IBil ililra Iflf f / ^ i • P lnl ,1 *\v»v pa 1 \v 9 wnl Is • M \ | [ Jw/ ’t /all ll ■iliwk ^ V ■ MiM iBav^ V® I . 71 m \«V i jkT^ ^Jjtj! If' jg 1 dj^riVltt f/ 1 j Bk. JtJsHK i. B n fi M il§nmBflr jM V i* J/ ■ ’9r ' r ll| Fig. I. The Solar Spectrum. Fig. III. Suhjtctivc Colour, Fig. IV Colour as related to idea < f Distance. The Primary , Secondary, and Tertiary Colours Fig. V. Fig. VI. El fee on Colours of Apposition. Mixture of Colours l>y d pfosition. Fig. VIII. Fig. VI 1. Indistinctness of Related Colours in contact. Effect of Black and White in separating Colours. Fig. IX. Fig. X. Fig XI. Effect of a Grey Ground Fffect of a Black Ground Effect of a White Ground on Colours. on Colours. on Colours. Cassell’s Technical Educator. See Lessons on Theory 0/ Colour THE a. ^ TECHNICAL EDUCATOR : &tt (Snrgrlopariiia OF TECHNICAL EDUCATION. VOLUME I. CASSELL PETTER & GALPIN: LONDON, PARIS &■ NEW YORK. INDEX TO CONTENTS, -4- PAGE AGRICULTURAL CHEMISTRY: On the Elementary Consti- tuents of Plants . .13 The Elementary Parts of Plants . . • .52 How Plants Grow . . 106 Formation and Composi- tion of Soils . . • 170 Influence of Cultivation and Drainage upon Soils 238 On the Improvement of Soils . . • -298 AGRICULTURAL DRAINAGE AND IRRIGATION : Introduction — Definitions of Drainage and Irriga- tion — Early History of the Science . . .19 Water-logged Soil— Advan- tages of Land Drainage . 77 Water Economy of Soils . 78 Causes of Efficacy of Drain- age-Action of Drains on the Soil — Various Me- thods of Drainage — Capil- lary Attraction and its Effects . . . .139 Various Methods of Drain- age — Materials . .174 Mole Plough — Draining Trench — Draining Tools, etc 219 Cost of Drainage, etc. . 250 ANIMAL COMMERCIAL PRO- DUCTS : Introduction ... 3 Zoological Classification . 4 Products of the Class Mam- malia .... 4 I. Purs — Quadrumana . . 5 Carnivora — 1. Digitigradcc . 5, 35, 74 2. Plantigradse . .74 3. Pinnigrad® . . 74 Rodentia . . .75 Ruminantia . . 75, 110 II. Perfumes — Musk, Civet, Ambergris . 110 III. Stearine and Oils — Whale, Sperm Whale, Tallow, etc. . . 142 IV. Food Products — Live Stock — Meats. . 143 V. Wool- Merino Sheep — Angora Goat — Thibet Goat — Al- paca, etc. . . 144, 149 VI. Leather — Russia and Morocco Leather, etc. . . 150 VII. Hair and Bristles— Human Hair — Horsehair, etc. .... 173 VIII. Horns and Allied Substances — Horns . . . 182, 174 PAGE Whalebone— Osseous Sub- stances . . .182 Products of the Class Aves — Food — Feathers . . 203 Bed Feathers — Quill Pens . 234 Products of the Class Rep- tilia .... 234 Products of the Class Am- phibia .... 235 Products of the Class Pisces 253 Herring, Pilchard, Sprat, Whitebait, Sardine, Mack- erel, Salmon, Cod . . 269 Cod (continued), Turbot, Sole, Lamprey, Sturgeon, Caviare, Isinglass . . 289 Products of the Sub-King- dom Mollusca . . 289 Dyes — Shells . . .321 Oyster, Mussel, etc. . . 344 Products of the Sub-King- dom Annulosa — Leech, Silkworm Moth, Honey Bee .... 344 The Honey Bee ( continued ) — Cochineal . . . 367 Blister Fly, Lac Insect . 382 Products of the Sub-King- dom Radiata — Coral, etc. 382 Products of the Sub-King- dom Protozoa — Sponge, etc. .... 382 APPLIED MECHANICS : Applications of the Lever and the Screw . . 33 ThePulley — Largeand Small Pulleys — Theory of the Pulley Block, including Friction — Experiments upon the Three - Sheave Pulley Block ... 93 Experiments upontheThree- Sheave Pulley Block — Differential Pulley — Epi- cycloidal Pulley . . 129 The Crane — Framework— Wheelwork . . . 206 Hydraulic Machinery. . 241 Common Tools — The Ham- mer, Saw, File, and Chisel 274 Machinery used in Agricul- ture — Mechanical Appli- ances used in Preparing the Soil — Machines used for Sowing — Machines used in Reaping . . 290 Mechanical Principles of Bridges — The Girder — The Wooden Bridge — The Arch . . .340 The Steam - Hammer and Rolling-Mills . . . 410 BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS : Captain Andrew Yarranton 22 Sir Humphry Davy . .51 PAGE / Robert Stevenson, Engineer 83 James Taylor . . . 147 | James Brindley, Engineer . 179 j Sir Robert Strange . . 218 j John Smeaton . . . 235 | James Horsburgh, F.R.S. . 346 George Stephenson . . 370 . BUILDING CONSTRUCTION : | Introduction . . . 2 j . Of the Drawings required j for Building Purposes . 2 j Elevations. . . . 3 . Sections . . . 3 ! Working Drawings . . 3 | Scales— To Construct aPlain j Scale, etc. . . . 38 j General Principles of Build- ing Construction . 38 | Foundations . . . 38 | Foundations under Water . 79 j Masonry . . . . 97 j Brickwork . . 141, 171, 195 ; Arches . 196, 225, 263, 295 j Drawing for Bricklayers . 226 j Drawing for Masons . . 297 Stone Arches— Woodwork, j etc 327 : Drawing for Carpenters and j Joiners — Joints in Tim- ber . . 330, 355, 395 I CHEMISTRY APPLIED THE ARTS: Bleaching . TO 45 Dyeing Calico Printing Tanning Soda . Soap Boiling 75, 130 197, 266 ' . 309 . 330 . 337 CIVIL ENGINEERING: Introduction — Early His tory of the Science . 29 Draining . . 113 Waterworks . 226 Roads — Canals . . 314 Canals ( continued ) . 385 COLOUR : Introduction — Connection of the Science of Optics with Colour . . .61 Composition of Light — Complementary Colours — The Spectrum . . 125 : Relation of Colours . . 177 Maxwell’s Theory of Prim- ary Colours . . . 211 j Secondary and Tertiary Colours — Contrasts of Tone and Colour . . 215 Colours with White, Grey, and Black — Ocular Modi- fications of Colour— Per- sistence of Colour Im- pressions — Irradiation — • Subjective Colours— Con- tact and Separation of Colours .... 318 i PAGE The Cultivation of the Sense of Colour — Triple Com- binations of Colour— Dis- • tribution, Balance, and Quality of Colour . . 394 Applications of Triple Prin- ciples of Distribution, Balance, and Quality, in estimating the Agreeable- ness of certain Assort- ments of Colours . . 407 DESIGN, PRINCIPLES OF: Introduction — Value of Art Knowledge — Meaning conveyed by Ancient Ornamentation . . 49 Egyptian Ornament — Greek Ornament — Early Chris- tian Symbolism . . 87 Truth, Beauty, and Power in Ornamentation . . 120 Employment of the Gro- tesque in Ornament . 151 Colour in Design — General Considerations — Contrast — Harmony — Qualities of Cblours — Teachings of Experience — Analytical Table of Colours . . 191 Harmonies and Contrasts of Colour . . 221, 229 Some General Art Princi- ples .... 277 Art Furniture . 311, 376, 403 ELECTRIC TELEGRAPH, THE: The Batteries Employed- Insulators — Line Wires . 60 Insulators : Mode of Test- ing them — Mode of Mat- ing Joints — Lightning Conductors — Covered Wire : Mode of Making Joints in it . . . 127 Subterranean Lines — Sub- marine Cables — First Cable from Dover to Calais — Atlantic Cables — Persian Gulf Cable — Sie- men’s Cable . . . 180 Interruptions in Communi- cation-Mode of Testing for and Localising Faults 255 O tlierFaults — C on tact— De- fective Earth — Lightning Guards— Mode of Render- ing Signals Intelligible — Single Needle Instrument — Code .... 303 Construction of SingleNeedle Instruments — The Com- mutator — The Coil — Switches— Swiss Commu- tator-Mode of Joining up Circuits . . . 369 Another Form of Commu- tator — The Double Needle Instrument — Its Code — Ordinary Alarum — Self- Acting Alarum . . '401 IV INDEX TO CONTENTS. TAGE FORTIFICATIONS : Preliminary Remarks — De- finition of Scales — Defini- tion of Terms used in Geometrical Drawing — Slopes : how Expressed — Definition of the Term F ortifi cation — C onditions that, if possible, every Fortification should ful- fil — Erroneous Impres- sions held with regard to the uses of Fortification — Subject divided into Two Branches — Field Fortification — Permanent Fortification — Definition of a Parapet — Materials of which Parapets are constructed . . .21 Types of Field Profiles on Level Ground — Defini- tions — Names of Slopes, etc. — Uses of various Parts of Profile — Pene- tration of Rifle Bullets — Penetration of Artillery — Necessity of variety of Profiles to Suit theGround — Definition of Defilade — Means of affording Ad- ditional Security to Men firing over the Parapet . 103 Profiles of Hasty and Irre- gular Defences — Trenches — Stoccades, etc. . . 161 Trace of Works — Definition of various Methods of Ar- tillery Attack, and Modes of obtaining Protection from them . . . 223 Closed Works ... . 287 MINERAL COMMERCIAL PRO- DUCTS. Introduction — Mineral Raw Produce . . .10 I. Metals — Iron . . .11, 26 Gold — Platinum — Silver — Mercury — Tin . . 26 Lead — Zinc— Aluminium — Antim ony — Bismuth — Cobalt —Nickel— Ar- senic — Manganese — Chromium . . .54 II. Minerals Proper — Coal — Bituminous Sub- stances . . .67 Calcareous Substances . 86 Silicious Substances . 87 Igneous and Metamor- phic Rocks . 87, 115 Clays and Allied Sub- stances . . . 115 Earths of Sodium, Potas- sium, Boron, Sulphur, etc. . . . lie, 138 Precious Stones . . 138 NOTABLE INVENTIONS AND INVENTORS: Printing . . , .27 Gas-lighting . . .93 Clocks and Watches 166, 190, 253 The Mariner’s Compass 322, 342 Pottery and Porcelain 366,378,402 OPTICAL INSTRUMENTS : Spectacle — TheNormalEye 110 The Abnormal Eye . . 159 Diagnosis for Spectacles . 257 Spectacles for the Presby- opic . . . 306, 350 Spectacles for the Myopic . 353 Spectacles for the Hyperme- tropic . . . .354 PAGE Spectacles for Eyes of Dif- ferent Foci . . . 354 Astigmatism . . 355 PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING . . .63, 123, 187, 251, 308, 372 PRACTICAL PERSPECTIVE 292, 332, 363, 382, 388 PROJECTION : Introduction ... 7 Elementary Principles of Projection ... 8 Projection of Lines . . 8 Projection of Planes or Sur- faces .... 9 Projection of Door — Trap DoorandFraming — Cubes and Prism — To Project a Cube — Shade Lines — To Develop a Cube . . 23 Projection of Prisms— Sec- tions . . . .40 Projection on the Inclined Plane — Side or End Ele- vations . . . .71 To Project a Pentagonal Prism — Of Pyramids — Projection of Circles and Cylinders . . .84 Projection of Cylinders . 100 Cylinders and Cones— Speed Pulley — Sections of Cones . . . 132 Sections of Cones and Pene- tration of Solids 164, 204, 235 Projection of Buildings . 235 Isometrical Projection . 267 Questions for Examina- tion . . . 282, 298 SEATS OF INDUSTRY: Birmingham . . .42 Sheffield . . . - 92 Liege and Pittsburg . . 118 ManchesteranditsSuburbs : their Chief Industries . 213 Manchester and its Suburbs: their Minor Industries . 302 Lowell and Rouen . . 338 Glasgow .... 386 STEAM ENGINE, The: Prime Movers — Source of the Power — Mechanical Equivalent of Heat — Pro- perties of Steam — The Boiler — Wagon, Cornish, Flue, and Tubular Boilers — Superheater . . 81 Superheater ( continued ) — Locomotive Boilers— Ar- tificial Draught — Con- struction of Boilers — Man-hole— Blow-off Cock —Gauge Glass, etc. . 145 Feed Apparatus — Stand Pipe for Low Pressure Boilers — “ Giffard’s In- jector ” — “ Bucket Boiler Feed” — Safety Valves — Pressure Gauge . . 209 Boilers (concluded) — TheFur- naca — Relative Values of Different Kinds of Coal — Draught — Smoke Con- suming Arrangements — Temperature and Pres- sure .... 283 Steam Pipes — The Cylinder Principle of Alternate Motion — The Piston and Rod — Packing of the Pis- — ton . . . .350 The Cylinder ( continued ) Stuffing Box — Slide Valves .... 399 PAGE TECHNICAL DRAWING: Introduction . . 11 How to use Mathematical Instruments . . .12 Technical . Drawing Box — Technical Pencils — Hints on Colouring Drawings— Linear Drawings by means of Instruments . 31 Linear Drawing in Parallel Lines— Free-Hand Draw- ing .... 46 Linear Drawing by means of Instruments . . .55 Free - Hand Drawing — Linear Drawing by means of Instruments . . 68 Drawing tor Carpenters— Coffer Dams — Wooden Bridges . . . .94 Wooden Bridges 107, 116, 135 Roofs, Development of Sur- face . . . 156, 167 Drawing for Joiners — Doors— Parquet Work . 183 Dovetailing — Mouldings — Free-Hand Drawing for Joiners .... 199 Gothic Tracery . . . 216 Drawing for Machinists and Engineers— Mechanical Drawing Gene- rally . . . 231, 247 Free-Hand Drawing . 259, 316 Practical Geometry . 259, 279 Mechanical Drawing 299,317, 323 Projection and Development 347 The Teeth of Wheels . 349, 359 Mechanical Drawing from Rough Sketches . 381, 392 Projection and Penetra- tions . . . . 392 Of Cams — Of Screws . . 407 TECHNICAL EDUCATION ON THE CONTINENT: Technical Education Gene- rally ... 15, 42 Models used in Teaching Animal Physiology 71 Polytechnic Schoolin Hano- ver . 71, 102, 134, 162 Parish Workmen’s Schools of Wurtemburg . . 202 Technical Education Ap- plied to Females . . 239 Trade Schools at Stuttgard 239 Trade Schools at Uhn . 240 Trade Schools of Wurtem- burg : Statistics and Working . . . 262 School of Practical Build- ing at Stuttgard . . 262 The Grand Duchy of Hesse — Polytechnic School at Darmstadt . . . 294 The Working Men’s Union in Berlin . . . 326 Technical Education in France . . . 327, 362 Method of Teaching Draw- ing in France . . 367 The Netherlands . . 397 VEGETABLE COMMERCIAL PRODUCTS : Introduction . . .17 Food Plants— I. Farinaceous Plants : Wheat — Oats — Barley — Rye — Rice — Maize — Guinea Com . . .17 Peas, Beaus, etc.— Ground- Nuts— CarobBean — Chick Pea . . . .58 PAGB II. Starches of Commerce and the Plants which produce them — Arrowroot — Tapioca- Sago . . . .56 III. Plants Yielding Spices and Condiments — Cinnamon — Nutmeg- Clove . . . .59 Allspice — Pepper — Gin- ger — Vanilla . . 90 Cardamoms — Umbelli- ferous Plants : Cara- way, Coriander, Anise, Mustard, etc. . . 122 IV. Plants Yielding Sugar— Sugar-Cane — Beetroot— Sugar-Maple— Date . 122 V. Plants used in the Pre- paration of Nutritious and Stimulating Beverages — The Tea Plant . .158 Paraguay Tea, Coffee, Cocoa . . . 186 Grape, Hops . . .214 VI. Plants producingWhole- some and Nutritious Fruits — Orange, Seville Orange, Citron . . . 215 Lemon, Grapes, Fig, Prune, Date, Palm, Pomegranate, Banana, Tamarind, Pine-apple, Hazel-nut . . . 243 Walnut — Hickory and Pecan Nuts — Brazil Nut, Chestnut, Almond 273 The Palm Family . . 273 VII. Miscellaneous Food Plants — Onion, Soy Bean, Truffles, Morel, Carrageen or Irish Moss . . . 274 Industrial and Medicinal Plants. I. Textile Plants — Flax, Hemp, Cotton . 305 Cotton ( continued ), Jute, New Zealand Flax, Coir Fibre, Carludovica Pal- mata, Manilla Hemp . 337 II. Oleaginous Plants — Cocoa-nut Oil — Castor Oil — Olive Oil — Rape Seed- Linseed — Sesame — Cro- ton Oil .... 338 Volatile or Essential Oils . 374 III. Tinctorial or Dye Plants — Alkanet Root — Sumach — Amotto — Myrobalans — Safflower — Logwood — Madder .... 374 Indigo — Turmeric — Quer- citron — Yellow Berries — Fustic — Woad — Nicara- gua or Peach Wood — Sapan Wood — Red Sanders Wood . .406 WEAPONS OF WAR: Introduction ... 5 Portable Arms ... 6 Fire-Arms— Brown Bess — Brunswick Rifle — Minie Rifle — -Enfield Rifle . 65 Gunpowder . . . 154 . Small- Arms — Snider Rifle — Enfield Rifle— Caps, etc. 193 Breecli-loading Small Arms ■ — Boxer Cartridge, etc. 272 Breech-loading Small Arms (continued) — Martini- Henry Rifle . . .334 Great Guns and their Pro- jectiles .... 389 THE TECHNICAL BEING THE TECHNICAL SERIES OF INTKOD Before entering upon the course of lessons which we are about to lay before our readers in The Technical Educator (which is intended to furnish a practical sequel to the theoretical lessons contained in The Popular Educator, and to which work indeed it forms a necessary supplement), it appears desirable to state what is understood by Technical Education, and to (five some general idea of the system upon which it is & our intention to proceed. Technical Education, as we have already explained in the address “To our Readers” in the concluding volume of The Popular Educator, means literally education in any special art, and in this sense, of course, it is capable of almost the widest application There is, in fact, no calling in life, no profession, voca- tion, or employment, from statecraft and diplomacy downwards, through the long lines of brain-work and hand-work, whose followers do not require a technical education peculiarly suited to it to enable them to pursue it with the best results to themselves and the largest amount of benefit to others. At the present day, how- ever, the term “Technical Education” is not generally understood in so wide a signification, but it is confined to special instruction designed to enable men who live by hand labour to apply to their handicraft the leading principles of science which bear more especially upon it. Without going to the length of giving a detailed list of all the different classes of hand- workers to whom this special kind of art instruction may be of benefit, WG . ma y least indicate in general terms the course of instruction we purpose to adopt in these volumes. J . subject which primarily affects those’ who would receive benefit from Technical Education, is Drawing m its practical application to the various Constructive Arts, as well as to Design and Ornamentation. Papers on these subjects, together with the kindred ones of Perspective, Projection, and Practical Geometry, will run through the volumes of The Technical Educator, those on Technical Drawing for Trade Purposes em- bracing Drawing for Carpenters and Joiners, Masons, Metal Workers, and several others. Design will be treated under its various conditions and in its different -yles, both as regards purity and correctness of form, and harmony and balance of colour. With regard to the -atter portion of the subject, special information will be given in a series of papers upon the Theory of Colour. The subject of Drawing is in one branch intimately connected with that of Practical Building 1— Vol. I. EDUCATOR: “CASSELL’S POPULAR EDUCATOR.” UCTION. Construction, which will form another portion of our series : these will treat of such points as the prin- ciples of construction generally, of scaffolding, and the strength, resistance, and applicability of different build- in g materials. The principles of Mechanics and Mhchmery have already been laid down in The Popular Educator. In the present volumes we shall supplement this infor- mation by describing the practical application of these pi inciples to the machinery, tools, and agricultural inrplements in ordinary use. Special papers will also be devoted to the Steam-engine, in its various applications to locomotive and mechanical purposes. A set of papers upon the principles and practice of Electric Telegraphy will form a practical continuation to the information alieady given on that subject in The Popular Educator. Another very important subject which will form part of our scheme is Civil Engineering, as well as the kindred one of Military Engineering and Fortification, and also what may be termed Agricultural Engineering, the drainage and irrigation of land, and the making of fences and roads. A portion of our space will be devoted to an ac- count of the various Animal, Vegetable, and Mineral Products used in Trade, and the processes of their manufacture from the raw material into articles of utility and ornament. Closely allied to these subjects is Practical Chemistry, which will be treated of in its application to Trade Purposes and Manufactures, and also to Agriculture. The course of instruction we have thus laid down will be sufficiently comprehensive to include every branch of handicraft work ; but in addition to this, some special branches of manufacture will also recen e separate treatment ; among these we may mention the Manufacture of Optical and Philosophical Instru- ments, and Weapons of War. We have now enumerated some of the subjects in which direct instruction will be given, and we have thought it advisable to add to them some others which will form a very interesting portion of the Work, being at the same time of a character both practical and instructive. Among these will be given descrip- tions of the Principal Seats of Industry in this and other countries ; Biographies of Notable Inventors and Manufacturers, with accounts of their work ; a sketch of the Progress and Practice of Technical Education ; and an account of the Museums and Schools of Design which have been already established for aiding Technical Education in this country. 2 THE TECHNICAL EDUCATOR. BUILDING CONSTRUCTION.— I. INTRODUCTION. The purpose of the present course of lessons is to give a general knowledge of “ Building Construction,” the special branches of which will be separately treated in subsequent articles. * The instruction given in this course is simplified as much as is consistent with the proper working out of the subject, whilst the illustrations are rendered as clear as possible, in order that they may serve not only as illustrations of construction, but also as drawing copies — of which a further series will be given in the lessons on “ Technical Drawing.” The student is strongly advised not to merely read the text and look at the examples, under the idea that the distinctive forms will be thus impressed on his mind, and that he will be able to reproduce or apply them when required. Long ex- perience has shown us that this plan is unsafe, and that lessons of this kind cannot be merely read as tales ; though in these, too, it is now admitted that the illustrations of the events depicted serve to fix the acts, actors, and scenes on the memory. This purpose may to a certain extent be accomplished by merely seeing the drawings ; but our object is twofold. We wish not only to teach the student to read a new language, and that language a universal one, but to speak it fluently. We wish to teach a workman not only to be able to work from a drawing, but to make one. This applies not only to masons and brick- layers, but to all artisans ; and if once the pleasure of being able to sketch with a piece of chalk from his pocket, or his rough flat pencil, so as to satisfy and please his employer, is felt, we have no fear but that the artisan will continue his study of drawing with increased interest. In plain words, we wish these lessons to afford mental study combined with manual practice, so as to accustom the student not only to think, but to act— a glorious combination which the education of the workers is most likely to bring about. The system therefore advised is that the student should first read the section carefully, referring to the cuts, and accurately observing the lettering. The illustration should next be drawn to a larger scale, and lettered to correspond ; and then the references or description written underneath it : not necessarily the whole text, but an abstract of the principles. The student will then lie able to look over his drawings occasionally, and will see the constructions at a glance ; these glances will serve as reminders, and each will awaken a chain of ideas which may for the moment have glided away, but which such a gentle touch may call back again. It is further necessary to remind the student that the con- structions treated of in these lessons, and in those diverging from thorn, are all more or less dependent upon the geometrical principles, forms, developments, and projections which are exemplified in other lessons given in these pages ; and he is urged not to rest satisfied with merely copying the diagrams, but to vary the studies, to apply the principles, and to attempt, however humbly, to design for himself. Let him look at the revival of architecture now going on around us, and reflect that this is being accomplished by the careful and conscientious study of the sciences upon which the glorious edifices of old were constructed, not by merely copying them ; and therefore it is that we would have the student throw his whole spirit into his vocation, and not merely to hew stone or cut wood, but to remember the words— “ Stamp each stone with earnest feeling. In the rock thy soul revealing.” Thus did the men of olden time. Their heart and soul were in their work, and when we look on it in the cathedrals and in the museums, with our spirit enchained and enraptured, we fail to ask, “How much did it cost ?” for, to the man who would do his duty, the question, “ How much shall I get for it ? ” must for the moment sink before the one great resolution, “ I will do my best.” But the artisan will ask, “ Will this bring me wages ? ” and we unhesitatingly answer, “ Yes, it will ; ” for we may fearlessly assert that never in the whole history of labour has there been a * It will be of advantage to the student, if he has not already done so, to go through the papers on “Practical Geometry" which have appeared in The Popular Educator. He must also follow the further development of that subject, together with the lessons on “ Projection," which will appear in these pages. period when the workman has been deemed more worthy of his hire, or when greater efforts have been made, first to teach the artisan, and then to show appreciation of his work, than the present. Let him but show that he possesses, in the words o: Beynolds, “ a love of art, and a desire to excel,” and he may be assured that he will not want encouragement for his efforts. OP THE DRAWINGS REQUIRED FOR BUILDING PURPOSES. The drawings required for the general purposes of building may be classed under four heads, viz. : — Plans. I Elevations. Sections. | Working Drawings. To these must be added “ Perspective Drawings,” which, how- ever, are not used in absolute construction, but are intended to represent the building when seen from various points of view ; and “ projections,” by which the widths, etc., of elevations, and the true shapes of the sections are obtained. The terms plan, elevation, and section are fully explained and practically demonstrated in the lessons on “ Projection,” which in its turn is based on the construction of geometrical forms, treated of in the lessons on “Practical Geometry” in the Popular Educator. It must be obvious that the course of instruction would be impeded were we to repeat the definitions and examples already given in explanation of these terms, before entering on our present subject. We would therefore earnestly advise the student to study the lessons referred to ; not to be content with the mere possession of the pages, but to work each example carefully; by this means he will have laid (to use a term adapted to our theme) a firm foundation, the benefits of which he will experience during the whole course of his subsequent studies. We will merely, then, remind the reader that the plan of a building, etc., is the exact form of the ground on which it stands or which it overhangs. (See lessons on “ Projection.”) Plans are spoken of as — 1. Block Plans. — These show the mere outlines of the build- ings, and their position in relation to the surrounding objects. In most cases the block plans are accompanied by drawings showing the levels of the ground and neighbourhood, the drains, gas and water mains, already existing, and the method by which the new works are to be connected with the old. These drawings are, in fact, maps of the whole property, on which the general shape and position of the buildings are marked. 2. Excavation Plans. — This term is almost self-explanatory. These drawings give the exact shape of the excavations that is, of the hollows to be sunk for the required buildings. The term is derived from ex, “ out,” and cavus, “ hollow (Latin). They show the trenches to be dug for the walls to stand in, and also give the plans from which the works below ground, such as cellars, etc., are to be excavated. 3. Basement Plans. — These show the foundations and works, up to the ground-line or level of the ground. 4. Floor Plans, sometimes called Chamber Plans. — These show the exact disposition of the rooms, etc., on each floor, the staircases, etc. The beginner might at first think that one drawing could show all this ; but the idea would be erroneous, because on the ground floor some apartments, such as store- rooms, larders, etc., or other outbuildings might project from the house and cover more ground than the upper floors; secondly, the rooms in upper floors might be divided by parti- tions, which would make their plans different from those below, although covering the same area. Under this head, therefore, would be comprehended the ground-floor plan, showing the dining-rooms and drawing-rooms (where the latter are on the ground floor), the entrance hall, staircase, etc. ; the chamber plans, showing the bed-rooms, dressing-rooms, and bath-rooms (and, of course, such a plan would be necessary for each floor) ; and the attic plan, showing how the space is apportioned in the highest floor of the house. 5. Roof Plans. — These show the exact manner in which the building is to be covered, and the gutters by which the water is to flow to the heads of the spouts by which it is to be conveyed away. It is usual to show parts of the roof plan uncovered, or naked ; that is, with the slates or tiles removed, so as to allow of a plan of the roof timbers being shown. ANIMAL COMMERCIAL PEODUCTS. 3 ELEVATIONS. Elevations are exact geometrical views of each sidfe of the building. By the term “ geometrical view ” is meant a drawing where every part is represented as it really is, without any attempt at showing the sides or parts which would be seen if the building were looked at from any particular point of view ; for in a perspective drawing, the various parts, such as windows, doors, mouldings, etc., would be rendered smaller as they become more distant, and thus the drawing could not be measured from ; but in an elevation, the eye is supposed to be exactly in front of every part of the side of the building which is to be delineated, so that all the sizes and forms remain unal- tered. As the subject of projecting elevations from given plans will be fully treated of in our lessons in “ Projection,” it is unnecessary to enter further into it in this place, especially as several opportunities will occur in the cohrse of our study, in which the principles taught may be practically applied. It will be readily understood that as many elevations are required as there are sides to the building ; thus, in erecting a detached villa — that is, one which stands alone — it will be neces- sary to prepare the front elevation, the back elevation, and two side elevations; whilst for a house in a street, situated between two others, only the front and back elevations would be required. On all the plans and elevations figures are placed to show the measurements. Those on the plans give the widths of the different parts, whilst those on the elevations give for the most part the heights ; in order that it may be clear to which parts the dimensions apply, an arrow-head is placed at each extremity. These are connected by a dotted or coloured line. This is broken off in the middle, and the necessary figures inserted. Of course, plans and elevations are drawn very much smaller than the real size, yet all the parts are represented in such accurate proportion, that the figures may be readily translated to the required dimensions ; this is called “ working to scale,” and the proportion in which the drawing is made is always stated on it. Thus you will notice in the margin, “ Scale, § inch to a foot;” this means, that every part of the drawing which measures i of an inch is to be 1 foot long in the building ; and as there are eight-eighths in an inch, and twelve inches in a foot, it will be clear that the drawing is one ninety-sixth of the real size. When one dash (') is placed over a figure, it means that that figure represents feet; whilst two dashes (") mark inches; and it is no doubt known to the student that X means “ multiplied by,” or, as it is generally termed, “by;” thus, if a room is marked 14'G" X 12 / 3", it means that it is to be fourteen feet six inches long, by twelve feet three inches wide. The mode of making scales will be shown further on. SECTIONS, The drawings next required are called sections. The study of “Projection ” will show what sections really are, and how they are obtained. It is, then, only necessary here to give a very simple definition of them, for it must be clearly understood that Projection is not to be taught in the present lessons, but applied; and therefore students are urged to take up that study either prior to (which is the more advisable), or together with this, otherwise they will be likely to become truly “ mechanical draughtsmen, that is, men who simply draw mechanically , who work from a copy, and rightly or wrongly measure and draw the lines because they are in the drawing before them, thus becoming mere drawing machines; whereas the study of Pro- jection will teach them to obtain an elevation from a given plan and other data, and to work out the sections according to the required position. A section, then, is the form which would be presented if an object were cut in any given direction and one part removed. Thus a plan may be said to be an horizontal section ; that is, the form which would be presented if a large knife were passed through a building parallel to the floors, and the upper portion were removed. Sections are, however, usually understood to mean vertical (or upright) cuttings, generally parallel to one of the elevations ; thus, a longitudinal section is a cutting parallel to the front, while a transverse section is a cutting across; viz., parallel to the sides of the building. Sections need not necessarily be parallel to either side, but may be taken in any direction that may be required, their position being shown by a line on the plan. Now the section of a solid body shows just the shape of the cutting, or, in common terms, the “ slice ” taken on a given line ; but if the object were hollow, its internal surface would be presented to view ; thus, if a house be supposed to be cut from back to front, the whole of the interior structure will become visible ; and thus, by giving sectional drawings taken on different lines, the entire modes of construction of the floors, roofs, staircases, etc., are shown, as are also the manner in which the rooms are placed over each other, and the walls and chimney stacks are carried up. WORKING DRAWINGS. Next we come to the working drawings, or as they are some- times called, the detailed drawings. These are to show exactly all the detail of the various parts, which could, of course, only be rendered on a very small scale in the general drawings. Working drawings, therefore, are made much larger; it is necessary, in fact, that the drawings of some of the parts be made of the real size, in order that the detail may be perfectly intelligible to the workman, so that drawings may be made for other parts which are to fit exactly to them. Working drawings are required not only for the builder, but for the purposes of the decorator as well, in order that the ornamentation may be designed so as to be adapted to the size and form of the surface to be covered. They are also necessary for the mason, in order that from them he may make his templets, or pieces of metal, cut to the exact shape of the section, etc., of the moulding or string course, and that by them he may make all the single pieces of stone which are to form tracery, of tho exact form and size required. Detailed drawings are also required in making the patterns in wood from which the iron girders and other castings are made, and for the carpenter and joiner, to show the method of framing- in the doors, windows, shutter-boxes, etc. It therefore becomes necessary that a separate set of drawings be provided for each trade. When it is intended that any part of a drawing is to represent in section, it is usual to cover such part with lines drawn at an angle of 45°. This is easily done by placing the T-square with its cross-head against the left-hand edge of the drawing-board, and moving the set square (of 45°) along the edge of the blade as each line is drawn. The section lines should not bo placed too closely together, and if the drawing is to bo coloured, the colour should be applied first, and allowed to dry thoroughly before the section lines are drawn ; for if the lines have been drawn first, the colour would be likely to “ wash up ” the Indian ink, and so cause a smeared and blotched appearance. The lines which represent the sections of stone, bricks, etc., are straight, but those which are to show the sections of wood are so placed that they may either represent the grain or the curves which are seen in the ends of timbers, and which are parts of the rings of woody fibre of which the wood is formed. Care must be taken that none of these effects are overdone. The student must remember that he is not making a picturesque drawing (and even if he were, excessive elaboration of such detail would be out of place), but that “ trade drawings,” the “ drawings of the workshop,” must be purely indicative, so that they may show at a glance the different materials of which the object is to be constructed. This purpose is much assisted by tinting each part with the colours which are generally under- stood to represent the various materials. A few plain instructions on the method of colouring draw- ings, and the colours used to express the various materials, will be given in the lessons on “ Technical Drawing.” ANIMAL COMMERCIAL PRODUCTS.— I. INTRODUCTION. In the animal as in the plant world, we find progressive organic development, boundless diversity of structure, and a beautiful subserviency of means to ends. The highest type of life is Man. The different grades of organisation have their purposes to fulfil, and each animated being has its own position indepen- dent of the rest, yet subordinate with reference to others of more complicated form and frame, especially with reference to man, for whose benefit all seem to exist. With the scientific classification and description of living creatures has lately arisen a desire for a scientific designation of 4 THE TECHNICAL EEHCATOE. tlieir economic uses, and a statement of their comparative com- mercial value, in order that the appliances of social life and the claims of civilisation may advance with the progress of inquiry and the diffusion of knowledge. Energy and skill are alike taxed for the discovery of new properties in the animal, the vegetable, and the mineral king- doms ; or for the further utilisation of properties long known. A caref ul study, then, of the contents of a collection like that in the South Kensington Museum, together with the greater variety passing through our Custom-house from the cargoes of all nations, must bo highly important, while it can hardly fail to be interesting. There is but one path for the successful pursuit of knowledge so valuable and so honourable— the path of science; for science is the track of truth, plain in all simplicity, yet revealing the symmetry and the beauty of the works of the Creator. ZOOLOGICAL CLASSIFICATION. Naturalists have arranged the animal kingdom into two grand divisions. I. Vertebrata (Latin, verto , I turn), or vertebrated animals, having the central portion of the ner- vous system, or the brain and spinal cord enclosed, the former in a cavity called the cranium or skull, and the 'latter in a canal composed of a suc- cession of united vertebrae, or bony segments, cr, as in some fishes, of car- tilage. The vertebrated animals are ar- ranged in five divi- sions or classes : — 1. Mammalia (Latin, mamma, a teat). — Animals which possess mam- mary glands and suckle their young, bringing them forth alive. Examples : the monkey, ox, seal, elephant, and whale. 2. Aves (Latin, avis, a bird). — Ovi- parous vertebrated animals covered with feathers and organised for flight, swan, pheasant, and eagle. 3. R.eptilia (Latin, repo, to creep). — Cold-blooded vertebrated animals, covered with scales or hard bony plates, terrestrial or aquatic, air-breathing, and endowed with extraordinary powers of endurance under abstinence, or against bodily injury. Examples : the turtle, snake, crocodile, lizard. 4. Amphibia (Greek, amphibios) . — Fisli-like in the early period of their existence, breathing exclusively by gills, and having a two-chambered heart, finally becoming air-breathers, acquiring lungs and a three-chambered heart, losing wholly or partially their piscine character, and becoming more or less terrestrial. Examples : the frog, toad, and proteus. 5. Pisces (Latin, piscis, a fish). — Oviparous vertebrated animals having a branchial respiration, a covering of scales, and an organisation for life in the water. Examples : the sturgeon, cod, and herring. II. Invertebrata, or animals destitute of a cranium or skull, and a vertebral column. The invertebrated animals comprise four sub-kingdoms : — 1. Mollusca (Latin, mollis, soft), or soft-bodied animals, popularly known as shell-fish. Examples : the oyster, pearl- oyster, and mussel. 2. Annulosa (Latin, annulus, a ring), or ringed animals, Examples : crabs, leeches, and insects. 3. Radiata (Latin, radius, a ray), or radiated animals, Examples : the sea-anemone and red coral. 4. Protozoa (Greek, protos, first, and zoon, animal), or first animals. Example : the common sponge. We now purpose to take up the various animal products in succession according to the above zoological arrangement. We begin with the highest and most useful class of Vertebrata, or the PRODUCTS OF THE CLASS MAMMALIA. This class comprises twelve orders, viz. : — 1. Bimana (Latin, bis, twice, and manus, the hand), or two- handed animals. Example : man. 2. Quadrumana (Latin, quatuor, four, and manus, the hand), or four-handed animals. Example : the monkey. 3. Cheiroptera (Greek, cheir, the hand, and pteron, a wing), or hand-winged animals. Example : the bat. 4. Insectivora (Latin, insecta, insects, and voro, I devour), ! insect-eaters. Examples : the hedgehog, mole, and shrew. 5. C am iv ora (Latin, caro, carnis, flesh, and voro, I de- vour), flesh-eaters Examples: the lion, tiger, fox, and er- THE ORNITHORHYNCHUS, OR DUCK-MOLE OF AUSTRALIA. Examples : the ostrich, 6. Cetacea (Gr. lcetos, a whale), or whale-like animals. Examples: the por- poise and whale. 7. PachAjdermata (Greek, pachus, thick, and derma, skin), or thick- skinned animals. Examples : the ele- phant, horse, and pig- 8. Ruminantia (Latin, ruminare, to ruminate), rumi- nating animals. Ex- amples : the stag, ox, and sheep. 9. Edentata (La- tin, edentatus, with- out teeth) , toothless animals. Examples : the sloth and arma- dillo. 10. Rodentia (Latin, rodere, to gnaw), gnawing animals. Examples : the squirrel, rat, rabbit, and hare. 11. Marsupialia (Latin, marsupium, a pouch), or poucned animals. Examples : the kangaroo, opossum. 12. Monotremata (signifying with one orifice or outlet), beaked, non-placental mammals. Examples : the echidna, or porcupine ant-eater, and the ornithorhynchus or duck-mole of Australia, to which country these monotrematous animals are peculiar. _ The Mammalia, living or dead, supply us with food m the form of flesh and milk : also with fur, wool, skins, hides, horns, hair, hoofs, fats, oils, bone, ivory, etc. In some instances every part is available — as, for example, in the horse. Leather is made from the skin ; the hair is manufactured into hair-cloth and bags for crushing seed in oil-mills ; the flesh furnishes food for dogs, poultry, and even men ; the intestines, a covering for sausages ; glue and gelatine are formed from the tendons ; knife-handles and phosphorus from the bones ; and buttons and snuff-boxes from the hoofs. I. FURS. We derive furs from all the orders of the Mammalia, witxi o\yo exceptions — Bimana and Cetacea. Man and the whales are well WEAPONS OF WAR. 5 known to be smooth-skinned animals. It is, however, the Carnivora and Eodentia principally which supply the market with furs. All our furs, both home and foreign, are either felted or dressed ; the former are used in the manufacture of hats, the latter as articles of' clothing. Fur is one of the most perfect non-conductors of heat, and therefore, if properly pre- pared, makes the most comfortable clothing that can be worn in cold climates. We find the animals there provided by Nature with this substance for their own protection, and therefore man has adopted it as the most suitable clothing for himself. In the prepared state skins are called furs ; without preparation, ’peltry . The hunter, as soon as the animal is captured and killed, strips off the skin, and hangs it up to dry, either in the open air or in a warm room. If the skin is well dried and properly packed, it may be sent to any distance, and will be received in good condition ; but if any moisture is left in the skin, or if it becomes exposed to damp on the voyage, putrefaction ensues, the hair falls off, and it is unfit for use so far as the furrier is concerned. A minute examination of the skins received is therefore the first thing to be done ; the grease is removed by steeping them in a liquid containing bran, alum, and salt, and by washing and scouring them ; and the oil is extracted from the fur with soap and soda. By subsequent treatment, each skin is tanned and converted into thin leather. It is now washed in clean water and dried, and is then ready to be made up into articles of dress. Felting is a process by which the different kinds of hair and wool are interlaced or intertwined, so as to form a close com- pact texture or mat. The felting capabilities of fur depend on the peculiar structure of the hair. Hair capable of felting has its surface covered with little serratures, which may be seen with the microscope ; and the felting consists in simply en- tangling these serratures with each other, and so matting the hairs together. Hair which is devoid of this serrated structure will not felt. The felting furs are confined to a few animals, such as the hare, rabbit, beaver, etc. These animals have two kinds of hair : a long and coarse kind, forming their visible external covering, which does not felt ; and a shorter, finer, and more abundant kind, which lies close to the skin, and is called the fur, and which does felt easily. When the skins are intended to be felted, these long hairs are first removed, either by being plucked out, or by very careful shearing. In the case of the beaver and rabbit, the long hair is pulled out with a short knife, the thumb of the operator being protected by a leather shield. The long hairs thus removed are of no use to the hatter, but are sold for stuffing chairs. The fur is then cut from the skin in a light fleecy mass, and the flocks are tossed about by the strokes of a vibrating string or bow, until matted together into a thin sheet of soft spongy felt ; a second sheet is pressed upon it, and then a third, until the required degree of strength and thickness of felt is obtained. The following are the most important of the fur-bearing animals : — QUADRUMANA. The chief monkey-furs imported are those obtained from the howlers, the largest of the New World monkeys. They are made up into muffs. CARNIVORA. These animals, next to the monkeys, are the most closely allied to man in organisation. Naturalists have divided them according to their mode of progression, which depends on certain peculiarities in the structure of their feet, into three leading groups : — 1. The Digitigradce, or finger-walkers (Latin, digitus, a finger, and gradior, I walk), from the habit of walking on their toes. Examples : the lion, tiger, and cat. 2. Plantigrades, or sole-walkers (Latin, planta, the sole of the foot), because applying the whole or the greater part of the sole to the ground when walking. Examples : the bear, racoon, wolverine, and badger. 3. Pinnigradce, or fin-walkers (Latin, pinna, a fin or feather), having their feet well adapted for progression through the water, by an expansion of the skin or web between the digits, and also for some slight degree of progression on land. Examples : the seal and walrus. I. DIGITIGRADA3. This division of the Carnivora includes the family Felidce (Latin, felis, a cat), so named by Linnseus, because an excellent example is furnished in the common domestic cat. These are characterised by the strong, sharp, retractile talons with which all their toes are armed ; they have teeth to correspond, pecu- liarly adapted for destroying other animals, and for tearing, dividing, and crushing flesh. Their sight is keen, to enable them to discern their prey, and they have great power of dis- sembling, so as to be able to lure their victims to destruction. It is most fortunate for mankind that these formidable animals have not the instinct of sociality ; otherwise, what could with- stand a troop of lions or tigers hunting in concert like wolves ? The most celebrated species of this genus is — The Lion ( Felis leo ). — This magnificent animal is distributed over the African continent and the southern parts of Asia. The long flowing mane of the male gives him a majestic appearance. His courage and strength are both indisputable, but he is as genuine a cat as the tiger, and quite as bloodthirsty and cruel in his disposition. About one hundred lion skins are annually imported into this country, chiefly from Africa. WEAPONS OF WAR.— I. BY AN OFFICER OF THE ROYAL ARTILLERY. INTRODUCTION. In order properly to appreciate the various improvements which through successive centuries have been introduced in weapons of war, and of which we see the combined results in the per- fected arms with which the modern soldier is provided, it is essential first to recognise distinctly the object which weapons are required to fulfil. In this way alone can we hope to obtain a firm grasp of the relative merits of particular types and classes of arms, and of the considerations which have recom- mended this simplification and that modification, which have determined the rejection of one weapon and the introduction of another. What, then, is the use and object of weapons of war ? What principle has ever governed the advance of this branch of the world’s industry and ingenuity ? The answer to these questions is best furnished by a brief reference to the general history of the subject. The theoretical starting-point is that remote epoch when man attacked his enemy and his prey wdth the weapons with which Nature had provided him. We say “ theo<. retical,” because the actual existence of such an epoch is. extremely doubtful, and in any case it must have been of insignificantly brief duration. That quality which distinguishes man from the brutes must early, if not immediately, have en- lightened him as to the advantages to be derived from the employment of accessory means of attack or defence. By a strange contradiction, the stream of almost Satanic ingenuity which since the time of Adam or of Cain has gone on widen- ing, and deepening, and strengthening — the tide of invention which has brought us the cannon and the rifle, the shell and the torpedo, which has improved the rude guns of the fifteenth or sixteenth centuries into the Armstrong of the present, which has changed Brown Bess into the Martini-Henry, which, .has developed the “infernal machine” of Fieschi into the mitrail- leur of our own day — this stream took its rise in the God-like quality of reason. Man’s intelligence at once prompted him to do that which was to the beasts, against whom his earliest wars were made, impossible, viz., to second his efforts by such assistance as he could draw from material resources. To weight the fist with a stone, to add force to the blow by means of a stick or club — such were the expedients at first adopted, and which we know, on the highest of all authorities, were employed in the daybreak of the world’s history with fatal success. But, by degrees, that faculty which had suggested these rude auxi- liary weapons, reached forward to other developments, and gave us the fashioned side-arm of definite form, the shaped weapon of stone or flint, of wood and bronze, of iron and steel. And then, as the study of the art expanded, it became obvious that a great advantage would result from the adoption of con- trivances. which would enable the enemy to be struck at a greater distance than hand weapons permitted ; and so we get to the . class of missile weapons — to the javelin, the assegai, and others, to be thrown by hand, and the projectile weapons, such as the blow-pipe, for projecting poisoned darts, the bow, the cross-bow and the sling, and the more powerful engines of 6 THE TECHNICAL EDUCATOR. war, sucli as tlie catapult and ballista. And now wo strike the track which leads more directly down to our own age. The range of these projectile weapons was so small, and their accuracy was so imperfect, while the importance of range and accuracy became so conclusively established, that the next con- siderable development naturally took these directions. At this point we mark the introduction of gunpowder, by which the ranges of offensive weapons and their practical importance were at once immensely increased. With the introduction of fire-arms we mark, indeed, a new epoch, although'the object remained the same — the killing or disabling of your enemy at the greatest distance, and with the greatest ease and certainty. The art received a new impulse ; the “villainous saltpetre” breathed into it a new life; and since this time men have laboured with an unfailing zest at the per- fecting of fire-arms, to the gradual pushing into the background of mere hand or missile weapons. During this period the suc- cessive improvements have nearly all taken the form of some advance in the production of long-range arms of precision of increased destructiveness. The greatest distance, the greatest and most irresistible certainty of destruction — these were the two main elements of success, the attempted achievement of which has advanced us from the blunderbuss to Brown Bess, from Brown Bess to the Brunswick rifle, from the Brunswick rifle to the Enfield, from the Enfield to the Henry, and Whit- worth, and Metford. With cannon, in the same way, pressed by the same considerations, we have advanced from the rude appliances of the sixteenth and seventeenth centuries to the smooth bores which won the victories of Nelson and of Wel- lington, and, again, to the rifled guns of Armstrong, and Whit- worth, and Woolwich. Again, from the simple round shot of an early age, or the rude and imperfect shell of the seventeenth century, we have travelled forward, always in the direction of increased destructiveness, to the shrapnel, and the segment, and the huge, far-reaching common and double shell, with their enormous charges of powder, and to the Palliser projectiles, which set at defiance the stoutest armour-plating. But, beyond a point, precision and range lose their practical walue. Where exactly that line is to be drawn it is difficult to say. Some enthusiasts would probably place it at the limits of human vision ; practical soldiers, however, know that other considerations than these really determine the limits. At all events, when men had got to military rifles, which would shoot with accuracy for half a mile or three-quarters, their instinct instructed them to seek to exercise their ingenuity in another direction. To multiply the rate of fire, within the limits already attained, became the problem of the day, and the result of this movement has been the introduction of breecli-loading rifles of immense variety, and many of surprising excellence. This brief and imperfect outline of the history of the subject will enable us to note the direction in which the tide of im- provement has gradually but surely set, and to recognise, in a general way, the objects which the artillerist and the rifleman have endeavoured to attain. But it is also important to recognise the influence of other considerations besides those of achieving determinate results. War is an art essentially of practice and not of theory ; and while theorists have been elaborating complex contrivances for the destruction of human life on the largest possible scale, the ..soldier, in his blunt way, has been ever at hand to exclaim : “ C’est magnifique, mais ce n’est pas la guerre.” Simplicity in warlike appliances is a necessity of their existence, which unpractised designers are apt to overlook. Economy, too, is a consideration which the soldier cannot afford to disregard. Capability of resisting rough usage, transport, exposure, and climatic changes may also be classed among the essentials of engines of war, the due observance of which limits the channel along which the military inventor must travel. In the ca.se of warlike stores for English use, these considerations are especially important, on account of the scattered nature of ■our dependencies, the variety of climates to which the stores are likely to be exposed, and the certainty that, in transport to our distant possessions, they will have much rough treatment to endure. This is a lesson which inventors, unfortunately, are slow to learn. They pursue a phantom of theoretical excellence in utter disregard of the consideration that the soldier wants the real, not the ideal. They trample ruthlessly on the prac- tical arguments which are opposed to their headlong progress, and push impatiently on one side the objections which those who know what war is venture to suggest. Even so dis- tinguished a man as Sir William Armstrong has not steered clear of this rock. It is noticeable that, where his inventions in war materiel have trenched upon the province of the artilleryman proper — in his breech-closing arrangement, for example, in his fuses, and his shells — they have all been more or less failures. When only mechanical, as distinguished from practical military considerations, were concerned, as in the structure of his guns, they have been eminently successful. To those readers who may now, or at some future time, conceive the idea of designing some weapon of war, we would give this serious advice : What- ever you may propose, be practical. Seek the advice, if you can, of some plain-spoken soldier ; one who has seen service ; one who knows something of the hurry and confusion and destruc- tion of action, of the roughness of military transport ; who can tell you of the rains and heats of India ; who knows how clumsy are a soldier’s fingers, and how little suited to ingenious refine- ments; one who can tell you, too, something of the brilliant failures of scores of clever but unpractical inventions, of fair hopes and extravagant promises wrecked on the first contact with the rough touchstone of practice — one, above all, who will not mince matters, but will say plainly, if need be, “Yours is the silliest and most unpractical invention which I have ever seen.” He is the best friend to the inventor who speaks thus ; he is the best friend also to his country, for he thus directs the inventive genius of the country into a useful course, instead of allowing it to filter itself away through vain channels into dreamland. On the other hand, we desire fully to recognise that the inventive mechanical genius and resource of England are among her native advantages, as substantial and important as her coal mines — advantages to be fostered and cherished by all means, and to be promoted by a liberal policy of encourage- ment on the part of both soldiers and the Government. If the present papers should have the effect of directing attention to war material, and stimulating the ingenuity of some who may honour them with their perusal, they will have accomplished more than the writer can dare to expect. He, on his side, would fail of his duty if he did not, with all emphasis, urge those who would enter upon the difficult and precarious path of improving our war material, to be, above all things, simple and practical. As Frederick the Great said, “ What is not simple is not possible in war.” Weapons of war may be conveniently grouped into three main classes* : — 1. Portable Arms. 2. Artillery. S. Special Instruments of Warfare. Each of these classes admits of further and almost indefinite subdivision. We will proceed to consider them separately, under their particular heads. I. PORTABLE ARMS. Under this head are included all weapons which are borne upon a man’s person. They are of two principal divisions : — (1.) Side-arms. (2.) Fire-arms. (1.) Under the head of side-arms are included swords, spears, lances, daggers, bayonets, pikes, javelins, arrows, and the like. The class is really a more comprehensive one than many persons suppose. The great advances made with fire-arms must be acknowledged to tend to push such weapons as swords and bayonets into a more subordinate position. If you can kill your enemy a mile off, the prospects of his being able to close with you are evidently less than when the range of your weapons was only a few score yards. Similarly, the great increase in the rapidity of fire of modern fire-arms renders less possible a successful charge of cavalry upon an infantry line or square, and by so much reduces the value of the sabre or the lance. But these considerations, which are perfectly just in themselves, have been pushed too far by theorists, and many have hastily and improperly jumped to the conclusion that the days of the bayonet and sword are gone by. To this the experience of the Franco-Prussian war furnished an * The classes have been placed in the above order because that order is, to some extent, historical, and indicates roughly where the most ancient and most modern contrivances will generally be found. PROJECTION. emphatic contradiction. It is quite clear that despite the im- provements in fire-arms, hand-weapons still possess consider- able importance — that they may even determine the crisis of a stubborn fight. If an obstinate enemy cannot be dislodged from his entrenchments by a musketry or artillery fire, against which his defences may afford him ample protection, he must be driven out with the bayonet, at whatever cost, and this was actually done more than once in the war already alluded to; while, although cavalry may no longer be employed to ride down infantry squares, they will still be required to sweep over the fields of battle, to complete a disorganisation already com- menced, to convert a retreat into a rout, to drive home the wedge which the rifle and cannon have inserted. Here, there- fore, we see a continued use for the bayonet, the sword, and the lance ; and, accordingly, we find all those weapons retaining their place in the British service. There are a considerable variety of swords in use in our army — the whole being made at the Eoyal Small Arms Factory at Enfield. The principal types of swords are those for the cavalry, and the navy cutlass. Of the other ten sorts of swords enumerated in the official vocabulary, the greater part are for serjeants, for Highland regiments, for volunteer non-com- missioned officers, etc. Pioneers have a sword with a saw- back, which is found useful in sawing through wood, removing obstacles, and doing some of the special work which pioneers are required to perform. It is noticeable that there is a grow- ing tendency to utilise hand- weapons for more than one purpose. This is perhaps a natural result of the decreased importance of these weapons for the particular purpose to fulfil which they were originally introduced. We thus find that the latest pattern of bayonet— that which has been proposed for use with the Martini-Henry rifle — is at once a sword, a saw, and a bayonet. This weapon has been favourably reported upon. It serves to saw fire-wood on an ■emergency ; it may be useful for clearing away light obstacles ; it gives the infantry soldier what the simple bayonet does not, an efficient hand-weapon for personal defence or attack. This is a more useful combination than that which has been proposed by some inventors— viz., to combine in one a spade or trowel and a bayonet, or to make the bayonet so broad and flat that it could be worn round the neck as a piece of defensive armour for the breast. We have seen specimens of both these weapons, and "have recognised in them the handiwork of the unpractical inventor. If the bayonet is to be utilised for more than one purpose, the best combination is undoubtedly that described above — of a sword, a saw, and a bayonet, the handle serving to attach it to the barrel of the rifle. Some of the best — probably the best — swords in Europe are manufactured at Solingen, in Rhenish Prussia. Not less re- markable than the excellence of these weapons and their fine temper, is their cheapness. An infantry officer’s regulation sword, with scabbard complete, can be bought at Solingen for something under =£1 ; an artillery officer’s sword for about a guinea. If purchased of good London makers, these weapons cost from =£4 to £5 ; but the London swords, the blades for which are generally obtained from Birmingham, are in no respect better than those made at Solingen. Visitors to the Paris Exhibition of 1867 will not readily forget the magnificent exhibition of sword cutlery furnished by M. Carl Reinh Kirsclibaum, of Solingen, and which, although surpassed in decorative excellence by some of the French makers, whose highly ornamental and costly swords are rather examples of goldsmiths’ than of cutlers’ work, was unequalled for solid excellence and cheapness by any swords in the Exhibition. The Solingen makers prefer cast steel to damascened blades ; the introduction of the iron by which the damascened appearance is produced being considered apt to soften the sword and spoil its high character, which is estimated in a great degree by the just and complete “return” of a blade after bending. All sword- makers are very far from agreed upon this point. By some it is thought that the extent to which a sword will bend is even more important than its perfectly accurate return to straight- ness after bending. On this point the following remarks occur in the official report on the “ Portable Arms ” in the Paris Exhibition : — - “The power which a blade may have of straightening again is accepted by the Solingen makers almost as a crucial test of its excellence ; and when a sword is bent to a point beyond which it can return perfectly straight, they would almost prefer it to break than that it should exhibit softness and remain crooked. On the other hgmd, it is argued by some that, although it is well that a sword should straighten, it is better that it should remain permanently bent than that it should break, a bent sword being more serviceable than a broken one ; and the Solingen makers are considered to lay undue stress upon the straightening qualities of the sword. As, however, the flexibility of a blade depends, after its quality, upon its transverse section, and as Solingen exhibits swords which will bend almost round a man’s body, it would seem as though all the flexibility that could possibly be desired can be obtained without any admixture of iron. When a Solingen maker says he prefers that his sword if it be bent beyond what it is capable of standing — should break rather than remain crooked, the burden of proof rests upon others of showing what useful purpose would be served by making a blade capable of bending further at the expense of some softness.” Next to the sword and the bayonet — weapons which we have seen are coming, in the hand of the infantry soldier, to be com- bined — the lance is the most important of military hand- weapons. Skilfully used, the lance is a most formidable weapon ; unskilfully used, it becomes a terrible encumbrance. In India the lance is largely employed. It is peculiarly useful in pursuits or in isolated combats. A few years ago, the bamboo staff was adopted for the lance of the British soldier, as being lighter than ash. Of the head of the lance there is not much to be said, except that it should be made of a good quality of steel, and of a form favourable to inflicting a serious wound. In the British service, the triangular head is preferred to the simple conical point. It is unnecessary, we think, to dwell at any greater length upon the subject of weapons of the sword and lance class ; nor is it worth while to touch upon the assegais of Africa, the arrows of the Indian, or the javelins and spears still in vogue among some of the ruder nations. The consideration of these weapons can have no practical value. They are interesting rather from an antiquarian point of view, and as so many examples of the ingenuity of man in producing a large variety of means of attack and defence. The projectile weapons — such as the javelin, the djerid, and the arrow — have completely lost their importance now that fire-arms have reached so high a pitch of development, and can be procured even by the poorest and most savage nations. Even hand-arms proper, such as swords, lances, and bayonets, have faded into a subordinate and wholly secondary position, alth®ugh, for special purposes, they must ever retain a certain value. But we must hasten oa to the more interesting branch of our subject, and to the consideration of fire-arms, about which we shall have much to say. PROJECTION.— I. INTKODU CTION. In the Lessons in Plane Geometry given in the Popular Educator, the figures treated of are such as possess length and breadth only, these figures being considered as traced upon a flat surface, called a plane, thus showing their exact forms as they are really known to be. In these papers we shall treat of the delineation of Solids — that is, bodies which possess not only length and breadth, but thickness as well ; and the science by which lines are so disposed that the representation of the object may seem to stand out, or project, from the flat surface of the paper, is called Projection, which is a branch of Solid or Descriptive Geometry. The subject may be divided into — Orthographic Projection, by means of which objects are pro- jected by parallel lines from given plans, elevations, or other data, the object being placed in any given position. Isometrical* Projection, by means of which a view of an object is projected at one definite angle, a uniform scale, pro- portionate to the real measurement, being retained throughout. Perspective, by which objects are drawn as they appear to the eye of the spectator from any point of view that may be selected. * From two Greek words, meaning equal measures. 8 THE TECHNICAL EDUCATOR The present course of lessons will embrace the whole of these divisions ; combining also the mode of obtaining required sec- tions, the methods of describing the peculiar curves generated by one solid body intersecting or penetrating another, and the development of surfaces — that is, the construction of the exact shape to which a metal plate or other material is to be cut, so as to form or cover the required object in the most ready and accurate manner, and with the least waste — a branch which will be further considered in subsequent studies, devoted to the technical drawing adapted to the requirements of the metal plate-worker, boiler-maker, and tinman. The lessons are given in as simple a manner as possible, so that the student may be able to follow them with interest, and may be led to desire still further instruction than is here afforded ; and it is hoped that the pleasure and benefit he receives from knowledge may awaken ELEMENTARY PRINCIPLES OF PROJECTION. Fig. 1. — If we place two planes or surfaces at right angles to each other, so as to form a floor and a wall, the floor, A B, is called the horizontal, and the wall, c d, the vertical, planes of projection. THE PROJECTION OP LINES. No. 1. — Let us take a piece of wire, and fix it in an upright position, a b, then the point on which the wire rests is called the horizontal projection, or plan; and if we carry lines directly back from its extremities until they cut the vertical plane in c and d, the line c d is the vertical projection or elevation of the wire. No. 2. — If a wire, e /, be fixed at right angles to the vertical plane, the point/, in which it is fixed, is the elevation, being in him that spirit of enthusiasm which is the mainspring of ail progress. It has been from the want of enthusiasm that our workmen have been content with the small amount of know- ledge which they have obtained from their “ mates in the shop. It has been this apathy which has caused so many to be satisfied with the “ rule of thumb” instead of the rule of science. It is not the province of these lessons to dilate on the natural history of enthusiasm ; but our object is to warm up the spirit of our fellow-countrymen — to convince them that, if they will but study the principles of the sciences on which their trades are based, they will, with their acknowledged manual superiority, hold their own against the men of every country in the world. Let us, therefore, interpret interest in their occupation to imply enthusiasm ; and let us translate enthusiasm to mean that spirit which urges every man to do his worlc as well as it can possibly be done, and to develop the mental powers with which his Creator has endowed him to their fullest extent, so that when he leaves the workshop of life he may, in the words of Longfellow, leave “ footprints in the sands of time.” the view which would be obtained if the model were placed ok an exact level with the eye, the point e being immediately opposite the spectator, so that the end only of the wire could be seen. If now perpendiculars are dropped from e and / until they meet the horizontal plane in g and h, the line uniting g and h will be the plan of the wire, or the view obtained by looking straight down on it. It must be remembered that in projection the visual rays are supposed to be parallel to each other, and not convergent* as in pictorial perspective. Further, if we suppose a wire, i j, to be suspended in space, perpendiculars dropped from its extremities to cut the hori- zontal plane will give the plan Tel; then, if lines be drawn from k and l to meet the vertical plane in to and n, and perpen- diculars be raised from these points, intersected by lines drawn from the ends of the wire parallel to k m and l n, the points o and p will be obtained, and the line joining thesj will be the elevation of the wire i j. * Convergent. From con, with, and vergo, to incline (Latin). Arising in various points, and approaching each other until they meet. PROJECTION. 9 In the model used for illustrating this lesson, the vertical and horizontal planes are connected by hinges, and are kept at right angles to each other by means of a brass loop. If now the wires be removed, and the pin, r, be withdrawn, so as to allow the plane, C D, to fall backwards, the two planes of pro- jection will form one surface, separated only by the line I L (Fig. 2), and the plans and elevations will be seen in the posi- tions in which they are placed in projection. The line separating the two planes is called the intersecting line, and will be lettered i l throughout these lessons. It must be borne in mind that the plan of an object does not mean merely the piece of ground it stands upon, but the space it overhangs as well : thus, the piece of ground on which the small lodge (Fig. 3) would stand, is represented by the dotted square in the plan, whilst the true space which the build- ing covers or overhangs is represented by the outer square. It will be seen that in all the figures hitherto shown the lengths of the plans and the heights of the elevations are the same as the heights and lengths of the objects they represent ; thus c d is the same length as a b, and k l and o p are the same length as i j ; but plans are not always the size, nor are eleva- tions always the full height, of the object, both being dependent on the position or angle in which the subject to be drawn is i l. From d drop a perpendicular to cut this line ; then a e is the plan of b d in the position in which it is now placed (viz., parallel to the vertical, and inclined at 60° to the horizontal plane) ; and if the movement of the wire were continued until it reached / (it would then be parallel to both planes), the plan would be the same line extended to g. The line b d is said to be placed at a simple angle, because it is inclined to one plane, but remains parallel to the other. Let us now suppose the wire fixed in this slanting position, as far as its inclination to the horizontal plane is concerned — but if the whole hinge is made to rotate on a pivot, so that, without alter- ing the slant, the end d may be turned forward — the line will then be at a compound angle, that is, it will be inclined, or slanting, to both planes. Now it will be remembered, that although we have turned the wire round, we have not altered its slant to the horizontal plane ; it will therefore overhang a piece of ground of exactly the same shape and size as it did in Fig. 4 ; but the position of that space will be changed. Let us now assume that, in addition to the wire being inclined at 60° to the horizontal, it is required to slant at 452 to the vertical plane. Place the plan, hi (Fig. 5), at 45° to the intersecting line, and draw perpendiculars from its extremities ; the line from h will cut the intersecting line iri placed. Before proceeding to treat of the changes which lines undergo by alteration of position, it is necessary that the terms used to define such positions should be understood, and for this purpose we again refer to Figs. 1 and 2. Here we have the line a b standing upright on the floor of the model, and as its distance from the wall is the same through- out its entire length, it is said to be at right angles (or perpen- dicular) to the horizontal, and parallel to the vertical plane. The line ef is said to be at right angles to the vertical, and parallel to the horizontal plane ; and it is evident that the line i j is parallel to both planes. It will be seen that whilst the plan of a line when standing upright is a mere point (Fig. 2, a), the plan of the same line when placed horizontally, as 7c l, is the full length of the original. Figs. 7, 8, 9, and 10 will account for this difference, and will show how the length of the plan is dependent on the angle at which the line is inclined. Let the original position of a wire (Fig. 4) be perfectly upright, then its plan will be the point a, and its elevation the line b c. Now, if this wire be made to work on a hinge-joint at b, and if the end c be moved from left to right, as from c to d, the end d being kept the same distance from the wall of the model, the wire will still be parallel to the vertical, but inclined to the horizontal plane (of course it may be inclined at any angle ; in this case it is at 60°). To find the plan of this wire, draw a line from a, parallel to j, and will give the base of the line. To find its height, we must remember that, although we turned the wire round, we did not alter its slant, and therefore the height of the end d remains the same as it was ; so that an horizontal line being drawn from d (Fig. 4), to meet the perpendicular drawn from i in the point fe, the line j k will be the projection of the wire inclined to both planes at the required angles. It will be seen that in this case both plan and elevation are shorter than the line itself. Exercise. — To find the real length of a line when it is inclined to both planes, and its plan, h i, and the height of the end is given. Draw a line, i l, at right angles to h i, and make it equal to the given height. Then the line h l will be the real length; for the plan, the original line, and a perpendicular dropped from its end form a right-angled triangle ; and this triangle, instead of standing upright, as in Fig. 4, is placed horizontally in Fig. 5 ; and the line h l will thus be found to be of the same length as b d. This may be illustrated by holding a set-square vertically, and rotating it on its edge until it lies on the horizontal plane ; the real length of the long edge (or hypothenuse), which when the set-square was vertical was repre- sented by its plan, h i, will then become visible. Fig. 6. — Again, it has been shown that if a wire were fixed at o, at right angles to the vertical and parallel to the hori- zontal plane, its plan would be m n, and its elevation the point o ; and if it were rotated on the point n until it became parallel to I l, its plan would be n p, and its elevation oq; 10 THE TECHNICAL EDUCATOR. but, on tbe principle shown in Pigs. 4 and 5, it will be evident that if the wire be rotated only as far as r, the elevation of it will be the line o s. PROJECTION OF PLANES OR SURFACES. The same laws which guide the projection of single lines will also govern the delineation of planes, which are flat surfaces bounded by lines. Let abed (Fig. 7) be a metal plate, the surface of which is parallel to the vertical and perpendicular to the horizontal plane : its plan will then be the line o' b' . If now this plane be turned, so as to be at right angles to both planes, its plan — that is, the line oil which it would stand — - will be a’ b' (Fig. 8), and its elevation the line a" c", or the view obtained when looking straight at the long edge. Now let this plane rotate on the line a” c", as a door on its binges, until the plan reaches b", then a perpendicular drawn from b' will give the rectangle a" c" b'" d'", which will be the projection of the plane, when perpendicular to the horizontal and inclined to the vertical plane, the height remaining unaltered. The other rectangles show the projections of the plane when further rotated. Fig. 9 . — In this figure the plane again rests on a b, its edge, b d, only being visible in the elevation ; but this edge hides the opposite one, which is parallel to it, and therefore the points a and c" are immediately at the back of, or “ beyond,” b d. Let us now rotate the plane on a b, as in closing a box-lid or trap- door, then the plan of the plane will be the rectangle a b c" d" ; and the more the plane is lowered, the longer the plan will become, as is shown at e and/. Notwithstanding the slanting direction which the plane has assumed in relation to the hori- zontal plane, it still remains at right angles to the vertical plane. This is shown in the plan, where the lines a b and c' d", which represent the upper and lower edge of the plane, are per- pendicular to i l. Let us now place the plane at a compound angle ; this will be done by rotating the plan ( carefully lettered, a& in Fig. 9) ; then, perpendiculars drawn from each of the points, intersected by horizontal lines from the corresponding points in the elevation, will give the required projection. The process is so plainly shown in the illustration (Fig. 10) that it is believed further explanation will be unnecessary. The student is urgently recommended not to be content with simple copying the diagrams herein given, which are merely to be considered as illustrations of principles ; and thus, unless those principles be understood and applied, nothing will be gained. He is therefore advised to vary the form of the plane, •and to project it at various angles. MINERAL COMMERCIAL PRODUCTS.— I. INTRODUCTION— MINERAL RAW PRODUCE. While we are indebted to the animal and vegetable worlds for a vast variety of useful products used for food, clothing, medi- cine, the constructive arts, and a countless number of other purposes, it is from the mineral kingdom that we obtain our coal, iron, building stone, precious metals, salt, etc. Of the uses of these and other mineral commercial products named in the annexed table, it is our purpose to give some account in this and subsequent lessons in this important subject. Mineral raw produce may be conveniently divided and considered as follows : — I. Metals and Metalliferous Minerals. Iron : Magnetic iron ore, titaniferous iron ore, red haema- tite, brown hcematite, spathic ores, clay ironstones, other ores. Process of smelting, puddling, etc. ; steel, supply of iron. Gold, silver, quicksilver, platinum, tin, copper, lead, zinc, aluminum, antimony, bismuth, cobalt, arsenic, manganese, chromium {with their chief ores, uses, locali- ties, etc.). II. Earthy Minerals. (a) Coals and allied Substances. Coal : Lignite, bituminous coal, steam coal, anthracite. Supply of coal. Jet, amber, naphtha, petroleum, asphalt, mineral pitch. (b) Limestones, Limes, and Cements. Common limestones, ornamental limestones, and so-called marbles ; marble, coral limestone, marl, calcareous sand, gypsum ; composition of limes, stuccoes, and cements. (c) Siliceous and Felspathic Substances. Bock crystal, quartz, and flint ; sandstones, paving, mill, and building stones ; siliceous sands, rottenstone, Bath bricks, Tripoli powder, Bilin powder, berg-mehl, tellurine. (d) Igneous and Metamorphic Rocks. Granites : Syenite, mica, talc, asbestos, serpentine, basaltic rocks ; greenstone, whinstone, trap, lava, obsidian, pumice- stone, pozzuolano, and trass. (e) Clays and allied Substances. Common clay, yellow, brown, and blue ; kaolin and pe- tuntse, pipe clay, fire clays, Stourbridge clay, fuller’s earth, red and yellow ochres, slates, hone stones. (/) Earths of Sodium, Potassium, Boron, Sulphur, etc. Common salt, rock salt, soda, chlorine, alum, natron, borax, saltpetre or nitre, cubic nitre, heavy spar, celestine, strontianite, fluor spar, sulphur, sulphuric acid, graphite or plumbago ; mineral manures, phosphates of lime. ( g ) Precious Stones. 1 . Carbonaceous : diamond. 2. Aluminous .- ruby, sapphire, emerald, topaz, corundum, garnet, beryl. 3. Siliceous : amethyst, Cairngorm stone, agate, sardonyx, opal, chalcedony, carnelian, jasper, lapis-lazuli, turquoise. 1.— METALS. IRON. This valuable and indispensable metal is, in a variety of forms, almost universally diffused throughout the earth. It is of incalculable use in all the appliances of modem civilisation — in machinery of every description, instruments, implements, and tools of all kinds ; architecture and domestic fittings and utensils ; conveyance, both inland and maritime ; apparatus for warming, lighting, and water supply ; and even in medicine, to impart renewed vigour to the failing human frame. It occurs in all parts of the earth, in all geological formations, to which it contributes a great part of their colouring matter; it is found in all spring and river waters ; and it enters into the composition of both plants and animals. It is present, too, as the principal ingredient, in the extraordinary fragments called meteoric stones, and is thus a constituent of worlds beyond our own. It can be melted and cast into moulds, softened, and hammered out into plates, drawn out into bars and wires, tem- pered to almost any degree of flexibility, hardened so as to scratch glass, and sharpened to the keenest cutting edge. In some of its natural forms, and also when heated to redness, iron is highly magnetic. Pure iron is white, or greyish-white, lustrous, soft, and tough, and it is one of the most infusible of metals (fusible at 3,480° Fahr.). Its specific gravity is 7'84. When beaten out it appears granular in structure ; when drawn, fibrous ; and to this latter peculiarity is attributed its extra- ordinary tenacity. Metallic iron as it occurs in meteoric stones is usually alloyed with nickel and other metals, but its occurrence as terrestrial native iron is doubtful. There are many minerals containing iron, but of these only the oxides and carbonates are so used by the smelter ; they are magnetic iron or loadstone, specular and micaceous iron ores, the red and brown haematites, the spathose ore and the clay ironstones. The maximum development of iron ores appears to be in the palaeozoic rocks, the largest and richest deposits being con- tained in the Laurentian rocks of North America and Scandi- navia ; they are abundant in the Devonian rocks of Germany and south-west of England. The Carboniferous system is espe- cially marked by the presence of interstratified argillaceous carbonates, both in America and Europe. The celebrated kidney ore of Cumberland is found in Permian strata, the Secondary rocks are rich in bedded deposits of ironstone, and the Tertiary series yields limonites. Magnetic iron ore, or Magnetite, is the black oxide (Fe 3 0 4 , or FeO + Fe 2 0 3 ), and contains 72 ‘41 per cent, of iron. It occurs in many parts of the earth in huge masses, forming the substance of hills and even mountains, as in the mountain of Blagod, among the Urals, and in some hills of Swedish Lapland, Mexico, and Styria. In Canada magnetite is found abundantly in the gneiss and crystalline limestones constituting the Laurentian rocks ; it occurs in irregular beds, often of considerable thick- ness, in one instance as much as 200 feet. In the State of New York this mineral occupies the Valley of Adirondac and TECHNICAL DRAWING. 11 its neighbourhood for a mile in width and twenty miles in length. In our own country it occurs in Dartmoor, at Rose- dale, and in Antrim ; and it is found also in New Jersey, Penn- sylvania, Nova Scotia, and parts of the East Indies. This ore is not only the richest in pure metal, but furnishes also the finest qualities. It is remarkable, however, that some veins, without any apparent chemical difference, produce finer iron than others. The produce of the mines of Dannemora in Sweden is of the finest description, and is employed in the pro- duction of the highest class of steel. Magnetic iron ore occurs chiefly in veins and fissures in diorites or dolerites, or in inter- stratified masses in metamorphic rocks. Titaniferous iron ore contafhs proto- and per-oxide of iron, titanic acid (an oxygen compound of the metal titanium), and magnesia in variable proportions. The bar iron or steel made from titaniferous iron ore possesses unusual strength and a peculiar mottled appearance. This ore is chiefly employed with others to impart a high degree of toughness to the metal produced. Red haematite is a sesquioxide of iron (Fe 2 0,), with 70 per cent, of iron. It is distinguished from the less rich brown haematite by its red streak, that of the latter mineral being brown in colour. Red haematite is known by special names, according to its different varieties : — Specular iron ore, oligiste, or iron glance, is brilliant, hard, and distinctly crystallised. It is found in Elba, Brazil, etc. Micaceous iron ore is scaly, crystalline, loosely coherent, and similar to graphite in structure. It is met with in South Devon. Kidney ore is a hard botryoidal variety, devoid of lustre, such as that of Cumberland. Red ochre is a compact, earthy, and more or less clayey variety, and is usually employed in the preparation of red and yellow ochres and umbers. Red haematite occurs abundantly in England and Wales, and, being rich, is much used for mixing with the poorer ores of the coal formations in the process of smelting. The red ore is worked in Cumberland, at Ulverstone, in the Forest of Dean, Cornwall, North Wales, Ireland, Belgium, Nova Scotia, Elba, Sweden, Missouri, and the neighbourhood of Lake Superior. Brown iron ore or haematite consists essentially of three equi- valents of water united to two of peroxide of iron, or 2Fe 2 0 3 + 3H 2 0, and is compact and earthy. Gotliite is another hydrated oxide (Ee 2 0 3 + H 2 0), but it is crystallised. Both minerals are usually included in the smelter’s term “brown haematite,” and, though resembling the red in outward appearance, are distinguished by their brown streak. Bog-iron ores, and those deposited in the beds ©f lakes by the action of infusorial life, belong to this group of iron ores. Brown haematites are largely worked in the Carboniferous rocks of England and South Wales ; in the Lias of Oxfordshire, Northamptonshire, and Yorkshire; in the Lower Greensand near Devizes, and in Buckinghamshire ; in Oolitic strata in France, Bavaria, Wurtemburg, Luxemburg, etc. ; and in the Wealden rocks of the Boulonnais. Bog-iron ore is abundantly developed in North Germany, Sweden, Norway, Finland, and Canada. Siderite, spathose iron, or brown spar, is a carbonate of the protoxide of iron (FeO,CO„), or, commonly speaking, carbonate of iron. The spathic ores are sparry or crystalline, and are associated with varying quantities of carbonate of lime and of magnesia. Spathic ore, when pure, is white ; but it becomes reddish on exposure to the air. It is particularly abundant in Styria, where the mountain Erzberg, near Eisenerz, is capped by the mineral to a thickness varying from 200 to 600 feet ; in Carinthia and other parts of Austria ; at Siegen, in the Stahl- berg, or “ steel mountain ” (Rhenish Prussia) ; and in the United States (New York and Ohio). The principal English deposits are those of Weardale, in Durham ; Exmoor, Devon- shire ; and Brendon Hill, in Somersetshire. Clay ironstone is an amorphous argillaceous carbonate of iron, mixed with small quantities of lime and magnesia, and sometimes, as in the “ black band,” with bituminous matters. The poorest of the serviceable ores, they are, nevertheless, in Britain, the most important, furnishing nearly two-thirds of the total yield of iron. Being mostly connected with the Coal formations, they are cheaply worked, having in immediate proximity a plentiful supply of fuel and limestone for their reduction. There are . many varieties — that called the “black band” being among the most valuable, from the ease and cheapness with which the ore may be calcined, by burning it in heaps without any additional fuel. The ores are extensively worked in South Wales, Monmouth- shire, Shropshire, Staffordshire, Yorkshire, Derbyshire, Lanark- shire, Stirlingshire, County Antrim ; in Belgium, Silesia, United States, North China, Japan, India, Brazil, and Tasmania. Ireland has large deposits, which are not much worked. Clay ironstones are not confined to the Carboniferous rocks, but are extensively met with in the Lias, Oolite, and Wealden, and even among Tertiary rocks. Of this character are thefrich iron district of Cleveland, in Yorkshire, and similar deposits in France. TECHNICAL DRAWING.— I. INTRODUCTION. The practice of Drawing is of such paramount importance in the mechanical arts, that in addition to the scientific principles given under the titles of Practical Geometry, Projection, Per- spective, Building Construction, etc., a chapter devoted specially to Drawing applied to various trades will now be given in each weekly number of the Technical Educator. In these lessons the various methods of delineation of brickwork, timber con- structions, masonry, mechanism, screws, teeth of wheels, etc. etc., Will be given; the principles of construction and their application being in every case fully described. The course of lessons will be so arranged as to combine Linear and Freehand Drawing, whilst Object and Model Draw- ing will be combined with Perspective and Projection in another set of lessons, the first of which appears simultaneously with this. Each of these branches will be again divided and sub-divided, and thus, in Linear Drawing, foundations, piles, coffer-dams, wooden bridges, roofs, staircases, doors, gates, machines of various kinds, and steam-engines, with all their details enlarged, will form the subjects of lessons. Alternately with these will be given drawings of masons’ and bricklayers’ work, etc. etc. Mouldings, borders, scrolls, etc., the forms of tools, etc., form portions of the Freehand section; whilst practical instruction in the uses of mathematical instruments, and in the method of colouring drawings, will complete the course, which it is hoped will be found practically useful to the artisan, whatever may be his particular branch of industry. Some description of mathematical instruments lias already appeared in an early volume of the Popular Educator. It is therefore intended here to give instruction in the practical use of them. It must be understood, however, that it is only by constant practice that the power over the instruments is acquired ; and the student is therefore urged to rule lines of various thicknesses, to describe articles of different sizes, and to repeat the most elementary figures, first in pencil and then in Indian ink, so as to achieve that manual dexterity and refine- ment which are so necessary for the mechanical draughtsman. Let your paper be rather smaller than your drawing-board, so that the edges may not project. To fasten the paper down, wet the back, and then paste the edges to the board ; let it lie flat whilst drying. This is only necessary when the drawing is likely to be some time in hand . for exercises such as are con- tained in this volume, it will be sufficient to fasten the paper down by means of drawing-pins, which may be bought at one halfpenny each. The best T-squares are those where the blade is screwed over the butt-end, as in the illustra- tion (Fig. 1), as this allows of the “set-square” (or triangle) passing freely along ; whilst, when the blade is mortised into the butt-end, the set-square is stopped when it comes against the projecting edge. The T-square is to be worked against the left-hand edge of the drawing-board, and should be used for horizontal lines only —perpendiculars are best drawn by working the set-square, as above, against the T-square ; for if the T-square be used for perpendicular as well as horizontal lines, the slightest inaccu- 12 THE TECHNICAL EDUCATOR. racy in the truth of the edges of the board would prevent the lines being at right angles to each other. There is in some cases of mathematical instruments an implement called a “parallel rule,” made of two flat pieces of ebony or ivory, connected by two bars of brass. The student is not advised to use this in obtaining parallel lines, as, unless the instrument be in very good order, and very carefully used, the lines drawn will not be parallel. The best way to draw lines parallel to each other is by means of two set- squares.* Thus, let it be required to draw several lines parallel to A B (Fig. 2). Place the edge of one of your set- squares, c, against the line, and place the other set-square, D, against the first ; hold i> firmly down, and move C along the edge of D, and thus any number of parallel lines may be drawn ; and if lines at right angles to the parallels are required, it is only necessary to hold c, and place d on it, as shown in the dotted portion of the figure. In inking the drawings, use Indian ink, not writing ink, which rusts the steel of the instruments, and so destroys their refinement. Indian ink may be obtained from twopence the stick. If you intend inking the drawings, you must work the original pencilling very lightly. From the very onset aim at refinement, neatness, and abso- lute accuracy. Do not be satisfied if your work is nearly right. Try again, and, if necessary, again ; and, with in- creased care and perseverance, success will be the certain result. HOW TO USE MATHEMATICAL INSTRUMENTS. The most important instrument is the compass. A complete pair of compasses consists of the body of the instrument and three movable parts — viz., the steel, the pencil, and the inking- legs, which are fixed in their places either by a screw, or by the end of the leg fitting accurately into a socket in the end of the shorter leg of the compass, and kept in its place by a pro- jecting ledge, which runs in a slit in the upper side of the socket. This is by far the better method, and is used in nearly all modern instruments ; its advantages over the screw form are, first, that the movable leg only remains firm in its place as long as the thread of the screw is in good order, but the very force used to tighten the pressure wears the thread away, and then the leg shakes. The consequence of this can be very well imagined, when we remember that one of the leading purposes of compasses is to draw circles, for unless the leg be absolutely firm the circle will not be true, and the point of the pencil or inking-leg will not meet the starting-point, and so an ugly break will be caused ; and, secondly, that the screw, being but small, is very liable to be lost. Be careful that in drawing the movable legs out you do not wrench or bend them from side to side, with the view of getting them out more easily, for by that means you will widen the socket, and cause the instrument to work inaccurately : the proper way is to draw the leg straight out. The steel point is used when distances are to be accurately measured or divided, and therefore compasses which have both points of steel are called “ dividers.” A pair of these is found in most cases of instruments. The pencil-leg is used for drawing arcs, circles, etc. Be careful that you keep it exactly the same length as the steel one ; this is accomplished by drawing the pencil out a little after each sharpening. In very old-fashioned instruments the pencil is held in a split tube, which is tightened around it by means of a sliding ring ; but in those of modern make a short split tube is placed at the end of a solid leg, and the cheeks of this “cannon-leg” are tightened by a screw. This is by far the better construction, as by its means the pencil is not only more firmly held, but the points of the compass may be brought more closely together than in the older form. The use of the inking-leg (as its name implies) is to repeat * Get two set-squares (about sixpence each), the one having’ angles Of 45°, 45°, and 90 c , and the other 30°, 60°, 90°. the pencil-work in ink ; the ink must be Indian ink, as already mentioned, and it is advisable to mix a small quantity of indigo with it, as otherwise it has a tendency to turn brown. When you mix the Indian ink, do not rub it very hard, as by that means you roughen the edges, and break off small pieces— they may be small indeed (and do we not frequently find failures caused by very trifling obstacles?), but they work between the nibs of the pen, and cause roughnesses and irregularities of thickness which materially damage a drawing. On examining the inking-leg, you will find a joint in it. The purpose of this is to enable you to bend the leg at that point, so that the part which contains the ink may be kept perpen- dicular to the surface of the paper whilst describing a circle, for if the inking-leg were kept straight as the steel one, when the compass is opened to any extent, only one of the nibs (the inner one) will touch the paper, and thus the outer edge of the circle drawn wil'l be ragged and rough. In drawing circles, be careful to lean as lightly as possible on the steel point, so that your centre may -not be pricked through the paper, for then, as each concentric circle is drawn, the hole will become larger, until all chance of following the exact curve will be lost, and when you come to ink the drawing you will find the difficulty still further increased. “ Horn centres ” are sometimes used. These are small circular pieces of horn with three needle-points fixed in them ; one of these may be placed over the centre on the paper, and pressed down ; the horn being transparent, the centre-point will be visible through the small plate, and the steel point of the compass may be placed exactly over it. This is all very well in large drawings, and where the circles to be drawn are at some distance from the centre; but where numerous small circles, immediately surrounding the centre, are required, as in the projections of the sections of cones, the horn plate is useless, as it will cover some of the space on which circles are to be drawn ; and further, the point resting on it is raised above the surface on which the other is working, and in small circles this will be a disadvantage. The student is therefore reminded of the old adage, “ Prevention is better than cure,” and he is assured that if from the outset he en- deavours to lean lightly on the instrument, practice will soon place him beyond the necessity for the aid of the horn centre. The following hints will be found useful : — 1. See that the steel point of your compass is round, and not triangular, which latter form opens the little hole far more than the point would if it were round. 2. See that this point is not too thin ; it should be rather a blunt point than otherwise, only just sharp enough to prevent it slipping away from the centre. Should either of these two faults exist, they may be easily remedied by drawing the point a few times over an oil-stone, remembering to keep turning it round whilst moving it along. 3. Hold the compass loosely between the thumb and forefinger only, allowing the instrument to rest with equal weight on both points, and merely using the finger and thumb to support and guide it. When a circle is required of a larger radius than can be reached with the compass in its usual form, a “ lengthening- bar ’ ’ is used. This is an extra brass rod, which fits into the socket in the leg of the compass, and has at its other end a socket into which the end of the pencil or inking-leg fits. This forms a pair of compasses with one leg very much longer than the other, and which is, therefore, rather awkward to manage. Here again the student is reminded that the pencil-leg and inking-pen must be bent at the joint, so that they may be per- pendicular to the surface of the paper. The full-sized compass is, however, not well adapted for drawing small circles, and therefore a complete case of instru- ments contains the bow-pencil and the bow-pen. These are simply small pairs of compasses, the first of which has a pencil and the other an inking-leg. These will be found very useful, and may be purchased separately if not in the case. For still smaller purposes, “spring-bows” are used. These constitute in themselves a small set consisting of dividers, pencil, and inking-bows. The legs, instead of being united by a hinge-joint, are made in one piece, so as to form a spring, which by its action tends to force the points apart ; they are then acted upon by a nut, which, screwing upon a bar fixed in one leg and passing through the other, closes the legs in the most minute degree possible. These will be found of immense AGRICULTURAL CHEMISTRY. 13 service in the higher branches of mechanical and architectural drawing, where very small arcs and circles are required, as in the delineation of the teeth of wheels, mouldings, and other architectural details. Another important instrument is the drawing-pen, which is something like the inking-leg of the compasses already described ; it is, however, generally smaller in its nibs, and is fitted on to an ivory or ebony handle. The ink should be placed between the nibs by means of a camel’s-hair brush. The pen should be held nearly upright, with its flatter side next to the rule, the end of the middle finger resting on the head of the screw. Before you ink any line of your drawing, be careful to try your pen on another piece of paper, in order that you may ascertain whether the line drawn by the pen would be of the proper thickness, and if not the pen may be adjusted by means of the screw, which acts in a way similar to the screw on the spring-bows already described. Before putting your inking-leg or drawing-pen away, be sure to wipe it well, and finally to pass a piece of paper between the nibs, so as to remove any ink that may have dried, or any grit which may have been deposited. The rule, or straight-edge, which you use when inking your lines, must have a bevelled edge ; and further, the bevel must be turned downwards towards the paper. This will avoid any smearing which might occur if the edge of the rule were to touch the paper whilst the line is wet. Scales of different sorts are used in mechanical and archi- tectural drawing; but as the subject of the present lesson does not necessarily involve working “ to scale,” the uses and construction of these will be found appended to the lessons on the above-named sections of scientific drawing. The protractor, used in measuring and constructing angles, is described, and its uses explained, in the lessons in Practical Geo- metry (Popular Educator, Vol. I., page 113) ; repetition here is therefore unneces- sary, and we proceed to mention what are called “French curves” (Fig. 3). These are rules cut into an almost end- less variety of shapes, one of which is here shown : they are used in inking curves. To do this, you must turn your French curve about, until some part of it corresponds with the form already drawn in pencil, which may then be repeated in ink, the pen being guided by the French curve. If you cannot find any portion of your rule which will correspond with the whole of your pencilled curve, draw as much of it as you can, and then find the remainder at some other part of your French curve, or on another one. As these useful implements may be had in innumerable patterns, at a very moderate price, the student is advised to provide himself with two or three of them ; but the writer wishes it to be plainly understood that he does not imply that by means of French curves freehand drawing may be dispensed with. On the contrary, he urges this practice on all students ; for there is such variety of form in drawing, that no mechanical means can possibly supersede the necessity for the accurate and refined education of the eye which is obtained by that study ; and further, a little practice will enable students to draw many curves by hand in less time than it would take them to find their places on the French curve. AGRICULTURAL CHEMISTRY.— I. BY CHARLES A. CAMERON, M.D., PH.D., Professor of Hygiene in the Royal College of Surgeons, Ireland; Analyst to the City of Dublin ; Honorary Member of the New York State Agricultural Society, etc. etc. CHAPTER I.— ON THE ELEMENTARY CONSTITUENTS OF PLANTS. During recent years Agricultural Chemistry, like most of the other branches of experimental science, has made great and permanent progress. Not many years since it was regarded as a mere philosophical pursuit, which, however interesting the abstract truths revealed by it might be, afforded no useful information for the benefit of the practical farmer. Less than a quarter of a century ago, that distinguished agriculturist, Mr. Pusey, stated that husbandry was only indebted to Chemistry for a receipt for making bone manure and a suggestion to utilise flax-steepings as a fertilising agent. However unfounded such assertions may have been twenty-five years ago, it is now gene- rally conceded that Chemistry has conferred the most important and lasting benefits upon agriculture. It has thoroughly inves- tigated the composition of plants ; it has shed a flood of light upon those wonderful processes by which the vegetable mechanism organises into the most complex substances the lifeless mineral matters furnished by air, soil, and water ; and it has discovered inexhaustible sources of fertilising materials, with which the exhaustion of our heavily-taxed fields may be indefinitely post- poned. By its aid farmers are protected from fraud in the purchase of artificial manures and “artificial foods” for cattle. These are but examples of the benefits which Agricultural Chemistry has conferred upon the cultivator of the soil ; and those who would aspire to be really enlightened agriculturists should not remain ignorant of a science so intimately affecting their pursuit. In the following chapters we purpose describing the chemical history of the vegetable creation, in so far as it is of interest to agriculture. We shall endeavour to show how the plant grows, of what materials it is composed, and by what means its food is absorbed ; and we shall point out the conditions which, according to both theory and practice, are found to be most favourable for the full development of the cultivated plants. Finally, we shall consider the means by which vegetable sub- stances are re-organised into still higher combinations of matter - — into the meat, milk, and butter which constitute so large a portion of the food of man. At present the Chemistry of the feeding-house is of equal importance with the Chemistry of the field. The solid crust of the earth, so far as it is accessible to our research, the atmosphere which surrounds our globe, the waters which cover so large a portion of its surface, the innumerable vegetable forms which clothe and adorn the world, and the animals which find subsistence on its broad bosom, all have formed the subject of chemical investigation. Minerals, vege- tables, animals, all are found to be composed of a comparatively small number of substances, termed simple bodies, or elements. Chalk is a compound mineral substance. By analysing — that is, by decomposing — it, two other substances, termed lime and carbonic acid gas, can be extracted from it. By a further analysis, lime is resolvable into a white metal, called calcium, and a gas termed oxygen ; whilst from carbonic acid gas a solid substance — carbon or charcoal — and oxygen gas are obtainable. Chemical analysis shows us, therefore, that the compound mineral substance chalk is proximately a compound of lime and carbonic acid, and ultimately constituted of carbon, calcium, and oxygen. Carbon, calcium, and oxygen are regarded as simple, or elementary substances, because up to the present no chemist has succeeded in decomposing them. Whilst we can extract from chalk, oil of vitriol, nitre, bones, starch, flesh, and thousands of other articles, from two to nearly a score of different kinds of matter, we fail in procuring from oxygen anything save oxygen, from calcium anything save calcium, or from carbon any substance except carbon. There are known to exist sixty-three kinds of matter which resemble carbon and oxygen in being undecomposable. These are the raw materials with which Nature builds up her multitu- dinous structures. Some of them are found in a free or uncom- bined state — gold, oxygen, and nitrogen, for example — but the great majority always exist in combinations. Water is a com- pound of two elements — oxygen and hydrogen; oil of vitriol contains three — namely, oxygen, hydrogen, and sulphur ; alum is composed of four — aluminum, potassium, sulphur, and oxygen. A large proportion of the elements occur in very minute quan- tities, and at present we know not the functions which they perform in the economy of Nature. Four simple substances— oxygen, hydrogen, carbon, and nitrogen — constitute the atmo- sphere, water, nearly half of the weight of the crust of the globe, and by far the greater part of all animal and vegetable substances. About twenty-four of the elements form the familiar objects of every-day life, and of these the greater number are found in the organic kingdoms of Nature. The 14 THE TECHNICAL EDUCATOR. following elementary bodies have been found in vegetable sub- stances, but some of them are only occasionally and merely accidentally present : — ELEMENTS POUND IN PLANTS. Non-Metallic Elements. Oxygen Hydrogen Nitrogen Carbon Sulphur Phosphorus Silicon Chlorine Iodine Fluorine Bromine ) Essential. I J ( Essentialness j doubtful. Non-Essential. Metals. Potassium Calcium Magnesium Iron Sodium Lithium Manganese Caesium Rubidium Copper Lead Arsenic Zinc Titanium Barium >Essential. Essentialness doubtful. 1 y Non-Essential. J Oxygen is a colourless, odourless, flavourless gas, about eight hundred times lighter than water. It exists free in, and con- stitutes about one-fifth of, the atmosphere. Eight-ninths of the weight of water and more than one-third of the crust of the earth are made up of this element ; and it enters largely into the composition of animals and plants. This gas plays a prime part in the processes of combustion and respiration, the decay and dissolution of organic matter, and the decomposition of rocks. Nitrogen in a free state constitutes four-fifths of the atmo- sphere. In combination with other elements it forms the important manurial agents, ammonia and nitre. It is a con- stituent of a numerous class of organic bodies, termed nitro- genous or albuminous. In a free state, nitrogen cannot be burned, neither does it support combustion or respiration. Its chief function is to moderate the action of the atmospheric oxygen, which, in a pure or undiluted condition, would act too energetically in the processes of respiration and combustion. Nitrogen is without colour, flavour, or odour, and is a little lighter than oxygen. Hydrogen is a colourless, odourless, and flavourless gas, fourteen and a half times lighter than atmospheric air, and by far the least ponderable form of matter in Nature. It is very rarely found free. Hydrogen is inflammable, producing water by its combustion in air or oxygen. This element is an impor- tant constituent of plants, and is abundantly present in fats, oils, petroleum, and resins. Carbon is a solid body, which, in a crystalline state, constitutes the most costly substance in commerce— -the diamond. Lamp- black, charcoal, coke, anthracite, and blacklead are essentially carbon. At the highest attainable temperature, this element remains infusible so long as it does not combine with other elements. Heated to redness in presence of oxygen, it unites with that element, and produces carbonic acid gas. Carbon is the characteristic element of organic bodies, as it is invariably found in every substance elaborated under the influence of the vital powers. Sulphur is a yellow, inflammable solid, twice the weight of water. It occurs both . free and combined, but much more abundantly in the latter state. Iron pyrites, gypsum (plaster of Paris), and sulphate of barium contain sulphur. Certain compounds of sulphur with oxygen and metals are termed sulphates ; and some of these substances occur in soils, and furnish plants with the small proportion of sulphur which they require. Phosphorus is an extremely inflammable substance. In colour and consistency it resembles white wax. It is seven- tenths heavier than water. Exposed to the air, it unites slowly with oxygen, forming a compound termed phosphorous acid ; rapidly burned, it produces another compound with oxygen, which, under the name of phosphoric acid, is familiarly known to scientific agriculturists. This element is so inflammable that it cannot be handled without danger, and must be pre- served under water. Phosphorus is never found free. In soils it occurs chiefly in the form of phosphate of calcium (a com- pound of phosphorus, oxygen, and calcium), but even the most fertile land seldom contains more than a half per cent, of this compound. The amount of phosphorus in whole plants probably varies from about a fourth to less than a tenth per cent. ; and the proportion of phosphoric acid compounds in vegetable ashes to from 20 to 40 per cent. Sulphur com- pounds are less abundantly present. The six non-metallic bodies which we have described are invariably present in plants, and they are indispensable to vegetable existence. When a plant is burned, its carbon, uniting with oxygen, passes off under the form of carbonic acid ; and its hydrogen, combining with oxygen, is dissipated in the condition of water. The nitrogen in general combines with hydrogen, and produces ammonia, the “volatile alkali;” but occasionally a 'portion, or perhaps the whole, of the nitrogen, uniting with carbon, forms cyanogen, which generally remains as a solid ingredient of the incombustible part of the plant. The phosphorus and sulphur are, by combustion, generally con- verted into solid substances fixed in the fire ; but occasionally a little of the sulphur may be dissipated in the form of sul- phurous acid. The substances which remain after the combustion of the plant are termed its mineral or inorganic constituents, or its ashes. They contain phosphorus, sulphur, carbon, and oxygen (in an incombustible form, combined with metals), and the metals potassium, calcium, magnesium, and iron, beside other elements, the essentialness of which is open to doubt. There are also occasionally present elements which can hardly be regarded as other than accidental impurities. Potassium is a silvery-white metal, lighter than water. It rusts or oxidises the instant it is exposed to the air. In con- tact with any fluid containing oxygen, it burns with great brilliancy, evolving a rich violet light. In order, therefore, to preserve this metal, it must be covered with a layer of naphtha, a liquid which contains no oxygen. A compound of potassium with oxygen is well known under the term potash, or potassa. Potassium salts are very abundant in plants, constituting often more than half the weight of their ashes. We have made numerous attempts to grow plants in artificial soils destitute of potash, but they invariably failed, except in one instance, where rubidium, a metal which very closely resembles potassium, appeared to have been substituted for potassium. Under ordinary circumstances, however, potassium salts must be abundantly supplied to plants. Calcium is a white metal, the oxide (oxygen compound) of which is common lime. Chalk, marble, limestone (three forms of carbonate of calcium), and gypsum (sulphate of calcium) are calcium compounds. Lime constitutes from 10 to 20 per cent, of the mineral part of plants. Magnesium is a light white metal. It burns at a high tem- perature, evolving an extremely brilliant white light. Its oxide is the well-known earth magnesia. In the ashes of the seeds of plants, especially of the cereals, magnesia is abundantly pre- sent, sometimes amounting to 12 per cent. In the ashes of the whole plant, however, it seldom exceeds 4 or 5 per cent. , Iron, when pure, is a whitish metal, about seven times heavier than an equal volume of water. It unites with oxygen in four proportions, producing ferrous oxide (protoxide of iron), ferric oxide (per or red oxide), ferroso-ferric oxide (black or magnetic oxide), and ferric acid. Iron, we have no doubt, is an indis- pensable ingredient of plants. Kekule detected 3 per cent, of ferric oxide in the ash of gluten from wheat, and Gorup-Besanez found 68 pen cent, in the ash of the fruit envelope of the Trapa natans. Knop could not get maize to grow when utterly deprived of iron. In general, the amount of ferric oxide found in the ash of plants is under 1 per cent., and proportions ex- ceeding that amount are probably useless. Sodium is a whitish metal, very little lighter than water. It resembles potassium in many respects, but it does not quite so- rapidly tarnish as that metal. Its oxide is termed soda (sodic oxide), and its compound with oxygen and carbon is the well- known carbonate of soda — in modern chemical language, sodic carbonate. Common culinary salt is a compound of sodium with chlorine. Here we should explain that none of the metals, except small quantities of iron, found in plants occur in an uncombined state in Nature. Although sodium compounds are generally, and often very largely, present in plants, yet we are quite satisfied that this metal is neither indispensable nor useful to vegetables. The results of the experiments of Knop, Nobbe, Peligo, Siegert, and other chemists sustain this view. Our own experimentsj con- TECHNICAL EDUCATION ON THE CONTINENT. 15 ducted during several years, and performed with various species of plants, lead to the conclusion that sodium compounds are not requisite for the full development of plants (see Chemical News, May and June, 1862). On the other hand, Stohmann, the Prince of Salm-Horstmar, and other investigators, assert that sodium compounds are indispensable to plant life; though xhey have to admit that only the merest traces are often present m healthy and fully-matured plants. It may be said that as sodium compounds (common salt, for example) are indispensable to animal life, Nature would have furnished a sufficient supply of it, as well as of the other principles of food, through the agency of the vegetable kingdom. It must, however, be borne in mind that, with the exception of water, common salt is the only mineral food which animals use ; for every other food sub- stance is, directly or indirectly, derived from plants. If Nature intended that salt should be an indispensable constituent of vegetables, animals would not have been endowed with an in- stinctive longing for the mineral form of that substance. Lithium, cassium, and rubidium are three metals allied (especially the latter two) to potassium. They are widely dif- fused throughout Nature, but they occur in excessively minute quantities. We have found them in several vegetable substances, but they are not invariably present, and in all probability they are not essential ingredients of plants. Salm-Horstmar, how- ever, believes lithium to be useful in the flowering of certain plants. The remarkable resemblance between potassium and rubidium and their compounds renders it probable that the latter might be capable of replacing wholly or partially the former as an ingredient of plants. Manganese is a metal somewhat allied to iron, and often found associated with the latter. Salm-Horstmar believes the oxide of manganese to be an indispensable ingredient of plants. Such, however, is not our opinion, for we have often found whole plants completely free from even traces of this substance. The metals aluminum, barium, copper, lead, arsenic, zinc, and titanium have been detected in plants, but their presence therein must have been purely accidental. The non-metal, silicon— or rather its compound with oxygen, silica — is invariably found in all plants grown under natural conditions. Sachs, Nobbe, Knop, Siegert, Rautenberg, Stoh- mann, Kiihn, Birner, Lucanus, and others, have notwithstand- ing, grown plants of various kinds with perfect exclusion of silica, and apparently without injury to the plants. Pierre has proved that the common opinion, attributing the “laying” or “lodging” of corn to a deficiency of silica in the straw, is not founded on facts. It appears probable that, if silica be really requisite for plants, a very small proportion of it only is neces- sary. Silicon is a chemical curiosity, never being found in a free state. It occurs either as an olive-brown powder, or in the form of very hard brownish crystals. Its compound with oxygen is termed silica, silex, or silic acid. Rock-crystal is very pure silica ; in a less pure state silica exists as quartz, jasper, agate, and flint. Most rocks and soils are largely composed of silica. Chlorine gas is a yellowish-green, non-metallic body, possessed of a powerful and disagreeable odour. It is twice and a half the weight of atmospheric air. The bleaching and disinfecting properties of this gas — and of its compound, chloride of lime, or bleaching powder — are well known. Chlorine, united with potas- sium or sodium, is rarely, perhaps never, altogether absent from plants. Except in the case of marine and sea-side vegetables, it seldom constitutes more than 1 per cent, of the ashes of plants. Many of the most distinguished agricultural chemists assert that chlorine is not one of the necessary ingredients of cultivated plants. Iodine is a black, solid non-metal, about five times as heavy as water ; its odour somewhat resembles that of chlorine largely diluted. Its vapour possesses a splendid violet colour. In sea- side plants it is found in somewhat large proportions, and it is prepared from the ashes of sea- weeds. It rarely occurs in cultivated plants, and even in the case of marine vegetables we believe that it is not indispensable. Fluorine (a non-metal, as yet not satisfactorily isolated) is believed by Salm-Horstmar to be indispensable to vegetable life. It is, however, certain that the quantity of this element hitherto found in plants has been quite insignificant. Bromine (a liquid resembling in its chemical relations chlorine and iodine) has been detected in plants ; but there can be little doubt as to the accidental nature of its occurrence in the vege- table kingdom. With the exception of sulphur, all the non-metals found in plants exist naturally in combination with other elements, and it is only by means of the chemist’s art that these elements have been exhibited to us in their free or uncombined state. The average amount of carbon in dried plants is about 47 per cent.; of oxygen, 42 per cent.; of hydrogen, 6 per cent.; of nitrogen, 2§ per cent.; and of ashes, 2 4 per cent. TECHNICAL EDUCATION ON THE CONTINENT. — I. BY ELLIS A. DAVIDSON. TECHNICAL EDUCATION GENEEALLY. The purpose of the present series of papers is to give an account of the rise and progress of Technical Schools on the Continent, their systems of management, their courses of instruction, and such other particulars in connection with them as have been gleaned by personal inspection, correspon- dence with the professors, and from documents furnished by the local authorities of the various institutions. From a careful study of the general constitution of these important schools, from an investigation of the intellectual ground they cover, and from the facts, details, and results, which will be here presented, it is hoped that additional impetus may be derived in the promotion of technical educa- tion in this country. Before, however, entering upon the general consideration of the subject, it is necessary that the real meaning of the words “technical education” should be in some degree made clear. The term has been so bandied about, so misapplied, and so mis- understood, that many who really stand in need of such a. course of training are now asking, “ What is technical educa- tion ? ” Technical instruction, then, may be briefly defined as the application of the great principles of science to the various branches of industry ; it gives, in fact, a knowledge of practical science and art, adapted to the required purposes, and to the conditions imposed by the nature of the materials employed ; and it teaches the principles upon which the processes of working are based, of what nature soever the occupation of the worker may be. It will be seen, then, that technical instruction cannot be taken as a distinct and separate branch ; it must grow out of, and depend entirely upon, a sound elementary education, and a knowledge of the fundamental principles of science. To attempt technical instruction, therefore, without this basis is as absurd as to build and decorate a house without provision having been made for the security of the foundation. Taking up the subject, as we have only recently done in this country, after long years of neglect, we must do the best we can with our artisans whose elementary education is deficient, and whose time for study is necessarily very limited. The work requires, therefore, the earnest exertions of authors, in the compilation of text-books of such a character as shall teach the rudimentary principles of science and art, and also show their practical application in the simplest manner ; it requires the enterprise and energy of publishers, in the production of such works ; and it requires the greatest tact on the part of our lecturers and teachers, in popularising and simplifying those studies which their adult students have become accustomed to regard as abstruse and difficult, and which they consequently approach with fear and dread. These students require cheering and encouraging by the way ; they require that the obstacles and roughnesses which obstruct their path should be removed or smoothened down; they truly want “words to guide and hands to lead;” and it is to assist both teachers and pupils in this great work, that the lessons put forth in the Technical Educator, and in the Technical Manuals, have been compiled. As regards our youths, however— admitting the early age at which they are generally taken from school — a sound primary education is now within the reach of all ; and this will, it is hoped, be soon greatly improved, so as to become the basis for a higher system, to be carried out either in the day-schools or in the science classes which are happily spreading all over the country. 16 THE TECHNICAL EDUCATOR. With the view, then, of encouraging working men and others to take up the various branches of study promulgated in these pages, and in the hope of inducing them to give their children — for it is scarcely now a question of means — a sound primary education, as the best foundation for a technical course, the detailed plans of study on the Continent are given. At this stage no comment on these systems will be made, such being reserved until the programme of the studies of each Continental school and institute is before the reader. A comparison of these with the classes held in our mechanics’ institutions, with some exceptions, may, perhaps, furnish some food for reflection as to the failure of so many of these institutions in this country, whilst they flourish luxuriantly abroad. Before, however, we can fairly appreciate the value of the systems pursued on the Continent, and derive practical advan- tage of the knowledge gained, we must review the former and present position of technical instruction in England. It was immediately after the great International Exhibition ■of 1851 that Dr. Lyon Playfair published his report on the state of technical education on the Continent ; and in a communica- tion made more recently to Lord Taunton, on “ The Industrial Arts of Great Britain,” as exemplified in the Paris Exhibition of 1867, the learned professor states that, “ with very few excep- tions, a singular coincidence of opinion prevailed that our country had shown but little inventiveness, and made but little progress in the arts of industry since 1862.” All who are sensible of Dr. Playfair’s comprehensive know- ledge of the subject, his warm interest in everything that concerns the intellectual development of his fellow-creatures, and his unswerving truth, must feel grateful to him for thus calling public attention to a great national deficiency, and so enabling us to devise means which shall prevent our being intellectually lowered in the scale of nations, and which shall bring about a system of education so healthy and sound as to have a practical bearing on the trade, manufactures, and com- merce of our country. The Exhibition of 1851 showed us that in ornamental art as applied to manufactures we were behind other countries, and the notion obtained that we were essentially a nation of shop- keepers — a people devoid of taste ; but, on investigation, it soon became evident that we were not so deficient of taste as of art ■education. The Government Department of Practical Art was instituted, teachers were trained and spread over the length and breadth of the country, Art was made popular, and the application of its principles to trade purposes was shown. It is now admitted on all hands that the seeds thus broadly sown have fructified fairly, and that in the period which has since elapsed a great and permanent improvement has been made. Daily is this progress becoming more evident, and daily is the measure of success increasing, because, in addition to the Schools of Art, which are intended for youths and adults, the teaching of elementary freehand drawing, geometry, and model drawing has, since 1852, been actively carried on in most of our National and British Schools, by teachers who have been taught elementary practical art in the colleges in which they were trained, or by the masters and assistants of the neighbouring Schools of Art. And thus the system, because it begins at the root, and provides for primary instruction, prospers. These pupils grow up, they feed the classes in the art schools, and the result is a trained body of designers and art workmen, who are fast supplying the designs and executing the works which were formerly imported from abroad. It has, however, now become evident that a corresponding progress has not taken place in the scientific and mechanical branches of industry, and this must, no doubt, be attributed to the unpractioal character of the elementary education given in most of our primary and other schools, which renders much of the teaching of the science classes recently established unavail- ing to adult students, whose elementary education has been of such an inefficient character that many of them cannot follow or take notes of the clearest lecture, or spell even the simplest scientific terms ; and whilst some of them have learnt Euclid (from the book), they have never obtained any idea of the practical use of the study of Geometry. It is with the view, therefore, of showing how education, to be ultimately useful, must, from the very beginning, be of a defined character ; how the tendency of all teaching, from the moment that the tools to be used in the acquirement of know- ledge — reading, writing, and elementary arithmetic — have been mastered, should be such that every lesson may be a part and parcel of a course to be subsequently carried further — even as every brick, however low may be its situation in a wall, supports others in the superstructure — that the plans carried out in the different grades of schools on the Continent will be here described. Before, however, proceeding to show the courses of education open to working men and their children abroad, let us glance at the early instruction and apprenticeship of an English artisan. As a boy, he attends a National or British School, where he may be, and in most cases is, well taught by a man who is earnest, energetic, self-sacrificing, and conscientious. But the course of study and the standards of examination are fixed by the Education Office, and the income derived from that source is dependent on “ results.” The master cannot, therefore, afford that time should be devoted to other branches — in fact, some find it difficult to allow even one hour per week for draw- ing. Again, in many cases the masters are not competent to give a technical tendency to their teaching, their own education having been merely literary in its character ; some are, in fact, unacquainted with the commonest principles of construction and mechanism, although they may have read the science of Mechanics. Their own education having been purely theoretical, and as young men are appointed to schools in different parts of the country by the authorities of the training college in which they have resided, sometimes being posted in neighbourhoods wholly new to them, they are in most cases unacquainted with the processes carried on in the industries of the locality, whilst the elementary principles upon which these are founded should certainly form branches of study in the school. Elementary Chemistry, Geology, Metallurgy, Economic Botany, etc., are not amongst the subjects aimed at in our primary schools, and thus the children do not acquire a knowledge of the sources or qualities of the raw materials in which they may subsequently have to work. Even “object cases” do not form a general portion of school apparatus, and the lessons given on their contents are desultory and unsatisfactory. The natural and unavoidable consequences of such a state of things is that, excepting in some of our ragged and industrial schools, where gardening, shoemaking, tailoring, etc., are carried on as occupations — not as studies, but merely classed with wood-chopping — the boy leaves school without having received any notions of what may be called the theory of work, or of the sciences upon which the practical arts are based, thinking of Chemistry as a mysterious art by which the druggist com- pounds medicines, and naturally associating Physics therewith. He looks upon a locomotive as a machine which somehow or other pulls the train along ; and building is to his mind merely the work of the mason, bricklayer, and carpenter. As a rule, chance, not talent or predisposition, guides the placing of the boy in an occupation by which he is to earn a livelihood, the parents being naturally anxious to send their sons out, so that their earnings may assist in the maintenance of the family. Let us follow the boy, and see him placed in an engineer’s or railway works. He is in most cases merely an errand boy, or fag, being fit, in fact, for little else. He is subsequently posted in one of the departments, his instructor being the man under whom he works ; but this man having his own work to attend to, has not time to teach, and even were it not so he could only show the boy the manual operations. It is but rarely that a boy placed in such a position will have been able to acquire any of the scientific principles of his trade ; some bril- liant exceptions there are, of course, but this is the general rule. When the piece of work on which the apprentice has been engaged is finished, it has to pass the foreman of the depart- ment, generally a man who, through honesty, sobriety, and manipulative skill, has risen from the ranks of the workmen, and whose education has been of a character similar to those around him. The foreman’s duties, of course, leave him no time, even if he were competent, to give instruction, and thus the lad goes on. In time he becomes a journeyman — he may become a foreman, to govern others. Thus the “ rule of thumb ” — viz., each man working as his shopmates do — proceeds, and thus has ignorance of principles been carried on from one genera- tion to another. VEGETABLE COMMERCIAL PRODUCTS. 17 VEGETABLE COMMERCIAL PRODUCTS.— I. INTRODUCTION. A plant is only earth and air, transmuted into those nutrient principles which form the food of animals. Plants form the basis of organised life. In the great laboratory of Nature they are employed in supplying the atmosphere with oxygen, and in removing its carbonic acid. No true naturalist will speak of any portion of the vegetable world as useless weeds. But there are some plants which are especially useful to man, as sources of food, clothing, and medicine ; and others are very valuable, as furnishing building materials, barks, gums, resins, balsams, dyes, oils, and perfumes. These plants are found in different countries and climates, to which, by a wise arrange- ment of Providence, they have been restricted. It is natural and useful to inquire, “ From what countries are they brought ? What quantity of them is annually imported economic uses made of their products ?” Obviously, the pursuit of such inquiries must open a wide and in- structive field of research. Numerous as are the vege- table products, hitherto dis- covered, capable of utilisa- tion, they are few when com- pared with the inexhaustible wealth of Nature. Not a year but adds in this respect something to our knowledge. When public attention shall be fully directed to this sub- ject, an immense harvest will be reaped. Our limits will only admit of the discussion of the most valuable of them. They may be sub- divided into two groups — 1. Food Plants; 2. Industrial and Medicinal Plants. What are the POOD PLANTS. I. FARINACEOUS PLANTS. The grasses (natural order, Graminacece ) constitute one of the largest and most widely distributed of the natural orders of plants appearing in temperate cli- mates in numbers so vast that they form the principal mass of the verdure which covers the landscape. The grasses of tropical climates are generally much loftier than those of the temperate zones, less gregarious, and more tufted. We give the first consideration to the Cerealia, or corn plants, the caryopsis or grain of which contains an abundant farinaceous albumen, capable of great im- provement in quantity and quality. The Cerealia have been cultivated from the remotest antiquity, and were thought by i he ancients to be the gift of the goddess Ceres. Their native country is unknown, and they have been so changed by cultiva- tion, that we are ignorant, except in one or two plants, of the wild stock from which they are lineally descended. The Cerealia ot temperate climates include the European cultivated grasses, wheau, oats, barley, and rye; maize and rice are the chief cereals of the tropics. (a.) The Cerealia of Temperate Climates. Wheat (Triticum vulgar e, Linnaeus).— Wheat is the chief grain o temperate and sub-temperate climates. Its geographical range extends from 30° to 60° N. lat, and 30° to 40° S lat m the Eastern continent and Australia. Along the Atlantic portions of the Western continent the wheat region embraces the .ract lying between 30° and 50° N. lat. In the tropics 2— Vol. I. 1. KICK (OEYZA SATIVA). 2. MAIZE (ZEA MAYS). wheat is cultivated only in mountainous districts, where the land is sufficiently elevated to be of the proper temperature. It is estimated that in Great Britain 5,000,000 acres are annually covered with this grain. Wheat is imported into the United Kingdom chiefly from Europe and America. We get red and white wheat from Prussia and Austria, Spanish wheat from Bilbao, and Saxanka wheat from St. Petersburg. We also import largely from the United States, Turkey, and Egypt. The finest kind of European wheat is from Dantzic, the grain being large, white, and very thin-skinned. 34,645,569 cwt. of wheat were imported in 1867. The largest amounts were received from the southern parts of Russia, Prussia, and the United States. Wheat was formerly sown broadcast — that is, thrown from the hand of the sower over soil previously prepared by the plough. This is the most ancient mode. In modern times the plan of drilling or dibbling has been adopted — that is, depositing the seed in holes, formed in straight furrows at regular intervals. When wheat is crushed be- tween the stones of the mill, it is separated into two parts, the bran and the flour. The bran is the outside harder part or coating of the grain, which, intermingled with the flour, darkens its colour, and is generally sifted or bolted out to a greater or less extent. Bran is used for fattening the stock on the farm, and is of some commercial value in tanning, calico printing, for filling dolls, cushions, etc. The finest kind of bran is called middlings. Pollard is a coarse product of wheat from the mill, but finer than bran. The whole meal, or the mixture of flour and bran obtained by simply grinding the grain, is as nutritious as the grain itself ; and as bran is an alimentary sub- stance, and equal to one- fourth the weight of the whole grain, by its separa- tion much waste of whole- some food is caused. The great importance attached to bread perfectly white is a prejudice. Brown bread, made from the whole meal, should be adopted not merely on a principle of economy, but as containing the most nutriment. Flour is largely imported from California and other parts of the United States. We received in 1866, from all sources of supply, 4,972,280 cwt. ; but in 1867 only 3,592,969 cwt. Oats (Avena sativa, L.).— The oat is the hardiest of all the cereal plants, and one of the most elegant of grasses. It can be cultivated in countries where wheat and barley will not grow. Its adaptability to climate is so great that it is cultivated in Bengal as low as 25° N. lat., but it refuses to yield profitable crops as we approach the equator. The oat is cultivated in England, principally in the north and north-eastern counties and in most parts of Wales and Scotland. It grows luxuriantly in Australia, in Northern and Central Asia, in South America, and over the whole of the cultivated districts of North America. The meal of this grain is remarkable for its richness in gluten, and for containing more fatty matter than any other of the cereals. To these two circumstances it owes its nutritious and wholesome character. It is therefore very suitable, and much in use, as an article of diet for invalids. The variety called the potato-oat is a great favourite in Scotland, and is 18 THE TECHNICAL EDUCATOR. almost the only kind now cultivated there. Oatmeal forms a ] very considerable portion of the daily food of the Scotch, and oat- cakes are muck eaten in the northern counties of England. "VVe export no oats, as our domestic consumption is equal to the amount grown. The crop of this grain annually raised in the United Kingdom is twice as large as that of wheat. . The use of the oat is very ancient. It is not mentioned in the Bible, but it is alluded to by the Greek and Roman writers, Dioscorides and Pliny. Caligula is said to have fed his horses •with gilded oats ; but this report was probably an allusion to tho colour of the grain. 9,407,136 cwt. of oats were imported into the United Kingdom in 1867. The greatest quantities came from Russia, Sweden, and British North America. Barley (. Hordeum distichon, L.).— This grain is one of the staple crops of Northern Europe and Asia, growing as far north of the equator as 70°, and as far south of it as 42 , in favourable seasons and situations. In the New Worid its growth is chiefly confined to Mexico, the middle, western, and northern States, and Canada. In Asia, it is cultivated in the Himalayas and Thibet, replacing wheat in many districts, and producing admirable flour. Barley is chiefly used for malting and distilling purposes, in making beer and spirits. When tho outer coat of this grain is removed, it is called pearl barley, and in this form it is valuable for thickening broths and soups. _ Barley-water is a mucilaginous drink for invalids, made by boiling pearl barley .. About 10,000,000 quarters of barley are grown annually in the United Kingdom. Our imports of this grain in 1866 amounted to 8,433,863 cwt., but in 186/ to only 5,683,721. The greatest quantities were received from Denmark, Prussia, Prance, and Turkey proper. Barley is a very ancient article of human food. It is men- tioned in the Bible in the book of Exodus. It has been culti- vated in Egypt and Syria for more than 3,000 years. Pliny calls barley the most ancient food of man. It requires very little dressing when sent to the mill, having no husk, and con- sequently no bran. Rye ( Secale cereale, L.). — This is a highly nutritious gram, but not much raised in this country, except as green fodder for cattle. In Bohemia and most parts of Germany, however, rye forms the principal crop. It is also much cultivated in the north of Europe, and in Elanders, where, mixed with wheat, and sometimes with barley, it forms a leading article of sub- sistence. The peasantry of Sweden live very generally on rye- cakes, baking them only twice a year ; they are, therefore, the greater part of the time as hard as a board. Geographically, the diffusion of rye and barley is pretty much the same, as these plants generally grow in similar soils and situations. Rye-straw is useless as fodder for cattle, but forms excellent thatching material, and a superior article for stuffing horse- collars, so that saddlers will usually pay a good price for it. The amount of rye imported in 1866 was 368,392 cwt. Rye is much infested by a very poisonous fungus. When attacked in this manner, it is called in England “ horned rye,, and in Prance ergot, from a fancied resemblance to a cock s spur. The poisonous influence of this fungus extends not only to human beings, but insects settling on it are killed, and swine, poultry, and other animals, die miserably in strong convulsions, and with mortifying ulcers. Ergot of rye is, however, in the hands of a skilful physician, useful as a remedial agent. The principal granaries of Europe are Hungary, Russia. Moldavia, and Wallachia; and the chief ports for the exporta- tion of grain, Archangel, St. Petersburg, Riga, Konigsberg, Dantzic, Stettin, Rostock, Kiel, and Hamburg, in the north, and Taganrog, Kertch, Odessa, and Trieste, in the south. Large flour mills have been recently erected at Mayence on the Rhine, which is now a very important place for this branch of commerce. . ( b .) The Cerealia of Warm Chmates. Rice ( Oryza saliva., L.).- — This useful grass is a native of the East Indies, whence it has spread to all the warm parts of Asia, Africa, and America. It is a marsh plant, and grows very much like the oat, the grain hanging gracefully from the very- thin, hair-like pedicles, forming a loose panicle. Rice is culti- vated throughout the torrid zone, wherever there is a plentiful supply of water. Under favourable circumstances it matures on the Eastern continent as high as 45° N. latitude, and as low as 38° S. latitude. Its cultivation is principally confined to India, China, Japan, Ceylon, Italy, Madagascar, South Carolina, and Central America. The rice from the Southern States of America is decidedly the best, being much sweeter, larger, and better coloured than that- from Asia, where its cultivation is not so well managed. It is necessary to except Bengal rice, which now nearly equals that growing in the Carolinas. South Carolina produces the best American rice, and Patna the best East Indian variety. n*xcel- lent rice is also grown in tho Spanish provinces of Andalusia, Valencia, and Catalonia, as well as in the marshes of Upper Italy, especially Lombardy and Venice, and in the plains of Milan, Mantua, Verona, Parma, and Modena, along the river Po. In 1867 we imported 2,785,423 cwt. of rice, besides 44,943 qrs. in the husk. Most of our rice comes from the British and Dutch East Indies, tho Carolinas, Brazil, and Egypt. The Carolinas and Louisiana now produce annually about 800,000 cwt. of rice, of which 300,000 cwt. are exported mo, Charleston and New Orleans ; the Brazilian rice comes into commerce from Rio Janiero, and the Egyptian (500,000 cwt.) from the Delta of the Nile, via Damietta and Rosetta. Immense quantities of rice are consumed in England in the form of puddings and confectionery. The straw is plaited for bonnets. Rice-paper is not manufactured from this grain, but is the pith of a shrub called by the Chinese “ taccada, and by botanists Aralia papyrifera, L. The pith, carefully removed from the stem of this plant, is first cut spirally with a sharp knife, then unrolled, spread out, and pressed flat. This paper is much used by the Chinese for water-colour paintings o. insects and flowers. Rice, although regarded by us more as a cheap luxury than a necessary article of food, forms the chief subsistence of the Hindoos', Chinese, Japanese, and other Eastern nations. The Burmese and Siamese are the greatest consumers of this grain. A Malay labourer requires 56 pounds monthly ; but a Burmese or Siamese 64 pounds. The people of South Carolina do not consume much rice themselves ; they raise it principally to supply tho foreign demand, the swamps of that State — both those which are occasioned by the periodical visits of the tides, and those which arc caused by the inland flooding of the rivers being well suited to its production. The mountain-rices of India are grown without irrigation, at elevations of 3,000 to 6,000 feet above the level of the sea ; the dampness of the summer months compensating for the want of artificial moisture. Rice which comes to us in the husk is called by its Indian name “ paddy.” Before it can be used for food this liusk must be removed ; this is done in India amongst the poorer people by rubbing the grain between flat stones, and winnowing or blow- ing the husks away. Paddy is now imported into the United Kingdom in larger quantities than it used to be, though pre- ference is still given to rice in its shelled state. In 1856 32,694 qrs. of rice in husk were imported to 3,692,001 cwt. of shelled rice ; while in 1863 the relative proportions were only 152 qrs. of the former to 3,070,292 cwt. of the latter. In 1868 45,404 qrs. or about 252,308 cwt. of rice in husk were imported to 4,735,997 cwt. of shelled rice. The cultivation of rice undoubtedly dates from the oldest period of which we have any historical record. “ Cast thy bread upon the waters, for thou shalt find it after many days” (Eccles. xi. 1), evidently applies to rice, which in Egypt is always sown whilst the waters of the Nile still cover the land, the retreating floods leaving a rich deposit of thick alluvial silt, in which the rice vegetates luxuriantly. A spirituous liquor ( arrack ) is distilled from rice. , Maize, or Indian Corn (Zea Mays, L.). — This plant has a strong reedy-jointed stem, as thick as a _ broom-handle, with large alternate leaves springing from each joint. In favourable situations this stem attains a height of from seven to ten feet ; it terminates in a large compound panicle of male flowers called the tassel. The female flowers are situated below the male, and spring from the sides of the stem. They consist o ten or more rows of grains or caryopses, situated on the surlace of a thick cylindrical pithy axis or stem called the cob, from eight to ten inches in length. From each of these grains pro- ceeds a long hairy filament, the whole cob being enveloped by several layers of thin leaves, forming the husk or wrapper ihe filaments of the individual grains hang together in a thick cluster out of the husk, and are called the silk. The filaments receive the pollen or fertilising matter from the anthers of the t asset* AGRICULTURAL DRAINAGE AND IRRIGATION. 19 a fact easily proved by cutting off the tassel, when the ears prove abortive. After fertilisation, both tassel and silk dry up. Thi3 plant, when grown up to some height, usually sends out several suckers from the lower joints of its stem, which help to maintain its upright position, acting as props or buttresses. Maize may be raised on the American continent as far to the north and south of the equator as the 40th parallels of latitude, whilst in Europe its geographical range on either side of the equator extends even to 50° and 52°. Naturalists are at no loss to determine the native country of maize, which is undoubtedly America, as the Indians through- out the continent were engaged in its cultivation when the New World was first discovered. It now forms the staple grain crop of the United States and Mexico. Since the discovery of America, maize has been introduced into the Old World, and is now grown abundantly in Hungary, Transylvania, Moldavia, and Wallaehia. From these countries large quantities are annually sent down the Danube, via the Wallachian port and fortress of Galatz, into the Mediterranean as far as Malta, and Trieste. Maize is also largely grown in the countries around the Mediterranean, and in Southern Germany. It is raised in India, the East Indies, and in Australia ; in a word, in all those regions of the tropical and temperate zones where the white man has established himself. Like the other cereals, maize may be reduced to meal, the coat of the grain or bran remaining mixed with the flour. Owing to its deficiency in gluten it is not much used for making bread. In the United States, however, it is made into cakes, and eaten under the name of “ corn bread.” In this country it is not regarded with much favour as human food, although it is both sweet and nutritious. We import it largely from America, principally for feeding and fattening cattle. In the preparation called hominy, the grain is first soaked, and then exposed to a dry heat, which causes the bran or outer coat of the grain to crack and peel off, when it is easily separated. Pop-corn is another American preparation of maize made by slightly baking the unripe grains. The corn cobs form a very cheap and useful fuel. We imported in 1866 14,322,863 cwt., and in 1867 8,540,429 cwt. of maize, chiefly from the United States and the Turkish dominions. Guinea Coen, Dubra, or Turkish Millet ( Sorghum vulgare , Pers.). — A roundish grain, in shape not unlike maize, but not of greater bulk than a small grain of wheat ; its colour is a yellowish-white. It is borne in loose tufts or panicles ; the stalks are about eighteen inches to two feet in height, and when dry are very rigid ; in this state they are much used in the manufacture of carpet-brooms and whisks. The grain itself is chiefly used in this country for feeding poultry ; it is, however, strongly suspected that wheaten flour is not unfrequently adulterated with it, but this can only occasionally take place, as the importation of durra is very irregular. It is much used as food for the black population in the West Indies, whence it has been called negro corn ; they make of it cakes about an inch thick, which are white, and tolerably palatable. It is also used by the poorer peasants of Italy. We receive it chiefly from Northern Africa; it i3, however, cultivated largely in the United States, West and East Indies, and in Southern Europe. India is its native country.” (Archer’s “ Economic Botany,” p. 8.) AGRICULTURAL DRAINAGE AND IRRIGATION.— I. By Professor Wrightson, Royal Agricultural College, Cirencester. INTRODUCTION DEFINITIONS OF DRAINAGE AND IRRIGATION EARLY HISTORY OF THE SCIENCE. Agricultural drainage may be defined as the art of freeing land from superfluous water. In its more restricted sense it has reference to the improvement of land already under cultiva- tion ; in a more extended signification it includes the reclama- tion of land from the sea and the drainage of lakes and marshes. Viewed in connection with the natural drainage of the country by means of rivers, artificial drainage becomes of high import- ance is the art of improving natural outfalls ; and when used for this . purpose the term trunk drainage is applied, in contra- distinction to underground drainage, by which' is meant the more localised use of the art in draining wet soils. Although to the landowner or occupier the drainage of land surcharged with water by means of pipes may appear the more important,, yet the first place must be given to trunk drainage, since with- out a perfect river economy much of what is now available land would be a mere swamp. Rivers may, indeed, from the drainer’s point of view, be looked upon as gigantic “ main drains,” into which smaller streams, brooks, brooklets, and ditches, empty themselves. The series thus sketched out is rendered complete by the underground pipe drains laid in every furrow. The wholo system may, indeed, be compared to a tree, the smallest twigs of which are represented by the furrow drains : just as the sprigs gradually unite into larger twigs, branches, and boughs in passing to the trunk, so in the case of land drainage do we find drains discharging into water-courses, these again into brooks and streams, which finally add to the bulk of some im- portant river. Looking at drainage from this extended view, it at once assumes a national importance. Not only is it a means of enriching landlords and farmers, or giving an increased supply of food to the population, but it vitally affects the whole question of the water supply of the country. There is also the sanitary aspect of the drainage question, which adds to its inte- rest and importance. Of late years much attention has been given to urban drainage, and through the value of sewage as a manure there is a close connection between this section of the subject and agriculture, insomuch that the sewage question is keenly watched and discussed by agriculturists. The climate of large districts of the country is altered and improved by the drainer’s art, and instances are not wanting of certain diseases having disappeared from localities where drainage works have been extensively carried out. Hence, from an agricultural, national, and sanitary point of view, drainage is a subject of vast importance, and well deserves our close consideration. Irrigation may be spoken of as the art of carrying water on to- land in order to increase its fertility. This art has been prac- tised from the earliest historical times in all civilised countries. Water-meadows have been established in this country for hun- dreds of years, but of late public attention has been aroused to the importance of still further extending the area of land thus treated. Although drainage and irrigation appear at first sight to aim at two opposite objects — the first to take water from the land, and the second to cause water to flow into it — yet they must not be looked upon as antagonistic. It may, indeed, be readily shown that, while draining frees land from superfluous moisture, it is the means of causing a larger body of water than formerly to pass through any given section of the soil. The same rainfall descends upon the drained as upon the undrained field, but owing to the arrangement of underground channels there is in the former case no puddling of the surface, no trickling over the land into contiguous ditches, evaporation is checked, and the land is dry because the water has quickly passed through it. Drainage, therefore, is a means for altering the condition of water in the soil, rather than of depriving the soil of so valuable an element of fertility. By it a stagnant condition is changed into a state of movement, and the full advantages of the rain are realised. Without it the land is waterlogged, and showers which ought to find their way down to the roots of plants soak the surface and feed the neighbour- ing gutters. The benefit of irrigation may likewise be traced to the constant change of the water as it passes over the sur- face of the meadow, giving up its riches to the herbage over which it flows. Thus drainage and irrigation may be shown to have much in common, and the idea of their being opposed to each other may be dispelled. Nay, further, as a preparatory step in the formation of water-meadows, it is often considered advisable to under-drain the field, thus showing that the two operations, so far from neutralising, may assist each other in improving the same land. In considering such a subject as agricultural drainage and irrigation, we shall postpone the treatment of the latter for the present. Drainage may best be viewed, first, from a theoretical, and, secondly, from a practical point of view. After a few remarks on the history of the art, we shall proceed to the study of the theory of drainage, which comprises the reasons of its efficacy, and the study of the action of drains in soils of varying character. To thoroughly understand this part of our subject, considerable knowledge of Physics, Chemistry, and Geology is needed, all these sciences bearing directly upon it. The practice of drainage will include a description of the ■ various systems in vogue, a consideration of the materials fitted 20 THE TECHNICAL EDUCATOE. for underground channels, the modo of carrying on the work, the practical good effects which may be expected to follow the j operation, and the cost. I * In treating of the history of drainage we shall be brief. Those who wish to study this subject fully will find abundant j information, of a somewhat prosy character, in “The History of Embanking and Draining divers Fens and Marshes, both in Foreign Parts and in this Kingdom,” by William Dugdale, Esq., Norroy King-at-Arms. In this work the earliest accounts of drainage, from the draining, embankments, and outfalls used in the economy of Egyptian agriculture down to the Christian era, are given ; and the author cites the names of Mysis, Sesostris, Sabacon, Darius, Amasis, Alexander, the Ptolemies, Cleopatra, C'sesar Augustus, etc., as among the patrons of this useful art. To us it is more interesting to learn that the Belgic drainage works were commenced about j the year 863 A.D., by Baldwin I., son-in-law of the Emperor j Charles the Bold, who undertook the work of reclamation in j the neighbourhood of Bruges. We also find that a marsh i common law existed as early as 796 a.d. in this country, in j which powers for levying rates were conferred. In the reign of i Henry III. Henry de Batho framed ordinances which settled | the laws and customs of Romney Marsh on the occasion of a threatened irruption of the sea through the sea-wall. Such facts sufficiently demonstrate the antiquity of drainage and reclamation on a large scale. It is hardly necessary to trace tiio history of the gradual change of the fen lands of the •eastern counties from the home of fish and wild fowl to their present high value as corn-growing districts. The work has been accomplished by the individual energy of private individuals, by Dutch settlers, and by the powerful house of Bedford. In tracing the history of drainage we find that, although the art was understood and practised even in the most ancient times, the subject for improvement was always submerged or marshy land. If we seek for the origin of modern ideas upon drainage -we shall find little mention made of the drainage of land already under cultivation, as a further improvement, until comparatively recent times. This is well exemplified by the following quota- tion from the late Thomas Gisborne’s excellent essay on ■drainage, which first appeared as a contribution to the Quar- terly Review , and was afterwards revised and published with several other essays on agricultural subjects. After stating that the first phase of the controversy between agriculture and water might rather be described as the recovery of land than its improvement, he says: “ Two other cases remain in which water appears as an opponent of agriculture. The first is that in which l’ain, falling on pervious lands, filters through them and reappears in the shape of springs on the surface of lower lands not equally pervious, much to their injury. The second is the case of lands which, from closeness of texture, are not able to pass down the rain which falls upon them. The combat with these two cases marks two distinct eras in the history and progress of drainage.” We must view the adoption of covered drains as an improve- ment upon the more ancient and simple open ditch. Both plans are, however, old, and both were used by the Romans, as appears from the writings of Cato, Varro, Columella, Pliny, and Palladius. The energy of the Romans was, however, principally directed -a, gainst soils wet from springs, or the filtration of water from a higher level, and they do not appear to have attempted the im- provement of soils of a more tenacious character, wet from their own inherent imperviousness. In tracing the history of English drainage down to the present time, it is striking to note how completely the drainage of cul- tivated land is a modern notion. Fen lands and marshes were early reclaimed, and from time to time a note of warning was sounded, urging the importance of a more close attention to this means of utilising waste lands. Mr. Fitz Herbert, who wrote on agricultural topics in 1534, says, “There is none other remedy I for marry s ground but first to drain the water clean away, and j this has to be accomplished by means of open ditches, having j an outfall into larger or main ditches. “And,” says he, “if j this manner of ditching will not make the marsh ground dry, j then must you make a slough (drain or hollow ditch) underneath the earth ; and if that will not serve, then keep out your cattle for fear of drowning.” The earliest notice, says Mr. Gisborne, that we have of English draining is contained in a broadside in Vol. IV. of the “ Collection of Proclamations, etc.,” once belonging to James II., and now in the library of the Society of Antiquaries, London. “Herein,” says the writer, who dates from Paine’s End, No- vember 16, 1583, “is taught, even for the capacity of tlhe meanest, how to drain moores and all other wet grounds or bogges, and lay them dry for ever.” It is also directed that the drains should be shallow, arranged in a herring-bone pattern, and filled with stones. Captain Walter Blythe published his “ Improver Improved ” in 1640, and Andrew Yarranton (see page 22) wrote, in 1677 , “ Eng- land’s Improvement by Sea and Land.” Both were authorities on draining, and the former has been frequently quoted to show how little the last two centuries have done to improve the drainer’s art. Blythe describes in somewhat quaint language the essentials to success in draining wet soils, when he says, “ And for thy drayning trench it must be made so deepe, it go to the bottome of the cold spewing moyst water that feeds the flag and rush .... and a yard or four feet if ever thou wilt drain to purpose.” It would occupy too much space to quote more from a work interesting not only from its merit as an agricultural treatise, but also from its quaintness. In it we are recommended to use fagots of “ willow, alder, elm, or thorns, and lay in the bottom of thy works, or take great pebble stones, or flint stones, and so fill up the bottom of thy trench about fifteen inches high, and then, having covered it all over with earth, and made it even as thy other ground, wait,” says the gallant old Cromwellian, “ and expect a wonderfull effect through the blessing of God.” In 1727, R. Bradley, Professor of Botany in the University of Cambridge, gives us, in his “ Complete Body of Husbandry, some valuable information upon the then state of knowledge upon the question of land drainage. Good practical directions are given for open ditching and “ hollow ditching” (covered drains) ; but his attention appears to have been directed to the drainage of land “ which lies wet and is a kind of lake, so that one cannot tread upon it but the water feels like a quag under one’s feet.” Then follow directions, which resemble those given by Captain Blythe eighty years previously, but whose valuable work appears to have at that time sunk into obscurity. “ This improvement (drainage) is chiefly practised in Essex. . I have seen it at Navestock, on the forest, at an estate belonging to Aaron Hai’rington, Esquire, and it is lately brought from that part of the county to the north of Essex, about Wicken- Benant, and near Sir Kane James’s ; and I doubt not but will be generally used upon all the squally, wet grounds in England when it comes to be known, for it is but a late invention. I his author also describes the use of windmills in raising water from a dead level, as commonly seen in Lincolnshire and the fen county ; the Persian wheel and the syphon, or, as it is termed, the “crane,” is also described and figured as an appliance for lifting water over an embankment ; “ but,” adds the conscien- tious author, “ I canndt take this thought to myself no more than I have done any others that have been communicated to me. I received it from Mr. Harding, a very ingenious founder and master of mechanicks, near Cupid’s Stair, over against Summerset House, London” (even professors at Cambridge were not particular in their spelling one hundred and fifty years since). The next great luminary in the history of the art of agricultural drainage was Mr. Joseph Elkington, of Princo- thorpe, Warwickshire, who commenced farming in 1730. The principles upon which Elkington based his practice were not canable of extensive application, but under certain conditions of soil and subsoil they have been carried out with excellent results. We shall again have occasion to refer to this period when speaking of the practice of drainage. From 1797, the year in which Elkington’s system was given to the world by John Johnston, surveyor, in the form of a work, illustrated with numerous diagrams, down to 1823, little attention was bestowed on the subject of land drainage. It was at this time that the late Mr. Smith, of Deanstone, introduced the subject of “ thorough draining ” to the British public, and gave an impetus to the good work which has sent it rolling onwards ever since. Finally, the use of the cylindrical draining pipe, both by cheapen- ing the material of the underground channel, and reducing the trench to the narrowest possible width, brings us down to the present day, when draining is universally looked upon as the foundation upon which all other agricultural improvements must be based. FORTIFICATION. 21 FORTIFICATION.— I. BY AN OFFICER OF THE ROYAL ENGINEERS. PRELIMINARY REMARKS DEFINITION OF SCALES DEFINITION OF TERMS USED IN GEOMETRICAL DRAWING SLOPES : HOW EXPRESSED DEFINITION OF THE TERM FORTIFICATION CONDITIONS THAT, IF POSSIBLE, EVERY FORTIFICATION SHOULD FULFIL — ERRONEOUS IMPRESSIONS HELD WITH REGARD TO THE USES OF FORTIFICATION SUBJECT DIVIDED INTO TWO BRANCHES— FIELD FORTIFICATION PERMANENT FORTIFICATION DEFINITION OF A PARAPET MATERIALS OF WHICH PARAPETS ARE CONSTRUCTED. Preliminary Remarks. — The science of Fortification is one so intimately connected with other branches of military art, that it can hardly be rendered interesting or even intelligible to a student who has not previously acquired a certain amount of general military knowledge, sufficient to enable him to realise fully the. main principles and conditions under which modern warfare is carried on. Unless the reader clearly understands the differences existing between the uses and powers of the three great combatant branches of every army — viz., infantry, cavalry, and artillery— it would be useless to attempt to describe to him the defensive arrangements best suited to either of these arms. A certain knowledge of military matters will, therefore, be assumed in these papers, but when technical expressions occur they will be explained. Most of the operations of fortification are those of practical building or construction, and it is often necessary to express, on the flat surface of the paper, solids of very varied forms ; consequently the methods of doing this by means of plans, sections, etc., must be learnt before any real progress can be made. These methods form the subject of a separate study, termed Geometrical Drawing, and will therefore only be so far explained as may be necessary to enable a reader to understand the diagrams attached to these papers. In order that the meaning of a drawing of this description may be clearly understood, it is necessary that it should convey not only an idea of the shape and appearance, but also of the actual size of the object it represents. Definition of Scales.— It is evident that it will often be impossible to make drawings as large as the objects they re- present, and it becomes necessary, therefore, that in every im- portant drawing a certain fixed proportion should exist between it and the object represented. This proportion is termed the scale ' of that drawing, and is usually expressed by means of a fraction written on the drawing itself — thus, scale — n , or scale j|u, would denote that the objects represented were 120 or 480 times as large as the respective drawings. The shapes of solids are usually denoted on paper by means of plans, profiles, and elevations. t Definition of Terms used in Geometrical Drawing. — The plan gives the length, breadth, and general direction of every part of a work, and is a representation on a horizontal plane of the various lines or edges formed by the intersection of the plane surfaces that bound the solid. The t? ace of a work is the plan of its guiding or magistral line. The section of a work is the outline of the surface that would be exposed by a plane cutting through the solid in any direction. The profile is a vertical section at right angles to the trace, and shows the true heights and breadths of the object. I he elevation is the outline of an object projected on a vertical plane, and gives the heights and general appearance of the various parts. Slopes : how Expressed. — The degrees of inclination, or steepness of slopes, are expressed by fractions ; the slope being considered as the hypothenuse of a right-angled triangle, of which the height is represented by the numerator of the fraction, and the base by the denominator ; thus, a slope of t means that the height = base. V >, height = | base. t » ,, height = double the base, f » » height = f of the base. The i.oregoing elementary definitions being understood, we should next get a clear notion of the principles of the science before becoming involved in its details. In all ages we find that men, prompted by the instinct of self-preservation, have availed themselves of artificial aids in war, either simply as a means of protection from the missiles of an enemy, or to enable a weaker force to neutralise the ad- vantage that superior numbers or armaments would give to their opponents. Definition of the term “ Fortification.” — The various practical operations resorted to are essentially defensive in their nature, and the science which treats of the different ways of applying them to strengthen positions held by troops is termed Fortification. These operations present an ahnost infinite variety of detail, for they depend necessarily on the special objects for which they are intended, and the time and means available for their construction. A knowledge of details is undoubtedly essential in fortifica- tion, as in every other practical science ; at the same time it will be more important for the student at first to realise the fact that he is not dealing with an abstruse or complicated subject, but merely applying practical common sense to the art of defensive warfare, his object being in all cases to make such arrangements as will oblige the enemy to fight under the most disadvantageous circumstances possible. Conditions, that, if possible, every Fortification should fulfil. To attain this object thoroughly, every work should fulfil the following conditions : — 1. To afford cover and protection from the enemy’s missiles. 2. To enable the defenders to use their weapons with the greatest effect, and with the least exposure to themselves. 3. To render the advance of the assailants as difficult and slow as possible while within the effective range of the works. These principles are often very difficult to combine, and their application to positions where the circumstances are unfavour- able will require the exercise of much thought and ingenuity. Fortification is necessarily a progressive science, ever chang- ing in some important details as the development of the sister- science of Artillery may require ; hence it is that we find such a variety in the forms and appearance of the defensive works constructed at different periods and in different countries. A close study of them will show that, however unlike they may appear in some respects, the same principles may bo clearly traced through all ; not less, perhaps, in the New Zealand “pah” than in the mediaeval castle or the modern fortress, if the weapons for which each were intended are borne in mind. There can bo no doubt that, when properly applied and these conditions fulfilled, fortification must ever be of vast assistance to the defence ; it can, however, only give a passive assistance, and should not be confounded, as is so frequently the case, with the defence proper, or actual fighting power of the defenders. Good defensive works undoubtedly enable a small force to fight a much larger one on tolerably equal terms, and, more, over, a less amount of training and organisation is necessary to enable troops to defend fortifications than would be required for manoeuvring in the field. It must, however, be remembered that fortifications without sufficient men and guns to defend them would offer no real obstacle to an enemy, and that unless the offensive powers of the defenders be considerable, they may, in spite of their de- fences, be defeated by a superior force. Erroneous Impressions held with Regard to the Uses of Fortification. — Nothing is more common than to hear it argued that because a fortified position is carried by assault, there- fore the fortifications were useless, ignoring the fact that if the defenders were unable to repel their assailants when assisted by artificial aid, they would not have had a chance of victory in open fight, and that the loss they have inflicted, as compared with their own, is probably far greater than it otherwise would have been. Another favourite argument against the use of fortifications is that if they are well placed, and well constructed, the enemy will probably not attack them at all, but will endeavour to pass round, or turn them, as it is termed, and that, therefore, they are useless. Let us examine this for a moment. It is evident in an attack on any position or territory, there must be a certain definite object in view, and that, in order to obtain this object, there must be certain parts of that position or territory which will be most essential for the assailant to get possession of. Now, if THE TECHNICAL EDUCATOR. these vital points are so strengthened by artificial means that, in spite of his superiority of force, the assailant prefers to adopt some other less advantageous scheme, to the certainty of heavy loss and possible defeat in attacking the works, it is clear that these fortifications will have materially assisted in protecting the position or territory, although they themselves were not actually attacked. . . . Subject divided into Two Branches . — For convenience m in- struction, the subject is usually divided into two branches, termed Field and Permanent fortification, although it is by no means de- sirable that they should be considered as separate studies, for precisely the same principles apply to both ; and in permanent fortification we merely see them combined in a complete form, whereas this can only be imperfectly attained in field fortification. Field Fortification . — This has reference to temporary works constructed during a campaign, within a limited time, and with such unskilled labour and ordinary materials as can be obtained on the spot. . . . The strength of this class of works varies considerably, from the carefully constructed redoubt, in which all the requisite conditions are fulfilled, to the hasty shelter-trench, or the rough lines of felled timber that so often afforded bullet-proof pro- tection to the troops in the battles of the late American war. 'PJiq weak point of all field works, as compared with per- manent fortifications, is that, from the fact of their being con- structed in a short time, the obstacle they oppose to the advance of the enemy is very much less formidable. Permanent Fortification . — Permanent fortifications, as the name implies, are constructed of durable materials, and during times of peace, when the choice of materials is unlimited, and wlien everything is done that skilled labour and elaborate design can accomplish, to render the defence as perfect as possible. They are intended to secure from immediate capture the arsenals, dockyards, and other points of vital importance in a country liable to attack. Permanent fortifications are necessarily very costly to con- struct, and unless destroyed by an enemy will endure for centuries, outliving the men who built them, and the artillery, and even the objects for which they were designed. Hence it is that we so frequently find examples of fortifications that are now obsolete, and we are apt to consider that it was a groat mistake ever to have built them, forgetting that they, perhaps, have been of the greatest national importance for many genera- tions, and would be so still, had the art of war remained stationary during that period. , Definition of a Parapet . — To fulfil the conditions of inter- cepting the projectiles of an enemy, and of enabling the de- fenders to use their arms with effect, a covering mass of somo material is necessary, which must have sufficient strength to resist the enemy’s shot, and over or through which the defenders may fire. This mass is called the parapet (derived, from the Italian words “ para petto,” guard the breast), and its dimen- sions as regards height are dependent to a great extent on the ordinary stature of men, whilst its thickness must depend on tne materials of which it is formed, and the nature of projectile it is intended to resist. This parapet is usually constructed of earth or sand, as being the material most readily obtained, and most indesti uctible by an enemy. Materials of which Parapets are Constructed .— In countries where timber abounds, and where the heavy fire of artillery lias not to be provided against, parapets may be constructed of logs of wood placed touching one another, so as to give good bullet-proof cover. These are called stockades, and have the •disadvantage of being liable to be burnt, and if struck by shot the splinters of the wood are dangerous. In some cases where it is impossible to obtain sufficient earth, or where, from the small area available, it is necessary to economise space as much as possible, masonry, and even iron, may be used as materials for parapets. The time required to construct them, and their cost, prevent the employment of these latter materials for any but permanent works. I hey are chiefly employed in harbour and coast defences, where it frequently happens that the small islands or rocks that are most ad- vantageously situated for the defence of the coast, are too small to admit of a sufficient number of large guns being placed on them, if they are to be surrounded by thick and massive earthen parapets. BIOGRAPHICAL SKETCHES OP EMINENT INVENTORS AND MANUFACTURERS. I— CAPTAIN ANDREW YARRANTON. BY JAMES GRANT. Andrew Yarranton — a man whose views were in advance of his time by perhaps more than two hundred years the projector of schemes for improving the inland navigation of England and her agriculture, of plans for docks m London, of a great public bank, and many other brilliant speculations, was born in a humble farmhouse at Larford, in Worcestershire, in the year 1616. When in his boyhood, in 1632, he was bound ap- prentice to a linendraper, whose services he quitted to become a soldier, when the great Civil War broke out.. Being a Presby- terian, he enlisted in the army of the Parliament, where his ability and zeal soon won him promotion, and thus a year or two saw him attain the rank of captain. He must have seen some service against the Royalists, and probably against the Scots, as he records of himself that, “ while a soldier, I had sometimes the honour and misfortune to lodge and dislodge. an army;” but, modestly, he tells us no more of his fighting career. In 1648 he received the sum of =£5,000 from Parlia- ment to reward his “valour and discretion” in frustrating a bold design, conceived by the Royalists, to capture Doylely House, in Herefordshire ; but after this we hear little more of Andrew Yarranton in connection with the army, as on the assumption of supreme power by Oliver Cromwell, he quitted it, and, with the money he had won, devoted himself entirely to the cause of trade and industry. . In 1652 he was actively engaged with certain ironworks near Bewdley, in Worcestershire, and with the aid of his wife he established there a linen manufactory, with great success. As regards iron, he early learned to see that it would be the chief means of England’s greatness and prosperity, and of her peril then in case of a foreign war. “ When the greatest part of the ironworks are asleep,” he wrote, “if there should be occasion for great quantities of guns and bullets, and other sorts of iron commodities for a present and unexpected war, and the Sound happen to be locked up, and so prevent iron coming to us, truly we should then be in a fine case ! ” In the course, of his double trade, perceiving the difficulty of communication by roads that were utterly neglected, and to develop the great natural sources of the west of England, he applied, himself to a survey of the rivers at his own expense, that he might improve the navigation ; and he was thus employed when the Restora- tion of Charles II. took place. The journeys of Yarranton from point to point soon excited the surprise and comment of those in local office, even as his success in trade had already aroused their enmity and envy. Then came whispers that the Puritan captain was engaged in a Presbyterian plot, and the 13th of November, 1660, saw him m prison for “ refusing to obey the authority ” of Lord Windsor, who was lord-lieutenant of Worcestershire. On a false charge of conspiring against the king, he was kept in durance till May, 1662, when he made his escape ; and though a party of norso scoured the country, he made his way to London. Ere June came, he was again in prison, and brought before “ John _rom- field, Oeorge Moore, and Thomas Lee, Esqrs., justices of Surrey,” accused of having “ broken out of the Marshalsea of Worcester.” But he was no more molested, and returned to his favourite schemes for widening and deepening the rivers of the West. His first attempts were on the Salwarp, a small stream, so that Droitwich might be opened to the Severn, and the transport of salt by barges be facilitated; and m grafitudo for this, the people of Droitwich gave him a reward of aYOU, and eight salt vats in Upwich valued at =£80 per annum. So lately as 1789, some of the barges used by Yarranton in his navigation were found in the bed of the stream. In 16n6 he projected the opening up of the Stour by connecting it wit i ie Trent through a canal, passing by both Stourport and Kidder- minster ; but money fell short, and more than a hundred years after Yarranton was gone, James Brindley, a kindred spirit, carried out his plans to the letter. To connect the Thames with the Severn, by means of a canal, was another of Yarranton’ s far-seeing projects ; and by his plans he proposed to cut it at the very place where, as m the I preceding case, more than a hundred years after his denth, it PROJECTION. 23 was ultimately constructed by others. In his own time,, how- ever, this son of industry had the pleasure of opening up the Avon, and was the first to have barges rowed thereon from Stafford to Tewkesbury. Amid all these watery schemes, the improvement of agriculture occupied his attention largely ; and perceiving that the land had become exhausted by repeated crops of rye and the tillage of centuries, he urged the adoption of a new system precisely similar to that of the Scottish farmers in the present day — the rotation of green and white crops ; and with this view he supplied clover-seed in great quantities xo the agriculturists of the western counties, where by his advice and measures the land soon became very nearly doubled in value. Seeing that England was almost without proper harbours or accommodation for merchant shipping, his next, and perhaps his boldest plans, were those of docks for the city of London, where the importers were content to ship and unship their goods by barges in the densely-crowded tideway of the Thames. But poor Yarranton found few supporters, while many laughed at his proposals as Utopian, and they were crushed ! While carrying on his ironworks near Bewdley, it had occurred to him that the manufacture of tin-plate would be a valuable addition to English industry, as we were then entirely dependent for that commodity on foreign markets, and all previous attempts to make it at home had completely failed. With this view, the in- defatigable Yarranton sailed for Hamburg, and went to Dresden, where then the Duke of Saxony held his court ; and from thence to the little town of Au, among the mountains of the district named the Erzebirge or Ore Hills (otherwise known as the Giant Mountains), where at this day more than 500 mines are open and worked. There he learnt that it was a country- man of his own — an aged miner, “ a Protestant banished out of England for his religion in Queen Mary’s time” — who had first discovered the tin mines of Saxony ; and the result was that, at the time of Yarranton’s visit, 80,000 men were ■at work in them, and they had, in gratitude, erected a statue to the memory of the old Cornish refugee. Returning from thence to England with a company of well-skilled workmen, he began to manufacture, in the Eorest of Dean, for the home market ; .and at his works were made many thousand tin plates, which were “pronounced of better quality than those of Saxony; ” but an opposition was soon established, for the Crown, harbour- ing, perhaps, a grudge against the old Cromwellian officer, gave a Mr. William Chamberlain, in 1673, the sole patent “ for plating ■and tinning iron, copper,” etc. ; so Yarranton’s works were abandoned, and those of Chamberlain failed; hence England had to import tin plate from Saxony and elsewhere for more than sixty years afterwards, till a new manufactory, on Yar- ranton’s plan, was started at Capel Hanbury, in Monmouth- shire, where it still exists. Yarranton now proceeded to Holland to inspect the linen factories and the canals of the Dutch, then the most thriving and industrious nation in the world ; and, by what he has written, he seemed to have been delighted with the wealth, •enterprise, and comfort of Germany and Holland. “ For as the honesty of all governments,” said he, “ so shall be their riches ; and as their honour, honesty, and riches are, so will be their strength ; and as their honour, honesty, riches, and strength, so will be their trade. These are five sisters that go hand in hand, and must not be parted.” Inspired by a knowledge that the fleets of the Dutch were in every sea, and that their herring-fishers swept all the east coast i of England and the shores of the Scottish isles, bn his return he ! at once began a new movement for the development of the wealth and resources of the British fisheries, and made several journeys to Ireland for the same purpose. He afterwards surveyed the Dee, to connect it with the Severn. The encouragement of the linen manufacture in the central counties of England, where the soil is so well adapted for the ■cultivation of flax, next occupied his restless attention, as he hoped that the two millions, or thereabouts, sent yearly out of the country for the foreign markets, would be spent at homo in the- employment of our own people ; but as he said himself, "sloth and envy discouraged all my pious endeavours to pro- mote our future happiness.” The first part of his new literary work, “ England’s Improve- ments by Land and Sea,” appeared at London in 1677 ; and in its pages, as if gifted with a spirit of prophecy, he foresaw or foretold the future commercial glory of England, his native country, “ whose future flourishing is the only reward I ever hope to see to all my labours.” The formation of harbours, the extension of the iron, the woollen, and the linen trades; the internal navigation by rivers and canals ; the deep-sea fisheries, and the establishment of a public bank based upon the security of freehold land, enabling its notes to pass in transactions equally with bullion ; and the scheme of a voluntary register of property, are all breached in his work ; and, strangely enough, the year 1862 saw an Act passed in the very spirit of Yar- ranton’s last idea. His project for a Land Bank was revived in 1695, and received the sanction of Parliament; but the Bank of England, then only one year old, petitioned against it, and it was immediately dropped. We know not whether he was then alive. In 1681 he published the second part of his singular book, “ England’s Improvement.” In limited growths and manufac- tures, he stated that England and Ireland (to Scotland he made no reference) were the only northern kingdoms remaining un- improved. He again urged the registration of real property ; the development of the fisheries ; the improvement of the Royal Navy ; the fortification of Tangiers (the dowry of Queen Katharine of Braganza), which might thus have become to England then what Gibraltar is now; the reduction of the expense of the Trained Bands, of which England then had eight regiments ; the formation of a harbour at Newhaven in Sussex ; the development of the vast resources of the Cornish tin mines ; and many other projects, all fraught with deep thought and foresight. In the last portion of his book, he suggested that the Cornish tin, if combined with the Roman cinders and iron- stone in the Forest of Dean, would make the best metal in the world. Of this he had some practical experience, having once discovered a vast quantity of Roman cinders near the walls of TV orcester, from whence he carried many thousand tons by barges up the Severn “to be melted down into iron with a mixture of the Forest of Dean iron-stone.” After the close of his work was published, he proceeded to Dunkirk (a port then belonging to Britain), for the purpose of making a personal survey thereof ; and on returning to London he published a map of the fortress, harbour, and town, with some letter-press remarks, wisely recommending the utter demo- lition of all the military works, as being more likely to be of service to the French than us. At the close of the same year, 1681, he published his “ Full Discovery of the First Presby- terian Sham Plot,” referring to the old persecution he had undergone at the Restoration ; and after this event his name disappears for ever, nor can any trace be found of where, or when, or how he died, or even where he was interred ; but such was the singular and restless career of one whose ideas were far before tnose of the age in which he lived ; and though his writings and even his name are all but forgotten now, in the exhortations to honest industry he sowed good seed in his time ; and in Andrew Yarranton we may recognise one of the most earnest pioneers of England’s present and future greatness. PROJECTION.— II. PROJECTION OF DOOR — TRAP-DOOR AND FRAMING — CUBES AND PRISMS — TO PROJECT A CUBE — SHADE LINES TO DEVELOP A CUBE. It will be remembered that in the previous lesson the method of projecting first single lines, and then planes at various angles, was treated of. The present studies are familiar appili- cations of the principles laid down. Fig. 11 represents a door when the wall is parallel to the vertical plane, the door being at an angle to it. The plan should be drawn first, and the elevation projected from it. Fig. 12 represents a trap-door and framing, the door being inclined to the horizontal plane, supported in that position by a piece of timber. In this figure the plan of the framing should be drawn first ; then its elevation. To this elevation the edge of the trap-door should be added, which should then be pro- jected on to the plan. In Fig. 13 the entire plan rotated should be drawn first, and the projection obtained by drawing perpendiculars from the angles, and intersecting them by horizontals drawn from the corresponding points in the elevation. 24 THE TECHNICAL EDUCATOR. Tig. 14. — Here a plane square is placed -with its surface pa- rallel to the horizontal plane, and its edges, a, b, c, d, making angles of 45° with the vertical plane. As this plane is sup- posed to possess little or no thickness, its elevation, when lying flat, is merely the line a' d; the angle c, and b which lies directly above it, being marked b c . If we now raise the square, allowing it to rest on the angle a, the extremities of the diagonals, d, c, and b, will travel through parts of circles. Thus, let it be required that the diagonal a d shall be parallel to the vertical plane, and inclined to the horizontal at 45°. Draw a perpendicular from a to the intersecting line, and thus obtain a'. From a' draw a line at 45°, and with radius a' c and a d describe arcs cutting the in- clined line in and d' ; the ex- tremities of the diagonals are thus transferred from the hori- zontal to the inclined elevation. Now the points b and d, in rising higher, will also have moved towards a in the plan, in the track indicated by dotted lines ; their present position is determined by dropping perpen- diculars from b c ' and d' to cut the dotted lines ; and the points being united by lines, the plan of the square in the required position will be obtained. Let it now be required to ob- tain the projection of this square, when, in addition to the diagonal a d being inclined at 45° to the horizontal, it is inclined at 60° to the vertical plane ; in other words, keeping the square resting on the point a, inclined at its present angle, and rotating it. The plan then will be the same as in Fig. 14, but turned round until a' d' is at 60° to the in- tersecting line; thenperpendiculars raised from each of the angles, intersected by h o ri z o nt als from the corre- spondingpoints in the previous elevation, will give the projec- tion in Fig. 15. The same plan turned so that a d is at — , right angles to the intersect- ing line, and worked out as in the last figure, will give the projection of the square when resting on one of its angles, its plane being at 45° to both the planes of pro- jection. It will be seen that Fig. 11. [ -~v_u []=== 1 ^ — 1 ■■ | i it ii 1 1 1 1 • j 1 l II i i 1 • i i ! i : ! ill Hiss Fig. 12 — the diagonal c b has, in all threes figures, remained parallel to the horizontal plane ; but in Fig'. 16 it will be observed to b© parallel to both planes. The student who has tho>- roughly mastered the foregoing lessons will have seen that, when he understood the projection of single lines, he soon compre- hended the delineation of planes, since planes are but forms bounded by lines. It is hoped, that the next step, the projec- - tion of solids (from the Latin solidus, compact), may be di- vested of some of its apparent difficulties, by the reflection that solids (excepting the sphere an d its allied forms, no portions of which are absolute planes) are * made up of planes, and that thus, when planes can be projected separately, it will be easy to work out several combined in one object. Thus a cube, or solid square, is formed of six equal squares ; and as each of these sides is parallel to the opposite one, the trouble will not be much more than project- ing three planes. CUBES AND PRISMS. When three or more planes meet at one point, as the corners of a cube, they form a solid angle. A prism is a solid whose oppo- site ends are equal and similar plane figures, and whose sides, uniting the ends, are parallelo- grams. The ends of prisms may be either ^triangles, squares, or polygons. . A line drawn from the centre of one end of a prism jO _lie centre of the other is called the axis. TO PROJECT A CUBE. ■When standing on the horizontal plane, its axis being vertical, and its sides at 45 degrees to the vertical plane. Let abed be the plan of the cube, and e the plan of the axis. Draw perpen- diculars from each of the angles of the plan, and make the height above the in- tersecting line equal to the side of the plan. Draw the top line, a d, which will complete the elevation, the axis being hidden by the edge, c. First Position (Fig. 17) PKOJECTION. 25 Second Position (Fig. 18). — When resting on the solid angle, a, its axis being inclined at 65? to the horizontal, and parallel to> the vertical plane. As the axis of a prism is parallel to its edges, it will only be necessary to place the elevation of Fig. 17 so that the edges are at 65°, then the axis will be between the edge c c in the front, and b b beyond ; and as the diagonal, a d, which forms the intersecting line. Draw perpendiculars from the solid angles of the plan, and horizontals from the corresponding points in the elevation of Fig. 18. The intersections of these two sets of lines will give the points for the projections. _ Shade Lines. — The light has been supposed to come in the direction of the parallel lines on the left of the point a. Thus the sides c d and d b are in shade. This is indicated by the the breadth of the base, is at right angles (90°) to the edge, a a, the plane of the base will be at 25° to the horizontal plane. Perpendiculars dropped from the angles of this elevation, intersected by horizontals drawn from the corresponding points in the plan of Fig. 17, will give the plan of Fig. 18, or the view obtained by looking down on the elevation, in the direction of the arrow. The axis, e /, will now be seen. lines on the plan being darker than the others, and all per- pendiculars rising from them will be dark also. Development. — The development is formed by the shapes of all the sides of an object being laid down on a flat surface, so that when folded, or connected, a given solid may be either constructed or covered. By solid is here meant an object that has the external appearance of solidity. Whether the body ct ci The student is urged to letter with the utmost care until dxO has become accustomed, to follow each point through its various changes of position. In Figs. 17, 18, 19, 20, and all subsequent projections of prisms, the points of the base, or lower end, will be marked with the same letters as those of the opposite or upper end, but in smaller characters. Fig. 19.— When the axis of the cube is at 65° to the hori- zontal and 30° to the vertical plane. Place the plan so that the line of the axis, e f, is at 30° to be really solid or hollow will be subsequently determined by sections or cuttings. To Develop a Cube (Fig. 20).- — A cube consists of six square sides. Let a, b , c, d be four of these, which, uniting at Hi Hi "will form the walls, then e and / will be the top and bottom. A very useful model may be thus formed. The strips left at the edges will be found useful in fastening the sides together. If the model is made of cardboard the lines should be cut half through, and half the thickness of the strips peeled off. 26 THE TECHNICAL EDUCATOR. MINERAL COMMERCIAL PRODUCTS.— II. iron ( continued ). tellurium, and other metals ; and often associated with the sul- phides of iron and silver. The modes of occurrence and association of gold are as Iron pyrites, mundic, the bisulphide of iron (FeS 2 ), is diffused through rocks of all ages, but the presence of sulphur makes it valueless for the production of iron. It is important, how- ever, both directly as a source of sulphur and sulphuric acid, and indirectly in the immense number of the useful applica- tions of this latter product. Pyrites sometimes contains gold, and it is then called auriferous pyrites. Wicklow, Cleveland, Bohemia, Spain, Portugal, and Norway possess very large quan- tities of this mineral. Phosphates of iron are worked in Canada, and silicates in Switzerland. The principal processes to which iron ores have to be sub- jected, in the preparation of iron and steel for manufacturing purposes, are roasting and smelting, refining and puddling, cementation and tempering, varying with the nature of the ores. The roasting process — chiefly necessary for impure ores — gets rid of combustible matter, water, and carbonic acid. The smelting, conducted in large blast furnaces, disengages the metal from the oxygen and earths of the ores, and brings it into the marketable form of cast-iron, in pigs. This is really a carbide of iron, containing a considerable proportion of carbon, with small quantities of some other substances, such as silica and potash, derived either from the ores or the fuel. It is -very brittle, and suitable only for castings : and, according to its quality, it is grey iron, which is the best ; mottled ; and white, which is the worst. Refining, a re-melting of the metal with coke or charcoal, removes some of the carbon and silicon, and produces what is called fine metal. The puddling, which is carried on in a reverberatory furnace, disengages further quanti- ties of these impurities, and makes the iron malleable, prepared :in bars or sheets, as required. By cementation, or heating with •charcoal, bar-iron is made into blistered steel. From this, by welding, shear-steel is made; and by re-melting and casting, the cheaper cast steel is obtained. Spathose pig-iron can be converted into steel without any intermediate processes. This is done in Styria and other parts of the Continent, and in Borneo. The produce is called natural steel, and is of very fine quality. Ordinary cast-iron, annealed — called “run-steel” — can some- times be substituted for steel. The tempering of steel, to adapt it, as regards hardness and ductility, for. its various purposes, is effected by the processes of re-heating and sudden cooling — the temperature being made to vary with the quality sought to be produced. The quantity of iron obtained from the principal mining countries is nearly as follows : — Tons. Great Britain . . . . 4,819,254 France (1867) .... 1,035,000 (and upwards) Prussia and Zollverein . 400,000 Austria 250,00# Sweden and Norway . . 150,000 Tons. Bussia 200,000 Belgium 200,000 United States .... 750,000 Spain 80,000 Italy •. 48,000 Other sources, about . . 300,000 follow : — 1. In quartz veins of the older rocks, those in the Lower Silurian containing the greatest quantity of gold. Examples are furnished by the auriferous lodes of North Wales. 2. In quartz veins in such Secondary rocks as have been penetrated by certain igneous eruptions, either in the intrusive rock, or in the Secondary strata, and then for a limited distance only beyond the junction of the two rocks. Such an association prevails in California, Central America, and Peru. 3. As auriferous detritus in Secondary and Tertiary deposits, and in the debris and alluvia of rivers, such having been derived from gold-bearing rocks. The placer mining of California, Aus- tralia, New Zealand, -etc., is prosecuted in superficial drift deposits. Gold has been found in streams in Cornwall, Devon- shire, Wicklow, and Scotland ; and the sands and alluvia of rivers in many parts of the world are washed for this metal. Our great supplies are drawn from all these sources. The chief are Australia and New Zealand, California and British Columbia, Brazil, Peru, Mexico, and Central America ; the Ural, Altai, and Carpathian Mountains. Gold is also obtained from Thibet, China, Japan, Further India, and Borneo ; from the sands of African rivers, especially in Guinea, and from those of the Rhine, Rhone, Danube, and Tagus. Small quanti- ties are procured in mining districts from iron and arsenical pyrites, and other sources, as in Silesia, Saxony, and parts of our own country. The total annual supply is about as follows: — Australia .... £12,000,000 New Zealand (1868) . 2,504,326 California .... 13,0 0 0,000 Bussia 3,000,000 Mexico and Central America .... 500,000 South America East Indies . Africa Austria , Britain . Nova Scotia £500,000 500.000 200.000 200,000 3,000 ' 90,000 PLATINUM. Platinum ranks with gold in its resistance to the influence of air, moisture, and ordinary acids, and is the heaviest sub- stance known (sp. gr. 21‘5). It is white, exceedingly malleable and ductile, and extremely difficult of fusion. On account of its indestructibility it is of great use in the laboratory for crucibles. It is valuable in the arts, and has been employed for coinage by Russia. Platinum rarely occurs pure. It is principally found alloyed with palladium, rhodium, iridium, iron, gold, or other metals, and generally in alluvial deposits. In the Ural Mountains it has been observed disseminated throughout the whole mass of certain crystalline rocks. The pure metal is got by adding sal- ammoniac to a solution of the alloy in nitro-hydrochloric acid, and washing and heating the compound thus produced. The sources of supply are the Ural Mountains, Brazil, Peru, Spain, Borneo, and Ceylon. The quantity furnished by Russia is 800 cwt. SILVER. From these figures it appears that the British produce of iron is more than double that of the rest of the globe. GOLD. This noble metal is unaffected either by air or water, and is of great and almost universal use. In civilised countries it forms, as coin, the principal medium of exchange, besides being used in the form of gold-dust for a similar purpose among semi- barbarous nations ; and from the richness of its colour and its imperishable nature, it enters very largely into the composition and ornamentation of such articles of utility and luxury as require to be both durable and beautiful. For all these pur- poses it is peculiarly fitted by its weight (sp. gr. 19 - 5) and its extraordinary malleability and ductility. In virtue of these latter qualities it can be hammered out into leaves of 282,000 to an inch, and a single grain can be extended into 500 feet of wire. Its natural softness can be corrected by a slight alloy of silver or copper, and in this state it is commonly em- ployed. Gold is more generally diffused throughout the globe than any other metal except iron, but not in all places in sufficient abundance to render its collection or extraction profitable. It occurs mostly native, being either pure or alloyed with silver, Silver, like gold, is a noble metal, and is used very extensively for similar purposes. It also needs an alloy to harden it ; and being less precious, as well as loss weighty (sp. gr. 10’5), is more available for common uses, especially many domestic ones. Its chemical preparations are valuable in photography and surgery. In colour silver is a beautifully brilliant white ; it is sonorous, highly malleable and ductile, and perhaps the best conductor of heat and electricity. This metal occurs pure in some rocks in very fine threads, and large masses of pure silver are occasionally met with in veins. But its supply is principally derived from ores, of which the chief are the chloride (AgCl), or horn-silver, a greyish crys- talline mass, which looks like horn ; the sulphide or silver- glance, and its combinations with the sulphides of antimony and arsenic, which are known as the dark and light red silver ore3 ; and argentiferous galena (sulphide of . lead), which often contains very considerable quantities. Silver is obtained from its ores chiefly by roasting, crushing, and amalgamation with mercury. The separation from Lad was formerly effected by the superior affinity of lead with oxygen in the process called cupellation, which was in every way costly ; and unless the per-centage of silver in the lead was large, it was not separated. A process known as Patiin- NOTABLE INVENTIONS AND INVENTOES. 27 son’s is now employed for desilverising lead ; it is based upon the discovery that lead crystallises or consolidates at a higher temperature than an alloy of lead and silver. Consequently, if argentiferous lead be kept at the lowest temperature at which the fluid state could be maintained, solid masses of pure lead are gradually formed and removed, the fluid portion remaining being exceedingly rich in silver. Finally, the lead is subjected to the process of cupellation, and the silver separated. lhe most abundant supply of silver is yielded by the mines of Mexico, Chili, and Peru, especially those of Pasco. These mines occur in elevated districts, some upwards of 16,000 feet above the sea-level. Considerable supplies are also obtained from other parts of South America, in the Ural and Altai Mountains, from China, Japan, Cochin-China, Thibet, Asiatic Turkey, Norway and Sweden, the Harz Mountains, Saxony, Hungary, Austria, and the lead districts of the British Isles. The annual quantities are : — Mexico £2,420,000 South America . . 1,650,000 Zollverein .... 450,000 Spain 400,000 Austria 250,000 Britain £180,000 France 60,000 East Indies (1860). . 50,000 Norway and Sweden . 30,000 MERCURY. This extraordinary metal — quicksilver, as it is often called — fluid at ordinary temperatures, is the heaviest liquid with which we are acquainted (sp. gr. 13'59). It becomes solid at -40° Fahrenheit, when it is both malleable and ductile. It is used for the extraction of gold and silver ; as an amalgam in che- mistry, and in the construction of scientific instruments ; in manufactures, for silvering mirrors, and for vermilion; and in medicine, for the valuable products calomel and corrosive sub- limate, the subchloride and chloride of the metal respectively. Quicksilver is met with pure in minute globules, but for the purposes of commerce it is obtained from one of its ores— cinnabar, a, red sulphide of mercury. This ore occurs in the older rocks, but chiefly in those of the Carboniferous system, and the metal is procured from it by a process of distillation. The principal sources of supply are Almaden in Spain, and Idria in Austria, both very rich ; Peru, California, Mexico, Aus- tralia, China, Japan, Ceylon, Bavaria, Bohemia, Tuscany, and Hungary ; and the quantities of mercury annually obtained are about as follows : — Pounds. Austria . 500,000 to 1,000,000 Spain 3,500,000 California .... 1,500,000 Po unds. Peru 324,000 Germany .... 21,000 Tuscany .... 55,000 TIN. This very useful metal is rather a rare one. It is but slightly acted upon by either air or water, is of a white silvery colour, malleable, and easily fused. Its specific gravity is 73. Besides being largely used in coating or tinning more oxidable metals, as iron, ior instance, in the well-known material called tin-place, and combining as an alloy to form pewter, bell-metal, type- metal, and solder, it is employed in its chemical combinations fer a great variety of purposes in the useful arts. It is found as an oxide, chiefly in the metalliferous veins of the older rocks, also in association with wolfram (a double tungstate of iron and manganese), and, like gold, in alluvial districts, as stream- tin. By the processes of roasting, smelting, and refining, the stream ores produce the grain tin, which is the most esteemed, and the others the bar or block tin. The most productive dis- uicts are Cornwall and Devonshire, the Malayan peninsula and islands, especially Banca and Billiton, to the south of it. and Tenasserim, in the East Indies, China, Saxony, Bohemia’ Hungary, Peru, New Granada, Bolivia, Mexico, France, Spain, Siberia, and Australia. Annual supply, about — Tons. Britain 10,000 China 127 I Austria 30 ! East Indies .... 5,000 | Tons. Japan 1x3 Australia (Victoria) . . 816 Siam 53 COPPER. Copper is a metal of great commercial value, and of very extensive use. It is of a fine red colour, very malleable, ductile, and tenacious, highly sonorous, and a good conductor of heat and electricity. Its specific gravity is 8'96. Independently of its use for coin, sheathing for ships, boilers, and domestic uten- sils, and of its alloys with gold and silver to harden those metals, copper enters into the composition of brass, bronze, pinchbeck, ormolu, gun-metal, bell-metal, German silver, and the biddery ware of India. It is also largely employed in the production of colours (blue and green), in telegraphy, and in medicine. It occurs native in fine threads, and occasionally in large masses, the most remarkable of which have been found in Brazil, the district of Lake Superior, and Australia. The prin- cipal ores, which occur either in veins or beds, and are most abundant in the primary rocks, are copper pyrites, a sulphide of the metal combined with sulphide of iron ; the red oxide (Cu„0), the black oxide, the green and blue carbonates of copper, and the purple and grey copper ores, the latter associated with iron, antimony, and arsenic. The reduction of the ores is a matter of some difficulty. In Britain it is chiefly carried on in the neighbourhood of Swansea. Ores of copper are found in Cornwall, Devonshire, Flintshire, Wicklow, and other parts of the British Isles; Chili, South Australia, the Ural Mountains, United States and Canada, near Lakes Superior and Huron ; associated with trap rock in Brazil and Cuba; in the copper schists of Mansfeld, in the Harz, Saxony, and other parts of Germany ; in Sweden, Tyrol, Hun- gar y, Tuscany, Spain, Persia, India, China, Japan, Algiers, South Africa, and New Zealand. Malachite, a beautiful ore of copper (carbonate), found abundantly in Russia and Australia, can be used as an ornamental stone. The annual supply of copper may be thus stated : — • Tons. Britain 12,000’ Chili 21,000 South Australia . . 6,700 Austria 2,330 Zollverein 2,650 Tons. Sweden 2,000 Cape of Good Hope (ore) 4,327 France 3,000 United States (Lake Su- perior) 3,000 NOTABLE INVENTIONS AND INVENTORS. I— PRINTING. BY JOHN TIMES, The origin and history of the “ noble craft and mystery ” of printing can scarcely be told within a moderate compass, since its principle can be traced in so many forms of producing a copy by pressure, as practised in very remote ages. Seals were impressed upon soft material nearly four thousand years ago, and characters were stamped upon clay m forming the bricks of Babylon. Of this art, Wilkinson and others have brought examples from Egypt, and Rawiinson and Layard from the ruins of the buried cities of Asia; 1 while wooden stamps, with which these inscriptions were impressed, 'are to be seen in the British Museum. Brass or bronze stamps, with raised characters for printing with colour upon papyrus, linen, or parchment, have also been found ; but though the Romans used these stamps, it did not occur to them to engrave whole sentences upon blocks — showing how very nearly we may approach to an important discovery, and yet miss it. The Chinese printing from blocks, at this day, closely resembles the old Roman, and they claim to have practised it before it was known in Europe. Printing from pictures, engraved upon wooden blocks, was accomplished in the thirteenth century; and next, the engravings of the Biblia Pauper urn (Poor Men’s Bible), with the text printed from movable types. From this period dates the practice of printing, in the present sense of the term. Whether wooden movable types were ever employed to print an entire book is very question- able ; but no expedient of the kind could have fulfilled the great purposes of this invention, until it was perfected by founding metal types in a matrix or mould, the essential characteristics of printing, as distinguished from other arts which bear some analogy to it. This important advance was made by Gutenberg, whose claim to the invention was disputed in an action at law with his partner in 1439, and evidence produced to show that one of the witnesses had learnt from Gutenberg to take the pages from the presses, and by remov- ing two screws thoroughly separate them (the letters) from one another, so that no man may know what it is ; ” thus proving 28 THE TECHNICAL EDUCATOR. that separated types were used, as well as some sort of press, as the transfers were no longer taken by a burnisher or roller. Gutenberg died in 1468, and a statue of him by Thorwaldsen was erected at Mayence, by subscription, in 1837. The capture of the city, in 1462, interrupted the labours of Fust and Schoeffer, Gutenberg’s partners; they with their work fled into the neighbouring states, and thus spread printing over the whole civilised world, and, within fifteen years, to every town of consideration in Christian Europe. Henceforth, down to the close of the last century, there appears to have been no alteration in the operation ; the improvements consisting in the gradual increase of the size and power of the press, together with the great beauty and variety of the types. The press used in Gutenberg’s office differed in no essential points from that in use until 1600-20. In woodcuts of Guten- berg’s press (1405-1535), the table, with the “forme” of type, remains, and the platen is brought down by a powerful screw, by means of a lever inserted in the spindle, such as might be seen in our time in a London printing-office. It also appears that the matrices and punches used early in the fifteenth century England, remained with him, and succeeded to his business t his works amount to 408. The English printers were for a long time supplied with type from the Continent ; but early in the eighteenth century William Caslon established the Caslon Foundry, which still exists. Another eminent founder was John Baskerville, of Birmingham. We have already referred to the form of presses used to the year 1620. Improvements were from time to time introduced; but they were all superseded early in the present century, when the old wooden press gave way to Earl Stanhope’s invention of tho iron press which bears his name, and in which the power, instead of being derived from the screw, was obtained from a bent lever that impressed the platen, or iron plate, upon the paper, which is brought down on the surface of the type. The peculiar property of this press is, that when the platen first moves downward its motion is rapid ; while, when the power is about to be applied, it is slow, so that the greatest amount of force is concentrated just at the time when it can be of the greatest efficiency. The principle has been followed out by several subsequent inventors. The printing press, however. marinoni’s printing machine. were much in the same form as at the present time. For a long period the printers were their own type-founders ; but as the art spread, the casting of letters became a separate business. To William Caxton and his successor, Wynkyn de Worde — who established for themselves a high reputation, both as printers and letter-founders — we owe the introduction of print- ing into England. Caxton was born in Kent, 1422-3, and apprenticed to a mercer in London. About 1441 Caxton was sent to Bruges, where he was engaged for thirty-five years in commercial pursuits, and subsequently devoted himself to literature and printing. In 1469 he translated, from French into English, tho “ Romance of Troy,” the demand for which was so great that he could not transcribe copies sufficiently fast, which led Caxton to employ the new invention of printing as a means of multiplying his copies. He derived from Colard Mansion, the first printer at Bruges, his types and his method of working, as shown by Mr. Blades, in kis “ Life of Caxton,” whose first book was printed in 1472, by Mansion himself, at Bruges, and not at Cologne, as hitherto believed. At West- minster he printed the first book in England, “ The Game and Playe of Chess,” completed in 1476. For fifteen years he continued translating and printing, and died in 1491, about eighty years old. Wynkyn de Worde, who came with Caxton to proved inadequate to render the rate of production equal to the urgent demand ; and as early as 1790 Mr. W. Nicholson patented a printing machine, in which “ the type, being rubbed or scraped narrower towards the bottom, was fixed upon a cylinder, in order, as it were, to radiate from the centre of it.” The cylinder, with its type, was to revolve in gear with another cylinder, covered with soft leather (the impression cylinder), and the type received its ink from another cylinder, to which the inking apparatus was applied ; the paper being impressed by passing between the types and impression cylinders. Such was the first printing machine, which was never brought into use, although most of Nicholson’s plans were modified and adopted by after constructors. Konig, a German, conceived nearly the same idea, and constructed for Mr. Walter a printing machine, by which, November 28, 1814, the Times newspaper was first printed by machinery driven by steam power, and working 1,100 impressions per hour. In this machine the type was laid upon a flat surface, the impression being given by the type passing under a cylinder of great size. This machine was super- seded by that of Applegath and Cowper. in which the novel points were accuracy in the register (one page falling precisely upon the back of the other), the method of inking the types, and the comparative perfection of the impression. CIVIL ENGINEERING. 29 Konig’s next improvement was the construction of a “ per- fecting” machine, which delivered the sheet of paper printed on both sides at the rate of 800 to 900 sheets per hour, equal to 1,600 and 1,800 impressions. Various improvements were made upon the existing machines, increased production and superior work being the result, until Mr. Applegath, in 182-7, combined in one leviathan machine four single or two perfecting machines. The product of this machine was 6,000 impressions per hour. The increasing circulation of newspapers, however, the competition among publishers, and the necessity of delaying the “ going to press ” to the last moment, in order to secure the insertion of the latent intelligence, soon made it evident that something superior even to the great Applegath was required, and the ingenuity of inventors was again taxed. Messrs. Hoe i and Co., of New York, introduced their famous “ feeders ” into London, in 1858, with a result so successful, that the entire system of printing newspapers was revolutionised. The Hoe 8-feeders turned out no less than 20,000 impressions per hour. The “ Hoe,” being constantly improved, held its own for ten years, and nearly every newspaper of importance in Britain and America used no other. The “ Marinoni ” machine appeared in 1868. Four of these machines were erected in the office of Le Petit Journal, a small paper sold at a sou, and these produced the extraordinary number of 144,000 copies per hour, being 36,000 for each machine ! In the same year the proprietors of the Echo introduced the “ Marinoni” into Loudon, and that popular evening paper has been hitherto printed by them at the rate of 20,000 perfect copies per hour ; the sheet, however, being much larger than Le Petit Journal. Four years later (1872) another and more remarkable advance was made. The “ Walter Press,” so named after the proprietor of the Times, made its appearance. It was the joint invention of Mr. Walter and Messrs. Macdonald and Calverley, of the engineering depart- ment of the Times. This machine differed from its predeces- sors. The paper is printed from a web of several miles in length, wound on a reel, perfected or printed on both sides, cut and delivered at the other end, at the rate of 17,000 copies per hour ! The illustration shows a 4-feeder “ Marinoni” machine, but those in use at the Echo office are 6-feeders. CIVIL ENGINEERING.— I. By E. G. Bartholomew, C.E., M.S.E. INTRODUCTION EARLY HISTORY OR THE SCIENCE. Civil Engineering is a term so comprehensive as almost to defy a complete and detailed explanation, whilst its importance is only equalled by its comprehensiveness. Its history is even more difficult to deal with, for it runs parallel with almost that of the world itself. Some idea of the scope of this vast science may be formed by stating what are some of the subjects it em- braces ; for it must not be imagined that the building of bridges, and the formation of canals and railroads, constitutes the whole of the occupation of the civil engineer. The civil engineer is one who applies the principles of mechanical and physical philosophy to the construction of the machines and public works by which the arts and accommoda- tion of civil life are rendered more efficient, extensive, and secure ; and hence Civil Engineering is the term applied to that science which treats of the construction of canals, railroads, roads, bridges, gas and water works, sewage and drainage works, aqueducts, piers, harbours, docks, viaducts, lighthouses, break- waters, and such like. Each of these subjects involves an acquaintance with detail in their design and carrying out which is by no means apparent on the surface. For instance, in the one subject of drainage is involved the arrangement of the dams, sluices, syphons, and machinery of every kind, whether actuated by steam-power, water-power, or the wind, for removing the surplus water, and the canals which by their intersection com- municate with every part qf the district to be drained. Ho must be acquainted with all the principles and details of machinery, which is after all but the handmaid of civil engineering, and must be enabled to utilise it to the utmost for facilitating and economising his work. He must also be practically acquainted with the strength of materials, and with those principles of com- bination by which the greatest amount of strength is gained with the least- expenditure of material. He must also have a clear knowledge of brickwork and masonry, and carpenter’s work in general. From the foregoing it is evident that the occu- pation of the civil engineer is far from limited, and that his attainments, if he would excel, 'must not be few. He must be a man of strong determination to combat with the difficulties he is sure to encounter, and one of ready thought to devise ex- pedients to overcome them. Inasmuch as the civil engineer must be well acquainted with mechanical engineering, and not altogether ignorant even of many points of military engineering, he stands at the head of his profession, and the vastness and variety of his works renders a merely superficial acquaintance with details useless to him ; and no man need aspire to any eminence as an engineer who has not climbed the ladder of ex- I perience from its lowest round. Some of our best engineers have been men trained in the school of the hardest manual labour, and have risen step by step, gaining experience at each advance, and employing that experience to the development of further achievements ; and it is a fact that all our most cele- brated engineers have made themselves conspicuous by works essentially their own. It may, under certain circumstances, be desirable for an engineer to have the assistance of an architect; but that engineer who is able himself to proportion his structures to the rules of architecture, and to produce a work as elegant as it is useful, and as useful as it is solid, has an immense advantage over others. Similarly, as many of the public works which the civil engineer is called upon to carry out involve very largely the employment of machinery, both in the course of the work and permanently afterwards, an intimate knowledge of mechan- ism and mechanics is of the utmost value to him ; and certainly no individual is so well qualified to adapt mechanism to the par- ticular function it is intended to perform as the man who under- takes the general design. The architect and the mechanician have each their sphere of usefulness, and very many works are required in which architecture or machinery alone are needed. Such works are not, stricly speaking, in the province of the civil engineer to carry out. One more remark we would make is that an intimate acquaint- ance with geometry is indispensable for the civil engineer to possess. His operations are very frequently of such a nature as to need great strength, and structural strength necessarily implies that a strain has to be withstood. The engineer must therefore be prepared to meet any strain that may be applied, in the most effective and economical manner. Any unnecessary use of material must be avoided, and therefore, particularly where lightness has to be combined with strength, a clear know- ledge of direction of force and strain is an obvious necessity. That civil engineering is certainly one of the most ancient, if not the most ancient of all the sciences, is evident from the magnificent relics which continue, after the lapse of thousands of years, to be the wonder and admiration even of the present age. No doubt the different conditions of society at different periods of the wor-ld’a history have caused various modes of development of the science of engineering. In the earlier ages war engrossed more attention than the arts of peace, and we might expect to find more attention paid to the arts of war in those days ; and hence the works of the early engineers tyould embrace the defence of their cities by the erection of massive walls and towers, or the construction of engines to demolish them. But although many of the arts of peace may have lain dormant for a while, commerce was not neglected ; and we find the Phoenicians, who were the earliest traders on record, more than 1,200 years before Christ, settling upon the coasts of the Mediterranean, building Sidon, Tyre, and other coast-towns, and forming moles and harbours for the protection of their shipping, and for facilitating their loading and unloading. The defence and siege of Tyre (332 b.c.) form most interesting records of early engineering — not, perhaps, strictly civil, but nevertheless, a record of ingenious devices to meet emergencies which many a modern engineer would do well to study. When we turn to Egypt we are again met with most remarkable remains of early engineering skill. One of their monarchs, Menes, who lived 2,320 years before Christ, actually diverted the course of the Nile, and, by cutting water-courses and raising embankments, converted the immense marsh which existed upon both sides of the river into the finest agricultural district in the world. The great lake Moeris, which, according to Herodotus, was 30 THE TECHNICAL EDUCATOE. 450 miles in circumference, was artificially constructed, and 1 intended as a vast reservoir to receive the overflowing water of ; the Nile, that it might be subsequently utilised for irrigation. < This great work of engineering was accomplished 1385 B.c. The canal which connected the lake with the river still remains. : That remarkable work of modern engineering, a work recently completed, the Suez Canal, was accomplished by Ptolemy II. hundreds of years prior to the Christian era. A passing remark ; is all we can give to the Pyramids — those stupendous works of ancient engineering which, from their construction, must have called into action the highest skill of the Egyptian engineers. These royal sepulchres are not entirely composed of huge blocks of chiselled stone, but are built upon a core or foundation of the original mountain, the native rock itself being excavated to form the burial-chamber ; and the manner in which the large masses of stone which form the facing of the rock were cut, carried, and lifted to their respective levels, furnishes an inte- resting study for the engineer. The great pyramid contains at the present day more than six millions of tons of hewn stone. The Pharos, or lighthouse of Alexandria, built by that cele- brated civil engineer, Sostratus, was considerably higher than St. Paul’s Cathedral. It was constructed entirely of stone, and divided into five storeys. But the engineering works of the early Egyptians were not confined to masonry. The people were acquainted with metallurgy and hydraulics. The process of refining gold and silver, and the forging of iron, were practised by them largely. It is not surprising that the science of hydraulics reached an advanced stage in a country so intimately associated with water supply, and the advantages and dis- advantages connected with it. To bring the forces of Nature to serve the convenience of man is one of the great aims of the engineer, and this the ancients knew well how to effect. Naturally, Egypt was a marsh ; hence their engineers raised dams and banks to restrain the river within bounds. But Egypt altogether without the Nile would be a barren waste, lying as it does under almost a tropical sun, and rarely watered by a shower ; hence the Egyptians made lakes and canals to irrigate the land ; and to avail themselves of the water when sunk below the level of the soil they devised engines, influenced by wind or water, whereby the lowered waters of the river might be raised, and poured again upon the thirsty soil. We pass on now to Greece, and here we find engineering directed principally to the erection of temples, and buildings for the celebration of religious rites, chaste and beautiful, but grand and massive ; not that the ancient Greeks by any means neglected either commerce or the arts of war. They built | magnificent walls to protect their cities from the incursions of man, and capacious harbours to guard their ships from the assaults of Nature. To Hippodamus, a celebrated Greek engineer, the city of Rhodes owed its beauty. Philon and Callicrates were Greek engineers, who lived about 400 b.c. The siege of Rhodes by Demetrius, and its defence by Diognetus and others, form an interesting record of the advance of civil and military engineering in these early times. But probably no individual of the period was so truly an engineer, in the strictest sense of the word, as Archimedes, a man fruitful of resources, and quick of invention, many of whose contrivances are employed to the present day. He was as clever as a mechanician as he was correct as an engineer ; and the combi- nation of these two sciences in his person, and the success resulting therefrom, form the best proof we can Have of the advantage to be gained in all engineering matters by uniting theory and practice. The stately Parthenon, and other grand Grecian temples, are, it is true, rather monuments of archi- tectural than engineering skill ; but the man who could design and erect such massive edifices would require to be an engineer of a high order. To design an architrave 21 feet long, 5 feet 8 inches wide, and 6 feet 9 inches deep, might be easy ; but who shall estimate the skill requisite to convey a single block of stone of these dimensions to the spot, and elevate it to its site more than 40 feet from the ground — a block containing 803 cubic feet, and weighing at least 50 tons ! But we must not linger amongst the relics of engineering art in Greece. There are greater works to be found in Rome and its neighbourhood, and Vitruvius has left us much information of Roman engineering works, many of which have in part or altogether disappeared. Conscious of the advantage derived from the selection of a healthy site for their towns, the Romans were very careful to avoid such places as, by their natural position, would render a, discharge of sewage a matter either of doubt or difficulty. Ini this respect the Romans wore in advance of ourselves, for we select our position and afterwards endeavour how best to draim it, and if the general level prove lower than the means of dis- charge we are compelled to erect costly machinery to convey ifc away. The Romans were equally alive to the importance of a, good water supply. If, from other causes, they desired to build upon a badly-watered locality, they expended incredible labour, and spared no expense to bring water to their town ; and the aqueducts of the Romans are to this day Standing monuments of engineering skill. The engineering works of the Romans were not confined to any particular region. Wherever their arms carried conquest, there they displayed the same wonderful ingenuity. The whole of Europe abounds more or less with the remains of the labours of their engineers. Their walls, their gates, their harbours, their temples, bridges, roads, aqueducts, public buildings, the materials they employed, their triumphs over Nature, the height of civilisation they attained to, are all so many proofs of the advanced state of civil engineering science amongst them. Their introduction of the arch in masonry is by itself a memorial to their engineering greatness ; for although the existence of the arch in some of the pyramids of Egypt points, to an era far before the building of Rome, yet it must be remembered that the Egyptian arches were con- structed rather as ornaments, or as covers to sarcophagi, than as the bearers of superincumbent weights, and that therefore the true value of that form was unknown to the Egyptians. But look how profusely the arch is made use of in the amphi- theatre of Vespasian, where they stand tier over tier ; see the wonderful lightness and immense strength of that enduring monument, so perfect after the lapse of eighteen centuries ! What work of modern engineering skill do we find to compare with it ? Modern engineers have followed the plan adopted by the Romans, of forming breakwaters by the immersion of large blocks of stone or concrete, piling them up without regard to order, until they appeared above the water. Of course the base of such a structure is greatly larger than the top, but the pris- matic form thus obtained conduces greatly to its stability and. strength. Plymouth breakwater is constructed thus, and is only a reproduction of the breakwater at Centocella, now Civita. Vecchia. The Romans eminently excelled in their roads. As a rule the.se roads were carried forward in a straight line, regardless of all natural obstacles. They are to be found in almost every country of Europe, not excepting our own. Twenty-nine great military roads centered in Rome, and extended thence to the utmost limits of the empire. They were most substantially constructed, and profusely decorated on both sides with temples and other ornamental structures. The Romans are stated to have constructed about 53,000 miles of road. The description of the Appian Way reads almost like a fable. It was 360 miles long, and paved throughout with large blocks of stone, squared and dressed with the chisel, and so intimately united that the interstices between them are scarcely visible. When the roads passed through towns they were built upon vast sewers, which effectually drained their streets. The bridges built by the Romans have withstood the storms and floods which have carried away many a modern structure. Their aqueducts are marvels of engineering skill, and evidence a perfect knowledge of hydrostatics and hydraulics. The finest of these were the Aqua Claudia, which was fifty miles long, and conveyed water to the capital from Porta Maggiore, and the Anio Novus, sixty miles in length, six miles of which was carried upon arches, some being 100 feet high. Not only were the Romans exceedingly particular in their choice of sites for their towns and cities ; but if necessity com- pelled them to select a position too contiguous for health to marshy ground, they in the most complete manner removed the evil by an elaborate system of drainage. Rome itself was perfectly drained, most of these subterranean channels remain- ing to the present day. Tunnels, some of great length, were amongst the engineering works of the ancient Romans. The temples built for their gods, although not equal in massiveness to the temples of the Egyptians, yet far excelled them in mag- nificence and architectural beauty. Indeed, in all the works TECHNICAL DRAWING. 31 of the Roman engineer* we trace a master hand. Centuries have elapsed since they were completed, and although discoveries have since been made, and many great works carried out, we mu.st still yield the palm of merit to the Romans in almost all points of structural and architectural engineering. Our brief history now passes in silence over several centuries. From the decline of the Roman empire to the middle of the fifteenth century the arts were in a declining state, and little or nothing of an engineering character was undertaken. The first revival of civil engineering in Europe took place in Holland, when the known rich and valuable character of the low-lying land adjoining the sea-coast, and subject to the overflowing of the tides, began to attract attention, and the idea of reclaiming it from the German Ocean was entertained. We merely refer to this now as a matter of history, that the first engineering works of more modern days have been those of drainage, which in the case we have alluded to consisted of the twofold operation of erecting a barrier against the encroachments of the ocean, and then removing the enclosed waters. Indeed, so important was this kind of work, and so valuable the results-, that for a long series of years, both in this country and on the neighbour- ing coasts of Holland, tnis was the only work of an engineering character attempted. It was owing to the great success which attended the efforts of the Dutch engineers, that some of them, particularly Vermuyden, were invited to England to superintend the drainage of the great fen district in Norfolk, a work which the Romans attempted, but without success. But we now enter upon a period when we are enabled to give a more connected and detailed account of our own engineer- ing works, premising, however, that as our object in the suc- ceeding chapters upon this subject is to explain the principles and practice of the various branches it may be divided into, we shall only allude to particular works of an engineering kind which have been carried out, in order better to illustrate the subject. TECHNICAL DRAWING.— II. TECHNICAL DRAWING BOX TECHNICAL PENCILS HINTS ON COLOURING DRAWINGS — LINEAR DRAWING BY MEANS OP INSTRUMENTS. The writer has frequently been asked by students, “ Which is the cheapest box of instruments to get?” whilst others have put to him the question, “Which is the best case to buy?” Now, it is not within the province of this work to recommend the instruments of any particular maker, nor to suggest the prices which should be given, as this last depends on the means at the command of the purchaser. But smallness of price is not always real cheapness, and a good article, manu- factured by, and bearing the name of, a respectable English house will be found by far the most economical in the end. Of course the price of a case of drawing implements must depend on what is contained in it. The following articles are indispensable ; and these having been obtained as a beginning, single instruments or colours can from time to time be added as occasion may require : — A set of instruments, which should at least comprise a pair of compasses with steel, pencil, and inking leg ; a draw-pen ; a twelve-inch rule, divided into eighths or tenths on the one side, and twelfths on the other ; if pos- sible, a protractor ; and certainly a stick of Indian ink. In addition to these, the mechanical draughtsman requires colours ; and, proceeding again to name the smallest stock he can do with, we advise him to get at starting three only — viz., indigo, lake, and yellow-ochre — from which he will be able to mix most of the tints used in Technical Drawings, according to methods which will be given presently. Of course he will add to the three colours from time to time. Then he will require a small slab — one with three divisions will be found the most useful — and a few brushes with sticks. As to pencils, the degrees most generally useful are those marked hb and h, the latter of which, being harder than the former, is more adapted for very minute work ; but, as a rule, hard pencils are not the best for mechanical drawings which are to be inked, as they are liable to make grooves in the paper, the bottom of which the nib of the drawing-pen does not touch, and hence the edges of the line will be ragged ; and further, lines which are drawn with very hard pencils are difficult to rub out. For mechanical drawing, it is best to cut a flat point to the pencil ; this is done by cutting away the wood, and leaving about an eighth of an inch of lead projecting, which is then to be cut until it is thinned to a flat, broad point like a chisel ; the broad side of this point is moved along against the rule, and the line thus drawn will be found to be much finer than one drawn with a round point. The chisel-point is economical in various ways, for it will not break so often, and the point once cut can be rubbed from time to time on a piece of fine glass- paper or a file, or even on the edge of the drawing-paper. Many of our readers will have experienced the annoyance, of a point breaking in the midst of a lesson, just at the moment when following the teacher’s illustration line by line. The student is therefore recommended to employ two pencils of the same kind, and to make a point at each end of both before beginning to work ; to keep the spare pencil at his side ; as the point he is using becomes blunt or breaks, he turns, his pencil; and when the same occurs to the second point, he takes up the spare pencil. He has thus the use of four points, more than which he is not likely to want in one evening. Once again the student is urged to remember that the mere possession of a case of instruments, however good, will not constitute a draughtsman. The instruments are merely the tools — the mechanical agents through which the mind acts ; and it cannot be denied that the more the mind comprehends of the subject to be drawn, the more willing and intelligent servants will the hands become, and the more accurately will they guide the compass or the drawing-pen. Geometrical drawing, then, should be looked upon as a mental exercise more than a merely manual occupation or employment, giving us not only subject for thought and earnest reflection, but enabling us to communi- cate our plans to others in such a manner that they can under- stand us and work out our designs better than they could haves done from the most eloquent description. The student will, no doubt, find it difficult at first to draw very fine lines, or to get them to intersect each other exactly as required, especially if he has been engaged in some hard manual occupation during the day ; but he will find a little practice will soon overcome this, if he but starts with patience, energy, and the earnest desire to excel. A PEW PLAIN HINTS ON COLOURING DRAWINGS. When you are about rubbing up some colour, first see that the slab is not dusty. Then drop some water on it from one of the larger brushes ; but on no account dip the cake of colour into the cup or glass of water, which is a most wasteful plan, as it softens the cake, and causes it to crumble off in rubbing. Rub the paint firmly, but not too heavily, or you will not get the colour smooth. Be careful to hold the cake upright, so as to keep the edge flat. When you have rubbed as much colour as you think you are likely to want, do not at once put the cake back into its place in the box, but stand it on one of its edges so as to allow it to dry, otherwise it will stick to the box. Blue, red, and yellow are called the three primary colours,. 'When two primaries are mixed they produce a secondary colour . Thus:— Primaries. Secondary. Yellow and Red produce Orange. Yellow and Blue „ Green. Red and Blue ,, Purple. When you wish to mix a secondary colour, such as green, from the two primaries blue and yellow, rub the blue in one division of the slab, and the yellow in another, leaving a space between them. Then, with your brush, mix the two colours in this vacant space ; but on no account rub either of the cakes in the colour obtained from the other, as this would leave the end soaked in another tint, and when you used it again you would find the colour would be impure. Of course, these remarks apply to the mixing of any two colours. In order that colour may flow easily, and cover a surface evenly, it is necessary that it should be thin. It is always easy to wash it over again if it is not dark enough, but it is very difficult to wash off the colour if it be too dark. "When you have laid on your colour, do not touch it again whilst wet. If it should require re-touching, let this be done 32 THE TECHNICAL EDUCATOB. ■when it has dried, as you will generally make it worse by stirring about in the wet colour, and will be likely to rub up the surface of the paper. Wherever it is possible, use a large brush in preference to a smaller one, as you will by this means be the more likely to succeed in getting a flat wash, whilst a small brush might make the tint lie in streaks. Care is, however, necessary in using a large brush, so that you may not pass over the outlines. To lay a flat wash of colour is of great importance, and to be able to accomplish this some practice is required, in order to obtain which you are recommended to draw several triangles, squares, or other figures, of different sizes. Commence by colouring the smallest, and then work on ^ in order of size, as it is more difficult to spread the wash over a large than a small surface. Let your brush be quite full of thin colour, and, holding it nearly upright, pass it boldly over the upper part of the figure; then gradually bring the colour down, spreading it equally over the whole work as rapidly as you can, so as to pre- vent, if possible, any one part drying be- fore the whole surface has been covered with colour. The following is a list of the colours used by most architects to express the various substances Colour. Material. Brickwork to he exe cuted (in the plan and sections) Brickwork in Eleva tious . The lighter Woods such as Eir . Oak or Teak . Granite . Stone generally Concrete Works Wrought Iron Cast Iron Steel Brass Lead Clay or Earth . Slate Crimson Lake. ( Crimson Lake with Burnt ( or Venetian Bed. | Baw Sienna. Vandyke Brown. Pale Indian Ink. f Yellow Ochre, or Pale | Sepia. ( Sepia with dark mark- \ iugs. Indigo. f Payne’s Grey, or ( Neutral Tint. ( Pale Indigo tinged 1 with Lake. ( Gamboge, or Eoman ( Ochre. j Pale Indian Ink tinged ( with Indigo. Burnt Umber. Indigo and Lake. Having thus given a few of the ele- mentary principles of drawing and colour- ing, we will now proceed with our subject, showing the application of these prin- ciples, and developing others as the lessons advance. The principles of foundations being enunciated in the lessons on “ Building Construction,” it is here proposed to give some studies of the various assemblages of timber employed in such works, in order to afford some useful practice in drawing parallel lines at right angles to each other. UNEAB DRAWING BY MEANS OE INSTRUMENTS. Big. 4 is the plan of a network of timber supporting a plat- form on which a foundation is to be erected. Here the transverse sleepers, a a a a a, rest directly on a site which, although not soft enough to render piling necessary, is still not sufficiently firm to allow the walls of the structure to be raised without the foundation being extended and equalised. Fig. 5 is the sectional elevation of the sleepers and wall, a being the elevation of the cross-sleepers, which are shaded in the plan. With thus much information as to the meaning of the sub- jects before him, the student can now commence work ; and as we have often known learners waste half of their evening, and when reproached with idleness, say, don’t know where to begin,” we may here, once for all, lay down the principle, that when the general position of the whole subject on the paper has been decided upon, the sure plan is to draw first that which would be laid down, or built first. It is also necessary to say that all the drawings in these lessons are to be worked to at least twice the size of these examples. Well, then, the sleepers, a a a a a, would, of course, be laid down first ; and therefore these must be drawn first. Draw the line A b, the front edge of the first cross-sleeper (Fig. 4). This line is to be drawn with the T-square, holding the butt- _ end tightly against the left-hand edge of |D the drawing-board. Do not draw it exactly the length of A b, but longer, and set off the length A B upon it, leaving a little of the indefinite line on each side of A b. The purpose of this will be pointed out to you presently. Next, keeping your T-square in its place against the edge of your board, move it by its butt-end a trifle lower down, place your set-square against it as shown in the cut, and draw perpendiculars from A and B (as shown in Fig. 4). The immediate purpose of these is to give the ends of all the cross-sleepers ; but as they will be wanted for another purpose by- and-by, draw them much higher than they are for the present required : in fact, in all architectural drawing, it is very useful to draw your 'pencil lines past their abso- lute extremities, for reasons which I will explain to you when speaking of inking the drawings. You will now find it useful to employ two pairs of compasses or dividers. In the one, take the thickness of the sleepers ; and in the other, the width of the space between them. From A b set off on the perpendicular, A C, the width of the first one, then a space, then another sleeper, and so on ; and draw the lines which give ijB the edges of the sleepers. It will, of course, be remembered that too hard a pencil should not be used, so that the superfluous lines may be easily rubbed out after inking, and that the pencilling must be done as lightly as possible, so that no more of the grit of the lead than is absolutely necessary may be left on the paper, for this will work up between the nibs of your draw-pen, and cause endless annoyance and diffi- culty. With the same width in your compasses, mark off the sizes of the longitudinal sleepers, b b b b, which rest on aaaaa; and across these again draw the planking, c c c c c, the lines forming the ends of these planks to be drawn within the lines A c and b d. To draw the sectional elevation (Fig. 5), draw the ground- line, e f, and the line above it, d e, representing the height ot the cross-sleepers, of which a is the elevation. Produce the lines of the longitudinal sleepers in the plan ; these will give the sides of their sections in Fig. 5, and across these draw the edges of the planking, c, parallel to the lower sleeper. It will be seen that the under sides of these sections are lower than the upper edge of the lower sleeper ; this is because they are notched on to it in the manner shown m the lessons on “ Building Construction. On the platform thus constructed draw the section ot the pier or wall. , ,, . It may be mentioned that the spaces between the sleepers should be well rammed or flushed up to the top of the sleepers — the planking may be then said to rest upon a solid Dasin and planks should be spiked to the sleepers with wooden pms. Fig. 5. APPLIED MECHANICS. 33 APPLIED MECHANICS.— I. BY ROBERT STAT7ELL BALL, M.A., LL.D., Astronomer-Royal for Ireland. APPLICATIONS OF THE LEVER AND THE SCREW. It is proposed in this series of lessons to give an account of the practical applications of mechanical principles. The general laws of Mechanics have been already laid down in our “Lessons in Mechanics ” in The Popular Educator. Our business is with the application of these laws to practice, and therefore we shall not unfrequently have to refer to them. For example, in the present lesson we shall often assume that the reader is familiar with the different forms of lever and their mechanical properties, of which an account will be found in Lesson VIII. of the series referred to. So also in what we shall have to say of the applications of the screw, we shall suppose that the reader already possesses the knowledge which may be gained by a perusal of Lesson XII. Occasional glances have been given in these lessons of the useful applications of the mechanical powers. It shall be our duty to follow out the useful part to its details. We shall- describe and give a practical account of many tools, implements, and machines ; we shall select those which are of interest either from the fact that they are of very extensive use, or that they are connected with some impor- tant branch of manufacture. We shall occasionally describe a very common tool, and occasionally a colossal machine or struc- ture. It is hoped that an account such as this is designed to be will not only prove of interest to the student of Mechanics, but be of actual service to those who are in any way connected with manufacturing industry. The lever is susceptible of a vast variety of forms, and it will be useful for the student to practise himself in trying to recognise its presence under its different aspects. In machines of any complexity, which contain a great number of moving parts, many of these parts are levers of one form or another. We shall mention a few of the different cases in which this contrivance is met with. We begin with one that is very simple and well known — the ordinary pincers. This is shown in Fig. 1, in which the familiar process of pulling out a nail is represented. This tool consists of two levers of the first order; the common fulcrum of both is the pin at E, about which they work. The power is applied at h, by squeezing the ends of the levers together. The load is at R, and consists in the grip with which the nail is held. In the figure the leverage is about sixfold — that is, the jaws grip the nail with six times the force that the ends, H, h, are forced together. The nail is held in the jaws by friction, which in- creases with the pressure, and consequently, the more powerful the force with which the jaws are pressed together, the more secure is the hold which they have of the nail. Hence we see the principle of the lever of the first order applied in taking hold of the nail, and we shall now recognise it in the sub- sequent process. When the nail is to be extracted, the side, s, of the jaw is pressed against the surface, and s becomes now the fulcrum, h is pressed down to- wards the surface by the hand, and this pressure constitutes the power. The load to be overcome is now the tenacity with which the nail resists being withdrawn. This is principally due to the friction of the wood upon the driven, and of course varies with the nature of the wood and the size of the nail. We shall take one instance. It has been found that a nail called a three- penny brad, which is 1'25 inches long, when hammered to a depth of 0'5 inch into dry Christiana deal, required a force of 58 lb. to extract it. Let us suppose that it is a nail of this size which we have represented in the figure. Now, the action ol the hand is twofold — it first squeezes the jaws together, and then, while holding them firmly, presses the whole tool in the direction of the arrow on h h. It is only the latter part of the action of the hand that we are at present concerned with. Let rail the perpendicular s f on h h. Then, by the principle of 3— Vol. I. the bent lever, the power of the hand must be to the resistance- of the nail, as the line s T is to the line s p. Now, on the scale on which the figure is drawn, s T is about one-eighth part of s p ; hence the power necessary to be applied at h is only 58 -T- 8, that is, about 7 or 8 lb. There is another advantage gained by the use of this tool, which it is important to notice, as the same case is met with in many different tools and machines. The pincers enable the whole power of the arm to be concentrated on withdrawing the nail. The fingers applied directly would be bruised in fruitless efforts even to stir the nail ; but the pincers, by giving a good object to grasp, enable the whole power of the arm to be applied, and then they magnify this power eightfold. No wonder, then, at the remark- able efficiency of this useful tool. Levers are not unfrequently used when there is no mechanical advantage to be gained in the way of power, but where the direction of a force is desired to be changed. In such cases it is sometimes a little difficult to see that the piece is a lever. We must then carefully remember the definition, that a piece capable of turning around a centre, to one point of which the power is applied, while to another point the load is applied, is a lever. A common illustration of this form is shown in Fig. 2, which repre- sents the well-known bell-crank. Bell-wires being stiff and rigid, it would be impossible to change their direction by means of pulleys, and so the beautiful and ingenious contrivance of the bell-crank has been adopted. It consists of a quadrant, usually of brass. It is supported at the centre, r, upon a pin which is firmly fastened to the wall, and about this pin it is free to turn. The power is applied to the circumfer- ence of the quadrant at the point p, the direction of its applica- tion being perpendicular to the radius F P ; this is the point to which the wire is attached by which the pull is given. Now, the effect of the pull on p is to turn the crank round slightly in the direction of the arrow, and this can only be done by raising R ; hence at r the wire to transmit the pull is attached. The load is in this case only equal to the power, so there is no gain, in that respect; in fact, if anything, there is a slight loss, owing to the friction of the crank about the pin. A very useful application of the lever of the third order is met with in the common treadle used in turning the foot-lathe. Here the power consists of the pressure of the foot which is applied between the fulcrum at one end, which is the centre about which the treadle moves, and the load at the other end, which is communicated by means of the connecting-rod and crank to the main shaft of the lathe. The power is here diminished, as is always the case in the lever of the third order - but the object aimed at is convenience, and it is found by ex- perience to be easier for the foot to exert a pressure sufficient to move the lathe through a short distance, rather than a less pressure through a longer distance. The real resistance which the lathe has to overcome is not the raising of a weight, but the shearing force necessary to cut off with a tool shavings of wood, ivory, iron, or other work on which the lathe may be engaged. The lathe apparently gives an increase of power, because in turning iron, for instance, the shavings that are- cut off are far greater than could have been removed from the work by the direct application of the tool. One reason of this is, that in the latter case only a few muscles of the hand and arm can be employed, while, with the aid of the lathe, all the powerful muscles of the leg can be concentrated on the work. The screw is a mechanical power of the utmost importance. Its theory has been already fully given in Lesson XII. We shall, then, point out some practical considerations in connection with the use of the instrument. The efficiency of the screw is largely diminished by friction. In fact, sometimes the power of a screw is found to be only one- fourth of what it would have been had not this force been present. This contrasts the screw with the lever, for in the latter the effect of friction is quite imperceptible. Theory at once in the lever gives the relation between the power and the 34 THE TECHNICAL EDUCATOK. load ; so docs theory in the screw also ; but then it must be preceded by and based upon actual experiment. In order to make this clear we shall fully describe experiments which have been made upon a screw-jack, with a view of deter- mining the relation between the power and the load. The screw-jack employed is represented in Fig. 3. It consists of a stout tripod of iron, two legs of which are shown in the figure. The top of this, A, is made of brass, and forms the nut of the screw. The screw itself is very carefully turned from a cylinder of wrought iron. Its pitch is two threads to the inch, and its diameter about two inches. The top of the screw is enlarged, as seen at b. This contains two holes, one of which is shown, while through the other the arm b e is passed. This arm is for the purpose of turning round the screw. At c is the crown. Tins is so arranged that it can turn round on B, so that after it has bitten into the surface which is being pressed upwards it shall cease to revolve, though b is turned round. The object of this is to diminish the great friction which would be experienced by making the top revolve against the surface, and placing the fric- tion instead between the top of the screw and the under surface of the crown, where it can be reduced by having a smooth and well-oiled bearing. Another reason is, that the surface acted on would be torn and injured by the action of the crown. There are slight ridges round the margin in order to make it take firm hold. The bottom of the tripod is also furnished with short projecting points which embed them- selves in the surface and prevent the tripod from turning round with the screw. The screw-jack used in the experiments now described was one adapted for weights up to two tons. The arm is about 33 inches long. When the arm makes one revolution it moves through a space of oo 2 x -- x 33 = 208 inches. But it must perform two revolutions in order to raise the screw 1 inch. Hence the power must have been exerted through a distance of 416 inches to raise the screw 1 inch. According, therefore, to the principles laid down, if there wore no friction the mechanical efficiency of this screw should be 416-fold. Let •us see how much it is in reality. A weight of 1,000 pounds is placed upon the screw, and it is found that a power of 8'2 pounds applied to the extremity of the arm is just sufficient to raise it. Hence the real mechanical efficiency is — have moved 754 inches. This would be the mechanical efficiemcy without friction; with friction it may be assumed about ome quarter of this, or 188. Hence, in order that the nut may exert a pressure of one ton in drawing the surfaces together, it is only requisite that the hand exert a pressure of 2240 188 = 11-9 lb. 1000 8-2 = 122 lb. In fact, since ijjgo = 29, the true mechanical efficiency is only 29 per cent, of what it would Lave been had there been no friction — less, in fact, than one-third. It is important to understand this thoroughly, and in general it will be safe to calculate on not getting from a screw more than one-fourth of the power it would yield without friction. The most useful contrivance by which the dif- ferent parts of a structure can be united together owes its efficiency to the screw. This is the well- known screw-bolt represented in Fig. 4. Bolts are the stitches by which machines are put together. They owe their utility to several distinct reasons. 1. They enable the parts to be drawn together very forcibly. Thus, suppose a bolt have ten threads to the inch, and that its nut be turned by a wrench, the arm of which is a foot long, the hand must move in one revolution through_a circum- ference of 22 x 2 x 12 = 75’4 inches. Hence, when the nut has been moved one inch, the hand must Thus, with a force of 12 lb., which can be exerted with little effort, the parts are pulled together by a force of a ton ; and with a little exertion a force four or five times this amount is readily produced. 2. The strength with which they hold the parts together is very remarkable. Not only does a bolt bring the parts into intimate contact, but it keeps them there. In fact, if the screw be properly made, and the size of the nut properly proportioned, the bolt may be considered as formed of solid iron when once the nut is screwed home. But wrought iron, when good, requires a force of about twenty tons per square inch of section to tear it asunder ; consequently a nut whose diameter is an inch will not be overcome by a force less than about fifteen tons. Though the two means just men- tioned are the most important, yet there Tig. 3. are several subsidiary reasons why bolts , are so extensively used. 3. Their simplicity. A bolt consists only of two parts, for the nut requires no catch to prevent it from slipping back along the screw after it has been brought home. This is due to fric- tion. Without friction every nut would require to be provided with some complicated arrangement to prevent its motion. Bolts connecting parts subject to extreme vibration can gene- rally have their nuts kept tight by the simple process of screw- ing a second nut down home on the top of the first. 4. Another great practical convenience of bolts is the very different sizes of the work they can grasp. A bolt 12 inches long, and with 2 inches of screw on the end, can bind together any two pieces whose united thickness is a little greater than 1 0 and a little less than 12 inches. But with the simple addition of washers — which are little iron plates with holes large enough to allow the bolt free passage — a 12-inch bolt can be made to grasp any two pieces whose united thickness is less than one foot. 5. Bolts require very little to be done to the work to which they are applied. All that is necessary is that a hole be bored large enough to admit the bolt. It is not necessary that this hole fit closely ; a loose fit acts as well as a tight one. 6. Nor do bolts injure the work when the pres- sure is applied to them, because by the use of washers of proper size the force can be distributed over a sufficiently large area on the surface of the work, and consequently bruising it can be avoided. 7. Bolts can be very readily applied, removed, or changed, and only a most simple tool- — a screw-wrench or spanner — is necessary for the purpose. No skilled workman is required. 8. Bolts being made of wrought iron are ever- lasting if rust be prevented. They are very cheap, as thousands of tons of iron are annually manufactured into bolts by machinery. They are kept in stock, of all sizes and forms, in shops where they are sold, and they are very portable. These reasons being considered, we need not wonder at the enormously varied circumstances under which bolts are employed ; they load us with a heavy debt of gratitude to that most beautiful of the mechanical powers — the screw. Little need be said of the common wood-screw. The thread of this screw is sharp, as it has to cut a nut for itself in the wood through which it passes. Its point must first be inserted into a hole, some of its threads then embed themselves slightly in the wood, and thus form the beginning of a nut. When the screwdriver is applied the screw advances, and thus makes its nut more perfect. It may be remarked that a screw should always be at right angles to the grain of the wood, so as to ANIMAL COMMERCIAL PRODUCTS. 35 enable the thread to insinuate itself between the interstices of the fibres. It is obvious that this cannot be done properly if the grain be parallel to the axis of the screw. I^Ve so all conclude this lesson with an account of a common aneil useful machine, which combines in itself examples both of the lever and the screw. This is the vice, of which, in its W ordinary form, a diagram Fig. 5. is given in Pig. 5. It consists of two jaws, A B and a'c. a b is continued downwards into what is called the tail, r, which rests upon the ground. The object of the tail is to support the vice when, as is often the case, the work between the jaws at w receives a blow from a hammer. a' is firmly secured to the bench by means of a strap of iron, t, which passes around it, and is then bolted to the bench at d. Thus the jaw A b is fixed; while the other jaw a' g is capable of turning around the pin shown at a’. Thus c can either be brought into contact with b, or re- moved to a considerable distance from it. The object of. the vice is to seize the work, w, and hold it very, firmly while it is being filed, or drilled, or cut with a chisel, or undergoing some other operation. Of course, it is only for comparatively small pieces of work that such an instrument is used or, indeed, required. The necessary pressure is given to the jaw a' c by means of a screw, s. In Fig. 6 are shown the pieces, of lead which are used for putting on the jaws of the vice when holding work which would be injured by the .steel faces of the vice 5 unprotected. ' • ru •». . • Wiien the handle, h, is turned so as to move the screw into Lhe nut, the jaw a' c is brought forcibly towards A b. a' c is then a lever of the third order, as the fulcrum is at one end, the load at the other, and the power in the middie. The power of the screw is therefore slightly diminished, when applied to the work at c ; but as a force of a ton or more can easily be exerted by the screw, it will, even though it loses a third of its amount by the nature of the leverage, exert a tremendous pressure on the work. I he surfaces of the jaws are roughened, so that they can take ■a firm grip of what is between them, and hold it by the friction. At E, a spring acting upon the jaw a' c is shown. The object of this is t® move the jaws asunder when the pressure of the screw is relaxed. The screw and its nut are quite independent of the jaws, and require to be renewed occasionally, as the thread of the .uut is apt to wear out by constant use. There are multitudes of other applications of the screw and lever, and it will be useful for the student to exercise himself in endeavouring to examine them ANIMAL COMMERCIAL PRODUCTS.— II. CARNIVORA. DIGITIGR ADiE ( continued ) . The Tiger ( Felis tigris ) inhabits the Asiatic continent, and is especially abundant in Hindostan. He is nocturnal in his habits, and during the day generally lies asleep in some shady spot’ gorged with his last meal. He frequents the neighbourhood of springs and the banks of rivers, where the weaker animals, forced by the scorching heats of the tropics, seek coolness and drink The skin is a bright tawny yellow, shaded into pure white beneath the body, and beautifully marked with dark bands and stripes. It is used to cover the seats of justice in China, and is also employed for rugs and mats. Prom 200 to 250 tiger-skins are annually imported into the United Kingdom. The Leopard ( Felis leopardus, Cuvier). — This animal is found in Africa and India : it inhabits the deepest recesses of the forest. thus rendering pursuit nearly impossible. Taken usually in tiaps, it is also hunted with dogs, until, being an expert climber, it takes refuge in a tree, and when the hunters come up it is easily shot. The skin is a tawny yellow, the lower parts white, and covered all over with dark spots, which vary in size and form. It is worn as a mantle by the Hungarian nobles who form the royal body-guard of Austria, it is als® used as a saddle-cloth in some of our cavalry regiments, as a mark of rank amongst the officers. About 200 leopard-skims are sent annually to the English fur market. The Jaguar , or American Panther (Felis onca , Linnaeus). — A native of the warm parts of America, especially Paraguay and the Brazils. Next to the tiger, the strongest species of the genus ; also an expert climber. The skin is beautifully marked with deep chocolate-brown spots upon a rich yellowish ground. From 300 to 400 skins of this animal are annually imported, and used as rugs, or for ornamental purposes. The Puma, or American Lion ( Felis concolor, L.). — Extern sively distributed throughout the Southern American continent, found also in the warmer parts of North America, More fre- quently met with in grassy plains and marshy meadow-lands bordering rivers than in the forest. This animal lives upon deer, hogs, and sheep, to which it is very destructive ; for it is not satisfied with the simple seizure of prey, but, meeting with a herd of animals, will kill as many as possible, sucking only a portion of the blood from each. The fur of the puma is thick, close, and reddish-brown in colour, changing on the belly to a pale reddish-white. The skin, when imported, is used for car- riage wrappers. The Canadian Lynx ( Felis Canadensis, Geoffroy).— This is a timid creature, common in the wooded districts of Canada as far north as 66°, incapable of attacking the larger quadrupeds, but well armed for the capture of the American hare, on which it principally feeds. It makes a poor fight when attacked by the hunter, spits and sets up its hair like an angry cat, but is easily destroyed by a blow on the back with a slender stick. Prom 15,000 to 20,000 lynx-skins are annually sent over to this country by the Hudson’s Bay Company. The Common Cat (Felis domesticus, L.). — In Holland the cat is bred for its fur, being fed on fish, and carefully tended until it arrives at perfection. We import annually 20,000 cat-skins, and the English fur-market also receives a considerable quantity from home. The cat’s skin makes an excellent rubber for electrical machinery, and is also used for sleigh coverings, rail- way rugs, etc. The Family Canidce (Latin, canis, a dog) forms the next group of Digitigrade Carnivora, and includes dogs, wolves, and foxes. The different varieties of dog are supposed by some naturalists to have been derived from the wolf. The common dog (Canis familiaris, L.) is distinguished from the wolf and jackal by its recurved tail ; but the species vary very much in size, form, and the colour and quality of hair. In most col- lections of fur a few dog-skins will be found, although there is no regular trade in them. The Wolf ( Canis lupus, L.) has a valuable skin. This animal, once indigenous to this country, but now exterminated, still lingers in the forests of Northern and Southern Europe, and is particularly abundant in Russia, North America, and the northern parts of Asia. From 9,000 to 10,000 wolf-skins are annually imported from Europe, the United States, and British North America. They are serviceable for the linings of coats and cloaks, for sleigh coverings, and wherever additional warmth is desirable. The Red Fox (Vulpes julvus). — It is not the common European fox that is found in the furriers’ shops of this country, but different varieties of the American (equally well known for its cunning and mischievous attacks on the poultry-yard). The fox is easily distinguished by its long, sharp nose and bushy tail. Foxes have been formed by zoologists into a distinct' group amongst the Canidce, or dogs, on the ground that the pupil of their eye is vertical, whilst in the dog it is circular. The tail of the fox is longer and more bushy, its head broader and more pointed in the muzzle, and its gait and attitude crouching. The red fox of America is ferruginous in colour, and strongly re- sembles the fox of Europe. About 8,000 sldns are annually imported into England, most of them to be re-exported, chiefly into the markets of Turkey. The Cross Fox ( Vulpes decussatus). — This is probably only a 3b THE TECHNICAL EDUCATOK. variety of the red fox. It is distinguished by a black cross on the neck and shoulders, and is a South American animal. Its skin is valuable, selling for <£4 or <£5. The Arctic Fox (Vulpes lag opus). — This animal is very com- mon within the Arctic circle, and exhibits in a remarkable manner that mutation of colour which polar animals undergo with the change of the seasons. In winter it is a pure white ; in summer a dorsal line of a darker colour is observable, with transverse stripes upon the shoulders. This circumstance has led to its being mistaken for the cross fox. Late in autumn these animals collect in vast numbers on the shores of Hudson’s Bay, and migrate southward, returning early in the following spring along the sea-coast to the northward. The southern limit of their migrations in North America is 50° north latitude. The Arctic fox is very cleanly in its habits, very unsuspicious, and easily snared. There is a dark variety known as the sooty or blue fox ( Vulpes fuliginosus) . Both the blue and the white otter, and wolverine. These animals, from their peculiar appearance and habits, have been called vermiform quadru- peds. They are distinguished by the length and slender- ness of their bodies, which enable them to wind like worms into very small openings and crevices, whither they easily follow the smaller mammalia and birds on which they prey. Several of them, as the polecat, emit a very offensive odour ; nevertheless, they yield the most costly and highly-priced of our furs. The Ermine ( Mustela erminea). — This, the most interesting species of the weasel family, resembles the common English weasel, and inhabits Siberia, Russia, Norway, and Sweden. In winter it is clothed by Nature with a fur as white as the snow which then covers the ground, and is thus rendered invisible to its numerous enemies ; in summer its garb changes to a dingy brown. The white fur of the ermine is highly esteemed. It is th© THE RUSSIAN SABLE (MUSTELA ZIBELLINA). skins are imported in considerable quantities, but they do not fetch so high a price in the English market as the skins of the red fox. The Blade or Silver Fox (Vulpes argentatus). — This species is distinguished from the others by its intensely black fur, which is intermingled with silvery hairs, and has a white spot at the end of the tail. It is a native of the northern parts of the American continent. “ An unusually fine skin of one of these animals has been sold in London for £1100. The imperial pelisse of the Emperor of Russia, made of the black necks of the silver fox (exhibited at Hyde Park, in 1851), was valued at £13,500.” The Cossach Fox ( Vulpes Cossac). — This fox inhabits the vast plains of Tartary. Its skin, which is of a clear ferruginous- yellow colour, is much prized in Russia and Turkey. Not fewer than from 40,000 to 50,000 of these animals are annually taken and sold. The Family Mustelidce (Latin, mustela, a weasel) forms the last group of Digitigrade Carnivora whose skins supply our fur markets. This family includes the sable, polecat, weasel, royal fur of England, and of the sovereigns and emperors of Europe. The Pope and his cardinals have their ecclesiastical robes adorned with capes and trimmings of ermine, according to their rank. The tail alone of the ermine is jet black, and this is inserted at intervals into the prepared furs as an ornament. “ In England there is now no restriction on the wearing of this fur, but in the reign of Edward III. it was forbidden to all but the royal family, and a similar prohibition still exists in Austria. There is, however, a characteristic distinction made in the mode of ornamenting the fur employed on state occa- sions, according as it is worn by the sovereign, or by peers, peeresses, judges, etc. The sovereign and royal family can alone wear ermine trimmings in which the fur is spotted all over with black — a spot in about every square inch of the fur. These spots are not formed of the tail of the ermine, but of the paws of the black Astracan lamb. The crown is also adorned with a band of ermine with a single row of spots. Peeresses wear capes of ermine, in which the spots are arranged in rows, the number of rows denoting their degrees ANIMAL COMMERCIAL PRODUCTS. 3? of rank. Peers wear robes of scarlet cloth, trimmed with pure white ermine without any spots. But the number of rows, or bars of pure ermine, in this case also denotes the rank. The robes of judges are also scarlet and pure white ermine.”* The number of ermine skins annually imported is upwards of 100,000, and of these very few are exported. The fur of the ermine is manufactured into ladies’ muffs, tippets, trimmings, and linings. The Russian Sable ( Mustela Zibellina). — This is the next fur to ermine in value and in general use. The animal which yields it lives in the wilds of Siberia, and is hunted in the depths of winter, when its fur is most valuable. The fur is brown, with some grey spots on the head. The darkest in colour are the best. The skins are small, but they are sold at prices varying from three to ten guineas. Only about 2,000 of these valuable furs are received in England, because so much prized in Russia, where about 25,000 skins are annually collected. This fur is usually manufactured into linings, sometimes valued as high as 1,000 guineas. The Lord Mayor, aldermen, and sheriffs of the City of London have their robes and gowns lined with Russian sable, according to their respective ranks. 206,000 marten skins were imported. Of these the greater number belonged to this species. The Polecat (Mustela putorius) is common throughout Europe. It is very destructive in the poultry-yard, and very courageous. Its flexibility is so great, that when seized improperly by a terrier, or not griped in the right place, it will turn and fasten on the dog, so as to prevent further attack. This animal has a soft black fur, with a rich yellow ground. The natural odour of the fur is unpleasant, but processes have recently been adopted which effect its removal : 150,000 to 200,000 of these skins are annually sold in the London fur markets. The finest are ob- tained in Scotland. More than 25,000 are exported yearly from this country to America, where the fur is much sought after. The Pine Marten ( Mustela abietum, Ray) is found abundantly in the forests of Northern Europe and America. It shuns the habitations of man, and preys on birds and the smaller animals — mice and hares. When its retreat is cut off, it shows its teeth, sets up its hair, arches its back, and hisses like a cat. Upwards of 100,000 pine marten skins are annually imported into England from the territories of the Hudson’s Bay Company and Canada. The Beech Marten (Mustela Foina). — This animal has a white MUSTELA ERMINEA AND MUSTELA VULGARIS IN WINTER. “The tails of sables are used in the manufacture of artists’ pencils and brushes. The Minx (Mustela vison). — This animal is a native of North America, and its skin comes to us principally through the Hudson’s Bay Company. In the month of March this Company holds annually, in London, a public fur sale, which attracts great numbers of foreigners. Through them the furs destined for the Continent find their way to Leipsic, whence they are distributed throughout Europe. The fur of the minx resembles the sable in colour, but is considerably shorter and more glossy. It is much used for ladies’ wear, and is made into victorines, cloaks, muffs, etc. In a single year, the number of skins of this little animal received in this country have amounted to a quarter of a million. Their price varies from ten to fifteen shillings a-piece. When this skin is of a silver-grey colour, it is additionally valuable. A muff made of six of such skins is worth twenty-live guineas. The American Sable (Mustela leucopus). — The fur of this animal varies from a tawny colour to a deep black. The animal itself is known by it3 white feet. The fur is much worn in England, and is made into cuffs, muffs, and boas. In 1856, * “ Cyclopmdia of Useful Arts.” By Charles Tomlinson. Vol. I., p. 729. throat, and is thus distinguished from the pine marten, the throat of which is yellow. It is found in woods and forests in. Northern Europe, but nearer the habitations of man than the pine marten. It is imported in considerable quantities froiT the north of Europe, and its fur is dyed to imitate sable. The Stone Marten (Mustela saxorum). — This animal is dis* tributed throughout Europe. Its under fur is bluish-white, with the top hairs a dark brown ; its throat a pure white, by which it is generally distinguished. The French excel in the art of dyeing this fur, and for that reason it is frequently sold under the name of French sable. The Tartar Sable (Mustela Siberica). — This little animal is caught in the northern parts of Russia and Siberia. The fur is bright yellow, the colour being remarkably uniform all over the body. The skin is used both in its natural state and dyed ; the tail is employed for artists’ pencils. In 1856 we imported as many as 70,000 skins of this animal. The Woodshoclc, cr Pehan (Mustela Canadensis). — The pekan inhabits North America, and is also called Hudson’s Bay Sable. As the natural colour of this skin is much lighter than the prevailing taste, it is dyed of a darker hue. Thus treated, it is scarcely inferior to the Russian sable, which it i3 intended to imitate. We import annually about 18,000 of these skins. 38 THE TECHNICAL EDUCATOR. BUILDING CONSTRUCTION.— II. SCALES. It has already been said that block plans, elevations, etc., are drawings which show the whole property, building, or machine, and that working drawings are executed of a larger, in. fact, sometimes of the read size of each portion, so as to guide the workman. Now it will be clearly understood that although the drawing may be much smaller than the object it represents, it must, for any useful purpose, have all its parts in proper proportion ; and not only this, but the drawing must be made in such a manner that it may at once be evident what the true size would be. This is called the “ scale.” TO CONSTRUCT A PLAIN SCALE. Let it be required to construct a scale of 1 inch to the foot. This has been taken for the first example, owing to its great simplicity ; for it will be at once understood that a 12 -inch rule will represent 12 feet, and therefore the drawing executed on this scale will be one-twelfth (A) of the real size. This is called the representative fraction. Draw a line of any length, and mark on it several inches. Mark the left-hand end of the line 0, the first space 1, and so on. This, however, only gives feet ; it is necessary, therefore, to divide the inches into twelfths,* and then each twelfth will represent an inch of the real measurement. It will be obvious that the same principle will apply to the construction of scales, whatever the representative fraction may be ; thus — TO CONSTRUCT A SCALE OF T |g, that is, one of one-tenth of an inch to the foot ; because there are 10 tenths in an inch, and 12 inches in a foot. Draw a line of indefinite length, and mark off on it any number of tenths of an inch ; these will represent feet. It is not neces- sary to figure every division, nor to carry them beyond 10 feet in single feet ; after that they may be marked in 5-feet lengths. Of course, on such a small scale separate inches would not be required ; it is only necessary, therefore, to divide one of the tenths into four parts, each of which will represent three inches. The detail would then be drawn on a larger scale, as already explained. GENERAL PRINCIPLES OE BUILDING CONSTRUCTION. The term construction, as applied in practical art, is generally understood to mean fabrication rather than form, its object being the adaptation of such materials as are most fitted for the purpose intended, and the art of the constructor being devoted to combining them so as to ensure permanency and stability. If an upright wall be properly constructed upon a sufficient foundation, the combined mass will retain its position, and bear pressure in the direction of gravity to any extent that the ground on which it stands and the component materials of the wall can sustain. The aim of the constructor then must be, first, to secure a firm basis on which the fabric is to rest, and secondly, so to dispose his structure, and so to combine all the parts, that the whole pressure may act in the required direc- tion : for instance, when a building is to be roofed, the rafters, if butting merely on the top of the walls and meeting at the ridge, would of course be liable to press the wall outward. The constructor, therefore, designs a “ truss ” in a manner best adapted to the particular case. A truss consists, in the first place, of a tie-beam, which is a strong piece of timber. The lower ends of the rafters are mortised into this, and their upper ends are inserted into the top of an upright piece called a “ ling-post,” which, acting as a keystone of an arch, keeps the rafters in their places ; whilst their lower ends, being inserted into the tie-beam, cannot spread outward. A firm triangular assemblage of timbers is thus formed, and when this is raised to its place on the walls, there is not any pressure outward, the entire weight bearing vertically, that is, in the direction in which the wall is best calculated to bear it ; and should the design of the building not permit of the introduction of the tie- beam, the constructor applies buttresses outside the walls, to * To divide a line into any number of equal parts, see “ Lessons on Practical Geometry,” page 64. enable them to resist the thrust caused by the weight of the roof. The numerous ways in which scientific construction is practically applied in building, will be exemplified according to the requirements of the different materials treated of in the following pages; and we will proceed, in the first place, to speak of FOUNDATIONS. By the term foundation is meant — 1. The surface or bed of earth on which a building rests j and 2. The manner in which the lower portions of the building are constructed so as to afford the best possible bearing for the superstructure. Foundations are spoken of as (1) natural and (2) artificial. Although both these terms seem self-explanatory, it is still deemed advisable to refer briefly to their exact signification in accordance with the principle adopted in this series of papers ; viz., not to assume any previous knowledge ; and although this plan may be open to the objection that information may be supplied which many students have already acquired, yet this is by far safer than that any one who may be totally unlearned on the subject should seek information in these pages and be disappointed. A natural foundation, then, is such as will be found where the site is underlaid by a solid rock, or any kind of incompressible, resisting substances, free from water. Of course this must depend entirely on the locality ; and it must be borne in mind that it is not so important that the ground should be per- fectly rocky and hard, as that it should be compact and of similar consistence throughout ; it is not so necessary that it should be absolutely unyielding as that it should yield equally throughout. Artificial foundations are such as are constructed so as to render the ground, which is too soft to bear the building, fitted for the purpose required. Of course the means adopted must depend on the situation, the nature of the soil, the character or purpose of the building, etc. ; and some of the methods mostly used will be here described and illustrated. Bad foundations have been the cause of the ruin of many modern buildings. This has arisen from the costly nature of the work in making good the site, when the soil is not naturally suitable. But it is clear that the saving of the first expense is an unwise economy, as the entire stability of the superstructure necessarily depends on the firmness of the foundation. The first process in connection with laying the foundations is sinking the trenches in which the bases of the walls, etc., are to rest, and in digging out the hollows for cellars, etc. This is called the excavation. If the surface be found to be perfectly rocky, or to consist of a gravelly soil embedded with stone, it becomes a good natural foundation when it has been reduced to a level. If the soil prove generally firm, the looser parts, if not very deep, may bo dug up until a solid bed be reached, and the hollow may then bo filled up with broken stones and concrete ; if the soil be not- very loose, it may be made good by ramming into it large stones,, closely packed together, or dry brick rubbish widely- spread ; but if the ground be very bad, it must be piled and planked, or covered with a bed of concrete, according to the circumstances. In a building to be erected on a slanting site, the foundation must rise with the inclination of the ground, which must be “ benched out ” — that is, cut into a series of broad steps ; this will ensure a firm bed for the courses, and prevent them from sliding, as they would be likely to do if built on an inclined plane. When a good hard foundation is easily accessible, as solid gravel, chalk, or rock, we have nothing to do but to excavate the surface mould to the sound bottom, and build at once, first putting in the “footings,” which are one or more courses form- ing a sort of steps, each projecting a little beyond the other. These footings will be referred to and illustrated further on. On hard ground, one course of masonry, about half as wide again as the wall, is ample, but of course this must depend on the discretion of the architect. The rule, however, which must always guide the builder, is that the broader the base the safer the construction, and therefore the softer the ground, the wider it will be necessary to spread the foundation; and thus on ] softer ground, in many cases, footings have been employed BUILDING- CONSTRUCTION. 39 extending not only double the width of the wall, but even more. But the invention, or rather the re-introduction of concrete, has altered much of the system formerly adopted. When the ground is a deep clay, the building material, be it what it may, should go so deep as not to be influenced by changes of tem- perature or the rising or falling of springs, as the alternate shrinking or swelling of the ground must affect the stability of the building. It has been satisfactorily proved that in this country frost seldom penetrates beyond a foot into the ground, but in clayey soils, cracks and fissures, caused by the drying of the ground, frequently extend to the depth of two or three feet. Under such circumstances the bases of the foundation should be below such level. If the ground be springy, it should be drained, if possible ; if not, a foundation must be laid with concrete as low as the lowest level of the water, or, if very deep and boggy, piles must be used. The plan of building on sleepers or planking has now been almost entirely discarded ; for experi- ence has shown that timber, where exposed to alternations of wet and dry, soon rots, and is liable to be crushed, thus allow- ing the walls to sink. Where the ground is wet at one time and dry at another, the best timber soon decays, and therefore piles used in supporting buildings should, where possible, be so placed as not to be liable to such alternations. The use of concrete, except under very peculiar circumstances, has entirely superseded all other substances used in artificial or semi-artificial foundations. Concrete may be defined as a sort of rough masonry, composed of broken pieces of stone or gravel, not laid by hand, but thrown at random into the trenches, cemented together with lime in various ways, and thoroughly mixed with it before it is thrown in. In England, the lime is generally ground, and mixed, when hot, with the stones. In France, however, the lime is first made into a paste, and the mixture is called bdton. Beton has been much used in foundations of breakwaters, bridges, etc., as it has the property of hardening under water. The use of this composition is of very ancient date, and many examples of its use by the Romans still remain to us on the coast of Italy; it is supposed to be the “ Signinum opus” men- tioned by Vitruvius.* It was in very common use in the Middle Ages, walls, and even arches, having been frequently made of it. Smeaton f states that he was induced to use it from his observation of the ruins of Corfe Castle. £ in Dorsetshire. Dance, the architect of Newgate Prison, employed a sort of concrete in rebuilding that structure in 1770-78. The site of part of the new building was a deep bog, and it was rendered available by shooting a quantity of broken bricks into the holes, mixed with occasional loads of mortar, in proportion of 4 to 1, and suffering them to find their bed. * Vitruvius, Marcus, a celebrated Eomau architect, who was born about 80 b.c. He received a liberal education, and pursued those studies which were calculated to fit him for the profession of an engineer and architect, and was engaged in the Roman army as superintendent of military engines. He wrote a work called “ De Architectural' in ten books, treating of the different branches of architecture and civil engineering. t Smeaton, John, an eminent civil engineer, was born at Austhorpe, near Leeds, in 1724, and early showed a bent towards mechanical pursuits. In 1755, an event occurred which was to afford him the opportunity of reaching the very summit of his profession. The second wooden lighthouse which had been erected on Eddy stone rock (which is one of a group of rocks daily submerged by the tide, situated in the English Channel, nine miles off the Cornish coast) was destroyed by fire. The speedy re-ei-ection of another beacon was of the Utmost importance, and the execution of the work was entrusted to Smeaton. The new lighthouse was built of stone. The cutting of the rock for the foundation commenced in 1756 ; the building was executed between June, 1757, and October, 1759; and the lantern lighted on the 16th of October of that year. This work, the greatest of its kind hitherto undertaken, remains to this day a stable monument of Smeaton’s engineering skill. + This castle stands in the middle of a village, to which it gives its name. In the vicinity are stone and marble quarries, clay works, and potteries. The castle was founded in the tenth century, and was long one of the strongest fortresses in the kingdom. Here King Edward the Martyr was murdered by his mother, Elfrida, about a.d. 960 ; and King John, during his disputes with the barons, kept his regalia here for surety. Here, also, in 1642, Lady Ba.nkes defended the castle for six weeks against Charles I. It was dismantled by Fairfax in 1645. Any hard substance, broken into small pieces, will serve for the solid part of concrete. That most used is gravel or ballast. This should not be sifted too fine, as the sand which is left will mix with the lime, and form a sort of mortar, and so assist to cement the stones together. If broken stones or masons’ chips are used, it is well to mix some sharp sand with them. The general rule is, that no piece should exceed a hen’s egg in size. In this country, the lime is generally ground, and used hot. It is mixed with the ballast by scattering it amongst the stones, and turning them over with a shovel, water being at the same time thrown upon the mass. It is then immediately filled into the trenches. This has sometimes been done by shooting it from stages erected for the purpose. This practice has, how- ever, been much and justly censured by the greatest engineers ; the proper method being to put the concrete down in layers of about one foot in thickness, to level each course, and ram it well down. In support of this plan we may quote the words of Mr. George Burnell, C.E. (on limes, concretes, and cements) : “ In almost every work upon the art of construction we meet with descriptions of modes of making concrete. It is, however, very discouraging to observe that, in spite of all that may be said, the majority of architects and engineers treat the matter with such utter indifference that the old imperfect systems are still retained, and the conduct of these works is left almost invariably to some rule-of-thumb workman, who only knows that he has been accustomed to make concrete in a certain manner, without knowing any one of the principles which, regulate the action of the materials he works with. We thus find that the bulk of the concrete made in and near London, where the building art ought to be the most advanced, is made simply by turning over the ground stone-lime, a very moderately- hydraulic one, by the way,* amongst the gravel. It is then put into barrows and shot down from a stage. Such a mode of proceeding is rapid and economical, but it is eminently un- scientific, leading, 'doubtlessly, to the waste of material we so often witness ; for the practice is to make the concrete about one-third thicker than would be at all necessary if the process of making it were more perfect. It cannot be too often repeated, that the first condition necessary to obtain a good concrete or b6ton, is that the lime should be brought to tho state of a perfect hydrate, f before being mixed with the nuclei £ which it is to surround. It should, therefore, be reduced to tho state of a thick paste, and made into a mortar, before it is mingled with the gravel. Instead of being thrown down from a. height, and left to arrange itself as it best may, it should bo wheeled in on a level, and beaten with a rammer ; for we find that when thrown thus from a height the materials separate, and the bottom parts of a thick bed of concrete are without tho proper proportion of lime. The advantage of making the lime into mortar previously, is that it fills in a much more perfect, manner the intervals of the gravel or stones, and, in fact, renders the concrete what it is meant to be, an imperfect species, of rubble masonry.” Where the soil consists of running sand or soft clay, the area of the foundation must be enclosed by sheet piling. This con- sists of piles driven close to each other, so as to form a wall which encloses the soil, and prevents the softer portion from spreading out under the superincumbent weight of the building. Sometimes as much as possible of the soft matter is removed and replaced by beton, or concrete, the heads of the piles sawn off level, and a kind of wooden platform built on this support. In other cases piles may be driven in at certain distances apart over the entire area enclosed by the sheet piling, the spaces between these piles being filled in with stones or concrete, and a solid flooring constructed on this foundation. It may be remarked that concrete is now used in making the walls of buildings as well as their foundations, the walls being raised about one or two feet at a time by throwing concrete into a frame-work or box formed of iron plates, which is raised from time to time as often as is necessary until the wall has been built up to the height required. * Hydraulic lime is such as possesses the quality of setting ejr hardening under water. f Hydrates are substances in which a definite quantity of water is- chemically combined with a definite quantity of some other con- stituent. f Nuclei, plural of nucleus, a substance, however small, which forms a centre around which other matters gather. 40 THE TECHNICAL EDUCATOR. PROJECTION. — III. PROJECTION OF PRISMS- SECTIONS. A prism lias already been defined to be a solid whose opposite ends are equal and similar plane figures, and whose sides uniting the ends are parallelograms. It will be clear, then, that the lessons previously given are but stepping-stones to the present, and we can therefore at once proceed to PROJECTION OP PRISMS. To Project a Square Prism.- (or 1‘5) inch. The dined, the plan, which was previously a point, becomes a line, the length of which increases as the object approaches the hori- zontal. (See Fig. 4.) But although the position of the lines is altered, as far as their relation to the horizontal plane is concerned, they still remain parallel to the vertical plane ; and if the eye were placed immediately over the object, the widths across from the front to the back would be seen to be the same throughout the motion. Therefore, from the angles of the plan of Fig. 21 draw prism is in this les- son placed so that its axis is vertical, and its long faces are at 45° to the vertical plane. Draw the square, Fig. 21 , which is the plan of the prism, its sides being at 45° to the inter- secting line ; per- pendiculars drawn from the angles will give the edges of the elevation, which are to be terminated by an horizontal line at 14 inch from the base. Fig. 22. — It is now required to draw the elevation and plan when the axis, although ■Width of side 4 inch, length If [ horizontal lines, which will give the widths of the two upper maining parallel to the vertical, is at 35° to the horizontal plane. Now it will be evident that as far as the elevation is con- cerned, it will merely be altered in position, not in form, which change is effected by allowing the object to rest on one angle of the base, and continuing the motion until one edge of the eleva- tion (the edges being parallel to the axis) is at 35° to the hori- zontal plane. It will therefore only be necessary to copy the previous elevation, inclining it at the required angle. This motion, however, whilst causing so slight an alteration in the elevation, causes an entire change in the plan ; for whilst in the first position the plans of the edges were mere points (see Fig. 1), which united form the base, the square of the top being imme- diately over this, as in a line placed vertically, the upper extre- mity is directly over the lower ; but the moment the line is in- sides ; the two under them, being the same, will be hid- den by them. The length of the dia- gonal of the top and bottom, which is at right angles to the vertical plane, thus remains unal- tered, but the dia- gonal which is in- clined will neces- sarily become short- ened. This will be seen in continuing the projection of the plan. Draw per- pendiculars from the two extremities of the line which is the edge elevation of the end, to cut the middle line of the three horizontals previously drawn in the lower plane. From the middle point of the edge elevation then draw a perpendicular which will cut the two outer hori- zontal lines, and thus four points will be obtained, and these united will give the lozenge, which is the plan of the square end when inclined. (Refer to Fig. 14.) The lower end of the prism will be obtained in a similar manner. Fig. 23. — It is now required that the object shall be rotated on its solid angle, so that the axis shall be at a compound angle — that is, it shall not only be obliquely placed in relation to the horizontal, but to the vertical plane. This operation has been shown in Fig. 5, and it is therefore only necessary to remind the student that, so long as the inclination of a line in relation to the horizontal plane is not altered, no change but that of posi- tion will occur in the plan ; fov however much the object may PROJECTION. 41 be rotated horizontally, the length of the space it overhangs will not be extended, nor will the heights of any of the points be altered ; and this knowledge is the key to the projection of Fig. 23. Place the plan of Fig. 22 so that its axis and the edges parallel to it are at 45° to the intersecting line, then from each point in the plan raise perpendiculars, and intersect them by horizontals drawn from the corresponding angles in the eleva- tion of Fig. 22. Join the points so obtained, and the result will be the form shown in the upper projection of Fig. 23. to that of the section-line, and the width, a c, as in the last figure. In Fig. 26 the section-plane passes from a line connecting the middle points of two adjacent edges of the top, to a similar line on the two opposite edges of the base. The width of the section at its middle will be equal to the diagonal a c, and at the top and bottom it will be equal to g h. It is usual to cover sections with lines at 45° to their central line. Fig. 27 is the plan and elevation of a square prism, similar to that which formed the subject of the last exerciso. Now if this be made of wood, and cut so that the section passes through the axis at 45°, and a pin, c, be fixed in the centre of the section, at right angles to its surface, the upper portion may be ro- tated on the pin, so that the short line (a) will move to b, and be at right angles to it, and the object will be represented by the elevation and plan in Fig. 28. Fig. 29 is the de- velopment, which will show how a metal plate may be cut without waste, so as to make a square pipe to turn a corner, or form SECTIONS. Fig. 24 is the plan and elevation of. the square prism forming the subject of the last exercise. It is required to find the true shape of a section or cutting, caused by a plane passing through the prism in the direc- tion of the line a d. This plane of sec- tion would cut through the dia- gonal a c of the top, and the angle d of the bottom. Draw the dotted lines a c and d d! at right angles to the line of section, and at any part draw d' e pa- rallel to a d. Now it will be evident that this will be the greatest length of the section, and that the ividth will be somewhere on each side of e ; but where ? How wide will the section be ? These are questions which the student will do well to ask himself. Now it is clear that in passing through a c, the section-line cuts the object in the widest part; therefore, if the eye be carried down from a in the elevation to a c in the plan, it will be seen that the real width on each side of the centre e is ea and e c ; therefore, if these lengths be set off on each side of e in the section -line, and the points joined to d', then a c d' will be the true section. In Fig. 25 the section-plane passes from one angle of the top to the opposite angle of the bottom, cutting through the middle of the two edges. The length will of course be equal being equal to d e, and its width to fg. Fig. 31 shows the plan and elevation of a piece of a square wooden pipe, when the plane of the section, instead of passing from angle to angle, as in the last figure, passes from side to side, so that the section will be a rectangle, the length of which will be equal to c d, and the width to ef, instead of a lozenge form, as in the former case. Here, too, the upper portion may be rotated on a centre, so as to join in a right angle. Fig. 32 is a projection of the object when placed at an angle to the vertical plane. Fig. 33 is the development, with the shape of the section attached. It will be seen that this form will give both parts of 42 THE TECHNICAL EDUCATOR. the object, the only difference being that in the portion formed by the fine lines the joint or seam will be in one of the edges at the back, whilst in the other it will be in the front. Fig. 34 shows how this form is applied in constructing a common sheet-iron coal-scuttle, the lid being the covering of the section. TECHNICAL EDUCATION ON THE CONTINENT.— II. BY ELLIS A. DAVIDSON. TECHNICAL EDUCATION GENERALLY (continued). In order, however, fully to appreciate the schools for the various olasses of society existing on the Continent, we must carry our examination into our own deficiency otill farther. Let us, there- fore, take the case of a young gentleman who is to be an engineer, and who is placed for a few years in “the works.” He has had the benefit of what is called a good education in a private school, or, perhaps, in one of our public seminaries. He has spent many hours on classics, has gone through the usual school course of mathematics; he has perhaps learnt chemistry and mechanics from books; his powers of drawing have been cultivated to the extent of manufacturing “ Views on the Rhine,” “Ruined Castles by moonlight” (the only true parts of which are the ruin and the moonsltine of such a system), and a few shaded heads. These look well to take home, when mounted, etc., by the drawing-master. In a few instances he may have drawn a steam-engine from a copy, without knowing anything of its action. Again, drawing being in many schools treated as an extra, taught on the half -holidays, the pupils attend instead of enjoy- ing their freedom, and the lesson is merely thought of as another form of amusement. The studies of Practical Geometry, projec- tion, Mechanical Drawing proper, and Perspective are ignored, whilst the teachers are mostly artists, incompetent to give the instruction a technical tendency. Chemistry and Practical Mechanics are scarcely better taught, for it may safely be asserted that a proper laboratory and a col- lection of working models of machinery, or parts of them, form features in but few of our public or private schools ; and it is scarcely necessary to point out that, unless the pupil receives his chemistry lessons in the laboratory, and is allowed to work out experiments there, the time spent in book-learning is almost wasted. The instruction our lads receive in architectural drawing whilst at school is, as a rule, of a similarly unpractical character, the highest achievement being a measured drawing, copied from an elevation or plan, without the slightest knowledge of the scientific principles of building construction, or of the method by which the elevations or sections are projected from given data. On entering the office of an architect or civil engineer, the youth has to attend to various office duties — -to make tracings, etc., and to get a knowledge of his profession in the best way he can ; for it must be remembered that in a place where all are engaged in their business, it is not any one’s especial duty to teach him, though it must be said that the clerks and draughts- men are always most willing to impart such instruction as they are able to give ; but their competency, like their time, is limited, so that our embryo architect, like the young artisan whose progress has been sketched, grows up to repeat what has been done by others, not daring to invent, being by very virtue of his education (or rather the want of it) wholly deficient of the materials necessary for invention, and of the scientific principles which should guide him in designing. Happily, these remarks do not apply to all our schools, but the few which form exceptions only serve by their very brilliancy to show the prevailing deficiency. The evening classes for science which have been established under the auspices of the Department of Science and Art, are doing a great and useful work in offering to young men sound instruction by properly certificated teachers ; but it is scarcely the purpose of such classes to teach the elementary portions of the various subjects. These should form a part of the work of primary schools for all classes of society, and the science schools should take up the studies at a higher stage, when the pupils, more advanced in years, and with intellect improved by previous training, feeling in their daily avocations the use of the elementary education they have received apd the necessity for extended knowledge, enter into the lessons with earnest- ness and appreciation. Whereas, to adults totally uninitiated, the necessary ruggedness of the first few steps of the road to learning, however much the tact and power of a clever teacher may enable him to smoothen it, is still irksome in some cases, causing many to droop by the way and to discon- tinue their attendance. On the Continent, under the heads of “ Gewerbschulen,” “Real Schulen,” and “ ficoles Polytechniques, ’’institutions for practical studies have been in operation for many years past ; and it is proposed in these papers to give a detailed account of the systems pursued, and the results attained in a number of these schools as obtained from the most authentic sources, in the hope that some hints may be taken from the information given, which may be applied in the promulgation and manage- ment of similar schools in this country. The numerous sets of works executed in the various technical schools of France and Germany, which were shown in the Paris International Exhibition in 1867, prove the great value attached to scientific drawing ; and it is intended in these papers to give a general account of these, reserving the practical working out of them for the lessons in “ Technical Drawing.” In the schools referred to the studies are, as their names imply, of a real and practical character. Students learn not only how to make a drawing of a machine, but to make the working drawings from which a machine may be constructed, and in many cases to make the objects from the drawings. This must tend to show the pupils the importance of accurate measurement and correct delineation. They learn not only that the drawings must be exact, or they could not be worked from but in turning or putting together the various parts, they do so with more readiness from having studied the construction on paper. The various models, etc., used in the Continental schools will be referred to as these papers proceed. The leading sets of studies show an excellent mode of combining several elementary manual processes with scientific instruction, and so avoiding a difficulty often experienced in instructing persons whose minds are in advance of their hands, who can “ think out” a subject, but who cannot execute it. Many practical teachers will have observed the diffidence with which a student, who has been allowed to continue his geometrical drawing in pencil for a long period, commences to work in ink, and the tendency to spoil a drawing scientifically correct by the tinting, either with the draw-pen or with the brush. The system pursued in the Austrian schools seems calculated to overcome the manual difficulties contemporaneously with the elementary scientific instruction. When the geometrical figures have been correctly executed with the pencil, they are from, the first lessons inked, great neatness of line and accuracy of intersection being insisted upon ; they are then coloured with flat-washes, or sectioned over variously with the pen, the inscribed and containing figures being tinted with complemen- tary colours. Where parts of circles cover each other, each circle is coloured with a primary, so that the part overlapped becomes a secondary colour, etc. This system is thoroughly carried out, and thus at the same period the student is learning practical geometry, shading with the pen, the use of the brush and elementary colouring ; and thus, by the time he reaches the studies of mechanical or architectural construction, he is able to draw and colour with tolerable correctness. In these studies, too, all the shading is scientifically worked out, all the shadows of or on the sphere are projected in circles, each circle separately according to position, and so accurately that at but a short distance the separate circles are not observable, but a beautiful roundness of form is the result. Amongst the excellent collection of scientific drawings ex- hibited in Paris in 1867, was a set shown by the Industrial Union of the Grand Duchy of Hesse, which will be again re- ferred to, being the works of pupils in schools for workmen of the duchy. These works were the more valuable, as it was evident that they had not been specially executed for exhibition, but had been taken from the daily studies of the pupils. They indicate, as indeed do all the works of the Continental schools, an absolute connection between the scientific and artistic SEATS OP INDUSTRY. 43 studies, since all the science students seem to learn free-hand and ornamental drawing, shading, etc., as well as mechanical drawing. The whole subject of technical drawing, whilst it has been much neglected in this country, has been thoroughly system- atised on the Continent, and the foreign schools possess com- pletely organised sets of examples, combining the study of drawing with that of construction adapted to the various branches, in which we have hitherto been very deficient. It is hoped, however, that this want is now being gradually dimi- nished. The Technical Manuals, published by the proprietors of The Popular Educator, and the Technical Lessons given in these pages, are designed specially to remedy the evil so long and so deeply felt ; and it is encouraging to our English artisans to know that in the compilation of these the author has received and is daily receiving assistance and the warmest co-operation from the heads of the Continental schools, and from the Royal Board of Workmen’s Schools of Wurtemberg, etc. etc. Amongst the most important features in the systems of teaching in the Continental schools are the excellent collections of models for teaching science. The experience of all practical teachers tends to show that however good printed diagrams may be, no real conception of forms can be obtained without the aid of solid models, for even though the pupils thoroughly understand the diagram , the form there given is only such as would be correct in one position, and it is sometimes impossible from that one view to form an accurate idea of what shape may be presented by the smallest rotation, depression, or elevation of the object. In this “ Projection ” differs from “ Perspec- tive,” the first rendering the object as it is, the other as it appears ; and in this the knowledge of the form and the imagination generally offer some assistance ; but in Projection it is not so, point by point has to be obtained, which, when united by lines, develop forms which to the student are often surprising. Even if the subject has been worked out on the black board, and followed line by line by the students, they get the diagram copied, but they do not receive a lesson such as might have been given by the aid of a block or two of wood or a sheet of cardboard or tin. The sets of models used on the Continent for illustrating lectures on projection, mechanism, building construction, etc., are of infinite use to the teacher. Some of them have already been reproduced in this country, and it is intended to arrange for the production of sets of models adapted to each branch of industry, and at a price which shall bring them within the means of working men’s classes and schools. In the whole group of studies adapted for boiler-makers, tin- plate workers, etc. etc., the study of “ development ” is of the utmost importance — how the shape the metal is to be cut when flat, so that when rolled, folded, or bent, it may assume the required form, may be worked out on the black board ; but how much is the value of the lesson increased if a model, made of cardboard or some other material, be used, so that it may be first exhibited in its complete form, then flattened out, and the students shown how the result is obtained. They then work with confidence, for they know what they are working for, whilst if they only copy the lines as worked by the teacher they are in a degree in the dark until the whole is completed, and even then the black board cannot be bent or folded, so that after all they believe because they are told that the form is correct. Again, let it be required to teach a class of artisans to shape metal so as to form a pipe with two elbow-joints. These students will most likely have been accustomed to cut, file, and alter separate pieces of piping so as to get the joints at the angles, and it would be difficult to convince them that the flat metal may at once be cut in properly constructed curves, so that the parts on being rolled into a cylindrical form will fit each other at the required angles without any waste of metal or time ; ■ but if a cardboard model has been obtained and exhibited in the course of the lesson, first complete, then the two ends rotated until at the required angle, and finally the three parts opened out to show the development of the surfaces and sections, the students will understand what they are about, will work with infinite pleasure, and will be encouraged to think out similar developments adapted to their own trades. This and numerous subjects are fully worked out in our lessons on “ Projection.” SEATS OF INDUSTRY.— I. BIRMINGHAM. BY H. R. FOX BOURNE, Among the seats of modern industry, English and foreign, which in this series of papers will be briefly described, Bir- mingham is fairly entitled to the first place. “ I sell here,” Matthew Boulton, Watt’s partner in the manufacture of steam- engines, said to Boswell in 1776 — “ I sell here, sir, what all the world desires to have, power.” And long before the steam- engine was invented, Birmingham took the lead in the produc- tion of the various tools by which other towns have been able to grow as homes of special industries. Now the busiest hardware town in England, it is also, per- haps, the oldest. Tradition and local antiquities support the belief that it was a place of note — -“very eminent for most commodities made of iron,” according to the historian Dugdale — even before Britain was a Roman province. Its primitive inhabitants may have made Boadicea’s war-chariots, and spears for her warriors ; at any rate, they set the fashion of metal- working, which has thriven among their successors ever since. “I came through a pretty street as ever I entered,” says Leland, the quaint traveller of Henry VIII.’s reign, “into Birmingham town. There be many smiths in the town, that use to make knives and all manner of cutting tools, and many lorimers that make bits, and a great many nailers, so that a great part of the town is maintained by smiths, who have iron and coal out of Staffordshire.” Iron and coal out of Staffordshire have con- tinued to feed the staple trades of Birmingham, and by those trades it has been made more than a hundred times as great as it was in Leland’s day. Its growth, however, has been rapid only in recent times. Two centuries ago it had about 5.000 inhabitants, and ninety years ago some 50,000. At the time of the census taken in 1861, the population numbered nearly 300,000, and there cannot now be fewer than 350,000 persons crowded into an area little more than two miles long and nearly as broad, and most of them directly connected with the great hardware industries which, having their centres in Birmingham itself, spread over all the adjoining districts and help to supply all the world with steam-engines and pins, pens, guns, and a, thousand and one other articles of various sort and use. Steam-engines rank first. Boulton said truly that in selling them he sold power ; and the new power, that has effected a revolution in all manufacturing enterprise, has wrought a won- derful change in the industries of Birmingham. A hundred years ago, when Boulton was a young man, the town was fairly described by Burke as “ the toy-shop of Europe.” In it swords, nails, and sober implements of many kinds were made and sold ; but it was especially famous for its production of trinkets and. nicknacks. John Taylor, then its richest and most influential manufacturer, made his fortune out of buttons, buckles, snuff- boxes, ornamental clocks, and other fancy articles. During some years, <£800 worth of buttons were turned out of his workshop every week, and one of his workmen earned twelve shillings a day by painting snuff-boxes for a farthing a-piece ; while his shop-sweepings, containing quicksilver and scraps of gold, silver, and brass, were sold for £1 000 a year. Boulton carried on the same sort of trade at Snow Hill, then the centre of manufacturing energy in the town, during some years pre- vious to 1762, when he transferred his business to Soho, a miserable village two miles out of tae town, where a water- mill had been set up, and he saw an opportunity of carrying on his old trade of toy-making with greater advantage. That ho did, and Soho became famous for its manufacture of buckles, buttons, and watch-chains, candlesticks, urns, ormolu wares, and the like. He made in it every variety of “ Brummagem goods,” trying always to redeem the town from the ill repute which then, even more than now, it had by reason of the trumpery articles which inferior and dishonest manufacturers produced. “The prejudice that Birmingham hath so justly established against itself,” he said, “makes every fault con- spicuous in all articles that have the least pretensions to taste. How can I expect the public to countenance rubbish from Soho while they can procure sound and perfect work from any other quarter?” Boulton’s work was sound and perfect, and he made great profit out of it before it whs applied in a new and very notable way in 1774. In that year he entered into part- 44 THE TECHNICAL EDUCATOK. nership with James Watt, whose invention of the steam-engine had been lying idle during nine years for want of a shrewd man of business to work out the ideas of the brilliant man of genius. This is not the place for rehearsal of the memorable exploits of Boulton and Watt in manufacturing steam-engines and convincing the world of their value. But the partnership and its results must be noted as forming the chief episode in the industrial history of Birmingham. The first steam-engine was made at Soho in 1775. The Soho Foundry now covers an area of ten acres, and in it, prior to 1866, there had been manu- factured 1,878 steam-engines, with a nominal horse-power of 70,958, but able to do more actual work than could be per- formed by 250,000 horses. Bearing the illustrious title of Boulton and Watt until 1848, the firm conducting this foundry is now known as James Watt and Co. In Soho and its neigh- bourhood other great establishments for the construction of steam-engines have grown out of the good example of Matthew Boulton, “ the father of Birmingham,” who may also be claimed as a foster-parent by every one of the hundred towns, in and out of England, which find their profit in engine-making. The staple industries of Birmingham, however, are concerned rather with the construction of metal and other goods by help of steam-engines than with the manufacture of steam-engines themselves. Among these brass manufactures are the most important. About 90,000 tons of copper are consumed each year in all parts of the world. Of that quantity some 60,000 tons are procured in England, or brought into it, and nearly 20,000 tons go to Birmingham, to be converted into brass by the addition of 11,000 or more tons of zinc. The entire supply of copper and zinc worked up in Birmingham, including old brass re-wrought, in 1865, was nearly 40,000 tons, and its value as raw material about .£2,400,000. There were 50 manufac- turers of brass and brass goods in the town in 1800. In 1835 the number had risen to 160, and in 1865 to 216. In the latter year about 7,000 men and over 2,000 women were directly engaged in these trades. As they require delicate manipulation, and furnish good wages to all who work at them, their import- ance to the town is very great. Another highly-paid calling, closely connected with brass- work, for which Birmingham is famous, is the gun-trade. The story goes that William III., soon after his accession, was com- plaining that England made no guns, and that he had to send all the way to Holland for them, when Sir Richard Newdigate reminded him that “the men of Birmingham were masters of all that skill and metal could do,” and showed him that their guns were at any rate as good as any to be procured abroad. Thereupon the local manufacturers were ordered to make weapons for the English soldiers, and the business has been mainly carried on by their successors ever since. Besides the great Government factories, more than 600 employers are con- cerned in gun-making and kindred trades. Nearly 4,000 men and boys are engaged in producing the materials, and rather more in setting up and finishing them. Besides the weapons supplied for the English troops, others — good, bad, and in- different are made in great numbers for private customers at Rome and foreigners of every nation. A more harmless trade connected with brass manufacture, in which Birmingham excels, is pin-making. Pins used to be made much of, as illustrating the value of division of labour, the services of fourteen persons being required for the perfecting of a single pin. Now, however, the whole work is done almost instantaneously by help of an ingenious machine invented in 1824 by an American named Wright. During a single revolu- tion of a wheel the requisite length of brass wire is cut off, pointed at one end, and provided with a head at the other, leaving nothing to be done but the whitening, which is effected by boiling in a copper vessel with tin and bitartrate of potash. One Birmingham house, that of Edelsten and Williams, turns three tons of brass wire into pins each week ; and there arc twenty other houses devoted to the same trade. There are also twenty steel-pen manufactories, and most of them much larger than the pin-shops, in Birmingham. The growth of this trade is remarkable. Sixty years ago a steel pen was a curiosity, and, clumsily shaped as it was, could hardly be bought for five shillings. Ten years later the price was about a shilling ; but before then Joseph Gillott had em- barked in the business, and to him and to J osiah Mason are mainly due the improvements m the manufacture. Steel pens 1 soon came into favour, and their increased use quickly reduced the price. In 1865 the Birmingham makers produced about 100,000 gross every week, and gave employment to nearly 400 men and boys and more than 2,000 women and girls. Unlike pins, pens are still produced by minute division of labour. They pass through at least twelve processes, yet the wholesale value of’the commoner sorts is often as low as three-halfpence a gross. Pins and pens will serve to show how, in Birmingham, the heaping of small things goes to make a great trade. The names of the trades, still justifying Burke’s epithet, “ the toy- shop of Europe,” are legion. Of button-making alone there are still two or three dozen varieties, altogether giving work to about 180 employers and more than 6,000 labourers. The old gold and silver buttons that suited the foppery of last century have gone out of fashion, but their places have been taken by cheaper and more convenient articles. Linen, silk, and velvet buttons, steel, brass, bone, glass, pearl, and wood, are turned out by the million every week. Then there is a large trade in gilt watch- keys and cheap jewellery of every sort, a larger trade in screws and nails, chisels and other tools, and one larger still in fenders and stoves, bedsteads and other ironmongery. One of the most interesting developments of the old “ toy *“ trades of Birmingham is the manufacture of electro-plated goods. Silver-plating was introduced at Soho by Matthew Boulton more than a hundred years ago, and the rude chemistry of his day made it necessary for the silver coating upon copper to be very solid unless the article produced was in the course of a few weeks to become good for nothing. Tho modem pro- cess of electro-plating was only adopted about forty years ago. In 1838 Messrs. Elkington were employed in coating military and other metal ornaments with gold and silver in the old way, when they, or some chemists in their employ, conceived the plan of depositing costly metals on cheap ones by utilising the decomposing powers of an electric current. Out of their experiments resulted the finished process for which their house is still famous. They have now more than fifty rivals in Bir- mingham, and the trade, also carried on extensively in Sheffield and elsewhere, has become an important branch of British industry. There is electro-plating in gold as well as in silver, and by it Birmingham is able to give cheap gratification to the vanity of young men and maidens too poor to buy good trinkets. An instance of electro-plating at its cheapest and flimsiest appears in those miniature gilt lockets, supplied with tolerable likenesses of the Prince and Princess of Wales, which a few years ago were sold wholesale for a halfpenny a-piece. Birmingham has some trades, also, which are not concerned in metal-working. In papier-mache manufacture, started by Henry Clay, a native of the town, in 1772, it has had almost a monopoly ever since ; and it is famous for its dressing-cases and other products of leather-working, its tortoiseshell goods, and the like. Nearly every month, it has been truly said, produces in Birmingham some new invention or some new trade. The old and the new industries combine to make the town wonderfully prosperous. “ The history of every trade and every manufactory,” says Mr. Timmins, a competent local authority, “ is one of rapid growth. Beginning as a small master, often working in his own house, with his wife and children to help him, the Birmingham workman has become a master, his trade has extended, his buildings have increased. He has used his house as a workshop, has annexed another, has built upon the garden or the yard, and consequently a large number of the manufactories are most irregular in style. Whenever the busi- ness has overgrown its early home, and it is necessary to remove or to rebuild, a better class of building is invariably adopted. The warehouses, the workshops, and the offices erected during the last few years, all show not only great attention to physical wants and sanitary laws, but generally some appreciation of ornament and some love of art. Birmingham is, in fact — Sheffield, perhaps, only excepted — the town of all others where social and personal freedom is extreme. The large number of small manufacturers are practically, independent of the nume- rous factors and merchants they supply. The workmen, mostly untrammelled by trades’ unions, are paid according to their merits, and skilled labour of all sorts is nearly always in demand. The enormous variety of the trades renders general bad trade almost impossible ; for if one branch is slack, another is usually working full or even over time. In no town in England CHEMISTRY APPLIED TO THE ARTS. 4. is comfort more common, or wealth more equally diffused. If millionaires are few, absolute poverty and wretchedness are also rare. Dwellings, however humble, are not overcrowded, as in many large towns, and very rarely is more than one family found in one house.” Birmingham is thus, on social grounds as well as on commercial, one of the most interesting of the great seats of English industry. CHEMISTRY APPLIED TO THE ARTS.— I. BY GEORGE GLADSTONE, F.C.S. BLEACHING. All the fabrics used for clothing and other purposes, which are made of cotton, flax, wool, jute, silk, and such like articles, are more or less coloured when they are first produced. Raw cotton is naturally almost white ; but it is liable to be mixed with minute fragments of the husk, and other extraneous sub- stances, besides grease and dirt, which destroy the purity of its character, and render it quite grey by the time it has passed ifhrough the spinning-mill and loom. Flax and jute are by nature rather dark-coloured ; silk is always yellow ; and wool is anything but white when in the fleece. None, therefore, of the goods made from these articles present a clean and inviting aspect when they leave the hands or machine of the weaver. In order to render them fit for the market, they must not merely be washed, which would only remove the dirt, but they must generally be bleached, or, in other words, made white. Grey calicoes are not bleached, but the tint they possess prevents their being used for a great variety of purposes. If they have to be dyed or printed with patterns, it is still more important that the fabric should be bleached, because otherwise the colours or patterns would appear indistinct and dirty. The bleaching process is therefore a very important one. It is one, however, that is continually going on without man’s interference, of which most housewives find too many instances. We are all familiar with the power of the sunlight in fading carpets, curtains, etc., which are much exposed to its influence. Almost every article that can be named is subject to the same, timber and even stone losing much of their colour by exposure. The effect is increased by occasional showers of rain. In the early ages man copied the process of Nature, and exposed his manufactures to these influences for the purpose of rendering them white. Water is generally so cheap, and sun- light costs nothing at all, that modern science has not alto- gether supplanted this plan ; but in these days, dispatch is a matter of so much importance that we cannot wait while Dame Nature does her work, and we must therefore either hurry her on, or find some more expeditious method. About 100 years ago, the attention of chemists was drawn to a substance which is now known to be one of the most common, and at the same time important, chemical elements — chlorine. In combination with sodium, it forms the well-known table-salt (chloride of sodium), and is therefore one of the most wide- spread substances in Nature. It was not long before its bleach- ing qualities were discovered, and then commenced a new era in the art of which wo are now writing. The best manner of using the chlorine was the subject of many experiments, and improvements have from time to time been suggested ; but still chlorine, in one form or another, is the article upon which the bleacher of cotton relies. A great economy, both of time and labour, is the result ; the effect which could formerly have been gained only by a vast amount of labour, and an exposure of months to the atmospheric influences, being now attained within an equal number of days. What is the principle upon which chlorine acts in the bleach- ing of goods made of vegetable fibres F Let us get at the philosophy of the matter first, and then proceed to the working of it out in actual practice. The chemical process amounts simply to this — to give the chlorine employed the opportunity of entering into combination with the colouring matter in the fabric to be bleached, the result of which is the formation of a white compound which can be readily separated from the manu- factured article. There are, however, many niceties in the operation which need to be borne in mind, in order to produce a satisfactory result. Raw cotton imbibes a certain amount of dirt and grease in the processes of picking, ginning, and sending from the place of growth to the manufacturing district ; and in the subsequent processes of spinning into yarn, and of weaving into calico or other fabrics, a good deal more of both these impurities is acquired. It is important to get rid of these, and more particu- larly the grease, before the goods are subjected to the actual operation of bleaching. The mere dirt is easily removed by the ordinary process of washing, which is therefore one of the first things to be done. Grease or oil is not, however, to be got rid of by this means, and the quantity of these troublesome ingredients when the goods come out of the loom is by no means inconsider- able. The simplest and cheapest way of purifying the fabric from these is to convert them into a soap, by boiling the goods in a solution of lime-water or any alkali. The soap thus formed is easily separated, and the material is then ready to be sub- jected to the bleaching process. During these preparatory operations, which consist of alternate washings in lime-water, acids, and caustic alkalis, between each of which the fabric is thoroughly rinsed in pure water, the article operated upon loses a good deal of its colour, though the most important have yet to follow. There are two ways of conducting the succeeding process : the one is by bringing the goods under the influence of chlorine in its free state (either as a gas or dissolved in water), and the other by using the chlorine in combination with a base, such as calcium, of which lime is the oxide. The former is adopted more generally on the Continent, the latter in England. The former is very effective and rapid in its operation, but it involves a certain amount of risk, because the chlorine in that case is liable to do too much, and destroy or burn the fibre itself ; the latter is more easily regulated, so that there is less risk of injuring the strength of the calico. Even in this case, it is necessary to adjust with care the strength of the solution of chloride of lime, its temperature, and the time employed ; be- cause an increase of temperature, or a prolongation of the time, will operate as prejudicially as an excessive quantity of the bleaching powder. The colouring matter is the first attacked, and as soon as that has been sufficiently acted upon, the fabric should be withdrawn from any further influence. The chloride of lime is dissolved in a large quantity of water , to make a bath into which the goods are to be placed after it is reduced to such strength as is desired, a point which varies con- siderably according to the quality and character of the goods to be bleached. Into this solution the cloth is put, and remains there generally for about six hours, by which time the chloride of lime has been taken up. It then passes into a weak bath of sulphuric acid, when the acid attacks the calcium, forming sulphate of calcium, and leaving the chlorine free to act upon the colouring matter. The sulphate is easily removed by steep- ing in water for eight or ten hours ; and the colouring matter, having been already decomposed by the chlorine, is got rid of by boiling for about eight hours in a solution of caustic or carbonate of soda. The goods are finally passed through a bath of weak acid, to prevent the chance of their subsequently turn- ing colour in consequence of any resinous matter remaining behind, and are then dressed and prepared for market. The time occupied in bleaching cotton goods by the agency of chlorine need not occupy more than two days. It is, however, better to take rather more time, as the most expeditious mode involves the use of rather stronger solutions than are desirable ; and a very thorough washing between the various steps of the process is of importance, because otherwise the fabric is liable, in course of time, to turn yellowish and spotty in some places. Care in this respect is all the more important if the goods are intended to be dyed or printed, because the colours are certain to be more or less affected if any of the ingredients used should remain behind, or have entered into combination with the fibre itself. The minute details vary considerably in different esta- blishments, as well as according to the class of goods in hand. The solutions of the alkalis are generally prepared by dissolving a certain weight of the substance in a given quantity of water j but as chloride of lime is very apt to lose its strength* by keep- ing, it is usually tested, by observing in a graduated tube how much is required to neutralise a standard solution of indigo, a test which is found in practice to be sufficiently exact. The process of bleaching linen is somewhat different from the foregoing, though the same in principle. While cotton goods lose at the outside 10 per cent, of their weight, linens lose at 46 THE TECHNICAL EDUCATOR. least 30 per cent, by being bleached. This arises from the large amount of colouring matter in the flax, some of which is even imbibed during the process of retting to which the flax plant is subjected in order to separate the fibre from the husk. The great quantity of colouring and resinous matters which have to be got rid of, render the bleaching of flax a much more tedious process than that of cotton, because they prevent the chloride of lime from penetrating the fibre completely during the short time that it is exposed to the influence of this agent ; and many bleachers combine the modern chemical process with the old system of exposure to the elements, which, though longer, saves the repetition of some of the mechanical operations. Upon this plan the process generally occupies from six weeks, to two months, though by adopting the artificial expedients it need not occupy more than about one-third of this time. The animal substances used in the manufacture of clothing cannot be treated in the same way, for were they subjected to the operation adopted in the bleaching of vegetable fibres, the material itself would be so far destroyed as to render the goods comparatively valueless. The most important of these sub- stances are wool and silk. They must be described separately. Wool, it is well known, contains a very large amount of grease, and this is only very imperfectly removed by the process of scouring to which it is subjected before the wool is made into yarn. As in the case of cotton goods, the first thing to be done is to get rid of the greasy substances, but the alkaline leys used by the bleachers of calico to saponify the fatty matters would destroy the wool itself, so that another means of achieving this end has to be resorted to. The best article for the purpose, and which is therefore commonly used, is a mixture of water and stale urine, into a cold bath of which the wool is placed for about twenty minutes. During this time the carbonate of ammonia, evolved in the decomposition of the urea, combines with the grease, forming a substance which is readily removed by washing. If woollen goods are subjected to this treatment there is some difficulty, however, in getting rid of the disagree- able smell which clings to them, in consequence of which carbonate of soda and soap are generally substituted, though they are not so satisfactory in their action. Though heat facilitates all the operations of the bleacher, it is necessary to avoid it when dealing with wool, because it would not only injure the fibre, but also make it shrink too much. Even in using cold water, the latter result has to be guarded against by keeping the goods stretched on a frame while passing through the various baths. To effect this with the greatest possible economy of liquid, the baths are fitted with two series of rollers, one near the bottom and the other near the top, and the fabric is drawn tightly over and under the rollers alternately. Having thus prepared the article for the actual bleaching operation, it is now subjected to the action of sulphur, and not chlorine as in the case of cotton. The object of this treatment is not to remove the colouring matter from the wool, but merely to deprive the substance of its colour. It is applied in the form of sulphurous acid, which is a gas readily soluble in water, and may be used in either of these conditions according to the pre- ference of the operator. Those who employ it in the gaseous state have large chambers provided in which the goods are hung up on wooden rails ; the door is then hermetically shut, and the burning sulphur is introduced through an aperture in the floor, which is at once closed. In this way the air that is in the chamber becomes thoroughly impregnated with the gas, and the cloth, after an exposure of about twenty-four hours, is completely bleached. An immersion of four hours in water saturated with the gas is sufficient to produce the same result. The aqueous solution may easily be prepared by heating a mixture of sulphate of iron and sulphur in a retort connected” by a pipe witli the bath, so that the gas evolved should pass into the water, and be absorbed by it until thoroughly saturated, or until a sufficient strength be attained. The process of bleaching silk is much simpler. In fact, except for special purposes, , it can hardly be said to be actually bleached. The very pale tint to which it is usually reduced is attained by repeated boilings in water with soap, then im- mersion in a bath in which a little carbonate of soda is dissolved, and finally a short exposure to the action of a weak acid, the silk being well rinsed between each operation. A further de- colorisation is, however, necessary, if tho silk is subsequently to be dyed of a very delicate colour, in which case a weak solution of sulphurous acid is used. Much care has to be exercised throughout, lest the fibre should be affected, which would not only destroy its strength, but also deprive it of the brilliance which adds so much to its value. The manufacture of the chloride of lime which is now the great agent in the bleaching of goods made of vegetable fibres, is a separate trade, and is principally carried on at the large chemical works in the neighbourhood of Glasgow, New- castle, and Liverpool. Machinery is used wherever practicable, in order to economise the cost of labour, and also time. The dash wheel, as it is called, is a most useful and simple contrivance, and one in almost constant requisition, being used in the frequent washings above described. It consists of a large cylinder or drum, divided lengthwise into four compartments, with a large aper- ture in the end of each, through which two or more pieces of cloth are inserted ; water is then added, and connection being I made with the steam-engine, the cylinder revolves rapidly, and the motion thus given to the pieces of cloth inside washes them thoroughly in less than ten minutes. TECHNICAL DRAWING— III. LINEAR DRAWING IN PARALLEL LINES FREE-HAND DRAWING. We now proceed to give another example for practice in draw- ing parallel lines. Eig. 6 is the plan and Fig. 7 is the sectional elevation of a platform in which the longitudinal sleepers, b b b, rest directly on the ground, and are kept in their places by the cross-sleepers, a a a a a a, which rest upon them. These are notched down, so that only half their thickness stands above the longitudinal sleepers. The spaces between these having been duly flushed up as in the previous example, the planking, c c c c, is placed between the cross-sleepers, of a thickness equal to the portion of their thickness which stands above the longitudinal timbers, the upper faces of the cross-sleepers themselves thus covering a portion of tho surface of the platform. To draw these figures, draw a line at A b, for the ends of the longitudinal sleepers ; mark off the widths of these and of the spaces between them. Now, knowing that the elevation is to be projected from the plan, you may as well carry on the process at the same time that you are drawing the first figure ; therefore, at the proper distance, draw the ground-line of the elevation, c D (Fig. 7), and as you draw the longitudinal sleepers, carry down the lines which will give you the ends or sections of the timbers lettered b b in the elevation. lieturning to the plan, draw the cross-sleepers, a a a a a, a a, and the lines parallel to the longitudinal sleepers (not shown in the example) which bound the ends of the cross-sleepers, carried up, will give also the end3 of the same timbers, and of the planking, in both plan and elevation. It will be seen that the portion of the cross-sleeper which is notched down on to the longitudinal timbers is represented by the width at a in the sectional elevation. The section of the wall may, of course, now be drawn either to pattern, or may be worked to represent brickwork from either of the footings of walls which will be given in the lessons on Building Construction. These drawings may now be coloured to represent fir, the colour usually employed for this purpose being raw sienna. This should be washed thinly over all the wood-work, and when dry the lower sleepers should be covered with sepia, the shadows cast by the upper on the lower timbers to be subsequently added with colour rather darker. When all the colouring is dry, the lines representing the graining are to be freely, but not too heavily, executed with this last darker shade of sepia ; and it must be borne in mind that the graining is but secondary, and must not be over-done, and that in tho example the lines are engraved closely in order to darken the lower timbers, so that the cross-sleepers may be more plainly visible; but in your drawing you attain this end by the wash of sepia, and therefore you are not required to shade your work in lines. In the ends of the sleepers shown in Fig. 7 it is, however, neces- sary to draw lines at 45°, in order to show that they are meant to represent sections. TECHNICAL DRAWING. 47 Fig. 8 is the plan and Fig. 9 is the sectional elevation of the planking for the foundations of walls meeting at right angles. This plan, taken from an excellent German example, is such as might be applied in a case where it might not be necessary that the whole of the area should be planked. To draw this example, draw the line A B (Fig. 8), and BC at right angles to it. On b c mark off the widths of the lower sleepers and the spaces between them, and from these points draw the lines required for the timbers. On a b mark off the widths of the upper sleepers and the spaces between them. I ends or to patch the line, which is exceedingly difficult to do j neatly. But if you have drawn out the pencil-lines forming the j edges of the sleepers, you at once see the exact length you are to ink ; and this same result in inking the long lines will be attained by the pencil-line previously drawn at D E. You are further advised never to scratch out any extraneous line until after you have coloured, and -the drawing has tho- roughly dried, as otherwise the colour will run into the roughened paper and cause a blotched appearance. The sectional elevation (Fig. 9) can now be projected from the plan in the manner already explained. The shadow cast by the wall (which is a section on the line yx) is to be washed in Although only three of these are continuous, it is advisable •to draw all in pencil as if they were so, which ensures the dis- tant set being immediately opposite to those in the front ; and this mode of working is decidedly the more rapid. It has been mentioned that it is desirable to draw all pencil lines longer than they will be required. We will now inquire why it is so. Let us suppose the whole plan finished, as far as the pencil- ling is concerned, and that the next process is that of inking. Now, of course, you know that the bevelled edge of your rule must be turned downward, in order to raise the edge so that the ink from the ruling-pen may not drag against it. This edge, however, obstructs, in a degree, your view of the lines you are to ink, and you either draw your pen past the angles of them or do not rule quite up to them. In either case the result is dis- agreeable, for you have either to scratch out the superfluous with sepia. Be careful not to mix your colour too thick. Bather repeat the wash in order to darken it. The lines for the courses of stones should be drawn after the colouring and shadowing, so that they may not be washed away. OF FREEHAND DRAWING. At this stage it is advisable that the student should be in- formed that a ll the drawing which is necessary for the artisan cannot be done with rules and compasses, but that some portion of the work must be drawn by “freehand.” It is important that a workman should be able, with his piece of chalk or pencil, to sketch roughly, by hand, the form of any object he is required to make, or that, visiting any exhibition or foreign country, he should be able to bring away with him drawings, however roughly done, of any tool, appliance, useful or ornamental article which may have attracted his attention. 48 THE TECHNICAL EDUCATOR. f Again, as the examples contained in this or any other work of a similar character advance, it will be seen that curved lines are of constant occurrence ; and although some of them, which may be composed of arcs of circles, may be done with compasses, and others may be inked by means of the French curve, there are many which cannot be executed by any other means than by freehand, and there will occur little pieces of curved lines continuous with straight ones, which can always be more neatly joined by hand than by instruments, or which a certain amount of practice will enable the draughtsman to execute with his pen or pencil in less time than it would take him to find the centres. But this is not all. The study and practice of freehand drawing gives ac- curacy to the eye and refines the perceptive facul- ties; it enables a man to raise his ideas beyond mere straight lines, to cultivate his taste, and in many ways to add beauty to utility. To the joiner these remarks apply with even greater force than to the carpenter, for there is so much in his work that requires taste and refine* ment, that to him hand-drawing and a proper culti- vation of taste are absolutely indispensable. The Germans (amongst whom technical education has from early times been well attended to) imply this in the very names they give to the different depart- ments of the workers in wood. They do not seem to consider the work of the house-carpenter to be merely making a good joint or planing wood very skilfully, and therefore do not use the term “ joiner.” They call the workman “ Bau-tischler ” (the building, cabinet, or table maker), and the “ Fein-zimmermann ” (the fine-room man) ; and these terms will at once be understood as conveying the meaning that from the jofner not only neatness but taste is required ; and he cannot acquire this, or even cultivate that which may be (and in many cases is) natural to him, without patiently studying' and practising the delineation of beautiful forms which Nature spreads so bountifully around, and which men of former periods have produced. The South Kensington Museum, a perfect art-world, contains innumerable specimens of the application of art to trade purposes, and the student is strongly urged to avail himself of the advantages of such an exhibition, and of the excellent tuition given in the numerous schools of science and art, spread not only over London, but throughout the pro- vinces. The object of introducing freehand drawing at this stage is that the student may practise it, little by little, as he progresses with his linear drawing, and so cultivate both branches equally. This will be found more satisfactory than allowing the study of ruling- work to outstrip hand- work ; for, where this is the case, whilst the ruled lines may be exceedingly well done, the curved parts will be so clumsily added that the appearance of the drawing will be quite spoiled. It is intended to in- troduce at a further stage the elements of ornamental forms; but in commencing, it is deemed best that the subjects should be such as are well known to the student. He will then be able to check his own work, for he will at once see whether his drawing is really like the tool he has in his basket ; and I would hope that it may lead him to try to make draw- ings of others direct from the objects and unaided by copies. We commence, then, with Fig. 10, which is intended to repre- sent a joiner’s screwdriver ; and this example, simple as it is, will afford excellent practice in a most important branch of the study — the balancing of parts. Here the perpendicular, A b, is to be drawn first, and, when this is accomplished (by hand, not by means of the rule), pro- ceed in the following manner : — Draw the lines c d and e /, crossing A B at right angles ; observing, but not measuring, the distance between them. Next draw the line g h, which is to form the edge of the blade ; and also dot fine lines across at ij and k l. All these lines are, in the first instance, to be drawn of in- definite length. The two points to be observed are — 1. That they are at the proper distances apart. 2. That they are all really at right angles to A b. Now mark off on each side of the central perpen- dicular the length of half the diameter of the brass ring, and draw the lines c e and d f. The handle is to be drawn next, and this is formed' of a continuous curve. Begin at A, and in the lightest manner possible sketch the curve extending to c. Adopt as a constant rule, that when two curves are to be balanced, it is advisable to draw the left side first, for if the right side were drawn before the other, you would most likely cover it with, your hand whilst sketching the left ; this would, of course, render your getting your two sides alike very difficult. When, then, you feel in some degree satisfied that the left side of the handle is nearly correct, add the curve from A to d. Observe. — There must not be a sharp point at A. The two sides must merge smoothly into each other at the top, so as to form one complete curve. You can well imagine how very absurd a screw- driver would appear, and how very unfit it would be for work, if it had a sharp point at the top of the handle. Now commence the blade, by drawing the per- pendiculars ei and fj; then the curve ik on the left side, and j l on the right. Mark off on g h, on each side of the perpendicular,, half the width of the edge of the blade, and then draw the lines lch and Ig, which will complete the form. Now this will constitute the rough sketch. The next step is to convert it into a drawing. Pass your india-rubber lightly over the pencil lines, so as to remove as much lead as possible, without entirely erasing the form. Fig. 11 is a sketch of a carpenter’s chisel. In beginning this, draw the central horizontal line, and across this draw the lines for the edge of the chisel, and the upper and lower ends of the handle. Next draw the sides of the blade, which, differing from those of the screwdriver, are parallel to the central line. The lines for the edges of the handle are not, however, parallel, as the handle is wider at the upper than at the lower end. Observe. — In using india-rubber, it is" better to rub in the direction of the lines rather than across them ; and when there is much lead upon the paper, it is better that the friction should be rapid and light rather than slow and hard. The rubbing should not be backward and forward, by which the lead rubbed off by one stroke is rubbed on again by the next ; but the action should be like planing or filing — viz., in one direction, the rubber being raised in the backward motion. The paper should at this stage present a perfectly clean ap- pearance, with a very clear but slight trace of the form. Now, with a fine, cleanly-cut point to your pencil, trace over the outline, avoiding all raggedness, and endeavouring to get each line of the same thickness throughout ; those on the right side are to be rendered a little darker than the others. This process is called “lining in.” By following these directions closely, which are similar to those given for outline-work in the earlier “ Lessons in Draw- ing ” in The Popular Educator, and taking an example for practice from any tool that he may be in the constant habit of using, the beginner will soon find himself able to produce creditable drawings. PRINCIPLES OP DESIGN. 49 PRINCIPLES OF DESIGN.— I. By Christopher Dresser, Ph.D., F.L.S., etc. INTRODUCTION — VALUE OF ART - KNOWLEDGE — MEANING CONVEYED BY ANCIENT ORNAMENTATION, At the very commencement of this series of articles on Orna- mental Design, which I have undertaken to write at the request of the Editor of The Technical Educator, I desire to say that I address myself especially to working men, and that my sole object will be to teach what I consider useful to them. There are many handicrafts in which a knowledge of the true prin- ciples of ornamentation are almost essential to success, and there are few in which a knowledge of decorative laws cannot be utilised. The man who can form a bowl or a vase well is an artist, and so is the man who can make a beautiful chair or table. These are truths ; but the converse of these facts is also true; for if a man be not an artist he can- not form an elegant bowl, nor make a beautiful chair. At the very outset we must recognise the fact that the beautiful has a com- mercial or money value. We may even say that art may lend to an object a value greater than that of the mate- rial of which it consists, even when the object be formed of precious matter, as of rare marbles, scarce woods, or silver, or gold. This being the case, it follows that the workman who can endow his produc- tions with those qualities or beauties which give value to his works, must be more useful to his employer than the man who produces ob- jects devoid of such beauty, and his time must be of higher value than that of his loss skilful companion. If a man, who has been born and brought up as a “ son of toil,” has that laudable ambition which causes him to seek to rise above his fellows by fairly becoming their superior, I would say to him that I know of no means of his so readily doing so, as by his acquaint- ing himself with the laws of beauty, and studying till he learns to perceive the differ- ence between the beautiful and the ugly, the graceful and the deformed, the re- iined and the coarse. To perceive delicate beauties is not by any means an easy task to those who have not devoted them- selves to the consideration of the beautiful for a long period of time, and of this be assured, that what now appears to you to be beautiful, you will shortly regard as less so, and what now bails to attract you, will ultimately become charming to your eye. In your study of the beautiful, do not be led away by the false judgment of ignorant persons who may suppose themselves possessed of good taste. It is very common to assume that women have better taste than men, and some women seem to consider themselves the possessors of even authoritative taste trom which there can be no appeal. This may be the case, only 4 — 7ol. l. we must be pardoned for not accepting such authority, for should there be any over-estimation of the accuracy of this good taste, serious loss of progress in art-judgment might result. It may be taken as an invariable truth that knowledge, and knowledge alone, can enable us to form an accurate judgment respecting the beauty or want of beauty of an object, and he who has the greater knowledge of art can judge best of the ornamental qualities of an object. He who would judge rightly of art-works must have knowledge. Let him apply himself, then, to earnest study, for thereby he shall have wisdom, and by his wise reasonings he shall be led to perceive beauty, and thus have opened to him a new source of pleasure. Art-knowledge is of value to the individual and to the country at large. To the individual it is riches and wealth, and to the nation it saves impoverishment. Take, for example, clay as a natu- ral material : in the hands of one man this material becomes flower-pots, worth eighteen-pence a “cast” (a number varying from sixty to twelve according to size) ; in the hands of another it becomes a tazza, or a vase, worth five pounds, or per- haps fifty. It is the art which gives the value, and not the material. To the nation it saves impoverish- ment. A wise policy induces a country to draw to itself all the wealth that it can, without parting with more of its natural material than is absolutely necessary. If for every pound of clay that a nation parts with, it can draw to itself that amount of gold which we value at five pounds sterling, it is ob- viously better thus to part with but little material and yet secure wealth, than it is to part with the material either in its native condi- tion, or worked into coarse vessels, at a low rate, there- by rendering a great im- poverishment of the native resources of the country necessary in order to its wealth. Men of the lowest degree of intelligence can dig clay, iron, or copper, or quarry stone ; but these materials, if bearing the impress of mind, are ennobled and ren- dered valuable, and the more strongly the material is marked with this ennobling impress the more valuable it becomes. I must qualify my last statement, for there are possible cases in which the impress of mind may degrade rather than exalt, and take from rather than enhance, the value of a material. To ennoble, the mind must be noble; if debased, it can only debase. Let the mind be refined and pure, and the more fully it impresses itself upon a material, the more lovely does the material become, for thereby it has received the impress of refinement and purity ; but if the mind be debased and impure, the more does the matter to which its nature is transmitted become degraded. Let me have a simple mass of clay as a candle-holder rather than the earthen candlestick which only FIG. 1. THE LOTUS (blue WATER-LILY) OF THE EGYPTIANS, AS CONVENTIONALLY TREATED BY THEM. A. Open flower and bud on mummy-ease. B. Flower and bud on bordei or cornice. C. Lotus flower and stalk. 50 THE TECHNICAL EDUCATOK. presents such a form as is the natural outgoing of a degraded mind. There is another reason why the material of which beautiful objects are formed should be of little intrinsic value, besides that arising out of a consideration of the exhaustion of the country, and this leads me to say that it is desirable in all cases to form beautiful objects of an inexpensive material as far as possible. Clay, wood, iron, stone, and copper are materials which may well be fashioned into beautiful forms ; but beware of silver, and of gold, and of precious stones. The most fragile material often endures for a long period of time, while the almost in- corrosible silver and gold rarely escape the ruthless hand of the destroyer. “ Beautiful though gold and silver are, and worthy, even though they were the commonest of things, to be fashioned into the most exquisite devices, their money value makes them a perilous material for works of art. How many of the choicest relics of antiquity are lost to us, because they tempted the thief to steal them, and then to hide his, theft by melting them! How many unique designs in gold and silver have the vicissi- tudes of war reduced in fierce haste into money-changers’ nuggets ! Yfhore are Benvenuto Cellini’s vases, Lorenzo Ghi- berti’s cups, or the silver lamps of Ghirlandajo ? Gone almost as completely as Aaron’s golden pot of manna, of which, for another reason than that which kept St. Paul silent, ! we cannot now speak particularly.’ Nor is it only because this is a world < where thieves break through and steal ’ that the fine gold becomes dim and the silver perishes. This, too, is a world where ‘ love is strong as death ; ’ and what has not love — love of family, love of brother, love of child, love of lover — prompted man and woman to do with the costliest things, when they could be exchanged as more bullion for the lives of those who were beloved ?” * Work- man ! it is fortunate for us that the best vehicles for art are the least costly materials. Having uiado these general remarks, I may explain to my readers what I am about to attempt in the series of papers which I have now commenced. My primary object will be the bringing about refinement of mind in all who may accompany me through my studies, so that they may individually be enabled to judge correctly of the nature of any decorated object, and enjoy its beauties— -should it present any — and detect its faults, if such be present. This refinement I shall attempt to bring about by presenting to the mind considerations which it must digest and assimilate, so that its new formations, if I may thus speak, may be of knowledge. We shall carefully consider cer- tain general principles, which are either common to all fine arts or govern the production or arrangement of ornamental forms. Then we shall notice the laws which regulate the combination of colours, and the application of colours to objects ; after which we shall review our various art manufactures, and consider art as associated with the industrial arts. We shall thus be led to consider art furniture, earthenware, table and window glass, wall decorations, carpets, floor-cloths, window-hangings, dress fabrics, works in silver and gold, jewellery, hardware, and what- ever is a combination of art with manufacture. I shall address myself, then, to the carpenter, the cabinet-maker, potter, glass- blower, paper-stainer, weaver and dyer, silversmith, jeweller, blacksmith, gas-finisher, mason, designer, and all who are in any way engaged in the production of art objects. But before we commence our regular work, let me say that without laborious study no satisfactory progress can be made. Labour is the means whereby we raise ourselves above our fellows; labour is the means by which we arrive at affluence. Think not that there is a royal road to success — the road is through toil. Deceive not yourself with the idea that you are born a genius, that you were born an artist. If you are endowed with a love for art, remember that it is by labour alone that you oan get that knowledge which will enable you to present your art ideas in a manner acceptable to refined and educated people. Be content, then, to labour. In the case of an individual, success appears to me to depend upon the time which he devotes to the study of that which he desires to master. One man works six hours a day; another works eighteen. One has three days in one ; and what is the natural result ? Simply this — that the one wno works the eighteen hours progresses with three times the rapidity of the one who only works six hours. It is true * From a lecture by the late Professor George Wilson, of Edinburgh. that individuals differ in mental capacity, but my experience has led me to believe that those who work the hardest almost invariably succeed best. While I write, I have in my mind’s eye one or two on whom Nature appeared to have lavishly bestowed art gifts ; yet those have made but little progress in life. I see, as it were, before me others who were less gifted by Nature, but who industriously persevered in then’ studies, and were content to labour lor success ; and these have achieved positions which the natural genius has failed even to approach. Workman ! I am a worker, and a believer in the efficacy of work. We will commence our systematic course by observing that good ornament, good decorations of any character, have qualities which appeal to the educated, but are silent to the ignorant, and that these qualities make utterance of interesting facts ; but before we can rightly understand what I may term the hidden utterance of ornament, we must inquire into the general revelation which the ornament of any particular people, or of any historic age, makes to us, and also the utterances of individual forms. As an illustration of my meaning, let us take the ornament produced by the Egyptians. In order to see this it may be necessary that we visit a museum — say the British Museum where we search out the mummy-cases ; but a3 most provincial museums boast one or more mummy-cases, we are almost certain to find in the leading county towns illustrations that will serve our present purpose. On a mummy-case you. may find a singular ornament, which is a conventional drawing of the Egyptian lotus, or blue water-lily* (see Fig. 1), and in all probability you will find this ornamental device repeated over and over again on the one mummy-case. Notice this pecu- liarity of the drawing of this lotus — a peculiarity common to Egyptian ornaments — that there is a severity, a rigidity of line, a sort of sternness about it. This rigidity or severity of drawing is a great peculiarity or characteristic of Egyptian drawing. But mark ! with this severity there is always coupled an amount of dignity, and in some cases this dignity is very apparent. Length of line, firmness of drawing, severity of form, and subtlety of curve, are the great characteristics of Egyptian ornamentation. What does all this express ? It expresses the character of the people who created the ornaments. The ornaments of the ancient Egyptians were all ordered by the priesthood, amongst whom the learning of these people was stored. The priests were the dictators to the people not only of religion, but of the forms which their ornaments were to assume. Mark, then, the expres- sion of the severity of character and dignified bearing of the priesthood : in the very drawing of a simple flower we have presented t* us the character of the men who brought about its production. But this is only what we are in the . constant habit of witnessing. A man of knowledge writes with power and force; while the man of wavering opinions writes timidly and with feebleness. The force of the one character (which character has been made forcible by knowledge) and the weak- ness of the other is manifested by his written words. So it is with ornaments : power or feebleness of character is manifest by the forms produced. The Egyptians were a severe people : they were hard task- masters. When a great work had to be performed, a number of slaves were selected for the work, and a portion of food allotted to each, which was to last till the work was completed ; and if the work was not finished when the food was consumed, the slaves perished. We do not wonder at the severity of Egyptian drawing. But they were a noble people — noble in knowledge of the arts, noble in the erection of vast and massive buildings, noble in the greatness of their power. Hence we have nobility of drawing — power and dignity mingled with severity in every ornamental form which they produced. We have thus noticed the general utterance oi* expression of Egyptian drawing ; but what specific communication does this particular lotus make? Most of the ornaments of the Egyptians — whether the adornments of sarcophagi, of water-vessels, or mere charms to be worn pendent from the neck — were symbols of some truth or dogma inculcated by the priests. Hence Egyptian ornament is said to be symbolic. * This can be seen growing in the water-tanks in the New Gardens’ I conservatories and in the Crystal Palace at Sydenham. 51 BIO GRAPHICAL SKETCHES OF The fertility of the Nile valley was chiefly due to the river annually overflowing its banks. In spreading over the land, the water carried with it a quantity of rich alluvial earth, which gave fecundity to the country on which it was deposited. When the water which had overspread the surrounding land had nearly subsided, the corn which was to produce the harvest was set by being cast upon the retiring water, through which it sank into the rich alluvial earth. The water being now well-nigh within the^ river-banks, the first flower that sprang up was the lotus. This flower was to the Egyptians the harbinger of coming plenty, for it symbolised the springing forth of the wheat. It was the first flower of spring, or their primrose (first rose). The priest- hood, perceiving the interest with which this flower was viewed, and the watchfulness manifested for its appearance, taught that in it abode a god, and that it must be worshipped. The acknow- ledgment of this flower as a fit and primary object of worship caused it to be delineated on the mummy-cases, and sarcophagi, and on all sacred edifices. We shall have frequent occasion, while considering decorative art, to notice symbolic forms ; but we must not forget the fact that all good ornaments make utterance. Let us in all eases, when beholding them, give ear to their teachings ! BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS. II.— SIR HUMPHRY DAVY. BY JAMES GRANT. ■Sir Humphry Davy, Bart., LL.D., F.R.S., Member of the Foreign Institute of France, the eminent chemical analyst and discoverer, and inventor of the famous safety lamp, was the eldest of the four children of Robert and Grace Davy, and was born in the old municipal borough of Penzance, in Cornwall on the shore of Mounts Bay, on the 17th of December, 1778. In’the adjacent parish of Ludgvan his ancestors had long possessed the estate of Varfell, and there he resided in his earlier days. In the church are several tablets of the family, and one bears the date 1635. A strong and healthy child, he walked at nine months old ; and at two years of age he could speak with fluency, and accurately recite stories and copy the figures from “Alsop’s Fables.” He was taught reading and writing by a Mr. Bushell, and was then sent to Truro Grammar .School, under Dr. Cardew, where he was chiefly famous among the pupils . as a narrator of tales and stories, especially from the “ Arabian Nights.” Much of his enthusiasm for the poetic and the marvellous was fed by the grand scenery of his native county, and the traditions of giants and hobgoblins with which local superstition still peoples it. His quitting Dr. Car-dew's school in 1793 was an important era in his life. At fifteen his school education was deemed com- plete ; thus to his future self-education he owed all. In the following^ year his father died, an event which gave a steadfast- ness to ail his resolutions. In 1795 he was apprenticed to Mr. Bingham Barlow, then surgeon and apothecary in Penzance, and in after years a distinguished physician. Young Davy’s note-books, show the ardour with which he entered on his new career,. during which he published some poems of considerable merit ^ 1G ‘‘ Annual Anthology.” In 1797 he was working hard at Euclid and algebra, and was deep in the study of -jocke, Hartley, and Helvetius, together with the writings of Reid, Hume, and others, who are designated by him as “ the Scottish metaphysicians.” The house in which he passed the years of his apprenticeship has recently been removed to make way for the Town Hall. He now commenced in earnest the study of natural philosophy, and went more deeply into chemistry on the system of Lavoisier, and at the same time he became a skilful draughtsman. In 1798 he began to form these peculiar views respecting heat and light, in opposition to those then commonly received ; and on this subject corresponded with Dr. Beddoes, who ' became a convert to his principle. Among his earliest researches at Penzance are those on the respiration ol fishes and of zoophytes, in which he maintains that oxygen is essential to the existence of those classes of animals ; that they breathe the air contained in the water, and, like the higher class of land animals, convert the oxygen, by the addition of carbon, into carbonic acid gas. EMINENT INVENTORS, ETC. In October that year, before he was twenty-one years of age, he left home to enter on a new and enlarged sphere of existence — a public career in the Pneumatic Institution at Clifton where, however, he was only two years and a half, when, at the suggestion of Count Rumford, he was appointed Professor of Chemistry in the Royal Institution of Great Britain ; and then he completed and gave to the world his first views of heat and light. At this time his chief friends and correspondents were Southey and. Gregory Watt (son of the famous James Watt), whose acquaintance he had made when the latter was travelling in Cornwall for the benefit of his health ; but he soon found other intimate friends and colleagues in Herschel, Dalton, Wollaston, Cavendish, Knight, Warburton, and Allen. His success as a lecturer was most eminent, and the theatre capable of holding a thousand persons — was always crowded to excess when he appeared. The best specimen of his powers is supposed to be contained in a lecture on electro-chemical science, delivered on the 12th of March, 1808, in which, after Bacon, he vindicated the benefits accruing to mankind from experimental science and natural knowledge in general, against all cui bo-no Carpers. This was to him a happy period of his life : enjoying the best society in London as only a young man can enjoy it, and when his duties set him free, travelling to the -wildest parts of Scot- land, Ireland, and Wales as a geologist and angler, returning always with numerous specimens, which now remain in the museum of the Royal Institution. But amid ail his occupations he never forgot his Cornish home, and to write a New Year’s letter to his mother, with regular Christmas-boxes of “ten shillings to Betty White and ten shillings to Mary Lander,” her old servants, as his published correspondence shows. The years 1806 and 1807 saw him immersed in the study of the use of electro-chemical science, and the extreme delight he felt when he first saw the metallic basis cf potash can only be conceived by those who are familiar with the operations of the laboratory, and the exciting nature of original research ; but illness, the result of over-work, came upon him now — an illness consequent, as some supposed, on a visit he had paid Newgate for the purpose of inquiring into the sanitary condition of that great and then foul prison. For a time he feared it would prove fatal, and his greatest apprehension was that he should die before he had given his discoveries to the world. After the 23rd of November — ho was nine weeks ill — he was con- valescent, and during that period he again amused and solaced himself by writing verses, a species of amusement to which he had occasional recourse during his life-time. His friend Beddoes died on Christmas Day, 180/, and on that occasion Davy wrote a touching letter to their friend Coleridge, saying that “ he had gone at the moment when his mind was purified and exalted for noble affections and great works. My heart is heavy.” In 1810 and 1811 he visited Dublin, where he met with a most enthusiastic reception, and the degree of D.C.L. was con- ferred upon him by Trinity College. He received 1,150 guineas for two lectures, and it was then that Cuvier wrote of him as — Davy, not yet thirty-two, in the opinion of all who can judge of such labours, holds the first rank among the chemists cf this or any other age.” After his marriage with Mrs. Apreece, in 1812, he wrote of her with enthusiasm to his brother John as “a noble creature who every day added to his contentment by the powers of her under standing and delightful tones of feeling ; ” and to her he dedi- cated his “Elements of Chemical Philosophy.” In 1814 he was in Italy, and his researches while there appeared in the “Philosophical Transactions” of the Royal Society for that year. He studied deeply all the marine productions of the shores of the Mediterranean; and in a letter to his brother says of this tour, “ I have lived much with Berthoilet, Cuvier, Chaptal, Vauqueiin, Humboldt, Morveau, Clement, Chevreul, and Gay Lussac, and they were all kind and attentive to me.” At Florence and Rome he entered upon a new subject of inquiry — the nature of the diamond, and discovered that it was merely - crystallised carbon. He also mentions that he saw old Pius i VIII. carried in triumph into the Eternal City on the shoulders j of the most distinguished artists, one of whom -was Canova. In 1818 he was created a baronet. At Milan in 1814 he visited Yolta (the inventor of the Voltaic battery), then in his seventieth year. From thence he crossed the Alps by the Simplon ; and wherever he wandered in Italy 52 THE TECHNICAL EDUCATOR. he was never idle— the laboratory, the flora, and the study of antiquities affording him incessant occupation. His observa- tions on the fast colours used in painting by the ancients experiments on the solid compound of iodine and oxygen, and the action of acids on salt— usually called hyper-oxymuriates and the gases produced from them, all appeared m the papers of the Royal Society in quick succession In March he visited Vesuvius, and gave an interesting sketch of the visible strata. , ,, While travelling in the Tyrol he made the acquaintance of the old mountain patriot, Speckbacker, who oddly enough presented •him with the identical musket with which he shot thirty Bavarian soldiers in one day; this trophy Davy afterwards presented to his friend Scott, and it is now preserved m the armoury at Abbotsford. May found him and Lady Davy in London, when he entered on a new train of inquiry, the investigation of fire- damp, with a view to the more efficient protection of mines and also of the workmen who are exposed to its destructive agency — objects of vast importance in regard to the interests of humanity, and which were ultimately accomplished by his famous invention of the safety lamp, which was calculated, as his paper stated, “ for preventing explosion in mines, houses lighted by gas, spirit warehouses, and ship-magazines.” . In 1815 he gave his entire attention to this important subject. After reasoning on all the various phenomena and causes of fire- damp, “it occurred to me,” he continues, “as a considerable heat was required for the inflammation of the fire-damp, and as it is produced by the burning of a comparatively small degree of heat, that tho effect of carbonic acid and azote, and of the surfaces of small tubes in preventing its explosion, depended upon their cooling powers, and upon their lowering the tempera- ture of the exploding mixture so much that it was no longer sufficient for its continuous inflammation.” His safety lamp was simply a cage of wire-gauze, which actually made prisoner the flame of the fire-damp ; and whilst it confined the dangerous and explosive flame (consuming it at the same time), permitted the air to pass and the light to escape; and though, from the combustion of the fire-damp, the cage might become red-hot, yet it acted the part of a safety lamp, and restrained the flaming element within its narrow bounds : hence the imprisoned flame was not capable of rising high enough to explode with the fire-damp without, or to allow the flame kindled within to pass unextinguished. Letters now poured in upon him from pro- prietors of mines and collieries, expressing their gratitude for his invention. A public banquet, presided over by the future Earl of Durham, was given to him at Newcastle, and he was presented with a service of plate valued at .£2,500. The year 1817 saw his researches on the subject of fire-damp brought to a close ; and after visiting Orkney, he departed on a second Continental tour through Austria, Hungary, Vienna, along the shores of the Adriatic, and thence again to Rome. Of this journey he left an interesting journal, and during it made experiments on tho papyri found in the ruins of Herculaneum, which he published together with some observations on vol- canoes, having witnessed the eruptions of Vesuvius in 1819 and 1820. On the death of Sir Joseph Banks, in the latter year, he became president of the Royal Society — an office held by his predecessor for forty-two years. He continued his scientific labours, espe- cially on magnetism, tho liquefaction of gases, and researches into the corrosion and protection of- the copper sheathing of vessels. In 1824 he made a tour through Scandinavia, Holstein, and Hanover, travelling more than 2,000 miles. He was graciously received by the Crown Prince of Sweden, and at dinner sat on the left of the princess— the grand-daughter of the Empress Josephine. At Altona— of which Blucher was then governor— he visited the tomb of Klopstock. The following year f ound him rusticating amid the beautiful scenery of Westmoreland. But 1826 saw his health breaking, indisposition creeping upon him, rheumatism impeding his literary labours ; and then the death of his mother, to whom he was tenderly attached, gave him a severe mental shock that was soon afterwards followed by a bodily one. At the meeting of the Royal Society on St. Andrew's Day, it was evident to all that his discourse was delivered by a great effort ; and fourteen days after, his whole left side was affected by paralysis, which came on him suddenly when shooting with Lord Gage. He immediately sought the aid cf his friend Dr. Babington ; but in this prostrate condition actually corrected the proofs of his “Discourses,” which were published in quarto in 1827. The 22nd of January saw him so far recovered as to be able once more to seek the Continent. He crossed France and Mont Cenis to Italy, and by the kindness of the Vice-Legate was lodged in the Apostolic Palace at Ravenna, where he resumed his journal, his diary, and wrote several poems of great sweetness and pathos ; but came home more than ever broken in health. Again he sought the Con- tinent, visiting Austria, Flanders, thence to the Noric Alps, Styria, and Trieste, that, ailing as he was, he might test the experiments he had long been meditating on the torpedo, and on returning to Laybach ho communicated his views to the society. May, 1829, saw him at Geneva, where he took up his residence at the Hotel la Couronne. At five o’clock on the 28th he dined as usual, and at nine o’clock accidentally struck an elbow against a sofa. The effect was extraordinary ; a universal tremor passed over his frame, and he exclaimed that he was “ dying.” He was put to bed as soon as possible, but gradually sank into a state of insensibility, and expired at three o’clock in the morning of the 29th ; his eyes being closed by his faithful brother John. On the 1st of June his remains were de- posited in the burying-ground without the walls, and close to those of Professor Pictet, where Lady Davy afterwards erected a tomb with a suitable inscription in Latin. No post-mortem examination was made, as he had throughout his life shown a. nervous horror of such searches. By his will he bequeathed to the grammar school of his native town £100, “ on condition that the boys were to be allowed an annual holiday on his birthday.” Thus, at the early age of fifty-one, passed away one of the brightest luminaries and best men in the world of science ; a mere enumeration of whose writings would go far beyond our limits. AGRICULTURAL CHEMISTRY.— II. BY CHARLES A. CAMERON, M.D., PH. D. qjXAPTER XI. — THE ELEMENTARY PARTS OF PLANTS. The almost infinite variety of form, colour, weight, and every other attribute of the multitudinous objects in the vast store- house of Nature, naturally suggests to most minds the idea that, the number of raw materials from which they have been elabo- rated must necessarily be very great. We have, however, shown in a previous chapter that such is not the case, and that tho number of first principles is very small. A mass of any one of these first principles or elements is, there is good reason to suppose, an aggregation of minute particles, which, from a belief in their indivisibility by chemical or physical means, are termed atoms* In a strictly mathematical sense we cannot consider atoms to bo indivisible, because matter, however minute in quantity, possesses weight, length, breadth, thick- ness, and extension. An atom, however, may be regarded as an aggregation of innumerable smaller particles, which cannot be separated from each other, at least by any power at man s disposal. The Greek philosopher, Democritus, by an ingenious illustration exhibited intelligibly tho impossibility of dividing an atom. He likened the matter of which our earth is com- posed to the starry firmament, each member of which being so small compared with its distance from the others and the immensity of the universe, may really be termed an atom; for although it is composed of a number of particles ot matter, yet all these particles are bound together by a force which no external influence can affect. Neither can its form or its distance from tho other heavenly bodies be altered. From this point of view the universe may bo re- garded as a vast aggregation of indivisible and unchangeable atoms. . , As in the inanimate the apparently insignificant atom is. believed to play the most important part, so in the animate creations wo find the essential functions of life discharged in. those parts of animals and plants which are apparently so low in the scale of organisation as to be all but unworthy of our attention. Animate as well as inanimate matter is composed of small and, in a physiological sense, indivisible atoms. As an amorphous (uncrystalline) mass of mineral matter possesses 1 From the Greek words, a, a privative particle, and Umno, I cut. AGRICULTURAL CHEMISTRY. 63 only the properties which distinguish a single atom of it, so also are there immense masses of living matter (simple cellular plar.ts) composed of organic atoms, each of which possesses all the properties which we recognise in their aggregated unity. And again, as the grouping of atoms of a particular kind of substance — say carbon — into crystalline masses causes them are numerous points of resemblance between the two classes of atoms, there is believed to be this important difference — the inorganic atom is conceived homogeneous, whereas the atoms of organised structures are, so to speak, heterogeneous. But certain botanical microscopists affirm that the cell takes its origin from an exceedingly minute and homogeneous particle of II. Examples of Forms assumed by Woody Fibre. III. Examples of I. Examples of Forms assumed by Vegetable Cells Forms assumed by Starch Granules. 5 ' cells^°5 anvSar cpUs TT °^ lar ve p^ We cells ; 2, polyhedral form induced by compression; 3, ovoid or spheroid cell - 4 stelliform flactifCus vessel ’7°°^ “unified ; 2, striated and punctated vessels of melon; 3, spiral fibres or trachea of plants 6 - •» - 7 - «•>»*»■ «•* - <*• “il: to acquire in combination properties whieh individually they did not possess, so the various arrangements of atoms of organic matter give rise to structures which manifest properties un- recognised in the simple atom. The organic atom is simply the nucleated cell of the vege- table physiologist. Its external configuration is probably similar to that of the mineral atom, and as the latter gains in weight at least in different inanimate substances, so does the former vary in size in different animate bodies. Although there spherical form, which they have termed the cell germ. It is, however, not probable that this germ is the ultimate atom of vegetable substances, inasmuch as it is easily visible through the microscope, whilst the same instrument reveals the existence of plants so minute that hundreds of millions occupy the limited space of one cubic inch without interfering with each other ! As each of these minute organisms must be composed of numerous parts or atoms, excessive minuteness of the latter presents an impassable barrier to all save speculative inquiries 54 THE TECHNICAL EDUCATOR. relative to their size and form. The cell may, therefore, for the purposes of research, be regarded as the elementary organ or atom of organised structures. The cell consists of a little bladder formed by an elastic trans- parent and extremely thin membrane. The cavity ^contains semi-liquid and sometimes gaseous matters. The wall of the cell is apparently devoid of definite structure ; it is composed chiefly of cellulose, a substance resembling starch in composi- tion. On the inner side of the cell there is a thick, mucilage- like substance, termed protoplasm or formative layer. In the cell there is a small spherical, termed the nucleus, which closely invests a smaller body — according to some, a cavity — called the nucleolus. The nucleus and the protoplasm are destined to form into new cells. The shape of cells is influenced by the condition under which they are developed. "When their growth is unopposed, or when they are exposed only to gentle and equable pressure, their form is most frequently that of a sphere or spheroid. Owing to unequal pressure, cells, however, are found to present a great variety of forms, many being tube-like. The engraving in the preceding page (Fig. I.) exhibits the varied forms assumed by translucent or transparent. Its function is to sustain th© elementary membrane, and to prevent any of its folds from coming into actual contact with each other. In fiibro -cel lul ar tissue we find cells having one or several fibres wound in a spiral direction round its inner side. As the sides of cells con- taining fibres are kept well apart, they are generally found to contain air. Woody fibre consists of long tubes (formed from cells) having tapering extremities ; their ends overlap each other. They are more or less filled with sclerogen or lignine. This kind of tissue is particularly abundant in forest trees. Vascular tissue is found only hi the higher forms of vegetable life. It consists of long unbranched tubes or ducts, which, however, are only a series of cells opening into each other. These tubes are believed to be chiefly employed in conveying air throughout the vegetable mechanism, and they may be regarded as somewhat analogous to the kings of animals. Woody tissue is a species of vascular tissue, and so also are the branched tubes termed lactiferous vessels, in which the milk -like liquid found in certain plants is contained. cells. Wood is in great part composed of tube-like cells. When the tubes are very long and narrow, they are termed vessels. Cells vary much in size ; sometimes they are easily recognisable by the unassisted eye ; but in general they are at least only the one-thousandth of an inch in diameter. In the lowest forms of vegetable life the cells are all but unconnected, and all perform the same functions ; but' in the higher forms of plants they coalesce and form structures, each of^which discharges a different function in the economy of the plant. The least organised plants are termed cellulars. In these lowly forms of vegetable life the cells touch, each at a limited number of points, forming intermediate spaces, termed intercellular canals oi’ passages. Compact tissue is produced when the cells lie close together. In the higher plants there are both loose and compact tissue. The majority .of physio- logists believe that there are numerous minute pores in the cell- walls ; a very probable hypothesis, for otherwise it would be difficult to account for the fact that gases and liquids pass through the cell-walls. The important food substances, starch and albuminoid bodies, are found in cells. ■ The former, according to Mulder, is com- posed of nuclei, in which matter destined for the nutrition of the offspring of the plant is stored up. The engraving (Fig. III.) represents the various appearance of some of the starch granules contained in cells. In the cells we also find the matter termed chlorophyll * which confers upon plants their green colour. The circulation of the juices of the plant is carried on by means of the cellular tissue, and in thousands of species the circulation is solely carried on through this agency. Owing to the looseness of the cellular tissue, and to the tenacity of the individual cells, these structures render plants strong and elastic at the same time. The substance of which cell tissue is formed is supposed to consist of extremely minute round bodies placed side by side, leaving very minute spaces between them. In young cells the tissue or membrane is extremely thin, and is translucent ; but after a time it generally becomes thicker and more opaque. Chemically, the membrane is composed of carbon, hydrogen, and oxygen, and is almost identical in composition with starch. By chemical treatment it is readily converted into a species of sugar. In certain parts of numerous plants the cell-wall is lined with a very hard substance, termed sclerogen, which appears to be almost, if not quite, identical in composition with the cell-wall. The hardness of various kinds of nuts is due to the sclerogen in their cellular tissue. The hardness of wood is in great part due to the sclerogen or lignine contained in its cells. Cellulose occurs nearly pure in elder pith, cotton, and linen. It constituted the celebrated papyrus or paper so extensively employed by the ancient Egyptians and Greeks. Examples of varieties of plant-fibre are given in Fig. II. in the preceding page. Elementary fibre is identical in composition with elementary membrane, on the side of which it is deposited from the proto- plasm. It is solid, body generally rounded, and almost always * From the Greek chloros, green, ancl phyllon, a leaf. MINERAL COMMERCIAL PRODUCTS.— III. LEAD. This metal, the heaviest of the baser metals (sp. gr. 11-45), is soft, easily fused, and very slightly sonorous. It is largely used in roofing, lining, plumbing, and bullet and shot making. It also enters into the composition of pewter, solder, and type- metal; and in its chemical combinations it forms litharge (the oxide), a yellow paint ; red lead (red oxide), a cheap substitute for vermilion ; white lead (carbonate), manufactured on an immense scale for the painter; and sugar of lead (the acetate), of great value to the chemist. These substances are highly poisonous. . The most abundant and important of the ores of lead is galena, a sulphide of the metal, yielding 86 per cent, of lead, and almost always containing silver, which is separated when the quantity is not less than four ounces to the ton. The other ores are : the carbonate of lead, the vanadiate of lead , the cupreous sulphate of lead, and the arsenio-phosphate of lead. Galena is found very abundantly in the limestones of the Car- boniferous series, and to a less extent in older rocks. Its reduction is effected by pounding, washing, and smelting in a reverberatory furnace. Bead-mining is carried on in Britain (Northumberland, Cumberland, Durham, Derbyshire, Flintshire, Cornwall, Isle of Man, and Bead -hills), also in Spain and Portu- gal, France, Belgium, the Harz Mountains, Saxony, Rhine Provinces, Bohemia, Carinthia, Hungary, Norway, _ and Sweden ; Altai Mountains, China, and Indo-Chinese Peninsula, South Africa, Peru, California, United States, and Canada. The annual supply of lead from the different countries of Europe is — Tons. Britain 67,000 Austria (with litharge) 6,800 Zollverein .... 38,800 Tons. Spain 313,000 Sweden 500 France (metriquintals) 20,000 ZINC. This metal, of a bluish-white colour, and specific gravity about 7, has the remarkable peculiarity of being malleable and ductile only between the temperatures of about 250° and 300° Fahr., and of retaining its malleability when coded. It forms a cheap substitute for many of the applications of lead, such as tanks, pipes, roofs, and for bronze in ornamental works. It enters into the composition of brass, and is now exten- sively employed in domestic manufactures, printing, engraving, sheathing of ships, coating of galvanised iron, electrical appa- ratus, and medicine. Its oxides form valuable white and grey paints. t The principal ores of zinc are, calamine, a carbonate (ZnO,CO a ); blende or blackjack, a sulphide; and a silicate, or electric cala- mine. They occur often in association with the ores of lead, and frequently with the ores of copper and tin, chiefly in lime- stones of the Carboniferous and Devonian systems. The pure metal is obtained by roasting and distillation, as it is very volatile at a red heat. The ores are largely worked in Belgium, Silesia, Rhine Provinces, and Hungary. Zinc is also produced TECHNICAL DRAWING. ■56 in Flintshire, Derbysmre, Cumberland, Cornwall, Devon, Ire- land, Wales, Isle of Man, Sweden, Bohemia, Carinthia, Spain, the Harz, Canada, New Hampshire, and New Jersey, in which last place the metal occurs in the mineral red zinc ore, an oxide of zinc. The average annual production of zinc from United States is : — Tons. Britain Silesia Austria Spain 4,460 36,000 1,500 1,000 Sweden (ore) Zollverein Belgium . United States Europe and the Tons. . . . 10,000 . . . 76,000 ' . ; . 16,000 . . . 5,000 ALUMINUM. This metal is white, resembling silver, and is of low specific gravity (2’G). It exists abundantly in Nature as the metallic base of argillaceous and felspathic rocks, which are silicates of alumina, and as sulphate of alumina, an important constituent of the alums. The pure metal has lately been obtained in quantities available for manufacturing purposes ; and from its extreme lightness, its freedom from tarnishing, and its sono- rousness, it promises to become a most useful product. The metal can be separated from the earth alumina, or from the chloride ; but it is obtained economically only from Cryolite, a double fluoride of aluminum and sodium, found in Greenland. ANTIMONY. Antimony is white and brittle, with a specific gravity of G’8. As a simple metal it is not used, but it forms valuable alloys. With lead and bismuth it is largely used in the preparation of type-metal, which consists of 6 parts of- lead and 2 of anti- mony ; with lead and tin for plates on which music is engraved, a,nd with the same for stereotype metal. A small proportion of antimony combined with tin forms hard pewter ; and with tin, bismuth, and copper, the white or Britannia metal. It is also \cry extensively employed in medicine. It occasionally occurs in a pure state, but usually combined with sulphur, or sulphur and lead ; it is also found in combination with arsenic, and with nickel, silver, and copper. Grey antimony, a tersulphide, affords nearly all the antimony of commerce. It is found in Hungary, Saxony, and tho Harz, Belgium, France, Italy, Spain, Siberia, Mexico, Malacca, the Indian Archipelago, and was at one period produced in consider- able quantities in Cornwall and Dumfriesshire ; but now the principal part of our supply of antimony is from Borneo and the East Indies. Central Italy furnishes 700 tons; Spain, 58 tons. BISMUTH. Bismuth is a brittle reddish-white metal (sp. gr. 9*9) which fuses at a very low temperature. It fuses still lower in com- bination with lead and tin, with which it is used as a solder, and with which it also forms the metal called “ Newton’s,” fusible at the boiling-point of water. It enters, too, into the composition of Britannia metal, pewter, and type-metal, and is of some use in medicine. It is found, tolerably pure, usually associated with ores of tin, copper, and silver, in Cornwall, France, Bohemia, Saxony, and Sweden. COBALT. Cobalt is a white, brittle, and very tenacious metal. Its specific gravity is 8'5, and it is strongly magnetic. It is very useful in its chemical preparations as producing fine colouring’ ' substances, chiefly blue, such as smalts, cobalt-ultramarine, and ! zaffra or saflor (a corruption from sapphire). The principal i ores are cobalt-glance, a combination with arsenic, the black i oxide, and cobalt-bloom ; they are found in Norway and Sweden, ! Saxony, Hungary, Rhenish Prussia, and the United States! ! The annual yield of zaffre or smalt amounts to, in Saxony, 8.000 cwt. ; Bohemia, 4,000 cwt. ; Prussia, 600 cwt. ; Norwav, 4.000 cwt. NICKEL. This metal is also found combined with arsenic. It is white, malleable, and but slightly affected by air and moisture. Its specific gravity is 8'5, and it is magnetic until subjected to great heat. With copper it forms German silver, and its alloys form excellent bases for electro-plating. A fine green colour is obtained from its preparations. Nickel has been used in the United States for coin. Its chief ore, “ knpfer- I nickel ” or speiss, often associated with cobalt, is found in Westphalia, Saxony, Hesse, Hungary, and Sweden. Nickel occurs in meteoric iron. ARSENIC. Metallic arsenic is grey, highly lustrous, crystalline, and brittle (sp. gr. 5'7). The arsenic of medicine is the white oxide, or arsenious acid, a virulent poison; this is also largely em- ployed in preparing some of the finer skins and furs of Russia. Ihis metal enters into the composition of some valuable pig- ments, especially a brilliant green and an orange red. It is also combined with lead in the manufacture of shot. Arsenic is rather widely diffused ; and although sometimes pure, it is usually found combined with other metals, with sulphur, and with oxygen. The chief amount is obtained from the arsenides of iron, nickel, and cobalt, and the supply is chiefly derived from Bohemia, Hungary, Saxony, Salzburg, Transylvania, Rhine Provinces, and France. Realgar, a red sulphide (AsS 2 ),is found in Bohemia and Saxony; and orpiment, another sulphide (AsS 3 ), a fine yellow, in China and South America. Arsenic is also procured from the tin mines of Cornwall; the produce of the metal from this source for 1866 being 1 , 1164 - tons. MANGANESE. Manganese oxidises at ordinary temperatures, and is never used in the arts in the pure state. It is of a reddish hue, brittle, so hard as to scratch glass, and has a specific gravity of 7T3. The binoxide (MnO a ) is an important article of com- merce, largely employed in glass manufacture and for colouring pottery, and by the chemist in the preparation of oxygen. Sulphate and chloride of manganese arc used in calico printing; the former gives a valuable brown dye. It is found that a slight addition of this metal much improves the cast steel made from British iron. The principal ores of manganese are Pyro- lusite and Psilomelane, both binoxides, tho former anhydrous,, the latter containing 1 per cent, of water. Wad, an impure manganese ore, may be employed, like the preceding, in bleach- ing, and also for umber paint. Manganese ores are procured from the Harz Mountains, Piedmont, France, Spain, Nova Scotia, Somerset, Devon, Isle of Man, and were formerly ob- tained from Cornwall, Italy, etc. Britain produces 5,000 tons. CHROMIUM. This metal, in its pure state brittle, difficult of fusion, and like iron in colour’, is important in the arts for tho beautiful colours produced by its combinations. The most important of these are the sesquioxide of chromium, a fine green, bichromate of potash, and bichromate of lead, yellow and orange. The principal ores are chromic iron (chromate of iron) and chromate of load, the former occurring usually in serpentine rocks in tho Shetland Isles, France, Norway, and the United States, and the latter in Siberia, the Urals, and Brazil. TECHNICAL DRAWING.— IY. LINEAR DRAWING BY MEANS OP INSTRUMENTS ( continued ). Returning now to the practice of drawing by means of instruments, a useful series of examples is here given for the student’s use. The subject of which Fig. 12 is the plan and Fig. 13 the section, is a network platform for a foundation where the soil is of a soft character, and liable to be pressed outward by the weight resting upon it, but still not sufficiently so to render absolute sheet-piling necessary. Strong piles (c c cc) are driven down to the firm soil, and these are connected by horizontal planks (e e), placed on each side and bolted through tho piles. Now in the space left between these planks a wall is formed of timbers, d d d d, which are driven down by hand-ramming, not extending downward further than the circumstances may render necessary. These planks are jointed in various ways, with some of which you will become acquainted in the study of “Building Con- struction Fig. 14, rebated ; Fig. 15, splayed at one edge and recessed at the other; Fig. 16, ploughed and tongued. In the example, the tongue is shown square and tapered, and in Fig. 17 it is worked in the dovetail form, whilst- Fig, 18 shows the planks joined by an inserted tongue. 56 THE TECHNICAL EDUCATOR. Now, to draw this series of examples — ■ First draw the piles, c c c c (Fig. 12), and continue the lines forming the edges of them, so that these may give you the sides of the piles shown in the section (Fig. 13). Next draw the top of the wall of planks between the piles, and in the example it will be seen these are one-third the thick- ness of the piles ; therefore, divide the edge of one of the piles on each side into three equal parts, and use the middle division for the thickness of the wall. This thickness, again, projected “Building Construction.” The cuts (Figs. 19, 20, 21, and 22) are here introduced in order that they may be used as studies for drawing and shading. It may, however, be well to inform you that the points of the single or corner piles (Fig. 19) are four-square, whilst those of sheet-piles are only bevelled from two sides, and the edge is cut so as to slant downwards (Fig. 20). Piles are generally worked of square timber, and if the trees admit of it, those which are to be rammed entirely into the upwards, will give the elevation of the edge of the planks (cl cl). Now outside and inside of the piles draw the tying-planks, eeee, and project them on to Fig. 13, e e e e, where it will be evident they will appear as sections. Next draw the lower course of sleepers, a a a a a, and the elevation of them shown at a, in Fig. 13 ; then follow in their order the upper course of sleepers (b h b b), their projection in section (bbb b), and in these last the flooring of the platform which has not been shown in the plan. The difference in the form of the piles when used separately, or at angles of foundations, and those called sheet-piles, will be fully described when treating of the principles of foundation in ground are mostly slightly tapered downwards throughout their whole length, and are shod with iron at their points (unless the piles be small and the ground not very hard) ; and an iron ring is placed around the upper end, to prevent the piles from splitting by the violence of the blows necessary to force them down. Sometimes, however, the piles which are to be driven quite below ground may be used without squaring ; two illustrations of such (Figs. 21 and 22) are here given, to afford practice in shading cylindrical bodies. Having pencilled and inked the outlines of the four piles shown in the example, wash over the part representing wood TECHNICAL DRAWING. 57 with a pale tint of raw sienna. In the two square piles this wash may be perfectly flat, but in the round piles the tinting must be in accordance with the form. It will be evident that when a cylindrical body is placed up- right, the light will fall in a stream straight down the part which projects the most, and this part must, therefore, be preserved as bright as possible ; in fact, there must be a per- fectly white streak extending all the way down. To effect this, you must use two brushes, the one rather larger than the other. Take some colour in the smaller one, and dip the other in water ; touch the points of both on another piece of paper, so that they may not be overcharged, and by gently turning each round as you draw it along the waste paper you will bring the hairs to a point. Now commence by drawing the brush containing the colour down the left side of the round pile, carefully avoiding passing over the line by which it is bounded. In this way colour a ( strip about one-eighth of an inch wide ; do not leave a pool of I colour, but merely tint the paper. Before this has time to ! The rammer, which is made of beech or other hard wood, should be tinted of a lighter colour than that given to the guide-posts. The pile is to be coloured and shaded as in the previous examples, but you will observe that there is on it the shadow cast by the rammer above; this is called the “cast-shadow,” and must not have its lower edge smoothened off, as the sharp edge of the bottom of the rammer will cause the shadow cast on the cylindrical pile to be very well defined. Big. 24 is the front elevation of the same object, and will give further practice. The student is urged to observe the forms and tones of shadows cast by different objects ; this he can easily manage a cubical piece of wood or two, and a cylin- drical piece, may be disposed in hundreds of ways, each affording a new study. This is the only way to gain real practice ; for so long as the pupil only copies, he is merely repeating other men’s works, and will only gain manual practice ; whilst by studying and maLing his own observations he will be laying up a store of information of which he will hourly find the value. become dry, take your water-brush, and passing the point down the inner side of the part you have coloured, soften the edge away so that the colour may merge gradually into the bright white. Leave about the eighth of an inch quite dry, then pass your water-brush down, and next to this the colour, so as to produce the effect as on the other side ; the colour becoming gradually fuller as it becomes further removed from the light. Whilst the dark strip is still moist, wash off its edges, and merge it off into the local colour of the pile, and this should be done so gradually that as you ought not to be able to discover where the white light merges into the raw sienna, so you should not be able to discern the meeting of that colour with the sepia ; but do not work your brushes up and down so as to produce a sleek or woolly effect. The shading and tinting should be bold and clear : a little practice will enable you to accomplish this. You are therefore advised to repeat such studies until you succeed. The iron shoe of the pile will, of course, be coloured with pale indigo. Fig. 23 will afford another example for colouring and shading. The drawing represents the side elevation of the monkey (or rammer) and guide-posts of a simple pile-driving machine, with head of a round pile. . The shading is to be done in sepia ; in the square piles this will simply consist in tinting the shaded sides with a flat tint. In the round piles, however, the shading must be managed in a similar manner to the colouring; dipping your middle-sized brush into the sepia, colour a strip the whole length of the pile. This darkest part, however, you will observe, is near, but not really on the outer edge of the cylindrical body. Further to the right side, you will notice the shade becomes lighter, and this is called the reflected light. It may happen with beginners that the tints may not dry quite as smooth or as flat as they expected — irregularities, dark patches, or light spots, may appear. In the one case, a brush just moist should be worked over the dark part, by which means some of the superfluous colour may be removed. In some cases it may be necessary to rub the spot with a soft piece of india- rubber or bread. If neither of these processes is successful, a sponge should be drawn over the whole, and the work repeated when dry. In case of light spots appearing, they should be touched with the point of a brush containing colour ; but care must be taken that only the light spot is touched. This is called stippling, and should only be used as a remedy. Tinting and shading should always be done in as free and bold a manner as possible. 58 THE TECHNICAL EDUCATOR. VEGETABLE COMMERCIAL PRODUCTS.— II. farinaceous plants ( continued ). (c.) The Leguminosx ( Pulse Family). This great natural family of plants contains numerous species With, wholesome nutritious seeds, which, under the general term pulse, form important articles of commerce. These legumes comprise, in temperate climates, the Common Pea (Pisum sativum, L.), the Horse Bean ( Faba vulgaris, Moench), the Haricot or French Bean ( Phaseolus vulgaris, Sari), the Lentil (Ervum lens, L.) ; and, in the tropics, the Ground Nut (Arachis hypogcea, L.), the Chick Pea ( Cicer arietinum, L.), and the Carob Bean, or St. John’s Bread ( Qeratonia siliqua, L.). The legumes of temperate climates are familiar plants, and their mode of culture well known. Peas, beans, and lentils are grown in great quantities in Poland, Prussia, Pomerania, Den- mark, East Friesland, and other countries. They create con- siderable business in the large sea-port towns on the Baltic and German seas, wh»le cargoes being brought to those places as provisions for ships. In 1866, 1,211,835 cwt. of peas were imported to this country, chiefly from Prussia and British North America; and the same year, 1,324,173 cwt. of beans were received, of which 615,912 cwt. wore from Egypt, and the remainder from other countries. The tropical species of pulse are not so well known, and require description. Ground Nut, ( Arachis hypogcea, L.). — This plant is culti- vated in America, in the Southern States, and forms an impor- tant article of food in many parts of Africa. It is a low, creeping plant, indigenous to the western coast of Africa, with yellow flowers, having the general appearance of a dwarf garden pea, although more bushy. After the flowers drop off, and the pods begin to form, the stalk or support of the pod elongates, thrusting the pod under ground, where it comes to maturity. The seeds contain a considerable quantity of oil. They are roasted in the pods, and are sold in the United States in large quantities, being a favourite dainty with children. This plant is very prolific, and in warm climates requires but little care and attention in its culture. In the green state it is greedily devoured by cattle. Carob Bean, or St. John’s Bread ( Qeratonia siliqua, L.). — The carob tree is peculiarly Oriental, and abundant in Palestine. It has large pods, the seeds of which are enveloped in a sweet, nutritious pulp. It is supposed to be the locust bean on which St. John the Baptist fed when in the wilderness. This tree is common in the Levant and the south of Europe, where its beans are used as food. Most of the carob beans imported into this country come from Sicily and Naples. During the Peninsular war the horses of the British cavalry were frequently fed on these beans. Chick Pea ( Cicer arietinum, L.). — This plant is a native of Southern Europe and the East. Its seeds are parched, and in Spain are sold in the shops for food. They are also abundant in the bazaars at Calcutta, and, under the name of gram, are sold as food for horses. Every part of this plant exudes oxalic acid, and it is used by tho ryots of India in their curries instead of vinegar. When roasted, it is said to sustain life longer than other food in similarly small quantities ; hence it is much used by travellers through the deserts, where the carriage of bulky food is inconvenient. II. THE STARCHES OP COMMERCE, AND THE PLANTS WHICH PRODUCE THEM Starch is an abundant product of the vegetable kingdom, and is in large demand for domestic and manufacturing purposes. It exists in all mealy farinaceous seeds, fruits, and roots, differ- ing in its appearance according to the plants from which it is obtained. Starch is the nutritive matter of plants, and is changed by light to chlorophyll, and by oxygen to a sugary gum called diastase, which is carried into the circulation for the support of the new growths of plants. Starch is turned blue by iodine, an excellent test for detecting its presence in plants. The Arrowroot Plant ( Maranta arundinacea, L. ; natural order, Marantacea ?,) is a native of tropical America and the West Indies, In arrowroot, tapioca, and sago, starch exists in a state of almost absolute purity. The arrowroot plant has large, herbaceous, very handsomely-striped leaves, and tuberous roots, which abound in fecula or starch. These roots 'are bruised, thrown into a vessel ot water, and well stirred, when the fibrous portion comes to the surface, and is rejected, tho starch settling at the bottom of the vessel as soon as the fluid is permitted to rest. This, after repeated washings, is dried in the sun, and constitutes the arrowroot of commerce, so much employed as a nutritive diet for invalids and young children. Zamia integrijolia, Wild. ( Coontie ) ; natural order, Cycadece. — An arrowroot is now manufactured at Key West, in South Florida, . from the stem of this plant, which is short and globular, and abounds in starch. This cycad, which was called by the Indians coontie, grows abundantly over an immense area of otherwise barren land. These manufactures bid fair to become as extensive and profitable as those of Bermuda, from whence at present our chief supplies of arrowroot are received. Tous-le-mois, the starch of the rhizome of a species of canna (0. coccinea ?) ; natural order, Marantacece.— This starch re- sembles a fine quality of arrowroot ; but the granules are much larger than those, or of any known starch. Tous-les-mois comes from the island of St. Kitts, and is only used as food. Tapioca Plant ( Manihot utilissima, Plum. ; natural order, Euphorbiacece) . — -Tapioca is another form of starch, obtained by grating and washing the roots of this plant, which, under the name of manioc or cassava, forms a most important article of food in South America. This washing removes a narcotic poisonous principle which exists in the sap. The Indians dissi- pate it by heat, simply roasting the root. Tho starch thus washed, softened by heat, and afterwards granulated, consti- tutes tapioca. The ungranulated starch is the Brazilian arrow- root of commerce. The tapioca plant, in its native clime, is a shrub about five feet high, with roots which, when ripe, are about as largd as a Swedish turnip, containing large quantities of this nutritive starch, and weighing sometimes thirty pounds. The common starch of the shops, used in domestic economy, is obtained from wheat, rice, and potatoes, and is almost, if not entirely, home-manufactured. Sago Palms ( Saguerus Bumphii, Wild. ; and Sagus Icevis, Goertn.). — Sago is obtained from several species of palm. The sago of commerce is, however, chiefly produced by these two plants. It is obtained from the cellular tissue, or pith, in the interior of the trunk. The sago palm produces, like rice, a chief means of nourish- ment for millions in warm climates, since sago powder is gene- rally used for making bread. It grows in the south of China, Japan, and all over the East Indies, but principally in the islands of the Indian Archipelago. This palm generally grows in swampy ground, where it flourishes best, a good plantation, being often in a marsh, selected for that purpose. Its trunk is from five to six feet in circumference, rising to a height of about twenty feet. The pith, from which the sago is obtained, is of no use until the tree is fourteen or fifteen years old. A single tree is said to yield from five to six hundred pounds of sago. Most of the sago imported into the United Kingdom comes to us in its granulated form from the island of Singapore, where it is manufactured as follows : — The pith, which is soft, white, spongy, and mealy, is first removed from the interior of the stem, then bruised, and put into large tubs of cold water ; the woody particles of course float,, and are easily removed, and the weightier starch or sago powder settles at the bottom of the vessel. The water is then poured off, and the dried sago powder passed through small sieves made of the fibres of the palm leaves. In passing through these sieves, the sago powder acquires its granulated character. The preparation is then finished, and the sago is ready to be put into boxes, or placed in bags, for shipment. The exports from Singapore in the year 1847 exceeded 6,500,000 lb., but are now much larger. Sago is insoluble in cold water, but by boiling becomes soft, and at last forms a gelatinous solution. In England it is much used for puddings ; and as it is both nutritive and easy of digestion, it constitutes an excellent article of diet for the invalid and the convalescent. A great deal of German or potato sago, from the manufac- tories of Vienna, Nuremberg, Schweinfurt, Erfurt, Halle, etc., comes into the European market, and it is with difficulty dis- tinguishable from the real East Indian sago. III. PLANTS YIELDING SPICES AND CONDIMENTS. Cinnamon ( Cinnamomnm Zeylanicum, Nees. ; natural order, Lauracece). — This plant is an evergreen aromatic tree, ' bout VEGETABLE COMMERCIAL PRODUCTS. m thirty feet in height, and indigenous to the island of Ceylon. Its leaves are oval, smooth, entire, with three prominent curvi- linear ribs on the under surface. The young leaves are at first red, but change gradually to a yellowish-green, possessing the same flavour as the bark, but in a less degree ; flowers panicled, white, with a brownish centre, devoid of fragrance, and about the same size as those of the lilac. The inner bark of this tree constitutes the cinnamon of com- merce, and the young twigs furnish the best. After the trees are nine years of age, the twigs are cut annually in the month of May, by the cinnamon peelers, or Ckoliahs, as they are called in Ceylon. This is done with a sharp iron instrument. The bark is removed by making a longitudinal and then a transverse incision into the shoot, inserting under the bark the point of the peeling-knife, and raising the handle of the knife as a lever. The next day the inner fibrous bark, in which resides the delightful flavour of cinnamon, is easily removed from the outer bark, and this, as it dries, curls up and forms quills. Before these quills become quite dry, hard, and brittle, the smaller are inserted into the larger ; space in packing is thus saved, and compact sticks are formed, which are not so liable to breakage as the single quills. The wood from which the bark has been removed is sold for fuel. “ After hearing so much about the spicy gales from Ceylon,” says Bishop Heber, “ I was much disappointed at not being able to discover any scent, at least from the plants, in passing through the cinnamon gardens. There is a very fragrant- smelling flower growing under them, which at first led us into a belief that we smelt the cinnamon, but we were soon unde- ceived. On pulling off a leaf or a twig, one perceives the spicy odour very strongly ; but I was surprised to hear that the flower has little or none.” Since neither the leaves nor the flower of the cinnamon-tree give forth any smell, it is only when the season arrives for gathering bark that the visitor to the gardens will enjoy the perfume of this plant. A walk through the cinnamon gardens during the busy season is truly charming. The grove is then full of fragrance, and a scene of cheerful industry. Everywhere are to be seen groups of Cingalese peeling the twigs, which they do with astsnishing quickness, making a great deal of money whilst the season lasts. The Choliahs form a distinct caste, and are considered very low, socially, so that, according to Cingalese notions, it is personally degrading for any one else to follow the business. The largest of the cinnamon gardens in Ceylon is that near Colombo, which covers upwards of 17,000 acres of land. Cinnamon-trees are preserved with the greatest care by their proprietors. By tho old Dutch law the penalty for cutting or injuring them was amputation of the hand ; at present a fine is imposed upon the delinquent. In 1866 932,729 lb., and in 1867 859,034 lb. of cinnamon were imported into this country, a great part of which we re- exported to our colonies. Considering the extreme lightness of cinnamon bark, this i.s a largo quantity. Cinnamon is usually brought home in bags or bales of from eighty to ninety pounds’ weight. The best comes from Ceylon, but the cinnamon-tree grows plentifully in J ava, Sumatra, Malabar, and Cochin-China, and it has been recently transplanted to the Mauritius, the Brazils, and Guiana, and to the West India islands of Tobago, Guadaloupe, Martinique, and Jamaica. The cinnamon produced in the West is, however, not so good as the Oriental. Cinnamon is an aromatic tonic of an agreeable odour and taste, which acts as a grateful stimulant or carminative, creating warmth of stomach, removing nausea, expelling flatulency, and relieving . colic or intestinal pain. It owes these properties to the volatile oil which it contains. Cinnamon is much employed as a condiment in culinary preparations, and is also frequently used for flavouring and disguising unpleasant medicines, or as an adjuvant — that is to say, an assistant. Cinnamomum Cassia seems to be the chief source of the Cassia lignea, or bastard cinnamon of commerce. This plant differs from the true cinnamon-tree in many particulars. Its leaves are oblong-lanceolate, and have the taste of cinnamon, to which also its bark bears a great resemblance, but is thicker, rougher, denser, and not so agreeable in flavour. It is culti- vated in China, and is imported from Canton, vid Singapore, in chests similar to those in which the tea is packed. 349,349 lb. of Cassia lignea were imported in 1866. Nutmeg-tree (Myristica moschata, Thunberg). — This tree, from twenty to twenty- five feet in height, strongly resembles our pear-tree in its general appearance, and also in its fruit, which is not unlike the round Burgundy pear. The leaves are alter- nate, smooth, entire, oblong-pointed, short-petioled, and aromatic when bruised ; the flowers axillary, racemose, pale, bell-shaped, without a calyx. The fruit is a fleshy pericarp, opening by two valves when ripe, and displaying the beautiful scarlet reticu- lated arillus, or mace, enveloping the thin, dark-brown, glossy, oval shell, which covers the kernel, the nutmeg of the shops’ Each fruit contains a single seed, or nutmeg. The mace and the nutmeg are both valuable spices. The former, although a brilliant scarlet colour when fresh, becomes yellow, brown, and brittle when dry. Whilst the clove has spread over Asia, Africa, and the West Indies, the nutmeg-tree refuses to flourish, except in the islands of the Malayan Archipelago, where it appears to be indigenous. In 1819, 100,000 of these trees were transplanted by the British Government to Ceylon and Bengal, but the plantations were not successful. All attempts to introduce the nutmeg-tree into other tropical countries have failed. The Dutch endeavoured to extirpate the nutmeg from all the islands of the Moluccas except Banda, and they had all the trees removed thither for better inspection ; but this attempted monopoly was completely frustrated by the mace-feeding wood- pigeons. These birds ' conveyed and dropped the fruit beyond the assigned limits, spreading it over the whole of the islands of the Malayan Archipelago, from the Moluccas and New Guinea. About 251 tons of nutmegs, and 68 tons of mace, were imported into the United Kingdom in 1866, nearly half of ’which were re-exported. The nutmeg and clove trees were first introduced into this country by Sir Joseph Banks, as ornamental hot-house plants about 1797. Nutmegs and mace are employed chiefly as condiments for culinary purposes, for which they are admirably suited by their agreeable taste and stimulating properties. As remedial agents they owe their activity to the volatile oil ' which they contain, and when administered in moderate quantities, produce the usual effect of the other spices. The Clove-tree ( Caryophyllus aromaticus, Linn. ; natural order, Myrtaceas, the Myrtle family).— Cloves are the unex- pandod flower-buds of this tree, which is an evergreen, the trunk rising from fifteen to twenty feet above the ground. The leaves are opposite, rigid, ovate-lanceolate, smooth, entire, petioled. The flowers are produced in great profusion, in short terminal panicles of from nine to eighteen in each bunch. The four leaves or sepals of the calyx are united ; the base of the calyx is tapering and somewhat quadrangular. The corolla is red, and before expansion, forms a ball or sphere at the top of the calyx. The peduncles, or flower-stalks, are divided into threes, and articulated or jointed. This greatly facilitates the fall of the buds when the gatherers beat the trees with reeds or wands. They are also gathered by hand — a method adopted when the season has been unfavourable. The clove-tree is a native of the Moluccas, where it was very abundant before the conquest of these islands by the Dutch. They extirpated it from all the Moluccas except Amboyna, axd even there they allowed only a limited number of trees to be planted, lest the price should fall too low ! This narrow policy stimulated other nations to try to get so valuable a spice. In 1770 the French obtained the plant, and introduced it into the Isle of Bourbon, and from thence to Cayenne and to their other possessions in America. But the best cloves still come from the Moluccas. We receive cloves from the East and West Indies, from the Mauritius, and indirectly from Holland. The quantity imported in 1866 was 541 tons. Dr. Ruschenberger, who visited Zanzibar, on the eastern coast of Africa, in 1835, thus speaks of the clove plantations there : — “ As far as the eye could reach over a beautifully undulating land, nothing was. to be seen but clove-trees of different ages, varying in height from five to twenty feet. The form of the tree is conical ; the branches grow at nearly right angles with the trunk, and they begin to shoot a few inches from the ground. The plantation contains nearly 4,000 trees, and each tree yields, on an average, six pounds of cloves 60 THE TECHNICAL EDUCATOE. annually. They are carefully picked by hand, and then dried in the shade. We saw numbers of slaves standing on ladders gathering the spice, while others were at work clearing the ground of dead leaves. The whole is in the finest order, pre- senting a picture of industry and of admirable neatness and beauty.” Cloves, when good, are dark, heavy, and strongly fragrant, the ball on the top being unbroken, and yielding oil when pressed with the nail. This oil is sometimes extracted, and the cloves so treated are mixed with the others. They are also sometimes adulterated with water, which they absorb readily, becoming plumper and heavier. Cloves are much employed in cookery as a condiment, being the most stimulating of the spices. The oil of cloves is a popular remedy for the toothache, and the infusion a warm and grateful stomachic. Cloves are frequently employed by medical men to disguise the nauseous properties of their drugs, and thus render them more palatable to the patient. THE ELECTRIC TELEGRAPH.— I. By J. M. Wigner, B.A. THE BATTERIES EMPLOYED INSULATORS LINE WIRES. One of the features by which the present century has been rendered especially remarkable is the number and importance of its scientific inventions. Among these there is none more wonderful than the electric telegraph, and none which has more rapidly passed from being a mere scientific toy, valuable only for the elucidation of certain principles and facts, into becoming a, great and important instrument in the conduct of our every- day business. Scarcely half a century has elapsed since Pro- fessor Oersted made the discovery that a magnetised needle was deflected by the passage of an electric current along a wire placed near to it, and the mode of converting a bar of iron into a temporary magnet by 'means of the electric current was not discovered till several years subsequently, and yet, at the present time, the messages weekly transmitted, in this country alone, by instruments based on these principles are numbered by the hundred thousand ; and there is scarcely any part of the globe that is not traversed by wires, along which our thoughts are constantly being flashed with a speed almost equal to their own. In the articles on “Voltaic Electricity,” which have already appeared in The Popular Educator, a general account has been given of the principle on which the various forms of telegraph instruments act. In the present series we propose to give a practical explanation of the construction of the dif- ferent instruments and the manner of using them, so as to enable the intelligent amateur to construct such instruments for himself, and to help the telegraphist to understand the mechanism of the apparatus he is employing. To transmit messages by electricity, it is, of course, necessary in the first place to have some means of generating an electric current of sufficient quantity and intensity. We must further have some way of conveying this to the desired place, and also of causing it to produce at that place such effects as shall enable us to make our messages understood. For generating an electric current, any one ot the many forms of battery already described may be employed. The Cruick- shank battery, consisting of alternate plates of copper and zinc excited by a solution of dilute sulphuric acid, was for a long time that generally adopted. Very frequently the cells were filled in with fine sand, over which the solution was poured. This form was commonly known as the Sand battery. Smee's and other forms have also occasionally been tried, but m almost all cases these batteries have now been superseded, and some modification of Daniell’s sulphate of copper battery adopted. In the large cellars under the Central Telegraph Offices in Lothbury, there are thousands of cells of these bat- teries constantly at work. The standard form now adopted consists ot a trough about two or two and a-half feet long. This is made of hard wood, and carefully coated inside with a resinous composition so as to prevent the acid from eating it away. Water-tight compartments are then fixed at about equal distances, so as to divide the trough into ten cells, and each of these is subdivided by a plate of porous or unglazed earthen- ware, represented in Fig. 1 by the thinner lines. Plates of sheet copper are then cut about four or five inches square, and zinc is cast into thicker cakes of a similar size. A piece of copper and one of zinc are then connected together by a copper band riveted to each, as shown in Fig. 2. The band or strap is then bent in the middle, so that the copper plate may be in one cell and the zinc in the next. A lid is provided to each trough ; this serves to exclude the dust, and at the same time, by checking evaporation, renders the action of the battery much more uniform. The cells which contain the zincs are charged with dilute sulphuric acid, or with a solution of sulphate of zinc ; those in r^\ ^ /"A ^ _ /] i I Tj 11 1 i 1 i 1 Fig. 1. which the copper plates are placed contain a saturated solution of sulphate of copper (blue-stone), and, as the copper is pre- cipitated on the plate by the action of the battery, the cells are usually filled up with crystals, so as to maintain the strength of the solution. If it gets exhausted, a portion of the zinc solu- tion passes through the porous partition, and this metal is thrown down on the copper, rendering it almost black. For each equivalent (26 parts) of zinc dissolved in any cell, an equivalent (25) parts) of copper is precipitated in the corre- sponding cell, and hence the copper plate increases in thickness while the zinc is eaten away. When the acid becomes saturated with zinc the action of the battery is much diminished ; a portion of the solution should therefore be removed, and the cell filled up with water. Care must be taken not to let the zinc plate rest in contact with the diaphragm, as in that case metallic copper is deposited on it, and it is soon broken. After having been used the par- tition should also be kept moist, as, if allowed to dry, the sulphate of zinc effloresces round the edges and chips away small pieces. The porous diaphragm does not entirely prevent the two solutions mixing, though it checks it very considerably. Some of the copper passes into the zinc cell, and, being there decom- posed by the action of the zinc, falls to the bottom as a dark powder usually known as the “mud” of Darnell's battery. When an inner porous cell is used instead of a partition, it is usually greased all over, except on the portion opposite to the copper plate, so as to check as far as possible this mixture. In some instances the porous diaphragm is entirely dispensed with, and the two solutions are kept separate by their respective weights alone. The copper solution, having the greater density, is first poured into the cell so as to half fill it ; the acid is then carefully put in above it. In this form of battery the copper plate is placed at the lower part of the cell, and the zinc plate at the upper portion, so that the two do not overlap. The copper solution, however, in time mixes with the acid, and this battery is not very much employed. Bio- 2 In working batteries it is found that the same amount of zinc is consumed in each cell ; it is advisable, therefore, only to employ plates of similar size in the same circuit. A single weak or defective cell will retard the passage of the entire current, and thus cause a very considerable waste of power. It should be remembered that the quantify of electricity generated is not augmented by increasing the number of the cells ; it is only the intensity that is thus affected. To increase the quantity we must increase the size of our cells, or, which practically amounts to the same thing, arrange two or three side by side, their zinc and copper plates being respectively connected. As a general rule, for distances of a few miles, a single trough containing ten or twelve cells is amply sufficient, provided it be working well. If it is losing its power, or the message has to be sent to a much greater distance, two or more of the troughs may be joined together. Having now seen the manner in which the electric current is generated, we have next to ascertain the mode in which it can be conveyed to any required place. As we have already COLOUR. 61 learnt, the fluid very easily escapes, unless the conductor along which it is travelling is carefully insulated. When the wires are laid under the surface of the ground or at the bottom of the sea, this is accomplished by coating them with some insulating material in a way that will shortly be explained. In most cases, however, the lines are suspended in the air, which is, for all practical purposes, a non-conductor. All need for coating the wire is then at an end, and it is only necessary to make some arrangements which shall prevent the escape of the electricity at the points of support. This is accomplished by means of “insulators,” a few of the forms of which were figured in the papers on “Voltaic Electricity.” In large towns the insulators are very frequently attached to the corners of lofty buildings, or to stacks of chimneys, and in this way much expense is avoided, and the wires are at the same time so much elevated that they do not interfere with the ordinary traffic of the streets. In tho open country, however, they are supported on posts specially erected for the purpose, which under ordinary circumstances are placed at distances of about sixty yards apart, and the wires are about eighteen or twenty feet above the surface of the ground. Young fir or larch trees are usually chosen for the purpose, and roughly trimmed. Sometimes the wood is impregnated with a preser- vative compound to guard against decay. When this is not d*ne, the pole is charred along the lower end for a length of several feet. The charred ends are sometimes allowed to stand in gas-tar for several hour3 as a further protection ; but still, with every precaution, it is found that the post will decay at the ground-line, where it is exposed to the air as well as to the moisture of the earth. In different parts of the Continent and in India, where wooden posts are far less durable, substitutes have been tried, and iron tubes and posts of different forms have been used to a considerable extent. The first cost of these is, of course, con- siderably greater, but in the long run a great saving is effected by their employment, and it seems probable that in England they may eventually become much more generally adopted. When the line is straight the strain is but small, but at an angle it is considerably increased, and struts or stays are usually employed to strengthen the posts. In some places the plan has been tried of affixing the insu- lators to the stems of living trees, and this has been found to answer very well. The swaying of trees during storms is a slight objection, but a swinging insulator designed by a Prus- sian officer, Lieut. -Colonel Chauvin, meets this difficulty. Tho construction of this will easily be understood by reference to Fig. 3. The bent iron rod, A b, is cut at one end into a screw, and fixed firmly into the tree, while the other end is flattened out, and fastened by means of a screw. The insu- lator, C, is sus- pended from the ring d by the hook f, the end of which is turned back so as to prevent the wire jerking out when the tree is shaken. In the lower part of the insulator is fixed another hook through which the line wire passes. This is, of course, quite insulated from f, and is so bent that when the insulator swings to and fro with the wind, only the porcelain comes in contact with the tree or the support. Almost every telegraph engineer has his preference for some special form of insulator, and hence there is a great variety. That most generally employed in this country is represented in Fig. 4. It consists of two inverted cups of brown earthenware, fitting inside one another. To tho inner one is fixed the steel stalk by means of which the insulator is firmly bolted to tho post, while round the outer is a groove to which the line wire is fastened. The two are fixed together by means of a non- conducting cement. On about one post in every ten a stretch- ing-insulator is placed. The wire is found to give a little by the continued strain, and also to vary in tension with changes in the temperature. The result of this, if unchecked, would be to cause the wires to hang so loosely that when, as is generally the case, there were several on one post, they would strike against one another, and thus greatly in- terfere with the communica- tion. These insulators are accordingly provided, and by means of them the wires are kept duly strained. Frequently, especially in lines supported on buildings, the wire is fixed to every insulator, instead of merely resting in a loop, and then there is less need of stretch- ing-insulators. The impor- tance of careful insulation is very great, especially in long lines, as a very trifling loss at each point of support will soon seriously weaken the current, and render much more battery power necessary to transmit the message. Copper wire is the best conductor by far, and might there- fore be used of much smaller size than the iron wire usually employed. This would probably cause a considerable ultimate saving, as the posts and insulators need not be so strong ; but tho value of the wire would render it so strong a temptation, that the lines would not unfrequently be cut. From this and other causes iron wire is always employed. For general purposes that known as No. 8 gauge is used, its diameter being 0T70 inch, and its breaking weight about 16 cwt. Unless, however, the wire be protected in some way it soon rusts, and becomes corroded by the influence of the air and moisture. Sometimes it is coated with tar or boiled linseed oil. More frequently, however, in this country, tho wire is “ galvanised,” or coated with metallic zinc, and this serves as a very good protection, except in the neighbourhood of manufacturing towns, where the smoke from the various factories soon corrodes away the zinc. In some cases, instead of a single wire, a strand com- posed of seven wires of No. 20 gauge is used, and this is by many considered preferable. COLOUR.— 1. By Professor Church, lioyal Agricultural College, Cirencester. INTRODU CTION CONNECTION OF THE SCIENCE OF OPTICS WITH COLOUR. Owing to the dependence of colour upon light we must begin our study of its laws and their applications by a statement of two or three of the chief facts of Optics. We wish now to direct our readers’ attention to the reflection, the emission, the transmission, the absorption, the refraction, and the dispersion of light. Everything that we can see is visible owing to its reflection of light, or to its emission of it : the former action produces or characterises illuminated bodies ; the latter, luminous 1 * lies- Uluminated bodies are marked out and distinguished from one another by the different amounts and qualities of the light which they reflect. A piece of black cloth on a white porcelain plate reflects but a very small part of the light which falls upon it ; the plate, on the other hand, reflects much. Had the black cloth possessed no power of reflecting light, it would have been invisible ; black velvet, which reflects less light, sometimes produces to the eye the effect of absolute blackness, that is, of an empty and dark space. Similarly, a sheet of plate glass may appear lustrous and visible enough if the light which falls on it is sent back to the eye ; but if we are so placed in front of the glass that these rays escape us, it ceases to be visible, and we may, perchance, stretch out our hand to take something from behind the glass, wholly unconscious of its existence. But it is possible to render a piece of polished glass Fig. 4. 62 THE TECHNICAL EDUCATOR. permanently visible. Crush it to powder, and then in what- ever direction the light falls upon its particles the surfaces of those particles will turn back or reflect some of the rays, and so render themselves visible. The clear glass has become opaque. For the very same reason dense clouds, which appear black when between the observer’s eye and the sky, owing to the complete way in which they cut off the light, may become brilliantly white when the sun’s rays fall upon their constituent particles, owing to the very same action ; for the light, which cannot get through the cloud, is continually reflected to and fro from the surfaces of its minute parts, and thus illuminates it. Thus it happens that the lower half of a cloud against a dark mountain may appear white, while the upper part of the same cloud against a luminous sky may appear a dull grey. The lessening of reflection, on the other hand, diminishes visibility. The numerous small reflections which occur between the surfaces of the fibres in a piece of paper may be greatly reduced by wetting or oiling the paper, when it becomes less opaque and ■at the same time greyer and clearer : to this cause the trans- parency of tracing paper and tracing cloth is due. We said above that bodies differ not only in the amount but in the quality of the light which they reflect. Now one of the chief differences as to quality of light is the difference of colour. Powdered vermilion reflects much light to the eye ; this light, however, is chiefly red light, though there is some white light mixed with it. A stick of red sealing-wax shows in some posi- tions a bar of white reflected light in the direction of its length, _ while in other positions we see only the red light reflected from the particles at its surface and a small depth below. Why this light happens to be red in the vermilion we shall discuss further on : we would only point out here that while the reflection from a polished surface is regular, that from a rough surface is irre- gular, and that from a coloured surface coloured. A polished plane metallic surface affords an example of the first kind of reflection, a piece of chalk of the second. So great is the differ- ence in effect produced by regular reflection from that produced by irregular reflection, that if an illuminated polished body could be found which was wholly incapable of irregularly re- flecting any part of the light falling upon it, that b©dy would be invisible. We may, therefore, say that we discern bodies by “the aid of the light which they reflect irregularly, or scatter ; a perfectly regular reflection gives, on the contrary, an image of the source of light, not of the object illuminated. It is only light which is regularly reflected which can be shown to obey the great law cf reflection, which is this : — The angle which an incident ray of light makes with a perpendicular to the reflect- ing surface, is equal to the angle which the reflected ray makes with that perpendicular ; in other words, the angle of incidence and the angle of reflection are equal. Another law here to be mentioned is, that both the incident and the reflected rays of light are in the same plane, which is perpendicular to the reflect- ing surface. We shall have to refer to these laws of reflection, to reflection at varying angles and from different substances, and to the different kinds of reflection enumerated above, when we proceed to discuss the subject of Colour. A few words may now be said on luminous bodies, or those which emit light. A candle flame, a glowing piece of charcoal, and the sun, are examples of luminous bodies. From those sources of light luminous rays are sent out ; these rays are the lines in which the light is propagated ; luminous pencils are bundles of such rays. From such luminous bodies as are near the eye the rays emitted are divergent, but the rays from the sun and distant bright bodies are practically parallel. Highly luminous bodies can only be clearly seen when much of the light which they emit is cut off by a special contrivance, such as a piece of smoked or dark-green glass. It is thus quite possible to see the form and changes of the coke-points of the electric lamp, intense as its light is. The light emitted from bodies travels in straight lines, and causes the production of shadows. The form and sharpness of shadows is influenced not only by the shape and the relative size of the opaque body which casts the shadow, but by the form of the luminous body, the light of which is intercepted. A luminous point gives a sharply-defined shadow, while a luminous surface, on the other hand, gives a dark shadow sur- rounded by a paler and less definite one which goes by the namo of a penumbra. We have so far spoken of the reflection and of the emission of light: the transmission of light has now to be considered. Bodies are said to be transparent when they permit light freely to pass, so as to allow objects to be distinguished through them ; translucent , when they allow light to pass less perfectly, and objects on the other side of them cannot be clearly discerned ; opaque, when light is wholly cut off. But in reality no bodies are perfectly transparent or perfectly opaque. The most colour- less and flawless polished glass cuts off some rays, while sub- stances, such as metals, which are commonly considered quite opaque, become transparent when reduced to the form of thin leaves. The sun may be conveniently viewed through a glass thinly coated with silver, while the light transmitted by an ordinary piece of gold-leaf is grass-green. In addition to this, it may be remarked that different trans- parent bodies permit the light to pass through them with more or less facility, but they also variously affect the light which finds its way into them. Suppose the case of water. A beam of light made up, we will suppose, of 1,000 rays, strikes the water perpendicularly ; 18 rays will then be reflected towards the lumi- nous source, while 982 will find their way through the water un- changed, unless the layer of water be of considerable thickness. Now introduce into the water a drop of some red solution ; the light transmitted will be filtered light, the red solution having strained off some of the constituent rays and left the others. The intensity of the light and its quality will thus have been altered by transmission, just as they are by reflection. Colour, in fact, may be produced from white light, either by the absorp- tion of some parts of the luminous rays and the reflection of others, or by the absorption of some parts and the transmission of others ; but, as we shall point out presently, there are several other ways of producing colour without the intervention of an absorbent body. Before, however, we can profitably study these ways, and the curious phenomenon of absorption itself, wo must become acquainted with the main features of the theory of light. This theory is called the undulatory theory. The undulatory theory supposes the existence, throughout all space and throughout all matter, of an infinitely thin, elastic medium called the luminiferous or fight-bearing ether. It must be supposed that this ether is not only universally present, but present without break in its continuity. It exists in space, in all solids, liquids, and gases, and it cannot be excluded from what we call a vacuum. It can hardly be material in the sense in which the sixty- three elements of the chemist are material ; but to account for the properties of fight, we must presume the medium which conveys it to have some at least of the properties of matter. The movement of this ether is fight. It undulates in waves, the undulations of the particles of the ether being across the direction in which the fight is propagated. Light is supposed to originate in the following manner : — The particles or mole- cules which constitute a luminous body are in a state of dis- turbance, a state of intensely rapid motion. This motion of the molecules is communicated to the ether and sets it in vibration, and is propagated in all directions in tho form of spherical waves. Beaching the retina, this fine motion of the ether excites vision and becomes sensible as fight. With these statements of the main assumptions of the wave-theory of fight before us, we shall be able to consider with exactness not only the absorption and refraction of fight, but the several modes of the production of colour. The waves of the ether are of different lengths ; in pure white fight, such as that emitted by the electric arc, waves of all lengths occur between the limits of about 33*33 of an inch on the one hand, and about 33300 an in (; h on the other hand. Now the colour of fight is solely dependent upon the length of the wave. The longest wave that is perceived by the retina is the red wave, the shortest the violet. Longer waves than the red waves possess a high heating power ; shorter waves than the violet, invisible to the eye, and with scarcely any action on the thermometer, are gifted with a great degree of chemical energy : they are called actinic. If we use the electric fight, which is really a more perfect fight than that of the sun, we shall find that it emits or causes undulations, the waves of which are of much wider differences as to length than those of the red and violet fights above mentioned. By means of various solutions wo can absorb some of the rays : those of fight can, for instance, be strained off, and those of heat and actinism trans- PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING. 63 mitted. Tlie waves of certain lengths cannot undulate in a solu- tion of iodine in carbon disulphide, they are arrested or quenched thereby. Such a solution, indeed, permits only the rays of dark heat to pass through it ; but the undulations of this dark heat may be changed, and their wave-lengths may be diminished by allowing the invisible heat-rays to be concentrated in a focus and to fall upon a solid, infusible body. This solid will become hot and then luminous — heat has been changed into light. This passage of calorific into luminous rays is known as calorescence, and may be made so complete a change that all the colours of the rainbow may be thus obtained from a perfectly dark source of heat. But exactly the same sort of change may be effected with the invisible actinic rays, the wave-lengths of which are shorter even than those of light. By using a solution of blue vitriol in ammonia, dark rays of chemical energy may be trans- mitted and freed from the visible rays. Receive these dark rays upon a screen of fluor spar, or Canary glass, or solution of quinine sulphate, light and colour are produced. The wave- lengths of the actinic undulations have been increased ; the invisible chemical rays have passed into visible luminous rays ; this passage is called fluorescence. Another name for the change in wave-length which we have just described is change in ref rangibility . Wo will now proceed to describe the meaning of the expres- sions refraction and rcfrangibility . When a beam of light falls perpendicularly upon water, more than 98 per cent, of the rays pursue a straight course through the water. Let the incidence of the beam be oblique, and then it will be found that fewer rays will penetrate the surface, and that those which do will not pass through the water in a straight line, but will be more or less bent out of that line : this bonding is called refraction. Refraction takes place when a beam of light passes obliquely from a rarer to a denser medium, or vice versd. Instances of refraction have been already alluded to and described in The Popular Educator (see “ Recreative Science,” Yol. Y., p. 223) in the case of a stick half immersed in water, which appears broken owing to refraction ; and of a coin, which, lying invisible at the bottom of a basin, may be made to appear by pouring water upon it, and so bending back the rays, which are reflected'by the coin, till they reach the eye. In passing from air into water or glass the refracted ray is bent towards the perpendicular ; in passing out of water or glass into air the reverse refraction occurs, and to a precisely equivalent extent. If, therefore, a beam of light enters obliquely a piece of glass, the faces of which aro parallel, the refraction towards the perpendicular on entering the glass will be exactly compensated by the refraction from the perpendicular on leaving the lower surface, and so the emergent ray will necessarily be parallel with the incident ray. But supposing wo omploy a prism of glass instead of a flat plate, then the ray is permanently refracted. The prism so much employed in Optics is a wedge-shaped piece of flint glass, and is an indispensable instrument in the study of colour. The angle enclosed by two oblique sides of this prism is called the refracting angle. If we place the prism so that this angle shall be below, and the opposite side of the prism horizontal, then a beam of light falling from above on to one of the oblique sides will be refracted towards the refracting angle, and passing across to the other oblique side will pass out, with its path changed again, but now in an upward direction. But something more will have commonly happened to the beam besides its permanent refraction. If the light be simple, if its wave-lengths be of one measure only, it will be simply deflected ; but if, as is nearly always the case, the light be compound — if its waves are of different lengths — than tho prism will differently affect them. It will retard the short waves more than the long ones, and so we shall find that these short waves are more refracted: The more refrangible rays are then the short violet rays, the less refrangible rays are the longer red rays. In every case, there- fore, where a luminous body emits rays of various refrangibili- ties, these rays can be separated from each other by means of the prism. As solar light consists of an enormous number of says of different refrangibilities, it may bo decomposed, analysed, Dr split into an enormous number of coloured lights, the wave- length of each of which belongs to a particular ray. The electric light gives an infinite number of such coloured lights, for there are no breaks in its series of rays, such as exist in the light of the sun. Burning metals and glowing gases emit, on the other hand, fewer rays, and give fewer colours, when their light is prismatically decomposed. The decomposition, or splitting up of light by the prism, is called the dispersion of light ; the coloured image formed is called a spectrum. We are enabled to study the origin, the properties, and the changes of colours by means of this spectrum. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— I. It is intended in the present course of lessons to show the practical application of Geometry to trade and manufactures, in order to give to students engaged in the several constructive arts, and the various branches of industry involving skilled labour, a thorough and practical knowledge of the methods of describing the various figures required, by the most ready and correct processes. It is impossible to over-estimate the importance of a know- ledge of Geometry, forming as it does the basis of all mechanical and decorative arts, constituting, in fact, the grand highway from which the various branches of Drawing diverge. Nor must the study of Practical Geometry be estimated by its mechanical value only, for its uses extend far beyond the neces- sities of trade and manufactures. It gives to the eye that ab- solute correctness of perception, that clear idea of form and size, which, as branches of education, render it most important to all ; and, further, it will be found that it gives to the mind that habit of accurate arrangement, that order in mental pro- cesses, which must act beneficially on all persons, whatever may be their position. In the present course, it is not proposed to give more of the definitions or elementary figures than may be absolutely neces- sary, the object being to apply knowledge to practice. Still the lessons will, as far as possible, be made self-explanatory, and the methods of drawing figures will be thoroughly ex- plained. The subject, then, is not to be treated as a mathematical, but as a thoroughly practical one, and therefore no absolute system of reasoning is attempted. Still, it has been thought right to give some simple and familiar explanations of the properties of the various figures, and the principles upon which their con- structions are based, as it must be obvious that the more the mind comprehends of the • relation cf one line and form to another, the more will the eye appreciate beauty and refine- ment, and the more accurately and intelligently will the hand execute. In erder to guide students in using these lessons for self- instruction, the processes in each figure are lettered in the order of the alphabet ; the consecutive steps by which the result is attained will thus become evident. This plan is assisted by the imaginary or constructive portions being, drawn in dots, or fine lines, the given figures in medium, and the resultant forms in full black lines. The lessons are intended, therefore, as stepping-stones to Technical Drawing in all its branches, and it is hoped that by their means the artisan may be enabled to construct the forms required in his trade by rapid and certain means, instead of blindly following the traditional methods existing amongst the men in “the shop;” and it is hoped that when ho has thus become acquainted with the “ grammar of form,” he may be able himself to originate and invent, and so be able to keep pace with the progress made, not only in foreign countries but in our own. We commence, then, with certain figures constantly used in mechanical drawing, repeating such of tho early studies as may be required in any particular figure, thus avoiding reference to back numbers as much as possible. The student is, however, supposed to have mastered such problems as bisecting lines, etc., and if he has not done so he will find them thoroughly explained in the “ Lessons in Geometry ” in The Popular Educator. One of the most frequently occurring processes is that of dividing lines into a certain number of equal parts. The want of knowledge of rapid methods causes waste of time, and by constant trials the paper becomes frayed and roughened, to the great detriment of the drawing. The following figure and its application is therefore given : — 64 THE TECHNICAL EDUCATOK. To divide the line A B into any number of equal parts (in this case ten). (Pig. 1.) Draw a line (c d) parallel to A b. (The line c d may be any length, that is, it may be drawn indefinitely for the present.). Prom e set off along this line the number of parts into which the line A b is to be divided— viz., 1 to 10. These parts may be any convenient size, but must be all equal. Draw c A and 10 b, and produce* both lines until they meet in E. From each of the points 1, 2, 3, etc., draw lines to the point E, which passing through A B will divide it into 1 0 equal parts . Application No. 1 of the foregoing figure (Fig. 2). This problem may also be used for dividing a line propor- tionally to another, that is, to find divisions on a line, which shall be in the same proportion to it, that certain divisions are to another line either larger or smaller. Thus, let it be required to cut off from A ““ ”B a part which shall have the same proportion to it that the division E D has to the line c v. C " E " ^ Place A b parallel to c r>, as in Pig. 2. Join C A and D B, and produce the lines until they meet in F. Prom E draw E F, which passing through A b will cut off G B, which will have the same proportion to A B that E D has to C D. This process is con- stantly used in find- ing the proportions of architectural mouldings, windows, mechanical details, etc., in making re- duced or enlarged drawings. This problem is also most useful in finding a particular point in a line which may be so small as to render accurate division very difficult. Example : The length from a to B in a spurf wheel (Fig. 3), * To “produce” a line mean3 to carry it on further, or to make it longer in the same direction. + A spur wheel is one in which the teeth are of iron, cast or cut in the rim ; a cog wheel has wooden teeth mortised into the iron rim, this is used principally in mill-work. Now although in many drawings the space and tooth are made equal, they are not so in a real spur wheel, the space being a very little larger than the tooth. This small difference is most important, for if the tooth and space were equal, the tooth of a wheel when in gear with another would not clear itself. The difference of one-eleventh is found in practice to be sufficient for all purposes. Thus, if the “pitch” is divided into eleven equal parts, the tooth will be five-elevenths, and the space six- elevenths. But dividing the space A b (which in many cases is much smaller than as given above) will be found liable to some inac- curacy : by this problem, however, the required point of division may be found with ease and exactness. Let A b (Fig. 4) be the length of the pitch, measured from A B in Fig. 3. Draw any line, C D, parallel to A b, and set off on it 11 equal divisions (any length). Draw C B and D A, and produce the lines to meet in e. From point 5 draw a line to E, which will divide A B as re- quired, the one part being ^ and the other Set off these lengths on the pitch circle.* To construct an equilateral triangle on the given line A b (Fig. 5). From A, with radius A B, describe an arc. From B, with the same radius, describe a corresponding arc, cutting the former one in c. Lines joining A C and B c will complete the triangle, which will be equilateral, that is, all its sides will be equal. A triangle having only two of its sides equal, is called an Tig. 5. isosceles triangle (a). When all three sides are of unequal length, the figure is called a scalene triangle, as b. In a right-angled triangle, one of the angles, as C, is a right angle. A right-angled triangle may be either isosceles, as D, or scalene, as e. The longest side of a right-angled triangle, viz., the side opposite to the right angle, viz., f, is called the hypothenuse. When a line, C D (Fig. 6), stands perpendicularly on another line, A B, it divides the space into two right angles ; if produced beyond c, four right angles will be formed but if the line c e be drawn, dividing the space unequally, the angle a e e is an obtuse (or wide) angle, being more than a right angle, and the remaining portion, b c e, is an acute tor sharp) angle, being less than a right angle. To construct a triangle of given dimensions (Fig. 7). Let it be required that the sides of the triangle should be 1 \ ,r , 1", and 1’-''. (The sign" attached to a number denotes inches.) Make A B 1.) in. long. From b, with a radius of 1J in., describe an arc. From A, with a radius of 1 in., describe an arc cutting the former one in C. Draw A C and B C, which will complete the triangle of the required dimensions. * For full instruction concerning the modes of drawing the various forms of teeth of wheels, the student is referred to the lessons or. I Technical Drawing. WEAPONS OF WAR. 65 WEAPONS OF WAR— II. BY AN OFFICER OF THE ROYAL ARTILLERY. FIRE-ARMS. The. division of our subject which we have now to consider is I the important one of fire-arms. We have seen how the intro- duction of fire-arms has had the effect of pushing side-arms into the background, how each successive development of fire- arms has by so much reduced the practical value of swords, and spears, and lances, and the like. We have noted also that the tide of improve- ment has always set in the direction of increased range, increased accuracy, in- creased destructiveness, increased rapidity of fire. These are the elements of the problem which the gun-maker has for several centuries been striving to solve, checked, however, and circumscribed in his action by the practical considerations which military necessities impose. Thus the exquisitely accurate match-shootinrg rifles which we see at Wimbledon, with all their refinements for ensuring good shoot- ing the carefully weighed charges, each in separate bottles, the delicate sights, the light triggers, have never come in for mili- tary use, because they fail in the first ele- ment of a military arm — simplicity. Again, the far-reaching Metford rifle, with which good practice has been made at 2,000 yards, is not a possible military weapon because of its refinements, and because also of its weight, and of the heavy charge which it requires. Many of the ingenious breech- loaders, in the production of which un- happy inventors have spent their time, their brains, and their money, fail alto- gether — despite their points of excel- lence and their rapidity — to satisfy the simpler wants of the soldier. But although let and hindered by these con- siderations — although continually being turned back from the dazzling path of ideal excellence, and warned out of the dangerous byeways of theoretical refine- ments — although continually being re- minded of the necessity of keeping to the somewhat tame and dusty high-road on which the soldiers are soberly tramping a road which to some probably appears as straight and dull as those famous mili- tary roads of the Romans — despite these restrictions, the gunmaker has succeeded in making very considerable advance in the direction required. For many years the arm of the British soldier was a smooth-bore musket, fami- liarly known as “Brown Bess.” This arm had a barrel of about three-quarter inch diameter (‘753 in.), and threw a spherical leaden ball, which weighed 483 grains, with a charge of four and a-half drams of powder. It will easily be understood that such an arm was neither accurate nor far-reaching. The charge of powder was large enough, it is true, to project the bullet with a high velocity, but the size of the bullet caused it to meet with great resistance from the air, and thus soon to lose its velocity, besides being liable to be easily deflected. More- °^ e ^’ fir e( l from a smooth-bore barrel, it was subject to all the disturbing causes common to smooth-bore projectiles. Among these causes may be prominently named : — (1) windage which is the difference between the diameter of the bullet and that of the bore, and which, by allowing the passage of the gas over the bullet, causes it to proceed through the bore with a sort of bounding motion, and to leave it in an accidental direc- tion, according to the position of the last impact against the bore ; (2) irregularity of form and surface of the projectile ; and (3) eccentricity of projectile. The result of these accumulated • 55 ' — > Bullet used in 5 — Vol. I. defects was that Brown Bess, although it would range effec- tively up to about 200 yards, could hardly be depended upon for even approximate accuracy up to half that distance. There used to be a saying among soldiers that if you fired at the church, you might think yourself lucky if you hit the parish ! The smooth-bore musket is not to this day entirely obsolete in our army. For example, the native infantry regiments in India are armed with a smooth-bore musket, which is in some respects superior to “ Brown Bess,” and has a smaller bore ('656 inch). The native Indian police have also smooth- bore carbines ; and some of our coast-guard are still armed .with smooth-bore pistols. Indeed, in some distant colonies we believe that even “ Brown Bess ” herself may still be found. After Messrs. Minie and Delvigne had shown how, by the adoption of a conical expanding bullet, an effective military rifle might be made, several of the old smooth- bore muskets were rifled with three grooves, and re-issued as rifled muskets — chiefly for naval use. By this means the weight of the bullet was increased to 825 grains, and the range, accuracy, and effectivepower of the arm were immenselyimproved. Com- pared with Brown Bess plain, Brown Bess rifled was an excellent weapon ; although in these days of small bores we should smile at a bullet three-quarters of an inch in diameter. The first rifled arm possessed by the British soldier was the Brunswick rifle. This arm had two grooves, and fired a belted ball, which was covered with a patch, the grease upon which, according to Mr. Kaye, determined the outbreak of the Indian mutiny. The bullet weighed 555 grains. The loading was tedious and inconvenient, owing to the belt on the ball having to be carefully adjusted in the groove, and to the great amount of fric- tion ; and the weapon, although vastly superior in range and accuracy to the smooth-bore, was comparatively inefficient as a rifled arm. Our rifle regiments and sharp-shooters were armed with it. The Sikh regiments in India are, if we mis- take not, still armed with the Brunswick rifle. But the really important improvement in military fire-arms was due to the labours of Messrs. Minie' and Delvigne. We by no means wish to underrate the exertions of other workers in the same field; and prominent among those who laboured to bring into notice the principle upon which the success of Messrs. Minie and Delvigne depended, was Captain Norton, who unquestionably invented and exhibited at Woolwich, as far back as 1823, an elongated expanding shot and shell, identical in principle with the Minie bullet. But it was not until 1851 that the Minie rifle was introduced. The arm was rifled with four grooves, and was intended to fire a conical leaden ball with a hollow in the base, into which was fitted an iron cup. The object of thi 3 arrangement was to enable the bullet to be readily loaded, the diameter being less than that of the bore, while by the action of discharge the iron cup would be driven forward into the conical hollow, expanding the bullet. A French colonel named Thouvenin had tried to accomplish the same object in a different way. He placed a small iron pillar or tige at the bottom of the bore, and on to this the bullet was rammed until it was expanded. . The carabine A tige was used by the Chasseurs d’Afrique in 1846 in Algeria, but it was obviously open to some strong objections, such as the liability of the tige to become bent or broken, the delay in loading, the want of uni- formity in expansion, and the disfigurement of the bullet. Tho Enfield Rifle. 36 THE TECHNICAL EDUCATOB. Delvigne -Minie system was a great improvement on this. The loading was effected almost as easily and rapidly as in a smooth- bore ; and the expansion of the bullet depended not upon the exact amount of force or hammering given to it by the soldier, but upon the pressure exerted upon the iron cup by the powder gases at the moment of discharge. The arm .as at first intro- duced was, however, open to some practical objections. In the first place, the iron cup was found liable in some instances to be blown through the bullet, which was left a distorted cylinder of lead inside the barrel, the weapon being thus rendered for the time unserviceable. In the next place, the calibre was too large for accurate long-range shooting — viz., '702 inch. The weight of the bullet was also objectionably great from a military point of view, being 670 grains. With so heavy a bullet the soldier, if provided with a sufficient supply of ammu- nition, was inconveniently over-burdened. So, in 1853, a modified Minie rifle was introduced, with a bore of only ’577 inch, and three grooves, which fired a bullet of 530 grains with 70 grains of powder. The iron cup was replaced by a box- wood plug. The reduction in the weight of the arm with sixty rounds of ammunition was three pounds. This was the famous Enfield rifle — the weapon which won Alma and Inkermann, and which at this moment, whether in its muzzle-loading or con- verted breech-loading condition, is the arm of the greater part of our regular army and reserve forces. But, since the intro- duction of the Enfield rifle in 1853, several improvements have been made in the ammunition, which have greatly increased the efficiency of the weapon. The two most important of these improvements were, the substitution of bees’-wax for a mixture of bees’-wax and tallow, for the lubricating material ; and the reduction in the diameter of the bullet. Both these changes were suggested by Colonel (now Major-General) Boxer, and contributed in an important degree to the efficiency of the ammunition and the arm. The adoption of bees’-wax was recom- mended on the ground that in hot climates the tallow melted, leaving the rifle unlubricated, besides which the acid in the tallow caused the corrosion of the bullets. The wisdom of adopting pure bees’-wax was stoutly disputed at the time, and has been frequently disputed since. But repeated experiments and inquiries have fully established the efficiency of bees’ -wax, and in the advertisement which was issued to the competing gun-makers in 1866, it was laid down that “ wax on the bullets is indispensable ; ” and the evidence which the late committee on small-arms took upon this subject led them to lay down posi- tively that “the lubrication should be pure bees’-wax, as. best adapted to withstand variations of climate and long keeping. This is a practical point upon which it seems important , to insist. Inventors of ammunition are very fond of submitting fancy lubrications of their own, and it is well, therefore, that it should be distinctly understood that the question of lubrication for military small-arm ammunition has been most fully and patiently considered, and decided definitively in favour of pure bees’-wax. In the Royal Laboratory at Woolwich, the greatest care is taken to ensure the perfect purity of the bees’-wax, which is all subjected to a careful chemical examination. . The second important change which was made in the ammu- nition was in the reduction of the diameter of the bullet. It vas found in India, during the mutiny, that great difficulties occurred in loading, owing to the size of the bullet, which was at first fixed at “568 inch, leaving a windage of only '009 inch — quite insufficient, when the rifle became foul, to admit of easy loading. Many instances occurred in which loading was almost impossible. The men were seen striking the ends of their ram- rods against walls and trees, to drive home the bullet, and the evil was so serious as to have threatened at one time to lead to the abandonment of the Enfield rifle. But some experiments, which were carried out by Colonel Boxer, showed that it was pos- sible to reduce the diameter of the bullet considerably without affecting the accuracy of shooting. He found that a reduction of diameter from 0“568 inch to “55 inch (giving a windage of ‘022 inch) might be safely made, and the loading difficulty was thus completely overcome. Other minor changes have been made, as, for example, the addition of a cut through the paper sur- rounding the bullet, in order to cause the paper to disengage itself from the bullet in flight ; the adoption of an improved powder, more uniform in its action, and better adapted to secure the just expansion of the bullet ; the substitution of a baked clay plug for one of box- wood, which, as before stated, has super- seded the iron cup of the original Minie. The iron cup was given up because it was liable to be blown through the bullet ; the box-wood plug was given up on account of the cost of box-wood ; and the clay plug was adopted as being inexpensive and efficient. The part which the plug plays in the action of the bullet must be noticed. It is generally spoken of as the expanding agent. This is true to a certain extent ; but the expansion can also be secured without any plug. In the Pritchett bullet, for. example, which for some short time was used with the Enfield rifle, there is only a shallow hollow, and the expansion is due partly to the action of the gas within this hollow, and partly to the ‘ upset- ting” of the bullet, which is due to its inertia. Other bullets— the Whitworth, for example— depend entirely upon the “upset- ting ” or “ over-taking ” action. But the plug serves a further and important purpose. It is a supporting as well as an ex- panding agent. The Pritchett bullet was found to foul, from the simple reasons that the expansion was not so piomptly effected as in a plugged bullet, and thus a rush of gas over the bullet became possible, and that when the barrel had become foul, the expanded sides of the bullet, having no internal support, collapsed on coming into contact with the fouling deposit. The plug," therefore, serves a threefold purpose : — 1. It ensures the ex- pansion. 2. It makes that expansion so prompt and rapid that the chance of an escape of gas over the bullet is diminished. 3. It supports the expanded sides when the rifle has become foul. The construction of the Enfield rifle cartridge is shown in the illustrations in the preceding page. It consists of a hollow rolled cylinder of paper, or rather a double cylinder, since . the part which contains the powder is a separate cylinder contained in the outer envelope, by which the bullet is attached. The lubrication is applied on the outside of the paper which sur- rounds the bullet— up to the shoulder of the bullet — which, as every rifle volunteer knows, is loaded with the paper upon it, the top of the cartridge being first torn off, the powder poured into the barrel, the papered bullet inserted in the muzzle, the rest of the cartridge being torn off and thrown away, and. the bullet rammed home. The ease of loading, with the “55-inch bullet is so great, that in a clean arm it is possible to load without the ramrod, by striking the butt against the ground. The bullets are made of perfectly pure lead, the purity of which is tested by chemical analysis. Any impurity tends to alter the weight and to affect the expansion, and thus to spoil the shooting of the arm. The bullets are all made by compression . the lead being first squirted into long rods — and then formed in a machine, which is one of the sights of W oolwich Arsenal, into bullets. The weight of each bullet, with the plug, is 530 grains ; and the accuracy of manufacture is so great that the working limits are only two grains over and . under the niean weight. The charge of powder is seventy grains. The Enfield rifle is capable of shooting with great accuracy, up to about 800 yards, and good practice has been made with it occasionally at longer distances. But 800 yards may practically be regarded as the extreme limit of accuracy of a bore so large as '577 inch, unless the weights of bullet and powder were unlimited, which, in view of the soldier’s requirements, of the quantity of. ammu- nition which he has to carry, and of the amount of “kick or recoil which he can endure, they cannot be. We have omitted, to mention that the pitch of rifling of the Enfield is one turn m six feet six inches ; the grooves are “235 inches wide, and ’005 inch deep at the muzzle, and ‘013 inch deep at the breech. The weight of the arm is as nearly as possible nine pounds. The weight of sixty rounds, packed for service, with the proportion of ninety caps, is about five pounds eleven ounces. The same ammunition is used with all muzzle-loading rifled muskets ot •577 bore. A similar cartridge — differing only in the weight of the charge of powder, which is reduced ho two drams— is used with all muzzle-loading carbines of ‘577 bore. Ihe carbines and the short rifles are for the most part rifled with five grooves, and a pitch of one turn in forty-eight inches, lhis disposition of rifling is more favourable to accuracy than the three grooves and slow pitch. Some oval-bore Lancaster rifles are in use in the service. This rifle has no grooves. Ihe bore is oval, and the oval being disposed spirally along the barrel gives the necessary spin to the bullet. The oval is at muzz e, major axis = -593 inch ; minor axis = '577 inch. At breech, major axis = ‘598 inch ; minor axis = 580 inch. le same ammunition is used with the Lancaster as with the n e n e. The shooting of the Lancaster is, however, decidedly superior. MINERAL COMMERCIAL PRODUCTS. MINERAL COMMERCIAL PRODUCTS. II.— MINERALS PROPER. COAL. 67 -IY. Coal is a mineral substance very generally diffused throughout d . earth s surface ; it occurs of different geological ages in various parts of the world, but by far the greater proportion of valuable workable coal is derived from the Carboniferous series of formations. Good workable coals are obtained in the Lias and Oolite ; brown coals and lignites are of Tertiary age Coal consists of vast collections of carbonised vegetable matter im- pregnated m varying degrees with the pitchy and resinous substances now so characteristic of the fir family. Peat bo^-s m superficial beds present perhaps the first stage in such a , rheS ° passes of vegetable matter, though containing much water, can be made available for house fuel, fuel for manu- fcmture, very fair charcoal, and for the extraction of naphtha, paraffin, tar, etc In the presence of an abundant supply of coal, pea,t cannot be economically employed, but it is extremely nseM where coal is scarce, as in Holland, many parts off Prance, Germany, and Ireland. A nearer approach to true coal is the £t fr° 0 y V 0r h T Vn C ° aL This minCT alised vegetable pro- Pea;t ’ C ° n r amS a consld erable quantity of moisture, and it. suffers, m quality on exposure to the air. It is a Tertiary deposit, and is found in Breslau, on the Rhine, in Germany, on the Danube, and the shores of the Baltic, in Styria, Tuscany, Nova Scotia, Lew Zealand, Devonshire, and County Antrim S e fih 0al 13 T 7 co , mpact > has for th e most part lost its woody “If™ character, and contains a very small quantity of earthy matter. It consists of two principal varieties, the bitu- minous and the anthracitic. Bituminous coals contain a large proportion of gas tar, paraffin, and such substances, and burn aSrfo" a L llliant flame - They are ’ imnee, peculiarly adapted for domestic consumption, for gas, manufactures, coke, ^ - , ^mminous coal richest in volatile constituents is the variety called Cannel m Scotland the “ Parrot ’’—which burns with great brilliancy. Other varieties are splint and cubic r a ffidifv A rr T m0US COa1, burning with less brilliancy and rapidity, but affording great heat, is called “ steam coal,” from its use m furnishing the supplies of steam-vessels taking long voyages. The middle part of the South Wales coal-field (thS wor£ri niS bl , tummon ® > a ? d a part of the Newcastle field recently worked, contain excellent coal of this character y Anthracite coal is very hard and glossy, not soiling the fingers. It is almost pure carbon, containing but a very^mall proportion of gaseous products. It burns lith a very feeble flame, but gives an intense heat. From its comparative diffi! culty of combustion it was formerly but little used; but by the introductaon of the hot-air blast, and other improvements in furnaces, it can be made available for many manufacturing pro- cesses, particularly that of the preparation of iron, for which it is now extensively used in Wales (the eastern part of the coal! field being anthracite) and the United States. Notwithstanding the enormous consumption of this important fuel, the supply will, perhaps, never be exhausted. Immense areas in the New World must be added to the still profusely abundant districts of the Old. The coal area of Great Britain and Ireland is about 9,000 square miles, that of the rest of Europe about the same or rather less ; and to known deposits i^lfoOO S America, Australia, and Africa, must be added UO OOO square miles in the United States and Canada. The following table may not oe devoid of interest in showing the ^adual but steady increase in the exports of coal from the United Kingdom from 18,54 to 1868. The quantities in the second column include all the different kinds of coal whfie'the thi' exp0rted + for an F Purpose whatever in tons’ while the third column contains the declared value thJ h ltr? Se P1 ' 0dUCG 0f the Principal coal districts of the globe, according to a recent return, is as follows : Tons. i Tons. Britain . 101,620,000 Zollverein ') (with i 25,000,000 lignite) J France . 11,000,000 United States Belgium . Austria Spain . - 16,172,000 4,000,000 2,270,000 400,000 Sweden . . India Australia China Nova Scotia Tons. 230.0 00 370.000 450.000 100.000 651,300 Tears. Tons. 1854 1855 1856 1857 1858 1859 1860 1861 4,309,255 4,976,902 5,879,779 6,737,718 6,529,483 7,006,949 7,321,832 7,855,115 Dec. Value. Tears. Tons. £2,127,156 1862 8,301,852 2,446,341 1863 8,275,212 2,826,582 1864 8,809,908 3,210,666 1865 9,170,477 3,045,434 1866 9,953,712 3,270,013 1867 10,415,778 3,316,281 1868 10,837,513 3,604,790 Dec. Value. £3,750,867 3,713,798 4,165,773 4,427,177 5,102,805 5,392,452 5,355,791 BITUMINOUS SUBSTANCES. Ma,ny bituminous substances are produced in vegetable matter during its conversion into coal ; the chief of these are naphtha,, petroleum, and asphalte, which are all hydro-carbons 0 varying proportions, and of an inflammable nature. The bituminous substances are widely distributed, especially in the tropical . and sub-tropical regions— a circumstance which evi- dently indicates that the substances are due to extensively operating natural causes, and not, as usually supposed, to the accidental combination of special agencies. The modes, of occurrence of asphalte deposits seem referable tif rmC1P JT 10 " 3 -- 1 ' In the rocks of felons origin ; this is the case m Cuba, and at Mount Lebanon. 2. In stratified rocks of the Palaeozoic and Mesozoic epochs, usually dissemi- nated m a granular form throughout the entire stratum, or issuing from the soil, or exuding from fissures in the rocks, in the form of springs of petroleum, naphtha, etc. 3. In rocks of Tertiar y age, usually accompanied by lignite or brown coal. Ihese are the most abundant sources of asphaltic substances and include those of Pegu, Trinidad, etc. ’ Naphtha is a transparent and nearly colourless fluid, burning Wl baGOpi °- ar ? d st rong odour, and leaving no residuum. . Peh ; oleum is dark-coloured, and thicker than common tar. It rises m immense quantities from some of our coal-beds, and impregnates the earth so as to form springs and wells. Petro- leum springs contain a mixture of petroleum and the various Pa b rmr C Tf S i aUl p d ^ n °° CUr “ abundanc e in Modena and 1 arrna, Italy, Persia, Canada, United States, etc., but the most powerful are those m the province of Pegu, in the Burman Empire. In many parts of the world petroleum is now the most abundant source of photogen and paraffin. The petroleum or lock-oil of the United States is refined for illuminating pur- poses while m the crude state it is a good lubricant. Bit umen or Asphalte, is an inspissated mineral oil, of a dark- brown or black colour, wff.i a strong odour of tar; the most valuable is hard, brittle,. of a brilliant lustre, and eminently conchoidal fracture ; a variety occurs of the consistency of jelly and bearing some resemblance to soft india-rubber. It is very abundant on the shores of the Dead Sea, occupies the so-called pitch-lake in Trinidad, and occurs in Cuba, Peru, Mexico, Ionian TT®?’ Portugal, etc. The Rangoon tar or Burmese naphtha is istilled from a number of volatile hydro-carbons, chiefly used as lamp fuels ; those known as Sherwoodole and Belmontine ave considerable detergent power, removing stains from silk without impairing delicate colours. Beds of limestone and clay occur impregnated with bitumen, and from such paraffin is dis- tilled m Britain, Germany, France, Austria, etc. . Jet, so much prized in the manufacture of ornaments for its intense blackness, its lightness, and its beautiful polish, is a variety of lignite highly bituminised and free from earthy im- purities and resembles Cannel coal, but it is blacker, and has a more brilliant lustre. It occurs in the Upper Lias of Whitby in which it is very abundant, in Languedoc, Asturias, the Alps’ f wi. 1 -\ and J ^ assacbusetts - The value of the jet manufacture of Whitby is about «£20 5 000 por annum. Amber is a fossil resin, the origin of which has been traced to coniferous trees, and is found in alluvial gravels. It occurs too, m the Cretaceous marls of France and Germany. It is procured from Prussia, the shores of the Baltic, the Adriatic and Smffian shores, and from Japan, Madagascar, and the Philippine Islands. Gam Copal, is a semi-fossilised gum found in a sandy soil in the hilly districts all along the coasts of Angola, the total yearly o X onn aaa A hlcb from a11 the dis tricts of Angola is estimated at 2,600,000 lb. A gum copal is obtained under similar condi- tions from Sierra Leone and Zanzibar, the origin of which, as well as that of Angola, is still unknown. Some copal resins are exudations from living trees, as that furnished by Guibortia copallifera of Sierra Leone, and others. 68 THE TECHNICAL EDUCATOR. TECHNICAL DRAWING.- V. freehand drawing ( continued ). Agreeably with the plan already laid down, to practise free- hand concurrently with linear drawing, the following figures are given as examples of objects which are so nearly flat that they can be rendered by their outlines only, without a know- ledge of perspective, which the student has yet to acquire, and in which les- sons will be given further on. Fig. 25 repre- sents a pair of compasses, such as are commonly used by joiners. Inbeginning this simple subject, draw a horizontal line, and on it erect the perpen- dicular A B. From A set off A c and A D, and joining B C and b D, complete the triangle CB D. The apex of this triangle will be the centre of the rivet. Draw the small circle around this point, and the larger circle for the head ■ of the compasses. Next draw the lines e c and F D, which form the outer sides of the instru- ment, and which are slightly curved. The inner sides to G and H are straight, and are portions of the triangle previously drawn. The lines i and J correspond with the outer edges, of which, indeed, they form portions when the compass is closed. Fig. 26 is an outline of a shaping-knife, and but very few instructions will This habit of observation is one of the beneficial results of mental training, and no instruction is so likely to induce it as drawing ; for a man who accustoms himself to draw from objects, will, in the old-fashioned words, “walk through the world with his eyes open,” and every day, nay, every hour, will add to his stock of information, and of his power of delineating the objects he sees. To workmen this is especially important, and practice in drawing tools will be both interesting and useful. In the figure now before us, the long oblique line, a b, forming the back of the saw, is to be drawn first, and then b c at right angles to a b. At a, a short curve will lead to the line d, which is a continua- tion of the back.; thence the line turns to e, form- ing the end of the saw. From e draw a fine line on which to rest the edge, and on this set off the distances of the points of the teeth ; on these points the short lines forming the front edges of the teeth are to be drawn. It is advisable that these should all be drawn first, as it is then easier to see whether they are all at equal distances, or parallel to each other, or not. When these are satisfactorily done, the back line of each tooth may be drawn. The handle must now be added, and this requires some little care. Carry on the line from b in a curve downwards, and then the eye must di- rect you in following the be required for copying it. Draw a horizontal line for the back of the tool, and two lines at right angles to it, which are to form the centre lines of the handles. The instructions given in relation to the handle of the screwdriver will serve for these ! as well ; but you must be careful to get the two handles . precisely alike. When this is accomplished, draw the edge of the blade parallel to the back, and then complete the curved portions by which the blade is united to the handle. Fig. 27 is a drawing of a tool with which the carpenter will be well acquainted ; but it often happens that although we may have seen a thing daily, we have never noticed the peculiarities in its form which may strike a casual observer. form until you come to g. Returning to /, draw / h, and follow the curve to i ; next, the under side of the handle, i j, then the curve g j will complete the external form of the handle. Now return to the point i, and carry the curve round so as to form the inside of the handle. The screws are to be drawn next, and no workman will require to be reminded that these must be placed inside the line be; in fact, it was to make sure that the screws should be rightly placed that the whole line b c has been drawn, whilst only the portion i c is re- quired. _ , . Now, ail saw-handles are not precisely alike, and further, their edges are bevelled off, so that at fh i, etc., double lines would be TECHNICAL DBA WING. 69 seen. All this is, however, omitted here, so as to keep the example as simple as possible. When, however, this is mastered, the student is advised to make a drawing from his own saw, and having sketched the general form as in the present figure, to fill in any detail he may ■Fig. 28 observe But he should also at- tempt to draw it in some other position : for in- stance, hanging by the handle from a nail in the wall. Whilst making such a sketch, the paper must be kept perfectly straight in front of the student ; but when the form is completed, he should turn it so that it may be in the position of that in Fig. 27, and he will then possibly see many points requiring correc- tion. Still, it is neces- sary that he should be- come accustomed to sketching objects in any position in which they may be placed, and this will soon be accom- plished by practice and perseverance. LINEAR DRAWING BY MEANS OP INSTRUMENTS (continued). Fig. 28 is the section of a dam, or wall of planks, which confines the soil subject to the action of water. Of course, the strength required for such a dam must depend on the height of the water- level — that is, the wall must be strong in proportion to its height. Fig. 28 is one of the simplest examples of these constructions, and consists of piles, placed at a distance from each other, which must be regulated, first, by the nature of the soil at the back of tho dam, and its tendency to press forward ; and secondly, by the thickness of the planks employed for the wall, which must be such as to resist their being bent by the force of the soil they confine. Of course, the more such pres- sure is to be expected, the closer must the piles be placed. The piles are in the above example connected at the top by a cross-timber, into which they are mortised. The planks are then placed horizontally at the back of the piles, and may be united by the methods shown in previous lessons. The drawing in this subject is very simple. First, the pile a, with section of the cross-beam b ; next, a line parallel to the inner side of the pile, and at a distance from it equal to the thickness of the planks of which the wall is to be constructed ; between these two lines short horizontals are to be drawn, or the joints of the edges shown, according to the method adopted. Fig. 29 is the section of a dam used in cases where the soil is very swampy in character, or where the external water might pass through fissures in the bed of the stream, and so Fig. 29. enter the foundation at a lower level than tho bottom of the wall adopted in the previous case. The plan hero adopted is to drive in the strong piles a, and to connect these by the cross-timber b, partially sunk and temporarily fastened on to them. Another timber, d, is then to be laid on the bed of the water, parallel to b, and this is also to be bolted on to the piles, and at the back of these the wall of perpendicular planks, united at their edge by one of the methods al- ready shown ; or sheet- piles, c, may be used — these are driven down far below the bed of the water, as the circum- stances may require. Each of these planks having been driven until it reaches more solid soil, the strong rail, e, is placed at the back of them, and a bolt passing through e, b, and a binds them all firmly together; the heads of the planks are then sawn off to one level. Fig. 30 is a section of one of the walls of a coffer-dam. A coffer-dam may be defined as a water-tight wall, enclosing the site on which the pile of a bridge or other structure surrounded by water is to be erected. Coffer-dams are, of course, constructed of a strength sufficient to bear the pressure of the water from without, which would sometimes damage, or even demolish them alto- gether, were it not that they are secured by struts, and otherwise strengthened. The coffer-dam, of which Fig. 30 is a section, is on? of the simplest used ; it con, sists of a double row of piles, a, a, united by the head-piece, b, the rows of piles being kept at equal distances from each other by cross-timbers, c, which, as will be seen in the illus- tration, act as a cramp in preventing them either spreading outward, or being pressed inward. Walls of planks, d, d, are next attached to the inner sides of the piles, the in- ternal space being then rammed with clay, etc. In drawing this and the future examples, the stu- dents are reminded that they are arranged progressively, and that as the subjects increase in difficulty, addi- tional care and accuracy are required. Again they are urged not to be content with their work being nearly right. To carpenters and joiners this accuracy is especially important, for the different parts, got out by separate workmen, must, when required, fit exactly to each other, and this would not be the case if either one of them had been careless or inaccurate. This exactitude is only to be obtained by accustoming yourself, from the very outset,, to measure with care, and to draw your lines exactly through the proper points. 70 THE TECHNICAL EDUCATOK. TECHNICAL EDUCATION ON THE CONTINENT.— III. By Ellis A. Davidson. MODELS USED IN TEACHING ANIMAL PHYSIOLOGY THE POLYTECHNIC SCHOOL IN HANOVEB. The great number and variety of tlie sets of models for teaching practical art which are published on the Continent, show their extensive use in the schools and the appreciation of the teachers. Opportunities will be taken, when describing the leading schools, to give some account of the models and teaching apparatus employed. Such methods of illustration are not, however, confined to the mechanical arts, nor is the education of the workman on the Continent limited to the precise branches which he may require in his occupation. This arises from the circumstance that he has overcome the rougher and more irksome portions of study in his youth, and thus in maturer years he has time and mind to spare, so that as he passes through the garden of this world, he need not spend all his time in simply gathering sticks for his immediate use as fuel, but retains enough of the freedom or elasticity of youth to rejoice at the sight of the lovely flowers which ornament his path, to gather and examine into their wonderful structure ; he has time to study the elaborate construction of his own frame, and the natural history of the bird which gaily floats past him in the air. These studies tend to elevate and refine ; they give the life of an artisan an aim beyond hewing wood and drawing water ; they give him sources of happiness and amusement which he can take up after his day’s toil — amuse- ments which can be pursued at home, and in which his wife and children can partake — amusements which, as he walks to his work next morning, afford him happy reflection, thus causing him to meet his fellow-men with a cheerful and contented mien : how different from that of the man who in his shop- mates only sees the boon-companions of the previous evening’s carousal, on the details of which each in his sober moments looks back with shame ! There is more religion, more morality, brought about by this popularising of science than many persons think. The man who has made the works of God his study during the week, will not waste the morning of the Sabbath day in listless idleness and the evening in smoking and drinking. He will look upon it as a day when, together with his family, he may undisturbedly contemplate God’s works, and walk hand-in-hand to tho house of prayer, realising the truth of the text, “ Man doth not live by bread only, but by every word that proceedeth out of the mouth of the Lord doth man live.” The subject of physiology is one of importance in the instruction of working men. We see many who, when a hinge of a door in their house happens to have given way, a board of the floor become loosened, or an article of furniture out of order, bring home with them the necessary screws, nails, etc., and at once set about repairing ; but, owing to the neglect in their education, they know nothing of the “ house they live in,” the body in which their Creator has placed that spirit with which he has endowed them, and for the care of which he holds them responsible. They will learn that tem- perance in food and drink, cleanliness, and proper exercise will double the value of their own lives and those of their children. Human physiology and zoology ought to form portions of general education, and no doubt will become so in this country, as they are on the Continent, when our teachers shall have be- -come duly qualified ; and for this purpose we require such models as are about to be described. A learned English professor, in reviewing the study of physiology in a school, remarked that “ the teacher should obtain heads, hearts, etc., of sheep, oxen, and other animals, and dissect in the presence of the boys.” Now it is scarcely necessary to say that this is wholly imprac- ticable in schools for boys, and difficult of accomplishment in those for adults. This obstacle is in a great measure overcome by the excellent— it may be said wonderful — models of natural objects used in the schools on the Continent. Foremost amongst these rank the “ clastic anatomical models,” by Dr. Auzoux, of Paris. The term “ clastic ” is derived from the Greek /cAaco, I break, and is applied because the models are composed of an immense number of separate pieces, each of which may be removed as in a real dissection, and can be replaced. Amongst these there is a complete life-sized model of the human body, composed of 130 parts, all of which may be detached, thus exposing to view upwards of 1,000 objects, comprising the leading features of the bony, muscular, nervous, arterial, and venous systems ; the heart, brain, lungs, viscera, etc., all coloured to nature. This is, of course, a most complex object, adapted for a very high order of teaching, such as would be pursued in a technical course prescribed for persons who are subsequently to follow the study of medicine, and serves ad- mirably to prepare for, though of course it cannot supply the place of, absolute dissection; but as it illustrates perfectly the descriptions contained in the most complete treatises on anatomy, it is invaluable to the lecturer. This model may also be had of a smaller size (3| feet high), but containing the same number of parts as the one before-mentioned. The model adapted for teaching human physiology in schools and science classes, where the instruction is of a more general character, is 5 feet 9 inches high. It represents on the one side the muscles and vessels of the superficial layer, and on the other the muscles, vessels, and nerves of the inner layer, besides other organs, as in the complete model. This, too, is used of a smaller size. Another model shows the eye greatly enlarged, with parts of the orbit, the muscles, vessels, nerves, membranes, vitreous humour, crystalline lens, etc. ; also models showing sections of the heart, brain, etc. Next we find a complete model of a horse, size of life, divisible into 200 pieces, comprising more than 3,000 minutiae ; a model of the foot of a horse, showing the disposition of the hoof, of the vessels, nerves, etc., all the parts separating ; another, illustrating the affections of the bone in the horse, showing from the commencement to their full development the diseases known under the names of splints, spavins, etc. The boa constrictor, 7 feet in length, with its complete anatomy ; the silk-worm, 2 feet 6 inches long, show- ing the alimentary canal, muscles, nerves, trachea, and tho apparatus for the formation of the silk ; bees, magnified to about 3 inches in length, showing the male, queen, honey, and wax bees, the honey cells, the development of the larva, etc. We also find in use a set of models by the same author for exhibiting the functional distinctions of mammalia, birds, reptiles, fishes, and protozoa, and the different orders into which they are divided. Dr. Auzoux has also published a set of very large models of plants, showing the most minute portions of vegetable organisation in the various stages of development — the seed, flowers, and fruit. The whole collection is of infinite interest, teeming with instruction, whilst the size of the models is such as to enable the lecturer to explain the position and use of even the smallest organ ; but, unfortunately, the prices of these models is necessarily so high as to place them far beyond the reach of most schools or institutions. Were, however, a workmen’s “ verein,” or union, formed, single models might be obtained, which could be circulated to the classes in connection with the parent institution, in the same manner that books, pictures, etc., are lent to local schools by the Government Department of Science and Art. It is impossible to understand clearly the action of any machine without a knowledge of its various parts ; and as both the animal and vegetable structures ar6 by far more complex, and contain more minute parts, each having its special function, it is certain that physiology cannot be successfully taught without tangible illustrations such as these, which, as already said, are second only to absolute dissection. These models have been thus fully described, and their high price hinted at, in the hope that some of the skilled workmen who read these papers may be induced to attempt an imitation of at least a few of the simpler ones ; and even in this admir- able set there are omissions which possibly might be supplied by Englishmen. Amongst models which may be suggested to be made are longitudinal and cross sections of bone, showing the Haversian canals ; a joint, such as that at the knee, show- ing the synovial bursa (or, as machinists would call it, the “ oil cup ”), by means of which the joint is lubricated or greased ; it would also be useful to have a model of a section of the skin, with the perspiratory glands, etc., showing the ill effects of the want of cleanliness in allowing the pores to-be- come stopped up. The material employed might b^ plaster of Paris, papier-mache, gutta-percha, or composition of various kinds, coloured and varnished. The fine exhibition at the Agricultural Hall, London, in 1870, well showed what artisans could do ; and this suggestion is made with every hope that it will be well received and acted upon. - - Another set of models for teaching botany is manufactured PROJECTION. 71 in Breslau, and is, as it deserves to be, very extensively used. It consists of buds, flowers, fruit, etc., made of thin metal coloured to nature, mounted on stands, and arranged accord- ing to both the Linnman and natural systems. Amongst the models of the first series are plants exhibiting the difference between monocotyledons and dicotyledons, etc., the second series shows the germination and development of various leading families of plants. Another series is, we hear, in preparation, which, when a knowledge of the previous sets has been acquired, will be of immense service in the study of economic botany. In this series will be given the leading plants used in trade, manu- factures, food, etc., and will thus enable the teachers to show imitations of objects when they would be out of season, and to show the natural growth of such as only reach this country in a dried or manufactured condition. _ The most extensive set of illustrations of objects of natural history is one which, originating in Prague, has spread far and wide. It consists, in the first place, of the real skeletons of animals, bleached and jointed with wire ; next, the animals complete, stuffed. Then follow such as a squirrel, bird, crab, lizard, snake, frog, fish, etc., the blood-vessels, etc., being in- jected with coloured fluids to show the circulation ; and this set is completed by collections of animals preserved in spirit. Another section comprises dried specimens of animal life, and contains such creatures as the lobster, the water-spider, various fishes, the sea-urchin, sea-star, sponge, etc. Next follow col- lections of insects, shells, and corals, arranged according to the most modern classification ; collections of minerals, crystals, petrifactions, and fossils, either real or imitated in plaster of Paris. This comprehensive set embraces also 100 models in plaster of polycystinae and foraminiferse (see “ Cassell’s Animal Kingdom ), each being five or six inches high, and are exceed- bigly useful in class teaching, being absolute reproductions on an immensely increased scale of these minute microscopic organisms to which we owe so much of the earth’s crust. Together with these a technical collection is used ; this com- prehends, amongst numerous other objects, skins, furs, and leathers ; wool, raw and manufactured ; silk, and silk fabrics ; cotton, raw and manufactured ; linen goods, paper, woods, etc. This collection differs from the miscellaneous one used in English schools under the name of “ object boxes.” In one moderate-sized case there are above 600 substances, contained in 300 cardboard boxes, and about 140 others, either placed in bottles or mounted on cards. These placed around the schools, their names and some few particulars being appended, must attract the attention of children, and this silent teaching goes imperceptibly on; and when the right time comes the little pupils do not approach the lessons in fear of difficulty, but are interested in the subjects and anxious to learn about them. In Austria we also find in use a fine collection of models of fish, all correctly coloured to nature. This is found very useful, for as a rule we see fewer members of the finny tribes than of any other, the knowledge of the form of most of them being in many cases limited to such as belong to the locality. This set places before the pupils well-executed models properly classified, and thus is of material service. In Austria, too, we have collections of seeds, arranged in sunk compartments on trays, like coin-boxes, sets of birds’ eggs, cocoons, etc. Having thus given a general description of some of the appliances used in technical institutions on the Continent, the various educational establishments must now occupy our atten- tion, the models, apparatus, diagrams, etc., employed in each being described in connection with the systems under con- sideration. THE POLYTECHNIC SCHOOL IN HANOVER. This institution, which ranks as one of the most important in Europe, is under the administration of the Koyal Commission for Trade Schools (Gewerbeschulen), organised by the decree of the Ministry for Finance and Commerce, dated June 15, 1835. This royal commission is also charged with the direction of the school for building construction in Nienburg, the higher working school in Hildesheim (hohere Gewerkenschule), and the collective trade schools in the provinces. It is especially the duty of this body to see that the authorised arrangements and course of studies are rigidly carried out — that the school regulations are observed by all concerned, to appoint the teachers in the various trade schools, and to supervise the proper appropriation of the pecuniary resources. The commission, which is directly under the Minister of the Interior, and by the enactment of September, 1863, consists of seven persons, namely, four members who do not belong to the Polytechnic School, together with the director, one professor, and the principal (syndicus) of that institution. PROJECTION.— IV. PROJECTION ON THE INCLINED PLANE. On referring to the projection of the cube (Fig. 17), it will be seen that it is there represented as if placed with its faces at 45° to the vertical plane, the line of the diagonal of the plan being parallel to the vertical plane. We must now consider the mode of projecting views of objects, at whatever angle they may be placed in relation to both planes. Let it be required, then, to project the cube when its faces are at 30° and 60° to the vertical, and when it stands on a plane inclined at 26° to the horizontal plane. It may here be pointed out, that in projecting views it is necessary to raise the objects at one side, or to place them on inclined planes ; for otherwise, as they are supposed to be exactly on the level of the eye, the elevation only (as in Fig. 17) would be seen, but when raised at one side the top becomes visible. Place the plan (Fig. 35) at the required angles to the inter- secting line. Draw the line A (Fig. 36) at 25° above the line. This line represents the edge (or side elevation) of the inclined plane on which the cube is supposed to stand. Draw the line B (Fig. 35) at right angles to the intersecting line,, and from abed draw lines at right angles to it, and cutting it in a' b' c' d 1 . Now it will be evident that these would be the widths which would be presented to the view of the spectator when looking at the sides a c d from the point c in direction of the arrow, and therefore, if perpendiculars equal to the height of the cube be drawn on a' V c' d', and their extremities joined by a line parallel to b, d will be the elevation of those sides. Fig. 36. — Transfer the points a‘ V c' d' to the inclined plane (a), and on them construct the elevation as at D. The per- pendicular at b is to be a dotted line ; for, although known to exist, it would not be seen from c unless the object were sup- posed to be transparent. Now, by drawing perpendiculars from tho points in the plan, and intersecting them by horizontals from the points correspond- ingly lettered in the elevation, the projection e (Fig. 37) will be obtained. It is now necessary to obtain the upper projection of the object — that is, the view from r, looking in the direction of the arrow. Now it must be remembered that the elevation on the inclined plane is the view obtained from c (Fig. 35). It is therefore necessary that as this elevation has been turned round, the widths of the plan should be turned round also. Take the line e f, which in the plan is at right angles to the vertical plane, and place it (indefinite in length) parallel to the intersecting line (Fig. 38). Draw a perpendicular from a, in the elevation (Fig. 36), to cut e/in a. This gives the plan of the one angle of the top of the cube. From b draw a perpendicular, cutting e f in g, and from g set off on this perpendicular the distance b g' in the plan (Fig. 35), viz., to b. From c (Fig. 36) draw a perpendicular, cutting e f in h; from h set off h' c of the plan — viz., to c. From d draw a perpendicular cutting e f in i. From i set off the length i d of the plan. Join abed, and this figure will be the plan of the upper surface of the cube. From each of these points draw lines parallel to I L, intersect these by per- pendiculars from the corresponding points in the bottom of the elevation, and lines connecting these points will complete the projection of the cube when viewed from above. SIDE OR END ELEVATIONS. The last lesson will have shown us that other views besides front elevations are necessary. These are called side or end elevations. In objects which are uniform in character, such as the cube (Fig. 37), the elevation of each end may be the same; but in a locomotive engine, a lathe, etc., the end elevations differ materially from each other, and in such cases several 72 THE TECHNICAL EDUCATOR. drawings are necessary in their construction and in their projection. The model shown in Fig. 39 is similar to that given in the first lesson ; hut the vertical plane, instead of being made of one piece, rotates on hinges at a b, and may be brought forward to c, so as to be at right angles to both planes. Let us now place a thin metal plate, d ef g, perpendicularly on the horizontal plane, with its surface parallel to the vertical plane ; then it will be seen that h i j h is the front elevation, and that the view when looking at its edge, in the direction of the arrow, will be the line l m projected in the plane ah c n, and this is the end elevation. If now this plane be turned back to its original position (that is, rotated on the line a b) until it forms a continuation of the vertical plane, and c has moved to c', the end and front elevation will appear on the edges are parallel to the vertical plane : the elevation is then shown in the dotted parallelogram, b c d e. Let us now raise the prism at one end (Fig. 45), so that its under side is at 20° to the horizontal plane. In this case it will be seen that the prism rests upon the line e /, and the points of the end eleva- tion will now become visible in the plan, and if this plan be turned (as at Fig. 46) at an angle (say 45°) to I L, perpendicular lines from the points of the plan intersected by horizontal lines from the elevation will give the projection of the object at a compound angle (Fig. 47). Fig. 48 shows the plan, and Fig. 49 the elevation of four such prisms meeting at a point, a figure which very frequently occurs in designing or drawing the roofs of houses, churches, etc. The plan is formed of two figures similar to the plan of the uame plane ; it will then be seen that the height of V m' is the same as h j, and that in its motion the point l will have travelled through a quarter of a circle. If now the vertical and horizontal plane be converted into, one flat surface, by withdrawing the pin r, the plan and the front and end elevation will be found to be those represented in Fig. 40. Fig. 41 is the end elevation, and Fig. 42 is the plan of a triangular prism when lying on one of its long sides, its edges being at right angles and its end parallel to the vertical plane ; thus the exact shape of the end — that of an equilateral triangle — is presented to view. But when the prism is turned, so that the plan is at an angle to the vertical plane (Fig. 43a), the elevation (Fig. 436) becomes materially altered; for as the object has rotated on the point 6, a has receded, whilst / has advanced, and the apex, d, of the opposite end, w'hich in Fig. 41 was hidden beyond c, now becomes visible ; the height, how- ever, remains the same as in the original figure. Eig. 44. — Here the plan ab e f is further rotated until its last prism, crossing each other at right angles, and from this the elevation is easily projected. Figs. 50 and 51 show the projections of the object when placed at an angle to the vertical plane ; and Fig. 52 is the development of one of the four parts of which the model is composed. To construct this development on a straight line, set off three spaces equal in width to the sides of the prism, a' b f a, and erect perpendiculars from the points. Make these perpendiculars equal to the lines similarly'lettered in the plan. Now it will be clear that when two parallelograms, like those forming the plan of the prism, cross each other, they will form four right angles at the centre. Therefore, at d' and e con- struct angles of 45°, which will meet in c and form the required right angle, and this will complete the under side. Draw c h and c i at right angles to e c and d' c, and equal to the altitude of the triangle g c in Fig. 41. Join d! i and h e. Then the right-angled triangles, d' c i and e c h, turned up at right angles to ab c d e, will form the upright sides of the mitre ; i and h will then come together. The triangular end, which is repre- PROJECTION. 73 to the vertical plane ; as in all the planes in a similar position, the elevation would be merely a line marking the greatest width, as ace (Fig. 54). Now let it be required to con- struct the plan of this figure, when the plane resting on A B is raised to an angle of 30° to the horizontal plane. Then, as each of the points c d and e will travel through portions of circles, draw a line at 30° at A on the inter- secting line, and from A, with sented as bent down, being now turned upward at right angles to the under side, the two upper sides are to be bent over. Then c will meet h i, f will meet c", and d a will meet d' a'. THE PROJECTION OP POLYGONS. In Figs. 53 to 60 the mode of projecting a plane pentagon is shown. Fig. 53. — Let ABODE be the geometrical figure when lying flat on the hori- zontal plane with one edge, A and t B, at right angles Fig. 54. Fig. 49. Fig. 51. Fig. 58. Fig. 60. O c A e, describe arcs cutting the line in points corre- spondingly let- tered. This, then, will be the eleva- tion. From e draw a perpen- dicular cutting e/ in e'. From c and D draw lines parallel to e /. Then perpendicu- lars drawn from £ in the elevation will cut these last- mentionedlines in c d 1 . Join B d', d’ e', e' c', c ' A, which will com- plete the plan of the figure. 74 THE TECHNICAL EDUCATOR. Ilg. 55. — Here the plan is turned, so that a' U is at 45° to the vertical plane, and it will be seen that by drawing perpen- diculars from the angles of the plan, and intersecting these by horizontals drawn from the corresponding points in the eleva- tion, the projection of the plane will be obtained. It must be remembered that the pentagon being “ regular,’' * a line joining C and D will be parallel to A B, and will remain so, however much the plane may be raised. Thus, this line d d' is represented in the elevation by the point the line itself being horizontal and at right angles to the vertical plane (see Fig. 2, page 8). Now when the object is turned round this horizontal line becomes visible, and the perpendiculars from c' cl' intersecting it, give the points c" and cT, and it will then be seen, that as the line joining these points was horizontal and parallel to A B in the previous figure, it will remain so in the projection ; and this will explain the cause of two points in the plan coming on one line in the projec- tion — a case which will frequently occur in the projection of polygons. Figs. 57 to 60 show the same process adapted to a regular hexagon when resting on one of its angles, which it is expected the student will be able to work out without further in- structions. ANIMAL COMMERCIAL PRODUCTS.— III. BiGiTiGBADiE ( continued ). The Skunk ( Mephitis Americana) is common in North America, especially in the States of Pennsylvania and New Jersey. It is well known for its power of ejecting, when hunted, from a small bag placed at the root of the tail, a very offensive fluid, which produces one of the most powerful and intolerable stenches in nature. This animal is allied to the polecat of Europe. Its fur is soft and black, with two white stripes running from head to tail. The fur is purified by exposure to heat. The Hudson’s Bay Company send to Europe annually about 10,000 skins, which are mostly exported to other parts of the world. The American Otter ( Lutra Canadensis) is aquatic in its habits, and lives principally upon fish, which it pursues in the water. The colour of the fur changes with the seasons : in summer it is short and almost black, but on the approach of winter it alters to a beautiful reddish-brown. The motions of the otter in the water are very easy and graceful. The short, close, fine fur keeps the body at a proper temperature, and the short legs, webbed feet, and rudder-like tail enable it to move swiftly in any direction in pursuit of its agile prey. In 1864, 21,319 otter-skins, valued at =£14,461, were imported into this country by the Hudson’s Bay Company. The Sea Otter ( Enhydra marina). — The fur of the sea-otter is thick, soft, and woolly, and much prized in Russia and China, where it is the fur of royalty ; to those countries most of the skins are exported. The animal is found in the North Pacific, from Kamtschatka to the Yellow Sea, on the Asiatic coast, and from Alaska to California, on the American coast. It is a rare animal, and not more than 1,000 skins are annually procured. In 1864 we imported 641, valued at =£7,891. The sea-otter haunts sea-washed rocks, lives mostly in the water, and ap- proximates to the seal in its habits. Its fur is generally employed for collars, cuffs, and trimmings. It is very beautiful, of a deep velvety maroon brown, the anterior parts being of a silvery grey. A fine skin of the sea-otter is worth about <£40, and a muff of this skin costs about twenty-five guineas. 2. PLANTIGBADiE. This group includes the family of the Ursidoe, or bears — heavy, stout-bodied animals, with thick limbs and a very stout tail — which inhabit the wooded and mountain districts of the arctic, temperate, and sub-temperate regions of the northern hemisphere. The commonest bear-skin in the English fur- market is that of the Blade Bear (TJrsus Americanus), which is imported into this country generally from British North America, and chiefly for military accoutrements. It is made into caps, rugs, pistol holsters, etc. In 1864 we imported 13,311 black bear skins, valued at <£21,047. The skins of the polar bear ( Thalassarctos maritimus), the brown bear ( TJrsus arctos), and the grisly bear ( TJrsus ferox), are also imported by us in small quantities. The Raccoon ( Procyon Lotor) is indigenous to North America, and usually frequents the sea-shore and the margins of rivers and swamps, where it lives upon small animals, birds, insects, and mollusca, with the addition of roots and succulent vege- tables. In 1864, 639,657 skins of the raccoon, valued at <£74,538, were imported into the United Kingdom. Two-thirds of this number were re-exported, principally to Germany, where they are used for making hats. The hair of the upper part and sides of the body is of uniform length and colour, and is employed for the linings of coats, for rugs, etc. The Badger ( Meles vulgaris, Desmarest) is found throughout the northern parts of Europe, Asia, and America. Its habits are nocturnal, inoffensive, and slothful. Its feet are planti- grade, and its long claws enable it to dig with effect, and burrow in the woods. It feeds on roots, earth-nuts, fruits, insects, frogs, and the eggs of birds. Its muscular strength is great, and its bite proverbially powerful. The American badger ( M . Labradoricus) is larger than the European species. About 5,000 skins are annually sent over to this country by the Hudson’s Bay Company. The long hairs are employed for making shaving brushes and painters’ pencils. In Europe, badgers are hunted with dogs ; in America, they are caught in early spring, whilst the ground is frozen, by pouring water into their holes. The Glutton, or Wolverine ( Gulo luscus), inhabits the northern parts of the American continent. Wolverines feed chiefly upon the carcases of beasts which have been killed by accident. They are very troublesome to the Hudson’s Bay trappers, for they will follow the marten hunters’ path round a line of traps extending from forty to sixty miles, and render the whole unserviceable, by removing the baits, which are generally the heads of partridges or bits of dried venison. They resemble the bear in their gait, and feed well ; they are generally, when caught, found to be very fat. The fur is a fine deep chestnut colour, with a dark disc on the back. About 1,000 skins are annually received in this country. The fur of the wolverine is much esteemed in Germany and Russia, and used for cloak linings, muffs, and sleigh robes. 3. PINNIGBAD2E. This group includes the family Phocidce (Latin phoca, a seal), and comprises the seals, sea-bears, and walruses, which are found chiefly in the arctic and antarctic seas, and are of great value alike for their oil, bones, and skins. The chief hunting- grounds are the fields of pack ice in the Greenland seas, and around the shores of Spitzbergen. The Saddleback or Harp Seal (Calocephalus Grcenlandicus). — This species, which is the most important of the Phocidce in commerce, is at all times gregarious, but never seen to assemble in such numbers as during the months of March and April, when it takes to the ice to bring forth its young. During those months a pack of ice three miles in diameter has been calculated to have no fewer than four millions of seals upon it. Its length does not exceed eight feet. The name saddle- back is given to it from an aggregation of black well-defined spots scattered over a yellowish-white ground in the form of a saddle or harp. For the capture of this seal, especially during the breeding season, many ships are annually sent out, and the number taken yearly amounts to hundreds of thousands. The success of the sealers varies ; for a ship one year may obtain as many as 20,000 seals, and next year not capture a hundred. The chief art of sealing lies in finding out where the main body of seals is located ; a sort of instinct directs these animals in flocks of hundreds to a common centre, where they remain in one great group till the young are capable of taking to the water. This species is highly prized. From its blubber the Green- lander and Esquimaux procure light and heat ; they cover their boats and bodies with its skin, make thongs with its entrails, a derg or float with its stomach, and ingeniously fashion the teeth into tips for their arrows and harpoons. The Bladder-note Seal ( Stemmatopus cristatus) inhabits, as the last, the Greenland seas, and is found in small groups of * A regular pentagon is one which has all its sides and angles equal. OHEMISTRY APPLIED TO THE ARTS. 75 k three or four. On account of the beauty of its fur, and the immense amount of its blubber, it is much sought after. It differs from the other species in having a thick black — in the young, delicate brown — woolly coat, which lies beneath its out- side bristly hair. The Common Seal ( Phoca vitulina, L.) is found on the coasts of Scotland, France, and other parts of Europe. . The usual haunt of this species is a hollow or cavern in a rock near the sea, and above high-water mark. They are extremely watchful, seldom sleep more than a minute, raise their heads, and, if nothing is to be seen or heard, lie down again ; but if disturbed, they instantly tumble off the rocks into the sea. They are usually shot when asleep. If surprised by the hunter at a distance from the shore, they hasten to the water, flinging stones and dirt behind as they scramble along, and expressing their fears by piteous moans. When overtaken, they make a vigorous defence with their feet and teeth until killed. We imported from Greenland, British North America, and the United States, as well as from Norway, Russia, and other parts of Europe, in 1867, 743,511 undressed seal-skins, valued at £1 74,998. The skin of the seal, when tanned, is employed in the making of shoes ; and when dressed by the furrier, serves for the covering of trunks, and for articles of clothing, such as caps and hats, mantles and muffs, coats and boots. RODENTIA. The Rodentia (Latin, rodo, I gnaw), or gnawing mammalia, are, for the most part, of small size, but numerous and prolific. They are distributed all over the world, even in Australia, which possesses some few indigenous species. They have two pairs of curved cutting or incisor teeth, which project from the front of each jaw, and from two to six molars on each side, but they are devoid of canine teeth. The rodents of the greatest value in the fur market are — • The Beaver ( Castor fiber, L.).- — This animal is found in Canada, where it frequents the banks of rivers and marshes, making large dams with the stems of trees plastered with mud to keep out the water, and building rude dwellings in the water, with considerable engineering skill and ingenuity. The fur of the beaver consists of two kinds of hair, one long and rigid, form- ing the outer coat, the other soft and downy ; it is the latter which is employed for coat linings, muffs, and other articles of dress. About 80,000 beaver-skins are annually sent over to this country from North America by the Hudson’s Bay Com- pany. The Music Rat, or Musquash ( Fiber zibethicus). — This animal is a native of Canada. It is much smaller -than the beaver, which it resembles in its fur and habits, and with which it associates. Above a million are annually taken by the Canadian trappers, and their skins sent over to the fur markets of. this country ; dressed in the same way as beaver-skin, they form a cheap and durable fur for ladies’ wear. The Nutria, or Coypu Rat ( Myopotamus Coypus ), inhabits South America, living near streams, and burrowing in their banks. It is smaller than the beaver, and also differs in the possession of a round, hairy tail. Its skin forms a good substi- tute for that of the beaver, and is dressed in a similar manner. In some years one million nutria-skins have been imported from South America into the United Kingdom. The Squirrel (Sciurus vulgams, L.). — Light, nimble, and grace- ful animals, living on the branches of trees, feeding on nuts and other hard fruits, which they gnaw through with their sharp front teeth, carefully removing every particle of skin from the kernel before eating it. Squirrels are distributed through all parts of the world except Australia, but are espe- cially abundant in North America. Their skins are used entirely for ladies’ and children’s wear, and are sent in enormous num- bers to our fur markets under the name of calabar. About 2,000,000 are annually imported. The fur is sometimes dyed to imitate sable. The tail is used in the manufacture of boas and artists’ pencils. Besides the common squirrel, Sciurus cinereus (the grey squirrel), S.niger (the black), S. Caroliniensis and S. Hudsonius (the American red squirrel), yield useful and ornamental furs. The Chinchilla ( Chinchilla lanigera). — An elegant, active little animal, inhabiting the Andes of South America, in Chili and Peru, and living at a considerable altitude. The posterior legs are longer than the anterior, and the animal when feeding sits upon its haunches, holding its food between its short fore- paws. The ears are very large and broad. The fur, which is very thick, soft, and of a greyish colour, reaches us through the South American markets. Chinchilla fur is greatly admired for winter clothing, and is made into muffs, mantles, boas, cloak linings, trimmings, and other articles for ladies’ and children’s wear. The Hare ( Lepus timidus ) and Rabbit ( Lepus cuniculus ). — The skin of the rabbit, when dressed and dyed, is made into all sorts of cheap and warm winter clothing ; that of the hare is frequently worn over the chest as a protection against external cold. We have large supplies of rabbit-skins sent to our markets from the rabbit warrens of Norfolk, the Orkney and Shetland Islands, and Ostend. Upwards of 1,000,000 rabbits are sold yearly in London, and more than a quarter of a million of hare-skins are annually imported into this country from Russia, Germany, Denmark, Friesland, Poland, Wallachia, Turkey, Greece, and Sicily. The best and the greatest number come from Russia. RLTMINANTIA. The animals of this order are distinguished from the other mammalia by the remarkable facilities which they possess for ruminating, or chewing their food twice over. In the majority the lower jaw alone is furnished with incisor teeth, their place in the upper jaw being occupied by the hardened gum. The molars are separated from the incisors by a considerable gap in the jaw. Examples : sheep and deer. The American Buffalo, or Bison ( Bison Americanus, L.). — Yast herds of buffaloes roam over the western prairies of North America, and hundreds of thousands of them are annually killed. Buffalo robes are much esteemed in America as sleigh coverings ; about 70,000 are annually made up and sold in New York. During the Crimean war our soldiers found these robes of great service ; about 20,000 buffalo robes were furnished by the English Government amongst other army supplies. CHEMISTRY APPLIED TO THE ARTS.— II. BY GEORGE GLADSTONE, E.C.S. DYEING. The art of dyeing was discovered at a very early period of human history, and is practised by nearly all races of men ; nevertheless, it has greatly profited by the advance of science, and even within the present generation it has been the subject of very great improvement. Many of the colours now regarded with most favour were altogether unknown to our fathers, while others have been rendered more permanent, and most have been cheapened in cost. The materials used in dyeing are derived from very various sources, and their number is legion. There is, indeed, scarcely any limit to the variety that might be employed, and in an article like the present we can only pretend to name a few of those which are most commonly used by dyers. They form two distinct classes, which must be constantly borne in mind, in order to arrive at a clear comprehension of the dyeing process : — (1) The colouring matters ; (2) The mordants and alterants 1. The great majority of the colouring matters in use are derived from the vegetable kingdom, though some of the others are of the very greatest importance. Of these it may suffice to name alkanet root, aloes, annatto, orchella and other lichens, barberry root, barwood, Brazil wood, camwood, logwood, Saun- ders’ wood, yellow berries, indigo, madder root, quercitron, safflower, turmeric, woad, and weld. The animal kingdom sup- plies the cochineal and kermes, which, as well as lac, an exu- dation produced by an insect, furnish very beautiful varieties of red. The metals arsenic, chromium, copper, iron, etc. in the form of salts, all produce valuable colours, though the compounds of arsenic are very deleterious both to the dyer and to the wearer of clothes so dyed, and should certainly be dis- couraged. There are also some artificial products which have been successfully prepared by modern chemists, and which bid fair to revolutionise the art of dyeing ; thus, what are called the aniline compounds have furnished some of the most favourite dyes of the last few years ; and alizarine, a still more recent 76 THE TECHNICAL EDUCATOR. $ production, will probably soon dispense to a great extent with the use of madder roots, the bulkiness of which considerably enhances the cost of bringing them from abroad. 2. The most important mordants and alterants are the alums, the salts of iron and tin, and a variety of vegetable substances which contain tannin. Of these last the principal are catechu, fustic, sumach, gall-nuts, dividivi, valonia, myro- balans, etc. Some of them exercise a double function, and might be included amongst the list of colouring matters, but their chief value brings them more appropriately under the second category. The operation of the first class needs little explanation, but that of the latter lies at the very root of the art. It will readily be understood that a highly coloured liquid may be obtained by boiling down or steeping certain substances in water, and that if a piece of calico be immersed in the solution, it will take up a certain amount of the colour ; but it follows almost as a necessary consequence that a dye so produced can be washed out again with almost equal readiness. If this were all, dyeing would be of no value. The importance of mordants consists in their so fixing the colours that they shall not wash out or otherwise lose their depth or brilliance ; and that of alterants in their bringing out or changing the tint produced by the dye stuff. By means of the latter a much greater variety of shades is obtained, and even some colours which can scarcely be derived at all from a mere com- bination of dyes. Some very interesting chemical reactions take place in the use of the dyes mentioned under the first head, which must be noted, as they are highly instructive. By far the most important in the list of vegetable substances is indigo. It is commonly known in this country as a lump of purplish stuff, having a bloom upon it like a ripe plum. In the dye vat, however, it presents a very different appearance. Indigo, in the state in which it is imported, is actually insoluble in water, and most other solvents will not even touch it ; but by expelling the oxygen which it has absorbed in the course of preparation, it returns to its original condition of white indigo, which is soluble in an alkaline liquid. The blue indigo of commerce is therefore ground up with water till it forms a thin paste, then put into a vat of water and stirred up with sulphate of iron (copperas) and lime, in the proportion of 1 lb. of indigo to 2 lb. of sulphate of iron and 3 lb. of lime ; the result is that the sulphuric acid leaves the iron and combines with an equal quantity of the lime, the oxygen of the blue indigo takes the place of the sulphuric acid which has left the iron, forming an oxide of iron, and the excess of lime which remains in the water renders the indigo soluble. The indigo having parted with its oxygen is no longer blue, but has returned to its original colourless con- dition. When the sulphate of lime and oxide of iron which have been produced in the vat have thoroughly settled to the bottom, the cotton fabric or yam which has to be dyed is dipped into the liquor, and the fibres become filled with the solution. The goods are then taken out of the vat, hung up, and exposed to the action of the air, when the oxygen out of the atmosphere again enters into combination with the white indigo in the fibre of the cloth, and restores its blue colour. This blue indigo being, as already mentioned, altogether insolu- ble in water, we have here a permanent colour which cannot be washed out. Wool may be dyed by precisely the same process, except that the liquor in the vat must be maintained at a high temperature, whereas cotton i3 dyed cold. Other modes of using indigo are employed by some dyers, or for special purposes, in which madder is a principal ingredient, but in every case the result is due to the chemical action above described. Indigo naturally leads to the consideration of what are commonly known as the aniline dyes, so named from their chemical relation to this substance, anil being the name given by the Spaniards to indigo. The terms mauve, magenta, etc., are now familiar as household words, though it is scarcely f eighteen years since the colours represented by them were quite new to the public. Aniline itself, which was originally made from indigo, had been produced from coal-tar by two or three different processes ; until the date above referred to, however, the substance had not attracted any very special attention, and its compounds were not known to produce the colours now so familiar. This discovery was due to Mr. Perkin, and the demand which suddenly sprung up for the dye soon led to the manufacture of aniline from coal-tar, on a scale never before attempted, and, by subsequent improvements in the process, at a much more moderate price than heretofore. The mode of application of these dyes will have to be considered later on. Madder is perhaps next in importance to indigo, and possesses some special features of interest, though the processes involved in its use are by no means so simple as those above described. This dye has hitherto been obtained from the roots of the rubia tinctorum, a plant which is largely cultivated in the south of Europe and in Asia Minor. Its value consists in its containing a substance called garancine or alizarine. This article will furnish, in combination with various other ingredients, a variety of tints, from yellow to orange, and up to a deep red. Unlike indigo, it requires the presence of a mordant in order to secure a satisfactory result. The one generally used in dyeing with madder is alum. The cloth to be dyed is first steeped in a solution of alum, and being thoroughly impregnated with this article, it is ready for the reception of the dye which may be intended. Let us suppose that an intense red is required ; a solution of alizarine with one of the alkalis (such as ammonia or soda) would be used, and into this the cloth, already permeated with the alum, would be introduced. The mordant would take up the alizarine until it was thoroughly saturated with it, the cloth thus acquiring the desired colour ; but were the process to be continued beyond this point, the excess of alizarine in the liquor would be liable to further decomposition,, producing a new compound, called rubiacin, which would have the effect of rendering the colour more dull ; it is therefore important so to regulate the relative proportions that this after effect may not take place. The madder roots themselves contain but a small per-centage of the colouring matter, the inevitable result of which is that the dye is costly. So important an article is it, however, that, notwithstanding the price, it is very largely used both in this country and on the Continent. Chemists have, in consequence, been led to study the composition of this dye, and their labours have recently been rewarded by discovering a means of producing artificial alizarine which shall fulfil all the reactions of the natural product. The history of this achievement is one of the deepest interest to the experimental philosopher, as well as to those who are likely to profit by it in a commercial point of view. It would take up too much space to describe all the steps by which the result was finally attained ; suffice it to say that from a study of the chemical formula (consisting of definite pro- portions of carbon, hydrogen, and oxygen (C 14 H 8 0.,), it was believed to bear a certain relation to other substances which are produced artificially. This view was confirmed by con- verting some of the alizarine taken from the madder roots into anthracene (C 14 H 10 ), which is obtained by the distillation of coal tar. This having been proved, it only needed a means of reversing the operation, which has since been discovered — alizarine, absolutely identical in all its properties with the dye obtained from the madder roots, having been made from anthracene. A second source of supply of an article quite indispensable to the dyer is thus provided by the mineral kingdom. Chromium, in the form of bichromate of potash, is a metal which is very extensively used, especially in the formation of yellows, orange, and reds. In dyeing cottons the process depends upon a chemical reaction, the fabric being first immersed in a solution of one of the salts of lead, so as to supply a base which possesses a greater affinity for the chromium than potash does. Thus, if the goods be impregnated with nitrate of lead, and subsequently with bichromate of potash, the chromium will leave the potash and combine with the lead, forming chromate of lead, which produces a yellow dye. Again, should an orange colour be required, the process can be carried a step further ; the article so dyed yellow would then be boiled in a bath of lime-water, during which operation the lime will take up a portion of the chromium, leaving a subchromate of lead behind, which produces a rich orange. Some persons use acetate of lead in preference to the nitrate, but the principle involved in either case is the same. Chrome is also employed in dyeing woollen goods with various colours, in combination with many of the vegetable dyes ; in these operations alum is almost always used as a mordant, and the solution into which the AGRICULTURAL DRAINAGE AND IRRIGATION. 77 article to be dyed is dipped must be maintained at the boiling- point. The use of a mordant has incidentally been mentioned in treating of madder and the chromates of potash. Its proper function is to fix the dye, so that it shall not wash out again. Alum, as wo hare seen, has this property ; a fabric which has previously been dipped into a solution of alum being able, not only to taka up a much larger quantity of some colouring matters than it would otherwise, but also to retain them so persistently that the colour becomes fast. In some cases the mordant and the dye are applied separately, while in others the two are mixed, forming a coloured liquor in which the article to be dyed is steeped, and so far reducing the number of operations. It appears probable that the action of such a mordant as alum is to enter into actual combination with the substance of the thread or cloth, and not merely to fill the capillary tubes with a substance insoluble in water, as in the case of cotton dyed with indigo ; hence, in consequence of the greater affinity of alum for animal substances than for other materials, the effect of this mordant is much more decided when applied to wool and silk than to cotton and flax. Various salts of iron exercise, in a pre-eminent degree, the double function of mordant and alterant. Sulphate of iron, or copperas, is, for instance, used as such in dyeing cotton blue with ferrocyanide of potassium or the red prussiate of potash, while the nitrate or sesquichloride of iron, combined with the ferrocyanide or yellow prussiate of potash, will produce the same result ; the chemical action in either case is the same — ■ the acid leaves the iron and combines with the potash, while the cyanogen completes the exchange by uniting with the iron, thus forming a compound cyanide of iron, commonly known as Prussian blue. Here we have an illustration of the effect of an alterant, the resulting colour having no relation to that of the ingredients which are brought into combination, but being due to chemical action only. Of all the metals, however, tin is the most important as a mordant, the various oxides of tin having a very powerful affinity both for vegetable colouring matters and for the materials which are to be dyed. The effect of these salts (or spirits, as they are called by the dyers) is to produce very permanent colours. The salts generally used in the dye-house are the chlorides ; the oxides being insoluble except in the presence of an acid, or in combination with an alkali, such as soda, in which case the tin itself acts the part of an acid, forming stannate of soda. A great variety of vegetable substances, all containing tannin in more or less quantity, are used in dyeing, which act both as mordants and alterants. The tannic and gallic acids which they furnish exercise a very powerful chemical action upon some of the other materials employed, especially the metallic salts. With sulphate of iron, for instance, these acids produce a deep black, of which the common writing-ink furnishes a familiar example. To give a description in detail of all the various processes for dyeing different kinds of goods, and of the several combinations which are best adapted to produce the almost endless varieties of tint, would fill a goodly volume. In the next article some of the most important general directions will be given, and one or two of the principal colours will be treated at length, as an illustration of the nature of the dyer’s art. AGRICULTURAL DRAINAGE AND IRRIGATION.— II. By Prof. Wrightson, Royal Agricultural College, Cirencester. WATER-LOGGED SOIL ADVANTAGES OR LAND DRAINAGE. The beneficial action of land drainage may at first sight appear somewhat paradoxical. That the partial removal of water, the want of which is often so keenly felt, which may be beneficially poured over growing crops in quantities far exceeding the natural rainfall, and which not unfrequently composes ninety per cent, of the actual weight of fresh vegetables — that the removal of this most essential constituent of plants from the soil should be attended with good effects certainly appears puzzling, and demands our careful attention. It will, then, be our first object to explain why the drainage of land is beneficial; and, secondly, we shall point out the nature of those practical good effects which have rendered the art popular. Let us consider the condition of a soil surcharged with moisture, and compare it with one in which, from natural or artificial means, the superfluous water finds egress. The fact that the land is wet is sufficient proof that some obstacle exists preventing the escape of water. The subsoil may be sufficiently impervious to prevent the downward passage of water to lower strata, or there may be a source of water in the form of springs too plentiful to allow of its sufficiently rapid removal by natural drainage. From either or both of these reasons the land is “water-logged,” by which we mean that all the interstices of the soil that would otherwise be filled with air are occupied by water. This water is in a stationary condition. If it is not, it will move in the line of least resistance, and the soil will be more or less perfectly drained. Having, however, assumed that the soil is wet, we must conclude that its condition is the effect of the water not being able to escape. (1.) What, then, are the consequences of this stagnant condition ? In the first place, air is excluded. Now the effect of air upon the soil is most beneficial, and without it it is impossible for any plant to develop. The first conse- quence of an insufficient supply of oxygen is the formation in the soil of organic and inorganic substances of a decidedly deleterious character. Vegetable matters remain in a state of partial or imperfect decomposition. Such a condition is un- favourable to plant life; and its evils are the more apparent when we remember that with a sufficient supply of oxygen such compounds would not only be removed from an actively hurtful state, but would become a source of carbonic acid and ammonia (the products of perfect combustion), and thus directly nourish growing crops. Lower oxides and sulphides of iron are also the result of decaying vegetable matter in the soil, which, in its condition of arrested decay, removes the oxygen previously associated with iron, thereby reducing the peroxide to the condition of protoxide. The removal of superfluous water at once admits air, and with it oxygen, and by this means the soil is brought into a “ sweeter ” and more whole- some condition. (2.) Water, when it exists in a stationary or stagnant con- dition in a soil, fails to exert those beneficial influences that constitute its peculiar value. Rain-water contains traces of carbonic acid, as well as of other valuable substances. This carbonic acid exerts a solvent action upon the mineral matter in the soil, gradually changing it from an insoluble and un- available condition into one in which it can be assimilated by the roots of plants. It is only, therefore, in drained or naturally dry soils that the valuable qualities of rain can be thoroughly realised. (3.) Not only is rain comparatively valueless to wet soils, but there is a danger of its becoming actively injurious. Not being able to sink into the already occupied soil, it washes the sur- face, and, as it trickles into the water-furrows and ditches, carries with it the finest particles of earth, as well as manurial substances that have been applied as fertilisers. This is, how- ever, not the worst evil consequent upon defective drainage. The top layer of soil becomes surcharged with moisture, and this can only be got rid of by evaporation. The larger the surface, and the more completely it is exposed to the air, the greater will be the evaporation. In the case of drained soils, the water is quickly removed from the effect of drying winds, and evaporation is proportionally checked. In wet soils, on the contrary, the conversion of water into vapour is the cause of a greatly diminished temperature. It has been calculated that the heat given off from the combustion of 1 lb. of charcoal is required to evaporate 12 J lb. of water, and when we remember that the rainfall upon an acre of land is equal to something like 6,000,000 lb., it will be readily seen that, where a large proportion of this is to be evaporated, much of the sun’s heat, which would otherwise be warming the ground, will be taken up. (4.) Another reason for the wonderful improvement of land by drainage is the altered texture of the soil. So long as land is constantly wet, its condition, although unfavourable to plant life, is in some respects constant. It is not subjected to the modifying influences of contraction and expansion to so great an extent as drained soils. A drained field is alternately, and 78 THE TECHNICAL EDUCATOR. within a very short period, dry and wet ; it is also acted upon by the atmosphere, and that weathering action which, in the long course of time, has broken down and pulverised rocks, and so formed soils, is promoted, so that further pulverisation and a finer mechanical condition of the soil is the result. The alternate contraction and expansion also causes the formation of a deeper layer of available soil, and renders lighter the work of cultivation. As water rises from the deeper layers of the soil to the surface, it brings with it the saline substances it has taken up in solution. These are carried by capillary action to the surface, where, as the water is evaporated, they are left in the form of an incrustation, which to a great extent pre- vents the entrance of air into the soil. This phenomenon is frequently noticed in the case of flower-pots watered by means of a saucer. In this case the water, as it evaporates from the upper surface of the soil, leaves a white efflorescence which, from the cause already referred to, is prejudicial to the plant, and requires to be frequently broken up in order to admit air. The Same phenomenon has been observed in the case of agricultural soils. Having traced the causes of the beneficial action of land drain- age, let us now glance at those many practical advantages which appeal to the common sense of the landowner, the farmer, and the public. That drained land grows a better crop than undrained land is easily accounted for when we remember the improved chemical and mechanical state of the soil. As every reason we have given points in the direction of an improved condition of soil, it need not surprise us that one quarter (eight bushels) of wheat has often been estimated as the average increase that may be expected after drainage. Instances are not wanting where land has been brought from a worthless into a valuable condition simply by draining it, but the above given measure of the benefit is applicable to soils which, although requiring drainage, were previously useful agricultural soils. An earlier harvest is a palpable advantage from drainage, and can be explained by the general improvement of the land, and the higher temperature of the soil consequent upon diminished evaporation. Mr. Parkes, the eminent drainage engineer, found, from the mean of thirty-five observations, that a drained peaty soil at seven inches in depth was 10° Fahrenheit warmer than a similar undrained soil at the same depth. This, it will be seen on inspection of any table of temperatures throughout the year, is equivalent to the differ- ence between the climates of February and May. The result of this improvement is harvest a fortnight earlier, and an im- proved quality as well as quantity of produce. The same causes operate in increasing the number of species of plants which the farmer can cultivate. Thus we find the bare fallow disappearing, and root and forage crops occupying the ground. Sheep stock also can be maintained, whereas previously they could not have been profitably kept. Every tillage operation is easier and more effectively performed, and, owing to the water being quickly carried away, the actual number of work- ing days is increased. Thus either a smaller number of horses will be required, or those that are kept will be more equally worked and less expensively fed. Manures are much more effective upon drained soils ,• hence this operation is now looked upon as the foundation of good husbandry, and the best farmers consider that it should pre- cede every other improvement. Grass land derives great benefit from drainage. It sooner assumes a beautiful green colour in the spring ; it is firmer under the foot ; rushes, sedges, and other water-loving and inferior herbage disappear, and are replaced by nutritious grasses. The health of the live stock is unquestionably improved, and land drainage is followed by the disappearance of “ black- quarter,” or inflammatory fever, which in unfavourable situa- tions is a cause of annual loss. The health of the human population is also improved. Before leaving this most interesting part of the subject, we would recall the attention of our readers to the fact that drainage owes its efficacy to the alteration in the condition of the water in the soil rather than to its withdrawal. If we remove water, it is only because it has accomplished its work, and we facilitate its exit to make room for a new supply. Thus the drainer’s art consists, as has been well remarked, not only in getting the water out of the land, but also in j getting water into the land, and thoroughly using its valuable properties. We propose, upon a future occasion, after considering the cost of drainage, to select a few instances showing the extent to which land has been improved by the operation; but at present we must pass on to another important point in the theory of drainage — namely, the action of drains in removing water from the land. THE WATER ECONOMT OF SOILS. Soils are wet from three causes : — (1) The direct fall of rain; (2) springs ; and (3) moisture which finds its way from higher porous strata on to lower ground in a diffused condition. How far these three sources of wetness are the cause of injury in any given case depends upon the structure of the soil and subsoil. Clay soils, with retentive subsoils, are liable to be wet from the first cause, and they may receive an additional supply from the percolation of water from higher grounds. In soils of a light character resting upon a tenacious clay (a com- bination not unfrequently met with), the natural rainfall may also be the direct cause of wetness. Springs are met with when a porous soil is underlaid by a clay bed. The rain sinks at once through the upper stratum until it is arrested by the impervious bed beneath. There it accumulates and rises until it either wets the surface or, following the line of least resist- ance, bursts out at a lower level in the form of a spring. Springs are very commonly seen upon the sides of hills. The accompanying diagram (Fig. 1) shows the conditions under which springs often occur. A represents a porous stratum ; b represents a clay bed which obstructs the downward passage of water ; c D represents the level to which water will require to rise before it overflows in the form of a spring at d. In dry weather, when the “reservoir” or “water-table” sinks below the line C r>, the spring will be dry ; but on the return of wet weather it will again become active. These facts exert an important influence upon the practice of drainage. The drainage of porous soils is exceedingly simple. All they require is an outfall for their superabundant water. They are wet simply because the water they receive direct from the clouds, or from higher levels, cannot escape ; and when egress is given to this superfluous moisture, they at once take their place among naturally dry or drained soils. With clay soils the case is somewhat different. Not only must an outfall be given, but the whole bulk of the soil between the drains must be thoroughly aerated before their drainage is complete. Such soils hold the water which incommodes them with a tight grasp, and a much more close and complete system of under- ground channels, supplemented by steam or other deep cultiva- tion, is necessary before the same effect is produced as in the case of lighter soils. Thus, in light, porous soils the distance between the drains is sometimes as great as sixty yards, while in clay soils they are often placed only six yards apart. In order to understand the action of drains, it is necessary to bear in mind that in all wet soils there exists, at a greater or less distance from the surface, a something which prevents the escape of water ; that the effect of continued rain, or an ac- cession of water from other causes, tends to accumulate water upon this obstruction, thereby forming a “ water-table” or level of supersaturation ; and lastly, that above this supercharged level the soil is wet by capillary attraction, which lifts the water to a greater or less height according to its texture and condition. Before land can be thoroughly drained it is essential, not only to lower the “water-table,” but to so lower it that capillarity shall not so saturate the superimposed stratum as to render it injurious to growing vegetables. In our next paper we hope to still further elucidate this portion of our subject, and to point out the important action of capillary Attraction in the water economy of soils. BUILDING CONSTRUCTION. 79 BUILDING CONSTRUCTION.— III. FOUNDATIONS UNDER WATER. In our previous lessons on this subject we have insisted on the necessity that exists for procuring a good foundation for build- ings of all kinds, and have explained the methods of effecting this by the employment of concrete and piles in soft soil of any description. We now pass to the mode of making foundations under water. Foundations under water are constructed in various ways. The most ancient, and certainly the most simple, is that called by the French “ pierre perdue ” (or lost stones). This method consists in shooting rough stones, etc.,, into the water, and leaving them to settle themselves as they happen to fall. When the heap rises to the surface, it is levelled, and the superstructure raised upon it. This system has been used principally for the erection of piers* and breakwaters, but is not adapted for structures of a permanent character, as light- houses, being erected upon it, as the external portions are liable to be washed away, and therefore the mound requires frequent repair. Nor do the stones always fall exactly within the prescribed area, but may reach a greater distance than was intended. The system is, therefore, not adapted for river works, where any narrowing of the water-way for vessels is of consequence. A breakwater is a barrier intended for the protection of shipping in harbours or anchorages, by breaking the force of the waders as the mighty waves roll towards the shore. Some- times a small island is situated opposite a bay, and thus forms a natural breakwater. This is in some degree the case with the Isle of Wight, which occupies such a position as to protect Portsmouth and Southampton. The Plymouth breakwater (Fig. 1), built by John Rennie,* is the best known of these constructions. The Sound, or harbour, being open to the south, was so much exposed to storms, that early in the present century it was determined to erect a breakwater across it, with openings on either side between it and the shore to allow of the passage of vessels. The works were commenced in 1812, by transporting along a tramroad large blocks of limestone from a neighbouring quarry. These were then carried by vessels fitted with trap-doors, and were thus deposited on the required spot. The good effect of the mound was felt as soon as it began to rise above the surface, but the great storm in November, 1824, threw a large quantity of the stones over into the Sound, and it was not until 1841 that the works were finally completed by the deposition of more than 3,000,000 tons of stone, and the ex- penditure of =£1,300,000. The breakwater is nearly a mile long. The central portion is 1,000 yards, and two wings, of 330 yards each, extend from the ends of this at a slight angle. The open channels at each end, between the breakwater and the shore, are each about half a mile wide, and their depth is respectively 40 feet and 22 feet at low water. The breakwater is 133 yards wide at the base, and 15 yards at the top, the two * Jolm Rennie was born at Phantassie, in East Lothian, in 1761. His early education was obtained in the parish school of East Linton, and he subsequently learned mathematics at Dunbar. He was for some time a workman in the employ of Mr. Andrew Meikle, an ingenious Scotch mechanic, who in 1787 invented the threshing machine. After attending various lectures on Natural Philosophy and Chemistry, he was taken into the employ of Messrs. Boulton and Watt, near Birmingham, and soon displayed such mechanical genius that Watt, in 1789, entrusted him with the direction of the construction and fitting up of the Albion Mills, London. His improvements in millwork were so striking that he at once rose into general notice as an engineer of great promise, and the thorough efficiency of his work- manship greatly contributed to his fame. To this branch of engineering he added, in 1799, another — the construction of bridges ; and, amongst numerous others, he huilt Waterloo and Southwark bridges over the Thames, the latter built of cast-iron arch girders resting on stone piers. He also drew up the plans for London Bridge, which was not, how- ever, commenced until after his death. In addition to numerous bridges, the London Docks, the East and West India Docks at Blackwall, with their goods sheds, the Hull Docks, the Prince’s Docks, Liverpool, and those of Dublin, were all designed and wholly or partially executed under his superintendence. Besides the Plymouth Breakwater, Rennie planned many improvements in harbours and dockyards in Portsmouth, Chatham, and Sheerness. He died in October, 1821, and was buried in St. Paul's Cathedral. sides being made very sloping for the security of the stones ; the slopes and top are faced with masonry. The water-space or area forming Plymouth Sound, which is protected by this breakwater, comprises 1,120 acres. There are breakwaters at Holyhead, Portland, and Dover, but the limits of the present lessons preclude descriptions of them. The above description of the Plymouth breakwater will therefore serve as an illustration of the system of “ pierre perdue” or “random” foundation. In some cases blocks of bHon have been used with success. Foundations under water are sometimes laid in coffer-dams. This is done by driving parallel rows of piling around the site on which the pier is to be built ; these piles are kept in their places by horizontal timbers, so as to form a coffer or strong box around the site. The space between the parallel rows of piling is filled with clay, puddle, etc., well rammed down, so as to render the wall thus formed water-tight ; this is one of the principal difficulties in the system, whilst another presents itself in the pressure of the water on the outside, which is resisted by struts placed inside the coffer-dam, extending from side to side. When the coffer-dam takes the form of a wall, and is intended to keep out the water during the building of a wharf, quay, etc., the struts are placed obliquely, and act as buttresses. When the structure is deemed satisfactory, the water is pumped out of the enclosed space, the bottom of which is then excavated and levelled until a solid stratum be reached, or, if there be any difficulty in doing this, a bed of concrete or beton is laid down. If solid ground is not found within available depth, the plan adopted is to drive piles a few feet apart all over the area. These are then surrounded by sheet-piling, to prevent the soft soil escaping. Stones, concrete, etc., are then rammed in between the piles ; the heads of the piles are cut off at one level; sleepers are laid across and fastened to them, and on these massive planking of great thickness is placed, on which the building is erected. Before the application of steam power to pumping, this system was very expensive, and another was introduced into this country by a Swiss architect, named Labelye, and was first used in the erection of old Westminster Bridge, which was com- menced in 1739. The method adopted by Labelye (which, however, did not prove a good one) was the using of a caisson, or large water- tight chest (the word “ caisson” meaning a large box or caisse). The bed of the stream was first carefully levelled by dredging. Strong frames of timber were then constructed, having upright sides like those of a box. These were floated over the place where the piers were to be built, and the masonry of each pier was commenced inside the caissons. When the first course was laid and cramped together, water was admitted by sluices into the caisson, which then sank. The bottom was not, however, found to be sufficiently level ; the sluices were there- fore closed, the water was pumped out of the caisson, and it was floated again. The ground was then again dredged and levelled, and this operation was performed three times before the mass of stone settled on a level bed. The pier was then built on this foundation, after which the sides of the caisson were removed and used for the next pier. Blackfriars Bridge, erected in 1760, was also built by caissons. In both these cases, however, the foundations proved failures, and both of the bridges have been removed, and that at Westminster is replaced by the elegant structure designed by Mr. Page, completed in 1862 ; and the new Blackfriars Bridge was, it will be re- membered, opened by Her Majesty in person on the 6th of November, 1869. Hitherto we have spoken of wooden piles, ana before pro- ceeding to mention those formed of iron, which are now so much used, it is deemed advisable to give the student some little information concerning piles and pile-driving. The piles, then, are squared beams of timber pointed at the bottom. The timber used for this purpose is oak, beech, fir, and larch. The piles are bound at the top by strong iron hoops, in order to prevent their being split by the force of the blows which drive them down ; they are also protected at the bottom by iron shoes. When the piles are to be placed singly, the point is pyramidical, that is, cut to a square point (Fig. 2) ; but for sheet- piling the ends are cut flat (Fig. 3), so as to present an edge 80 THE TECHNICAL EDUCATOR rather than a point, and this edge, too, is a little slanting, that is, the triangular face is a little longer at one side than the other. (This has already been referred to in lessons in “ Tech- nical Drawing,” but is here repeated in order to render the instruction as clear as possible.) The purpose of this is, that as the pile is being driven down, it will have the tendency towards the last pile which has been driven, and so a closer wall of piles will be formed. When sheet-piling is constructed, one pile is placed at each end of the required width, and a few others at intervals. These are called guide piles, and to these horizontal timbers are attached, called wales, which guide the rest of the piles, so that they may be placed in a straight line. Piles are forced into the ground by pile-drivers or engines. The subject of these lessons precludes any lengthened de- scription of such machines ; it will be sufficient to say that a pile-driver consists of vertical guide-bars, between which a weight called the “monkey” is drawn up, either by a number of men or by steam power, and is suddenly released, when its weight descends like a huge hammer on the head of the pile, which in this way is driven into the soil. Nasmyth’s steam pile-driver consists of Fig. 1. ends of these cylinders the platform of girders and planking is constructed. The screw-piles, introduced by Mr. Mitchell, are admirably adapted for loose, movable, and even sandy soils, and have been found very useful in situations where all other means have failed. These piles are of wrought iron and are hollow, and terminate at their lower end in screws of various shapes (see Figs. 4 and 5). They are screwed down into the bed of the river or the bottom of the sea until the pile is firmly fixed ; their heads are then connected by sleepers, and the superstructure raised upon the base thus formed. The lighthouse on the Chapman Sand, in the mouth of the Thames, is built on such piles seven inches in diameter and about forty feet long ; the blade of the screw, which is of cast iron, is four. feet in diameter. They are screwed down to the depth of about thirty-seven feet ; on their heads iron girders, braces, etc., are bolted ; and on these the lighthouse, which is entirely of wrought iron, is erected. The piles are seven in number, one driven in the centre, and the others at equal distances around it. The plan which was adopted by Mr. Page, C.E., for getting in the piles of the new bridge designed by him at Westminster, described by Mr. AShpital, a guide-bar, with the required machinery for hoisting the hammer, etc. This hammer is an important application of Nasmyth’s steam-hammer. The “ monkey” is attached to the piston-rod, working, as in the steam-hammer, downwards from the cylinders ; it acts in an iron guide-bar, resting on the top of the pile which is being driven, the steam being led from the boiler to the cylinder by jointed pipes, which allow of the motion as the pipe sinks. Another important pile - driver, which was first used in the construction of St. Katherine’s Docks, Lon- don, is the atmospheric engine, which is worked by an air-pump and a steam-engine. We shall have an opportunity of entering at greater length into the con- struction of these important engines in another series of lessons, and at the same time give some illustrations of them. When piles have only been used for a temporary purpose they are either cut off at the level of the ground or are drawn up ; the latter plan, however, must always be adopted with great care, lest the vacuum caused by the withdrawal of them should weaken the foundation. Piles of cast iron were first employed in the construction of Bridlington harbour. The piles used in this work were formed of plates of iron, so contrived at the sides that each pile was united by a dove-tailed joint with the adjoining one. In 1822 Mr. Ewart took out a patent for iron piling, and the success of those employed by him emboldened others ; eventually cylindrical iron piles were introduced, and are now largely employed. These vary, according to the nature of the work, from three to seven feet in diameter. They are first lowered into the water, and driven as far as they will go without great difficulty into the ground ; a quantity of clay is then placed around the outside of them, for the purpose of preventing the water forcing its way underneath the bottom. The water is pumped from the inside, and the workmen then descend into the cylinder and dig away the soil, which they send up in buckets, thus literally undermining the cylinder, which then sinks either by its own weight or by additional pressure. The pile is formed of parts, and at the top of the first part are flanges, which also exist at both ends of the other section. As one part sinks, another is bolted on to it, until the required depth is reached. On the - 2 ' 0 " so novel and important that no course of lessons could be deemed complete without a slight description of it. Bows of strong elm piles, about thirty feet long, are driven into the bed of the river, passing first through the gravel, which is about four or five feet thick, and then going about twenty feet into the London clay. There are about 140 or 150 piles to each pier, ranged alternately in threes and fives ; around these a range of cast-iron piles is driven, about four feet apart. These are round, fifteen inches in diameter, and have strong grooves cast on each side of them ; they, how- ever, go into the clay only ten or twelve feet. Into these grooves large plates of iron, which the engineer calls “ plate piles,” are fitted, and driven down between the piles ; they go about ten feet into the blue clay, and extend about a foot or two above the natural bed of gravel. Upon these is a series of slabs of granite, placed edgewise, retained in their places in the following manner : — The bottom rests on the plate-piles, the edges are secured to the round iron piles, and the tops to the other masonry ; the plate-piles are secured together by two sets of ranges of iron rods, passing through the pier and tying them together ; these are all fixed by the divers. It will be seen, therefore, a sort of case or box is made, which surrounds the wooden piles on all sides ; the loose standing mud is then dredged out, and the case filled up solid with hydraulic concrete, in which, of course, the piles are embedded, and the whole forms one solid mass to about a foot above low-water mark. At this level the tops of the piles are cut off, and on each top a stone, 2 feet square, and 1 J> feet thick, is bedded, the spaces between which are again filled in with concrete. The gravel is then dredged out around the pier on the outside of the case, and the space also filled with concrete. It has been urged that the steamers would come into collision with the round piles, and break them so that the granite slabs will escape, as it were, and fall into the river. This, however, cannot be as long as the concrete remains in its place, as the top of the slab is secured by the masonry, and the bottom would not be accessible. It is, however, intended to protect the piles by floating booms, which will prevent the chance of collision, and will act as safeguards for the steamers as well as tho bridge. 4'0"- THE STEAM-ENGINE. 81 THE STEAM-ENGINE.— I. By J. M. Wigner, B.A. PRIME MOYERS SOURCE OE THE POWER — MECHANICAL EQUIVALENT OE HEAT PROPERTIES OP STEAM — THE BOILER — WAGON, CORNISH, ELUE, AND TUBULAR BOILERS SUPERHEATER. In early times the advance of civilisation rendered the employ- ment of machinery almost a necessity, and the need of some prime mover, other than the power of man, soon began to be felt. The force of the wind, and the power developed in running streams, would be the first to suggest themselves, and were early employed. A great inconvenience, however, attended the use of these agents, as they were uncertain and irregular in their action. A long-continued drought would so far reduce the level of many streams, that any hydraulio contrivances which had been set in motion by them would stand idle and useless, however much they might be needed. The uncertainty of the wind was also pro- verbially great, and a calm might occur just at the time when the machinery was required to act. The power of ani- mals was, of course, in these cases, turned to account; but here again in- convenience and difficulty were ex- perienced. The ani- mals had to be fed and tended whether any work were re- quired or not — thus entailing con- stant expense. At- tention was, there- fore, very naturally turned to the dis- covery of some source of power which should be certain and uni- form in its action, well under control, and, withal, economical in its employment. The power which has up to the present time most perfectly succeeded in carry- ing out these various conditions is that of Steam. Many other prime movers — among which may be mentioned Electricity, Heated Air, and Gas — have at various times been suggested, and tried with varying degrees of success. None of them have as yet exceeded, or even equalled, the force of Steam; but it is the opinion of many who are best competent to form a judgment on such a subject, that some of these will ulti- mately take the place that steam now occupies, and that the steam-engine will thus become among the things of the past. Be this as it may, the undoubted fact is that in the present day steam is all but universally adopted as the moving power in all our factories, large and small ; and there is scarcely any article that we employ in our daily life, but in some stage or stages of its manufacture has been operated upon by its agency. Even before the Christian era the attempt was made by Hero, the well-known philosopher of Alexandria, to drive an engine by the power of steam issuing from two small apertures, much in the same way as the hydraulio machine, known as Barker’s .Mill, is set in motion by the reaction of the water as it issues from openings in the two arms. A scientific toy, acting on precisely the same principle, was a short time since brought out by the London Stereoscopic Com- pany, under the title of “The Little Marvel” steam-engine, and was sold in large numbers. It would be very interesting and instructive to trace the gradual development of the steam-engine from this, its earliest germ, down to the present time, but this would be foreign to the scope of the present papers, which is to furnish a practical description of its construction and action. We must, however, pay a passing tribute to James Watt, to whom more is due than to any other of the almost numberless engineers who have made or suggested improvements. In fact, we may say that, in most of its essential features, the steam-engine of the present day is the same as completed and perfected by Watt. We must first inquire into the actual source of the power produced by the steam-engine ; for it must be carefully remembered that no machine can create force — all that it can do is to control or modify its action. The source of the power, then, must be sought for in the fuel consumed in the furnace. As was explained in our lessons on Heat in The Popular Educator, heat and force are to a certain extent mutually convertible. Illustrations of the conversion of force into heat are familiar to al- most every one. We have a practical ex- emplification of it every time we strike a luoifer match, and, by the friction, generate sufficient heat to ignite the inflammable com- pound with which it is tipped. We are not, however, so familiar with the fact that heat may be converted into mechanical force. Such, however, is - the case ; and as the result of a long * series of experi- ments, very care- fully conducted by Dr. Joule and others, we learn that the amount of heat required to raise 1 lb. of water 1° Eahr., is sufficient to exert a mechanical force equal to raising a weight of 770 pounds to a height of one foot. Every pound of coal or other combustible consumed in a furnace is capable of performing a certain definite amount of work, and tlm steam-engine may therefore ba defined as “a machine in which the motive power of heat is utilised and made to accomplish any desired work.” The problem to be solved is to discover in what manner the largest portion of this heat may be rendered available, and most of the im- provements made in its construction have this as their aim. At present, however, we cannot consider this problem as by any means satisfactorily disposed of, for, even in our best con- structed machines, the actual work accomplished is seldom, if ever, more than one-eighth of the theoretical amount, and in the large majority of cases it falls considerably below even this. This subject is, of course, one which demands and has obtained much attention from practical men. One great cause of the waste appears to be that the extremes of temperature in the boiler and condenser are not sufficiently removed from one another. The greater this interval, the greater is the power obtained ; in the engine, however, it is seldom above 200° ; for although the temperature in parts of the furnace is frequently 3,000°, that of the steam is seldom much above 300° or 350°, there being practical difficulties in the way of employing it at a higher temperature. If we take a vessel of water, and apply heat to it, the tem- VOL. i. 6 THE TECHNICAL EDUCATOR. «2 perature will gradually rise till it reaches 212°. At this point, if the vessel be an open one, it becomes stationary, and bubbles of invisible vapour, or steam, are formed at the surface exposed to the source of heat. These rise through the liquid, causing ebul- lition, and then escape into the air, where they soon become par- tially condensed, and are thus rendered visible. If the water be contained in a close vessel, the pressure of the steam generated gradually increases, until at last, if no escape be provided, it bursts the vessel. By allowing the steam to enter an empty vessel, we find that it occupies a very large space as compared with the water from which it is produced, the increase in bulk being rather more than 1,700 times. As an easy mode of remembering this, we may state it thus A cubic inch of water, when converted into steam at the ordinary pressure of the atmosphere (15 lb. per square inch), occupies the space of a cubic foot. If the pressure be increased, the volume will be diminished in a corre- sponding degree ; thus the steam produced from a cubic inch of water will only occupy half a cubic foot when at a pressure of two atmospheres. On removing this pressure, it will at once expand. We see, then, that dry steam — that is, steam when above the point at which it is condensed— possesses the proper- ties of an elastic gas, and it is to these properties, and to its great increase in bulk compared with that of the water from which it is generated, that we owe its employment in the engine. It may be well here, as a caution, just to remind the student that true steam is an invisible gas. That which we see issuing from the funnel of an engine or the spout of a kettle, is in reality partially condensed steam, that is, minutely divided particles of water suspended in the air. We must not imagine that it is sufficient merely to raise the water in the boiler to a temperature of 212°, and that then it will at once be converted into steam. Were this the case, no vessel would be strong enough to withstand the sudden pressure thus produced, for the water would, on attaining the boiling- point, explode with a violence almost equal to that of gun- powder. The real fact is, that a large amount of heat is ab- sorbed in the conversion of water into steam. If we take any vessel containing water at a temperature of 32° — that is,, just at the freezing-point — and having placed a thermometer in it, expose it to a uniform source of heat, we can easily ascertain the exact time it requires to attain the boiling-point. Now let the heat continue uniform, the water will slowly boil away and be converted into steam, and we shall find that about five and a-half time 3 as long is required to evaporate all the water as was taken to raise it from the freezing to the boiling point. The temperature of the steam has, however, at no time exceeded 2 1 2' b ; it is clear, therefore, that this additional quantity of heat has all been stored up or rendered latent in the steam. This may easily be proved. If we close the vessel, and allow the steam to pas3 along a pipe into another vessel filled with ice-cold water, we shall find that it has sufficient heat in it to raise five and a-half times its own weight of water to the boiling-point. Having in this way just explained the more important pro- perties of steam, so far as they relate to the engine, we must proceed practically to explain the mechanism and action of the different varieties of engine generally employed. To do this, the simplest plan will be first of all to explain in detail the construction of some one form, which may, to a certain extent, be regarded as a typical form, and then to trace the various deviations from this, which are rendered necessary by the different requirements of each particular case. The engine which we shall select for this detailed description is that techni- cally known as a Double-acting, Condensing, Beam Engine ; the meaning of these terms has been explained in the papers on this subject which have already appeared in The Popular Educa- tor, and will shortly become more apparent. From what has been said, it is clear that the first requisite is a vessel an which the water may be contained for conversion into steam. This is technically known as the boiler, and must j of necessity be so made as to be water-tight, and of sufficient j strength to resist the outward pressure of the steam. It must, j further, have such a form, that heat may be easily and eco- , nomically applied to it. The construction of the furnace is thus intimately connected with that of the boiler, and, as we shall see, the utmost variety exists in the forms given to the two The object sought is the means of generating the largest amount of steam with the smallest expenditure of fuel ; economy of space is also in many cases an important requisite, and hence the form given to the boiler depends partly upon the special exigencies of the case. There are three main classes of boilers, viz., land, marine, and locomotive boilers. The two first- named are stationary, being usually firmly fixed in the position they are intended permanently to occupy. Space is usually more valuable in marine boilers, and hence special arrange- ments have to be made, even at the expense of m increased expenditure of fuel in proportion to the work accomplished. At the present time, however, the construction of land boilers is, in many respects, becoming more closely assimilated to that of those intended for marine use. The form known as the “ wagon” boiler, and represented in Fig. 1, was introduced by Watt, and for a long time was re- garded as a standard form. It has, however, gradually been falling into disuse. Perhaps that most generally employed in the present day is the “ Cornish ” boiler, a section of which is shown in Fig. 2. It consists of a cylindrical shell, usually made with flat ends, and has one or two large internal circular flues, in which the furnaces are placed; the hot air, having passed along these, returns by flues made in the surrounding brickwork at the sides or bottom. The cylindrical form is much better calcu- lated to resist the strong internal pressure to which boilers are subjected. In other forms strong internal stays are nearly always introduced, to impart additional strength. The internal flues are firmly riveted to the ends, and materially add to the strength of the boiler. There are some objections to this form, the main ones being that the space for the furnaces is rather limited, and a sufficient slope cannot well be given to the bars. The tubes, too, unless carefully strengthened, will sometimes collapse from the pres- sure; but these difficulties may be overcome, and the boiler is reckoned one of the best for ordinary circumstances. The plan of allowing the flame and heated gases from the furnace to play outside tubes containing the water, instead of passing through tubes filled with it, has been adopted in many instances with beneficial results. An application of this prin- ciple has been patented by Messrs. Galloway, and been con- siderably employed. Conical tubes are made to pass right through the central flues, beyond the combustion-chamber and the fire-bridge, on the plan shown in Fig. 3, which represents an ordinary Cornish boiler with these tubes, which are known as “ Galloway Tubes,” fitted to it. Owing to their conical form, the flange at the lower end will pass through the opening in the upper side of the flue, and thus save much trouble in the fixing. They are found to serve as a support to the flues, rendering them much less liable to collapse, and at the same time they afford increased and very effective heating surface, and improve the circulation of the water in the boiler. This latter is found to be a very important point. When two furnaces exist, they are usually fired alternately, and in this way the production of smoke is found to be considerably lessenedi The boilers employed for the earlier marine engines were of the class known as flue boilers, and they attained a high degree of efficiency. In these the flues were wholly internal, so that they were surrounded on all sides by a thin layer of water, and the products of combustion were thus made to circulate through the boiler before escaping into the chimney. As will easily be understood, the great object required to be obtained is to absorb as much as possible of the heat, without rendering the draught too feeble. When the heated air escapes into the chimney at a very high temperature, there is, of course, a corresponding waste of heat ; the object, therefore, in having these long flues is to enable the water in the boilers to take up as much heat as possible. It will easily be seen that when the flues are internal, that portion of heat which is usually absorbed by the brickwork, and which is by no means incon- siderable in quantity, is saved. A tubular boiler is, however, now nearly always employed in marine engines. In this the heated products from the furnace, instead of passing along one large flue, are broken up into a number of small streams, which pass through a series of tubes, and thus give up nearly all their heat to the water. In this way it is found that a great economy of space is effected, the heat being much more rapidly abstracted from these small streams. Sometimes multi-tubular boilers are constructed on a BIOGRAPHICAL SKETCHES OF | plan very similar to the Cornish boiler already figured. The front part of the flue is fitted with a sloping grate, and serves as a combustion-chamber, which extends only part of the length of the boiler ; at the back of this is placed the fire-bridge, ; against which the flames first impinge. The rest of the flue is replaced by a series of small tubes about two and a-half inches internal diameter. These are, of course, firmly fixed into a tube-plate at each end, so as to render the joints water-tight. A packing of wood is often introduced for this purpose. Care must be taken not to place the tubes so close together [ as to impede the circulation of water, as it has sometimes been found that the additional heating surface thus attained is more than counterbalanced by the impaired circulation ; in these cases an increased production of steam has been caused by removing a few of the tubes. With a boiler of this form a return flue is usually unneces- sary, and the smoke is allowed to pass directly into the chimney ; much of the cost and labour of setting in brickwork is therefore dispensed with. Another form of boiler, now very frequently employed in steam-vessels, is represented in Pig. 4. In this the furnace passes from end to end of the boilers, and the tubes are placed above it, so that the smoke passes back again along the boiler before escaping into the chimney. A is the furnace-door, b b the fire-bars, which slope away from the front, so that the fuel gradually passes along to the further end, as fresh is sup- plied in front. In this way the smoke produced, when the furnace is coaled, has to pass over the surface of the highly incandescent fuel at the further end before it reaches the flues, and thus it is to a considerable extent consumed. The gases then strike against the fire-bridge, E, and pass into the space d. From this they travel along the horizontal tubes till they escape into the flue, f. In this way there is but little waste of heat : even the ash-pit, c, is, as will be seen by the figure, within the boiler, so that the heat from it is not wasted. The tubes in this boiler are, it will be observed, entirely surrounded by water. Sometimes another set is placed above these, so as to be in the steam space, and these serve to raise the temperature of the steam, and thus render it more perfectly dry. This second set is technically known as the “ superheater.” Steam in most of its properties resembles a gas, and, like any gas, expands on the application of heat to it. If, then, the steam be exposed to a higher temperature, either its volume J or its pressure will be increased, and a greater mechanical j effect may therefore be obtained from it. Another advantage is also obtained by superheating the steam. Under ordinary circumstances, when the steam is not at a very high temperature, it is partly condensed by contact with the cylinder and other I working parti j and hence there is a deposit of water in them, and a corresponding loss of power. By superheating the steam this is guarded against. A few years ago the tendency was to superheat the steam as much as possible. It is found, however, that if its temperature be raised above 315°, the packing of the stuffing-boxes is liable to become charred, and the oil or other lubricant used in the engine to be injured. The practice, therefore, seems to be gradually diminishing, and is ; not usually carried much beyond the degree that is requisite to render the steam thoroughly dry. Very many different forms of superheater have been pro- posed, and tried with varying degrees of success. The usual plan is to cause the steam to pass through a series of tubes placed at the lower part of the chimney, so that the heat employed is that which would otherwise escape with the smoke. It is not found that when fresh fuel has to be employed, any * advantage is gained by employing it in superheating the steam, ' instead of applying it to the boiler in the ordinary manner. I — BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS. III.— EOBERT STEVENSON, ENGINEEE. BY JAMES GRANT. Robert Stevenson, the creator of the modern lighthouse | system in Scotland, the great engineer by whose skill and I courage that wonderful structure on the Bell Rock was erected, was born on the 8th of June, 1772, in the city of Glasgow, where EMINENT INVENTORS, ETC. his father, Allan Stevenson, was a merchant connected with St. Christopher s. By the death of that parent, when on a visit there, Robert Stevenson was left fatherless at an early age, amid many pecuniary difficulties, on the care of his mother] Jane Lillie, who, with the ambition so usual with the Scottish matrons of the middle and humbler classes, designed her boy for the Church ; but, ere his fifteenth year, she had contracted a second marriage with Mr. Thomas Smith, a tinsmith of Edin- burgh, a man whose mind was far in advance of his station, and whose studies were devoted to the construction of lighthouses and beacons — a department of engineering in which he had the merit of substituting for the open coal fire and grates pre- viously used, lamps fed with oil and furnished with parabolic reflectors. This matrimonial alliance caused a change in the prospects of young Stevenson, who threw aside his Latin, Greek, and Hebrew, and devoted all his energies to the views and plans of his stepfather, by whom, so early as his nineteenth year, he was entrusted with the erection of a lighthouse on one of the Cumbrae Isles in the Firth of Clyde — a commission ordered by the Trustees of the River Navigation; and, pleased with the skill he evinced, Smith soon after took him as a partner in his business. In 1799 he married a daughter of Mr. Smith, whom he succeeded as Superintendent of Scottish Lighthouses, an office which he resigned as lately as 1843. During the progress of the work at the Cumbrae, he attended the lectures of the Andersonian University of Glasgow, and mastered the mathe- matical and mechanical sciences necessary for success in his new profession ; in this having the good fortune to obtain for a preceptor, Dr. Anderson, the founder of the institution. His next work was the erection of a lighthouse on the dangerous P entland Skerries in Orkney, and the close of every summer's work found him studying hard at the University of Edinburgh, where he rapidly passed through a curriculum that included mathematics, natural and moral philosophy, chemistry, natural history, logic, and agriculture. He was a striking example of the hard, resolute, and persevering Scottish student, and ere long he beeame a most accomplished and scientific scholar. He made his first tour of inspection as Superintendent of Light- houses in 1797, and during his term of office he erected no less than twenty-three of these edifices in the far Northern Isles, many of them being constructed in perilous situations, the difficulties of which, by land and water, could alone be over- come by the most anxious thought, courage, and scientific care. In 1824 he published an account of the most durable monu- ment of his high attainments and success — the erection of the lighthouse on the Bell Rock, a dangerous and sunken reef of red sandstone, near the mouth of the Firth of Tay, in west longitude from Greenwich 2° 22', and in north latitude 56° 29'. In ancient times it was named the Inch Cape, and thereon in the Middle Ages an abbot of St. Mary’s of Arbroath hung a bell, which was rung by the waves and wind, as a warning to sea- men ; and this bell is said to have been spitefully destroyed by a famous rover, named Sir Ralph, whose ship perished on the fatal reef a year and a day thereafter. So much for Southey’a ballad and old Scottish tradition ; but every winter saw many vessels cast away there, and among others, in the great storm of December, 1799, H.M.S. York, of 74 guns, when running for the Forth, foundered thereon, and every man onboard perished. The wreck alone survived to tell their story. This catastrophe made the outcry for a lighthouse general, and that on the Eddystone was proposed as a model. But the obstacles to be overcome in this instance were greater than in those of the former, which occupies a reef barely covered by the tide at flow, while the Bell Rock was barely uncovered at its lowest ebb. The Trinity House at Leith (a humane endow- ment of Mary of Guise, Queen Regent of Scotland) had erected no less than three great beacons on the rock ; but these the sea swept away in rapid succession. In the summer of 1800 it was visited by Robert Stevenson, who had modelled a pillar- formed lighthouse for the place, even before the loss of the York ; but he saw that it would prove unsuitable, though he deemed it quite practicable to erect a solid stone tower on the Eddystone plan, and his drawings for this purpose, with esti- mates for the expense, amounting to <£42,685 8s., were sub- mitted to the Lighthouse Board, and at once accepted. He procured a Prussian vessel of 82 tons — a prize taken during the war — as a habitation for his workmen, which ho 84 THE TECHNICAL EDUCATOR. named the Smeaton, in honour of the constructor of the Eddy- stone lighthouse, and prior to mooring her off the reef, he rounded both her stem and stern that she might ride more easily. She -was rigged with three masts, each surmounted by a copper lantern, while another vessel of 40 tons conveyed the stones from Aberdeen, where they were hewn in the granite quarries of Rubislaw, and also from Mylnefield, near Dundee. On the 12th of August, 1807, the foundation-stone was laid, and soon “ such was the clink of hammers, the hurrying of feet, and the din of human voices, which now invaded the solitude, that the affrighted seals, who had hitherto regarded the Bell Rock as their own exclusive property, went off in shoals in quest of new settlements.” The erection was a seven years’ task, beset by hourly diffi- culties, and an incessant struggle with the shifting elements. On one occasion the Smeaton broke from her moorings and was drifted into the German Sea, leaving Robert Stevenson with thirty-two workmen on the desolate rock, which by the flowing tide would soon be submerged to the depth of twelve feet, while the two boats they had would not have carried off more than half their number. It was a perilous and terrible situation. Who were to go, and who were to be left to drown P Stevenson was not without hope that the drifting Smeaton might pcik up the boats if she came to leeward ; accordingly, he was on the point of haranguing his terrified men on the perils that menaced them, and urging them to be of good courage and put their trust in God. His idea was, that all should strip and cast away their clothes as an unnecessary incumbrance and additional weight, and that a specified number should cling to the gunwales in the water, while others rowed them all towards the .shore. But when he attempted to speak, his tongue was so parched by excitement and the saline atmosphere, that speech failed him ; however, at that critical juncture, there was a cry of “A boat! a boat!” and through the mist one was seen approaching. It proved to be the pilot craft with letters for the workmen, and all quitted the Bell Rock that evening, happy at escaping a too probable death ; but all were drenched to the neck by the surf. During the first season the Smeaton floating-light was Steven- son’s abode while the worn progressed ; many a hard gale he rode out in the old Prussian hulk, and many a night the adven- turous engineer endured all the horrors that precede a ship- wreck — of being blown adrift on the one hand, or dashed on the rock itself, as a sudden and final catastrophe, on the other. After a time he got a kind of “ pigeon-house,” as ha names it, built of logs, exposed, however, to the assault of every wave. In fine weather the breakers rolled sixteen feet high against it, while in gales the spray rose ninety feet above the sea- level. At four o’clock one evening, as Stevenson records, “ the water broke into the cook’s berth, when he rang the alarm-bell, and turned up all hands to attend to their personal safety. The floor was completely burst up by the force of the sea, while the whole of the deals and articles remaining on the floor Were swept away, such as the cast-iron mortar tubs, the iron hearth of the foi’ge ; the smith’s bellows and even his anvil were thrown down on the rock. Before the tide rose to its full height to-day, some of the artificers passed along the bridge into the lighthouse to observe the effect of the sea upon it, and they re- ported that they felt a slightly tremulous motion in the building when the great waves struck it in a certain direction about high- water mark. It was quite impossible for me to do anything for their relief, until the gale should pass off.” Amid such obstacles and enduring toils, the Bell Rock light- house was completed in December, 1810, and since then, far over the wild German Sea, night after night, its lamps have shone as a guiding-star ; while in the haze and snow, its great bell is heard to clang as in the days of the humane abbot of St. Mary’s, amid the dense atmosphere, a warning to seamen, and the means of saving many a human life. In July, 1814, it was visited by Sir Walter Scott, whose “Diary” records the pleasure and novelty he experienced on that occasion ; and when there he mote in the album some lines which Stevenson adopted as the motto for the title-page of the history of the undertaking. Stevenson next contemplated a lighthouse on the Skerry Vhor, in the Isle of Tiree, one of the Hebrides, a design after- wards carried out successfully by his son Allan, also a talented engineer, in 1842. Robert Stevenson always acknowledged that the Eddystone lighthouse suggested to him the more difficult erection on the sunken Bell Rock, while his plans of the jib and balance-cranes, and the changes he adopted in the masonry of the tower, in laying the floors so that the stones of each should form a portion of the outer wall — thus binding the whole mass together — were im- provements on the plans of Smeaton, whom he was ever proud to call “ his master.” The lamps were also an invention of Stevenson’s, being intermittent and flashing ; the former disap- pearing at irregular intervals, and the latter emitting a power- ful gleam every five seconds. For this he received no reward from his own country, or native sovereign, but the King of the Netherlands presented him with a gold medal. Ultimately, he made the system of the Scottish lighthouses so perfect, as to be a model to other maritime nations. He was a frequent co-operator with Rennie, Telford, and other great engineers of the time ; and after the peace of 1815, he was the principal adviser in the construction of all those new harbours, bridges, roads, canals, and railways, towards the formation of which Scottish energy and capital became suddenly directed ; and the new and beautiful approach to Edinburgh from the east, by the Calton Hill and Regent Bridge, was cut through the rocks under his immediate direction. He suggested the new form of suspension bridge applicable to small spans, avoiding tall piers ; and this form was partially adopted in the bridge over the Thames at Hammersmith. For a timber bridge at Meikle Ferry ne designed an arcff or a new construction. It was composed of thin layers of p .arm- ing bent into circular form, ana stiffened by ring-post-pieces, on which the level roadway rested , ana tms xorm is now ir. general use in the construction of railway bridges. He was author of many articles in the - Encyclopaedia Britannica,” in Sir David Brewster’s “ Edinburgh Encyclopae- dia,” and the old “ Scot’s Magazine,” etc. ; his professional con- tributions making altogether four good-sized quarto volumes. In 1815 he was made a Member of the Royal Society of Edinburgh, of the Geological Society of London, and of the "Wernerian and Antiquarian Societies of Scotland. In private life ho was universally esteemed as intelligent, kind, amiable, and benevolent, and he died universally regretted in his seventy-ninth year, at Baxter’s Place, Edinburgh, on the 12th of July, 1850. A bust of him was subsequently executed by Samuel Josephs, and, oddly enough, placed by the Commissioners of the Northern Lighthouses — where few indeed will care to visit it — in the library of the tower on the Bell Rock. PROJECTION.— V. TO PROJECT A PENTAGONAL PRISM. Let abode (Fig. 61) be the plan, and e 'l a, e' c , a' (Fig. 62) the elevation when one of the long faces, A B, is at right angles to the vertical plane. Fig. 63 is the elevation, looking directly at the point e. The mode of obtaining this elevation has been shown in Fig. 40. The upper end of the axis is shown at g in the centre of the plan,* and its position in the elevation is at / g. Now it will be remembered that the ends of a right prism are equal and similar planes, parallel to each other, f these ends being united by lines at right angles to their surfaces ; and it will therefore be evident, that projecting a prism is only re- peating the process of projecting a plane. Thus let it be required to draw the plan of the prism when resting on A B, its axis at 45° to the horizontal, and parallel to the vertical plane. It has already been shown that the axis is parallel to the edges of a prism ; consequently, as the axis is at 60°, so will be the edges. Therefore, place the line a a ^Fig. 64) at 45°, and on this line construct the elevation of Fig. 61 ; project the ends (Fig. 65) by dropping perpendiculars from the points in the elevation (Fig. 64), and intersecting these by horizontals from the * To find the centre of a regular polygon Bisect two of the angles of sides which adjoin each other, and the point where the bisecting lines meet will be the centre. t When the planes forming the ends of the prism are at right angles to the long sides (that is, so that if the prism stands on one of the ends, the long sides may he vertical)»it is called “a right prism.” When the planes of the ends are slanting to the length of the prism, it is called “ oblique.” In these lessons all prisms are assumed to he “ right,” unless otherwise expressed. PROJECTION. 85 called the apex. When the axis rises from the centre of the base, and is per- pendicular to it, the sides will be all equal trian- gles, and the solid is called a right pyramid. When the axis is not at right an- gles to the base, the pyramid is called “oblique.” When the upper part of a pyra- mid or cone is cut off, the solid is said to be “ truncated.” Fig. 68 is the plan, and Fig. 69 the elevation of a hexagons? the intersecting line, viz., Fig. 67; then perpendicu- lars drawn from the angles, in- tersected by ho- rizontals drawn from the corre- sponding points in the elevation, will give the pro- jection. OF PYRAMIDS. A pyramid is a solid which stands on a tri- angle, square, or polygon, and ter- minates in a point, all its sides being, therefore, triangles. The axis of a pyramid is the line joining the centre of the base to its summit, Fig. 64. Fig. 63. Fig. 61. corresponding points in the plan of Fig. 61. Unite the points of these two plans by lines representing the long edges of the prism, which will then be seen to be parallel to the vertical plane (Fig. 65). Fig. 66 shows the prism when the axis is at 45° to the hori- zontal, and 30° to the vertical plane. In- this figure it will only be necessary to place the plan of Fig. 65 at the re- quired angle with Fig Pig. 74 Fig Fi 86 THE TECHNICAL EDUCATOR pyramid when two sides of the plan, b c and E F, are at right angles to the vertical plane, and its axis vertical. Now let it be required to draw the plan of the pyramid when lying on the side bcg. The elevation (Fig. 70) will be precisely the same as in Fig. 69, altered only in position. It will be self-evident that if a pyramid stood on a plan, and, whilst resting on the line B C, it were gradually turned over until it should lie on one of its triangular faces, the widths f e, b c, and A i> would remain the same, notwithstanding the change of position ; for, supposing pieces of board were placed upright on the lines h h, the angles A, d would touch these “ wooden walls ” throughout the movement ; but this is not so with regard to the widths from e to c, and from f to b, which are altered according to the position of the plane of the base in relation to the hori- zontal plane. The points for the plan (Fig. 71) will therefore be found by producing the straight lines e c, f b in the plan, and intersecting them by perpendiculars from the corresponding points in the elevation. A line drawn from G in the plan parallel to the in- tersecting line, intersected by a perpendicular from g' in the elevation, will give g", which will be the plan of the apex. Fig. 72 is the projection of the pyramid when lying on one of its faces, with its axis at 45° to the vertical plane. In order to test the student’s comprehension of the foregoing lessons, this figure is left unlettered. It is now required to find the true shape of the section a d, H i (Fig. 69). It will be evident that, as a d in the elevation represents A d in the plan (Fig. 68), a d will be the width of the section at its base. Therefore, draw A d (Fig. 73), and erect a perpendicular at its centre. Make this perpendicular equal to a h, and draw a line through i parallel to A d. From £ (Fig. 69) draw a perpendicular cutting the radii f and e of the plan in l- Join h i, i A, h d. Then ad i li will be the plan of the section> or the view of it looking downward in the direction of the arrow. On each side of i, in the true section (Fig. 73), set off half the length of the line i li in the plan — viz., i' h'. Join h‘ a and %' d, which will complete the form of the section. The next step is to develop the covering of such a solid. It is hoped that, after the instructions already given, this will prove an easy task. From G in the plan (Fig. 68) draw a line, G j, perpendicular to f c, and equal to the height of the pyramid (^ g). Draw f j, c J, which represents the section which would be bounded by a diagonal of the base and two of the edges ( not sides ) of the pyramid. With j f as radius, describe an arc. (Fig. 74), and set off on it the lengths equal to the sides of the base. Join all these points to each other* and to j . On c b, or any other of the sides, construct a regular hexagon, which will complete the development of the pyramid and base. Bisect e f by the line. e , and on this line set off the height, e i, on the elevation (Fig. 69), and through i draw i h. Join these points to each other and to A, d ; this will give the section-line marked in the development. PROJECTION OF CIRCLES AND CYLINDERS. We now approach a branch of our subject which is of especial importance to engineers and metal plate-workers — namely, the projection of circles and cylinders, and their development. As, however, the previous lessons have gradually led up to this point, it is hoped that the student will have been so prepared for the subsequent studies that he will find but little difficulty in them. Fig. 75 is the front elevation of a circular plane ; and it will be seen that the plan of this is a mere line, A b, equal to the diameter of the circle. (The aperture in a child’s money-box is the plan of the penny which drops through it.) To prepare this disc for projection, divide its circumference into any num- ber of equal parts, as a e, e d, etc., and from the points a, e, d, etc., drop perpendiculars to cut the plan A B in the points simi- larly lettered. If now we rotate the disc so that its plan is at right angles to the intersecting line (Fig. 76), the elevation, too, will be a line, c c , equal to the diameter. To project this circle, transfer the points c, d, d, and E, e to plan A b (Fig. 76). Let it then be required to find the forms of elevations when the plane of the disc is at 60° and 30° to the vertical plane. Place the plan at each of these angles, as A b' and A b". Taking j A as a centre, describe arcs from the points in the plan to cut the plans A b' and A b" in c' d' e'. From each of these points draw perpendiculars, and from the points similarly lettered in the elevation draw horizontals. The intersections of these two sets of lines will give the points c, d, e, etc., through which the curve is to be drawn by hand in the first instance, but it may subsequently be inked by means of the French curve, or centres may be found from which parts of the ellipse may be struck. The principle on which the projection of a circle is founded having thus been shown, Fig. 77 gives a simplified method. Let it be required to draw the plan of a circle when resting on one end of a diameter which is parallel to the vertical plane, the surface being at 30° to the horizontal plane. The line A b, placed at 308 to the intersecting line, will then represent the elevation of the disc. From the centre of this line, with the radius of the circle it is intended to project, describe a semi- circle, and divide it into a number of equal parts, ae, ed, etc. From each of the points A, e, D, etc., draw lines meeting a b at right angles in the points c, d, d, e, e. Draw any fine parallel to the intersecting line, and draw perpendiculars to it from a and b ; then this line a' b' will be the plan of the diameter which is parallel to the vertical plane. The semicircle drawn on A b represents one-half of the disc lifted up until it is parallel to the vertical plane. The lines c c, D cl, and e e thus show the distance which each of these points in the circumference is from the diameter A b. Therefore, from e, e, c, d, d in the ele- vation draw perpendiculars passing through the plan of the diameter a' b' in e', d 1 , c', d' , e. From these points set off on the lines drawn through them, and on each side of a' b, the lengths e' e, d' d, c' c, etc., and through the points thus obtained the plan is to be drawn. Fig. 78 shows the mode of projecting a circle when its sur- face is at 30 Q to the horizontal, and one of its diameters at 45° to the vertical plane. Place ab at 45° to the intersecting line, and on it construct the plan by measurement from Fig. 77. This is best done by drawing a line, c c, at right angles to the diameter, a b, and on each side of the intersection marking off the distances e, e, d, d. By drawing lines through these points at right angles to A B, and making them the same length as in the plan of Fig. 77, the points for the present figure will be obtained. From these points in the plan draw perpendiculars, and from the points correspondingly lettered in the elevation of Fig. 77 draw horizontals, and the intersections will give the points through which the projection of the circle is to be drawn. MINERAL COMMERCIxiL PRODUCTS.— V. CALCAREOUS* SUBSTANCES. The metal calcium very readily oxidises and forms lime, which easily enters into combination with carbonic acid, forming car- bonate of lime (the base of limestone, chalk, marble, and calc-spar), and with sulphuric acid and water to form gypsum. Carbonate of lime in its various forms is a most abundant sub- stance, and of the most extensive use, whether in its native condition as stone for building, paving, statuary, and smelting, or in its preparations — mortars and cements, in glass-making, leather-dressing, bleaching, agriculture, and medicine. Common limestone is found in almost every geological forma- tion ; compact and often crystalline in the older rocks, but generally loose and more earthy in the newer. It is abundant in nearly all countries, in varying qualities and degrees of adaptation to its numerous uses. In England it chiefly occurs in the rocks of the Devonian and Carboniferous series — moun- tain limestone especially — and in the Liassic and Oolitic sys- tems. The dolomite or magnesian limestone belongs to the Permian group of rocks. The best kinds of limestones for building are those of Portland, Bath, Box, and Corsham, all of which are Oolitic, and the magnesian limestone of Notts and Yorkshire. The oolite of Bavaria furnishes a very fine litho- graphic stone ; these stones are also supplied from older rocks in Canada, and from France, Greece, and Portugal. Of ornamental limestones, those of South Devon are exten- sively worked. Some interesting varieties of the red, grey, and variegated marbles (so called) are obtained near Torquay. Many blocks are almost entirely formed of fossil corals, and * That is, having the nature of limestone. PRINCIPLES OF DESIGN. 87 known as madrepore marbles. The Carboniferous rocks of Derbyshire are rich in ornamental limestones, the chief varieties of which are the entrochal or encrinital marble, productal marble, and black marble. The former of the first two is built up of the stony fragments of stone-lilies (Encrinites) , whilst the latter is composed almost entirely of shells of the genus Producta. Other marbles of a like character are obtained in Staffordshire, Somersetshire, and Ireland. The Purbeck and Petworth marbles are limestones charged with the fossil shell Paludina, and hence are sometimes called paludinal marbles ; they belong to the Purbeck and Wealden series respectively, and were formerly used extensively in ecclesiastical architecture. The true marbles are altered limestones or dolomites. The finest is the pure white or statuary marble ; others are red or yellow in colour, and either pure or streaked. They are firm in texture, finely grained, and susceptible of a beautiful polish ; hence their use for ornamental purposes. Italy is pre-eminently a marble-producing country, and has of late years produced an average of 250,000 tons per annum of statuary marble. The best white marble is now obtained from Carrara, quarried in the Apennines where they approach the Mediterranean. India, Sicily, Spain, Ireland, the United States, and other countries also furnish it. Coral limestone belongs to this group of mineral products. It is a recent formation, and the rock is sometimes used as a building stone in the South Sea Islands. Great numbers of these islands, as well as numerous others in the Indian Ocean, are themselves natural coral structures. Coral reefs are abun- dant in tropical seas and the North Atlantic and Pacific Oceans. Marl, a mixture of clay with carbonate of lime, occurs as clay-marl, marl-clay, and shell-marl. It is procured from valleys which have formed the beds of lakes, and from the neighbourhood of existing lakes, and is useful as a manure. Calcareous sand, formed chiefly of crushed shells, and found on ancient and modern beaches, is also used in agriculture. Of such sand, 8,000,000 cubic feet are annually removed from the Cornish coast into the interior. The shelly deposits of the Crag formations, in the east of England, are similarly used. Gypsum is a very valuable mineral, occurring chiefly in the New Red Sandstone and in Tertiary deposits, but also among earlier rocks. It is abundant in England, Ireland, France, Canada, Nova Scotia, and in many other places. Gypsum forms the plaster of Paris, of such utility in building and modelling ; crystallised, it is met with in selenite, satin gypsum, and ala- baster. The use of this last, for statuary and ornamental work, dates from the remotest times of Etruscan art. Statuary ala- baster is obtained from the Miocene and Pliocene strata in Tuscany and in Egypt. Limes, stucooes, and cement, so indispensable in all building operations, are obtained from various carbonates. Pure car- bonates make rich limes, which are such as set only in dry air ; impure ones (with mixtures of clay) yield hydraulic limes, which possess the valuable property of setting in moist air, and even under water. The septaria or calcareous nodules in London clay, at Sheppey, those procured at Harwich, the cement stones of the Lias at Whitby, and of the Speeton Clay of Yorkshire, the Lower Lias Limestone, etc., furnish suitable limestone for hydraulic cements. SILICIOUS SUBSTANCES. Another very important mineral substance is silica, which is a combination of oxygen with the metalloid silicium or silicon. The purest examples of silica are rock-crystal, quartz, and flint. The colourless crystals, especially the so-called Brazilian pebble, are much used for lenses. Quartz, which, crystallised, constitutes several of the gems, is an important constituent of granitic rocks ; and, in the form of sand, it is the principal ingredient in all sandstones. Quartz, well powdered, is com- bined with fine clays in the manufacture of porcelain in China, as flint is also in this country. Flints are irregular masses of nearly pure silica, occurring in nodules distributed in layers, in the Chalk formation especially. Reduced to powder, they enter into the composition of china, porcelain, and glass ; and, whole, they furnish a rough building material. Sandstones are of very various composition and of different degrees of hardness. They consist of silicious sands, often mixed with other substances, all cemented together by means of carbonate of lime, oxide of iron, silica, or clay. They are of all geological ages, the oldest being usually the most compact. When hard and coarse-grained they are denominated grits. If pebbles very largely predominate, they are called conglome- rates, and these are either pudding stones with rounded pebbles, or breccia with angular fragments. The extremely hard and schistose grits are very useful for flag-paving. The best qualities of these are supplied from Forfarshire and Caithness. Millstones are obtained from the Millstone Grit of Newcastle, from Yorkshire, Belgium, France (especially at La Ferte), and Wurtemburg. They are also made from a silicious limestone near Paris, and out of lava at Andernacli. For building pur- poses, the finest sandstone is quarried at Craigleith and other localities in the Carboniferous formations of Scotland. Good stone is obtained from rocks of the same age in Durham, York- shire, Derbyshire, etc., and from Queen’s County and other parts of Ireland. Silicious sands are much in request in the arts, as in building for mortars, in moulding and casting, and in glass-making. The most valuable for the last-named purpose are procured from Senlis in France, from the Isle of Wight, Lynn Regis, Aylesbury, and Reigate. Rottenstone, found in Derbyshire and elsewhere, is a decomposed silicious limestone, and is used for polishing. Bath brick, Tripoli powder, the polishing powder from Bilin, in Bohemia, the Berg-meld of Sweden and America, and the French tellurine, are peculiar mealy forms of silica. IGNEOUS AND METAMORFHIC ROCKS. Granites, and their allied rocks, gneiss, mica-schist, and fel- stones, consist largely of silica. Their chief mineral consti- tuents are quartz, felspar, and mica (white, green, or black). Felspar is a silicate of alumina and potash, or, in the case of albite, the white felspar of Cornish granite, of alumina and soda. Mica is a silicate of lime and alumina or iron. Where hornblende, a dark-green silicate of lime and magnesia, has taken the place of mica, the stone is called syenite. These rocks assume a structure termed porphyritic — that is, they are composed of crystals embedded in an amorphous matrix — and are highly valued for ornamental purposes. These latter, and white granite, are obtained from Cornwall and Devon, red and grey granites from Aberdeen and Peterhead, and a very hard and dark variety from Guernsey, the Malvern Hills, and Leices- tershire. Granitic rocks are abundant in many parts of the world, Ireland, Norway and Sweden, India, and China among others ; and Egypt is famed for its syenite and red porphyritic felstone. They furnish a durable and highly polishable building material, particularly well suited for bridges, quays, and monu- mental works. The coloured varieties are eminently adapted for ornamental purposes. Mica is often found in large crystals, which can be split up into plates and used as glass. This is the material known as Siberian glass, from the country whence it is supplied. Talc is a similar mineral, and is employed in the porcelain and crayon manufactures : it forms, besides, the French chalk. Asbestos is a fibrous variety of hornblende. It can be woven into a fire-proof cloth, and is also made available in open gas stoves. PRINCIPLES OF DESIGN.— II. By Christopher Dresser, Pli.D., F.L.S., etc. EGYPTIAN ORNAMENT — GREEK ORNAMENT — EARLY CHRISTIAN SYMBOLISM. In my former article I observed that ornamental forms in many cases make utterance of truths which are so far hidden as to be imperceptible to the untutored, and this utterance was illustrated by reference to the Egyptian lotus, which spoke to those for whom it was intended of coining plenty, and thus became first looked for with pleasure, then reverenced, and finally worshipped as the abode or personification of a god. Egyptian ornament is so full of forms which have interesting significance that I cannot forbear giving one or two other illus- trations ; and of this I am sure, that not only does a knowledge of the intention of each form employed in a decorative scheme cause the beholder to receive a special amount of pleasure when viewing it, but also that without such knowledge no one can rightly judge of the nature of any ornamental work. There is a device in Egyptian ornament which the most casual observer cannot have failed to notice ; it is what is termed the “winged globe,” and consists of a small ball cr globe, imm^« 88 THE TECHNICAL EDUCATOR diately at the sides of which are two asps, and from which extend two wings, each wing being in length about five to eight times that of the diameter of the ball (Fig. 2). The drawing of this device is very grand. The force with which the wings are Museum library*, where several interesting works on Egyptian ornament may be seen ; from the “ Grammar of Ornament” by Mr. Owen Jones, the works on Egypt by Sir Gardiner Wilkinson ; and, especially, by a visit to the Egyptian Court of the Crystal delineated well represents the powerful character of the pro- tection which the kingdom of Egypt afforded, and which was symbolised by ta.o extended and overshadowing pinions. I know of few instances in which forms of an ornamental character have been com- bined in a manner either more quaint or more interesting than in the example before us. The composition presents a charm which few orna- ments do, and is worthy of careful consideration. But this ornament derives a very special and unusual interest when we consider its purpose, the blow which was once aimed at ita and the shock which its perpetuators must have received, upon finding it powerless to act as they had taught, if not be- lieved, it would. The priesthood in- structed the people that this was the symbol of protection, and that it so effectually appealed to the preserving spirits that no evil could enter where it was portrayed. With the view of giving a secure protection to the inmates of Egyptian dwellings, this device, or symbol of protection, was ordered to be placed on the lintel (the post over the door) of every house of the Egyp- tians, whether residence or temple. It was to nullify this symbol, and to show the vain character of the Egyptian gods, that Moses was commanded to have the blood, of the lamb slain at the passover, placed upon the lintel, in the very position of this winged globe. It was also enjoined as a further duty, that the blood be sprinkled on the door- post ; but this was merely a new duty, tending further to show that even in position as well as in nature this winged globe was powerless to secure protection. This device, then, is of special interest, both as a symbolic ornament, and as throwing light on Scripture history Besides the two ornamental forms mentioned, i.e., the lotus and the winged globe, we might notice many others also of great interest, but our space will not enable ue to do so : further in- formation may, however, be got from the South Kensington Palace at Sydenham, and by a careful perusal of the hand-bock to that court .f Much might also be said respecting Egyptian architecture, but on this we can say little ; yet, as the columns of the temples are of a very ornamental character, we may notice that in most cases they are formed of a bundle of papyrus stems bound together by thongs or straps — the heads of the plant forming the capital of the column, and the stems the shaft (Fig. 3). In some cases the lotus was substituted for the papyrus, £ and in other instances the palm leaf ; these modifications can be seen in the Egyp- tian Court at Sydenham with great advantage, and many varieties of form, resulting from the use of the one plant, as of the papyrus, may also be observed. We have here an op- portunity of noticing how the mode of building, how- ever simple or primitive in character, first em- ployed by a nation may become embodied in its ultimate architecture; for, undoubtedly, the rude houses first erected in Egypt were formed largely of bundles of the papyrus, which were gathered from the river side — for wood was rare in Egypt — and, ultimately, when buildings were formed of stone, an attempt was made at imi- tating in the new mate- rial the form which the old reeds presented. But mark, the imitation was no gross copy of the original work, but a well- considered and perfectly idealised work, having the true architectural qualities of a noble-look- ing and useful column. * Any person can have admission to the South Kensington Museum Art library and its Educational library, for a week, *by payment of sixpence. t A hand-book to each of the historic courts erected in the Sydenham Palace was prepared at the time the courts were built. These are still to be got in the literary department, in the north-east gallery of the building. They are all worthy of careful study. t The papyrus was the plant from which Egyptian paper was made. It was also the bulrush of the Scriptures, in which the infant Moses was found. PRINCIPLES OF DESIGN. 89 We must now pass from the ornament of the Egyptians to that of the Greeks, and here we meet with decorative forms having a different object and different aim from those already considered. Egyptian ornament was symbolical in character. Its individual forms had specific meanings — the purport of each shape being taught by the priests — but we find no such thing as symbolism in Greek decoration. The Greeks were a refined people, who sought not to express their power by their works so much as their refinement. Before the mental eye they always had a perfect ideal, and their most earnest efforts were made at the realisation of the perfections of the mental conception of absolute refine- ment. In one respect the Greeks resembled the Egyptians, for they rarely created new forms. When once a form became sacred to the Egyptians, it could not be altered ; but with the Greeks, while bound by no law, the love of old forms was great ; yet the Greeks did not seek simply to repro- duce what they had before created, for they Athens* (Fig. 5). The idea presented by this column is that of an energetic upward growth which has come in contact with some super-imposed mass, the weight of which presses upon the column from above, while the energy of the upward growth of the column causes it to appear fully equal to the task of supporting the superincum- bent structure. Mark this — that by pres- sure from above, or weight, the shaft of the column is distended, or bent out, about one- third of the distance from its base to its apex (just where this distension would occur, were the column formed of a slightly plastic material), and yet this distension of the shaft is not such as to give any idea of weakness, for the column appears to rise with the energy of such vigorous life, as to be more than able to bear the weight which it has to sustain. Mark also the singularly delicate curve of the capital of the column, which appears as a slightly plastic cushion intervening between the shaft and the superincumbent mass which it has to support. The delicacy and refine- laboured hard to improve and refine what they had before done, and even through succeeding centuries they worked at the refinement of simple forms and ornamental compositions, which have become characteristic of them as a people. The general expression of Greek art is that of refinement, and the manner in which the delicately cultivated taste of some of the Greeks is expressed by their ornaments is perfectly astonishing. One decorative device, which we term the Greek Anthemion, may be regarded as their principal ornament — (the original ornamental composition by one of my pupils, Fig. 4, consists primarily of three anthemions) — and the variety of refined forms in which it appears is most interesting. But it must not be thought that the Greek ornaments and architectural forms present nothing but refinement made manifest in form, for this is not the case. Great as is the refinement of some of these forms, we yet notice that they speak of more than the perfected taste of their producers, for they reveal to us this fact — that their creators had great knowledge of natural forces and the laws by which natural forces are governed. This becomes apparent in a marked degree when we inquire into the manner in which they arranged the proportion of the various parts of their works to the whole, and especially by a consideration of the subtle nature of the curves which they em- ployed both in architectural members and in deco- rative terms ; but into this matter we must not enter. Yet, by way of throwing some faint light upon the manner in which knowledge is em- bodied in Greek forms, I may refer to the Doric column, such as was employed In the Parthenon at Fig 5. ment of form presented by this capital is perhaps greater than that of any other with which we are acquainted. The same principle of life and energy coming in contact with resistance or pressure from above is constantly met with in the enrichments of Greek cornices and mouldings ; but having called attention to the fact, I must leave the student to observe and think upon these interesting facts for himself. Let me, however, say that there are few classic build- ings in England which will aid the learner in his researches ; there is now but little poetry in archi- tectural buildings, and but little refinement in the forms of the parts ; and, added to this, Greek art without Greek colouring is dead, being almost as the marble statue to the living form. For the purposes of my readers, the Greek Court at the Crystal Palace will be the best example for study. I might now review Roman ornament, and show that in the hour of pride the materials of which the works were formed were considered, rather than the shapes which they assumed ; and how we thus get little worthy of praise from the all-con- quering Romans — how the sunny climate and religious superstitions of the East called forth the gorgeous and beautiful developments of art which have existed, or still exist, with the Persians, Indians, Turks, Moors, Chinese, and Japanese ; but * A capital and portion of the shaft of one of these columns are to he seen in the British Museum Sculp- ture-room, and a cast of the same at the Crystal Palace, Sydenham. This Doric column is employed in the Greek Court of the Crystal Palace. 90 THE TECHNICAL EDUCATOR. I have not space to do so ; yet all the forms of ornament which these peoples have created are worthy of the most careful and exhaustive consideration, as they present art-qualities of the highest kind. I know of no ornament more intricately beauti- ful and mingled than the Persian — no geometrical strapwork, or systems of interlacing lines, so rich as those of the Moors (the Alhambraic) — no fabrics so gorgeous as those of India — none so quaintly harmonious as those of China ; and Japan can supply the world with the most beautiful domestic articles that we can anywhere procure. We must pass on, however, to what we may term Christian art, or that development of ornament which had its rise with the Christian religion, and has associated itself in a special manner with Christianity. Neither the Egyptians nor early Greeks appear to have used the arch structurally in their buildings ; the Romans, however, had the round arch as a primary element in the construction of their edifices. This round arch was also used by the Byzantines, and amongst their ornaments we find those combinations of circles and parts of circles, which we find so constantly recurring in later times in Gothic architecture and Gothic ornament. Norman buildings, again, show us the round arch, and present us with such intersected arcs as would naturally suggest the pointed arch of later times, with which came the full development of Gothic or Christian architecture and ornamentation. There was a very fine and marvellously clever development of decorative art, enthusiastically worked at by the Christian monks of the seventh and eighth centuries, called Celtic, of which we have many very beautiful examples in Professor Westwood’s great work on early illuminated manuscripts ; but what is generally understood by Christian or Gothic art had its finest development about the thirteenth century. Gothic ornament, like the Egyptian, is essentially symbolic. Its forms have in many instances specific significance. Thus the common equilateral triangle is in some cases used to symbolise the Holy Trinity ; so are the two entwined triangles. But there are many other symbols employed in Gothic orna- ment which set forth the mystery of the Unity of the Trinity. Thus in Fig. 6 we have three interlaced circles, which beauti- fully express the eternal Unity of the Trinity, for the circle alone symbolises eternity, being without beginning and without end, and the three parts point to the Three Persons of the Godhead. A very curious and clever symbol of the Trinity is portrayed in Fig. 7, where three faces are so combined as to form an orna- mental figure. Baptism under the immediate sanction of the Divine Trinity was represented by three fishes placed together in the manner of a triangle (Fig. 8) ; but so numerous were Christian symbols after the ninth century, that to enumerate them merely would occupy much space. Every trefoil symbolised the Holy Trinity, every quatrefoil the four evangelists, every cross the Cruci- fixion, or the martyrdom of some saint. And into Gothic ornamentation the chalice, the crown of thorns, the dice, the sop, the hammer and nails, the flagellum, and other symbols of our Lord’s passion, have entered. But, besides these, we have more purely architectural forms making gentle utterance : the chureh spire points heavenwards, and the long lines of the clustered columns direct the thoughts upwards to heaven and to God. Gothic ornament, having passed from its purity towards undue elaboration, began to lose its hold on the people for whom it was created, and the form of religion with which it had long been associated had become old, when the great overthrow of old traditions and usages occurred, commonly called the Reformation. With the reformation of religion came a revival of classic learning, and a general diffusion of know- ledge, and thus the immediate necessity for art symbols was passing away, it being especially to an unlettered people that an extended system of symbolism appeals. With this revival of classic learning came the investigation of classic remains — the exploration of Greek and Roman ruins ; and while this was going on, a dislike to whatever had been associated with the old form of religion had sprung up, which dislike turned to hate as the struggle advanced, till the feeling against Gothic architecture and ornament became so strong, that anything was preferred to it. Now arose Renaissance architecture and ornament (revival work), which was based on the Roman remains, but was yet re- moulded or formed anew ; so that the ornament of the Renais- sance is not Roman ornament, but a new decorative scheme, somewhat of the same genus as that of the Roman. Here, however, all my sympathies end. I confess that all Renaissance ornament, whether developed under the soft sky of I'.aly (Italian ornament), in more northerly France (French Renais- sance), or on our own soil (Elizabethan, or English Renaissance), fails to awaken any feeling of sympathy in my breast ; and that it, on the contrary, chills and repels me. I enjoy the power and vigour of Egyptian ornament, the refinement of the Greek, the gorgeousness of the Alhambraic, the richness of the Persian and Indian, the simple honesty and boldness of the Gothic ; but vith the coarse Assyrian, the haughty Roman, and the cold Renais- sance, I have no kindred feeling, no sympathy. They strike notes which have no chords in my nature : hence from them I instinctively fly. I must be pardoned for this my feeling by those who differ from me in judgment, but my continued studies of these styles only separate me further from them in feeling. It will be said that in my writings I mingle together orna- ment and architecture, and that my sphere is ornament, and not building. I cannot separate the two. The material at command, the religion of the people, and the climate, have, to a great extent, determined the character of the architecture of all ages and nations ; but they have, to the same extent, deter- mined the nature of the ornamentation of the edifices raised. Ornament always has arisen out of architecture, or been a mere reflex of the art-principles of the building decorated. We cannot rightly consider ornament without architecture ; but I will promise to take no further notice of architecture than is absolutely necessary to the proper understanding of our subject. VEGETABLE COMMERCIAL PRODUCTS.-III. PLANTS YIELDING SPICES AND CONDIMENTS ( Continued ). Allspice, Pimento, or Jamaica Peppee (Eugenia Pimento, De Candolle; natural order, Myrtacece). — This plant is called all- spice because it has the combined flavour of all the other spices — that of cinnamon, cloves, and nutmegs entering into its com- position. The unripe berries of this plant, dried in the sun, form the allspice. The plant itself is a handsome evergreen, with a straight trunk about thirty feet high, covered with a smooth, grey bark. Its leaves are opposite, short-petioled, elliptical, smooth, and pellucid-dotted, abounding in an essential oil, to which the pimento owes its aromatic properties. The flowers are greenish-white, and the fruit is a smooth, shining, succulent berry, black when ripe, and containing two uniform seeds, the flavour of which resides within the shell. The allspice is a native of the West Indies, where it is culti- vated — particularly in Jamaica, in the hilly parts of the country — in plantations, having broad walks between the trees, called “ pimento walks.” It begins to bear fruit when three years of age, and arrives at maturity in seven years. Nothing can be more fragrant than the odour of the pimento trees, especially when in bloom ; even the leaf emits a fine aromatic odour when bruised. The berries are collected before they are ripe, at which time the essential oil, to which they owe their pungency, is most abundant. They are spread out, exposed to the sun, and often turned. In about a week they have lost their green colour, and have acquired that reddish-brown tint which renders them marketable ; they are then packed in bags and casks for expor- tation. When dried, the berries are rather larger than a peppercorn. Some plantations kiln-dry them, which expedites the process very considerably. The consumption of allspice in this country is very great, as it is both cheap and useful ; 22,000 bags, weighing 1,022 tons, were imported into Liverpool and London in 1850, and about one-fifth of that quantity was re-exported. This spice is used as a condiment, and its oil, like that of cloves, is employed as a remedy for toothache. Pepper ( Piper nigrum, L. ; natural order, Piper acece). — This is a climbing vine, with alternate, ovate, acuminate, dark-green leaves, five to seven-nerved beneath, and small inconspicuous flowers, in long, slender, drooping spikes, which are opposite. Its fruit is a round, sessile, one-celled berry, first green, then red, and finally black. VEGETABLE COMMERCIAL PRODUCTS. 91 The pepper vine is indigenous to the East Indies, and is ex- tensively cultivated in Sumatra, Java, and on the Malabar coast. A little pepper is also grown in the Mauritius and in the West India islands. The berries, which resemble those of our holly in size and colour, are gathered as soon as they begin to redden ; for if ! allowed to ripen fully, they lose their pungency. They are • dried in the sun, and they become wrinkled and black on the outside. In this state they are known as black pepper, which is the most powerful variety. White and black pepper are produced by the same plant. This difference in colour is only the result of a difference in the preparation of the berries. To obtain white pepper the berries are allowed to ripen, then dried and soaked in water, and the softened black outer coat is removed by rubbing. The internal seed is of a whitish-grey colour, and, when dried, forms white pepper. Pepper is a warm carminative stimulant, which is added to food principally for the object of correcting the flatulent and griping character of certain articles of diet — peas and beans, for instance. Both varieties of black and white pepper are some- times used whole in soups and pickles, but they are mostly ground in a mill, and sold in the form of a powder. The quantity of pepper annually imported into the United Kingdom is immense. About 6,523 tons of the dried unripe black berries and white ripened seeds of the pepper plant reached this country from the East Indies in 1866, chiefly from Sumatra and Java, and also from Malacca, Siam, and Singapore. The pepper vine is strictly tropical, but it will grow freely from cuttings wherever the soil and climate are suitable. It is allowed to climb props from ten to thirteen feet in height. These props root freely, the tree from which they are cut being selected with that object in view. The props thus afford both shade and support to the plants. Great care is necessary in the management of the vine, especially in training and tying it to the props. An acre of pepper vines affords an average annual yield of 1,161 lb. of clean pepper. Long Pepper ( Piper longum, L. ; natural order, Piperacece). —This species, which is wholly different from the black pepper, is found wild in India, and is cultivated in Bengal. The long pepper consists of the frrfit catkins of the plant dried in the sun. Long pepper is expensive, and therefore not much used either as a condiment or a medicine. Cayenne Pepper ( Capsicum annuum, L. ; natural order, Solanacece). — Cayenne or red pepper is not the produce of a pepper plant, but of one belonging to a totally different natural order. It is prepared from the large, red, inflated, pod-like berries of the capsicum, dried and reduced to powder. The capsicum is a native of the East and West Indies, but cultivated in England, where it can be grown with a very little care. There are numerous species of capsicum, named after the form and colour of the pod, which varies considerably. All are, however, included under the general Mexican name of “ chillies.” In tropical countries chillies are used in great quantities, the consumption as a condiment being almost universal, and nearly equal to that of salt. In India they are the principal ingredients in all curries, and form the only seasoning which the millions of the poor of that country can obtain to eat with their insipid rice. The natives of the tropics can eat and relish them raw, which cannot be done by strangers from temperate climates without suffering, the pungent and acrid action of the chillies affecting the mouth and throat. Capsicums or chillies are imported into this country in the form of red and brown pods, which are broken, dried, and packed in bales, weighing 2% cwt., principally for making red pepper. Different varieties are cultivated for pickles, and are imported in the pickled state in vinegar from the East Indies. The annual imports from the East and West Indies are from 80 to 100 tons. Capsicums are useful in cases of putrid sore throat, in malig- nant scarlet fever, as a powerful irritant to be applied in the condition of a saturated infusion externally, so as to draw the internal inflammation to the surface, and thus relieve the throat. Ginger ( Zingiber officinale, Roscoe ; natural order, Zingi- ber acece). — This is an elegant, reed-like, tropical plant, which rises from a creeping rhizome or underground stem. The aerial stem is formed by the cohering bases of the leaves, which are alternate, lanceolate, and sheathing, the nervures diverging from the mid-ribs. The flower-stem springs froiq the rhizome. The dark-purple flowers are arranged in spikes. The ginger-plant is a native of the East and West Indies, and is now cultivated generally in hot climates. The ginger of commerce is the dry, wrinkled rhizomes of the plant, which aro called “races,” and are usually from two to three inches in length, branched, flat, and white in colour. Sometimes the root is dug up when a year old, scalded to prevent germination, and then dried. So prepared, it is called “ black ginger,” although this term is very erroneous, as the darkest ginger is only a dirty stone colour. Again, the best pieces are selected, the outer skin is scraped off before the ginger is dried, and the pieces, bleached with chloride of lime, constitute what is known in the market as “ white ginger.” This bleaching process renders the ginger beautifully smooth, but certainly does not improve its quality. Lastly, the races, newly formed in spring, are cut off, and boiled in syrup ; and the ginger, so treated, is imported in jars under the name of preserved ginger, forming a well-known sweetmeat. The varieties of ginger recognised in commerce are the Jamaica white ginger, and the Jamaica and Malabar black gingers ; also the black varieties, or the Barbadoes, African, and East Indian gingers. Jamaica ginger is considered to be the best. The amount of ginger annually imported into the United Kingdom is about 700 tons. The principal use of this spice is as a condiment. Medicinally, it is an excellent sto- machic, removing flatulence and griping pains. When used in the form of a poultice, it forms a good rubefacient or counter- irritant. Vanilla ( Vanilla aromatica, Swammerdam ; natural order, Orchidacece) . — The vanilla is an epiphyte, or air-plant, with a trailing stem, not unlike the common ivy, which attaches itself to trees not as a source of food, like the mistletoe and other parasites, but as a mere point of support, deriving its nourishment entirely from the atmosphere. It grows from eighteen to twenty feet in length. The flowers are greenish-yellow mixed with white, and these are followed by a long slender pod, the fragrance of which is owing to the presence of benzoic acid, crystals of which form upon the pod if left undisturbed. This is, perhaps, the most important genus of the whole orchidaceous family, and the only one which possesses any marked economic value. It grows in the tropical parts of South America, in the Brazils, Peru, on the banks of the Orinoco, and in all places where heat, moisture, and shade prevail. The pods or fruit of the vanilla are sub-cylindrical, about eight inches long, one-celled, and pulpy within, filled through- out their entire length with very minute black oily seeds, having the appearance of a black paste. The following is a good account of the method used in pre- paring vanilla for market — •“ When about 12,000 of the pods are collected, they are strung like a garland by their lower ends, a3 near as possible to their foot-stalks ; the whole are plunged for an instant into boiling water to blanch them ; they are then hung up in the open air, and exposed to the sun for a few hours. Next day they are lightly smeared with oil, by means of a feather or the fingers, and surrounded with oiled cotton to prevent the valves from opening. As they become dry on inverting their upper end, they discharge a viscid liquor from it, and they are pressed several times with oiled fingers to promote its flow. The dry pods lose their appearance, grow brown, wrinkled, and soft, and shrink into one-fourth of their original size. In this state they are touched a second time with oil, but only very sparingly, because, if oiled too much, they would lose a great deal of their delicious perfume. They are then packed for the market in small bundles of 50 to 100 in each, enclosed in lead-foil or light metallic cases.”* As an aromatic, vanilla is much used by confectioners for flavouring ices and custards. The Spaniards employ it exten- sively in perfuming their chocolate. It is difficult to reduce it to small particles, but it may be sufficiently attenuated by cutting it into little bits, and grinding these along with sugar. The quantity imported into the United Kingdom is very small, amounting to not more than five and six cwt. per annum- * See Ure’s “ Dictionary of Arts and Manufactures,” Vol. III., p. 974. 1867. 9i THE TECHNICAL EDUCATOR. SEATS OF INDUSTRY.— II. SHEFFIELD. BY H. B. FOX BOTJENE. Sheffield, smaller than Birmingham by about a third, is the second hardware town in England. It has an old as well as a modern history. A castle built on a field at the junction of the little river Sheaf with the Don, was the centre of the old lordship of Hallamshire in feudal times, and here Cardinal Wolsey was imprisoned for eighteen days, and Mary Queen of Scots for the best part of fourteen years. Before that, how- ever, the village that had grown up round about began to follow the trade which, till very recently, has been the staple manufacture of the inhabitants. Chaucer speaks of “ Sheffield whittles,” and from an earlier day the rude knives so known, and other cutlery wares, were chiefly supplied to the Yorkshire districts by Sheffield, while Birmingham carried on a like trade with the midland counties. Neither town could then produce such delicate workmanship as some of the Continental factories. In the reign of Henry VIII. we read of “ knives of Almayne, knives of France, and knives of Collogne,” but only of whittles from Sheffield. The whittles gradually improved. A case of them was thought dainty enough to serve as a present from the Earl of Shrewsbury, lord of Hallamshire, to Queen Elizabeth. At that time there existed in Sheffield a corpo- I'ation of cutlers, which in 1624, by charter from James I., became the Cutlers’ Company that still has famous influence in the town. But Sheffield was then small and poor. In 1615 it had a population of 2,207, of whom, according to a con- temporary record, 100 were “ householders which relieve others, )pd though the best sort, are but poor artificers;” 160 were householders <: not able to relieve others, such, though they beg not, as are not able to abide the storm of one fortnight’s sick- ness, but would be thereby driven to beggary 1,222 were “ children and servants of the said householders, the greatest part of which are such as 'live on small wages, and are con- strained to work even to provide them necessaries and the remaining 750 were “all begging poor, not able to live without the charity of their neighbours.” The inhabitants numbered 9,625 in 1736 ; 45,755 in 1801 ; and 185,157 in 1861. During the last two centuries the population has nearly doubled in every twenty-five years, and the importance of the town has grown in far greater proportion. Most of the 240,000 or more persons now resident in it are concerned, directly or indirectly, in the production of every sort of cutlery, from pen-knives to sword-blades, or of tools, trinkets, cannon-balls, and armour- plates, and the thousand other varieties of hardware manufac- ture, some of them peculiar to Sheffield, and others in which Sheffield is a formidable rival of Birmingham. Steel is to Sheffield what brass is to Birmingham. Swedish iron comes into the town in vast supplies by way of Hull, and is skilfully worked up with the help of the coal that is plentiful in the neighbourhood. By far the larger part of the 50,000 or more tons of steel made annually in England — the produce of all the rest of the world being about as great — comes from Sheffield and its outlying districts, along the shores of the Don, and with this trade is extensively carried on the kindred and older process of cast-iron manufacture. Both cast iron and steel are combinations of pure iron and carbon, the proportion of carbon in cast iron being four or five times as great as in steel. All the efforts of old iron-workers were directed to the removal of every extraneous substance from the ore, so as to render it as ductile and malleable as possible. About 300 years ago it was discovered that the presence of carbon, while rendering iron less fit for ordinary purposes, gave it some special advantages, and accordingly the ore was so treated as that four or five per cent, of carbon should be left in it. The treatment, however, caused manganese and other bodies to be also left in the metal, and the presence of these substances lessens the value of cast iron for all delicate uses. To produce a suitable metal for these uses, therefore, the iron was at first purified as thoroughly as it could be, and then a portion of the carbon extracted from it was restored, the new metal being known as steel. Most of the various methods adopted for thus manufac- turing steel are pursued in Sheffield. In the Cyclops Works of Messrs. Charles Cammell and Co., the most common process, that of cementation, is pursued. The purest malleable iron, generally brought from Sweden or Russia, is broken into short bars, mixed up with powdered charcoal, and subjected to a uniform red heat for ten or eleven days, until a sufficient quantity of carbon is absorbed, and what, from its peculiar appearance, is called blister-steel is produced. Blister-steel is turned into cast steel by another melting and a slight hammer- ing, or into shear steel by hammering alone. Coarser varieties are manufactured by modifications of this treatment, or by sub- jecting the cast steel to the ordinary puddling process until only the requisite quantity, from one-half to one per cent., of carbon is left in it. All these, however, are costly ; and an important innovation is Mr. Bessemer’s method of directly converting the crude metal, as it comes from the blast-furnace, into steel. The secret of this method is the sudden application of intense heat, under a rapid current of air, to the rough iron, whereby violent boiling and decarbonisation are secured, and tolerably pure steel is turned out with remarkable ease and speed. The process, invented in 1855, has yet to be thoroughly perfected ; but vast benefits have already resulted from it. Not only is the manufacture of steel rendered much cheaper than by any other plan, but it can also be produced in larger masses than there were facilities for previously, and thus tho metal can be applied to new and valuable uses. One of these uses, directly due to Mr. Bessemer’s fertile invention, is the manufacture of steel cannon-balls. “ To facilitate this manufacture,” says Mr. Fair bairn, “Mr. Besse- mer designed a rolling-mill, now in use at his works in Sheffield, in which lumps of steel are fashioned into spherical balls, from 68 to 300 pounds each in weight, with the greatest rapidity, and with a degree of accuracy never attained in cast- iron shot. The mass to be acted upon is cut from a solid cylinder. The angles of the cylindrical lump are then reduced by pressure between curved surfaces. In this approximate form they are put, at a bright red heat, into the rolling-mill, which consists simply of a revolving table, in which an annular channel is formed. The channel being in section part of a circle of the diameter of the intended shot, a similarly grooved table is fixed above it. The axis of the lower one may be moved end-wise by a hydraulic ram, there being a recess formed in the ram to receive the end of the axis. When a mass of steel is put into this annular channel, and the table set in motion by powerful gearing, the hydraulic ram is made to act on the lower end of the axis, and compress the revolving mass between the grooved surfaces. The lump of steel in its passage round the central shaft also revolves on its own axis, which constantly varies in position, and thus ensures the most per- fectly spherical form. To prevent the scale of the metal from roughening its surface, a jet of water passing down the hollow axis is projected against the shot as it revolves, and causes the scale to be thrown off as quickly as it is formed, while a blast of air passing down another passage in the axis blows all these detached scales out of the annular channel. Three balls are best acted upon at one time, so that in three or four minutes this simple apparatus is capable of producing three large spheres, more accurate in size and form than a workman with a slide-lathe could produce in as many days.” That “simple apparatus ” will serve as a specimen of the numberless methods by which mechanical skill is made to supersede, or rather to economise, hand labour in Sheffield, as in all other manufac- turing towns. A more important illustration of the way in which warlike needs are served in Sheffield, to the great enrichment of the town, is furnished by its manufacture of armour-plates. Iron ships have already virtually superseded the more graceful wooden men-of-war for purposes of naval fighting ; but their adoption was long delayed by the peculiar dangers arising from the effects of shot upon ordinary iron steamers. The innovation was opposed by the English Admiralty in 1834 and subsequent years, until 1855, when the Emperor Napoleon caused thick iron plates to be constructed for casing the sides of his iron war- ships, and their successful use in the Crimean war brought iron-clads into fashion. The Sheffield manufacturers quickly set themselves to supply the new commodity. Messrs. John Brown and Co., who started their huge Atlas Works in 1857, began the enterprise in 1860. They constructed immense rolling- mills adapted for the production of armour-plates, some of them twelve inches thick, nineteen feet long, and four feet wide, and weighing twenty tons. Their example was soon followed by APPLIED MECHANICS. 93 Messrs. Cammell and Co. at their Cyclops Works, and thus the two largest establishments in Sheffield find a considerable part of their business in providing the munitions of war. Armour-plates, however, sre only special items in the multi- tudinous productions of these groat hardware factories. Other factories have their own specialities ; among the most notable being the steel cannon-balls of Messrs. Thomas Firth and Sons, who follow in Mr. Bessemer’s lead, using their own homogeneous steel in lieu of the Bessemer steel ; the saws of Messrs. Spear and Jackson, manufactured at their iEtna Works ; and the cast- steel bells of Messrs. Naylor, Vicker3, and Co. Making bells weighing 2,000 or more pounds apiece, the latter firm has proved that steel is for this purpose as serviceable as bronze, and nearly two-tbirds cheaper. These new manufactures have partly ousted knife-making from its old place as the staple trade of Sheffield ; but Sheffield is still the great haunt of cutlers, some 1,500 employers having here their workshops, besides about 250 makers of files, while the makers of edged tools number about 150, the saw-makers as many, the makers of hammers about 60, and the engineers’ tool-makers about 100. These associated trades provide occu- pation for a large part of the community, and in them all the appliances of modern science and art are brought to bear. Each one of the millions of pen-knives manufactured every year in Sheffield, and sent for sale to all quarters of the world, goes through ten or a dozen hands. One man forges th9 blade ; another roughly grinds it ; a third softens the metal and affixes the trade-mark of the maker ; a fourth hardens and tempers it ; a fifth grinds it over again until a fine edge is produced ; a sixth fastens it to the handle, which has been prepared by a separate rrain of workpeople, from wood, horn, ivory, mother-of-pearl, or any of the other substances employed. In file-making and all the other trades of the town there is a like subdivision of labour. Wire manufacture is another important trade of Sheffield, some wire, for watchmakers’ use, being so fine that a hundred miles’ length of it would hardly weigh a pound. When steel wire was in fashion for ladies’ crinolines, Sheffield produced 10,000 tons of it in a year. The trade in which Sheffield competes most directly with Birmingham is that concerned in the manufacture of plated goods. This trade was born in the Yorkshire town. In 1742 one Thomas Bolsover was employed to repair the handle of a knife made partly of silver and partly of copper. It occurred to him that, by placing a thin coat of silver over a thick base of copper, and rolling them together at a high temperature, they might be welded into one mass, and a marketable commodity produced. He experimented successfully, and soon drove a thriving trade in plated snuff-boxes, buttons, and the like. Matthew Boulton adopted the device in Birmingham, and before long both towns were busy with silver-plating and gold-plating. The electro-plating process, begun at Birmingham a century later, was soon copied in Sheffield, and thus each town has helped the other to a new source of wealth. The kindred trade in Britannia metal — an amalgamation of tin, regulus of anti- mony, copper, and brass — was started in 1770 by two Sheffield workmen named Jessop and Hancock, and now gives employ- ment to one large house and many smaller ones. Rivalling Birmingham in the general character of its em- ployments, and especially in some of their details, Sheffield differs widely from it in one important respect. The War- wickshire hardware town is a model of freedom from restraint among workpeople, and of harmony between them and their masters. The Yorkshire hardware town, as was painfully shown a few years ago, furnished an ugly example of the tyranny of trades’ unions, and of the mischievous disposition that leads to strikes and trade-outrages. The social condition of the workpeople, who are generally paid highly for the skilled labour of which they are masters, is favourable ; and there is now no counterpart to the state of things which, as we have seen, prevailed in the town 250 years ago, when one-third of the inhabitants were “begging poor,” and most of the rest were “ constrained to work even to provide them neces- saries.” There are signs of wealth in the cottages as well as in the mansions ; but the very prosperity of the labourers has begotten an evil. Jealous of all rivalry, they strive, by foul means as well as fair, to maintain their advantage over the majority of English workpeople. The result is a vicious temper, which dominates the whole class, though most of its members may be free from it, and which threatens to retard the future growth of Sheffield, and drive some of its trades into healthier homes. 0 00 0 APPLIED MECHANICS.— II. BY ROBERT BALL, M.A. THE PULLEY. INTRODUCTION — LARGE AND SMALL PULLEYS — THEORY OF THE PULLEY-BLOCK, INCLUDING FRICTION — EXPERIMENTS UPON THE THREE-SHEAVE PULLEY-BLOCK. Before commencing this lesson the student should make him- self familiar with what has been said on the subject of Pulleys in Lessons X., XI. of the series of lessons on “ Mechanics.” It will also be necessary to fully understand what is in Lesson XI. called the “ golden rule of Mechanics.” This law may be thus stated : — In any mechanical 'power the distance through which the poiver moves multiplied by its magnitude is equal to the distance through which the resistance moves multiplied by its magnitude. This rule must be thoroughly grasped before any real advance can be made in the practical side of the subject which we now approach. It is often called the “law of virtual velocities,” and we shall use this name, though in reality virtual velocities means a gene- ral and profound truth in Mechanics, of which the golden rule is only a par- ticular case. We shall also use the term velocity ratio ; this may be de- fined as the proportion of the distance though which the power moves in a given time to the distance over which the load is moved in the same time. It would follow then, from the principle of virtual velocities, that the mechanical efficiency of a machine is to be expressed ^ }. by its velocity ratio. This is the usual supposition, and by it various problems in pulleys are solved in Lesson XI. But when we turn to practice, we find that the mechanical efficiency of a pulley is very much less than its velocity ratio. This is because friction has stepped in and robbed us of our force. No matter how well made be the axles and their bearings, no matter how carefully they be oiled, there is invariably loss of power produced by friction. The student will do well to read the account of friction given in Lesson XII. It is the presence of this force which impera- tively demands that to study the mechanical powers we must first resort to experiment, and then theory will aid us in making our experiments, and afterwards discussing them. We shall find that friction, which at first sight seems embarrassing, and destructive of whatever is symmetrical or elegant in the treat- ment of the problem, does not really prove so : on the contrary , it leads, when properly studied, to truths of a beauty and pro- fundity beyond any we can attain by theoretical studies of the mechanical powers which do not recognise its presence. EXPERIMENTS ON LARGE AND SMALL PULLEYS. We shall commence our experiments upon a single pulley, which is merely used for the purpose of changing the direction of a force. This can only be done at a little sacrifice of power, whatever be the size of the pulley; but the loss is greater with a small pulley than a large one. We can study the sub- ject by the apparatus of Fig. 1. This represents an horizontal axle around which the piece A B . is capable of turning quite freely. A B is ap- ‘ parently composed of two pulleys fastened toge- ther ; it is in reality one piece, one of these sheaves being 4' 7 times the size of the other. We may place the rope on either the larger groove or the smaller groove, as is shown in Fig. 2. We shall first describe the mode of experimenting with the larger groove, and the same process is to be afterwards carried out with reference to the smaller groove. A rope being placed on the pulley, let a weight, r, be hung at one end. If then an equal weight, p, were placed on the other side, the two would balance. Now, if tb» pulley M B Fig. 2. 94 THE TECHNICAL EDUCATOR. had no friction, we should find that the slightest addition made to either of the weights would cause it to descend and raise up the other ; but on account of friction, a very appre- ciable addition must be made to one of the weights before it does this. We shall give the details of one experiment, in which a piece of flexible rope was used, which carried a hook fastened to each end, the hooks having equal weights. A weight of 141b. was then placed on each of the hooks. We have now a number of pieces of wire, each of which weighs exactly O'l lb. We add one of them to P, but there is still equilibrium, 01 lb. not being sufficient to overcome the friction; another and another is added, till we find that when p has received 0'4 lb. it begins slowly to descend ; the friction is then conquered, and it is measured by 0’4 lb. Let us now remove the stone weights from the two hooks, and attach to them weights of 56 lb. each. We find that 0'4 lb., which was sufficient to overcome the friction before, is not now enough ; 12 lb. must be added to the weight p before it descends and raises r. This experiment teaches us that the friction of a pulley about its axle increases with the weights that the pulley is lifting : here the weights are incx-eased fourfold, and the friction has increased threefold. Speaking very roughly, we may often take the friction as proportional to the load raised. This rule gives rather too high a value for large weights, ~ and too low for small weights, but it may be taken as sufficiently correct for ordinary purposes. Let us remove the rope from the large groove, and place it on the small groove, adding 141b. to each of the hooks. The condition of things is so far the same as in the first of the two cases already described, that the two grooves turn as one piece upon the same axle ; if, therefore, we find any difference in the amount of friction, it is to be attributed solely to the difference in the size of the two grooves. We load p as before, but we find before it descends we must add to it 3'6 lb. ; this, then, is the measure of the friction. It is nine times as large as it was when we used the larger pulley. This difference is not to be attributed to friction only ; the rope opposes more resistance to being bent around the small pulley than it does about the large pulley, and this resistance and the friction account for the loss. It will be easy, by examining Fig. 2, to see that friction must have a greater effect on the small pulley than on the large pulley. The friction is at the circumference of the axle, and always acts to oppose the motion. Supposing p be acting to raise R, p acts at an arm o b, while the friction acts at the arm o c ; the leverage of p, therefore, in overcoming the friction is greater than that of x in the proportion of the lengths o A and o b ; hence the friction should be 4'7 times larger in the small pulley, that is, 4'7 x 0’4 = 1'88 = T9 lb. approximately. The difference between this amount and that which was observed, 3 6 - 1*9 = 17 lb.. expresses the power that is expended in overcoming the other Bource of loss, viz., the rigidity of the rope. The practical conclusion to be dei’ived from these considera- tions is this : always use pulleys as large as possible. In coal- pits the cage containing trucks of coal is raised to the surface by a wire rope ; this generally passes over a large pulley, and from thence to the engine-house. The pulley is large, both for the purpose of avoiding friction, and also to avoid bending the rope too quickly, a process that not only entails loss of power, but also injures the rope. By having a large pulley for the rope to pass over, sudden flexure is not required. The pulleys used in coal-mining are from six or eight feet in diameter up to nearly double this size. P = A + BE, where A and B are numerical constants whose values nust bo determined by experiment. The form of this expressior sl.ould be noticed Friction is not strictly proportional to tie pres- sure. It is found that the friction is best represented by two terms : one, B r, which bears a certain ratio to the lord ; the other a constant quantity, A, which is generally small. A also implicitly contains the amount of power necessary to rxise the actual weight of the lower block ; so that R means only the actual number of pounds attached to the hook. We car easily conceive how A and b can be determined. Suppose we hang a load, r, to the load-hook, and find tlat a power, p 1 , is necessary to raise it, we have, by the formula— P, = A + BE,. If now we take another load, R 2 , and find the power to raise it P a - A + BE.. be p,, we have- There are thus two equations between the two unknowns, a and b. From these two equations the values of a and b can be determined by the well-known process which is described in Lessons in Algebra. It will then be found that if any other load, r 3 , be raised, the power necessary to lift it will be A + BE,, thus verifying the formula. Actual values of A and B for one system of pulleys will presently be given. They are found by taking the mean of several different experiments. The principle is essentially the same as here explained, but is a litt'.e more accurate. It need not be dwelt on fui'ther, as the process is somewhat difficult, and requires considerable calculation. Let us now deduce from this formula the mechanical effi- ciency of the machine. This is to be obtained by dividing r by A -j- B r. We have for quotient — R _ 1 A+ BB“ b + a* R When r is considerable, A is very small, and therefore the me. E 1 chanical efficiency is represented by g very nearly. It will also be useful to ascertain the quantity of energy or work which is usefully employed, and therefore, of course, the quantity which is wasted in overcoming friction. In order to raise R pounds one foot, p must be exerted over n feet, hence n p units of work must be expended to do r units of work ; but n P = n A + nBR ; aixd out of this quantity only r is employed, hence the per- centage is R nA + xiBE * 100 100 E n(A + BE) 100 n (r + ®)* If R be very large, - is small, and may be neglected ; and we R find the per-centage of work utilised to be 100 iiB’ TECHNICAL DRAWING.— VI. THEORY OF THE PULLEY-BLOCK, INCLUDING FRICTION. Let n be the virtual velocity of a pulley-block, or, indeed, of any other mechanical power, for the investigation now given applies to all machines. Let r be the load to be raised, p the power which raises it. If there were no friction, we should have P = U; but the presence of friction prevents this equation being true. The power required is always greater than the value given by it. It is found that the power should be expressed by a formula of this kind — DRAWING FOE CARPENTERS— COFFER-DAMS ( continued ). Fig. 31 is the section of a much stronger coffer-dam, which is so constructed as to preserve its firmness throughout its entire height. This consists of three rows of piles, a b c ; the two nearest the water, a and b, being of the full height of the coffer- dam, and the third, c, being half the height. These piles are placed at certain distances apart, and are united at the top and at a point just below the middle by cross-timbers, d 1 , d 2 , placed horizontally on each side of the piles, and attached by being notched on to the piles; an iron bolt passing through all three timbers. The outer row of piles are connected in a similar manner by the cross-pieces, e, which are on a level with the rails, d 1 and d 2 . Resting on these, timbers, /, are laid across TECHNICAL DRAWING. 95 In pairs — that is, on each side of the piles, so that each pair grasps the piles, and also the strut, g, between them ; bolts tightened up by means of nuts passing through all three. The transverse pieces at the top of the long piles rest on the longi- tudinal joists, and are in this example shown notched down upon them, for the purpose already explained in the previous study. The student must now be reminded that up to this stage the construction is a mere skeleton, the piles being six or eight feet apart. This space is filled in by sheet-piling — that is, piles placed in a sheet or wall. These are narrower than the true piles, and are driven down between the longitudinal cross- pieces or walls, so as to render the whole construction com- plete. This hollow wall is now to be filled in with clay, puddle, etc., and the water having been pumped out cf the site en- closed by the coffer-dam, the ground must be dredged, and, if required, a bed of b4ton* must be laid down on which to erect the intended pier or other structure. The following practical hints by Mr. Dobson are quoted for the instruction of the student : — “ Leakage between the puddle and the surface of the ground will generally take place unless all the loose, soft, or porous surface-soil be carefully removed by dredging before the puddle is put in. This dredging may be done before or after the piles have been driven. Leakage through the puddle-wall itself may arise from various causes, but may generally be prevented by careful work, and selection of good materials. In the first place, the piles should all be fitted to each other before driving, and should be truly and carefully driven: next, the framing and strutting should be sufficiently strong to prevent any straining or movement under the varying pressure to which the dam may be exposed by alternations in the height of the water ; and lastly, the material used for the puddle should be such as will settle down into a solid mass, and should be carefully punned in thin layers so as to secure that no vacuities are left in any part. For this reason it is desirable, when the piles have been driven between the double wallings, to remove the inside walls after the piles are home, as any projections of this kind increase the difficulty of punning the puddle. In order to resist the evil effects which might arise from the swelling of the puddle, the inner and outer rows of piles are usually connected with iron bolts passing through the piles, and secured by nuts, with iron plates and large wooden washers to prevent the former from being drawn into the piles by extreme pressure. These tie-bolts are often found to be very troublesome sources of leakage, as the water soaks in round the bolt-holes, and it is difficult to keep the puddle from settling away from the bolts, and leaving a channel for the passage of water through the dam.” With this information as to the construction of the coffer- dam, the student will not, it is presumed, require any instruc- tions as to copying the example ; and he will, as has been already mentioned, do well to draw the various parts in precisely the same order in which they have been mentioned in the description. WOODEN BRIDGES. Wooden bridges maybe looked upon as the origin of all other constructions for crossing water or roads, whether of stone or iron ; for it seems natural to suppose that in the earliest times the simple method of throwing a plank across a stream may have been adopted — in fact, the falling in that position of a tree on the bank would have suggested such an expedient. A plank placed across from one bank of a stream to the other is, then, the most elementary form of a timber bridge ; it is at the same time the most perfect, and the principle on which it is suspended, or kept in its proper position, is worthy of con- sideration. “For,” says Mr. Peter Nicholson, “we may learn how to construct the best and most advantageous kind of bridge suitable for immense spans from this unpretending and apparently unpremeditated contrivance.” When a strong plank is thus laid upon two supports, that part of it which lies midway between them has to sustain its own weight, and that of anything crossing over it, by the co- hesion between its particles — that is, by the power with which * Beton, a kind of concrete, which, owing to its composition, has the property of hardening under water. (See "Lessons on Building Construction.") the atoms or fibres of which it is built up, cling together ; for as that part of the plank has nothing to rest upon, it will be clear that it will have a tendency to break somewhere between the supports when the strain upon it exceeds its strength. But owing to the cohesion of the particles, which attracts them one to another, such a plank cannot snap asunder with absolute suddenness, because the cells of which timber is formed are lengthened out into fibres or hollow threads, and these are so interwoven one with another that one particle or atom ot the material will not readily be separated from its fellow as long as such material remains in a sound state.* This being the case, the weight upon the beam will cause it to bend, or what is technically termed to “ sag,” and it is to prevent such bonding extending beyond a safe amount of elasticity that the efforts of the constructor of wooden bridges are mainly directed. Absolute construction does not come within the province of these lessons, but, as already stated, the better acquainted a man is with the principles involved in what he is doing, the better will he do his work, and certainly the more interest will he take in it ; and therefore, although nothing like a scientific treatise would be in character with the object in view, it is hoped that the following notes on wooden bridges, their his- tory, and peculiarities of construction, may be of interest to those who are now, or who may at any time become, engaged in such works. It will be easily understood that when a plank is laid across from wall to wall, and a weight is placed on any part of it. it bends, because the particles of which it is formed are pressed close together on the upper side, whilst on the under side they are drawn out. If across a plank so placed you had previously drawn lines exactly corresponding with each other, you would find that when a weight is placed on the plank the lines on the lower will be further apart than those on the upper surface. Thus you will understand that two forces are acting on the beam at the same moment, for the upper portion is subjected to a compressing force, whilst a tensile or stretching force is acting upon the lower side. It is the strength with which these two forces counteract each other that constitutes the rigidity of timber, and it will be evident that there must be some intermediate plane between the upper and lower surfaces of the beam in which the two opposite contending forces will meet, in which, of course, neither will preponderate. This is denominated the neutral plane, and will be differently situated according to the thickness of the beam, and the power of cohesion which is possessed by the fibres of the various kinds of timber. In looking back to the early history of wooden bridges, we shall find that where rivers were broad and their channels deep, it would be impossible to cross them by single beams of timber. In such cases a timber framing or scaffolding would be formed in the bed of the river by driving piles, or a pier might be formed of stones or other materials. On these, beams of timber would be placed with one extremity resting upon the pier, and the other on the bank of the river, or on an abutment raised at the water’s edge, and upon several piers in the water, as the case might be. Where the distances between the supports were too great for the dimensions of the timber forming the roadway, the main beams were propped up by struts projecting from the sides of the piers or piles, which were sometimes made to meet in the centre ; or if that was not practicable, on account of the dis- tance between the supports, they could each be made to sustain the beam, either by running directly to it from the abutment at about an angle of 45°, or a cross-piece, on which their ends should abut, be placed between them and fastened to the under side of the beam. These struts or stays were then multiplied and disposed in various ways, until at length a rib or arch of timber was formed to support the roadway, while the spandrels f were filled up with struts and ties to resist compression. * For an account of wood, and how it is formed, see “ Out Houses,” and “The Uses of Plants” (Cassell’s Primary Series). f Spandrel . — The irregular triangular space bounded on one side by the curve of the arch, on the second by the vertical, and on ths top by the horizontal lines forming the sides of the angular space in which an arch is contained. 96 THE TECHNICAL EDUCATOR. The ribs of bridges constructed in this manner were com- posed of frames, the lower portion of which form segments of circles, frequently made up of several pieces of wood placed immediately over each other and joggled together, so arranged however, that their ends should break joint.. To these circular arcs, or polygonal frames, upright pieces were attached, either by bolts, mortises, or iron straps, by which the weight of beams supporting the roadway was sustained at intervals, and so dis- posed as that each part might, as far as possible, conduce to the strength of the whole. Tho following historical notes as to timber bridges are given in order that the student may glean some intelligence as to what has been done — the best possible guidance as to what may be done. The extensive use of iron in tubular, girder, and suspension bridges, has in modern times superseded, in a great degree, the use of wood, but not entirely so ; and as the principles are applicable to so many other timber constructions, no apology will be necessary for describing some of them, especially as they constitute, both in their complete form and in their details, such excel- lent studies in drawing for all those engaged in wood- work. The “ Pons Sublicius ” was the first bridge ever built across the Tiber. It was at first constructed of timber in the reign of Ancus Martius. It ivas 'put together without either bolts or ties, so that it could readily be taken asunder, and was built for the purpose of connecting together the Aventine and Janiculum hills. The bridge over the Danube, by Trajan, is almost one of the oldest timber bridges of which we have a detailed ac- count. It was supported on twenty stone piers, which were 150 feet high and six feet broad. On these were framed timber arches each 170 feet span, and formed of three concentric timber rings bound to- gether by radiating pend- ants. These, together with the arches, supported the longitudinal beams on which the flooring joists were placed across the bridge. The timber bridge of Schaffhausen, built over the Rhine by Ulrick Grubenmann, was remarkable for its ingenious con- struction. It consisted of two openings, one of 170ieet span, and the other about 190. Its abutments and centre pier were of stone. On these were laid a kind of compound beam formed of three rails or walings, each of which consisted of two longi- tudinal beams bolted together and toothed into each other so as to be perfectly united ; these were supported by an infinity of struts, kept in their places by vertical binding pieces, all tending to transfer the thrust to the supports of the bridge. It was roofed in for the ostensible purpose of protecting the timber, but there can be no doubt that the roof added greatly to its strength. This bridge (which was demolished in the year 1800), and others designed by the brothers Grubenmann, were, in fact, timber tubular bridges. The timber bridge of St. Clair, over the Rhone at Lyons, has seventeen openings, the centre one having a span of forty-five feet, and the others diminishing towards each bank. This bridge has a roadway of aboxit thirty-six feet, which is supported upon piers, each formed of thirteen piles arranged in a single row, running parallel with the banks of the river. On the top of these piles a sill was framed, and longitudinal timbers were made to bear over the head of each pile, and upon these the flooring of the bridge was laid. The bridge of Grenelle, over the Seine near Paris, built by M. Mallet, consists of two equal and symmetrical bridges, separated by an intermediate piece of dry ground ; each of these is formed of three timber bays of eighty-two feet span, sup. ported upon two abutments and two piers of masonry. The width of this bridge is nearly thirty-three feet. The ground in the centre measuring eighty-five feet, the whole bridge, reckoning the entire distance from the abutments on either side of the Seine, is 632 feet long. All the foundations were bxiilt on piles, upon which a planking was laid. These foundations were formed by means of coffer-dams, which at low water were not more than five feet deep. A bridge similar to this was built over the Seine at Ivry in 1828. Besides these, which are merely mentioned as well- known specimens, there is an almost endless number of wooden bridges erected throughout the world, amongst which may be named that at Trenton, in America, of 180 feet span ; a bridge over the Tees, 150 feet span ; the bridge of Neucetringen, in Bavaria, 102 feet span ; that over the Necker, 210 feet span ; the bridge of Bamberg, with an opening of 206 feet, erected by M. Wiebe- king, an engineer who has constructed an immense number of timber bridges ; the bridge of Feldriclc, with a span of 65 feet; the bridge of Zeto, built by M. Coffinet, with a span of 125 ft. ; besides several put up by the celebrated M. Perronet, a French engi- neer, who was extremely skilful in forming con- structions of this kind. Before giving some ex- amples for drawing pur- poses, acting upon my often-repeated wish that my readers should con- sider drawing as a mental as well as a manual exercise, I ask their attention to the following principles of construction. Timber bridges are either supported upon piers and abut- ments of masonry, built on the solid foundation of the ground, or on a platform constructed upon piles driven into the earth, or they are supported upon piets formed upon one or more rows of piles driven in a line with the road or river passing under the bridge. There is almost an infinite variety of ways in which such props or piers may be made. It is, however, usual to drive the piles about a yard apart, from centre to centre, and to bolt capping-pieces or walings to the top of such piles, and either filling up the spaces between with large stones laid dry or else grouted with mortar. On this the masonry for the sup- ports should be placed, or a timber framing, if desired, or else the piles may be carried up to the height of the roadway, being kept in their places by walings and diagonal pieces, bolted on each side of them. These piles should be about a foot square, and when they are driven in salt water or in tidal rivers, their surfaces, up to high-water mark, should be sheathed with copper, or otherwise protected from the ravages of the worm. BUILDING CONSTRUCTION. 9 BUILDING CONSTRUCTION. — IV, FOUNDATIONS. It will be remembered that the term foundation refers not only to the surface or bed on which a building stands, but to the manner in which the lower portions of the walls are con- structed. Now, as walls are built either of stones or brick, we think it advisable to give the principles connected with the laying of both these materials before proceeding with the subject of the foundations in which they are to be employed : otherwise several of the terms used might not be understood by the be- ginner MASONRY. — PART I, Stonemasons class the methods of building walls into (1) rubble work and (2) ashlar work. Rubble work is either uncowrscd or coursed. In uncoursed 'rubble (Fig. 6), stones of any size and shape are used without any reference to their heights. The workman merely uses a tool, called the scabling hammer, to chip off any portion which may be unsightly or project from the general sur- face of the wall ; an intelligent mason is, however, careful so to dispose his variously - shaped stones that they may fit into each other, packing in every interstice with smaller stones, filling in every crevice with mortar, and using his plumb-rule to keep his wall perpendicular. It must be borne in mind that the wall is to be composed of stone, which is compact, and mortar, which is yielding ; and therefore the more stone, and the less mortar put in, the better. As the mortar will continue to shrink until it is dry and hard, it will be easily under- stood that a thick bed of soft material will necessarily allow of a greater settlement at the part where it exists than in any other ; nor should any stone be placed so as to rest on one part which may project more than another, and be bedded up with mortar, which would, of course, cause unequal settlement when other stones are placed upon it. It will thus be seen that even in the simplest operation there is a scope for in- telligent application of thought, and necessity for knowledge of principles. In coursed rubble (Fig. 7), the workman roughly dresses the stones before he begins to lay them. He is careful to get good beds to them, that is, to get the under and upper surfaces of the stones perfectly parallel ; he also gets the front of them at right angles to the beds, and tolerably level. The wall is built in courses, which are kept of one height all along in each, although the different courses need not be equally high, nor need the separate stones of which a course may be composed necessarily be equal, but some may be laid on others to make up the height. The stones at the corners are called “ quoins,” and are always laid with care, a3 they serve as gauges by which the height of the course is regulated, the workman using the line md level to guide him. Ashlar work (Fig. 8) is a sort of facing to a wall built either by one of the other methods or of bricks. Ashlar stones, oi ashlars, as they are usually called, are neatly squared and tooled on their surface, and arc made of various sizes according to convenience or the character of the building. The following is given on the authority of Mr. Peter Nicholson : — Walls are most commonly built with an ashiar facing, and backed with brick or rubble work. Brick backings are common in London, where bricks are cheaper ; and stone backing h} the north of England and Scotland, where stone is plentiful. Walls faced with ashlar and backed with brick or uncoursed rubble are liable to become convex on the outside, from the greater number of joints and from the greater quantity of mortar placed in each joint, as the shrinking of the mortar will be in proportion to the quantity ; and therefore a wall of this description is much inferior t( one of which the facing and backing are of the same kind, and built with equal care, even though both sides were uncoursed rubble, which is the worst of all walling. Where the outside of a wall is of ashlar facing, and the inside coursed rubble, the courses of the backing should be as high as possible, and set in thin beds of mortar. In Scotland, where stone abounds, and where perhaps as good ashlar facings are con- structed as any in Great Britain, the backing of the walls most commonly consists of uncoursed rubble, built with very little care. In the north of England, where the ashlar facings of walls are done with less neatness, they are much more particular in the coursing of their backings. Coursed rubble and backings are favourable to the insertion of bond timbers ; but in good masonry wooden bonds should never be in continued lengths, as in case of fire or rot the wood will perish, and the masonry, being reduced by the breadth of the timbers, will be liable to bend at the place where it was inserted. When it is necessary to have wall timber, for the fastening of bat- tens for lath and plaster, the pieces of timber ought to be built with the fibres of the wood per- pendicular to the surface of the wall, or otherwise in unconnected short pieces not exceeding nine inches in length. In an ashlar facing the stones generally run from twenty-eight to thirty inches in length, twelve inches in height, and eight or nine inches in thickness. Al- though both the upper and lower beds of an ashlar, as well as the vertical joints, should be at right angles to the face of the stone, and the face-bed and ver- tical joints at right angles to the beds, in an ashlar facing, where the stones run nearly of the same thickness, it is of some advantage in respect of bond that the back of the stone should be inclined to the face, and that all the backs thus in- clined should run in the same direction, as this gives a small degree of lap in the setting of the next course ; whereas, if the backs were parallel to the fronts, there could be no lap where the stones run of an even length in the thickness of the wall. It is of some advantage, likewise, to select the stones so that a thicker and a thinner one may follow each other alternately. The disposition of the stones in the next superior course should follow the same order as in the inferior course, and every vertical joint should follow as nearly as possible in the middle of the stone below. By the term beds of a stone is meant the upper and lower surfaces of the block. In usual walling these are horizontal. j n„ III] mil ? ^M\\ j ■'Hint ~«A ■llll'l f /Af/n [ *»urr i f m -W.4 "5=7 1 <*«/ ,/fl( w/l 1 ^1111 ~4,di U "III /H mill Lull- -ilfi mil ,,/l ‘ [ - — " 1 M U m"\ u VyJi ^in ,,lHl III ( L-.. ( i •" 1 '.i ■/.. .J- ^ i i ,,'•"/ carbon particles shrink together and form compounds of greater complexity, being some of the dense vapours which exist in a gas- flame ; and even the soot produced by a gas-flame is not pure, but requires intense and prolonged ignition to free it from. Hydrogen. A gas-flame is also perfectly transparent, and gives equal light in different positions. In the comparison of light of equal intensity, obtained from different materials, it is found that coal-gas, and especially gas from cannel coal, is the least unhealthy of all ordinary lights, which is contrary to the usual opinion. The illuminating power of coal-gas has been greatly improved of late years, but the inquiry is too extensive for our limits. We must be content to mention the passing of gas ever naph- thaline, when it takes up its vapour, thirty grains of which to one foot of gas increases the light seven or eight times ; with oil the result exceeds from four to five times, but even this is an important gain. Gas has been made from oil and resin, but both are too costly for street-lighting. Wood and peat are also used, and a village in Ireland has been lighted with gas made from bog-turf. The lime-ball and the electric lights are costly. The Bude light was lirst used for lighting the House of Commons in the year 1812 ; its flame, acted upon by a current of oxygen, has its brilliancy increased by a current of atmospheric air. It has been calculated that an ordinary candle consumes as much air while burning as a man does in the act of breathing ; the same may be said with regard to gas, oil-lamps, etc., bear- ing a proportion to the amount of light evolved. One hour after the gas of London is lighted, the air is deoxidised as much as if 500,000 people had been added to the population. During the combustion of oil, tallow, gas, etc., water is pro- duced. In cold weather we see it condensed on the windows of ill- ventilated shops. By the burning of gas in London during twenty-four hours, more water is produced than would supply a ship laden with emigrants on a voyage from London to Adelaide. Dr. Johnson is said to have had a prevision of gas lighting streets, when one evening, from the window of his house in Bolt Court, he observed the parish lamp-lighter ascend a ladder to light one of the glimmering pil-lamps ; he had scarcely descended the ladder half way when the flame expired ; quickly returning, he lifted the cover partially, and thrusting the end of his torch beneath it, the flame was instantly communicated to the wick by the thick vapour which had issued from it. “ Ah !” exclaimed the doctor, “ one of these days the streets of London will be lighted by smoke!” PROJECTION.— VI. THE PROJECTION OF CYLINDERS A cylinder is a solid body of the character of a prism, but its ends are circles. The axis, or line on which a cylinder might be turned, unites the centres of the ends ; and if the ends are at right angles to the axis, the solid is called a right cylinder. If the ends are inclined to the axis, so that if the cylinder were placed on one of them it would be slanting instead Df upright, it is called an oblique cylinder. In the first case the ends would be circles ; but in the second, although all the sections at right angles to the axis are circles, the ends being at an angle to it are ellipses. It will be readily understood that all sections passing from one end of a cylinder to the other, 2 parallel to the axis , will be parallelograms ; and by rolling up a rectangular piece of paper it will be seen that the surface of development of a cylinder is a parallelogram, the height of which is equal to the length of the cylinder, and the breadth to its circumference. Fig. 79 is the plan and elevation of a cylinder when standing on its base, and it will be evident that then, although the cylinder might be rotated on its axis, that axis would remain at right angles to the horizontal, and parallel to the vertical plane. Fig. 80 shows the elevation of the cylinder when its axis is at 45° to the horizontal, and parallel to the vertical plane. To project the plan of this, on A B describe a semicircle which will represent half of the end. Divide this semicircle into any number of equal parts, c d, d e, etc., as in Fig. 77 in the last lesson. From the points c, D, e, etc., draw lines parallel to the axis of the cylinder, which, passing from end to end, will give the same points in both. Draw a line for the axis of the plan parallel to the intersecting line, and perpendiculars from the various points in the elevation. Mark off the lengths, c c, etc., on each side of the axis, and through the points thus obtained draw the ellipses forming the plans of the ends. Unite taese by lines parallel to the axis, which will complete the plan. Fig. 81 is the projection of the cylinder when the axis is at 45° to both of the planes of projection. No description of the working is deemed necessary, as it is simply a repetition of Fig. 78 in the last lesson, and will, no doubt, be readily j understood. On referring to Figs. 27, 28, 29, 30, the student will be re- ! minded that if a, solid be cut across the parts will, when rotated on a centre, form an “ elbow ” — that is, they may be joined so as to turn a corner. This principle holds equally good in re- lation to cylinders. Fig. 82 is the plan and elevation of a cylinder which it is required to cut so that the parts may be joined to form an angle of 90°. The following rule must be impressed on the minds of students, viz. : Whatever may be the required angle, the section must be made at half that angle with the axis. Thus, if a pipe is to follow two walls which meet at an angle of 120°, each part must be cut at 60° ; and, therefore, in the present figure, draw the section-line, A B, at 45° (half of 90° required). If now the upper part of the cylinder be rotated on a centre (c), the point b will meet A, and the line b f will become A G. Now divide the plan into any number of equal parts at E, D, etc., and carry up perpendiculars from these points to cut the section-line in cl', cl', e', e'. To find the true section, draw A b (Fig. 83), equal to the section-line A b in Fig. 82, and set off on this line all the dis- tances, A e', e' d, etc. Through the points e', d', etc., draw lines at right angles to A B, and set off on them, on each side of the line A B, the distances which the. points similarly lettered are from the central line A B in the plan, thus obtaining the points c, c, d, d, E, e. Draw the curve of the ellipse, which forms the true section, through these points. Fig. 84. — To develop this cylinder, draw a horizontal line and a perpendicular, A. On each side of a set off the six equal spaces into which the two parts of the plan in Fig. 82 are divided, viz., a e, e d, etc., and A e, e d , etc., placing the letters E, D, etc., e, cl, etc., in the order in which they follow on each side of A. Erect perpendiculars from each cf these points, making B F equal to the height of the original cylinder (Fig. 82). Join f f, and the parallelogram b f f b will be the development of the entire cylinder. To trace the section-line on this development — that is, to draw the line in which the material is to be cut so as to form both the parts of the cylinder — erect perpendiculars from each of the points between B, b, and make them the height of those similarly lettered in the elevation. This is best done by drawing horizon- tals from the points in the section-line to cut the perpendiculars in the development which are similarly lettered. The points A, e, e, d, d, c, c, d, cl, e, e, b, B, will be thus obtained; and through these the curve is to be traced, which will be the development of the line of section ; and if a piece of sheet iron, or any other material, were so cut, the parts when rolled and joined will give exactly the same figures, the joint or seam being at the highest point in the one, and at the lowest in the other part. Fig. 85 is a view of the lower portion projected from the plan, when the diameter, A B, is at an angle instead of being parallel to the vertical plane. Fig. 86 shows the elevation and half-plan of a cylinder, which, on being cut twice at 45°, may be converted into a “ double-elbow.” Having drawn the half -plan (only the half is required, as the points in the other half would be immediately at the back of those here given), project the elevation from it; then divide the ! semicircle into any number of equal parts, and from these : points of division draw perpendiculars. Next draw the section- | lines at the required angle (in this case 45°), and at the two j extremities of the lower one draw lines at right angles to the elevation of the cylinder ; make these lines equal in length to the middle portion of the cylinder, and join them by a line at 45°. Erect perpendiculars at tneir extremities eoual respec- tively to the corresponding lines in the lower portion, of the object. Join these by a horizontal line, and this will complete 1 the elevation. PROJECTION. 101 The develop- ment of the piece of metal of which this double-elbow is to be cut must now receive our attention. Pro- duce the base-line of the cylinder, and at any part of it erect a per- pendicular (Fig-. 87), from which set off on each side the same number of equal parts as that into which the half-plan of the cylinder is di- vided, and draw perpendiculars from the points. From the top of the original erect cylinder draw a horizontal line, | Fig. 79 Fig. 81. and this, uniting the two external perpendiculars, will complete the general develop- ment. Returning now to the eleva- tion of the ori- ginal cylinder, it will be seen that the perpendicu- lars which were drawn from the points of division in the plan, cut both of the sec- tion - lines, and from these points of intersection draw horizontal lines to cut the perpendiculars in the develop- ment, that drawn from the highest point (viz., the point where the section-line starts from the side of the elevation) to cut the central perpendicular, and that from each of the other points to cut the next pair of per- pendiculars in suc- cession; through these points the curve, which is the development of the section- line, is to be drawn. The lower section-line will, of course, be de- veloped in pre- cisely the same manner from the corresponding points of inter- section occurring on it. Fig. 88 is the elevation and plan of one of the ends of the 102 THE TECHNICAL EDUCATOR. above object when resting on its section. On a horizontal line mark off the length of the section-line in the elevation, and at the extremities draw lines at 45° ; make these equal to the length of the longer and shorter sides of one of the end pieces of the elevation, and join them by a line which will (if their lengths be correct) be at right angles to them. Divide this line into two equal parts, and from the bisecting point draw a line parallel to the sides already drawn : this will be the axis. On ^ach side of this draw lines parallel to it, and at distances apart corresponding with those in the elevation, to meet the inter- secting line. Drop perpendiculars from these intersections, passing through a horizontal line drawn in the lower plane ; on these set off from the horizontal line the widths of the corre- sponding lines in the plan ; join the extremities by tracing an -ellipse to touch each, and this will.be the true section on which the object now rests. From each of the points through which the ellipse has been traced draw horizontal lines, and intersect these by perpendiculars drawn from the points occurring in the encl of the object ; through these intersections draw the ellipse, which will be the plan of the end. TECHNICAL EDUCATION ON THE CONTINENT.— IT. BY ELLIS A. DAVIDSON. POLYTECHNIC SCHOOL IN HANOVER— THE DIRECTION. The management of the general affairs of the school is vested by the Eoyal Commission in (1) the Director, and (2) the Prin- cipal (syndieus). The Director, whilst virtually responsible for the conduct of the whole Institution, takes especial charge of the monetary department and accounts ; he also supervises the collections of models, specimens, etc., which are entrusted to the teachers of the different departments. The library is under his direct care ; he exercises a general supervision over all persons employed in the establishment, and regulates the discipline of the students. The Principal holds his office under the general superinten- dence of the Director, his duties relating more to. the internal mana gement of the institution. Thus amongst them are com- prised — 1. The receiving and enrolling of pupils and attendants at lectures, in connection with the Director. 2. The conduct of the School Eegister in all the departments of the establishment. 3. Correspondence with parents of pupils, etc. 4. The receiving of returns from the teaching and domestic staffs, the compilation of reports, etc., in relation to students, lectures, teachers, and household matters. GENERAL MANAGEMENT OE THE INSTITUTION. The general conduct of the institution is vested in — • 1. A selection from the body of teachers and professors asso- ciated with the Director. 2. A sub-committee for all matters affecting the discipline of the establishment, consisting of five members of the general teaching staff and Board of Management, together with the Principal of the Polytechnic School. 3. The general board, called the “Plenum.” The duties of the body named in Section 1 constitute them what may be properly called the working school board. They administer the laws and regulations, decide on all cases which may arise, and legislate for all circumstances occurring which are not provided for by existing laws ; they prepare the course of studies, attend to matters of general discipline, and re-organise 'and modify arrangements i the internal wor’dnr? of the school, according to the requirements of the period. This body also decides on the applications for admission as free students and exhibitioners ; they confer with the Director, and make such suggestions as to alterations, etc., as their experience of the practical working of the school may from time to time show them to be necessary. The general board, or “ Plenum,” is composed of the entire body of professors and teachers, and in its meetings the Prin- cipal of the school presides. The duty of this body at their conferences is (1), so to regulate the scholastic matters that all the teachers may work harmoniously, and that the classes may oe so arranged as to assist, instead of obstructing, each other. (2) To receive the income and regulate the expenditure thereof in conjunction with the Director. (3) To select the students for premiums and other rewards. (4) To select the in-coming stu- dents from the gross number of applicants, according to the result of a preliminary examination. (5) To select the sub- committee for discipline alluded to above. THE SCHOOL. The school is divided into Upper and Lower. The students of the Lower School are, as a body, required to take all the subjects prescribed. This regulation is only re- laxed in exceptional cases, such as (1) whero an independent student (that is, one who is his own master) wishes to attend certain of the classes ; (2) where a student in the Upper School, who may be backward in any individual subject, desires to receive further elementary instruction not given in the Upper School. All are admitted to the freehand and linear drawing classes without reference to attendance for other subjects. The students of the Upper School are free to attend such lectures as they may find adapted to the course they are pur- suing ; this permission being subject to the capacities of the class-rooms. The students are, however, required to attend the classes and lectures belonging to their course with the utmost regularity and punctuality ; to prepare their studies, designs, and general work with the greatest care and diligence ; and to obey in every respect the code of rules, a copy of which is handed to them on their admission. Eespectable persons who are above twenty-one years of age, or who have studied in one of the universities, are admitted to the school as “ auditors” (zuhorer). ENTRANCE TO THE SCHOOLS. Candidates for admission to the Lower School must be at least sixteen years, and to tho Upper School at least seventeen years of age. They must present testimonials as to conduct and acquirements, and must be prepared to submit to the preliminary examination as under (a.) German language, stylo, and idiom ; an essay to bo written on a given theme, which shall be correct in composition, grammar, and orthography, and which shall show an acquaint- ance with, and an intellectual method of treating .the subject. ( b .) Facility in arithmetic, including decimals. (c.) An acquaintance with tho elements of algebra. ( d .) A knowledge of plane geometry. (e.) A general knowledge of geography and history. The preliminary examination for admission to the Upper School is based upon the course of studies in the Lower School, since the one serves as a stepping-stone to the other. Students who enter the Upper School expressly for the study of natural history are not compelled to take the mathematical examination ; they must, however, give proof that they possess sufficient education to enable them to understand tho lectures and to work them out. Students of freehand drawing or modelling are not required to undergo any educational test, and are admitted at sixteen years of age. Having thus given the history, constitution, and system of management of this noble institution, we can now proceed to consider the courses of study pursued in the school. We cannot, however, in reviewing the constitution of the governing bodies, avoid being struck by the circumstance that the professors and teachers are those who regulate the whole. Does not this in some degree account for the great measuro of success which has been achieved by this school and other- on the Continent of a similar character ? In England on ? managing committees are elected by their social and pecuniary position, not by their educational status ; it is not admitted that the masters are really the school, but they hold^ merely the position of journeymen who do a given amount of labour for a given wage ; and since the latter is, as a rule, far 1 below what ought to bo paid to gentlemen of education and position, the quality of the former is in many cases of a secondary character, or is very grudgingly given. COURSE OF STUDY IN THE LOWER SCHOOL. 1. Lower Mathematics. (First course, five hours weekly.) Arithmetic: powers— the binomial theorem— the theory of numbers — decimal and vulgar ir actions — evolution — equations FORTIFICATION. 103 of second, third, and fourth degrees — imaginary quantities — logarithms — simple and compound interest — stocks, etc. (Second course, five hours weekly.) Plane geometry — similar figures — measurement of surfaces — regular polygons and circles — plane trigonometry — stereotomy — the relations of the vertical to the horizontal, and of plane to plane — solid angles and spherical triangles — determining the volume and development of solids bounded by planes — cylinders — cones and spheres. This syllabus may at first sight appear rather high ; but it must be borne in mind that the students are all above sixteen years of age, and that they have all attended schools of a class which will be hereafter described ; in these the steps of instruc- tion have been such as to lead up to the course of study as carried on in the Polytechnic School. 2. Zoology and Botany. (Five hours per week.) Zoology in winter, botany in summer : general classification of animals and plants, with special reference to the animal and vegetable products used in trade. Practical study from natural objects, and modelled imitations of them, is combined with the lectures. In addition to this there is a class for the practice of microscopic investigation, and also in the summer excursions for the collection and examination of living specimens. 3. Mineralogy. (Five hours per week.) The elements of geology, mineralogy, and crystallography, by lessons, lectures, and practical observation. 4. Freehand Drawing. (In three divisions — lower, middle, and upper. Ten hours per week.) Ornamental drawing from flat examples and easts — in the upper divisions from casts of heads, figures, etc. 5. Linear Drawing. The elements of projection— geometrical constructions as studies of the combinations of straight and curved lines — linear drawing from copies. It may here be pointed out, that students who pass from the Lower to the Upper School, and intend devoting themselves to the study of either architecture or engineering, must show that they have advanced in freehand and linear drawing, at least as far as the middle division. COURSE OF STUDIES IN THE UPPER SCHOOL. 1. Higher Mathematics. (First course, five hours per week.) Analytical plane geometry — differential calculus — -differen- tiation and continued differentiation of the explicit and implicit functions of one or several variables — Taylor’s theorem — maxima and minima — the apparently indeterminate forms, jj etc. — integral calculus. 2. Higher Mathematics. (Second course, four hours weekly.) Spherical trigonometry — analytical geometry of surfaces — double and multiplied integrals — general and partial differential equations — interpolations — methods of the least squares — ma- thematical statistics, etc. 3. Solid Geometry. (Six hours weekly.) Orthographic projection of a point — line and plane — sections and developments — the projection of shadows — perspective, etc. 4. Practical Geometry. (First course.) (Lectures, three hours per week ; plan drawing and surveying, four hours per week in the summer ; and drawing from given measurements in tho winter.) Fundamental principles of practical geometry and its object — description, construction, and practical use of the instru- ments used in measuring, surveying, and levelling, map-drawing and measuring heights — the surveyor’s table — levelling-pole, chain, theodolite, etc. Students, before entering upon this course, are required to show their previous knowledge of the subject as far as taught in the Lower School, and are also expected to be acquainted with the elementary principles of physics. 5. Practical Geometry. (Second course.) (Lectures, two hours weekly ; plan drawing and surveying, four hours per week in the summer, and drawing from given data in the winter.) t The higher study and application of the subjects of Course 1 — trigonometrical and barometrical measurements of heights — geodesy — map-drawing from actual survey. C. Mechanics. (First course, five hours wee"kly.) In the first ten weeks of the course, lectures are given show., ing the practical application of higher mathematics to the present subject. 7. Mechanics. (Second course, five hours weekly.) The conditions of entering on this course are, a sound know- ledge of higher mathematics, Course 2 ; and of mechanics, Course 1. 8. Mechanical Construction. (First course, lectures, five hours $ study, eight hours weekly.) (a.) Introduction — the component parts of machinery — nuts and screws — gibs and cottars • — plummer-blocks — axles— cylinders — couplings — friction and tooth-wheels — levers — cranks — beams — direct motion — pipes — valves — glands and collars — pistons, etc. (6.) Arrangements for regulating motion — fly-wheels — gover- nors — breaks — also simple crabs, pumps, and presses. 9. Mechanical Construction. (Second course.) (c.) Continuation — crabs and cranes — the construction of water-wheels — turbines, steam-engines — pumps and blowing engines — railway machinery, with especial reference to the con- struction of locomotive engines and railway wagons — wheel gearing — kinematics. 10. Mechanism. (First course, general consideration, five hours weekly.) (a.) The popular importance of machinery — quantity, quality, and price of mechanical work, illustrated by examples — advantages and disadvantages of certain constructions — machines for measuring and counting — clockwork for measur- ing time and other purposes — registering machines — water and gas meters — dynamometers — weighing machines — historical review of machines for producing motion, and for changing the places or forms of bodies — classification of machines. (b.) Specialties of machines for producing motion — water* wheels, vertical and horizontal — hydraulic pressure engines, for reciprocating or rotary motion — windmills— steam, calorio (including gas-power) engines — machines for moving bodies * foad and railway locomotives — steamships — windlasses cranes and other raising machines — water-raising machines and fire- engines — blast and suction machinery — machines for altering the shape of bodies, especially mills — agricultural and domestic machinery. 11. Mechanism. (Second course, five hours weekly.) Recapitulation of the principles of mechanics, with special reference to the solution of problems in kinematics, and tho regulating of motion in machinery — experimental hydraulics — the theory of water-wheels and of blast and suction machines — the theory of vertical and horizontal water-wheels — the theory of hydraulic pressure engines, for reciprocating or rotary motion — the theory of steam-engines, railway locomotive, and streeb- transport engines — the theory of the steam-ship tho paddle screw and reaction propellers — theory of blast and suction machines — hammering, stamping, and rolling machinery. FORTIFICATION.— II. BY AN OFFICER OF THE ROYAL ENGINEERS. TYPES OF FIELD PROFILES ON LEVEL GROUND — DEFINITIONS NAMES OF SLOPES, ETC. USES OF VARIOUS PARTS OF PROFILE PENETRATION OF RIFLE BULLETS PENETRA- TION OF ARTILLERY NECESSITY FOR VARIETY OF PROFILE TO SUIT THE GROUND DEFINITION OF DEFILADE MEANS OF AFFORDING ADDITIONAL SECURITY. TO MEN FIRING OVER THE PARAPET. Types of Field Profiles .— The ordinary earthen parapet is a mound of earth thrown out from an excavation near it. When this excavation is behind the mound it is called a trench, and when it is between the mound and the enemy it is called a ditch. . . In the latter case* the defenders either fight on the same level 104 THE TECHNICAL EDUCATOR. as their opponents, or are raised above them, and the excava- tion serves as an obstacle to the enemy’s advance. When (as in permanent fortification) it is possible to make the ditch both broad and deep, it forms a serious obstacle, and affords sufficient earth for the formation of a really impor- tant parapet (Fig. 1). In field works, however, it rarely happens that the ditches can be made more than ten or twelve feet deep, in which case the obstacle is not sufficiently formidable, and ad- ditional arrangements must be made to delay the enemy under the close fire of the work. When completed with a suffi- ciently high parapet, this is •the best formation, as it offers the advantages of a command- ing position to the defenders, and protects them by an obstacle in front ; it is not, however, a rapid method of obtaining cover. Cover is more rapidly ob- tained by excavating a trench, in which the defenders can stand to fire over the mound of excavated earth ; because by this arrangement they are pro- tected by the parapet as well as by the depth of the excavation. Thus, for instance, a trench three feet deep will afford about six feet of cover. Th6 trench formation is therefore generally adopted for hasty entrench- ments in the field, and for the parallels and approaches em- ployed in sieges, to enable tho besiegers to advance towards the well-armed and formidable works of a fortress (Fig. 2). It must, however, be observed that there is no obstacle what- soever opposed to the enemy, and that as the defenders are standing in the trench, they are lower and consequently fight- ing to a certain extent at a disadvantage with an enemy outside. Occasionally, when there is plenty of labour available, but when the time for the construc- tion of the parapet is limited, or when it is desirable to con- struct a thicker parapet in a given time than could have been obtained by either of the above methods, a double set of workmen are employed — one party digging a ditch and the other a trench, and throwing up the earth between them (Fig. 3). This arrangement has many advantages ; it has, however, the defect belonging to all trench formations, viz., that the trenches are liable to be flooded in rainy weather, unless special arrangements are made to drain them ; and that, unless the parapet is unusually high, the defenders are only under cover while standing in the trench. It is applicable to rocky or marshy sites, where neither ditch nor trench can be made deep enough to provide sufficient earth for the parapet. Definitions. — The following terms are frequently made use of with reference to the profiles of works, and should be understood : — A revetment is an arrangement for supporting earth at a steeper slope than it would naturally assume, and various materials may be used for this purpose. The command is the height of the highest point or crest of a work above the level of the ground on which it stands ; or above some other work over which it has to fire. The former is termed the absolute command, the latter the relative command. A work is said to have a command of fire over another work, when its relative command is such as will admit of a direct fire from both parapets being kept up simul- taneously, without danger to the defenders of the front work. Assuming the work to be on level ground, in the same plane with the enemy’s position, and that the parapet should be capa- ble of giving cover and protec- tion to men of ordinary stature standing a certain distance in rear, it is evident that the crest must at least be six feet higher than the level on which they stand ; and when it is remem- bered that the trajectory or path of the enemy’s projectile is a curved line, it is plain that this height must be exceeded. A command of eight feet gives a fair amount of protection, but a greater command would, of course, be better. The relief is the difference of level between the crest of the parapet and the bottom of the ditch, or the command + depth of ditch. The ierreplein of a work is the level surface within it on which the active operations of the defence — such as working the guns, etc. — are carried on. In field-works with a low com- mand, the terreplein is usually the original ground-line (Fig. 4) ; but in permanent works, with a command of twenty or thirty feet, the terreplein is the level surface on the top of the embankment or rampart (Fig. 5). These terms “ rampart” and “parapet” are so frequently misapplied, that it would be well to note that the rampart is simply an embankment or mass of some material which raises the parapet to the re- quired level. Names of Slopes, etc. — The names of the various parts of a profile (Fig. 6) are — A b. Slope of the banquette, b c. Ban- quette. C D. Interior slope of parapet, d e. Superior slope of parapet, d e. Thickness of parapet. e f. Exterior slope of parapet. F a. Berm, g h. Escarp, h i. Bottom of ditch, i K. Counterscarp. k l m. Glacis. K L. Interior slope of glacis. L m. Slope of glacis. Uses of various parts of Profile. — When the parapet is high enough to give cover to those not actually defending it, a plat- form or step must be made at a convenient level (usually 4 feet 6 inches) below the crest, to enable the defenders to fire over the top of the parapet, with as little exposure to them- selves as possible. This step is called a banquette ; its breadth is 4 j feet when two ranks of men are to fire, and 3 feet when only one rank is required. The level of the banquette is gained either by steps or by a slope of about £, called the slope of the banquette, which is a sufficiently easy incline to enable men to go up or down with ease. To enable the men, when firing, to stand close up to the FORTIFICATION, 105 parapet, its interior slope is made about f, and as ordinary loose earth will not stand at so steep an angle for any length of time, it is supported by a revetment of sods, or some other material. The thickness of parapet is the horizontal distance between the crest and the exterior slope, or, in other words, it is the base of the superior slope. It is regulated so as to exceed the pene- tration of the projectiles it is intended to resist. Penetrations of Rifle Bullets. — These penetrations are very various with different guns at different ranges, and of course vary with the hardness of the resisting medium. The details of the various experiments on this subject would be too numerous to state here, and it will, perhaps, be sufficient to note some of the results. First, with reference to the penetration of the most im- proved specimen of small arms, viz., the Martini-Henry rifle, the following results were ob- tained ( vide “ Proceedings of the Artillery Institution,” 1869) : — Mantlets of four thicknesses of three-inch rope were proof against bullets at 400 yards. A gabion (or cylindrical basket two feet in diameter) filled with clay was penetrated at twenty- five yards, but not at longer distances. Two planks of green oak were not penetrated at 100 yards. Twelve inches’ thick- ness of fir planking was pene- trated at 100 yards. Earthen parapets, or sand- bags filled with earth, 2 feet or 2 feet 6 inches thick, are proof against any small arms what- ever. Penetration of Artillery . — The penetrating power of artil- lery has increased enormously in the last few years, and the earthen parapets of field-works, which a few years ago would have been made 6 or 18 feet thick, must now (if time admits of its being done) be increased to 12 or 24 feet thick to resist field artillery ; and in perma- nent works, to withstand the heaviest artillery, earth para- pets from 45 to 50 feet thick will be required. The top of the parapet is made to slop# to the front, to admit of the musketry fire from the work sweeping the ground on the further side of the ditch. This is termed the superior slope, and is usually about A. In an earthen work it should never be made more than |, as if it were so, the thickness near the crest would be too weak to resist the enemy’s projectiles. The exterior slope is the outside portion of the parapet most exposed to fire, and consequently should be built at the inclina- tion that the soil of which it is composed would assume when loosely thrown up. Made-earth will rarely stand at a steeper angle than 45°, or I, and in sand or loose soils the angle is less ; it must therefore be understood that, although the exterior slope will be assumed as f for purposes of calculation, etc., it would in reality depend on the soil, and probably would be less steep than this. Berm is a space left between the foot of a slope and the edge of the excavation near it. The berm at the foot of the exterior Blope is useful, as it facilitates the repair of the parapet, and tends to prevent the weight of the parapet from breaking down the earthen slope of the escarp, and slipping into the ditch. The escarp is the side of the ditch nearest to the work. In order to make it difficult for the enemy to get up, it would be desirable to make the escarp vertical ; but the weight of the parapet prevents this being possible in field-works with unrevetted ditches. It therefore is a slope varying from s to a, according to the tenacity of the soil. In permanent works, the escarp is a very formidable obstacle, usually a wall about thirty feet high, placed in the ditch so as to be hidden from the distant view and fire of the enemy, and where it can only be destroyed with great difficulty . The ditch provides the earth for the parapet, and, if deep enough, serves as an obstacle. Owing to the difficulty of throwing the earth higher than twelve feet, the ditches of field- works rarely exceed that depth, In permanent fortifications, when time and labour are available, the ditches are much deeper — in some cases exceed- ing 50 feet in depth, as, for in- stance, at Portland and at Malta. The width of the ditches in field-works is never very great, but in permanent works it varies from about 50 feet to 60 yards. N.B, The ditches of the new works at Antwerp are 60 or 80 metres in width. The counterscarp is the sido of the ditch opposite to the escarp, and as there is but little weight to bear on it, this slope in field-works may be made as steep as the soil will admit of. In a firm soil, and with moderate level strata, it will stand for some time at a slope of i ; but all steep earthen slopes should be revetted to withstand the effects of rain and frost. In permanent for- tifications the counterscarp is usually a wall which, in some cases, has a gallery behind it, and is loopholed to allow of a musketry fire being brought to bear on the bottom of the ditch. The glacis is a mass of earth placed on the outer side of the ditch, to bring the ground beyond the counterscarp under the fire from the parapet ; and is also used in field-works to protect, from the enemy’s fire, the various obstacles in- tended to delay his advance (Fig. 7). The earth necessary for this latter object can be obtained by excavating, as shown above. In all the foregoing examples it has been assumed that the works were on level ground, and that a parapet eight feet high would protect men standing in rear of it ; and that men, whilo firing over an earthen parapet, are only protected breast high. Let us now consider how these arrangements must be modified when the ground is sloping, or the enemy is on a higher level than the interior of the work ; and then how better protection can be obtained for the men firing over the parapet. Necessity for variety of Profile to suit the Ground.- — From Figs. 8, 9, 10 it will bo seen that, although a height of eight 106 THE TECHNICAL EDUCATOR. feet of parapet may be sufficient on level ground to protect men standing behind (Fig. 8), it will be necessary to obtain more cover by either raising the crest or lowering the terreplein when (as in Pig. 9) the enemy is on higher ground, or (as in Fig. 10) when the enemy is on the same level as the work, but the ground rises behind it. Definition of Defilade .— The various practical operations that are gone through to ascertain how much the parapets should be raised to obtain cover, are called defilade, and will be further explained hereafter. To protect the head and shoulders of men firing over the parapet, loopholes are made on the superior slope, by laying two filled sand-bags on the slope, as shown in Fig. 11, and then laying two other filled sand- bags across ’ them, as in Fig. 12. When sand-bags are not available, a stout log of timber may be laid lengthwise along the crest, and supported at intervals, so as to leave room under- neath for men to fire between it and the crest (Fig. 13). This gives good bullet-proof cover ; but if hit by a shot or splinter of a shell, the beam will probably be carried away, and may kill the men standing behind it. Fig. 14 shows a section of a rifle-pit with sand-bag loophole. AGRICULTURAL CHEMISTRY.— III. BY CHARLES A. CAMERON, M.D., PH.D., Professor of Hygiene in the Royal College of Surgeons, Ireland, etc. CHAPTER III.— HOW PLANTS GROW. The final act of vegetation is the production of seed, after the performance of which function the individual plants of many species immediately perish, having in the reproduction of similar organisms accomplished their destined career. The seed developed by the mature plant contains the germ of the future individual, which may therefore be regarded as the heir to the plant ; and as the provident human parent lays by a store for his offspring, intended to supply their wants until the time arrives when they shall be able to provide for themselves, so also does the parent plant ceaselessly occupy itself during a portion of its existence, in accumulating provisionary stores destined to nourish its offspring during the earlier stages of its growth. This analogy is interesting, and it admits of being further extended. The first process which takes place when the embryo plant contained in the seed is about to assume an independent existence is termed germination. In order to describe this pro- cess, we must first explain the structure of the seed. We will take the common garden bean as an example. It consists of an integument, covering, or case, termed the testa, within which is enclosed the embryo, or immature plant. On dissecting the seed, two large oblong and flat bodies are observed, which bear some resemblance to leaves, and are termed cotyledons. The bean contains two of these organs, but other kinds of plants have a greater number, whilst a few species are destitute of them. On separating the cotyledons, a small bud-like projec- tion is seen ; this is called the plumule, and it consists of ex- tremely minute leaves. At the base of the plumule is the corcule, or germ of the future plant. From the lower part of the corcule tapers an elon- gation, which, during the pro- cess of germination, is termed the radicle, and is subsequently developed into the root. The corcule is connected with the cotyledons, from which it de- rives its nutriment, by suitable vessels. When the seed is placed in the soil, and supplied with the heat and moisture necessary for germination, that process soon takes splace. The seed absorbs moisture, becomes soft, increases greatly in size, and finally bursts. The temperature at which this first effort of the vital force takes place is dif- ferent in the cr.se of different plants ; for all varieties it must be above 32° Fahr. The seeds of the plants of temperate climates require, with few exceptions, a temperature of at least 40° ; whilst the seeds of tropical plants do noi in general germinate under 70 p . According to Sachs, plants do not grow vigorously when produced from seeds which have been IV. Garden Bean. a. Testa or outer covering. V. Garden Bean Germinating!. a. Cotyledon ; b. Plumule ; c. Radicle. germinated at a low temperature ; on the other hand, seeds germinated at too high a temperature do not produce healthy plants. When the testa bursts, two shoots issue from the seed : one — the plumule — springs upwards, and is gradually developed into the stem of the plant ; whilst the other, sinking into the soil, becomes in process of time the root. During these changes, the composition of the seed undergoes important alterations. Its insoluble starch is converted into solu- ble sugar and a gum - like substance termed dextrine, with which the young plant is chiefly nourished. The albuminoids, or nitrogenous matters originally present in the seed, also are employed in feeding the young plant, and they gradually disappear from the seed. The cotyledons being thus deprived of the great bulk of their starchy and albuminous constituents, sometimes perish ; but very often they make their appearance over ground, acquire a green colour, and for a brief time discharge the functions of leaves. When the cotyledons begin to act upon the atmosphere, the independent existence of the young plant commences. Up to this point oxygen gas is absorbed, and carbonic acid gas ex- haled ; but in future the plant will absorb carbonic acid and exhale oxygen. The great bulk of the seed is made up of starchy matter, which, being insoluble, is not capable of nourishing the plantlet. There is also present in the seed albu- minoid bodies — substances containing nitrogen — which are very liable to enter into a state of fermentation. During germina- tion a portion of the nitro- genous matter ferments, and becomes the peculiar sub- stance termed diastase, which possesses the property of con- verting starch into sugar and dextrine. It is stated that one part of diastase is capable of converting 2,000 parts of insoluble starch into soluble dextrine and sugar. This curious attribute of diastase is common to the albuminoid bodies found in plants ; they are termed ferments. The albuminoids are like starch, insoluble in the ungerminated seeds ; but during fermenta- tion they become more or less soluble, and thus contri- bute to the nutrition of the plantlet. So soon as the young plant has exhausted the stores of organic food supplied by its parent, it enters upon the second stage of its existence, and now begins to vegetate. Henceforth it must depend upon air, soil, and water for its existence, and it must elaborate these mineral sub- stances into the various tis- sues of its structure. We shall now explain the nature of the mineral food of plants, and the means by which they absorb it. We have already stated that the great bulk of vegetable matter is composed of the elements oxygen, hydrogen, nitrogen, and carbon. These elements exist in the air — carbon as car- bonic dioxide (carbonic acid, a compound of twelve parts of carbon with twenty-four parts of oxygen) ; hydrogen as water (hydrio oxide, composed of two parts of hydrogen united with sixteen parts of oxygen) ; nitrogen in a free state and in the form of rmmonia (a compound of fourteen parts of nitrogen and three VI. Germination op Garden Bean in Advanced Stage. a. Cotyledons ; b. Plumule ; c. Corcule; d. Root-fibres^ TECHNICAL DBA WING-. 107 parts of hydrogen) ; and oxygen free and (combined with hydrogen and carbon) in the forms of water and carbonic acid. The greater part of the food of plants is undoubtedly supplied by the atmosphere, but it would appear that the free oxygen and nitrogen of the air are not assimilable by plants. A-Vere the free nitrogen of the air capable of furnishing plants with the amount of this element which they require, there would be_ no necessity for applying ammoniacal manures to our soils. • Bcforo further considering this point, we shall state the composition of the atmosphere which surrounds our globe, extending to a height of at least forty-six miles from its surface. AVERAGE COMPOSITION OF THE ATMOSPHERE. Essential . . Non-Essential Nitrogen Oxygen . . Watery vapour Carbonic dioxide Ozone Ammonia . Nitric acid . Carbonic oxide Carburetted hydrogen Sulphuretted hydrogen Organic and solid mineral 1 latter Parts. 77-95 20- Cl 1-40 •04 > traces 100-00 According to Yille, there is but one part of ammonia in 28,000,000 parts of air ; but Angus Smith found a larger pro- portion — one grain in 412'42 cubic feet in the air of Man- chester. Small as this proportion of atmospheric ammonia is, it appears to be sufficient for the purpose of supplying unculti- vated vegetables with sufficient amounts of nitrogen. In the case of most kinds of cultivated plants, it is, however, found neces- sary to supplement the atmospheric ammonia with nitrogenous manures, such as Peruvian guano, ammonic sulphate (sulphate of ammonia), sodic nitrate (nitrate of soda, or cubic nitre), and the various “ natural manures ” obtained in the farm-yard and -elsewhere. By the decay of organic matter in the soil, ammonia and nitric acid are produced, and both are sources of nitrogen to vegetation. Nitric acid is formed in the atmosphere by the oxidation of ammonia under electrical influences ; and "very year several pounds’ weight of this substance descends upon every acre. Potassic cyanide (cyanide of potassium) is capable of yielding nitrogen to plants, as is also, as I have shown (“Transactions of the British Association, 1857 ”), urea, the chief nitrogenous matter in fresh liquid manure. It has been contended that the soluble organic matters in the soil directly furnish nitrogen to plants ; but the weight of scientific evidence is against this assumption, as it is also opposed to the statement that vegetables are capable of assimilating the free nitrogen of the atmosphere. The absorption of carbonic dioxide by plants takes place chiefly through the “ breathing pores,” or stomata,” of their leaves. In agricultural plants the stomata are nearly altogether found on the under side of the leaves ; they are very numerous, the leaves of some species of plants containing more than 150,000 per square inch of surface. The stomata communicate with the intercellular spaces in the plant, and consequently the air has ready access through them to the interior of the vegetable mechanism. It is chiefly by means of the stomata that the excessive water absorbed by the root is exhaled ; and through these openings the gas generated within the plant, and not required for its nutrition, is got rid of. Plants cannot grow in the dark. Fungi appear to be excep- tions to this rule, but they are not in reality, for they cannot /row in the absence of light, except at the expense of the juices of other kinds of vegetables. The carbonic dioxide, water, and ammonia, taken into the vegetable mechanism, are decomposed under the stimulus or the solar beams, and their elements organised into the various structures and products of the plant. All the oxygen taken into plants in the form of carbonic dioxide is not required, and therefore a large proportion of it is exhaled through the stomata into the atmosphere. Carbonic dioxide is a poisonous gas to animals, whilst oxygen is the vital prin- ciple of the air which they breathe. Plants, therefore, by absorbing carbonic dioxide and exhaling pure oxygen, act as purifiers of the atmosphere ; while, on the other hand, -animals, by inspiring oxygen and expiring carbonic dioxide, indirectly contribute in an important manner to the nutrition cf the v ege- table creation. The stomata have contractile powers, which subserve useful purposes. For example, under the influence of a dry atmo- sphere, the size of these openings decreases, and thereby pre- vents too rapid an exhalation of moisture from the plant. Moisture is indispensable to vegetable life ; and if growing plants were deprived of all, or nearly all, the water which tucy contain, they would speedily perish. Under the stimulus of light the stomata increase in size, and absorb more carbonic dioxide. Plants grow, other conditions being equal, in propor- tion to the amount of the sun’s light and heat which they re- The mineral or ash ingredients of plants are absorbed through the roots. Some cf these ingredients — the alkaline salts for example — are soluble in pure water ; others — sue*, as, for in- stance, calcic phosphate — require for their solution water con- taining carbonic dioxide, and certain saline matters which in- crease the solvent power of water. The water contained in the soil holds in solution carbonic dioxide, and other matters, by means of which it is enabled to dissolve all the mineral substances required by plants. The term spongioles lias been applied to the fine points of the branches of the root, and until recently it was the belief of vegetable physiologists that absorption of water and other matters took place only through these fibril or rootlet terminations. Ohlert, however, has shown that the real absorbing surface is close to, but not actually at, the tips of the roots. Every part of the roots, the epidermis, or covering of which is young, thin, and soft, appears to be more or less capable of absorbing plant-food ; but they have not pores corresponding with the stomata of the leaves and stems. . The green colour of the leaves and stems of plants is duo to the presence of a pigment termed chlorophyll. When the green colour of the leaves disappears, the growth of the plant is wholly or in part arrested, and the inorganic forces are at work. The parts of the plant engaged in the absorption of carbonic dioxide possess colour, generally green. When parts of growing plants arc kept in darkened situations, the forma- tion of chlorophyll is prevented. It is by this means that the blanching of that favourite esculent, celery, is effected. TECHNICAL DRAWING. — VII. wooden bridges ( continued ). At each end of the piers in the water, in cases where several rows of piles are driven, a sort of cutwater should be formed, in order to ward off heavy bodies, such as floating trees, ice, etc., and prevent them from injuring the superstructure (caked in German constructions, “ Eisbrecher,” or ice-breaker). ^his is usually done by driving one pile by itself in advance of tho rest, or by forming what is called a “dolphin at each end ot the pier. The piers and abutments should, of course, be made in every case sufficiently strong to resist the thrust of the arch. In the case of small bridges, where the distance between tho supports is sometimes as much as twenty or thirty feet, longitudinal scarfed girders may be laid upon the caps of the pile's. Under such circumstances, as we have seen, there is nothing but tho weight or perpendicular pressure to be pro- vided for ; and tho same may be said of timber bridges of greater width for roads, and even for railways, provided the distance between the piers does not greatly exceed ten or fifteen feet. Beyond that opening, however, bridges are usually sus- tained by struts or tension-rods, or the roadway timbers arc trussed so as to exert an oblique pressure upon the supports ; indeed, in all instances of the kind, where the bays are formed upon the principle of compression or tension, the piers must be so formed as to counteract the tendency constantly exeited to force them out of their perpendicular position. This must be done either by making the piers of sufficient weight and strength to overcome any force that may be exerted against them, or else to counterbalance the efforts of one bay or arch acting in one direction, by a similarly acting arch or timber frame exerting a like amount of force in the contrary direction. The former of these methods is employed in the abutments of 108 THE TECHNICAL EDUCATOE. a bridge, whilst the latter is invariably adopted with respect to piers. The roadway of timber bridges is usually a flooring of boards laid upon the joists, for, in cases where sand and stones are employed, it is found that their weight, 1 together with the Jiumidity they engender, causes the timDers of such bridges speedily to decay. This, however, is far from being a general rule, and many splendid erections of this description are rapidly being destroyed, owing to a want of attention to this important particular. Some have proposed to cover the surface of the roadway with lead, iron, copper, etc., but the increased expense will be a great obstacle to their frequent introduction. Wood pavement forms an excellent covering for timber bridges, and is highly recommended by various engineers. The parapet, or hand-rail, of these bridges is frequently of wood, or it may be of cast and wrought iron. Now, however, Returning, then, to the drawing (Fig. 32), the horizontal line drawn is to be the top line of the cross-beams, which in Figs. 36 and 37 are lettered c. Now, in the front elevation these are seen in section ; but, as you will require the same height in the cross-section (Fig. 33), draw this line of indefi- nite length at once ; and this system of projecting one view from the other is to be carried on throughout, as thereby much time will be saved, and greater accuracy ensured, for it is by far easier to continue a line at once than to “piece” it afterwards. Next draw a second horizontal line under the other, at such a distance from it as to give the lower edge of the cross-pieces, c, and then, having drawn the irregular line representing the bed of the stream, draw the vertical lines, which will form the sides of the struts, d d (seen in front elevation). Now, on referring to the cross-section (Fig. 33), it will be seen that precisely this same arrangement exists in regard to the that it has been shown how impor- tant an addition to the strength of a bridge the sides of a beam are, and that it acts usefully in the direction of its depth, if it has only sufficient breadth to pre- vent its yielding laterally, it ought in every case to be made available to sustain the bridge, in addition to its present pur- poses of ornament and protection. Fig. 32 is one of three bays of a wooden girder bridge, which is the simplest class of such constructions, consisting merely of beams laid across the stream and supported by piers formed of wooden framework, from which struts spread out on either side, which extend the bearing effect of the piers, and so diminish the length of the girder which is left unsup- ported. In copying this example first draw a horizontal line, to form the top of the elevation of one of the cross-pieces, which, rest- ing on purlins, clamp the piles forming the piers between them. As this portion of the structure is shown on an enlarged scale in Fig. 36, the lettering here given will apply to that illustration. a' a', then, is the front elevation of the pile against which the struts, d, are firmly bolted, and on to these the purlins, /, are notched. Those struts, too, are halved on to the pile at their upper ends, so that they clamp it between them. This arrangement is shown in Fig. 37, which is the side elevation. middle pile — namely, that it is clamped between two cross-pieces, and against these two struts abut. These cross-pieces are shown in sec- tion in Fig. 33, the struts being merely represented by the three perpendicular lines under these. They are, however, shown in elevation in Fig. 32, where their effect of adding to the steadiness of the frame will be evident. The foundation of the pier being thus completed, next draw the uprights and the cross-timber resting upon them. This is shown in its full length in Fig. 33, and in section on each of the piles in Fig. 32. The upper line of this cross-timber will, of course, form the lower line of the main girders resting upon the cross-pieces. Now draw the upper edge of these gii’ders, which, of course, are seen in elevation in Fig. 32, and are represented by seven shaded squares in Fig. 33, these squares representing the sections of the seven ribs, which will thus be seen to be made of square timber. Each of these girders rests immediately on a pile, so that the bridge is supported bj seven ribs. You will now draw the struts, and as these are here placed at an angle of 45°, you can use your set-square, or, of course, you can find the exact inclination, whatever that may be, by measuring the distances of the upper and lower ends of the strut from the right angle. These struts arc now to be added to the cross-section (Fig. 33), from which it will be seen that they are narrower in this direction than in the other. TECHNICAL DRAWING. 109 The horizontal line forming the toy the flooring of the bridge is now to be drawn, and as these nlr-iiiS, of course, run at right angles to the girders, their ends are shown in Fig. 32, whilst their length is shown in Fig. 33. Fig. 34 is an example of a bridge in which the struts abut against centre-pieces, placed on the under side of the girders. They do not, however, touch these centre-pieces directly, but Fig. 40 is an illustration taken from a five-bay girder bridge in Germany. This is supported on stone abutments and piers, the bearing of which is extended, first, by two saddle-pieces, the upper projecting below the under one, which, in its turn, projects beyond the pier. Next, the bridge itself is formed of double girders, one above the other. Now the upper one is supported by struts, which are shown in the longitudinal sec- cross-timbers, the sections of which are shown in the elevation, I are placed as end-ties, and against these the struts abut. The heads of the piles are united by a waling-piece, on which, over each pile, a saddle-piece rests, supported by struts. This gives a much broader surface on which to rest the girders, which are scarfed at this point. In drawing this bridge, the system is precisely similar to that adopted in the former example, and therefore no further ex- planation need be given. Figs. 38 and 39 are examples of scarfing the girders, and of the methods of supporting them. The latter method is that adopted in the preceding study. The subject of scarfing will | be treated in “ Building Construction.” tion (Fig. 41), and as cross-timbers passing transversely beneath the lower girders are bolted through to the upper ones, the lower girders may bo said to be suspended from those above them. From Fig. 42, which is a transverse section on the line a b, it will be seen that the footway is raised to a higher level than the roadway by means of square timbers resting on trans- verse beams. The roadway is laid upon round timbers, which are extensively used in Germany. Although only one bay is given in the example, the student is advised to draw more than this (of course to a larger scale), as the practice thus obtained will be of great service to him. In commencing, rule a straight line for the bed of the river, and draw the foundations and embankments. Next erect per- 110 THE TECHNICAL EDUCATOR. pendiculars on the middle of the foundations, to act as centre- lines for the piers. On these perpendiculars, mark off the heights of the cornice and capping of the piers and abutments, and draw the required horizontals ; on these, mark off the re- spective widths from the centre-line, and complete the piers both above and below the capping. The profile (or side view) of the abutment now requires our attention, the next task being that of drawing it at the same slant as the sides of the piers. Now, in this bridge the space between the abutment and the pier is the same as that between any two of the piers; therefore, measure that distance from centre to centre , and from the central perpendicular of the last pier mark off this distance on either of the horizontals, and through the point thus obtained draw a perpendicular, which will be to the profile of the abutment as the central perpen- diculars are to the piers ; therefore, procoed in the same manner to set off half the . width of the pier on the horizontals, and thus complete the abutments. The double saddle-pieces resting on the piers and abutments are to be drawn next, and then the double girders. ANIMAL COMMERCIAL PRODUCTS.— IY. ruminantia ( continued ), The skin of the lamb is made into collars, muffs, gloves, and coat-linings. The most valued of these skins are furnished by Southern Russia, Greece, and Hungary. Beautiful black lamb-skins are imported from the Crimea, and others still more rich and glossy, with a short fur, from Astracan. The lamb- skins from Persia are known by the curl of the hair, which is produced artificially by tying up the lamb, as soon as born, in a leathern skin, and thus preventing the hair from expanding. These Persian lamb-skins are used for coats and other garments. The skin of the foetal calf is used for covering trunks. The principal fur marts for the English or Canadian furs are London, in Upper Canada; Fort William, on Lake Superior; and in Lower Canada, Montreal, on the River St. Lawrence. II. — PERFUMES. The Mush Deer ( Moschus moschiferus, L. ; order, Ruminantia). — This animal, which furnishes the well-known perfume called musk, is about the size of a roebuck, without horns, legs very slender, and in all its movements exceedingly active and graceful. The musk deer is found in herds in the mountains of Central Asia, and in some of the larger islands of the Indian Ocean, such as Ceylon, Java, Sumatra, and Borneo. It is a shy animal, fond of precipices and almost inaccessible crags, and therefore very difficult to shoot. The musk is produced in a glandular pcuch in the abdomen, and is peculiar to the male. It is in the form of reddish-brown coarse granules, and greasy to tho touch. The average quantity which can be removed from one pouch is about 190 grains. Musk is known in commerce under two forms — as Tenquin or Thibet musk, which is the most valuable, and Siberian, Kabardinian, or Russian musk, of inferior quality. The Oriental or Tonquin musk, from Cochin-China and Tonquin, is imported in small oblong, rectangular boxes, which are lined with lead, to prevent the escape of the odour ; the musk bags, wrapped in thin blue or red paper covered with Chinese characters, are placed in these boxes. These musk bags are usually covered with hairs, which all converge towards the little narrow opening in the bag. The weight of each bag varies, some not exceeding half an ounce, whilst others weigh upwards of two ounces. Large numbers of musk deer are annually killed. The annual import of musk into the United Kingdom is upwards of 10,000 ounces. Besides these uses, musk also possesses valuable remedial qualities. When genuine, it is one of the most powerful of the anti-spasmodics, and is applied with advantage in cases of infantile spasms, when not accompanied with inflammation. Civet Cat (Viverra civetta. Gmelin; order, Carnivora). — Anative of Northern Africa, and especially common in Abyssinia, allied to the pole-cat and marten. Body from two to three feet long, r.nd from ten tc twelvi inches high ; tail half a3 long as the t ody. This animal yields a perfume which is thus obtained : — The civet, when captured, is enclosed in a small cage, in which it cannot turn round, and while thus confined, the secretion is removed from its large anal pouch two or three times a week with a spoon or spatula. The interior of the pouch is glandular, the glands secreting the perfume from tae blood of the animal. The substance itself is of a pale-yellow colour, and of the consistence of honey. It is not unlike musk, and to most persons smells disagreeably ; but when mixed with butter, wax, lard, and alcohol, in the proportion of 1 part to 1,000, it loses its offensive character, and becomes aromatic and delicately fragrant. Thus prepared it is used in perfumery, and when employed renders more perceptible other scents with which it is mixed. Lavender and other scented waters become more agreeable by the addition of minute quantities of civet. The substance is not so much in use now as formerly ; never- theless, there is still a cons’ icrable consumption of it in this country, and as much as forty shillings an ounce is paid for it. Viverra zibetha is another species of civet cat, peculiar to the Asiatic continent, and found from Arabia to Malabar, and in the larger islands of the Malayan Archipelago. It is much milder in its disposition than the African species, and is domes- ticated by the Arabs and Malays. Our supplies of civet are also derived from this animal, although to a less extent than from the African species. Castoreum, which strongly resembles musk in its medicinal qualities and applications, is furnished by the beaver ( Castor fiber, L.). This substance is secreted in tho interior of a little bag or pouch, with which the beaver is supplied. It is brought to market, like the musk, ilL tho pouch. The best Castoreum is that from Russia and Siberia ; a very good quality is furnished also by Poland, Prussia, Bavaria, Germany, Sweden, and Norway ; an inferior kind comes from Canada and the territories formerly belonging to the Hudson’s Bay Company. Ambergris. — This substance is obtained from the sperm whale. It is an expensive drug, because not frequently found, and is valued on account of the excellency of its fragrance. Amber- gris is a morbid or diseased concretion formed in the stomach, or probably in the gall-ducts, of the sperm whale, in masses cf considerable size, sometimes weighing thirty or forty pounds. It is usually found floating on the surface of the water, probably disengaged from the floating body of one of these monsters, and is rarely sought for in the intestines of tho sperm whale, although it is worth a guinea an ounce. It is fished up in the Indian Ocean, near the Moluccas and Philippine Islands ; also near Sumatra, Madagascar, and on the coast of Coromandel. In the Atlantic Ocean it is found near the West Indies and tho Brazils. Ambergris is used as a costly frankincense, principally for perfumes, especially in France. It has also the property cf increasing the power of other perfumes when mixed with them, and it is principally for this purpose that it is used. OPTICAL INSTRUMENTS.— I. By Samuel Hiohiey. SPECTACLES TIIE NOEMU EYE. One of the first offices the optician is called on to perform is to aid humanity, when through age, defect, or absolute disease, the organs of vision deviate from the very perfect optical arrange- ment that characterises the normal eye. The Normal Eye. — Every perfect (or as it is technically termed, normal) eye possesses tho power of “accommodation,” that is, of adjusting itself for different distances, now looking at something near, as a book at reading distance, then at somo' far distant object, presently taking in at a glance the range of an extensive view. In a normal eye the whole apparatus of accommodation is so beautifully balanced, its functions performed with such ease and accuracy, that although in reality a voluntary act, its duties are from early childhood fulfilled intuitively, . impercep- tibly, and unconsciously. A familiar exemplification of the power of accommodation maybe made by placing one object at a yard distance from tho eye, and another at six yards beyond it ; on looking intently at either we are conscious of ilie presence of the other, but we do not discriminate its details ; on fixing one, we lose the definition of the ether. Again, if tho letters cf a book, held at somo distanco from the eye, bo looked at through a gauze veil placed, I OPTICAL INSTRUMENTS. Ill nearer the eye, it will be found that when the letters are seen distinctly the veil will be seen indistinctly ; and conversely, if the veil is seen distinctly, the letters will be seen indistinctly. These experiments demonstrate that images of objects at different distances from the eye cannot be defined at the same time upon the retina. The human eye is a camera obscura, furnished with an achro- matic lens, compounded of three principal parts, namely, the aqueous humour, k (Fig. 1), held in place by a transparent horny capsule, the cornea, g ; the crystalline lens, n, the principal refracting medium ; and the vitreous humour, q, which constitutes the main body of the eye, in which optical combina- tion the iris, m, placed between the aqueous humour and the crystalline lens, plays the part of a self-adjusting diaphragm ; the circular opening or “ stop ” in the pupil expanding when the light is feeble or the object viewed is distant, and contract- ing as the light becomes more and more intense or when the object viewed is near. This compound lens projects an inverted image of an object on the retina, o, which corresponds to the focussing glass of the photographer’s camera. The retina is a delicate and sensitive network of nervous filaments springing from the optic nerve, x, that conveys to the brain the impression of an image focussed on. the retina. The sclerotic, h, a tough white membrane, forms the wall of the eye, and corresponds to the rigid box of a camera, and to this wall are attached the various muscles that (like the hands of the photographer) direct the eyeball to the object. The sclerotic is lined with a delicate membrane, the choroid, e, coated on its inner surface with black colouring matter ( pigmentum nigrum), shown behind o, which serves the same purpose as the black paint or velvet on the inside of a camera, viz., to reduce to a minimum all internal reflections. So far tho comparison between the eye and a camera is perfect, but here the parallelism of properties ceases. In tho ordinary camera the image of an object is received on a flat plato of glass ; but, as a consequence of every lens being subject more or less fo the defects of spherical aberration, if the central portion of the object is perfectly depicted on the screen, tho marginal portion will be distorted and indistinct, through the marginal rays emanating from that object being blurred by the focal point falling short of the focussing glass; conversely, if the marginal rays are brought to focus on tho screen, tho central portion of tho image will become indistinct through being out of focus. In the human eye, however, the retina being the most perfect form of focussing screen that could be designed — viz., hemispherical or basin-shaped — the delineating rays fall on its surface in the precise ratio of their lengths. In the above general description of the component parts of tho human eye it is stated that the external walls or sclerotic correspond to a rigid camera, that is to say, one wherein tho box is not made with a telescopic draw, to obtain facility for focussing near and distant objects. In a telescopic camera, on pointing the lens to a near object, we have to draw the focussing glass away from the lens to secure a sharp image on the ground-glass screen (or retina of the camera), while on pointing to a distant object we must push the screen nearer the lens to obtain the same result. Now it might be supposed that the act of focussing (or power of “ ac- commodation,” as it is termed) was obtained through the elasticity of the walls of the eyeball (acted on by sympathetic muscular power), in the one case elongating, in the other con- tracting in length in the direction of its axis ; but this is not tie case. Great has been the discussion among physiologists as to the exact means by which the accommodation of the eye to far and distant objects is really effected, but general opinion at the present day is in favour of the view that it is through curvature of the crystalline lens being increased when near objects are viewed, and decreased when distant objects are observed, and further by its change of relative distance between the iris and retina. The experiments of Dr. Young on persons deprived of the crystalline lens, and who were thereby incapacitated from focussing their sight, seemed to put the question of the power possessed by this portion of the eye beyond dispute ; while the recent investigations of Cramer and Helmholtz have definitely settled it. When the normal eye in a state of rest is adjusted for an object, d, at an infinite distance* (at or beyond 18 feet from the eye), the rays emanating from such an object being parallel are brought to a focus on the retina, (as shown at i, Fig. 2) without any effort of accommodation ; but when an object is viewed at a finite distance, n (say, 12 inches from the eye), tho rays emanating from such an object becoming then divergent, they will no longer be brought to a focus on the retina, but to a point behind it, as at /(Fig. 2), if tho eye does not undergo some change which will increase its refractive power, and bring these divergent rays to a focus upon the retina. The normal eye does by its power of accommodation effect such a refractive process, and, as Helmholtz found, by means of his ophthalmometer, in the following manner : — 1st. The pupil diminishes in size. 2nd. The pupillary edge of the iris moves forward. 3rd. The peripheral portion of the iris moves backwards. 4th. The anterior surface of the crystalline lens becomes nioro convex (and so acquiring a higher power of refraction, and consequently a shorter focal length), and its vertex moves forward. 5th. The posterior surface of the crystalline lens also becomes slightly more arched, but does not perceptibly change its position; the lens, therefore, become^ thicker in the centre. And from calculation he found that these changes in the crystal- line lens are quite sufficient to account for all accommodative purposes. The diagram in the next page, after Helmholtz (Fig. 3), shows the changes which the eye undergoes during accommoda- tion. The anterior portion is divided into two equal parts : the one half, I, shows the position of the parts where tho eye is adjusted for distance ; the other, F, when it is accommodated for -fc ig. li. near objects. When the eye is in a state of rest, the iris forms a curve at a ; when accommodated for near objects, the fibres of the iris become contracted, the periphery of the iris straightened at b, and the anterior chamber lengthened, thus making up for its loss in depth, through the advance of the anterior surface of the crystalline lens. The anatomical mechanism by which this accommodation is effected is yet an open question, but as it is one of physiological rather than optical importance, it need not be herein discussed. * The rays emanating from a far distant object, such as the sun, moon, or a star, are regarded optically as parallel, hut practically, even when an object is only placed at eighteen or twenty feet distance the rays from it, though really divergent, are yet so slightly so, tha^ to all intents and purposes they impinge parallel upon the eye. We therefore consider rays coming from an object further than eighteen feet as parallel, and emanating from an object at an infinite distance. On the other hand, rays coming from a nearer object fall upon the eye in a divergent direction (the divergence being in proportion to its proximity), and are then considered as coming from a J'nite distance. 112 THE TECHNICAL EDUCATOR. It is assumed that when the normal eye is in a state of absolute rest, parallel rays (emanating from objects at an infinite distance) are brought to a focus on the retina, and that a positive change in the accommodative apparatus of the eye is only required for objects at a finite distance ; but it is thought by some ophthalmists that the eye when in a state of rest is adjusted neither for its far nor for its near point, but for a distance between the two, and that adjustment for either nearer or more distant objects necessitates an effort of accommodation. Such authorities call the adjustment for near objects positive, and that for distant objects nega- tive accommodation, It may be here noted that every eye has its “ blind spot,” which is situated at the point where the optic nerve enters the eye, and from which it ramifies to form the network of the re- tina ; and if the image of f an object is made to fall upon that spot it will be invisible, as the punctum caecum, as it is called, is insensible to the action of light. This may be proved in the fol- lowing manner : — Lay two black wafers on a sheet of white paper three inches apart, and at a distance of ten or eleven inches, bring the right eye exactly over the left-hand wafer, so that the line joining the two eyes shall be parallel to the line joining the two wafers. On closing the left eye, and looking steadily with the right at the left-hand wafer, the right-hand one ceases to be visible, as in this position its image falls upon the “ blind spot.” As the normal eye performs its delicate functions to perfection, it is evident that the interference of the optician can never be required, excepting to give relief when the organs of vision are weak or suffering from inflammation, in which case an ordinary spectacle-frame •■fitted with a flat piece of tinted glass may be furnished to the patient ; or when it is necessary to carry this protective appliance to greater perfection, a frame may be supplied with what are called “ glazed wings,” shown in Fig. 4, while the most perfect guard is to be found in a frame fitted with tinted glasses and a shield of fine black gauze that fits close around the socket of the eye, shown in Fig. 5. The glass employed in the construction of these “ Pro- tectors * ’ may be obtained of various colours and tints, green and blue being chiefly employed ; but the tint that admits the least amount of glare, and yet allows of the greatest amount of distinct vision, is a neutral blue, the value of which has been recognised by most ophthalmic surgeons and oculists. Tinted protectors of this nature may also be given with advantage to travellers to guard them against the injurious reflections from Alpine snows or the radiation from hot desert sands. Fitted with very dark glasses, they may also be recommended to those who have re- ceived injury to the eyes, in order to disguise the dis- figurement. In violent or in chronic inflamma- tion of the eyes the optician is often applied to for a shade that will give more ventilation than the home-made article will allow of ; the best arrangement is one wherein the shade is supported on the bead by a metal frame in such a manner as to throw the upper edge of the shade slightly from the forehead so as to ■ llew a current of air to pass over the eyes, while by a pivot attached to the frame the shade can be thrown back when necessary. The optician is also often required to furnish an “ eye douche,” by which the organ can, in certain cases of irritation or weakness, be bathed. These usually consist of ail elastic syringe, by which water or medicated liquid can be projected on the eye with any amount of force, connected by an india- rubber tube with a glass cup that surrounds the eye while being used, and to this cup another tube is attached to carry off the liquid into a basin. Where the eye is to be subjected to the influence of stimulating vapours, a stoppered bottle, con- structed with an oval-shaped cup to fit the socket of the eye is employed. The optician is frequently requested to supply eye-glasses or spectacles to persons who, they soon discover, are in no way affected in their organs of vision — in fact, are blessed with a normal eye. As a rule, such individuals desire what may bo called a “dandy glass ” to stick in their eye-sockets, with which to assume a supposed fashion- able appearance, and further, that this shall be supplied at the lowest possible price. The article best suited to meet the want in such cases is a disc of plane white glass with a hole drilled in it for the insertion cf a thin silk cord, by which it can be at- tached to the person. It need scarcely be stated that such a glass must be perfectly devoid of all optical properties. In other and similar cases spec- tacles are desired to give the wearer a thoughtful or learned appearance ; in such instances two plain glasses (not lenses) are required instead of one, which might be called “ snob glasses.” In rare cases it may be found that aged persons of good constitution are desirous of purchasing a pair of spectacles, not from any absolute shortcoming of sight, but from a notion that as friends of similar or greater age required the optician’s aid, they also ought to wear them. In such instances the applicants may be tested with convex and concave lenses before the real state of the case is discovered, as they see better with the naked eye than with spectacles of the lowest power. The proper course is to state that spectacles would do more harm than good, a piece of advice that would be quite thrown away in the former cases. Range of Accommodation . — When the eye has assumed its highest state of refraction, it is accommodated for its nearest point of distinct vision ; when, on the other hand, its state of refraction is relaxed to the utmost, it is adjusted for its furthest point. « The distance between the furthest and nearest point of distinct vision is called “ the range of accommodation.” As increase in the convexity of the crystalline lens is limited, its power of accommodation for near objects is also limited, and the “ near point ” cannot be brought nearer than a certain distance to the eye. In normal eyes the nearest point of distinct vision lies at about 3,V inches to 4 inches from the eye ; this varies, however, according to age, for the near point re- cedes further and further from the eye with increasing years. Where profes- sional occupation, such as engraving, needlework, etc., necessitates con- tinued work at near objects, the near point for distinct vision lies at about five inches from the eye. Few eyes, it should be observed, can bear to work for any length of time with the object nearer than this. The furthest point of distinct vision in the normal eye is at an infinite distance. The amount of this “ range of accommo- dation” varies according to the strength of the ciliary muscles, the elasticity of the crystalline lens, and other minor causes. It is most important that the optician should carefully determine the “ range )f accommodation” for each patient according to the method hereafter given, as it affords a means of safely dis- covering whether the eye is normal, presbyopic, hypermetropic, or myopic, and the kind ef lens exactly suited to each particular case, together with the most suitable focus for such lens. CIVIL ENGINEERING. 113 CIVIL ENGINEERING.— II. BY E. G. BARTHOLOMEW, C.E., M.S.E. DRAINING. Works of drainage are of two kinds : — 1st. Those which relate to the reclamation of land from the encroachments or accu- mulation of tidal and other large bodies of water. 2nd. Those which relate to the removal of sewage from towns. As respects agricultural drainage — by which we mean the improvement of the soil by the removal of mere surface moisture — as it does not come within the province of Civil Engineering, we shall make no further allusion to it. The value of the land overflowed by tidal waters, or by waters subject to rise and fall through floods and drought, is almost always very considerable, owing to the marine or alluvial de- posits which remain upon the soil. Some of the component parts of sea-water are highly fertilising; indeed, in many districts, especially in Scotland and Ireland, sea-weed forms the only manure employed by the farmer. Hence it has been found worth while to expend vast sums of money in order to shut out the water, and to drain the soil over which it had spread. It is a matter of no ordinary difficulty to contend against the variations and alternations of pressure produced by water whose level is perpetually and rapidly changing. This difficulty reaches its maximum in the case of tidal waters, especially of such tides as are experienced upon our own shores, where, in less than the space of twelve hours, there is a rise and fall of from fifteen to twenty-four feet. The immense rush of water in or out of any passage communicating with the tides, renders the greatest caution ne- cessary, lest the barriers intended to withstand the pressure should be carried away before being sufficiently consolidated. And yet in the face of these engineering diffi- culties, a vast portion of the low land in Holland has been reclaimed from the sea ; and in this country upwards of half a million of acres of land in Norfolk overflowed at one period by the joint action of the sea, and the rivers Witham, Welland, Ouse, and others, have been converted into somo of the richest agricultural districts in England, from being, at one time, pestilent marshes. How these particular results were brought about it is not our purpose to explain; our object is rather to state briefly the usual course adopted in operations of this kind. It is not, however, possible to lay down any rule of action, since each operation will require some special arrangements applicable to the particular locality ; these matters must be left to the discretion of the engineer. Before commencing a main barrier of any kind, whether of piles, earth, or caissons, it is desirable to ascertain, by a careful survey of the flooded districts and an examination of the levels, how far a judicious arrangement of canals and ditches may not avail to carry away a large amount of water by the mere effect of gravity, and also whether or not an ordinary dyke or bank of earth, stretched across a back-lying portion of drowned land, may not successfully diminish its area, and thus render less difficult the final operation of closing the entrance to the tide, when this has been reduced to a minimum by sub- sequent operations. These simple operations will frequently save an immense amount of labour, for it is obvious that the larger the area of the submerged land, the greater will be the rush or scour of the tide as it flows over it. Whenever banks are erected across a flooded district, they should be constructed with sluAces or flood-gates , which can be opened or closed when required, so that advantage may be taken of a lower state of the water-level upon the tidal or outlet side, to discharge the excess upon the land side. It is also of advantage to construct self-acting sluices or outfalls, which are VOL. i. simply strong doors or flaps of timber, iron-hinged at their upper edge, and opening only outwards, so that whenever the level is higher upon the land side, the greater pressure of water automatically opens these doors, and a discharge continues until uniformity of level is gained, when the doors close by their own weight, and falling against a sill, effectually prevent the return of the discharged water. These sluices, to be of most service, must be constructed low down in the dyke, and being usually out of sight, should be constructed with great care, as any derangement in them would cause disastrous results. It frequently occurs that an accumulation of fresh water arises from the simple overflow of a river during heavy and continuous rains, or a sudden thaw. Such floods are of fre- quent occurrence in the south of France, and cause serious loss of property and life. The remedy in this case is simple and obvious, although it may involve a considerable outlay. The banks must either be raised and strengthened, or the channel must be deepened and widened, or additional channels must be cut ; the end being in either case gained when the sectional area of the water-course is equal in every point to the volume of water which has to pass it in a unit of time. In the case of tidal waters, the operations are very difficult ; the rush of the in-flowing water at every flood-tide, and of the out-flowing at every ebb and the consequent scour pro- duced by this rush, has to be ; net, and the smaller the opening or gap, as compared with the tract of land covered at each tide, the greater will this rush be ; and it is only a barrier far more substantial than it is possible to place across any large opening, in the short period allowed be- tween tide and tide, that will suffice to withstand the force of the current in the tide-way. Hence it is necessary to reduce the width of the tide-way to a minimum before at- tempting to close it. The most substantial barrier, and the cheapest when- ever it can be employed, is earth ; but this is use- less to stop an opening through which a violent rush of water occurs, as the soil will be carried away as fast as it is de- posited. Earth call, however, be safely and advantageously employed as a base for further operations ; using it in all cases where the flow of water is inconsiderable, and thus gradually narrowing the tide-way. When this embankment (strength- ened according to discretion with piles) has been carried as far as it can be with safety, there then remains the tide-way to close up. There are two methods of doing this. If the depth of water in the channel will admit of it, a double semi-circular or curved row of piles (p p p, Fig. 1) n ay be driven at short intervals apart across the opening, leaving a space (s s s) of twelve or eighteen inches between the two vows, which are to be strengthened by cross-ties, braces, and struts (t t t). The curve must be outwards, and the driving of the piles should commence from each side and finish in the centre. At the ends of the curve, the piles abut upon other piles driven closely together, and forming a protection for the extremities of the earthen dyke, which would, otherwise be subject to injury by the scour of the water. Barges of stiff, broken clay and stones should be floated near the outside of the piles, and plenty of labour ought to be at hand in order to take prompt advantage of the moment of low water. The clay and stones must then be rapidly shot into the space between the rows of piles ; and if the organisation of labour be good, it will be quite possible to keep pace with the rise of the tide in the deposit of the soil, and even to impart a certain degree of solidity to it by ramming. Such a barrier has the elements of great strength in it ; and although it may not be altogether impervious to water, it will suffice to prevent any considerable flow, and will entirely stop 3 Fig. 1. — BARRIER at the mouth op a tidal basin. 114 THE TECHNICAL EDUCATOR. a rush or scour, thus enabling the permanent embankment to be completed, after which the piles can be removed. The plan we have indicated will not, however, avail in all cases. The depth of water in the tide-way may be too great to admit of piles being sunk sufficiently deep into the soil to gain a firm standing, or the area of the land overflowed at every tide may be so extensive, that it will be found impossible to narrow the tide-way by a continuous earthen embankment sufficiently to admit of a barrier of piles withstanding the pressure. In such cases the following course may be adopted : — Let the embankment contain, at frequent intervals, large flood-gates, constructed during the progress of the work, which can be opened and shut at pleasure. When the gates are open, the flow of the tide is spread over an opening equal to the joint area of the space between the extremities of the embankment and that of the flood-gates, and will, consequently, be less in the un- finished opening when the gates are open than when they are closed. The scour of the tide being thus reduced, the embank- ment can be continued until the space of the tide-way is reduced to a point sufficiently narrow to admit of the same course being adopted as shown in Fig. 1. The embankment can then be completed, and the gates being closed at low tide, the level of water over the enclosed space will be proportionately re- duced. Under almost all conditions of the drainage of flooded lands, a surplus of water will remain even after all communication with the tide has been cut off, and this surplus must be removed or kept under by pumping. Wind or steam power may be necessary, indeed will be, if the submerged district is ex- tensive. The better kind of pump for the purpose is the “V,” the “ chain,” or the “ centrifugal,” as the grit which enters the pump with the water is sure to act detrimentally upon the ordinary barrel and bucket pump, destroying the leather and choking the valves. Constant attention must be paid to the sluices, “ clows,” and gates, owing to the great pressure they are frequently sub- jected to, and in consequence of the serious results which would ensue from their failure. An idea of the pressure exerted by water, when any considerable difference of level exists, is formed by the fact that, at the mean height of the tide — sixteen feet above low-water mark — the pressure exerted upon each square foot of surface at the bottom is 1,152 lb., and half this, or 576 lb., represents the actual mean pressure exerted by a high tide upon every vertical square foot of an embankment. The magnificent stone embankment recently constructed on portions of both the north and south sides of the Thames, and which has for its object, amongst others, t ’10 narrowing of the channel in order to cause a greater scour of water to remove the accumulated mud, was carried out behind a protecting wall of closely-fitting piles, in one portion, and of cast-iron shields, dovetailed together with piles, in another. The percolation of water from the river, which was considerable, was kept under by steam-pumps. The granite wall was completed behind the wall of piles, and soil afterwards “tipped” into the space on the land side. The foul black mud has thus been buried, and the Space it formerly occupied devoted to a splendid carriage way, a subterranean railway, and one of the principal culverts connected with the main drainage system of the Metropolis. Sanitary Drainage. — But one opinion can exist as to the necessity for removing sewage from the vicinity of an inhabited district, although a variety of opinions are held as to the best mode of disposing of it. It is foreign to our purpose to adduce the various arguments which have been raised for or against any particular system of drainage, and we shall merely state what are the various plans adopted. I. We consider the most desirable plan, when practicable, is entirely to remove the offensive matter as far as possible from the inhabited locality. This plan has been carried out at great expense in the drainage of London. In all cases of sanitary drainage it is necessary to provide for the passage of rain-water as well as of mere sewage. An estimate of the rainfall in any particular locality, formed by taking an average of a succession of years, is hardly sufficient ; it is better to select the maximum rainfall in one day of a series of years, and provide an excessive area in the culverts for such a maximum, so that no danger from the flushing of the sewers shall arise, even during a period of flood. This question was very carefully considered in dealing with the main drainage of the Metropolis. To reduce the amount of pumping to a minimum, it is de- sirable so to arrange the levels of the sewers as that as muck as possible of the sewage shall pass away by gravitation. If the area to be drained were either a uniform level standing a definite height above the river or sea into which it is intended to discharge the sewage, or stood upon a regular slope down to the point of discharge, no pumping would be needed ; but when the ground is uneven, and some of it lies lower even than the level of the outfall, it will become necessary to pump the drainage from the lower levels into the higher, from which alone the discharge can be effected. How best to arrange these levels is a question of the highest moment in planning out the positions of the sewers. The uneven nature of the ground occupied by the Metropolis necessitated three different lines of sewers, each occupying a different level. These, known as the High, Middle, and Low level sewers, are thus arranged : — Upon the north side of the Thames the three lines converge and unite at Abbey Mills, near Bow, where the contents of the Low Level are pumped into the Upper Level sewer, and the aggregate stream carried across the marshes to Barking Creek, through the northern outfall, and there discharged into the river at the period of high water. The theory involved in this arrangement is, that as the flow of water towards the sea consists, during the period of ebb tide, of the land water plus the tidal water, the period of ebb tide is longer than the period of flow; hence any object free to move up and down the channel of the river by the action of the tide, will be carried nearer and nearer the sea at each successive tide. Such occurs with the sewage. It is retained in an immense reservoir near the outfall, until the period of high water, and then discharged during a certain time, the time at which the discharge is stopped being regulated by the state of the tide : the reservoir being arranged to con- tain an accumulation of eleven hours’ sewage. The great object is that the sewage, after its discharge into the river, shall never be brought back by the action of the tide to the Metropolis, and this is entirely effected by placing the outfalls from twelve to thirteen and a-half miles by river below London Bridge. The section of the sewers is for the most part circular, as combining the greatest strength and capacity with the least cost of labour and material. The smaller and subsidiary branches are egg-shaped, in order to obtain the greatest scour with a minimum amount of flow. This shape was adopted by the Romans in the Cloaca Maxima which drains the whole of Rome as well as the Campagna. This culvert is fourteen feet wide and thirty -two feet high, and 'its area is nearly sufficient to drain the whole of the metro- politan district. Its section manifests a considerable knowledge of the power of deep water for scouring the bottom of a sewer, and thus removing the deposits. The metropolitan culverts are for the most part constructed of brickwork set in cement. Their area varies from four feet diameter to nine feet six inches by twelve feet. The thick- ness of the brickwork also varies from nine to twenty-seven inches. The necessity for maintaining a nearly uniform gradient in the lines of sewers, and more particularly the necessity of making the gradient always in one direction, compelled them to be carried over or under every obstacle. As an instance of this, we may state that the Middle Level sewer, on the north j tide of the river, is carried over the Metropolitan Railway near Farringdon Street by a wrought-iron aqueduct of 150 feet span ; its weight being 240 tons. A similar system of drainage is carried out on the south side of the river, the convergence of the three levels being at Deptford Creek, where also is situated the pumping-engine for raising the sewage from the Low Level to the High Level sewer, a height of eighteen feet. The southern outfall passes thence to Crossness, about one and a-half miles further down, the river than Barking Creek. We append a summary of the principal points of engineering interest in this great work. The total cost of the mam drainage i works, when completed, will be about .£4, 100, 000, a sum raised MINERAL COMMERCIAL PRODUCTS. 1L5 by loan, and paid off by a 3d. rate levied on the Metropolis, producing' .£180, 262 per annum. It will require forty years to pay off both principal and interest. There are 1,300 miles of sewers in London, and eighty-two miles of main sewers; ^318,000,000 bricks, and 880,000 cubic yards of concrete have been consumed; and 3,500,000 cubic yards of earth have been removed in the progress of the work. The total pumping power employed is 2,380 horse-power nominal, and the annual consumption of coal is about 20,000 tons. The sewage on the north side of the Thames is over 10,000,000 cubic feet per day, and over 5,000,000 on the south side. In addition to this, provision is made for 28,500,000 cubic feet of rainfall per day on the north side, and 17,250,000 on the south side ; the total being equivalent to a lake fifteen times p,s large as the Serpentine. The reservoir at Barking is 16| feet deep, and covers an area of about 94 acres ; that at Crossness, with an equal depth, has an area of 64 acres. The importance of this great engineering work cannot be overrated. It has totally changed the sanitary condition of large areas of the Metropolis ; and although not fully completed, has effected an improvement in a sanitary point of view of which the cost of the undertaking forms no criterion. We have entered somewhat largely into the details of this work, as it forms the best example of that system of drainage which aims at conveying away bodily the refuse matter. II. Many persons are of opinion that to convey away and discharge into a river so enormous a quantity of sewage is a twofold evil : it poisons the water, and wastes a valuable fer- tilising agent. Those who hold this opinion differ, however, as to the manner in which they would treat the sewage. In some instances, as at Croydon, the sewage is applied to the entire level surface, irrigating the plants or grass at once. In other cases, as at Romford, the ground is intersected by numerous shallow trenches, into which the sewage is pumped, the plants being embedded in the soil adjoining the trenches. The sewage thus passes to the roots through the medium of the soil. The whole district thus irrigated is itself drained, and the eflluent water pumped back into the trenches. There can be no question as to the value of sewage for agricultural pur- poses. The sewage of London is estimated as worth =£1,500,000 annually. Its value, as shown at South Norwood, is such, that over fifty tons of Italian rye-grass have been grown the acre in each year, worth from =£30 to <£40. This grass has been pro- duced from six successive crops in the twelve months, and the aggregate length of the blades is equal to fifteen feet. At the same time it is asserted that the sewage, after being thus utilised, is actually as pure as the water supplied by some of the Metropolitan water companies, in the proportion of 23 to 21 grains of organic matter per gallon. Iff* There is yet another system adopted with respect to sewage. Leamington and Hastings are the chief localities where this system has been carried out. It is known as the ‘"ABC” process. Under this system the sewage is first deodorised and precipitated, the effluent water being allowed to pass away into the sea or river, the solid residuum bein°- utilised as manure. The “A B C ” is a patented process, and obtains its name from the initial letters of the three principal ingredients used in the process of defcecation, alum, blood , and clay. Other sub- stances are employed : for instance, the sulphate or carbonate of magnesia, manganate of potash, chloride of sodium, animal and vegetable charcoal. A mixture in certain proportions of these substances is added to the sewage so long as precipi- tation takes place ; the average quantity required being 4 pounds of mixture to 1,000 gallons of sewage. The partially dried precipitate has a small quantity of sulphuric aoid added to it to fix the ammonia, and it is then regarded by the patentees as a valuable manure. MINERAL COMMERCIAL PRODUCTS.— VI. siLiciotrs substances ( continued ). Serpentine, so called from the supposed resemblance of the mineral to the skin of a serpent, is a silicate of magnesia with adventitious admixtures of lime, alumina, iron, chromium, etc., and occurs as a rock or in association with other minerals' constituting rock masses. The west of Mayo and Galway are remarkable for their serpentine rocks, which afford the beautiful variegated green and white varieties worked into pilasters, columns, etc. Serpentines and serpentine limestones of great beauty and excellent quality are also quarried in different parts of the county of Cornwall, the Shetland Isles, Canada, the United States, Italy, etc. Basaltic and kindred rocks — greenstone, whinstone, and trap — are intrusive rocks, for the most part felspathic. Some of these are well adapted for building, but their great use is for paving and macadamising roads, for which purposes they are unrivalled. The columnar structure of basalt is in some places taken advantage of for the construction of stone posts and window-sills. These rooks are abundant in many parts of Scotland, and occur also in Ireland, various districts of Germany, and Nova Scotia. Lava, a volcanic production, is often similar to trap, and equally useful. It occurs in recent and extinct volcanic dis- tricts. Obsidian, a volcanic glass, usually black, and somewhat resembling the slag of a glass furnace, is found in Mexico, Central America, Peru, Iceland, etc. Pumice-stone, a well< known porous and extremely light stone, used for polishing, etc., and Pozzuolano and trass, silicious earths much used to mix with limes for hydraulic cements, are also volcanic produc- tions, of which the chief mineral ingredients are augite and felspar. Pumice-stone is quarried in the small islands that lie off the coast of Sicily. Pozzuolano and trass are obtained from Italy, and from many districts of France, Germany, and Scotland. CLAYS AND ALLIED SUBSTANCES. Clays, which are silicates of alumina more or less pure, occur in all formations from the firmest slates of the older rocks, and the loose shales of the Carboniferous and the Secondary, to the plastic clays of the Tertiary and the alluvial deposits. They enter largely into the materials and processes of build- ing, as slates, tiles (both for roofing, paving, and ornamental purposes), and bricks ; into the manufacture of pottery and earthenware of all sorts, terra-cotta, and many other useful applications. Common clay, so abundantly diffused over the earth’s surface, and chiefly distinguished into three varieties — yellow, brown, and blue — furnishes material for the builder and the maker of the common pottery wares. China and porcelain are made from the fine clays called kaolin and 'petuntse, which are almost pure, and are due to the decomposition of the felspars of granitic rocks, the felspar containing soda being especially liable to disintegration. These clays are found in Cornwall, Devon, France, Belgium, and Germany, but can also bo artificially pre- pared. Pipe-clay is a white, pure variety, with an excess of silica. It is obtained from Poole and Purbeck. Fire or refrac- tory clays, used in the manufacture of fire-bricks, retorts, and crucibles, contain a preponderance of silica over alumina, and occur chiefly in the Carboniferous strata. In England the Stourbridge clay is famous for these purposes. Belgium, and Siegburg in Germany, also furnish fine clays. Others, however, sufficiently pure, can be made available to some extent by the addition of silicious sand. Fuller’s earth is a very useful clayey substance, having in its composition a large proportion of silica and a quantity of water. It is employed in the preparation of wool, and is abundantly met with in Surrey, Buckingham, Hampshire, Gloucestershire, and Bedford. The ochres, chiefly red and yellow, are mixtures of clay and oxides of iron. They are used in the manufacture of colours ; the most suitable for this purpose being obtained near Oxford, in Fife, in Antrim, Italy, and other places. Slates, from their natural cleavage and their great durability, are of extreme utility for a variety of purposes, chiefly roofing, the construction of cisterns, and the manufacture of school slates and pencils. The best are those which are hardest and finest in grain. Besides the common colour, there are green, purple, and grey slates. The laminae are of different thick- nesses, and are used accordingly. Slates are quarried chiefly from rocks of ancient date (Silurian and Cambrian), and are abundantly supplied from Penrhyn, Llanberis, Festiniog, and other parts of Wales, as well as from Cornwall, Devonshire, Westmoreland, Scotland, Ireland, France, Belgium, Germany, and Asia. 116 THE TECHNICAL EDUCATOR Hone stones, of which there are many varieties, are slaty stones which are used in straight pieces for sharpening tools after they have been ground on grindstones. The most im- portant varieties are the following: — Norway ragstone, the coarsest variety, imported in large quantities from Norway ; Charnwood Forest stone, one of the best substitutes for the Turkey oil-stone, much in request by joiners and others, and obtained from Charnwood Forest, Leicestershire : -turkey oil- stone, of which there are two varieties, white and black, the latter being the harder, surpassing every other oil-stone, used by the engraver, and obtained from the interior of Asia Minor ; Ayr stone ; -snake stone ; Scotch stone, used especially for polishing copperplate ; Welsh oil-stone, second only to the Charnwood Forest stone, and obtained at Llyn Idwall, near Snowdon, whence is also obtained the c cutler s green stone ; and the German razor hone, derived from a yellow band in the blue slates of the neighbourhood of Ratisbon. EARTHS OF SODIUM, POTASSIUM, BORON, SULPHUR, ETC. The elements, of the combination of which we are about to speak, do not, for the most part, occur naturally in their simple state, but their compounds, especially those of sodium, potassium, and sulphur (which is also native), are numerous, abundant, and valuable. Common salt (chloride of sodium) is an extremely abundant and quite an indispensable commodity. It exists in sea-water and salt lakes, in the proportion of from 3 to 4 per cent., or even more in some of the lakes, and can be extracted by evapo- ration. It occurs in a much larger proportion in many brine- springs connected with geological deposits of salt, but these deposits themselves form now by far the best sources of supply. Rock-salt is obtained in England principally from the mines of Cheshire, and also near Belfast ; culinary salt is manufactured in large quantities in Cheshire and Worcestershire from brine springs ; in both cases, the salt is derived from the Keuper marls of the New Red Sandstone system, in which it occurs in basin-shaped deposits, and is arranged in wedge-shaped masses. Salt-beds occur in rocks of various ages ; those of Nova Scotia in the Carboniferous system ; the rock-salt of Ireland, England, and Prussian Saxony in the Keuper formation ; that of the Carpathian Alps in the Upper Oolite ; that of Poland and the Pyrenees in the Cretaceous series ; and that of Pisa and Cuba in the Miocene rocks. Beds of salt occur also in China, and many districts of North America. Some of the salt mines of Europe furnish perhaps the most stupendous examples of mining industry. Salt for domestic purposes is refined from the more or less impure native product, and from it also common soda (carbonate of soda) — formerly made, like barilla, from the ashes of sea-weeds, etc. — is manufactured on an im- mense scale. Chlorine for bleaching and disinfecting purposes is also very largely supplied from the same source. Many parts of the earth being deficient in the supply of salt, it is an important article of commerce, and 600,000 tons are annually exported from this country, the yearly produce of which exceeds 1,500,000 tons. The Alums, already alluded to under the head of Aluminum, are important compounds of sulphate of alumina with sulphate of potash, or soda, or ammonia, potash being the most common. Alum occurs native to a small extent, but from its great value in the arts, especially in dyeing and calico printing, it is manu- factured on a large scale. One process is to treat clay with sulphuric acid, by which a sulphate of alumina is formed, to which potash, soda, or ammonia is added, and the resulting crystallised salt is accordingly either a potash, soda, or am- monia alum. Alum is also made from alum slate or shale ; this substance contains alumina, protoxide of iron, a trace of potash, and iron pyrites dispersed through it. This pyritous shale, on exposure to the atmosphere, undergoes decomposition, which is accelerated by the manufacturer, who, availing himself of the carbonaceous character of the shale, applies fire to the alum shale heap. The iron pyrites is changed into sulphate of iron, which forms, with the alumina, a double sulphate of iron and alumina ; this is subsequently purified by evaporation, and by the addition of potash the salt is rendered crystailisable. Glasgow, Whitby, and Newcastle are the chief localities of aium manufacture in this country. The best alums are those prepared in Asia Minor and Italy. China produces a consider- able quantity, and Tuscany an average of 7,000 tons per annum. TECHNICAL DRAWING.— VIII. wooden bridges ( continued .) The structural portions of the bridge having been completed, the hand-rail may now be commenced. Having drawn the top rail and the standards which divide the length into ten equal rectangles, draw diagonals in each ; then the lines forming the cross-struts are to be drawn parallel to these. The longitudinal and transverse sections will not, it is presumed, require further instruction, and we can therefore turn our attention to the next series of examples of hand-rails. The most simple of these is Fig. 43. In beginning this it is best to draw the section (Fig. 44) first, as from it the elevation of the cornice and of the horizontal bars must be projected. Having, then, drawn Fig. 44, draw horizontals from the different points in the section of the cornice, a, and from the top and bottom of the section of the top rail, h. Next draw the standards, c c; then from the angles of the square middle rail, tZ, project the elevation, d, which will com- plete the figure. Fig. 45 is an enlarged elevation of the hand-rail already shown in Fig. 40. Here the section (Fig. 46) is to be drawn first, excepting the part d d, which is determined according to the angle at which the struts cross each other. Having, then, projected the elevation of the top rail and cornice from the section, draw the standards, c c, and diagonals in the rectangle. Now let us suppose (as would in practice, of course, bo the case) that the struts are to be of a definite width. To set this off accurately, draw a line through each diagonal, at any part, but at right angles to it. On these, on each side of the diagonals, set off from the intersection half of the width of the struts ; then lines drawn through these points parallel to the diagonals will give the sides of the cross-pieces required. It will be seen that the lines thus drawn will at their inter- section form a lozenge or diamond-shape : from the lower and upper angle of this figure draw horizontals, which will give the section, d d, in Fig. 46, and in this the central vertical line will show that the struts in crossing are “ halved ” into each other, so they are “ flush ” with the uprights and with the upper rail. The splaying of the edges can, of course, be done without any further guidance. Fig. 47 is a hand-rail of a similar character to the last, but the space between the standards is to be filled with two pairs of struts at right angles to each other. Now the space is doubly as long as it is wide ; therefore divide it into two equal squares, in which draw diagonals. On these, set off from their intersection half of the width of the struts, and draw the lines which form the edges of them ; the section (Fig. 48) can then, as in the last figure, be completed from the elevation. Fig. 50 is a mere trellis-rail, and will be found very easy to draw ; but care is required so that all the interstices may be equal squares. Having drawn the section (Fig. 49), and projected the cornice and upper rail in tho elevation (Fig. 50), draw centre-lines for each of the cross-pieces, which will be readily accomplished by means of your set-square of 45°. On each side of the intersection set off half tho width of the pieces, and diaw tho lines ; it will thus be seen that this is a repetition of the last figure, but with a multiplication of parts. We still continue using wooden bridges as examples for drawing, not because they are as much used in this country as they were in times gone by, but because the principles of theii construction convey so much instruction, which will bo of service in the subsequent section on “ Roofs.” And further, in these days of railways and emigration, some knowledge of the construction of bridges of a material which is so generally available cannot fail to be of service. Fig. 51 is partly an elevation and partly a longitudinal section of a covered wooden truss-bridge, such as is frequently used for passengers to pass from one platform of a railway to the other. Here it is necessary briefly to remind the student of tho action of a king-post, viz., that when the lower ends of tho principal rafters (two strong timbers, which together are longer than the space to be bridged over) are mortised or otherwise fixed by their lower ends to the tie-beam, the upper ends abutting against the head of the king-post, this acts as the key- stone of an arch, and being lengthened, the tie-beam is belted or strapped up to it. This orincipie, illustrated by the necessary 118 THE TECHNICAL EDUCATOR. diagrams, is treated of in “Building Construction,” and will be further worked out in connection with roofs. In the present example the tie-beam is built up of two equal timbers, which are scarfed or toothed into each other, and the king-post, being also double, clasps the tie-beam at the bottom. Underneath the tie-beam a transverse bearer passes from one king-post to the other, and these being screwed up by means of screw-bolts, the tie-beam is drawn up into a curve. The principals, too, are made up of two equal lengths. In addition to this there are queen-posts, which are supported at the top by means of a collar-beam and struts ; and to these, bearers passing transversely under the tie-beams are bolted, like those under the king-posts. There are also intermediate suspending posts, from which bearers are not suspended, but to which bolts pass through the tie-beams. The half of Fig. 51, which is given in section, will show the manner in which the planks forming the floor of the bridge are laid, and the longitudinal girders resting on the transverse bearers are shown in the section (Fig. 52), in which the simple roof timbers are also shown. Fig. 53 is a horizontal section, showing the diagonal straining- pieces between the bearers. A few instructions on the method of drawing this subject (Fig. 51) will now be given. First draw the piers, and a straight line uniting their spring- ing points. Bisect this line, and in the perpendicular set off from the intersection the height of the curve from the horizontal line. There will then be three fixed points — viz., the two springing points, and that in the perpendicular. Now it will be remembered that if these points be joined, and the lines uniting them be bisected, the intersection of the bisecting lines will be the centre of the circle of which the arc is a part. (See Fig. 10, “ Practical Geometry.”) Having, then, thus found the centre, describe the arc forming the under side of the tie-beam. The arcs under this are to be drawn with the same radius, moving the centres a little lower down on the perpendicular. The tie-beam is rather broader in the middle than at the ends, and therefore the upper arc must be struck with a rather shorter radius, the centre being slightly higher than that from which the under side was drawn ; from a point half-way between these two centres an arc must be struck, exactly between the upper and lower edges of the tie-beam, and on this the toothing of the scarf is to be drawn. Now proceed to draw the king-post, measuring half its width on each side of the central perpendicular, then the principal rafters, the collar-beam, and the longitudinal joist above it ; then follow the queen-posts, the suspension-pieces, and the ends of the bearers. The foundation for the fronts, and the fronts themselves, are now to be drawn ; then the ridge and the rafters. After this the boarding of the sides of the bridge is to be filled in, and any other detail which may not have required separate mention. Figs. 52 and 53 are too simple in their lines for the student to need any instructions as to the mode of drawing them ; he is simply advised to draw the different parts in the order in which they have been explained in the elevation. Fig. 54 is a side elevation of a small bridge constructed on the “ bow suspension truss ” principle. Here the bow, consisting of a single beam, is mortised into the ends of the tie-beam, which are in their turn strengthened by saddle-pieces, bolts passing through these saddle-pieces, the tie-beam, and the bow. At regular intervals perpendicular posts are placed between the tie-beam and the bow. Underneath these are placed the transverse bearers, bolts passing through these, the tie-beam, th6 perpendiculars, and bow. On the bearers timbers are laid parallel to the truss, and on these the flooring of the bridge rests. This arrangement will be clearly understood on referring to the section (Fig. 55). In commencing to copy this example, draw the horizontal line •which forms the tops of the abutments, and then add the oblique lines representing the imposts. Next draw another horizontal line, and between this and the last mark off the widths of the ends of the cross-timbers which act as wall-plates, on which the trusses are to rest. This horizontal will also give the lower side of the saddle- pieces, and the horizontal which will give the top of these will also form the under side of the tie-beam, the upper side of which, and the ends of the saddle-pieces, may now be drawn. The points at which the outer arc of the bow meets the upper lino of the tie-beam are next to be marked, and the height of the bow set off on a central perpendicular. From these three points, the centre from which the arc is struck will be found in the manner already mentioned. The internal arc and the mortises at the ends will then complete the bow. Having divided the space on each side into four equal parts by dotted perpendiculars, set off on each side of these half the thickness of the uprights, draw the ends of the bearers, the rail-bolts, etc. The section is so very simple, that no further instruction connected with its delineation is deemed necessary. It can be well understood that the system of forming the bow of a single timber must be limited to bridges of small span, and an improvement was effected in this respect by the introduction of a system invented by Philibert de Lorme, a celebrated French architect. This system was not new, its author having proposed it in the sixteenth century, and it had been used more or less from that period ; but it seems to have been first applied to bridges in that over the Weser, near filinden, in Westphalia, in the year 1800. The De Lorme system will be fully described and illustrated in connection with “Roofs,” in the construction of which it has been principally used ; it may, however, be briefly stated here that it consists in building up the bow of separate pieces of timber placed edge-wise, and united in the manner called break- joint — that is, the joints in the pieces of each layer of timber composing the bow are alternated, so that those in the one are over the whole part of the other, nails and bolts passing through the complete thickness SEATS OF INDUSTRY.— III. LlfiGE AND PITTSBUKG. BY H. R. BOX BOURNE. Ip Birmingham and Sheffield vie with one another as the lead- ing hardware towns of England, Liege is without a rival among the hardware towns of the continent of Europe, and Pittsburg has a like rank in America. The main features of these cities are interesting in themselves, and worth comparing with their English prototypes. Liege is older as a town, though not as a hardware centre, thnn Sheffield or, perhaps, even Birmingham. There was a village of Legia in the seventh century ; and the old cathedral, which was destroyed by the French revolutionary forces in 1794, was founded as early as the year 702. Its early history is chiefly ecclesiastical. In the tenth century its bishops became independent sovereigns, yielding feudal homage only to the kings of France ; and even that was often refused. They had an influential position in mediaeval Europe until Liege was captured by Charles the Bold in 1408, to be thenceforward annexed to Burgundy . until it passed into the hands of the Spanish and Austrian monarchs, and ultimately became part of the new state of Belgium. Like all the other towns of that busy corner of Europe, it early applied itself to trade and com- merce, and shared in the old prosperity of Ghent, Bruges, and Antwerp. It throve most after they had begun to decline. “ Lidge,” it was written a hundred years ago, “ is a very large and well-fortified city, on the left of the river Meuse, and con- tains a cathedral, seven collegiate and thirty parish churches ; five abbeys for men, and a like number for women ; thirty -two cloisters for both sexes, two colleges for Jesuits (now turned into seminaries), and ten hospitals ; besides other charitable foundations. The manufactures here are very considerable, consisting of serges and other stuffs, all sorts of military weapons, nails and leather, and great numbers of brewers. There is pit-coal in its neighbourhood, with which they supply Holland very much.” That pit-coal has made the modern fortune of Liege. The wonderful coal-field, about six miles wide, stretching for a hundred miles from Mons to • Liege, has seams as rich as any in the world, some of the pits being the deepest that are anywhere SEATS OF INDUSTEY. 119 -worked. In the neighbourhood of Liege occupation is thus given to about 10,000 coal-miners ; and the same district is rich in iron, besides yielding smaller supplies of zinc, lead, and copper. Thus the old city of bishops and churches has ready at hand an abundance of mineral wealth, put to good use by its thrifty inhabitants. The old fortifications have been well-nigh demolished; and the old streets— narrow, and often so steep that they are more like long flights of steps — are ill adapted for trading purposes ; but trade flourishes. Though the town, which in the middle of the fifteenth century is reported to have contained a population of 120,000, now has only about 100,000 inhabitants, it has ten busy suburbs which share its occupa- tion and contribute to its wealth. Seraing, the chief of these suburbs, on the opposite side of the Meuse, and being to Liege what Southwark is to London, is the chief centre of the new life of the district. In it an old palace of the prince-bishops was, in 1817, converted into a great factory by an enterprising Englishman named John Cockerill. He followed the example of his countrymen at home, and began to use the coal and iron of the neighbourhood in making steam- engines and machinery of every sort. One of his first coke- blast furnaces was set up in 1823, and his establishment soon became, what it has ever since been, the largest of its kind on the Continent. King William I. took a great interest in the movement, and after a time, buying up the share of John Cockerill’ s brother, became a partner in it. Cockerill embarked in more than sixty other enterprises, in and out of Belgium, and was for a long period the greatest manufacturer out of England. His speculations brought him into some trouble, especially during the time of revolution ; but he rode through all his difficulties, and his establishment was at the height of its prosperity during the few years previous to his death in 1840. After that it passed into the hands of a company known as the “Societe de John Cockerill;” and the works now com- prise a coal-mine, six blast-furnaces, a steel puddling-mill, an iron-foundry, and a general machine factory. Many kindred establishments have been founded, and by their energy Liege has been made the Birmingham of Belgium. Liege is especially famous for its manufacture of cannon and fire-arms. The Royal Cannon Foundry, started in 1802, produces on an average nine large pieces of ordnance every week. The small arms are chiefly made by the workmen in their own houses ; but the total produce is very large. It has more than quad- rupled in the last fifty years, and is now much larger than that of Birmingham. In the ten years ending with 1864 there were made in Birmingham 5,611,000 guns ; in Liege, 6,842,000. The estimated value of the English work, however, was about =£10, 500, 000 ; that of the Belgian being only =£8,200,000. The average price of an English gun is 32s., a government arm being twice as costly ; that of a Belgian weapon is 24s. In the same ten years Liege produced 2,305,000 pocket-pistols, Birmingham only 588,000 ; yet the gross value of the latter rather exceeded that of the former. Most of the Belgian pistols cost only from one to two shillings a-piece. Vast numbers of these inferior weapons, as well as guns, are sold in this country and elsewhere at greatly enhanced prices, with counterfeited English trade-marks. In the manufacture of fire-arms Liege cannot rival the ex- cellence of Birmingham workmanship ; but in rougher branches of the hardware trade there is successful competition, and Belgium, like France and Prussia, has the advantage over England in cheapness of labour and often in better training of the labourers. French ironworks are inconsiderable as com- pared with English ; yet in them are adopted methods that England might well follow. “ Some of the French mining manufacturers,” said an English workman, describing the Paris Exhibition of 1867, “ exhibited models, plans, and drawings not only of their works, but of schools, chapels, and workmen’s ■dwellings, showing that they consider it in some measure a duty to attend to the social, moral, and intellectual condition of the workpeople ; and from facts coming to our knowledge respecting the means of education supplied, the care taken oi sick workmen, and the provision made for them in old age, it really does appear to us that the right steps are being taken by manufacturers for the purpose of surrounding themselves with intelligent and contented populations. This circumstance might possibly account to some extent for the fact that there is more economy in the use of fuel, and more care in utilising mate- rials in connection with the ironworks in that country than in this. We saw no such plans or models in the English col- lections.” If Liege and the Continental iron towns differ in some im- portant respects from those of England, there is yet greater difference in the case of the American towns, of which Pittsburg alone is considerable. Its history hardly covers more than a century ; yet it has belonged to three nations. In February, 1754, the English, then engaged in fighting with the French and Indians, set up a stockade on the point at which the Alleghany and Monongahela join to form the river Ohio. In April they were driven out by the French, who chose the site for their Fort Duquesne, a famous centre of resistance to the English. Several attempts were made to regain it, and its conquest was effected in 1758. Fort Duquesne was replaced by Fort Pitt in 1759, and in 1764 the town of Pittsburg was begun. It was abandoned by the English in 1772, and then, after some years of rivalry between Virginia and Pennsylvania for its possession, it wafe assigned to the latter state. At that time the life of the United States was almost confined to their Atlantic coast- line. Save in traffic with the Indians for furs, there was but little done in the interior, and Pittsburg, though now reckoned one of the eastern towns of the country, was then one of the most western outposts of civilisation. Its early growth was slow. Not till the Ohio and the Missis- sippi were found to furnish rare conveniences of transit between the northern and the southern states, and the splendid coal- fields of the district began to be recognised as the best source of fuel possessed by the country, was Pittsburg much thought of. The discovery once made, however, its later progress has been wonderfully rapid. In 1840 it contained 21,115 inhabi- tants ; in 1850 the number amounted to 46,601 ; and in 1860 the town and its suburbs had a population of 115,000. “ Com- pactly and well built,” said one who visited it in 1848, “ with wide streets, handsome squares and public gardens, it is thoroughly begrimed with smoke, and is certainly the darkest and dirtiest place I ever saw. Its great importance is due to its manufactories, for which it has every facility in the way of water-power and supplies of coal and iron ; indeed, Pittsburg is a city of iron, hardware, and cutlery works. It annually manu- factures large quantities of every kind of ironmongery, includ- ing steam-engines and machinery, cutlery and nails, and builds ships and steamboats on a large scale. It was a busy, grimy, sooty, dusty, coaly, dirty, Staffordshire-like kind of place.” The Pennsylvanian coal-fields cover an area of about 15,000 square miles, and are estimated to contain three times as much coal as all the fields of Great Britain — more than the whole of Europe. Most of the seams are easy of access, and there are excellent river facilities for concentrating the produce of the mines in Pittsburg, and thence dispatching it to all parts. More than a hundred collieries are within easy reach of the town. Ten or twelve are in its immediate vicinity ; and these, giving employment to about 1,500 colliers, are known as the “City Mines,” and feed the local manufactures. Of these manufactures, iron and steel are the most important. In 1860 Pittsburg contained twenty -three great establishments devoted to their production ; the number of workmen so engaged being about 6,000, and the value of their produce about =£2,500,000. It had also sixteen foundries ; one for cannon — from which was sent out, in January, 1861, the famous “Union” gun, weighing 49,050 pounds. In 1860 the town produced about 350 steam- engines for ships and factories. It had two copper-mills, six cotton-mills, nine white-lead factories, and several establish- ments for constructing river steamboats. The town may be considered to have about doubled in popula- tion and in trade between 1860 and 1870. Unlike most of the American towns, it gained instead of losing in the unfortunate war between North and South. A great impetus was given to its manufacture of large and small guns ; and the Americans, who before that time went chiefly to Birmingham and Liege for their weapons, now have their wants supplied amply and more cheaply by Pittsburg The town makes wonderful pro- gress every year in all branches Df hardware manufacture. Besides its abundant stores of coal, it has plenty of iron, copper, zinc, and lead in the neighbourhood; and by continuing to make good use of these advantages, it promises not only to hold its position as the chief hardware town in America, but also, in so doing, to surpass its rivals in the Old World. 120 THE TECHNICAL EDUCATOR. PRINCIPLES OF DESIGN.— III. By Christopher Dresser, Ph.D., F.L.S., etc. TRUTH, BEAUTY, AND POWER IN ORNAMENTATION. In my two previous chapters I have attempted to set forth some of the first principles of ornament, and to call attention to the purport or intention of certain of the leading historic styles, and the manner in which they make utterance to us of the faith or sentiments of their producers. But there are other utterances of ornament, and other general expressions which decorative forms convey to the mind. Thus sharp, angular, or spiny forms are more or less exciting (Fig. 9) ; while bold and broad forms are soothing, or tend to give repose. Sharp or angular forms, where combined in ornament, act upon the senses much as racy and pointed sayings do. Thus “cut” or angular glass, spinose metal-work, as the pointed foliation of some wrought-iron gates, and other works in which there is a prevalence of angles and points, so act upon the mind as to stimulate it, and thus produce an effect opposite to repose ; while “ breadth” of form and “ largeness ” of treatment induce tranquillity and meditation. Nothing can be more important to the ornamentist than the scientific study of art. The meta- physical inquiry into cause and effect, as relating to decorative ideas, is very important — indeed, all-im- portant — to the true decorator. He must constantly ask himself what effect such and such forms have upon the mind— which effects are soothing, which cheerful, which me- lancholy, which rich, which ethereal, which gorgeous, which solid, which graceful, which lovable, and so on ; and in order to do this he must sepa- rate the various elements of orna- mental composition, and consider these apart, so as to be sure that he is not mistaken as to what affects the mind in any particular manner, and he must then combine these elements in various proportions, and consider the effects of the various combinations on his own mind and that of others, and thus he will discover what will enable him to so act on the senses as to induce effects such as he may desire to produce. Are we to decorate a dining-room, let the decoration give the sense of richness ; a drawing-room, let it give cheerfulness ; a library, let it give worth ; a bedroom, repose ; but glitter must never occur in large quantities, for that which excites can only be sparingly indulged in ; for if it is too freely employed, it gives the sense of vulgarity. In this chapter I have to speak primarily of Truth, Beauty, and Pouter. Long since I was so fully impressed with the idea that true art- principles are so perfectly manifested in these three words, that I embodied them in an ornamental device which I painted on my study door, so that all who entered might learn the principles which I sought to manifest in my works. There can be morality or immorality in art, the utterance of truth or of falsehood ; and by his art the ornamentist may exalt or debase a nation. Truth. — How noble, how beautiful, how righteous to utter it ; and how debasing is falsehood ; yet we see falsehood preferred to truth — that which debases to that which exalts, in art as well as morals ; and I fear that there is almost as much that is false, degrading, and untrue in my beautiful art as there is of the noble, righteous, and exalting, although art should only be prac- tised by ennobling hands. It is this grovelling art, this so- called ornamentation, which tends to debase rather than exalt, to degrade rather than make noble, to foster a lie rather than utter truth, which brings about the abasement of our calling, and causes our art to fail in many instances in laying hold of, Fig. 9. and clinging to, the affections of the noble and the great. Ornamentation is in the highest sense of the word a Fine Art ; there is no art more noble, none more exalted. It can cheer the sorrowing ; it can soothe the troubled ; it can enhance the joys of those who make merry ; it can inculcate the doctrine of truth ; it can refine, elevate, purify, and point onward and upward to heaven and to God. It is a fine art, for it embodies and ex- presses the feelings of the soul of man — that inward spirit which was breathed by the Creator into the lifeless clay as the image of His life, however noble, pure, or holy. This being the case, those who ignore decoration cast aside a source of refinement, and deprive themselves of what may induce their elevation in virtue and morals. Such a neglect on the part of those who can afford luxuries would be highly censurable were it not that the professors of the art are for the most part false pretenders, knowing not what they practise, and men ignorant of the powers which they hold in their hands. The true artist is a rare creature ; he is often unknown, frequently misunderstood, or not understood at all, and is not unfrequently lost to a people that prefer shallowness to deep meaning, falsehood to truth, and glitter to repose. We now see the utter folly of appealing simply to what is called “taste” in matters of art, and the uselessness of yielding to the caprice (falsely called taste) of the uneducated in such matters, especially as this so-called taste is often of the most vulgar and de- based order. We also see the ab- surdity of persons who employ a true artist interfering with his judg- ment and ideas. The true artist is a noble teacher ; shall he be told, then, what morals he shall incul- cate, and what lofty truths he shall embody in his works, or omit from them ? Do we tell the preacher what he shall say, and ask him to withhold whatever is refining and elevating ? We do not, and iix art we must leave the professors free to teach, and hold them respon- sible for their teachings. If I thought that I had now con- vinced my reader that decorative art does not consist in the placing together forms merely, however beau- tiful they may be individually or col- lectively ; nor in rendering objects simply what is called pretty ; but that it is a power for good or evil ; that it is what will elevate or debase — that which cannot be neutral in its tendency — I would advance to consider its principles ; but I cannot teach, nor can I be understood, unless the reader feels that he who practises art wields a vast power, for the rightful use of which he must be held responsible. All graining of wood is false, inasmuch as it attempts to deceive, the effort being made at causing one material to look like another which it is not. All “marbling” is false also : a floor-cloth made in imitation of carpet or matting is false a Brussels carpet that imitates a Turkey carpet is false ; so is a jug that imitates wicker-work, a printed fabric that imitates one which is woven, a gas-lamp that imitates an oil- lamp. These are all untruths in expression, and are, besides, vulgar absurdities which are the more lamentable, as the imita- tion is always less beautiful than the thing imitated ; and as each material has the power of expressing beauty truthfully, thus truth has its own reward. A deal door is beautiful, but it: will not keep clean ; let it then be varnished. It is now pre- served, and its own characteristic features are enhanced by the varnish, so that its individuality is emphasised, and no untruth is told. A floor-cloth can present a pattern with true and beautiful curves — how absurd, then, to try and imitate the dotty effect of a carpet ; and the Brussels carpet can express truer curves than the Turkey carpet, then why imitate the latter ? But perhaps the most senseless of all these absurdities is the ORNAMENT COMPOSED OP SHARP AND SPINY FORMS. PRINCIPLES OF DESIGN. 121 making an earthen jug in imitation of wicker-work, when if so formed it would be useless as a water- vessel. I can imagine a fool in his simplicity priding himself on such a bright thought as the production of a vessel of this kind, but I cannot imagine any rightly constituted mind producing or commending such an idea. Let the expression our art ever be truthful. Beauty. — I will say little on this head, for decorative forms must be beau- tiful. Shapes which are not beautiful are rarely decora- tive. I will not now attempt to express what character forms should have in order that they be considered beautiful, but will content my- self by saying that they must be truthful in expression, and graceful, deli- cate, and refined in contour, manifesting no coarseness, vul- garity, or ob- trusiveness of character. My views of the beautiful must be gathered from the series of articles which will follow, but this I may here say, that the beautiful mani- fests no want, no shortcoming. A composition that is beautiful must have no parts which can be taken from it and yet leave the remainder equally good or better. The per- fectly beautiful is that which admits of no im- provement. The beautiful is lovable, and, as that which is lovable, takes hold of the affec- tions and clings to them, bind- ing itself firmer and firmer to them as time rolls on. If an object is really beautiful we do not tire of it ; fashion does not induce us to change it; the merely new does not displace it. It becomes as an old friend, more loved as its good qualities are better understood. Power . — We now come to consider an art-element or principle of great importance, for if absent from any composition, feeble- ness or weakness is the result, the manifestation of which is not pleasant. Weakness is childish, it is infantine ; power is manly — power is God-like. With what power do the plants burst from the earth in spring ! With what power do the buds develop into branches ! The powerful orator is a man to be admired, the powerful thinker a man we esteem. Even the simple power, or brute- force, of animals we involuntarily approve — the powerful tiger and the power- ful horse call forth our com- mendation, for power is antag- onistic to weak- ness. Power also manifests ear- nestness; power means energy ; power implies a conqueror. Our compositions, then, must be powerful. But besides all this, we, the professors of decorative art, must manifest power in our works, for we are teachers sent forth to instruct, and en- noble, and ele- vate our fellow- creatures. We shall not be be- lieved if we do not utter our truths with power ; let truth, then, be uttered with power, and in the form of beauty. I have given in this chapter an original sketch (Fig. 10), in which I have sought to em- body chiefly the one idea of power, energy, force, or vigour, as a dominant idea ; and in order to do this, I have employed such lines as we see in the burst- ing buds of spring, when the energy of growth is at its maximum, and especially such as are to be seen in the spring growth of a luxuriant tropical vegetation ; and I have also availed myself of those forms which we see in certain bones of birds which are associated with the organs of flight, and which give us an impression of great power, as well as those which we observe in the powerful propelling fins of certain species of fish. of Fig. 10. — DESIGN EXEMPLIFYING POWEK. 122 THE TECHNICAL EDUCATOR. VEGETABLE COMMERCIAL PRODUCTS. -IV. PLANTS YIELDING SPICES AND CONDIMENTS ( Continued ). Cardamoms ( Elettaria cardamomum, Maton ; natural order, Zingiberacece) . — Cardamom seeds are obtained from several other allied plants, but those of the ab-T e species of Elettaria constitute the true officinal Malabar cardamoms. The cardamom is an obtusely triangular three-celled pod, about half an inch in length, of a pale-straw colour, and fur- rowed longitudinally on its outer surface. This pod contains numerous reddish-brown, rugose seeds, about the size of mus- tard seeds, internally white, and having a pleasant aromatic odour and an agreeable taste. Cardamoms are principally employed here in medicine as a flavouring ingredient, and occasionally as a stimulant and car- minative, especially in the form of a simple or compound tinc- ture. In India they are much used as a favourite condiment for various kinds of food, as curries, ketchups, and soups. Their active principle is a pungent volatile oil. Cardamoms are shipped to this country from Ceylon, the Malay peninsula, Sumatra, Java, Siam, Cochin-China, and the Malabar coast. The quantity of all kinds imported is about twenty-five tons per annum. UMBELLIFEROUS PLANTS WITH AROMATIC FRUITS. There are a few seeds which, from their pungent aromatic flavour, are used as condiments, and may very properly be classed with the spices. The fruits of the caraway, coriander, and anise — called in commerce -seeds — although cultivated in this country, are im- ported somewhat largely from the Continent, and are therefore deserving of notice. Caraway (Carum carui, L.). — The caraway is indigenous to most parts of Europe, as well as to this country. It is cultivated to some extent in Essex and Kent. The taste of the seeds is aromatic and warm, and their odour is fragrant, but peculiar. The seeds are much used by the confectioner, and are some- times added to bread ; coated with sugar, they form the well- known “caraway comfits” to which children are so partial. We import about 500 tons of caraway seeds annually from Ger- many and Holland, nearly the whole of which are retained for home consumption. Coriander ( Coriandrum sativum, L.). — The fruit of this plant is globose, having a peculiar smell, and a pleasant, aromatio taste. In a fresh state both the fruit and foliage have an extremely disagreeable odour ; nevertheless, the Tartars are said to use it in the preparation of a favourite soup. The coriander is indigenous to Southern Europe and Italy, but has a wide geographical range, bearing the climate of India and Britain equally well. It is cultivated in this country, par- ticularly in Suffolk and Essex, and is valued both by the apothecary and the distiller. Coriander is used in medicine for its carminative and aromatic properties,- as a corrective to the griping qualities of cathartics. It is more used in confectionery than in medicine. Coriander-seed is also employed in adulterat- ing beer. The poor Indian mixes these seeds with his curry, and they are equally welcome at the table of the rich. Our im- ports from Germany average fifty tons per annum Anise (Pimpinella anisum, L.). — This is a perennial plant, with an erect, round, striated, rough, or downy stem ; pinnati- sect leaves, white flowers, and an ovate, downy, aromatic fruit, resembling the finer kinds of parsley-seed in shape, and grateful and sweetish to the taste. The oil of anise is obtained by distillation from the seed, about one cwt. of seed yielding two pounds of the oil. It is used in confectionery and in medicine. Anise is indigenous to Egypt, but is now largely grown in Malta, Spain, Italy, France, Germany, and the East Indies. The principal imports are from Alicant in Spain, and Hamburg in Germany, and average about seventy tons per annum. Other umbelliferous, plants used as condiments are cumin {Cuminum cymium, L.) and angelica (Archangelica officinalis, Hoffm.). Star Anise ( Illicium amsatum ,■ natural order, Magnoliacece). This plant is so called because the flavour of aniseed pervades the whole of it, especially the fruit ; but it is not at all allied to anise, belonging to a totally different natural order. It is a ©hrub indigenous to Chma and Japan: its fruit is used to flavour sweetmeats, confectionery, and liquors. The aromatic oil of star anise, singularly enough, in every respect resembles anise oil, for which it is often substituted. In India, star anise is an important article of commerce, and sold in all the bazaars. Mustard. — The seeds of Sinapis nigra, L., often mixed with S. alba (natural order, Crucifer os). — The spherical seeds of these two species are crushed, pounded, and then sifted through a fine sieve ; the fine, powdery product is the “ flour of mustard ” in common use. The outer skin of the seeds, separated by sifting, forms a coarse powder, which is sold for adulterating pepper. Mustard-seed is largely imported from the East Indies for the expression of oil ; and white-mustard seed is imported from Northern Germany, in small quantities, for grinding with the black mustard-seed grown in this country. IV. PLANTS YIELDING SUGAR. Sugar-cane ( Saccharum officinarum, L. ; natural order, Oraminece) . — This plant, next to rice and maize, is the most valuable of the tropical grasses. Its stem* which is solid, cylindrical, and jointed, is two inches in diameter, and from twelve to fifteen feet in height ; its leaves are long, narrow, and drooping ; flowers very handsome, appearing like a plume of white feathers, tinged with lilac. A field of sugar-canes in blossom presents a very beautiful appearance. The sugar-cane is seldom permitted to flower under cultiva- tion. It is propagated by sections of the culm, or stem, with buds in them. Trenches are cut, and the pieces of the culm are laid horizontally in them ; the earth is then thrown into the trench, and the canes soon develop from the nodes or joints of the culm. As they grow up, and the wind gains power over them, the lower leaves are removed, and the stems are strengthened by being fastened to bamboo supports. The sugar-cane plant is very sensitive to cold, and therefore its cultivation is restricted to the tropics, and to regions on their borders where there is little or no frost. In the Old World sugar plantations are mostly confined to countries lying between the 40th parallel of north latitude and a corresponding degree south ; in America, along the Atlantic seaboard, they do not thrive beyond 33° north latitude and 35° south latitude ; whilst on the Pacific side the sugar-cane matures about 5° further to the north and south of the equator. The principal countries -where sugar is largely grown are the West Indies, Venezuela, Brazil, Mauritius, British India, China, Japan, the Sunda, Philippine, and Sandwich Islands, and the Southern United States of America. Moreton Bay and the northern parts of Australia are admirably suited, both in soil and climate, to sugar culture. Manufacture of Sugar. — When the cane is ripe, it is cut down, deprived of its top and leaves, cut up into convenient lengths, tied up in bundles, and taken to the mill. Hero the canes are crushed between iron rollers, the juice from them flowing into vessels, where it is boiled with the addition of lime, and evaporated to the consistence of syrup, care being taken to remove any scum which appears on the surface during this part of the process. The lime is added to remove any acidity, and prevent fermentation. The material of the fire consists of the refuse crushed cane, dried for that purpose in the sun. Six or eight pounds of cane-juice will yield one pound of raw sugar ; and from sixteen to twenty cart-loads of cane ought to make a hogshead of sugar, when thoroughly ripe. The cane syrup thus prepared is transferred to shallow vessels, or coolers, in which it is stirred until it becomes granulated ; it is then put into hogsheads having holes in the bottom, which are placed in an upright position over a large cistern, and allowed to drain. In this state it is called muscovado or brown sugar, and the drainings molasses. The casks are then headed down and shipped. This muscovado is purchased by the grocers, and constitutes the brown or moist sugar of the shops. The planters in the West Indies generally send their sugar to England in the form of muscovado; but in the French, Spanish, and Portuguese settlements, it is usually converted into clayed sugar before exportation. The process is as follows : — The sugar from the coolers is placed in conical pots with holes at the bottom, having their points downward. A quantity of clay is laid on the top and kept moistened with water, which, oozing gently from the clay through the sugar, dilutes the molasses, and causes more of it to come away than in the hogs- head, leaving it whiter and purer than the muscovado sugar. 123 PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING. Loaf or refined sugar is made from the muscovado by the sugar-bakers in England. The muscovado is re-boiled, and refined with the serum of bullock’s blood or the white of eggs ; it is then transferred to conical moulds, and clayed repeatedly until perfectly white. The sugar is then removed from the moulds, and set in a stove to dry. The sugar-cane, a plant originally confined to Asia, and which grew wild in India, was introduced into the south of Europe from the East by the Saracens, soon after then- con- quests in the ninth century. In the twelfth century, sugar plantations were established in Cyprus, Rhodes, Candia, Malta, Sicily, and Spain ; and as early as the beginning of the fifteenth century they had been extended to Granada, Murcia, Portugal, Madeira, and the Canary Islands. The sugar-cane is now cultivated at only a few places in Europe, viz., Malta, Sicily, and the south of Spain. The rest of the sugar plantations have disappeared from the coun- tries about the Mediterranean, in consequence of the ex- tent of the great American plantations, and thoso in the West Indies. In the middle of the sixteenth century the sugar-cane was transplanted by the Portuguese to Brazil, and by the Spaniards to the West Indies, where the greatest quantity of sugar is now produced. Brazil has now 900 sugar plantations, pro- ducing annually about 50,000 tons of sugar ; and of the West India Islands, Cuba and Jamaica alone raise 150,000 tons for exportation yearly. Porto- Rico, and the French, Dutch, and Danish colonies in the West Indies, export sugar largely, as do also Louisiana and Alabama, by way of New Orleans. The ex- ports of sugar from Mexico go mostly to New Granada, Caracas, and Ecuador in South America. The East Indies, Java, Sumatra, the Philippine Islands, Siam, Cochin-China, Bengal, and Ceylon, all produce sugar for exportation. Sugar has been made in China, indeed, from very remote antiquity, and large quantities also have been exported from India in all ages. In 1866, 10,639,085 cwt. of raw sugar were imported into the United Kingdom, of which 5,823,729 cwt. were received from our colonies, and the rest from foreign countries. Of this amount 10,297,196 cwt. were retained for home consumption, and the remainder exported. Rum, or Brandy of Sugar.- — The best is distilled from the pure juice of sugar; the inferior kind is made from treacle, and from the residuum in the sugar refineries. Jamaica rum is the finest, about three millions of gallons being annually imported into England from the West Indies. Rum is also distilled for exportation in Bengal, Madras, Batavia, and Manilla. The native arrack of India has been nearly driven out of the market by this spirit. Besides the sugar-cane, many other plants yield sugar. The principal of these are : — - 1. Beet-boot and Mangold-wurtzel (two varieties of Beta vulgaris, Tournef ; natural order, Chenopodiaceoe) are cul- tivated very extensively on the continent of Europe, especially in France, where a great portion of the supply of sugar is ob- tained from the juice of these sap-roots. In Great Britain beet-root is eaten as a salad, and mangold-wurtzel is largely grown as winter food for cattle. 2. Sugar-maple (Acer saccharinum, Wang. ; natural order, Aceracece). — From the juice which flows from incisions made in the stem of this, and probably other species of maple, large quantities of a coarse uncrystallisable sugar are manufactured in North America. 3. Date (Phoenix dactylifera, L. ; natural order, P ahnaceai) . — From this useful palm, and also from P. sylvestris, L., and Saguerus saccharifer, sugar is produced by boiling the ! juice, which flows from incisions made in the flower-heads; from P. sylvestris, L., alone, as much as 6,000 tons are made annually. These sugars are mostly consumed in India ; much, however, is supposed to be imported to this country as cano sugar. The fruit of the date is well known and highly appre- ciated in this country. It is remarkable for its nutritious and life-sustaining qualities ; the Arabs, while crossing vast desert tracts, requiring no other food than a handful or two of this fruit per day. The best grow in the regions on the southern slopes of the Atlas mountains. This, part of Africa is said to be the natural habitat of the date-palm, and is called Bil-ed-ul- jerid, or the Date Country. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— II. It has been explained in previous lessons that “ to bisect ” means to cut into two equal portions ; this requires to be pro- perly understood in dividing angles, for it will be evident that if a line were drawn across the angle, the one part would be much wider than the other, even though the line might cross exactly in the middle of one of the lines forming the angle. The following problem shows the correct method of overcoming the difficulty, and subsequent figures show the application of the lesson. To bisect an angle, a b c (Fig. 8). — From B, with any radius, describe an arc, cutting the lines B A and B c in D and E. From D and e, with any radius, describs arcs cutting each other in F. Draw B p, which will bisect the angle. To inscribe a circle in the triangle ABC (Fig. 9). — Bisect any two of the angles (by Fig. 8). c Produce the bisecting lines until they meet in D. From D, with the radius d e, which is a perpendicular from D on A B, a circle may be described which will touch all three sides of the triangle. This is called the inscribed circle. To draw a circle through three points, however they may be placed, provided they are not in an absolutely straight line (Fig. 10). Let A B and c be the three given points. Join A B and b c. Bisect A b and b c, and produce the bisecting lines until they cut each other in the point D. Then D will be equally distant from each of the three points. Therefore, from D, with radius D A, D B, or D C, a circle may be drawn which will pass through the three given points. It will be evident that if A and C were joined, the figure would be a triangle ; and thus this problem serves also for describing a circle which shall touch the three angles of a triangle. This is called the circumscribing circle. 124 THE TECHNICAL EDUCATOR. ■ The Gothic trefoil (Fig. 11).— The trefoil is a figure much used in Gothic architecture. It is formed of three leaves, or lobes (hence its name), meeting at a centre, as in the three- leaved clover. It is sometimes enclosed in a circle, as in window tracery, but not always, as in many wall-piercings. This figure will serve as an application of the construction of the equilateral triangle and the bisecting of angles. It is here introduced with the view of showing students the importance of absolute accuracy in the early problems, as well as in the subsequent operations. Construct an equilateral triangle, a be. Bisect the angles, and produce the bisecting lines, cl, e, f. Observe, that in an equilateral triangle, the lines which triangle, describe the arcs j, Je, l, and the others, which it will be plain are concentric (that is, drawn from the same centre) with them. The arcs m and n, and those corresponding to them, are also drawn from the same centres. The outer circles and the arcs p, q, etc., are drawn from the centre of the triangle o. To construct on the given line, u e, an angle similar to the angle A b c (Fig. 12). From B, with any radius, describe an arc cutting the sides of the angle in c d. From E, with the same radius, describe an arc, cutting E D in r. Measure the length from point c to d. Mark off the same on the arc from F — viz., to point g. Draw a line from E through G. The angle peg will be equal to A B C. On the given line, a b, to construct a triangle similar * to * When a figure is said to he similar to another, it means that it is of the same shape. When it is said to be equal, it means that it is of the same area — that is, it contains precisely the same space. A figure may be equal to another without being similar in shape : thus a square may be equal in area to a rectangle ; and a figure may be similar without being equal, as in Figs. 13, 14. “Similar and equal’’ means being of both the same shape and size as another figure, as in Figs. 18 and 19 CEE (Figs. 13 and 14). — At A construct an angle sim.lar to the angle h c G — viz., j a i. Definitions concerning four-sided figures which are not paral- lelograms . — A figure having four sides, which are neither equal nor parallel to each other, is called a trapezium, as A (Fig. 15). But any two of its adjacent (or adjoining) sides maybe equal to each other, so long as they are not parallel to the opposite sides, as B (Fig. 16). If any two of the sides are parallel to each other, the figure is called a trapezoid, as c (Fig. 17). To construct a trapezium similar and equal to another, c d e f (Figs. 18 and 19). ] Draw A B equal to c r>. At A construct an angle similar to that at c. Make A G equal to C E. At B construct an angle similar to that at D. Make b h equal to d f. Join h G, and the trapezium on A b will be similar and equal to C D E F. It is advisable that the students should be repeatedly exer- cised in constructing figures similar and equal to each other ; and as the correct result of the higher figures depends on the refinement of their con- struction, the most intense accuracy should, from the very outset, be aimed at. Having thus illustrated the difference between the trapezium and the trapezoid, and between similar and equal, we now pro- ceed to construct these figures similar to others, and of given dimensions. The artisan cannot too soon begin to work to “ scale,” and he is therefore recommended to take the measure- ments from his rule, not from these pages ; the result must be the same, even though the mere sizes may be different. To construct on the given diagonal, ab (Fig. 20), a trapezium similar to another, c E d f (Fig. 21). Draw the diagonal c d in the given trapezium. From c and D, with any radius, draw arcs cutting the diagonal c D in G and H, c f and C E in I and j, and D E and d f in K and L. From A and B, with the same radius, describe arcs cutting the diagonal A b in m and N. From the point M, cut off on the arc the length G J — viz., to O, and also the length g i — viz., to p. From the point n, cut off on the arc the length h k — viz., to Q, and also the length H l — viz., to r. Draw B q and be; also ao and ap. Produce these lines until they meet in s and T. atbs will be the trapezium required. Fig. 18. Fig. 19. COLOUR 125 This result would be the same, whatever might be the length of the diagonal or the relative sizes of the figures, as an angl e is not altered by the length of the lines of which it may be formed. To construct a trapezium from the following given dimensions (Fig. 22). — Sides c A and c b are to be adjacent to each other, forming an angle similar to A b c. c A is to be If inches long ; C B, li in. ; A D, 1 in. ; bd, 1} in. Fig 22. Now, in the figure here required, the first fixed condition is, that the sides o a x and c B are to make an angle similar to the given angle A B c. Therefore at any point, construct this angle (a C b), and produce the lines until c A is If inches, and c B inches long — -viz., to A and b. From A, with 1 inch radius, describe an arc. From B, with inch radius, describe another arc cutting the former in d. Draw a d and b d, which will complete Fig. 23 from the given dimensions. COLOUR— II. B. The ray will be refracted, of course, but it will show but one colour, as before, and its image will not be elongated. We have already learnt that every ray of coloured light has its own wave-length, and therefore that all the colours of the spectrum, however similar they may seem, are really distinct tints. But this consideration does not take in all the facts of the case. The green of the solar spectrum is not compound, but simple ; and yet we know that many substances of a green colour may be split into two components, one blue and the other yellow. Supposing for a moment we can exactly imitate the Fig. 2. green of the solar spectrum by mixing yellow and blue pigments together, this fact would not of itself suffice to prove that the solar green was really a mixed hue ; but it would show that tha sensation of vision is similarly excited by the waves that reach the eye from these two colours — one simple, the other apparently compound. Precisely the converse of this holds good. We can, as might be expected, re-form white light by re-uniting all the seven dispersed coloured lights of the solar spectrum (we will describe how to do this presently) ; but we can reach the same result by re-uniting merely certain pairs of these coloured lights. Thus, the following unions of two colours generate white, or nearly white light : — By Professor Church, Eoyal Agricultural College, Cirencester. COMPOSITION OF LIGHT — COMPLEMENTARY COLOURS — THE SPECTRUM. It was Newton who first discovered the compound nature of white light. In order to split up a ray of the solar light into its constituent parts, the following contrivance (Fig. 1) may be adopted : — Through a hole in the shutter of a darkened room a beam of light, s, is allowed to enter. This small beam must fall upon a prisia of flint-glass, A, so arranged that the side, P, oppo- site to its refracting angle is uppermost and horizontal. The beam will be refracted and dispersed, as described in our last paper; and if the refracting angle of the prism be 60°, a vertical Fig. 1. band of rainbow colours will be produced on a screen placed at a distance of five yards or so from the prism, a. This band, H I, is the solar spectrum. It consists of a very large number of different tints, amongst which it is easy to distinguish seven prinfipal colours. Beginning at the end of the spectrum which is ntarest to the spot, K, the beam would have reached had no prism bint it out of its path, we find the order of the colours is as follovs : — Bed, orange, yellow, green, blue, indigo, violet. Now the node in which these colours have been separated from white light is sufficient proof that they cannot be further sepa- rated into other kinds of colour. This anticipation is realised by actual trial ; for if, as in Fig. 2, one of the colours of the spectrum, v, be allowed to pass through a hole in the screen, E, on which the band of decomposed light has been received, it cannot be altered by being transmitted through a second prism, 1. Bed— greenish-blue. I 3. Yellow — indigo-blue. 2. Orange — Prussian-blue. | 4. Greenish-yellow — violet. These pairs of colours, and many others less easy to distinguish by intelligible names, when united lose their respective colours and become white. They are called complementary colours. It will be seen that we have followed in our grouping of them the sequence of the colours of the spectrum, beginning with the red or least refrangible rays ; but in order to produce white light by the combination of any couple of the above colours, two con- ditions must be fulfilled — the intensity and the quantity of the component rays must be adjusted with care. By receiving two such coloured pencils of light upon a lens which condenses and brings them to the same focus on a white screen placed at a suitable distance, the result is a perfectly white light ; but, to secure this result, the constituents of a coloured ray are as important as its apparent quality of colour. Thus Helmholtz has found that the red and bluish-green of the spectrum produce yellow, not white ; while red, with the bluish-green formed by the union of green and indigo, does yield white. Green and red have indeed a relation to each other which is different in some particulars from that of many other pairs of colours. They, how- ever, are often included among the pairs of so-called comple- mentary colours for reasons to be hereafter noticed. That there is something very peculiar in the relation of green to red may be also concluded from the frequency with which these two colours are confounded by persons who suffer from colour-blind- ness or Daltonism. One of the most curious of all the results of studying the re-composition of white light is the relation of yellow to blue. It is a matter of observation that a yellow and blue liquid and a yellow and blue powder, when mixed together, pro- duce respectively a green liquid and a green powder. But a very different result ensues on mixing blue and yellow light together. When the blue and yellow rays of the spectrum are mixed together, white light is produced. The same effect results from receiving upon the eye the reflected image of a disc painted with gamboge along with the direct image of a second disc painted with cobalt-blue. Though a disc painted with these two pigments mixed together would have appeared green, yet when the lights these pigments respectively reflect are con- veyed to the retina as above described, then, where the two images coincide, whiteness is the result. We must now describe some of the peculiarities of different spectra, and afterwards a few of the more recondite method* by which colour is produced. * 126 THE TECHNICAL EDUCATOR. Our purest source of coloured lights is a spectrum. We may use the spectrum of the solar beams, or that from the electric lamp : the latter is more convenient, and yields, as we have previously stated, a light more complex than the sun ; for in the solar spectrum there are some three thousand or more gaps where rays are missing. These are the black lines first noticed by Wollaston, in 1802, afterwards mapped out by Fraunhofer, and at last explained by Bunsen and Kirchholf. These black lines indicate lost rays — rays which have been blotted out by absorption. The absorption takes place in the following manner : — In the sun’s gaseous envelope certain vapours exist. These vapours are opaque to certain rays of light : they do not allow them to pass, but quench them. There is, for instance, the metal sodium in the sun’s gaseous covering. Now sodium vapour is opaque to a certain yellow ray which it itself origi- nates when it is burnt. Consequently, the place which should be occupied by a bright yellow band in the solar spectrum is a dark line, or rather group of lines, called D. In like manner the other black lines, or many of them, have been traced to the special absorptive powers possessed by the sun’s gaseous enve- lope, and exercised upon certain rays of light emanating from within. These black lines, however, in the solar spectrum, though rendering it imperfect in continuity, are of great service in referring to the localities of particular colours. Yet we must not forget that the material of the prism exercises some influence upon the position of the lines and the relative extent of the coloured bands. With a future part a coloured plate will be given in which will be shown the positions occupied by the most important of the black lines and coloured spaces in the solar spectrum when obtained by means of a flint-glass prism in the spectroscope. The conditions of success in obtaining these lines dis- tinctly are a narrow, clean-edged slit, a collimating lens to make the luminous rays parallel, and Cj prism of highly-refractive and dispersive glass, quite free from striae and flaws. The instruments known as spectroscopes are, however, always of more complicated construction than these con- ditions seem to involve ; for it is desirable to use a battery of prisms instead of one prism, and to obtain a magnified image of the spectrum by means of a combination of lenses in a telescope. Let us turn now to the consideration of the spectra as ob- tained by means of the spectroscope. Most of our sources of artificial light yield spectra without lines. An oil-lamp, gas-flame, the electric light, are instances of this kind. But it is easy to secure a flame which shall yield a very simple spectrum, reduced by the absence of so large a number of rays that it shall merely consist of a few bright bands, or merely of one. Dissolve a little common salt, for instance, in some methylated spirit of wine, and introduce the solution into a spirit-lamp. The flame will, to the eye, appear tolerably luminous and distinctly yellow. The spectrum of this flamo shows little more than a single brilliant yellow band, occupying the dark space of the solar spectrum called D. The metal sodium is distinguished from other metals by its flame emitting rays of that particular refrangibility only. If a salt of lithium be taken, and dissolved in spirit, the flame of the lamp will be crimson, and two coloured bands will characterise the spectrum. One of them is red, and very distinct ; the other is of a faint orange tint. Other metals produce different spectra, though in many cases the colour which they impart to the flame cf a Bunsen gas-burner or a spirit-lamp may seem to the unassisted eye identical. In trying experiments with coloured flames, in order to study their effects on the appearance of different objects, the following contrivance may be used : — -A (Fig. 3) is a Bunsen gas-burner (which is best made of steatite) ; B is a bundle of fine platinum wires, dipping into a small vessel containing a mixture of a solution of the metallic salt to be experimented with, and am- monium chloride. A ball of pumice attached to a bundle of asbestos fibres may be substituted for the platinum wires. The following is a list of substances which give colours of different hues to the flame of a burner under the circumstances described the metallic salts most applicable being those known as chlo- rides, chlorates, and nitrates : — • Substances. Calcium nitrate . . . Lithium chloride Strontium nitrate or chlorate Sodium chloride . Barium chloride or chlorate Boracic acid Thallium perchloride . . Copper chloride . Indium chloride . Potassium chlorate . . Colours of Flame. Bed. Carmine. Crimson. Yellow. Y ellowish-green. Green. Green. Bluish-green. Indigo-blue. Violet. The above substances give, for the most part, spectra with many bright lines of different colours ; but the red lines will dominate in one spectrum, and the green in another. Thus far we have been studying light and colour by means of the prism : we will now see how the colours of the spectrum may be separated without that instrument, and yet without loss of any of their component parts. Some of the most beautiful phenomena of colour are produced by a modification which light undergoes when it passes the edge of an opaque body, or when it traverses a small opening. Light then turns a corner. This bending of the waves of light has been termed diffraction. The source of light in studying the phenomena of diffraction should be a luminous or highly illuminated point. A silvered bead, or steel globule, or the focus of rays ob- tained by the action of a lens on a beam of light entering a dark chamber by means of a small hole — all these contrivances furnish a suitable light. If a narrow rectangular slit between two metallic edges be placed in a beam of light, between the focus of a lens and a screen, the space between the edges will be occupied by bands of coloured light. If one colour only be used, as by the interposition of a screen of red glass, then alternate bands of that colour and black will be seen. By using, instead of a simple rectangular slit, apertures differing in size, number, and shape, very beautiful chromatic appear- ances may be developed. Those may be obtained by looking at a bright point or line of light through a bird’s feather mounted in a card-frame, through a piece of glass dusted with lycopodium spores, through a fine wire-grating, through a- piece of very fine cambric, or through a plate of smoked glass ruled with fine lines. The halo of colours sometimes seen round the moon and the- sun is a phenomenon of the same kind, produced by the diffrac- tion of light by the globules of water constituting the fog. Imperfectly polished metals, the feathers of many birds, and the surfaces of mother-of-pearl, owe part, at least, of the peculiar coloured effects which they exhibit, and which are known as iridescence, to the diffraction of the light reflected from the small striae, filaments, or folds of their surfaces. Now, without entering into the minute particulars necessary to elucidate these appearances thoroughly, we may state that the phenomena of diffraction are due to two causes. One of these is the bending of light round a corner, as waves of water bend round a rock in a lake ; the other, the interference of the waves of the light-rays so bent with one another. Interference of one set of oscillations with those of another set may even extinguish the light altogether. This takes place when the crests of the undulations of a ray coincide with the hollows of the undulations of another ray : thus there will be rays on either side of a slit which, bent by diffraction, will by this kind of interference exactly neutralise each other and abolish the light. The dark bands and lines produced by diffraction are ex- plicable in this way. As to the cause of the colours seen under the conditions just mentioned we may refer to th3 THE ELECTRIC TELEGRAPH. 127 obliquity of the paths of the diffracted rays. If red light be employed, black and red rings or bars alternate ; but with violet light, black and violet rings or bars are seen. The violet rings are nearer together than the red, because then- waves are smaller than the red. We can obtain bands of colours intermediate in width between red and violet by employing, for example, green light. Hence, when ivliite light passes through a slit, we obtain a series of coloured spectra side by side, be- cause the constituent colours are not superposed, owing to the obliquity of the paths of the rays and their different wave- lengths. More or less obliquity in the path of a diffracted ray will cause it to differ, by various parts of a wave-length, from other diffracted rays of the same beam. The colours of thin plates correspond in sequence, as do those of diffraction, to the colours of the prismatic spectrum. They are produced by the interference of the ray which enters the thin transparent film, and is reflected from its second surface, with the ray which is directly reflected from its first surface. A soap-bubble may be of such a thickness as to retard the beam reflected from its second surface by half a wave-length, or by any number of half wave-lengths. Then it will be found that the bubble is black, because the two reflected beams are in com- plete discordance ; and a destruction of light follows. Then, again, soap-bubbles may vary very much in the thickness of different parts. As the waves of light differ in length, so they will require different thicknesses to produce accordance and dis- cordance. The result of this is that a thickness of film which is competent to extinguish one colour will not extinguish other colours. Thin films of variable and changing thicknesses, illuminated by white light, will therefore display in their different parts variable %nd changing colours. The colours of the precious opal are due to the interference of the internal reflections from its minute vacuous fissures. The colours of tar-films upon water, of many insects’ wings, and of lead-skim- mings, are due also to interference. So also are the splendid chromatic appearances of certain crystals when viewed in polarised light, and, to some extent also, the colours previously alluded to as iridescent. We will next turn our attention to the production of colour by “ selective absorption,” to the re-composition of white light by the re-union of its scattered elements, and then to the mutual relations of those coloured elements. THE ELECTRIC TELEGRAPH.— II. By J. M. Wigner, B.A. insulators ( continued ) — testing t!hem — mode of making JOINTS LIGHTNING CONDUCTORS COVERED WIRE MODE OF MAKING JOINTS IN IT. However perfect the insulators employed on any line may be, there is sure to be some slight escape of the current, and our care is to reduce this to a minimum. Dust and dirt settle on the insulators, especially when they are damp, and thus allow some portion of the electricity to escape to the post. Formerly a screen was placed over the insulator, to shield it from the rain ; but it is now found that when there is a good glaze to the earthenware, the rain washes off the dirt, so that after long- continued dry weather a smart shower will frequently mate- rially improve the insulation of a long line : the screen is consequently dispensed with. Glass and different glazes also condense the moisture of the air on their surfaces, and thus produce a damp layer, by which the current escapes. In this respect ebonite is found to be superior to any substance of a vitreous nature, but at present its durability and economy have not been sufficiently tested, and it is but little adopted for general purposes. When, through defective insulators, or in any other way, the current leaks to the ground, the line said to be “ earthy,” and usually the defect may be remedied by an increase of the battery power. If a full contact is made with the ground, so that the whole or the greater portion of the current is lost, there is said to be “ dead earth.” Very frequently a portion of tho current leaks from one wire to another, and in this way the messages along both lines are endered more or less indistinct. There is then said to be •contact.” Spiders’ webs round the wires will, when they become damp, act thus, and where the lines cross public streets, they are frequently fouled by the strings of kites. These strings becoming broken in the attempts made to save the kite, get twisted round the wires, and in damp weather greatly interfere with the communication. In earthenware insulators cracks are not unfrequently pro- duced by the unequal shrinking of the wire in drying or baking, and if these are covered with a glaze they may escape deueccion at first. After a while, however, the glaze cracks, and then the flaw becomes apparent by the escape of the current. A good glaze is useful, since it hinders the adherence of dirt and dust, but it must not be depended upon as an insulator. All insulators should, before being employed, be carefully tested, so that defective ones may be rejected. This is usually done by immersing the porcelain or earthenware portion for a few hours in dilute sulphuric acid, or in salt and water. One pole of a battery is then applied to the stalk of the insulator, and tho other is immersed in the liquid, a delicate galvanometer being introduced into the circuit, and in this way a flaw is easily detected. In a few cases a portion of the glaze is removed, so as to test the quality of the ware itself. On a very wet day it is often found difficult to communicate with distant stations on account of “weather contact,” or the leakage of the current along the insulators and posts. In such a case it is frequently found very advantageous to join a fresh set of batteries side by side with the others, so as to increase the quantity rather than the intensity. Two batteries thus joined side by side are, of course, equivalent to one having cells double the size. The following experiments tried by Mr. Walker, of the South- Eastern Railway, illustrate this well. The figures in the last column indicate the strength of the current received at the further end, as shown by a quantity galvanometer. The line was a defective portion, five or six miles long : — Cells. Size. Strength. Cells . Size. Strength. 24 . . Ordinary . . 10 48 . . Double . . 37 24 . . Double . , . 24 72 . . Ordinary . 21 24 . . Treble . . . 27 72 . . Double . . . 43 24 . . Sixfold . . . 32 96 . . Ordinary . 23 48 . . Ordinary . . 19 From this it will bo seen that a greater power was obtained from forty-eight cells connected in pairs (twenty-four double cells) than from ninety-six connected in the ordinary way. In many of the telegraph wires that cross the roofs of houses in large towns, a form of insulator different from any hitherto described is employed. It consists of a short cylinder of porce- lain (Fig. 5), with a hole pierced along its centre, and a broad groove round it, so that it somewhat resembles a short and stout reel. The wire is then passed round the groove, and fastened off as at an ordinary terminal insulator. Another wire is passed through the central hole, and by this it is affixed to the post. The wire at the other side of the post is fastened in a similar way, so that two insulators are required at every post. As, however, they are of a very simple form, consisting merely of a lump of porcelain, their cost is but small. A short link of wire is connected beyond the insulators on each side, and forms the passage along which the electric current passes. This plan is found much more simple and economical for carrying the wires over houses. If any wire breaks, only the length between the two posts is affected, and can easily be repaired ; it is also easier to stretch the wires when fastened in this way. Wire cannot easily be obtained in lengths of more than about a thousand yards, and usually it is made in shorter pieces ; frequent joints have, therefore, to be made, and the manner of making these is. a thing of very great importance. It is not sufficient merely to make a strong joint, which shall bear the strain : we must also ensure a complete electrical contact ; and as, after a while, the wire becomes more or less oxidised, great care is necessary, or else in a short time the current would be seriously impeded, or even altogether interrupted. The joint most frequently employed in England is that known as the Britannia joint, and is represented in Fig. 6. The ends of each of the pieces of wire to be joined are first carefully scraped and cleaned, so as to remove all oxide. About half an inch at the end of each is then turned up at right angles, and the two pieces being laid side by side for two or three inches, are care- fully and tightly bound round with galvanised binding wire. The bent ends should then be cut short, as otherwise, when 128 THE TECHNICAL EDUCATOR. blown about by the wind, they are apt to hook the next wire, and thus make a false contact. In order to make the joint more secure, the whole is very frequently made tight by soldering, and many engineers con- sider this of the utmost importance but in towns it is almost given up, and little or no practical inconvenience is found to accrue. It adds, however, to the strength to employ solder, since the wires sometimes become injured by the twisting, and then, after a time, yield and break. The other joint commonly employed is known as the twist joint, and in France it is almost universally adopted. To make this it is necessary to have the ends of the wires quite soft and pliable, as otherwise they will break oil short, and cause much inconvenience and delay. When carefully cleaned, they are laid side by side for about five or six inches ; the end of each is then carefully and tightly twisted round the other, a space of about an inch being left in the middle, to avoid turning the wire too sharply, and thus injuring it. In order to make this joint, it is necessary to have a clip of some kind to hold the wires firm whilo they are being twisted. The French usually employ two small screw- clamps fitted with handles, and with the aid of these the joint is easily made. In this country an ingenious arrange- ment, consisting of two steel bars, jointed in the middle, is used. One or other of these two joints is almost universally adopted. The wire employed is carefully tested for strength, and also for ductility. Short pieces of it are gripped between two vices six inches apart, which are then twisted in opposite directions, and the wire should stand from fifteen to thirty twists, according to its size, before it breaks ; it is also tested by the application of weights so as to find its break- ing strain. As few welds as possible should be allowed, and these should be carefully tested, as it is usually at these places that the wire breaks. It is a very good plan, when stretching the wires, to draw them as tight as practicable by means of a block, and then let them be pulled sideways with consider- able force. In this way they will be straightened, and the weak places very probably detected. They may then be pulled tighter and fastened to the insulators. When a number of wires are placed on the same posts, care is required to ensure a sufficient distance between them, as otherwise, when they become a little slack, and are swayed by the wind, they will touch. The lateral interval, when the posts are at the usual distance of about sixty yards, should be at least twelve or thirteen inches, and the vertical distance ten inches. If the posts are further apart, greater distances should be given. When the wire is affixed to a terminal insulator it should not be twisted, as in that case it is very likely to break. The end should be slightly turned up and then passed round the insulator, and .securely bound after the plan shown in section at Fig. 8. Telegraph posts should always be provided with a pointed wire projecting above the top, and connected with the ground, so as to servo as a lightning conductor. From their elevation they attract the lightning, and were it not for these conductors, it would pass along the lines and often do serious damage to the instruments or fittings. In most cases the wires are suspended in the air in the way we have been explaining. Occasionally, however, they are placed beneath the surface of the ground or the sea ; and then, of course, they must be insulated along their entire length. Sometimes, to avoid the inconvenience of fixing wires on the roofs of houses, or the danger of their crossing public thorough- fares, they are laid under the paving stones at the side of a street. The usual plan is to lay a metal pipe in a narrow trench, and to place the wires inside this pipe so as to protect them from accidental injury. Copper wire is usually employed, and as it is a much better conductor than iron, and has no strain to support, it may be used of a much less diameter. The simplest plan of insulating it, and that almost univer- sally adopted, is to apply a coating of gutta-percha to it. This is carefully laid on when quite soft and warm, and on cooling forms a firm protection, and being a good insulator pre- vents the escape of the fluid. Sometimes a second or third coating of gutta-percha is applied outside the first, so that if an accidental flaw exists in the one, the other may cover it. The wires are usually brought up at dis- tances of about a mile, into iron pillars arranged for the purpose, so that in the event of any interruption of the communication, the wires can be tested, and the exact position of the fault ascertained. In this way much unnecessary trouble in breaking up the streets to discover the place of the injury is avoided. In many parts of London, a small cable may be seen overhead, suspended from two wires placed a little above it. This cable contains a large number of separate insu- lated wires bound together in one bundle. Most of these are private wires employed by different business houses, for communicating with branch offices, or manufactories. The instruments commonly used in these cases will be described in a future paper. The wires being coated with gutta-percha are completely insulated from one another, and single ones are brought out of the bundle at any required place. In a few instances subterranean lines are laid for considerable distances, but in these cases some additional protection is usually given, as it is found that the gutta-percha alone, if exposed to the air, or to moist ground, perishes in a few years and becomes almost useless. On this apcount all external con- nections from offices which are made with this wire (and most are made with it) ought to be covered with tape, and to receive a good coating of Stockholm tar once or twice every year. When this is done they will last almost indefinitely. In very exposed positions, it is better to protect them still further by enclosing them in a pipe, or putting a wood-casing round them. As this wire is so much used, especially in important positions, it will be well here to explain the way in which joints may be made in it, according to the instructions given by the Gutta Percha Company, who are the chief manufacturers of the ware. A few narrow strips of the very thin sheet gutta-porcha should be in readiness, and also a little warm gutta-percha about one-eighth of an inch thick. One or two tools for heat- ing, and a spirit-lamp are also required. Having softened the wire by warmth, the covering may very easily be stripped off with a knife for just as far as is requisite to make the joint. The ends should be well cleaned, joined, and soldered in the usual way with the twist joint. Sometimes, as an additional precaution, 1 the joint is bound with thin wire before soldering. The gutta-percha on the wire beyond the joint should be softened and tapered down to tho wire. Now take a narrow strip of the thin sheet, and fixing it to the warm tapered part, twist it spirally along all the joint, and fasten at the other side. Having done this, gently warm the surface ; then lay on in the same way as before a second strip, wrapping it round in the reverse direction, and warm again. Sometimes a third strip is added as an additional safeguard, and in important places it is well to do so. Outside this lay on a layer of the thicker gutta-percha, taking care Jjo make a good contact with that covering the wire beyond the joint, and smooth and finish off the whole with a warm tool. With care and cleanliness, a joint thus made is as secure as the rest of the wire. Moisture or dirt, however, if allowed to enter during the process, will impair the joint very much. Fig. 7. Fig. 8. APPLIED MECHANICS. 129 APPLIED MECHANICS.— III. BY S03BET STAWELL BALL, LL.D., Astronomer- Royal for Ireland. EXPERIMENTS ON THE THREE - SHEAVE PULLEY - BLOCK DIFFERENTIAL PULLEY EPIC Y CLOIDAL PULLEY CON- CLUDING REMARKS. The three-sheave pulley-block has been described in “ Me- chanics.” — XI. (Popular Educator, Vol. II., page 61, Fig. 74). Our duty is to describe the mode of experimenting with it, to record the results, and to explain their significance. One experiment will be fully explained, as by this means th8 process will be better understood. The sheaves were about 2” - 5 in diameter, and the rope used was what is called technically “imperial patent sash line.” A weight of 228 lb., not including the weight of the block itself, was attached to the hook of the lower block. According to the theory of virtual velocities, a power one-seventh .of this should be sufficient to raise this load, but a power of 38 lb. was found not sufficient, though if the load were raised a little, 38 lb., or indeed less, would prevent it from overhauling. It was found that a power of 56 lb. was necessary in •order to raise the weight, so that the power is seen to be about one-fourth of the load, instead of one-sixth. A series of experiments with 'different loads was tried, and the result is given in the table below. The first column shows the number of each experiment, (there were eight in all) ; the second column gives the load, which was in each case suspended from the lower pulley-block ; and the third column gives the corre- sponding value of the power. ’From columns 2 and 3 the formula — P - 2-33 -+■ 0-238 R has been calculated to be that which represents the relation between the power P and the load R with the greatest fidelity. The calcu- lated values are shown in the fourth column, and they are compared with the observed values in the fifth column, which shows the difference between the two. Thus, for example, in Experiment 7 a load of 395 lb. was found to be raised by a power of 97’0 lb. ; but had we used the formula we should have found — 2-36 + 0-238 x 97 = 96-4. three-sheave pulley-block, sheaves 2"-5 ON WROUGHT- IRON AXLES. FORMULA P — 2’36 + 0'238 R. Number of Experiment. R Load in ib. Observed Power in lb. R Calculated Power in lb. Difference of Observed and Calcu- lated Values. 1 57 15-5 15-9 + 0-4 2 114 29-5 29-5 + o-o 3 171 43-5 431 - 0-4 4 223 56-0 56-6 + 0-6 5 281 70-0 69-2 - 0-8 6 338 83-0 82-8 - 0-2 7 395 97-0 96-4 - 0-6 8 452 109-0 109-9 + 0-9 On examining the table it will be seen that the difference, 0'6, between the calculated power and the observed power is shown in the fifth eolumn. It will be noticed that the dif- ferences between the calculated and the observed values are always very small. This shows that the formula represents the experiments with accuracy. THE DIFFERENTIAL PULLEY-BLOCK. A pulley-block which has been introduced within the last few years, and which has been found of the utmost practical utility, has been called the Differential Pulley-block. It is a. convenient adaptation of a mechanical principle * which i 3 of considerable antiquity, but has never been embodied in a practicable machine until this happy invention. The principle of the machine will be understood from Fig. 2, which shows in a diagrammatic form the action of the pulley, while its general appear- ance is given in Fig. 1. It consists of a fixed and a movable block, and an endless chain. The upper block, A (Fig. 2), is composed of two sheaves, which are, however, in one piece, and turn to- gether. One of these sheaves is a little greater in diameter than the other. The lower sheave, b, only differs from the ordinary movable pulley in having small ridges in its groove, in order to receive the links of the chain pro- perly. An endless chain con- nects the two blocks ; the course of this chain is indi- cated in the diagram by the arrows. From p, where the power is applied by the hand, the chain passes over the larger sheave, then down under the movable pulley, then up again around the smaller sheave, and back again to p. The action of the machine will now be easily seen. The upper sheave winds up the chain on the side marked C, and at the same time lowers it on the side marked d, as indicated by the arrow ; but since the groove by which the chain is raised is larger than that by which it is lowered, it follows that the chain must be wound in a little faster than it is lowered out ; hence the pulley, b, must be raised gradually. The origin of the name is then evident : the raising of the load is due to the difference of these actions. By having the chain endless, a much smaller length of chain will suffice than would otherwise be necessary. The velocity ratio of the differential pulley is most easily ascertained by measurement. Thus, in a pulley of this class which is adapted for raising weights up to a quarter of a ton, the velociiy ratio is 16. This was found by observing that sixteen feet of chain must be pulled out of the upper block in order to raise the hook one foot. But the mechanical efficiency of this machine is by no means sixteenfold. Attaching 5 cwt. to the hook, it is found that 86 pounds must be attached to the chain in order to raise it. The power is most conve- niently attached to the chain by means of little hooks, which pass through the links, and can receive the rings attached to the weights. Hence from this experiment we see that the mechanical efficiency is 6"6, or roughly, six or seven-fold. Thus, in the use of this machine, though the power of a man is enabled to lift a weight six times greater than would be pos- * “ Mechanics.”— IX., Fig. 65 (Popular Educator, Yol. I., p. 316). 9— Vol. I. 130 THE TECHNICAL EDUCATOR. sible without this assistance, yet more than half of the energy or work which ho puts into it is consumed by friction. This apparent loss of energy is not only useless, but, unfortunately, as energy is never really lost, what is not usefully employed expends itself gradually in abrading the parts of the pulley, producing what is known as wear and tear. To resist this as far as possible, the working parts of the differential pulley are specially hardened. It often excites surprise in one who see3 for the first time a differential pulley in action, that when the weight has been raised it will remain suspended without the chain being held or fastened. This property of not overhauling is one of the most useful features of the pulley. It is not only very con- venient, but is a source of safety, as accidents often occur when heavy weights are raised by machines which do not possess this property. In fact, in the use of the differential pulley, when the weight is to be lowered the chain Q must be pulled, just as p must be pulled when it is being raised ; by holding one of these chains in each hand, then position of the weight can be adjusted with the greatest nicety. This adds very much to the g'eneral utility of the differential pulley and renders it a mechanical aid of great value. That the differential pulley does not overhaul, arises solely from the fact that more than half the power which is applied is lost by friction, and therefore when friction acts to prevent motion it is more than sufficient for the purpose. This pro- perty applies to all the mechanical powers where the mechani- cal efficiency is less than half the velocity ratio ; as, for example, in the screw, but not in the three-sheave pulley-block. The handle which is attached to the upper block of Fig. 1 shows a modification of the differential pulley, which is some- times useful ; by turning this lever the block is turned round, and therefore the load is raised ; by having a long lever the power can be greatly increased. By this means a man is enabled to lift a ton or even more without using any very great exertion, but the rate at which the weight is raised is, of course, very slow. EXPERIMENTS UPON THE EPICYCLOIDAL PULLEY. In Fig. 3 wo have represented another kind of pulley, which is often called the epicycloidal pulley-block. In this there are two chains — -one stout chain with a hook at each end, on which, the load is carried ; the other a smaller chain, which passes over a sheave in the upper block, and by means of which the power is applied. Holding one part, p, in one hand, and the other part, Q, in the other hand, the weight can be raised and loivered with the greatest facility. The mechanical power of this pulley is about fivefold, and as its velocity ratio is 12, it follows from the principle already laid down that tho weight cannot overhaul. There being two distinct hooks on the load-chain, one of these hooks is always low down and convenient for raising, when the other has carried up its load. This is a practical convenience which, as the student may have noticed, is not met with in the differential pulley. CONCLUDING REMARKS. The values of the velocity ratios and mechanical efficiencies which have been given in this lesson for differential pulleys apply only, of course, to the actual specimens which have been examined. Various sizes of differential pulley-blocks are made, but the one hero referred to is that size adapted for lifting a quarter of a ton ; the more general principles apply to all sizes, but it was thought better to describe fully one form. Tho same remark may be made about the epicycloidal pulley-blocks. Various other blocks differing more cr less from those men- tioned are met with. The way to study them is to perform the two processes here described. First, measure the distance through which the power must be moved when the load is raised one foot ; then attaching a given load to the load-hook, see what power will raise it. The first operation gives the velocity ratio ; the second, the mechanical efficiency. A com- parison of these numbers, which would be equal in a perfectly frictionless machine, shows how much of the power is lost by friction. And we cannot repeat too often, that when the mechanical efficiency is reduced by friction to less than half the velocity ratio, tho machine does not overhaul. CHEMISTRY APPLIED TO THE ARTS.— III. BY GEORGE GLADSTONE, E.C.S. DYEING (continued). In the practical operation of dyeing the first thing that has to be considered is the material to be dyed. The same processes cannot be applied to cotton, flax, wool, silk, etc., indiscrimi- nately ; in fact, it may be taken almost as a general rule that one which will suit a vegetable fibre will not suit those derived from the animal kingdom. It is not, however, sufficient merely to divide the articles to bo dyed into these two classes, for cotton and flax will not dye equally well by the same process, nor will a given amount of dye-stuff produce the same effect upon wool after it is spun or woven as before — one quality, too, of either wool ©r cotton will take up colours much more readily than another. Nowadays there is a great disposition to use mixed goods as articles both of dress and furniture, in which cotton and silk, or cotton and wool, or a mixture of the latter with goats’ -hair, are woven together. All such, if they are to be subsequently dyed, demand much consideration as to the- means to be adopted. The animal substances are, in nearly all cases, the most sus- ceptible to the dyer’s art, more brilliant colours being produced upon silk than on any other material. Woollen goods also dye very well; the scarlet of our soldiers’ coats, which is produced by cochineal mordanted with oxide of tin, being a colour the equal of which cannot be attained on any vegetable tissue. It is, therefore, a matter of no little difficulty to dye a mixed fabric of an even colour. By the aid of chemical solvents, if other means fail, the dyer can at once detect any mixture in the materials of which the cloth to be dyed is made. For instance, bichloride of tin, when heated moderately, will turn vegetable fibres black, while, animal substances will remain unaltered. If a mixed fabric of cotton and wool be boiled in caustic soda, the Wool will be dissolved and the cotton will remain untouched. Again, cotton is whitened by chlorine, but silk and wool are turned yellow. Having determined this point, the next step is to prepare the article for dyeing. Of whatever material the goods may be made, it is necessary to free them from grease, iron-mould, or any other accidental impurity ; and if they are to receive any light or delicate tints, they must be properly bleached. If the goods are fresh from the manufactory, they are sure to contain either grease or some dressing ; and if they are old, there will probably be some accidental stains, which will re- appear more or less after dyeing, if they are not first eradicated. The material being thus prepared, the subsequent processes will depend much upon the article of which it may be made. Confining our attention at present to simple fabrics, we must take them separately. Silk . — To produce a good colour, silks should first be im- mersed for some hours in a strong solution of alum, which must be dissolved in cold water, for if applied hot it is injurious to the lustre of the silk. After tho aluming, they should be tho- roughly washed in pure water. A good permanent red may then be produced by a mixture of cochineal with bitartrate of potash and spirits of tin. For a yellow, weld is very commonly employed, the silk being put into a hot solution in which some soda is dissolved, the quantity of the latter depending upon the shade desired, an increase of the soda rendering the colour more intense. For blues, recourse is generally had to indigo, with tho addition of a little potash and madder, the vat being kept moderately warm during the process. There is, however, considerable difficulty in producing an even colour with this dye, and the silk should be dried rapidly when taken out of the vat. To obtain an intense black, it is necessary to deprive the silk, as much as possible, of the gummy substance naturally belonging to it, which is done by boiling it in a strong solution of soap — a desirable thing, by the way, in every case, as all the colours take better the more thoroughly the gum is removed. This being done, it is steeped for a day or a day and a half in a very strong decoction of galls, or one of the other substances mentioned in the previous article as having the same chemical property, after which it is immersed in a solution of sulphate of iron. Greens are usually produced by dyeing the silk yellow in the first instance, and then blue. Violets and purples may be obtained by dyeing first with cochineal (no tin being added to it in this case) and subsequently with indigo, the relative CHEMISTRY APPLIED TO THE ARTS. 131 strengths of the two dyes being adjusted according to the tint desired. For all these combinations, however, the aniline dyes are now superseding the others. Magenta and mauve have a great affinity for silk, and the operation is consequently very simple : a solution of the dye is made in cold water, and the silk worked in it until it has acquired the requisite depth of colour. In all cases the silk, after being taken out of the dye, must ■ be washed in cold water before being hung up to dry. Wool . — Care must be taken to rid the stuff of the grease it always contains by scouring it well in soap and water or a strong solution of soda for several hours. It is then ready to receive the dye, which is always to be applied hot, the wool being afterwards washed in cold water. It can be dyed blue by indigo in the manner described in the previous article for dyeing cotton, except that the vat must be kept at an elevated temperature. For woollens, however, the vat is more generally prepared in another way, and goes by the name of the “ pastel vat.” The difference consists in substituting for the sulphate of iron and the large quantity of lime, other ingredients for deoxidising the indigo, one of them acting the part of a dye at the same time. Pastel or woad was, indeed, used almost ex- clusively 200 years ago for dyeing blue, but has since been nearly superseded by indigo, on account of the latter giving a richer colour. To prepare a vat, about 400 lb. of woad, 20 lb. of madder, 10 lb. of bran, and 8 lb. of lime have to be boiled up together. In the course of twenty -four hours it will be in a state of fermentation, and the bath will have acquired a yel- lowish tint. It is then ready to receive the indigo — -say about 20 lb., with a further addition of about half that weight of lime — and in about six hours more the indigo will be converted into the white soluble state previously described. The wool is then dipped in the vat for about an hour, after which it is hung up in the air to dry, during which process it turns blue ; the dipping being repeated several times if very deep shades are required. This vat, when once prepared, will last for months, but the supply of indigo must be renewed from time to time as its strength becomes exhausted. The substances employed for dyeing red in all cases require a mordant to fix them. If madder be used, the cloth should bo first steeped in a solution of alum and bitartrate of potash. To produce a brilliant scarlet, a little cochineal should be boiled up with bitartrate of potash and spirits of tin ; and after the wool has been dipped in this mixture, washed, and dried, it should be immersed in a second bath containing a strong solu- tion of cochineal. Lac is used for the same purpose, and with the same mordants. To obtain a good black, the wool is first dyed blue, then boiled in a solution of galls or any of the other articles previously named which possess the same properties, and finally in a bath of sulphate of iron. For a green it is generally found best to dye the stuff blue first, and afterwards yellow. For violets and purples the blue should form the foundation, though some shades of these compound colours may be made in the bath by a mixture of the various ingre- dients, by which a saving is effected in the number of operations. Mauve and the other aniline dyes also act very readily upon wool by merely working it in a lukewarm aqueous solution. Vegetable fibres are not so readily dyed as those already con- sidered, nor can colours of equal brilliancy be produced upon them. After the fabrics made of them have been properly cleansed they are subjected to the operations of aluming and galling. The materials used for these purposes are sufficiently indicated by the respective terms. Flax . — After being thus prepared, it may be dyed red with madder by a process similar to that used in dyeing cotton Turkey red, which will be considered presently. This is almost the only shade of red which can be produced as a fast colour on vegetable tissues. Quercitron furnishes a beautiful and perma- nent yellow. For blues, indigo is almost invariably employed. A thorough black is not readily obtained, but the most approved plan is first to dye the linen with a deep blue, then steep it in a strong decoction of galls, and finally in a bath containing one of the salts of iron along with acetic acid. Cotton is generally dyed in the same way as flax. The mode of using indigo has already been described in detail in the pre- vious article. The Turkey red process is certainly the most complicated of all, but it demands special notice, as it is very extensively earned on, particularly in Glasgow and Manchester, and produces one of the most durable colours known. The little minutias must inevitably be omitted for the sake of brevity, and only the most characteristic operations described, though very great exactitude in all the details is necessary in order to produce a thoroughly satisfactory result. The cloth, having been carefully freed from the weavers’ dressing, is steeped three successive times (being dried on the grass between each) in a bath containing the following ingredients to 15 gallons of cold water -. — 1 gallon of olive oil, 11/ of sheeps’ or cows’ dung, 4 gallons of a solution of carbonate of soda, and 1 gallon of a solution of pearlash. The steeping in this liquor should last for a fortnight at least. The cloth is then passed through a warm and weak solution of pearlash, steeped again three times as before in a bath containing 1 gallon of olive oil and 3 of soda lye to 18 of water ; and then passed again through a wash of soda and pearlash. These may be considered the pre- paratory processes, the chief peculiarity of which consists in the use of oil and dung, which together act as a mordant upon the outer surface of the cotton fibre, and prepare it to take up the dye that is subsequently to be applied. The alkali through which the fabric is passed saponifies and carries off any excess of oil remaining over from the preceding operations, the rest being apparently decomposed by the action of the other in- gredients with which it is mixed. The cloth is next galled with a decoction either of gall-nuts or sumach, and then alumed, without which the dye would not be permanent. The colouring matter used is madder, to which some bullocks’ blood is added, the quantities varying according to the intensity of the colours required. The fabric is put into the dye when cold, which is then raised to the boiling-point, and kept at that temperature for a couple of hours. It is finally boiled in an alkaline solu- tion in which a little protochloride of tin is dissolved, and then spread out to dry. The great peculiarity of this process is, that while the usual object to be attained in dyeing is to fill the internal cavity of the transparent fibre with a colouring matter which shall be insoluble, the Turkey red dye is princi- pally deposited on the outer surface, and has entered into actual combination with the fibre itself — a circumstance to which both the permanence and the brilliance of this dye is attributed. Mauve, or any of the aniline colours, will dye cotton ; unlike silk or wool, however, the fabric must be mordanted in order to produce a fast dye. It is best to soak it first in a decoction of sumach, galls, or other article rich in tannin, and then pass it through a weak solution of stannate of sodium. Being thus prepared, the cotton will absorb the dye most readily. Hitherto' attention has been directed to the dyeing of fabrics made exclusively of one material. The mixed goods have also to be dyed, and that either of one or more colours ; for instance, a damask may be dyed of one uniform colour, or the cotton may be of one and the wool of another. In either operation the affinity of the materials for different colouring matters has to be taken into consideration, as well as the manner of apply- ing them ; picric and rosolic acids, for instance, cannot be used for dyeing cottons, nor are the compound cyanides of potassium and iron applicable to woollens. With mixtures of cotton and wool it is nearly always necessary to dye the latter first, as it is more tenacious of the colours imparted to it ; but if the cotton is to be blue the order of proceeding is reversed, the indigo dye being so fast as to be unaffected by the subsequent operations upon the wool. It is not so easy to produce different colours upon a mixture of silk and wool, because they are both animal, substances, and are each more or less acted upon by the same ingredients ; the silk, being more retentive, is, however, gene- rally dyed first. With a mixed fabric composed of silk and. cotton the same order is followed. There are two ways of dyeing mixed fabrics of one uniform colour — either separately or at one process. Let' us suppose that a mixture of cotton and wool has to be dyed black. The latter can be dyed first with camwood and sulphate of iron in the manner already described, and then the cotton in a solution of sumach followed by sulphate of iron. They may, however, be dyed simultaneously (and even if the fabric should also con- tain silk the process will apply) by steeping the article in a decoction of sumach, and then in a solution containing equal parts of bitartrate of potash, sulphate of iron, and sulphate of copper ; after this with logwood, and again with the sulphate of iron. Other colours besides black may be produced upon mixed goods by a single, process ; the adjustment of the in- 132 THE TECHNICAL EDUCATOR. gradients needs, however, considerable nicety, in order to adapt them to the varied powers of the materials in taking up the different dyes. Throughout the paper it has always been taken for granted that the materials are the best of their respective sorts. Many of them unavoidably vary considerably in quality, while others, again, are in such a condition as to be easily adulterated. It is very important, therefore, that the operator should be tho- roughly assured both as to the purity and quality of the in- gredients, or he may be grievously disappointed in the result. PRO JECTION.— VII. CYLINDERS AND CONES. PLAN AND PROJECTION OF A SPEED-PULLET (Fig. 89). This is a further application of the lessons on the projection of cylinders, wheels being, as it were, sections cut from cylinders. The subject is composed of three pairs of parallel circles. Having drawn the plan, describe on A b a semicircle, and divide it into any number of equal parts in c, d, e, /, g. From each of these points draw lines meeting a b at right angles in c' d' e' f g'. These lines will cut c d in c", d", e ", /', g". Draw a line, x x, at a height above I l equal to the radius of the circle — viz., e' e. From A B, and all the points between them, draw perpendiculars passing through x x, and on these per- pendiculars set off on each side of x x distances corresponding to the distance between the point similarly lettered in the semi- circle and the line A b, as e e', d d', etc., and this will give the points a', b', c', d', e', f', g', through which the ellipse is to be drawn. From each of the points last mentioned, draw hori- zontal lines, and intersect them by perpendiculars from the points c, d", e", etc., in the plan, and the intersections of the lines correspondingly lettered will give the points e", d", a", etc. The other two wheels are to be projected in precisely the same manner from semicircles equal to half their surface. The lettering of these is omitted in order to avoid confusion in the diagram ; but the student, who is expected to work on a much larger scale, is advised carefully to letter every point. CONES AND THEIR PROJECTION. A cone is a solid, the base of which is a circle, and the body of which tapers to a point called the apex. The straight line drawn from the centre of the base to the apex of the cone is called the axis. When the axis of the cone is perpendicular to the base, the cone is called a ‘‘ right ” cone ; but when otherwise, it is called an “ oblique ” cone. The curved surface of a cone is equal to the sector* of a circle, the radius of which is equal to a straight line drawn from any point in the circumference of the base to the apex, and the arc-line of the sector is equal to the circumference of the base of the cone. Fig. 90 is the plan and elevation of a cone when standing on its base, its axis being perpendicular to the horizontal and parallel to the vertical plane. The apex is thus over the centre of the plan, and the solid is therefore called a right cone. Fig. 91. — To draw the plan of this cone when lying on the horizontal plane with its axis parallel to the vertical plane, draw the elevation lying on I l. To do this, at any point in I L con- struct an angle similar to ab a in the elevation ; make the sides of the angle equal to those of the elevation, and join a' c'. Bisect the angle, and produce the bisecting line to d. This will be the axis. Now begin the plan by drawing c b parallel to i l. From d in the elevation, with radius d a, describe a semicircle, and divide it into any number of equal parts in e,f, g, h. From each of these points draw lines meeting A c at right angles, and from these points of meeting drop perpendiculars passing through c b on the points e, /, d, g, h. Set off from these points on their respective perpendiculars, and on each side of c b, the lengths of the lines between A c and the semicircle, and by this means the points through which the ellipse is to be drawn will be obtained. Join the point b to each end of the ellipse, which will thus complete the plan. The students should now, as an exercise, turn the plan so that its axis is at a given angle to I l, and then make a projection from it and the present elevation. * A sector is a part of a circle contained between two radii and a portion of the circumference. Fig. 92 shows the elevation and plan of the cone when resting on the extremity of one diameter of the base, the plane of which is at 30° to the horizontal plane. It will be evident that whether the cone lies on the paper, or stands on one extremity of a diameter of its base, so long as the axis remains parallel to the vertical plane, the elevation will be the same in form — changed only in position — and therefore the line which is the elevation of the base has been placed at the required angle. Construct on it an isosceles triangle of the given altitude, which will form the elevation of the cone. It must here be remarked that this figure and the next have been left unlettered, so that the student may become gradually accus- tomed to follow the points through their various change of position ; and, with Fig. 91 to guide him, it is thought that he will be able to complete this projection of the plan from the instructions here given. It will be remembered that although the base of the cone is rendered by a straight line in the elevation, that line is the edge elevation of a circle ; therefore, from the middle point in the line describe a semicircle, which will represent one-half of the base, turned up so as to be parallel instead of at right angles to the vertical plane. Now divide this semicircle into any number of equal parts, and from each of these draw lines at right angles to the diameter. Next draw a line in the horizontal (or lower plane) parallel to I L, and a portion of this line will become the axis of the cone. From each of the points in the base of the cone draw perpendiculars passing through this horizontal, and make them the same length on each side as the lines drawn from the points in the semicircle to the diameter. Through these points trace by hand the ellipse, which repre- sents the plan of the base, being the view from a point imme- PROJECTION, 133 diately over it. Drop a perpendicular from the apex of the elevation to cut the horizontal, and this intersection will be the plan of the apex. Join this by straight lines to the widest parts of the ellipse, and this will complete the projection. Fig. 93 is the projection of the cone when the base is at 30° to the horizontal, and its axis at 45° to the vertical plane. It has been shown in several previous figures that an object may be rotated without the height of any part of it being altered ; and thus, as in the pro- jection now required, the base of the cone is to be at an angle to the horizontal plane similar to that of the last figure, the plan will be the same in shape, but altered in position ; there- fore, repeat plan of Fig. 92, placing it so that the axis is at 45° to il; then draw perpendiculars from all the points in the ellipse, and cut them by hori- zontals from the points in the elevation. Draw the projection of the base through the intersections. Draw a perpendicular from the point which is the plan of the apex, and a horizontal from the apex in the elevation. The intersection of these will give the apex of the projection. Join this point to the ellipse represent- ing the base, which will complete the figure. SECTIONS OF CONES- If a cone be cut across, so that the plane of section may pass through the axis at an angle, and cut the slanting surface of the cone on the opposite sides, the section is called an ellipse* TO DRAW AN ELLIPSE WHICH SHALL BE THE TRUE SECTION OF A CONE ON A GIVEN LINE. Let Fig. 94 be the plan and elevation of the cone, and A b the line of section. Divide the circumference of the plan into any number of equal parts in c, D, e, f, g, h, i, and d', e', f', g', h', The line e" j" in the elevation is therefore the radius e j in the plan, and thus the plan of any point marked on e" j’ r must fall somewhere on the radius E J. Now the section-line A b cuts through all the lines drawn to the apex of the cone in the points d, e, f, g, h, and it will be remembered that, although in the elevation the section is represented by a single line, A b, it will assume a different form in the plan. From points a and b draw perpen- diculars cutting the diameter ci in ft and b, and from d, e, g, h in the elevation draw perpendiculars cutting the radii of the plan which bear the same letters. Draw the curve, which will unite e'd'ade , and also the curve uniting g’h'bhg. It will at once be seen that these two curves form the ends of an ellipse which is to be the plan of the section, but that a point is wanted on f and f' in order to complete the figure. But we cannot draw a perpendicular from the point / in the elevation, to cut the radius f in the plan, as we have done in the other lines, because the radii F f' are but portions of the same perpendicular on which the point f is situated, and there- fore no intersection can be obtained. Now let us remember that the line f" j", though appearing perpendicular to i L when looked at in its present posi- tion, would, if looked at from K, in the direction of the arrow, be seen to be as much a portion of the slanting surface of the cone as i" j", and therefore the line f" j" would be seen to make the same angle with the horizontal plane as i" j". If therefore wo rotate the cone on its axis, the point / will move to f f, and a per- pendicular drawn from // will give us // in the plan. If now we turn the cone to its original position (which will be repre- sented by drawing a quadrant from the centre of the plan with radius j //), the quadrant will cut the radius F inf and f' inf". Join e and g and e‘ and g' by curves passing through / and f, which will complete the plan of the section. This is not the i', and draw radii. Project these points on to the base of the cone, and from c", d", etc., draw lines to the apex j". The diagram up to this point represents a cone, up the slanting surface of which straight lines have been drawn, which on looking down on the apex would appear as radii of the circle forming the plan. * An ellipse differs from an oval by being the same shape at both ends ; but in an oval, the one end is more pointed than the other. true section, but the view when looking straight down upon it, and as it is slanting, its length from a to b will seem shorter than it really is. It will be evident that the true length of the section is the line a b. From these points, and also from d, e,f, g, h, draw lines at right angles to the section-line, and a' b' parallel to it. On each side of the points d, e,f, g, h, in the line a' b', set off the distances which the points similarly lettered are from c i in the plan, and these will give the points through which the true section may be drawn. 134 THE TECHNICAL EDUCATOR. TECHNICAL EDUCATION ON THE CONTINENT. — V. BY ELLIS A. DAVIDSON. THE POLYTECHNIC SCHOOL IN HANOYEB-COUESE OP STUDY (continued). 12. Architecture. (First course, lectures, three hours per week, and six hours drawing.) The course is divided into three sections. (a.) The setting out of plans; stone, wood, and iron con- structions. (b.) Ancient architecture, and architectural form, one hour lecture, and four hours drawing, weekly ; aesthetics ; illustra- tion of the forms of Greek architecture ; its constructive and aesthetic principles ; the general principles of Greek orna- mentation. (c.) The construction of simple buildings (three hours weekly). 13. Architecture. (Second course, two hours lectures, and four hours drawing, weekly.) (a.) Building construction : — The construction of staircases ; arrangements for heating ; the work of the carpenter ; plasterers and decorators. (b.) Architectural form : — Perspective (two hours lecture and four hours practice weekly) : — Study of form as developed in the Roman, Early Christian, and Romanesque architecture; their aesthetic and constructive principles, and their history ; the principles of Gothic architecture. (c.) Rural architecture (one "hour lecture and two hours drawing per week) : — The construction and arrangement of various classes of rustic dwellings and agricultural buildings r the arrangements of farms, etc. (cZ.) Ornament (one lecture weekly, and drawing three hours): * Special characteristics of Antique ornament ; Early Christian and Romanesque styles ; drawing from models and designs. 14. Architecture. (Third course, four hours weekly.) (a.) Designing of circular buildings. (b.) (Two hours weekly.) The planning and arrangement of public buildings and private dwellings of the highest class; dwellings for middle and working classes ; toll-houses ; station- masters’ and porters’ houses, etc. ; factories ; railway-sheds ; post-offices ; inns ; exchanges ; warehouses ; shops ; markets ; granaries ; slaughterhouses ; baths and laundries ; hospitals ; prisons ; asylums ; dispensaries ; school-houses ; blind, deaf and dumb institutes ; workhouses ; gymnasia ; barracks ; exercise and riding-houses. (c.) Details of building construction, (one hour lecture, and three hours drawing, per week) Designing of mouldings, columns and arches ; window and door-framing, etc., with particular regard to the material employed ; building stone ; brick ; wood ; iron ; glass, etc. (cl.) General considerations in relation to architecture, build- ing works, and materials (two hours weekly) : — General and special cost; valuation of old buildings; building works; the plans ; letting of buildings ; building contracts ; building ac- counts ; technical and financial specifications; measuring up; general survey ; reporting ; drawing up inventories ; building materials — stone, mortar, wood, metal, etc. etc. (e.) Ornament (one lecture weekly, two hours drawing) : — The Romanesque and Gothic styles ; drawings from casts and designs. (/.) Architectural history (six hours weekly) — German anti- quities and memorials in America ; early Asiatic and Egyptian art ; the architecture of the Greeks, Etruscans, and Romans ; Early Christian art ; the Mohammedan style ; Medieval art generally ; the Renaissance ; review of the works and progress in architecture in modern times. 15. Architecture. (Fourth course.) (a.) Building construction as applied to extensive works ; heating and ventilation (two hours weekly) : — The various con- siderations involved in the construction of large buildings ; heating ; ventilation ; circulation of water ; baths, lighting, arrangements for telegraphy, etc. (b.) The most important kinds of public and private buildings; civic architecture (two hours weekly) : — Dwellings of the most expensive class — palaces ; country houses ; theatres ; circuses ; panoramas ; concert halls ; places of amusement ; guildhalls ; Houses of Parliament ; courts of justice : watch-houses and gates; academies; libraries; museums; exhibitions; churches; dead-houses : monuments ; garden arrangements ; town building and fortification, etc. etc. (c.) The design and decoration of buildings (two hours weekly) : — Design and decoration of houses ; the most im- portant classes of public and private buildings ; civic archi- tecture ; and necessary arrangements. ( d .) Designs for public buildings (five hours weekly) : — The buildings specially treated of in this section are such as require the highest application of science and art, such as churches, public schools, assembly rooms, town halls, etc. The designs are all worked to an especially large scale, and consist of plans, elevations, sections, and interior and exterior perspective. (e.) Designing for coloured decoration (one lecture and three hours designing per week) : — Ancient and Middle Age wall- painting, glass- painting, and mosaic work ; designing complete systems of interior and exterior decorations ; with details to an enlarged scale. (/.) Ornamentation and “ small ” architecture (one hour lecture and four hours drawing weekly) : — Details of orna- ■ mental design in architecture applied in the construction and ornamentation of furniture and objects of domestic use, the purpose being to bring about a perfect system of harmony in a household, so that if the architecture of a room be classic, the carpet may not be Louis Quartorze and the furniture Gothic. This is not a question of expense, but of knowledge, and hence the instruction is of exceeding importance. (g.) Mediaeval architecture (two lectures and two hours drawing per week) : — Church architecture ; plans of churches ; crypts ; columns ; bases, shafts, and capitals ; buttresses ; windows and tracery ; towers ; spires ; porches ; elevations ; profiles and ornaments ; brick architecture ; timber construc- tions ; carpenters’ work ; metal works ; floor tiles ; wall and window decoration. 16. The Elements of Waterworks ancl Bridge-building. (Two lectures and two hours drawing per week.) Waterworks : — The regulation and utilisation of small and great streams ; the arrangement and carrying out of works for this purpose ; arrangements for utilising and controlling back waters and mill-streams ; arrangements for the drainage and irrigation of land. Bridge-building : — Foundations under water ; embankments ; the general principles of the construction of bridges ; the usual methods of building stone, wood, iron, sus- pension, and moving bridges.. 17. The Construction of Roads and Railways, Streets and Bridges. (Three lectures weekly ; two hours drawing.) Introduction ; the history of the means of transport em- ployed in early times ; general considerations in relation to the planning of streets and railways ; the composition of tho crust of the earth ; the elements of planning ; considerations as to geological formations of the site ; working out of the plans ; earthworks ; measurement and translation of scales ; the arrangement of payment and commission, etc. ; plans for irrigation, cuttings, vaults and yiaducts, canals, railways on similar, higher, and lower levels ; the construction of roadways, railways, and railway bridges, etc. etc. 18. Streets, Railways, and Bridges. (Three lectures weekly and four hours study.) Iron Bridges: — The principles of bridge construction: methods of working, and properties of wrought iron and steel ; rivetting ; bearers ; girders ; rails ; sleepers ; tramways for streets ; tho equilibrium of bridges ; bridges of timber and iron combined ; girder and tubular bridges ; estimates of cost ; practice in bridge construction ; excursions to inspect works in progress.. The further history of means of transport ; investigation of best systems ; direction of the line ; its breadth, curve, and level ; arrangements of railway works ; tunnelling, etc. etc. 19. Iron Bridges ( continued ) : — Further development of his- tory; springs and reservoirs of water, and means of filtering and conducting it over land ; arrangements for damming water ; weirs, watercoursos, and waterworks generally ; methods of irri- gating and draining tracts of land ; canals and sluices ; rivers and streams; foundations in streams and rivers; sea-walls, harbours, and docks ; methods of designing and preparing the necessary drawings and estimates for the construction of stone, wood, iron, suspension, and moving bridges. TECHNICAL DRAWING. 135 20. Mineralogy as applied to Building Purposes. (Two hours weekly.) The elements of mineralogy, with particular reference to the portions of the earth’s crust used for building purposes; the elements of petrology ; application of the various mineral substances. 21. Geognosy. Eecapitulation of the principles of mineralogy and petrology ; the elements of palaeontology in connection with geology. In connection with lectures, rock specimens and petrifactions are examined and described. (Natural history of animals, plants, and minerals is supposed to have been previously studied.) 22. Elements of Physics. (Two hours weekly.) Condensed instruction on the leading facts and principles of Physics. 23. Pure Physics. (Five hours weekly.) The progressive development of Physical theories, and Ex- perimental Physics : — Lectures and practice. 24. Applied Physics. (Five hours weekly.) Popular astronomy ; mathematical and physical geography ; meteorology ; weighing and measuring apparatus ; musical and optical instruments ; lighting apparatus ; the mechanical principles of heating apparatus ; application of the theory of heat to fireplaces. The lectures are illustrated by experiments. 25. Elementary Chemistry. (Two hours weekly.) Brief introduction to Chemistry, with especial reference to building and building materials, illustrated by experiments. 26. Pure Chemistry. (Five hours weekly.) Inorganic and Organic Chemistry, illustrated by numerous ■experiments. 27. Technical Chemistry. (Five hours weekly.) Apparatus for carrying out chemical operations on a large scale ; the processes of manufacture of chemical products. The instruction given in this course is by means of lectures, experi- ments, excursions, and visits to laboratories and manufactories. 28. Practical Chemistry. (Twenty-four hours weekly.) In this course, in addition to practical work, three hours per week are devoted to lectures on analytical chemistry ■ the students having previously attended the courses 25 and 26. 29. Mechanical Technology. (Five hours weekly.) Working in metal and wood ; spinning and weaving ; manu- facture of paper ; and numerous other processes employed in the mechanical arts. 30. Building Technology . (Two hours weekly.) Brief recapitulation of the practice of building art, with espe- cial reference to materials used in finishing or decorating build- ings, as glass, paper-hangings, iron, stone, and plaster works. 31. Telegraphy. (Two hours weekly.) 32. Modelling. (Ten hours weekly.) Modelling, ornament, human and animal forms in clay and wax from drawings and casts ; moulding and casting ; finishing rough casts. 33. Architectural Modelling. (Ten hours weekly.) Modelling in wood, roofs, trussed bridges, staircases, etc. ; modelling in plaster, arches, vaults, etc. etc. TECHNICAL DRAWING.— IX. DRAWING FOR CARPENTERS ( continued ). ■WOODEN BRIDGES. Fig. 56 is the elevation of the bridge over the Wcser alluded to in the last lesson. The bow, built up as described, abuts against oak blocks, toothed and bolted on to the ends of the tie-beam. From the bow, transverse bearers are suspended by means of seven iron rods, placed as in the drawing, and on these the beams supporting - the roadway rest. It is deemed necessary, in relation to the drawing of this example, to remark that the lines forming the joints (that is, the ends of each piece of timber) must be radii of the circle of which the arc is a part. In the present instance the arc is that sub- tending an angle of 60°; therefore, having drawn the tie-beam, and marked the points at which the under side of the bow meet it, with distance between these two points as radius, describe arcs cutting each other in a point below, which would be the apex of an equilateral triangle, and from this centre the arcs are to be described. The disadvantages connected with the De Lorme system are, first, that the stiffness of the span must depend mainly upon the natural strength with which the fibres of the wood adhere to each other ; and as this is of course limited, it is necessary to construct the curved rafters of greater width than would other- wise be required, in order to ensure them against the strain to which they may be subjected. Secondly, there is, from the circumstance above alluded to, and from the necessity of sawing the segments out of straight timber, a great waste of material, time, and labour. These considerations naturally prevented the system becoming very general, and in 1809 an improvement thereon was proposed by a celebrated Prussian architect named Wiebeking, which was in 1817 'perfected by Colonel Emys, a French military engineer, and which has since been extensively used. By Emys’ system, the arched ribs are laminated — that is, formed of “laminae,” or thin layers of timbers — not placed edge- ways, as in the De Lorme plan, but laid flat on each other, the break-joint system being still preserved, and the planks being held together by iron straps with which they are sur- rounded. The whole rib is then confined by its ends fitting into cast- iron shoes bolted on to the tie-beam. Thus all the fibres of the wood coincide with the curvature of the rib, and thus not only are they not liable to be torn asunder, but a great amount of elasticity is obtained. As this system has been extensively used in the construction of roofs, it will be further described in the section devoted to that subject, and the attention of the student is now directed to the elevation of one of three arched ribs of a wooden railway bridge (Fig. 57). Here the tie-beam is formed of double timbers, resting on an additional piece at each end. The bow is made up of seven layers of timber, united in the manner shown in Fig. 58, which is an enlarged drawing of the middle portion of the truss. Seven perpendiculars are placed between the bow and the tie- beam, by which the latter is suspended, as by king and queen posts. The mode in which the iron bands, nuts, and screws act in such cases is described in connection with Roofs in “Lessons on Building Construction.” The trusses arc further stiffened by diagonal struts between the perpendiculars. Across the tie-beams of the three ribs the sleepers are placed on which the flooring of the bridge and the rails are laid. The piers,, saddle-pieces, and tie-beams having been drawn, the arc forming the upper edge of the bow is next to be described. The cast-iron shoes necessarily follow. In the smaller view (Fig. 57) their outer edge is shown as continuous with the arc of the bow ; but in working this figure to a larger scale, this should be drawn with a rather wider radius, so that the iron shoes may project to allow for the thickness of the material. As in the case of the cross-joints of the timbers in the Ds Lorme bow truss, the third side of the cast-iron shoes and the bands by which the laminae are clamped together are radii of the circle of which the bow is a part, and therefore converge to the same centre. This is not, however, the case with the irons by which the uprights arc suspended. These plates, which end in screws, are, of course, placed parallel to the posts ; at the top a cross-plate unites the screws, on which are washers and nuts. The irons at the bottom of the perpendiculars are similar in character. When the bow has been completed, the perpendiculars for the centres of the uprights are to be dotted in, and on each side of these half the thickness of the supports is to be drawn. The upper and 'lower ends of these are, of course, wider than the middle part, the two widths being joined by short oblique lines. Now, from the points where these oblique lines join the outer to the inner width, and so form a “ head,” draw diagonals in the interspaces, which will form the centre-lines for the struts. It will be observed that the oblique lines, which form part of the ends of the struts, are at right angles to their sides. It is presumed that this drawing can be finished without any further instructions. The student is required, in the first case, to draw Fig. 57 to the size of Fig. 58, and then to repeat the whole figure, making TECHNICAL DBAWING. 137 the drawing on a scale half as large again as Fig. 58. In both of these cases great care will be necessary in drawing the parallel arcs, and the student is reminded of the purpose of the joint in the inking-leg of the compass— namely, so that by bending the leg both nibs may touch the paper, and thus roughness of the edge of the line may be avoided. The lengthening bar will also bo needed, and it is then advisable to hold the steel end of the compass in it3 place with the left hand whilst describing the arcs with the right, for the instrument, thus lengthened, becomes rather unwieldy, and the point is then liable to slip out of the centre. Fig. 59 is the elevation, Fig. 60 a section, and Fig. 61 a half Fig. 63 is the half section of the upper portion of this arch, showing the manner in which the four ribs are connected by iron tie-rods, the longitudinal girders, transverse bearers, the flooring, and the hand-rail. With this knowledge as to the construction of the bridge, the student will not, it is believed, require any information as to the mode of drawing the example, and therefore will be left to apply the instruction he has received in relation to the previous studies. Fig. 64 is the half elevation of an American timber bridge, by which the Erie Bailway is carried over a span of 300 feet. The arch ribs of this structure consist of two separate bows, plan of one of the three arches of the wooden railway bridge from Paris to St. Germain. This bridge is supported upon, instead of being suspended from, the four arch trusses. These bows are formed of fifteen laminae, or layers ; but not only is the break-joint system carried out in the length, but in the breadth, as will be seen in the transverse section of the bows (Fig. 62). The planks of which the bows are formed are tarred, excepting on the outermost edge ; and further, coarse paper saturated with tar was laid between them before binding to the template. When the required curve was attained, the planks were united by strong oak pins, plates of lead being previously inserted to prevent the wood suffering from the stress. The planks are further secured by iron bands, as in the former example. The ends of the be>w3 abut in cast-iron shoes, firmly fixed in the springings of the piers. clamped between cross-timbers, and stiffened by struts placed diagonally. The bows are constructed of three layers each, with extra pieces above and below at each end, all being, of course, firmly bolted together. These ribs abut against iron plates attached to the rocks, and support perpendiculars. On these rest trans-- verse beams bearing longitudinal joists, across which sleepers are again placed for the support of the floor-joists of the road. This construction will be best understood by referring to the section (Fig. 65), from which it will be seen that four such ribs are employed in the bridge, two of which, as in the last example, are placed close together in the middle, the whole being strength- ened in a transverse direction by cross-struts. The longitudinal joists being thus secured on the top of trans- verse head-pieces resting on the perpendiculars, the bows are 138 THE TECHNICAL EDUCATOR. braced up to them by means of straining-pieces clamping these and all the other timbers between them. This is shown in the section, from which it will also bo seen that each of the three layers in the bows is made of two timbers, placed side by side, each single bow being thus formed of six square beams in the middle, and twelve at its extremities. This being the last study connected with bridges, the student is expected to be able to draw it without any instructions, but is advised to copy it on a much larger scale. Figs. 66, 67, 68, with its section 69, are different methods used in the abutments of bow trusses. MINERAL COMMERCIAL PRODUCTS.— VII. earths or sodium, etc. ( continued ). Natron, a native sesquicarbonate of soda called trona, and mineral soda, is found in sandy soils in Egypt, Mexico, Hungary, etc. Large quantities are collected from the lakes of Sukena in Africa, and chiefly used for native consumption. Borax, an important article, very useful in chemistry and the arts, is a compound of boracic acid and soda. It occurs in the waters of some lakes in Thibet and Persia, and is imported in an impure state, as tincal, from the East Indies. Much, how- ever, is manufactured from boracic acid obtained in a native state by the evaporation of the mineral waters from the extra- ordinary volcanic lagoons of Tuscany, and from hayescine, a borate of lime found in Peru. The annual produce of boracic acid from Tuscany ha3 of late years been about from 1,800 to 2.000 tons. Saltpetre, nitre, or nitrate of potash, is a natural product occurring on the surface of the soil in some hot and dry coun- tries. It can also be prepared artificially, as is done in France, Germany, and other places. The British supply comes chiefly from the East Indies, to the amount of 18,000 tons annually; the annual importation from other sources is about 5,000 tons. Besides being the chief ingredient in gunpowder, it is largely used in chemistry, medicine, and the arts. Nitrate of soda, or cubic nitre, is found native in immense quantities as a geological deposit in Northern Chili and Peru, and is probably abundant over the salt plains of the same conti- nent. It is largely imported by this country, to the extent of 50.000 tons annually (value ,£500,000), and used in agri- culture as manure, and for many of the purposes to which salt- petre is applied. Sulphate of baryta, or heavy spar, is a beautifully crystal- lised mineral, occurring in mineral veins in Cumberland, West- moreland, Derbyshire (as cawk), Carinthia, Algiers, and Nova Scotia, and is a spurious substitute for white lead. The mine- rals celestine (sulphate of strontia) and strontianitc (a car- bonate of strontia) are used in the arts for the manufacture of the nitrate of strontia, which is employed for producing a red colour in fireworks. The salts of strontia are remarkable for the red colour which they impart to flame, whilst those of baryta give a green colour. Fluor spar (fluoride of calcium) is also a beautiful mineral, and important as the principal natural source of hydrofluoric acid and other combinations of fluorine. It occurs in the lead veins of Yorkshire and Derbyshire, and, from its rich colours, is used in the ornamental manufacture of tazzas of various kinds. Sulphur is an element existing abundantly in various metallic and non-metallic compounds ; but it also occurs native in quan- tities sufficient to render its extraction from its combinations almost unnecessary ; it is, however, separated for economic pur- poses from iron pyrites. It is found native in all volcanic regions, either as an efflorescence on the surface or largely impregnated with earths. Sicily and Iceland possess it as a volcanic product, and from the former our chief supply, 50,000 tons annually, is obtained. Spain also supplies this substance. Sulphur is a very important article as an ingredient in gun- powder. Sulphuric acid (vitriol), so indispensable in the arts, together with other valuable sulphur compounds, has already been referred to. Graphite, plumbago, or blaclt lead, although pure carbon, contains a variable quantity of iron up to a pro- portion of 5 per cent. It occurs in beds and embedded masses, in fissures in granitic and slate rocks, in nodules in greenstone, and, rarely, in mineral veins. This mineral, well known as the material from which the black-lead pencils of the finest quality are produced, is comparatively rare. It has been found on the right bank of the great river Tungouska, in a country pre- viously little known. In the depths of pine-forests, and it the level of the waters of the wild Tunbusi, torn and abracbd by the ice, one continuous mass of graphite has also been Paced, 3,000 yards or more in length, with an ascertained de;th of thirty yards. The famous mine of Borrowdalc is almost ex- hausted. Considerable quantities are, however, procured from Ceylon (3,547 tons) and Austria (660 tons), as well as some from Spain, Mexico, Greenland, and the Cape Colony. Besides its more common uses, plumbago is of great utility in the manufacture of crucibles or melting pots for metallurgical and chemical purposes. Among mineral productions available as articles of utility and commerce, mention must not.be omitted of some tint are of great use in agriculture, especially in such farming as must be carried on in densely-peopled countries, where all quilities of soil must be brought under cultivation. In addition to the silica, alumina, and lime, which are the common chemical con- stituents of arable soils, there must be a due supply of silts of potash, phosphoric acid, nitrogen, and some other ingredients. Organic remains, in the shape of natural vegetable decay, and of ordinary farm manures, supply these ; but mineral minures are also highly valuable and much used. Limes, clays, sands, and marls are all useful under certain circumstances. Salt- petre (nitrate of potash) is a valuable addition to soils requiring nitrogen, but it is costly. The cubic nitre already alluded to exists, however, in great abundance, and is largely available for the same purpose. Phosphates of lime are used to furnish the phosphoric acid. The supply is now chiefly obtained from the small hard nodules of various sizes, composed in part of ancient organic remains ( coprolites ) which are found in the C:ag of Suffolk, and in the Greensand at Farnham, Cambridge, Ihtchin, Isle of Wight, Havre and other parts of France. Phosphatic nodules are also abundant in the Lias. Thousands of ions of these are annually raised, crushed, and, by the action of sul- phuric acid, converted into superphosphate of lime ; and they are, in this form, extensively employed as manure. Phosphate of lime is quarried in Spain, and at Sombrero, one of the West Indian isles, and prepared for agricultural purposes. PRECIOUS STONES. Important mineral products, on account of their great in- trinsic value, are precious stones. These occur in mineral veins, and, as is the case with some of the metals and their ores, in river sands and alluvial deposits brought down from metalliferous districts. Brazil, India, the Ural Mountains, and the mining districts in general, especially those of the older formations, furnish the chief supply. Precious stones are either carbonaceous, aluminous, or silicious. The diamond is the only one consisting of carbon, and is well known as the hardest and most valuable gem. Diamonds are prized according to their purity and freedom from colour, or if coloured, according to the depth of the tint. Besides their extensive use fo? orna- mental purposes, they are, in the form of fragments, of much service in the arts — as in glass-cutting, watch-making, ar.d dia- mond polishing. The aluminous gems comprise the sapphires (the red sapphire, or Oriental ruby, next in value to the diamond; the blue, or true sapphire; the green, or Oriental e'inerald ; and the yellow, or Oriental topaz) ; the corundum, or adaman- tine spar, the hardest substance next to diamond, and employed for emery-powder ; the rubies of various reds ; the topaz of various yellows ; and the garnets, of which the carbuncle is the choicest. The emerald, of a beautiful green, and the leryl — ■ yellow, blue, or colourless — are compounds of silica, alumina, and glucina. The most valuable of the silicious gems are the amethyst, of a purplish-violet hue ; the Cairngorm stone, the opal, sardonyx, agate (which is also employed as a burnisher), chalcedony, carnelian, and jasper. The lapis-lazuli, from which ultramarine used to be prepared, is a beautiful mineral, found in China, Persia, and Siberia. The turquoise may be considered as a phosphate of alumina, lime, and silica, with iron and copper. The chief supply is drawn from the peninsula of Sinai, which appears to have been the great mining district of the ancient Egyptians. The turquoises, so much admired for their beau- tiful blue colour, occur more or less in veins of sandstone. With this notice of precious stones we bring our brief account of the Mineral Commercial Products of the earth to an end. AGRICULTURAL DRAINAGE AND IRRIGATION. 139 AGRICULTURAL DRAINAGE AND IRRIGATION.— III. By Prof. Wrightsox, Royal Agricultural College, Cirencester. CAUSES OF EFFICACY OF DRAINAGE ACTION OF DRAINS ON THE SOIL VARIOUS METHODS OF DRAINAGE CAPILLARY ATTRACTION AND ITS EFFECTS. In the last paper we considered the causes of the efficacy of drainage as a means of improving land. These causes may be briefly summarised as follows : — 1. Diminished evaporation, rendering the soil warmer. 2. Removal of stagnant water, allowing access to rainfall. 3. The introduction of air, and therefore of oxygen, into the land. ' 4. Washing of the surface by heavy rains prevented. 5. Improved texture, owing to alternate contraction and ex- pansion of both soil and subsoil. These causes are followed by good effects readily appre- ciated by landowners and occupiers. Thus increase in tem- perature is followed by an earlier and more abundant harvest, by the cultivation of a larger number of plant species being rendered possible, and by greater healthiness in the animals maintained on the farm. Causes 2 and 3 operate in a similar direction, and, in the phraseology of the farmer, “sweeten” the land, while the remaining two causes render manures more efficacious and lasting, and especially the last cause renders the land easier to work and more accessible to the roots of plants. The effects of drainage in improving definite areas of land, and the comparison between the advantages secured and the cost entailed, will be considered hereafter. At present it is only my wish to point out the relation between the causes that occupied us in the last paper, and those practical good effects which alone render the drainer’s art valuable. Our next consideration is the action of drains in the soil. We shall endeavour to come to a truthful conclusion as to the mode in which water is removed by drains. But, before doing so, we must carefully consider the condition of wet soils, the causes of their wetness, and afterwards the effect of intro- ducing a means by which surplus water may be removed. Before proceeding another step, however, it is well to bear in mind that soils are exceedingly various in their textures, and that their relations to water must not be looked upon as con- stant and invariable. A few simple natural laws account for all the phenomena of drainage, but the action of these laws is modified according to the character of the soil and subsoil, and these modifications occasionally give rise to apparent contra- dictions in practice. In approaching this subject, it is also requisite to free the mind from false notions as to the action of drains. Thus, too often we hear a drain spoken of as “ draw- ing,” as though an underground channel exerted an active instead of a merely passive effect. All idea of suction on the part of drains must then be given up, and with it the notion of land being “ over-drained.” Land may, of course, be over-dry for some purposes ; but supposing drains to be multiplied to an indefinite extent beneath the surface, it would be impossible for them to remove more than the surplus water of a field. They could not carry off that portion which tho varying character of the soil allows it to hold, as a sponge holds a certain amount of water after it ceases to drip. Soils are wet from three causes — from direct rainfall, from springs, and the soaldng down of water from higher grounds. The greater part of our retentive soils are wet from the arrested descent of rain-water as it seeks a lower stratum. Springs usually occur on the sides of hills, and owe their existence to the presence of a bed of clay, or other retentive material, at a greater or less distance from the surface. When rain falls upon a porous soil it sinks in without difficulty, until it meets with an obstruction. Here it accumulates, and may be reached by boring a well down to it. Supposing, however, that this obstruction, probably clay, crops out upon a hill-side at no great distance, there you will have springs. As soon as the water rises in the natural reser- voir until the lip of the basin is reached, it will overflow, and cause wetness in the land immediately beneath it. Again, water may find its way from the point at which it fell, and incommode land more or less remote by a slower soaking pro- cess, in which definite gushing springs do not occur. This is usually met with in free soils, and is defined by Mr. Bailey Denton as that moisture which is caused by water of distant and adjacent higher ground pressing up through free soils of a lower level, and which may be called “ diffluent water.” Now the treatment of land wet from these three causes has given rise to two distinct methods of drainage : one in which the drainer effects his purpose by means of pipes laid at regular intervals, adapted to soils suffering from the first kind of wet- ness ; and another in which the object of the drainer is rather to attack the source of water and cut off the supply, than to attempt to drain by regular channels at stated distances apart. The first method is identified with Mr. Smith, of Deanston; the second with the name of Elkington, who flourished in the latter half of the last century. The principle upon which Elkington’ s system of draining was based will be rendered more intelligible when his practice is described. It is evident, however, that it is only under peculiar conditions of soil and subsoil that it can be effective. It is comparatively seldom that the source of wetness can be localised so as to allow of its removal by a single drain, and althdugh such cases occur, yet, more ordinarily, land is wet because the rainfall is prevented from finding its way through the soil to depths at which it would be harmless to growing plants. Let us, then, investigate an ordinary ease. A field is wet, and requires draining. It is wet simply because the water cannot escape, and this may be due to general retentiveness throughout the mass, a»s is the case in clay soils ; or to an ob- structing bed at some little distance beneath the surface. Taking the first case, we are at once introduced to the difficult ques- tion of the action of drains in stiff clay soils. That water will penetrate such soils has been proved, as Mr. Morton has tersely observed, by the fact that they are wet. Their power of reten- tion is, however, very great, and this is a force which, while it exists, cannot be overcome by any number of drains. Clay soil will hold, according to the experiments of Schiibler, 48 pounds of water per cubic foot, and it is only the excess over this amount which would find its way into a drain. When, however, such soils are furnished with a series of underground channels, and when the work of tho drainer is supplemented by deep cultiva- tion, the character of the soil is gradually altered. The con- tinuity of the soil is broken, air gains access, pulverisation takes place, and the altered soil becomes amenable to the ordinary rules which govern more usual cases. Vigorous treat- ment is, however, requisite, and no system of wide intervals between drains would be successful. The drains must be close enough to exert what Mr. Bailey Denton has termed a reci- procating effect upon one another, that is, so close that the action of one shall extend into the region of action of its neigh- bour. After the full effects of thorough drainage have been brought to bear upon a clay soil, the water will pass through it and find its way to the drains in the same manner, but never with the same facility, as in lighter soils. Let us, then, turn to the case of a more porous soil, wet from direct rainfall. Here we must suppose a definite obstruction to the down- ward passage of water. The water tends to pass through the soil in straight lines, according to the law of gravity. It meets with the obstruction, and begins to rise upon it towards the surface. There is no limit to its rise. It may form a lake, or it may be the cause of a marsh. In other cases it will not rise to the surface, but form what is known as a “ water-table ” one, two, or more feet beneath. Now this water-table, or level of supersaturation, is not the limit of wetness. Over it is a stratum of greater or less thick- ness, depending upon the character of the soil, wet from capil- lary attraction ; and if this force raises water to the surface, the land requires draining. Capillary attraction may be defined as a triumph of adhesion over cohesion and gravity. When a piece of wood or metal is dipped into water and withdrawn, its wetness may be explained by the fact that tho adhesion of the liquid to the object introduced is stronger than its cohesion to the remaining water it has left, or to the downward force of gravity. A similar attraction is exerted by the soil and many fami- liar porous substances when placed in contact with water. The superior force of adhesion lifts a tiny column of water through the interstices of the porous material presented until the weight of the column thus lifted counterbalances the attrac- tion of adhesion, and the limit of the force is reached. A healthy soil should have a layer of earth at its surface a few inches in thickness, which must not be continually wet 140 THE TECHNICAL EDUCATOR. even from water raised by capillary attraction. It will be readily fieen tbat if such a layer does not exist, capillarity and evapora- tion will between them lower the temperature of the soil con- siderably. Growing plants will also suffer from the same causes which render saucer-watering, in the case of potted plants, objectionable. It is, indeed, a case closely analogous to saucer-watering, and the sooner it is altered the better for the crops. The question as to the height to which soils will thus lift water has been assumed and guessed at; but data of a precise kind are still needed. A few years ago I undertook a series of experiments for the purpose of throwing light upon this point, and the results obtained were as follows : — When air-dried clay or sand is placed in a tube, one end of which is immersed in water, the fluid rises rapidly, especially in the case of sand. Thus, twenty minutes after the experiment was com- menced, the fine sand was wet 9 inches above the level of the water in the saucer, and seven hours after it was wet 15 inches up the tube. Clay, in a finely-powdered state, had during this time only raised water 3 and 5 inches in height, taking two tubes containing similar soils. The capillary power of the sand was, however, almost exhausted in this short period, and although the experiment was conducted for 132 days the column of water was never raised higher than 23 inches. The clay behaved very differently. Although water rose slowly, it rose very steadily, and at the termination of the experiment, 132 days after its commencement, it was wet 35 and 33 inches, taking again the results of two tubes. During the last six weeks of the experi- ment the rise was exceedingly slow, and only 1'8 inch of extra height was obtained. As this was partially due to the upper soil becoming wet by evaporation and condensation of water from the part wet by the force of capillarity, the limit of the force was considered to have been reached, and we may, there- fore, take 3 feet as the height to which water may be raised by clay in a fine state of division. There was one more point worthy of attention in these experiments, namely, that a pre- cisely similar soil to the clay just mentioned, but in a somewhat coarser state of division, was only able to lift a column of water 15‘5 inch, showing that physical condition even more than material is an important constituent in this power possessed by soils. It is the object, then, of the drainer to so lower the water- table that a thin layer of dry soil may intervene between the surface and the portion wet by capillary attraction. A drain is constructed, say four feet beneath the surface, and immediately water flows from it, the water-table begins to sink, until it is on a level with the bottom of the drain, just as the water in a cask would sink to the level of the lowest portion of a hole made through the wood. Remembering that water falling on the surfaoe makes its way down through the soil as straight as possible, it is evident that rain feeds the water-table, constantly tending to raise it ; but as the water-table will have a difficulty to rise higher than the drain, it will be seen that the water, for the most part, enters the bottom, and not the top of the drain. It can only enter the top when, by heavy rains, the water-table is unnaturally raised; but on the return of ordinary weather the lowest portion of the draining tile will once more become the upward limit of the saturated portion. The area over which one drain will act is, of course, very limited, and the limits of its action are soon reached. The water-table, although kept down to the level of the drain in its immediate proximity, just as a river keeps down the water-table of a district through which it passses, yet rises as we recede from the drain until it extends to a point completely out of its influence. Hence a series of drains is required so near to each other that the level of supersaturation is sufficiently lowered throughout the intervening space. It is generally believed that the action of drains is intensified by the near proximity of other drains. This is mostly owing to the aeration of the soil. A bed of sand or gravel underlying a clay soil will not drain the field, although such a gravel bed may be looked upon as a continuous drain, or means of escape for water. Under such circumstances, however, a few drains placed at wide intervals would bring the drying power of the porous bed into immediate action by the admittance of air, and the field would be easily and effectually dried. It is, indeed, surprising to what distances drains, under such circumstances, will draw. Instances are not want- ing in which the channels have been effective at sixty yards apart. Such cases at once lead us to the consideration of the means of draining employed by Elkington and other drainers, and introduce us to the more purely practical part of our subject. BUILDING CONSTRUCTION.— V. BRICKWORK. Bricks may be considered as artificial stones, and seem to have been used from a very early period in the history of man. Their average size in this country is a trifle less than nine inches long, four and a-half inches wide, and two and a-half inches thick. Their uniformity in size enables builders to describe the thickness of walls by the number of bricks extend- ing across it ; thus, a slight brick partition wall being formed of bricks lying on their broad side, with their length in the direction of the length of the wall, is called a “ half -brick thick,” its thickness being four and a-half inches ; a wall in which the length of the brick extends through the thickness is called a “ one-brick thick;” a wall 14 inches through is called a “ brick and a-half thick ” (though to speak more accurately it would be 13£ inches, that is, 9 for the whole brick and 4$ for the half) ; an 18-inch wall is said to be a “ two-brick thick,” and so on. If we suppose a wall of only half a brick thick, all the bricks used would, of course, be laid lengthwise, so as to show their whole length in the face of the wall. In laying a second course of bricks, care would be taken to prevent any two vertical joints from coinciding. This would be effected by placing the joints or meeting of the ends of the bricks forming the second course over the middle of the bricks of the course below. This arrangement would be attended to in all the succeeding courses, and is technically called breaking joints : a wall thus built i3 said to have a proper bond, a term which implies that the parts are well connected. It must, however, be remarked, that the above supposition of a building only half a brick thick has been introduced merely to illustrate the principle of what is technically called bond in building ; no brick wall so slight as the above should ever be used, this dimension being much too weak to afford proper stability even to the smallest buildings, unless the brickwork be held together by wooden framing, of which it fills the vacant spaces. This style of work, used for economy, is altogether unsuitable for public buildings, unless of a temporary nature, and is called “ brick nogging,” of which specimens are very common, especially in villages. Brick nogging is also some- times used for the partitions of dwelling-houses. It is important that brick walls should be kept perfectly vertical; and it must be remembered that if a wall at the bottom is in the slightest degree “out,” the evil (like every other) will go on increasing, the top will gradually extend be- yond the foundations and fall. But this is not all ; the wall must be kept “plumb,” which does not necessarily mean upright, but a straight surface ; thus, a wall may be slanting, as against a bank, or the side of a tower which tapers towards the top ; but in whatever position it may be, it must be kept plumb ; and the plumb-rule* may not only be used for this purpose, but to keep the vertical joints regularly over each other. This is generally termed “keeping the perpends.” Next in importance to this, or we may say equal to it, is the subject of bond- ing. By bond, is meant that method of com- biningthe bricks that each indi- vidual may be supported by as many others as possible ; and this is done by Fig. 9. the judicious arrangement of the joints, which will be seen on reference to the annexed illustrations. * A plumb-rule is a straight piece of wood, to which is attached a string with a plummet or lump of lead. The name is derived from the Latin word plumbum (lead), and the line formed by the weighted cord, when perfectly still, is a true vertical hue. A F B G C H D 1 E J BUILDING CONSTRUCTION. 141 Let us suppose that an attempt were made to build a wall as in Fig. 9, viz., by placing rows of bricks over each other : it will be evident that here none of the stones receive any other support than is afforded by those immediately under them. Thus A is supported by b, c, d, and E, and this is the greatest amount of support it could receive ; nor would it be less liable to sink (supposing the ground to give way under it), even if it rested on a greater number of bricks so disposed, for in case of failure in the foundation, the whole column abode would sink, sliding dovra at the side of F g h i j. Now let us turn to Fig. 10. Here, by the simple arrange- ment of “ breaking joint,” we get the brick A supported by two others, b and c ; these rest on three bricks, d, e, f ; which in their turn are supported by fowr, g, H, I, j ; and these again rest A r B C s D E F t C H 1 J u K L M N 0 V Fig. 10. Q on five, K, l, m, n, o. Thus the brick A is supported by fourteen others, and its foundation rests on the entire space extending from p to Q; further, this breadth of foundation does not refer to this brick only, but to every individual one composing the wall : thus, r rests on c, s ; e, f, t ; H, i, j, u ; and L, m, n, o, v ; and any brick taken promiscuously is similarly supported ; thus D rests on G, H, and G, H rest on K, l, m, etc. In this illustration all the bricks are supposed to be laid on their broad sides, with their length parallel to the front of the wall ; in this position they are called stretchers. When bricks are laid so that their ends are to- wards the surface, and their length extends into the thickness of the wall, as in the group shown in Fig. 11, they are called headers. Now, on referring to the previous diagram (Fig. 10), it will be seen that the wall there represented would be a “ half -brick thick” one; and that even if we were to build one three times as thick on the same system, the wall would consist of three separate ones of half-brick thickness each, neither having any connection ivith the other; and thus the front might fall forward, the Fig. 11. ( E. B 1 H C E D Fig. 14. J Fig. 12. j Fig. 15. Fig. 13. hindermost one might fall backward, or the middle one might sink; for neither one would give any support to the other, not being in any way built in to each other, the bonding being merely longitudinal or lengthwise, but no cross bond existing between them. Combinations of stretchers and headers have therefore been devised, by which the entire thickness of the wall is so bonded as to form one compact structure. Thus, in the one system called “English bond,” one course of bricks Fig. 17. ! ! Fig, 116. : -/■f Fig. 19. Fig. 18. is laid lengthwise, or as stretchers ; and the next crosswise, or as headers. The annexed illustration (Fig. 12) shows the commencement of a wall of one-brick thickness, built in what is called English bond. In this it will be seen that the one course consists entirely of stretchers, and the other entirely of headers. The plan of the lower course (Fig. 13) is given below the elevation, and the plan of the upper course (Fig. 14) is placed above it. Now bricks are exactly half as broad as they are long, and thus, if when the first course of stretchers had been laid, we followed the simple idea of placing the next course as headers, and commenced at A (Fig. 12), we should not produce a bond at all, for the second header, b, would fall over the end of the first stretcher at c ; thus one joint would bs immediately over another; and of course, if this were carried up, one portion of the wall would soon separate itself from the other. Tfce bricklayer, therefore, having laid his lower course, places D, his first header, at A ; he then cuts a brick in halves lengthwise, and lays this half-brick next to the stretcher. This is called a “ closer,” e. He can after that proceed to lay the headers regularly, for the next header, p, will then be placed so that half of its width will be on each side of the joint c. Then will follow another header, G, which will leave a quarter of the length of the stretcher exposed, and this will be covered by the next header, H, which will overlap the joint by half its width. Fig. 15 shows the end of the wall which has been described. Fig. 16 illustrates a 14-inch or “ brick and a-half ” wall. The eleva- tion is the same in this as in the last ; for of course the thick- ness of a wall is not visible on its surface ; the plans, however, show how the bonds are arranged. Fig. 17 shows the plan of the first course, and all alternate i 1 \ (8" Fig. 20. S Fig. 21. Fig. 22. 142 THE TECHNICAL EDUCATOR. courses above it ; in this it will be seen why the wall is called “ brick and a-half.” Fig. 18 is the plan of the second course, and the alternate courses above it ; and Fig. 19 shows the end of sucn a wall. Fig. 20 shows the end, and Figs. 21 and 22 are the plans of a two-brick thick wall, built in old English bond, and from these it will be seen how the thickness i3 made up. In the lower course, there is a row of stretchers on each side, between which headers are placed ; thus the thickness is made up of the widths of two half and one whole bricks, whilst in the upper course two headers laid transversely to the face of the wall give the required width. The dotted lines on each of these plans show where the joints would fall when the one course should be worked over the other. In copying these examples, the student is advised to work to a scale, so that the bricks and half-bricks may be drawn in their proper proportion ; and it may be well to state here I L Fig. 24. Fig. 25. longitudinal bond ; but although uniformity in the bond on the surface may be thus preserved, it is at a sacrifice of the cross- tie. It must be taken as a rule, therefore, that a brick should never be cut. if by any skill on the part of the workman it can be laid whole ; for when a brick is cut, an extra joint is created Fig. 29. in a structure, in the erection of which the greatest difficulty arises from the great number of joints. The utmost care, then, should be taken to avoid making more than are absolutely indispensable. Figs. 26 and 27 represent plans of first and second courses of a brick and a-half wall, built in Flemish bond. Figs. 28 and 29 show plans of the same wall, built so as to avoid the half-bricks without interfering with the strength of the bond. This, however, leaves an open space on each side of tho header in the thickness of the wall, which may either be filled up with a bat or left open. that this plan is desirable in working all the exercises in these lessons ; for if every line be simply measured, the studies will not convey all the instruction intended, whilst by. working them to a larger scale they will afford excellent practice. The student is also advisod to attempt simple colouring from the commencement, so that the use of compass, pencil, and brush may be practised together. Another kind of bond in very general use is that called “ Flemish bond.” _ . This consists of stretchers and headers laid alternately m uhe same course. Fig. 23 is the elevation, and Figs. 24 and 25 are Fig. 26. 2 1 2 Fig. 27. plans of two courses according to this method. It is neater in appearance than the English bond ; but, owing to there being less headers in it, the cross bonding is not considered to be as strong. In walls of almost all thicknesses above nine inches it is often necessary to use half -bricks, in order not to break the ANIMAL COMMERCIAL PRODUCTS.— V. III. — STEARINE AND OILS. The chief supply of animal oil is derived from various species of seals (order Carnivora, family Phocida) and whales (order Cetacea). In order to meet the needs of the creature it defends, the true skin of whales is modified, forming the layer o'f blubber, called by whalers the blanket, probably in allusion to its office of preserving the animal heat. The blubber is composed of a number of interlacing fibres, capable of containing a very large quantity of oily matter. The thickness of the blubber varies in the several species ; those inhabiting the frigid zones have it of greater thickness than those which habitually live in warmer seas. It is never less than several inches, and in many parts of a whale is two feet deep, and, moreover, as elastic as caoutchouc, offering an admirable buffer to the force of the waves and tho pressure of the water, as well as a defence from cold. In a large whale the blubber will weigh thirty tons. The species of whales that are regularly hunted for the sake of their oil are— • The Greenland Whale ( Baloena mysticetus), which is confined to the Greenland and Spitzbergen seas, its migrations being regulated by the extent of the perpetual ice. The Hump-backed Whale ( Megaptera lonaimana) attains * length of sixty to seventy feet, and inhabits the Greenland seas, where it is found in great abundance. Though its oil is said to be superior to that which is furnished by the Greenland whale, and not much Inferior to the oil of the sperm whale, yet it is not eagerly sought after. The Pike, or Finned Whale ( Balcenoptera rostrata) is a native of the seas that wash the shores of Greenland,, and is sometimes seen near Iceland and Norway. The flesh is in some repute as a delicacy among the natives of these northern regions. The oil which it furnishes is said to be particularly delicate. . , Sperm Whale ( Cdtodon macrocephalus) . — This species, which measures from seventy to eighty feet in length, is chiefly notable on account of the valuable substances which are ob- tained from its body — oil, spermaceti, teeth, ambergris. It differs from the tru’e whales in having no baleen plates in the ANIMAL COMMERCIAL PRODUCTS. 143 palate, but from forty to fifty conical teeth in the lower jaw, which fit into cavities in the upper, so that the mouth is capable of being completely closed. The head is of an enormous size, forming about one- third of the entire length of the animal. It is cylindrical, truncated, not composed of a bone, but of a sort of cartilaginous envelope, containing an oily fluid, which hardens by exposure to the air, and is then known as sper- maceti. This substance is also diffused through the blubber. The sperm whale, or cachelot, is generally distributed in all seas, but principally in those of the southern hemisphere. The oil is obtained from the blubber, which is only fourteen inches in depth on the breast, and eleven inches on the other parts of the body, and is therefore not so abundant in propor- tion to the size of the animal as that which is extracted, from the Greenland whale. Its superior quality, however, compen- sates fully for its deficiency in quantity. It is much used for burning in lamps. The spermaceti from the head is very valuable as an oint- ment, and for the manufacture of candles. The United States fit out more ships than any other nation for this whale fishery, bringing home annually more than 200,000 casks of train oil, and 150,000 casks of spermaceti. Next to the United States, England is the country most engaged in the whale fisheries, the principal port, Hull, having about 200 ships. France em- ploys 145 ships in this business, the principal port being Havre. Norway, Sweden, Denmark, and the Hanseatic Towns take some part in the whale fisheries, though not to any very great extent. Spermaceti candles are mostly manufactured in England. Spermaceti is imported from the United States ; the value per ton in 1866 was <£123 15s. Gd. The Beluga ( Beluga cdtodon), also called the white whale, on account of the colour of its skin, is an inhabitant of the higher latitudes, being found in great numbers in Hudson’s Bay and Davis’s Straits, and frequenting the mouths of large rivers on the northern coasts of Asia and America. The oil furnished by the beluga is of very good quality, although small in quantity, and is sufficiently valuable to have led to the esta- blishment of regular beluga hunts in the great North American rivers, which they ascend for some distance in search of prey. The skin can be made into a peculiarly strong tough leather, and is said to resist an ordinary musket-ball. The Seals, which have been described in page 74, are also hunted for the sake of their oil ; and the pursuit of them is superseding that of the Greenland whale, for the latter has been greatly reduced in numbers by continued persecution at the hand of whalers for upwards of one hundred years past. A large number of British vessels are engaged each year in the capture of whales and seals ; and the importation of train or blubber oil from British North America for 1867 was 15,945 tuns, the average for the last fifteen years being, however, 20,000 tuns. The price per tun in 1866 was <£44 Us. lOd. Tallow. — This is an article of great commercial value. It is animal fat separated from membranous matter by fusion, and consists chiefly of stearine, with a small quantity of oleine. It is manufactured into candles and soap, and is extensively used in dressing leather, and in various other processes in the arts. TVe are supplied extensively with native tallow, and we annually import a large quantity, principally from Russia, Hungary, and Turkey altogether about 30,000 tons a year. Our imports of callow from Australia and the Argentine Confederation average also from 2,000 to 3,000 tons annually. The entire imports from all parts were — in 1865, 3,125,282 cwt. ; in 1866, 3,008,807 cwt. ; and in 1867, 2,419,594 cwt. respectively. The tallow we receive from Australia is chiefly obtained from sheep, the carcases of which are boiled down for this product alone ; that from South America is from oxen and even horses, which roam in a half -wild state over the grassy plains of Monte Video, La Plata, etc. The animals are slaughtered for their hides, tallow, and bones. IV.— FOOD PRODUCTS. Butter is extensively made in the counties of Cambridge- shire, Suffolk, Yorkshire, Somerset, Gloucestershire, Oxford- shire, and Essex. In Scotland excellent butter is made in Clydesdale and Aberdeenshire. The butter produced in Great Britain is, however, insufficient for home consumption, and large quantities are imported, principally from Ireland, where it is°a staple commodity ; and from Holland, Belgium, the Hanse Towns, France, and the United States. The foreign imports for 1869 were 1,142,262 cwt. . Cheese is the curd of milk compressed into solid masses of different sizes and shapes, salted and dried, and sometimes coloured and flavoured. Besides our own supply of Gloucester, Wiltshire, Cheshire, and Stilton cheeses, which are the most in demand, we import a considerable number of foreign cheeses, amongst which are Limburg cheese from Belgium, Swiss cheese from Switzerland, Parmesan cheeses from Parma and other places in Lombardy, American cheeses from the United States, Edam and Gouda cheeses from Holland, and German cheeses from Westphalia. The last come to market made up into round balls, or short cylinders, under a pound weight each. The rich flavour of Parmesan cheese is owing to the aromatic plants which abound in the Italian pastures. Stilton cheese, so named from the. town in Huntingdonshire where it was first brought into notice, is the dearest of all English cheeses, the price being generally to that of Cheshire as 2 to 1, or 2 to II. To produce premature decay, and consequently an appear- ance of age, in these cheeses, the manufacturers are said to bury them in masses of fermenting straw ; also to spread the curd out on the ground over night, by which it becomes sooner liable to the blue mould. The quantity of cheese of all kinds imported during the year 1867 was 905,476 cwt., the principal countries which supplied us being Holland and the United States. Lard. — The melted fat of swine is imported chiefly from the United States. In 1867 we received 246,839 cwt., of the average value of .£3 9s. per cwt, LIVE STOCK. Oxen. — The numbers imported were— in 1865, 283,271 ; in 1866, 237,739; in 1867, 177,948 respectively. The average price per head in 1867 was <£17 19s. ; and the principal coun- tries whence imported were Schleswig, Holstein, and Holland. Sheep and Lambs, principally imported from Holland, amounted, _ in 1865, to the number of 914,170; in 1866, 790,880; in 1867, 540,326, of the average price per head, in 1867, of >£2 10s. MEATS. Bacon and Hams. — The imports in 1863 were as much as 1,877,813 cwt., since which year the importation has been on the decline ; in 1867 the number of cwt. was only 537,114, of the value of £21,391,779. The greatest supply was from the Hanse Towns and the United States. Beef (salted). — The imports, chiefly from the Hanse Towns and the United States, were, in 1867. 246,767 cwt., of the value of <£623,392, Pork (salted), not including hams, is imported from the Hanse Towns and the United States ; the quantity which was re- ceived in 1867—150,285 cwt., of the computed real value of <£351,871 — is much below the annual average. Preservation of Meat.—— How to meet the growing demand for butclier-meat, consequent on an increase of population and a decrease of stock, arising in great measure from pasture- lands being brought under tillage, is a question of grave im- portance in relation to the commercial prosperity of this and other countries, and calls for the earnest attention of legislators and scientific men. Though the stock of sheep and cattle raised in England is large, and that of cattle in Ireland and Scotland is a source of wealth to those two countries, yet enormous quantities of meat are imported. When we turn our attention to Australia and the Argentine States, we find the flesh of cattle and sheep sacrificed for other parts of the animal ; and he who shall devise a method by which these meats can be economically imported into this country will be hailed as one of the greatest public benefactors of the age. The im- portation of the living animals seems out of the question, not- withstanding the arrival of one or two cargoes ; and as the jerked or sun-dried beef, though brought in at low rates from Monte Video, etc., has not found favour, there only remains the discovery of a process by which the meat can be preserved in a fresh state a sufficient length cf time to admit of its transportation from regions so distant. _ This art of preserving meat is one of modern times, and differs entirely from the old and common methods by means of salt, saltpetre, sugar, etc. These substances, when in solution, 144 THE TECHNICAL EDUCATOE. do not absorb oxygen, and therefore they prevent decomposi- tion. The history of the art of preserving meat in a fresh state is associated with the earliest Arctic explorations. Scientific observers found that scorbutic diseases arising from living exclusively on salt meat were fearfully aggravated by extreme cold ; the Admiralty, therefore, offered inducements to merchants to devise plans for preserving unsalted meat, cooked or in a raw state, thus doing away with the use of salt meat altogether. It is hardly possible to over-estimate the impor- tance of this subject, as is evident from the fact that preserved provisions, cooked or raw, are an absolute preventive of sea scurvy. , . M. Appert, a French gentleman, was the first to succeed m the attempt to preserve unsalted or fresh meat, and in 1810 he received a prize of 12,000 francs from the Parisian Board of Arts and Manufactures. In the following year, M. Durant, a colleague of M. Appert, took out, in this country, a pa- tent, which was subsequently purchased by Messrs. Donkin, Hall, and Gam- ble, for <£1,000. M. Appert’ s process con- sisted in partly cooking the meat, placing it in a glass ves- sel in a bath of chloride of cal- cium, heating it to about 240° Fahr., and then hermetically sealing the lid. Appert’s plan, as adopted and improved by Messrs.Donkin, Hall, and Gam- ble, is as fol- lows : — Tin canisters are substituted for the glass ves- sels, and the meat (pre- viously par- boiled) is placed in them, with a rich gravy or soup. The lids, which are pierced with a small hole, are then soldered down air-tight, and the canisters immersed in a bath of brine or chloride of calcium, heated to boiling point. On the steam issuing from the hole in the canister lid, it is suddenly condensed by the application of a cold wet rag, and a drop of molten solder being dexterously applied to the hole at the same moment, the case becomes hermetically sealed. On cooling, the ends of the canisters are slightly concave, from the effect of atmospheric pressure, if the process has been successful ; but if the ends have flattened, or become convex instead of concave, then either the case has not been properly soldered, and is not air-tight, or the meat has decomposed and liberated gases. As soon as this modification of Appert’s process was made practically perfect, it was tested by order of the Admiralty, and ships were dispatched by them to the Arctic regions with an abundant supply of these meat canisters. On their return, the officers in command of the expedition reported favourably of the whole. Their value in cold climates having thus been clearly demonstrated, the experiment was tried with equal success by vessels trading in the tropical regions. For ship use these preserved meats are invaluable, and hardly a vessel now leaves this country without a supply. In India they are extensively used as luxuries in the towns, and as necessaries in the remote districts, where fresh meat of any kind is scarce and bad. It may be noted here that most of the ocean steam- ships belonging to ports of the United States and Europe are provisioned with fresh meats conserved in ice. Y. WOOL. In commercial phraseology the term “wool” is applied to the hair of the alpaca, goat, beaver, and rabbit, and to allied substances ; but, more strictly speaking, it belongs to the sheep alone, the hair of which, from time immemorial, has been woven into cloth. Wools are divided into two great classes — clothing wools and combing wools, or short wools and long wools ; and the fabrics woven from them are termedwoollens or worsteds, ac- cording as the one or the other is employed. The fibres of clothing wools felt or inter- lace with one another, form- ing thereby a dense com- pact material, suitable for warm and heavy clothing ; these wools are manu- factured into broad cloths, narrow cloths, felt for hats, blankets, car- pets, serges, flannels, and tartans. Comb- wools, on contrary, though long in fibre, do not felt, and are therefore em- ployed in the manufacture of light and loose, but still warm garments — such as stuffs, bombazines, merinos, hosiery, camlets, and shawls, and various mixed goods, as damasks, plushes, and velvets. The wool of the sheep has been greatly improved since tiro animal has been brought under the fostering care of man. The mouflon, which is considered by some zoologists as the parent stock of the common domestic sheep, inhabits the mountains of Sardinia, Corsica, Greece, Barbary, and Asia Minor. This animal has a very short and coarse fleece, more like hair than wool. When domesticated, the rank hair disappears, and the soft wool around the hair-roots, which is hardly visible in the wild animal, becomes singularly developed. If sheep are left to themselves on downs and moors, there is a tendency to the for- mation of this hair amongst the wool; its occurrence in the fleece of domestic sheep is therefore rare, and is always re- garded as proving defective sheep-farming. The climate of this country is unfavourable to the growth of the best wools ; hence the superiority of the Merino, Saxony, and Australian wools, the produce of countries having a higher average temperature. THE SPERM WHALE (CATODON MACROCEPHALH8). THE STEAM-ENGINE. 145 THE STEAM-ENGINE.— II. By J. M. Whiner, B.A. SUPERHEATER ( continued ) — LOCOMOTIVE BOILERS — ARTIFICIAL DRAUGHT CONSTRUCTION OF BOILERS MANHOLE BLOW-OFF COCK GAUGE GLASS, ETC. In some forms of superheater the steam passes through a set I of pipes arranged in a chamber, through which the smoke and heated air pass on their way to the chimney. In other varieties f the smoke is made to traverse a series of small tubes, while I the steam passes outside them. This plan was adopted in the I Great Eastern steamer, the steam-pipe opening into a large [ rectangular chamber, placed at the foot of the chimney, and traversed by a large number of vertical tubes through which the smoke had to pass. The area of the superheater varies, of I course, very considerably ; but a common proportion is about ! one and a-half square foot of surface for each nominal horse- power of the engine. A somewhat similar arrangement is some- times made in tubular boilers, vertical tubes being introduced, weight. A cylindrical tubular boiler is accordingly employed ; but the tubes are made of smaller diameter and greater length than those ordinarily adopted, their usual diameter being about two inches, while in length they often run from ten to twelve feet. The number employed, too, is very large ; in some powerful engines as many as 300 will be found, and in this way a large heating surface is obtained without unduly increasing the dimensions of the boiler. There is one difficulty produced by the employment of so many small tubes, the draught is considerably diminished ; and as a locomotive engine is obliged to have a very short chimney, no increase can be produced in this way. It is necessary, there- fore, to resort to some other means of producing a draught sufficiently powerful to maintain the necessary heat in the furnace, and the way in which this is usually accomplished is by placing at the base of the chimney a steam-pipe, the blast from which quickens the draught to the required extent. This pipe should be fitted with a funnel-shaped mouth-piece, as in this way a much larger body of air is thrown into motion Fig. 10. which are filled with the water, while the smoke finds its way between them, and thus imparts its heat to their outer surfaces, instead of their inner surfaces, as is usual. This plan was suggested by the Earl of Dundonald, and in Fig. 5 we have an. illustration of its use. This figure shows a section of the boilers of the Atlantic steam-ship. Two furnaces are employed here, one bekig placed above the other ; the smoke from the two unites, and, after passing in and out among the vertical tubes, strikes against the bridge at the further end, and thence escapes into the chimney. We must not stay here to notice the many other modifications often made in various marine boilers ; for these, and all other details, the practical student should consult Bourne’s various works on the subject, in which he will find almost every variety figured and described, and in many cases full details as to dimensions and heating surface, for the particulars of which we cannot find space. Locomotive boilers differ in some respects from any of those already described. Instead of being built and fixed in a given place which they are permanently to occupy, they are, as their name implies, portable. The special requirements of the case demand, therefore, that they be made of small dimensions, and as light as practicable. Economy of fuel, though still an im- portant point, is, in these, subservient to economy in space and 10— Vol. I. by it. There is usually a small pipe fitted to this, so that when the engine is at rest, or getting up steam, a small stream may be allowed to escape. When the engine is in action, the waste steam from the cylinders, which escapes at a con- siderable pressure, is commonly employed, and this it is which produces the series of puffs which may so frequently be observed issuing from the funnel of a locomotive. The draught produced in this manner is so strong that sometimes small pieces of ash or cinder are drawn from the furnace and thrown out of the funnel. These are, of course, very dangerous, and in dry weather crops have thus been set on fire ; a screen is therefore employed to intercept them, and let them fall down to the foot of the chimney. In American locomotives the top of the funnel is usually con- siderably enlarged, and fitted with a contrivance known as a “spark-trap” or “spark-arrester.” This is more necessary there on account of the prairies, which in a dry season are very easily fired, and also because wood is often burnt, and this throws off more sparks than coal does. The details of this trap will easily be understood by reference to Fig. 6. The two inverted curves, h h, placed above the central funnel g, arrest the sparks, and throw them down into the chambers, i i, where they remain, while the smoke and hot air escape through tha shaded apertures. 146 THE TECHNICAL EDUCATOR. Coke alone ought to be burnt in locomotive boilers, so as to prevent the smoke which is often produced in considerable quantity ; but this regulation is by no means rigidly adhered to, and often dense volumes of smoke may be seen issuing from the funnel. The furnace-bars are usually placed so as to slope considerably, and by carefully introducing the coal in front it becomes coked, the smoke given off being mixed with the air and partially burnt in the further part of the furnace ; but even with this precaution a good deal of smoke is often given off when coal is employed. Locomotives for use in countries where wood is plentiful and cheaper than coal, are made with special furnaces for burning wood. The main difference consists in the necessity for an increased area of heating surface, as the heat produced is less than where coal is employed. In an ordinary locomotive about five square feet of heating surface per nominal horse-power is the usual allowance. The following details of a locomotive passenger engine, ex- hibited by Messrs. JR. Stephenson and Co. at the Paris Exhibition in 1867, will give a general idea of the dimensions of ordinary passenger locomotives. Goods engines are, of course, made much heavier and more powerful, speed being in them of much less importance than tractive force. The diameter of the cylinders was 16 inches, and the length of stroke 22 inches. The heating surface of the firebox was 83 square feet, and in addition to this there were 161 tubes, 2 inches in external diameter and 11 feet 4 inches long, pre- senting in the aggregate a heating surface of 960 square feet. The boiler was 4 feet in diameter, and might be safely worked up to 190 pounds pressure per square inch, being made of 4-inch boiler plate. The driving-wheels were 6 .V feet in diameter, and sustained nearly one-half the weight of the engine, which was about 30 tons. There are many general features common to nearly all forms of boilers, to which we must now turn our attention, for at present we have mainly been concerned with the shape and arrangement of the various parts. Copper has occasionally been employed as the material of which they are constructed, and in many respects it is the best material, as it is less liable to become incrusted with the deposit from the water, and is also more durable than iron. The greatly increased expense, however, precludes its adoption, and boilers are almost uni- versally constructed of wrought-iron plates. The best plate- iron should be chosen for this purpose, and it should be very tough, so as to withstand the pressure. The plates are cut so as to overlap one another to a slight extent, and, after being bent to the proper curvature, are firmly riveted together in the manner shown in Fig. 7. The holes should be very carefully punched or drilled, so as to be just the same distance apart in the two plates ; if this is carelessly done, so that the holes do not exactly correspond, and the plates have to be forced together by “ drifts,” and then riveted, the strength of the boiler is much impaired. When the plates are brought to- gether they are temporarily secured, and then a rivet is inserted in each of the holes. The rivets, which should be of the best Lowmoor iron, are first heated in a furnace till they are quite soft ; they are then inserted, and immediately hammered down so as to form a good and solid head. As it cools and con- tracts the rivet draws the plates closer together, and thus forms a tight joint without any packing being introduced. The rivets should be placed at distances of about two inches from centre to centre. When the boiler is completed, the joints are carefully caulked — that is, the inner edge is forced into closer contact by means of a hammer and cold chisel or punch, and before being used it should be tested by forcing cold water into it till the pressure exceeds that to which it will ever be subjected when at work. Any leak will thus be easily detected. Eings of well-made angle iron are placed round the ends, and also at intervals along the length. Internal stays or struts are also introduced wherever they are considered necessary, to guard against the boiler bulging or collapsing. The different plates should be so arranged that the seams do not form a continuous line either round or along the boiler, each being intermediate to those in the adjoining plates. The reason of this is that the plates become somewhat weakened by the rivet-holes, and the boiler might under pressure part at the seams. The thickness of the plate-iron employed depends upon the pressure at which the boiler is to be worked, and also upon its diameter. The following is a rule which will give the minimum thickness of plate that ought to be employed, and it is, of course, better to be on the safe side, and exceed rather than fall short of this : — - Multiply the internal diameter of the boiler expressed in inches by the maximum pressure in pounds per square inch of surface, and divide the product by 8,900 ; the result will give the thickness of the plate in inches. An example will render this more clear. Suppose we have a boiler whose diameter is 4 feet, and it is required to work it to a pressure of 70 pounds, what thickness should the plate be ? Multiplying 48 by 70 we get the product 3,360, which, divided by 8,900, gives us - 377 as the thickness required. The usual thickness of the plate employed is about three- eighths of an inch, and the rivets have a mean diameter of about five-eighths of an inch, though they vary more or less from this. The plates to which the tubes are fastened in tubular boilers are made considerably thicker, as the number of holes drilled in them materially lessens their strength. For the same reason, whenever an opening is cut in the boiler to admit the steam-pipe or any other fitting, it is well to rivet an internal block round the opening, so as to compensate for the diminished strength. As a result of many experiments, it is found that the tenacity of boiler-plate increases with the tem- perature up to about 500° or 600° Fahr., but beyond this it diminishes. In every boiler it is necessary to provide some opening suf- ficiently large to enable a man or boy to get inside, in case of any repairs being necessary. This opening is known as the “ manhole,” and must be so arranged that it can at pleasure be closed so as to be perfectly steam-tight. The plan for a long time adopted was to cut an oval hole in the boiler, and procure a plate about an inch or two larger on each side. This could be inserted sideways through the opening, and the edge being smeared with red lead or some similar substance, it was held in its, place by means of a screw fixed to it, which passed through a hole cut in a movable arch, placed outside the boiler over the opening. By screwing t'he nut on the screw, the plate was drawn tightly against the boiler ; and the pressure of the steam being exerted outwards, aided in keeping it firm in its position. This plan has, however, gone almost out of use, and man- holes are now constructed on the plan shown in Fig. 8. A circular or oval aperture is cut in a convenient portion of the upper surface of the boiler, and a short tube with a flange at the lower end, so made as exactly to fit the curvature of the boiler, is fitted on over the opening. This tube is securely fastened to the boiler by means of screw-bolts and nuts ; pack- ing is also introduced to render the joint tight. On the upper end of the tube is another flange, made quite true, so that a thick plate of iron may be firmly bolted to it, and close the opening steam-tight. Copper wire is sometimes employed in this case as a packing, a ring of it being laid on the surface of the flange, and as the screws are tightened the wire becomes flattened, so as to give a very perfect joint, and one not likely to become injured by the heat. In addition to this opening, another is required to enable the boiler to be emptied when necessary. The water used often contains a large amount of various mineral salts in solution, and as these cannot pass away with the steam, the water in the boiler becomes so saturated that it deposits a portion as a crust on the internal surface. It is therefore advisable occasionally to let a considerable portion of the water in the boiler escape, and this may be effected by opening this blow-off cock, as it is termed. (Fig. 9). At a convenient portion of the under-side of the boiler an opening is made through the plate, and one end of a large pipe is inserted in this, the other end being closed by a valve able to withstand the pressure of the steam. This valve has a square spindle, and is usually situated just in front of the boiler, or in the ashpit, so that it may easily be got at when required, without being in the way under ordinary circumstances. Were the boiler left quite unprotected externally, a very large amount of heat would be lost by radiation from its sur- face, and the building in which it was placed would soon become extremely hot. To guard against these inconveniences, the boiler should be surrounded by some material which is a bad conductor of heat, and which will therefore prevent its escape. For this purpose sawdust is found to answer very well indeed. BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS, ETC. 147 ii many cases, therefore, the boiler is surrounded with a casing >r ■•lagging” of wood stuffed with sawdust, and when this is one the boiler-room will be quite cool. The steam-pipes and the cylinder of the engine are frequently icketed in a similar way. Patent felt and various fibrous ubstances are in some cases employed in place of sawdust, and nswer the same end. In locomotive boilers some protection of his kind is very necessary, since they are so much exposed to ;he air and weather that the loss of heat would be very large Lnd serious. An incidental advantage of casing the boilers is chat when protected they may be touched with impunity, and thus many burns are avoided. If we examine any boiler we shall find several appendages pifixed to various parts : these we must now describe. When a, boiler is started it is filled with water up to a certain fixed Level, and it is very important that this level should be main- tained almost uniform. The flues are so arranged that no portion of the boiler-plate or tubes shall be exposed to the direct action of the heated air, unless it is protected by being covered inside with water. Some of this^ water, as soon as the temperature rises, becomes con- certed into steam, and thus keeps the plate from becoming in duly heated. If now the level of the water falls too low, a portion of the surface will be exposed, and may not improbably be injured by being overheated, and thus rendered so soft as to bulge. Many explosions have arisen from this cause, and the need of great care will therefore be easily seen. As the engine -S at work, a portion of the water is converted into steam, and thus the level inside the boiler is continually falling : we want, therefore, some easy mode of indicating at all times the exact Level, and also of introducing fresh supplies of water to take the place of that evaporated. The simplest mode of indicating this is by means of a ‘water gauge,” which is shown fixed on the end of the boiler it B (Fig. 10). This consists of a thick glass tube communi- cating above and below with the boiler, so that the level of the water in the glass is the same as that of the water inside the boiler. The gauge is usually provided with cocks, as shown in Fig. 11 ; by means of those at A and B it may be quite cut off from connection with the boiler, so that in case of the glass becoming accidentally broken, the steam and water can at once be prevented from escaping, and a fresh glass can easily be introduced. An additional cock is placed at c, by which the water in the tube can be allowed to escape from it. The tube is usually fixed into its sockets, D, D, by a screw-ring, an india- rubber packing being introduced to render the joint steam-tight. Another plan frequently employed for ascertaining the level of the water is to place two cocks, A, a (Fig. 10), in the end of the boiler, the one being an inch or two above the other, and the level of these is so arranged that the one shall be a little below the normal level of the water, and the other about as much above it. When, therefore, the water is at the proper height, steam should issue from the upper one when it is opened, and water from the lower one. Should it at anv time fall too low, steam will issue from both, and the engineer should then immediately set the feed-pump in action, so as to introduce 1 fresh supply of water. If, on the other hand, water issues from both cocks, it shows at once that there is too much water, whereby steam space is curtailed, and the proper action of the boiler is somewhat interfered with. As a, general rule it is found best to have as much steam 3pace in the boiler as is equivalent to about eight times the contents of the cylinders ; in a small boiler it is well, however, to allow rather more. One disadvantage of curtailing the steam space is that the steam carries with it a larger amount of water in a fine state of division, and this is deposited in the cylinder. To guard against this as much as possible a steam dome (c, Fig. 10) should be provided, and the steam-pipe should start from its highest point. lhe door by which fuel is introduced into the furnace of the engine shown in Fig. 10 is at d, while the ashpit is imme- diately below it. The cock at E shows the appliance by which the quantity of water in the boiler can be reduced at pleasure, or by which the boiler may be emptied when necessary. This sock, and the manner in which it is affixed to the bdiler, is shown on a larger scale in Fig. 9. I .The description of the arrangements usually employed for injecting water into the boiler we must defer to our next lesson. BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS. IV.— JAMES TAYLOR. BY JAMES GRANT. James Taylor, generally understood to be the first person who applied the power of steam to inland navigation, was bom on the 3rd of May, 1758, at Leadhills, a Lanarkshire village, which is perched amid a complete wilderness of dismal and heathy mountains, the most sterile and bare perhaps in Scotland. This victim for such he proved to be — of a life of disappoint- ments received the rudiments of his education at the academy of Closeburn, in Dumfriesshire, a free school, which was hand- somely endowed by a gentleman named Wallace in 1723. Iso- lated though his native village is still, it has possessed a good library since 1741 ; and of the contents of its volumes young Taylor is said to have amply availed himself. After graduating in medicine, he was employed by Mr. Patrick Miller, of Dalswinton, as tutor to his two sons, who were study- ing at the University of Edinburgh. It was the wish of Mr. Miller that Mr. Taylor, whoso scientific attainments had been warmly praised by a mutual friend, should assist him in certain mechanical pursuits, with which he was in the habit of amusing his leisure hours ; and in the year mentioned, he happened to be engaged in a series of operations for adding paddle-wheels to sailing-ships, with the view of rendering them independent of wind and tide, so that they could be enabled to avoid currents or lee-shores, and extricate themselves from various perilous positions — somewhat of the old Archimedean "idea of machinery driven by human agency. Taylor, who had a strong love of mechanics, entered warmly into the idea, and aided his patron in the construction of a doublo vessel, sixty feet long, having intermediate paddles which were revolved by a capstan that was worked by human labour ; and this craft they launched and tried with success on the waters of the Forth in the spring of 1/87, and easily succeeded in distancing a smart custom-house vessel which was contented to sail under canvas. The success of this attempt convinced Taylor of the great utility of paddles ; but perceiving that the crew at the capstan soon became exhausted, he conceived that some superior mecha- nical labour was necessary to render their invention of value to the nautical world. After much thought, he wrote to Mr. Miller on the subject, and received a reply which showed that their ideas were similar. “ I am of the same opinion,” he wrote, “and that power is just what I am in search of. My object is to add mechanical aid to the natural power of the wind, to enable vessels to avoid and to extricate themselves from dangerous situations, which they cannot do on their present construction.” The letter concluded by requesting him to suggest some plan calculated to accomplish this purpose. Mr. Taylor applied himself to a close consideration of all the mechanical powers already in use, but failed to be convinced of the possibility of applying any of them to this new purpose, till at length the steam-engine presented itself to him. This idea was not entirely new, for though Taylor may never have heard of Blasco de Garay, a Spanish merchant captain of that name, in the year 1543, during the reign of the Emperor Charles V., conceived the idea “of an engine able to move large vessels in calm weather, without the use of oars or sails;” and this engine he actually tried on board of a 200-ton ship named Let Trinidad , in the harbour of Barcelona ; but all we know of it is, that it consisted of a boiler, and an axle laid across the ■vessel’s deck, with a wooden wheel at each end— and that some- how it proved a failure eventually. On suggesting the adoption of the steam-engine to nautical purposes, Taylor found that he excited in Mr. Miller more astonishment at the novelty than respect for the feasibility of the plan ; but though somewhat startled himself at the boldness of his own conception, he was, nevertheless, convinced of its being perfectly practicable. Though well skilled in mechanics, Mr. Miller made many objec- tions, some of which were on the score of expense and risk, thinking that steam-power would be unavailing in those critical circumstances which it had been his chief project to obviate or conquer. “ In such cases,” he wrote, “as that disastrous event which happened lately, the wreck of a whole fleet upon a lee-shore off the coast of Spain, every fire on board must be extinguished. 143 THE TECHNICAL EDUCATOE. and of course such, an engine could be of no use.” But Taylor bad thoroughly considered tbe subject, and, undaunted by ob- stacles, urged that, if inapplicable to sea-going vessels, the new motive power might at least prove useful on canals, estuaries, and inland lakes. After long consideration, Mr. Miller con- sented to assist him in the matter, and asked him to prepare sections and other drawings to show how the engine and external paddle-wheels were to be connected. Taylor did so, and his friend, though still unconvinced that the project was possible, agreed to be at the expense of the experiment, provided the sum required was not too heavy, as he candidly confessed that of the power of steam he knew nothing. They were then in the country, at Mr. Miller’s mansion of Dalswinton, and it was fully arranged that on their return to Edinburgh in winter, the engine was to be constructed. During the summer of that year Mr. Miller had drawn up an account of all his experiments upon shipping, and, at Taylor’s suggestion, introduced an allusion to steam as an agent probably to be employed in the propulsion of his vessels ; and copies of this work were transmitted to the King, the Ministry, to the leading members of the Upper and Lower Houses, the President of the United States of America, and to all the maritime powers of Europe. In the winter of 1787, when Mr. Miller had returned to the Scottish capital, he empowered Mr. Taylor to set about the construction of the intended engine ; and the latter employed a young engineer named Symington, who was then residing in Edinburgh for the study of mechanics, and who had already attempted some improvements on the steam-engine. After long discussion, it was agreed that the latter should form it on a plan of his own, and that the great experiment should be made almost privately, ill the ensuing summer, on the Loch of Dal- swinton, in Dumfriesshire. Several months were occupied in the construction of the engine, to see after which Mr. Taylor remained in town, while his patron and pupils returned to the country. At length, to his joy, it was completed, and he pro- ceeded with Symington to Dalswinton, where, on the 14th of October, 1788, the great experiment was made. The event had been noised abroad, however, and on that day the beautiful little lake which lay on Mr. Miller’s property was surrounded by a great crowd of spectators. The vessel built for the purpose was a double one, and the engine, which was furnished with a four-inch cylinder, was placed in a species of framework on the deck, and the experiment, which was ultimately destined to effect such a revolution in nautical matters, proved a perfect success. The little vessel moved at the rate of five miles an hour, and the connection between the engine and the paddles was free from all clumsiness ; while it also appeared that all dread from the introduction of a furnace into a structure so inflammable as a wooden ship could be obviated. For several days the experiment was repeated, and thus the first steamship continued to traverse in safety the little inland lake, to the wonder and delight of all who came to see her; and a full account of his invention, or adaptation of steam to seafaring purposes, was drawn up by Mr. Taylor and inserted in the Scot’s Magazine of the following month. Before applying for a patent to protect their joint invention, Messrs. Taylor and Miller deemed it necessary to test it more fully, by its applica- tion to a vessel of a larger size ; and the former, accompanied by Symington, had one constructed at the Carron Foundry in the summer of 1789. This craft was of considerable dimensions, and had an engine the cylinder of which was eighteen inches in diameter. Winter drew near before she was completely fitted up and launched on the Forth and Clyde Canal, in presence of the Carron committee of management, and of all who were interested in the matter. » The steam was got up, and the vessel moved smoothly for a considerable distance beyond Lock Sixteen ; but on giving the engine full play, the flat boards of the paddle-wheels, which had been too slenderly constructed, broke, and put an end to the voyage. Re-constructed on a stronger principle, she made a second trip on the 26th of December, when she attained seven miles per hour ; and a full account of the invention, written bv the future Lord Cullen for the Edinburgh newspapers of 4v90, brought it prominently before the country as a new means for extending inland navigation. But here for a time the matter ended ; for Mr. Miller became so deterred by the excessive expense on one hand, and a necessity for improving his estate on the other, that he declined to proceed further with the project. He was somewhat disappointed by the ex- travagance of the engineer, whose expenses had gone far beyond his estimate ; and Taylor was quite unable personally to pro- secute the scheme so auspiciously commenced. Our Government ignored the. inventor and the invention ; and Mr. Fergusson, younger, of Craigdarroch, pitying his disappointment, sought, but in vain, to engage the interest of the Emperor of Austria on the subject. The sudden indifference of Mr. Miller, the attention of tho public to the war of the French Revolution, and the obscure position of Taylor, who was himself unable to do anything — his pecuniary means being most limited — all combined to throw the ■ steamboat into abeyance, and for several years it was forgotten by all but the bold projector, who for some time was thankful to find employment in superintending the working of coal, lime, and other minerals on the estate of the Earl of Dumfries. Eleven years after the second steamer had been permitted to rot at the Carron, Symington, who had commenced business at Falkirk, constructed a third, called the Bundas, on the old plan, and tried her on the Forth and Clyde' Canal; but the company prevented her being set in motion again, as her paddles proved injurious to the banks ; so she, too, was laid up at Lock Sixteen, where she lay forgotten for several years more, though Lord Stanhope, in 1790, had been in communication with Mr. Rennie as to the best mode of applying this novel power, and in that year actually took out a patent for the propulsion of ships by steam. But his plan, though ingenious, was never put in effect, his paddles being placed under tho vessel’s quarter, and made to open and shut like the feet of a duck. Symington was in treaty with the Duke of Bridgewater to introduce steam on his grace’s famous canal, and six boats on his supposed plan — utterly ignoring Mr. Taylor’s — were ordered ; but the duke’s death caused the abandonment of the scheme. Mr. Fulton from America, and Mr. Henry Bell from Dundee, now came to Carron and inspected the Bundas, and the result was that in 1807 the former gentleman launched a steam-vessel on the Hudson, and in 1812 Mr. Bell placed another on the Clyde, each being the first vessels of the kind used for public service in the new and old hemispheres. “ Thus, after all the primary difficulties of the invention had been over- come — when the barque was ready, as it were, to start from the shore, and waited only for the master to give the word — did two individuals, altogether alien to the project, come in and appropriate the honour of launching it into the open sea ! ” On finding that the credit of this important invention, which was his own undoubtedly, was now assigned to others, Taylor lost neither time nor opportunity in asserting his claims. He urged Mr. Miller of Dalswinton to move in the matter, but without success. He kept his own name, however, before the public eye, and on finding that Symington had actually secured a patent, forced him into agreements of sharing the profits, which, however, were never realised. Taylor’s pecuniary cir- cumstances were far from prosperous, and when the mighty importance of steam navigation to the world at large became fully established and understood, his friends urged that he should solicit some reward from Government. In 1824 a state- ment of his invention and his claims was printed and addressed to Sir Henry Parnell, the chairman of a select committee of the House of Commons on steamboats, in the humble hope that his narrative might procure him some remuneration in his old age, for the benefits he had conferred on mankind in general and his country in particular ; but poor Taylor prayed in vain. Not a penny was ever accorded him. Broken in health, crushed and soured by disappointments, and oppressed by penury, this ingenious but unfortunate inventor died on the 18th of Septem- ber, 1825, when verging on his seventieth year. ANIMAL COMMERCIAL PRODUCTS.— VL WOOL (continued). Merino wool is obtained from the migratory sheep of Spain, a breed which is distinguished from the British by bearing wool on the forehead and cheeks ; the horns are large, pon- derous, and convoluted laterally ; the wool is long, soft, and twisted into silky-looking spiral ringlets, and is very superior in its fineness and felting properties. Its closeness and a luxu- riant supply, from the glands of the skin, of yolk or natural oil, ANIMAL COMMERCIAL PRODUCTS. 149 which serves to nourish it and mats the fibres together, render it an excellent natural defence against the extremes of heat and cold. These migratory sheep, amounting in Spain to 10,000,000, are led twice a year (in April and October) a journey of 400 miles, passing the summer in the pastures on the slopes of the Pyrenean mountains, and the winter on the plains towards the south. The word merino signifies an overseer of pasture lands, and is applied to these sheep because in Spain they travel in detach- ments of 10,000 each, under the care of fifty shepherds and as many dogs, with a mayoral or chief shepherd at their head, and have a general right of pasturage all over the kingdom. This celebrated breed is now reared in Saxony and in Aus- tralia, . which has become one of the principal wool-growin^ countries m the world. In 1464 Spain imported ew-s and rams from the Cotswold hills. The Cretan orWallachian sheep, remarkable for the enormous development and magnificent formation of its horns, possesses a fleece composed of a soft woolly under-coat, covered with and protected by long drooping hairs. The wool is extremely fine in quality, and is employed in the manufacture of warm cloaks which are largely used by the peasantry, and which are so thick and warm that they defend the wearer against the bitterest cold to which man can be exposed, MERINO SHEEP. Several of the sheep are tamed and taught to obey the signals m the shepherds ; these follow the leading shepherd (for there is no driving), and the rest quietly follow them. The flocks travel through the country at the rate of eighteen to twenty miles a day, but in open country, with good pasturage, more lei- surely. Much damage is done to the country over which these immense flocks are passing; the free sheep-walk which the landed proprietors are forced to keep open interferes with en- closure and good husbandry ; the commons, also, are so com- pletely eaten down that the sheep of the neighbourhood are for a time half-starved. The sheep know as well as the shepherds when the procession has arrived at the end of its journey. In April their migratory instinct renders them restless, and, if not guided, they set forth unattended to the cooler hills. In spite of the vigilance of the shepherds, great numbers often escape ; if not destroyed by the wolves, there is no danger of losing these stragglers,, for they are found in their old pasture, quietly awaiting the arrival of their companions.” The chief countries which supply us with sheep and lambs’ wool are Russia, Hanse Towns, Argentine Confederation, British Possessions, Africa, British India, and Australia. There are other ruminant animals from which the wools of commerce are obtained besides the sheep. The following are the chief of these : — Angora Goat (Ccupra Angorensis, Hasselquist). — This animal inhabits the mountains in the vicinity of Angora, in Asia Minor. In colour it is milk white ; legs short and black, horns spirally twisted and spreading ; the hair on the whole body is disposed m long, pendulous, spiral ringlets, and is highly valued in Turkey, the finest and most costly Turkish robes being manu- factured from the fleece, which is as soft and fine as silk. It was first brought into the markets of Europe under the name of mohair. Its. exportation, unless in the shape of yarn, was formerly prohibited, but it is now allowed to be exported un- spun. Mohair is transmitted to England principally from Smyrna 35tr THE TECHNICAL EDUCATOR. and Constantinople. It is manufactured into fine shawls, cam- lets, velveteens, plushes, braidings, decorative laces, and trnn- xnin °'3 for gentlemen’s coats. The manufacture is principally carried on at Bradford and Norwich. In 1864, 4,737,330 lb. of mohair, valued at ,11650,191, were imported into the United Kingdom. Thibet Goat ( Capra lvircus ).— The costly and beautiful Cashmere shawls are made from the delicate downy wool found about the roots of the hair of this animal, which inhabits the high table-lands of Thibet, where these shawls are manufactured. These Oriental fabrics are woven by very slow processes, and are therefore very expensive, being sold in Paris at from 4,000 to 10,000 francs a-piece, and in London at from <£100 to =£400. “ The wool is spun by women, and afterwards coloured. A fine shawl, with a pattern all over it, takes nearly a year in making. 1 persons employed sit on a bench at the frame sometimes four people at each ; but if the shawl is a plain one, only two. The borders are worked with wooden needles, there being a separate needle for each colour, and the rough part of the shawl is uppermost whilst it is in progress of manufacture.” To the people of Cashmere this manufacture is very important; about 16,000 looms are continually at work, each one giving employment to three men. The annual sale there is calculated at 30,000 shawls. It has long been the aim of European nations, on account of the beauty and value of these shawls, to imitate them, if possi- ble, and apply to their manufacture the more speedy and elabo- rate methods which modern science has placed within our reach. The French have been most successful, and shawls are now pro- duced at Parisj Lyons, and Nismes, known in commerce as French cashmere, which closely approximate in stuff and style of work to the Oriental, while much lower in price, although still costly. Norwich, Bristol, Paisley, and Edinburgh have also manufac- tured very good imitations of these shawls. The Cashmere wool imported for this purpose comes into Europe through Kasan, on tho eastern bank of tho Volga, and also directly from India and Persia. The quantity of goats’ hair or wool imported in 1867 was 2,648,360 lb. ; tho imports of the same material manufactured were of the value of .£127,093. Alpaca ( Llama Pacos, Gray).— The llamas may be regarded as the camels of South America, to which tribe of animals they belong. They inhabit the slopes of the Peruvian Andes, and the mountains of Chili, keeping together in herds of from 100 to 200, and never drinking when they have a sufficiency of green herbage. Tho alpaca is about tho size of a full-grown deer, and very graceful in appearance. Its fleece is superior to that of the sheep in length and softness, spins easily, and yields an even, strong, and true thread. Pizarro found this animal used as a boast of burden, and its wool employed for slothing by the natives of that country. Alpaca wool arrives in this country in small bales, called bal- lots, weighing about 70 lb., and generally in a very dirty state. It is sorted into eight different varieties, each fitted for a par- ticular class of goods, and then washed and combed by ma- chinery. The principal articles manufactured from it consist of alpaca lustres, fancy alpacas, and alpaca mixtures. Nearly all the alpaca wool imported into England is worked up in the Bradford district. In 1863 our imports from Peru were 2,772,836 lb.; from New Granada, 622,889 lb. ; and from other places in South America, 6,857 lb. The Llama vicuna and L. guanaco, other species of these animals inhabiting the same regions, yield fine hair, but at present of little commercial value. In 1867 we imported 233,703,184 lb. of wool (sheep, lamb, and alpaca) from Europe, South America, South Africa, the East Indies, and Australia. Our exports of wool in 1867, to foreign countries and our colonial possessions, amounted to 90,832,584 lb. The best wool is grown in Germany, which annually produces 67,200,000 lb. The finest kind passes in commerce under the name of “ electoral wool.” Next to Germany, Australia ranks in importance as a wool-growing country ; the merino breed of sheep has been introduced there with unexampled success. In 1807 the first importation of Australian merino wool was re- ceived in England, amounting to only 245 lb. It has now grown to national importance, amounting in 1852 to 36,000,000 lb., valued at £2,000,000 sterling. Probably a more extensive and instructive collection of wools was never brought together than that contributed to the Great Exhibition of 1851, in this country; showing, in a remarkable manner, the extent to which wool-bearing ruminants have been fostered by man, their wide geographical diffusion, and the influence of climate in modifying the characters of their fleeces. Samples of wool were there for inspection and comparison, from Chinese Tartary, Thibet, and India in the East, to the lately redeemed tracts of the United States in the far West ; and from Iceland and Scandinavia to the Cape of Good Hope and Australia. Although Europe now surpasses Oriental nations in the artistic working of cotton and silk, yet the same cannot be said of the manufacture of shawls and carpets ; for, besides the Cashmere shawls made at Kashmir, in the kingdom of Lahore in Thibet, and also at Delhi in British India, carpets of peculiar and unequalled beauty still come exclusively from Persia and ^0 Levani '- VI— LEATHER. Leather is an animal’s skin chemically changed by the process called tanning. The skin is prevented from putrefying, and rendered comparatively impervious to water, by the vegetable astringent, tannin, found in the bark, fruit, and leaves of various plants ; this uniting with the gelatine of the skin, forms a tannate of gelatine. The skin, thus changed, was called by our Saxon ancestors “ lith,” “lithe,” or “lither” — that is, soft or yielding, whence our term “leather.” The skins are first cleansed from hair and cuticle, by being soaked for several days in a pit of lime water ; this loosens tho hair and cuticle, so that it is easily scraped off with a curved knife, upon a half cylinder of wood, called a beam. The hair thus removed is sold to plasterers, who use it in their mortar. The skins are now steeped for a few days in a sour liquor of fer- mented rye or barley, or in weak sulphuric acid. By this pro- cess, called “ the raising,” the pores are distended and rendered more susceptible of the action of the tan. The skins are then put into the tan-pit, in alternate layers, with crushed oak bark, valonia, catechu, dividivi, and other vegetable astringents, and the pit is filled with water. As the tannin is taken up by the skins, it becomes necessary to empty the tan-pit, and add fresh supplies of tanning material and water. The time required to tan the skins, or transform them to leather, depends on their thickness and other circumstances, and varies from four months to two years. When fully tanned, the leather, if cut through, is of a uniform brown colour — anything like a white streak in the centre showing incompleteness in the process. It is now stretched upon a convex piece of wood called a “horse, beater and smoothed, or passed between cylinders to make it more solid and supple, and lastly, dried by suspension in an airy covered building. Tanned leather often undergoes the further operation o: currying, or impregnation with oil. Leather, prepared a already described, when it is received by the currier is by him rendered smooth, shining, and pliable, so as to make it suitable for tho purposes of the shoemaker, coachmaker, saddler, and harness-maker. First, it is soaked in water to render it pliable, then stretched upon the beam and shaved smooth with a knife next rubbed with a polishing stone, and while still wet besmearei with a mixture of fish-oil and tallow, and hung up in a loft ti dry. As it dries, tho water only evaporates, the oil penetrat ing the pores of the leather. The grain, or hair side, is thor blackened with copperas water, or sulphate of iron in solution the iron uniting with the gallic acid of the tan, and producing an inky dye, or a gallate of iron. Leather so prepared ii chiefly used for the uppers of ladies’ shoes. Leather for th< uppers of men’s boots and shoes is blackened on the flesh side or waxed, as it is termed, with lampblack and oil, which i rubbed in with a hard brush. The thick leather for the soles o boots and shoes is simply tanned without being curried. But leather can be made without tannic acid. Skins maj be preserved by means of alum and salt, and leather so made i called in tho trade “ tawed leather,” and is quite as durable am much softer. Gloves are usually made from tawed leather Skins intended to be tawed pass through a series ot preliminar; operations, resembling those by which skins are made ready fo tanning (the use of ordures is, however, indispensable). _ The; are then immersed in a solution of alum and salt, to which, fo the superior kinds of leather, flour and yolk of eggs are addec They are next dried in a loft, smoothed with a warm iron, an PRINCIPLES OF DESIGN. 151 then softened on a stake, when they are dyed of various colours for gloves and ladies’ boots. The French are skilled in this art. At Annonay, a town about fifty miles from Lyons, tawing operations are carried on so largely, that 4,000,000 kid-skins are dressed there annually. It has been computed that France and England consume 6,000,000 eggs yearly in preparing kid leather. These eggs are kept in lime-water by the leather dresser, to preserve them until they are wanted. The average quantity of leather gloves annually made in the United King- dom has been estimated at 12,000,000 pairs. We import also largely from France. In 1867, 10,893,780 pairs were received from that country. The imports of tanned and untanned hides in 1867 were 975,168 cwt. The leathers known in commerce as chamois and buff leather are prepared much in the same way as tanned and tawed leather, only that oil is substituted for the alum and tannic acid. The skin of the chamois is not always used ; more frequently sheep and doe skin. Wash leather is an example of this kind of preparation. Russia leather, the smell of which is so agreeable, is pre- pared in the usual way, then tanned with the bark of the willows ( Salix cinerea and Salix caproea), and afterwards curried with the empyreumatic oil from the bark of the birch tree, which imparts to it its peculiar odour. M. Chevreul, who in- vestigated the chemical nature of this odoriferous substance, called it betuline. Morocco leather of the finer qualities is made from goat- skins tanned with sumach, and inferior morocco, or roan, from sheep-skins. The hair, wool, and grease are removed as usual, and the skin, thoroughly cleansed, is reduced to the state of simple membrane, called pelt. Each skin is then sewn by its edges into the form of a bag, the grain, or hair side, being out- wards. A strong solution of sumach having been put into the bag, it is distended with air like a blown bladder, and the aper- ture tied up. About fifty of these skins, so distended, are thrown into a tub containing a warm solution of sumach — the tanning liquor — in which they are allowed to float. In a few hours they are tanned, removed from the bath, the sewing is then undone, and they are scraped and hung up in the drying loft. Red morocco leather derives its colour from cochineal, which, boiled in water with a little alum, forms a red liquor, in which the skins are immersed before being put into the sumach bath. In the case of black morocco, the skins are sumached without any previous dyeing, and the black colour is given by applying with a brush, to the grain side, a solution of red acetate of iron ; blue is communicated by indigo ; puce colour by logwood, with a little alum: green is derived from Saxon blue, followed by a yellow dye made from the chopped roots of the barberry ; and for olive, the skins are first immersed in a weak solution of green vitriol, and then in a decoction of bar- berry root, containing a little Saxon blue. The thickest and most substantial leather now in general use is that made from the hides of the wild horses found throughout the pampas in South America. It is employed for the soles of boots and shoes, harness, saddlery, leather trunks, hose for fire- engines, pump-valves, military gloves and belts. Deer-skins are used for the finer kinds of morocco leather, and for bookbinding. Calf-skins, tawed, are used by bookbinders ; tanned and curried, by boot and shoemakers. Sheep-skins, simply tanned, are em- ployed for inferior bookbinding, for leathering bellows, and other purposes where a cheap leather is required. Morocco leather is used for coach linings, for covering chairs and sofas, bookbind- ing, pocket-books, etc. A thin leather, called shiver, is used for hat linings. There is an immense demand for thin leathers, and machinery for this purpose is now constructed with such accuracy that it will split a sheep-skin into three parts. The grain side of the skin is then used for skiver, the middle for vellum and parchment, and the flesh side is transferred to the glue maker. On parchment we inscribe our deeds, and on velhttn all our State documents. The leather manufacture of Great Britain is of great import- ance, and ranks iiext in value and extent to those of cotton, wool, and iron. The census of 1851 showed that 350,000 persons were engaged in the different branches of the leather manufacture, and its entire annual value has been computed at more than .£20,000,000 sterling, the leather for boots and shoes alone being valued at .£12, 000,000. Most of the leather made in the kingdom, and the articles manufactured from it, are used at home. Our exports are, however, considerable, and in 1867 were as follows : — Tanned unwrought 43,584 cwt. Boots and shoes 3,284,883 pairs. Saddlery and harness .... Wrought leather of other sorts . 1,176,1461b. Value. £428,268 950,794 220,475 258,541 The Australian colonies are the great purchasers of these goods. PRINCIPLES OF DESIG N.— I V. By Christopher Dresser, Ph.D., F.L.S, etc. EMPLOYMENT OP THE GROTESQUE IN ORNAMENT. OME other principles of a less noble character than those which wo have already noticed as entering into ornament yet remain to be men- tioned. Man will be amused as well as in- structed ; he must be pleased as well as en- nobled by what he sees. I hold it is a first principle that ornamen- tation, as a true fine art, can administer to man in all his varying moods, and under all phases of feel- ing. Decora- tion, if properly understood, would at once be seen to be a high art in the truest sense of the word, as it can teach, elevate, refine, induce lofty aspirations, and allay sorrows ; but we have now to notice it as a fine art, administer- ing to man in his various modds, rather than as the handmaid to religion or morals. Humour seems to be as much an attribute of our nature as love, and, like it, varies in intensity with different individuals. There are few in whom there is not an amount of humour, and in some this one quality predominates over all others. It not unfrequently happens that men who are great thinkers are also great humorists — great talent and great humour being often combined in the one individual. The feeling for humour is ministered to in ornament by the grotesque, and the grotesque occurs as the work of almost all ages and all peoples. The Ancient Egyptians employed it, so did the Assyrians, the Greeks, and the Romans ; but none of these nations used it to the extent of the artists of the Celtic, Byzantine, and the “ Gothic” periods. Hideous “ evil spirits” occurred on the outside of almost every sacred Christian edifice at one time, and much of the Celtic ornament produced by the early monks consisted of an anastomosis, or network of often grotesque creatures. The old Irish crosses were enriched with this kind of orna- mentation,* and some of these decorative embellishments are of extraordinary interest ; but those who have access to the beautiful work of Professor Westwood on Celtic manuscripts will there see this grotesque form of ornament to perfection. As regards the Eastern nation’s, while nearly all have employed the grotesque as an element of decorative art, the Chinese and Japanese have employed it most largely, and for it they manifest a most decided partiality. The drawings of dragons, celestial lions (always spotted), mythical birds, beasts, fishes, insects, * Casts of one or two of these can he seen in the central transept of the Crystal Palace at Sydenham. 152 THE TECHNICAL EDUCATOK. and other supposed inhabitants of the Elysian plains which these peoples produce, are most interesting and extraordinary. Without in any way going into a history of the grotesque, let us look at the characteristic forms which it has assumed, and what is necessary to its successful production. We have said that the grotesque in ornament is the analogue of humour in literature. This is the case; but the grotesque may represent the truly horrible or repellant, and be simply repulsive. This form is so seldom re- quired in ornamention \that I shall not dwell upon it, and when required it should always be associated with power ; for if the horrible is feeble it cannot be correc- tive, but only revolting, like a miserable deformed animal. I think that it may be taken as a principle, that the further the grotesque is removed from an imitation of a natural object the better it is, provided that it be energetic and vigorous ■ — lifelike. Nothing is worse than a feeble joke, unless it be a feeble grotesque. The amusing must appear to be earnest. In conjunction with this chapter we engrave a series of grotesques, with the view of illustrating my meaning, and I would fain give more, but my space will not permit me to do so. The initial letter at the commencement of this lesson is a Celtic letter S, formed of a bird. It is quaint and interesting, and is sufficiently unlike a living creature to avoid giving any sense of pain to the beholder, while it is yet in a most unnatural position. It is, in truth, rather an ornament than a copy of a bird, yet it is so suggestive as to call forth the thought of one of the “feathered tribe.” It should be noticed, in connectisn wth this figure, that the inter- stices between certain portions of the creaturo are filled by a knot. This is well — the whole thing being an ornament, and not a naturalistic representation. Fig. 11 is a Siamese grotesque head, and a fine sample it is of the curious form of ornament which it represents. Mark, it is in no way a copy of a human head, but is a true ornament, with its parts so arranged as to call up the idea of a face, and nothing more. Notice the volutes forming the chin; the grotesque, yet highly ornamental, lines forming the mouth and the upper boundary of the forehead, and the flambeauant ears : the whole thing is worthy of the most careful study. Fig. 12 is a Gothic foliated face ; but here we have features which are much too naturalistic. We have, indeed, only a hideous human face with a marginal excrescence of leafage. This is a type to be avoided ; it is not droll, nor quaint ; but is simply unpleasant to look upon. Fig. 13 is a fish, with the feeling of the grotesques of the Middle Ages ; it is modified from one in Colling’ s “ Ar t rofiage.” It is a good type, being truly ornamental, and yet sufficiently suggestive. In order that I may convey to the reader a fuller idea of my views respecting the grotesque than I otherwise could- I have sketched one or two original illustrations — Fig. 14 being suggestive of a face, Fig. 15 of a skeleton (old bogey), and Fig. 16 of an impossible animal. They are intentionally far from imitative. If naturalistic some would awaken a sense of pain, as they are con- torted into curious posi- tions, whereas that which induces no thought of life or feeling induces no sense of pain. Of all grotesques with which I am acquainted, the dragons of the Chinese and Japanese are those which represent a combination of power, vigour, energy, and passion most fully. This is to be accounted for by the fact that these peoples are believers in dragons. When the sun or moon is eclipsed they believe that the luminous orb has been swallowed by some fierce monster which they give form to in the dragon, and upon the occurrence of such a phenomenon they come with cans and kettles to make rough music, and thus cause the monster to disgorge the luminary, the brilliancy of which it would otherwise have for ever extin- guished. I can imagine a believer in dragons drawing these monsters with the power and spirit that the Chinese and Japanese do ; but I can scarcely fancy that a disbeliever could do so — a man’s very nature must be saturated with a belief in their existence and mischievous power, in order that he may embody in his delineation such ex- pressions of the assumed character of this ima- ginary creature as do the Chinese and Japanese.* Although I am not now considering the struc- ture of objects, I may say that the grotesque should frequently be used where we meet with naturalistic imitations. We not unfrequently see a figure, naturally imitated, placed as a support to a superincumbent weight — a female figure as an archi- tectural pillar bearing the weight of the entablature above, men crouched into the most painful positions supporting the bowl of some colossal fountain. Natural- istic figures in such positions are simply revolting, however perfect as works of sculpture. If weight has to be supported by that which has a resemblance to a living crea- ture of any kind, the semblance' should only be suggested ; and the more unreal and woodeny (if I may make such a word) the support, if possessing the quaintness and humour of a true grotesque, the better. It is not the business of the ornamentdst to produce that which shall induce the feeling of con- tinued pain, unless there is some exceptional reason for his so doing, and such a reason is of rare occurrence. * I have met with many fine Japanese and Chinese grotesques at the warehouse of Mr. Goode, of 32, King William Street, City, whose taste in importing these things is great. 154 THE TECHNICAL EDUCATOR. WEAPONS OF WAR.— III. EY AN OFFICES OF THE ROYAL ARTILLERY. GUNPOWDER. The powder used for the charges of small arms necessarily influences in a great degree the efficiency of the weapons. There is no direction in which English artillerymen have laboured so determinedly, and, on the whole, successfully, as in the direction of the improvement of the powder for guns and small arms. For the moment we are engaged with small arms only ; but it will, perhaps, be convenient if we deal with the subject of powder as a whole, and take this occasion to speak generally of the different descriptions of gunpowder in use in the British service. 'Gunpowder, as all the world knows, is an intimate mixture of saltpetre, sulphur, and charcoal. The proportions of the ingredients differ in various countries. The following table, extracted from Captain Goodenough’s “ Notes on Gunpowder, Prepared for the Use of the Gentlemen Cadets,” shows the rates, or per-centage, of the several ingre- dients in the powder of different countries : — Saltpetre. Sulphur. Charcoal. England (Government powder) Prance 'l 75 10 15 Prussia United States 1 75 12-5 12-5 Russia . 73 '78 12-63 13-59 Austria 76 12-5 11-5 Spain . 76-47 12-75 10-78 Sweden 75 16 9 China . • • . 73 14-4 9-6 Switzerland . 76 14 10 English powder has long held almost undisputed supremacy as to excellence of quality and strength. The purity of the ingredients employed, and the elaborate care which is bestowed upon all the processes of manufacture, result in the production of an explosive and propellant agent of great power. Indeed, the chief objection to the English powder has been that it is too strong. We believe that we may safely affirm that there is no powder in the world equal to that which is produced at the Government mills at Waltham Abbey, unless it be the powder which is turned out from the mills of some of the leading English makers, such as Curtis and Harvey, Hall and Sons, and others. The action of gunpowder is due to the almost instantaneous decomposition of the saltpetre by the charcoal, the latter being burned by the oxygen of the saltpetre, with which it combines in the act of burning to form carbonic acid gas. At the same time the oxygen in the saltpetre becomes separated from the nitrogen with which it was combined. The explosive force of gunpowder is mainly due to the sudden evolution at a high temperature of these two gases — carbonic acid and nitrogen. In this action, it will be observed, the sulphur plays apparently no part. Indeed, it is a fact that gunpowder may be made without sulphur at all ; but the ex- plosive force of a mixture of saltpetre and charcoal is com- paratively feeble, because the evolution of the gases in such a mixture is very slow, and the temperature of the gases, and the consequent expansion, relatively small. Sulphur, therefore, which ignites at a much lower temperature than either of the other two ingredients, is added to render the action more rapid, and, by raising the temperature of the gases, to increase their expansive power. Sulphur also increases the volume of the gas, by combining with the potassium in the saltpetre, and so liberating the oxygen with which that potassium was combined, the liberated oxygen becoming available for the burning of the charcoal. It is to the presence of the sulphur that we owe the white smoke and the solid residue' of fired gunpowder. The smoke and residue are chiefly sulphate of potassa (K 2 S0 4 ) and car- bonate of potassa (K 2 C0 3 ), resulting from the combination of the sulphur with the potassium. Some of the sulphide of potas- sium is carried out by the escaping gases, when it catches fire and burns— forming flash and smoke ; that portion of it which is not carried out being left in the form of a solid residue. .The explosion of a charge of gunpowder can be effected by | raising a single grain of the powder to a temperature of about j 600°, which is about the temperature at which the sulphur sublimes. Alien one grain is ignited, the resulting gases are transmitted by their own expansive power through the inter- stices, igniting other grains, and finally consuming the whole charge. From this it follows that the ignition of a charge of gunpowder is not necessarily — indeed, it is not under any cir- cumstances — really instantaneous. Gunpowder, in fact, burns, but the combustion generally takes place at so great a rate that, it practically amounts to instantaneous ignition. This consideration brings us to a very important branch of our subject. Those who have followed us thus far will have recognised that the explosive force of gunpowder is not determined alone by the amount of gas developed. It depends upon three main causes : the amount of gas developed ; the heat evolved, by v - hich the expansion of the gases is influenced ; and the rapidity with which the gases are produced. As to the first two points, we have said all that is necessary for the purposes of the present, paper. As to the third point, it is clear that if the rapidity of the inflammation of the charge depend, cceteris paribus, upon the rapidity with which each grain successively becomes ignited and consumed, it is possible largely to influ- ence the action of the powder by altering the size and shape of the grains. Thus, for example, to put an extreme case: — If the powder were not disposed in grains at all, but existed in the form of a solid mass, like what is technically known as “ press cake,” the inflammation of the mass would be very slow indeed; the flame applied to one portion would flash over the whole surface, and then proceed to consume the mass from outside to within, burning it slowly away in successive layers. If the mass, however, be broken up into an infinite number of small particles, the effect is to open a large number of passages through which the gases at once rush, thus practically igniting each grain in the same instant of time ; and in proportion as the individual grains are of a size and shape which permit of their being readily consumed, so will the burning of the whole mass of powder, and consequently its conversion into gases, be rapidly effected. Here we have the two extremes — of slow and rapid ignition ; extremes which are susceptible of modification at will, and between which lie the various applications which the artillerist makes use of. In short, it comes to this, that the action of gunpowder can be largely influenced by mechanical means, and without prejudice to its chemical character. Of course, the chemical character can be influenced by a change in the propor- tion of the ingredients, in their purity, in their mode of manu- facture, etc. ; but obviously the better course is first to discover, by theory and practice, the best chemical constitution for gun- powder that constitution which is capable of producing the maximum results from the three ingredients of which "gun- powder is composed — and then to seek mechanically to control the violence or rapidity of the action. In practice; this is what we do in England, and the field of experimental inquiry thus opened out is exceedingly wide. One interesting application of this theory is that which was proposed by Mr. Gale, the well-known experimentist, of Plymouth. Mr. Gale, following— although perhaps uncon- sciously— the steps of the French artillerist, Piobert, and those of the Russian chemist, Fadeieff, filled up the interstices of gun- powder with an inexplosive substance, such as finely-powdered glass, and in this way, by cutting off communication between one grain and another, made the powder absolutely inexplosive. Mr. Gale proposed to dilute all powder in store with the ground- glass, and when required for use to sift out the glass, when the powder would resume its natural explosiveness. The idea was ingenious, but it was open to many practical objections, which, in spite of the success that, on the whole, attended the long series of costly experiments which were made, ultimately deter- mined the rejection of the proposition, although at first sight it had appeared to be feasible enough. More useful advantage is taken of the fact that the explosive violence of gunpowder can be readily controlled by mechanical means, in connection with the adoption, for the different natures of fire-arms, of the powder most suited to them. The size of the charge, the nature of the work required to be done, and the reduc- tion of the strain upon the weapon, are the three considerations which mainly influence the determination of the most suitable WEAPONS OP WAR. 155 powder. A few words upon each of these points in succession may be useful. 1. The size oj the charge. — It might be hastily assumed that the size of the charge could not have much influence upon the nature of the combustion, and therefore could not affect the selection of the powder for particular arms. The popular notion would probably be — that if a powder, of a particular size and form of grain and density, burn quicker than another powder in any fire-arm, it must burn quicker in all arms. And this argu- ment would probably go forward to the conclusion that fine- grain powder must, under all circumstances, burn quicker than large grain. Both these opinions would be erroneous. The rapidity of action of gunpowder depends upon (a) the rate of burning of each grain, called the “velocity of combustion;” and (b) the rate at which the grains successively become ignited, called the “velocity of ignition.” In the case of an open train of powder, the velocity of ignition is independent of the interstices between the grains — the flash travels over and along the train, not through it. So also with small enclosed charges. When the distance which the flame has to traverse is inconsiderable, the velocity of ignition is an element of subordinate importance to the velocity of combustion. In the case of very large charges, however, it is otherwise : the velocity of ignition then becomes a more important element. Consequently, according to the size of the charge, those elements which favour velocity of ignition will have a varying importance, and thus it is impossible to predicate from the size and shape of the grain — which are the elements that mainly influence the velocity of ignition— whether a certain powder will be quick or slow. Other conditions being the same, a fine-grain powder will generally burn quicker than a large grain, except in very large charges, where a very fine-grain powder will not burn so quickly as the same powder disposed in larger pieces. 2. The nature of the work to be done bears, of course, directly upon the selection of powder. Thus, in a smooth-bore musket the chief point is rapidity of action ; while, with rifled small arms, regularity of combustion and uniformity of action are of greater importance. Indeed, a very quick powder is unsuited for rifled small arms. In the case of an expanding bullet, such as is used in the Enfield rifle, and which was described in our last paper, it is desirable to make the pressure upon the plug as little of a blow as possible ; hence a comparatively slow action is preferred. And in the case of arms firing non-expanding bullets, such as the Martini-Henry — which will presently be described — too rapid a powder, by escaping over the bullet, tends to cause fouling. Therefore, we find that the powder which was used for the old smooth-bore arms, and which was known as “ fine grain,” wa3 of a size to be retained upon a sieve of 36 meshes to the inch, and to pass through one of 16 meshes. The powder used for the Enfield rifle is of a size to bo retained upon a sieve of 20 meshes to the inch, and to pass through one of 12 meshes. The powder for the Enfield rifle is, however, different from the old smooth-bore powder in other respects than size of grain. It is made with dogwood instead of alder charcoal, the ingredients are more thoroughly incorporated, the density is rather less, and the grains are more rounded, more uniform in form, and more highly glazed. Again, as an example of the adaptation of powder to the work to be done, may be instanced the use of an exceedingly quick powder for the bursting charges of Shrapnel shell, where the powder is required to effect the rupture of the shell and the release of the bullets as instantaneously a3 possible, so as to diminish the possibility of the charge acting upon the balls. Finally, in the case of all rifled guns, it is necessary to select as uniform a powder as possible, and for rifled guns a special powder has generally been employed. 3. The reduction of the strain upon the weapon. — When we have to deal with large guns, we are met by the third consideration which we have named, viz., the importance of reducing the strain upon the gun as much as possible. In the use of small arms this consideration may be ignored. The strength of the barrel is largely in excess of what is requisite to resist the explosion of the regulated charge of gunpowder, however rapid in its action ; and the same holds good with regard to field-guns and guns of moderate calibre. But it is far different when passing from weapons which fire only 70 or 80 grains of powder, or guns which fire only a few pounds, we get among the weapons which consume 40, 60, and 100 pounds of powder at each discharge. The great 35-ton guns built at Woolwich fire 120 pounds of powder — that is, about a barrel and a quarter each. With such charges as these it is necessary to modify the action as much as possible ; it is desirable at the same time to do this without diminishing the power of the gun by any reduction in the strength of the powder. This is a problem which has each year become of increasing importance, as the guns and charges have become larger and the strain more severe. It is a problem which accordingly has actively occupied the attention of artillerists for the last few years. The strain which the gun suffers from most is the violent initial strain at the moment of the first ignition of the charge. If the development of gas be intensely sudden, we have a violent local effect, an expression of irresistible force upon the sides and end of the bore before the shot is moved. A familiar experiment illustrates this. If a charge of powder be placed in a thin glass tube, and a charge of fulminating mercury — which, compared with gunpowder, is intensely sudden and violent in its action — be placed in another ; and if the two tubes be closed with a cork, and their respective charges exploded, the cork will be blown out of the tube which contains the gunpowder, while the tube which contains the fulminate will be shattered to pieces. What we require in a gun is, not to burst it, but to blow out the shot. It is desirable, therefore, with very heavy charges to modify the action of the powder, and this without altering its chemical character and strength. Accordingly, the size and shape of the grains, their density, and the degree of glazing imparted to them — physical conditions which all affect the rate of explosion — are modified in such a way as to make the explo- sion less rapid, and to distribute the pressure more evenly through the bore. With this view the Russians, Prussians, and others employ what is called “prismatic powder powder which is com- pressed into hexagonal prisms, perforated to allow of the passage of the gases. This powder is, no doubt, a great im- provement upon the granulated powders ; but in England it has been found inferior to both “pellet” and “pebble” powders. “ Pellet” powder was adopted provisionally in 1866 for use in very heavy charges. It consists of cylindrical pellets instead of grains — the diameter of the pellets being three-fourths of an inch, and their thickness about half an inch. Latterly, a special committee, which is still sitting, has recommended the adoption of a powder, which, from its representing in form and dimen- sions large pebbles of the size of the top of a man’s thumb, has received the name of “ pebble ” powder. This powder has lately been adopted for use with the heavier rifled guns. Not merely does the use of this powder greatly decrease the local strain upon the breech end of the gun, being far more gradual in ignition ; but it is capable of imparting, with a reduced strain, a far higher velocity to the projectile. Thus, not only is the power of our guns greatly increased, but their time of ser- vice is prolonged in proportion to the less strain imposed upon them. The uniformity of action of, this powder is also greater than that of the ordinary, old-fashioned cannon powder. The maximum pressure exerted upon an 8-inch gun with 35 pounds of pebble powder is estimated at 15'4 tons per inch, as against 29'8 tons exerted by the former cannon powder (“ rifle large grain ”), and the initial velocity of the projectile has been increased from 1,363 to 1,410 feet per second. These are important results to have achieved, and we hope, before this series of papers is concluded, to say something of the instru- ments and means by which this powder question has been worked. It appears, then, that while the chemical constitution of all English powder is the same, the physical characteristics of different powder differ widely, the size of grain ranging from the fine “ pistol” powder, of- which the grains are retained upon a sieve of 72 meshes to the inch and pass through one of 44, up to the leviathan “ pebble ” powder, of which the lumps (for they are hardly to be called grains) are retained between sieves of | and | inch meshes respectively. There is no more important subject to the artillerist and the rifleman than that of powder. It has been appropriately called “ the soul of artillery.” So comprehensive and difficult a subject cannot be exhaustively discussed in a single article, and the foregoing remarks make no pretensions to an exhaustive character. They merely furnish a slight sketch of the more marked features of a very great and interesting subject. 156 THE TECHNICAL EDUCATOR. TECHNICAL DRAWING.— X. DRAWING FOR CARPENTERS: ROOFS. The whole subject of roofs being very fully treated of in the lessons on “ Building Construction,” it will not be necessary in this course to give many examples of them. The following examples are illustrations of roofs in which iron is combined with wood, by which means far greater light- ness is attained than when wood only is employed. In Fig. 70 A A and B B are tension-rods ; by screwing up the nuts at the ends of these, the straining-pieces, d d, are forced upward, and being perpendicular to the principals, they give support to them at their middle points. When these tension-rods are tightened, it will be seen that the tie-rod, c, is also strained, and perfect stiffness is thus attained. Fig. 71 shows the manner in which the principals meet. The apex is covered by an iron plate ; this is bent downward so as to form a base for the the support of the ridge-timber ; a plate extends below the shoe for the attachment of the tension-rods. Fig. 76 is a similar subject, with an extra breadth of plate and a third hole into which the end of a vertical tension-rod 5 which acts as a king-post, is bolted. Fig. 77 shows the cast-iron shoe for the reception of the lower ends of the principals. Fig. 78 is a truss used in a railway-shed in Paris, designed by. M. Armand. This is an application of Emys’ system of building up the arch-beam of plates of timber, and to this is added a drought-iron tie-rod, by which the ends are confined ; this is tightened up by the tension-rod, A b, in the middle. Figs. 79 and 80 are the elevation and plan of the junction at B, showing the means by which the tie-rod is tightened up. Fig. 81 shows another arrange- ment for attaching and tighten- ing a tension-rod. In drawing these examples, the student cannot do better than follow the construction as de- scribed, and draw the various auts, which shall, be at right angles to the tension-rods. The nuts are double in order to cause them to act upon a greater length of the rod than would be the case if single ones were employed. Fig. 72 illustrates the manner in which the nuts act at the lower ends of the principals, a cast-iron boss being attached to the wood-work, with one face slanting, so that in this case also the faces of the nuts may be at right angles to the tension-rods. X* * S roo ^"^ russ on precisely the same principle as the other, the difference being merely that the straining-pieces, A A, are of wood instead of cast iron ; at their lower end, how- ever, they are fitted with a wrought- iron shoe (Fig. 74, b b), into the ringed end of which the tension-rods hook. These hooks are confined by rings, and their ends are then bent round as shown at c c and A. Fig. 75 is a section of a cast-iron double shoe, or housing, for the reception of the upper ends of the principals, and also for members in the order in which they would be employed in the construction. He will, by this mode of proceeding, learn to make a drawing in an intelligent manner, instead of merely copying the lines. It is advisable that the drawing should be made of at least twice the size of the original, and if neatly inked and nicely coloured it will become an important addition to the portfolio. This affords an opportunity of advising each student to provide himself with a portfolio, and to keep his drawings flat. When drawings are rolled one over another, they are put away in a drawer or cupboard (if indeed they are so taken care of) ; those which were drawn first are buried in the depths of the roll, are seldom seen, and are often entirely forgotten; even if taken out for reference, they will not keep flat, but are wrinkled and difficult to measure from. On the other, hand, if the drawings are neatly cut off the board, and kept in a portfolio, they are constantly kept before the eye, and the student is thus reminded of subjects and of principles, TECHNICAL DRAWING. 157 which would otherwise have formed only a single study, possibly never to be looked at again. Portfolios may now be had at a very low price, and the student is assured that the amount will be very well laid out. Having drawn the sections of the walls in Fig. 70, draw a horizontal line across from top to top, and projecting beyond the walls as far as the eaves at e e are intended to overhang the walls of the building. failure, each fault will become worse and worse as the work proceeds, and the incorrectness will be so evident that he will have to give up the work in an incomplete state, thus wasting all the time and trouble that have been bestowed upon it. If, however, the student, in making a drawing from any of the examples that have been brought under his notice, should find that either from inattention to some preliminary point of detail or miscalculation of the scale, he is going so far wrong’ Fig. 81. At the middle point of this horizontal erect a perpendicular, and mark on this the height of the angle where the rafters meet. Next draw the rafters, the straining-pieces, D D, and the tension-rods, a a, b b, and the tie-rod c ; then follow the purlins, and the rest of the roof, as shown in the example. The construction at the apex has been shown in Fig. 71, and this is to be followed in the complete drawing. The nuts at the ends of the rafters, too, are to be copied from Fig. 72. The student is again urged to aim at absolute accuracy and refinement in his work, and is warned that unless he is very careful in the elementary operations the drawing will be a that he is obliged to give up the piece of work that he is engaged on, he should not be discouraged, but renew the attempt on fresh paper until he has succeeded to his satis- faction. Perseverance, he must remember, never fails to bring its reward. In drawing the ends of the purlins, for instance, the greatest care must be taken that they are all one size, and that the spaces between them are equal. This will be best accomplished by using two pairs of dividers, the one to be kept to the width of the purlins, and the other for the spaces. This will avoid the inaccuracy caused by frequently changing the size held in the instrument, and will be by far the more rapid plan. 158 THE TECHNICAL EDUCATOR. VEGETABLE COMMERCIAL PRODUCTS.— V. Y. PLAIT2JS USEFUL IN THE PREPARATION OF NUTRITIOUS AND STIMULATING BEVERAGES. The Tea-Plant ( Thea viridis, L., and Thea Bohea, L. ; natural order, Camelliacece). — These two species are probably only varieties of the same plant. Native region, China and Japan. The tea-plant is an evergreen shrub which attains in a state of nature a height of from twenty-five to thirty feet, but under cultivation seldom exceeds five or six feet in height, owing to the removal of its foliage by the cultivator. The leaves are alternate, short-petioled, smooth, shining, ovate-oblong, stiff and coriaceous, and slightly dentate. All the numerous varieties of tea known in commerce are referable to one or other of the two grand divisions of green and black tea. Both are most undoubtedly produced by the same plant, the difference in their colour resulting simply from a difference in their mode of preparation. The green teas comprise Twankay, so called after the name of a stream in Chehkiang, where this sort is produced ; Hyson, or, in Chinese, yu-tsien, meaning “ before the rains,” in allu- sion to the time of gathering; Gunpowder, or ma-chu, “ hemp- pearl, referring to the peculiar globular form into which the leaves are twisted ; Imperial — the finest kind of green tea — so named because it is only used by the emperor and the man- darins : this tea consists of the smallest and most tender light- green leaves of the first gathering ; it is not easily obtained in Europe in the pure state. Ihe black teas include Bohea, named with reference to the range of the Bu-i hills, where it is grown ; Congou, or Jcoong- foo, signifying labour or assiduity ; Souchong, or siau-chung, meaning small or scarce sort ; and Pekoe, or pe-kow, “ white hairs,” in allusion to the down on the epidermis of the young spring leaves. The two last are the finest and most expensive of the black teas. The preparation of green tea may be described in general terms as follows : — The leaves are gathered from the shrub, and placed in bamboo baskets ; they are then put into shallow iron pans, placed over charcoal fires, and stirred continually and briskly, the rising steam being fanned away ; after this, they are removed from the pans, and whilst still flaccid with the contained moisture, are placed before the twisters, on a table made of split bamboo, and therefore presenting ridges ; the twisters roll them over with their hands until twisted. The leaves are then spread out and exposed to the action of the air, and afterwards returned to the drying-pans, exposed there to additional heat, and kept continually stirred until the drying is complete, when they are picked, sifted, sorted, and so prepared for packing. Black tea is prepared in the same manner, with this difference, that the fresh leaves, as soon as collected, are thrown together into heaps, and allowed to lie until a slight degree of fermentation ensues, or a spontaneous heating, similar to that which tabes place in a damp hay-stack. This partial fer- mentation of the tea-leaves darkens their colour. All the black teas are grown in Pokien, a hilly and populous district about 200 miles to the north-east of Canton. The green teas are raised in the district of Kianguan, about 750 miles from the same city. Owing to certain peculiarities in Chinese legislation, landed property is much subdivided, so that the tea is generally culti- vated in small gardens or plantations, the leaves being picked by the family of the cultivator. The first gathering takes place in early spring, in the month of April : pekoe and hyson are made from, this crop. It is scarcely over before the air becomes charged with moisture, rain falls, and this, combined with the warmth of the atmosphere, causes the tea-shrubs soon to put forth, in the month of May, the leaves of the second crop. A third gathering is made about the middle of June, and a fourth in August. The leaves of the first gathering are the most valuable, and from these the finest imperial and hyson, with pekoe and similar qualities of black teas, are prepared. The leaves of the last crop are large and old, and consequently make preparations very inferior in flavour and value. During the harvest season, when the weather is dry, the Chinese may be seen in little family groups on every hillside, engaged in gathering the tea-leaves. They strip off the leaves with astonishing rapidity, and throw them into small round baskets made for the purpose out of split bamboo or rattan. •These baskets, when filled, are emptied into larger ones, and immediately conveyed to market, where a class of Chinese make it a business to collect them in large quantities, and partly manufacture them, drying them under a shed. A. second class, known as the tea-merchants, purchase the tea in this half-prepared state, and complete the manufacture, employing in the operation women and children. The tea-mer- chants begin to arrive in Canton about the middle of October and the busy season continues until the beginning of March* being at the height in November, December, and January. The tea . is brought to Canton either by land-carriage or by inland navigation. The roads are' too bad to admit of beasts of burden attached to wheeled vehicles, so that the land-carriage is usually effected by porters. In China tea is the common beverage of the people, being sold in the public-houses in every town, and along the public roads, like beer in England. It is quite common for travellers on foot to lay down their load, refresh themselves with a cup of warm tea, and then proceed on their journey. A Chinaman never drinks cold water, which he abhors and considers unholy; tea is his favourite drink from morning to night, not mixed with milk or sugar, but the essence of the herb itself, drawn out with pure water. The Chinese empire could hardly exist were it deprived of the tea-plant, so habituated are the people to its use ; and there is no doubt that it adds greatly to their health and comfort as a nation. The Japanese usually make tea by pouring boiling water on the leaves, after having first reduced them to powder. Neither the Chinese nor the Japanese use milk or sugar with tea ; and certainly the peculiar taste and aroma of the tea are better appreciated without these additions. Tea. is imported in chests always lined with thin sheet-lead, and with a paper which the Chinese manufacture from the liber or inner bark of the paper mulberry ( Broussonetia papyrifera, L.). It is silky in texture, straw-coloured, and made without size. When the tea is put into the boxes, it is pressed down first with the hand, and then with the feet, after which the boxes are nailed down and stamped with the name of the district-grower or manufacturer. The Chinese colour with Prussian blue the teas which they ship for the foreign market. Only a little of this dye is em- ployed, so that its use is not productive of evil results ; still, the tea would be better without it. The Chinese never dye the teas which they retain for their own use. The green teas of commerce are too often only black teas coloured with Prussian blue. Nevertheless, comparatively speaking, very little adultera- tion of tea is practised by the Chinese. A few leaves of the Camellia and of a species of Rhamnus or buckthorn indigenous to China are found occasionally amongst the tea-leaves, but not to any very great extent. The leaves of such British plants as the beech, elm, willow, poplar, hawthorn, and sloe, are far more abundant, proving that the tea is adulterated after it has arrived in this country. The adulteration is easily detected by comparing the leaves from the teapot with the genuine tea- leaf. Tea is also adulterated with old exhausted tea-leaves, which are re-dried and used again. In 1866, 139,610,0441b. of tea were imported into the United Kingdom, of which quantity 102,265,531 lb. were retained for home consumption ; in the same year we exported 20,245,454 lb. to foreign parts. The consumption of tea by the Chinese themselves is enor- mous. They drink four times as much as we do. With rich and poor of all that swarming population, tea — not such as our working classes here drink, but fresh and strong, and with no second watering — accompanies every meal. The population of China, according to an official census taken in 1825, was 352,866,012, which is more than ten times our population. Estimating our annual consumption of tea at 33,600,000 lb., that of China must be forty times that quantity, or 1,444,000,000 lb. In addition to this there is a very heavy exportation in native vessels from China to all parts of the East where Chinese emigrants are settled, such as Tonquin, Cochin-China, Cambodia, Siam, the Philippines, Borneo, the settlements in the Straits of Malacca, California, and Australia. In comparison with such an enormous amount as this our own consumption sinks into insignificance. The caravan or Russian teas are the best and most expensive of those used in Europe. They are brought overland from China by Russian merchants, who go there annually in caravans, viA OPTICAL INSTRUMENTS. 159 Kyachta. These caravan teas, purchased by the wealthier Russian families, are preferred to those shipped in Canton, which are said to deteriorate in some degree through the sea air, and from being stowed away in the narrow and close holds of the -vessels. Tea was first brought to Europe by the Dutch in 1610, and they had for a long time the monopoly of the trade. But the British East India Company, entering the field as a competitor, soon obtained a fair share of the business. The sole object of the company was to provide tea for the English market ; of this they had the exclusive monopoly until 1834, when the British Government passed an Act which threw open the tea-trade to all disposed to engage in this important branch of commerce. Formerly all the tea received in Europe was cultivated exclu- sively by the Chinese ; now the culture of the tea-shrub is suc- cessfully carried on in other countries. The Dutch were the first to break the charm of the Chinese monopoly by introducing and cultivating the tea-plant in the rich and fertile island of Java. Their first experiment was so successful that numerous tea-gardens were soon under cultiva- tion on the mountain range which runs through the centre of the island, where the plant escapes the scorching heat of the torrid zone, and finds a climate by height, rather than by lati- tude, adapted to its nature. A considerable quantity of tea is now annually shipped from Java to Amsterdam. In 1810 an attempt was made to cultivate the tea-shrub in the Brazils, near Rio de Janeiro, and a colony of Chinese were induced to settle there, and attend to the plantations. But the experiment did not succeed : the shrubs became diseased, and the Chinese formally abandoned them. Another effort made in the same country in 1817 was unsuccessful, owing to difficulties arising from climate, the high price of labour, and the natural indolence of the natives. The experiment, however, was tried once more, and this time successfully, and tea culture is now prosecuted with energy in the Brazils, and with a commensurate amount of success. The Rio Janeiro market is entirely supplied with tea of domestic growth, and the public of Brazil are satis- fied that no plant is more profitable or deserving of attention. Tea is now cultivated in British India. Some years ago it was discovered that the tea-plant was indigenous to our Indian territory of Upper Assam. This plant, supposed to be a distinct species, has received the name of Thea Assamica. It is a more vigorous plant than the Chinese species, and has much larger leaves. It grows in the warm, moist valleys of the Himalaya mountains, the temperature and other conditions there being similar to the circumstances under which the Chinese plant is raised. The! Assam Tea Company was started, and several thousand acres were soon under cultivation in the district stretching fnrom Kumaon to the hill tracts acquired from the Sikhs- The plants grown are chiefly those raised from Chinese seed, the remainder are the indigenous plants of the district. The seeds of the Chinese plant were obtained by Mr. Fortune in China in the summer of 1850, and by him planted in Wardian cases. They germinated during the voyage, and reached their final destination — the plantations of the Himalayas— in fine condition. About 14,000 plants were thus added to the Assam collection. Chinese tea-curers have been induced to settle in Assam, and both black and green tea are now manufactured from the Chinese and Assam plants. The latter produces a very strong tea, which answers well to mix with the low sorts of China tea, and is chiefly used for this purpose. Several large cargoes of tea from Assam have already been received in this country. Land suitable for the culture of tea exists amongst the Himalayas to an almost unlimited extent, and the quantity raised annually and exported must increase as the plantations are extended and multiplied. OPTICAL INSTRUMENTS.— II. By Sasiusl Highley. THE ABNORMAL EVE. Having described the characteristics of the perfect and healthy organ of vision, we have now to describe the deviations from the normal eye, and those defects or diseases that require the optician’s aid for their correction or alleviation. Between thirty and fifty years of age indications of natural decay in the perfect organ of sight may be detected, and it will be found, as a rule, that while distant objects are as distinctly discernible as in youth, it becomes necessary to hold near objects — such as the newspaper, needlework, etc. — further from the eye than the person has hitherto been accustomed to do, especially at candle or gas light — it is, in fact, becoming long-sighted „ The average distance for distinct vision for near objects in the normal eye is about eight inches from the eye ; but on long-sightedness setting in, near objects cannot be distinctly discerned till removed to a distance of fourteen, sixteen, eighteen inches, or further, from it. This defect is termed presbyopia. The commencement and progress of this deterioration of the normal eye depends upon how it has been used, and upon the health of the individual. At thirty years of age some eyes are more defective than others are at fifty years, but the average period of the commencement of decay in the eye is about the forty-fifth year, and is first indi- cated by feeling the necessity of removing small type further from the eye when reading by candle or gas light, and the con- sequent necessity for using spectacles. This will be about a year before their assistance during daylight is recognised as absolutely essential for the comfort of the organs of vision. Presbyopia, it may be stated, is often accompanied by that “ weakness of sight” termed amblyopia ; and the latter is some- times mistaken for the former, as the amblyopic person also cannot see small objects distinctly, and convex spectacles (as with presbyopia) improve his vision by affording larger retinal images ; but the purely presbyopic eye is free from amblyopia. About the age of fifty the far point, in the normal eye, also begins to recede somewhat, so that the eye then becomes slightly hypermetropic (or of the defective nature next described), and with increasing years may become absolute, so that the patient is not only unable to accommodate for divergent rays from near objects, but even for parallel rays from distant objects. Another shortcoming, which may be present in youth, is where the eye, when in a state of rest, is incapable of bringing- the parallel rays emanating from distant objects to a distinct focus on the retina, and can only do so by an effort of accom- modation more or less considerable, according to the amount of defect, while no great inconvenience may be experienced in regard to near objects, when reading, writing, sewing, etc. — in fact, may never be detected till age sends the person so affected to the optician or oculist, especially if he has good accommo- dative power, when the defect is unconsciously corrected with but slight effort. If, however, this defect is absolute, vision will not be perfect at any point. This is termed hypermetropia, an affection which was little noticed, or not properly understood, until within the last few years. Another deviation from the normal eye (which has no connection with age, but is, as a rule, a natural, often hereditary defect from birth, though seldom dis- covered by the person so affected till the age of puberty, or till the commencement of earnest study, or occupation at some trade or profession involving the use of the eye at its near point, or in other cases resulting from occupations teazing to the eyes) is short-sightedness, or myopia, as it is professionally termed. In this case persons can see the very smallest object perfectly when brought unnaturally close to the eye, while large ones at a distance, or even a moderate distance, are involved in such haziness, that they would not be justified in swearing to the recognition of an accused person in a court of justice. All eyes — the emmetropic,* hypermetropic, and myopic — suffer change in the near point with the advent of old age. The eye is not adjusted at the same time for equally distant horizon- tal and vertical objects, being greater for horizontal lines than vertical ones, which may be proved in the following manner : — - Draw on paper two ink lines at right angles to each other, and place one horizontal. At the distanco of distinct vision, this will appear black and sharp, while the other will be indistinct, as if drawn in paler ink ; adjust the eye for the vertical line, and the effect will be reversed. In some cases this difference in the curvature of the eye in two directions may become so great as to require optical correction by means of “cylindrical lenses.” This defect is termed astigmatism. Some persons (always affected with slight myopia) complain j that after reading for a short time without glasses, the letters become confused, blurred, and appear to run into each other ; * The presbyopic is classed with the emmetropic eye, being in fact a normal eye defective through age and not by congenital malfor- mation. ISO THE TECHNICAL EDUCATOR. pain in the eye and around the orbit is experienced, and, if persisted in, the eyes become red and watery. After resting 1 the eyes for a few minutes, reading may be proceeded with, but only to entail a speedy return of the same train of symptoms. If we request such a patient to look at our own forefinger, while we gradually approach it towards his eye, we shall find that when it is within a distance of about six inches, one eye becomes a little unsteady in its fixedness, and then gradually, suddenly, or spasmodically deviates outwards. Again, this deviation occurs even, perhaps, if the object be some feet distant, when we cover one eye, so as to exclude it from par- ticipating in the act of vision of the other. This outward deviation indicates insufficiency or weakness in the recti interni muscles of the eyeball, which tends to the production of double images of the objects observed (or what is professionally termed ■diplopia), which the patient intuitively suppresses, unless the object be brought too near to the eye. If such a person persists in employing the eye on near objects, the affected eye moves outwards and produces a permanent divergent squint ( strabismus ), in which case the patient again suppresses the image of the squinting eye, to avoid the production of diplopia, which leads to more or less of that “ weakness of sight” of the affected eye termed asthenopia. By the judicious selection and employment of prisms of suitable refractive power, this weakness of the muscles, if attacked in the early stages, may be cured, and thus the surgical operation of tenotomy may be avoided. Such prisms must be weak at first, and then be 'gradually increased in power. The prism must be placed with the base outwards before the affected eye, so that the rays from a candle, placed about eight inches distant, may fall upon a portion of the retina slightly to the outer side of what is known as the yellow spot ( fovea centralis). To avoid the production of double images arising from this, the eye will instinctively move inwards, in order to bring the rays exactly upon the yellow spot. During these exercises of the internal rectus, short-sighted eyes must be furnished with concave spectacles, so that the object may be distinctly seen. This mode of treat- ment requires great patience on the part of oculist and patient. Oculists classify eyes according to their diopteric charac- teristics when tested for their furthest point of distinct vision, and four kinds may be specified : — - 1. The Normal, or Emmetropic Eye, in which, when in a state of rest, parallel rays are brought to a focus on the retina, as shown at i (Fig. 2, page 111). 2. The Presbyopic, or Long-sighted Eye (aged emmetropic), in which, through the loss of accommodative power, caused partly by the weakening of the ciliary muscles, partly by the hardening and discolouration of the crystalline lens,* and the flattening of the cornea, the faculty of bringing near objects to a focus on the retina is lost, unless the object be removed to an abnormal distance from the eye ; though the eye, in a state of rest, is capable of bringing parallel rays emanating from a distant object to a focus on the retina, and so far is a normal * The crystalline lens is as transparent as water till about the twenty-fifth or thirtieth year, when it begins to be slightly tinged with yellow towards its centre, which very gradually extends towards the surface, and becomes deeper and deeper in tint, till in extreme old age it may resemble a piece of yellow amber. eye still, while the converging rays from a near object come to a focus behind the retina, as shown in Fig. 6. This defect is remedied by holding the object at a distance from the eye, so as to lessen the divergence of its rays, or by placing a convex lens before the eye, so as to help it to produce the necessary conver- gence, as shown by the dotted lines in Fig. 7. 3. The Hypermetropic, or Over-sighted Eye (hyper presbyopic, or hyperopic), which is adjusted for convergent rays, but in which parallel rays are brought to a focus behind the retina when the eye is in a state of rest, as shown in Fig. 8. This results from the length of the axis being too short — in other words, the retina being too near the cornea — or through the refracting surfaces of the eye being slightly flattened, or both causes may be co-existent. In either instance the refracting part of the organ of vision is incapable of converging parallel rays from a distant object, so as to bring them to a focus on the retina. The hypermetropic eye may be diagnosed by its peculiar shape, as it appears flatter and shorter than the normal eye, and it does not fill out the aperture of the lid, a little pouch being left between the eyeball and lid. Hypermetropia is remedied by placing a convex lens before the eye, so as to help it to produce the necessary convergence of the parallel rays, and bring them to a focus on the retina, as shown by the lines (Fig. 9). 4. The Myopic, or Short-sighted Eye (br achy metropic), which, when in a state of rest, is adjusted for divergent rays, and wherein parallel rays are, even when the eye accommodates itself for its farthest point, brought to a focus before the retina, as shown in Fig. 10, so that distinct images are formed on the retina only when the rays emanating from such object fall upon the eye divergently. This results from the axis of the eye being too long, or tho curvature of the refracting surfaces being too great. This defect is remedied by holding the object very close to the eye, so as to increase the divergence of its rays, or by placing a, concave lens before the eye, so as to produce the necessary divergence, as shown by the dotted lines (Fig. 11). FORTIFICATION. 161 ' FORTIFICATION.— III. BY AN OFFICER OF THE ROYAL ENGINEERS. PROFILES OF HASTY AND IRREGULAR DEFENCES. The destructive effects of rifled arms render it absolutely necessary that cover of some kind should be rapidly provided for the troops acting on the defensive, and it must often happen that a regular profile cannot be given to works only intended for the temporary occupation of a field of battle. Advantage must then be taken of all such materials existing on the spot (walls, hedges, etc.), as are capable of being readily converted into parapets ; and where no such materials exist, oover must be ob- tained by means of what are called •Shelter Trenches (Fig. 15). The object of these is to secure for the defenders, hy a small amount of labour, consider- able protection whilst firing (as may be accurately with the blades of their shovels, which are about 1 foot in length. Care must be taken that after the parapet has been raised to a height of 1 foot 6 inches, the additional earth is not allowed to increase this height, as it would then be too high to be fired over by men kneeling in the trench. In rear of each company, short trenches will be dug for the officers and non- commissioned officers (Fig. 17), who will then be in their right places for superintending the firing, and only so far back from the line, that when the main trench is completed, their own parapet shall not be interfered with. As will be seen in the accompanying cuts, the men in these trenches are much less exposed than those in the open, and as they are absolutely out of sight when lying down and not actually engaged, many lives j must be saved by the cover they afford ; at the same time the propor- tion of fatal wounds to the total f SCALE JL Fig. 17. SCALE jjig. Fig. 23. seen by comparing the men shown in the open in the figure and those in the trench) ; and, at the same time, not to obstruct their rapid advance when the moment for a forward movement arrives. The method of executing them i3 as follows : — As soon as a regiment arrives on the ground it is intended to defend, one rank is extended as a line of workmen, at six feet intervals from one another. In the first instance, a continuous trench 1 foot 3 inches deep, and 2 feet broad, is dug, the earth being thrown in front to form a parapet 1 foot 3 inches high. This trench can be excavated in from ten to twenty minutes, and is then capable of giving cover to one rank kneeling in it, and to a rear rank lying down on the ground behind (Fig. 16). If more time is available, the trench is then gradually widened until it is 7 feet broad, when it is wide enough to allow of the men lying down in it, and being perfectly hidden until required to fire (Fig. 17). As soon as it is 4 feet wide, there is room for both ranks kneeling. iNo tracing or special measurements are necessary for this work ; for if the men are placed in line, two full paces apart, they can measure the depth and breadth sufficiently numbers of men hit must be larger than before, since the men’s heads are almost the only parts exposed. This result appears to have been noticed in some of the late battles in France, where trenches of this description were employed. In woods, where large trees can be easily obtained, parapets may be formed by felling the trees, and, after removing the branches, laying them lengthways one above another, as represented in Fig. 18. If shovels are available, a small trench should be excavated, and the earth thrown over the logs. A very service- able parapet may thus be readily formed, as the crest, which is usually the weak part of all earthen parapets, is in this case quite bullet-proof. The intrenchments used by the Maories or New Zealanders are worthy of notice, both on account of their being somewhat different from the ordinary profile, and also because the same method may be advantageously applied in cases where it is desirable to defend a hill-side with several rows of men in shelter trenches, one behind the other. *Their pahs, or in- trenched positions, were generally admirably chosen on the slopes of hills, inaccessible or difficult of approach, and the 11 VOL. I. 162 THE TECHNICAL EDUCATOR. ground most liable to attack thoroughly well swept by their fire. These works generally consisted of an irregular line of deep rifle-pits, as represented in Figs. 19a, 20a, placed close to one another, connected either by a trench ( b ) or a small underground passage, and the earth being thrown up behind the trench instead of in front, as is usually the case. This mound served the double purpose of affording cover to their huts and dwelling-places, and, if necessary, could be manned to bring a second line of fire to bear on the attack. The men in the pits, firing at the level of the ground, were very little exposed, besides which the narrowness of the pits and their irregular outline made it difficult to dislodge the defenders by the fire of shells. The front was usually protected by a stout palisade, or post-and-rail fence, on which a screen of flax was hung (c)- — the former as an obstacle to prevent the assailants closing with the men in the pits, who were hidden from view by the screen, and were able to fire under it close along the ground. Some of the pits were partially roofed in and lined with fern to serve as sleeping-places, as may be seen from the enlarged section through rifle-pit in Fig. 20. An inte- resting detailed account of these may be found in Vols. VI. and XIV. of the “ Professional Papers of the Royal Engineers.” Stoccades are formidable parapets constructed entirely of wood in situations not exposed to artillery fire. They are so high as to necessitate the use of ladders to get over them, and being bullet-proof and loopholed are troublesome to attack, as unless they can be approached by surprise, many casualties must occur in attempting either to escalade them, or to blow them in with gunpowder. Stoccades are the type of work usually met with in wars with uncivilised nations who do not possess artillery, such as the Hill tribes on our Indian frontiers, etc. One of these Works in Bhootan proved a very formidable obstacle, formed of long bamboos firmly lashed together, and was not demolished by the explosion of 60 lb. of powder placed in a bag against its foot. Ordinary stoccades consist of a row of upright timbers 12 or 14 inches in diameter, and from 10 to 15 feet in length, placed touching one another, with their butt ends buried in a trench 3 or 4 feet deep. These logs are kept together by being spiked to two rails, or cross-pieces, near the top and bottom of the logs on the inside (Fig. 21). To increase the difficulty of getting over them, their tops should be pointed, and where they come in contact the logs should be squared, by having slabs cut off each side. If this cannot be done, smaller logs should bo placed in front and in roar, to strengthen the weak points between the large timbers. The larger the logs are the better, both on account of the greater security they afford, and also because they are not so liable to be dangerously weakened by cutting a loophole through them. This is generally managed by cutting a notch equal to half a loophole out of each of two adjacent logs, and placing them together. As the usual method of demolishing a stoccado is by explod- ing bags of powder placed against them, it is desirable to prevent this as far as possible, by digging a ditch in front, and piling the earth at a steep slope against the stoccade on the out- side. This should generally be done, unless the lower portion of the stoccade requires to be loopholed so as to allow of a second tier of musketry fire, when a temporary platform or “ banquette” must be erected inside to enable one row of men to fire over it, while another rank stand in a trench at the first of the timbers, and fire through close to the ground level (Fig. 22). With regard to loopholes generally, it will be well to re- member that they should invariably be made at a level either too high or too low for Ihe enemy to use for firing into the work from the outside ; and, at the same time, they must be at a convenient height on the inside for use by the defenders. About 15 feet of ordinary stoccade work can be constructed by a party of eight men in eight hours. This does not include cutting down, or bringing the timber to the spot. Strong hedges afford excellent defensive obstacles, and are capable of being converted with little trouble into good parapets. When a hedge is less than 6 feet high, a ditch should be dug, and the earth thrown over to the other side to form a parapet, as the hedge is then utilised as an obstacle, and also as a revetment to the earth behind (Fig. 23a). This method gives the men firing over the hedge a command over their assailants. When time presses, and the hedge is high and strong enough to form a good obstacle, a slight trench with the earth piled against the hedge will suffice to obtain cover- A small ditch (Fig. 23 b) should be added outside to keep the enemy from closing with the breastwork. In some instances it will be better to make the trench deeper, and having cut away the lower branches, to fire close to the ground (Fig. 23c). Hedges intended a3 obstacles maybe very much strengthened, and made difficult to cut down, by having thick iron wire run through them and made fast to the largest trees in the hedge. As it is the ex- ception to find hedges without some sort of bank or ditch on one side of them, the excavations that have been indicated in these diagrams will generally require very slight work to complete, and consequently this species of defence may be very rapidly prepared. Walls of moderate thickness may be rendered defensible by either breaking loopholes through them at the required levels, or cutting openings down from the top, care being taken that the wall is not too much weakened by this treatment, and that the enemy is prevented from closing with the loopholes from outside. On level ground, walls under four feet high are useless as parapets, but may be of service as a partial revetment to earthen ones thrown up in front of them (Fig. 24). tow walls, under 7 feet high, require that a ditch and a trench should be dug in order to obtain sufficient cover. High walls may be arranged for two tiers of musketry fire, in the same way as has been described for a stoccade (Fig. 25). In the hasty defence of villages and towns, rough barricades formed of carts, furniture, etc., may be employed both as obstacles and parapets. No rules can be laid down for their construction, except that they should be placed at points where their fire can bo assisted from loopholes in adjacent buildings, and where artillery fire cannot be brought to bear on them from a distance. Four-wheeled carts filled with stones, earth, etc., would form a good commencement for a barricade if drawn up in a line across a street, and their hind wheels taken off. Behind these, logs of wood, sacks filled with coals, barrels, etc., would be accumulated until a sufficient parapet and banquette had been formed; a pile of broken wheelbarrows, furniture, etc., being arranged in front as an obstacle, but so as not to afford cover. TECHNICAL EDUCATION ON THE CONTINENT. — YI. BY ELLIS A. DAVIDSON. THE POLYTECHNIC SCHOOL AT HANOVER (continued). Having thus given an outline of the comprehensive course of studies carried out in this school, which may be termed a Technical University, it is now only necessary to mention that the courses are arranged for each student according to the profession he intends following, the technical or special branches, however, not being taken up in the Higher School until the complete general course in the Lower School has been gone through. REGULATIONS AS TO CONDUCT AND DISCIPLINE, ESTABLISHED BY DECREE OP THE MINISTER OP THE INTERIOR. The regulations of this school are so admirable in their character that they are calculated to exercise as great an influence over the general life and moral training, as the course of study has upon the intellectual career of the student.. An extract only from the code of rules will be given here with the view of showing that in the conduct of such establishments for youth there are other subjects to be considered than thie mere course of studies. 1. The students and persons attending the Polytechnic School must conduct themselves in a decorous and blameless manner, and must show the lecturers, teachers, and othier per- sons concerned in the management, the utmost obedien ce and respect. 2. They must, during lectures and lessons, be orderly and attentive, and must be in their places in the class or lecture room before ten minutes after the time fixed. The cause of absence must in every case be explained in writing, and in case* of illness a medical certificate must be produced. TECHNICAL EDUCATION ON THE CONTINENT. m 3. Each student must provide such books, or other school material, as the teacher may prescribe, without delay. 4. The exercises and notes given out by the lecturers and teachers to be worked out in leisure hours, must be carefully prepared and delivered at the specified time. 5. The students in the Lower School must, as a body, take the entire course of studies, unless exempted from any branches by permission of the Direction. In the Upper School the students are free to select the classes or lectures they may wish to attend ; but they are urged to avoid disturbing the course laid down for each profession, since each branch has necessarily an important bearing upon the other. A student, however, having entered himself for any complete course, is not permitted to omit any individual subject comprised in it without written permission, of the professor. 6. Models, tools, apparatus, examples, etc., used in the lectures and lessons, must be carefully preserved, and any damage thereto must at once be made good. Where the indi- vidual student is not discovered, the entire class is held respon- sible for restoration of damaged property. Students are not allowed to take books or examples home, unless by special permission. 7. The school buildings, furniture, and fittings must also be kept from damage, under the previous rule. 8. Proper obedience must be shown to the officers anid attendants, whose duty it is to carry out the rules and to main- tain the order of the establishment outside the class-rooms. Violations of this rule are reported to the Direction. 9. Students wishing to form amongst themselves a club or union, are permitted to do so provided their object be their mental,- moral, and social benefit. The rules of such union must be submitted for the approval of the Direction, and every student under age wishing to join must present the written permission of his parent or guardian. The members are free to withdraw themselves from such union at any time, but new members can only join at the commencement of a school year. 10. Disorderly conduct of any kind is severely punished. 11. Improper conduct in the streets, or any other public place, although it may not be absolutely legislated for in the code of regulations, will be recognised and punished as com- promising the reputation of the school, causing annoyance, and setting an evil example to others. The means taken to secure discipline are — (a.) Warning of dismissal. (b.) Suspension from a class. (c.) Dismissal from the school. (d.) Formal expulsion. The extreme punishments are, however, never inflicted without frequent admonitions and warnings, and in every case the parents or guardians are communicated with. SUPERVISION OF STUDENTS. It is incumbent on every teacher of lower classes in the Polytechnic School to exercise the most careful supervision over the students, and to register their attendance. It is also the teachers’ duty to keep a continuous watch over the conduct and attention of the students, so that they may be prepared at the end of the year to give an accurate and truthful report of each. THE LABORATORY. The laboratory is open for the use of students at stated hours. Experiments or processes, which could not otherwise be completed by dinner-time, are begun at eight in the morning. Except under special circumstances, only such work as is prescribed by the teachers is allowed to be done in the laboratory. The laboratory is well supplied with complete apparatus, etc., for carrying out experiments on a large scale, and for lecture purposes ; but the students are required to provide themselves with the smaller utensils — test-tubes, beakers, flasks, funnels, and other apparatus. The laboratory students are supplied with a certain quantity of spirits of wine (for lamps), filter paper, litmus paper, etc. Students requiring more must purchase it. Such students as desire the accommodation can be supplied with a complete set of glass beakers for a moderate sum, which is returned to them at the end of the school year, if the glasses are restored unbroken. The chemicals students may require for their private study may be purchased at numerous shops, or can be supplied at moderate prices from the laboratory ; the payment must, however, be “ cash,” the laboratory not undertaking to keep credit accounts of goods supplied. For the maintenance of proper order, for the economy of the laboratory, and to render its resources as widely beneficial as possible, the following rules have been established, and these are given here, as indeed are all the other details, in order to afford hints for the establishment of similar institutions in this country. 1. Each student must keep his own place in the laboratory in order/ and before leaving must restore the apparatus he has used to its proper place, so that it may be ready for the next comer. 2. Such apparatus as may be the property of the student, oar which has been specially entrusted to his care, may be locked up in cabinets. 3. The students are bound to see that under no circumstances whatever is anything put into the jars or bottles but the chemical stated on the label, and to be careful that the proper stoppers are put in the bottles, so that the purity of the contents may not be impaired, or that evaporation may not take place through inaccurate fitting of the stoppers or covers. 4. The apparatus in the lecture theatre are reserved fo^ lectures, and must not be removed for any other purpose. 5. Although according to a previous regulation students are bound to make good any damage done to the school property, this rule, in consideration of the fragile nature of some of the chemical apparatus, and the dangers to which they are subjected whilst in legitimate use in the laboratory, is thus far relaxed, that payment is only exacted when the damage has been kept secret, or is proved to have taken place through absolute neglect. In the following cases, however, full restitution is demanded : (a.) Where a student has injured the balances used, so that repairs are necessary. (b.) When any of the apparatus has been so damaged as to be of no further use. (c.) When books of reference used in the laboratory have been soiled or stained. ( d .) When the hand-towels have been used for wiping up acids, or subjected to other destructive treatment. A fine is also inflicted on students leaving gas burning in the laboratory, or neglecting to see that the taps are properly turned off. The teaching staff in this admirable institution comprises above forty professors— not professors in name only, but absolutely professional men of the highest position, architects, consulting engineers, analytical chemists, and mathematicians ; and the inspectors are all practical men, appointed by the Direction for their status in the branch in which they are to examine. In addition to the various branches of science and art already mentioned, classes are held for instruction in languages and other subjects connected with the intellectual development of the students, and which serve to promote their progress in either their own country or any other. Amongst these are — languages, English, French, etc. ; building arts ; history — not merely of their own country, but universal history — and social science. Some statistics in relation to this Technical University, which may be taken as a type of what such an institution should be, cannot fail to be interesting to the reader. In the year 1869-70 the Polytechnic School was attended by 384 persons, of whom 197 were students of the previous year and 187 were new ; of this number 322 were regular students, and 62 persons admitted to individual courses of lectures ; 88 entered the Lower, and 296 the Upper School. This shows that although the standard of the matriculation to the Upper School is very high, the Lower School is doing its work of prepara- tion efficiently ; and even more than this, it proves that the scientific culture in other schools in Germany must be of a most efficient character, for supposing that the whole of the 197 students remaining from the previous year had been drafted into the Upper School — which, as the courses of study in the Upper School extends over four or five years, is not likely there would still remain 99 students who have been sup- plied by other schools, without counting the 62 who have 164 THE TECHNICAL EDUCATOR. entered for special courses of lectures only, from whom, as already stated, no examination is demanded on entering ; but it is evident that as all the lectures are of a sound and eminently practical character, and not likely to attract persons who could not follow the teaching and benefit thereby, the rudimentary teaching these have received must be of an eflicient character. . It is necessary to say that the advantages of this mstitution have not been confined to Germany, but that students have entered from various parts of Europe ; thus, the 384 students of 1870 are composed of 195 from the province of Hanover, 154 from other parts of Germany, 4 from Norway and Sweden, 5 from Russia, 2 from Finland, 4 from England, 12 from the Netherlands, 1 from Italy, and 7 from America. The advantages to be derived from institutions of the kind we have just described cannot be rated too highly. Up to the present time nothing approaching the Polytechnic School of Hanover, either in constitution, management, or purpose, has been established in this country ; but the movement in this j direction in the establishment of the Whitworth Scholarships, and i other aids to the advancement of practical science, will doubt- less end in the formation of a university which shall stand in the same relation to art-knowledge and science that Oxford and Cambridge now occupy towards the learned professions. LENDING AND REFERENCE LIBRARY. The library is open on all week days from nine to twelve in the morning, and on Mondays, Tuesdays, Wednesdays, Thursdays, and Fridays, from half -past two to four o’clock in the afternoon. The library is also open from twelve to one o clock on all week days during vacations — a great privilege to students residing in the neighbourhood who may wish to consult some book of reference. Students borrowing books are enjoined to take great care of them, and are strictly forbidden to make any notes or remarks on the pages ; they are, however, requested, should they feel that any remark they might make, or any solution of a problem, etc., which may occur to them might be of service to others, to write the same on a separate slip of paper, and place it in the book. The benefits of the library are not restricted to the students, but persons resident in Hanover and the neighbourhood are permitted to borrow books — an introduction and guarantee being signed by a householder or other person of position. Persons borrowing books from the library are not allowed to lend them to others, without special permission in writing from the secretary of the library. The original borrower is still, how- ever, held responsible for the book. He is required to sign the receipt for it, and to insert in it the name and address of the person for whom he is borrowing the book. School books, dictionaries, and other books of reference are not lent out, neither are books of engravings. These are, however, allowed to be taken into the class-rooms when required fop the purposes of study ; but in that case they are considered as borrowed, and the proper receipt must be signed for them before they are taken from the library. Having thus given a detailed account of this great Polytechnic University, we will next proceed to consider the extended system for the education of workmen and their children, and for this purpose we will describe the whole group of schools so efficiently carried on in the kingdom of Wurtemberg. PROJECTION.— VIII. SECTIONS OP CONES AND PENETRATIONS OP SOLIDS. THE PARABOLA. If a cone be cut by a plane parallel to one of the sides of the triangle which forms its elevation, the section is called a parabola. Fig. 95 . — To draw the parabola which shall be the true shape of the section of the cone ABC , on the line D E, which is parallel to c B. Divide E D into any number of parts, in f g h, and through these points draw lines parallel to the base, meeting the sides of the triangle in /, g, h, i on each side. Now it will be evident that vll sections of a right cone which are parallel to the base must be circles ; and therefore, as the base A b of the elevation is represented in the plan by the circle a' b', the line f f in the elevation will be represented by the circle / in the plan ; and similarly, the lines g and h in the elevation become the circles g and h in the plan. From E in the elevation draw a perpendicular, which, passing through the plan, will give the fine e' e'. This is the line where the section-plane, entering the cone at D, will cut the base. A perpendicular dropped from D will mark on the diameter the plan of the top of the section — viz., d'. An additional point, i, has been inserted between h and d, in order to gain more points for tracing the curve. This point is to be worked similarly to the others. It has been shown that the section-plane cuts the elevations of circles f g hi inv am, and therefore perpendiculars dropped from these points to cut the plans of these circles, will give the points /, g, h, i in the plan. The curve drawn through these points, together with the straight line e' e', forms the plan of the parabola, being the view of the slanting surface E d as seen from a point of view immediately over the cone. # To draw the true shape of the section, draw a line d" e" parallel to d e, and from d, e, f, g, h, i draw lines at right angles to d e, passing through d" e" in f' , g', h', i . On each side of these points, mark on the lines drawn through them the distances which the points e’, e’,/, g, h in the plan are from the diameter A b — viz., /, g, h. Through these points draw the curve, which will be the true parabola formed by the plane cutting the cone in the line d e. THE HYPERBOLA. Pig 96. — When a cone is cut by a plane which is parallel to the axis, the section is called the hyperbola. In this case the object of the lesson is to find the true section of the cone, caused by a plane, of which d e is the edge elevation, cutting it parallel to the axis. Rotate the cone on its axis so that the section shall face the spectator, in which position (Fig. 97) it will evidently be parallel to the vertical plane. Now from c in the plan, draw any number of circles, cutting the line e e in /, g, h. The diameters of these circles will be marked, by the points /', g', h'. From these draw perpendiculars cutting the side of the cone ; and the lines f", g", h" drawn parallel to the base will give their elevations. Now from the points in the plan where the section-line cuts the circles — viz., points /, g, h — draw perpendiculars cutting the lines f, g ,h in f,g, and h ; then from d (Fig. 96) draw a line to cut the axis in d', and perpendiculars from e 1 e to cut the base of the elevation in e e. The curve drawn through all these points will be the required hyperbola. THB pENETEATI0N of solids. When one solid meets another it is said to penetrate it, and the development of the form generated at the intersection of the bodies is a study of the utmost importance to artisans. The lessons we are now giving on this subject commence with those of the most elementary character, and advance by very gradual stages. Only fundamental principles are, however, developed, in order to prepare the student for the advanced studies which will be given in subsequent lessons adapted to the respective branches of industry. Fig. 98 represents the plan and elevation of a square prism penetrated by another of smaller size, their axes* being at right angles to each other, and two of their faces being parallel. The figure at this stage is so simple that it requires but little explanation. The points not visible in the present view, owing to their lying exactly beyond others, are marked with letters corresponding to those on the points which are in front of them, with the addition of a dash ('), and the points themselves will become visible in Fig. 99, where the object is rotated. pig 99. — Place the plan at any angle (as required). The projection will then be accomplished, as in previous figures, by drawing perpendiculars from the points in the plan, and inter- secting them by horizontals from the corresponding points in the elevation. Points G and h will mark the line of penetra- tion that is, the line at which the smaller prism enters the larger. Fig. 100 is the development. The widths of the sides being equal to A B, and the length to the height of larger prism, the squares represent the cavities through which the smaller Axes, plural of axis. PROJECTION. 165 prism would pass if the develop- ment were folded into a square form. Fig. 101 repre- sents the plan and elevation of a square prism penetrated by a smaller one, when the axis of the latter is at an angle to that of the former. The student who has followed the lessons to this point will find no difficulty in pro- jecting the plan from the eleva- tion, and by turn- Fig. 98. draw horizontals from A and b, which will give the top and bot- tom of the oblong, which is to be made of the width e f. The aper- ture on the oppo- site side is to bo projected in the same manner from through all the degrees of the zodiac, together with the days of the month, the sun and moon’s place in the ecliptic the moon’s southing, etc. Langley Bradley repaired it m 1714 and it was again altered and repaired somewhere between 1760 and 1800. The astronomical furniture is in- correctly attributed to Thomas Tompion, the celebrated clock- maker, but he died in 1669, or about 129 years after its con- struction, though he might have been employed upon it (see Hendersons “Horology,” pp. 16, 18, 2nd edit. 1836). The -dial, and part of the wheel attached to the back of the dial still remain. About the year 1560, the Danish astronomer’ lycho Brahe, possessed four clocks, which indicated the hours minutes, and seconds ; the largest of these had only three wheels ; one was about three feet in diameter, and had 1200 teeth m it, a proof that clockwork was then in a very imperfect state. _ In 1577, Moestlin had a clock so constructed as to make just 2,528 beats in an hour, 146 of which were counted during the sun’s passage over a meridian or azimuth line and thereby determined his diameter to be 34' 13''- so the science of astronomy began thus early to be promoted by clock- work ; and astronomy, m its turn, gave rise to some of the most essential improvements in clockmaking. Martinelli in his work printed at Venice, 1663, describes an old clock going in his time m the Grand Piazza, in which two Moors struck the hour upon a bell, three kings entered from a door, and after making obeisance to figures of the Virgin and Child, placed in a niche, retired through a door on the opposite side. John Evelyn relates that about the middle of the seventeenth century a man was killed by this famous clock : “While repairing the works, he stooped his head in such a position, and in such a nick of fame, that the quarter boy struck it with his hammer, and knocked him over the battlements.” In the palace of Versailles are two curious clocks, one being the clock of the king’s death, in the Cour de Marbre This c ock has no mechanism, and has only one hand, whioh is plaoed at tne precise moment of the death of the last king of Prance, and is not moved during the whole of his successor’s reign. This custom dates from the time of Louis XIII In the saloon of Mercury is a clock dated 1706 ; each time that it strikes, two cocks flap their wings, small doors open, and two figures advance, holding bucklers, on which Cupids strike the quarters ; a figure of Louis XIV. steps forth, fffnd from a cloud, Victory descends and plaoes a crown on the king’s head • the puppets all disappear, and the hour strikes. A story told of Louis XI (King of France from 1461 to 1483) shows that horology had then made great advances. A gentleman who had lost a great deal at play, stole a clock belonging to the king, and hid it in his sleeve ; in a short time, the clock, which continued to go, notwithstanding its removal, struck the hour, and the theft, of course, was discovered. Louis, as capricious m kindness as in tyranny, not only pardoned the culprit, but made him a present of the clock. It was customary formerly m several French towns, to make clocks tell the hour by means of one or more statues, which struck the bell with hammers A similar custom prevails in Italy. In the little town of Lambex there is on the top of a tower the figure of a man who strikes the hour in this manner ; at the same instant, a woman appears, and makes him a low curtsey, and then walks once round him. Portable clockwork exhibitions of sceneries, the life and death of our Saviour and the Blessed Virgin, and models of Nazareth, Jerusalem, and Mount Calvary, are among* the attrac* tions of French fetes. Invention was, for a time, limited to enriching clocks by the addition of moving figures, processions of saints,, with the Virgin, representations of mysteries and pious subjects ; while others were made by the more learned to represent the motions of the heavenly bodies. Of this class were the two “wooden horologists” of St. Dunstan’s, Fleet Street, which struck the quarters upon a suspended bell, each moving his head at the same time. These figures of savages, life size, carved in wood, stood beneath a pediment, each having in his right hand a club, with which he struck the bell. When the church was taken down, in 1830, they were purchased, with the bells, for A 2 00. by the Marquis of Hertford, for his villa in Regent’s Park. There is a like contrivance to the above in B orwich Cathedral ; and a general name for these figures was “ Jacks of the Clockhouse.” TECHNICAL DRAWING.— XI. DRAWING FOE CARPENTERS AND BUILDERS. DEVELOPMENT OE THE SURFACES OF ROOFS. Although the whole subject of the development of prisms is treated in lessons on “Projection,” it is deemed desirable to give two examples here, showing the immediate application of the principles to roofs, in order to enable the student to find the exact shapes of the surfaces of which they are com- posed ; and, as in the case of a hipped roof, the length of the hip-rafters. Fig. 82. — In this figure, a b c d is the plan of the building to be covered with a hipped roof. To draw the plan of the roof, bisect the angles of the paral- lelogram, and the bisecting lines meeting in e and / will form the plans of the hip-lines, and the line joining e and /will be the plan of the ridge. It is now required to project the elevation from this plan. To do this, draw any horizontal line, as A B (Fig. 83), and the perpendiculars from c, e, /, d, cutting a b in g, h, i, j, and pro- duce li and i indefinitely. Produce the perpendicular at e until it reaches l ; then it will be clear that Jc l is the width of the roof-trusses (at h l and m n), which would be at right angles to the sides a b and c d. Draw k l (Fig. 84) equal to kl in Fig. 82, and at the middle point, o, draw the perpendicular, o p, equal to the real height of the truss, which is, of course, a matter dependent on the design of the architect. This triangle, then, will be the shape of the truss at this point, and is the section across the roof. Make h q and i r in Fig. 83 equal to op in Fig. 84 ; draw g q, qr, and rj, which wall complete the elevation; and this will also be the longitudinal section through the ridge. We now have to find the real length of the hip j to do this 168 THE TECHNICAL EDTJCATOB. draw / s (Fig. 82) equal to op (Fig. 84), and at right angles to / d ; join d s ; then the right-angled triangle d f s is the true shape of the hip-truss. This will be understood by cutting a piece of cardboard of this shape, and placing it on its edge on df, then it will be seen that d s will be the length of the hip. To develop the covering of this roof : — It will, of course, be then the trapezoid c v w d is the development of one of the planes forming the side of the roof -covering. The same length set off on the perpendiculars l, n will give the points x, y, which will complete the fourth plane. We will now proceed to find the form of the hip when the roof is a groined one. understood that this will consist of four planes, which will meet *t the hip-lines. Now, it has already been shown that the ends are triangles, of which a e c and b f d are the plans ; the length of lines a c and b d remains unaltered, but the real length of c e, a e,b f, and df has been proved to bed s ; therefore on d b and a c construct isoscdies triangles, having d s for the two remaining sides ; these triangles then, ate and bud, are the true shape of the coverings of the ends of the roof. Now from c and d, with radius c t, describe arcs cutting the perpendiculars Tc and m in v and w ; join d iv, v c. and w v ; Let me ask you to imagine yourself standing on the platform of a railway at the side of a semi-circular arch by which a road is carried over it you will then see that whilst the face or elevation of the arch where it crosses the railway at right angles is semi-circular, its span being of course the diameter of the circle of which it is the half, the length from the springing near which you are standing, to the most distant springing (that is, the one on the opposite side of the line at the other end of the arch) will be much longer ; yet the arch there is not any higher, although its span thus taken crosswise is longer. TECHNICAL DRAWING. 169 because the diagonal of a square or other rectangle is longer than either of its sides. The principle on which to find the shape of the curve which would reach from the springing at which you are standing to the one referred to, is also shown in Fig. 85. On a 6 describe a semicirole, and divide it into any number of equal parts in the points 1, 2, 3, 4, etc. From these points let fall perpendiculars on a b, and produce them downwards till they cut the diagonal a c in the points 1', 2', 3', 4', etc. Now, from the points where the lines 1', 2', 3', 4', etc., cut a c, draw lines perpendicular toac; make each of these equal in height to those correspondingly lettered in the semicircle, and the curve drawn through their extremities will be the form required. Fig. 86. — Here A b c d is the plan of a building to be covered by a groined roof. The arch, the springing of which is A c and B d, is a semi- cylinder. The arch which has its springing in A B and c D, being of the same height but of wider span, is a semi -cylindroid. A cylindroid is a solid body of the cha- racter of a cylinder. But whilst in a cylin- der all sections taken at right angles to the axis are circles, in the cylindroid all such sections are ellipses. It is, in fact, a flat- tened cylinder. The curve at the groin, then, is gene- rated by the penetra- tion of a cylindroid and cylinder. On A b describe the semicircle which re- presents the form of the arch at the ends a b and c r>, and divide it into any number of equal parts, a, b, c, etc. It is only necessary to use the quadrant, as throughout the work- ing the measurements are the same on each side. Draw the diagonals A D and b c. From a, b, c, d, e, J draw lines perpen-’ dicular to A b, and cutting the diagonal A d in a', b', c', d', e', f , and set off the same distances on the other half of the diagonal. > From these points draw lines at right angles to A c, and passing through it in points 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ; mark off on the perpendicular 6 the height of 6 / equal to the height of the semicircle /, and on the perpendiculars 5, 4, 3, 2, 1 mark off in succession the heights of the perpendiculars e, d,f, c, b, a, as contained between the semicircle and the diameter. Set off ■“ihe same heights on the corresponding perpendicular 3 on the other side of 6 /, and the curve traced through these points will be a semi-ellipse, which is the section of the semi-cylindroid forming the arch of which A b and c D are the springings. We now proceed to find the curve of the groin ; and it will be evident that, although the span is still further increased in length, the heights of the different points in the curve will be the same as in both the previous elevations. The span, then, of the arch at the groin is the diagonal A d (or b c), to which the divisions a', V, c, d', e', /' have already been transferred from the semicircle, and from these the lines were carried at right angles to A c, on which the heights of the points in the curve were set off. These points on the diagonal, then, will be seen to be common to both arches, since they are the plans of the points in the roof where the cylindrical and cylindroidal bodies penetrate each other. At these points, therefore, draw lines perpendicular to the diagonal, and mark off on these the heights of the per- pendiculars in the semicircle from which the points on which they stand were deduced. These extremities being connected, the curve so traced is the groin curve, and will give the shape for the centering for the groin, as the semi-circle and semi-ellipse will for those used in the elevations of the arches. It now only remains to develop the soffits or under surfaces. Fig. 87. — Draw any straight line, and commencing at A set off on it the distances into which the curve a c is divided (measuring on the curve, not on the springing-line), namely, the distances A a, a, bb, c c, etc. At the points on the straight line thus marked, draw per- pendiculars ; make the middle one equal to 6 f. those on e, e equal to 5 e, those on d, d equal to 4 d, those on c, c equal to 3 c, those on b, b to 2 b, and these on a, a equal to 1 a. Join the extremities of these perpendiculars, and the two curves meeting in a point* and joined by the original straight line, will form the develop- ment of the soffit of the cylindroidal arch. Fig. 88 is the de- velopment of the semi-cylindrical arch. As this is worked in precisely the same manner from the semicircle, no further instructions are deemed necessary. Fig. 89 is the plan of a building to be covered by a roof of a pyramidical form, the hips, however, being curved instead of straight, so that the roof is really a square dome. Now in this case, the given rib crossing from b to b, and that which would cross it at right angles through the centre, is shown at b, which is the form of wooden centering which would be used to divide the semicircle ,._into any number of equal parts. Draw diagonals in the square, and from the divisions in the semicircle draw lines perpendicular to the diameter, and cutting the diagonal ; at these points erect, perpendiculars, and make them equal to those in the semi- circle ; then the curve drawn through their extremities will be the shape of the hip. This is shown lying down in the illustration, and the student is advised to cut the form in cardboard, when by standing it on its edge against a semi- circle placed on the line b b, he will be able thoroughly to comprehend the difference between the forms caused by their positions. When a roof is constructed as in this figure, but the curve is truncated, or cut short by a flat surface, it is called “ coved and flat.” Ceilings are sometimes built in this manner. They form a sort of compromise between a flat ceiling and the various arched forms practised by the ancients. They do not require so much height as the latter mode, and have therefore been of considerable use in the finishing of modern apartments ; but although the form is admired by many, it naturally is wanting in the elegance and grandeur of entire arched ceilings, nor does it admit of that beauty of decoration of which they are susceptible. 170 THE TECHNICAL EDUCATOR AGRICULTURAL CHEMISTRY.— IV. BT CHARLES A. CAMERON, M.D., PH. D., Professor of Hygiene in the Royal College of Surgeons, Ireland, etc. CHAPTER IV.— FORMATION AND COMPOSITION OF SOILS. The solid “crust” of the globe is composed of substances termed rocks by the geologist, whether they exist in the enor- mous compact masses popularly known as rocks, or in the slightly coherent states called clay, gravel, sand, etc. Granite, gneiss, trap, basalt, sandstones, limestone, and various other minerals, constitute the solid rocks. They are composed of the metals potassium, sodium, magnesium, calcium, aluminum, and iron, united with the metalloids (non-metals) oxygen, car- bon, silicon, sulphur, and phosphorus. The metal manganese occurs also (and very commonly) in rocks, but only in small quantities ; and the metals barium and strontium are also occasionally found in masses of rock. Fluorine combined with calcium (fluoride of calcium, or fluor spar) is also met with in rocks, but in comparatively minute quantities. The great bulk of rocks is made up of the elementary substances silicon, oxygen, carbon, aluminum, and calcium. Silica, or silicic acid, is composed of 46‘7 parts of silicon combined with 533 parts of oxygen. It constitutes the great bulk of most kinds of rock, such as granite, gneiss, and basalt, and it is the chief constituent of such common minerals as felspar, mica, hornblende, and meerschaum. Quartz, flint, rock crystal, jasper, chalcedony, and agate are varieties of silica. Aluminum is a white, malleable metal, about one-third the weight of silver. It is but very slightly affected by the air. 53'39 parts of this metal combined with 46'G1 parts of oxygen constitute the earth alumina. The latter, when artificially pre- pared, is a white substance, insoluble in water, but possessed of a great tendency to combine with that liquid. The in- tensely hard mineral corundum is pure alumina; and emery, and the beautiful gems termed the sapphire and the ruby, are slightly impure varieties of this earth. The plastic constituent of clays and porcelain earths is alumina ; and this body is the basis of bricks and pottery. The affinity which alumina has for moisture may easily be proved by applying the tongue to a brick or piece of unglazed porcelain. The metal calcium, united with oxygen in the proportion of 71 '43 parts of the former with 28'57 parts of the latter, consti- tutes the earth lime, or calcic oxide. This body is white, and is about three times the weight of water. When water is poured upon lime, they combine, the earth swells up, and (unless there be too much water) crumbles into a fine powder. During this process a large amount of heat is evolved. This compound of water and lime is termed slaked lime, or calcic hydrate (formerly, hydrate of lime), and is largely employed as an ingredient of mortars and cements. Limestone and marble are essentially composed of lime, or calcium in union with car- bonic dioxide. When either mineral is highly heated, carbonic dioxide is expelled, and calcic oxide (quick or burnt lime) remains. The important earthy salt gypsum, or plaster of Paris, is calcic sulphate ; and tricalcic diphosphate is one of the most valuable earthy compounds used in agriculture. A large number of minerals containing tricalcic diphosphate exist, and are employed for agricultural purposes. y The metal magnesium occurs far less abundantly than calcium. 60-28 parts of this metal and 39 - 72 parts of oxygen form the earth magnesia — a bulky, white, tasteless powder. Dolomite is a compound of calcic carbonate and magnesic carbonate, and the well-known Epsom salts are magnesic sulphate. Magnesium occurs in all fertile soils, and in a great variety of minerals, such as, for example, chrysolite, French chalk or steatite, meer- schaum, serpentine, and asbestos. Geologists have not been able to penetrate very far beneath the surface of the earth ; consequently, the composition of all but the mere skin, so to speak, of our globe is unknown to us. So far as we have penetrated, certain kinds of rocks have been found in layers or beds termed strata, overlying each other in regular succession. Occasionally the strata have a horizontal direction, but more frequently they form angles with the sur- face of the earth. The stratified* rocks are termed aqueous, because it is be- lieved that they have been formed out of older rocks by the action of water. The hardest kinds of rock crumble away under atmospheric influences, and the debris or fragments be- come transported to considerable distances by means of drainage water, rivulets, rivers, the sea, and even by glaciers and ice- bergs. The pulverised particles of rock deposited in various places out of water undergo a kind of cementation and form new rocks. The latter, being produced from a gradually-de- posited sediment, necessarily have a stratified or leaf -like struc- ture. Some stratified rocks are derived from the remains of animals. Chalk and limestone are composed chiefly of the remains of shell-fish and other animals. So great is the rock- forming power of large rivers that, according to Sir Charles Lyell, the Nile annually deposits 3,702,758,400 cubic feet of solid earthy matter beneath the waters of the Mediterranean. The greater part of Egypt was believed by Herodotus to be “ the gift of the Nile.” The rocks termed igneous are those which have been sub- jected to, or formed under the influence of, intense heat. They are generally composed of small crystals or vitreous (glass or slag-like) substances. They generally underlie the stratified rocks, but often pass up through the latter in a wedge-like form. Granite and trap are igneous rocks, and lava, or other volcanic rock, also belong to this group, and are the latest members of it. Limestone, oolite, and sandstones are familiar examples of stratified rocks. Rocks intermediate between aqueous and primary rocks are termed metamorphic : gneiss is a metamorphic rock. Fig. VII. shows the appearance presented by a vertical section of stratified rocks. The greater portion of the surface of the “dry land” is covered with loose fragments of rocks, mixed with the remains, more or less altered, of plants and animals. These matters are termed soils, and they extend downwards to distances varying from an inch to more than twenty feet. There are two kinds of soil, the super and the sub. The former term is confined to the layer next the surface, which contains nearly all the organic matter ( i.e ., animal and vegetable substances), and throughout which the roots of plants ramify. Tho sub-soil generally closely resembles the super-soil so far as their mineral ingredi- ents are concerned, but the condition in which these ingredients exist is somewhat different in the two soils. Both super- and sub-soils are often formed by the disintegra- tion of the hard rocks underlying them ; but sometimes thej are produced from the ddbris of rocks transported by aqueous agency from distances more or less considerable. The agencies which form soils are frost, rain, damp, oxygen, and carbonic dioxide. Wafer, when it is" converted into ice, expands about 10 per cent, of its volume. In the densest rocks there are little cavities containing water, which in winter often expand with irresistible force into ice, and thereby in- crease the size of the cavity. This process, carried on for centuries, produces tho disintegration of enormous quantities of rock. The mere mechanical action of rain and hail upon rocks also crumbles away in process of time the densest stone sur- faces — witness the rough and decayed aspect presented by so many of our stone buildings. Carbonic dioxide has a great affinity for potassium and sodium ; and as these metals are common ingredients of rocks, they are often abstracted from them by the free carbonic dioxide of the atmosphere — a circum- stance which renders the rocks more porous and friable. Tho ferrous oxide (protoxide of iron) in rocks is often converted into ferric oxide (per- or sesqui-oxide) by the atmospheric oxygen, and this process tends to break up the structure of tho rock. The influences of air and moisture upon the solid crust of the globe are, of course, confined to the surface, and take place with an extreme degree of slowness ; but influences, however small, exerted during a considerable period of time, ultimately produce great effects. The stratified rocks (which include soils) now in existence have been produced by the atmospheric influences of countless ages. It is, indeed, pro- bable that, as Liebig remarks, the atmospheric influences of a * From the Latiu stratum, a layer, and faccre, to make. BUILDING CONSTRUCTION. m thousand years are necessary to form from any kind of rock a layer of arable soil one-twelfth of an inch thick, suitable for the growth of plants. The composition of soils varies greatly. Some contain con- siderable amounts of calcic carbonate, others are very rich in organic matter, whilst many are composed of but little more than silica. As a rule, silica is by far the most abundant mine- ral ingredient of soils ; next oomes alumina ; and ferric oxide and calcic carbonate are about equally abundant. The follow- ing is the composition, according to Yoelcker, of a sandy soil (Tubney Warren, Abingdon), deficient in lime, alkalies, and phos- phoric acid. 100 parts of the dried soil contain — Organic matter . . . . . . . . 5‘88 Oxides of iron, and alumina . . . . . 4 - ll Carbonate of lime (calcic carbonate) .... O' 62 Magnesia . . . . . . . . . 0 '22 Potash and soda 0 14 Phosphoric acid . . . . . . . 0'07 SulplWic acid . . . . . . . . 0 '04 Insoluble silicious matter (fine sand) . . . . 88 '92 . 100-00 The amount of silica is generally from 80 to 94 per cent, in sandy soils, from 70 to 80 in clay lands, from 60 to 70 in loams and rich moulds, from 40 to 60 in marly clays, from 5 to 40 in calcareous or limy soils, and in marls. The proportion of alumina is greatest in rich loams, but it rarely exceeds 15 per cent. In clay soils alumina exists on the average to the extent of about 7 per cent. ; in sandy soils its per-centage varies from 1 to 5. Marls, calcareous soils, and vegetable moulds contain from 1 to 8 per cent, of alumina. The larger the proportion of alumina in the soil, the more diffi- cult is its cultivation — the adhesive character of the earth offer- ing a stubborn resistance to the passage of the plough and the spade through it. Porcelain and brick clays contain from 30 to 40 per cent, of alumina. The per-centage of calcic carbonate varies from 90 per cent, in the case of marls and limestone soils to mere traces. Clays and loams generally contain from 1 to 3 per cent, of this sub- stance. Less than 1 per cent, may be regarded as a defective proportion. Potash exists in soil from the merest trace to nearly 3 per cent. Soils rich in alumina are, with rare exceptions, also rich in potash. Sandy and peaty soils and marls- are in general deficient in this alkali. Soda is not so important a constituent of plants as potash ; and, except near the coast, it is not quite so abundant in soils as potash. Its proportion varies from a trace to 5s per cent. Magnesia is found in all fertile soils, and in per-centages which range from '05 to 1'5. Marly, peaty, and calcareous soils contain very minute amounts of phosphoric acid, but in clays its per-centage is occasionally 1’5. In general, even very fertile land contains less than 1 per cent., and the average amount is probably about 0'4 per cent. Sulphuric acid and chlorine occur very sparingly in soils. Carbonic dioxide is abundant in all cases where there is much lime. It is generally found in the form of calcic carbonate and magnesic carbonate. Organic matter (animal and vegetable substances more or less decomposed) is present in all soils capable of producing good crops. Sometimes, as in the case of bogs and peaty mosses, it is too abundant. It is most deficient in sandy soils, which often contain less than 1 per cent, of this ingredient. Cold clays are in general poor in organic matter. Fertile loams include from 10 to 14 per cent, of this valuable element of fertility. BUILDING CONSTRUCTION.— VI. BRICKWORK ( continued ). FOUNDATIONS. Having in the previous lesson shown the difference between English and Flemish bonds, we now purpose illustrating the method by which these may be worked together. Figs. 30 and Boulton’s were one-inch pipes, and it is an inte- resting fact (which we derive from Mr. Gisborne’s valuable essay) that these were made of porcelain by Wedgwood at Etruria, showing that in the same works where exquisite medallions and vases of a character adapted to elevate public taste were being executed, attention was also being given to the development of a less beautiful but equally important manufacture. The general adoption of pipe-tiles did not, however, take place for some years later. In Yol. IV. of the Royal Agricultural Society’s Journal for 1843 two excellent papers appeared upon land- drainage, the first by Mr. Thomas Arkell, of Stratton St. Mar- garet’s, Swindon, and the second by Mr. Robert Beart, but in neither of them is any other tile mentioned or figured, but the ordinary horse-shoe tile with soles. In the same volume is to be found a report by Mr. Josiah Parkes, consulting engineer to the Society, upon drain-tiles and drainage. “The society had offered a premium of ten sovereigns for the drain - tile which should fulfil certain specified condi- tions, but it was found quite impos- sible in the show- yard to authenti- cate the facts required ; conse- quently this prize was not adjudged.’,’ A silver medal was awarded by the judges to Mr. John Read, 35, Regent Circus, Piccadilly, for specimens of cylindrical or pipe tiles invented by him. These tiles were from 1 to 2 in. internal diameter, twelve inches in length, and were offered at £ 1 to £\ 14s. and ,£1 18s. per thousand. “It does not appear,” writes Mr. Parkes, “ that pipes have been anywhere used for land drains at a period more remote than thirty-five years since, about which time Mr. John Read made and employed them, when servant to the late Rev. Dr. Marriott, of Horsemonden, in Kent. These were about three inches in diameter, and were made by bending a sheet of clay over a wooden cylindrical mandril. This simple form of tile was well adapted for a more rapid mode of manufacture.” It would occupy too much space to enter at any length into particulars regarding the different machines which have been brought out for perfecting the manufacture of tiles. Mr. Pusey relates, in Vol. III. of the Royal Agricultural Society’s Journal (1842), how the cost of tiles had been a great check to their employment, and how, about two years previously, while 40s., 50s., and 60s. per thousand were paid for tiles in the south of England, Mr. Beart, of Godmanchester, had five years before invented a simple machine by which he had reduced the price of tiles from 40s. to 22s. throughout Huntingdonshire. The Marquis of Tweeddale followed with a most ingenious machine, and at the Bristol meeting Mr. Irving exhibited an apparatus for the same purpose. Formerly tiles, whether cylindrical or horse-shoe shaped, were perforated with occasional holes to allow water to enter easily. This is, however, quite unneces- sary, as water will have no difficulty in penetrating through the porous material of which they are formed, and when we re- member the joints which occur between each tile, it is evident that there is enough space for its entrance. COLOUR. 177 COLOUR— III. By Professor Church, Eoyal Agricultural College, Cirencester. PRODUCTION OP COLOUR BY TRANSMISSION, ETC. — MUTUAL RELATION OP COLOURS. The absorption and reflection of light are very closely related, yet there are many coloured bodies which instead of absorbing some rays and reflecting others, transmit those rays which they do not reflect. Even a third condition exists, in which a sub- stance reflects some rays of the incident light, transmits others, and absorbs the remainder. We may now briefly consider the production of colour by these three methods. Let us suppose a substance which appears ted by reflected light and red also by trans- mitted light. Of the white light which has fallen upon it and which it has decomposed, it has absorbed or quenched all the colours save the red; while of the red it has trans- mitted part and reflected part. But the instances in which a substance appears of a very distinct colour owing to reflection are rare. A few metals may be cited as ex- amples along with such sub- stances as murexide, magne- sium platinocyanide, potas- sium permanganate, and indigo. The yellow colour of gold is due to selective re- flection. A plate of this metal reflects much of the incident light unchanged, but it quen- ches in another portion muoh of the violet and other very refrangible rays, and so leaves the residual red, orange, and yellow rays to produce their colouring effect. It might seem likely that gold would transmit when in sufficiently thin leaves all those coloured rays which it does not reflect. This is true to a great extent ; still the grass-green light which a leaf of gold transmits is not perfectly complementary to the orange-yellow which it reflects, some of the constituent rays of the original white light having been absorbed. Solid indigo affords us a similar ex- ample of selective absorption and re- flection. If a lump of pure indigo be pressed with an agate burnisher, a copper-coloured streak makes its ap- pearance. As long as the substance of the indigo is not coherent — that is, as long as it is in minute powdery particles — so long it shows no symptom of a copper-coloured reflection, but is blue. Now the blueness of powdered in- digo thus seen by reflection is not really produced by or in reflection, but rather during transmission of light from particle to particle of the powder. A chromatic selection is thus made, and the light finally reflected to the eye has been deprived of several of its coloured elements. Increase the coherence of the blue indigo powder either by pressure, or by the chemical process of sublimation, by which crystals may be formed, and then, though the transmitted light will remain blue as before, the reflected light will be chiefly copper-coloured, having been deprived by reflection itself of its blue and some other constituent rays. The foregoing facts often suffice to ex- plain the great difference in oolour between a solid substance and its powder. Substances which are commonly regarded as transparent are never perfectly so. Neither water, nor flint glass, nor rock crystal, permit all light-rays to travel freely through them. Some substances, such as solutions of the rare metal didymium, P^nd certain specimens of the mineral known as zircon, absorb rft cut off several of the rays of solar light, and yet do not VOL. i. Fig. 4. Fig. 5. appear perceptibly coloured. The residual transmitted rays in such cases suffice to produce white light. Very thin layers of coloured substances, such as films of tinted liquids, may seem colourless, and yet, when we increase their thickness, colour be- comes perceptible. Not only does colour become perceptible, but the colour varies with the thickness. A crystal of blue vitriol shows on its thinnest edges a greenish tint, which alters to a pure blue in the mass. Such a change as this is easily ex- plained. A thin plate of blue vitriol transmits all the blue, a good deal of the green, and a very little of the remaining rays of the spectrum. If we double the thickness of the plate the effect is increased, not in arithmetical but in geometrical proportion. Ultimately, by the extinction of all the rays save the blue, the transmitted light becomes sensibly an homo- geneous blue. A very easy mode of observing the striking differences in colour between thin and thick layers was devised by Professor Stokes. A fine slit (one-fiftieth of an inch across) between two blac&ened metallic edges is adjusted vertically in a blackened piece of board ; behind the slit is a source of light, such as a bright flame of the sky. Hold the prism, having an angle of 60°, against the*eye ; by adjusting the position of the prism a pure spectrum will be ob- tained, showing, if solar light be used, the principal fixed lines. Now, to observe the absorption of any liquid, fix a test tube or flat cell contain- ing the liquid to be examined behind the slit. Begin the experiment by using a very pale solution, and then gradu- ally increase the strength, noting the gradual appearance of dark, lines or spaces in the spectrum and the blotting out of colour after colour. If a wedge-shaped trough be used to hold the coloured liquid behind the slit, it may be gradually moved so as to interpose thicker and thicker layers of the coloured liquids, and thus to produce the same results as those ob- tained by gradually increasing the strength of the solution. This method is of service when we wish to know the result of diluting any coloured liquid which has to be employed for artistic purposes. Thus, it will be found that some reds, when diluted, instead of becoming pink, pass through orange to yellow ; while some blues, instead of becoming paler blues when weak- ened, become either green on the one hand or violet on the other. We turn now to the re-composition of white light from its constituent elements. There are several ways of accomplishing this result. If we receive the spectrum of coloured rays pro- duced by one prism on another precisely similar prism, but in- verted (Fig. 4), the emergent beam, e, will be white. The con- centration of a spectrum by a bi-convex lens or a concave mirror gives a white and not a variegated image. Or the seven so- called principal colours of a spectrum may be received upon seven little mirrors (as shown in Fig. 5), and then these mirrors may be so adjusted that their separate images are superposed. In this case also a single white image is obtained. A less perfect mode of re-uniting oolours so as to form white may be accomplished in the manner suggested by Newton. A disc (Fig. 6) is painted in radiating segments with the nearest approach afforded by pigments to the seven colours of the spec- trum, the centre and edges being made black. The relative areas of the several colours must be adjusted so as to correspond as far as possible with the normal spectrum, introducing, however, such 12 178 THE TECHNICAL EDUCATOR. differences as the imperfections of the pigments used may de- mand. As red, green, and blue are the most prominent colours of the spectrum, they should be used in larger proportion than the orange, yellow, indigo, and violet. Indeed, a very respect- able kind of whitish grey may be obtained by the use of fewer colours than seven ; but of this point we shall have occasion to speak mere definitely further on. The best pigments, however, even when used in proper proportions, do not produce a per- fect white when the disc painted with them is rapidly revolved (see Fig. 7), so that the retina receives in quick succession the impression of the whole series. All coloured bodies absorb much light and do not reflect really homogeneous rays, and a grey is the reult. If several series of similarly coloured segments be painted on the disc the grey more nearly approaches white. In the latter case the eye receives simultaneously the impressions of the several colours, and so the effect does not wholly depend upon the long persistence on the retina of these impressions. We may now turn our attention to the mutual relations of the several colours. Reverting for a moment to the pure solar spectrum obtained by means of a prism and a slit, apd with the exclusion of all ex- traneous light, we may first of alf notice that it consists mainly of three colours — red, green, and blue. These coloured bands occupy by far the largest area of its most brilliant portion. The orange, yellow, and sea-green, though more brilliant, are very limited in extent, while the indigo and violet region of the spectrum is much less conspicuous. Now for many practical purposes the theory of the existence of only three primary or elementary colours will be found very useful. The selection of these primary odours has, however, been far from unanimous, one set of observers choosing scarlet, green, and blue, another vellow red, and blue. Nearly all writers on the artistic aspects of colours, such authors as Chevreul, Field, Redgrave and Hay, have accepted the latter selection ; but though it undoubtedly affords an easier means of studying the nature of the mixed colours which pigments and paints afford, it is but partially supported by experiments with the pure colours of the spectrum, and in some points is positively contradicted by them. The rival theory, in which the three primaries assumed are scarlet, green, and’ blue, has been profoundly studied by Maxwell, and has been made the basis of a small treatise on the science of colour by Mr. W. Benson, a London architect, who has done much to further the acceptance of this comparatively modern theory. We shall proceed to give an outline of both views as to the relations of the colours of the spectrum ; thus our readers will be able to form their own judgments on the two theories. For OUr owh. part we regard Maxwell’s experiments as conclu- sively proving most of the positions he has laid down when pure coloured lights are the subject of comparison and experiment. Yet in actual work with pigments themselves, the older theory affords a more immediate, though often a less exact, answer to any question which may arise. In order to study the primary or simple, and the secondary or mixed colours, several methods may be pursued. We here name three of the most important of these methods. Tint two pieces of paper with the two colours to be examined, place the coloured pieces an inch or two apart on a piece ot black velvet, and set up, equidistant between them, a slip ot thin, colourless plate glass; then adjust the eye so that one coloured patch may be seen by reflection from the near surface of the glass, coincident with the other patch as seen directly through the glass. By inclining the glass the reflected image of one colour may be altered in intensity, and so the relative proportions of the two colours may be varied at pleasure. . # i Another plan, devised, like the last, by Helmholtz, consists m / obtaining two intersecting spectra. Two clean-edged narrow slits, forming together a right angle, thus V , are made in a metallic plate. When this compound slit, brightly illuminated from behind, is viewed by means of a prism about twelve teet off two overlapping spectra will be seen, the prism being he d vertically. As each coloured band of one spectrum crosses all the coloured bands of the other, the result of combining two o the spectrum colours together may be studied. For this pur- pose it is desirable to employ solar light, the fixed lines of which afford a means of identification of the several colours, and may be readily seen in the above-named spectra by means of a telescope. The telescope is furnished with cross wires, and a diaphragm for limiting the field of view, placed a short dis- lig. 8. tance frctin the eye-piece of the telescope and close to tie eye. A third slit may be used, if it be desired to unite three caoured rays. A modification of this method of producing overlipping spectra consists in cutting out from a piece of white cariboard three pieces of the shape indicated in Fig. 8 by the black spaces. The perforated cardboard, which should be of larje size, is placed in a bright light with a piece of black velvet beow it. It is then to be viewed six or seven yards off with a prism laving its refracting angle turned away from the eye, and placed ah right angles with the edge a b of the cardboard figure. No desc?iption can give an idea of the beauty of the overlapping spectra thus produced. The results obtained by Helmholtz and Max- well, by means of experiments conducted by the method of overlapping spectra, will be described below. A third method of combining colours is by means of a revolving disc such as that represented in Fig. 7. The disc may be painted with the colours it is desired to combine, and then rotated. Of course the proportions of the colours used may be varied not only by painted segments having different areas, but by the superposition of a second or third disc upon the original one, the additional discs having segments of different areas cut out, and being themselves either white, black, or coloured. The various kinds of colour-tops and kaleidoscopic tops may be used for these experiments. We may n portant fortresses or military stations with one another. In case i of an invasion all ordinary lines would at once be cut ; but if an i underground wire has been laid by a circuitous and well-chosen b route,' "’it is very difficult to discover it. In the present French , wa r several of these lines, connecting different fortresses, have ) been discovered and cut, but not till after they had rendered r good service to the besieged. I Submarine lines are of much greater importance than these, j an( J have demanded in their manufacture all the skill and in- a genuity that could be brought to bear. To us, in our snug island home, they are especially important, and by their means - we are now linked in electrical circuits with all neighbouring t countries as well as with several s which are very remote from us. y The first attempt at a sub- e marine cable consisted of a wire 3 coated with gutta percha, which e was laid between Dover and t Calais in 1850; but this was so y imperfect that it failed after the d first day. A fresh attempt was, s however, made the next year with much increased success. The d cable laid on this occasion is re- ,t presented in Fig. 9, which shows y a section of the true size, g The conductor consisted of four copper wires (No. 10 Bir- II mingham wire gauge), each of which was separately insulated d by being covered with gutta-percha. These wires were laid e side by side, a little hemp being placed between them to prevent n their chafing ; tarred hemp was then laid on so as to form a i . solid rope, and outside all, as a protection against accidental d injury, there were galvanised iron wires (No. 1 Birmingham 3 - wire gauge) spirally wound. The cable, when complete, weighed )- about seven tons per mile, and possessed very great strength. THE ELECTRIC TELEGRAPH. 181 It was found to answer admirably, and has remained in working order ever since. This experiment having succeeded so thoroughly, many other lines were speedily projected and laid, most of which answered well. There have, however, been several failures, and these very costly ones ; but they have been the means of drawing attention to defects in the mode of manufacture, so that in the present day success is almost certain, even when the length of the cable is very great. It will easily be seen that the risk and difficulty increase in a very rapid degree with the length. A few very minute imper- fections, so trifling as only to be discovered by the greatest care and scientific skill, will suffice to render a long cable almost useless, and it is very difficult to get at them so as to repair them when once the cable is laid. The pressure of the water, too, at the bottom of the sea is very great, and thus any flaw soon becomes manifest, as the water is forced into it, and makes an escape for the electricity. The whole of a cable is now constantly and carefully tested during all the processes of its manufacture, so that there is but little chance of a defect passing unobserved. The core after being made is submerged in water, and after remaining so some hours is carefully tested ; should any portion prove defective, the exact position of the fault is ascertained, the defective piece is removed, and the core spliced again. The same pro- cess is repeated when the cable is complete; and during the process of laying currents are continually transmitted along it, so that faults, should there be any, may at once be detected and removed. In 1853 a cable was laid between Dover and Ostend; this was very similar in construction to that already figured, but it contained six conducting wires instead of four. More recently this plan has been almost given up, and each cable now usually contains only one conductor, though this is often composed of several wires twisted together. In 1856, so rapid had been the advance in the manufacture of telegraph cables that a project was started for making one to connect England and America, and in the summer of 1858 this was completed and laid. The deep- sea portion of this (Fig. 10) was much lighter Fig. 10. than those already described, weighing only one ton per mile. The conductor here consisted of seven copper wires, No. 22£ gauge, twisted together. It was con- sidered preferable to employ these instead of a single wire of larger diameter, as in case of any defect in one wire the current would easily be transmitted along the remaining six without being perceptibly interrupted. This strand was carefully covered by three coatinp of gutta-percha, so as fully to insulate it ; addi- tional protection and strength were then imparted by a serving of jute saturated with tar and other preservative materials, and outside this, eighteen strands of iron wire were carefully wound on, each strand consisting of seven wires No. 22 gauge! Near the shore there is, of course, a much greater risk of accident than in the deep sea, where, when the cable is once laid, it soon becomes covered with sand or silt, and is practically safe from injury. In the shallow water the bottom is more affected by currents and storms, and hence a much stronger portion, known as the shore end, is spliced to the deep-sea part of the cable. In this first Atlantic cable the same core was used as for the deep-sea portion, but instead of the strands of fine iron wire, an extra serving of hemp was laid on, and outside this twelve stout iron wires were coiled, so that the diameter of this portion was nearly three times as great as that of the rest. The total length of the whole was a little over 2,000 miles. It was, however, far from successful ; sufficient care was not taken in testing it ; hence there were faults in it from the very first, and only a few messages were passed along it before communication entirely ceased. This experiment, being a very costly one, checked a little the manufacture of cables ; but the causes of the want of success soon became apparent, and thus much valuable informa- tion was obtained even by the failure. Two cables have since this been laid between England and America, both of which have answered well, though some serious difficulties were encountered in laying them. Faults have occasionally been discovered, but these have been found to arise from injuries inflicted either by design or acci- dent, and have been repaired. In laying one of these, the cable Fig. 11. broke and the end was lost. The exact position was, however, noted, and suitable drags being obtained, the end was fished up from the bottom, spliced on to the new cable, and the whole completed. The fact of thus being able to find the end of a cable, lost at a very great depth, is perhaps one of the most wonderful recorded in connection with the laying of submarine cables. The former of these two cables is represented in Fig. 11. The core con- sists of seven No. 18 gauge wires, twisted into a spiral ; this is covered with four coats of gutta-percha, alter- nating with thin layers of Chatterton’s compound, which consists of 3 parts of gutta-percha, 1 of Stockholm tar, and 1 of resin. These bring the dia- meter of the core nearly up to half an inch. Outside this is a covering of hemp, well saturated with salt water, and an outer layer of ten wires of homogeneous iron. The peculiarity here is that each of these* is separately sur- rounded by Manilla yarn, saturated with a preservative com- pound. For the shore end a portion of the completed deep-sea cable is used, but it is furthei’ strengthened by another layer of hemp, and some more wire strands. For submerging this cable the Great Eastern steamer was employed, fitted with large tanks, in which the cable was coiled and kept submerged till it was laid. All the core was tested in water at a considerable pressure before it was made up into the cable. One of the most recent cables laid is that along the Persian Gulf, between Teheran and Bushire. The core of this consists of copper wire of good quality covered with Hooper's india- rubber compound to a diameter of ’320 inch. Two servings of hemp saturated with tar-water were then laid on in reverse directions, and strength was imparted by twelve galvanised wires T92 inch diameter. These were separately covered with a mix- ture of tar and asphalte, and the whole then coated externally with two layers of Clark’s Patent Asphalte Covering, so as to give it a smooth and even surface. Fig. 12 shows a portion of the cable, each layer being separately removed to show the construction, while Fig. 13 shows a section. Many other forms of covering have been tried with varying degrees of success, tll0 objeet in all being to reduce as far as possible the size, and consequently the weight of the cable. This, how- ever, must not be done at the expense of strength or durability. One cable, constructed by Messrs. Siemens, con- sisted of a small core, protected in the usual way by fine hemp, and out- side this four strips of thin copper sheet were wound round in such a way as partially to overlap one another. This cable, which was laid between Carthagena and Oran, worked uncommonly well for a little time, but it was laid on a very bad bottom, and consequently was soon chafed and broken. When the bed of the sea is rocky the cable is very apt to chafe, especially if there be any great inequalities. The best Ig ’ ~ J ' bottom is a flat one covered with fine sand or siliceous deposit. In this a cable is thoroughly protected, and should last almost indefinitely. We have now carefully inquired into the different ways in which the electric fluid can be conveyed from place to place. It is, however, necessary, as we have seen in our lessons on “Electricity,” to have a complete circuit in order for the current to produce any effects ; in other words, we must provide some return path for the current, as well as a conductor along which it may travel to its destination. For this purpose a 182 THE TECHNICAL EDUCATOR. special wire used to be erected, so that the current might pass along the one and return by the other. This was, however, soon found to be unnecessary, since the earth will answer every purpose of a return wire. All that is requisite is to bury a large plate of metal in the earth near each station, and let the earth wire of the distant station be connected with the one there, while one pole of the battery at the transmitting station is connected with its own earth plate. The current then passes along the wire, through the instrument, on to the earth plate, and back again by the earth plate to the battery, thus completing the circuit. There are, however, a few occasions in which a return wire is a great ad- vantage. Strong currents of elec- tricity at times appear to travel from one part of the earth’s surface to another. This is especially noticed during the appearance of the Aurora Borealis. Sometimes they continue to flow steadily in one direction, at other times they change very rapidly. These are known as “ earth currents,” and they seem to enter the wires by one of their earth connections and travel along them, deflect- ing the needles in their way. If the earth connections be severed, these currents at once cease in the wires ; but while they are passing messages are considerably interfered with. Sometimes, when they are steady and uniform, communication may be maintained by cutting the batteries altogether out of circuit, and signalling by the earth current alone. It is not often, however, that this can be done, and the best course then, if there are several wires between the stations, is to alter the connections so as to make one a return wire, joining on the earth wires from the instruments to it instead of to the earth plate. When this is done the whole circuit is completely insulated and cut off from all communication with the earth ; the earth currents cannot therefore pass along the wires, and if they affect the working at all, only do so by their inductive action. Any line of telegraphs — whether aerial, subterranean, or sub- marine — is liable to injury, as, e.g., by the breaking of an insu- lator or a wound in the insulating covering, and at first it was a somewhat difficult matter to discover the exact place of the fault, or, as it is termed, to “ localise” it, the only plan being to test at intervals all along the line until the exact place at which the communication became defective was discovered. The rapid advance, however, made recently in the construction of delicate pieces of apparatus, and our increased knowledge as to the laws which regulate the passage of electric currents, now enable the operator, without leaving the station at which he is, to discover the exact place of the fault, and thus without loss of time to have it repaired. The manner in which this is accomplished we must explain in our next lesson. ANIMAL COMMERCIAL PRODUCTS. — VIII. HORNS AND ALLIED SUBSTANCES (continued). Horn is manufactured into many other articles besides combs. Snuff-boxes, drinking-cups, shoe-horns, and powder-horns are all made of horn. The fragments of horn, melted and com- pressed into a solid mass in moulds, form bell-pulls, handles for table knives and forks, knobs for drawers, and many other useful articles ; or, if exposed to a decomposing heat in close vessels, these fragments develop prussic acid, and for this reason are in demand among the manufacturers of Prussian blue, and of the beautiful yellow prussiate of potash. The solid tips of the horns are always sawn off, because these parts are not lamellated, and therefore incapable of separation into plates. They are made into knife and umbrella handles, the tops of whips, buttons, and various other articles both useful and ornamental. The quantity of horn annually worked up in the manufac- tures of Great Britain, including the produce of our own animals, is estimated at 6,400 tons, of the value of <£180,000. The comb manufacturers alone consume 1,300 tons, which pro- duce d>320, 000 worth of combs. Horns of oxen are largely ©sported from South America, from Buenos Ayres, Monte Video, and Brazil, the last taking, as regards size and quality the first rank. The Indian buffalo from Siam furnishes a very valuable horn, of which we receive annually about 26,000 j the Cape of Good Hope and New South Wales also supply our markets with ox-horns. The manufacture of articles from hoofs and horns is carried on very extensively at Aberdeen in Scot- land, where an immense establishment exists. The hoofs of horses and ruminant animals, though similar tc horn in character, are not so useful as horns, because they are much heavier and are less easily worked. They are, however, tc some extent made available in the manufacture of buttons cheap combs, and similar articles. II. WHALEBONE. Whale ( Balcena mysticetus ). — This animal furnishes the baleen, or whalebone of commerce. Commonly regarded as a fish, they are nevertheless true mammals, producing their young alive, and suckling them for a considerable time. They are very sociable, swimming in large shoals, and sporting or the surface of the water in their native Arctic seas. Whalebone or baleen consists of numerous parallel lamina descending perpendicularly from the palate of the animal. The object of this structure is to form an efficient sieve or strainer for the food of the whale, as it comes in with the water. Although provided with an immense mouth, this enormouB creature has an oesophagus or food-pipe so small, that he iB compelled to nourish his vast bulk by the consumption of some of the smallest inhabitants of the sea, his food consisting of small mollusca and Crustacea. “ To procure these insignificant; morsels, he engulfs a whole shoal of them at once in his capa- cious jaws, where they are of course entangled among the fibres of the baleen ; the water is then strained off and expelled through the blow-holes, and the monster is thus enabled to pass his diminutive prey at his leisure into his stomach.”* The length of the largest pieces of baleen in a whale sixty feet long is about twelve feet, and the pieces are arranged in two rows, 300 in each. The average weight of each piece is seven pounds, and the weight of the whole is therefore 4,200 pounds, or upwards of one ton and three quarters, worth about <£160 a ton. Whalebone is prepared for use by immersion for twelve hours in boiling water, which softens and renders it fit for manu- facturing purposes. It is valued for its flexibility, tenacity, compactness, and lightness, and is cut into quadrangular sticks for the ribs of umbrellas and parasols, the supports of stays and other articles of ladies’ wear. In thin strips whalebone is used for covering whip-handles, walking-sticks, and telescopes. These strips also are plaited like straw to form hats and bonnets, whilst the fino shavings arc employed by the upholsterers as a stuffing for cushions, for filling fire-grates in summer, and for other useful purposes. III. OSSEOUS SUBSTANCES. Antlers . — The antlers of the different species of deet are very valuable for making a variety of useful and ornamental articles. The chief supply is furnished by the elk, wapiti, stag or red deer, and fallow deer. In Switzerland, brooches, pins, and bracelets are made from stag’s horn ; in Sheffield the whole shaft of the horn is used in making the handles of carving- knives, or it is cut up into small plates and riveted on to an iron case for the handles of pocket and pen knives. About 400 tons are annually imported from Hindostan and Ceylon for this purpose ; another 100 tons come from Germany, Bussia, Spain, and Italy, and from our own parks. About 18,000 head of deer are annually killed in Greenland, and their horns sent over to this country. The shavings of the horns are employed for the purpose of making ammonia, which has therefore long been popularly known as “ hartshorn.” Ivory . — Our supplies of ivory are derived chiefly from the Asiatic and African elephants ; the tusks or canine teeth of these animals furnish the article, but those of the African species are the most valuable. Elephants’ tusks from two to ten feet in length, and weighing from 6 to 160 pounds, are Imported into this country from Senegambia, Guinea, Mozambique, and Sofala; and also brought from the interior of Africa * “Natural History of the Animal Kingdom.” By W. S. Dallas, F.L.S. 1856. Fig. 13. TECHNICAL DRAWING. 183 in caravans and shipped at Alexandria, Tunis, Tripoli, and Cairo. We receive them, besides, from Bengal, Birmah, Siam, Cochin-China, Ceylon, Sumatra, and Java. There are large buildings erected in Birmingham for the manufacture of ivory, and also at Nuremberg in Germany. The Chinese are unrivalled in this manufacture. Their ivory balls, carved one inside another, are marvels of patience, industry, and ingenuity ; and their chessmen, cabinets, drinking-cups, and numerous other articles made of this material are most elaborate in their ornamentation. Generally and technically under the name of ivory are com- prised the teeth of the narwhal ( Monodon monoceros), walrus { Trichecus rosmarus), and hippopotamus ( Hippopotamus amphi- bius), which, like ivory, are worked up into a variety of things, and always keep white. Ivory is largely consumed in the manufacture of billiard-balls, which cost from six to twelve shillings each, and are so nicely turned that they are perfectly spherical, and made to corre- spond accurately in size and weight, even to a single grain. The greatest consumption of ivory is undoubtedly in connection with the cutlery trade. A large amount is also worked up in the manufacture of the backs and handles of the best hair and tooth brushes. The miniature tablets, so invaluable to the artist, are cut from off the tusk by an extremely thin saw acting horizontally, just as we pare an apple ; so that from a solid tusk, of the ordinary size, a sheet of very considerable length can be obtained. In the Great Exhibition of 1851, one manufacturer exhibited a sheet of ivory sixty feet in length, obtained without joining, and which had thus been pared off from a single tusk. We import annually 50,000 elephants’ tusks, weighing 10,000 cwts., and consequently we may calculate that not less than 25,000 elephants are killed annually to supply the English market alone. The material of ivory is so valuable, that economy in its use is necessarily studied, and the smallest fragments are preserved. The refuse of ivory is used for making the finest black colour ( noir d’ivoire) by converting it into charcoal in air-tight vessels. Such ivory refuse, consisting of ivory scrapings, shavings, and sawdust, when boiled, makes an excellent jelly, quite as good as calf’s-foot jelly, and with the advantage that it suffers no change by keeping. Ivory refuse is therefore saleable to the confectioner and pastrycook, by whom it is very frequently employed in this way. Bone. — The skeleton, or framework of animal bodies consists of bones articulated with each other, which protect the vital organs, and form a basis or support for the softer parts, and for the attachment of the muscles, or organs of locomotion. In the arts, bones are extensively employed by the cutler, comb and brush maker, chemist, confectioner, and agriculturist. Common bone is manufactured into buttons, combs, knife, fork, and brush handles, card cases, parasol handles, book folders, and numerous other articles. The chemist obtains phosphorus, sal-ammoniac, and charcoal from bone, and the farmer a most valuable manure — super-phosphate of lime — which has a quick and efficient action on the crop. Large quantities of bones of oxen are imported to Great Britain from Buenos Ayres, etc., for this purpose ; and also the bones of seals, captured in the North Seas for their fur and oil, and brought home by the sealers. The number of tons imported during the year 1867 amounted to 83,814. TECHNICAL DRAWING.— XII. DRAWING FOR JOINERS. The limits of these lessons now render it necessary that some attention should be paid to such examples as form studies for drawing for joiners. Tet we would not wish to be understood that the lessons hitherto given do not appertain to joiners, or that those about to be given possess no value to carpenters. It is difficult to say what is the exact boundary which divides the two branches of wood-work. The general rule, however, is that carpenters’ work is structural, and connected with the carcase, whilst that of a joiner comprehends the finishings of the outside and inside of a building. Of course, greater refinement and nicety is required by the joiner in practice ; but this will not .hurt the carpenter, nor can the structural knowledge required by the carpenter fail to benefit the joiner. In fact, a general knowledge of the practice of each will make both work with greater economy, for one will work into the other’s hands ; their work will, to use a technical term, “ dovetail ” together, therefore the two branches are not separated here by a hard line ; and that the student may see that the higher branches of joinery approach cabinet-making and wood-carving, examples belonging to both of these branches are introduced. We all know the pleasure it is to meet with a joiner who, in addition to the work of laying down floors, putting up wainscots, or fixing window-sashes, can, when required, set out and execute a piece of Gothic panelling or an organ screen, or who is able to carve any portion of the turn of a moulding which cannot be worked with the plane or struck by the machine. We therefore strongly urge the student to work from the examples herein with the utmost care, and subsequently to follow up the system as he will find it laid down in the special technical lessons devoted to his trade. Eig. 90 shows the method of uniting the boards a and b in a flat surface, called “ dowelling.” The edges of the boards having been accurately planed, holes are bored, pins (as at e) are glued into the one, and the projecting ends being inserted into corresponding holes in the edge of the other board, unite them firmly — the edge of the board c and the end of the pin being glued. Square pieces of hard wood, or dowels, are often used in the place of pins, and are shown at d. Fig. 91 is a method frequently adopted in floor-boards and panelling. It is called rebating, and consists in planing away half the thickness of the edge, so as to leave a ledge standing ; all the boards being thus rebated, the ledge left on the one fills up the rebate, or “ abated ” edge of the other. This will be clearly understood on referring to the illustration. Fig. 92 is a method of joining boards called 11 roughed and tongued.” In this case a groove is planed in the one edge, and a tongue left (by planing away the angles) at the other edge of each board ; the tongue of the one then fits into the groove of the other. In very good work it is usual to plough both edges, and insert a separate tongue. This tongue is formed of strips cut the cross way of the wood, as shown in Fig. 93. Fig. 94. — This method consists in working grooves across the back of the pieces, a, and forcing rabbets into them, as b b. The bottom of this groove is flat (a), and its sides slant in- wards towards the bottom. The sides of the rabbet are also cut slantingly, and a joint is thus formed called the “ dovetail notch.’’ This method is exceedingly well adapted for making drawing- boards. The rabbets must not then be glued, or otherwise fastened in, and thus, by means of their dovetailed edges, they keep the board from warping, whilst at the same time they allow of its expansion and contraction, and thus splitting and twisting are prevented. Fig. 95 is an illustration of the method of clamping the ends of boards, a b, by tongueing the board and ploughing the piece which is to cross it, c. Sometimes, instead of bring- ing the end of the cross-piece flush with the edge of the board, it is cut off at an angle, the board being cut correspondingly to admit of the insertion. This last method is called mitre clamping. Fig. 96 shows a very common method of joining up a flat surface by means of framing and panelling. A groove is run in the edge of the frame, the edges of the pand'l are rebated, and the whole brought up flush. Fig. 97 shows a portion of a panel inserted into a frame where a flush surface is not required. Fig. 98 represents one of the many methods employed for angle joints. It is the simple mortise and tenon, a shoulder being left on the outer side of the tenon by which the one piece is secured against being forced out of perpendicular. Fig. 99 is another method, which is accomplished by means of a mitre, part of the wood being left as a tenon at the end of the one part, which is inserted into the mortise at the end of the other. A pin is then passed through the whole. DOORS. The most common kinds of doors are constructed of several simple boards, not fixed with glue or any tenacious substance, but by nailing transverse pieces upon the back of the boards 184 THE TECHNICAL EDUCATOE. laid edge to edge. The transverse pieces thus nailed are called ledges or bars, whence the door is said to be lodged or barred. In this case one of the edges at every joint is beaded on both sides, or at least on the face which is outside, the edges being placed on the inside. Doors of this description are generally employed in cottages or out-houses. Where doors are required to combine r ■ - . ■ ■ strength, beauty, and durability, a frame, joined with mortise and tenon, must be constructed, with one or more intermediate openings, each of which must be sur- rounded by three or more parts of the frame, which have grooves ploughed in the edges for the re- ception of boards to close the openings, in- serted as in Fig. 97. The parts of the framing which are horizontal when the door is hung or fixed upon its hinges are called rails — upper, middle, and lower. The extreme parts of the frame, to which the rails are fixed, are called the stiles, and the intermediate ones are termed mount- ings. The boards by which the interstices are closed ‘are called panels. Fig. 100 is the ele- vation of a pair of folding - doors, with mouldings and cor- nice. In this example it is desirable to com- menee by drawing the entire framing and cornice, with their mouldings. Then draw a central per- pendicular, on which mark off the heights of the various rails and panels, and draw horizontal lines for the upper and lower edges of these. From the central perpendi- cular next set off the width of the stiles, etc., and draw the necessary perpendi- culars. The mould- ings to the panels may now be added. Fig. 101 is the section, on a larger scale, of the frieze and cornice, showing how the various members are put together. The ornamental moulding, /, is in this design supposed to be made of pressed zinc, in which some very beautiful patterns are now worked, which are by far more durable than those made of composition. Fig. 102 shows the manner in which such doors meet in the middle. Fig. 103 is the plan of a folding (or French) window and shutter-box. a is the framing of the window ; b, the window ; c d, the folding shutter closed ; cd, ditto folded ; efi, the casing; of the shutter-box ; g, the wall ; h, the inner casing. PARQUET WORK. Parquetry is a beautiful species of flooring, consisting of various patterns formed of different woods — such as cherry,, oak, ebony, walnut, mahogany, maple, etc. It is very much used both in Germany and. . — , . France, and is now becoming fashionabla in England. The wood of which the par- quetry consists is, usually one inch, thick, grooved,, ton- gue d, and keyed at the back and corners. It is well adapted for reception rooms and picture galleries, for. borders round Turkey carpets, as well as for landings and panel- ling of rooms. Fig. 104 is a design based on the square only, and is too simple to require any in- structions as to draw- ing, further than the advice already so fre- quently given — to work with the utmost' accuracy, for in sucli repeating patterns, any one of the com- ponent figures, being' inaccurately formed* throws out the whole design. Fig. 105. — This design is drawn by setting out a number of squares. Draw- diagonals and circles from tire angles. All the other lines em- ployed will be found- to be parallel to» these. Fig. 106 is also# based on the square. Having set out a, number of squares, divide the sides of each into three equal parts, and draw lines- across so as to divide- each of the squares into nine smaller ones. In each of the* four small squares occupying the corners of the larger ones, draw one diagonal ; and in each of the four squares occupy- ing the middle of the sides draw two diagonals. By shading the portions as in the example, the design will be developed- Fig. 107 is based upon the hexagon. To draw this pattern, construct a line of regular hexagons, t3ach touching two others, by their angles ; divide each hexagon ihto six equilateral tri- angles by diagonals. Find the middle of the sides, and draw lines to the middle points of the alternate sides ; these will give two equilateral triangles crossing each other ; and the required- portions being coloured, the star in the centre will be left. The, darker lines are drawn parallel to the sides of the hexagon- 186 THE TECHNICAL EDUCATOR. VEGETABLE COMMERCIAL PRODTJCTS.-VI. PLANTS USED IN THE PREPARATION OP NUTRITIOUS AND stimulating beverages ( continued ). Paraguay Tea, or Mate (Hex Paraguayensis ; natural order, Aquifoliacece) . — A small shrub with oval, wedge- form, or oblong-lanceolate, toothed, smooth leaves, somewhat like those of the orange. This plant, which is, in fact, a species of holly, occupies the same important position in the domestic economy of South America that the Chinese plant does in this country. The leaves are prepared by drying and roasting — -not in the manner of the Chinese teas, in which each leaf is gathered sepa- rately ; but small branches with the leaves attached to them are cut from the plant, placed on hurdles over a wood lire, roasted, and then beaten on a hard floor with sticks. The dried leaves and stems thus knocked off are collected, reduced to powder, and packed in hide sacks. Each of these sacks, when full, contains from 200 to 250 pounds of the tea. The sacks are sewed up, and as the hide dries and tightens by exposure to the sun over its contents, at the end of a couple of days the tea forms a substance as hard as stone, and almost as heavy. As found in commerce, Paraguay tea is, therefore, in the form of a greenish-yellow powder, mixed with broken leaves and stems. This is infused in boiling water, and the decoction is drunk, or rather sucked up, by means of a tube perforated with small holes. It is usually imbibed out of a small gourd or cup with a little sugar, and sometimes an aromatic is added, such as orange or lemon-peel, or cinnamon, to give it an additional flavour. Mate is generally disagreeable to those unaccustomed to its use, but a taste for it is soon acquired, and it is very refreshing and acts as a restorative to the human frame after great fatigue. It has been calculated that 40,000,000 pounds of Paraguay tea are annually consumed in the various South American Republics. Coffee Tree ( Coffea Arabica, L. ; natural order, Rubiacece; sub-order, Cinchonacece). — An evergreen shrub, from fifteen to twenty feet in height, with an erect stem covered with a brownish bark, and opposite branches with a slightly downward inclination, giving to the whole shrub an elegantly beautiful pyramidal contour or outline. Leaves opposite, short-stalked, ovate-lanceolate, entire, glossy dark-green above, paler beneath, and from two to three inches long ; flowers, white and funnel- shaped ; fruit, a globular two-celled and two-seeded berry, about the size of a cherry. The seeds, freed from their hard, horny, parchment-like husk, are hemispherical, with one side convex, and the other flat and furrowed. The flowers of the coffee-tree resemble those of the white jessamine, and appear in clusters in the axils of the leaves. The trees are very beautiful and fragrant when in bloom, and not less attractive when the berries are ripe and ready for cropping, for these are then of a deep scarlet colour, and show to great advantage amongst the dark-green glossy leaves. The home of the coffee-tree is said to be Abyssinia, where it still grows wild ; thence it wai transplanted to Arabia towards the close of the fifteenth century. It was introduced by the Dutch into Batavia in 1690, and thence carried to the West Indies in the beginning of the eighteenth century, and after- wards to the Brazils. Coffee is now grown in almost every tropical country having an average temperature of above 55°. We receive it from Java in the East Indies, from Trinidad in the West Indies, and from Rio Janeiro in South America. The best coffee comes from Mocha in Yemen, the southernmost pro- vince of Arabia. As soon as the crimson colour of the coffee berry indicates the time for harvesting, the berries, which drop readily when mature, are shaken from the trees upon cloths or mats spread under them. They are then piled together in heaps for forty- eight hours to soften the pulp, and afterwards put into tanks through which water flows continually, to wash off the pulp ; the berries are then spread out on the platform, with which every coffee estate is furnished, to dry in the sun. But there still exists the husk, which is broken off by means of heavy rollers ; the seeds are then winnowed, and put into bags for sale. Raw coffee is roasted, after it arrives in this country, in a hollow iron cylinder, which is kept turning for half an hour over a charcoal fire until the berries are coloured sufficiently brown. Roasting coffee improves its flavour and power as a stimulant. Coffee owes its properties to a peculiar principle, which has been called by chemists caffeine, and which is identical both with the theine of the tea and the theobromine of the cocoa plant. If is worthy of note that the common beverages of man — tea, coffee, and cocoa — although found in the most dis- similar plants, nevertheless contain identically the same peculiar principle which gives them their nutritious and stimulating properties. Coffee is said to have been first used by the Persians as a beverage as early as 875 a.d., and from them the Arabs learned its value. The first Arab who drank coffee was Megalledin, Mufti of Aden, in Arabia Felix, who had become acquainted with this use of the coffee berry when in Persia. The con- sumption of coffee was not at all rapid at first, and it was not until 1554 that it was publicly sold at Constantinople. It afterwards became very popular with the Turks, but as it fre- quantly led to social and festive meetings, which were considered incompatible with the strictness of Mahometan discipline, its use was restricted by the Turkish Government, though without effect. In vain the Turkish priests complained to the authorities that the mosques were deserted, whilst the coffee-houses were crowded ; in vain the latter were shut up by order of the Mufti, and the police employed to prevent any one from drinking coffee ; the Turks found means to elude their vigilance. They would have their coffee. The law, therefore, became only a dead letter, and although never repealed, the Government acknowledged its defeat by finally laying a tax on the beverage, thus making it a source of considerable revenue. The consumption of coffee in Turkey is very great. This is probably owing to the strict prohibition which the Moslem religion lay3 against wine and spirituous liquors. So necessary is coffee to the Turks, that the refusal of it in reasonable quantities to a wife is considered to be a sufficient ground for a divorce. The coffee-houses in Turkey are very numerous, and some of them spacious and handsome. In Constantinople, such as are regularly licensed are gaudily painted, and furnished with mats, platforms, and benches. Sometimes there is a fountain in the middle of the room, which renders the atmosphere de- lightfully cool ; and also a gallery for the musicians. Towards evening these houses become thronged with a motley assemblage of Armenians, Greeks, and Jews, all smoking and indulging in tiny cups of coffee, generally drunk without either sugar or milk. It is in the Turkish coffee-houses that the vagrant story- teller finds his stage and his audience. He walks to and fro, stopping when the sense of his story requires some emphatic expression or attitude, and generally contrives to break off in the most interesting part of his tale, making his escape from the room despite every precaution that may be taken to prevent him. His auditors thus compelled to restrain their curiosity, are induced to return at the same hour to the coffee-room. As soon as he has made his exit, the company present commence an animated discussion, in separate parties, as to the character of the drama, and the principal events of the story. The following account, by Mr. M'Farlane, is characteristic of Turkish manners, and of the mode in Turkey of setting aside the laws in reference to coffee : — “ I was surprised to see in Smyrna, and in numerous other towns, the scarcity of coffee-houses and the quantity of barbers’ shops. It was explained when, on wishing to rest a while, my servant David led me into one of them, which in appearance was devoted to shaving, but which concealed behind a wooden screen, that looked like the end of a room, a spacious recess hung with chibouks, or common pipes, narghiles, or water pipes, and tiny coffee-cups. The small characteristic fire for the preparation of the fragrant berry was burning in the usual corner, and there were the usual supplies of benches and stools — in short, it was a bond fide coffee-house, screened by a barber’s shop, and a group of Osmanlis shuffled in after us, not to be shaved, but to smoke their pipes and drink their cup of coffee. “ ‘ David,’ said I, ‘are all these hundreds of barbers’ shops nothing but veils for coffee-houses ?’ “ ‘ Not all, but the greater part of them,’ was the answer. “ ‘ Yet the disguise may be easily penetrated. Any bostangi might discover the recess, and arrest a crowd of delinquents, as here, for example.’ “ ‘ That is all very true,’ said David, * but what would the bostangi get by that P The fact is, the Turks cannot live PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING. 187 without coffee-houses ; besides, the order to shut them up is now an old affair. Each proprietor may make it worth his while not to see, and so you understand the bostangi and his officers need not look beyond the barber’s shop.’ During the latter part of this speech, a Mollah, a stout advocate of both law and gospel, stepped in, and called for his narghile and coffee ! ” Coffee was first sold in London in 1652, by a Turkish mer- chant, who kept a house for that purpose in George Yard, Lombard Street. It soon became very popular, and in 1660 a tax of f ourpence on the gallon was levied on all coffee made and sold. It spread amongst the English for reasons very similar to those which caused its spread among the Turks. According to Macaulay,* it extended most rapidly. To be able to spend the evening sociably at a small charge soon become fashionable. The coffee-house was “ the Londoner’s home.” Nobody was excluded who laid down his penny at the bar. There were coffee-houses where politics were discussed, where literary men held their meetings, and where doctors, divines, and lawyers congregated, and might bo consulted. “ There were Puritan coffee-houses, where no oaths were ever heard, and where lank- haired men discussed election and reprobation through their noses ; Popish coffee-houses, where good Protestants believed over their cups that the Jesuits were planning another Gun- powder Plot, and oasting silver bullets, to shoot the king ; and Jew coffee-houses, where the money-changers of different nations greeted each other.” Such was the respectable position of a London coffee-house in 1685. Lloyd’s was originally a coffee- house at which insurers and underwriters met. These houses have long ceased to be the favourite haunts of literary men and fashion, and, although still retaining their ancient name, they are now on a level with an ordinary restaurant, having been superseded as places of entertainment by the numerous music- halls and club-rooms in the metropolis, where something more stimulating than coffee is usually in demand. . Coffee, like tea, is frequently adulterated. Of these adultera- tions the most common one is chicory ( Cichorium intybus, L.), a plant resembling a dandelion, with blue flowers, belonging to the natural order Composite. The large tap-roots of this plant are sliced and dried in kilns ; they are then roasted and reduced to powder, and this, when boiled, yields a drink not unlike coffee. Chicory is perfectly wholesome, containing no alkaloid or oil, and only a small amount of narcotic matter. When added to coffee in small quantities, it rather improves its flavour, neutralises its oil, and renders it less difficult of digestion. The sale of chicory is now legalised. Many persons prefer the coffee with chicory. The adulteration of coffee with chicory is easily detected. Roasted ooffee imparts its oolour very slightly to cold water, but chicory colours the water a deep-reddish brown. Coffee is light, and floats on the surface of the water chicory is heavy, and sinks to the bottom. The best coffee, called Mocha coffee, comes from Yemen in Southern Arabia ; Loheia and Mocha are the principal ports for its exportation on the Red Sea, besides which, Aden, acquired by England in 1838, will soon become an important coffee mart. About 4,000 tons of this coffee are annually exported. East Indian coffee ranks next in commerce, chiefly the coffees of Ceylon and Batavia. About 50,000 tons of East Indian coffee are annually produced. An inferior kind, called green coffee, is raised in the West Indies — in Jamaica, Cuba, St. Domingo, Trinidad, Guadaloupe, Porto-Rico, and Martinique — to an annual amount of about 70,000 tons. Other American coffees also come from the free States of Venezuela and New Granada, from the Brazils, Cayenne, and Surinam. The annual produce of coffee in South America may be estimated at 81,000 tons. In 1867 about 61,486 tons were imported into the United Kingdom, principally from our foreign possessions. We export ooffee also largely to our colonies and Australia. Hamburg and Amsterdam are the most important coffee markets, and next to these London, Rotterdam, Antwerp, Havre, and Trieste. Cocoa ( Theobroma cacao, L. ; natural order, Byttneriacece). —A tree, about twenty feet in height, with dark-green leaves, from four to six inches in length and about three inches in breadth, elliptical, obloiig, and pointed, the margin entire, and slightly wavy ; the flowers are small and white, growing directly History of England, from the Accession of James II.,” by Lord Macaulay, Yol. I., p. 175.— People’s Edition, 1864. both from the stem and branches ; the fruit somewhat resembles a cucumber ; it is about five inches in length, and three inches and a, half in diameter, at first green, but when ripe, yellow. Within this fruit, embedded in the pulp, are from forty to fifty cocoa-beans or seeds, packed closely together in five rows, around a common centre. The cocoa-trees will only grow well in the shade. They are planted at intervals of twelve feet apart, and are protected from the fierce heat of the tropical sun by the broad-leaved banana and the stately and beautiful Brythrina, or coral-tree. The rays of the sun cannot penetrate the foliage of these trees j and the ground below them is constantly wet. When the fruit is ripe, it is plucked and opened ; and the beans, cleared of the spongy pulp, aro spread upon mats to dry in the sun. Chocolate and cocoa are both made from these beans. Chocolate is made by first freeing the beans from their husk, and then roasting them over a fire in an iron cylinder, with holes in its end for the escape of the vapour. The apparatus is very similar to that of a coffee-roaster. When the aroma is well developed, the beans are roasted ; they are then turned out of the cylinder, and ground to a powder, which, mixed with sugar, flavoured with vanilla, and brought to a paste, forms the chocolate cakes of commerce. Cocoa is prepared by grinding up the entire nut— both husk and kernel— after roasting, a quantity of suet being added during the process of grinding. Sometimes the beans are roasted and simply crushed. This preparation is sold in the shops under the name of cocoa nibs. The cocoa-tree is a native of South America, Mexico, and the West Indies, where it formerly grew wild, but is now culti- vated in extensive plantations. The beans of this tree have always been the chief means of nourishment of the natives of those countries. From them the Spaniards learnt to make both chocolate and cocoa. The cocoa bean, which is about the size and colour of an almond, oontains a peculiar solid oil called butter of cocoa, and an alkaloid called theobromine, which produces on the nervous system analogous effects to those of caffeine and theine. Chocolate and cocoa yield highly nutritious beverages. Linnaeus was so convinced of this, that he called the plant Theobroma. Cocoa is imported into this country chiefly in the raw state, that is, the beans with the husks on. The following are the principal sorts which are brought into Europe. The preparation, Chocolat Menier, is from cacao grown in the district of Rivas, Nicaragua. Soconusco, the best sort, comes from the district of the same name in the free state of Guatemala. This seldom comes into the market. Caracas, the next in quality, comes from La Guayra, the commercial port of Caracas in Venezuela, also from Guayaquil in Ecuador. Our largest supplies come from these ports. We receive also heavy shipments from Eng- lish, Dutch, and French Guiana, Brazil, Mexico, and the West Indies, especially from the island of Trinidad. In 1867, 11,954,862 lb. of cocoa were imported into the United Kingdom. Its consumption in France, Spain, and Portugal is continually increasing. Chocolate is more used in Franco and Spain than in England. It forms the ordinary breakfast of the Mexicans. Both chocolate and cocoa are much adulterated with wheaten and potato flour. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— III. It is now intended to show the construction of Gothic tracery. Some of the figures used in the designs of windows, etc., in churches of the Middle Ages are extremely beautiful ; yet all the forms grow out of others of the most simple character, dependent on correct geometrical construction. The quatre- f oil, which forms the subject of the present lesson, is based upon a square drawn on given diagonals ; and this elementary figure, and one of a similar character, are therefore given as steps in the construction. To construct a square on a given diagonal, a b (Fig. 24). Bisect the diagonal a b in the point C. From c, with radius C A, describe a circle cutting the bisecting line in r> and E. Draw A D, D b, b E, E a, which will complete the square on the given diagonal A b. To construct a parallelogram when the diagonal A B and the length of one pair of sides c are given (Fig. 25). 188 THE TECHNICAL. EDUCJATOB. Bisect A b in the point o. From o, with radius o A, describe a circle. From A and b set off the length of the line c on the circle — viz., A i) and b e. Join these points, and the required figure will be completed. To construct a Gothic quatre- foil* (Fig. 26). Construct a square on the dia- gonal A b (see Fig. 24). Bisect the sides by the lines e g, f h, cutting the lines A c, c b, b d, and d A, in i, j, k, l • From A, C, B, and D, with radius A i — - that is, half the side of the square — draw the arcs V, m, n, o, and those concentric with them. Tho outer circles are drawn from the centre o. To inscribe a square in any triangle, ABC (Fig. 27). From c drop a perpendicular, c d. From c draw a line parallel to A b — viz., c e. From c, with radius c D, describe a quadrant cutting c e in f. Draw f a, cutting c B in G. From G draw G H parallel to A B. And from G apd H draw lines G i and h j parallel to c d, which will com- plete the square in the triangle. To inscribe a square in a given trapezium, A b c d (Fig. 28). Draw the diagonals A C and B D. Draw i> E at right angles and equal to D B. Draw E A, _ cutting } c d in F. Draw f g parallel to A C. f i parallel to db in the trapezium. To inscribe a circle in a given trapezium, ABC D, of which the adjacent sides are equal (Fig. 29) To trisect* a right angle, ABC (Fig. 30). From b, with any radius, describe the quadrant D e. From P, with the radius B b, describe an arc cutting e d in F. From e, with the same radius, describe an arc cutting e d in g. Draw lines b f and b g, which will trisect right angle. THE MEASUREMENT OF ANGLES (Fig. 31). Angies are estimated accord- ing to the position which the two lines of which they are formed occupy as radii of a circle. The circle being divided into 360 equal parts, called “de- grees,” it will be evident that the lines A o c contain 90 degrees (written 90°), or a right angle. Similarly, B O C is a right angle. Now, if these right angles be trisected (as per last problem), each of the divisions will contain. 30°, thus : — A o E is an angle of 30° A o F A o c A O G A O H 60 c 90° 120 ° 150° ^ Draw G H and Join H i, which will complete the square A o B is in reality not any angle at all, being a perfectly straight line ; but the slightest divergence from it would cause it to become an angle ; as 179°, etc. _ _ Each of these angles being again divided into three parts will give tens, which may again be divided into units ; and thus angles may be constructed or measured with the greatest accuracy. Draw the diagonal A b, which will bisect the angles c b d and cad. Bisect the angle a d b. Produce the bisecting line until it cuts A B in O. Then O is the centre from which a circle maybe described, touching all four sides of the trapezium. \ * The Quatrefoil is a figure based on four leaves or lobes. See remarks on the Trefoil (Fig. 11). Example No. 1 of the foregoing (Fig. 32). — To find the angle contained by the lines A b c. Erect a perpendicular at B. Draw the quadrant D E, and trisect it. Divide the arc G e into three equal parts by points h and i (70° and 80°). Bisect the arc h i, and it will be seen Trisect. To cut into three equal parts. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING. 189 that the line b c falls precisely on the bisecting point. A b c is therefore an angle of 75°. Had the line B c not fallen exactly in the bisecting point, further subdivision would have been necessary. Example No. 2 (Fig. 33). — To construct at a given point b an angle of a required number of degrees, say 100°. At b erect a perpendicular, b c. Trisect the right angle, carrying on the arc beyond the perpendi- cular, c. Divide any one of the three divi- sions into three equal parts representing tens. Set off one of these tens beyond c, viz., to D. Draw B D. Then A b d will be an angle of 100°. To construct a tri- angle, when the length of the lase and the angles at the base are given (Fig. 34). — Let it be required that the base should be 2’5 (2, decimal 5, or 2 and 5 tenths, which is 2|) inches long, that the angle at a should be 50°, and that at b 45°. Draw the base 2 - 5 inches long. At A erect a perpendicular ; draw a quadrant and trisect it in ed. Divide the middle portion, D e, into three equal parts, and the second division from k will be 50°. Draw a line from a through point 50, and produce it. At b erect a perpen- dicular, and bisect the right angle thus formed (as 45° is one-half of 90°). Produce the bisecting line until it meets the line of the opposite angle in f. Then a b f will be the required triangle. Note. — All the three angles of a triangle are always equal to Fig. 32. given to show its practical application. This has a short line marked at c, and two rows of figures round the rim — the one reading from right to left, and the other the reverse way. In order to measure an angle by means of the protractor, place the edge a b on the straight line which is to form one of the sides of the angle, with the point c exactly against the point of the angle to be measured. Then the line c d will be seen to correspond qm . with the point 60°, and b c d is therefore an angle of 60° ; or, reading from the left side, A c d is an angle of 120°. In constructing an angle, place c against the point at which it is desired to construct an angle ; mark a point on your paper exactly against the figure corresponding to the number of de- grees required ; re- move the protractor, and draw a line through the point thus obtained, to c, which will give the desired angle. Protractors are sometimes made of wood or ivory, and of a rectangular form, as e f. These are used in a manner similar to the semi- circular instruments, but are not generally thought as useful or exact in practice. To construct an isosceles triangle on a given base, and having a given vertical angle (say 30°). (Fig. 36.) Before commencing to work this 'figure, it is desirable that attention should be called to the principle upon which the con- struction is based. . A c Fig. 33. 3 v\ 10 J- / two right angles, that is, 180°; and therefore, as one of the above angles is 50°, and the other 45° — total 95° — the vertical angle, that is, that opposite the base, will be 85°. THE PROTRACTOR (Fig. 35). For measuring and constructing angles, there is in most cases of mathematical instruments a brass semicircle called a protractor. This has already been referred to, and is here It has been shown that all the angles of a triangle, of what- ever shape it may be, will always be equal to two right angles (viz., 180°). Every straight line then is equal to the bases of two right angles ; for a perpendicular drawn at any point will at once form two right angles, equal to 180°, upon it (Fig. 37). ... Now let it be supposed that <£180 are to be divided between 190 THE TECHNICAL EDUCATOR. three persons, that one of them is to receive <£30, and the re- mainder to be equally divided by the other two. It will be seen at once that, when the first condition has been fulfilled, and <£30 deducted from <£180, the remainder will be £150, or £75 for each of the remaining claimants. It is on a similar principle that this operation is based ; and this mode of procedure is rendered necessary because we cannot commence by constructing the vertical angle; for, as the base A b is fixed, we should not know where to commence the vertical angle, so that the sides might not cut through a b (Fig. 38), or pass beyond it (Fig. 39) ; and thus we are com- pelled to construct the angles at the base firstly, and of such a number of degrees, that they should meet in the required angle. Now it has been shown that 180° stand on every line. Returning now to Fig. 36, produce A b, and at a construct an angle of 30°— viz., cab. So that out of the whole sum of 180° we have set aside 30°, the fixed number. Bisect the remaining angle d A b in e. Draw a e. ' At b con- struct an angle a b f, similar to the angle b a e. Produce lines A E and b f, which will meet in g, and will form the required angle of 30°. NOTABLE INVENTIONS AND INVENTORS. IV.— CLOCKS AND WATCHES ( continued ). BY JOHN TIMBS. The middle of the fourteenth century seems to be the time which affords the first certain evidence of the existence of what would now be called a clock, or regulated horological machine ; for although the term “ horologia ” had been of frequent occur- rence in preceding ages, there is every reason to believe it was applied to other horological instruments. It appears from a letter written by Ambrosiua Camalodunensis to Nicolaus of Florence, that clocks were pot very uncommon in private fami- lies on the Continent about the end of the fifteenth century, and there is good reason for supposing that they began to become general in England about the same period ; for we find in Chaucer, who was born in 1328 and died about 1400, the following lines : — “ Full sickerer was his crowing in his loge. As is a clock, or an abbey orloge.” It is also believed, on good grounds, that a clock is not the invention of one man, but a compound of successive inventions, each worthy of a separate contriver. Thus, (1) wheelwork was known and applied in the time of Archimedes. (2) A weight being applied as a maintaining power would, in all probability, have at first a fly similar to that of a kitchen- jack, to regulate the velocity. (3) The ratchet-wheel and click for winding up the weight, without detaching the teeth or main wheel from those of the pinion in which they were engaged, would soon be found an indispensable contrivance. (4) The regulation by a fly, being subject to such great changes from the variations of density in the atmosphere, and the ten- dency of a falling body to accelerate its motion, would neces- sarily give rise to the alternate motion of the balance, with which invention an escapement of some kind must have been coupled. (5) The last-mentioned two inventions are most im- portant ones, and would have induced such a degree of equability in the motion of the whole work, as would lead the way to a dial-plate, and to its necessary adjunct — a hand or pointer. Lastly, the striking part, to proclaim at a distance, without the aid of a person to watch, the hour that was indicated, completed the invention. And the supposition, that De Wyck’s clock was a combination of the successive inventions of different indi- viduals, is confirmed by analogy ; for the clocks and watches of the present day have been brought to their present degree of perfection by a series of successive inventions and improve- ments upon what may now be called the rude clock of De Wyck, which is the most ancient clock of which we have a description. This and, indeed, all clocks made with a balance for a regu- lator, without any regulating spring — must have been very impel feet machines ; yet as early as 1484 a balance clock was used for celestial observations, and was superseded by the use of a portable one for ascertaining the longitude at sea, about 1530. Ancient clocks must have been reduced to a portable size prior to 1544, when the mainspring was substituted for the weight as a moving power ; and this may be considered a second era in horology, from which may be dated the application of the fusee, round which is wound the chain or cord. Among the earliest of the wheel-clocks seen in England was that of St. Paul’s Cathedral, London, in 1286; and an agree- ment of 1344 shows that iron and steel were then used for the frame and clock, as they were until towards the end of the sixteenth century. The present clock at St. Paul’s is remark- able for the magnitude of its wheels and the fineness of its works ; it was made, by Langley Bradley, at a cost of £300. It has two dial-plates, each between 50 and 60 feet in circum- ference ; the hour numerals are a little over 2 feet in height ; the minute-hands, 8 or 9 feet long, weigh 75 pounds each, and the hour-hands, between 5 and 6 feet long, weigh 44 pounds each. The pendulum is 16 feet long, and its bob weighs 180 pounds, but it is suspended by a spring no thicker than a shilling. Its beat is 2 seconds — that is, a dead beat, of 30 to a minute, instead of 60. The clock, going 8 days, strikes the hour on the brim of the great bell with a hammer ; its head weighs 145 pounds, and is drawn by a wire to the back part of the clockwork, falling by its own weight on the bell, it can be heard at a distance of 22 miles; the clapper weighs 180 pounds; diameter of bell, 10 feet; weight, 102 cwt. Below this bell are the two quarter bells. The Horse Guards’ clock, we may here mention, made in 1756, was originally of coarse work. It was repaired and improved in 1815, and measures time sufficiently accurate for practical purposes, not connected with astronomical observations ; but much of its reputation is conventional, from its association with “ military time ” of the Horse Guards. Clocks remained with balances for the motive power until the middle of the seventeenth century, when the pendulum was first applied — it is said by Galileo observing the oscillations of a lamp suspended in the cathedral at Pisa. The discovery is also claimed for Huygens, Bergen, Hooke, and others, about the same time; but the “ancient astronomers of the East em- ployed pendulums in measuring the times of their observations, patiently counting their vibrations during the phases of an eclipse, or the transit of the stars, and renewing them by a little pressure of the finger when they languished ; and Gassendi, Riccioli, and others, in more recent times, followed their example.” (“ Encyclopaedia Britannica,” 8th edit.) “ Clocks and watches,” says Mr. Babbage, “ may be c®n- sidered as instruments for registering the number of vibrations formed by a pendulum or a balance. George Graham, in 1715, first applied a compensating power to counteract the effect of heat and cold upon the length of the pendulum ; and John Harrison, in 1726, used different metals to compensate each other, the rods being placed in the form of a gridiron. The mechanism by which these numbers are counted is technically called a scapement. A common clock is merely a pendulum, with wheelwork attached to it to record the number of the vibrations ; and with a weight, or spring, having force enough to counteract the retarding effects of friction and the resistance of the air. The wheels show how many swings or beats of the pendulum have taken place, because at every beat a tooth of the last wheel is allowed to pass. Now, if the wheel has sixty teeth (as is common), it will just turn round once for sixty beats of the pendulum, or seconds ; and a hand fixed on its axis, pro- jecting through the dial-plate, will be the second-hand of the clock. The other wheels are so connected with the first, and the number of the teeth on them so proportioned, that one turns sixty times slower than the first, to fit its axis to carry a minute-hand ; and another, by moving twelve times slower still, is fitted to carry an hour-hand.” A few public clocks may be noted here. The Bank of England clock, in the roof, is a marvel of mechanism, as it is connected with all the clocks in the Stock Offices. The hands of the several dials indicate precisely the same hour and second, by means of connecting brass rods (700 feet long, and weighing 6 cwt.), and 200 wheels ; the principal weight being about 300 lb. The General Post Office clock, by Vulliamy, is a beautiful work of art on a small scale ; its pendulum-bob weighs 448 lb., and requires only 33 lb. to cause it to vibrate 2' 20" on each side of zero — an extremely small motive power. The clock of the Royal Exchange, manufactured by Dent in 1843, has been pronounced by the Astronomer Royal as “ the best public clock in the world;” the pendulum, weighing nearly PRINCIPLES OF DESIGN. 191 4 cwt., is compensated, the first stroke of the hour is true to a second, and it can also be set to any fraction of a second. This was the first turret clock constructed by Mr. Dent. The Westminster Palace clock, designed by Mr. Denison, and made by Mr. Dent, jun., about 1855, has four dials, each 22 feet in diameter — the largest in the world with a minute-hand ; the 'great wheel of the going part is 27 inches diameter; the pendu- lum is 15 feet long; and weighs 680 lb. ; and the scape-wheel weighs about half an ounce. This clock is said to be eight times as large as a full-sized cathedral clock ; it requires two hours a week to wind it up, and reports its own time to Greenwich by electrical connection ; the cost has exceeded =£22,000, and the gilding of the clock-tower =£1,500. PRINCIPLES OE DESIGN.— Y. BY CHRISTOPHER DRESSER, PH.D., F.L.S., ETC. Having considered some of the chief principles involved in the production of decorative design so far as “expression” goes, we come to notice that constant adjunot, or handmaid, of form which has ever played an important part in all decorative schemes — namely, colour. Form can exist independently of colour, but it never has had any important development without the chromatic adjunct. From a consideration of history, we should be led to conclude that form alone is incapable of yielding such enrichments as satisfy ; for no national system of decoration has ever existed in the absence of colour. Mere outline-form may be good, but it is not satisfying ; mere light and shade may be pleasing, but it is not all that we require. With form our very nature seems to demand colour ; and it is only when we get well-proportioned forms which are graceful, or noble, or vigorous, in combination with colours harmoniously arranged, that we are satisfied. Possibly this feeling results from our contact with Nature. The flowers appear in a thousand hues, and the hills are of ever-varying tints. What a barren world ours would appear, were the earth, the hills, the trees and the flowers, the sky and the waters, all of one colour ! Form we should have, and that in its richest variety ; light and shade we should have, with ever-varying intensity and change ; but colour would be • gone. There would be no green to cheer, no blue to soothe, no red to excite ; and, indeed, there would be a deadness, although the world would be full of life, so appalling, that we can scarcely conceive of it, and cannot feel it. Colour alone seems to have almost greater charms than form alone. How entrancing is a sunset when the sky glows with its radiant hues ; the blue is almost lost in red, the yellow is as a sea of transparent gold, and the whole presents a variety and blending of tints, which charm, and soothe, and lull to reverie ; and yet all form is indistinct and obscure. If so charming when separate from form, what is colour when pro- perly combined with beautiful shapes P It is difficult, indeed, for many of those for whom I write to answer this question, even by a mental conception ; for I could scarcely point to a single building in England which would be in any way a satis- factory illustration of what may be done by the combination of forms and colours. There is a beauty in Art, which we in England do not even know of : it does not exist round us, it is little talked of, rarely thought about, and never seen. A decorator is called in to beautify a house, and yet not one in fifty of the so-called decorators know even the first principle of their art, and would not believe, were they told of the power of the art which they employ. They place on the walls a few sickly tints — so pale, that their want of harmony is not very apparent. The colours of the wall become the colours of the cornice and of the doors, because they know not how to produce a harmony of hues ; and the result is a house which may be clean, but which is in every other respect an offence against good taste. I do not wonder that persons- here in England do not care to have their houses “ decorated,” ^ nor do I wonder at their not appreciating the “ decorations ” ! when they are done. Colour, lovely colour, of itself would make our rooms charming, but where are the priests who un- derstand their mistress ? There are few objects to which colour may not be applied, and many articles which are now colourless might be coloured with advantage. Our reasons for applying colour to objects are twofold, and here we have the true use of colour. 1st. Colour lends to objects a new charm — a charm which they would not possess, if without it ; and, 2nd, Colour assists in the separation of objects, and thus gives assistance to form. These, then, are the two objects of colour. Mark, first, colour is to bestow on objects a charm, such as they could not have in its absence. In the hands of the man of knowledge it will do so— - it will make an object lovely or lovable, but the mere applica- tion of colour will not do this. Colour may be SO applied to objects as to render them infinitely more ugly than they were without it. I have seen many a white bowl so coloured at our potteries as to be much less satisfactory when coloured than when white — the colouring having marred, rather than im- proved, its general effect. Here, again, it is knowledge that we want. Knowledge will" enable us to transmute base materials into works of marvellous beauty, worth their weight in gold. Knowledge, then, is the true philosopher’s stone ; for if possessed by the artist it does, in truth, enable him to transmute the baser metals into gold. But a little knowledge will not do this. In order that we produce true beauty, we require muoh knowledge, and this can only be got by constant and diligent labour, as I have before said ; but the end to be gained is worth the plodding toil. Believe me, there is a pleasure in seeing your works develop as things of beauty, delighting all who see them — not the illiterate only, but also the eduoated thinker — such as words fail to express. Although there is no royal road to art power, and although the road is long, and lies through much toil and many difficulties ; yet as you go along, there is pleasure in feeling that one obstacle after another is cleared from your path, and at the end there is pleasure inexpressible. The second object of colour is that of assisting in the separation of form. If there is a series of objects placed near to one another, and these objects are all of the same colour, the be- holder will have much more difficulty in seeing the boundaries or terminations of each than he would, were they variously coloured ; he would have to come nearer to them in order to see the limits of each, were all coloured in the same manner, than he would, were they variously coloured : thus colour assists in the separation of form. This quality which colour has of separating forms is often lost sight of, and much confusion thereby results. If it is worth while to produce and place a decorative form, it is worth while to render it visible ; and yet, how much ornament, and even good ornament, is lost to the eye through not being manifested by colour ! Colour is the means whereby we manifest form. Colours, when placed together, can only please and satisfy the educated when combined harmoniously, or according to the laws of harmony. What, then, are the laws which govern the arrangement of colours P and how are they to be applied P We shall endeavour to answer these questions, by making a series of statements in axiomic form, and then we shall enlarge upon these propositions. GENERAL CONSIDERATIONS. 1. Regarded from an art point of view, there are but three colours — i.e., blue, red, and yellow. 2. Blue, red, and yellow have been termed primary colours ; they cannot be formed by the admixture of any other colours. 3. All colours, other than blue, red, and yellow, result from the admixture of the primary colours. 4. By the admixture of blue and red, purple is formed ; by the admixture of red and yellow, orange is formed * and by the admixture of yellow and blue, green is formed. 5. Colours resulting from the admixture of two primary colours are termed secondary : hence purple, orange, and green are secondary colours. 6. By the admixture of two secondary colours a tertiary colour is formed : thus, purple and orange produce russet (the red tertiary) ; orange and green produce citrine (the yellow tertiary) ; and green and purple, olive (the blue tertiary) ; russet, citrine, and olive are the three tertiary colours. CONTRAST. 7. When a light colour is juxtaposed to a dark colour, tho light colour appears lighter than it is, and the dark colour darker. 8. When colours are juxtaposed, they become influenced as to their hue. Thus, when red and green are placed side by side, the red appears redder than it actually is, and the green greener; and when blue and black are juxtaposed, the blue manifests 192 THE TECHNICAL EDUCATOE. PURPLE 13 RED 5. but little alteration, while the black assumes an orange tint or becomes “ rusty.” 9. No one colour can be viewed by the eye without another being created. Thus, if red is viewed, the eye creates for itself green, and this green is cast upon whatever is near. If it views green, red is in like manner created and cast upon ad- jacent objects ; thus, if red and green are juxtaposed, each creates the other in the eye, and the red created by the green is cast upon the red, and the green created by the red is cast upon the green ; and the red and the green become improved by being juxtaposed. The eye also demands the presence of the three primary colours, either in their purity or in com- bination; and if these are not present, whatever is deficient will be created in the eye, and this induced colour will be cast upon whatever is near. Thus, when we view blue, orange, which is a mixture of red and yellow, is created in the eye, and this colour is cast upon whatever is near : if black is in juxtaposition to the blue, this orange is cast upon it, and gives to it an orange tint, thus causing it to look “ rusty.” 10. In like manner, if we look upon red, green is formed in the eye, and is cast upon adjacent colours ; or, if we look upon yellow, purple is formed. HARMONY. 11. Harmony results from an agreeable contrast. 12. Colours which perfectly harmonise improve one another to the utmost. 13. In order to perfect harmony, the three colours are necessary, either in their purity or in combination. 14. Red and green combine to yield a harmony. Red is a primary colour, and green, which is a secondary colour, consists of blue and yellow — the other two primary colours. Blue and orange also produce a harmony, and yellow and purple ; for in each case the three primary colours are present. 15. It has been found that the primary colours in perfect purity produce exact har- monies in the proportions of 8 parts of blue, 5 of red, and 3 of yellow ; that the secondary colours harmonise in the proportions of 13 of purple, 11 of green, and 8 of orange; and that the tertiary colours harmonise in the proportions of olive 24, russet 21, and citrine 19. 16. There are, however, subtleties of har- mony which it is difficult to understand. 17. The rarest harmonies frequently lie . close on the verge of discord. 18. Harmony of colour is, in many respects, analogous to harmony of musical sounds. QUALITIES OF COLOURS. 19. Blue is a cold colour, and appears to recede from the eye. 20. Red is a warm colour, and is exciting; it remains station- ary as to distance. 21. Yellow is the colour most nearly allied to light ; it ap- pears to advance towards the spectator. 22. At twilight blue appears much lighter than it is, red much darker, and yellow slightly darker. By ordinary gas- light blue becomes darker, red brighter, and yellow lighter. By this artificial light a pure yellow appears lighter than white itself, when viewed in contrast with certain other colours. 23. By certain combinations colour may make glad or depress, convey the idea of purity, richness, or poverty, or may affect the mind in any desired manner, as does music. TEACHINGS OF EXPERIENCE. 24. When a colour is placed on a gold ground, it should be outlined with a darker shade of its own colour. 25. When a gold ornament falls on a coloured ground, it should bo outlined with black. 26. When an ornament falls on a ground which is in direct harmony with it, it must be outlined with a lighter tint of its own colour. Thus, when a red ornament falls on a green ground, the ornament must be outlined with a lighter red. 27. When the ornament and the ground are in two tints > of the same colour, if the ornament is darker than the ground, it will require outlining with a still darker tint of the same colour ; but if lighter than the ground, no outline will be required. ANALYTICAL TABLES OF COLOUR. When commencing my studies both in science and art, I found great advantage from reducing all facts to a tabular form so far as possible, and this mode of study I would recom- mend to others. To me this method appears to have great advantages, for by it we see at a glance what it is otherwise more difficult to understand ; if carefully done, it becomes an analysis of our work ; and by preparing these tabular arrange- ments of facts, the subject becomes impressed on the mind, and we see the relation of one fact to another, or of one part of a scheme to another. The following analytical tables will illustrate many of the facts stated in our propositions. The figures which follow the colours represent the proportions in which BLUE 8. they harmonise : — Primary Secondary Tertiary GREEN 11. Colours. Colours. Colours. Blue . . 8 Purple . . 13 Olive. . . 24 . * Bed . . 5 Green . 11 Busset . 21 Yellow . 3 Orange . . 8 Citrine . . 19 Primary Colours. Secondary Colours. Tertiary Colours. YELLOW 3. ORANGE 8. Fig. 17. PURPLE 13. Bed Yellow 5) Orange . . 8^ Citrine, or Yel- Blue . Yellow s 3 Green 11 J low tertiary 19 Blue . Bed 8 5 Purple • 13> Busset, or Bed Bed . Yellow 5 3 ■ Orange tertiary . . 21 Blue . Yellow. 8 3 • Green . . if Olive, or Blue Blue . Bed 8 5 • Purple .13j tertiary . . 24 CITRINE 19. Fig. 18. This latter table shows at a glance how each of the secondary and tertiary colours are formed, and the proportions in which they harmonise. It also shows why the three tertiary colours are called respectively the yellow tertiary, the red tertiary, and the blue tertiary, for into each tertiary two equivalents* of one primary enter, and one equivalent of each of the other primaries. Thus, in citrine we find two equivalents of yellow, and one each of red and blue; hence it is the yellow tertiary. In russet we find two equivalents of red, and one each of blue and of yellow ; and in olive two of blue, and one each of red and yellow. Hence they are respectively the red and blue tertiaries. Figs. 17 and 18 are diagrams of harmony. I have connected in the centre, by three similar lines, the colours which form a harmony ; thus, blue, red, and yellow harmonise when placed together. Purple, green, and orange also harmonise (I have con- nected them by dotted lines in the first of the two diagrams). But when two colours are to produce a harmony, the one will be a primary colour, and the other a secondary formed of the other two primary colours (for the presence of the three primary colours is necessary to a harmony), or the one will be a secondary, and the other a tertiary colour formed of the two remaining secondary colours. Such harmonies I have placed opposite to each other ; thus blue, a primary, harmonises with orange, a secondary ; yellow with purple ; and red with green ; and the secondary colour is placed between the two primary colours of which it is formed; thus, orange is formed of red and yellow, between which it stands ; green, of blue and yellow ; and purple, of blue and red. In the second of the two diagrams we see that purple, green, and orange produce a harmony, so do olive, russet, and citrine. We also see that purple and citrine harmonise, and green and russet, and orange and olive. * An equivalent of blue is 8, of red 5, of yellow 3. WEAPONS OP WAR. 193 Fig- 1. — SNIDER RIFLE OPEN FOR RECEPTION OF CARTRIDGE WEAPONS OF 'WAR. — IY. BY AN OFFICER OF THE ROYAL ARTILLERY. SMALL ARMS ( continued ). Before quitting the subject of muzzle-loading small arms, of which, together with the descriptions of powder used with them, we have given some account, it may be well to notice the means of ignition usually employed with arms of this class. Nearly the earliest and rudest mode of igniting the charge consisted of a fuse or slow match, which was applied to a small charge of powder placed over the “touch-hole,” or vent, as it is npw called. A grave inconvenience of this system consisted in the fact that arms could hardly be carried ready primed, at least for any length of time, because the priming was liable to drop out, or if it did not drop out, to become damp. Accordingly, • the soldier was com- pelled to prime his gun just before using it ; and as the operation had to be carefully per- formed, rapidity of fire under this system was out of the question ; moreover, the carrying of an ignited match at- tached to the gun was a source of inconveni- ence and danger. The match was superseded by the flint-lock, the flint being made to strike a spark as it descended on to the priming charge of powder. In some in- stances a metallic alloy of iron and antimony was substituted for the flint. The action in both cases was the same ; sparks being istruck into the priming- charge. Here we come more closely to our pre- sent lock and hammer. A spring-lock was neces- sary to bring the flint violently down, and the hammer by which the flint was held was the direct parent of the hammer by which the percussion cap was afterwards fired. The next important advance consisted in the appli- .cation of the percussion system to the firing of small arms. It is said that a Scotch gunsmith, called Forsyth, was the first who pro- posed a percussion fire-arm, for which he took out a patont in 1807 ; but it was not, we bolieve, until about 1822 that a percussion musket was introduced — at least in this country — Tor military use. It is hardly necessary to insist upon the advantages which the percussion cap presents over the match and flint-lock guns. A moment’s consideration will serve to show that the change was a most important one, scarcely less important in its way than the introduction at a later period of breech-loading. To fletail the various simplifications and improvements of the lock which have been effected would be tedious ; nor is it necessary to set forth the endless varieties of percussion caps and devices for igniting fire-arms by means of detonating composition which have been proposed and attempted since the subject of this improved method of firing was first suggested about sixty years ago. It will be sufficient to say, that the percussion caps for military arms, with the form and appearance of which all our readers are no doubt familiar, are made of pure copper of a Fig. 2.*— SNIDER RIFLE CLOSED AFTER INSERTION OF CARTRIDGE. superior quality. It is not only necessary to use good copper, because a very small admixture of foreign matter, by affecting its malleability, will interfere with the production of a cap of the required form, but because too hard or brittle a metal would be apt to fly and injure the firer. Partly on this account, and partly because of the liability of zinc to corrosion, the pro- position which has been frequently made to substitute that metal for copper has always been held to be inadmissible. For a similar reason our readers should be cautioned against employing, if they can avoid it, the cheap brass eaps which are not unfrequently manufactured and coloured to represent copper. In the Government establishments very careful atten- tion is paid to the selection of the copper. Cap composition varies with different makers, and from time to time it has been altered for military arms. Thus, the com- position for the caps for the Enfield rifle con- sisted of — Parts. Fulminate of Mercury . 4 Chlorate of Potash . . 6 Ground glass .... 2 — the latter ingredient being added to increase the sensitiveness of the composition, by pro- moting friction between the particles. When the Westley- Richards and Sharp’s breech-loaders were introduced, with whioh the cap was re- quired to ignite the powder contained in a paper cartridge, a more powerful composition was introduced, namely : — Parts. Fulminate of Mercury . 4 Chlorate of Potash . . 1 This composition proved, however, too vio- lent in its action for use on the nipples of the En- field rifle, which are of a different form from the nipples of the breech- loading rifles, with which the eaps were intended to be used, and a further change was made to a com- position consisting of Parts. Fulminate of Mercury . 6 Chlorate of Potash . . 6 Sulphide of Antimony . 4 The addition of the antimony secured the flash which was re- quired to pierce the paper envelope of the cartridge, while at the same time it modified the intense violence of action of the cap, and prevented it from “flying” into pieces, and causing inconvenience and injury to the firer. One more point with regard to percussion caps, and we pass on to another subject. This point is the waterproofing of the cap. Several methods have been tried, and are in vogue for rendering percussion caps waterproof ; or, which is of more im- portance, for enabling them to resist damp. Among these may be mentioned the covering of the composition with a thin metallic disc, or with a disc of india-rubber. The simplest \ and probably the most effective plan is that which is applied to the Government caps, viz., to subject the composition to considerable pressure, by which means it is reduced to a stony hardness, and is rendered almost impervious to moisture ; while by coating the cemposition with a strong varnish of shellac the caps are ultimately made completely waterproof. We have now dealt generally with all the points which oopv vol. x- r t94 THE TECHNICAL EDUCATOR. 3 iect themselves with muzzle-loading rifled small arms. We have considered the bullet, the charge, the means of ignition, the rifling, the weight and character of the arms. These elements, judiciously combined, gave us in the Enfield rifle a military weapon of great excellence. But there were two im- portant directions in which improvements seemed necessary and possible. The first and most important consisted m in- creasing the rapidity of fire ; the second in increasing the ballistic power of our weapons, an expression which covers all the shooting qualities of an arm— its accuracy, range, flatness of trajectory, penetrative powers, etc. — as distinguished from those qualities which connect themselves with easy and rapid loading, etc. t In short, the advantages of the Enfield rifle as an arm of precision were no sooner recognised than men began instinc- tively to endeavour to simplify and accelerate the operation of loading by introducing the cartridge at the breech. In the case of the cavalry soldier this was a matter of no small importance. The difficulties of loading a rifled arm on horseback were con- siderable ; and thus wo find that as early as 1857 steps had been taken towards the supply of breech-loaders to mounted men. In that year some Sharp’s breech-loading carbines were issued to two regiments of cavalry. The charge in this arm was inserted bodily at the breech ; and as the block ascended it cut off the end of the cartridge, and exposed the powder, which was fired in the same way as a muzzle-loader, with the ordinary percussion cap. The Sharp breech-loader, which is still used to some extent by our cavalry in India, is an extremely bad breech-loader, for several reasons— among them the great escape of gas which occurs at the breech on firing, and the employ- ment of a percussion cap. The W estley -Richards carbine was a great improvement on the Sharp, for the end of the cartridge was not cut off in load- ing, and tho escape of gas was prevented by means of a felt wad attached to the back of the cartridge. In this wad we see a sort of rude prototype of the present non-consuming cartridge an imperfect application of the present system of making the cartridge do the work of checking the escape of gas. We recog- nise here, also, in this half solution of the question, a dim per- ception of tho fact now so fully admitted, that the cartridge is the turning-pbint or hinge upon which the success of a breech-loading small-arm depends. Here, for example, we have, in the Westley-Richards, a superior combination to that which existed in the Sharp ; and why P Not because of the supe- riority of the breech-action of tho Westley-Richards, for it may be doubted if the Sharp action (upon which tho present admi- rable Henry breech-loader is based) is not in fact the better of the two. No ; but simply because Westley-Richards was on tho right track with regard to his cartridge, and Sharp was on tho wrong track. It should here be mentioned that, as an artn of precision, the Westley-Richards carbine was a very good one. It was a “small-bore” rifle— an expression to which we will assign a definite meaning hereafter and it threw a 400-grain bullet, with a 2-dram charge, with great accuracy to a long range. But the rifle (which is now, we believe,. in the hands of the yeomanry cavalry) is open to several objections — among them, that it is fired in the old way by means, of a. percussion cap. So long as this mode of ignition is retained, it is impos- sible to realise the full advantages of a breech-loader. It is fair, however, to observe that it was through no fault of the inventors that this objectionable feature in the Sharp, Westley-Richards, and other breech-loading rifles was retained. The fact is that the authorities set their faces determinedly against cartridges containing — like those now in use for the Snider — their own means of ignition. It was supposed that such cartridges wore liable to accidental explosion cn masse by the ignition of a single cartridge in the barrel or box, and the con- sequences of such an accident were likely to be so serious that any cartridge of this description was considered inadmissible. We thus perceive that a serious barrier- existed at this time to the development of the breech -loading question. It was re- garded as .essential to employ the old muzzle-loading means of ignition, and greatly accelerated rapidity of fire one of the principal, though not the only, advantage of breech-loading waslimpossible with a capping breech-loader ; so that for several years the question was considered mainly as a cavalry ques- tion, facility, but not rapidity, of loading being the thing aimed at. Indeed, rapidity of loading was rather deprecated than otherwise. Many good soldiers and experienced officers declared that if you gave a soldier a gun which he could load very quickly ho would expend all his ammunition before he came within effective fighting range. It may be admitted that breech-loaders are open to this objection, although not to any- thing like the extent commonly supposed, and the objection is one which can be remedied by discipline and an effective, careful training. The practice of the Prussians is an example of this. Here we have a nation which really understands the breech- loader, which is properly trained in its use and in the econo- mical expenditure of ammunition, and the results wo have seen in two great wars. On the other hand, wo have the excitable, and, we may be permitted to add, badly-trained, ill-drilled, ill- disciplined French soldier, blazing away at any number of metres from tho enemy, and running out of cartridges early in the day. Cannot the English soldier do what the Prussian does? Is our national temperament so excitable, so unlike that of the Prussians, that no training can teach our men that the fighting unit is a man plus a cartridge, not a man by himself with an empty pouch ? Then, again, it is to be observed that although a somewhat wasteful expenditure of ammunition may be one of the results of the introduction of breech-loaders, the non-issue of breech-loaders would be tantamount to the destruction of the army. If a soldier is likely to fire too rapidly in the one case, he is certain to be unable to fire rapidly enough in the other. The one defect may be corrected or controlled; the other, so long as muzzle-loaders are in use, cannot be. It is not a question of expediency, it is a question of sheer necessity. Whether or not breech-loading rifles may be attended with certain disadvan- tages is a point which admits of discussion, but it admits of .no discussion that breech-loading rifles are vital to the very exist- ence of an army. If tho disadvantages are there they must be made the best of; and the way to make the best of this special disadvantage is so to train the soldier, so to drill and discipline, so to hammer at him, that he will come to understand that a shot ought never to be thrown away. And if ne only act upon this principle, it will be no objection that he is able to fire a dozen shots a minute instead of three, and thus to do his work in one-fourth the time. , What we have written may appear to have an historical rather than a practical interest. A little consideration .will, however, servo to show that this is not the case. It is in the history of the subject that its foundations repose. In the recognition of the difficulties which beset the earlier attempts, and the objections which stunted the growth of the question.; in the perception of the growing importance of the cartridge question, and tho relatively inferior importance of the breech mechanism ; in the recognition of the fact that the question of breech-loading is quite distinct from and independent of the question of shooting — of ballistic power — we have the elements of the subject. Let us pass now to their practical application. Up to about 1864 the question of breech-loading was treated, for reasons which we have endeavoured to trace in outline, as one which principally affected the cavalry soldier. But in 1864, instructed by the experience ,of the Dano-German war, General Russell’s committee recommended that the British infantry be armed with breech-loaders. The question then arose, What breech-loader should be provided P I need not now trace all the discussion which took place at the time, or set forth, the monts which ultimately prevailed to secure the adoption of the Snider system of conversion. Tho Enfield rifle was thought, and properly thought, to be so excellent a shooting weapon, that it was considered that it would be sufficient, at least for the present, if this rifle were provided with an arrangement which, without affecting its shooting, would permit of its being fired more rapidly. In this way, while the British army could, be rapidly re-armed with an effective breech-loader, ample time would be given for working out the question which would still remain of a totally new breech-loader for future manufacture. About fifty systems of conversion were submitted to Govern- ment, in reply to an advertisement dated August, 1864. Of the five systems which were preferred by the committee only one was a non-capping breech-loader, and that, was the Snider. Ultimately, after some extensive trials, the Snider was adopted. Most of our readers are probably more or less familiar with the breech-action of the Snider rifle— the block hinged upon the side of the “ shoe,” and containing the piston or striker, by means of which the blow is communicated from the hammer to the capo BUILDING- CONSTRUCTION. 195 Those who are unacquainted with this arm will be able to under- stand its construction from the illustrations in page 193. The whole of the serviceable long and short Enfield rifles are rapidly being converted into breech-loaders on this system ; and these, with the addition of some thousands of new Snider- Enfields, will give us about 700,000 Sniders by the end of March, 1871. The regular army, and we believe the militia are already armed with this weapon; the armament of the volunteers is now proceeding. The Snider rifle was subjected to a, good deal of hostile criticism on its first introduction, which has been sufficiently answered by the experience of the past three or four years. We now hear little censure of the arm It is obviously open to the objection that the calibre is too large, and that it is inferior as an arm of precision, and even as a breech-loader, to some of the more modern examples of military breech-loading arms; but the simplicity, efficiency, and dura- bility of the breech mechanism are now universally admitted ; and as for its shooting qualities, the weapon is at least as efficient as the Enfield rifle. With regard to the durability of ifiiese arms, it may be mentioned that the writer of these papers has seen several Snider rifles which have fired 40,000 and 50,000 rounds : he has seen one which has fired over 70,000 rounds and which is still serviceable. We have yet to speak of a very important element in the new arm— the cartridge. It is not too much to say that it is rather to the cartridge than to the breech mechanism that the arm owes its success. The breech mechanism, it should also be understood, was not an easy one to construct a cartridge tor, because (1), in the event of a failure on the part of the cartridge, the block was liable to be blown open ; (2) the diffi- culty— we might say, the impossibility— of making the block fat accurately and closely against the base of the cartridge ren- dered the strain upon the cartridge case peculiarly severe; (3) the extraction of the empty case had to be performed by hand, and without any leverage or mechanical assistance, and therefore must be easier than is necessary for guns in which ‘power” can be applied. But there were other conditions besides those of strength and easy extraction which the car- tridge was required to fulfil. What they were, and how they have been satisfied, will be explained in another paoer. BUILDING CONSTRUCTION.— VII. plates, serve to spread the pressure over a wider surface than that on which the girders would otherwise rest. Fig. 43 shows the section of a girder resting on a template, how it is necessary, first, that pressure should be averted aa much as possible from the end of this girder; for, in ‘the event of damp striking it, or its rotting, it would give way under the weight. Secondly, the upper portion of the wall should receive no support from the girder by resting on it; for, should the 7 'amp / mIs, Fig. 43. girder warp, sag, or by any means shake, the brickwork de- pendent upon it would crack and give way. The arch, then turned over the end of the girder and lintel, not only supports eachffid« ab ° Ve ’ ^ “ dlscharges ” the weight over the walls on Lmtets are pieces of timber placed over the square-heads of ndows; they are used to preserve the square form, and for the attachment of the wooden lining of the under surface of the opening called the soffit, etc. They should not, however, be allowed to bear the weight of the wall above, under which they would certainly give way ; and any sagging in the middle would to ” Se ’> which the entire brickwork would be distuibed. It is therefore necessary to build “ discharging ” arches over them.- The principle on which arches are con- structed will be considered further on; it is therefore only necessary here to demonstrate their use in relieving the lintel from pressure. 6 Fig. 44 illustrates the position of a lintel, over which a dis- c larging arch is placed, for the same purpose as that above. Ifais cut also snows the application of wood -bricks, w, w. Those are used for the attachment of joiner’s work in the jambs BRICKWORK ( continued ). Brickwork should not be carried on in frosty weather, am oven if such is expected, it is advisable, where possible, to dela 1 the building. Unfinished walls should be covered with straw on which boards, called weather-boards, should be laid. Bi attention to this simple matter injury to walls might often bi prevented. The introduction of substances other than those composim the walls should be as far as possible avoided. In general however, some wooden members are required, but these shoulc be treated with the greatest caution, so that they may not be crushed by the weight above them, or lest the superstructure, u I? 1 ?! made to rest u P on them, might become liable to sinh should the wood decay. The principal wooden parts of the structure which are connected with the brickwork are the wall- plates, templates, lintels, and wood-bricks. Wall-plates are pieces of timber laid lengthwise on the top of a wall to receive the ends of the floor-joists, which rest upon mem.. This will be fully treated of under the head of Flooring and is only referred to in this place to explain the purpose of wall-plates in relation to the walls. It will be clear that if the joists were tailed singly on the walls themselves the pressure of each individual timber would be on a single brick and those which support it, whilst those between the joists would not in any way share the burden. The wall-plate then, resting as it does on the wail, distributes the weight over the whole length • and thus ail parts of it bear alike. The application of a wall- plate will be shown in an illustration in a future lesson. r ^° P ur P° se templates (called also templets) is similar to that of wall-plates. They are used in a stronger form of flooring, which will subsequently be treated of, called “ framed floors, the weight of which is borne by a few very large girders. Under theso are placed the templates, which are stout pieces of timber two or three feet long; these, like the wall- of the windows and doors, for their fittings, and along the walls at certain heights for the skirtings or wainscoting to be nailed to. It is scarcely necessary to remind workmen that it is worst'" than useless to drive nails into mortar between bricks; and that therefore when it is necessary to drive a nail into a wall already built, the wall must be plugged, that is, wedges of wood must be driven in, and into these the nails may be ham- mered. But the use of wood-bricks supersedes the necessity of wedges in a wall in course of building, and as it is known beforehand what fittings are to be attached, the blocks o£ wood 196 THE TECHNICAL EDUCATOE. cut to the exact shape and size of the bricks can be -worked in as bricks at the points in the wall where they will oe required by the joiner. Wood-bricks are, however, gradually going out of use. It is found better to insert a piece of timber of the thickness of the joint of the brickwork — viz., about I or f thick, which shrinks less than a wood-brick, and still affords sufficient hold for the Bond-timbers are long pieces of wood like continuous wood- bricks. They are not much used now. Their purpose is to bond the bricks together, and for the attachment of mouldings, wainscoting, etc. ; but they are liable to shrink, swell, and decay, according to the situation in which they may be placed ; and further, in the event of taking fire, they burn away, and if designed by another. Let us then state once for all, that every curved covering to an aperture is not necessarily an arch. Thus, the stone which rests on the piers shown in Fig. 45 is not an arch, being merely a stone hewn out in an arch-like shape ; but at its top, the very point (a) at which strength is required, it is the weakest, and would fracture the moment any great weight were placed upon it. Equally faulty is the annexed example of an early Egyptian attempt (Fig. 46), in which the first course of horizontal stones projects beyond the piers, and on these rest a third, hewn out to complete the form ; and here again wo have weakness where strength is required. . At Etruria, and also at Phigalia, constructions similar to Fig. I 47 have been found, which are, if possible, worse in principle thus the wall resting on them is weakened. Their use in England is now almost entirely superseded by hoop-iron. Thin and narrow strips of this metal, tarred, are laid in the bed- joints of the mortar, at intervals more or less frequent, accord- ing to the thickness of the wall ; and they are found in every way effective, whilst it has been shown that the joiner’s fittings may be attached to single wood-bricks, on which so much struc- tural strength or safety does not depend. ARCHES. Arches have been incidentally spoken of, but they form such an important feature in building- construction, that it is deemed advisable that they should be treated of separately. It is necessary, then, that the student should have a very clear con- ception as to what an arch really is. For if a positive con- clusion has not been arrived at, and if the “ arch principle ia not thoroughly understood, he cannot be expected to design arch, or to construct it with accuracy or intelligence, even than the previous ones ; for it is clear that, unless the upper slab be longer than the width of the opening, and the lower stones are weighted at their tail ends, the whole must full in the moment any weight rests on A. _ . We come, then, to the point at which it is required that we should state, as briefly as possible, what an arch really is. An arch, then, is an assemblage of stones or bricks, so arranged that they may by mutual pressure support not only each other, but any weight that may be placed upon them. The leading principles in the construction of an arch are — 1. That all the stones of which it is formed shall bo of the form of wedges ; that is, narrower at th i inner than the outer end. . 2. That all the joints formed by the meeting or the Siantir.g sides of the wedges should be radii of the circle, circles, or ellipse, forming the inner curve of the arch, and will therefore converge to the centro or centres from which these are struck. These two brief statements will serve at the present stage to CHEMISTRY APPLIED TO THE ARTS. 197 ma.i£e clear to the mind of the student the general principles of an arch ; the mathematical reasonings connected with the de- signing of arches to bear certain weights are omitted, as not coming within the scope of this course of lessons, but the writer is very anxious that the student should clearly comprehend and not misconstrue the cause of this omission. It is not because he deems this mathematical knowledge unnecessary , but simply because be wishes to give information to students who have not had opportunities of acquiring such. Elementary works on the various mathematical subjects connected herewith can, however, be easily obtained ; and all who would really study principles, a.nd appreciate the exquisite refinement of the examples herein given, are strongly urged to read them. Referring to Fig. 48, wo will first explain terms. The under surface is called the intrados, and the outer the extrados. The supports are called the piers or abutments, though the latter term is one of more extensive application, referring more generally to the supports which bridges obtain from the shore on each side than to other arches. The term piers is, as a rule, supposed to imply supports which receive vertical pressure, whilst “abutments” are such as resist outward thrust. The upper parts of the supports on which an arch rests are called the imposts. The span of an arch is the complete width between the points where the intrados meets the imposts on either side ; and a line connecting these points is called the springing or spanning line. The separate wedge-like stones composing an arch are called voussoirs, the central or uppermost one of which is called the key- stone ; whilst those next FIC to the imposts termed springers. The highest point in the intrados is called the vertex or crown, and the height of this point above the springing line is termed the rise of the arch. It will be evident that in a semi- circular arch, such as rig. 48, this would be the radius with which the semicircle is struck. The spaces between the vertex and the springing line are called the flanks or haunches. The following are the varieties of arches used : — The Semicircular, as shown in Fig. 48; the Segment (Fig. 49) , in which a portion only of the circle is used — the centre c is therefore not in the springing bne s, S ; the Elliptical (Fig. 50) ; the Hyperbolical (Fig. 51) ; the Parabolical (Fig. 52) ; the Cycloidal (Fig. 53). The methods of constructing these various curves are fully elucidated and illustrated in the lessons in “ Practical Geometry applied to Linear Drawing,” and it is therefore not necessary to repeat them in this place. The Catenarian (Fig. 54), the form of which is the reverse of the curve taken by a chain or heavy rope when suspended between two points, as a b. A simple mechanical method of describing this curve is as follows : — -Draw the springing or spanning line, A B, and bisect it by a perpendicular ; place your drawing-board upright, and having marked on the central per- pendicukar the length 4 c, equal to the height of the required arch (the rise), fasten a cord at A; place a nail at B, and, sus- pending the cord over it, draw it until it gradually reaches c ; then fasten it, and with your pencil carefully trace the curve thus formed, being guided by, but not disturbing the cord, which should be first wetted and drawn between the fingers. A further improvement on this method is to obtain a quantity of shot, drilled through their centres like beads, and thread them on a fine flexible cord, such as silk, having previously slightly rubbed them over with common black lead. When this loaded cord has been accurately placed, press gently on the shot, and thus a series of marks will be made on the paper. The curve drawn through these points will be the Catenary. Now set off any number of divisions on each side of the centre, and draw perpendiculars through them, cutting the curve in a, b, c, c, d, e, f, and passing through the span a b in 1, 2, 3, 4, 5 ’ 6, 7 ; set off all the perpendiculars above the spanning line, the lengths of 1 a, 2 b, 3 c, etc. ; join these points, and the curve will be the catenary inverted, as used in the catenarian arch. CHEMISTRY APPLIED TO THE A RTS. —IV. BY GEORGE GLADSTONE, F.C.S. CALICO PRINTING. Calico printing forms now one of the greatest industries of the country, and is destined steadily to increase as the great foreign markets become more and more opened up to British commerce. It is associated with the names of many of the wealthiest families of Lancashire and Glasgow, such as the Peels, whose enterprise in availing themselves without delay of every improvement in the art, led to the realisation of that fortune which enabled the late statesman to devote himself to a public career. From the earliest ages down to the end of last century, what is termed “hand-block printing” was universally practised, and it still continues to be to some extent. Block printing by machinery has since been introduced ; but though the machines employed for this purpose are very ingenious and beautiful, they would never have sufficed to meet the rapidly increasing demands of the trade. It is to the invention of the cylinder machine that the prosperity of our manufacturing districts is so largely indebted. Block printing, as distinguished from cylinder printing, con- sists in stamping the calico with a pattern raised in relief upon the block, after being moistened with the composition which is intended to be transferred to the cloth. The hand-block varies somewhat in size, according to the pattern or work required ; but it is commonly about nine inches long and six broad, with a handle for the sake of convenience. The pattern is some- times cut out in relief upon the wood, but this is liable to wear down very rapidly, so that it has been found greatly preferable to raise the pattern on the block, by inserting strips of oopper of the desired form and thickness into the wood, by which means a sharper and more durable design can be obtained. The mordant, or dye stuff, as the case may be, is applied to the block by pressing the latter upon what is termed a “ sieve ” (a box covered with woollen cloth), which is kept moist by the com- position below working its way up through the interstices, and then the cloth is stamped with it at the regular distances required to produce the pattern. Another mode of charging the block with the dye is to pass a moistened roller over it, after the manner generally adopted for applying ink to letter- press. Several colours may, however, be printed simultaneously with one block ; in which case the sieve must be divided into as many compartments as may be required, each division corre- sponding in shape and size with the portion of calico which is to receive a certain mordant or dye. If the several colours are to form parallel lines, whether straight or waved, the roller can also be readily adapted to this purpose. A piece of print would ordinarily require about 450 separate applications of the hand-block, involving a very serious expense for labour, as well as occupying a considerable time ; especially as each im- pression must bo adjusted with the utmost nicety, or there will appear to be breaks or irregularities in the pattern. In order to increase dispatch, and at the same time to secure great precision in the joining of the pattern, machinery has been adopted ; the most complete invention of the kind being the “ Perrothie,” so named because it was brought to perfection by M. Perrot, of Rouen, one of the chief centres of the French cotton manufacture. Cylinder printing has now almost superseded all the other processes, those previously employed having no chance of com- peting with it, either as to precision or dispatch. It dates from about the year 1785. It differs in several particulars from the block system. In the first place, the pattern is not raised upon the cylinder, as in the block, but cut into it, by which means fine lines can be produced without suffering much from wear and tear ; in the second, it can be arranged with, such precision that the pattern shall be continuous ; and in the- third, the printing can go on without intermission, so that there is an immense saving of time. The multiplication of different colours in one pattern can also be much more easily effected by the adoption of this system, as almost any number of cylinders can be adapted to the machine, according to the number of colours desired. The following description of the actual operations will be confined to cylinder machine printing, as the block system only varies from it in the mechanical arrangement. The several THE TECHNICAL EDUCATOK. *98 processes which a piece of goods ordinarily passes through at a printing establishment consist of printing, stoveing (in which ageing is included), dunging, dyeing, brightening, and dress- ing, There are, however, some special processes adopted to produce different styles, which will be described afterwards. They may be regarded as additions to, or variations from, the ordinary style. Printing . — It will be seen at once that the result depends upon the same chemical reactions as have been fully explained in the previous articles upon Dyeing ; and it will be necessary to bear in mind the special functions of mordants and alterants. The colours which the piece of goods is hereafter to assume are not printed upon it, but only the mordants, which are to take them up afterwards, and to fix them. The pattern being engraved upon the copper cylinder, it has to be charged with the mordant, which must be of such a consistency that it will neither run too freely, nor stick to the metal. With this object, it is usually thickened with flour, starch, pipeclay, sugar, glue, gum, etc., but the quantity of such ingredients varies a good deal, according to the character of the design ; and the thicken- ings themselves must be selected with reference to the substances contained in the mordants, some of the salts used for this purpose causing starch or flour to coagulate, while others have the same effect upon gums — which renders them quite unfit for the purpose. The mordants have, of course, to be likewise selected with reference to the colours which it is intended to produce, so that, on subsequently steeping the oloth in the dye, different chemical reactions may take place, and thus bring out the variety of colours or shades required. Thus mordants made with iron salts and alums in various proportions will serve to produce all kinds of tints from red to purple, and even to brown : by omitting the alum altogether, a black may be produoed ; and, on the other hand, an aluminous compound without any iron salts will serve as a mordant for orange. Each cylinder employed, being arranged so as to fit into its exact place in the pattern, and charged with its respec- tive mordant, passes over the cloth in succession, discharging the mordant upon it, which then passes at once into another ehamber, in order to undergo the next process. The printing, however, cannot be satisfactorily performed unless the cloth be damp, a certain amount of moisture being absolutely necessary in order to ensure the mordant’s thoroughly adhering to the fabric ; but if, on the contrary, it should be made too wet, the mordant would be liable to run, and the sharpness of the pattern would be marred. In order that the proper medium should be secured, and that the whole piece should be of uniform dampness, it is found best to let the goods lie in a damp atmo- sphere for some time, and that the printing-room should be maintained at a pretty high temperature with the air thoroughly saturated with moisture. Stoveing . — Immediately after coming off the printing-machine, the cloth is passed through a hot flue, in order to dry the sub- stance taken off the cylinders before it has time to spread, which action would be encouraged by the dampness of the fabric. In the act of drying, the mordants adhere more closely to the fabric, especially if acetates of iron have been used, the acetic acid being driven off by the heat, and leaving the iron free to unite with the cloth. The hot flue leads into the ageing-room, where the cloth remains suspended for about a couple cf days, to complete the fixing of the mordants, so far as exposure to the influence of the atmosphere will carry the process. Dunging . — This is a very necessary operation, and is so named from cow-dung being usually the material employed for the purpose. Other ingredients are sometimes used as sub- stitutes, and there are cases also when a bran-bath will suffice. The valuable properties of the dung appear to consist in the phosphorus compounds and the albuminous matters contained in it ; and the natural combination is preferable to the chemical preparations which are in some instances used instead. The result produced is a double one ; it fixes more thoroughly the iron salts and aluminous mordants which have been transferred to the cloth in the act of printing, while at" the same time it carries off the ingredients which have been introduced as thickenings, so as to expose the mordants to the full action of the dye which is presently to be applied. It is usual to pass the goods rapidly through two separate baths made of a solution of this material in warm water, the tanks being arranged with a series of rollers on each side, over which the fabric is drawn alternately, so that a very large surface is exposed to the action of the bath. Between each of these immersions the goods should be well scoured in the dash-wheel (similar to what is used in bleaching), so as to carry off the extraneous matters. Dyeing . — Up to this stage, although the pattern has been printed upon the cotton, the effect is not manifest, the slight colour which may have been conveyed to the cloth with the mordant having no reference to that which is intended to be ultimately produced. This comes out during the dyeing ; the mordanted portions of the cloth — which exactly correspond with the pattern, or combination of patterns, engraved upon the cylinders — taking up the dye, and producing, with the various mordants employed, the variety of colours required to produce the desired result. The chemical processes upon which this depends will be readily understood by those who have read the previous articles on Dyeing, but the practical details will need some further description. One of the dyes most commonly used for this purpose is madder. A solution of it is made in the dyebeck — a long vessel containing the dye in solution, above which a roller or reel extends for its whole length, over which the cloth passes; and, being made to revolve by a winch, it carries the fabric with it, so that the whole surface becomes equally exposed to the action of the dye, and by repeated revo- lutions has as large a surface as possible brought under its influ- ence within a given time. The immersion in the dyebeck should occupy four or five hours, during which period the temperature should be gradually raised from a tepid to the boiling heat. The addition of a little chalk, especially if the water should be very pure, greatly heightens the effect of the madder. Should it be intended that the mordant printed from any one cylinder shall take up no other dye than madder, the process above described must be repeated until the mordant is thoroughly saturated, so that it may be rendered incapable of taking up any of the dyes to be subsequently applied for other parts of the pattern. Suppose, however, an orange be desired, the mad- dering would be stopped sooner, in order that some of the mor- dant might remain free to combine with the yellow dye. The same plan is adopted when solutions of quercitron, sumach, and other dye stuffs are used. Brightening . — The next step (sometimes called “ clearing ”) is for the purpose of bringing up the colours to their full bril- liance, and at the same time of finishing the operation of fixing. This is attained by passing the goods through a soap bath two or more times, according to the dyes which have been previously applied, the second immersion being usually in a slightly acid solution. Between each bath the fabric should be thoroughly rinsed and exposed to the air. The effect of these operations is to clear the unmordanted portions of any colour that may be adhering to them, so as to obtain a perfectly white ground, . and also to discharge from the rest of the surface any excess either of mordant or dye which has not entered into combination with the other. Some dyes, however, will not bear the action of soap, and for clearing these a bath of bran is used instead, the goods being immersed for about half an hour, during which time the liquor is raised to the boiling-point. After this they only require dressing, in order to give them a proper finish for the market. Such is a brief description of the process in most general use for printing calicoes. The ingredients principally employed as mordants are alumina and the salts of tin and iron, different combinations of which are worked up with gum and other thickenings, in order to make the various pastes for feeding the cylinders upon which the several parts of the required pattern are engraved. The dye-stuffs which are subsequently used for producing a permanent colour with the various mordants have already been named in the articles on Bleaching, the calico printer having to consider the varied affinities of certain dyes for the several mordants which have been used in printing the pattern, so that they shall produce such colours, or combina- tions of colour, as shall make a harmonious whole. Madder, cochineal, and safflower are much used for various shades of red ; chromium, yellow berries, and quercitron, for yellows and orange ; the double cyanides of potassium for blue ; while com- binations of these, by successive applications in the dyebeck upon appropriate mordants, will produce the intermediate colours. The selection of the most suitable dye-stuffs - so as to realise the best effect, is a matter of considerable importance; TECHNICAL DRAWING. 199 nor is the order in which the dyes are applied a matter of indif- ference, the general rule, however, being that the darkest colours should be dealt with first. There are yet other processes connected with calico printing to be described, which must form the subject of another article. -XIII. TECHNICAL DRAWING. DOVETAILING. We do not know any branch of carpentry or joinery which so much shows whether the workman is a “ good hand ” or not, as the way in which he joins timber at the angles. Wo say “ car- pentry and joinery,” because carpenters are constantly called upon to build wooden cases for cisterns and similar construc- tions ; and, therefore, this lesson refers to them as well as to joiners. Certainly it applies to all young workmen, for they, above all, must learn accuracy in joining, and must acquire the power of cutting wood, so that every part may fit without being hacked, chopped, chiselled, or shaved, by which material, time, and patience are wasted, and, in consequence, bad work ensues. It is, of course, desirable that a joiner should work quickly ; but it is by far more important that he should work well ; that he should join his materials with firmness and accu- racy : that he should make the surfaces perfectly even and smooth, the mouldings true and regular, and the parts intended to move so that they may be used with ease and freedom. It is also of the greatest importance that the work when thus put together should be constructed of such dry and sound materials, and on such principles, that the whole should bear the various changes of temperature and of moisture and dryness, so that the least possible shrinkage or swelling should take place, and that frames, panels, or doors should not warp or twist. We have seen the great effects of encouraging good workmanship in iron and in the construction of machinery, which is now one of the industries for which this country is famed throughout the world : let us attach the same importance to our wood-work, and thero is no reason why we should not in that branch attain a similar position. One of the most important methods employed by the joiner is that termed dovetailing, which is of three kinds — namely, common, lap, and mitre. Common dovetailing shows the form of the pins or projecting parts, as well as the excava- tions made to receive them. Fig. 108 shows the ends of the two boards, a and b, to be thus, joined, and Fig. 109 shows the joint completed. Fig. 110 represents a variation of this form, used in attaching the fronts of drawers to the sides, and for similar purposes. Here the dovetail is shown on the one i S1 . d ® * .J ed f e being left at the end of a so that the ends I of the dovetails of the side b do not penetrate quite to the front Lap dovetailing is similar to this, but in that system the ends ot the dovetails of the side a are shortened, and the recesses which are to receive them in b are not cut through; when joined ' together, therefore, only the ledge is visible on the return side. ' i Mitre dgvetailmg— sometimes called also secret dovetailing— ! conceals the dovetails, and shows only the mitre at the edges Ihe manner in which this joint is effected will be understood xrom * l "‘ 1 | 1 > m ^bich the two parts a and b are given, each part being lettered to correspond with the position it is to occupy when the sides are joined. Concealed dovetailing is particularly useM where the faces of the boards are intended to form a salient angle, that is, one which is on the outside of any piece of work ; but where the faces form a re-entrant angle— that is, a joint to be seen from the inside— common dovetailing will answer best ; for, first, it is stronger, because the dovetails pass entirely instead of only partly through; secondly, it is cheaper, for the dovetails which go through the whole wood ta e up so much less time in working than where a mitre has to be left ; and further, if well executed, the dovetails are, by the very nature of the work, concealed internally. I'lg. 112 exhibits a method of joining two boards at right angies to each other. This is the simple mortise and tenon, and will not require any explanation. MOULDINGS. Mouldings are classed as Roman, Grecian, and Gothic. * xf K ° man mouldings are all formed of parts of circles, and can therefore be struck with compasses. The Grecian are prin- pal y composed of parts of curves known as the conic sections — such as the ellipse or hyperbola. They are otherwise nearly similar to the Roman, which are therefore illustrated in lhi« place as being the simpler and the more generally used. The modes of describing the conic sections will be found in the lessons in “ Practical Geometry applied to Linear Drawing.” Fig. 113. — The moulding of which this is a section is called the Ovolo, or quarter round. The fillet, or straight edge pro- jecting beyond the curved portion, is to be drawn first, and then the horizontal, which represents the depth or bottom line of the moulding. Now produce the bottom line of the fillet, and on it, from the point at which the curve is to start, mark off the width of the moulding. The point marked © in the cut, is the centre from which the quadrant is to be struck. Fig. 114 is called the Torus, or half-round. Having drawn the fillet, and the line representing the bottom of the moulding, draw a line at right angles to these. Bisect the width of the curved part, and the bisecting point will be the centre. Fig. 115 is the Cavetto, or hollow. This is a quarter-round, the curve turning inward. It is thus precisely the reverse of the ovolo. Fig. 116 is a section of the moulding called the Oyma Recta . The exact form of this moulding is to a certain extent a matter of taste, since the curve may be made more or less full, aa shown in the three examples, Figs. 116, 117, and 118. To describe Fig. 116, draw a perpendicular across the depth of the moulding, and bisect it. From the bisecting point as a centre point describe a quadrant; through the centre draw a horizontal I line, and from the point where the quadrant already drawn l touches this line mark off the radius ; then from this point as j a centre describe the second quadrant, which will complete the ] form. In this and the subsequent curves composed of com- ! bined arcs the greatest care is necessary, so that the one may ! glide smoothly into the other without showing any break or j thickening at the joining. To describe the Cyma Recta shown j in Fig, 117, which is the form most generally used, let n and o i be the points to be united by the moulding. Draw the line n o, J and bisect it ; with half no as a base describe an equilateral J triangle on the opposite sides of the line ; then the apices * of j the triangles will be the centres from which the curves are to | be struck. To describe Fig. 11 8, or others the curves of which are required to be more flat than in the last figure, draw the line j n 0 as before, and bisect it. Bisect these two divisions again. ! and tho centres will be on theso bisecting lines, according to the form required ; for, of course, the longer the radius the flatter the curve will be. * ' n, If it is required that the curve should be more full at the lower than at the upper part, it may be effected in the following Sww 1S 1 T in Fiff ; 119 - Havi1 ^ drawn n o, divide it mto three equal parts ; construct an equilateral triangle, the base of which is two of these thirds, and on the opposite side of tlie line another, the base of which is the remaining third. Thu apices of these triangles will be the centres for the curves'. Fig. 120 is the Ctyma Reversa. In this moulding the curve bulg-es outward at its upper part, its fulness being regulated by tne taste of the designer. Thus it may be formed of two quad- rants, as in Fig-. 120 ; or of two semicircles, as in Fig. 121 • or it may consist of the two arcs drawn from the apices of triangles as m the cyma recta already shown. i big- 122 is the Scotia. This is a hollow moulding, sometimes I consisting of a semicircle only— viz., the reverse of the torus In other instances, as in Fig. 122, it is composed of two quad- rants ; and m others it is drawn from three centres, as in Fig. 123, To draw this, divide the depth of the moulding into three equal parts, and with one third describe the quadrant r u; produce the horizontal r u, and from r set off i, equal to half u r. At n erect a, perpendicular, and mark on it n k, equal to i u; draw i k, and bisect it; produce the bisecting line until it cuts n k m s. Draw s i, and produce it. From i, with radius i u, draw ,, n ® t Portion of the curve, meeting s i produced ; then com- plete the curve by an arc drawn from s with radius s n. A fillet (from the French word filet, a band) is the small flat edging used to separate two larger mouldings, to strengthen ' then- edges, or to form a cap or crowning to a moulding. The nilet is one of the smallest members used in cornices, archi- - waves, bases, and pedestals. When placed against the flat i * Apices plural of apex. The upper point of a triangle. 200 THE TECHNICAL EDUCATOR surface of a pedestal, it is usually joined to it by a small quarter-round hollow called the Apophyge (Fig. 124). The torus, when worked very small, is called the Astragal (Fig. 125) ; but when worked so as not to project, as on the edge of boards to be joined, it is called a lead. Figs. 126 to 133 are sections of Gothic mouldings. The whole of the construction lines are given in the illustration, and it is hoped the student will be able to work from these without any further aid. The whole subject of “Gothic Architecture” will be fully treated of in a separate series of lessons. FREEHAND DRAWING FOR JOINERS. We now proceed to give some examples of free-hand drawing, Figs. 140 and 141 are ancient borders worked on the ogee or cyma reversa moulding. These are both to be started in. the same manner as Figs. 143 and 144 — namely, by dividing the width into equal parts for the middle line of the arch or of the tongue, and dividing each space again to obtain the middle line of the dart or flower. The main forms are then to be sketched in.. Fig. 142 is the Guilloche, or chain, and is formed by con- centric circles overlapping each other. This pattern is easily drawn with compasses, but is here given as a freehand study, in order to give the student an exercise in severity and accuracy of form. . Fig. 143 is a Greek border, composed of a leaf and dart, and is presented, of course, with the understanding that it is to he which we are sure will be acceptable to the student. In these examples Figs. 134 and 135 are studies of the wave-line. They are, in fact, the cyma recta repeated, the depth being lessened in Fig. 135. Fig. 136 is a study of the elementary lines of a running scroll, formed of the wave-line, with the addition of spirals. Care must be taken in drawing these spirals, so that they may pro- ceed from the stem in a smooth and continuous manner. They should start as a continuation of the wave-line so gradually, that if the stem beyond the spiral were removed, the scroll would be perfect, and that if the scroll were taken away the wave-line would remain uninjured. This should also be the case in Fig. 137, in which tendrils are added to the scrolls. Fig. 138 is a further elaboration of the same design, the lines being doubled. Fig. 139 is another simple running pattern based on the wave -line. copied on a very much larger scale ; and the student is again reminded that shading must be secondary to outline, and that therefore it is intended that each of the studies here given is to be drawn twice, first, as distinct practice in outline; and, secondly, another outline having been drawn, the shading may be added, but on no account is the shading to be begun until the outline can be drawn with facility. In commencing to draw this moulding, which is used as a decoration for the cyma reversa, set off the widths of the leaves, and draw perpendiculars, which will afterwards be the middle lines for the darts or tongues. Exactly in the middle of each of these spaces draw other per- pendiculars for the midribs of the leaves. The curves are next to be drawn, being careful to balance the sides accurately. Fig. 144 is the Greek ornament known as the Egg and Tongue. It is used as a decoration for the ovolo moulding. The method of commencing to draw this is the same as in the last example, and thus any further instructions are unnecessary. 202 THE TECHNICAL EDUCATOK. TECHNICAL EDUCATION ON THE CONTINENT.— VII. BY ELLIS A. DAVIDSON. THE PARISH WORKMEN’S SCHOOLS OF WURTEMBURG. The workmen’s schools of the kingdom of Wurtemburg afford, as a complete series, an admirable example of a great system by which thousands of young people of both sexes receive instruc- tion, such as may qualify them for entering on a future course of usefulness, and at the same time assist in developing the elementary instruction which they have received in the primary schools. These schools, admirably organised as they are, fulfil, however, a moral as well as an intellectual mission. It is just in the years when a boy leaves the primary school and goes to busi- ness that he begins to feel the desire to throw off the trammels which school discipline has during his early life imposed upon him. He enters a workshop ; is associated with other youths and men ; he earns money, and learns to spend it ; he acquires habits ©f manliness — not always such as add dignity to that term ; and thus in these few years the whole moral status of the youth is decided. It is in watching over this critical period of a boy’s life — in attaching him to the studies, the elements of which he as a child acquired — in showing him the advantages and the appli- cation of the rudimentary instruction he has received, that these schools acquire a charm and exercise an influence over the whole future life; whilst by the practical teaching of the “ R>eal- schulen” ( real schools, an admirable name), the “ Gewerbe- schulen” (trade or industrial schools), the “ Fort-bildung schu- len” ( continued education schools), and the “Bau-gewerke schu- len ” building (and the trades connected therewith) schools, the scientific branches of the boy’s futuro employment are thoroughly taught, and he enters the workshop, not a mere looker-on or errand-boy, but understanding the constructive principles of the work going on, and in some cases with a fair amount of manual skill. The original promoters of these schools said, “ It is, no doubt, a matter of great importance that in universities and academies professional men have an opportunity of acquiring every kind of scientific instruction” (would that this could be said of England) ; “ but a task has in these days become one of urgent necessity — namely, that of providing for the rising generation of the working and trading classes, not only the elementary knowledge offered in primary schools, but also that amount of technical and scientific instruction which tradesmen now require, in consequence of the increased compe- tition amongst themselves and between tradesmen and manu- facturers, as also in consequence of the improving taste of the public, and the great improvement made in all the different branches of industry.” The claims of the present age in regard to education have been well understood in Wurtemburg. As far back as 1818 a step was made in the direction indicated, by introducing into the Sunday-schools already established in the larger towns, for youths who had left the primary schools, special classes for drawing for apprentices. It is needless to say that such a step is not one advocated in these papers. Afterwards, however, preparations were made by the Board of Education for extending the principle to a greater number of schools. But it was in 1848 that the actual organisation of the “ working men’s schools,” as they are at present, was carried out, when the newly-created Board of Trade and Industry was charged also with the care of providing good instruction for the youths engaged in workshops and trade generally. To effect the latter purpose, a special commission, composed of members of the above-named body, was appointed. This commission, standing in direct communication with and in sub- ordination to the Ministry for educational matters, could not, however, turn to any enactments which would have empowered them to order parishes to establish the schools required ; and it was thus only by way of recommendation, and by treating with such of the parishes which had shown an interest for the sub- ject in question, that they could hope to succeed. They were, however, much aided in their efforts by the circumstance that pecuniary means were liberally granted by the State, in the form of subsidies, to such schools as had been organised in con- formity with the conditions fixed by the commission, the sums granted in this way amounting in general to half the yearly expenditure made by the parishes themselves for the support of the said schools, thus assisting but not superseding local effort. The conditions chiefly insisted upon by the commission in the organisation of the schools were, in the first place, the volun- tary principle with respect to the frequenting of the schools, and the demand that fees should be paid by the scholars- — a demand which, however small the fee might be, was considered of importance with regard to the well-known 'fact, that what is paid for is more appreciated than that which is given gra- tuitously. Thanks to the enlightenment of the Government and the ready assent given by the Chambers, the pecuniary means placed at the disposal of the commission were soon increased, and through the additional aid afforded by a large collection of educational works and appliances, maintained out of the funds of the Boyal Board of Trade and Commerce, the commissioners had the satisfaction of seeing their efforts crowned with much success. The principal task of the commissioners is to take measures that suitable localities, and all the necessary means of education, such as good books, models, diagrams, etc., are provided for the schools ; to control the appointment of tho managing boards and inspectors, as well as the training up of good teachers of drawing, etc. The commission did not, however, think it advisable to or- ganise all the schools after a uniform system, feeling that regard must be had to the different circumstances of each locality ; and therefore the general plans of some of the leading schools will be given in these papers, in order that the diversities may be rendered clear to the reader. The 135 schools now in existence in Wurtemburg (of which a statistical notice will be given further on) present, of course, various degrees of development, the studies being adapted to the requirements of the locality. In many of the smaller towns and villages the instruction is confined to arithmetic as adapted for trade purposes, commercial correspondence, compo- sition, and drawing ; this last subject, however, is in every case divided into geometrical, free-hand, and trade drawing, adapted to the wants of the district. Thus in Stuttgard the branches of drawing taught are especially those adapted for the work of builders, carpenters, locksmiths, saddlers, etc. Of course, the progress made by pupils must in a great measure depend upon the amount of elementary knowledge they have acquired in the primary schools, the purpose of these schools being supplemen- tary, not rudimentary. The schools are open to persons ®f all creeds without distinc- tion, and the Government insist that they shall be established in every town or village, however small, where trade of any kind is carried on. But the attendance of the pupils is not compul- sory ; on the contrary, only such as can produce testimonials of good conduct and industry are admitted, and indolent, irregular, and badly-conducted pupils, since they necessarily impede the progress of others and set a bad example, are dismissed. The examples used in the drawing-schools are of a large size, and are of n,v. eminently practical character, adapted for almost every br.v of construction and decorative industry. The pra>. final work done in these schools is, considering that it is executed by youths, truly satisfactory. It consists of models of machinery, buildings, and roofs, scientific apparatus, furniture, etc. In the art schools, excellent drawing from the flat and round is carried on, together with modelling in wax and clay ; casting figure and ornament in plaster ; metal work, chased and hammered ; carving in wood, etc. etc. The whole system, carried out under able and experienced teachers, shows to the utmost advantage the practical application of technical education. THE COMMERCIAL TRADE SCHOOLS. These are designed to enable young persons of cither sex to obtain those branches of theoretical and practical education which may be required in their trade, occupation, or domestic management. Those entering as pupils must have completed their four- teenth year, and the males must previously have had soma practice in manual work; The instruction in the Trade Schools is given in the hours after the close of business, and for tho special accommodation of workmen whose trades are only carried on in fine weather — as bricklayers, painters, slaters, etc. — day-classes are established. ANIMAL COMMERCIAL .PRODUCTS. 203 so that an opportunity is afforded for them to improve their education without losing wages ; and they are encouraged to ceme to the schools when not employed in their work, instead of lounging about in the manner so often and so painfully seen in this country. The course of study in these schools comprehends geometri- cal and free-hand drawing ; practical art adapted for special branches of industry ; arithmetic ; elementary geometry ; trigo- nometry and algebra ; stereometry ; commercial and trade ac- counts ; composition and correspondence ; book-keeping ; French, English, and Italian languages ; elementary chemistry and physics ; natural history ; physiology applied to health ; sani- tary knowledge ; domestic accounts and household management, the whole of the studies having reference to the present and future occupation of the learner, according to various necessary rules and regulations which will be given in connection with the individual schools. The Parish Workmen’s Schools of Wurtemburg may be divided into four classes, viz. : — 1. Commercial schools ; in which the instruction afforded is intended chiefly for the benefit of merchants, bankers’ clerks, and others engaged in trading and commercial pursuits of all kinds. 2. Trade schools ; in which the teaching afforded is adapted for artisans generally. 3. School of practical art; for ornamentists, designers, art- workmen, and teachers. 4. Female school ; to give instruction to girls and young women in domestic economy and household management — a description of school much required in this country, artisans’ wives, as a rule, not possessing much sound knowledge in these matters. Students above the age of sixteen have the privilege of elect- ing from amongst themselves a “ captain,” who in all matters represents the class. He acts as deputy before the arrival or in the absence of the teacher, whom he also supports and assists when present. These monitors are chosen from the Upper School, and must be above the ago of eighteen. The Students must, however, consult the teacher as to whether he wishes such assistance or not. In order to test the progress and to reward the perseverance and industry of the students, periodical exhibitions are held, when certificates, prizes, and other rewards are awarded, which are highly valued by the recipients, and prove a considerable stimulus to exertion and honourable competition among the members of the various classes. Although architecture and engineering, and the courses of study they require, have been principally mentioned, it must be understood that the technical instruction fakes the widest fange, including all the practical arts, and embracing the whole range of manufactures ; this will, perhaps, account for the repeated reference to the union of science and art. In carrying out this scheme the assistance of skilled workmen is obtained ; and, further, persons, whether male or female, professing and carrying on various trades, are invited, not only to visit the school and advise, but also to attend at regular and special hours. They are then entitled, should they require remuneration, to receive payment from the State according to a fixed tariff. By this means not only are the advantages of experience obtained, but the sympathy of the class who are employers of skilled labour is cultivated. In this regard we should not be wanting in this country. The noble example set by Sir Joseph Whitworth in the fur- therance of technical education, and the munificent amounts he has devoted to it ; the active measures taken by the late Herbert Minton in the promotion of education amongst his employes, and the liberality with which our leading manufacturers con- tribute not only money but practical aid in the support of any institution for the benefit of our working men, prove that if they show themselves desirous for a proper and extended system of education for themselves and their children, they will find plenty of co-operation. Thus this great country, so universally quoted for its liberality of sentiment, will at no very distant period make such strides in the training of her workmen as will enable hep by the united efforts of her own sons, to hold her own against the whole world ; and thus as the merciful Creator allows his light to shine as brightly into the pitman’s hovel as into the nobleman’s mansion, the work will prosper to the glory of His name and the honour of our native land. ANIMAL COMMERCIAL PRODUCTS.— IX. PRODUCTS OF THE CLASS AVES. Birds are warm-blooded, vertebrated animals, characterised by a double circulation and respiration, the adaptation of their anterior extremities for flight, oviparous reproduction, and a covering of feathers. The following classification, founded on certain modifications in the structure of the beak and foot, ia that which is generally adopted by naturalists : — 1. Raptores (Latin, raptor, a robber), or birds of prey, having a strong, curved, sharp-pointed beak, short robust legs, and a foot furnished with three toes before and one behind, which are armed with long, strong, crooked, and more or less retractile talons, adapted to seize and lacerate a living prey. Examples : eagle, hawk, and vulture. 2. Insessores (Latin, insideo, I sit on), or perching birds, having three toes before and one behind, slender and flexible, with claws, long, pointed, and slightly curved ; a foot, in fact, organised and adapted for the delicate operations of nest-build- ing, grasping the slender branches of trees, and perching on them. Examples: sparrow, robin, and crow. 3. Scansores (Latin, scando, I climb), or climbing birds, with the four toes arranged in pairs, two before and two behind — a conformation of the foot most suitable for climbing trees. Examples : woodpecker, cuckoo, and parrot. 4. ColumbidcB (Latin, coluniba, a pigeon), including pigeons and doves. 5. Rasores (Latin, rado, I scratch), or scratching birds, having three toes before and one behind, strong, straight, and terminated by robust, obtuse claws, adapted for scratching up the soil. Examples : turkey, pheasant, partridge, and the common barn-door fowl. 6. Cursores (Latin, curro, I run), or running birds, with wings unfitted for flight, and feet formed for running swiftly over the ground, with two and sometimes three toes in front, and none behind, except in the apteryx. Examples : ostrich and casso- wary. 7. Grallatores (Latin, grallator, a stalker), wading birds with long legs, the three anterior toes long and slender, and the posterior toe elevated and short — a form of foot and leg which enables the bird to seek its food in water along the margins of rivers, lakes, and seas. Examples : crane, heron, sandpiper. 8. Natatorcs (Latin, natator, a swimmer), swimming birds, including those which have the toes united by an intervening membrane. The body is protected by a dense covering of feathers, and a thick down next the skin ; the whole organisa- tion is adapted for aquatic life. Examples : duck, swan, and goose. The products of the class Aves consist of FOOD. All these orders of birds, with the exception of the first, afford flesh which may be eaten. The eggs of many of them are very , nutritious, especially those of the Basorial birds : 397,934,520 were imported from France in 1867. In one case, even the nest is available as food — namely, the Chinese edible birds’ nests, constructed by a Javanese swallow. The collecting of these nests employs numbers of people, as they are largely exported to China from Java, Ceylon, and New Guinea. It is calculated that 30,000 tons of shipping are engaged in this traffic, and that the value of their freights is above .£280,000. But the chief commercial value of birds lies in their feathers. FEATHERS. A feather consists of three parts — the quill, the shaft, and the vane. The quill is that part of the feather by which it is at- tached to the skin ; it is cylindrical, hollow, and semi-trans- parent, possessing in an eminent degree the qualities of light- ness and strength. The shaft is covered by an outer layer of firm, horny material, like that which forms the quill, and en- closes a soft elastic substance called the pith. The vane con- sists of barbs and barbules. The barbs are attached to the sides of the shaft, the barbules are given off from either side of the barb, and when long and loose they characterise the form of feather known as a “ plume ” — e.g., that of the ostrich, which, commercially considered, is the most valuable of feathers. The development of feathers is always preceded by that of down, which constitutes the first covering of young birds. Their colours are clue to peculiar organic pigments, which may 204 THE TECHNICAL EDUCATOR. be separated by appropriate solvents. The beautiful play of colours shown by some feathers is referable to a decomposition of light, analogous to that produced by mother-of-pearl, and other striated surfaces. The preparation of feathers for military decoration, or for the toilette, forms the art of the plumassier, the French term for the artisan who works on them. Feathers may be dyed a variety of beautiful colours, and of these, rose-colour or pink is given by safflower and lemon-juice, and deep red by a bath of Brazil wood boiling hot, after aluming ; indigo supplies the blues of every shade, and turmeric the yellows, alum being the usual mordant. Ornamental Feathers. — The most valuable and esteemed ornamental feathers are, unquestionably, those of The Ostrich (Struthio camelus). — The elegance of these feathers arises from their slender stems and disunited barbs. Those taken from the living or from recently killed birds are far more beautiful than the cast or dropped ones. The feathers from the back and above the wings are the best ; next, those of the wings and tail. Ostrich feathers dyed black — for which purpose logwood, copperas, and acetate of iron are used — are sold to undertakers as mourning plumes ; a full set is worth from .£200 to .£300. Ostrich feathers are scoured with soap, and then bleached. Fine white ones are worth from seven to eight guineas a pound. The finest white feathers of this bird, which is indigenous to Northern and Central Africa and Arabia, come from Aleppo in Syria. Good ostrich featherB are also reoeived from Algiers, Tunis, Alexandria, and Cairo, and in- ferior ones from Senegal and the island of Madagascar. The Little Egret ( Herodias leuce) is found in all the countries on the Mediterranean coast, and in Asia as far as the East Indies j an allied specieB, H. cegretta, is a native of tropical America. The feathers of both species are of the purest white, very delicately formed, six or eight inches in length, with slender shafts. The Turks and Persians embellish their turbans with them, and they form plumes for ladies’ head- dresses in this country and on the Continent. The Oreat White Heron ( Ardea alba) inhabits the shores of the Caspian, the Black Sea, and lakes of Tartary, and is also found in America and Africa. The largest and most expensive white heron feathers are furnished by the plumage of this bird. Common Heron ( Ardea cinerea). — The black heron feathers are supplied by this species, which is found throughout Europe, but especially in Prussia, Poland, and Russia. We receive the greatest quantity from Siberia. Adjutant (Leptoptilis Argdla), and a kindred species (L. Marabou), furnish the exquisitely fine and flowing plumes termed “Marabou feathers.” The former species is the well- known scavenger bird of India, its name being derived from its habit of frequenting the parade-grounds ; the latter is a native of Africa. It is impossible to enumerate all the birds whose beautiful plumage supplies us with ornamental feathers. The feathers of the Bird of Paradise, the gold and silver pheasants, the peacock, the several species of Ibises, the flamingo, the beau- tiful wing and tail feathers of the Argus pheasant, and the wing of the partridge and ptarmigan are all worn in children’s and ladies’ hats. Cocks’ feathers furnish plumes for soldiers ; eagles’ feathers are worn in the hat and bonnet in Scotland, and a plume of them is a mark of distinction amongst the Zulus in South Africa. The wing and side feathers of the turkey supply trimmings for articles of ladies’ apparel, and are made into victorines, boas, and muffs. Artificial flowers made from feathers are now much worn by ladies. The feathers selected for their manufacture are chiefly those of a purple, copper, or crimson oolour, from the breasts and heads of humming-birds. Feathers are also worn as articles of clothing. The skin of the swan, after being properly prepared, is used for muffs, linings, and a variety of other articles of dress ; the skin and feathers of the penguin, puffin, and grebe ( Podiceps cristatus) are worn as clothing on account of their beauty and warmth, supplying suitable material for victorines, tippets, boas, cuffs, and muffs, and other articles of winter attire. The native in- habitants of the Arctic regions, in some parts, make themselves coats of bird-skins, which are worn with the feathers inside. Confucius, the Chinese philosopher, writes, that ere the art of weaving silk and hemp was understood, mankind UBed to clothe themselves with the skins of beasts and with feathers ; and it is very certain that the Chinese are now very skilful and in- genious in the art of plumagery or feather-working. They manufacture garlands, chaplets, frontals, tiaras, and crowns of very thin copper, on which purple and blue feathers are placed with much taste and skill. PROJECTION.— IX. PENETRATIONS OF SOLIDS (continued). Fig. 105 is the plan and elevation of a square prism, penetrated at its edges by a smaller prism, their axes being at right angles to each other. Having drawn the square ABC d — the plan of the larger prism — draw the line E f through the centre, and make it equal to the required length of the smaller prism. At f draw j K, and at e draw G h, equal to the diagonal. On © h construct half the square of the end — viz., produce F e until E i equals E h, and join I H and I G. Draw H j and g k. These will complete the plan of the smaller prism, which will penetrate the sides of the plan of the larger prism inLMNO, Project the elevation c A d of the larger prism from the plan, and draw g' k' at right angles to the axis. On each side of gk set off the length E i — viz., points e, e ; F, f. Draw perpendiculars from L and m, cutting g' k' in i/ m'. Join cl'c, d m' d, which will be the lines marking the intersections of the two prisms. Fig. 106 shows the projection of this object when the axis of the smaller prism is at an angle to the vertical plane. Fig. 107 is the development of the longer prism, showing the shape of the openings through which the smaller prism is to pass. On a straight line set off four times the width of the side of the plan represented by adbca. Erect perpendiculars from these points equal to the height of the prism, and draw a horizontal line at their extremities. Produce ef, g' k', and E f, to cut line c in p Q R, and line D in p' q' r'. On each side of Q set off Q s and Q t, equal to c L in the plan, and set off the same measurement — viz., Q' s' and Q' T — on each side of q'. Join pset, and also p' s' r' t', and two lozenge-shaped figures will be formed. It will be observed that these are wider across than the prism which is to pass through the aperture, but it must be remembered that the two sides of the larger prism are bent at right angles to each other, and thus, when the perpen- diculars A and B are brought together, s and T approach each other until the distance between them is equal to m n in the plan, which, it will be seen, corresponds with the diagonal of the end of the smaller prism. Fig. 108 is the development of one of the projecting ends of the smaller prism. Here the widths are taken from g i in the plan of the smaller prism (Fig. 105), and the heights from DF, JO,MK. PLAN AND ELEVATION OF A CYLINDER PENETRATED BY A SMALLER ONE. The circle in the lower plane (Fig. 109) represents the plan of the larger, and the parallelogram d d' e' e that of the smaller cylinder. From this figure project the mere cross which forms the elevation. No explanation of this process is deemed neces- sary, the object of the lesson being to find the curve generated at the points where the penetration takes place. The student is here reminded that, as the plan is the view of the object when looking down upon it, the line CABO 1 , which is the top line of the smaller cylinder in the elevation, is the middle line in the plan ; and thus the line D e, which is the front or most promi- nent line of the cylinder in the plan, is represented by D e, the middle line in the elevation. From c' in the plan, with radius c' e, describe a semicircle, which represents half of the plane of the end of the cylinder.. This plane, although laid down flat, is supposed to stand up- right on the line E e' at right angles to the plan. Divide the semicircle into any number of equal parts, and from these divisions draw lines meeting E e' at right angles in F and a. Set off the lengths of these perpendiculars on each side of the line D E in the elevation — viz., F F and G G, and draw lines from these points across the whole length of the elevation of the smaller cylinder. Draw similar lines parallel to C c' from the corresponding points in the plan — viz., F F , G g', which lines will be seen to pass, not only through the smaller, but PROJECTION. 205 200 THE TECHNICAL EDUCATOK. also through the larger cylinder, representing as they do planes common to both the solids. From the points A and B, f g e, draw perpendiculars to meet the horizontals drawn from the points similarly lettered in the elevation, and the inter- sections e,f f, g g will give the points through which the curves of the penetrations are to be drawn. * Fig. 110 shows the projection of the objects when the plan has been rotated, so that the axis of the smaller cylinder is at an angle to the vertical plane. The lettering is omitted, but as all the lines of construction are shown, it is hoped that the student will be able to project the object with the aid of the instructions here given. It has repeatedly been shown that when an object is simply rotated on its axis, or on a solid angle, without altering the inclination, the heights of the various points will remain the same. This fact may be observed in a crane. When the weight has been raised as high as may be required, the crane is rotated, but the height of the top and of the weight will be exactly the same in which direction soever the crane may be turned, and thus the piece of ground over- hung by the crane and weight will remain the same in form though altered in position. If, therefore, the plan and elevation given in Fig. 109 has been prepared, it will only be necessary to repeat the plan, placing the axis of the smaller cylinder at the required angle ; then perpendiculars raised from the various points in the plan may be intersected by horizontals drawn from the corresponding points in the elevation, and the intersections thus obtained will give the points required for the pro- jection. But, in practice, the whole of the object shown in Fig. 110 might be projected without referring to the previous one, and it is important that the student should understand this, as otherwise time would be lost. To project the object when at any angle, therefore, proceed in the following manner : — Draw the circle which represents the plan of the larger cylinder. Draw a line through the centre of this, making an angle with the intersecting line corresponding to the angle which the axis of the smaller cylinder is to make with the vertical plane. On this line set off, on each side of the centre, half the length of the smaller cylinder, and at these points draw lines at right angles to the line of the axis. The plan of the object will then be com- plete, and we proceed to project the elevation from it. Draw a fine or dotted line through the centre parallel to the vertical plane, and from the extremities of this diameter carry up the perpendiculars which are to form the edges of the elevation of the larger cylinder. Now it must be borne in mind that these are not the points from which the elevation of the ctjlinder would he projected if the axis of the smaller one were parallel to the ver- tical plane. In that case the perpendiculars would be raised from the points where the axis of the smaller cylinder cuts the circumference of the plan of the larger one ; but if this were done in the present position of the plan, the elevation would be narrower than the cylinder. All vertical sections of a cylinder are parallelograms, and all those which pass through the centre are equal. Still, reference to Fig. 8 (page 9) will remind the student that the real size of a plane is only obtained in the ele- vation when it is parallel to the vertical plane ; and it will be seen that the elevation of the plane, of which the diameter of the plan, which is at an angle with the vertical plane, is the eleva- tion, would not therefore be the projection of the largest section, and would not represent the true width any more than the eleva- tion of the open door in Fig. 1 1 (page 24) represents its real width, and it thus becomes necessary to draw the dotted line referred to, so that the elevation may represent the greatest width of the cylinder. Now draw another diameter in the plan at right angles to the axis of the smaller cylinder, and the extremities of this line will be the front and back lines of the larger cylinder, which, if the axis of the smaller one were parallel to the verti- cal plane, would be the centre of the elevation ; but as it has of course rotated with the object, it is central no longer, but its relation to the heights remains the same, however the larger cylinder may be turned on its axis. On this perpendicular, therefore, set off from the intersecting line the real height, and draw the horizontal line, which repre- sents the top of the larger cylinder. Mark on the perpendicular, too, the height at which the axis * The points x, x, x are not used in this projection, but will be sub- sequently referred to. of the smaller cylinder intersects that of the larger, and draw a horizontal through the point. Returning now to the plan, the preparation for the projection of the circular end of the smaller cylinder, as shown in Fig. 77, is necessary. On the line which forms the end in the plan draw a semicircle, and divide it into any number of equal parts. Through these points of division draw lines parallel to the axis of the smaller cylinder, which will be seen to pass through the plan of the larger one, and the intersections will be the plans of points “ common to both ” cylinders. Now, from the points where these lines meet the straight line, which is the plan of the end of the smaller cylinder (on which the semicircle has been drawn), raise perpendiculars passing through the horizontal line which has been drawn across the elevation, and above and below this horizontal set off on the perpendiculars the lengths of the lines drawn from the points in the plan from which they started to the semicircle. Join the points thus obtained, and the projection of the end will be obtained. From each of the points through which the ellipse ha3 been drawn now draw horizontal lines, and raise perpendiculars from the points in the opposite end of the plan ; the curve of the end of the smaller cylinder which is turned away must then be traced through these points, and it will be observed that, as only one side of the ellipse could really be seen in this position of the object, the other half is drawn in dots. It now remains to find the shape of the curve of penetra- tion — that is, the curve generated where the smaller cylin- der penetrates the larger, and this will be accomplished by finding the elevations of the points which in the plan were spoken of as “ common to both ” cylinders. From these points — that is, from the points where the lines drawn parallel to the axis of the smaller cylinder cut the circle, which is the plan of the larger one — erect perpendiculars cutting the horizontal lines in the elevation, which are in fact the elevations of the lines in the plan. The curves must then be traced through the inter- sections of these two sets of lines. The perpendiculars must be drawn not only from the points on the front of the plan, but from those on the back part, and these cutting the horizontals will give the points through which the curve on the other side of the cylinder is to be drawn. The reason why the perpendiculars at the back are to cut the same horizontals as those in the front, is that already pointed out— viz., that a point is not altered in height when the object on which it exists rotates on its axis in the manner shown in the diagram. APPLIED MECHANICS.— IY. BY ROBERT STAWELL BALL, M.A., Professor of Applied Mathematics, Royal College of Science, Dublin. THE CRANE. INTRODUCTORY — THE FRAMEWORK THE WHEELWORK. In the various operations connected with manufactures, and with the transport of goods from one place to another, it frequently becomes necessary to raise weights and carry them about. When the weights are large, amounting as they often do to many tons, special mechanical appliances have to be used. It is our intention in this lesson to examine into some of the machines used for this purpose. In unloading a ship at the quay-side, some heavy weight — such, for example, as a block of marble weighing ten tons — must first of all be lifted from the hold. It must then be carried from the ship to the quay, and there be deposited in safety. The machine which is able to accomplish this must have three distinct properties. In the first place, it must be a sufficient mechanical power to overcome the resistance. In the next place, it must be sufficiently strong to sustain the load suspended from it ; and in the third place, it must be capable of moving the block, when suspended, from the ship to the quay. These three requisites are very beautifully combined in the useful machine known as the lifting crane. With its powerful aid three men would be easily able, at the cost of a little time, to unload the block of marble, even though it weighed ten tons. We shall consider the several parts of a crane sepa- rately, and show how each is adapted for the work it has to perform; we shall then describe some forms of crane whioh are used for various purposes in the arts of construction. APPLIED MECHANICS. 207 THE FRAMEWORK. The form of crane which is most familiarly known is that vhich is sometimes called the jib-crane . It is in reality a triangle, one side of which is held vertically, while the load is suspended from the opposite vertex. The framework of this crane — with which alone we are at present engaged— is repre- sented in Fig. 1 in a diagrammatic manner. ABC is a triangle of which the side A B is held constantly vertical, while the load is suspended from the vertex c. We shall first endeavour to ascertain tho nature and amount of the strains along the different parts of this structure. A knowledge of these strains is quite essential to a complete understanding of any machine. By this inquiry the proportions of the different parts can be pro- yQ perly adjusted, so that failure of strength on the one hand, or, what is also very unde- sirable, extravagant waste of material on the other, may be equally avoided. In Fig. 1, w is the position of the suspended weight. If I take a length, c o, which is propor- tional to the magnitude of w, and place an arrow to indicate, the direction of the force, the line co represents the force, as explained in the first lesson in “Mechanics” (Popular Educator, Yol. I., page 17). Now this force c o must be supported by bc and a c, and therefore there must be certain strains acting down these lines. In order to find them, draw o p parallel to b c, and o q parallel to A c. Then by Lesson III. (“ Mechanics”) the force o c can be decom- posed into two forces, c p and c Q. The directions of these forces are indicated by the arrows : that along c A is a force of compression, that along c b is a force of extension. Since o c and o p are parallel to a b and c B, the triangle o c p is similar to the triangle ABC, and hence the forces o c, c p, and c Q are proportional to the sides of the triangle abc. If, therefore, the load be represented by a b, the strains along b c and A c are represented by their lengths. The line b c is in a state of tension ; that is, the force is tending to tear it asunder. Now a force of this kind is called in mechanics a “tie,” and the amount of the force which is straining is called its tension. On the scale of the figure the line b c is double A b, and hence the tension of b c must be double the load. If, then, the crane were employed in raising a load of ten tons, the tension along b c would be twenty tons, and the tie must therefore be strong enough to bear this amount. But in constructions of this kind it is not sufficient that a piece be just sufficiently strong to bear the strain it has to carry : we must always allow a very considerable margin. This is especially true in a machine like a crane, which is subject to countless jerks and shocks, which for a moment place a far greater strain upon its parts than would be produced by the mere load it sup- ports. In the lowering of heavy weights this is especially the case, for sometimes slight slips occur in the links of the chain, or the load has to be stopped suddenly in its descent. Hence we are accustomed in mechanical construction to intro- duce what is called the “ factor of safety.” Thus, in the present case, instead of making the tie just strong enough to bear the utmost load the crane is intended to raise, we make it ten times as strong : the factor of safety is then said to be 10. In a crane the factor of safety should not be less than 10. It is sometimes even more than this ; but in other machines which are not exposed to the rough usage to which cranes are liable, the factor need not be so large. Wrought iron, from its great tenacity, is admirably adapted for making the ties of cranes. A rod of iron one square inch in section will require a force of nearly twenty tons to tear it asunder. Hence we must make a crane en the proportion of Fig. 1 with a wrought-iron tie ten square inches in section, as it will then be able to withstand any strain less than 200 tons — that is, it will be ten times as strong as would be absolutely required for the bare purpose of sustaining the weight. In every case the tie, if made of wrought iron, should have a total section in no place less than half an inch for each ton of strain. The jib A c has to withstand a thrust. In fact, it is a pillar, and tho component of the load which it supports is tending to crush it. It must therefore be made of materials which are capable of resisting a crushing force. In ordinary cranes it is very often made of a piece of timber, which is very well adapted for resisting a crushing force. A bar of wrought iron, such as would make an admirable tie, would be quite unequal to withstand the crushing without being of great size and cost. Sometimes both jib and tie are cast in one piece of cast iron. This arrangement answers well for cranes which are used for raising a few tons, but would be quite unfit for the largest cranes, on account of the massiveness which would be necessary to give sufficient strength. By far the best arrangement for the jib of a large crane is a girder of riveted wrought iron ; for by means of this arrangement the material is so disposed as to present a large amount of resistance to a force of crushing. The form which a wrought-iron jib may have will be under- stood from the section shown in Fig. 2. ab,cd are iron plates, which are riveted together in lengths. A good plan of fastening these plates together is shown in Fig. 3, where the plates overlap, and are riveted together, the object of the arrangement being to have the united pieces just as strong at the joint as else- where. Two plates the whole length of the jib are thus 'pre- pared, and they are shown in section in A b, ur ordinary red colours contain orange and yellow, or else blue and violet. A stick of sealing-wax examined by a prism is found to reflect all the rays up to the line D in the yellow — that is, the colour which it presents is made up of much orange and a little yellow in addition to the true red. The fugitive paint known as geranium colour is a purer red than that just named, the vermilion of sealing-wax, but it is not free from a tint of orange. Carmine and crimson lake, with other similar pig- ments, reflect to the eye a trace of the blue and violet, as well as nearly all the red, and some of the orange rays of the light which falls upon them. The best idea of pure redness may be got from the bright and broad red band in the spectrum of a burning lithium salt. Eed glass, at least that kind of red glass which is coloured by copper suboxide, does not transmit unmixed red rays, but many orange rays as well. Blue . — The third and least vivid of the primary colours is blue. It is also the most retiring and cool. We cannot point to any tolerably pure blue pigment. Beautiful as ultramarine undoubtedly is, its spectrum reveals the existence of several colours besides blue. Yet it would be hardly fair on this account to regard this or any other colour as impure. If the various coloured rays which a pigment reflects to the eye impart the sensation of blueness, it is enough. They may con- tain red, violet, and other constituents, but the resultant effect of the combination may be a blue indistinguishable in purity from the normal blue of the solar spectrum. A difficulty does, however, arise when such pigments as those above referred to are illuminated by artificial light, or are mixed with others to form secondary and tertiary colours ; the anticipated result being occasionally very far from being realised. Cobalt-blue reflects much green and violet light, as well as blue, and in fact shows a very remarkable combination of colours when its spectrum is examined. On mixing it with carmine, to form a violet hue, the green constituent in its light interferes with the purity of the resulting colour, which is much greyer than one would have expected. By lamp-light cobalt-blue appears violet. Prussian-blue and indigo absorb most of the red, orange, and yellow rays, but emit a very large part of the green, blue, and indigo. A crystal of blue vitriol (copper sulphate) cuts off all the red, orange, and yellow rays, together with the green rays up to line E, and transmits the remainder. The secondary and tertiary colours remain for discussion in our next lesson. SEATS OF INDUSTRY.— IY. MANCHESTER AND ITS SUBURBS : THEIR CHIEF INDUSTRY. Br H. R. Fox Bourne. Manchester has an antiquarian history, extending over nearly twenty centuries, and a commercial history, the authentic re- cords of which hardly cover five hundred years. Pt ranks however, with the oldest English towns that attained importance by their manufacture of clothing and other textile goods. Its first staple manufacture was not cotton but wool. When, in 1331, a few of those industrious Flemish emigrants who instructed the English in better ways of turning sheep’s wool into cloth settled in Manchester, they gave new life to a trade that for some time previously had been feebly carried on. Two centuries later, one of the three most famous clothiers in England was Martin Brian, or Byrom, of Manchester ; and at that time, in 1538, the town was spoken of by Leland as “ the fairest, best builded, quickest, and most populous town of all Lancashire.” Linen manufacture, as well as woollen manufacture, had a share in making what is now the greatest of all the great cotton towns. “ The town of Manchester,” it was written in 1542, “ is and hath of long time been inhabited, and the inhabitants of the said town have come into riches and wealthy livings, and have kept and set many artificers and poor folks to work within it ; and by reason of the great occupying, good order, straight and true dealing of the inhabitants, many strangers, as well of Ireland as of other places, have resorted to the said town with linen yarn, wool, and necessary wares for making of cloths, and have used to credit and trust the poor inhabitants, which had not ready money to pay in hand, unto such time as the said debtors with their industry, labour, and pains, might make cloths of the wools, yarns, and other necessary wares, and sell the same, to content and pay their creditors ; wherein hath consisted much of the common wealth of the town.” That account of the help given to poor Manchester weavers by rich Irish merchants fur- nishes a curious illustration of the relative position of Irish and English which has so strangely altered during the last three centuries. It is not necessary to note in detail the stages of the progress of Manchester during those three centuries. It grew steadily by help of wool and linen, although the progress was slow indeed in comparison with that of the past century, in which cotton has been the staple. In 1757, Manchester and Salford, then quite a distinct town, had between them hardly 20,000 inhabitants. In 1801 their population was 84,000, and in 1861 it was 460,000. The real Manchester, however, is very much more than the Manchester on the Irwell with its half a million inhabitants. Thirty or more important towns in southern Lancashire and western Yorkshire, and in the adjoining counties of Derbyshire and Cheshire, each with its own group of suburbs and outlying villages, constitute a vast network of cotton fac- tories, with Manchester for the head and centre of the whole. The development of the Lancashire cotton trade furnishes one of the most remarkable episodes in commercial history. It had a slender existence more than two centuries ago. “ They buy cotton wool in London that comes first from Cyprus and Smyrna,” it was said in 1641 of the Manchester manufacturers, “ and at home work the same and perfect it into fustians, dimities, and other such stuffs, and then return it to London, where the same is vended and sold, and not seldom sent into foreign parts.” While all the cotton wool that reached England came from the Levant, the supply was so small that no preju- dice was excited by its use. As soon, however, as the East India Company began to bring home larger quantities, which were worked up both in the Manchester districts and elsewhere in England, the dealers in woollen goods began to fear that their own trade would be interfered with, and accordingly, using all their influence in Parliament, they obtained the passing of a series of laws, by which such heavy taxes were laid on cotton manufactures that for a time they were virtually prohibited. In London, and along the Thames, where Huguenot settlers had planted the trade, it was nearly stamped out. In Manchester it was carried on with difficulty until 1774, when the foolish laws were rescinded. The trade, thus relieved, had a little while before begun to be quickened by the arrival of cotton wool from the West Indies, and the American colonies which have now become part of the United States. The trade in England encouraged these new importations. The invention of new machines for spinning and weaving further encouraged them ; and these causes, influencing and being influenced by the favour shown by the people for the new and cheap material for clothing, caused a marvellous extension of the trade. In 1768 the cotton goods manufactured in the whole of Great Britain were worth less than >£200,000. By 1788 the trade had been more than doubled, and it was then large enough to give employment in spinning and weaving to 159,000 men, 90,000 women, and 101,000 children. Of 142 water-mills used in these manufac- tures, 41 were in Lancashire, 22 in Derbyshire, and 8 in Cheshire ; that is, just half were in the district of which Manchester was the centre. In 1835 the number of factories in the Manchester district amounted to over a thousand, and the hands employed in them, and in connection with them, cannot have been far short of a million. The trade has more than trebled during the last generation. Manchester alone contains more than 200 factories, and in its far-reaching suburbs, from Preston to Mac- clesfield, and from Warrington to Eochdale, there are more than ten times as many. In 1860, said Mr. Bazley, “ the number of spindles employed was about 32,000,000, and the number of looms employed would be about 340,000. The p^jd investments, including the value of land and the right of water, amounted to not less than .£60,000,000, to which must be added a working 14 THE TECHNICAL EDUCATOR. capital of ,£20,000,000. Add to these again the value of mer- | chants’ and tradesmen’s stocks at home and abroad, the value of raw cotton and subsidiary materials, and of bankers’ capital, and the grand total of capital employed in t.he trade will not be less than £200,000,000.” No other single trade is so vast in its dimensions, or so important in its influences on society as the cotton manufacture, which has Manchester for its centre. All the circumstances of the trade have gyown in proportion. Dr. Aiken, the old historian of the town, tells how, a century and a half ago, “an eminent manufacturer used to be in his warehouse before six in the morning, accompanied by his children and apprentices. At noon they all came into breakfast, which consisted of one large dish of water pottage, made of oatmeal, water, and a little salt, boiled thick, and poured into a dish ; at the side was a pan or basin of milk, and the master and apprentices, each with a wooden spoon in his hand, without loss of time, dipped into the same dish, and thence into the milk-pan ; and as soon as it was finished they all returned to their work.” Those simple ways gradually gave place to more refinement and conventionality ; but the accounts of old Robert Peel’s early life, and of his commencement of calico printing, show a state of things almost as primitive. As Peel grew rich, and became the master of a score of mighty factories, giving work to 1,500 hands, so Manchester and its suburbs have grown. The old modes of labour, by which each cottage was generally a distinct workshop, and each workman his own master, have been displaced by arrangements which necessitate the presence of hundreds of workpeople under one roof to manage the complicated machinery now in vogue, and that ma- chinery enables each hand to get through fifty or a hundred times as much work as tho old tools rendered possible. The numerous stages of cotton manufacture may be grouped under three divisions. The first comprises all the processes by which the great lumps of cotton wool brought from the United States and other parts, through Liverpool, to Manchester and its suburbs, are reduced to yarn fit for weaving. The cotton is, in the first instance, cleaned by removing all impurities, and separating the coarser from the finer qualities. Then it is carded, that is, all tufts and knots are removed, and the fabric is laid out in a fleecy ribbon -like web. Next it is drawn, so that the ribbons may be all of the same quality and texture, and the filaments all exactly parallel. After that it is roved, a process by which each ribbon is greatly attenuated, and at the same time slightly twisted, so as to give it more strength and consis- tency. Fine roving follows, being, as the term implies, a more delicate repetition of the former operation. The sixth process is the spinning, which completes the production of the yarn, except that it has to be wound and packed before it i-3 ready to be passed over to tho weaving-shops. All these processes hang together, and are generally carried on in one department. The weaving is often conducted in the same factory, but it need not be so, and many cotton colonies are for spinning and nothing more. The weaving stage consists of fewer processes, but these are more complicated, some of the most wonderful exploits of modern invention being concerned in the adaptation to vast machinery of the same principles which guided the hands of the old weavers and websters during the thousands of years that preceded the introduction of machinery. We hope to be able to describe these in a future number, as well as the interesting processes of the third stage, in which the cotton wool, now converted into cloth, is dyed, printed, or otherwise finished, so that it may go out for sale as muslin or calico, wearing apparel, curtains, counterpanes, or anything else. Bleach-works, dye-works, print-works, and the like, all come under this category, and complete the circle of cotton manu- facture. The substitution of these comprehensive mechanical arrange- ments for the old-fashioned modes of handiwork has effected a mighty revolution in the social condition of the people. The history of that revolution is full of interest. Looking back at the Manchester people of bygone times, wo see a notably indus- trious and independent race. Looking at them now, we see that both industry and independence have increased, in spite of changes fraught with danger and discomfort". A century ago the Lancashire spinners and weavers thought themselves supe- rior to sT the vforld — as, indeed, they were — in their craft. The craft gave them unusual freedom, and sufficient profit to ensure for them more luxuries than any other craftsman could enjoy. They looked with extreme jealousy upon the improved ma- chinery that was introduced by Hargreaves, Arkwright, Cromp- ton, and others, seeing clearly that thereby their cottage-work- shops would soon be rendered impossible, and a new order of things would be introduced. Hence the Blackburn riots and other disturbances throughout Lancashire, which forced old Robert Peel and the other best friends of the cotton industries to use rough means for adopting the improvements and extend- ing their trade. They succeeded, and the trade has been indeed extended. The cotton lords have, perhaps, in many cases, gained an unfair share of the benefit that has ensued, but the cotton operatives have also gained very much. They have found out the way to preserve their old independence, while they have come to be, in one sense, merely well-wrought tools in a vast conglomeration of machinery. You cannot walk through the streets of Manchester, or any other cotton town, without being struck by the self-sufficient bearing, the rough, honest look, and the almost painful intentness of pur- pose shown in every movement and aspect of every man, woman, and child. There is room for much further education, and especially hygienic education, among the cotton operatives ; but England may be proud of them as they are, and the pride passes into reverence when we recall the history of their patient heroism, self-sacrifice, and mutual trust during tho terrible period of the cotton famine, consequent On the American civil war. Some mention of the multitudinous trades carried on in Man- chester and its suburbs in dependence on the cotton manufac- ture, or apart from it, must be reserved for another paper. VEGETABLE COMMERCIAL PRODUCTS. VII. PLANTS USED IN THE PREPARATION OF NUTRITIOUS AND stimulating beverages ( continued ). Grape ( Vitis vinifera, L. ; natural order, Vitacece) . — The wines of commerce are mostly prepared by fermentation irom the juice of the grape. The vine ranks next to the tea and coffee plant in importance. The excellence of its fruit, whether fresh, or dried in the form of raisins, is well known. The virtues of its fermented juice have been eulogised in song by poets, and its excessive abuse has furnished a theme for moralists of every age and nation. The grape varies in tho colour, form, size, and flavour of ita fruit. These varieties have all probably been produced by long- continued cultivation in different soils. This lengthened atten- tion which the vine has received has given it an extensive geographical range. The vine may be found in all countries on the earth’s surface included between the parallels of latitude 51° N. and 33° S. But the same latitude does not always permit the grape to ripen enough to make good wine ; this depends on the average clearness or cloudiness of the atmo- sphere throughout the year. The vine is generally supported by props and trellises, but in the sandy districts of Spain it is allowed to trail upon the ground. The time of the grape harvest, or vintage, is always regulated by the character of the wine to be made. For a brisk wine, such as champagne, the grapes are gathered before fully ripe ; foe a dry, full-flavoured wine, such as port, the mature grapes are selected ; and for German wines, the driest of ail wines, the vintage is made as late as possible. The process of wine-making is as follows : — The grapes are gathered into baskets, which are emptied into a tub, with holes at the bottom, called the wine-press. This tub is placed over another much larger, named the wine-vat. A man then gets into the upper tub, and presses or crushes the grapes by treading upon them — a mode of bruising the grape as ancient as wine-making itself. The juice or must, as it is termed, flows from the press into the vat, and sometimes within a few days, or even a few hours, depending on the temperature, begins to ferment. This fermentation makes the liquor turbid, increases its temperature and volume, so that it quickly com- mences to fill the vat. After a time the fermentation ceases, the liquor diminishes in temperature and bulk, and becomes cool and clear. When quite cold it is drawn off, or racked, as it is termed, from tho vat by a tap placed a few inches above tho VEGETABLE COMMERCIAL PRODUCTS. 215 bottom, into an open vessel, whence it is conveyed into the casks prepared for its reception. After entering the cask, a second, although much slighter, fermentation takes place, which further clarifies the wine ; its subsidence diminishes the bulk of the wine in the cask, and more wine is added so as nearly to fill the cask. This again slightly renews the fermentation, and the cask is kept open until filled to its utmost capacity with wine free from fermentation ; it is then closed, and is ready for the market. It requires great attention and practical skill to manage the fermenting process properly, as on this depends the quality of the wine. Wines vary according to the amount of sugar, alcohol, and acid which they contain. When wines contain much sugar, they are called sweet when little, “ dry.” Sweet wines, such as Malaga and Tokay, are wines which have been only half fermented ; their sweetness depends on the fer- mentation not having exhausted the sugar. Dry, strong wines, such as Madeira, sherry, Marsala, and port, are fully fermented wines, all the sugar of the grape having been converted into alcohol. Champagne and other sparkling wines owe their briskness to the presence of carbonic acid ; whilst hock and the Rhenish wines generally, and many of the French, contain much uncombined acid. The roughness and flavour of the red wines are usually derived from the husks of the fruit, but are often communicated to them by the addition of astringents, such as rhatany, kino, etc. The tints of wines are either natural or artificial. Their strength is frequently augmented by the addition of brandy. This brandy is itself distilled from wine. It is coloured with burnt sugar, and peach kernels are added during the distillation to give it that peculiar flavour by which it is distinguished. The principal wine countries in Europe are France, Spain, Portugal, Germany, Sicily, Italy, Hungary, Greece, and Turkey. France holds the first rank. The principal French wines are white and red champagne, white and red Burgundy, white and red Medocs from Bordeaux, Rhone wines, and wines from Languedoc, Roussillon, Orleans, Alsace, and Corsica. The infe- rior white wine of Bayonne, and Bordeaux wine, pass under the name of French wine, vin ordinaire. From Germany we receive the celebrated Rhine wines, so called from their place of culture — the valley of the Rhine and its tributary streams ; wines from the Palatinate, principally from Rhenish Bavaria; wines from the Bavarian province of Lower Franconia ; Moselle wines from Rhenish Prussia ; and Tauber wines from Baden and Wurtemburg. The chief places for these wines are Mayence, Coblentz, Frankfort-on- the-Maine, and Wurzburg. The vine is cultivated to some considerable extent on the Danube in Lower Austria, also in Tyrol and Illyria ; but the exportation is small. Moravia, Silesia, Bohemia, and Saxony grow inferior wines. Artificial champagne is made in many parts of Germany, especially at Esslingen, Stuttgart, and Mayence. The best Swiss vnnes are the Ryff wines, from the Canton de Vaud, the Vin de la cote from the shores of Lake Geneva. Of Hungarian wines, Tokay is the ohief, and is largely exported to Moravia, Silesia, Poland, and Prussia. Of Spanish wines, Malaga and Alicante are the most valued, and called after the names of the places which export them. From Oporto in Portugal we receive red and white port wine. Numerous varieties of Italian wines come into commerce. Europe also obtains Madeira wine from the island of Madeira, on the north- west coast of Africa ; Capo (Constantia) wine from the Cape of Good Hope, and palm wine from the East Indies.. Young and inferior wines, and the lees of wine, or the sediment at the bottom of the wine-vat, are used in the manufacture of cognac, or French brandy, and vinegar ; these come into the market from Bordeaux. In 18G7 the import of wines into the United Kingdom amounted to 15,442,581 gallons. Hops ( Humulus lupulus, L.). — The hop vine, so well known in England, is a native of Europe, and probably also indigenous in North America, as it has been found growing apparently wild on the banks of the Mississippi and Missouri. It is exten- sively cultivated for its strobiles or cones, so largely employed in the preparation of malt liquors. These strobiles, or female catkins, when fully ripe, are picked from the vines, dried in kilns, and packed in bags. Hops consist of thin, translucent, veined, leaf-like bracts or scales, of a greenish-yellow colour, having near their base two small, round, dark seeds. Hops are somewhat narcotic and their odour fragrant, the taste bitter, aromatic, and slightly astringent. These properties are owing to the presence of a peculiar resinous secretion in the glands, which has been called “ lupuline.” Ale and porter owe their bitter flavour and tonic properties to the hops added to them during the process of brewing — about one pound of hops being added for every bushel of malt. About 550,000,000 gallons of ale and porter are annually brewed in this country. The importation of hops in 1867, chiefly from the Hanse Towns, Holland, Belgium, and the United States, was 975,168 cwt., as compared with 1,133,131 cwt. in 1860. VI. PLANTS PRODUCING WHOLESOME AND NUTRITIOUS FRUITS. The fruits of commerce are very numerous and interesting. They come to us from almost every climate and country ; an immense amount of shipping is engaged in bringing them across the seas, and employment is thus given to hundreds of thousands of people. Besides furnishing us with nutritious food, these fruits give us much novel and interesting informa- tion in regard to the economy of vegetation in foreign countries. They are arranged naturally into two divisions, viz., fleshy fruits and nuts. (d.) FLESHY FRUITS. Of these one of the most important is the Sweet Orange ( Citrus aurantium, Risso ; natural order, Aurantiacece). — This is one of our commonest foreign fruits. The orange-tree is a medium-sized evergreen, with alternate, bright-green, elliptical, pellucid-glandular leaves, furnished with winged footstalks; the flowers are white, and very fragrant. Both the ripe and unripe fruits are frequently seen on the tree at the same time along with the flowers their presence amongst the foliage being truly ornamental, and adding greatly to its beauty. China is generally considered to be the native country of the orange-tree, where it still grows wild. It is said to have been brought to Portugal in 1520, and thence it has been trans- planted into every country possessing climate suitable for its culture. It is new grown in China, Portugal, India, Northern and Southern Africa, Southern Europe, Turkey, the islands of the Mediterranean, the Azores, the West Indies, and the Southern portion of the United States. The oranges imported into this country come chiefly from the Azores, Lisbon, Malta, Italy, Sicily, and Spain, in boxes and chests, and grow in those countries in the greatest profusion. It is said that a single orange-tree in’ St. Michael s has produced a crop of 20,000, exclusive of those unfit for use, calculated at 10,000 more. In 1866, 1,711,857 bushels of oranges and lemons were imported into the United Kingdom, valued at <£889,238. . , The rind of the orange yields by distillation a. fragrant oil much used in perfumery ; a still more agreeable oil, with which eau-de-Cologne is perfumed, is distilled from orange flowers. The rind is also boiled in sugar until it is candied, and thus converted into a sweetmeat. The orange contains much sac- charine matter and mucilage, forming, an agreeable acid, and hence is wholesome, cooling, and refreshing to the sick, especially in cases of fever and inflammation. The Bitter or Seville Orange ( Citrus vulgaris, L.).— This species closely resembles the sweet . orange, but is easily distinguished from it by the form and bitterness of its fruit. These oranges are chiefly used in making marmalade. .The i"nd has a place in the British Pharmacopoeia from- its qualities as a Citron ( Citrus medica, L.). — This kind closely approaches the lemon-tree in appearance, with which it has sometimes beer- confounded. The chief differences are its naked petiole, its greater number of stamens, and the superior thickness of the rind of its fruit. The fruit of the citron sometimes attains a very great size, weighing upwards of twenty pounds. Ilio citron itself is not eaten, but the thick rind is much used as a preserve, and reaches England either already candied or elso pickled in salt and water for the purpose of being candied on its arrival. We receive annually from Madeira about seventy tons of this preserved rind. An essential oil (Oleum citroneda) is obtained from the rind of the citron, very fragrant, and much I used in perfumery. 21G THE TECHNICAL EDUCATOR. TECHNICAL DE AWING. — XI Y. DRAWING FOR JOINERS ( continued ). Pigs. 145 and 146, combined into one view, are two designs for wooden gates, and are so simple that they will scarcely require any instructions as to copying. The posts m and n are, of course, to be drawn first ; then the base, k, and moulding, l ; next the framing, a, b, c, d, of each gate. In Fig. 145 the rail, e, is to be drawn next ; and in the upper compartments the quatrefoils, g, and in the lower, the bars, h, and curved stay are to be drawn. In the rectangle formed by the framing in Fig. 146 draw diagonals, and at their intersection the circular opening. Now draw the cross-framing, o p, and the vertical bars. The details will then be added without much difficulty. GOTHIC TRACERY. Although, as has already been stated, the whole subject of Gothic architecture, in both stone and wood, will be treated of in special lessons, still a few examples of tracery are given here, knowing that the joiner is often called upon to put such together on panels in churches or mansions, and that a knowledge of the basis of the construction will be of service to him. The limits of the present course of lessons, however, utteily preclude a systematic treatise on the characteris- tics of the several periods of mediaeval art. These exam- ples will, however, in some degree pre- pare the pupil for the subsequent and more extended study. Fig. 147 is the elementary figure upon which the sub- sequent design is based. Having drawn the circle, describe on the diameter two opposite semicircles, meeting at the centre, a. Divide one of these into six equal parts, and set off one of these sixths from i to n. Draw a n, and divide it into four equal parts. From the middle point of a n draw a line passing through the centre of the semicircle, and cutting it in c. From c set off on this line the length of one of the fourths of a n. This point and the two in a n will be the centres for the interior curves. Fig. 148 is the further working out of this elementary figure, ft is desirable that a larger circle should be drawn. Then, when the figure has been carried up to the stage shown in the last, all the rest of the curves will be drawn from the same centres. Fig. 149 is the elementary form of the tracery shown in Fig. 151, and is based on the problem, “ To inscribe three equal circles in a circle ” (in “ Practical Geometry applied to Linear Drawing”), which, in order to save the student the trouble of reference, in the event of his not being quite certain as to the construction, is here repeated in connection with Fig. 152. At any point, as A, draw a tangent, and A G at right angles to it. From A, with radius o A, cut the circle in b and c. From b and c draw lines through o, cutting the circle in e and d, and the tangent in the point f (and in another not given here, not being required). Bisect the angle e f a at F, and produce the bisecting line until it cuts A g in h. From o, with radius o h, cut the lines d c and eb in i and j. From h, i, and j, with ralius h a, draw the three required circles, each of which should touch the other two and the outer circle. Returning now to Fig. 149, having inscribed three equal circles in a circle, join their centres, thus forming an equilateral triangle. From the centre of the surrounding circle draw radii passing through the angles of the triangle and cutting the circle in points, as d and two others. Draw e d, and bisect it by eg; then the centres for the curves which are in the semicircle will be on the three lines d c, eg, and c e. These curves are called foliations, or featherings, and the points at which they meet are called cusps. The completion of this study is given in Fig. 151. Fig. 150 shows the elementary construction of Fig. 153. Draw two diameters at right angles to each other, and join their extremities, thus inscribing a square in the circle. Bisect the quad- rants by two dia- meters cutting the sides of the square in points, as g. Join these points, and a second square will be inscribed within the first. The middle points of the sides of this inner square, as b, c, d, are the centres of the arcs which start from the extremities of the diameters. From b, with radius b d, describe an arc, and from g, with radius g c, describe another cutting the former one in e. Then e is the centre for the arc i g, which will meet the arc struck from b in i. Of course, this pro- cess is to be carried on in each of the four lobes. Fig. 153 is the completed figure. The method of drawing the foliation will have been suggested by Fig. 148, and is further shown in the present illustration. Fig. 154 shows the skeleton lines of Fig. 155. Divide the diameter into four equal parts, and on the middle two, as a common base, construct the two equilateral triangles oin and o im. Draw lines through the middle points of the sides of the triangles, which, intersecting, will complete a six-pointed star in the circle, the angles of which will be the centres for the main lines of the tracery. Fig. 155 is the completed figure. The small figures, 156 and 157, will be understood without further instruction than is afforded by the examples. Fig. 158 shows the construction of the tracery in a square panel. From each of the angles of the square (the inner one in this figure), with a radius equal to the length of the side of the square, describe arcs ; these intersecting will give a four-sided curvilinear figure in the centre. Draw diagonals in the square. From the point b where the diagonal intersects the curve (the middle line of the three shown in the figure) set off on the diagonal the length b m equal to b c. From q, with radius m q, describe an arc o m r, cutting the original arc x in o. 218 THE TECHNICAL EDUCATOR. Make m r equal tomo. From o and r, with radius o r, describe arcs intersecting each other in i : extend these until they meet the curve p in n and a. The foliation and completion, as per Fig. 159, will now be found simplo Fig. 160 is a quatrefoil, and Fig. 161 a cinquefoil, the con- struction of which has been fully described in “ Practical Geo- metry applied to Linear Drawing ” (Figs. 26 and 41). Fig. 162 is given as a closing illustration of panel tracery ; and it is hoped that, with the instructions already given, and the elementary figures 163 and 164, the student will be able to draw this example without further aid. We shall in the next number commence a series of lessons in Drawing for machinists and engineers. BIOGRAPHICAL SKETCHES OE EMINENT INVENTORS AND MANUFACTURERS. VI.— SIR ROBERT STRANGE. BY JAMES GRANT. This eminent artist, the father of line engraving in Great Britain, was born on the 14th of July, 1721, in the island of Pomona, the principal of the Orkneys. He was lineally descended from Sir David Strange, or Strang, a younger son of the laird of Balcaskie, in Fifeshire, who had settled in those bleak northern isles at the time of the Reformation in Scotland. Under the care of Mr. Murdoch Mackenzie, teacher in Kirkwall, he received a classical education, and probably a knowledge of drawing, as his tutor has rendered good service to his country by the accurate surveys he published of the Orkney Isles, and of the British and Irish coasts. Young Strange was destined by his family for the study of the law ; but, disliking the monotony of the profession, he shipped on board of a man-of- war, and sailed for the Mediterranean. However, he soon left the sea service, his great talent for sketching having shown him the propriety of making Art his study and occupation. On his return to Scotland some of his Mediterranean sketches were shown to Mr. Richard Cooper, an engraver in Edinburgh, who at once took him as an apprentice, and he soon made rapid progress in the arts. He felt that now he was, for the first time, in the line of life for which Nature destined him ; but an interruption, for a time, was at hand. He was busy at his art on his own account, when in the month of September, 1745, the Highland foroes of Prince Charles Edward took possession of Edinburgh, and blockaded the fortress. Strange had keen Jacobite predilections, all the more so that he had formed an attachment to a Miss L'umsden, sister of Andrew Lumsden, a Stuart partisan of note, who long afterwards formed one of Charles’s exiled household at Rome, of the antiquities of which city he published an account. These circumstances, together with his local fame as an engraver, pointed him out as the most suitable person to undertake a print of Charles for his adherents and admirers ; and while employed on this work, his house in Stewart’s Close was the daily resort of the chiefs and officers of the revolted clans, and of all the ladies of high rank who were attached to their cause. The prince’s portrait is still entitled to praise, but when completed it was regarded by the Scottish Jacobites as a miracle of art ; yet to possess this por- trait was once in itself treason. It was a half-length, in an oval frame, placed on a pedestal, whereon was engraved the legend, “ E verso missus succurrere seeclo.” As a reward for this service he was offered a place in the Finance department of the prince, but preferred an appointment in his Life Guards — a body of horse commanded by Lord Elcho, clad in blue faced with red, and with these he served through- out that romantic and desperate campaign. He was in the advance to Derby, and at the victory of Falkirk ; and when riding along the shore, after the battle, had a narrow escape, as his sword was broken by a ball from a king’s ship a little way out in the Frith of Forth. After the final defeat of the few insurgent clans at Culloden, he was obliged to conceal himself for many months among the Highland mountains, where he endured great hardships ; but on the vigilance and cruelties of the Government toning down, he ventured back to Edinburgh and sought subsistence by selling his prints of the favourite Jacobite leaders who were in exile, and of those who had perished on the field or scaffold. In 1747 he married Miss Lumsden, and they proceeded together to London ; from thence they went to Rome, where many fugitive Scottish gentlemen, his comrades in the late; struggle, were at that time residing, and there he obtained' the honorary prize given by the Academy. After this Strange went to Paris, where he prosecuted his studies under the direc- tion of Le Bas, from whom he had the first hint of the use of the instrument known as the dry needle, which he afterwards so greatly improved by his own genius. The year 1751 found him in London, and settled as an engraver. He devoted himself almost entirely to historical, religious, or classical subjects, which he executed in a manner so masterly that he soon attracted considerable notice. As historical engraving had at that period made little or no progress in Britain, he may justly be deemed as also being tho father of that most difficult department of art. In 1759, Mr. Allan Ramsay, a Scottish artist (son of the poet of the same name), now intimated to him that it would be agreeable to tho Prince of Wales and Earl of Bute if he would undertake the engraving of two portraits he had just painted for those eminent personages. Mr. Strange, whose heart was still with the exiled Stuarts, declined, on the plea that he was about to start for Italy ; and he is said to have thus lost the favour of the royal preceptor, which was afterwards of great disadvantage to him; though the king, at a future period, approved of his conduct, on the ground that the portraits, which were after- wards engraved by Ryland and Woollett, “ were not worthy, as works of art, of being commemorated by him.” He had been long anxious to visit Italy, the seat of the fine arts, a second time ; and in 1760 he set forth on his tour, in the course of which he made many drawings, which were after- wards engraved. While in Italy, he was chosen a member of the Academies of Rome, Florence, and Bologna, and was made a Professor of the Royal Academy at Parma, while at the samo time he was elected a member of the Royal Academy of Paint- ing at Paris. His portrait was introduced by Roffanelli, among those of other distinguished engravers, into a painting on the ceiling of the library in the Palace of the Vatican, where engravings are stored up ; and he was permitted to erect a scaffold in one of the rooms of that princely dwelling — an un- usual honour — that he might make a drawing of the “ Parnassus of Raphael — “ a favour not granted for many years to any petitioning artist.” The Pope assigned him apartments for his own use while engaged in this task ; and the King of Naples conferred a similar honour upon him when he wished to copy a celebrated painting by Schedoni. His drawings were in coloured crayons — an invention of his own — and subsequently prints on a magnificent scale were published, from nearly fifty of the paintings he had thus copied in Italy. Among them may be mentioned : “ The Return from Market,” by Wouvermans ; “ Cupid,” by Vanloo ; “Mary Magdalene;” “Cleopatra;” “the Madonna ;” “ the Angel Gabriel ;” “ the Virgin with the Child asleep;” “Liberality and Modesty,” by Guido; “Apollo re- warding Merit and punishing Arrogance,” by Andrea Sacchi ; “ Joseph and Potiphar’s Wife,” by Guido ; “ Charles I.,” by Vandyke. The subsequent hie of Strange was spent in London, whero — owing to his Scottish birth and Jacobite sympathies — ho did not find Court favour until 1787, when he was knighted by George III. A letter by him to the Earl of Bute, reflecting on some instances of persecution which he thought were traceable to that nobleman, appeared in 1775, and was prefixed to an “ Inquiry into the Rise and Establishment of the Royal Academy of London,” which was drawn from his pen by a law of that institution passed against the admission of engravings into the exhibition. Prior to this he had published “A Descrip- tive Catalogue of a Collection of Pictures ” selected by him on the Continent. An authentic list of all his engravings will be found in the seventh edition of the “ Encyclopaedia Britannica.” Such was the chequered and busy life of our first line en- graver ; and after fifty years spent in the active exercise of his professional talents, he died of an asthmatical complaint, on the 5th of July, 17&2, in the seventy-first year of his age, and 1 was interred in the churchyard of Covent Garden. Besides his widow — one of those ladies who had seen the white cockade dis- i tributed at the Cross of Edinburgh — he left a daughter and l three sons. “ Sir Robert Strange has been described by his surviving friends as one of the most amiable and virtuous of AGRICULTURAL DRAINAGE AND IRRIGATION. 219 men, as he was unquestionably among the most able in his own peculiar walk. He was unassuming, benevolent, and liberal, and his industry was as remarkable as his talent. In the coldest seasons, when health permitted him, he went to work with the dawn, and the longest day was too short to fatigue his hand. Even the most mechanical parts of his labour he would gene- rally perform himself, choosing rather to undergo a drudgery so unsuitable to his talents than trust to others.” AGRICULTURAL DRAINAGE AND IRRIGATION.— Y. By Prof. Wiughtson, Eoyal Agricultural College, Cirencester. MOLE PLOUGH— DRAINING TRENCH DRAINING TOOLS, ETC. In the last lesson we considered two methods of draining land, associated with the names of Elkington and Smith, of Dean- stone, and concluded by giving a brief sketch of the materials used in forming underground channels. Such materials are, however, not always necessary, as it is possible to ensure a sufficient channel for water wichout their introduction, and also, in some cases, to dry land by open ditches. The last method of drainage need not detain us. Were we thoroughly to discuss it, we should be led into a very wide subject, em- bracing the surface drainage of upland pastures, the drainage of woodlands, where underground channels are not practicable, owing to the far-searching and insinuating character of the roots, and into the whole question of reclaiming marshes and fenny tracts. Under all these circumstances open ditches are used, and are occasionally of such magnitude as to resemble rivers and canals rather than ditches. Steam power is in such cases brought into requisition where the natural fall of the land is not sufficient to ensure an outfall, and the work assumes a magnitude requiring great engineering skill and a large ex- penditure of labour and capital. We must leave the con- sideration of such enterprises from sheer want of space, and restrict ourselves to more ordinary drainage operations. With reference to the formation of underground channels without the use of tiles, stones, or any other material, two practices prevail. Eirst, we have the wiolc -plough forcing its way through a tenacious clay, and leaving a hollow channel like the path of the animal after which it is named. Secondly, we have the drainage of peat, effected by leaving a space at the bottom of a trench. Draining by means of the “ mole-plough ” is principally used in pastures resting upon a tenacious soil. It may also be em- ployed as a means of drying arable land of similar character ; but owing to the fact that such draining is necessarily some- what shallow, and that arable soils are subjected to consider- able pressure from the passage over them of horses and tillage implements, it follows that in their case a deeper and more permanent system is desirable. Cheapness is the principal inducement for undertaking this work, the total cost being from £1 to <£1 8s. per acre. . The operation is effected by what may be termed a plough furnished with a stout coulter. This coulter, which is let down into the ground to the required depth, say thirty to thirty-two inches, is terminated by a conical or egg-formed piece of iron. The coulter cuts through the soil, and, after the passage of the im- plement, the earth again closes together, leaving the open channel, at the above-mentioned depth, caused by the passage of the “ mole.” The implement may be drawn by steam power, or by a wire rope wound around a capstan, on the headland. Peat when drained is always liable to sink. Thus, at the November meeting of the Farmers’ Club (1870), Mr. A. S. Suston, of Aylesby House, Chatteris, informed his audience that the surface of Whittlesea Mere is seven feet lower than it was eighteen years ago, when the drainage works were com- menced ; and that “in the ‘Middle Level,’ on all our old- drained lands, we find the subsidence is still going on at the rate of an inch per year.” While such a change of level is taking place, it would be unwise to adopt pipe-draining at the asual depths, as the lowering of the surface would subject the drains to injury from the treading of horses. The following plan is therefore used : — A trench is dug, thirty inches deep and twelve inches wide at the bottom. A narrow grafting tool (Fig. 4) is now used to deepen the trench, in such a manner as to leave shoulders on either side of the deepened portion. Thi3 is made plain by reference to Fig. 5. The sod taken from the surface is made to rest upon the shoulders just mentioned, and thus a hollow space is left as a drain. The trench is now filled up, and the work is complete (Fig. 5). In other cases, artificial channels are cut out of the substance of the peat by a tool constructed so as to form semi-cylinders of peat, which, when applied together and laid at the bottom of a trench, make a fair drain. We have in the next place to consider the work of drain" age as carried out upon the principles laid down by Mr. Smith of Deanstone. The tools with which the work is performed are worthy of consideration, and after briefly describing them we shall pass on to the consideration of the work itself. A line for marking off the work will be the first requisite in carrying out drainage work. The drainer will also require an ordinary spade (Fig.r7), which need not be de- scribed. The remaining tools for making the trench consist of two grafting tools (Figs. 4, 6). These are so designed as to economise the amount of ground removed to the greatest pos- sible extent. A glance at the sketches in the next page will show how the successive use of the spade and grafting tools must form a narrow trench, gradually decreasing in width with the breadth of the implements, until it is about four inches wide at the bottom. A shovel for paring and smoothing the sides (Fig. 7), a pickaxe for removing land-fast stones or cutting through rock, a “ swan-necked ” shovel for removing small fragments of earth and levelling the bottom of the trench (Fig. 8), a pipe- layer or wooden shaft, with a piece of iron at its extremity turned at right angles to the direction of its length (Fig. 9), a spirit-level, a drain-gauge for testing the depth of the trench, and a few boards and struts to support the sides of the trench where the ground happens to be of a very soft character. Such will be the most necessary tools with which to start the work of drainage. , , We have now explained the benefits of the drainer s art, discussed the water economy of the soil, the best materials for constructing underground channels, and the work-tools required for carrying out the necessary operations. We pro- ceed to the practice, first asking, How can we determine whether or not a field requires draining? Indications are numerous, both in the case of arable and of pasture lands. In the case of the former, wetness is indicated by the difficulty of working the soil for considerable periods after heavy rains have fallen. The ground cuts, or turns over from the plough in compact slices, whereas in contiguous and drained soils of similar quality the furrow is more friable, crumbling down after the passage of the plough. The undrained farm, therefore, cannot compete with its drier neighbour in the growth of root-crops, to which a fine tilth is absolutely necessary. Snow, too, has been observed. t OOOOOOO ' Blue. Yellow. 1 OOO I OOOOOO Blue. Yellow. ) OOO I 00 1 Blue. In all these cases it will be seen that we have eight parts of blue, five of red, and three of yellow, only the mode of com- bination varies. This variation may occur to any extent, pro- vided the totals of each be always the equivalent proportions. These remarks will apply equally to hues of colour, shades, and tints, and to shades and tints of hues. Care, and perhaps a little practice, will enable the learner to arrange colours into a number of degrees of depth, or shades, as they are generally called. (We do not here use the term as signify- ing pure colours darkened with black.) Ten shades of each colour differing obviously in degree of depth can readily be arranged by the experienced, the ten shades being equidistant from each other as regards depth — that is, shade 3 will be as much darker than shade 2 as shade 2 is darker than shade 1, and so on throughout the whole. Purple is a colour inter- mediate between blue and red. Imagine ten hues between the purple and the red, and ten more between the purple and the blue : thus we should have purple, then a slightly red purple, then a rather redder purple, then a purple still more red, and so on till we get purple-reds, and finally the pure red ; and the same variations of hue at the blue side also. Imagine, fui tlier, the green having ten hues extending towards blue, and ten more stretching towards the yellow ; and the orange having ten hues towards the red, and ten towards the yellow in all cases I count the colour from which we start as one of the ten, thus : — Blue. Purple. Red- 09876543212345678 9 0 — and we shall have 54 colours and hues of colour. Of each of these 54 colours and hues imagine 10 degrees of depth, and we get 540 colours, hues, tints, and shades, ail differing from one another to an obvious degree. Mark this fact, that any colour, tint, hue, or shade of such a diagram has its complement in one other of the colours, tints, FORTIFICATION. 223 hues, or shades of the diagram, and that only two of this series of 540 are complementary to each other; thus, if you fix on any one colour of the 540, there is but one colour in the whole that is complementary to it, and it is complementary to but this one other colour. The student will do well to try and make a colour-diagram of this kind, of a simple character, say such as the following, only using pigments for my numbers ; but in doing so he must exercise the utmost care, in order that he secure some degree of accuracy of tint or shade, and if he can call to his aid an experienced colourist it will be of great assistance to him. Blue. in tracing a work that the prolongations of the lines of parapet are directed on to points inaccessible or beyond the range of the enemy’s guns. Where this is impracticable, short earthen parapets, called traverses, must be built at right angles to the general line, to intercept the shot. Ricochet fire is that in which the charge and elevation of the guns are so arranged as to cause the shot to make a number of rebounds after its first graze in the work. It is consequently often employed for enfilading purposes. When a line of parapet is so placed that the fire from its guns passes parallel to and in front of another line, it is called a flank, and defends that line by a flanking fire. A glance at Purple-blue. Blue-purple. I 2 Purple. 1 Rcd- purple. Purple- i red. 3 4 2 0 4 5 3 , 5 5 3 » 4 5 3 4 5 2 4 5 5 o 3 4 5 5 5 ;1 2 3 z 4 4 3 5 5 4 1 Green-blue. 1 Blue-green. 1 Green. 4 4 3 Yello ro- lled. 1 3 4 2 3 Orange-red. 1 2 Bed-orange. 1 2 1 5 * ~ * green 5 4 5 A . 5 4 * 4 4 3 S 2 2 1 Orange-yellow. 1 Yellow-orange. 2 1 Green- yellow. 1 Yellow. Orange. Tins table is highly valuable, as it gives ninety harmonies, if carefully prepared in colour ; and the preparation of such a table is the very best practice that a student can possibly have. Let us for a moment consider this table, and suppose that we want to find the complement to some particular colour, as the third shade of red. We find the complement of this in the third shade of green opposite. If we want the complement of the second shade of orange-yellow, we find it in the second shade of blue-purple opposite, and so on. Thus we have a means of at once judging of the harmony of colours. FORTIFICATION.— IY. BY AN OFFICER OF THE ROYAL ENGINEERS. TRACE OF WORKS DEFINITIONS OF VARIOUS METHODS OF ARTILLERY ATTACK, AND MODES OF OBTAINING PROTEC- TION FROM THEM. Before considering the varieties of trace suitable for works under different circumstances, it will be well to examine the ways in which artillery and musketry fire can be employed for their attack and defence, and then what defensive arrangements can be made to guard against these. Various terms are em- ployed to express the direction, mode of firing, and special objects of artillery fire, with reference to the works attacked. Thus the terms direct, oblique, reverse, enfilade, flanking all express the horizontal direction of the fire ; whereas 'plunging, pitching, vertical, and ricochet denote varieties either in the mode of firing, or the results to be attained. The terms direct and oblique are applied to the fire of guns placed either immediately opposite or oblique to the direction of the works attacked. Reverse fire is that which is brought to bear on the interior of a work by guns firing into it from the rear. When the guns of the assailants are so placed as to bring either a direct or oblique fire to bear on the works, they must be opposed by parapets of sufficient strength and thickness to resist them ; but when protection from reverse fire is required, it becomes necessary to construct a sort of second parapet inside the work, behind the guns, which is called a parados. When the enemy’s guns are in prolongation of the line of work attacked, and can fire along the rear of that line, it is called enfilade fire. This is a very effective method of artillery attack, as any one shot may take effect on many more guns or men than it could if it merely passed directly through the parapet. To guard against this, great care should be taken Fig. 26. any ordinary profile (Fig. 26) will show that the ditch cannot be defended by the direct fire of the parapet behind it, and unless the ditch is defended by a flank fire from some other part of the work, the enemy might assemble in comparative safety in it before making his final assault. This defence is obtained either by means of flanks or by constructions in the ditch, and it is with reference to it that most of the varieties in the trace of works other than those dependent on the shape of the ground are made. Vertical fire is that from mortars firing shells at an angle of 45° so as to fall almost vertically. This is the least accurate of all the artillery fire we shall have occasion to consider, but is useful for bombarding towns, closed works, etc., where great accuracy is not essential. Protection from the effects of vertical fire can only be obtained by constructing buildings, the roofs of which are of sufficient thickness to resist the fall of the shells from a great height, and their subsequent ex- plosion. In all works intended to make a prolonged resistance to modern artillery, protection of this land, or “ bomb-proof cover ” as it is called, must be largely provided. When these buildings are of a permanent nature, they are called casemates, and where only temporary constructions, blindages. As a guide to the thickness of roof necessary for this purpose, it may be well to remember that the maximum penetration of the largest spherical shells in the British service (13 inches) was found to be as follows, viz. — penetration in earth, 6 feet ; in concrete or brickwork, 1 foot 6 inches. Pitching fire is similar to ricochet, except that the shot descend at such an angle as not to rebound. It is used in the attack of works, to strike objects that are hidden from view by some intervening mass, over which the shot must pass. Escarp walls and other masonry in permanent fortifications are liable to be breached by this means, unless they are kept considerably below the direct line of fire. Plunging fire is that from guns firing with full charges at objects on a much lower level than themselves. Owing to the considerable angle of depression of the guns the shot do not ricochet, and greater accuracy in firing is required ; it is not, therefore, very efficient against troops or small moving objects, but is most effective against ships, whose guns probably cannot elevate sufficiently to reply, and whose decks, even in iron- clads, are rarely invulnerable. The Bussian “Wasp” battery, which did so much damage to the English ships bombarding Sebastopol, was an example of this. Undoubtedly the ad- vantages of a commanding position are so considerable, and the difficulties of protecting the interior of a work from plunging fire are so great, that none but urgent reasons can justify works being placed in so disadvantageous a position ; it must not, however, be supposed that a slight difference of level con- stitutes plunging fire, or that a work is necessarily untenable because it is somewhat lower than the attacking guns ; for the Russian lines at Sebastopol withstood for more than a year the attack of the Allies, whose artillery was posted on a higher level than they were. The object of almost all works being that of enclosing or pro- tecting some particular area, it follows that few can consist of a mere straight line of parapet, and their trace or outline shape will depend — 224 THE TECHNICAL EDUCATOR. 1. On the number of men they are intended to head. 2. On the shape of the ground. 3. On the necessity for flank defence for the ditches and ground in front. The trace will, therefore, either be a curved line or consist of a number of lines forming angles with one another. When an angle points outwards from the work it is called a salient angle (Fig. 27) ; and when it points inwards, a re-entering angle. The former should be as obtuse as possible, and never less than 60°. The imaginary line bisecting a salient angle is termed the capital. The distance from a flank to the furthest point of the work flanked by it, measured in the direction of the flanking fire, is called a line of defence. The length of this line is dependent on the weapons used, although, as the same accuracy can never be obtained from men who are being fired at as from ordinary target practice, it is made considerably less than the effective range of these arms. In' field-works, therefore, the lines of defence should not, as a rule, be more than 200 yards long ; and in permanent w»rks, where the ditches are flanked by artillery, -cae, salient angle ; a d, capital ; c e, gorge ; bcef, flanks ; n c a, a e f, re-entering angles, or flanking angles, or angles of defence; c a, line of defence. they may vary from 300 to 500 yards, so as to be within range of case and grape-shot. The angle between a flank and a line of defence is called the flanking angle or angle of defence. This should never be less than a right angle, lest accidentally oblique fire should wound men defending the parapet that is being flanked ; and should not exceed 95°, as the fire would then become too divergent. When the parapets of a work entirely surround the site occupied, and its garrison is consequently capable of an inde- pendent resistance, nO matter on which side the attack may be made, it is called a closed work ; and when its parapets only afford a defence in certain directions, leaving an open side or gorge liable to attack, it is called an open work (Fig. 28). Closed works are suitable for isolated positions, and should, if possible, have their own flank defence. Open works are chiefly used as auxiliaries to other works, to afford a flank de- fence for the approaches to them, and are themselves defended by the flank-fire of the works in rear, which should be able to fire into their open gorges and prevent an enemy occupying them. Both open and closed works are frequently combined so as to mutually defend one another, for the occupation of a long line or position. They are then called lines of intrenchments. If a number of open works are connected by a line of parapet or obstacles, they are called continuous lines ; and if the works are isolated and the spaces between them only defended by the lire of the collateral works or works in rear, they are called lines with intervals (Fig. 29). Closed are better than open works for this latter case, unless there is a second line of works behind the first, in which case the gorges of the open works must be closed by obstacles, to prevent the enemy, by a temporary success, getting possession of them, and dismounting the guns or doing other damage before retiring. In permanent works an attack on the rear of the open works in connection with the fortress can rarely be made, owing to the formidable nature of the ditches that surround them When closed works are employed in the outer line, their gorge parapets should be made so thin as not to prevent the guns of the rear-line firing into them. The principal descriptions of open works employed in field defences are — redans, fliclies, double or triple redans, and lunettes ; and in permanent fortification more formidable works, answering the same purpose if not exactly of the same shape, are employed, called ravelins, lunettes, horn works, and crown works. Redans, fleches, and ravelins are all of much the same form, and consist of two lines of parapet meeting in a salient angle. A redan is a large field-work of this shape ; whereas a Jttclie is a smaller work, intended merely to protect a gate or somo similar small object. In Fig. 30 is shown Yauban’s Redan line, consisting of redans 180 yards apart, connected by a straight line of parapet. A ravelin is a permanent redan-shaped outwork, placed in advance of a permanent fortification to increase its defensive powers. All these works have the defects of being liable to be enfiladed, of being open at the gorge, and of having the space in front of the salient angle badly defended. This is owing to the fact that men firing over a parapet deliver their fire at right angles, or nearly so, to the crest (Fig. 31). This undefended space may be brought under fire by the addition of short auxiliary flanks (see Fig. 29), or by forming a short face at right angles to the capital. In some cases where the front fire of a ravelin may be much wanted, and its flank fire required in a direction at right angles to the capital, this principle may be still further applied (see Fig. 32). A double or triple redan consists of two or three redans com- bined as one work (Fig. 33). In these the flank defence of the salients is provided for, but the outer faces on either side are unflanked. A lunette is a redan with two extra faces parallel to the capital (Fig. 34). It is useful as an advanced outwork, but has all the defects of other open works. Open works are specially adapted for the protection of bridges or other positions where they cannot be attacked in rear. They are then called Utes du pont or bridge-heads. BUILDING CONSTRUCTION. 223 BUILDING CONSTRUCTION.— VIII. arches ( continued ). The scmi-circular arch was the kind of arch principally used by the Romans, who employed it largely in their aqueducts and triumphal arches. Other forms, however, are mentioned by some writers as having been employed by the ancients. In the Middle Ages forms still different to those already in use were generally introduced. Thus we have — The stilted arch, which it is scarcely necessary to say is but an adaptation of the semi-circular, the springing being raised above the capitals of the columns. The illustration below (Fig. 55), copied from Mr. Owen Jones’s admirable handbook to the Alhambra Court of the Crystal Palace, will afford the student a good example of this species of arch. Next we have the horseshoe arch, also used in, and almost J entirely restricted to, the Arabian style of architecture. In this form of arch the curve is carried below the line of centre or centres; for in some cases the arch is struck from one centre, a rule indicates the style called “Early English,” which pro* vailed in this country from about 1189 until 1307. Fig. 58 is the equilateral arch, the radius with which the arcs are struck being equal to the span of the arch, and the centres being the imposts; and thus, the crown and the imposts being united, an equilateral triangle is formed. This form was principally used in the “Decorated” period of Gothic archi- tecture, from about 1307 until about 1390, at which time the ogee arch (Fig. 59) was also occasionally used. At a later date, during the existence of th9 “ Perpendicular ” style of Gothic architecture — viz., from the close of the fourteenth century to about 1630— we find various forms of arch introduced, such as the segmental (Fig. 60), formed of segments of two circles, the centres of which are placed below the springing; and still later on we find the Tudor or four-centred arch (Fig, 61), in which two of the centres are on the springing and two below it. The arches at the later period of this style became flatter and flatter, and this forms one of the features of De- based Gothic, when the beautiful and graceful forms of that / @ \ Fig. 61. / \ V © i © Fig. 62. and in others from two, as in Fig. 56. Now it must not be supposed that the real bearing of the arch is at the imposts, A, A ; for if this were really so, it must be seen that any weight or pressure on the crown of the arch would cause it to break at b ; but the fact is simply that the real bear- ings of the arch are at b, b, and the prolongation of the arch beyond these points is merely a matter of form and has no structural significancy. The horse-shoe arch belongs especially to the Mahometan architecture, from its having originated with that creed, and from its having been used exclusively by its followers. Next in point of time, but by far the most graceful in form, is the pointed arch, which is essentially the mediaeval (or middle age) style, and is capable of almost endless variety. The origin of this form of arch has been the subject of much antiquarian discussion; but it is certain, that although the pointed arch was first generally used in the architecture of the Middle Ages, recent discoveries have shown that it was used many centuries previously in Assyria. The greater or less acuteness of the pointed arch depends on the position of the centres from which the flanks are struck. Thus the lancet arch (Fig. 57) is constructed by placing the centres C, c outside the span, but still on the same line with the imposts. This form of arch was first used in the Gothic, and as style gradually decayed, and for a time were lost. Happily, in the present century there has been a gradual and spirited re- vival of the Gothic style, and works are now being produced which bid fair to rival in beauty of form and in principles of construction the marvellous buildings of the Middle Ages. As the principles of Gothic Architecture will form the subject of another series of lessons, further description is here unneces- sary. We now return to the constructive principles of arches, and these may be conveniently treated of under the separate heads of brick arches and those constructed of stone, the main prin- ciples being the same — viz., that the bricks or stones composing the arch must be so placed that they act as wedges. In stone arches, this is accomplished by cutting the stones into the exact forms required. In bricks, they must either be “gauged,” that is, rubbed or cut to the shape required, or the difference must be made up by mortar ; the skill of the workman being in this case displayed by his so bonding his courses that the shrink- ing may be equally distributed, and that when the necessary settlement is arrived at, the structure may be found perfectly safe and strong. Arches in brickwork are plain, rough, and cut or gauged. Plain arches are built of uncut bricks, and those being blocks of equal thickness, must be “ made out ” with mortar (Fig. 62, a a); that is, the difference between the intradoa and the extrados muA 15 VOL. I. 226 THE TECHNICAL EDUCATOR. be filled in with mortar or cement. Thus, in building such an arch, the bricks at the inner line should all but touch, and the centering (the wooden framework upon which the arch is tempo- rarily built) should not be struck (or removed) until the arch has settled or the cement perfectly hardened. The cement used should be of greater consistency than for general purposes. In consequence of the unavoidable defect in plain brick arches — viz., that the bricks are not in themselves wedge-like in form, but are kept apart at the top by a matter liable to shrink — it is advisable in extensive and continuous works, such as tunnels, sewers, vaults, etc., to make them of thin independent rings of half-brick or one-brick thick — that is, a 9-inch arch should be in two half -brick arches, as is shown in the illustration (Fig. 62), and an 18-inch arch should be formed of rings consisting of alternate whole and half-bricks, the bricks being put in where they come naturally, as where three, four, or more bricks of the inner ring cut in with four, five, or more of the outer ring ; but by half -bricks we do not, in this case, mean bricks cut into halves, but merely laid on their edge, as headers, so as to be half-brick high. Each arch thus becomes bonded in itself with headers and stretchers, as in a brick wall. Bough arches are those in which the bricks are roughly cut with an axe to a wedge form, and are used over openings, such as doors and windows, when the work is to be plastered on the outside, or in plain back-fronts, outhouses, garden gates, etc. ; when, however, they are generally neatly finished off with what is called a “tuck joint.” This consists in marking the divisions by a neatly-raised line of fine white plaster, having previously pressed a blue mortar into the joints. Pointing is of two kinds, tuck, as above, and flat. This last consists in first raking out the mortar in front of the joints, and filling in with mortar, on which the line is then marked with the edge of the trowel. Semi-circular and elliptical arches, when large, are generally formed of uncut bricks ; but those composed of small segments of circles are either cut or axed. These are sometimes called scheme arches. Very flat arches are known by the name of “camber,” from the French word cambrer, to round like an arch. Gauged arches are formed of bricks which are cut and rubbed to gauges or moulds, according to a full-sized drawing of half an arch. Gauged arches are, of course, the neatest in appearance, and are therefore used in the fronts of houses. When the arches are semi-circular, the bricks will all be of one shape, and therefore, if the number of arches renders it worth while, the bricks may be all moulded ; that is, made specially of the exact size and form required. The arches over windows in fronts of houses are frequently straight. Such a window with a diagram (Fig. 63) will be shown in the next lesson. The outer :slant line of the arch is called the skew-back, and, as a rule, the skew-backs of both sides should meet on the centre line, at an angle of 60°. From the drawing it will be seen that the material between the two arcs struck from h is all that is really efficient in forming the arch, and that all between the arc and its chord is of no service. This breadth may be increased by making the angle at the centre less than 60° — that is, taking the centre lower down on the perpendicular line; the skew-back will not then slant so much, and the width at the crown will be more, the arch being flatter ; but that portion will be less secure than by the former system, for, as the radii diverge less, they are more nearly parallel, and hence are not so tightly wedged together. These arches require to be executed wfth the utmost nicety, being generally of only half a brick thick, and not being bonded to the work behind them. Bricklayers usually cut the joints of gauged arches slack at the back, so as to get a fine joint on the face ; the consequence is that the pres- sure of the load causes the arrises of the face to chip, and thus the bricks fall out; this should therefore be guarded against. DRAWING FOR BRICKLAYERS. In accordance with the plan laid down — viz., that the cuts in these lessons should serve not only as illustrations of the text, but as studies for drawing — we now proceed to give the student some instructions as to the method of drawing the subjects used as architectural illustrations. One illustration previously given may, however, require a few hints to guard the student against error, viz., Fig. 62. The subject of this is a “plain arch,” that is, one in which the bricks are not cut or altered in form, but are still made to radiate ; that is, the intrados of the arch is to be made smaller than the extrados, for otherwise an arch could not be formed ; and here it is to be remembered that the difference between the small intrados and the larger extrados is made up by mortar or rough pieces of bricks, but that the bricks themselves retain their original size. Now to draw such an arch : — The radius of the intrados being given — viz., A B — from A, with radius A b, describe the semicircle, half of which is here shown, and also the semicircle c ; the width between these two semicircles being equal to the width of a brick laid on its broad side, viz., 4| inches by scale. Divide the intrados into as many equal parts as there are to be bricks in the inner ring of the arch ; viz., 1, 2, 3, 4, etc. It will be evident that the centres of these bricks radiate from the centre of the circle, though their sides do not. Therefore, bisect each of the spaces 1, 2, 3, 4, etc., and draw radii through these bisecting points. Now, if a line were drawn along the end of a brick it would be at once seen that the edge of the top and bottom surface would be parallel with this line, and of course with each other; therefore, from points 1, 2, 3, 4, etc., draw lines between the semi- circles, parallel to the radii. This may easily be done with a pair of set-squares, by the method shown in the lessons in “Technical Drawing;” and thus a semicircle of oblongs will be obtained — that is, approximately so ; for were this drawing executed on a larger scale, it would be seen that the inner and outer edges of the ring are made up of pieces of straight lines equal to the width of the shorter edge of the end of each brick. For the second ring, mark off the width c D, equal to b c ; set off on the semicircle c the width of the narrow sides of the bricks, as at 1, 2, 3, 4, etc. ; bisect these spaces, and draw lines parallel to the bisecting lines as before. CIVIL ENGINEERING.— III. BY E. G. BARTHOLOMEW, C.E.,M.S.E.' WATER-WORKS. The term water-works is properly applied only to such works as have for their object the collection, supply, and conveyance of water to towns for drinking and sanitary purposes, but it is also applicable in a somewhat subordinate degree to the storage and utilisation of water for agricultural objects. We hav6 adverted to that great work of Egyptian engi- neering, Lake Moeris, which was intended as a reservoir to re- ceive the waters of the Nile at the period of overflow, to be employed afterwards for the irrigation of the surrounding dis- trict. In all countries where the rainfall is confined to certain seasons, and is then excessive, it is imperative to provide against the effects of the dry season. In Hindostan, where the greatest periods of drought occur at certain cycles of years, the construc- tion of reservoirs has been carried to an extreme that is not found in any other country. Advantage has been taken of every nook and ravine, and, by throwing across them banks of earth called bunds, they have been converted into storage reservoirs. . In the Madras Presidency alone, there exist at the present time upwards of 43,000 irrigation reservoirs available for use, whilst thousands besides have become useless through neglect. The length of these bunds varies from half a mile to thirty miles. The Poniary tank, now disused, was formed by the construction of a bund thirty miles across the opening of a valley, and em- braced an area of nearly eighty square miles. The Veranum reservoir is still in operation, and possesses an area of thirty-five square miles, the bund which effects the storage being twelve miles long. In the island of Ceylon there exist the remains of an embankment constructed for storage purposes fifteen miles long, composed of huge blocks of stone cemented together, 100 feet wide at the base, and sloping to a top width of forty feet. These semi-natural reservoirs are to be found in our own island, but in smaller proportions, as, for instance, in the Pent- land Hills, where one such reservoir forms the principal source of water-supply to Edinburgh. In determining the position for a reservoir of this kind, there are several matters which require consideration irrespective of the formation of the ground. It will be necessary to determine — CrVTL ENGINEERING. 22 ? J. What is the height of the proposed reservoir with respect to the town or district to he supplied from it ? 2. What is the nature of the soil composing the proposed site ; is it porous or otherwise ? 3. What is the source of supply ; is it regular, being derived from springs, or irregular, being dependent upon rainfall; and if the latter, may a sufficient amount be expected to be available in all ordinary periods of dry weather ? 4. What are the difficulties to be encountered in conveying the water from the reservoir to the town ? The question of rainfall is one of the highest importance in matters of water-supply. As a rule, the rainfall is greatest in those districts which are situated towards the coast- line, whence the prevailing winds blow. For instance, in Great Britain and Ireland, the south-western districts are the most rainy; but the presence of mountains which penetrate the cool moisture- charged regions of the air causes the atmosphere to part with its moisture by condensation, and hence the rainfall occurs on the lee side of the mountains. The rainfall over the whole globe varies in different localities from zero to 28 feet per annum. In addition to the foregoing considerations, if the water- supply of a town is to be entirely dependent upon a storage re- servoir, it will be necessary to determine its loss by absorption and evaporation, and then to proportion its area accordingly. The average annual loss by evaporation in the temperate zone, -with a mean temperature of 52-25°, is 36'5 inches. In South America, with a mean temperature of 81-86°, it exceeds 100 inches. The mean daily evaporation in Great Britain is less than - 1 inch. Equal in importance to proportioning the storage area to the •demand, is the consolidation of the embankment, so as to with- stand the pressure of water under every possible emergency. Neither is it enough to determine what will be the water- pressure, and to proportion the breadth and slope ( batter ) of "the earth-work to the strain upon it ; the character of the material composing it is equally important, for above all things ■ percolation must be prevented. The least trickle may be the ■commencement of wide-spread desolation. It is not necessary that the entire mass of the bank should be impervious to water, hut there must run throughout it an impenetrable layer. Well- puddled clay will answer the purpose, and the most advan- tageous position of this layer is on the side of the bank next to dhe water, its surface being protected from detrition by a closely packed layer of stones. The main body of earth lies upon the reverse side of the puddled wall, its use being simply to act as a buttress or support to it, all that is laid upon the water- side becoming valueless as a support, since the water will pene- trate it. A regularly-constructed weir or escape-pipe for the overflow must be provided, so as to prevent the water escaping over loose or removable soil, and if it be an escape-pipe or culvert it should not pass through the bank, as there is always a tendency to trickle along the line of pipe. A syphon passing over the bank may be employed with advantage, and may be kept always full and ready for use by a valve at the base of the longer leg. Having thus briefly considered the question of water-supply ■derived from a level above that of the district to be supplied, -we shall now consider how best to obtain and utilise it from a Homer level. There are few towns in existence which have not a river or ■stream of some kind either passing through or very near them, and these would naturally appear to offer the means of water- supply. But when we remember that the same streams are very generally the channels employed to convey away the ■sewage and refuse matter, the idea of using the water for drink- ing purposes vanishes. It is, however, possible under certain •conditions to render such water drinkable. Nature has pro- vided that the soil itself shall act as a filter and disinfectant do water passing through it; if, therefore, a reservoir be con- structed of a soil suitable for filtration, and the impure waters he pumped into it and allowed to filter through it into another receptacle, and the same process repeated through other reser- voirs,. the water may be rendered fit for use. There is, of course, a. limit to this process of purification, for there are streams so highly contaminated and indeed poisoned by the infiltration of chemical and animal impurities that no amount of artificial filtration will make their water pure. The black, stinking streams which flow through our northern manufacturing towns are long past all recovery as affording drinkable water. We are not, however, dependent upon streams and rivers for an efficient water-supply. The action of the soil in purifying water extends to the rainfall, which, absorbed by the ground passes downwards by gravitation, and, being obtained from a considerable depth, is found to be highly suitable for the use of man ; and here we have the great and never-ceasing water- supply, always and almost everywhere available, which Nature herself provides for us. We are thus led to a brief consideration of wells. These are various in contraction. ' There is the ordinary dug well, and the bored or Artesian well. Of ordinary dug wells there is the shallow pit into which surface water drains ; such is little better than a cesspool, not deserving of the name of well, and yet thousands of our popu- lation are wholly dependent upon such means for their water- supply, the use of which is a fruitful source of disease and death. Some of our most fearful epidemics may distinctly be traced to the use of water derived from such a source. The construction of deep wells is of very ancient date. The ancient wells of Cabul are from 300 to 350 feet deep, and many of them are only 3 feet across. A dug well at Tyre is said to be 3,780 feet deep. Jacob’s well at Samaria is 105 feet deep and 9 feet in diameter. Joseph’s well at Cairo is a won- derful piece of engineering skill. It consists of two shafts, one above the other, but not in the same vertical line. The upper shaft is 16o feet deep, and 24 feet by 18 feet in the opening. At the bottom is a spacious chamber cut down into the rock, which serves as a reservoir for the water raised from the lower shaft, which is loO feet deep, and 15 feet by 9 feet in the opening. This second shaft is sunk at the side of the reservoir, and is reached from the surface by a spiral gallery cut in the solid rock outside the upper shaft, the gallery being pierced with loopholes opening into the shaft to afford light. By this gal- lery pass the men and mules which raise the water from the lower shaft, and discharge it into the reservoir, whence it is raised to the surface. The mode of raising the water is the same in both the shafts, and consists of the ancient Eastern system of an endless band of twisted grass passing over a large drum suspended over the mouth of the well, and lashed to which are earthen jars having their mouths all in the same direction. The drum is caused to revolve by animal labour, and the jars which descend empty come up filled, discharging their water into a trough as they pass over the dram. The mode of construction of ordinary wells is as follows : — If the soil is of a sandy or loose nature, the sides of the well must be protected by a lining or steining, the most suitable materials for which are timber, stone, brick, and iron. Timber, which should be elm, may be employed as a preliminary support, or as a steining in saline strata, the salt preventing its decay. Under other circumstances timber is objectionable, as it is subject to rot. If stone is employed, it should be silicious. Brickwork is the material most usually employed, but if the water in the surrounding soil be impure, or if under considerable pressure, it is not suitable, as the water will percolate. The use both of brick and stone is, in fact, rather to keep back the soil than the water. Of all materials iron is the best by far for a steining. It is capable of bearing great strains and resisting great pressure; water cannot pass through it, and it is not liable to decay. The steining of wells, whether of brickwork or of iron, is per- formed in sections. If of bricks, the earth is taken out to as great a depth as is consistent with safety, and a “ curb,” or circular ring of jointed timber, is placed on the bottom, upon which is laid the brickwork which is carried up to the surface. The curb is suspended by iron rods to cross-beams laid over the mouth of the shaft, and is capable of being lowered bodily with the brickwork upon it when required. The earth below the curb is now removed, and the steining is gradually lowered, more brickwork being added above. This process is thus con- tinued until, if the well is deep or the soil very loose, the fric- tion of the earth outside prevents the steining sinking lower by its own weight ; it is then said to be “ earth-bound.” The excavation must now be continued below the first curb, and a second section of brickwork laid upon a second curb must be commenced below the upper piece, this being suspended inde- pendently of the first, and lowered in the same manner. Another mode of proceeding is to leave a portion of earth below the first curb to support it, and after a further excavation, the diameter 228 THE TECHNICAL EDUCATOR. of which is equal to that of the inside of the steining, to insert a fresh curb at a certain distance below the first, and gradually removing the earth above it, to fill in the space with superposed brickwork until the first curb is reached. When iron is em- ployed it is usually the cast metal, the steining being cast either entire as a cylinder, or in sections. If the latter, the sections are cast with flanges pointing imuards, by means of which they are bolted together, the joints being made water- tight by iron cement. The outer surface of the cylinder is thus smooth, and it may be driven down to a considerable depth before becoming earth-bound. The great advantage of a steining through which water will not percolate is that all surface and impure water is shut out from the well, and the water obtained only from the deep-seated springs, which are usually pure. The most useful well is the bored or Artesian well. Bored wells are of very ancient date. They are to be found in all parts of the world, and have existed in Egypt, China, and other Eastern countries from time immemorial. There is a well bored on this principle at the old convent of Chartreux, in the town of Lillier in France, which is said to have been executed as far back as the year 1126. The rationale of the Artesian well is easily explained. Certain soils — such as sand, gravel, chalk — are absorbent, and permit water to pass through them ; others — such as clay, loams — are non-absorbent, and do not permit the water to pass through them. Hence the rainfall is arrested in certain directions, and finds a free passage in others. But the tendency of water is to flow in all directions, and it will therefore move along horizontal strata if debarred from sinking lower by a clay formation. Water under these circum- stances may, and often does, find its way laterally beneath a bed of clay or rock, and if the clay or rock be perforated, the under- lying water will spring up, rising to a height equal to the height of water pressing upon it anywhere outside the clay. Suppose, then, a perforation be made in the soil, passing through various strata, but coming at length to a clay or rock stratum, the probabilities are greatly in favour of water rising in the bore from below the clay, and frequently to a height quite near the surface. There are even instances of the water rising above the surface, and forming a perpetual fountain of the purest water. The mode of well-boring is simple, although tedious and ex- pensive. The boring tool, which is of steel, is attached to an iron rod, to which a rotary motion is imparted. As the depth of the bore increases, the rod is lengthened by the addition of successive pieces attached one to the other by firmly-screwed joints. The shape of the boring tool varies with the kind of stratum it has to contend with. If it be rock, the tool is shaped like a chisel, so as to cut and break the stone ; if clay, the tool is shaped like an augur, which scoops it out. The broken soil has to be brought to the surface by tools specially adapted for the work. The great loss of time lies in raising and lowering the tool, which has frequently to be done, and in recovering a broken tool, every portion of which must be re- moved before the work can proceed. The Chinese adopt a system of “ jumping ” in boring for water. The rod is sus- pended by its upper end to a windlass placed some feet above the bore, and is frequently raised and allowed to fall, a rotary motion being applied to the rod at the same time. The plan is very effectual, but the tool suffers frequent fracture. Bored wells are only a few inches in diameter, and have in certain strata to be protected by iron steining. The joints of the successive sections of the tube are necessarily “flush” both inside and out, the mode of uniting them being shown in Fig. 2, Fig. 2. so as neither to prevent their sticking in the soil, nor yet to impede the action of the boring rod, nor the subsequent flow of water. The supply of water obtainable from Artesian wells is fre- quently enormous. At Birkenhead, one such well, about 400 feet deep, yields 2,000,000 gallons of good water in twenty-four hours. Another at Kingston-on-Hull, which is sunk in chalk to a depth of 281 feet, and having a diameter of 18 inches for 210 feet of this depth, yields nearly 4,000,000 gallons in the same period. A. well was commenced on Southampton Common some years since, and attained a depth— partly by digging, and partly by boring— ' of 1,317 feet from the surface, but water not being then obtained, it was abandoned. In all cases of water-supply for towns it is essential to provide reservoirs to meet any sudden demand for it which may ariset from fire, etc., or to provide against injury to the pumping machinery. The size of the reservoir must depend entirely upon circumstances. The mode of disseminating the water over the district to bo supplied must be briefly noticed. At the present day the water is conveyed in cast-iron pipes, the diameter and thickness of which are proportioned to the demand likely at any time to arise, care being taken to allow a fair margin for increase of population. In the early days of the New River Company, the water was conveyed in wooden troughs under the streets. The Company Fig. 3. possessed at one period 400 miles of this troughing, but the leakage was so great — equal to one-fourth of the original supply — owing to faulty joints, decay of material, and bursting after frost, that they were abandoned. The joints between the pipes have to be made with great care to prevent leakage ; they are made after the pipes are bedded in their place, and the ground must be taken out at each joint to an extent to permit a man to pass entirely round it. The pipes are cast with a lip at one end, and an enlargement at the other, as shown at Fig. 3, so that the end of one fits into the enlargement of the other, as seen at a b. Into the recess thus formed, a flat plait of spun yarn is driven with a caulking chisel and mallet, and melted lead run into the remaining space. The principal arteries or pumping mains are the largest and strongest, and have frequently to bear a very great pressure. From these mains branch off pipes of lesser size and diminished thickness, and from these again others smaller and thinner, and so on. The valves which regulate the supply consist for the most part of a sliding plate of iron, fitting accurately in a vertical groove, and raised or lowered by a rod working in a stuffing-box. The pressure of the water being thus at right angles to the plane of movement, it exerts a comparatively small influence upon it, whilst the surface of friction is greatly less than in an ordinary tap. A throttle or balance valve could not be rendered water- tight. Wien the reservoir stands upon the same or a lower level than the system of pipes through which the water has to pass, great care is necessary to render the flow in them equable. The action of the pumping-engine being intermittent, the flow of water would be reduced to a series of impulses, by which great strain would be thrown upon the machinery, without some means of keeping up the forward motion of the column of water between each stroke of the engine. There are two methods of doing this, by fixing either a vertical stand-pipe or an air-chamber over the main immediately in front of the pump. The action of the pump impels a certain quantity of water forward into the main, but the vis inertia of the mass of water opposes a certain amount of resistance to this effort, and some therefore rises into the stand-pipe — which is open at the top — or into the inverted air- chamber. In the case of the stand-pipe, the column of water takes up the force, which for a moment the engine has ceased to apply, and continues to urge forward the water in the main. In that of the air-chamber — which is simply a large and strong iron cylinder closed at the top, and communicating below with the main — the water is forced by the engine partly into the main, and partly into the air-chamber, thereby compressing the air, which, directly the pump stops, acts by its elasticity upon the water it contains, and thus continues its forward motion in l the main. PRINCIPLES OF DESIGN. 229 PRINCIPLES OF DESIGN.—' VII. By Christopher Dresser, Ph.D., F.L.S.etc. HARMONIES AND CONTRASTS OF COLOUR ( Continued ). Continuing our studies in colour-harmony, it must be noticed that while colours harmonise in the proportions stated, the areas may vary if there be a corresponding alteration in in- tensity. Thus eight of blue and eight of orange form a perfect harmony when both colours are of prismatic intensity ; but we shall still have a perfect harmony if the orange is diluted to one-half its strength with white, and thus formed into a tint, provided there be sixteen parts of this orange of half strength to the eight parts of blue of full strength. The orange might be further diluted to one-third of its full power, but then twenty-four parts would be necessary to a perfect harmony with eight parts of prismatic blue ; or to one- fourth of its strength, when thirty-two parts would be neces- sary to the harmony. It is not desirable that I occupy space with diagrams of these quantities, but the industrious student will prepare them for himself, and will strive to realise a true half-tint, quarter- tint, etc., which is not a very easy thing to do. By practice, however, it will readily be accomplished, and anything achieved is a new power gained. What I have said respecting the harmony of blue with tints of orange will apply in all similar cases. Thus red will har- monise with tints of gre°n, provided the area of the tint be increased as the intensity _s decreased ; and so will yellow har- monise with tints of purple under similar conditions. But we may reverse the conditions, and lower the primary to a tint, retaining the secondary in its intensity. Thus blue, if reduced to a half-tint, will harmonise with orange of prismatic intensity in the proportion of sixteen of blue to eight of orange ; or, if reduced to a quarter-tint, in the proportion of thirty-two of blue to eight of orange. Red, if reduced to a half -tint, will harmonise in the proportion of ten red to eleven of green ; and yellow as a half-tint in the proportion of six yellow to thirteen of purple. The same remarks might be made respecting the harmony of shades of colour with those of prismatic intensity. Thus, if orange is diluted to a shade of half intensity with black, it will harmonise with pure blue in the proportion of sixteen of orange to eight of blue, and so on, just as in the case of tints ; and this principle applies to the harmony of all hues of colour also. To go one step further : we scarcely ever deal with pure colours or their shades or tints, or even come as near them as we can. With great intensity of colour we seem to require an ethereal character, such as we have in those of light ; but our pigments are coarse and earthy— they are too real-looking, and are not ethereal — they may be said to be corporeal rather than spiritual in character. For this reason we have to avoid the use of our purest pigments in such quantities as render their poverty of nature manifest, and to use for large surfaces such tints as, through their subtlety of composition, interest and please. A tint the composition of which is not apparent is always preferable to one of a more obvious formation. Thus we are led to use tints which are subtly formed, and such as please by their newness and bewilder by the intricacy of forma- tion. To do what I here mean it is not necessary that many pig- ments be mixed together in order to their formation. The effect of which I speak can frequently be got by two well-chosen pigments. Thus a fine series of low-toned shades can be pro- duced by mixing together middle-chrome and brown-lake in various proportions, and in all of the shades thus formed the three primary colours will be represented, but in some yellow will predominate, and in others red ; while in many it will not be easy to discover to what proportionate extent the three primary colours are present. Let us suppose that we make a tint by adding white to cobalt blue. This blue contains a small amount of yellow, and is a slightly green-blue. But to this tint we add a small amount of raw umber with the view of imparting a greyness* or atmo- spheric character. Raw umber is a neutral colour, leaning * Cobalt, raw umber, and white make a magnificent grey, both in oil-colours in tempera (powder-colours mixed with gum-water) aud in distemper (powder-colours mixed with size). slightly to yellow — that is, it consists of red, blue, and yellow, with a slight excess of the latter. In order that an orange harmonise with this grey-blue of a slightly yellow tone, the orange must be slightly inclined to red, so as to neutralise the little green formed by the yellow in the blue. It may har- monise with the grey-blue as a pure tint if the area of the diluted and neutralised primary is sufficiently extended, or may itself be likewise reduced to a tint of the same depth, when both tints would have, in this instance, the same area. I might go on multiplying cases of this character to almost any extent, but these I must leave the student to work out for himself, and must pass on to notice that while it is desirable to use subtle tints (often called “broken tints”), it is rarely expedient to make up the full harmony by a large area of a tertiary tone and a single positive colour. Thus, we might have a shade or a tint of citrine spreading over a large surface as a ground on which we wished to place a figure. This figure would harmonise in pure purple were it of a certain size, and yet if thus coloured it would give a somewhat common-place effect when finished, for the harmony would be too simple and obvious. It would be much better to have the nineteen parts of citrine reduced, say, to half intensity, when the area would be in- creased to thirty-eight, with the figure of eight parts of blue and five of red, than of thirteen parts of purple. But it would be better still if there were the thirty-eight parts of reduced citrine, three parts of pure yellow, thirteen of purple, five of red, and eight of blue, together with white, black, or gold, or all three (these may be added without altering the conditions, as all act as neutrals), for here the harmony is of a more subtle character. If we count up the equivalents of the colours employed in this scheme of harmony, we shall see that wo have, in the citrine — Yellow 6 (two equivalents). Blue 8 (one equivalent). Bed 5 (one equivalent). In the purple — • Blue 8 (one equivalent). Bed 5 (one equivalent). Of the pure colours — Yellow 3 (one equivalent pure). Bed 5 (one equivalent pure). Blue 8 (one equivalent pure). Thus we have three equivalents of each primary, which give a perfect harmony. I must not say more respecting the laws of harmony, for the space at my disposal will not allow of my so doing, but must proceed to notice certain effects Or properties of colours, which I have as yet only, alluded to, or have passed altogether un- noticed. I have said that black, white, and gold are neutral as regards colour. This is the case, although many would suppose that gold was a yellow. Gold will act as a yellow, but it is generally employed as a neutral in decorative work, and it is more of a neutral than a yellow, for both red and blue exist largely in it. The pictorial artist frames his picture with gold because it, being a neutral, does not interfere with the tints of his work. It has the further advantage of being rich and costly in appear- ance, and thus of giving an impression of worth where it exists. Black, white, and gold, being neutral, may be advantageously employed to separate colours where a separation is necessary. Yellow and purple harmonise, but yellow is a light colour and purple is dark. These colours not only harmonise, but also contrast as to depth, the one being light and the other dark. The limit of each colour, wherever these are used in juxtaposi- tion, is therefore obvious. It is not so with red and green, for these harmonise when of the same depth. This being the case, and red being a glowing colour, if a red object is painted on a green ground, or a green object on a red ground, the “ figure ” and ground will appear to “swim” together, and will produce a dazzling effect. Colour must assist form, and not confuse it. It will do this in the instance just named if the figure is outlined with black, white, or gold, and there will be no loss of harmony. But experience has shown that this effect can also be averted by outlining the figure with a lighter tint of its own colour. Thus, if the figure is red and the ground green, an outline of lighter red (pink) may be employed. (See Proposition 26.) 230 THE TECHNICAL EDUCATOR. A blue figure on a red ground (as ultramarine on carmine), or a red figure on a blue ground, will also produce this swimming and unsatisfactory effect, but this is again obviated by an out- line of black, white, or gold. Employing the outline thus must not be regarded as a means of merely rendering what was actually unpleasant endurable, for it does much more — it indeed affords one of the richest means of effect. A carmine ground well covered with bold green ornament'having a gold outline is, if well managed, truly gorgeous ; and were the figure blue on the red ground, the lavish use of gold would render the employment of yellow unnecessary, as the slight predominance of this primary in the metal would, together with the yellow formed in the eye and cast upon the gold, satisfy all requirements. It is a curious fact that the eye will create any colour of which there is a deficiency. This it will do, but the colour so created is of little use to the composition unless white or gold are present ; if, however, there be white or gold in the composi- tion, the colour which is absent, or is insufficiently represented, will be formed in the eye and cast upon these neutrals, and the white or the gold, as the case may be, will assume the tint of the deficient or absent colour. (See Propositions 8 and 9.) While this occurs (and sometimes it occurs to a marked degree, as can be shown by experiment), it must not be sup- posed that a composition in which any element is wanting is as perfect as one which reveals no want. It is far otherwise ; only Nature here comes to our assistance, and is content to help herself rather than endure our shortcomings; but in the one case we give Nature the labour of completing the harmony ; while in the other, all being prepared, we receive a sense of satisfaction and repose. In Proposition 8 we show that when blue and black are juxtaposed the black becomes “rusty,” or assumes an orange tint ; and in Proposition 9 we give the cause of this effect. Let a blue spot be placed on a black silk necktie, and however black the silk, it will yet appear rusty. This is a fact ; but we sometimes desire to employ blue on black, and wish the black to look black, and not an orange-black. How can we do this ? Obviously by substituting for the black a very dark blue, as indigo. The bright blue spot induces orange (the complement of blue) in the eye. This orange, when cast upon black, causes the latter to look “rusty but if we place in the black an amount of blue sufficient to neutralise the orange cast upon it, the effect will be that of a jet black. We have now considered those qualities of colour, and those laws of contrast and harmony, which may be said to be of the grosser sort ; but we have scarcely touched on those considera- tions which pertain to special refinement or tenderness of effect. But let me close this part of my subject by repeating a state- ment already made — a statement, let me say, which first led me to perceive really harmony of colour — that those colours, and those particular hues of colour, which improve each other to the utmost, are those which perfectly harmonise. (Consider this statement in connection with Propositions 8, 9, 10, and 14.) We come now to consider delicacies and refinements in colour effects, which, although dependent upon the skilful exercise of the laws enunciated, are yet of a character the power to pro- duce which only results from the consideration of the works of the masters of great art nations ; but of these effects I can say little beyond that of pointing out what should be studied. This principle I cannot pass without notice — namely, that the finest colour effects are those of a rich, mingled, bloomy character. Imagine a luxuriant garden, the beds in which are filled with a thousand flowers, having all the colours of the rainbow, and imagine these arranged as closely together as will permit of their growth. When viewed from a distance the effect is soft and rich, and full and varied, and is all that is pleasant. This is Nature’s colouring. It is our work humbly to strive at pro- ducing like beauty with her. This leads me to notice that primary colours (and secondary colours, also, when of great intensity) should be used chiefly in Bmall masses, together with gold, white, or black. Visit the Indian Museum at 'Whitehall,* and consider the beautiful Indian shawls and scarves and table-covers ; or, if * This Museum is open free to the public. unable to do so, look in the windows of our large drapers in the chief towns, and see the true Indian fabrics,* and observe the manner in which small portions of intense reds, blues, yellows, greens, and a score of tertiary tints, are combined with white and black and gold to produce a very miracle of bloom. I know of nothing in the way of colour combination so rich, so beautiful, so gorgeous, and yet so soft, as some of these Indian shawls. It is curious that we never find a purely Indian work other- wise than in good taste as regards colour harmony. Their works, in this respect — whether carpets, or shawls, or dress materials, or lacquered boxes, or enamelled weapons — are almost perfect — perfect in harmony, perfect in richness, perfect in the softness of their general effect. How strangely these works contrast with ours, where an harmonious work in colours is scarcely ever seen. By the co-mingling (not co-mixing) of colours in the manner just described, a rich and bloomy effect can be got, having the general tone of a tertiary colour of any desired hue. Thus, if a wall be covered with little ornamental flowerets, by colouring all alike, and letting each contain two parts of yellow and one part of blue and one of red, the distant hue will be that of citrine : the same effect will result if the flowers are coloured variously, while the same proportions of the primaries are pre- served throughout. I can conceive of no decorative effects more subtle, rich, and lovely than those of which I now speak. Imagine three rooms, all connecte d "by open archways, and all decorated with a thousand flower-like ornaments, and these so coloured, in this mingled manner, that in one room blue predominates, in another red, and in another yellow ; we should then have a beautiful tertiary bloom in each — a subtle mingling of colour, an exquisite delicacy and refinement of treatment, a fulness such as always results from a rich mingling of hues, and an amount of detail which would interest when closely inspected ; besides which, we should have the harmony of the general effect of the three rooms, the one appearing as olive, another as citrine, and the other as russet. This mode of decoration has the advantage that it not only gives richness and beauty, but it also gives purity. If pigments are mixed together they are thereby reduced in intensity, as we have already seen ; but if placed side by side, when viewed from a distance the eye will mix them, but they will suffer no diminu- tion of brilliancy. With the view of cultivating the eye, Eastern works cannot be too carefully studied. The Indian Museum should be the home of all those who can avail themselves of the opportunity of study which it affords ; and the small Indian department of the South Kensington Museum should not be neglected, small though it is.f Chinese works must also be studied, for they likewise supply most valuable examples of colour harmony ; and although they do not present such a perfect colour-bloom as do the works of India, yet they are never inharmonious, and give clearness and sharpness, together with great brilliancy, in a manner not attempted by the Indians. The best works of Chinese embroidery are rarely seen in this, country ; but these are unsurpassed by the productions of any- other people. For richness, splendour, and purity of colour, to- gether with a delicious coolness, I know of nothing to equal them.. The works of the Japanese are not to be overlooked, for in certain branches of art they are inimitable, and as colourists they are almost perfect. On the commonest of their lacquer trays we generally have a bit of good colouring, and their coloured pictures are sometimes marvels of harmony. As to the styles of colouring adopted by the nations referred to, I should say that the Indians produce rich, mingled, bloomy, warm effects — that is, effects in which red and yellow prevail ; that the Chinese achieve clearness, re-pose, and coolness — a form * These will only be seen in very first-class shops, f It may not be generally known, blit nearly all our large manu- facturing towns have, in connection with the chamber of commerce, a collection of Indian fabrics, filling several large volumes, which were prepared, at the expense of Government, under the superintendence of Dr. Forbes "Watson, and which were given to the various towns on the condition that they be accessible to all persons who are trustworthy. Although these collections do not embrace the costly-decorated fabrics, yet much can be learned from them, and the combinations of colour are always harmonious. A much larger collection is now in course of; formation. TECHNICAL DRAWING. 231 of colouring in which blue and white prevail; and that the Japanese effects are tv arm, simple, and quiet. Besides studying the works of India, China, and Japan, study those also of Turkey, and even those of Algeria, for here the colouring is much better than with us, although not so good as in the countries first named. No aid to progress must be neglected, and no help must be despised. The South Kensington Museum has a very interesting collec- tion of art-works from China and Japan ; but the latter are chiefly lent. It is a strange thing that the perfect works of the East are so poorly illustrated in this national collection, while costly, yea, very costly works of inferior character, illus- trative of Renaissance art, swarm as thickly as flies in August. This can only be accounted for by the fact that the heads of the institution have a feeling for pictorial rather than decorative art, and the Renaissance ornament is that which has most of the pictorial elements. To me, the style appears to owe its very weakness to this fact, for decorative art should be wholly ideal. Pictorial art is of necessity more or less imitative. With the view of refining the judgment further in respect to colour, get a good colour-top,* and study its beautiful effects. See also the “gas tubes ” illuminated by electricity, as sold in the opticians’ shops, and let the prism yield you daily instruction. Soap-bubbles may also be blown, and the beautiful colours seen in them carefully noted. These and any other available means of cultivating the eye should constantly be resorted to, as by such means only can we become great colourists. As to works on colour, we have the writings of Field, to whom we are indebted for valuable discoveries ; of Hay, the decorator and friend of the late David Roberts, but some of his ideas are wild and Utopian ; of Chevreul, whose work will be most useful to the student ; and the small catechism of colour by Mr. Redgrave, of the South Kensington Museum, which is excellent. The student will also do well to carefully study the scientific articles on “Colour” by Professor Church in this work. TECHNICAL DRAWING.— XY. DRAWING FOR MACHINISTS AND ENGINEERS. The purpose of this portion of our lessons in “ Technical Draw- ing” is to give engineers and machinists a series of lessons in those branches of drawing which are connected with their work. The system laid down is elementary, but every endeavour has been made to render the instruction thorough, as far as it goes. It is not long ago since the study of mechanical drawing was supposed to consist in simply copying drawings of machinery, by accurate measurement and in very fine lines. This idea has now happily exploded, but the necessity for books which should show an artisan, first, what he ought to learn, and then how to acquire such knowledge, has been deeply felt. It is as a contribution towards the accomplishment of this purpose that the present course of lessons is put forth, in the earnest hope of aiding artisans to mount a step or two higher on the ladder of improvement. Each part of this course of Technical lessons is, as far as possible, complete in itself; but as a knowledge of practical geometry and projection should underlie all instruction in mechanical drawing, the student is advised to read the lessons on “ Practical Geometry applied to Linear Drawing” and “ Pro- jection,” either prior to, or simultaneously with this ; he will then be able to proceed with the advanced lessons in which the special application of those studies is shown. Free-hand drawing of a character adapted to the wants of machinists, drawing from objects, and isometrical projection form the subjects of the various sections, and several initiatory lessons in drawing from rough sketches will be introduced, these lessons being followed with a series of drawings of modern machinery and a few simple hints on the method of colouring mechanical drawings. * Not the so-called colour or chameleon top sold in the shops during the past winter, but the more scientific toy procurable of opticians, together with the perforated discs of Mr. John Graham, M.R.C.S., of Tunbridge, Kent. See also The Popular Educator, “Recreative Science” — NX. (Yol. VI., p. 231). These lessons have been prepared with the greatest care, and are based on the result of long and varied experience in teaching the subject. The lessons will therefore be found thoroughly practical, whilst the information given as to the history and principles of action of the different pieces of mechanism cannot fail to prove both useful and interesting to students. We cannot close our preliminary remarks without thanking the eminent engineers and machinists who have so kindly sent us contributions of drawings and information ; had the limits of our lessons permitted, we should have gladly availed ourselves of their liberality to a greater extent than it will be found we have done. Their willingness to assist in the education of work- men proves the spirit of employers towards the employed, which is one of the most glorious features of the age we live in. MECHANICAL DRAWING GENERALLY. The figures given in “ Practical Geometry applied to Linear Drawing,” and their application in “Projection,” will have shown the student the importance of absolute accuracy and refinement in mechanical drawing; and as the aim of this part of our lessons is to carry the subject to a higher stage, the necessity for perfect correctness of delineation will, as the studies advance, become more and more evident. The first lessons are therefore designed for the purpose of offering manual practice, so as to give the student, not only the power of measuring accurately, but of drawing his lines exactly where he knows they ought to be ; for, strange as it may seem to some, it is not so easy to draw lines which shall pass exactly through required points, or which shall be absolutely parallel to each other, as might be supposed, even though the student is furnished with rule, square, and compasses. It is hoped, however, that the practice afforded by the examples given in these lessons, and the hints accompanying them, may show the learner the obstacles with which he is likely to meet, and enable him to overcome them. We are aware that we are addressing a body of youths and men whose work is such as to cause them to be “ heavy-handed,” and that the hands accustomed to wield the hammer and file with such effect as to tell upon the metal which has become more practically useful than gold, will find difficulty at first in leaning so lightly on their dividers that their delicate points shall barely mark the paper, yet we have known hammermen who in their earliest lessons crushed the very points of their pencils, become with practice expert and refined draughtsmen. We are conscious, too, that we are writing for those who have been engaged for several hours in severe toil, whose occupation has not admitted of its being exercised in the open air, or even in airy apartments, as might be the case in many other walks of industry, but whose labour has been carried on for the most part in necessarily heated workshops, under the lurid glare of the forge-fire, amid the din of steam-hammers, and the thousand other noises inseparable from mechanical works. It might be thought that from men so situated a sacrifice is demanded when they are urged to attend evening classes, or even to pursue home study when their day’s work is over. We do not think so. We cannot believe that any man’s work is really done, until he has made an effort, however small, to (icvelop those mental powers with which he has been so merci- fully endowed ; and he will find, too, that the effect of the in- formation he gains will not be confined to the evenings, but that the knowledge he acquires will increase his interest in the form and action of the machines amongst which he is engaged, and his work will not only be done better, but with greater pleasure than before. The experience of many years has shown us that men who are desirous of working as intelligent beings, attend the evening classes with the greatest regularity, often bringing their sons to share the instruction given ; and that many hours are spent at home in working out the lessons which have been received. In such practice these lessons will be found especially useful, and therefore practical hints are given so that the student may not be delayed by not knowing “ how to go on.” Fig. 165 represents a drawing-board with T-square and set- square. The T-square should only be used for lines in one direc- tion ; for, unless the board be one which has recently been squared, it cannot be depended upon, and the lines drawn by means of the T-square, when guided by different sides of the board, will not generally be found to be at right angles to each other. 282 THE TECHNICAL EDUCATOR Although a few plain hints on linear drawing, and a plain description of some of the mathematical instruments mostly used, hare been given in our lessons on “Technical Drawing,” some few of the remarks there given are repeated here to avoid the trouble of reference, together with such additions as the subject of these lessons renders necessary. The best T-squares are those which have the blade screwed across the stock, which form (see Fig. 165) admits of the set-square being moved freely along, in order to draw a line near the edge of the paper, whilst it would be obstructed by the stock if the blade were mortised into it. It is important that the set-square should be true whichever way it may be worked, and this may be tested by drawing a line against its edge when placed as at A (Fig. 165), and then turning it over as at B, bring its edge up to the line drawn ; then if another drawn against the edge in its present position agrees perfectly with the former one, the square is true ; if not, it will require setting. Any working man or student will, with a little care, be able to do this for himself, by placing a sheet of very fine sand-paper on a ‘perfectly flat surface, and rubbing the edge of the set-square against it, keeping the square upright, and pressing a little heavier on the part which requires “easing” than on the other. It may be well, whilst speaking of this por-. tion of the subject, to advise you to rub off the angles of the edges of your square. We do not mean that you should actually bevel them, but merely rub off enough of the Sharp edge to raise it almost imperceptibly above the paper, when the square is lying flat ; and we recommend you to do this to all the edges, for a purpose of which wo will tell you presently. The T-square, then, being worked against the left-hand edge of the drawing-board, will give all the horizontal lines, and can be moved higher or lower without laying down the pencil or inking-pen. The lines perpen- dicular to the others are drawn by means of the set-square, as shown in Fig. 165. Should it be required to lengthen the line, it is only neces- sary to move the T-square downwards, keeping the set-square in its place against it. If these instructions are carefully followed, lines at right angles to each other will be ensured. In pencilling your work you will, as a general rule, find an hb pencil the best for the larger parts, and an h for the teeth of wheels and more minute portions. Be careful not to press too heavily on your pencil ; the lines should be so lightly done that they can, if required, bo easily rubbed out with india-rubber, without disturbing the grain on the surface of the paper. Remember that, as a rule, mechanical draw- ings are not left in pencil, but. that the pencil- lines are merely drawn as guides for inking. Therefore as little lead as possible should be deposited on the paper ; for as the nibs of the inking-pen are drawn over the lines they gather up the grit of the lead, which lodges between them, causing the line to become thick and irregular. When, therefore, the work is finished in pencil, it is advisable to pass the india-rubber lightly over the surface, by this means removing the loose par- ticles of lead without erasing the lines. Draw all pencil-lines past each other at right angles and in- tersections ; for as the edge of the rule partly obstructs your Tiew of the line when inking, you are liable to pass over the re- quired point, which annoyance will be prevented by another pencil line crossing at the exact spot at which you are to stop. If you have by mistake drawn a line too long, do not scratch out the superfluous length until after you have coloured, as the roughened surface will cause the colour to run. For rubbing out an ink-line, if ryjt too thick, you will find ink-eraser, or very fine glass-paper (No. 1), better than the knife, as it removes the surface of the paper more equally. Never use writing-ink in your mathematical instruments. Indian ink is sold in sticks, which may be purchased at from twopence to a shil- ling each. This should be rubbed in a small saucer, or slab, with a little water. You should put some in your pen to try on a slip of paper, in order that you may know if it is dark enough before you begin to work with it. A little indigo rubbed with the Indian ink darkens it, and removes the brown tinge. Drawing-boards of various kinds are sold ; some are framed, some clamped, and some rab- beted. The different methods are all so many plans to secure the board against twisting and cracking; and yet all of them, however inge- nious, fail, if the wood is not well seasoned be- fore the board is made up ; so that we advise you, if you are about having a drawing-board made, not to attend so much to the make as to the stuff it is made of. Most machinists who are connected with large works will have seen something of woodwork, and the carpenters with whom they may be associated will, no doubt, give them the benefit of their assistance in the matter. To persons not so situated we suggest, that it is safer to buy a ready-made board, from a stock which has been some time in hand. They will then have an opportunity of selecting such as are in some degree seasoned. For drawings such as the ele- mentary studies in these lessons, or simple geometrical figures which are soon finished, it will be sufficient to fasten the paper down by means of drawing-pins, which may be bought at one halfpenny each ; but if the draw- ing is likely to take some time, or is to be coloured, it is best to “ stretch” the paper. This is done as fol- lows : — Cut the sheet to a trifle smaller than your board, and turn up a margin about half an inch broad all round ; then lay the paper face downwards, and spread water over the surface (the back of the sheet) with a sponge ; allow the water to soak in for a minute or two, but keep the surface equally moist all over; raise the paper by its edges, turn it over, so that the wet side may rest on the board, and apply strong paste to the turned-up edges > rub these down, and in doing so draw the paper outward. It is a good plan to burnish the margin well with the handle of your penknife, by which means you press the air out, and make sure that the paper is properly pasted down. The board must then be pla.ced horizontally to dry. If, when nearly dry, one or two large blisters remain which do not seem to decrease, prick a small "hole or two in them with a needle to let out the air, which will, in most cases, remedy the evil ; if not, pass the sponge over the whole face of the paper, moistening it especially towards the outer part. It is advisable to operate upon a small sheet at first, until the “knack ” of stretching is acquired. The size of the paper most generally used by students is called “ imperial.” This has been fixed as the size for the competitive drawings sent to the Government Department of l A B. C D E F, G Fig. 166. TECHNICAL DRAWING. 238 Science and Art, and is found the most convenient for general purposes. It is, therefore, advisable to have your drawing- board made of the same size as the paper, thus avoiding waste. The whole sheet is 30 in. X 22 in. You will find it enough for the present to use the half sheet, the size of which will be 22 in. X 15 in. Your board should be a trifle larger all round. Fig. 167. LINEAR DRAWING BY MEANS OF INSTRUMENTS. "Fig. 160. — The object in this lesson is to give practice in ruling straight lines at equal distances apart, and of the same length and thickness. Draw a light line at the top and another at the bottom. These lines are to be ruled by the aid of the T-square, worked against the left-hand edge of the drawing-board. Take the distance between the lines A b in your dividers, and set it off as many times along the bottom line as may be re- quired. (The dividers are the smaller-sized compasses without the pencil or pen legs. If you have not one of these, you must use your compass, taking care to insert the steel leg instead of that which holds a pencil.) Having, then, set off from A the lengths b, c, d, e, f, g, keep the blade of your T-square horizontal, but moved a trifle lower down. Place your set-square against it, as shown in Pig. 165, and draw perpendiculars from the points marked. Be careful that you incline your pencil so onat its point ig guided by the set-square all along ; otherwise your lines will not be upright. When properly pencilled, dust off the lead on the surface with india-rubber, and then ink your work as already directed. Hold your draw-pen as upright as possible, leaning your first finger on the head of the screw. If you slant the pen only one of its nibs will touch the paper, then the edge of your line will be ragged. Before inking, rule a few lines on another piece of paper to try if your draw-pen is as open as is required to give the proper thickness of line, or if the ink is of the right colour, etc. You will find this little precaution will sometimes prevent great annoyance, and often save a drawing from being spoiled. Fig. 167. — This figure will afford practice in dividing a square into several smaller ones. The study of linear drawing will have shown the geometrical method of constructing the original figure and of dividing lines ; it is therefore only neces- sary here to advise you in drawing the square in pencil to carry the sides beyond the angles, which enables you when inking, and your rule covers the figure, to know the exact point at which to stop. This is important, for if you do not draw your ink -line quite long enough, you will have the trouble of “ piecing” it, which is always difficult, but especially so if the line be fine j THE TECHNICAL EDUCATOR. 234 and if too long, you will have to erase the superfluous length, which causes annoyance and trouble, and in doing which the angle of the square is often damaged. Fig. 168 is an exercise in the accurate use of the set-square of 45°. Having drawn the base (a), and one other side of the square (as b) at right angles to it, place the set-square of 45° so that its hypothenuse * may enter the right angle c ; draw the line which will subsequently become one of the diagonals. Now from the extremities of the two sides of the square draw lines for the other two sides, and these should meet at d, on the line c. If this is not the case, the lines are not at right angles to each other, or there is some other inaccuracy, and you had better rub your work out, to avoid being compelled to do so when further advanced. Having now drawn the square and one diagonal, draw the other. This must also be done with the set-square, for if your figure be accurate, the set-square placed against the one angle should give a line direct to the other. Divide the base into the required number of equal parts, and moving the set- square along the T-square, draw the lines across in each direction. The utmost care is necessary in doing this, for it must be pointed out that it is only required to mark the division on the base, since the lines drawn from these should give the points in the sides. Thus the line drawn from E will give the point a, and if the work be correctly done the hypothenuse of the set- square when reversed should give F H and the other lines parallel to it. Fig. 169 shows the mode of drawing lines to indicate that the drawing represents a section or cutting, and is another example of the use of the set-square, these lines being drawn at 45°. Care is necessary in keeping them all the same distance apart, and of the same thickness. The lines which on the right- hand side are thicker than those on the left are called shade lines. They indicate that a square open tube is represented, and that the light is proceeding from the left side. If it were intended to show that the walls of the tube are cut through, and that the space they enclose is filled up by a flat board not cut through, the lines A and B would be drawn of the same thickness as the other two. Fig. 170 is an application of Fig. 168, and represents an iron grating. To draw this figure, proceed as in Fig. 168, working all the crossing lines in dots or very finely. On each side of the intersections set off half the width of the bars, as shown at a, h, c, d, and through these points, by means of the set-square, draw the necessary lines, all of which must be parallel to those previously drawn. The rest of the subject will now be easily completed without further instructions. Fig. 171 is another application of the same study. Having drawn the original fine lines crossing the square, set off. half the thickness of the bars as shown at a, h, c, d in the previous figure. From the same points mark off the semi-diagonal of the square which is to be drawn at each intersection — viz., e, f, g, h. It will be seen that one square will guide those of two lines at right angles to each other ; thus e h and g f produced will give the horizontal lines of all the squares on the same line, whilst e g and h f will give the perpendiculars of all the squares above and below the square e g f h. If this plan be pursued, instead of measuring each square separately, much time will be saved. ANIMAL COMMERCIAL PRODUCTS.— X. PRODUCTS OF THE CLASS AYES ( continued ). BED-FEATHEKS. The lower barbs in feathers are usually loose, and form the down, which is called the “ accessory plume.” The quantity j{ this down varies in different species of birds, and even in the feathers taken from different portions of the body of the same bird. It is most abundant on aquatic birds, and as the value of bed-feathers depends on its amount, the feathers of ducks, swans, and geese — which have the “ accessory plume ” nearly as large as the feather — are the most esteemed. The qualities sought for in bed-feathers — softness, elasticity, lightness, and warmth — are combined in common goose feathers ; * Hypothenuse. The longest side of a right-angled triangle. they are considered best when plucked from the living bird, and this cruel operation is repeated from three to five times in a year. Young birds are plucked as well as those of mature growth — the early plucking being supposed to favour the growth of the feathers. The less valuable kinds of feathers, obtained from turkeys, ducks, and fowls, are also used for bed-stuffing, and are called “ poultry feathers.” Eider Duclc ( Anas mollissima). — This bird furnishes the softest, finest, and most valuable down-feathers that are in the market. Eider-down is procured from the nest of this bird, which robs its own breast of feathers in order to make a warm home for its young. The eider ducks build their nests in great numbers, in almost inaccessible rocky situations on the coasts of Ireland, Scotland, the Faroe Islands, Lapland, Nova Zembla, and Spitzbergen ; and these nests are, at great risk of life, annually plundered of their down by the fowlers. Eider-down comes to this country in the form of balls, about the size of a man’s fist, and weighing three or four pounds. It is so fine and soft, that if one of these balls is spread and warmed over hot coals, it will expand and fill a bed big enough for two persons. Eider-down is only used as a covering for beds, and never should be slept upon, as it thereby loses its elasticity. In 1864 our imports of bed-feathers from Russia, Hamburg, France, and other parts of the Continent, amounted to 8,786 cwt., valued at <£76,488 ; white ostrich feathers, 16,192 lb., valued at .£113,480 ; black ostrich feathers, 26,643 lb., valued at ,£80,583 ; and feathers of all other kinds, 24,186 lb., valued at .£11,485. QUILL PENS. The earliest pens, such as were used for writing on papyrus with a fluid ink, were made of reeds. Reed pens are still in use in Arabia, as they suit the Arabic character better than quill pens. These reeds are collected near the shores of the Persian Gulf, whence they are sent to various parts of the East. Quill pens are chiefly supplied by the goose, swan, and crow — the ostrich, turkey, and other birds occasionally contributing. Crow quills are usually employed in fine drawings, on account of the fine point to which they can be brought. Goose quills are employed for ordinary writing ; but swan and turkey quills, being larger, are preferable for copying. Two principal sorts of quills are known in commerce — viz., Dutch quills, which are transparent and glass-like ; and Ham- burg quills, which are milk-white and clouded. Dutch quills are much esteemed ; the Dutch were the first to find out the art of preparing quills for market, by removing the oil which im- pregnates them, and'prevents the ink from flowing freely along the pen. Quills are obtained in the greatest quantities from the countries along the Baltic ; Hamburg is still the principal place for preparing and exporting them. Next to the Ham- burg and Dutch quills, those of Riga are much liked, especially in England. The manufacture of steel pens does not appear to have dimi- nished the demand for quills. In 1855 we imported, indepen- dently of our home supply, 26,500,000 goose and swan quills. The quills used are the five outer feathers of the wing, which are classified according to the order in which they are fixed in the wing, the second and third being the best. With proper management, a goose may afford twenty quills during the year. In the fens of Lincolnshire, geese are kept in large numbers. During the breeding season they are lodged around the owner’s house. A gooseherd, it is said, can distinguish every goose in the flock by the tones of its voice. 4 PRODUCTS OF THE CLASS REPTILIA. Reptilia (Latin, reptilia, from repto, I creep). — Cold-blooded, vertebrated animals, having a heart so constructed as to trans- mit only a portion of the blood to the lungs. The blood is therefore imperfectly oxygenated, and there is a lower degree of animal heat. The amount of venous blood, however, trans- mitted to the general system varies in the different reptiles, and in proportion as there is less or more of it, is there a corre- sponding difference in their temperature and vital activity. As reptiles have no need of preserving a temperature many degrees warmer than that of the medium in which they live, they are covered with scales, or hard bony plates, and without the warm clothing of the birds and mammalia. PROJECTION. 235 The class Reptilia is divided into four orders, viz. 1. Chelonia (Greek, chelone, a tortoise), which are character- ised by the enclosure of the body in a double shield or shell, out of which extend the head, tail, and four extremities. Examples : tortoise and turtle. 2. Lacertilia, or Sauria (lizards), having the body and tail elongated, the jaws furnished with teeth, the skin covered with scales, and the feet generally four hi number. Examples : green lizard and blind- worm. 3. Crocodilia include the alligators of America, the true crocodiles of Africa, and the gavials of Asia. Gigantic lizards, covered with closely-set bony plates. 4. Ophidia (Greek, opliis, a serpent), ’which are distinguished by the absence of the extremities, as in the snake. The Chelonia are commercially the most valuable of the above orders, as we derive from them two important articles — turtle soup and tortoise-shell — the former the greatest luxury of the table, and the latter the most prized of horny materials. Green Turtle ( Chelonia mydas ). — This is one of the largest of the genus, often measuring five feet in length, and weighing between 500 and 600 pounds. It receives its name from the green colour of its fat. Its flesh is much esteemed, and in this country it is regarded as a great luxury, large quantities being continually imported for the supply of the London taverns alone. Green turtles are met with in the Atlantic Ocean, where they are widely distributed. They are found in great abundance near the Bahama Islands, and when they come ashore to deposit their eggs in holes in the sand are usually caught, either by harpooning or by turning them over on their backs, for when once turned they cannot get on their feet again. The Chinese catch them with the sucking- fish (Remora), which is put into the water with a string tied to its tail. The remora darts at the turtle, to which it firmly adheres by means of its sucking apparatus, and both fish and turtle are then drawn into the boat. Mr. Darwin thus describes the capture of this turtle at Keeling’s Island : “ The water is so clear and shallow that at first a turtle quickly dives out of sight ; yet, in a canoe or boat under sail, the pursuers, after no very long chase, come up to it. A man standing ready in the bows at this moment dashes through the water upon the turtle’s back ; then, clinging with both hands by the shell of the neck, he is carried away until the animal becomes exhausted and is secured. It was quite an interesting chase to see the animals thus doubling about, and the men dashing into the water trying to seize their prey.” HawTc’ s-Blill Turtle ( Chelonia imbricata).- — The horn-like plates of this animal, and also of the carett, or giant tortoise (Testudo carett a), which lives in all the seas of the torrid zone, furnish the tortoise-shell of commerce. The island of Ascension is a place of resort for these reptiles, and thousands of them are annually destroyed there. In most species of tortoise the scales which compose the carapace or upper covering adhere to each other by their edges, like inlaid work ; but in the hawk’s-bill turtle these scales are imbricated, or overlap one another, like the tiles on the voof of a house. The head is also smaller than in the other tortoises ; but the neck is longer, and the beak narrower, sharper, and more curved, resembling a hawk’s bill. The lamellae, or plates of the shell, are semi-transparent, and Variegated with whitish, yellowish, reddish, and dark-brown clouds and undulations, so as to constitute, when properly pre- pared and polished, an elegant article for ornamental purposes. The shell of this animal is therefore largely imported into this country, as much as thirty tons’ weight being annually con- sumed by the manufacturers. Tortoise-shell is used for the handles of penknives and razors, spectacle-frames, card-cases, ladies’ side, back, and dressing combs, and for inlaying work- boxes. The best tortoise-shell comes from the Indian Archi- pelago, where Singapore is the principal port for its exporta- tion. It is also sent from the West Indies; from the Galla- pagos Islands, situated on the west coast of South America ; and from the Mauritius, Cape Yerde, and Canary Islands. “ A large number of turtle eggs are secured every year for the sake of turtle oil. The eggs, when collected, are thrown into long troughs of water, and being broken and stirred with shovels, they remain exposed to the sun till the yolk, the oily part, is collected on the surface, and removed and boiled over a quick fire. This animal oil, or ‘turtle grease,’ is limpid, in- odorous, and scarcely yellow ; and it is used not merely to burn in lamps, but in dressing victuals, to which it imparts no dis- agreeable taste. The total gathering from the shores between the junction of the Orinoco and Apure is 5,000 jars, and it takes about 5,000 eggs to furnish one jar of oil.”* PRODUCTS OF THE CLASS AMPHIBIA. Rana esculent a (edible frog). — This species is eaten in France. Rana pipiens (American bull-frog). — The hind limbs are con- sidered a great luxury, and are exposed for sale in the markets of the United States. Siredon pisciforme (the axolotl). — Inhabits the lake near the city of Mexico, where it is very abundant, attaining a length of from ten to fifteen inches. Thousands are sold, and esteemed a. great delicacy by the Mexicans. PRODUCTS OF THE CLASS PISCES. Vertebrate animals inhabiting water, breathing by means of branchiae or gills — vascular organs into which the circulating- fluid enters, and which is submitted in a state of minute sub- division in the vessels of the gills to the air contained in the water, and so oxygenated — swimming by means of flattened ex- panded organs called fins, the entire body being mostly covered with cartilaginous scales. The specific gravity of fishes is nearly the same as that of the watery element in which they live. Most of them have a membranous bag at the lower side of the spinal column, known as the “air-bladder,” which is so organised that the fish can vary its specific gravity by contract- ing or expanding the bladder, expelling the air or taking it in, and so sink or rise in the water at pleasure. It is somewhat- remarkable that this air-bladder is quite rudimentary or alto- gether absent in fishes which live much at the bottom of the water, seldom or never coming to the surface, such as plaice, turbot, and sole. Progression in any direction is effected by the movements of the tail. The craving for food seems to be that which gives the chief impulse to their movements. Their rapacity has no bounds whatever ; even when taken out of the water, and just expiring, they will greedily swallow the very bait which lured them to destruction. The class of fishes has been sub-divided by Cuvier into two sub-classes. 1. Pisces ossei, or bony fishes, comprising those which have- a true bony skeleton. Examples : herrings, salmon, and cod. 2. Pisces cartilaginei, or cartilaginous fishes, including those in which the skeleton never passes beyond its primitive con- dition of gristle or cartilage. Examples : the sturgeon, ray, and shark. PROJECTION.— X. PENETRATIONS OF SOLIDS ( continued ). PROJECTION OF BUILDINGS. It is now necessary to develop the larger cylinder, and to draw accurately upon the development the form of the aperture through which the smaller one shall pass. Now it must bo borne in mind that this aperture, notwithstanding that it is to contain a cylinder, will not be a circle when the surface through which it is pierced is laid out flat. This will be evident on referring to the plan in Fig. 10P (page 205), where the length of the straight line e to e is the real width of the penetrating cylinder; whereas the distance between e and e' , when measured on the circumference of the plan, would be much more ; but as the axes of the two cylinders penetrate each other at right angles, the diameter in the eleva- tion will remain unaltered. The development of the general form of the cylinder will be accomplished by the method shown in Fig. 84f (page 101). On this development (Fig. Ill) draw a centre line A° repre- senting A in the plan. The outer perpendiculars b' b" will represent b in the plan. On each side of A° set off the lengths g f e, and erect perpendiculars ; then the heights of the points * See Bates' “Naturalist on the Amazon.” t The difference between this distance on the curve and on a straight line would be considerable, therefore divide it into several parts, x, x, x, and set them off separately, by which means the difference will be lessened. 236 THE TECHNICAL EDUCATOE. correspondingly lettered in the elevation, marked off on these j perpendiculars, will give points through which the development of the aperture may be traced. It now only remains to develop the form of one of the ends of the penetrating or smaller cylinder. To do this, draw a horizontal line (Fig. 112), and about the middle at e erect a perpendicular. On each side of e set off the distances/, g,c,g,f,~E, into which the end of the smaller cylinder is divided, and from these points erect perpendiculars. On these set off the lengths of the lines between e e (Fig. 109) and the plan of the larger cylinder — viz., e e, f /, G g, c' b, etc. The curve uniting the extremities of these perpendiculars will give the form in which the piece of metal is to be cut, so that when rolled and joined at its outer edges, it may form a part of a cylinder of the required size which will exactly fit to the aperture in the larger cylinder already explained. TO DRAW A CONE PENETRATED BY A CYLINDER, THEIR AXES BEING AT RIGHT ANGLES TO EACH OTHER (Fig. 113). Draw in the first place the mere elevation of the cone, A b c, and of the cylinder, D d' e e', intersecting each other in t f' g g' ; from these the general plan may be projected in the horizontal plane. The next problem for solution is the curve line may be followed throughout) the same lettering is given - — namely, d' V c'. From these points carry perpendiculars cutting the base line of the elevation of the cone in d' V c', and draw lines from these points to the apex, c, of the cone. Intersect these lines by others drawn from bed in the original semicircle, and through the points thus obtained the curve of penetration, starting at r and G, and ending in f and g', is to be drawn. It is now necessary to show on the plan the curve formed at the junction or penetration of the two bodies. Four points in these curves may at once be found by dropping perpendiculars from F, F* and G, g' in the elevation to cut x X in F, f' and G, g'. Now it will be remembered that every horizontal section of a right cone is a circle, and thus the lines parallel to the base on which the points b, c, d exist, are really edge elevations of circles, the diameter of which is regulated by their position on the cone. The length from point 1' on the edge of the cone to 1 in the axis is thus the radius of the circle on which the point b, and the corresponding point beyond it, are placed. Therefore, with this radius describe a circle from the centre of the plan, and drop a perpendicular from b, cutting it in b b. Draw a circle from the same centre of the plan with radius 2 2', and a perpendicular from c, cutting it in c c. Draw a circle from the same centre with radius 3 3', and Fig. 112 . -which will be generated by the intersection of the cylinder | (which is a round body of equal diameter) with the cone (which is a round body of ever decreasing diameter). At d d' draw the perpendicular H I equal to the altitude of the cone, and from J, the middle line of the elevation of the cylinder, describe a semicircle equal to half the end of the cylinder. From I draw a line touching this semicircle in c, and reaching the intersect- ing line in c'. Between D and c and c and D' mark off any number of divisions, as b, d, etc. It must, of course, be under- stood that the greater the number of divisions marked off, the greater will be the number of points subsequently obtained, and, of course, the greater the accuracy of the intersecting curve and development ; but the object of the author is to make the operations as clear as possible, and therefore, in order to avoid one set of lines passing over another, and causing difficulties and confusion, he has only marked one division (6) in the upper and one ( d ) in the lower portion of the elevation. The student, who is expected to work this figure to a much larger scale, will, however, do wisely to use many more points, all of which are worked in the same manner. From I draw a lino through b cutting the intersecting line in b', and from I draw a line through d cutting the intersecting line in d’ . Through the centre of the plan draw the line x x, and carry perpendiculars to it from c V d ' ; and from d', with radius d d, D b, D c, draw arcs cutting I H produced in points similarly lettered. From these points draw lines parallel to x x, cutting the plan of the cone in points to which (in order that the same a perpendicular from d, cutting it in d d. Draw the curve F d c b f' d c b, which will be the plan of the aperture required. (Of course the corresponding lines on the other side will give a similar result.) TO PROJECT A SMALL CHURCH FROM THE PLAN (Fig. 114). The church, it will be seen, is made up entirely of simple solids — viz., square prisms of various lengths, triangular prisms, and a square pyramid ; and as the student has already had some practice in these, he will find, it is believed, but little (if any) difficulty in following out the instructions, although the diagram is not lettered. The building is to be considered in the first instance formed of the square prisms only — that is, divested of the triangular prisms which form the roof, and also of the pyramid which forms the spire. These solids, then, will be represented in the plan by two rectangles crossing each other at right angles, and as they are equal in width their intersection is a square, which is the plan of the tower ; the shorter end of the longer rectangle then becomes the plan of the chancel, and the longer end the plan of the nave ; the smaller rectangles form the plans of the tran- septs. It is advisable now to proceed with the projection of the body of the church from the plan. This operation is very simple, requiring only that perpendiculars should be drawn from the various points. From the two front angles of the transept which faces the spectator, therefore, draw perpen, PROJECTION. 237 diculars, and a horizontal line cutting them off at a height above the intersecting line equal to the required height of the walls of the church. This horizontal line may be drawn of in- definite length, as it will regulate the height of the whole body of the building. A perpendicular drawn from the third angle of the transept ( i.e ., the front left-hand corner of the square) will give the one edge of the tower of which the square is the plan, and a perpendicular drawn from the right-hand corner of the square will give, not only the side of the transept, but will, if continued, give the right-hand line of the front of the tower : further, a perpendicular raised from the distant right-hand corner of the square will give the side, the height Next draw perpendiculars from the two angles of the right- hand end of the longer rectangle, and these carried up will give the projection of the rectangle, or wall forming the extreme end of the nave. We now return to the plan, and draw the diagonals, which constitute the plan of the edges of the pyramidical spire. From their intersection draw a perpendicular, and on this mark the height of the required pyramid, this line being the axis. From the apex thus fixed draw lines to the upper angles of the pro- jection of the tower, which will complete the spire. Again reverting to the plan, draw lines through the middle of the rectangles, which will give the plans of the ridges of the roof (Fig. 48, page 73). From the point where the ridge-line meets the front of the transept draw a perpendicular, and mark on this, above the top line of the walls, the perpendicular height shown in the dotted triangle annexed. Join this point to the upper corners of the front of the transept, and this will complete its gable. From the apex of this triangle draw a horizontal line, and intersect it by a perpendicular drawn from the point where the ridge-line in the plan cuts the front line of the square. This intersection will give the point where the ridge meets the front of the tower. From this point draw a line parallel to that side of the triangle, and this will complete the visible transept ; the opposite one is, of course, hidden by the body of the church, and could not therefore be seen in the present view. The student is, however, advised to project this object on the inclined plane, as shown in Lesson IY. (page 72), when the upper portion jected from the plan, and it now only remains to complete it by the addition of the gable. It must be obvious that the gable-point will be immediately over the point where the ridge-line meets the end of the nave in the plan ; and therefore from this point erect a perpendicular, and carry it up between the two lines which represent the edges of the end of the nave. Draw a perpendicular, too, from .the point where the ridge-line cuts the plan of the tower. A horizontal drawn from the gable-point of the transept will cut these perpendiculars, and give the corresponding point in the end of the nave, and in the part of the roof which meets the side of the tower. Produce this horizontal until it meets a perpen- dicular drawn from the end of the ridge of the chancel in the plan, and this will give the distant point in the ridge, and thus complete the projection of the church - 238 THE TECHNICAL EDUCATOR. AGRICULTURAL CHEMISTRY.— V. BY CHARLES A. CAMERON, M.D., PH.D., Professor of Hygiene in the Royal College of Surgeons, Ireland, etc. CHAPTER V— INFLUENCE OF CULTIVATION AND DRAINAGE UPON SOILS. "When crops are grown in a rich field year after year without any manure being applied to it, its soil soon ceases to be very productive. It was formerly the general' opinion amongst agriculturists, and even amongst agricultural chemists, that unmanured land, if heavily cropped, would soon become per- fectly infertile, or barren ; but the accurately conducted inves- tigations of Mr. J. B. Lawes, of Rotliamstead, and the prolonged experiment of the late Mr. Smith, of Lois Weedon, prove that it is not in man’s power to reduce fertile soils to a condition of absolute sterility. Indeed, it would appear that no system of husbandry, however improvident, is capable of permanently deteriorating the productive powers of the earth. Mr. J. B. Lawes and the Rev. Mr. Smith have grown crops year after year for a long period in the same field, without the use of any kind of manure. Nor were the crops obtained very inferior either with regard to quantity or quality. Under ordinary circumstances, however, it is found expedient to restore to the soil, wholly or partly, in the form of manure, the mineral substances removed from it by crops. Tillage, or cultivation, is to a great extent a substitute for manure ; and the less fertilising matter applied to the soil, the greater is the necessity for its thorough mechanical treatment. The quantity of fertilising matter present in most soils is practically in- exhaustible ; but only a minute proportion of it exists in a con- dition in which it can immediately contribute to the nourish- ment of plants. We have already shown that calcic phosphate is essential to plants, and that it is an abundant ingredient of their ashes. Now every soil capable of growing vegetables contains this substance, but chiefly as an ingredient of stones and coarse particles, upon which plants cannot feed. Any one who examines a specimen of clay will see how very little of it is in the state of even coarse powder. It is the very finest powder contained in the soil which supplies the great bulk of the mineral food of plants ; hence any process by which the coarse lumps and particles are pulverised increases the productiveness of the land. It was only by means of thorough cultivation that Mr. Lawes and the Rev. Mr. Smith succeeded in growing crop after crop of wheat in succession, in the same field, and without the use of manure. It would appear that the most exhaustive system of cropping may soon put land out of condition, but cannot affect its fertility. In practice, poor and inferior lands always remain so, whilst a rich soil can only for a brief time be reduced to an inferior condition. If, as Mr. Lawes truly observes, it were possible by any system of cropping to abstract all, or even the greater portion, of the elements of fertility from the ground, there would not now be a fertile field in these countries. Needy landlords and poor tenants would long since have taken every- thing worth abstracting from the fields of these islands. A good piece of land, well manured and sufficiently tilled, produces so many bushels of corn per acre. If the manure be discontinued, and the amount of tillage not augmented, an im- mediate and large decrease in the productiveness of the land results, and in two or three years it goes out of condition. The yield does not, however, continue to decrease, for after a short time it remains stationary for an indefinite period. The amounts of potash, phosphoric acid, and other of the mineral elements of the food of plants are so very large in loams and clays, that it would require centuries of cropping to wholly exhaust them. They are, however, bound up in the rocky portion of the soil, and only a minute proportion of them is annually set free. It is a wise arrangement of Providence that phosphoric acid and potash should be locked np in the soil, and even that the earth should contain such small proportions of these substances. Were it otherwise— were potash, phosphoric acid, and the other ash ingredients of plants supplied in an available form, and in unlimited quantities — the husbandman could not earn his bread by the sweat of his brow, in obedience to the wise fiat of the First Great Cause. It is not a mere accident that the minerals which are least abundant in the soil are the most abundant in plants. In very light soils, particularly those derived from the dis- integration of limestones, the system of tillage without manure could not be carried on for more than a few years, without reducing the yield to an extent that would be altogether un- remunerative. On the rich loams and stiff clays, which usually are very rich in potash and phosphoric acid, thorough cultiva- tion will, without the aid of manure, produce average crops for perhaps more than a century. The maximum of productiveness is, however, attained when the land is both well tilled and abundantly manured. The following figures show the large quantity of phosphoric acid contained in the soil, and the small proportion of it which is annually removed by crops. The soil of a field weighs a + least 100 tons per inch in depth. A good soil contains 0'25 pex cent, of phosphoric acid, or 5 cwt. per inch in depth. A crop of wheat removes from 12 to 15 lb. of phosphoric acid from each acre. If we assume the latter quantity, then an inch of soil would furnish sufficient phosphoric acid for 37 crops of wheat, and ten inches of soil would supply this compound to 370 crops of wheat. Other crops, no doubt, take much more phosphoric acid from the land ; but, on the other hand, the fertilising resources of the super-soil admit of being largely replenished from the stores of phosphoric acid and potash buried in the sub-soil. The chief objects accomplished by the operations of ploiigh- ing, subsoiling, grubbing, harrowing, and digging, are the exposure of the inner portions of the soil to the agencies of light and air. Under these stimulants the inert organic matter is converted into soluble plant-food, and the potash, phosphoric acid, and other fertilisers are abstracted from their stony cases, and prepared for the use of the crop. This mechanical treat- ment is also most beneficial in deepening the soil, whereby the roots of the plants grown in it can penetrate to greater depths in search of their food. Good cultivation also gets the land into fine tilth — that is, it reduces its particles to a tolerably uniform condition— increases its porosity, which augments its capacity of absorbing ammonia and carbonic dioxide from the air — and actually reduces a small portion of the soil to the finely pulverulent condition in which it proves most useful to vegetation. The sub-soil is poorer in organic matter than the super-soil, and it contains in general less 'potential or active phosphates, potash, and other mineral foods of plants. For these reasons it is not desirable to bring up to the surface too much of the sub-soil ; but it is useful to commingle annually a small quantity of the sub-soil with the surface one, so as to compensate for the loss of ithe fertilising matters which are continuously removed from the latter. A winter’s action upon the crude sub-soil brought close to the air will render some of its dormant fer- tilising constituents immediately available for the use of plants. It is most desirable that the mechanical treatment of the soil should not be deferred until spring. Autumn cultivation is now becoming the rule, and not, as was the case formerly, the exception. Land intended for green fallow crops should be ploughed very early in the winter, so as to render it more accessible to atmospheric influences. In the spring, grubbing is preferable to cross-ploughing, as it more thoroughly pul- verises the soil. It is surprising how greatly the yield of turnips and mangolds is affected by cultivation. If the land be not thoroughly prepared for these crops, no amount of manure ordinarily applied will produce a large crop. As for the cereals, we have already shown that good crops may be pro- duced without any manure, providing the tillage of the soil is thoroughly performed. Indeed, the term manure is derived from the Latin words manus, the hand, and opera, work, or hand- labour; and therefore, even according to etymology, manure and cultivation are equivalents. Thorough drainage is one of the most important means of increasing the productiveness of soils. Excessive moisture acts injuriously by keeping the land cold ; the sun’s heat, instead of being usefully expended in warming the soil, is wasted in evapo- rating the superfluous water contained in it. 3,700 tons of water often fall upon an acre. In order to convert this liquid into steam or vapour, the heat derived from the combustion of 550 tons would be required. In the case of stiff, nndrained clays, the large quantity of superfluous water which annually descends upon them is chiefly got rid of by evaporation — -a process effected by robbing the soil of the sun’s heat, which is TECHNICAL EDUCATION ON THE CONTINENT. 239 so indispensably requisite for the maintenance of the vigour of the cultivated plants. Heavy, tenacious loams and clays are rendered more porous and friable by drainage ; and after that operation their tillage can be performed with less difficulty and expense. Undrained soils are converted by heavy rains either (in the case of clays) into adhesive pastes, or (in the case of light lands) into puddles. On the contrary, a well-drained field will act under such circum- stances like a water-filter, through which the water readily passes without effecting any important alteration in the condi- tion of the filtering materials. Undrained stiff soils, when sub- jected to heavy rain, and then to strong heat, acquire a crust soj hard that it is difficult to penetrate it. We have often seen seeds and potato-cuttings so firmly baked up in an undrained tenacious clay, that their vital powers were quite destroyed. Unwelcome semi-aquatic plants often spring up in land which is badly drained, and they frequently succeed in overcoming and displacing no inconsiderable proportion of the plants under cultivation. When a marshy field is drained, the useless semi- aquatic plants spontaneously disappear. The organic matter in wet soils decomposes very slowly, because of the exclusion of air. When by drainage the soil is rendered porous, the atmospheric oxygen penetrates to the organic matter, and converts it more expeditiously into water, carbonic dioxide, and ammonia — the substances that furnish to the vegetable the greater portion of its food. Every farmer knows that a wet field requires more manure than a drained one ; in the former the manure remains much longer in an inert condition. The water drained off from soils contains fertilising matters, more particularly compounds of nitric acid and sodium salts. The important fertilising substances, ammonia, potash, and phosphoric acid, are retained by the jsoil with great tenacity ; and, on the whole, the water which passes off from cultivated soils carries with it but very small quantities of the food of plants. On the other hand, the soil is continuously receiving ammonia and nitric acid from the atmosphere. TECHNICAL EDUCATION ON THE CONTINENT. — YII I. BY ELLIS A. DAVIDSON. TECHNICAL EDUCATION APPLIED TO FEMALES. Whatever has been said of the unpractical character of the education of our boys refers with equal force to our girls, whose instruction in this country has until recently been of the most flimsy character, whilst in Germany it has always been recognised as in every way of equal importance with that of males. It has been shown that technical education is that kind of instruction which shall fit the student for the business of life ; and this applies to girls as well as boys. Is it not just as necessary that the one should be educated for her position as the other ? Assuredly females of every grade have sooner or later to take their share in the work of life ; and therefore, whilst we are educating our boys, who arc to carry on the work of this great country in the coming period, it is our bounden duty to extend equal care to their sisters : otherwise, although we shall render our future men more intellectual, and thus qualify them to elevate their positions, we shall be laying up for them a store of unhappiness, for as they become more enlightened, they will all the more require that those whom they may select as companions in life should be able to appre- ciate their acquirements and to sympathise with their labours. Technical education on the Continent, then, is brought to bear upon females as well as males. And here, no doubt, many in this country, where the neglect with which female education has been treated is a national disgrace, will ask, “ What can females learn ? ” For be it understood that, in order to account for their own selfishness and ignorance, it has been a fashion amongst some to speak disparagingly of female intellect. It is not within the scope of these papers to enter upon the discussion of this point, especially as most of our best teachers declare that their experience shows them that no difference in the capability of receiving instruction exists between pupils in schools of either sex ; whilst the desire to learn evinced by girls has always equalled, and often surpassed, that of boys. That the action of the female brain takes a different direction to that of the male there can be no doubt ; and is not this a beneficent ordination of an Allwise power who has assigned special duties and spheres of action to each? and thus it be- comes the province of practical education to qualify them (as far as instruction can qualify them) to fill ably (as religious education should fit them to fill worthily) the duties of their position, whether as wives, mistresses, mothers, teachers, nurses, servants, or workers in any branch of industry. It has been wisely said, “ Man’s home is the world, woman’s world is her home but we must add that proper — we may call it technical — education is required for the efficient discharge of the relative duties of each ; and further, that as many females are compelled by circumstances to make the world their home before they have a home in which to establish their world, as many have to enter the field of industrial work, it is necessary to inquire how these may be best fitted for the sphere in which they are to be placed. Nor are the mere subjects which are to be taught to girls the only matters which are to be considered. The reasoning and practical tone given to the mind, the general training, the regularity of habits, and the economy of daily life, are all most important in the education of those who are to be the wives of the present, and mothers of the future generation ; and if we would have the influence they will assuredly exert productive of good, we must let their instruction be such as will fit them to fill the important positions they are destined to occupy. It is on his mother’s knee that the child — “eyes raised to heaven, and small hands folded fair” — is taught to raise his heart to “ Him who all things sees it is whilst walking with her that he learns to turn aside, lest he should injure the worm so marvellously made, and to watch the opening of the budding leaf. It is of her he asks, “ Mother, what is the sun ?” and to her he says, “ What is there beyond the skies ? ” And then she reads to him out of this fair book of Nature ; and the instruction she gives to him is wrapped in veneration for that great power, whose law, which governs all around us, is science ; and the boy starts as a student with the best of all incentives to the acquirement of knowledge — a love of inquiry. Thus, then, does woman lay the foundation of all education, and is the pioneer for all future teachers; and, therefore, no system of primary or technical education can be complete unless it is extended to females as well as to males. THE TRADE SCHOOLS AT STUTTGARD. The name by which these schools are known in Wurtemburg, “ Fortbildungschulen,” really implies their purpose better than any single word in our language : they are really schools for further education of persons who wish to continue their studies after they have left school for business. For the full development of the purpose the schools are divided into the following departments : — 1. Evening schools, for pupils engaged in business in the day- time. 2. Sunday classes, for youth of both sexes, and adults. 3. Day school, for girls and women. 4. Drawing and modelling school, open throughout the whole day during the week. Pupils on entering have their choice of attending such classes as they may deem necessary for their occupation, provided their previous education has fitted them for taking only special sub- jects ; but pupils under sixteen must submit to the guidance of the teachers as to the branches which may be deemed neces- sary for them. Pupils attending school, whatever their age, must in every way conform to the regulations ; it being considered that the object of education (so eloquently expressed by the German word hildung, which means to “shape,” or “form”) is not merely to give literary or scientific instruction, but to form the habits and discipline the mind ; and thus these schools fit the pupil for the business of life in other ways than in intellectual improvement. Breaches of discipline are, after repeated warn- ings, punished by dismissal. Pupils under sixteen years must present a written introduc- tion from their parent, or other respectable person, who will be required to sign a document, undertaking to be responsible for the proper observance of the rules on the part of the pupil. The course of instruction, on the evenings of the week, com- prehends the following subjects, and is carried on during the winter months only, with the exception of the advanced drawing and modelling classes, which are continued throughout the year ■ 240 THE TECHNICAL EDUCATOR. Hrs. p. wk. Modelling in clay and was . 4 Free-liand, Figure (from copies and casts), Land- scapes, etc. . . .6 Free-hand Drawing for Wood and Copper-plate Engravers 4 Ornamental Drawing . . 6 Geometrical Drawing . . 2 Trade Drawing (for example) : Drawing for Carpenters, etc. 6 Drawing for Turners, Stonemasons, etc. . . 6 Drawing for Locksmiths, Braziers, etc. . . 6 Hrs. p. wk. Mechanical and Architectural Drawing . . . .6 Solid Geometry & Projection 4 Writing .... l.i Mercantile Correspondence . 14 Book-keeping . . . 14 Arithmetic . . . .3 Geometry . . .3 Mechanics . . . .3 Physics .... 3 Chemistry . . .3 French — - Elementary . . . 4-i Advanced . . .3 Before pupils are admitted to the modelling' class, they must have acquired a certain standard of power in ornamental and figure drawing. The pupils who practise wood and copper-plate engraving find their own materials and tools. The pupils in the geometrical drawing class are expected to have previously mastered the elements of practical geometry, the use of mathematical instru- ments, etc., and must either have attended, or must in the same term attend, the class for projection. In the “trade drawing” department the pupils are taught designing, and working out of the special drawing used in their branch of trade, to make or work from drawings. In the pro- jection class the instruction enables the pupils to project elevations from plans or given data, to make sections, develop- ments, etc. This branch is, in fact, the basis of all mechanical, architectural, and engineering drawing. In the class for the study of mechanics, the entire theories upon which machines are constructed are studied; and in the mechanical drawing class the designs are drawn to a given scale, together with details and working drawings. The instruction in arithmetic and geometry is adapted to practical purposes, and every opportunity is taken to show their application in the other studies. The lessons in physics and chemistry, too, are arranged with a view to their use in trade. DAY SCHOOL FOR GIRLS AND WOMEN. Hrs. p. wk. (a.) General Course — Arithmetic . . .2 Trade Rules aud Corre- spondence . . .2 Book-keeping . .2 Writing . . .1 (b.) Advanced Course — English Language • 3 French Language . . 3 German Language, etc. . 2 Geography and History . 2 Hrs. p. wk. Natural History, includ- ing also the knowledge of the food products used in a household, aud domestic economy 2 Physiology as applied to health and sanitary principles . . . 1^- Drawing and Painting . 3 Pattern Drawing and Designing . . .3 Besides the above-named, classes are formed for other subjects when a sufficient number of names are entered to guarantee the attendance. The teaching staff in the Stuttgard Fortbildung Schools is composed of professors of the highest standing, amongst them being three ladies. The following statistics will give some idea of the extent of the operations of this school : — - Number of pupils : — In the Evening School .... 32S with 20 teachers. ,, Sunday Evening School . . 4S1 ,, 23 „ ,, Commercial Evening School 178 „ 16 ,, ,, Female Evening School . 130 ,, 10 ,, 1117 60 ,» TRADE SCHOOL AT ULM. The Trade School at Ulm, though based on the same scheme as that of Stuttgard, has, like all the other schools, its individual peculiarities; and, therefore, in pursuance of the object in view — viz., to show the systems of various technical schools — a brief notice of it is here given. The classes begin in October, and close at the end of April ; but those for the study of the French and English languages are continued throughout the year. The hours of attendance are, for the general studies, from 8 to 9.30 in the evening ; and for languages, from 7 to 8 o’clock in the morning during the winter months, and from 6 to 7 in the summer. Besides this, there are art-classes open all day in the winter, to enable working men who may not be fully employed at that season — such as carpenters, masons, slaters, etc. — to improve themselves in the studies connected with their respec- tive occupations. The school consists of two departments — viz., the Commercial and the Trade Schools. Pupils having paid the fees for the commercial school are free to attend the trade school, should the arrangements of the lessons permit, without further pay- ment; students in the trade sohool are admitted free to the German classes in the commercial school, and, on the pay- ment of a very small extra fee, to the English and French classes. Below is given the time table in the Trade School at Ulm. The number of students attending the school at Ulm averages 739, under the care of 22 teachers. This teaching staff is perhaps the smallest of any in the great group of schools — - giving an average of rather more than 33 pupils to each teacher whilst it will be seen that, in the Stuttgard school, 1,117 pupils are taught by G9 teachers, or rather less than 17 to each. Seventeen pupils to each teacher seems to be about the average, throughout this class of schools in Wurtemburg. TIME-TABLE IN THE TRADE SCHOOL AT ULM. Monday. Tuesday. Wednesday. Thursday. Friday. Saturday. Drawing. Every Evening from 8 to 10. Free-hand Drawing and Modelling. Linear Drawing. Free-hand Drawing and Modelling. Free-hand Drawing and Modelling. Linear Drawing. Free-hand Drawing and Modelling. Free-hand Drawing and Modelling. Linear Drawing. Free-hand Drawing and Modelling. Trade Department. Elementary Course, 8 to 9.30 Evening. Trade Arithmetic. (Course A.) Trade Arithmetic. (Course A.) Business Compo- sition and Cor- respondence. Geometrical Drawing. Trade Arithmetic. (Course B.) Geometry. Trade Arithmetic. Business Composition & Correspondence. Geometry. Advanced Course, 8 to 9.30 Evening. Chemistry. Descriptive Geometry. Business Correspondence. Physics. Trade Book- keeping. Chemistry. Descriptive Geometry. Physics. Commercial Depart- ment. 7 to 8 Morning. English (A). French (B). English (B). French (A). English (A). French (B). English (B). French (A). English (A). French (B). English (B). French (A). 8 to 9.30 Evening. English and French Correspondence. Commercial Arithmetic. General Office Instruction. Commercial Arithmetic. Exchanges. Commercial Arithmetic. Office Instruction. German Literature. Commercial Arithmetic. APPLIED MECHANICS. 241 APPLIED MECHANICS.— V. BY BOBEET BTAWE1L BALL, LL.D,, Astronomer-Royal for Ireland. HYDRAULIC MACHINERY. The machines which may be classed under this heading contain some of the most beautiful examples of modern engineering skill. Water has been applied with the greatest success as a means of transmitting power for a great variety of objects. For this purpose its remarkable property of incompressibility is peculiarly adapted. We do not mean to say that water is absolutely incompressible ; but it may practically be so con- sidered, for the amount of com- pression it undergoes is exceed- ingly small. The principle and construction of the hydraulic press has been already fully explained in the pages of the Popular Educator (see “Hydrostatics” — I.,Vol. II., page 366). To this account we therefore refer the reader for a full description of this powerful machine. We shall mention one or two important applications of the hydraulic press, and we shall then consider some other ma- chines which are worked by water at high pressure. The first example we shall take is the application of the hydraulic press to the manufacture of leaden tubing. The quantity of lead annually consumed in making gas-pipes and water-pipes is enor- mous, so the aid of machinery has been called in whenever pos- sible. The process is one of great interest. The tubes are forced by pressure out of solid lead, which is warmed up to a certain temperature, though still far from being melted. The apparatus by which this is done is shown in Fig. 1. p q is the hydraulic press. This consists of a very massive iron cylinder, into which the piston, b c, fits. A is the pipe by which the water is forced into the space above the piston. The pumps which inject the water are not shown in the figure ; they are worked by a steam-engine. The piston is thus pushed downwards with enormous force. The plunger is narrowed at the end, and turned so as to fit tightly into a very powerful iron cylinder, g h. It is in the space D, in the hollow of this cylinder, that the lead is placed from which the pipes are to be made. This cylinder is filled by pouring in molten lead, which is then allowed to solidify. Round this cylinder is a second cylinder, k l, containing a fire for the purpose of keeping the lead at the temperature required. This lower cylinder, contain- ing the lead, is connected with the upper cylinder, p q, by means of very powerful framework, so that when the pressure is exerted the piston must be forced down into d. The most essential feature of the apparatus is shown at e. At o is a hole in the bottom of the cylinder, which is carefully turned, and is exactly the external size of the pipe required. A small arch is shown at E ; from the top of this a mandril descends down through the hole. This mandril is exactly the internal diameter of the pipe, so that when the lead is forced between the mandril and the cylindrical hole, it is formed into the required dimensions. Under the enormous force with which the lead is compressed it becomes as yielding as putty is to an ordinary pressure. It appears very surprising at first to find that the lead is forced around the sides of the arch at e, and yet that the pipe is perfect and bears no traces whatever of the division which it must have undergone. In the earlier stages of the manufacture it was not believed that the lead would be sufficiently plastic, and consequently the mandril was fixed directly into the plunger, c, so as to avoid the difficulty of the arch. It is, however, found that equally good tubes can be made when the mandril is supported by the arch, and so this more convenient arrangement is adopted. It is very remark- able to see the lead pipe rapidly flowing from the bottom of the 16 — Vol. I. cylinder. It is thus made in lengths, each of which contains one charge of the vessel, G H, called the container. By altering the size of the hole and of the mandril different sizes of.pipes can be produced. Hydraulic pressure is especially convenient for the purpose of transmitting power. Water can be conveyed through pipes to any distance, and if force be employed in compressing the water into a pipe at one end, the water will exert force to get out at the other end. Hence we may consider that the water is just the means of transmitting the power from one end of the pipe to the other. For this purpose water is more convenient than steam, for though the steam could be conveyed through pipes, yet special means must be employed to keep the steam hot enough to prevent its condensation. Air is sometimes used for the purpose of transmitting power when from any cause the use of water is inconvenient. As an example of this application of hydraulic power, we shall describe the machinery which is erected at Waterloo Dock, Liverpool, and at various other places throughout the country. The machinery at the place mentioned is on a very large scale, and has a great number of functions to fulfil : the dock-gates have to be closed and opened, the vessels have to be unloaded, the corn has to be raised and carried about to different parts of the immense granaries, which are capable of containing many thousands of tons. These different duties demand special machines in different parts where the work is required to be done. To accomplish this it would be very un- economical of power, and otherwise inconvenient, to have a special engine for each machine. Most of these machines are only worked occasionally : for example, to open the dock-gates an engine of very considerable power would be required, but the gates only require to be opened now and then, and it would be very undesirable to have to maintain a fire all day for the purpose of opening the gates a few times during the twenty- four hours. Similarly, the other machines are only worked intermittently, and out of all the machines that are employed, perhaps more than a quarter are never simultaneously in action. The case, therefore, is this : an engine, one-fourth of the power which would be necessary to turn all the machines together, will yet be sufficient for ordinary purposes, provided we have convenient means of applying its power wherever it may be wanted. Some of the machines require a great deal of power, others not so much, and therefore we also require to save up the power of the engine when working the small machines in order to have enough when a greater exertion is demanded. Water affords a most convenient means of obtaining these objects. An engine of sufficient power supplies the energy ; this energy is stored up by the engine in what is called an accumulator, and from the accumulator it is distributed by means of water-pressure to the different machines that require it. The accumulator is shown in Fig. 2. w is an immense weight of about ninety tons. There are guides intro- duced in order to restrain its motion to sliding up and down vertically, and prevent it from falling to one side. These guides are not shown in the figure. At the bottom of this weight is a plunger, p, which works tightly into a cylinder, A B. This cylinder is kept filled with water by the pipe c ; the water is pumped into it by very powerful force-pumps, to work which the whole power of the engine is employed ; forcing water through the pipe c into the cylinder is, in fact, the duty of the engine. Let us suppose a cock on the pipe d is turned off, then the water, when forced into the cylinder, must raise w. It is prevented from pushing ^ p entirely out of the cylinder by a self-acting contrivance. When the weight w ascends to a certain point it acts on a T lever which closes the valve supplying steam to the engine, and therefore stops the entry of water at c. Hence the engine will i be constantly striving to keep the cylinder full. The pipe D communicates with all the machines throughout 242 THE TECHNICAL EDUCATOK. the docks which are to be worked by the pressure of the water. The water is at an enormous pressure in the cylinder. We can easily calculate its amount when we know the diameter of the cylinder and the weight of w. Let us suppose that the diameter of the cylinder is 10", and that the load w is 90 tons. The area of a circle is iy x (radius) 2 . From this it will be seen at once that the area of the end of the plunger is 22 + 7 x 25 = 78 '5. Hence we have a pressure of 90 tons upon a surface of 78‘5 square inches, and therefore the pressure on each square inch is 93 -r- 78'5 = 1T5 tons. This enormous pressure is doubtless to some extent lost by friction through the ramifications of pipes by which the water is distributed ; but we may probably assume that in general the pressure must be nearly a ton on the square inch. At this enormous pressure a very little water does a very great quantity of work. Let us calculate how much work is done for every pint of water that leaves the cylinder. A pint of water contains 35 cubic inches ; hence, since the area of the plunger is 78'5 inches, the weight must descend 35 yg -5 = 0 45 inches, in order to expel a pint of water along the tube d. How, how many units of work has the cylinder exerted? This is to be found by multiplying its weight in pounds by the distance through which it descends in feet. 0-45 -T- 12 = 0-0375 is the distance in feet, and 2240 x 90 = 201600 is the weight in pounds, hence the number of units of work is 201600 x 0-0375 = 7560; that is, it would raise 7,560 pounds through one foot, or one ton through 756O 4- 2240 = 3' 4 nearly. Hence, by the consumption of one pint of water a ton weight can be raised in any part of tha building through a distance of more than a yard. The mode of working the machine will be easily understood. The weight is constantly rising or falling, rising when no largo machines arc drawing off the water through D, and falling when the machines are using the water faster than the engine is sending it in. Thus, when little water is used it is stored up until there is a greater demand for it. The machines which are worked by the power of the water are of different kinds. We shall say a few words about the con- struction of the most important of them. The corn is taken out of the vessels by the use of machinery. An arm projects from the warehouse, which supports an apparatus by means of which little buckets upon a band descend into the hold and return filled with corn. This corn, when the buckets reach the top of the arm, is discharged into a shoot that carries it into the store, and the empty buckets descend for another load. By this contrivance a vessel is unloaded with great expedition. This machine is worked by the pressure of the water. The com is also hoisted from the bottom of the warehouse to the top by means of an hydraulic hoist. • This is a very remark- able machine, and a description of it is the more necessary, as it has come into very extensive use. The principle of the hydraulic hoist may be understood by Fig. 3. This diagram shows the essential principle of the machine, reduced to as simple a form as possible for the purpose of explanation. In consists essentially of an hydraulic press, and two pulley-blocks, one of which is attached to the cylinder, and the other to the plunger. The corn is raised in loads of about a ton, from the bottom of the store up to tho Fig. 4, top, through, perhaps, a height of 60 feet or more. It is, there- fore, necessary to pull in the chain which is attached to the lift through a length of 60 feet. If we have a pair of four-sheave pulley blocks, and are raising weights in the ordinary way, it is evident from the account we have already given in Lesson II., that 8 feet of chain must be pulled out for every 1 foot that the load is raised. Now, if the pulley-block be so well constructed at the axles of the sheaves that there is as little friction as possible, the weight will overhaul ; that is, when lifting a weight, if we ■> 4 6 s release the lifting chain the weight will descend. It follows, then, that for every foot the weight descends 8 feet of chain will be pulled in between the blocks. For this to occur wo must have, as already explained, less than half the total force lost by friction. Supposing, now, there were a weight of 8 cwt. being raised, a force of 1 cwt. would be necessary to lift it without friction, and about 2, or a little less, with friction ; but suppose the weight to descend, what strain can it produce on the lifting chain ? It would produce a strain of 1 cwt. in a frictionless block, but owing to friction the actual strain is less than this. Let us suppose it to be £ cwt., then the weight of 8 cwt. descending will raise i cwt. 8 feet for every foot it descends. Hence we learn that, if the blocks of a pair are forced asunder by a great pressure, the chain will be drawn in through a distance 8 times as great as the distance through which the blocks are forced apart, and a strain will be exerted upon the chain thus drawn in, which we may take as about one-sixteenth of the force pushing the blocks asunder. Let us now apply these considerations to Fig. 3. The two blocks are shown at D and E ; but the chain is not introduced, for the purpose of keeping the figure clear. The block E is. firmly attached to the cylinder, and the lower block is forced away from it by admitting water at high pressure through the pipe A. The chain is attached to the upper block at o, it then passes down under the pulley 1, over 2, under 3, over 4, under 5, over 6, under 7, and over 8 ; to the free end hanging over 8 the lift is attached. Now, supposing the blocks be forced asunder with a pressure of about 16 tons, it is evident that the free end of the chain will be drawn in with a force of one ton, and will, therefore, be able to raise a load of 1 ton. If the stroke of the plunger be 8 feet, the lift will be raised 8x8 = 64 feet. As the pressure on the water is very great, the cylinder need not be very large in order to produce sufficient pressure. There is considerable loss of power by friction in this arrangement ; but its com- pactness and convenience quite outbalance this slight disadvantage. The hydraulic- hoist has but few parts, it cannot easily go out of repair, and it can be applied wherever a pipe can be laid to carry the water to it. After the load has been raised the water has done its work, and a valve is opened to permit its escape. The Weight of the lift then pulls the chain, this raises the plunger and expels the water, and the apparatus is ready for another load. The corn, when raised by the lift, is poured into a hopper, from which it descends to a weighing machine, which weighs it in loads of nearly a ton at a time. It is then, carried by machinery to that part of the store in which it is to remain. The machinery by which this distribution is effected is- very interesting. A large band, about 18" wide, runs along the top floor of the building. This band is supported by rollers, and is worked by a small water-pressure engine. A view of a water-pressure engine, suitable for such a purpose, is shown in Fig. 4. There are two small cylinders resembling steam cylinders, and the water is admitted to the sides of the piston alternately, just as the steam works the piston in the steam cylinder. These cylinders oscillate, and the rod of each is connected with a crank on the horizontal shaft. The cylinders need only be of small dimensions, for the VEGETABLE COMMERCIAL PRODUCTS. 243 pressure of the water vastly exceeds any steam-pressure which could be used. The machine shown in Fig. 4 has been constructed by Messrs. Ramsbottom, of Leeds. We cannot do better than give the account of its use in the makers’ own words : — “ The great requisite in water machinery is to maintain a constant and equal outflow to avoid concussion, for when the momentum of water has been generated in a given direction, and its motion is suddenly intercepted by a barrier in the form of a stop-tap, or imperfect valvular action, the result is not only destructive to the machine, but represents a considerable expenditure of mechanical effect. For water-engines are nearly always double acting, and in such eases the valvular action is duplicate, and we have made it a matter of the greatest import- ance in valvular construction to open and close the supply and exit ports slowly, and in such manner that the feed-way leading to one piston shall be in full effect when the other is absolutely closed at the termination of its stroke, and thus one set of feed and exit ways are dying gradually away to termination of stroke as the other set are opening towards full effect on return-stroke of its piston ; and thus a valvular action is obtained, which not only avoids concussion but the loss of effect by avoiding the counteraction of pressure and untimely supply. We have several hundreds of water-engines employed for various kinds of work, with valvular action, as above described, and their efficiency, compactness, and convenience clearly show how much the advantages of hydraulic power are under-estimated in many of our largest towns and cities, where numerous mechanical operations might be better performed by this than any other kind of power whatever. A constant supply and adequate pressure in London would be of immense value, for unlike steam this power is neither dangerous nor offensive, but is con- tributive to health and cleanliness ; and as in many cases the water passes directly in a pure state from the engines to the sewers, it forms a valuable flushing agent after use. Most machinery of a domestic character could be driven by water power, thus avoiding much personal attention ; and the folding, pressing, and raising of goods of various kinds, as well as the working of hoists, the grinding of coffee or drugs, the driving of book-printing machines, and other uses too numerous to mention, attest the importance of soliciting increased public attention to this most natural of all the sources of motive power.” On the shaft, which is turned round by a water-power engine, a large pulley is fastened. This pulley is enveloped by the band which runs on the rollers, and when it revolves it gives the band motion. After leaving the weighing machine the corn passes into a second hopper, from an opening in which it is poured out upon tho rapidly- moving band, and is carried along by the band at a prodigious rate. About 50 tons of corn can be carried on one of these bands in an hour. By an ingenious arrangement the com can be thrown from one band upon another at right angles, and can thus be made to turn round a corner. By means of shoots it can be delivered into any corner of the building. There are many other applications of water-pressure hardly less interesting than those we have been considering; but our space will not admit any further discussion of them. VEGETABLE COMMERCIAL PRODUCTS, vm. fleshy fruits ( continued ). The Lemon ( Citrus limonum, L.). — This plant is a native of the Himalaya mountains. It appears to have been brought to Europe about the time of the Crusades. The lemon is now cultivated in all warm climates. The principal supplies to our markets are received from Italy, Spain, Portugal, Trieste, and South Tyrol. The juice and rind are both officinal. Lemon- juice is peculiarly grateful and cooling, and is much used in the preparation of effervescing draughts, and as a beverage in febrile complaints. The juice owes its sourness to the presence of a peculiar acid, called citric, which is easily separated by chemical means. It is one of the most powerful anti-scorbutic medicines known. That dreadful disease, the scurvy, has hardly been known in our navy since limes and lemons were ordered by law to be carried by all vessels sailing to foreign parts. There are several other species of Citrus which are largely imported ; as, for instance, the Citrus Iwnetta, or lime, which is about one-third the size of a common lemon, and which is ex ported in the green state, in order to preserve the delight! aroma of its rind. The preserved lime comes to us in smatf kegs of about 7 lb. weight. The Citrus Bergamice, or bergamot, bears a fruit closely resembling the lemon. As a preserve it is used as a substitute for citron, but its chief value lies in the oil obtained from it — the well-known bergamot so much used in perfumery. Grapes ( Vitis vinifera, L.). — The fruit of this vine not only furnishes us with a variety of wines, but is itself imported into this country both in the fresh and the dried state. We receive comparatively few grapes in a fresh state ; about 300 tons arrive every autumn from Sicily, Lisbon, and Hamburg. They suffer in their flavour from being closely packed, and still more from the use of sawdust as a packing material. Raisins, or dried grapes, are far more abundantly imported. These are prepared sometimes by cutting the stalks of the bunches half through, and leaving them suspended to the vine until suf- ficiently dry, which in this state they rapidly become, without losing any of their fine flavour or bloom ; the usual mode is to expose the grapes to the sun and air for a while, then lay them out in rooms, and sprinkle them with water in which soda or potash has been dissolved. This causes the sugar of the grape to candy, forming those little sweet lumps so well known in the common raisin. The differences amongst the raisins are caused entirely by difference in their mode of culture or curing. Thus we receive stoneless sultana raisins from Smyrna, in Turkey ; fine muscatels, or sun-dried raisins, in bunches with the stalks still attached, from Malaga ; Damascus raisins, much larger than the sultanas, stoneless also, and preferred to the Smyrna raisins, from Damascus ; and lastly, the ordinary raisins from Valencia, and from the same countries and ports where the grape L cultivated. Currants are only the raisins of a small grape, also deficient in seeds or stones, growing in huge bunches, often as much as eighteen inches long, and of proportionate breadth. They are trod into large casks, and exported. Enormous quantities are cultivated m the Grecian islands, principally in Corfu, Zante. and Ithaca. Originally, Corinth was the principal place where they wore raised, whence the name “ Corinths,” from which the word “currants” has been derived. In 1867, 1,002,366 cwt. of this much-esteemed fruit were imported into the United Kingdom, and about 392,322 cwt. of the other and larger varieties of raisins. Fig ( Ficus carica, L. ; natural order, Urticaceas) . — ’Phis is a very valuable and extensive genus of tropical and sub-tropical plants, some of the species attaining an enormous size, as the Ficus Indica, or celebrated banyan tree. The fig tree, originally a native of Asia, now flourishes in Southern Europe, on all the islands in the Mediterranean, and especially in Asia Minor, Northern Africa, and the Canary Islands. The fig, considered botanically, is a very remarkable form of fruit, being just the reverse of that of the strawberry, in which the minute pistils are scattered over the exterior of the enlarged succulent receptacle ; whereas in the fig the inflorescence or position of the flowers is concealed within the body of the fruit. There is sometimes a failure in the fig crop, when it is not properly attended to, in consequence of the pistils of the florets not becoming duly fertilised by the pollen of the stamens. It i? supposed that this operation is caused naturally by the entry of insects through the very small orifice which remains open in the flowering fig ; the fig-growers therefore adopt an artificial means of ensuring fertilisation — a small feather is inserted and turned round in the internal cavity. This operation is called “ca- prification.” Figs are sent to us in large quantities from Turkey and Greece — those from Turkey being the best. The fig, after having been gathered from the trees and dried in the sun, is usuallv packed in square or circular boxes, the latter being called “drums.” A few bay leaves are put upon the top of each box, to keep the fruit from being injured by a grub, which feeds on it and is very destructive. The Maltese figs are very good, but those which come from Smyrna, called “Eleme,” or “Elemi,” are the best. The fig is nutritious, laxative, and demulcent, acting gently in cases of habitual constipation. Roasted and split it is some- 244 THE TECHNICAL EDUCATOR, times applied to gum-boils and other circumscribed maturating tumours. It was used by Hezekiah as a remedy for boils 2,400 years ago, (See Isaiah xxxviii. 21.) The annual import of figs into the United Kingdom is upwards of 700 tons. Prune ( Prunus domestica, variety, Juliana ; natural order, p.osacece). — Dried plums, under the names of prunes and French plums, form an important article of commerce. The prune is the Julian variety of the common plum dried in the sun ; the prunes are then thrown together and pressed into barrels. We receive them in large quantities from France. The imports in 1860 amounted to nearly 300 tons. Prunus domestica, variety Catlierinea, is the French plum or table prune. These are more carefully prepared for market. They generally come over in very elegant boxes called cartons, into which they are neatly packed one by one. In 1851 about 90 tons were im- ported. The Date Palm ( Phoenix dactylifera, L.). — This palm has been known and prized from the ear- liest antiquity ; it is frequently referred to in the Bible. The fruit is very nourish- ing and wholesome, and grows in bunches weighing from twenty to twenty-five pounds. Every part of this tree is useful. Its hard wood is employed for building ; its leaves are made by the natives into mats, baskets, and drinking bowls of great neat- ness ; its seeds are ground to make oil; and its fermented sap forms an excellent wine. In Corsica, Sar- dinia, and in Southern Greece the date palm is planted only as an ornamental tree, as its fruit does not mature in these parts, or ripens only imperfectly. In the very warmest districts of Spain, around Valencia, the fruit comes to perfec- tion, and is exported. The date palm is indigenous to Arabia and Northern Africa, where it is very abundant. In those countries plantations of these trees are sold as estates, and are often the wedding portion of the bride. In some parts of Arabia this palm sometimes forms almost impenetrable forests when neglected by the Arab of the desert, who usually considers every kind of cultivation beneath his dignity. More frequently, how- ever, it is found in a solitary state near a spring, thus present- ing to the thirsty traveller a welcome signal, which assures him of water for refreshment, and of a friendly shade for repose. The best dates come to U3 from Tunis vid Marseilles. The quantity annually imported into England is from ten to twelve tons. Pomegranate ( Punica granatum, L. ; natural order, Myrtacece). — A small evergreen shrub, resembling a myrtle, with numerous slender spinose branches ; leaves opposite, entire, lanceolate, bright green, and sessile ; flowers large, terminal, and rich crimson in colour. The fruit is about the size of a large poppy head, and similarly shaped ; its rind hard, leathery, and beautifully coloured ; when ripe, golden- yellow, with a rosy tinge. When the rind is broken, the interior of the fruit is found to be filled with numerous seeds, each enveloped in a rose- coloured pulp, packed together in two rows, with partitions of pith between them, and closely resembling red currants. There is scarcely a part of the pome- granate that is not either useful or agree- able. The pulp of the fruit is refreshing to persons suffering from fever. The seeds and flowers dried form a valuable medicine, and are used in dyeing, and the rind is em- ployed in tanning and preparing the finer kinds of leather, as the morocco, so much used for bookbinding. The pomegranate is a native of Northern Africa, Syria, and Persia, but it is now naturalised in the warmer parts of Eu- rope, the West Indies, and the Southern States of the American Union. It was known to the ancients, is mentioned by Homer, and also frequently referred to in the Bible. We receive annually a consider- able number of chests of pomegranates from Portugal, and some- times from Barbary. This tree is frequently cultivated as much for the beauty of its flowers and foliage as for its fruit. Tamarind (Tamarindus Indica, L. ; natural order, Legu- minosce). — This is a large tree, with spreading branches, and abruptly pinnate leaves, the leaflets closing in the evening or in cold, moist weather, like those of the sensitive plant. The flowers are in simple racemes, the petals yellowish, variegated with red veins ; these are succeeded by an oblong, compressed, one-celled, brittle, brown pod, from three to four inches in length, which encloses from six to twelve brown, flattened, hard, polished seeds, enveloped in a soft pulp, the whole being held together by a number of thick root-like fibres which pene- trate it in all directions. The tamarind is common in the East Indies, where it is indi- genous, and grows in great perfection. It is now introduced THE DATE PALM. COLOUE. 245 and extensively cultivated in the West Indies and in South America ; but the fruit there is not equal to the East Indian, having much less saccharine matter in the pulp. The tamarinds from the East Indies are darker, have a larger and sweeter pulp, and can be preserved without sugar ; those from the West Indies require sugar, and are sent over preserved in a thick saccharine syrup. The tamarind pods are gathered when ripe, a fact known by their brittleness ; the fruit is removed from the pod, placed in layers in a cask ; boiling syrup is poured in ; and when the cask is filled, and its contents have cooled, it is headed down for exportation. In tropical countries the tamarind is much esteemed for its cooling qualities ; its taste is acid and agreeable, and it assuages thirst. Tamarinds are principally employed in this country to form cooling medicinal drinks. Large quantities arrive annually from the East and West Indies. Banana ( Musa sapientum, Tournef. ; natural order, Musacece). — This may be called a stemless plant, for its . gigantic leaves, with their long petioles, are sheathing and imbricated at their base, and form, by their union, a spurious trunk, often many feet in height. The leaves are from four to six feet in length, rounded at each end, and about eighteen inches in breadth throughout their whole extent; they have a strong mid-rib parallel, lateral veins, and are of a beautiful emerald-green colour. The flowers are spathaceous, and produce large clusters of succulent indehiscent fruits, each fruit being an inch in dia- meter and about six inches in length. When ripe, the banana acquires a rich golden-yellow colour; the outer envelope or exte- rior of the fruit is easily removed ; the inner portion consisting of a rich cream-coloured pulp, containing a considerable quantity of sugar and starch. The banana forms an important article of food in the tropics. Some idea of its fruitfulness may be gathered from the statement of Humboldt, that the same space of ground which will grow thirty pounds of wheat, or ninety-nine pounds of potatoes, will afford 4,000 pounds of bananas. Those intended for exportation are generally gathered green and unripe, but soon acquire, on being kept, that golden tint which marks maturity* Several other species of Musa produce similar fruits. Musa paradisiaca yields the plantain, a fruit bearing a close resemblance to the banana, and equally nutritious. Pine -Apple ( Ananassa sativa, Lindl. ; natural order, Bromeliacece) . — This is a stemless plant with rigid, re-curved, channelled, and spinose leaves. The fruit is called in botany a sorosis, and consists of a union of the ovaries, floral envelopes, and the succulent axis of the inflorescence, which become pulpy and confluent with each other. The fruit is so acid in the wild state, that; when eaten it removes the skin from the lips and gums ; cultivated, it becomes sweet and agreeable to the palate, and richly aromatic. Originally indigenous to the Bahama and Bermuda Islands, the pine-apple, owing to its value as a fruit, and its capability of becoming naturalised, is now cultivated, not only in the East Indies and Africa, but in all parts of the world where it can be grown either by natural or artificial means. Owing to the in- troduction of steam navigation, vessels can now bring ripe pine- apples from the West Indies to England in pretty good con- dition ; and their importation has become an extensive trade, more than 200,000 having been brought from the Bahamas in 1851. Consequently, this fine fruit is often sold in London and other large towns at a cheap rate compared with the price asked for those grown in English hot-houses. English-grown pine- apples^ are worth from ten to twelve shillings per pound, whilst those, imported rarely exceed half-a-crown for the entire fruit. Inferior pine-apples are frequently sold in the streets in slices at a penny per slice. ( b .) NETS. Hazel Net (Corylus Avellana, L. ; natural order, Cupuli- ferce). — This familiar edible nut is found growing wild in the United Kingdom, in the forests of all parts of temperate Europe, and in many places in Asia. The consumption is immense, especially amongst children; and many thousand bushels are annually brought to this country from Spain, Sicily, Smyrna, and other places. The filbert is only an improved variety of the common hazel nut, and although occasionally imported, is usually cultivated in sufficient quantities in England to supplv the demand. COLOUR— y. By Professor Church, Royal Agricultural College, Cirencester. THE SECONDARY AND TERTIARY COLOERS CONTRASTS OP TONE AND OP COLOUR. Secondary colours may now engage our attention. On referring to the central figure in our coloured diagram, it will be seen that the three primaries occupy the angles of the first triangle, and the three secondaries the angles of the second. If we repre- sent the same arrangement without colour (Fig. 13), we sha.ll be able to point out very clearly the constituents of each com- pound colour. The three small triangles marked I. contain the three primary colours, while those marked II. contain the three secondary colours. When equivalent quantities of yellow and red are mixed, orange is the result — a secondary colour equally distant from yellow on the one side and red on the other. It is commonly held that, with material pigments, three parts (by surface measurement) of a good yellow require five parts of a good red to form the normal orange. The eight parts of the normal orange formed in this way will serve as a complementary equivalent to eight parts of the normal blue. But, after alt. these and similar numbers are merely approximate, serving just to indicate the direction in which one coloured constituent must preponderate over another in such mixtures as the secondary colours. When yellow and red are mixed in proportions differ- ing from those necessary to constitute the normal orange, the resulting colour becomes a yellowish-orange or a reddish-orange, according to the predominance of either of the constituent primaries : countless variations of a secondary colour in this direction are possible. Indeed, as wo have already shown, most of our coloured materials, usually regarded as exhibiting primary colours, in reality furnish us with secondary hues of this kind, though their mixed character is not perceived by the unassisted vision. The following list shows the imaginary or theoretical com- position of the three secondary colours, and their six chief modifications or hues. The letters Y, K, and B represent the equivalent proportions of the three primaries— yellow, red, and blue ; the equivalent of yellow being assumed to be 3, of red 5, and of blue 8 : — SECONDARY COLOURS. Y + R = Orange. R + B = Violet. B + Y = Green. SECONDARY HUES. 2Y + R = Yellowish-orange,. Y + 2R = Reddish-orange. 2R + B = Reddish-violet. R + 2B = Bluish-violet. 2B + Y = Bluish-green. B + 2Y == Yellowish-green. Ch-ange . — This colour is the most powerful and brilliant of the three normal secondaries. It is seen in the pigment known as cadmium yellow (the cadmium sulphide), and in the skin of a rich-coloured ripe orange. To make a pure and bright orange by mixture, it is essential that the yellow pigment should incline to red rather than to green, and the red pigment to orange rather than to blue. If the contrary be the case, and a greenish- 246 THE TECHNICAL EDUCATOR. yellow pigment be mixed with a red, or a yellow with a violet- red, a certain amount of grey is produced by the combination of the three primaries present, and a dulled tone of orange is the result. Th 9 worst effect of this kind is produced when a greenish-yellow is mixed with a violet-red. Gamboge and carmine form an orange far inferior in purity to that produced by the admixture of chrome yellow and -jermilion. Violet is the least powerful of the secondary colours. The aniline dye known as mauve may be taken as somewhat -near the normal violet. Many other artificial colouring matters made from the products of coal-distillation also approach this beauti- ful colour. Yiolet usually appears much redder and duller by candle or gas-light than by daylight. The yellow and orange rays which are present in peculiar abundance in most artificial lights, neutralise some of the blue in the violet, forming there- with grey, and at the same time setting free, as it were, the red element of this secondary combination. To make a pure and bright violet by mixture, it is essential that the red pig- ment should incline to blue rather than to orange, and that the blue pigment should incline to red rather than to green. Ver- milion and cobalt produce a very dull and earthy-looking com- bination, owing to the presence of orange in the former colour and green in the latter. Carmine and ultramarine afford a more satisfactory mixture. Green is more vivid than violet, but less so than orange. It occupies a considerable space in the solar spectrum, where, however, much of the green light has a yellowish hue, and some of it inclines towards blue. Emerald green is in reality far from reflecting pure green light only to the eye. Its spectrum is simply deficient in red and orange rays, yet even these are by no means absent. The new “ aniline green,” which retains its characteristic and brilliant cplour by artificial light, absorbs, when of sufficient purity and in sufficient amount, nearly all rays except the green. When a piece of cotton dyed with this green is interposed between a light and the spectroscope, it will be found that about six thicknesses of the fabric are requisite to strain off all the red rays. But this result may be accom- plished more easily by a solution of the colouring matter ; for in this case there are no interstices through which light can pass, and thus escape the selective absorption of the pigment. Viridian, the beautiful and permanent chrome green introduced very recently, transmits the green rays or green portion of the spectriim unchanged, but along with them a small portion of the red and of the blue - rays. In producing a green by ad- mixture of yellow and blue, it is important to take a yellow and a blue both free from red. A greenish-yellow and a greenish-blue, or else a pure yellow and a pure blue, may be successfully used. Notwithstanding its brilliancy, cadmium yellow, which is really an orange, cannot be made to yield a satisfactory green by the addition of any kind of blue pigment. Tertiary Colours have now to be considered. Referring back to our diagram (Fig. 13), we find six spaces marked III. Each of these spaces is immediately contiguous with a space (marked I.) assigned to a primary, or to a space (marked II.) assigned to a secondary colour. We have already alluded to the fact that the so-called tertiary colours ought, strictly speaking, to be regarded as nothing more than dulled tones of the primary and secondary colours. Indeed, it is impossible, on the theory of the three primaries together forming grey, to have any colour which shall exhibit the colour-effect of more than two of them together. An examination of the composition of the tertiary colours will explain this point. Using again our former sym- bols for the primaries, and letting Gy stand for grey, we may express the constituents of the six normal tertiaries thus : — 2Y + R B = Y + Gy = Yellow-grey, or citrine. 2Y + 2E+ B = Y + R + Gy = Orange-grey, or buff. Y + 2R+ B = R + Gy = Reddish-grey, or russet. Y + 2B + 2B = R + B + Gy = Violet-grey, or plum. Y -t- R + 2B = B + Gy = Bluisli-grey, or slate. 2Y + R-t-2B = Y + B + Gy= Greenish-grey, or sage. It is commonly stated that the tertiary colours are com- pounded of the secondary colours. Thus the two secondaries, orange and green, are assumed to give rise to the tertiary colour known as citrine. This hue is really nothing more than a yellow-grey ; for its orange constituent contains yellow and red, and its green constituent yellow and blue. Subtracting equivalents of the three primaries, so as to form grey, we have, therefore, nothing but a residue of the primary yellow, to pro- duce the whole colour-effect of the mixture of the secondaries orange and green. This residual yellow is dulled by the pre- sence of the grey which is the product of mixing equivalents of pigments representing the three primaries. The colour com- plementary with citrine or yellowish-grey is violet, which, of course, supplies the blue and red which have been extinguished in the former hue. The secondary colours orange and violet produce, when mixed together, the tertiary hue known as russet. It is really a reddish-grey. Some autumnal leaves present good examples of this colour. Its complementary is green, which supplies the yellow and blue which are wanting in russet. The secondary colours green and violet produce, when mixed together, the tertiary hue often called olive, but which may, perhaps, be more correctly designated slate. It is really a bluish-grey. The complementary colour is orange, which sup- plies the missing red and yellow constituents. We may here name, as other and very useful tertiary hues, those known as buff, plum, and sage. Buff, or orange modified by grey, may be produced by the addition of red to citrine, or by mixing the three primaries so that yellow and red pre- dominate. Sage-green is produced by the addition of yellow to slate-colour, or by mixing the three primaries so that both yellow and blue predominate. Plum-colour is a violet-grey produced by the addition of blue to russet, or by mixing the three primaries so that both blue and red predominate. Numerous other tertiary hues, besides the six just named, are constantly observed in natural objects, and may be reproduced with great advantage in decorative art. It is, however, very difficult to describe the composition and character of such colours. Contrasts of tone and of colour . — If there be the slightest difference either of tone or of colour in two contiguous or neigh- bouring coloured or shaded surfaces, that difference will not be seen exactly as it really exists. Under such conditions, either the retina of the eye receives an impression which does not actually reproduce the facts of the exterior phenomenon, or the message Jtransmitted to the brain is itself modified. Whatever the exact cause, the study of the subjective modifications of tone and colour is one of the most important branches of our pre- sent series of lessons. We shall describe, first of all, contrasts of tone, and then contrasts of colour. Contrasts of tone may be either successive or simultaneous- Of the first kind, we have examples in the facts that a dark- toned piece of cloth or paper looks lighter if we have imme- diately before been looking at a still darker piece ; and that a light-toned piece looks darker, if we have immediately before been looking at a still lighter piece. The following are illustra- tions of the facts of the simultaneous contrasts of tones : Wo first take two strips of pale-grey paper, and fix them a few inches apart towards one side of a piece of linen stretched across a window. Two similar strips are next prepared, but they are to be of a considerably darker tone. One of these is placed so as to touch one of the first strips ; the other is fixed at some few inches’ distance. The following sketch shows the arrangement of the strips : — Upon steadily looking at the four sheets for a short time, it will be perceived that a' close to b seems lighter than A, while B close to a ' seems darker than b'. The effect of contrast in altering the tone of the contiguous strips a' and B may be further studied in this way. ' Make such openings in a piece of card as to divide the strips A and B each into three portions. It will then be noticed that the two nearest portions are most contrasted in tone, and the others less so in proportion to their distance from the line of contact. But the effect of contrast of tone is still better seen when a more complete series of toned strips is placed in contiguity. In such a case the effect on all the strips, save the end ones, is that of a double contrast. The second strip, or second tone, has one side of it made apparently darker by reason of the contiguity of the lighter tone of strip 1, while the other side seems lighter by the contiguity of the I TECHNICAL DRAWING. 247 darker tone of strip 3. The general result of these double Contrasts is that the whole series or scale of tones presents the appearance of a number of hollows, although, in fact, the apparent hollows are perfectly fiat spaces of shading or colour- ing. The effect is approximately represented in Pig. 14, where 13 3 4 5 6 the real flatness of eaeh tone of the six may be verified by covering up all tho other spaces by a card. The same diagram of contrast of tone may be made more effective, by dividing a slip of card into several equal sections — say, six — by faint pencil lines, and then giving all six a light wash of Indian ink. Next, when this is dry, five sections receive a second similar wash. Afterwards the same process is repeated until the third section has received three washes, the fourth section four, the fifth section five, and the sixth section six. In carry- ing out the process, all sections, except those being submitted to the operation of washing, should be hid from view. Without this precaution it is difficult to secure a flat tint in each strip. If a series of pieces of grey paper of the same colour, but of different tones, are obtainable, they may be used in the con- struction of the same figure. They should be of equal size, and be pasted close together on a strip of cardboard ; or a strip of glass or gelatine may be so arranged as to present at one end one thickness of the material, and the other end six or more thicknesses. On looking through the series, especially if a piece of white enamel glass, or a sheet of white paper, be placed behind, the effect of simultaneous contrast of tone will be clearly perceived. It is scarcely necessary to state that the tones of any particular colour may be used as well as grey to illustrate this kind of contrast. Its characteristic effect is not seen unless the contrasting tones differ considerably in inten- sity, and are in close contiguity or absolute contact. Contrasts of colour are always more or less complex in cha- racter. There is, to begin with, the actual or objective differ- ence between two colours, and then, superadded to this, we have certain subjective modifications, of an ocular or mental kind, which all contrasted colours produce. Further than this, it is rare to find any contrast of colour in which the effects of con- trast of tone are not likewise present. We shall have to speak in a f uture lesson, and with considerable detail, of the practical results of all the circumstances which affect contrast of colours, and so now we merely introduce this subject by a few words on the successive and simultaneous contrast of colour. If the eyes have steadily regarded some coloured object, and then look at a colourless object, that object will assume a colour complementary to that of the former, or will present an image of that object in the complementary colour. If the second object be itself also coloured, but differently from that first viewed, then the complementary colour will mingle with that of the second object, and modify its proper colour accordingly. But even a third case of successive contrast may occur. Sup- posing we look steadily at a series of pieces of scarlet cloth, one after another being placed before us ; the eye, fatigued with the repeated calls on its perception and appreciation of scarlet, becomes incapable of estimating the series of identical speci- mens, and reports the last specimen to be duller than the first. The eye has become less appreciative of red, and more apprecia- tive of the other colours. It sees less red, and more green than before. This green mixes with the red of the later specimens of cloth, dulling and modifying them. The eye may be rested and restored to its proper condition by gazing upon a piece of green cloth, when its power of appreciating red will once more return. The simultaneous contrast of colours was first thoroughly worked out by the French chemist, Chevreul. It is the most fertile of all the laws of colour in the elucidation of the actual phenomena of contrasts, and in the suggestion of new com- binations. When two coloured objects are seen at the same time, they usually mutually affect each other both in colour and tone. A yellow object, for example, placed close to a blue one, will appear as if it inclined to orange, while the blue object will seem to incline towards violet. The reason of this, on the assumption that yellow, red, and blue are the primary colours, is that the eye looking at yellow becomes less able to appreciate it, and sees the remainder of the primary colours, red and blue, that is, violet. This violet mixing with the con- tiguous blue colour tinges it with a faint trace of red. So with the blue object : the eye looking at the blue becomes less able to appreciate it, and sees the remaining primaries, yellow and red, or orange, the complementary of blue, which orange is im- parted to the yellow, giving it a reddish hue. But blue and yellow differ much in their respective value as regards tone. The luminous and brilliant yellow becomes still more brilliant by contact with the richer and deeper blue, which itself is at the same time deepened, so that under ordinary circumstances these two colours afford a combined example of simultaneous contrast of tone and colour. But two complementary colours, such as red and green are presumed to be according to the common theory, do not modify one another’s colour by contiguity. Theoretically, they contain the three constituents of white light, and the eye perceives no deficiency or excess of any coloured elements in the combination. So red and green merely enhance each other’s characteristics when in contact. Thus it is with orange and its complementary blue, and with other pairs of complementary colours. By placing strips of coloured paper together, a few of the chief phenomena of simultaneous contrast may be easily ob- served. We here give a list of some of the modifications of hue which coloured surfaces seem to undergo when placed in contact in pairs : — • Red Red with orange Red Red with yellow Red Red with blue Red Red with violet Orange Orange with yellow Orange Orange with green inclines to violet. ,, yellow, violet. „ green. „ orange. ,, green. „ orange. ,, blue. „ red. „ green. „ red. „ blue. Orange inclines to yellow. Orange with violet,. „ blue. Yellow ,, „ orange. Yellow with green „ ,, blue. Yellow „ „ orange. Yellow with blue „ ,, violet. Green ,, ,, yellow. Green ivith blue „ „ violet. Green „ „ yellow. Green with violet „ „ red. Blue ,, „ green. Blue with violet ,, „ red. TECHNICAL DRAWING.— XVI. DRAWING FOR MACHINISTS AND ENGINEERS. Fig. 172. — This study is intended as an exercise in the use of the set-square of 60°. Having constructed the containing rectangle, draw diagonals by means of the set-square resting on its shortest side on the T-square. All lines drawn against the hypothenuse of the set- square in this position will be at 60° to the horizontal lines and at 30° to the perpendiculars. Now divide the base into the required number of equal parts, and draw lines from them parallel to both diagonals. This is done by turning the set-square. These lines will cut the per- pendicular sides of the containing figure, and from the points thus obtained lines parallel to the diagonals may again be drawn as before. To test the correctness of your work as you proceed, (1) Draw the horizontal line A B, which should pass through all the intersections at that height. (2.) Draw the perpendicular c d, which should pass through all the intersections at that distance from the side. (3.) Join any two of the points on a line drawn, as A B, and on E F construct two equilateral triangles ; the apex of the one should be on the intersection G, and the other at H. If the drawing does not fulfil all these conditions, there is some- thing incorrect in the construction ; and as the error would cause all the work based upon this original figure to be inaccurate, it is advisable to rub it completely out and start afresh. The most economical plan is, therefore, to work with the utmost care in the early stages, on which all the subsequent operations are based. Fig. 173 is another design for a cast-iron grating, as an appli- cation of the foregoing study. Having carried your work up to the stage shown in the last lesson, it becomes necessary to mark the width of the cross-barso 248 THE TECHNICAL EDUCATOR. Now in Fig. 170 this was done by setting off half the required thickness on each side of the intersection ; but it will be evident that in the present instance this would not answer the purpose, as the lines intersecting are not at right angles to each other, and therefore the measurement set off on them would not give the correct width. Therefore, at any point (as a) draw a line at right angles to one of the cross-lines, and on this, on each side of the intersection, set off the half-width of the bars — viz., b, c — and through these points draw the required lines cutting the cross-lines in d and e. This length, therefore, may be set off from each of the intersections, and the required widths of the bars will thus be obtained. The centres for the circles are, of course, the intersections of the primary lines. If a large circle is to be drawn, the inking-leg of the compass should be bent at the joint to allow of both the nibs of the pen touching the paper. If this is not done, the outer edge of the circle will be ragged. For small circles, bow-compasses are necessary. These, which have been already described (page 12), are small compasses with a neat handle at the top, by means of which they may be twirled round between the finger and thumb with the greatest ease. The best kind are made with joints in both legs, by means of which the steel point and the pen or pencil can be made upright, and thus far better work is secured. For still smaller circles “spring-bows” are used. These are very small and refined instruments, which open by means of a spring instead of a joint, and are regulated by a screw ; they are Figs. 174, 175, 176, 177. — These figures are simply intended to give practice in drawing concentric circles. The greatest care is necessary in this operation. The compass should be held loosely between the forefinger and thumb ; the pressure on the steel point should be so very little that scarcely a mark is made on the paper. If by carelessness or pressure the paper is pene- trated, the hole will be made larger as each circle is drawn, and of course the centre becomes no longer true. Thus the circles will not be parallel to each other, nor will the curve on ending meet the starting-point. As concentric circles are of constant occurrence in mechanical drawing, it is important that the student should acquire the power of drawing them with the utmost precision and facility. The pencil-leg should be allowed to trail over the paper, and where numerous concentric circles are required it will be found in many cases unnecessary to pencil them.; the radius of each may be merely marked on a line drawn through the centre, and the circles themselves can then be at once drawn in ink. only sold in the better class of boxes, but a set of bow-compasses (three) can be purchased in separate small cases. Fig. 178. — This study is designed to afford practice in joining arcs. The first line to be drawn in this case is the horizontal. On this describe a semicircle, A b. From the point where the semicircle meets the straight line (viz., b), set off the radius viz., b c), and from c describe the next semicircle on the opposite side of the line, carefully observing that the semicircle starts accurately from B, and that the joint is effected without any thickening, the curves running into each other so as to form one smooth wave-line. When the student can accomplish this, the drawing of a wave-line of a given breadth may be attempted. Having drawn the centre line as above, set off as the radius on each side of B half the required breadth — viz., b e and b f ; then with radius extending from the centre to each of these points in turn describe the semicircles required. Joining curves to straight lines occurs frequently in mechanioal drawing, and this is therefore made the subject of the following study. TECHNICAL DRAWING. 249 Fig. 179. — The object here represented is a portion of the framing of a small “ table engine.” Having set off from the centre line, A, the half-width of the framing, A b and A c, erect perpendiculars. Draw the horizontal surface at the top and the edging D, E. Now set off from a the distances f and a, for the width of the opening, and from a set off also A h and A i, so that f h and g i may be equal to b d and e c, the edging of the framing. the curves first, as it is easier to draw a straight line to meet a curve than the reverse. Fig. 180. — This is an elevation of the pillar supporting the “ governor,” from the same small engine. It is supposed that but little trouble will be found in drawing this figure, as far as the straight portions of it are concerned. Draw the ground line and central perpendicular, on which set off the heights for the horizontals. When these have been From H i g f erect perpendiculars, and at j k and L m draw horizontal lines. From l and m set off l n and m o equal to L j or m k, and at N and o erect perpendiculars, cutting J K in p and Q. From n and o, with radius n l or o m, describe quadrants joining l p and m Q. From N and o describe quadrants, with radius n b or o s, cutting n p and o Q in T and tr. Join p q and t it, which will complete the framing. The manner in which the curves at the foot of the framing are obtained being precisely similar to those above, no instruc- tions concerning them are deemed necessary. Observe . — When curves are to be joined to straight lines, draw drawn, the widths are to be set off from the centre line. The points a b and c d having been joined, it only remains to describe the curve at e f and that on the opposite side. This curve is the arc which is formed by using the apex of an equilateral triangle as the centre, and the side of the triangle as the radius. This part of the drawing is worked out on a large scale in the next example (Fig. 181). From e and /, with radius e /, describe arcs cutting each other in g ; then from g, with the same radius, describe the arc ef as required. Fig. 182 is the Cyma Recta moulding, and Fig. 183 is the Cyma Reversa. Both of these are of frequent occurrence in the 250 THE TECHNICAL EDUCATOR. framing of machinery, and the mode of constructing them is therefore introduced here. Draw a line between the points which are to be connected by the curve, as a b (Fig. 182), and bisect this line in c. From a, c and c, b describe arcs cutting each other in d and e ; these will be the centres for the two parts of the curves, which must glide smoothly into each other at c. The form of curve may be varied by moving the point c either higher or lower, or taking a shorter or longer radius with which to describe the arcs. AGRICULTURAL DRAINAGE AND IRRIGATION.— YI. By Professor Wrightson, Boyal Agricultural College, Cirencester. COST OP DRAINAGE, ETC. Land drainage under ordinary circumstances can hardly be spoken of as a very complicated process. The reasons which account for its marvellous effects, the changes it induces in the soil, the discussion as to the proper depth, distance, and direc- tion of the drains, and the practical advantages which follow its adoption, are all fertile subjects. The mere description of the process of laying the pipes, however, need not detain us long. Wo have already devoted some attention to this portion of the subject, and it now remains for us to consider some diffi- culties which the practical drainer will encounter. Where the land is very wet, it is occasionally difficult to keep the trench open, in which case support must be given to the sides by boards and struts until the tiles are laid. Sometimes a quicksand is met with, upon which it is impossible to lay tiles, as they would speedily sink out of regular line. Under such circumstances, a layer of straw (according to Mr. Wilson, of Edington) or a narrow board must be used in order to give support to the tiles until they have time to act on the sur- rounding mass of soil, and render it dry and firm. Tree and hedge roots are another source of danger. In order to avoid this, no drain should be laid nearer than five or six yards to a fence, unless special precautions are taken for prevent- ing the entrance of root-fibres. Thoms are sometimes placed over the tiles in such drains to prevent this occurrence, and, in other cases, close-fitting collars are used at every joint so as to secure them from the entrance of roots. It is occasionally necessary to carry a drain across a water- course, and when this is required it may be passed underneath with the assistance of a few feet of iron piping. Another difficulty frequently presents itself in obtaining a good outfall. Ditches which receive drainage water ought to be strengthened and deepened so as to offer the least possible resistance to its passage. Where the land to be drained is situated on a river-bank, it is sometimes difficult to contrive a suitable outfall for three or four feet drains. In such cases the main drain must be run parallel with the stream such a distance as to ensure an outfall for the higher-lying land. Landfast stones and rock also are frequent obstructions in cutting drains, but this is a difficulty which gives way before extra labour. If the rock is of a porous character it may occasionally be made use of as a vent for surface water. This plan is frequently followed in ohalk and other districts where the nature of the soil will allow of it. The water is brought by ordinary drains to a low point or focus, where a well is sunk down into the rock, and thus the water is discharged into the great reservoir which underlies the formation. The complete aeration of the soil is one of the principal functions of drains. It is, therefore, by no moans a matter of surprise that the idea of “air drainage” should have been maintained strongly by many agriculturists. All draining, so far as it admits air, and cannot act unless air is admitted, is air drainage, but the advocates of this system wish to go further. They found an able exponent in the late Mr. S. Hutchinson, agent to the late Earl Brownlow. An idea of this method may be best obtained by reference to Mr. Hutchin- son’s experiments as recorded in Vol. IX. of the Royal Agri- cultural Society’s Journal. He there makes the following statement : “ The field to which I refer is in the occupa- tion of Mr. Strafford, of Marnkam, near Newark-upon-Trent, and consists of ten acres of strong loamy soil, resting upon a clay subsoil. It was underdrained by Mr. Strafford in 1843, by twenty-five parallel drains, two feet deep and five yards apart, each discharging into a covered outfall at the bottom of the field. In the autumn of 1846 it occurred to me that this being a shallow-drained field, presented a good oppor- tunity for experiment. I divided it into five compartments, a' a' 1 %. 11 . (see Fig. 11), each containing five of the drains. With the two outside and the centre compartments I did not interfere. Into the two other compartments I introduced what I called an air- drain, a 1 a', across the upper ends of the five drains, in each case to join them together. I then connected the air-drain so cut with the adjacent open ditch at the top of the field, in order to increase the natural circulation of air through the ordinary drains.” This experiment was successful, and sub- sequently both Mr. Strafford and Mr. Hutchinson were struck with the benefit following the introduction of the air-drains, when the land under their influence was compared with the neighbouring compartments not so treated. With a view to test the accuracy of these observations, the produce per im- perial acre was accurately ascertained, both in wheat and turnips, and the result showed a palpable advantage in the air- drained plots. The prescribed method is exceedingly cheap, and may be resorted to without appreciably increasing the expense. Upon some soils an air-drain may be requirecWm order to facilitate the egress of water ; in others the porous character of the soil will allow a sufficient circulation of air without any additional help. We now approach the consideration of the cost of drainage. This will vary with the expense of digging the trenches, their depth, the distance between them, and the price of tiles. The cost of digging three-feet drains through homogeneous clay soils is often estimated at one penny per linear yard, but where stones and rock occur this price may be indefinitely increased. The distance between the drains resolves. itself, so far as cost is concerned, into a mere question of the numbers of rods or chains per acre ; and the price of tiles is very dependent upon that of coal. Whore this is abundant, 2-inch tiles (internal | diameter) may be obtained at from 17s. to 20s. per thousand, and three-inch tiles at about 30s. per thousand. The following tables, taken from Wilson’s “British Farming,” embody much valuable information upon several of the points touched upon. TABLE SHOWING THE NUMBER OP RODS OP DRAIN PER ACRE AT GIVEN DISTANCES APART, AND THE NUMBER OP PIPES OP GIVEN LENGTHS REQUIRED PER ACRE. Intervals between the drains. Rods per a ere. 12-inch pipes. 13-incli pipes. 14-inch pipes. 15-inch. pipes. IS feet 146§ 2120 2234 2074 1936 21 „ 125# 2074 1915 1778 1659 24 „ 110 1815 1676 1555 1452 27 „ 97# 1013 1489 1383 1290 30 „ 88 1452 1340 1244 1161 From the following table we learn the expense of draining land will, under ordinary circumstances, vary from £5 to rather more than £8 per acre, according to the distance between the channels. There are, however, other important elements con- nected with the materials used for forming the drains, the depth of the drains, and the tenacity or rockiness of the soil. With these ever-varying conditions, the cost may easily exceed or be less than the above estimates. Thus Mr. Stephens gives a list of prices ranging from <£2 7s. 6d. to £9 10s. per acre. The first case was that of a soil described as overlying irregular beds of gravel or sand, and irregular open strata, the material used being broken stones. In such a case the distance between PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING. 251 the drains might be increased easily to forty feet with good effect. Contrasted with this minimum expenditure, we have the high figure above given, in which the soil was described as “ hard till ” or clay, when it was found requisite to place the drains ten feet apart, and where stones were used as the material. TABLE SHOWING THE COST OF' DRAINING PER ACRE AT VARIOUS INTERVALS BETWEEN THE DRAINS. 18 feet 21 feet 24 feet 27 feet 30 feet apart. apart. apart. apart. apart. £ s. d. £ s. d. £ s. d. £ s. d. £ s. d. Labour — cutting and filling at 6d. per rod Material — pipes for 3 13 4 3 2 10 2 15 0 2 8 11 2 4 0 minor drains ISs. per 1,000 O 5 9 1 19 2 i 14 3 1 10 6 1 7 5 Haulage 2 miles and delivery in fields at 2s. 6d. per 1,000 . 0 6 4 0 5 5 0 4 9 0 4 3 0 3 9 Pipe-laying & finish- ing at Id. per rod. Superintendence 0 12 2 0 10 6 0 9 2 0 8 2 0 7 4 — foreman 0 5 0 0 5 j0 0 5 0 0 5 0 0 5 0 Extra for mains Iron outlet pipes and 0 2 0 0 2 0 0 2 0 0 2 0 0 2 0 masonry, and extra labour . 0 1 6 0 1 6 0 1 6 0 1 6 0 1 6 Total . 7 0 1 6 6 5 5 11 8 5 0 4 4 11 0 Add for collars if used , 1 2 10 0 19 ? o 17 1 0 15 3 0 13 8 £ 8 8 11 7 6 0 6 8 9 5 15 7 5 4 8 The Marquis of Tweeddale gives the expense of tile-draining as varying from £4 to <£10. The lower price is for cutting two-feet drains thirty feet apart at a cost of -£d. per yard, and the higher figure is for draining three and a-half feet deep, fifteen feet between the drains, and at a cost of more than Id. per yard (Stephens). Draining by means of the mole plough may be accomplished at a cost of from £1 per acre, according to a recent report upon Mr. Ruck’s farm, at Braydon Manor, to .£1 8s. and £1 10s., according to the nature of the soil, and the depth and distance. When, however, circumstances vary so widely, it is a difficult matter to fix any definite limit to the expense, almost every field requiring a different treatment to the last, and each case having its own special requirements with regard to depth, distance, and cost of labour. The effect of drainage in increasing the produce is, in some cases, exceedingly marked. Instances are not wanting in which the agricultural value of the land is entirely owing to this im- provement. In very many cases one quarter extra per acre of wheat, and a proportional increase in the yield of other crops, is looked upon as the advantage which may be expected. Again, looking at the benefits of land drainage from a general point of view, we find farmers willing to pay 6 per cent, upon money thus expended by their landlords, and at the end of the lease this per-centage is incorporated in the ordinary rent-charge, thereby showing that the improvement is looked upon as per- manent. Among the best examples of improvement are those collected by Mr. Stephens in the “ Book of the Farm.” There we are told that in the case of land belonging to Mr. Dalrymple of Cleland, Lanarkshire, one field of eighteen acres cost £5 9s. per acre to drain. Previously this field had been occupied with whins and rushes, and had been let for 12s. per acre ; but after draining, the wheat off one portion of it brought £13 per acre, the potatoes off another part dll 5 15s. per acre, and the turnips off the remainder <£21 per acre. Mr. James Howden, Winton- hill, East Lothian, asserted years ago that, although drains should cost as much as d7 per acre, yet on damp heavy land thorough drainage would repay from 15 to 20 per cent, upon the outlay. A farmer in Lanarkshire, who thoroughly drained one-half of a four-acre field, and left the other half nndrained, planted the whole field with potatoes. From the drained half he realised <£45, whilst the undrained half only realised £13 per Scotch acre. It appears almost unnecessary to multiply instances. We conclude by citing the results obtained on the Teddesley Hay Estate, the property of Lord Hatherton, where, after an expenditure of from £3 10s. to £4 per acre, the rental value of the land was increased in one case from 10s. to 27s. per acre, in another from 10s. to 35s. per acre, in a third from 16s. to 33s'., and in a fourth from 8s. to 22s. per acre. Su,ch examples, although matters of fact, may possibly mislead unless it be remembered that the ordinary result is much less striking, and that the more modest but satisfac- tory return first spoken of will be a more usual measure of the •* direct advantages derived from land drainage. No one now denies the advantage of draining arable land, although some persons hold that it is possible to overdrain even this. With regard, however, to pastures, there has been j a considerable amount of discussion, many farmers considering . that the amount of grass is diminished by the operation. Such seasons as 1868 and 1870 are well calculated to try the truth of such opinions : it was, therefore, exceedingly judi- cious in Mr. J. C. Morton, at the close of 1868, to request answers from correspondents in various parts of England upon the results, during the long-continued drought, of drainage upon pastures. In answer to the query, “Are there instances known to you of differences, as regards productiveness, during so dry a season, between drained and undrained land either arable or pasture ? ” Mr. Paget, of Ruddington, “ confesses that where the land had been very recently drained, and consequently the grasses proper to dry land were not fully established, they did not afford quite so much ‘ keep ’ as the corresponding undrained land ; but as soon as the rain fell in August, the advantage was on the side of the drained land. Those meadows which had been long drained had the advantage throughout.” This is an instructive case, and explains why, in some cases, drainage has temporarily lowered the yield of grass upon pasture lands. Mr. Wortley, of South Collingham, Newark, says, “ I must say that, according to my experience, there is some foundation for the popular belief that a certain kind of grass land is injured by under-draining ; that is to say, the inferior plants which previously made a show, if they did little more, are destroyed by the drainage, and they are very slowly replaced by better, if the land is left to itself. With such exceptions, however, my belief has always been that the draining of wet land, whether arable or grass, increases the productive power, even in such seasons as the last.” Mr. James Rawlence also says, “ I quite think with you that more corn or grass have been grown on drained than on undrained land, except on grass land which had been drained the previous autumn, in which case the aquatic plants all died out from the long drought and heat, and the more nutritious grasses had not time to fill up their places.” These concurrent testimonies to the effect of drainage upon grass lands are very conclusive, and reconcile apparently contradictory ob- servations, it being evident that although the ultimate effect of drainage upon grass land is beneficial, yet there is a period of trial between the dying out of sedges and water-grasses and the prevalence of a sweeter and better herbage. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— IY. DEFINITIONS CONCERNING POLYGONS. All figures having more than four sides are called polygons, and are distinguished by names denoting the number of their sides and angles— thus : A Polygon of 5 sides is called a Pentagon. 6 3 33 Hexagon. 7 3 3 Heptagon. 8 t 3 3 Octagon. 9 » 33 Nonagon. 10 Decagon. 11 Undecagon. 12 ,, Duodecagon. When all the sides of a polygon are equal, and all its angles equal, it is called regular. When they are not equal, the polygon is said to be irregular. By drawing lines from the angles of a regular polygon to the centre, the figure may be divided into as many triangle's as the polygon has. sides. In the regular hexagon these triangles will be equilateral, but in all other regular polygons they will bo isosceles. The methods of constructing the various polygons having been given in “ Lessons on Geometry” in The Popular Educator, 252 THE TECHNICAL EDUCATOR. it is only necessary in this place to give one or two, in order to show their application in mechanical drawing. To inscribe a regular pentagon in a circle, by a special method (Fig. 40). Draw the diameter A b, and bisect it, or divide it into two eqnal parts in o. At o erect a perpendicular, o c. Bisect o A in the point d, according to the method indicated in the figure. From D, with radius d c, describe an arc cutting A b in e. c From c, with radius c e, describe an arc cutting the circle in f. Draw c F, which will be one side of the pentagon. Set off the length c F around the circle in the points g, h, i. Draw lines f g, g h, h i, and i c, which will complete the figure. Application of the foregoing principle in the construction of Gothic tracery (Fig. 41). Draw a circle, divide it into five equal parts,' And draw the radii o A, o B, o c, o D, o E. Bisect one of the radii, and set A off the half on each of them in the points f, g, h, i, j. Join these points, and a regular pentagon will be formed. Bisect the sides of this pentagon by the lines o i, o l, o m, ON,OP. Draw a small circle in the centre, and another, Q, concentric with it. From Q to the sides of the pentagon draw lines parallel to o k, o l, etc., at a small distance on each side of them — viz., ss,t u, etc. Produce the sides of the pentagon indefinitely from f, g, h, i, j, and with radius h tj describe circles cutting the produced sides of the pentagon in v w and the corresponding points. Draw v c, w c, and similar lines from the other circles, and the remaining lines will be parallel to, and conoentric with, those already drawn. To construct a regular hexagon on the given line a b (Fig. 42), From A and B describe arcs cutting each other in O. From o, with radius o a or o b, describe a circle. The radius with which a circle is struck will divide it into six equal parts ; therefore set off the length o A, which is equal to A B, around the circle — viz., cdef. Join these points, and a regular hexagon will be formed. To inscribe a regular hexagon in a circle. Find the centre of the circle, set off the radius around it, and join the points. Example 1 of inscribing a hexagon in a circle. — To draw a simple fly-wheel (Fig. 43). Draw the circles A and b, representing the outer and inner edge of the rim. Divide the circle b into six equal parts, and draw the dia- meters c D, G F, E H. Next draw the circles I and j, representing the end of the shaft and the boss, or central part of the wheel ; the small paral- lelogram at the side of the inner circle represents the “ key,” by which the wheel is held on the shaft. On the edge of the boss set off equal distances, k l. Draw the circle m, and on it, on each side of the radii, set off distances rather less than k and L — viz., n and o. Draw the sides of the arms, K n and L o, etc. ; and with any convenient radius describe the small arcs connecting the arms with the rim at n and o. The length p Q set off from p and Q on the radius, will give the point R, which is the centre for striking the arc, caused by the elliptical arm meeting (called penetrating) the elliptical rim. NOTABLE INVENTIONS AND INVENTORS. 253 Example 2 of the application of the hexagon in mechanical d/rawing (Fig. 44). In this drawing of a nut and bolt, the plan — that is, the appearance it would have if your eye were directly over it, and you looked down upon it — is to be drawn first. The two largest circles being described, the inner one is to be divided into six equal parts, and a hexagon inscribed in it. Perpendiculars drawn from each of the angles of the hexagon will give the projection of the widths of the sides of the nut. Within the equilateral triangle , A b c, to inscribe six equal circles (Fig. 45). Draw the lines b d, a f, and c E, bisecting the sides and angles of the triangle, and intersecting each other in o. Bisect the angle o a e, and the point (g) where the bisecting line cuts c e, will be the centre of one of the three isosceles triangles, into which the equilateral triangle has been divided. c Through g draw H I parallel to A b, and from H and I draw H j and i j, cutting b d and A E in k and L. From ghijk and l, with radius G e, draw the six circles. To inscribe three equal circles in a circle (Fig. 46). At any point, as A, draw a tangent, and A g at right angles to it. From A, with radius o A, cut the circle in b and c. From b and c draw lines through o, cutting the circle in d and e, and the tangent in the point f (and in another not given here, not being required). Bisect the angle at f, and produce the bisecting line until it cuts a g in h. From o, with radius o ft, cut the lines d c and e b in i and J. From H, i, and J, with radius h a, draw the three required circles, each of which should touch the other two and the outer circle. To inscribe in an equilateral triangle, A b c, the three largest circles it will contain (Fig. 47). Draw A g, b f, and c E, bisecting the angles and sides of the triangle, and intersecting in o. Bisect the right angle A e o. Produce the bisecting line until it cuts A G in H. to b c. From h, i, and j, with radius h k, draw the three circles, each of which should touch the other two, and two sides of the triangle. NOTABLE INVENTIONS AND INVENTORS. Y.— CLOCKS AND WATCHES (concluded). BY JOHN TIMBS. Clerkenwell has long been noted as a clock-making parish. The most extensive establishment here has workshops for every branch of manufacture : as the brass-casting, the wheel and pinion cutting, the case-making, and the movement-making. Wooden clocks are made on the confines of the Black Forest, by peasant families — the export of clocks from Baden alone amounting to <£1,000,000 sterling. Of American clocks, in New Haven 50,000 brass eight-day clocks are made in a year at one factory ; the wheels and plate-holes are all stamped, and the maintaining power is a spring, in place of the gradual fall of a heavy weight. In electrical clocks, the indicator has a clock-face and an index, or hand, and the communicating disc is moved round by the oscillation of a pendulum, kept going by electricity ; thus one clock, by a wire, communicates its own time to any number of clocks at any distance, kept in perfect unison by the action of only one pendulum. Horological electricity also drops time-balls, fires time-guns, and exhibits an hourly signal from the 254 THE TECHNICAL EDUCATOR. parent electro-magnet clock at Greenwich. Observatory, to correct any error in the great clock at Westminster. Illu- minated clocks date from the “ fire-clock ” of Martinelli, in 1663, and in an old German work we find designs for illuminated dials ; in one the light is placed behind a transparent dial and opaque figures, which are reflected, much magnified ; in another, the light issuing from a lantern is so arranged as to fall on, and be continued to, the dial of a clock. It is curious to find, in the year 1869, the good citizens of Beauvais placing in its cathedral a monumental clock, composed of 14 different movements, and 90,000 pieces (weighing 35,000 lb.), and costing .£5,000. The body of the clock is 36 feet high, of carved oak ; it has a figure of the Supreme Being, and the twelve apostles, in enamel ; the main dial (there are 50 in all) has a figure of the Saviour — the largest enamel existing. The pendulum weighs nearly 1 cwt., and is moved by a steel ball weighing but the thirty-second part of an ounce, this movement impelling the fourteen others. The other dials indicate days of the week, movements of the planetary bodies, sunrise and sunset, seasons, signs of the zodiac, duration of daylight and night, saints’ days, months, phases and age of the moon, time at principal cities, solstices, movable feasts, age of the world, year of the century, bissextile years, longitudes, tides, eclipses, etc. In the seventeenth and eighteenth centuries several very curious clooks were constructed. Among these were Grollier’s model of a ball ascending and descending inclined planes, spiral grooves, and others swallowed' by serpents; lizards ascending columns, with the hours marked on them, and mice moving on a graduated cornice. The “invisible clock” at Yauxhall Gardens, in 1822, is thus explained : — “ An hour-hand pointed to the hours on a transparent dial, without visible connection with mechanism. This was effected by having two pieces of glass placed together, the hand being fixed in the centre of one of them, which, turning round once in twelve hours, by motion produced at a tangent, pointed to the hours marked on the other piece of glass, which was immovable.” Amongst the uses of time-keepers we find that by means ©f a clock, the Danish astronomer, Boomer, discovered that the eclipses of Jupiter’s satellites took place a few seconds later than he had calculated, when the earth was in that part of its orbit the farthest from Jupiter. Speculating on the cause of this phenomenon, he concluded that light was not propagated in- stantaneously, but took time to reach us ; and from calculations founded on this theory, light has been discovered to dart through space with a velocity of about 192,000 miles in a second ; thus the light of the sun takes eight minutes to reach the earth. Professor Airy has ascertained the variation of gravity at the surface and interior of the earth, by descending to the bottom of a deep mine, and the result of his computations is, “ supposing a clock adjusted to go true time at the top of the mine, it would gain 21 seconds per day at the bottom ; or it may be stated thus : that gravity is greater at the bottom of a mine than at the top, by 15x35th part.” Time-pieces with springs as the maintaining power (and now called watches) were imperfect machines, going with even less precision than an old clock. They had only an hour-hand, and most of them required winding twice a day. A watch differs from a clock (says Dr. Arnott) in having a vibrating wheel instead of a vibrating pendulum ; and as in a clock gravity is always pulling the pendulum down to the bottom of its arc, which is its natural place of rest, but does not fix it there, because the momentum acquired during its fall on one side carries it up to an equal height on the other — so in a watch, a spring, generally spiral, surrounding the axis of the balance- wheel, is always pulling this towards a middle position of rest, hut does not fix it there, because the momentum acquired during its approach to the middle position from either side carries it just as far past on the other, and the spring has to begin its work again. The balance-wheel, at each vibration, allows one tooth of the adjoining wheel to pass, as the pendulum does in a clock ; and as a spring acts equally well, whatever be its position, a watch keeps time whether carried in the pocket or in a moving ship. In winding up a watch, one turn of the axle on which the key is fixed is rendered equivalent, by the train of wheels, to about 400 turns or beats of the balance- wheel ; and thus the exertion, during a few seconds, of the hand which winds up, gives motion to twenty-four or thirty horn’s. The invention of the coiled spring in the watch dates from the close of the fifteenth century. It is claimed for Nuremberg, then famous for watches, but the priority is much disputed. Their introduction into England is equally uncertain. The watch of Abbot Whiting, dated 1536, is of accredited antiquity ; and Count D’Albanne’s silver watch, of English workmanship, is dated 1529. Henry VIII. had a watch that went for a week ; Anne Boleyn possessed another, as well as a small gilt clock, now in Windsor Castle. Edward VI. had, in 1542, a “watch of iron.” Mary Queen of Scots possessed a death’s head and a skull watch ; one in a case of crystal, coffin-shaped ; and another in which a piece of catgut supplied the place of a chain; but all these were foreign watches. Queen Elizabeth had a large collection of watches. A watch was found upon Guido Fawkes ; and of this period is a curious oval-shaped watch in a silver case, ornamented with mythological figures. The English watch- makers of the City of London were incorporated in 1631. In 1635 the value of a brass watch was 40s. Charles I. possessed several watches. In 1658 was constructed the spiral, or pendu- lum-spring, invented by Dr. Hooke and improved by Tompion. Next, Juare, by applying the pendulum-spring, added (to the hour-hand) minute-hand and wheel-hand. He also added the repeating movement in watches ; one of the first was presented by Charles II. to Louis XIV. of France. Juare also made repeating watches for James II. and William III. From 1698 all makers were compelled by law to put their names on their watches. In 1724 was invented the horizontal escapement by Graham, who also invented the mercurial compensation-pen- dulum. Graham’s escapement has been superseded by the duplex, and more recently by the lever, which is the dead-beat escapement applied to a watch. At the beginning of the last century was invented jewelling the pivot-hole of watches, to prevent friction. Next, John Harrison, by his famous chrono- meter, discovered the longitude, for which he received from Parliament £20,000. Among his other improvements, are the gridiron pendulum and the expansion balance-wheel — the one to equalise the movements of a clock ; the other, those of a watch, under all changes of temperature, by employing two different metals to form the rod of the pendulum and the circumference of the wheel, so that the contraction of the one exactly counterbalances the expansion of the other. Another of Harrison’s inventions is the going fusee, by which a watch can be wound up without interrupting its movement. A time- keeper of greater simplicity than Harrison’s was that of John Arnold, for which he and his son received the Government reward of £3,000 ; the extreme variation of this machine in twelve months has been thirty-seven-hundredths only. Arnold also made the smallest repeating-watch ever known, for which George III. presented him with 500 guineas. The next im- prover of the chronometer was Thomas Earnshaw ; and in this state it has remained for the last ninety years with scarcely any alteration. Among the celebrated French watchmakers was Breguet, who paid some of his workmen thirty francs a day, and none less than a napoleon. He invented the touch watch, by which a spring touched at any time struck the hour and minute ; one cost the Duke of Wellington 300 guineas. About ten years ago, it was maintained that our common watch is, in many of its parts, a very ill-constructed machine. The train of wheel-work, which transmits the motion of the mainspring, for example, is contrived on faulty principles, and the long-used methods and engines were alike condemned. Mr. Dent has stated that every watch consists of at least 202 pieces, em- ploying, probably, 215 persons, distributed among 40 trades — to say nothing of the tool-makers for all of them. It is next maintained that if we were then materially to alter the con- struction of the watch, all those trades would have to be re- learnt, new tools and wheel-cutting engines would have to be devised, and the majority of the workmen to begin life again. During this interval, the price of the instrument, it is asserted, would be enormously advanced. Watch-making in England suffers much from overstrained competition ; the annual importation of gold watches from Swit- zerland is about 35,000 ; while the total number of all kinds produced at home is but 26,000. In America watches are manufactured on a large scale by aid of machinery. We read of a manufactory with 250 hands, more than half of whom are females. The stamps and dies are THE ELECTBIC TELEGRAPH. 255 out by steam machinery, by which are effected the processes, also, of hardening and forming the barrels and chambers, coiling and fastening the mainsprings, gearing-wheels, and cutting their teeth ; shaping pinions and axles, cutting escape-wheels, trim- ming and marking the porcelain dials, drilling and shaping the jewels, and adjusting and fitting together the various parts. It has been confidently stated that the result of the intro- duction of machinery into the watch-making trade is already to be seen in the comparatively low price at which that necessary article is to be obtained ; but hitherto the great drawback has been that machinery was unable to compete with hand-work in the extremely delicate manipulation of the watch. The difficulty, however, is stated to have been entirely obviated by an American invention, which, with the exception of the hair-spring, makes every portion of the watch with a nicety scarcely to be surpassed. One of the chief advantages of this, it is stated, is that each part, being made by a separate machine, can, in the event of damage, be supplied through the post to any part of the world. THE ELECTRIC) TELEGRAPH.— IY. By J. M. Wigner, B.A. INTERRUPTION S IN COMMUNICATION — -MODE OF TESTING FOR AND LOCALISING FAULTS. As we have already seen, any electric circuit is liable to various interruptions, which often cause serious inconvenience. It is therefore a very important matter to be able to discover the eause of the interruption, and, if it be an injury to the line, to find the exact place at which it exists, so that it may be repaired as promptly as possible. "When any circuit is interrupted, the first question is to ascertain whether the fault exists in the battery, the instruments, the office, or the line. Suppose the clerk at any office presses the key of his instru- ment with a view of sending a message, but finds that his own needle is not affected at all, he at once knows that something is wrong. If his own battery or instruments are out of order, and will not act, that will fully account for the failure. His first duty, therefore, is to make sure that the fault is not in his own office., For this purpose the wire where it leaves the office should be temporarily connected with the earth-plate, so as to cut the line-wire and receiving station altogether out of the circuit, and a current should then be sent again. If now the instrument acts satisfactorily, the fault is either on the line or at the receiving station, and the reason why the current would not pass is that the circuit is interrupted at one of those places. If, however, when earth is thus put on, the needle still de- clines to move, the fault is evidently in the office, and may be a faulty connection, or a failure of the instruments or batteries. The latter should first be tested by connecting their two poles with a galvanometer, and noting the deflection. Should this indicate that the battery is enfeebled or impaired, it should be replaced, or set in order. It not unfrequently happens that a single cell in the trough is working badly, and has entirely stopped the passage of the current generated by the rest. In this case the defective cell must be replaced, or else bridged over by making a good connection between the cells on either side of it. If, however, the battery is in good order, the fault must be in the instruments or their connections, and its exact place may be discovered by affixing one end of a good wire to the terminal where the line-wire leaves the instrument, and having pressed down the key so as to send a constant current, bring the other end of the wire successively in contact with the different binding-screws or connections. As soon as the fault is passed, the needle will immediately be deflected, and thus the place of the interruption will be seen. Sometimes the injury will be found to be a rusted or dirty connection ; or sometimes, if inferior oil. has been used in any part of the apparatus, the dust may have settled on it, and become hardened, so that in this way a faulty contact is pro- duced. Too much care cannot be taken in ensuring the perfect cleanliness of all connections, as, even if the current passes at first, the surface, after the lapse of a little time, becomes more corroded, and a great amount of inconvenience and loss of time may be caused in discovering the exact place. A little of the I best salad oil should be applied to the pivots and points by I $vhicb a contact is made, as a safer connection is ensured j thereby, and this oil will not harden sufficiently to injure the contact. The contact-plate should, however, be frequently wiped to remove the dust which may have settled on it. In this way any faults in the office are easily discovered, and for the most part they may without much difficulty be rectified, unless, indeed, the needle has become demagnetised, or there is some injury to the instrument rendering necessary its return into the maker’s hands. More commonly, however, the fault exists along the line. An insulator may be broken, or the wires may be so slack as to come into contact with one another, or with some obstruction which carries away a part of the current. As considerable inconvenience and delay are caused by such faults on important lines, it is usual to test them every day with a view of discovering any flaw before it is sufficiently developed to interrupt the communications. In these tests two things are ascertained — the degree of insulation, and also the amount of resistance which is offered to the passage of the current, as sometimes the wire may be well insulated, but a defective place in it may offer such a resistance as totally to in- tercept a weak current. In all testing experiments the battery power employed should be as small as possible, since a powerful current will often pass a bad connection, which would quite intercept a feebler one. A well-made galvanometer is the most important thing in testing a line. There are two different forms of this instru- ment in common use. In the more sensitive of these the needle is placed horizontally, being poised on a fine steel point. Friction is thus reduced to a minimum, and the only force to be overcome by the current is the directive influence of the earth’s magnetism. The instrument is so placed that the needle may point to o on the graduated scale ; the current is then applied, and the amount of deflection when the needle comes to rest is noted. This instrument is represented in Fig. 14. In the other form of galvanometer, usually called the “ detector,” the needle hangs vertically inside the coils, a pointer being fixed on the same axis so as to indicate the posi- tion of the inner needle. In the more perfect instruments of this class, this outer needle is magnetised as well as the inner one, and is so mounted that its north pole shall point in the reverse direction to that of the inner one, and thus both are affected by the current round the coils, and the instrument is rendered much more sensitive. The lower end of the needle is slightly weighted, so that it hangs vertical when no current is passing. Hence this form of galvanometer is more used than the other, as it requires no adjustment of position. The gradu- ated scale is placed above the needle, as seen in Fig. 15. Without care the readings of a galvanometer may be mis- understood, for a deflection of 40 Q must not be taken as an indication that the current is just twice as strong as one pro- ducing a deflection of half that amount, or 20°. A special scale has accordingly to be provided for each instrument. In a well- made detector, the values of the degrees up to 30° were found very nearly to correspond with the strength of the current ; above that the following results were obtained : — 40° deflection represented a strength equivalent to 44° 50° „ 65° 60° „ • „ 93° 65° „ 150° In another galvanometer, the values of the reading would probably differ to a considerable extent ; it is necessary, there- fore, for each to be graduated by actual trial. The following is the simplest manner in which the daily tests for insulation and resistance are made Let A and B be the stations at the ends of the line. A puts a detector in his circuit, and then sends' a current through it along the line, having first informed B, who for a short time, say two minutes, disconnects his line-wire altogether, so as to leave it completely insulated. The deflection of the deteotor during this period shows the amount of loss by imperfect insulation, and if this amount is above the daily average, it plainly shows some defect, as, for instance, a broken insulator. B then, for a similar period, con- nects his end of the line-wire to a good earth, through his own detector, and the results now obtained show the resistance to the current. A very weak battery should be employed for this purpose, since otherwise “full deflection” would almost cer- tainly be obtained, even although a considerable fault existed. Only very rough tests can therefore be made in this way, and at all principal stations the resistances are accurately ascertained 256 THE TECHNICAL EDUCATOR. by means of a resistance coil and a differential galvanometer. The last-named instrument consists of a magnetised needle mounted with two independent coils, each of which exerts the same influence on the needle. If, then, the current be made to pass round these in opposite directions, the needle will remain at rest, one coil exactly neutralising the effect of the other. In order to use this galvanometer, two passages are provided for the current from the battery ; the resistance to be measured is made a part of one of these circuits, while in the ascertaining the position of a fault in any line, when it has been ascertained that there is one. We must, however, first know the different kind of faults that are met with. The first is a total interruption of the circuit arising from a broken wire or some similar cause, in which case no current whatever passes. There may also be a partial want of continuity in- dicated by the signals at the receiving station being less distinct | than usual ; so much so at times as to be unintelligible. Another defect is “ earth ” on the line — that is, a connection other is placed a series of resistance coils by which a known resistance can be introduced till it exactly balances the other, as shown by the needle remaining at zero. The annexed diagram (Fig. 16) will render this more clear. B is the battery, from each pole of which there are two con- ducting wires. The one leads to the binding-screw a, whence the current passes round one coil to e, thence along the line- wire l, whose resistance is to be ascertained, returning either by the earth or by another wire whose resistance is known, or else similar to that being tested. The other bat- tery wire leads to c, and from this the current passes round the other coil of the galvanometer to B, thence through the set of resistance coils r, and back to the other pole. Two courses are therefore open for the current, and it accordingly splits between them ; the greater portion, how- ever, passes along the route which offers the least resistance, and the needle is accordingly deflected by that. By means, however, of the various coils in R, the resistance in that circuit can be so ad- justed as exactly to balance that of the line, which is thus ascertained. If the current returns from L by a wire similar to itself, the resistance must be divided by 2 to give that of each wire. If it re- turns by a wire of known resistance, that must be deducted to give the resistance of L. s is a “ shunt ” affixed to one of the coils of the galvanometer, so as to reduce the effect of the current upon it by providing a short path for the greater portion of the current. A peg is inserted between the pieces of brass, and offers J5 or -jig the resistance of the coil, round which accord- ingly only or ^ of the current passes. The advantage of this is that by it a much smaller resistance coil is required, since one of 1,000 units may balance a resistance of 10,000 or at some place between the line-wire and the ground, so that a greater or less portion of the current escapes. If the connec- tion be a very good one, so that the whole of the current escapes, we have what is technically known as “ dead earth.” In this case the signals at the sending station are stronger than usual, since there is a shorter path for the current to travel along, but no signal whatever is received at the receiving station. When this happens, each station along the line should in succession transmit a current, and the interruption will evidently be beyond the last one from which a current is received. When it has been ascertained between which stations the fault lies, its place can be found by noting the resistance of that piece of line as compared with its usual resistance. If it be only half as great as usual, the fault is probably about mid-way along it, and so in proportion. Partial earth occurs when there is a fault by which only a portion of the current escapes, and this is a more difficult fault to test for. The signals at the sending station are still unusually strong, since two return paths are open for the current, one by the fault, the other in the usual way. The signals at the receiving station are, however, weakened considerably. The best plan of testing for a fault of this description will be understood by reference to Fig. 18, in which the battery, etc., are denoted by the same letters as before. If possible, a good wire, H, leading from the receiving station, should be used as a return wire, being connected to the faulty one at G. Let r be the place of the fault, and let the connections be made as shown. The current leaving c to the earth-plate will divide at E, a portion passing along by G, H, e, A, to z ; the other portion passes through the resistance coils R, and so to z. If Rwere 100,000 units, the proper shunt being employed. In this case the indicated resistances must of course be multiplied by 10 or 100. When the test for insulation is being made, 'the further end of the line is disconnected, and the corresponding pole of the battery put to earth, as seen in Fig. 17. This circuit then can only be completed by the escape of a portion of the current from the line-wires to the ground, owing to imperfect insula- tion. In keeping a record of these tests, it is important to note also the state of the weather at the time of taking them, since this makes a material difference in the state of the lines. We must now endeavour to explain roughly the manner of removed, the latter portion would clearly bo the stronger, since it has the shorter distance to travel ; by introducing a resist- ance, therefore, we can ascertain how much one exceeds the other, and from that we can calculate approximately the place of f. When this is done, there will probably be little difficulty in the line inspector ascertaining and repairing the damage. If any portion of covered wire or ^instruments exist in the circuit either way, allowance must be made for the extra resist- ance caused thereby, or else the calculation will mislead. In any testing experiments the copper pole should always be put to earth, since a negative current discovers a flaw much more readily than a positive current. OPTICAL INSTRUMENTS. 257 OPTICAL INSTRUMENTS.— III. BY SAMUEL H1GHLEY, P.G.S., ETC. DIAGNOSIS FOE SPECTACLES. To ascertain what form of lens is needed to correct the defec- tive vision of a patient, the optician or oculist must first deter- mine the true nature of the defect — whether it be presbyopic myopic, or hypermetropic; and if the person is not advanced in years, great care should be taken to ascertain whether or not the last defect exists, for by a faulty diagnosis great injury might be brought about through supplying unsuitable glasses. Again it must be determined whether failing sight is due to optical detects of vision, or to those weaknesses of sight known as amblyopia and asthenopia, which are due to irritation of parts Qi the eye. First, he must determine the patient’s “ acuteness of vision ” i S technically termed, by exercising the eye on Dr. Snellen’s le f fc These consist of carefully-drawn, square, litho- graphed letters, whose limbs have a width equal to one-fifth of the letter s height, such being generally distinctly visible to a normal eye at an angle of 5'. These letters are arranged singly or in groups, and of increasing size, with a number attached to each to indicate the number of feet at which the particular- sized letters must be placed from a normal eye, to subtend an angle of 5 for their height ; and, further, an angle of 1' for the breadth of the thick strokes, for determining “the minimum angular magnitude of distinct vision ” (which is taken at 1 ). These types range in size from the smallest letters, to be seen at 1 foot, to 3 4 inches m height, to be employed at 200 feet 1 wo diagrams are specially designed for testing the acuteness ol vision at an infinite distance, that is, from 20 feet to 200 ieet— one havmg black letters on a white ground ; the other similar letters, but white on a black ground. To normal eyes these seem nearly alike as to distinctness ; but should the white letters on a black ground appear more distinct to the patient a diminution of acuteness of vision is indicated, which probably results from diffuse light, arising from turbidity of the refractive media of .the eyes. The distance from which the tes -types can be distinctly recognised should be measured from the surface of the paper to the temple of the person under examination. These letters are grouped in irregular order, so ■'X ri< l, he P be S lyen to their recognition by juxtaposition with other letters, as would be the case were words employed • w lie, on the other hand, to attain, if possible, more uniform distinctness, certain letters that might lead to confusion with ? DerfecT? T Thua ever V care 18 taken to ensure a peilect and independent recognition of these letters without any extraneous help* The degree of acuteness of vision (V) is Expressed by the relation of the distance at which the letter is anSfof 7' e (I)) d t0 that ^ Which th ° letter is a PP ar ent at an d V = D’ at If Yv°' is dist inctly seen at a distance of one foot, and it "follow ■ that 611 * 7 feet ’ tllGn d and D are equal > and accordingly „ 1 20 V = ? = ™ = 1; An investigation of 281 cases of emmetropic eyes at different ages gives the following results : — At from ten to twenty years . . . . ~y At thirty years _ At fifty years __ At sixty years ... j ..... y = At eighty years . . . . » . . . s y _ Bh. 20 22 . 20 * 18 20 14 20 * n 20 * witha^T be ° bserved ’ the normal acuteness of vision decreases Besides these tests by jumbled groups of letters, the person may be tested by reading in different-sized type, but such ex- periments must not be identified with the recognition of isolated letters, for the reason previously stated ; but in other respects reading is a more difficult test, because the letters of words as ordinarily printed, are very close together, hence more confusing for immediate recognition. s For testing by reading, fluency is chiefly to be regarded for with a contracted or interrupted visual field reading is less ed» 0 ?t£ 10M “““ ttiS test C “ be «” Snellen’s reading tests are printed in type as nearly as pos- sible uniform with Ins letter tests, and the following numbers of his typos correspond in height with the less scientific system ri'Jf; u yPeS ° f Professor lager, which, however, have been pnncipally used m this country.* No. I. of Snellen’s = No. 1 of Jager’s Test-Types. Ir - „ 5 in. „ 7 IT. H V. „ 13 VII. „ 14 XVIII. „ is XXVII. „ 19 TAX VIII. „ 20 XX or, in other words, there is normal acuteness of vision. , on the other hand, No. I. is only distinct at six inches from the eye, and No. XX. at ten feet, then d is less than V y _ £ _ 10 _ 1 I 20 2' If No. XV can only be recognised at a distance of five feet Ten we get the following equation : — ’ V=^ XV 3’ _ be g fv ate i' than D ’ and No - XX - be thus visible at tbaU i WOnty feet ’ then acuteness of vision is more than the normal averag*e. A good series of reading test may be formed of short para- graphs set up m the following well-known printer’s type^ No. 1, brilliant ; No. 2, “ pearl ; ” No. 4, “ minion ; ’’No. 6, ,« bour S eois ; No. 8, “ small pica ; ” No. 10, “ pica ; ” No. 12 great primer; No. 14, “double pica;” No. 16, “two-line great primer ; ” No. 18, “canon;” No. 19, “four-line con- densed; No. 20, “ eight-line Roman.” An eye with normal acuteness of vision ought to be able to read Nos. 18, 19, and 20 of these types at a distance of twenty feet; but a person may be so amblyopic as not to be able to read the largest of Snellen at any distance. In such cases we may try whether the Person is able to count fingers at different distances, or whether he can distinguish light from darkness by placing him at six feet from an argand gas-flame in a dark room, then turning the light up and down slowly; or, if this fails, from hght to sudden darkness, and back again. If the patient cannot distinguish between such extremes, he must be “ stone blind. We must next test for the “range of accommodation” the patient s eyes possess, by first determining the “ near-point ” and then the “far-point,” which may be expressed by the following formula : — . benefit “ Test T ^ es '’ « published for the Soijate Ophthalmic Hospital, by Messrs. Williams 17 — Vol. I. in which p represents the {proximate) nearest point of distinct vision, and r ( remote ) the farthest point of distinct vision, and 1 ~ A the range of accommodation. For this purpose we employ an optometer, which consists of a carrier for a test-plate, and an adjustable scale that will give the exact distance between the face of the pla,te and the cornea of the patient’s eye. The test-plate may consist of a paragraph set up in •• 0 r “Pearl” type which corresponds to Nos. 1 and 2 of Jager’s reading tests • or of a little frame, 7-8ths wide in the opening, divided vertically into six parts by five fine black wires or horsehairs ; or of a black * C °P ies of Jager’s test-types may be obtained of the Secretary at the Eoyal Ophthalmic Hospital, Moorfields. 258 THE TECHNICAL EDUCATOR. plate, pierced with little holes from l-20th to l-6th of a line in diameter, behind which a background of ground-glass is placed : these rapidly emit rays, and lose their round form, if not perfectly focussed on the retina. The adjustable scale may be a winder measuring tape, the ring of which is looped on to the handle that supports the test-plate ; or it may be a shoemaker s rule, the fixed end of which is cut down and notched to receive the patient’s eye, the test-plate being fixed to the sliding upright ; or it may be a specially-designed piece of apparatus, consisting of a graduated brass rod, mounted on a firm telescopic foot by a shifting-hinged joint, on which a frame that carries the test- plate works freely up or down, and can be clamped at any desired position by means of a milled-headed screw. Whatever the arrangement, the test-plate should, as Donders has pointed out, be moved steadily up to, or away from, the eye under examina- tion for “ ordinary individuals accommodate for their farthest point only, when they actually look at a distant object, and for their nearest only, when they very distinctly see an object ap- proaching, whose diminishing distance they meanwhile observe and follow in their imagination. Then, by the effort actually to see the object distinctly as long as possible, the greatest power of accommodation is excited.” On sliding along the reading-test towards the eye, we soon find the nearest point at which the text can be read off. With the wire-test, the wires only appear sharply defined when the eye accommodates itself perfectly to them ; directly there is a deviation in this (the frame being too near or too far from the eye), the wires seem indistinct, thicken, or as if surrounded with a halo ; or even double-coloured images of them appear in the transparent intervals, as a white wall or the sky should in this test be used as a background. The same may be remarked in regard to the test-holes, for they rapidly lose their round form and emit rays when the eye is not in perfect accommodation with them. It will be readily seen that much depends upon the intelligence of the person under examination in appreciating the distinctness of the wires or the sharp form of the holes ; therefore the reading-test is, as a rule, the most readily applied ; for it is oftentimes absurd to what a distance persons will maintain that the wires and holes seem well defined ; while, by moving the reading-test alternately nearer to and further from the eyes, we can readily ascertain with exactitude both tho near and the far point of distinct vision. If to this optometer we add an arm fitted with a six-inch convex lens, the far-point may be ascertained in all cases. If for an eye (with suspended accommodation) we have to move the test-plate to six inches’ distance to secure distinct recogni- tion, it is emmetropic ; if nearer to the eye than six inches, it is myopic; if further off, it is hypermetropic. The systematic employment, in the optometer of Yon Groefe, of a convex lens of only six inches focus, presents advantages over those of longer foci, as it brings the normal eye to a condition that is very nearly myopic, and so in a state more favourable for comparison. By employing an optometer of the kind last described, the far ('/) and the near (p 1 ) , thus found, stand in such a relation to the patient’s real far (r) and near (p) point, that the rays coming from r' are refracted by the lens as if they proceeded from r, and those from p as if they emanated from p. . In the normal eye (with 6-inch convex) i would lie at six inches from the eye, for rays from an object at six inches’ distance falling on the lens would be rendered parallel by it, and would consequently impinge upon the eye as if they came from an infinite distance or the normal far-point. The near- point {p') would lie at about three inches, for this varies ac- cording to age. . If (with 6-inch convex) we find the far-pomt (r ) lies at six inches, and the near-point ( p ') at three inches, the eye is then emmetropic. If (with 6*inch convex) we find that '/ — 5 inches, and p' = 3, the, eye is then myopic, for it is not adjusted for the normal far- point (six inches), but for a nearer one, the rays from which impinge in a divergent direction upon the eye. If (with 6-inch convex) we find that / — 8 inches, and p — 3 inches, the eye is then hypermetropic, for its far-point lies beyond the normal far-point, namely, six inches. It has been stated above that these determinations may be made for an eye with suspended accommodation. Now in practice this is rarely met with, except in cases where the power of accommodation is paralysed (“paralysis of accommodation,” as it is tech- nically termed) ; but we have the power of producing such a state of rest artificially, by the application of a solution . of atropine (gr. iv. to Jj) two hours prior to making the trial. As the effects of atropine last for some days, I need hardly say that the ordinary optician would not be justified in using this agent on his customers, and that its employment must be confined to the practice of the medical oculist. Moreover, as decided cases of presbyopia and myopia are readily determined by optical tests, it is only in cases of suspected hypermetropia, or for determining the whole amount of a patient s hyperme- tropia, that atropine is needed. But when there is reason, from the form of the eye (see p. 160), together with complaint on the part of the patient of con- stant fatigue in the organs of vision, to suspect the existence of hypermetropia, the optician may make the following tnai. Try the patient’s eye on No. XX. of Snellen s test-types, at twenty feet distance, or on a paragraph set up in type of this size Canon If the eye is emmetropic, it will read this at the distance specified ; and a hypermetropic eye will most probably do the same, unless the hypermetropia be very great, or its accommoda- tion has been paralysed by atropine ! Now try the patient with spectacles glazed with 20-inch lenses on the same object at the same distance ; if the eye is emmetropic, it will no longer be able to read the test ; while if it be hypermetropic, it will read it with greater facility than before. In extreme hypermetropia the eyes may not be able to read the test with 20-inch lenses, but can without them. Thus assimilating to the characteristics of a normal eye makes its diagnosis by optical tests extremely difficult ; but a suspicion of its existence should be created when fatigue in the eye is constantly complained of ; and as the question must then be settled by ophthalmoscopic indications, it becomes the duty ot the optician to direct the patient to consult an ophthalmic surgeon ; for the diagnosis and mode of treatment must be medical as well as optical. . In testing for the range of accommodation, it is necessary to try both eyes of the patient ; for it will often be found that tho two eyes of the same individual may possess a difference m accommodative power. In other cases we may find that the near-point may be normal, but the far-point approaches nearer than an infinite distance to the eye, which might be mistaken for an indication of myopia ; or the far-point may be normal, and the near-point abnormally distant from the eye ; or both near and far point may have changed their normal position, and have become approximated to each other. We may also meet with a dislocation of accommodation, without any diminution in its range. _ . In making trials for the far and near point, we bear in mind that in the normal eye its far-point lies at an infinite distance (symbolised by <*>), so that parallel rays are united on the retina when it is adjusted for its far-point, while its near-pomt lies at from four to five inches from the eye, though even a near- point of seven inches is not to be regarded as sufficient y abnormal to amount to a defective state of vision. In testing for the near-point we may find that one person wxli clearly distinguish the test-plate as close as three inches while another cannot do so nearer than thirty inches. This indicates that the one has the power of increasing the convexity ot his crystalline lens by a quantity equivalent to a 3-mch glass lens ; while the second can only do so to an extent equivalent to a 30-inch glass lens ; and we say that the accommodation ot the first equals l-3rd, and that of the second equals l-30th. TECHNICAL DRAWING. 259 TECHNICAL DRAWING.— XVII. DRAWING FOR MACHINISTS AND ENGINEERS. FREE-HAND DRAWING. The great importance of Free-hand Drawing to artisans has already been insisted upon, and a few examples in this branch of the subject will be given in this part of our lessons in “ Tech- nical Drawing, in order to show the kind of practice which is deemed advisable for machinists and engineers. Our workmen have laboured under the mistaken idea, that so long as they could manage to measure and rule the lines from a copy with some degree of neatness, they were learning Mechanical Drawing. Nor were the teachers of the period im- mediately preceding the present competent to give them better instruction ; for whilst qualified mechanical draughtsmen were not teachers, the teachers were artists, but not engineers. It was only when the Government Department of Science and Art undertook the systematic training of masters of Schools of Art — in which not only ornamentists and designers, but arti- sans generally were to be taught— that this branch of the sub- ject began to receive proper attention, and was made a portion of the certificate examination 5 and not only is Linear Drawing by means of instruments taught, but the artisan is shown how to sketch from objects and to draw curves by hand ; in fact, an enlarged view of the whole subject has been given, of which’the fruits are daily becoming more obvious. The early training of foreign artisans has in this respect been superior to ours ; and in the different exhibitions which have been held in this country and on the Continent, workmen were to be seen with their note- books busily employed in collecting information, and sketching the appliances connected with their peculiar walks of industry. Such notes and sketches, however roughly done, must be a source, not only of great usefulness, but pleasure to them. Drawing, too, constitutes a universal language, which to artisans is a matter of the utmost importance ; for by its means they can illustrate the form of an object in an infinitely less period of time than by words, to persons who may not be able perfectly to understand the language of the country; in fact in the words of Sir Joshua Reynolds, “the pencil speaks the tongue of every land.” Ihe machinist must remember, too, that in making drawings from actual measurement, the instruments are not in the first instance employed. All the implements used are the pencil and the “ two-foot rule.” The draughtsman makes a rough sketch entirely by the hand and eye, measures the various parts, and jots down the measurements in his sketch. After this he reduces the whole to the required scale, and proceeds to make his mechanical drawing. As the lessons proceed, the student will be taught how to draw from objects seen perspectively. In commencing, how- ever, the practice is confined to a few well-known objects placed so as to present only one surface to the eye of the spectator, and which can thus be drawn as mere elevations. In the first instance tools have been chosen, because the student is sup- posed to be well acquainted with their forms ; thus, when he has sketched them, he will, as it were, be able to check his own work, and this may, it is hoped, lead him to try his hand on other objects ; he will thus gain power and courage, and will be gradually led on to attempt (and to succeed in) higher things. Drawing, in addition to its use as a universal language, is a means of strengthening the powers of observation, and, viewed in this light, it is a study of the greatest importance to work- men. . To “ look at” is not necessarily “to observe ”- — the latter term implies a careful examination of all the parts of an object, an accurate study of the points in which they differ from others, and their peculiar adaptation to their special purpose. In this drawing materially aids the student ; for as each line of the object is followed, and compared with others, the mind is led to appreciate forms which would have escaped casual observation. The artisan will understand what is meant by this accuracy in observing special forms, if he calls to mind the differences which exist in even the same tool, when adapted for the various branches of handicraft. Take, for instance, such a simple tool as a hammer, and note the variations in form between the joiner’s hammer, the fitter’s hammer, the smith’s hammer, the watchmaker’s hammer, etc. ; and it must be remembered that all the differences visible are of importance in the work in which the tools are to be used. Fig. 184 is a sketch of a pair of compasses, such as is com- monly used by machinists ; it is here given, in order that the student may compare it with Fig. 25, page 68, which repre- sents the same instrument used by the carpenter or joiner; and the difference will at once become evident. The method of drawing this object being in the main the same as that already given, is not repeated here. The student is reminded, too, that even in the same branch there are different forms of the same instrument — such as the compass with a quadrant and thumb- screw, and, for finer work, the spring-dividers ; all have their peculiarities, and each will afford a subject for careful study. Fig. 185 is a machinist’s screw-driver, which will afford another study as to the differences in form when compared with the joiner’s screw-driver, given in page 48. In this subject, too, the horizontal centre line A b having been drawn, the directions given in connection with the former subject are to be followed. Fig. 186 represents a pair of callipers. Draw the perpen- dicular A b, and the circles at the top. Next sketch the curve from c to b, and adopt as a general rule that the curve on the left side should be drawn first when another is to be drawn to balance it ; for if the right curve were sketched first, the hand would cover it when drawing the other, and thus the balancing; would be rendered difficult. When this curve, then, has been satisfactorily sketched, draw a line, D, across the widest part, and from F mark off the length f e equal to f d ; the curve G b may then be drawn. The inner lines to H and i are to be straight, and from these points the inner curves to the ends of the legs are to be drawn. It will be seen that, although the callipers are open, it is advis- able to continue the curves in the first instance to b, although only wanted as far as j, k. PRACTICAL GEOMETRY. A fair knowledge of Practical, Plane, and Solid Geometry is of the utmost importance in mechanical drawing, in which the various constructions are applied, and it is therefore assumed that the student has worked through the majority of the figures in lessons in “ Practical Geometry applied to Linear Drawing ” and “ Projection,” which are intended as stepping-stones to the present lessons. A few additional figures, however, bearing immediately on the subjects to be delineated, are here given, and the student will find that the application of these and other scientific methods will not only enable him to work with greater accuracy than any empirical means, but will save much time and trouble. Figs. 187 and 188 show the liability to inaccuracy where a straight line has to be drawn to touch a circle. In Fig. 187, owing to the great radius of the circle, it is almost impossible to say which is the exact point of tangent ; and in Fig. 188 it will be seen that, owing to there being no definite point at which to draw the straight line, it often occurs that it is so drawn as to cut off a portion of the circle. Fig. 189 shows two pulleys rotating in the same direction by means of a band wrapped round both. Now it will be clear that this band must touch the circles, without cutting off any portion of the circumferences, and must therefore be composed of true tangents. Fig. 190 will remind the student that a true tangent is at right angles to the radius drawn from the point of tangent. Having, therefore, set off on a. straight line, A b (Fig. 189), the centres of the two circles at their correct distance apart, and having described the circles, draw diameters at right angles to A b. These will cut the circles in cd and e f, thus giving the exact points which are to be joined by the straight lines of the connecting band. Fig. 191. — To draw tangents to a circle from a point, a, lying without it. From A draw a line to the centre of the circle, B. Bisect a b in c. From c, with radius c b, describe an arc cutting the circle in D and E. Draw a d and a e, which will be the required tangents ; and it will be seen that the radii drawn from d and e are at right angles to these. Fig, 192 shows the method of drawing tangents to two circles of different diameters. Draw a straight line through the centres A and B of the circles, and produce it. 260 THE TECHNICAL EDUCATOR. Draw any radius in either of the circles, as b c. second circle, draw a radius, A D, parallel to B C. From c draw a line through D, meeting the line of centres 11 The point e is therefore “a point lying without the circle,” from which it is required to draw a line which shall be a tangent to both circles, therefore proceed as in the last figure — viz. Bisect the line joining E and A in r. From F, with radius F A, describe an arc cutting the circle A in G and h. Draw the radii A G and A H. From b draw the radii B i and b j parallel to AG and A H. Then straight lines drawn from E through G and H will meet the circle B in I and J, and will thus be tangents to both circles. Fig. 193. — This figure shows a driving - band crossed, by which means the pulleys are made to rotate in opposite direc- tions. Join the centres of the circles by the straight line A b, and draw diameters at right angles to this line, cutting the circles in c, d and e, f. Draw c F cutting A B in G. Bisect A G in h. From H, with radius H A, describe an arc cutting the circle a in i and J. Draw the radii A i and A j. In the circle b draw the radius bk parallel to A I, and the radius B L parallel to A J. Draw i K and J L, which, passing through G, will be the two lines required, each being tangential to both circles. Before proceeding to the next lesson it may be men- tioned that the student should keep up the con- stant practice of free- hand drawing, since it is only by practice that any degree of proficiency can be obtained. Amongst other subjects which might furnish good practice for free-hand drawing, are the following : a vice, a hand- vice, a hammer, a pair of plyers, a pocket-knife with ; one of its blades open ; and 1 then the student is advised to try his hand on parts of machines, as a hanger, a plummer- block, a crank, a cone-pulley, etc. Many of these subjects for study are to be found in the lessons in “ Technical Drawing, and these may serve as guides ; but in the present stage the work is to be done by free-hand only. Again the student is urged to sketch very lightly at first, so that he may have an opportunity of reviewing his drawing as a whole before “ lining in he can then easily rub it out and repeat the lines. In starting any subject which, like the callipers and compasses, is equally balanced, a vertical line should always be drawn. Now, some persons have from habit acquired the power of drawing horizontal lines more easily than upright ones, and therefore turn the drawing-board in order to draw the line parallel to their chest. This is a very bad practice, and should be carefully guarded against in young people. Nor should the board be turned in drawing the object itself. The left side should be drawn first, and then balanced by the right, as already described. The drawing should then be held up, and the faults in balancing will at once become visible. It is best in sketching, whether the form is to be regular or otherwise, to generalise the Whole before drawing any single part definitely; by this means much time is spared, for the student will often, when he pursues the opposite plan, find he has bestowed much care on drawing one portion of the subject, which when he comes to draw the rest, he finds too large, too small, or otherwise useless. A few touches, scattered as it were over the paper, will, however, enable him to judge of the general proportions of the whole, and of the position and space which should be occupied by the details. To do this, it is best to look upon the whole sub- ject in the first instance as one mass, and having sketched this, find the points where it might be divided into two or three smaller portions ; not abso- lutely drawing the lines, but marking off the spaces. By this method room will be found for all the parts, and it will be easy to get all the proportions correct. Having thus generalised, some fixed point should next be decided upon, and this should then be sketched with some care, so that other parts de- pendent upon it may be properly placed. Thus proceeding, the minor details will follow in their places. It is a good plan for artisans to repeat their drawing in ink with a steel pen, instead of using the pencil ; in doing this the pen must not be pressed on, as in the down-strokes in writing, but the student must endeavour to keep a fine equal line throughout. In some cases a flat- wash of colour may be thinly and lightly spread over the representation of the object, which practice will m some degree prepare the student for the lessons to be given further on. In the TECHNICAL DRAWING. 261 262 THE TECHNICAL EDUCATOR. TECHNICAL EDUCATION ON THE CONTINENT.— IX. BY ELLIS A. DAVIDSON. THE TRADE SCHOOLS OF WURTEMBURG : STATISTICS AND WORKING. The general system of the trade schools having been thus dwelt upon, some statistics as to the attendance and teaching staff will be interesting, as showing the extent to which the population avail themselves of the great advantages held out to them. The total number of the trade schools in Wurtemburg in 1808 was 135— viz., 102 in towns and 33 in villages, against 122 schools (97 in towns and 25 in villages) in the previous year, showing an increase of 13 in the number of schools viz., 5 in towns and 8 in villages ; united population, 490,626. The average attendance of pupils in 135 schools is 8,352, of whom 6,533 are under and 1,819 are above the age of seventeen. The number of groups into which the trade schools are classed is as follows : — 1. Trade schools holding classes on Sunday evenings as well as on the evenings of the week, and in which a drawing school is open all day ; viz., Stuttgart, Ulm, Hoilbron, and Beutlingen . . 4 2. Trade schools (Sunday and week-day evenings) in which there are trade but not commercial classes, but still drawing schools open all day; viz., Eszlingen, Ludwigsburg^ Gmiind, Tubingen, Can- statt, Hall, Bavensburg, Biberach, Eottenburg, Kirchheim, Eottweil, Calw, Ellwangen, Ehingen, and Geislingen . . . . . . .15 3. Trade schools with evening classes on Sundays and week-days, but without separate drawing schools (63 towns and 22 villages) ... . .85 4. Trade schools with classes only on the evenings of week-days (6 in towns and 2 in villages) . . S 5. Drawing schools only (14 in towns and 9 in villages) 23 135 It must be remarked that by the “ drawing classes” are not meant the “ Schools of Art,” which are separate institutions, which although they give technical instruction of a high cha- racter, cannot be treated of in the circumscribed limits of these papers, and are therefore reserved for future consideration. The number of teachers in the 135 trade schools is 489 ; or, on the average, 1 to each 17 pupils. The separate classes are attended by the following numbers of pupils : — - Arithmetic, 4,292 ; free-hand drawing, 3,951 ; German lan- guage, 3,819 ; trade drawing, 2,157 ; geometrical drawing, 1,969; book-keeping, 1,264; plane geometry, 1,031. The following table shows the number of pupils and teachers in 24 of the principal schools : — Pupils. Teachers. Pupils. Teachers. Stuttgart . . 1117 69 Metzingen . . 100 4 Ulm . . . . 709 22 Aaien . . 98 6 Heilbron . 247 12 Giippingen . 96 7 Biberach . 222 12 Canstntt 94 7 Reutlingen . 219 16 Saulgau 91 8 Ludwigsburg . 199 9 Hall . . . 94 8 Ravensburg . 194 16 Niirtingen . 89 3 Eszlingen . . 182 15 Ellwangen . 83 3 Freudenstadt . 154 5 Rottenburg 88 5 Geislingen . . 104 7 Rottweil r 86 6 Heidenheim . 103 4 Tuttlingen . 86 4 Gmiind . . . 101 5 Ehingen 85 4 In their annual report of the working of the trade schools, the Eoyal Commissioners say, that whilst testifying to the satisfactory working of the whole system, they are especially happy to see the position taken by the drawing and modelling classes, and their influence on the industries of the country. The system on which drawing is taught is calculated to educe all the power, and to awaken the interest, of the pupils. Drawing from casts is studied at the same time as modelling from copies, the pupil thus obtaining sound notions of the relation between the “flat ’’and the “round.” In both cases the student works to a different scale to that of the work he is reproducing, and thus his ideas of proportion are developed. Although the greatest tact is exercised by the teachers so that the manual powers and the mental grasp of the students may not be overtaxed, and so that discouragement from failure may not ensue, still every impetus is given to progress, and every inducement to work is held out; thus, whilst idle or wilfully negligent pupils are dismissed, the utmost care is exercised, so that a pupil whose mind does not turn to any one study may be directed to another; and even if rather below the standard of the other pupils, he is placed amongst such as are willing and able to help him upward ; the system of men being mutually helpful being acted upon with every success: The work accomplished by the regular art schools (or such of the schools as possess special drawing schools) is being emulated by numerous others, and it is hoped that the results will be exhibited before long. The old-fashioned system of allowing a student to work many months at one subject requiring only manual skill — such as finely shading a drawing from a large cast with the chalk-point — is discouraged ; and whilst the projection of shadows is taught on the most correct scientific principles, the mere execution is carried out boldly, and in a broad manner. Drawing from memory is much practised, and the students are taught to carry out a design, the details or natural type having been previously studied. On the whole, therefore, drawing becomes a mental rather than a merely manual exercise. The travelling library, containing not merely books, but port- folios of engravings, which are circulated amongst the schools who apply for the loan, is a source of continual pleasure and inspiration to the pupils, who by reading of the works of the great masters, and studying illustrations of their masterpieces, see, and are led to think, that “ what man has done, man can do.” In old-fashioned “ copy slips” used in English schools, there used to be two trite sentences which sadly puzzled boys ; the one commencing the alphabet started with a capital A in the most extensive flourishes, and it said, “ Attempt not im- possibilities.” Here, then, was the bane to all youthful aspira- tions ; but in order to introduce the capital B the antidote came on the next page, “ By attempting -impossibilities men accomplish possibilities ; ” the question, however, as to what was possible or impossible, was left undecided. The copy on W was simply “Write with care.” The sentiment above given, “What man has done, man can do,” would have given some clue, though not a complete one ; for what the great men of old did, they did by dint of labour, method, and self-culture : how much more, therefore, can our youth be expected to accomplish with oppor- tunities such as are now at their disposal ! It is, indeed, satisfactory to know that in regard to the loans of books, pictures, etc., we are carrying out a similar system in this country, and th^t the most valuable and unique works are circulated from the magnificent museum and library at South Kensington to such schools of art as make arrangements to receive them, and enter into the proper guarantees for their safe keeping. The means for public instruction in Wurtemburg are so very numerous, that it is impossible here to do more than mention the various institutions. Amongst these may be named — The University of Tubingen, in which the curriculum of education is of the widest character — literary, classical, mathematical, medical, surgical, theological, philosophical, chemical, etc. ; the Agricultural School, comprising all the branches of knowledge comprehended by that term — farm management, farm buildings, gardening science, the commercial arrangements of farm land, measuring and valuing, agricultural botany, chemistry and geology, etc. ; the Veterinary Schools, with their concomitant courses of instruction ; the Polytechnic School of Stuttgart, of a character similar to that of Hanover, already described ; the Building School at Stuttgart, of which an account will be pre- sently given; the Schools of Art; the “Beal” Schools, for higher and extended education of middle and upper classes ; the Public Primary Schools ; Industrial, Blind, and Deaf and Dumb Schools, etc. All show the deep sense of the responsibility which the enlightened Government feel for the welfare of the people, and of the duty they recognise as incumbent upon them to provide a full and practical education for all classes of the community ; but this is not all — the great educational scheme is not a new one ; it has now been going on for many, many years, each year only showing further development. It is clear, then, that the authorities would not go on adding schools and assist- ance if they were not demanded by the people ; nor would the numerous institutions be kept up, were they not found of use or value ; the plan being, as has already been set forth, to assist, but not to supersede, local effort. BUILDING CONSTRUCTION. 263 The purpose, therefore, of these papers is to show to our people what is being done abroad, not merely as “ a tale that is told,” but to urge on them the necessity of a united effort ; first, to avail themselves of such opportunities as already exist ; secondly, to show by their attendance and numbers that they are willing to receive instruction, and to benefit by it ; and, thirdly, to demand a further development of the germs, so that every working man in this country may be able to obtain the instruc- tion which he finds necessary for his special branch of industry. We will conclude our notices of the excellent technical schools of Wurtemburg with a brief account of THE SCHOOL OF PRACTICAL BUILDING AT STUTTGART. The object of this school is to give a thoroughly systematic education, in the scientific principles of their trades, to the fol- lowing classes of persons engaged in the building trades : — 2. Skilled artisans, masons, stone-carvers, carpenters, etc. 2. Builders’ clerks, including clerks of works, surveyors, etc. 3. Sluice and mill builders. 4. All trades of which geometry forms the basis. In the general working of the school there are courses of instruction adapted for plasterers, bricklayers, tilers and slaters, millwrights, mechanics and locksmiths, carpenters, glaziers, plumbers, turners, house and room painters and decorators, ornamental carvers and mod-ellers, engravers, silver and gold workers, gardeners, and all other trades, in fact, dependent on drawing. The working of this school is carried on throughout the year ; and the work of each half-year is divided into five courses, so that a student has the opportunity of attending all the courses in one half-year or the other, of taking some in one half-year and some in the other, or of attending both. Further, students who, on completing the whole of the courses, wish to continue the study of architectural design and building construction, are permitted to remain for that purpose. The students who really intend following any branch of the building trades are not only instructed in theory but practice. There are workshops attached to the school in which manual work is taught, but only such branches are there carried on as are not practised in the locality, or are insufficiently known. Visits are constantly paid to large works in the neighbour- hood. The school is divided into five sections : — 1st Class. This class is intended for pupils who have received their previous education in a parish school, or who, although they may have attended any other schools, have not acquired sufficient knowledge to permit of their entering any higher class in the school. The subjects of instruction are German, French, history, geography, writing, arithmetic, elementary geometry, free-hand and geometrical drawing. 2nd Class. Advanced German, French and writing, geometry and stereometry, algebra, building drawing, drawing for builders, Gothic architecture, ornamental drawing. 3rd Class. Natural history and physics, descriptive geometry, trigonometry, practical geometry, architectural drawing, orna- mental drawing, architecture, building construction. 4th Class. Mechanics, applied practical geometry (including stone-cutting), the projection of shadows, perspective, archi- tectural and ornamental drawing, building materials, archi- tecture, building construction, practical building, the implements and mechanical apparatus used, arrangements for warming and ventilating, architectural styles, the construction of roads and railways, specifications and the cost of buildings, rural archi- tecture, practical mathematics. 5th Class. Architectural designing and construction of work- ing drawings for building purposes, applied mathematics and physics, considerations as to sites, account keeping, etc. There is also a separate section for the special instruction 6t “geometers” (i.e., all other trades or professions in which geometry forms the basis), a school of hydraulic architecture, and a class for the study of machinery. Visits are paid to workshops and buildings in course of erection, and excursions are made for the purpose of practising land-surveying. The students are classed as ordinary and extra-ordinary, the former being such as attend the entire course; while the latter are such as attend other schools, or are already engaged in trade, and who enter for certain courses only ; the admission of these depends on the vacancies in the regular school. BUILDING CONSTRUCTION.— IX. arches ( continued ). We now come to the square-headed window (Fig. 63), referred to in the last lesson. Draw a perpendicular, A B, and at the point C draw a hori- zontal line ; the point c representing the height of the top line of the sill from the ground, or some fixed horizontal line, such as a string course. On each side of c set off half the width of the window, D and E ; and at these points erect perpendiculars of indefinite height. Now as the whole height of the jamb is to be thirty bricks, take the height of ten bricks, or any other multiple of thirty, and set it off on the perpendicular D, as many times as may be required; then subdivide each of these spaces (5, 10, 15, etc.) into the proper number of bricks (this is more accurate than to set off the bricks separately) ; then from the highest point, draw the horizontal F G, cutting the perpendicular in I. This will complete the oblong for the window, and the line f g will form the intrados, or soffit, of the square arch. Now it has already been stated that the “ skew-back ” usually inclines at 60° ; therefore, on f G construct the equilateral triangle F G H, and produce the sides beyond f and G. The height of a gauged arch must be some multiple of the height of one brick, on the flat with its joint — viz., three or four courses— in this instance say four ; therefore, draw at that height the line k l, which will give the extrados of the arch. Set off on each side of the central perpendicular on the extrados half the thickness of a brick, and then fill up the re- maining portion of the line on each side with the widths of 264 THE TECHNICAL EDUCATOR. bricks. From each of these points draw lines to h, which will divide the general form of the arch into a number of wedges. This will complete the straight arch. As the whole thickness of such an arch, reckoning it obliquely according to the lines of the joints of the arch bricks, and which therefore varies according to the situation of those joints, cannot be obtained from one brick, the depth is usually made up of two pieces. But the horizontal lines, m and N, are not the real joints, but false ones, marked for effect ; the real joints are not hori- zontal, but perpendicular to the centre line of the brick. The real joint soon becomes visible when time has changed the colour of the bricks. Having done this, through the points of division in the sides draw horizontal lines, which may be carried over to right hand press on the blade, to prevent it rising at the middle or distant part. Where this occurs, the pencil or pen-point is liable to travel out of the required track. It is advisable to mark off with compasses on the last window, or on a line at the extreme right of the board, a few of the points, such as r> 5, d 10, etc. ; these will act as guide-points, and will serve to check the work. The rest of the window will be completed by marking off the whole bricks, halves, and closers, and drawing the necessary vertical lines. It will be seen that in this window the stone sill occupies the height of two bricks. When this has been drawn, the num- ber of courses of bricks under- neath may be added according to circumstances. Fig. 64 shows the plan of the same window. If the elevation is to be projected from a given the other side; in fact, if there are several windows, or even if the courses are to be marked, they may be carried along the whole elevation, and will save all the trouble of repeat- ing the measurement. A practical hint is, however, neces- sary, in order ito secure accuracy in this operation. First, be very careful that your T-square is held tightly against the left edge of your board, and as you move your pencil along, let your plan, this must be finished first ; and perpendiculars raised from O and p, which will give the width of the window. Fig. 65 is a study of the front elevation of a window, the head of which is formed by a segment arch, gauged. The general form of the aperture, and the courses of bricks, ,the sill, etc., will all be done by the method shown in the former subject. BUILDING- CONSTRUCTION. 263 The centre having been fixed at c, draw radii from it touch- ing the imposts I, i. The position of the centre will, of course, depend on the sweep or curve which is to constitute the intrados of the arch ; for, of course, the lower the centre be placed, the longer will be the radius, and hence the flatter the arc. Now set off D E equal to the intended height cf the arch — in this case 12 inches ; with c e as radius describe the extrados, and on it set off the width of the bricks ; that is, the length of their shortest edges. From these points draw radii to the centre, this is not so ; and as its thrust will be obliquely outwards, there will be the tendency to force the wall out of the perpendicular. Semi-circular and elliptical arches are not, however, open to this objection, as in these the thrust is more directly downwards. Fig. 67 is a semi-elliptical arch, using the term in an ap- proximate sense, for it will be remembered that, strictly speak- ing, no portion of an ellipse is a part of a circle. The figure, however, shows the form adopted for general purposes, and tho which will give the wedge-like divisions in the arch. Divide these alternately into brick and half-brick, and complete the rest of the brickwork and sill. Fig. 66 is the back or interior of the same window. Here it will be seen that the arch at the back is formed of two rings of half-a-brick each, worked as rough arches ; the lower portion of the width of the gauged arch is thus left, and forms the revel (or reveal). This elevation shows also the positions of the wood-bricks for the attachment of the woodwork. Segment arches are not deemed advisable in the elevations of detached or corner houses, for although they may be safe as far as the middle arches are concerned, since the thrust of each counteracts the other, and they receive mutual support from the pier, which is common to both, yet in regard to the outer arch construction of such an elliptical figure will be given in a future lesson of “ Practical Geometry applied to Linear Drawing.” The span and rise — that is, the long and half of the short diameter — being given, construct the ellipse, and another parallel to it, struck from the same centres. Set off on the outer curve the sizes of the bricks, and then the radii are to be drawn to the centres from which the arcs on which they are placed are struck. Thus all those between A and b will be drawn to the centre c, whilst all those between a and D and B and E will be drawn to F and G. This subject will be further treated of when the construction of stone arches is described. Fig. 68, taken from an excellent German example, shows the union of the straight with the segment arch. 266 THE TECHNICAL EDUCATOR. CHEMISTRY APPLIED TO THE ARTS.— V. BY GEOBGE GLADSTONE, F.C.S. CALICO PRINTING ( continued ). The style of printing described in the previous lesson relates exclusively to the production of a pattern in one or more oolours upon a white ground. There are, however, a variety of other effects which it is desirable to produce, that either call for a modification of the plan which has been detailed already, or for the introduction of fresh processes. These must now occupy our attention. In many finished goods the pattern is white or tinted, while the ground is coloured. There are various ways of producing this effect. We will take first a white pattern upon blue. A resist, as it is termed, composed of acetate and sulphate of copper, thickened with gum and pipeclay, would be printed upon those portions which are to remain white, and the cloth would then be suspended in a rather moist atmosphere for a couple of days, to secure its taking thorough hold of the fabric. It may then be dyed in the indigo vat in the usual way. The portions covered by the resist are preserved from contact with the dye, and the copper salts contained in it act as a double preventive, by also withdrawing the lime from the solution of indigo which comes into contact with them, and which is neces- sary to its solubility, thus producing an insoluble compound on the exterior of the resist, which is subsequently easily removed by washing. Sulphate of zinc is sometimes preferred to the salts of copper ; it produces the same result, by causing the oxidation of the indigo, and thus rendering it insoluble. A yellow pattern upon a blue ground would be obtained by printing the cloth with a resist as before, and then dyeing the ■cloth in the indigo vat ; but in this case the resist must contain nitrate of lead, as well as the copper salts and the usual thicken- ings ; and after having been dyed the cloth must be dipped in a weak solution of bichromate of potash, when the chromium will combine with the lead in the resist, and produce the yellow colour in the pattern which is due to chromate of lead. The vegetable colours described in the last lesson may be printed upon a cloth which is to be dyed blue by indigo ; thus, a pattern in red may be produced with madder, by adopting the following procedure. The resist must contain alum and other mordants, as in dyeing Turkey red, mixed with gum and pipeclay for thickening ; and the pattern be printed with it on the cloth in the usual way. After being left to age for a couple of days, the fabric has to be passed through the indigo vat, which will furnish the necessary grounding, then dunged and dyed with madder, and finally brightened with bran and soap. It will be readily seen from these instances that almost any combinations of colours may be produced in the pattern without affecting the blue grounds; just as any number of colours may be printed on a white ground, by making a proper selection of the ingredients composing the resist, the indigo having no effect upon the parts so protected, while, on the other hand, the dyes used for the pattern will not permanently fix upon any portions but those impregnated with the appropriate mordants and alterants. In dyeing the ground, however, it is not usual to immerse the goods in the indigo vat as described in Lesson II., but merely to pass them through the vat once, by carrying them over a series of rollers passing under the liquid, during the course of which they get sufficiently impregnated with the dye for this purpose. It may be desired to produce a pattern in white, upon a ground of some other colour than indigo blue, and one that can only be fixed by a fnordant. The resist will then be made of gum and pipeclay, mixed with lime-juice or other acid ingredient which shall be capable of combining with the mordant so as to produce a soluble compound. Such a resist will effectually pro- tect those portions of the cloth printed with it from the iron and aluminous mordants used in dyeing with madder and other vegetable colours. Tinted figures may also be produced with such groundings, by including the salts of tin in the resist. In these cases the usual processes of mordanting, ageing, dunging, and clearing will have to be gone through after the reserves have been printed with the resist. We must now consider a totally different plan of attaining the same result, and one which is adopted in many large works. Instead of preserving the pattern from the influence of the dye by means of resists, it consists in depriving portions of the cloth of the colour they possess, in order to produce a pattern. This is technically called discharging. It is the very opposite of the preceding operation. For this purpose the usual bleach- ing agents are in requisition, but they have to be differently applied, as their action has to be limited to those spots which are to constitute the pattern. The ordinary process of bleach- ing by chlorine is, comparatively speaking, a slow one, but it can be greatly expedited by the addition of an acid to set free the chlorine contained in the bleaching-powder. A piece of goods uniformly dyed with madder in the usual way can have a pattern printed upon it containing an acid discharger, and on immersing it afterwards in a solution of chloride of lime, the parts printed with the discharger will be bleached by the chlorine set free by the acid, before the liquor will have exer- cised any appreciable effect upon the portions not so printed. The operation is, of course, stopped the moment that the pattern has been properly developed, which ordinarily will not occupy more than two or three minutes, on which account it is found most convenient merely to draw the cloth through the liquid by passing it between squeezing rollers. After passing the second pair of these it goes into the dash-wheel, in order to be thoroughly washed. Another plan of applying the bleaching liquor to certain portions of the surface is largely adopted in printing handker- chiefs in imitation of the Indian bandanas, in which the aid of powerful machinery is brought into requisition. Hydraulic presses are employed, which convey motion to two plates, an upper and an under, which are perforated with holes exactly corresponding with the spots which are to be bleached. Upon the lower plate a number of pieces of Turkey red cloth are laid very evenly, and it is then raised by the hydraulic pump until it presses against the upper plate with the force of about 300 tons. The bleaching liquor is then poured into the interstices in the upper plate which form the pattern, and passing through the cloth and out by the corresponding spaces in the lower plate, it carries with it all the colour, while the rest of the cloth is preserved from any action of the chlorine by the extreme pressure put upon it. The action of the bleaching liquor is accelerated by mixing with it some sulphuric acid, and if a strong solution is used the chlorine is forced through by artificial pressure. As soon as this process is accomplished, pure water is passed through in the same manner, in order to wash away the chlorine. If, instead of a white pattern, one of some other colour be desired, it can be communicated without removing the goods from the press ; but when the whites are to be filled up with some parti-coloured device, the hand-block is generally used for the purpose. When a discharge is to be produced upon an article dyed with indigo, chromic acid is used instead of chlorine. The plan adopted is as follows : — The surface of the blue cloth is padded with a solution of bichlorate of potash, by passing it under a roller the lower portion of which is immersed in the liquid, then between the drying rollers to squeeze out the excess, and afterwards through a hot flue ; it is then printed with a discharger ordinarily made of oxalic and sulphuric acids thickened with starch, and immediately washed in water con- taining a little chalk. The acids contained in the discharger combine with the potash, leaving the chromic acid free to act upon the indigo, and so depriving the latter immediately of its colour. The cloth is then thoroughly washed in the dash-wheel. If some of the salts of lead be added to the discharger, a yellow instead of a white pattern will be the result. In cases where dyes are employed which require the presence of mordants or alterants, the dischargers are used before dyeing instead of afterwards. The object then is to annul the effect of the mordant, so that at the subsequent process of dyeing the colouring matter shall 'not take permanent hold of those parts which are to remain white. The mordants generally used for vegetable dyes — alum and the salts of iron — are best neutra- lised by lime-juice, tartaric and oxalic acids, thickened in the usual manner. Mineral colours are usually discharged in the same way as the mordants above described, and by means of the same acids, the result being that the salt of the metal enters into combi- nation with the acid, forming a compound which in some in- stances is colourless, and in others can be removed by washing ; in either case the desired effect is equally attained. If Prussian blue is the colouring material, the cloth must be first printed PROJECTION. 267 with a paste made with caustic alkali, and then immersed in oxalic acid. The process already described in dyeing with this colour will then be reversed on these portions of the fabric, and the resulting compounds will prove removable by washing. Sometimes, however, it is the object of the dyer to combine with the discharger other substances which shall act as mordants for colours to bo subsequently applied ; thus the protochloride of tin may bo used to decompose a brown produced by man- ganese, and at the same time form a mordant for such dye-stuffs as quercitron or logwood ; and further combinations may be made, each several discharger being applied in succession by a different cylinder, so as to produce at the subsequent dyeing so many different shades or colours in the pattern. There is again another process for printing a pattern in various shades of blue, which is a modification of the ordinary mode of dyeing with indigo. It is only applicable to this par- ticular dye, but is, nevertheless, of sufficient importance to warrant a detailed description. Instead of converting the blue indigo of commerce into the white soluble indigo in the vat, and then working the whole piece in the liquid, which would produce a uniform depth of colour throughout, the indigo is printed on the material in its blue state, and is afterwards dis- solved. By this means a permanent figure in blue can be pro- duced upon a white ground, and, by varying the strength of the composition communicated to it by the cylinder or block, any required shade or any number of shades can be obtained. The composition used for this purpose usually contains about equal weights of indigo and sulphate of iron, finely ground, and mixed up into a paste with a varying quantity of gum-water or starch, according to the depth of colour required. Sometimes the acetate of iron is substituted for the sulphate. As many pastes of different strengths as may be wished are printed from suc- cessive cylinders upon the white cloth, and it is then hung up to dry for about a couple of days. Three vats are then pre- pared, the first containing an aqueous solution of lime, the second of sulphate of iron, and the third of caustic soda. Into these vats the cloth is dipped in the following order — into the lime and iron twice alternately, then into the soda, next into the iron and lime twice alternately, then again into the iron, and lastly into the soda. Each dipping should occupy ten minutes, with an interval between each of five minutes, to allow for the solution draining off. The oxide of iron which will be deposited on the goods during these immersions is got rid of by passing them through a bath of dilute sulphuric acid, after which they are well washed in pure water. The materials employed will be seen to be nearly the same as those used for dyeing in the indigo vat, and the result is due to the same chemical action. At each immersion in the lime-vat a certain portion of the sulphate or acetate of iron is decomposed, and an equivalent quantity of the indigo rendered soluble, which then enters into the fabric, and becomes oxidised again while the cloth is hanging up to drain, so that by the time it has under- gone the series of dippings prescribed a sufficient depth of colour will have been attained. This style is generally known as “ China blue printing.” Vegetable dyes used with the salts of tin, commonly called “spirit colours,” produce brilliant patterns, but unfortunately they are not fast. Many colours may, however, be printed with a mordant, and then fixed by the action of steam, so as to pro- duce an effective and permanent design. For this purpose a steam-chest has to be provided, in the upper part of which the goods are suspended for half to three-quarters of an hour, while the steam is let in by a pipe from below, care being taken not to let the steam condense upon them, or the dyes would be apt to run. In some dye-works high-pressure steam is applied, when the duration of the steaming is reduced to one-half the time. A good red is obtained by this process with Brazil or sapan- wood printed with an aluminous mordant, and a very brilliant colour with cochineal combined with chloride of tin and oxalic acid. Yellow berries are generally used for the colour indicated by their name, which may be employed either alone or with a tin mordant, the latter communicating to them an additional brilliance. The ferrocyanide of potassium is always used when a steam blue is required. Black can be produced by this means ; an extract of logwood and galls combined with an iron mordant producing the reaction which has already been de- scribed in the lesson on dyeing. The intelligent reader will not fail to observe that the various processes described in this and the preceding article are capable of being combined, and some of the best effects are realised by a combination of one or more of them. In order to avoid confusion, the printing of cotton goods has been exclu- sively treated ; woollens and mixed fabrics have also to be dealt with in practice, but these are of so much less importance that the reader must be left to apply to them such modifications as will be suggested by a consideration of the principles which have already been laid down when speaking of the dyeing of these classes of goods. PROJECTION.— XI. ISOM ETHICAL PROJECTION.* In all the previous constructions, it will have been observed that the projections have been obtained by the union of plans and elevations. Isometrical Projection enables the draughtsman to work out views of buildings, etc., without these separate drawings, but still embodying both. This most useful system may be called the perspective of the workshop, as by its means we are enabled, not only to show in one drawing a view of the complete object, but all the lines of the projection maybe measured by a uniform scale ; and hence the name, isometrical, derived from two Greek words meaning “equal measures.” In this respect it differs from- perspective, in which the sizes of all objects and lines diminish as they recede into the dis- tance, according to distinct optical laws ; and it differs also from orthographic projection (which has formed the subject of our study hitherto), as in that branch of science the lengths of the lines are altered according to the angle at which the object may be placed. The whole system of isometrical projection is based on a cube resting on one of its solid angles, whilst its base is raised until the one solid diagonal — that is, the diagonal which connects the one angle of the top to the opposite angle of the bottom— is parallel to the horizontal plane. Then, if the cube be rotated on the angle on which it rests until the diagonal is at right angles to the vertical plane, the projection of the cube will be a regular hexagon. This will be clearly understood on referring to the following figures. THE ISOMETRICAL PROJECTION OF A CUBE. Fig. 115 is the plan and Fig. 116 is the elevation of a cube, when raised on the solid angle a, so that the solid diagonal, A b, is horizontal, and thus when rotated on a, until A B is at right angles to the vertical plane, as in Fig. 117, the point b is hidden by the point A, and the projection will be seen to be a regular hexagon. Now we know that when a regular hexagon stands on one angle, so that a line drawn from that angle to the centre may be quite upright, the two sides adjacent will be at 30° to the line on which the figure stands ; and this knowledge enables us to draw the isometrical projection of a cube without plan or elevation, but by means of the set-square of 30°, 60°, and 90°, by simply placing it with the long side of the right angle against the T-square (see Fig. 118), and having drawn one line of the hexagon, reversing the set-square and drawing the other, then either moving the square along until its short edge is at the point of meeting of the two previously drawn lines, or turning it so that the short edge rests on the set-square, and thus drawing the vertical line. These three lines are then to be made equal, and the upper lines of the hexagon may be drawn, by again placing the set-square in the first and second position when the T-square is moved higher up on the board. All the lines forming the projection of the cube will thus be seen to be equal, but they will not be the real size which they would be in the plan or elevation, but will all of them bear the same proportion to the original measurement, and may there- fore be measured by a uniform scale throughout. To understand the construction of the isometrical scale, observe that the square, ABCD (Fig. 115), is represented in the projection (Fig. 119) by the lozenge, a' c b d, and that all the other sides, which we know to be squares equal to abcd, are represented by lozenges similar and equal to a' c b d. In Fig. 119, therefore, this lozenge is placed within the square, and it will then be seen that the side D b of the square is at 45° to * Invented by Professor Parish, of Cambridge, about 1820. ANIMAL COMMERCIAL PRODUCTS. 269 D e, whilst the side of the lozenge, d b, is at 30° to d e. The difference, then, between the triangle de!i and the triangle dee, is the triangle d b b, the angle b db being 15°, and db b being 45°. It will therefore be plain that if a side of a cube be given, and we are required to find the side of the hexagon which should form the isometric projection of the cube, we need only take the given length as the base of a triangle, as d b. Construct an angle of 15° at one end (d) and of 45° at the other (b). Then the side d b of such triangle will be the required length of the side of the hexagon, and any divisions or parts marked on b d, as B /, may be transferred to b D, by drawing a line from /, parallel to B b, cutting b d in g ; then b g will have the same proportion to BD that B / has to B D. TO CONSTRUCT AN ISOMETRICAL SCALE. Now let it be required to construct an isometrical scale, so that the object delineated may be one-twelfth of the real size. It will, of course, be understood that this scale is one inch to the foot, as an inch is one-twelfth of a foot ; and further, that if this inch be divided into twelve equal parts, each of the twelfths will represent the inches of the real measurement ; that is, they will bear the same relation to an inch that an inch does to a foot — -viz., one-twelfth; and, therefore, as in the pro- posed scale an inch represents a foot, necessarily a twelfth of an inch represents an inch. The object to be projected is a box, V 6" long, 1' 0" wide, and 6" high ; the sides and bottom being 2" thick.* Draw the line B D (Fig. 120) an inch and a half long, repre- senting the real length of the box — viz., a foot and a half, and mark on this the twelfths of inches, which are to represent inches on the scale. Draw at d a line at 15° to d b (which is most accurately done by drawing a line with your 30° set-square, and bisecting the angle). Draw at b a line at 45° to b d, cutting the line drawn from B in b ; then the triangle B b d in Fig. 120 will be similar to the triangle D b B in Fig. 119, and therefore d b in Fig. 120 will have the same proportion to bd that the lines similarly lettered in Fig. 119 have to each other. From the points 1, 2, 3, 4, etc., in b d draw lines parallel to b b, and these will divide b d proportionately to b d, and the divisions will thus, on the isometrical drawing, represent inches, and the line D b is an isometrical scale of TO PROJECT A BOX ISOMETRICALLY. We can now attempt the object, Fig. 121. By means of the set-square of 30°, draw the lines A b and A c ; make abI' 6" long by the isometrical scale (the line d b), and make A c 1' long. At A b and c draw perpendiculars. Make a d 6" high, and from D draw lines parallel to A b and A c, and cutting the perpendiculars b and c in e and r. From E and f draw lines parallel to dp and d e, meeting in G, and this will complete the object as far as the mere block is concerned ; and as a rule, it is advisable to project the general block view before attempting the detail. From d, e, and f, mark off 2" by scale — viz., h, i,j, k, and from these draw lines parallel to d e, d f, which, intersecting in l, m, n, o, will give the inner edge of the sides of the box, which, it will be remembered, are 2" thick. The bottom of the box is also 2" thick, therefore on the per- pendicular A set off A p, and draw p q and p r parallel to ab and A c. From h, i, j, k draw perpendiculars to cut these lines in s,t,u,v, and from these points draw lines parallel to the sides of the box, cutting perpendiculars drawn from l, m, n, o in w > x ,y,z, which will show the junction of the inner sides of the walls and the bottom, and will complete the projection. TO PROJECT A FOUR-ARMED CROSS. Fig. 122 shows the isometrical projection of a four-armed cross standing on a square pedestal. Scale, I of an inch to the foot ; side of pedestal, 8 feet ; height of ditto, 2 feet ; com- plete height of cross, 14 feet. The pedestal having been projected in a manner precisely similar to that by which the box (Fig. 121) was drawn, carry up the perpendiculars from the angles ; make the perpendicular A b 14 feet high, and by drawing lines from b parallel to the * The student is reminded that one dash (') over a figure means feet, and two dashes (") inches ; thus 1' 6" is one foot six inches. sides of the base, complete the top of a block which would con- tain the entire object ; for, as the complete height of the cross is 14 feet, the top of the upright would be in the top of the block ; and as the arms are 8 feet long from end to end, their extremities would be in the sides of the block, which may thus represent a glass case exactly containing the cross. The thickness of the central upright is 2' 0" ; and as the width of the side of the pedestal is 8' 0”, it follows that if 3' 0" be marked off from c to e, from D to d, from c to f, and from B to g, the spaces d e and / g will each be 2' 0''. From d, c and /, g draw lines parallel to the sides of the pedestal, which, crossing, will give the lozenge hj i k, which is the plan of the central upright. From d, e,f, g draw perpendicu- lars to touch the edges of the top of the solid block, b f and b g in l, in, n, o, and lines drawn from these points parallel to the sides will give the top of the central upright. On the front perpendicular A mark off q at 9' 0", and P at 11' 0" from the bottom, and from these points draw lines parallel to the sides c d and c e. These will give the heights of the top and bottom edges of the arms. But the arms are not so thick as the central upright, being only 1' 0" ; therefore between d and e, and f and g, mark off half a foot from each of the points. This will leave the spaces r s and t u each V 0" wide. From these draw perpendiculars, which, cutting the lines drawn from p and q, will give the ends of the arms ; then draw lines parallel to the sides of the pedestal, cutting hj and h k in v, w and x, y, and from these points draw perpendiculars. From the angles of the ends of the arms draw lines parallel to the sides of the pedestal, cutting these perpendiculars, and these will complete the two arms which are turned towards the front. By pro- ducing these lines as shown in the diagram, the portions visible of the opposite arms may be drawn. All further detail will, it is hoped, be rendered clear by reference to the figure. the isometric circle. Projection does not deal with curves as such, but it becomes necessary to find points in rectilineal figures through which the curves pass, then to project the rectilineal figure, and trace the curve through the points so obtained. Thus for isometrical purposes (as in radial perspective) the circle is enclosed in a square (Fig. 123). Having drawn the circle, describe around it the square Abcd. Draw the diagonals, and also the two diameters, at right angles to each other, meeting the sides of the square in the tangent points E, F, G, H. The circle not only touches at these four points, but cuts through the diagonals in the points J, K, L, M. Draw lines through each of these points, cutting the sides of the square in j, k, l, m. Proceeding now to project the circle thus prepared, draw the diagonal CD in Fig. 124 equal to c D in Fig. 123. From c and D draw lines at 30° to C D, intersecting in A and B. This will be the isometrical representation of the enclosing square. The points e, f, G, H and j, k, l, m are obtained by marking from A the distances A j, j e, e l, and A j, j f, and F in, and drawing lines from these points parallel to the sides of the figure. The intersections J, K, L, M will thus be obtained through which the ellipse, which is the isometrical projection of the circle, is to be drawn. The study may be carried on to the projection of a cylinder, by repeating the operation for the bottom, and joining the intersections by perpendiculars. The limits of these papers necessarily preclude further illus- trations of this branch of projection. Various objects will, however, be delineated on this simple system in the lessons in Technical Drawing devoted to Architectural and Engineering Drawing. > ANIMAL COMMERCIAL PRODUCTS.— XI. products of the class pisces ( continued ). In our last lesson it was stated that Cuvier has divided the class Pisces into two sub-classes — 1. Pisces ossei, or bony fishes. 2. Pisces cartilaginei, or cartilaginous fishes. The first sub-class of osseous fishes are arranged according to the character of their organs of locomotion into — Acanthopterygii (Greek akantha, a spine, and pterugion, a fin), or spiny-finned fishes. Examples : perch, mackerel, and mullet. 270 THE TECHNICAL EDUCATOR. Malacoptemjgii (Greek malakos. soft, and pterugion, a fin), cr soft-finned fishes. Examples : herring, salmon, carp, and trout. Fish constitutes an important article of commerce, furnishing us with immense quantities of oil and an abundance of food. Great Britain possesses a coast-line of 3,000 miles in extent, while that of Ireland is above 1,000 miles, and the greater part of the shores of both islands abound in those species of fish which exist in the largest numbers and yield the most accept- able and nutritious food. Hence a hardy and adventurous race of fishermen have arisen, well supplied with vessels beautifully built, and with materials of the best description. We shall aotice only the fisheries commercially most valuable. Herring ( Clupea harengus). — This fish appears in vast shoals upon our coasts from July to November, when it forsakes the deeper portions of the sea where it habitually dwells, and comes into the shallow shore water for the purpose of spawning. These shoals, animated by a common impulse, are so enormous that the sea for miles round shines with a silvery lustre from their glittering scales. It is certainly a wise and beneficent law Which thus impels certain fish to approach the shore to deposit their ova ; for whilst the best means are being taken for the continuance of the species, there is brought within the reach of man an abundant supply of nutritious food, which would other- wise be lost in the depths of the ocean. The British herring fisheries are principally carried on off Galway, Mayo, in the estuary of the Shannon, at Banbury, and Waterford, in Ireland ; at Cardigan Bay and Swansea, in Wales ; at Yarmouth, Lowestoft, Hastings, and Folkestone, in England; and on the coasts of Caithness, Sutherland, Ross, Aberdeen, Banff, Moray, and Berwickshire, in Scotland. In the harbour of the small town of Wick, in Caithness, as many as 2,000 boats, each having five or six men, have been congregated at one time during the herring season. Some idea of the extent of this fishery may be inferred from the fact that independently of the home consumption of fresh herrings in 1858, 636,122 barrels of herrings were cured, and 350,204 were exported, valued at upwards of =£350,000. In Norway about 600,000 tons of these fish are annually taken and salted. Sweden, Denmark, Holland, and France are also largely engaged in this business. The Pilchard ( Clupea pilchardus) closely resembles the her- ring. This fish is very abundant on the coasts of Cornwall during the spawning season in July. Like the herring, it is taken with the net at night. The average annual produce of the Cornish pilchard fisheries is estimated at 21,000 hogsheads, each annually containing 2,500 fish, thus making the total number captured 52,500,000. About 10,521 persons, young and old, are employed, and the capital invested in boats, nets, and cellars for curing, is estimated at =£441,215. The Sprat ( Clupea sprattus), although smaller than the her- ring, is also very abundant, and furnishes an acceptable supply of cheap and agreeable food. It is caught during the winter months on the coasts of Kent, Essex, and Suffolk, and in such vast quantities as to give rise to the Stow Boat fisheries round the Thames estuary, where they are taken for manure, many thousand tons being sold to the farmers at from 6d. to 8d. per bushel for this purpose. Forty bushels of sprats serve for an acre of land. Whitebait ( Clupea alba). — Every one has doubtless heard of the whitebait dinner — or fish dinner, at which whitebait is the chief dish — for so many years annually held at Greenwich by the members of the British Cabinet, and the Lord Mayor and aldermen of London. This little fish, so much prized for its delicious flavour, was formerly regarded as the fry of the shad, while other naturalists maintain that it is quite a distinct species. Gunther, an authority of high repute, has recently pronounced that whitebait is the fry of the sprat. It has never been found with matured ova, and therefore does not ascend rivers for the purpose of spawning. Sardine ( Clupea sardina ) and Anchovy ( Engraulis encrasi- colus), both closely allied to the herring, replace that fish in the Mediterranean. The former is taken in great abundance off the shores of Sardinia and Brittany, and packed in small metallic boxes, and is much esteemed as a breakfast relish. The latter, a small silvery fish four or five inches in length, is found on the coasts of France and Portugal. The head and entrails having been removed, it is salted and packed in barrels, and forms the well-known condiment, anchovy sauce. About 140,000 pounds are annually imported. Mackerel ( Scomber scombrus). — This well-known and beautiful, fish, so valuable as an article of food, is found in abundance on the south and south-east shores of England. Out of the water it soon dies, and becomes quickly tainted. Those caught in the months of May and June are preferred. “ Mackerel will bite at almost any bait, hence quantities are taken by hook and line. A slice cut from the side of a mackerel near the tail is a successful lure, or even a strip of red leather or scarlet cloth.’ ’ * In 1823, 142 lasts of mackerel were taken at Yarmouth — a last is 10,000. This makes a total of no less than 1,420,000 indi- vidual mackerel. Salmon ( Salmo salar). — This is a soft-finned fish, the body being adorned with spots, and brilliantly coloured, and covered with cycloid scales. The species pass by almost insensible gradations into the clupeoid or herring family. Like the her- ring they inhabit the sea, and not only approach the land, but ascend the rivers nearly to their sources in order to deposit spawn. For this object the salmon reaches the small streams near the sources of rivers, displaying an amount of perseverance and activity in getting there which is astonishing. Cataracts and weirs ten and twelve feet in height are cleared at a single leap, and should the fish be foiled the first time, it tries again until successful. After spawning salmon are totally unfit for food. They descend the rivers to the sea with the floods, with which winter usually closes, where they soon recover their condition, and return ample in size and rich in human nourishment, exposing themselves in narrow streams as if Nature intended them as a special boon to man. Such salmon as are taken in estuaries or rivers are, of course, the property of those to whom the estuaries and rivers belong ; but latterly considerable quanti- ties have been caught in bays and in the open sea, where the fishing is free. The London markets are principally supplied with salmon sent up from the Tweed, Tay, Don, and Dee, and from Norway, preserved fresh by being packed in ice. The fish- ing is usually carried on in summer, and when the take is greater than can be conveniently sent off fresh, the residue are salted, pickled, or dried for winter consumption at home, or for foreign markets. Of late years there has been a decrease of salmon in the English and Scotch rivers, the result of poaching and over- fishing. Legislation has done something to remedy the evil. Pecuniary penalties are inflicted on poachers and trespassers ; and in Scotland the rivers are shut up — on the Tweed from October 15th to February 15th, and north of the Tweed from September 14th to February 1st. Cod ( Morrhua vulgaris). — This valuable fish is spread throughout the seas of Europe from Iceland to Gibraltar, and abounds on the eastern coast of North America from 40° to 60° N. lat., particularly around Newfoundland. It spawns in British waters about February, and is in the best condition as food from the end of October to Christmas. It is amazingly prolific, 9,384,000 ova or eggs having been counted by Leuwenhoeck in the roe of one female. As the cod frequents deep water it can only be taken by long deep sea lines, hooks being fastened at regular distances along their entire length. It is usual to fish for cod in water from twenty-five to forty fathoms in depth, with a hook and line. Cod is voracious, and easily taken with a variety of baits. The British cod fishery is parried on in a number of places contiguous to the shores of our islands. The most prodnetive home fisheries are those off the coasts of Norfolk, Suffolk, Essex, Lincolnshire, and the Orkney, Shetland, and other islands. The London market is supplied chiefly from the Norfolk and Lin- colnshire fisheries. Fresh cod are usually kept alive in welled smacks, and are in this manner brought in good condition from the most distant points of our coasts. The well is capable of holding about fifty score, and receives its water directly from the sea, through perforations in the bottom of the vessel. These vessels are either anchored in a tide-way, or one of the sails is kept set, so as to produce a constant heaving motion, and, in consequence, a perpetual change in the waters of the well. The smacks never go farther up the Thames than Gravesend, as the fresh water intermingles with the salt above that point, and proves destructive to the fish. * See article Fisheries, “ Encyclopaedia Britannica,” eighth edition. WEAPONS OP WAR. 271 WEAPONS OF AVAR. — V. BY AN OFFICER OF THE ROYAL ARTILLERY. BREECH-LOADING SMALL ARMS ( continued ). We have spoken of the introduction of the Snider-Enfield rifle, the present arm of the British soldier. It is necessary, however, to say something more on the subject of the cartridge for this arm, because it is now recognised that the cartridge really constitutes the soul of any system of breech-loading small arms. The cartridge has been compared to the hinge upon which the system turns ; once select a good cartridge, and the difficulty of finding a good rifle is more than half solved. The foundation of a good system is laid, at any rate ; and it becomes very much a matter of individual preference whether the cartridge shall be used with this or that breech-action. At this moment there are so many good rifles before the public that the difficulty consists rather in deciding which is the best than in deciding whether any one of them will do. All these systems have a point of contact in the cartridge. They do not all fire identically the same cartridge, although they could, of course, be made to do so ; but they all fire a metallic cartridge — a cartridge which forms a gas-check at the breech, and which has to be withdrawn after firing, and either thrown away or re-filled. There are two great classes of cartridges — those which belong to the class above described, cartouches obturatrices, as the French call them, for the reason that they “obturate,” or seal the breech at the moment of explosion; secondly, cartridges which are intended to be consumed by the explosion, the arm itself or some portion of the breech mecha- nism furnishing the gas-check. The English “ Boxer ” service cartridge, the solid metal cartridge, the stout pasteboard sport- ing cartridges, are all types of the first class; the Chassepot and needle-gun cartridges are types of the second class. The objections to the second class of cartridges are not inconside- rable. In the first place, the gas escape being taken by the breech of the gun, continued firing tends to make that check less effectual. In the needle-gun, for example, where there is only a mechanical fit of one metal upon another, the “spitting” of fire at the breech is inconveniently great. The same thing occurred in our own cavalry “ Sharp ” breech-loaders. In the Chassepot the spitting is prevented by an india-rubber ring or washer, which, however, is liable to become injured by use, or hard with frost, or rotten with heat, and which then, of course, fails to fulfil its object. Indeed, we are informed on credible authority that this defect exhibited itself to a very considerable and inconvenient extent during the recent war (1870-1). Again, although cartridges of this class are supposed to be consumed by the discharge, it is a fact that they frequently are not altogether consumed — debris collects and fouls the chamber of the gun, and loading, after a time, becomes difficult. Again, if made very thin, these cartridges are liable to be exploded en masse by the accidental ignition of one or two cartridges in their midst. The list of objections could be largely extended ; but the three j which we have named will suffice to show that the English mili- j tary authorities are not without reason in having set their faces I against the “consuming” cartridges, and in having adopted the ■ cartouche obturatrice for use with our military rifles. For with an obturating cartridge you renew your gas-check each time of firing ; you have a cartridge which cannot be exploded by the adjacent explosion of another cartridge ; you have a cartridge far more capable, because stronger, of resisting rough usage, transport, and damp ; you have a cartridge which, if a miss-fire occurs, can be withdrawn without the use of the ramrod, by simply applying the ordinary extractor ; you have a cartridge, also, which is less liable to miss fire, for the reason that its position in the chamber is always determined accurately by means of the projecting metallic base ; while with the paper cartridge the position in the chamber varies according to the exact size of the cartridge and of the chamber, the former being, of course, variable, according as the cartridges become deformed in handling and transport. All these advantages belong to the class of cartridges of which the English service cartridge — the invention of General Boxer, B. A.— forms the best known and most successful type. In this cartridge the maximum of strength is obtained with the minimum of metal. A pasteboard cartridge is inadmissible for military purposes, because it is liable to swell with damp, and is more or less susceptible to injury in other ways. We are, therefore — having narrowed our selection down to the obturating non-consuming class of cartridges, and having eliminated from this class the pasteboard cartridge— left to choose between a cartridge on the Boxer or coil system, and one on the solid metal system. The latter is much more costly than the former, more metal being used in it, and the loss in manufacture being greater. But it is urged that, as the cartridge-case is capable of being fired many times, it is, in the end, cheaper than a once- fired Boxer cartridge. To this there are two answers — first, that the operation of collecting and re-filling empty cartridges i3 not one which can be carried out by soldiers on service ; secondly, that the Boxer construction of cartridge is just as suitable for re-filling as — if not more so than — the solid-metal cartridge. We have ourselves seen these cartridges re-filled and fired as many as thirty-two times. The best authorities are, however, now generally agreed that the operation of re-filling cartridge-cases is not one to be entertained for military purposes, however practicable for sportsmen. Before proceeding to describe the Boxer, or service cartridge, it may be well to 'observe in passing that the self-consuming cartridge is not, as is frequently supposed, necessarily cheaper than the metallic cartridge ; on the contrary, the Chassepot is a very expensive cartridge, as it is all made by hand. Again, it is generally assumed that loss of time takes place in extract- ing the empty case of the non-consuming cartridge after firing. This is an error. Even in the Snider the loss of time is in- appreciable, and in the improved types of breech-loaders, such as the Martini-Henry, the operation of extracting is combined with that of opening the breech and cocking the arm ; there is, therefore, absolutely no loss of time whatever caused by extraction. The Boxer service cartridge for the Snider rifle (Fig. 3) consists of a case of thin brass, ’005 inch thick, rolled into a cylinder, and covered with paper, by which the coil is cemented together. The coiled case is fitted into a double base-cup of brass, with an iron disc forming the end of the cartridge which abuts against the breech-block of the rifle. The case is secured in its position by means of a rolled paper wad inside, which is squeezed out with great force against the sides of the case. The iron base is attached to the cartridge by means of the copper “ cap- chamber,” which contains the detonating arrangement ; the cap-chamber, being riveted over at each end, holds the base tightly to the cartridge. The ignition is effected by means of a percussion-cap, resting on a small shouldered brass anvil. To explode the cap, it is necessary that the crown of the cap should be indented (by the striker of the rifle, for example), when the detonating composition is brought into contact with the anvil, and the flash passes through the fire-hole at the bottom of the cap-chamber to the powder in the case. The top of the cartridge is closed by means of a small quantity of wool, over which is fitted the bullet. This bullet has four grooves or cannelures round it, which serve to carry the wax lubrication, which in this ammunition is distributed in a thin film around the bullet. The construction of the bullet is peculiar, the head as well as the base being hollowed out. The base is hollowed out for the same reason as in the bullet for the muzzle-loading , Enfield — viz., for the insertion of a clay plug, by which the bullet will be expanded into the grooves of the rifling. The head of the bullet is made hollow, in order to give the necessary length to the bullet without increasing the weight. The following are the details : — Length of bullet, F065" ; diameter (without lubrication), ‘573" ; weight, 480 grains. Length of cartridge, 2‘445" ; weight, 1 oz. 10 drs. 20 grs. ; charge, 70 grains. This bullet, although an ingenious contrivance for overcoming the difficulties inherent in a large bore slow-twist rifle, is the least satisfactory part of this ammunition; and repeated changes have been made, and innumerable experiments, with a view to the adoption of another bullet for this arm. Hitherto the results have been attended with little marked success, and all that can be said is that the present bullet gives an accuracy and general shooting power about equal to that of the old Enfield, and superior to it in one respect — viz., that the wounds inflicted by the hollow-headed bullet are much more severe than those inflicted by the solid-headed bullet. The conversion of the muzzle-loading arms may therefore be said to have fully answered its purpose. Let no one depreciate the Snider rifle. It is an admirable weapon, and, taken all 272 THE TECHNICAL EDUCATOB round, superior to most of the breech-loading - rifles in the hands of other military powers. It is simple, durable, eco- nomical, capable of a rapidity of fire of from twelve to eighteen shots per minute, according to the skill of the firer ; the ex- traction of the empty case is effected with ease and rapidity ; the ammunition is ‘exceedingly durable, strong, little susceptible to injury by damp, and as cheap, probably, as any equally ser- viceable ammunition can be made. It is important to notice that one characteristic feature of great excellence in this cartridge is the coiled case. The action of firing causes the case to expand immediately against the sides of the chamber; and this ex- pansion is followed by an instantaneous contraction, by means of which the withdrawal of the empty shell is greatly facilitated. Also, the arrangement of base is especially noteworthy — the solid end, which gives great stability to a part of the cartridge where strength and resistance are required, and which likewise serves for the claw of the. extractor to take hold of. The double cup affords the necessary strength round the back end of the cartridge, the part upon which the greatest strain comes, espe- cially if the block of the rifle should happen not to fit very and the accuracy of the weapon leaves much to be desired— so much, indeed, that we find the Prussians have taken the ad- vantage of the large number of Chassepots which have fallen into their hands to arm some of their troops with them. But the Chassepot, as we shall see when we compare it hereafter with the Martini-Henry, is far from a satisfactory arm. The ignition of the needle-gun cartridge is effected by means of a small patch of detonating composition placed at the back of the sabot, into which the needle penetrates when the arm is fired. The Chassepot cartridge is made of thin paper, covered with thin silk, the latter being intended to secure the blowing out of the* whole of the debris of the consumed cartridge when the arm is discharged. The ignition is effected by means of a percussion-cap, into which the needle strikes, disturbing the detonating composition, the flash passing through holes in the crown of the cap. The cap, it will be observed, is presented to the striker in the opposite direction to the cap in the Boxer cartridge, and the ignition is effected by means of a needle, instead of with a blunt piston. To prevent the gas from the ex- ploded cap escaping backwards, the mouth of the cap is covered ELEVATION. Fig. 6. ELEVATION. ELEVATION. Fig. 3. — BOXER CARTRIDGE FOR SNIDER RIFLE. Fig. 4. — AMMUNITION FOR PRUSSIAN NEEDLE GUN. Fig. 5. — AMMUNITION FOR FRENCH CHASSEPOT. Fig. 6. — BOXER CHARGE FOR BREECH-LOADING REVOLVER. accurately, or if, from any other cause, the cartridge should be subjected to undue strain round the rim. Having given a drawing of our own service cartridge, we think that the accompanying drawings of the cartridges for the Prussian needle-gun (Fig. 4) and the French Chassepot (Fig. 5), with the following details as to dimensions, weight, etc., may be of interest for comparison. These are, for Prussian needle- jgun: — Length of bullet, 1 ’OS*; diameter, - 533"; weight, 480 grs. Length of cartridge, 2'44"; weight, 1 oz. 6drs. 20 grs.; weight of charge, 66 grs. For French chassepot : — Length of bullet, l - "; diameter, - 463"; weight, 380 grs. Length of cartridge, 2 - 64"; weight, 1 oz. 2 drs. 2 grs. ; weight of charge, 85 grs. The needle-gun cartridge is made of paper. Rotation is given to the bullet by means of a paper sabot, which, being slightly larger than the bore, is forced into the rifling. The bullet thus does not touch the bore at all, but is spun by means of the sabot. This method is a clever plan for obtaining the ad- vantages of a large bore, in respect of shortness of cartridge, prompt ignition of the charge, etc., while preserving the advantages of a small bore as far as the bullet is concerned. But the needle-gun is not at all a satisfactory arm, considered as an arm of precision or as a breech-loader. The liability, under the latter head, to escape of gas at the breech, has been before remarked upon ; in addition, the mechanism is defective in some important particulars. As an arm of precision, the weapon is feeble. The velocity imparted to the bullet is small — only about 1,000 feet per second, as against 1,390 for the Chassepot, 1,260 for the Snider, and 1,335 for the Martini- Henry ; the trajectory is consequently high, the range is small, with a thin disc of india-rubber, through which the needle passes. Sometimes this india-rubber comes back with the needle, inter- fering with its action. This is one of the minor defects of the system. There are several other defects too numerous to be here enumerated, but to which the French are now only too fully alive. Other means of igniting breech-loading cartridges have been designed. There is the well-known “pin-fire,” so common in sporting cartridges, in which a blunt pin which projects from the cartridge, and one end of which rests in a percussion-cap inside the cartridge, is driven down by the hammer of the gun. There is also the “ rim-fire ” cartridge, a common American form, in which the fulminate is enclosed in the rim of the base of the cartridge. This method is objectionable on many accounts. Then, of “central-fire” cartridges, of which the Boxer is an example, there are infinite varieties ; but the system of cap and anvil is the one most generally in vogue. It is hardly possible to doubt, however, that this detail will in time be considerably simplified and improved upon. We will mention in this paper one other description of breech-loading cartridge, and one only — namely, the service cartridge for the breech-loading revolver. The construction ot this cartridge is sufficiently exhibited in Fig. 6. This ammu- nition has now entirely superseded the old skin or paper revolver cartridge, which was in vogue until a few years ago. The pistol with which it is used in Her Majesty’s service is aD Adams’ revolver — a simple, strong, quick, serviceable weapon. In our next paper we propose to treat of the Martini-Henry breech-loader and its ammunition, and to bring the subject of Small Arms to a conclusion. VEGETABLE COMMERCIAL PRODUCTS. 273 VEGETABLE COMMERCIAL PRODUCTS.— IX nuts ( continued ). Walnut ( Juglans regia, L. ; natural order, Jugla/ndacece ) . — This fine tree is too well known to need description. It grows not'only in England, but over the whole of Europe, and in Asia. It is especially abundant in Circassia, where it is extensively cultivated. There is a considerable number of English walnuts in the market, as the fruit ripens well in the southern parts of this country. We receive about 30,000 bushels of foreign walnuts ;i annually, chiefly from Ger- many, France, and Italy. Walnuts will not bear a long voyage without being kiln-dried, a process which certainly spoils them. Hickory and Pecan Nuts. — We receive from the United States, in small quantities, the hickory nut (Cary a alia, Nutt.), and the pecan nut ( Carya olivceformis, Nut-,), both of which belong to the same natural order, Juglandacece. These nuts have kernels very similar to those of the wal- nut, but their shells are very different. The hickory nut is smooth, whitish, marked on its ex- terior with three or four elevated ridges, extremely hard, and smaller than the wal- nut. The pecan nut is about the size of an olive, which it re- sembles in shape, as implied by its specific name ; its colour is a light reddish-brown. Brazil Nut { Bertholetia excelsa, Humboldt ; natural order, Lecythidacece ) . — Large fine trees, often 120 feet in height, and growing abundantly in the Brazilian forests. The nuts are closely packed in a hard woody capsule, to the number of twelve or twenty. This cap- sule is nearly round, but slightly pear-shaped, and is so hard and heavy that when ripe it is dangerous to pass under the trees, for a human head is not thick enough to escape fracture if it be struck by one of these fruits in falling. The capsules open at the top by a circular lid, whence they have been called monkey-pots. Sometimes, aa soon as the falling capsule strikes the ground it bursts open, and this is at once the signal for an amusing scramble amongst the monkeys, who, keeping sentinel on a hundred branches, instantly swing them- selves from tree to tree by the help of their prehensile tales, until they arrive at the spot, and then fight furiously for the coveted nuts. The Indians, in order to obtain the nuts, pelt the monkeys with stones, who in return gather the capsules to hurl at their opponents. In this manner large quantities are collected and THE WALNUT-TREE transferred to boats, and thence to vessels. We receive from the Brazils annually not less than 50,000 bushels of these nuts. Chestnut ( Castanea vesca, L. ; natural order, Cupuliferce ). — The chestnut- tree is a native of Great Britain and the temperate parts of Europe, but the nuts not coming to perfection in this country, we import nearly all that we use fflom Spain, whence they are usually called Spanish chestnuts. Upwards of 50,000 bushels are annually imported. Although not very nutritious, chestnuts are much more easy of digestion when roasted. The larger and better sort called Marones are the produce of Italy, Trance, Switzerland, and of some parts of Germany. Sweet Almond (Amygdalus com- munis, L. ; variety, dulcis ; natural order, Rosacece). — The al- mond-tree, a native of the warm parts of Asia, and of the coasts of Barbary, is now cultivated to some considerable extent in Southern Europe, especially in Italy and Spain. It grows to about the size of a common plum-tree. The cortex or outer en- velope of the fruit is not succulent like the peach ( Amygdalus Persica, L.), to which the almond is allied, but hard, green, and juiceless, so that when growing it looks not unlike an unripe apricot ; when fully ripe this green covering splits, and the almond in its rough shell drops out. There are two well-marked varieties of the sweet almond. (1.) The Jordan al- monds, the finest and best of the sweetest variety ; these, not- withstanding their Oriental name, we receive from Malaga, imported without their shells. (2.) The Yalentia almonds, which are broader and shorter than the Jordan variety, and (juglans regia). * usually imported in the shell. England receives yearly about 500 tons of this fruit, which is usually eaten with raisins. Bitter Almond ( Amygdalus communis, L. ; variety, amara). — This variety comes to us from Barbary, in Northern Africa, where it forms a staple article of trade. It is principally used for its oil, which imparts a pleasant flavour to confectionery. This almond is smaller and much rounder than the two preceding varieties of sweet almond, and very bitter to the taste. The annual imports amount to about 300 tons. the palm: family (natural order palmace^e). The palms, next to the cereal grasses and sugar-cane, are the most valuable order of food-plants. They are, however, of fa.r greater importance in the countries where they are produced than in our own, furnishing as they do to the inhabitants of 18— Vol. L 274 THE TECHNICAL EDUCATOK. those countries food, shelter, and clothing. The most useful plant of this order is The Cocoa-nut Palm ( Cocos nucifcra, L.). — This palm supplies the natives ©f the countries in which it grows with clothing, food, medicine, houses, and every description of do- mestic utensil. The aspect of the tree is very imposing. Its stem is tall and slender, without a branch, and at the top are seen from ten to two hundred cocoa-nuts, each as large as a man’s head ; over these are the gracefully drooping, green, glossy, and beautiful fronds. “ The blessings it confers are incalculable. Tear after year the islander reposes beneath its shade, both eating and drinking of its fruit ; he thatches his hut with its boughs, and weaves them into baskets to carry his food ; ho cools himself with a fan plaited from the young leaflets, and shields his head from the sun by a bonnet of its leaves ; some- times he clothes himself with the cloth-like substance which wraps round the base of the stalks, whose elastic rods, strung with filberts, are used as a taper. The larger nuts, thinned and polished, furnish him with a beautiful goblet, the smaller ones with bowls for pipes ; the dry husks kindle his fires, their fibres are twisted into fishing-lines and cords for his canoes. He heals his wounds with a balsam compounded from the juice of the nut, and with the oil extracted from it embalms the bodies of the dead. The noble trunk itself is far from being valueless. Sawn into posts, it upholds the islander’s dwelling; converted into charcoal, it cooks his food ; and supported on blocks of stone, rails in his lands. He impels his canoe through the water with a paddle of the wood, and goes to battle with clubs and spears of the same hard material.”* The cocoa-nut palm grows by the sea-side in most tropical countries, and is usually the first plant to establish itself on the newly-formed coral reefs in the Pacific and Indian Oceans. It is abundant throughout the South Sea Islands. The fibrous outer covering of the nut, when macerated and prepared, is termed coir, a substance extensively employed for making ropes, mats, and stuffing for cushions. Large quantities of oil are obtained from the nut, after it has been ground into a rough meal, called in Ceylon coperah. This oil has of late years been in great demand in England for the manufacture of composite candles and soap. Marine soap, so called because it washes linen with sea-water, is made from cocoa-nut oil. This nut is used largely in confectionery. The cocoa-nut forms a con- siderable article of export from many of our colonies; 3,500,000 were exported from Ceylon in 1847, whence coir and coperah are also largely shipped. VII. MISCELLANEOUS FOOD PLANTS. Onion ( Allium cepa, L. ; natural order, Liliacece). — The onions of Spain and Portugal and the south of France are superior to our common garden onion, larger, and more succulent ; we therefore import them from those countries in chests and boxes to the amount of about 700 or 800 tons. Soybean (Soja hispida ; natural order, Lcguminosm). — A sauce or catsup, as thick as treacle and of a clear black colour, called soy, which is much esteemed, is made from the beans of this plant by the Chinese, and sent to us from India in con- siderable .quantities. Prom 500 to GOO gallons are annually imported. Truffles ( Tuber dbarium ; natural order, Fungi). — These remarkable fungi grow beneath the soil, generally in beech woods, in this country somewhat sparingly, but more plentifully in France and Italy. The truffles of commerce, besides the above species, include several others, all of which are edible, and highly prized for their delicate flavour. In form the truffle is round, its surface in some species smooth, in others warted and tuber- culous; the colour, dark-brown outside, and brown, grey, or white within. They generally grow at the depth of five or six inches'. Dogs are trained to scent them out, and sows are also employed for the same purpose. We receive them from France and Italy preserved in oil. They are used generally in sauces and soups, and as stuffing for poultry. Morel (Morchella esculenta, Dill.). — This is one of the few fungi found in this country which may be eaten with safety. The stipes or stalk is hollow, from two to three inches high ; the pileus or cap is spheroidal, hollow within, and marked on the surface with numerous areola) resemble a honeycomb in structure ; the colour whitish. The morel is usually found abundantly where trees have been burnt, a fact which led in Germany to the practice ®f firing the forests for the sake of the morels, a practice so injurious that it became necessary to suppress it by law. This fungus occa- sionally occurs in woods and orchards in England, whence it finds it3 way to our markets ; it is found to be very valuable for cookery purposes, but is more frequently used in a dry state for sauce than when fresh. We import the greater proportion of the morels used in England from Italy. Carrageen or Irish Moss ( Chondrus crispus ; natural order, Algae ). — This is a very common plant on the rocky coasts of Ireland and Great Britain. The frond is tufted, fixed to the rock by a hard scutate base, dichotomous, the segments linear, wedge-shaped, frequently crisped and curled at the edges. The whole plant looks like yellow parchment. Carrageen or Irish moss is sold by all druggists and herbalists in the United Kingdom. It contains an abundance of gelatine, and is extensively used for feeding cattle, and for forming a light nutritive jelly for invalids, nearly the whole weight of the plant being convertible by boiling into the required substance. Carrageen moss is sometimes used in manufactories for dressing silks. Immense quantities of it are annually brought to England from the Irish coast, and from Northern Europe. A preparation of this moss is now sold under the name of Sea-Moss Farine, which is coming into very general use. Tho moss is apparently dried, and then ground or crushed into a kind of meal, re- sembling fine sand. The jelly obtained from this plant is made far more quickly from the meal than it is by boiling the moss in an entire state. We have now considered the principal, if not all, of the plants used for food, and some other purposes in commerce, in the lessons that have been brought under the notice of the reader. In our next lesson on this subject we shall commence a review of plants that are of importance in medicine and many of the industries of the United Kingdom, commencing with textile plants, or those from which we derive materials for clothing and cordage. APPLIED MECHANICS.— VI. BY ROBERT STAWELL BALL, M.A., LL.D., Astronomer-Royal for Ireland. COMMON TOOLS : THE HAMMER, SAW, FILE, AND CHISEL. THE HAMMER. This very well-known tool is a remarkable mechanical power. The study of its action is important, as it depends on some principles of the greatest consequence. We shall commence by an explanation of these principles, and we shall then apply them to certain different forms of hammer, reserving, however, the important subject of the steam-hammer for a separate lesson. We shall suppose that a hammer is employed for driving a nail into wood, and let us examine what is the resistance to be overcome by the nail, and compare it with the power which is applied to the hammer. In considering this subject, it is necessary to understand the structure of wood. Wood is composed of multitudes of fibres placed side by side. In this it differs from stone, which is a multitude of particles merely attached together. This constitu- tion of wood is the cause of many of its peculiar properties. The fibres are extremely tenacious in themselves, but they adhere together with comparatively weak force. This produces what is called the grain in wood. If I take a piece of pine one foot long and one inch square, I should find it impossible to break it when the fibres — that is, the grain — run along the length of the wood ; the reason of this is, that to break the piece the fibres would have to be torn across, and enormous force would be required. But if I take a piece of pine of the same dimensions, in which the grain runs across the wood, I find that it is broken with comparative ease. The reason is that in this case the fibres have not to be torn asunder, but only separated, and the force of adhesion is not great. In different woods, the grain varies, the fibres being much more compact in some cases than * Melville’s “ Adventures in the South Seas.” APPLIED MECHANICS. 275 in others. Splitting of wood is a separation between contiguous fibres. In fact, a pieee of wood is to some extent analogous to a rope, the fibres in each being placed side by side ; the diffe- rence lies in this, that in the first place the fibres of wood are not twisted like those of the rope, and in the second place that the fibres of the wood adhere together, while those of the rope do not. The fibres of wood are also short. Wrought-iron, when rolled into bars, presents somewhat of a fibrous structure in the direction of its length ; this is seen when one of these bars is torn asunder. The nail has two completely different resistances to overcome. It has, in the first place, to compress the fibres of the wood, so as to make a hole for its entry. After it has entered, as it is somewhat of a taper form, while the point is dividing the fibres and compressing them on each side, the sides of the nail must still be compressing the fibres, as the hole has to be made larger and larger, to admit the tapering nail. One part, then, of the force of the hammer is expended upon compression of the fibres ; but there is another force to be overcome by the nail, and that is the friction against the sides of the hole — the nail is pressed with great force against the wood, and there is, there- fore, a great deal of friction produced. The relative amounts of these forces it is not easy to determine ; it is probable that in hard woods the first is the most important, while in very soft woods the, proportion which the latter bears to the former is doubtless greater, but both added together produce a very large amount of force, which has to bo overcome by the blows of the hammer. Before driving a nail into wood it is often usual to bore a hole for it with a bradawl, and the exertion of making a hole is I a measure of the resistance produced by compression of the fibres. The extremity of the bradawl is bevelled, as shown in Pig. 1. This bevelled edge must, as every one knows, be placed at right angles to the grain of the wood. When pressed downwards it divides the fibres, and then compresses them in the direction of the length of the fibres. In so doing, there is little tendency to split the Pig. 1. wood, for the wedge-shaped extremity is never em- ployed in forcing the fibres apart. But if the edge of the bradawl be placed parallel to the fibres, then as the wedge enters it forces the fibres apart ; and if it be easier to split the wood than to compress the fibres together, the former catas- trophe happens. The resistance of the wood to splitting is mea- sured by the area of the surfaces which would have to be separated ; hence in the middle of a large piece of timber splitting will not occur, however the bradawl be introduced, because, though the resistance of the fibres to compression is still as great as before, yet the resistance to splitting has been increased to be greater than the resistance to compression. The hole having been bored for the reception of the nail, the amount of work to be done by the hammer is diminished until the nail completely fills the hole, and then, of course, the further resistance is the same as if no hole had been bored. In order to express the amount of force which the hammer exerts upon the nail, we must consider what weight must be laid upon the head of the nail in order to force it into the wood. This force must evidently be enormous. A nail requires a very large force to pull it out, when friction alone is retaining it, and to force it in must of course require a very much larger force. We may, therefore, be assured that a force at all events of some hundredweights would have to be laid upon the head of a two- inch nail, in order to force it into the wood. It is, of course, meant that the pressure of this weight is to be simply borne by the nail: we do not mean that the head is to receive a blow with this amount ; it would, of course, not be possible to place a heavy load on the head of the nail directly ; we must produce the effect by means of levers, or some similar contrivance. Now the head of the hammer must be capable, when it delivers a blow upon the head of the nail, of developing a force for a short time equal to the continued pressure that would be produced by a load of many hundredweights ; hence the hammer is a mechanical power, for it transforms the power of the hand into a far larger force. What is the cause of this property of the hammer ? It depends upon a remarkable force called the force of inertia, and may also be viewed in connection with the principle of work to which we have already so often re- ferred. We shall first consider it in the former aspect, and afterwards in the latter. To set a body in motion requires the exertion of force. This is so evident, following as it does from the definition of force, that it is not necessary to dwell upon it. To set the head of the hammer in motion the force of the hand is required. Bit when a body has been set in motion, it requires force to stop it. This is nearly as evident as the former statement. When a railway train is in motion, it would require a prodigious force to stop it. When a stone drops upon the ground, it is stopped by the force of reaction which the ground exerts upon it. In short, to change the condition of a body as to arrest a motion requires the exertion of force. Now action and reaction are equal and opposite ; this is a profound law of Nature not always easy to comprehend. In the present case it asserts that when any force acts upon a body to stop it, the body reacts with an equal force upon the body which endeavours to stop it. Hence, when the head of the hammer comes into contact with the nail, the head of the nail acts upon the hammer, and the hammer reacts upon the nail. This force of reaction may be enormously great. The amount of the force depends upon the amount of motion which the nail makes. If the nail move but a very small way, the force is great ; but if the nail yields easily, the force is comparatively small. This will be evident from the obvious circumstance, that a rapidly moving body exerts a prodigious force of reaction upon any body which endeavours to stop it suddenly, but if the body be stopped gradually it exerts a much less force. But the action of the hammer may be viewed in another way, which will perhaps make the matter clearer. Work or energy, as we have already explained it, may be stored up in a moving body. Thus, for example, a cannon-ball when in motion has a quantity of energy imparted to it by the explosion of the gun- powder ; this energy is stored in it until the cannon-ball meets a wall or other obstacle, the energy is then instantly transferred to the destruction of what is opposed to it, and the ball, having spent its energy, comes to rest. That work is actually in the ball may be at once realised, if we remember that a cannon-ball might be shot straight up into the air. Thus, suppose a ball of 100 lb. weight ascended 1,000 feet, the ball contained sufficient energy to accomplish 100 x 1,000 = 100,000 foot-pounds of work. Whatever bo the moving body, the way to estimate the quantity of energy it contains is to seo how high in the air its velocity would raise it. If a body were moving with a certain velocity, the laws of Mechanics tell us that the height to which it would ascend if projected vertically upwards with that velocity is (velocity) 2 61 If, therefore, wo multiply this height by the mass of the body, wo have as product the number of units of work that the body is capable of doing before it comes to rest. Let us apply these considerations to the case of the hammer. We shall suppose a hammer, the head of which weighs 1 pound. Now the head of the hammer is not merely allowed to fall upon the nail, but is impelled downwards upon it by a considerable velocity. We may suppose, at all events, that when the head of the hammer reaches the nail, it is at that instant moving with a velocity of 20 feet per second. Now, by the rule already given, a body projected vertically upwards with a velocity of 20 feet per second would ascend to a height — This is certainly within the mark, for it is probable the velocity exceeds 20 feet. The quantity of work stored in the hammer is, then, sufficient to raise 1 lb. 6'2 feet high, or, in other words, the hammer contains 6'2 units of work. All this work is ex- pended upon the nail, and let us suppose that the nail is forced into the wood one-tenth of an inch by one blow. The nail must then react upon a hammer with a sufficient force to consume the entire 6 - 2 units of work when the hammer moves through one-tenth of an inch. Let f be the force with which the hammer and nail react ©n each other, then the number of units of work done in forcing the nail into the wood is F x 0T" -r 13; 276 THE TECHNICAL EDUCATOR* but this must be equal to the number of units the hammer expends, hence we must have F x 0-1" -r 12 = 6-2, from which we find P = 744. of work which Hence the pressure exerted on the head of the nail is at least 744 lb. This is a very large force, equal to a third of a ton. But supposing the nail had only entered 0'05 ,/ , we shall easily find by the same process that the pressure exerted is 1,488 lb. Hence we see that, according as the wood is harder — that is, according as the nail enters less at each stroke the force of the blow becomes greater. Thus the hammer is a mechanical power most admirably adapted for the purposes it fulfils. The pile-driver is an example of the hammer which is well adapted to illustrate these principles. A pile is a large piece of timber, shod at one end with an iron point, and provided with a hoop of iron surrounding it at the other end ; the pointed end is forced into the ground by means of heavy blows delivered upon the other end. The mode in which these blows are given is extremely simple. A massive iron weight, called a “ monkey,” slides up and down on a vertical frame, by means of a lifting crab or a steam-engine ; this weight is raised to a considerable height, and then let fall upon the head of the pile ; these blows are repeated until the pile has been driven so far that the blows produce but little effect. Now, if we suppose that the mass of the monkey in a pile-engine is 500 lb., and that the monkey is raised to a height of 20 feet, and then allowed to fall, the number of units of work that have been stored up in the monkey, and which it is therefore capable of exerting, is 500 x 20 = 10,009. Hence 10,000 units of work will be expended upon the pile. Now suppose that the pile be only driven 1" into the ground by the blow. Let us calculate the pressure which has been exerted. Since 1" is one-twelfth of a foot, we have for the force f T \ F = 10,000 ; . ■ . F = 120,000. Hence the pile is urged downwards for the space of 1" by a pressure of 120,000 lb., that is, a force of upwards of 50 tons. When the pile has been driven some distance, it moves less and less under each blow ; consequently, as we have already explained, the magnitude of the force which each blow produces is increased. When the pile “ refuses,” . as it is technically termed, we are then assured that it can withstand a force of enormous magnitude, and, therefore, is capable of supporting the buildings or whatever else the pile may be intended to sustain. THE SAW. The ancients probably employed the simple process of splitting for the purpose of dividing timber ; but such a process is wasteful, both of material and time. This rude method has been replaced by the saw, which, in different forms, is doubtless the most important tool used in the working of wood. We shall afterwards return to the subject of the machinery used in saw-mills, and therefore we shall not here discuss the circular saw and other special applications of the saw, but shall confine ourselves to a general sketch of the process of sawing. We have already described the structure of wood as con- sisting ©f multitudes of fibres placed side by side. In sawing a piece of wood with the grain, the teeth of the saw tear away these fibres without necessarily cutting them across ; in sawing against the grain, however, the fibres have actually to be divided. This is the reason why a saw used for cutting along the grain, called a hand-saw, has larger teeth than a saw which is used for cutting against the grain, called a tenon-saw. The method of sawing is also applicable to other materials besides wood. Marble and other soft stones are frequently cut by saws specially adapted for the purpose. In these cases the sawing is really accompanied by a grinding process. The particles of stone which are removed are comminuted into very small particles. Some very valuable remarks upon saws and other tools are to be found in Holtzappfel’s treatise on “ Turning and Mechanical Manipulation.” From this work the following account is condensed : — “ The blade of the saw is a thin plate of steel rolled of equal thickness ; the teeth are then punched along its edge previously to the blade being hardened and tempered. After this process the saw is flattened by hammering. The blade is then ground upon a grindstone of considerable diameter, and principally crossways, so as to reduce the thickness of the metal from tho teeth towards the back. When, by means of the hammer, the blade has been rendered of uniform tension or elasticity, the teeth are sharpened with a file, and slightly bent to the right and left alternately, in order that they may cut a groove so much wider than the general thickness as to allow the blade to pass freely through the groove made by itself. The bending is called the ‘ set ’ of the saw. The angles of the points of tho saw-teeth are more acute in proportion to the softness of the material to be sawn. “ In using the hand-saw, the left hand is applied to the board, in order that the end of the thumb may be placed just above the teeth and against the smooth blade of the saw, to guide it to the line. The saw is then drawn backwards and forwards a few times with light pressure, to make a slight notch. In the first few strokes the length and vigour of the stroke of the saw are gradually increased, until the blade has made a cut of two to four inches in depth, after which the entire force of the right arm is employed, the saw is used from point to heel, and, in extreme cases, the whole force of both arms is used to urge the saw forwards. “ In order to acquire the habit of sawing well, or, in fact, of performing well most mechanical operations, it is desirable to become habituated to certain definite positions ; thus, in sawing, it is better the work should as often as practicable be placed either exactly horizontal or vertical ; the positions of the tools and the movements of the person will then be constantly either horizontal or vertical, instead of arbitrary and inclined.” THE FILE. This useful tool depends for its action upon the same prin- ciples as the action of the saw. The file is composed of a piece of steel which has first been roughened by a special process called file-cutting, and then rendered intensely hard. The file is used for removing small quantities of metal from a surface. The work is held firmly in a vice, and the file is moved back- wards and forwards by the workman. Simple as the process of fifing appears to be, a great deal of skill is demanded in order to do work with it as it should be done. The ridges on the file detach small particles of the work ; the finer the file, tho smaller are the particles which are removed. Polishing with rouge is in reality a process of fifing j the particles of rouge are extremely small and extremely hard, and they remove extremely small particles of the surface, and thus polish it, for a polished surface is not absolutely smooth. When magnified, it is seen to be rough, but the irregularities are very small ; the rouge removes all irregularities above a certain magnitude. Holtzappfel thus describes the manufacture of files : — “ The pieces of steel or the blanks intended for files are forged out of bars of steel that have been either tilted or rolled as nearly as possible to the sections required, so as to leave but little to be done at the forge ; the blanks are afterwards annealed with the greatest caution, so that in none of the processes the tem- perature known as the blood-red heat may be exceeded. Tho surfaces of the blanks are now rendered accurate in form and quite clean in surface, either by fifing or grinding. In Warring- ton, where small files are made, the blanks are mostly filed into shape, as the more exact method. In Sheffield, it is customary, in the manufacture of large files, to grind the blanks on the grindstone as the more expeditious method ; but the best of the small files are here also filed into shape, and in some few cases the blanks are placed in the planing machine for those called dead parallel files, the object being in every case to make the surface clean and smooth. The blank before being cut is slightly greased, that the chisel may slip freely over it, as will be explained. The file-cutter when at work is always seated before a square block or anvil, and he places the blank straight before him, with the tang towards his person ; the ends of the blank are held down by the leather straps or loops, one of which is held fast by each foot. “ The ridges are cut by means of a chisel, which, for larger files, at Sheffield, is 3 inches long, inches wide, and has a cutting-edge at an angle of 50°. The first cut is made at the point of the file ; the blow of the hammer upon the chisel causes the latter to indent and slightly drive forwards the steel, I thereby throwing up a trifling ridge or burr. The chisel is im- PRINCIPLES OE DESIGN. 277 mediately replaced upon the blank, and slid from the operator until it encounters the ridge previously thrown up, which arrests the chisel, or prevents it from slipping further back, and thereby determines the succeeding position of the chisel. The heavier the blow the greater the ridge, and the greater the distance from the preceding cut at which the chisel is arrested. The chisel having been placed in its second position is again struck by the hammer, which is made to give the blows as nearly as possible of uniform strength ; and the process is re- peated with considerable rapidity and regularity, sixty to eighty cuts being made in one minute, until the entire length of the file has been cut with inclined, parallel, and equidistant ridges, which are collectively denominated ‘ first course.’ So far as this one face is concerned, if the file is intended to be single-cut, it would then be ready for hardening. Most files are, however, double-cut, or have two courses of chisel cuts ; and for these the surface of the file is now smoothed, by passing a smooth file once or twice along the face of the teeth, to remove only so much of the roughness as would obstruct the chisel from sliding along the face in receiving its successive positions, and the file is again greased. If the file is flat, and to be cut on two faces, it is now turned over, but to protect the teeth from the hard face of the anvil a thin plate of pewter is interposed. In cutting files they almost always become more or less bent, and there would be danger of breaking them if they were set straight while cold ; they are consequently straightened whilst they are at the red heat, immediately prior to their being hardened and tem- pered. Previously to their being hardened, the files are drawn through beer-grounds, yeast, or other sticky matter, and then through common salt, mixed with cows’ -hoof, previously roasted and pounded, and which serves as a defence to protect the delicate teeth of the file from the direct action of the fire. The compound likewise serves as an index of the temperature, as on the fusion of the salt the hardening heat is attained. The file thus prepared is gradually raised to a dull red, and is then straightened with a leaden hammer on two small blocks of lead ; the temperature is afterwards increased until the salt just fines, when the file is immediately dipped in water. The tangs are next softened, to prevent their fracture : this is done by immersing the tang in a bath of melted lead. The tang is afterwards cooled in oil. When the file has been cleaned it is fit for use.” THE CHISEL. This tool depends for its action upon principles very different from those of the saw or file. We take the chisel as the type of a cutting tool, and we must first consider in what the act of cutting consists. We shall again borrow from the admirable authority (Holtzappfel) already referred to : — “ If we drive an axe or a thin wedge into the centre of a block of wood, it will split the same into two parts, through the natural line of the fibres, leaving rough uneven surfaces, and the rigidity of the mass will cause the rent to precede the edge of the tool. The same effect will partially occur when we attempt to remove a stout chip from off the side of a block of wood with the hatchet, adze, paring-knife, chisel, or any similar tool. So long as the chip is too rigid to bend to the edge of the tool, the rent will precede the edge, and with a naked tool the splitting will only finally cease when the instrument is so thin and sharp, and it is applied to so small a quantity of the material that the shading can bend to the tool, and then only will the edge bo cut, or will exhibit a true copy of the edge of the instrument, in opposition to its being split or rent, and con- sequently showing the natural disruption or tearing asunder of the fibres.” “For paring a large or nearly horizontal surface, the adze is the propel- instrument to be employed. The tool is held in both hands, whilst the operator stands upon his work in a stoop- ing position ; the handle being from twenty-four to thirty inches long, and the weight of the blade from two to four pounds. “ The adze is swung in a circular path almost of the same curvature as the blade, the shoulder-joint being the centre of motion, and the entire arm and tool forming as it were one in- flexible radius. The tool, therefore, makes a succession of small arcs, and in each blow the arm of the workman is brought in contact with the thigh, which thus serves as a stop to prevent accidents. In coarse preparatory works, the workman directs the adze into the space between his two feet ; he thus surprises us by the quantity of work removed. In fine works he fre- quently places his toes over the spot to be wrought, and the adze penetrates two or three inches beneath the sole of his shoe, and he thus surprises us by the apparent danger yet perfect working of the instrument, which, in the hands of the shipwright in particular, almost rivals the joiner’s plane ; it is with him the nearly universal paring instrument, and is used upon works in all positions.” “ The chisel when inserted in one of the several forms of stocks or guides becomes the plane, the general objects being to limit the extent to which the blade can penetrate the wood, te provide a definitive guide to its path or direction, and to re- strain the splitting in favour of the cutting action.” “ It is well known that most pieces of wood will plane better from one end than from the other, and that when such pieces are turned over they must be changed end for end likewise. The necessity for this will immediately appear if we remember the fibres of which the wood is composed. It rarely happens that the fibres will be exactly parallel to the face of the work ; the plane, then, when working with the grain, would cut smoothly, as it would rather press down the fibres than otherwise, whereas when the plane is used in the other direction it will meet the. fibres cropping out, and be liable to tear them up.” “The handsome characters of showy woods greatly depend’ upon all kinds of irregularities in the fibres, so that the direc- tion in which the plane should be applied is continually chang- ing. Even the most experienced workman will apply the smoothing-plane at various angles across the different parts of such wood according to his judgment. In extreme cases, when the wood is very knotty, the plane can scarcely be used at all, and such pieces are finished with the steel scraper.” PRINCIPLES OF DESIGN.- VIII. By Christopher Dresser, Ph.D., F.L.S., etc. SOME GENERAL ART PRINCIPLES. I intended devoting this chapter to the consideration of furni- ture, and of the art principles which are involved in its forma- tion ; but I feel that there are principles which have not yet been considered that are so important, and of such general ap- plication, that I cannot pass to consider any one art manufacture till these have been considered. The first principle to which I must ask your attention is utility, for the first aim of the designer of any article must be to render the object which he produces useful. I may go further to say, that an article must be made not only useful, but as perfectly suited to the purpose for which it is intended as it can be. It matters not how beautiful the object is in- tended to be ; it must first be formed as though it were a mcro work of utility, and, after it has been carefully created with this end in view, it may then be rendered as beautiful as you please. There are special reasons why our works should be useful as well as beautiful, for if an object, however beautiful it may be in shape, however riehly covered with beautiful ornaments, or however harmoniously coloured, be unsuitable for use, it will ultimately be set aside, and that which is more convenient for use will replace it, even if the latter be without beauty. As an illustration of this fact, let us suppose the balustrade railings of a staircase very beautiful, and yet furnished with such pro- jections as render it almost impossible that we walk up or down the stairs without tearing our dress, or injuring the person, and' how soon will our admiration of the beautiful railing disappear, and even be replaced by hatred ! In like manner let the handle of a door, or the head of a poker, be so formed as to hurt the hand, and the simple round knob, or round head, will be pre- ferred to it, however ornamentally or beautifully formed it- may be. In relation to this subject, Professor George Wilson has said: “ The conviction seems ineradicable from some minds, that a beautiful thing cannot be a useful thing, and that the more you increase the beauty of the necessary furniture or the implements of every-day life the more you lessen their utility. Make the Queen’s sceptre as beautiful as you please, but don’t try to beautify a poker, especially in cold weather. My lady’s vinai- grette carve and gild as you will, but leave untouched my pewter inkbottle. Put fine furniture, if you choose, into my drawing-room ; but I am a plain man, and like useful things in my parlour, and so on. Good folks of this sort seem to labour 378 THE TECHNICAL EDTJCATOK. under tlie impression tliat tlie secret desire of art is to rob them of all comfort. Its unconfessed but actual aim, they believe, is to realise the faith of their childhood, when it was understood that a monarch always wore his crown, held an orb in one hand and a sceptre in the other, and a literal interpreta- tion was put upon Shakespeare’s words, “ * Uneasy lies the head that wears a crown !’ Were art to prosper, farewell to fire-proof, shapeless slippers, which bask like salamanders unharmed in the hottest blaze. An [esthetic pair, modelled upon Cinderella’s foot, and covered with snow-white embroidery, must take their place, and dis- pense chilblains and frost-bite to miserable toes. Farewell to shooting-coats out a little at the elbows, to patched dressing- gowns, and hair-cloth sofas. Nothing but full dress, varnished boots, spider-legged chairs, white satin chair-covers, alabaster ink-bottles, velvet door-mats, and scrapers of silver or gold. It is astonishing how many people think that a thing cannot be comfortable if it is beautiful. ... If there be one truth which the Author of all has taught us in his works more clearly than another, it is the perfect compatibility of the highest utility with the greatest beauty. I offer you one example. All are familiar with the beautiful shell of the nautilus. Give the nautilus itself to a mathematician, and he will show you that one secret of its gracefulness lies in its following in its volute or whorl a particular geometrical curve with rigid precision. Pass it from the mathematician to the natural philosopher, and he will show you how the simple superposition of a great number of very thin transparent plates, and the close approxi- mation of a multitude of very fine engraved lines, are the cause of its exquisite pearly lustre. Pass it from the natural philo- sopher to tho engineer, and he will show you that this fairy shell is a most perfect practical machine, at once a sailing vessel and a diving-bell, in which its living possessor had, cen- turies before Archimedes, applied to utilitarian ends the law of specific gravity, and centuries before Halley had dived in his bell to the bottom of the sea. Pass it from the engineer to the anatomist, and he will show you how, without marring its beauty, it is occupied during its lifetime with a most orderly system of rowing and sailing tackle, chambers for food, pumps to keep blood circulating, ventilating apparatus, and hands to control all, so that it is a model ship with a model mariner on board. Pass it lastly from the anatomist to the chemist, and he will show you that every part of the shell and the creature is compounded of elements, the relative weights of which follow in each individual nautilus the same numerically identical ratio. “ Such is the nautilus, a thing so graceful, that when we look at it, we are content to say with Keats — “ ‘ A thing of beauty is a joy for ever;’ and yet a thing so thoroughly 'utilitarian, and fulfilling with the utmost perfection the purely practical aim of its construc- tion, that our shipbuilders would be only too thankful if, though sacrificing all beauty, they could make their vessels fulfil their business ends half so well.” Viewing our subject in another light, and with special re- ference to architecture, we notice that unless a building is fitted for the purpose intended, or, in other words, answers utilitarian ends, it cannot be esteemed as it otherwise might be, even though it be of great aesthetic beauty. In respect to this subject, Mr. Owen Jones has said, “ The nave and aisles of a Gothic church become absurd when filled with pews for Pro- testant worship, where all are required to see and hear. The columns of tho nave which impede sight and sound, the aisles for processions which no longer exist, rood-screens, and deep chancels for the concealment of mysteries, now no longer such, are all so many useless reproductions which must be thrown aside. Further, “ As architecture, so all works of the decora- tive arts, should possess fitness, proportion, harmony ; the result of all which is repose.” Sir Digby Wyatt has said, “ In- finite variety and unerring fitness govern all forms in Nature.” /itruvius : “ The perfection of all works depends on their fitness to answer the end proposed, and on principles resulting from a consideration of Nature itself.” Sir Charles L. Eastlake : “ In every case in Nature where fitness or utility can be traced, the characteristic quality, or relative beauty, is found to be identical with that of fitness.” A. W. Pugin : “ How many objects of ordinary use are rendered monstrous and ridiculous simply because the artist, instead of seeking the most con- venient form, and then decorating it, ha3 embodied some ex- travagance to conceal the real purpose for which the article has been made.” And with the view of pointing out how fitness for, or adaptation to the end proposed is manifested in the struc- ture and disposition upon the earth of plants, I have written in a little work now out of print : “ The trees which grow highest upon the mountains, and the plants which grow upon the unsheltered plain, have usually long, narrow, and rigid loaves, which, owing to their form, are enabled to bear the fury of the tempest, to which they are exposed, without injury. This is seen in the case of the species of fir which grow at great altitudes, where the leaves are more like needles than leaves as they commonly occur; and also in the species of heath which grow upon exposed moors : in both cases the plants are, owing to the form of the leaf, enabled to defy tlie blast, while those with broad leaves would be shattered and destroyed. “ Not only is the form of leaf such as fits these plants to dwell in such inhospitable regions, but other circumstances also tend to this result. The stems are in both cases woody and flexible, so that while they bend to the wind they resist its destroying influence by their strength and elasticity. In relation to the stem of the papyrus,” which is a plant constantly met with in Egyptian ornaments, “ Sir W. J. Hooker mentions an interesting fact which manifests adapta- tion to its position. This plant grows in water, and attaches itself to the margins of rivers and streams, by sending forth roots and evolving long underground stems in the alluvium of the sides of the waters. Owing to its position it is exposed to the influences of the current which it has to withstand, and this it does, not only by having its stems of a triangular form — a shape well adapted for withstanding pressure — but also by having them so placed in relation to the direction of the stream, that one angle always meets the current, and thus separates the waters as does the bow of a modern steam-ship.” I might multiply illustrations of this principle of fitness, or adaptation to purpose, as manifested in plants, to an almost in- definite extent ; but when all had been said, we should yet have but the simple truth before us, that the primary object which we should have in creating any object, is that of rendering it perfectly fitted to answer the proposed end. If those works which are beautiful were but invariably useful, as they should be ; if those objects which are most beautiful were also the most convenient and useful — and there is no reason why they should not be so — how the beautiful would become loved and sought after. Cost would be of little moment, the prico would not be complained of, if beautiful objects were works of perfect utility. But, alas ! it is far otherwise : that which is useful is often ugly, and that which is beautiful is often inconvenient to use. This very fact has given rise to the highly absurd fashion of having a second poker in a drawing-room sot of fire-irons. The one poker is ornamental, possibly, but it is to be looked at ; the other is for use, and as it is not to be looked at is hidden away in some corner, or close within the fender. I do not wonder at the second poker being required ; for nineteen out of every twenty pokers of an ornamental (P) character which I have seen during the last few years would hurt the hand so insufferably if they were used to break a lump of coal with, that it would almost be impossible to employ them con- stantly for such a purpose. But why not abolish the detest- able thing altogether ? If the poker is to be retained as an ornament, place it on the table or chimney-piece of your drawing-room, and not down on the hearth, where it is at such a distance from the eye that its beauties cannot be discovered. It is no use saying it would be out of place in such a position. If to poke the fire with, its place is within the fender , if it is an ornament, it should be placed where it can be best seen — in a glass case, if worthy of protection. I hope that sufficient has now been said upon this all-impor- tant necessity, that if an object is to be beautiful it should also be useful, to cause us to consider it as a primary principle of design that all objects which we create must be useful. To this as a first law we shall constantly have to refer. When we construct a chair we shall ask, is it useful P is it strong P is it properly put together ? could it be stronger without using more I or a stronger material P and then we should consider whether it TECHNICAL DRAWING. 279 is beautiful. When we design a bottle we shall inquire, is it useful ? is it all that a bottle should be f could it be more useful ? and then, is it beautiful? When we create a gas-branch we shall ask, does it fulfil all requirements, and perfectly answer the end for which it is intended ? and then, is it beautiful ? And in relation to patterns merely, we shall also have to make similar inquiries. Thus, if drawing a carpet design, we shall inquire, is this form of ornament suitable to a woven fabric ? is it suitable to the particular fabric for which it is intended P is the particular treatment of the ornament which we have adopted the best possible when we bear in mind that the carpet has to be walked over, is to act in relation to our furniture as a background does to a picture, and is to be viewed at some distance from the eye P and then, is it beautiful P Such inquiries we shall put respecting any object the formation of which we may suggest : hence, in all our inquiries, I shall, as I love art, consider utility before beauty, in order that my art may be fostered and not despised. There are many subjects not yet named in these chapters which we ought to consider, but I must content myself by merely mentioning them, and you must be willing to think of them, and consider them with care as their importance may demand. Some of them, however, we shall refer to when con- sidering the various manufactures. A principle of great importance in respect to design is, that the material of which an object is formed should be used in a manner consistent with its oivn nature, and in that particular way in which it can be most easily worked. Another principle of equal importance with that just set forth, is this : that when an object is about to be formed, that material (or those materials) which is most appropriate to its formation should be sought and employed. These two proposi- tions are of very great importance, and the principles which they set forth should never be lost sight of by the designer. They strike at the very root of successful designing, for if ignored the work produced cannot be satisfactory. Curves will be found to be beautiful just as they wre subtle in character ; those ivhich are most subtle in character being most beautiful. The arc is the least beautiful of curves (I do not here speak of a circle, but of the line, as a line, which bounds the circle) ; being struck from one centre, its origin is instantly detected ; while the mind requires that a line, the contemplation of which shall be pleasurable, must be in advance of its knowledge, and call into activity its powers of inquiry. The elliptic curve, or curve bounding the ellipse, is more beautiful than the arc, for its origin is not so strikingly apparent; being formed around two centres. The curve of the egg is more beautiful still, being formed around three centres. As the number of centres neces- sary to the formation of a curve increases, the difficulty of detecting its origin also increases, and the variety which the curve presents is also proportionally great ; the variety being obviously greater as the number of the centres from which it is struck is increased. Proportion, like the curve, must be of a subtle nature. A surface must never be divided for the purpose of decora- tion into halves. The proportion of 1 to 1 is bad. As pro- portion increases in subtlety it also increases in beauty. The proportion of 2 to 1 is little better ; the proportion of 3 to 8, or of 5 to 8, or of 5 to 13, is, however, good, the last named being the best of those which I have adduced ; for the pleasure derived from the contemplation of proportion increases with the difficulty of detecting it. This principle is true in relation to the division of a mass into primary segments, and of primary segments into secondary forms, as well as in relation to grouping together parts of various sizes ; hence it is worthy of special note. A principle of order must prevail in every ornamental com- position. Confusion is the result of accident, order of thought and care. The operation of mind cannot well be set forth in the absence of this principle ; at least, the presence of a principle of order renders the operation of mind at once manifest. The repetition of parts frequently aids in the production of ornamental effects. The kaleidoscope affords a wonderful example of what repeti- tion will do. The mere fragments of glass which we view in this instrument would altogether fail to please were they not repeated with regularity. Of themselves repetition and order can do much. Alternation is a principle of primary importance in certain ornamental compositions. In the case of a flower (as the buttercup, or chickweed, for example), the coloured leaves do not fall over the green leaves (the petals do not fall over the sepals), but between them — they alternate with them. This principle is not only manifested in plants, but also in many ornaments produced in the best periods of art. If plants arc employed as ornaments they must not be treated irniiatively , but must be conventionally treated, or rendered into orncmients. A monkey can imitate, man can create. These are the chief principles which we shall have to notice, as involved in the production of ornamental designs. The next paper will be devoted to the consideration of art furniture, but in it we shall have to discuss questions involved in the construction of all art objects. TECHNICAL DRAWING.— XVIII. DRAWING FOR MACHINISTS AND ENGINEERS. practical geometry ( continued ). Fig. 194. — To draw a curve which shall be a portion of a circle, when the centre is not available. Let A B be the chord of the arc, and D c its rise. From A and b as centres, with the radius A b, describe the arcs A E and B F. From A draw a line through c, cutting the arc Biino. From B draw a line through c, cutting the arc A E in H. Divide a h and B G into any number of equal parts, as, 1, 2, 3, 4, 5, and set off a number of these parts from G and h, as a, b, c, d, e. Draw lines from A to 1, 2, 3, 4, 5, and from B to a, b, c, d, e. Then it will be seen that the first line above H — viz., a — intersects the first line below G — viz., 1 — in the point x. In the s^-me manner line 2 will intersect b, line 3 will inter- sect c, and lines 4 and 5 will cut d and e Proceed in the same manner on the opposite side, and through, the intersections trace the curve by hand. For inking, a “templet” may be made; and as this plan will be recommended in several other cases, the mode of making this useful article is given. Draw the figure accurately on a smooth piece of veneer of other thin wood ; if of a light colour, so much the better ; or a small quantity of veneer may be kept by you, with thin white paper glued over it. Cut out the form near to the line required, and bring it exactly up to the mark by means of a fine file : a half-round file is best for this, as it enables you to finish up concave as well as convex curves. The final smoothing is then to be done with very fine glass-paper, and in this prooess the edges should be slightly bevelled off (as already advised in the case of set- squares), in order to prevent the ink dragging on the paper. Sets of curves of different radii and “French curves” of various forms may be purchased, and though these will be found very useful in their way, the above hints are given, as it is deemed advisable to promote self-help as much as possible. The student will remember that no portion of a true ellipse is a part of a circle, and the curve cannot, therefore, be drawn with compasses so as to be mathematically correct; but there are many ways in which figures nearly approximating to ellipses may be drawn by arcs of circles, which are very useful for general practical purposes. In mechanical drawing, therefore, figures approximating to ellipses are used, and have the advantage that they can be drawn by means of compasses instead of by hand. The following method is given in addition to those which will be found in “ Practical Geometry applied to Linear Drawing.” To construct an elliptical figure by means of arcs of circles (Fig. 195). Place the two diameters A B and c d at right angles, and intersecting each other at their middle point, E. From b on the line A B set off b f equal to e c. From e on e a set off e g equal to E F. Draw G f, and bisect it in i. From f set off f j equal to pi. Draw J K parallel to G f* From e set off E L and E M equal to E j. 280 THE TECHNICAL EDUCATOB. Complete the square j k l m, and produce the sides beyond j and l. The angles of the square are the centres from which the elliptical figure may be drawn. From k and M, with radius K D or M c, describe arcs cutting the produced sides of the square in n, o and p, q. From j and L, with radius la or j b, describe arcs joining N P and O Q, which will complete the figure. Fig. 196 . — To bisect the space contained betiveen two lines, a and b, inclined to each other when the point at which they would meet is inaccessible. Fig. 198 . — To divide a circle into any number of equal parts. The following constructions, which require the compasses alone, are best made with the steel dividers, and if two or three pairs can be em- ployed, the distances (such as the radius of the circle), often required, can be kept unaltered. With the given radius de- scribe the circle, and divide it into six parts in B, C, D, E, f, g. B e is a diameter, and therefore divides it into two. b d is the chord of § or i, and the circle is At any part of each line erect equal perpendiculars, as c E and D F, and from their extremities draw lines parallel to A and B, intersecting in G. Bisect the angle e G F, and the line G H will bi- sect the space contained between the lines A and b. Fig. 197 . — To describe a circle touching two given circles, A and b, and one of them in a given point of contact, c. Join the centres D and E. Draw a line from c, passing through D, and produce it. At E draw e f parallel to D C. Draw c F parallel to e d, and produce it to G. Draw G E, and produce it until it intersects c D produced in H. From H, with radius H c, describe the required circle, which will touch both the circles A and B, and one of them in the given point c. divided in B, d, f into three parts. From each end of the diameter B E, with the chord of b D or c e, de- scribe arcs intersecting in x* Then the distance ax being set off from b and e, the circumference will be divided into four parts in H, B, I, E. The arc described with the radius A b from x, x as centres will cut the circumference in k, l, m, and N, which points bisect the quadrants b h, h e, e i, and i B, and thus divide the circle into eight equal parts. The radius a b, set off from h, i to o, P, Q, R, bisects the arcs * In all these constructions, in order to ensure greater accuracy, the arcs should be described on both sides of the line joining the centres; thus the point x should be found on both sides of tho diameter b e. TECHNICAL DRAWING. 281 B c, d e, e p, and g b, which completes the trisection of each quadrant, and therefore divides the oircle into twelve parts. The radius A b, set off from k, l, m, and n, both ways from each point, will bisect the two arcs on each side of the extremi- ties of the diameters, b e, i h in s, y, tr, v, w, z, a, b, and thus complete the division of the circle into twenty-four parts. An y further subdivision may either be done by bisecting the arcs already formed, or by trial. Thus each of the twenty-four parts being bisected, the circle will be divided into forty-eight parts. All the foregoing constructions, by which the circumference is divided into twenty- four parts, are performed, it will be seen, by three distances only , the radius The division into forty parts may be effected by bisecting the arcs last found. These constructions will be found useful in drawing regular polygons, and in dividing the circles for toothed wheels. Of course no more of the figure need be worked than is necessary for the immediate purpose. Fig. 200. — To join two lines, a b, inclined to each other, by an, arc of a circle. Produce A and b until they meet in c. Bisect the angle a c b. At D. the extremity of one of the lines, erect a perpendicular, cutting the line of bisection in e. From e, with radius E d, describe the arc D f which will meet A in F. a b, the chord b d, and A x ; consequently, if these be kept unaltered in separate pairs of dividers, the operations are performed with the greatest accuracy. In order to avoid confusion, the continua- tion of this problem is given in a separate figure (Fig. 199). With the distance A x as a radius, from o, p, Q, R (these points having been found as in the last figure), describe arcs intersecting in y ' then the distance b t, or e v, will divide the circumference into five equal parts in b, c, d, p, and G. The distance A y will bisect the arcs b c, c d, d f, etc., in H, I, E, x, L, and thus divide the circle into ten parts. The distance b y, set off from s, T, the extremities of the diameter s t, perpendicular to b e, will bisect the arcs d e, b h, e p, b l in the points tr, v, w, z, and will thus give one-twentieth of the circumference. The same distance being set off from these points will bisect the other arcs of the decagon. If the point c is not accessible, the angle- must be bisected as shown in Fig. 196 in the preceding page. This method of bisecting an angle should be carefully practised by the learner. Fig. 201. — To draw a circle touching another circle in a given point, and passing through a given point lying without the circle. Let A be the point of contact in the given circle, and B the point lying without it. The centre of the required circle will evidently lie on th® radius o A produced, and on a perpendicular at the middle of a line joining A b, which line will be a chord of the required circle ; therefore Produce o A to as great a length as may be necessary. Draw a line from a to b, and bisect it in c. Produce the bisecting line until it cuts o A produced in D. The point d is the centre of the required circle, r> A being the radius. 232 THE TECHNICAL EDUCATOR. PROJECTION.— XII. QUESTIONS EOS EXAMINATION. Tee following questions, selected for the most part from the papers given at the Government and other examinations, are appended with the view of enabling the student to test his own knowledge, and as suggestions to teachers as to the mode of stating problems on this subject. It is hoped that the examples already given, and the application of them, will have shown the constructions upon which all the questions are based. 1. Give the plan and elevation of a line 3 inches long, when parallel to the vertical and horizontal plane, and 2 inches distant from each. 2. Give the plan and elevation of this line when it is at right angles to the vertical and parallel to the horizontal plane, its height being 2 inches from the ground. 3. Give the plan and elevation of the same line, when the former is a point, and the latter a vertical line 3 inches long. 4. Give the elevation and plan of the same line when it is parallel to the vertical, but is inclined to the horizontal plane at 70°. 5. Give the plan and elevation of the line, when it is inclined at 70° to the horizontal, and 45° to the vertical plane. 6. A wire 3 inches long projects from a wall at 60° to the surface, and is parallel to the ground. Give the plan and elevation. 7. A plane 2" X 3" rests on its narrow edge in such a manner that its surface is at right angles to both planes. Give plan and elevation. 8. Give plan and elevation of the same plane, when its surface is vertical, but inclined to the vertical plane at 45°. 9. Give plan and elevation of the same plane when its shorter edges are at right angles to the vertical plane, and its surface inclined to the horizontal plane at 60°. 10. Give plan and elevation when the plane rests on one of its short edges, its surface being inclined at 60 Q to the horizontal plane, and its long edges being at 45° to the vertical plane. 11. A square plane of 3 inches side lies on the horizontal plane, its one diagonal being at right angles to the vertical plane, and the other parallel to it. Give plan and elevation. 12. Give elevation and plan when the plane rests on one of its angles, its surface being inclined at 40° to the horizontal plane, but its one diagonal remaining at 90° to the vertical plane. 13. Give plan and elevation of the same plane when one of its diagonals is at 45° to the horizontal, and 60° to the vertical plane, the other diagonal being parallel to the horizontal plane. 14. A cube of 2 inches side stands on the horizontal plane, with two of its faces parallel to the vertical plane. Give its plan and elevation. 15. Draw its plan and elevation when standing on one of its sides, the opposite one being horizontal, and the others being at 45° to the vertical plane. 16. Give plan and elevation when resting on one of its solid angles, one diagonal of the base being at 50° to the horizontal, and the other at 90° to the vertical plane. 17. Draw elevation and plan of the same cube, when resting on one of its edges, so that two of its sides are vertical and the rest make angles of 45° with the horizontal, but are at right angles to the vertical plane. 18. Add the shape (the development ) of the piece of metal or other substance which on being folded would form the above- named cube. 19. There is a stick of timber 2 inches square at base, and 5 inches high. Give the true shape of a section caused by a plane entering at one angle of the top, and emerging at the opposite angle of the base. 20. Give the development of one portion of this square prism when it has been cut as in the last question. 21. Give plan and elevation of a triangular prism when resting on one of its long faces, the surface of the triangular end being at 50° to the vertical plane. The end is an equilateral triangle of 2 inch edge, and the length of the prism is 3£ inches. 22. Give plan and elevation of the same prism when the edge of the end on which it rests is at 50° to the vertical plane, and the under side is inclined to the horizontal pla,ne at 35°. 23. Add the development of this prism. 24. Draw the plan and elevation of a regular pentagon of 1 inch side when resting on one of its angles, so that its surfaco is at right angles to the vertical, and at 60° to the horizontal plane. 25. Give the projection of this polygon when the line joining the angle on which it rest3 to the middle of the opposite sido is at 40° to the vertical plane, the inclination to the horizontal plane remaining the same as in the last figure. 26. There is a hexagonal prism of 1 inch side and 4 inches long. Draw plan and elevation when standing on its end, with two cf its faces parallel to the vertical plane. 27. Give the plan and elevation of the same prism, when the axis is vertical and one of its faces is at 40° to the vertical plane. 28. Give elevation and plan of the same prism when two of its faces are parallel to the vertical plane, and the prism is so inclined that the axis is at 50° to the horizontal plane. 29. Draw the plan and elevation when the prism rests on one of the solid angles, and the axis is at 50° to the horizontal, and 45° to the vertical plane. 30. Project the prism when lying on one of its long faces, the axis being at 40° to the vertical plane. 31. Give the true section caused by a plane passing from one angle of the top to the opposite angle of the bottom. 32. Draw the development of the prism, marking on it the line of section, as per last figure. 33. There is a prism, the ends of which are regular octagons of f inch side, and the sides of which are 4 inches long. Give the plan and elevation of this object when the one edge of the base rests on the ground, and the corresponding edge of the top touches the edge of a cube of 2 inches side. 34. Give the plan and elevation of this group when rotated so that the sides of the cube are at 45° to the vertical plane. 35. Project the front view of an octagonal prism (size at pleasure), when its end rests in a plane inclined at 35°, neither of the long faces being parallel to the vertical plane. 86. Give a section of the prism named in Question 33, caused by a plane passing through it at 60° to the axis ; the prism to be hollow, and formed of wood §• inch thick. 37. Give plan and elevation of a hexagonal pyramid when two of the edges of the base (1 inch long) are at 20° to the vertical plane, the altitude being 2 4 inches. 38. Draw elevation and plan of this pyramid when lying on one of its triangular faces, with its axis parallel to the vertical plane. 39. Give the elevation and plan of this pyramid when resting on one angle of the base, and one of its edges being vertical. 40. A circular disc (1.) radius) stands so that one diameter is vertical, and another at right angles to the first is at 50° to the vertical plane. Give plan and elevation. 41. Give elevation and plan of the same circular disc, when resting on the end of one diameter, which is parallel to the vertical plane, the surface being at 40° to the horizontal plane. 42. Draw the plan and elevation of the same disc, when the diameter is at 408 to the horizontal and 60° to the vertical plane. 43. A circular slab of stone, such as a mill-stone, 4 feet diameter and 1 foot high (to be represented by inches for feet), lies on the horizontal plane. Give the plan and elevation. 44. A second circular slab, 3 feet diameter, and 1 foot high, rests on a slab, similar to the last ; their centres being coinci- dent. Draw the plan and elevation. 45. Draw the elevation, plan, and projection of these two slabs, one placed on the other, as above, when their circular- surfaces are inclined at 40° to the horizontal plane. 46. A cylinder, 4 inches long and 2 inches diameter, stands on its circular end. Give the plan and elevation. 47. Draw the plan and elevation of the same cylinder when lying on the horizontal plane, its axis being parallel to both planes of projection. 48. Give plan and elevation of the cylinder when lying on the horizontal plane, its axis being at 60° to the vertical plane. 49. Draw the plan and elevation of a cylinder 4 inches long and 2 inches diameter, when the axis is inclined at 60° to the horizontal and 45° to the vertical plane. 50. Give the true section caused by a plane passing through the middle point of the axis at 45° to it. 51. Draw the development of this cylinder, marking on it the line of section. THE STEAM-ENGINE. 283 52. A cylindrical pipe, of 2 inches diameter, is to be cut so as to turn a right angle. Give plan and elevation, showing the section-line. 53. Give the elevation and plan of one of the parts when resting on the sectional surface. 54. Give the true shape of the section, and the development, showing how both parts of the elbow may be cut out of the same piece of metal without any waste. 55. From piping of the same diameter, construct a double elbow-joint, one end of which bends one way and the other the opposite. Give development of the three parts to be cut out of one piece without waste. 56. The same piping is to be carried round three sides of a square room (size at pleasure). Give development, showing the section-line. 57. A pipe of sheet iron (2 inches diameter) is to be joined so as to turn an angle of 120°. Show on an elevation the inclina- tion of the line of section, and show on a development the line in which the metal must be cut to form the required parts without any waste. 58. Given a cone of 2 .) inches base and 3.j- inches altitude. Draw the plan and elevation of this cone when standing on its base. 59. Give elevation and plan, when the cone lies on the hori- zontal plane, its axis being parallel to the vertical plane. 60. Draw the projection of the cone, when lying on the hori- zontal, with its axis at 45° to the vertical plane. 61. Project the cone when resting on one end of the diameter of the base, the axis being inclined at 70° to the horizontal plane. 62. Project the cone, when the axis is inclined at 70° to the horizontal and 45° to the vertical plane. 63. Draw the true section of the same cone caused by a plane at 408 to the surface of the base, which enters at | inch from the bottom. 64. Draw the parabola resulting from a plane entering the base of a similar cone at f inch from the centre. 65. Draw the hyperbola resulting from a section-plane enter- ing the base of a similar cone at J inch from the axis. 66. A pipe 2 inches square is penetrated by another of 1 inch side. The smaller one passes through 2 sides of the larger, their axes being at right angles to each other. Give elevation and plan when two faces of each of the pipes are parallel to the vertical plane. 67. Project this object when the two faces, which in the last case were parallel to the vertical plane, are at 60° to it. 68. Give the development of the larger pipe, showing the exact shape of the aperture through which the smaller one is to pass. 69. Give the elevation and plan of the object when the smaller pipe penetrates the sides of the larger at 60°. 70. Draw the development of the larger pipe, showing the apertures, and of one piece of the smaller one. 71. A square pipe of 2 inches side is penetrated by another of inch side, their axes being at 60° to each other, and parallel to the vertical plane ; and two edges of the smaller meeting two edges of the larger pipe. Give the elevation and plan. 72. Draw the plan and elevation, when two faces of the larger pipe are parallel to the vertical plane. 73. Draw the development of the larger pipe, showing the shape of the apertures through which the smaller one is to pass, and also one of the ends of the smaller pipe. 74. A cube of 3 inches side stands on the horizontal plane, and is surmounted by a square pyramid, 3 inches high. Give elevation and plan, when two faces of the cube and two of the sides of the base of the pyramid are parallel to the vertical plane. 75. Draw the elevation and plan of this object, when the faces are parallel to the vertical plane, as in the last question, but when the base is inclined at 25° to the horizontal plane. 76. Draw the plan and elevation of the object, when the sides of the cube are at 50° and 40° to the vertical plane. 77. Give plan and elevation of the object, when the faces of the cube are at 45°, and two of the sides of the base of the pyramid are parallel to the vertical plane, their axes being coincident. 78. Draw the shape of the piece of metal to form a gas- shade, 20 inches wide across the circular base, 6 inches across the top, and 10 inches perpendicular height. (To be worked size.) 79. A cylindrical coal-scuttle is to be made of sheet iron ; it is to be 10 inches in diameter and 18 inches high at the highest part, the lid to be inclined at 45°. Draw the shape the metal is to be cut to form this object, and the exact shape of the lid. (To be worked £ size.) 80. A cylinder, 2^ inches diameter and 6 inches long, is penetrated by another of 1^ inch diameter and 5 inches long, their axes being at right angles to each other, and intersecting at their centres. Show the mode of obtaining the curves of penetration. Develop the larger cylinder and one of the ends of the smaller one. 81. Draw the plan and elevation of this object when the axis of the larger is parallel, and of the smaller at 60° to the vertical plane. THE STEAM-ENGINE.— IV. By J. M. Wigneb, B.A. BOILERS ( concluded ) THE furnace RELATIVE value of DIFFERENT KINDS OF COAL DRAUGHT SMOKE-CON- SUMING ARRANGEMENTS TEMPERATURE AND PRESSURE. We have now referred to those forms of boiler which have come into most general use. There are, however, many ether varieties, some of which are only available for special and peculiar work, while others are of comparatively recent intro- duction, and have as yet to stand the test of experience. Sec- tional wrought-iron boilers have been tried of late years, with apparently good results. In these the water is contained in wrought-iron tubes of comparatively small diameter, round which the flame and heated gases are made to play. These tubes are proved to a great pressure before being used, and arc so arranged that if by accident any one should become injured or ruptured it can easily be either cut out of communication with the rest of the boiler, or removed and replaced by a fresh one. In one form of boiler, on this principle, a number of parallel wrought-iron tubes are placed above the furnace, from each of which a small tube leads into the general steam-pipe. In other forms, the tubes are connected to one another at the ends, but the connections are so arranged that any defective one can easily be separated from the rest. Many advantages are claimed by the manufacturers of these boilers, among which are economy in use and greatly-increased safety — an injury being easily discovered and repaired, and an explosion of the whole being rendered almost impossible. One of the uses to which the steam-engine has been applied is to work a fire-engine. In large towns, where dwellings and warehouses are closely packed, fires spread very rapidly, and manual engines are found not to be sufficiently powerful to ex- tinguish them with promptitude. Steam is therefore employed ; but in this case the desideratum is an engine and boiler so constructed as to get up steam in a very short time, as other- wise the fire gains a very powerful hold before the engine can be set to work. Much attention has accordingly been directed to this point, and with such success that engines are now made capable of throwing very large jets of water within a few minutes of the time when their fires are lighted. The boilers usually employed are of very small dimensions, and contain a large number of short tubes very closely packed ; quick -burning fuel is also employed, so that a powerful draught is at once produced. The quantity of water in the boiler is of course very small, and thus a high pressure is quickly attained. The engine is so arranged that at every stroke a small quantity of water is injected into the boiler, sufficient to take the place of that converted into steam, without materially reducing the tem- perature of the rest. The amount of work accomplished by these engines is very great indeed, when considered with refer- ence to their size and weight. They are usually worked at great speed, and with steam at a pressure of from 100 to 150 pounds to the inch. In an official trial of fire-engines at the International Exhibition of 1862, steam was got up to a pressure of 100 pounds by two different engines in 12 minutes 10 seconds and 18g- minutes respectively, from the time of lighting the fires, the boiler in each case being filled with cold water at starting. Sometimes these engines are made to propel themselves along 284 THE TECHNICAL EDUCATOR. the road to the fire, but this plan is not generally adopted, as it is found better to start at once with horses, and get up steam while going along. One drawback to the use of boilers of this kind, with the tubes so closely placed, is that they soon become incrusted, and the fur deposited hinders the circulation of the water. As, however, fire-engines are not very often set to work, and then only for a comparatively short period, there is plenty of time for removing this accumulation, and the boiler is so constructed that the covering can easily be removed and the tubes laid bare for this purpose. We must now pass from the details of the boiler to notice the arrangements of the furnace, many of which have already been referred to in connection with the boilers of which we have spoken. The furnace is the source of all the power. The fuel sup- plied to it enters into chemical combination with the oxygen of the air, evolving thereby a large amount of heat, which, by the medium of the steam, becomes in time converted into force. The fuel usually employed is coal — a mineral substance con- sisting principally of carbon and hydrogen, together with some sulphur and various incombustible mineral ingredients which remain behind in the form of ash. During the process of com- bustion, the carbon, hydrogen, and sulphur unite with the oxygen of the air, producing various gaseous products, the principal of which are carbonic oxide, carbonic acid, and watery vapour. The exact products vary with the coal employed, different samples of which are found to differ very greatly in their composition, and accordingly in the duty they are capable of performing. Good coal ought to contain at least three- fourths its weight of carbon — often it contains considerably more. It will easily be seen that the amount of heat produced by the consumption of a given weight of coal is a very important point in connection with the economical employment of the engine. A large number of experiments have therefore been tried with coal of every variety. A very important series of trials of this kind, conducted under Government authority at Woolwich, was brought to a close a few years ago, and the results published as a Parliamentary paper which is well worthy the attention of all employers of steam-power. These trials had extended over many years, and were carried on with great care. Boilers were fed with water at a uniform tem- perature of 100° : the trial was then continued some days, the exact amount of coal consumed being noted, and also the amount of water evaporated. It would be impossible here to insert even a general abstract of these trials, but the following extracts will give an idea of the average duty which should, Generally, then, we may state that from 7 to 9 pounds of water at 100° (which may be taken as the average tempera- ture of feed-water) should be evaporated by each pound of coal consumed in the furnace. The best results are those obtained with a Cornish boiler, that being the form of boiler in which the greatest economy of fuel is obtained. This economy has been partly produced by the system, which has long prevailed in that district, of publishing the results obtained as compared with the coal used. This plan has produced a kind of com- petition that has acted very favourably. In many cases little care is taken as to the construction or management of the furnace, and the results then obtained are, of course, much inferior to those given above. By inquiring a little into the process of combustion that goes on in the furnace we shall be able to understand more clearly the different things requisite in order to ensure perfect com- bustion. Carbon itself burns almost without flame when heated to a temperature of 700° or 800°. The hydrogen in the coal is for the most part combined with some of the carbon, producing the gas known as carburetted hydrogen, and tins it is which produces the flame and smoke. The products of com- bustion are themselves invisible, but this gas carries with it small particles of the coal mechanically suspended, and, if not perfectly consumed, deposits, in addition, a portion of its carbon, in the form of dark smoke. All smoke that escapes will thus be seen to be a loss of so much fuel, and therefore, apart from the nuisance, motives of economy point to the need of fully consuming the smoke pro- duced in any furnace. To perfectly consume a pound of carbon requires 12 cubic feet of oxygen gas. In the air, however, this gas is diluted with four times its bulk of nitrogen ; 60 cubic feet of air are there- fore required to consume 1 lb. of carbon. It is not, however, to be supposed that all the oxygen is extracted from the air as it passes through the furnace : only a portion is removed, and the rest escapes up the chimney, with the products of com- bustion. We may, therefore, assume that about 150 cubic feet of air should pass into the furnace for each pound of coal con- sumed, the exact quantity varying considerably with the shape and construction of the furnace. If too little is admitted, com- bustion will be imperfectly carried on, and much smoke will accordingly be produced, while the heat obtained will be less than that required. On the other hand, too large a supply of cold air will materially reduce the temperature, besides carrying off a large amount of waste heat up the chimney. The usual manner in which a powerful draught is main- tained, so as to ensure a sufficient supply of air, is by means of a tall chimney. The air having passed through the furnace becomes intensely heated, and accordingly expands. In this way it is rendered much lighter than the air around, and ascends the chimney, while fresh air rushes through the furnace to supply its place. With a stationary furnace sufficient draught can always be obtained in this way, and dampers are introduced into the flues to reduce it when needful. In locomotives, however, where a long chimney is, of course, inadmissible, artificial expedients are employed to quicken the draught. Under ordinary circumstances, when a fresh supply of fuel is thrown into the furnace, the heat at once drives off a large portion of the carburetted hydrogen, which takes with it minute particles of dust, and the supply of air is for the time insufficient to consume these. Yolumes of dense smoke accord- ingly issue from the chimney, and much attention has been directed to the best mode of avoiding this. Very much depends upon the manner of feeding the furnace. If a large supply of coal is thrown carelessly into it, there is sure to be a large pro- duction of smoke. If, on the other hand, the fuel bo introduced in frequent small supplies, and placed near the furnace-door, the smoke produced will have to pass over the intensely-heated cinders beyond, and will be entirely consumed ; and this is the principle of most of the smoke-consuming arrangements at present in use. The fuel is introduced in small quantities and at frequent intervals, and the smoke is burnt by being com- pelled to pass over the surface of the highly incandescent fuel already in the furnace. Another plan by which smoke may also be reduced is by allowing an additional supply of air to enter the furnace and pass into the combustion chamber, where it mingles with the smoke, and aids in its complete combustion. The former of these plans is by far the most generally adopted, though, of course, there are very many ways in which the principle may be carried into practice. The most important thing of all is to procure a careful and intelligent stoker, for more, as a general rule, depends on this than on the apparatus used. A perfect self -feeding apparatus would be the best pre- ventive of smoke : this, however, has yet to be discovered. With an ordinary furnace little smoke will be caused if the fire is well managed. The fuel, as already stated, should be introduced frequently and in small quantities. Before doing so, the stoker should open the furnace-doors and push back a portion of the fuel, so as to make a space in front for the fresh supply, whioh should be spread evenly on the fire-bars. It will then first become coked— that is, the gases will be expelled, and, in passing over the rest of the furnace, will be entirely consumed. The coke then burns in a clear, smokeless way. . under favourable circumstances, be obtained : — Description of Coal. Pounds of Water evaporated for each pound of Coal consumed. Best Welsh Coal 9-493 Anthracite 9-014 Best Small Newcastle Coal . . . 8-524 Average Small Newcastle Coal 8-074 Average Welsh Coal 8-045 Large Newcastle Coal .... 7-658 Derbyshire 6-772 BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS, ETC. 285 This plan, however, requires constant care and watchfulness, which it is difficult at all times to ensure. Some furnaces are constructed with a self-feeding arrange- ment. The coal employed in these is usually crushed almost to dust, or else small coal is employed. It is introduced into a hopper above the furnace, and a small revolving scoop, driven by the engine, constantly and slowly sprinkles the coal into it. A slow motion is also imparted to the furnace-bars, so that the burning fuel is gradually carried to the back of the furnace as fresh coal or coal- dust is supplied in front. The main drawbacks to this system are the somewhat com- plicated nature of the mechan- ism and the power required to drive it, but, despite these, it is found in many places to answer very well, and to effect a saving in cost of fuel. The supply of coal is rendered quite .uniform, and all the smoke is consumed. Sometimes the fur- nace-bars are laid transversely and connected to the links of an endless chain, and then made to travel slowly along. In other forms they are longitudinal, and an oscillating movement is given to the alternate ones at the end nearest the furnace-door, so that the same effect is produced — the coal being slowly moved back in the furnace, and the ashes discharged at the further end. Frequently two furnaces are employed, being placed side by side, and alternately fed. These are so arranged that the smoke from the one passes through the other, and is consumed. But we cannot stay even to enumerate the different plans of smoke- consuming apparatus that have been tried. There is, however, one very ingenious and useful contrivance to which we must just refer. It is known as “ Prideaux’s Self-closing Furnace Valve,” and serves to regulate the supply of air admitted to the furnace. The apparatus, which is fitted as a, door to the furnace, consists of three series of vertical plates, placed behind one another, as shown in plan in Fig. 19. The two outer sets are a little inclined in opposite directions, so as to prevent any loss of heat by radiation. The air as it enters the furnace passes between these plates, and thus keeps the outer portion of them cool, while it becomes itself raised to a very high tem- perature, and thus aids more perfectly in carrying on com- bustion. In front of these partitions is a series of horizontal shutters, mounted so as to close somewhat after the manner of Venetian blinds (Fig. 20). A weight, c, fixed at the end of a lever, a, closes these. This weight is, however, prevented from falling rapidly by means of the cylinder, b, containing water. A piston works in this cylinder, and is so arranged that it can readily rise to the top, the water in the cylinder passing below it. There is, however, only a very small return channel for the water, the size of which can be regulated by a set-screw. The piston, there- fore, can only fall very slowly, and as the weight c is connected to it, the shutters likewise close very slowly and gradually. Usually the apparatus is so adjusted that it shall take seven or eight minutes Fig. 20. for the piston to fall. When the furnace-door is opened to introduce fresh fuel the piston is raised to the top, and the shutters are accordingly opened and admit a plentiful supply of air, which becomes heated on its way, and aids in consuming the smoke produced. As the fuel becomes coked less air is required, and the shutters gradually close, diminishing the supply. In this way the supply of air is nicely adjusted to meet the requirements of the furnace, while at the same time the air that enters is warmed, and consequently does not reduce the temperature as it otherwise would. Other arrangements have been suggested for the purpose of warming the air by means of the waste heat, ere it is allowed to enter the furnace, but these have not been at all generally adopted. The student will now have acquired a general acquaintance with the details of construction of the boiler and its appendages, and we can, therefore, pass on to inquire into the mechanism of the engine itself, and the different forms given to it. Before doing so, however, it will be useful to append a table, showing the temperature of steam at any given pressure. Under the ordinary pressure of the air water boils at 212°, and the tem- perature of the steam never exceeds this. When, however, we have a closed vessel like a boiler, and allow the pressure to become greater than that of the air, we find the temperature rises, and the ratio of this increase will at once be seen by reference to the table. Tempera- Pressure. Tempera- Pressure. ture. Atmospheres. Pounds. ture. Atmospheres. Pounds. 212° 1 15 293-7 4 60 234 u 22J 307-5 5 75 250-5 2 30 320-4 6 90 263-8 H 371 358-9 10 150 285 3 45 418-5 20 300 BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS. VII.— JOHN SMEATON. BY JAMES GRANT. John Smeaton, the eminent civil engineer, constructor of the Eddystone Lighthouse and many other great works, was born in 1724 at Austhorpe, near Leeds, and from his earliest years showed an eagerness for mechanical science. Thus, in his fifteenth year he constructed a machine for rose-engine turning. He commenced business in London as a maker of mathematical instruments about the year 1750, and among various desultory experiments in mechanics, he invented a compass, and improve- ments in wind and water-mill machinery, an “odometer” for ships, and many other useful things. His improvements ia mill-work— being found to increase the effective force of all such engines by fully one-third — were deemed of such value, that in 1759 he was awarded the Copley medal of the Royal Society. Three years before this, he had been elected a member of the Royal Society, and in 1753 he visited Holland, and in- spected the dykes, embankments, canals, and other works of note in that country, with a view to increase his knowledge of practical engineering; and soon after his return home in 1755, there occurred an event, which gave him the long-desired oppor- tunity of rising to the summit of his profession — the destruction by fire of the old wooden lighthouse on the Eddystone Rock, off the stormy coast of Cornwall. His essay was the third erection of the kind which had been attempted there. The Eddystone is a reef of gneiss rocks submerged daily by the tide, lying nine miles from Ram Head, and fourteen south- west of Plymouth harbour. Around them the water varies from 12 to 150 fathoms deep. They had long formed a dangerous obstacle to navigation, and many a valuable ship, after crossing the Atlantic in safety, had gone down there, in sight of land, with all its crew, even in the finest weather. The frequency of those disasters induced a wealthy and humane gentleman, named Winstanley, who had a decided turn for mechanics, to erect a lighthouse there in 1696, in the reign of William III. It was a wooden polygon, about 100 feet high, based on stone, constructed like a Chinese pagoda, and furnished with open galleries. So confident was Winstanley of its stability, that he expressed a hope to be in it “ during the greatest storm that ever blew under the face of heaven ; ’ ’ and his wish was gratified, for in a terrific tempest, which occurred on a November night in 1703, he and all therein perished. When day dawned, not a vestige of the building remained, save an iron chain, wedged in a fissure of the rocks. Three years after this, Mr. John Rudyerd, an opulent silk-mercer on Ludgate Hill, undertook the erection of a new lighthouse, in which twenty-four candles were to burn by night. It was constructed chiefly of timber, and in December, 1755, was destroyed by fire, a spark having probably ignited some of the flakes of soot that hung from the roof above the lights. The speedy re-erection of another beacon was of the utmost importance ; but before it was undertaken, the projectors pru- Eig. 19. 286 THE TECHNICAL EDUCATOB. dently consulted the President of the Royal Society, who re- commended Mr. John Smeaton, as the person best qualified to superintend its construction. He spent much time in consider- ing the best methods of grafting the foundations into the rock, so as to secure stability; and in planning the present structure he took, it is said, as his model, the trunk of an oak, which so seldom succumbs to the tempest. On the 12th of June, 1757, the first stone was laid, and the night of the 16th of October, 1759, saw the saving light from its summit once more stream across the waters of the British Channel. This great work is built on the sloping side of one of the rocks, and is formed of blocks, generally one or two tons in weight, of Portland oolite cased in granite, the latter being dovetailed solidly into the reef. To prepare a base for the tower, the shelving rock was cut into six steps, which are filled up with masonry, riveted to the living stone; and for the height of 12 feet above the base, the tower is one solid co- lumnar mass. The interior consists of four rooms, situated one over the other, the whole being surmounted by a glass lantern and iron gallery. The base is 26| feet in diameter ; the light, a fixed one, stands 72 feet above the water, and is visible for thirteen miles. Such was Smeaton’s greatest work, which survived without injury the memorable tempest of 1762, and is likely to endure for centuries ; but with all his engineering fame, he would seem to have had little employment for some time subsequently, as in 1764 he applied for and obtained the post of “ Receiver of the Derwentwater Estates,” the funds of which were appropriated for the benefit of Greenwich Hospital ; and this situation he held till 1777, when he was full of professional employment, and frequently consulted on the opening-up of river navigation. On this matter he reported so early as 1760 to the Provost and Bailies of Dumfries on the improvement of the shallow Nith ; but his advice to form a navigable canal, rather than to deepen the sandy river, could not be carried out for want of funds. He was consulted concerning the opening-up of the Don above Doncaster, the Chelmer to Chelmsford ; the lockage of the Wear, and the deepening of the Black Devon, which rises in the Saline Hills, and falls into the Forth at Clackmannan Pow ; the navi- gation of Tetney Haven, near Louth ; the improvement of the Lea ; and the extensive repairs of the lockage and dams of the Calder, in Yorkshire — a subject requiring much care and con- sideration, owing to the floods from Blackstone Edge in rainy seasons. The drainage of the Lincolnshire fens, and all the low-lying tract about Doncaster and Hull, were subjects on which he was frequently consulted. In reporting on this matter in 1761, he was associated with the Messrs. Grundy and Edwards, and the result of their labours was a proposal to improve the outfall by the formation of a new river, twelve miles long, from a place called Chapel- Hill to a little way above Boston ; the total estimate being more than <£40, 000. In 1762 he suggested the improve- ment of the Fossdyke, an old cut that joined the Trent and the Witham ; but though he was applied to on the same subject in 1782, the county was too poor to undertake the work. The greatest success attended his operations for the drainage of the isle of Axholme, by the diversion of the old river Trone ; the drainage of the lands adjacent to the Went ; those of Lord Kinnoul in Perthshire ; at Hotham Fens ; the Holderness Level, near Hull; and many other places, by which waste sheets of gloomy water — the local source of ague, fog, and fever ; the haunt of wild fowl and abode of mud-fed fishes — became fertile tracts of arable land. He was consulted concerning the repair of old Bristol bridge, and in 1758 he was engaged in improving and widening the ancient bridge of London, then overhung by houses above a dark and narrow thoroughfare; and the result of his advice was the proposal to erect a new bridge at Blackfriars, the reihoval of the houses from the old London Bridge, the demolition of the great middle pier, and erecting there a new arch to span the space of two. In 1763 he visited Perth, where he erected a handsome bridge, 900 feet in length, in lieu of the old one, swept away by a flood in the Tay; and now the fame of his skill brought him much engineering business in Scotland. At Edinburgh he was consulted about the supply of water for the city; at Glasgow about the security of its bridge ; but his most important Scot- tish work was the formation of the great canal between the Forth and Clyde, a project as old as the time of Charles II. Smeaton first estimated the expense at <£80,000 ; and after being opposed by Parliament, and having many difficulties to surmount, <£150, 000 were subscribed, chiefly in Glasgow, and the canal was begun under Smeaton’s direction in 1768, but made navigable only as far as Stockingfield, and in that state it re- mained until 1784, when it was completed by sums levied on the forfeited estates. It is 37£ miles long ; its medium width is 56 feet — at the bottom, 27 feet; its depth 9 feet; and it has 39 locks. It is supplied from 8 reservoirs covering 721 acres. A bridge across the Tweed at Coldstream was Smeaton’s next work. It consists of five arches founded on piles, and was opened for traffic in 1766, after costing =£6,000. Two years after, he was at the Carron Iron Works, the largest of the kind in Europe, where he constructed a highly-effective machine to aid the powerful blowing-apparatus. He also supplied the company with a design for a double-boring mill for cylinders and cannon, of which vast quantities, of the form known as “ carronades,” were cast there until recent years. The elegant bridge of seven arches across the Deveron, near Banff, was his next work, and there, as elsewhere, he adopted the elliptical outline. He was less successful in the construction of his only English county bridge — that across the Tyne at Hexham — in 1777. A subsi- dence in one of the piers occurred soon after it was finished. No remedies availed ; and in the spring of 1782, when flood swept down the Tyne, “ Smeaton’s beautiful Hexham bridge lay a wreck in the bottom of the river.” He felt this acutely, and it seemed strange that he, whose lighthouse bid defiance to the waves, was foiled by the current of an inland stream. Harbours next occupied his attention ; he constructed the pier at St. Ives in Cornwall, and was consulted concerning those at Dover, Rye, and Christchurch ; Workington, White- haven, and Bristol ; Yarmouth, Lynn, Scarborough, Sunderland, Aberdeen, Eyemouth, and Ramsgate. The latter he commenced in 1774, but it was not until ten years later that the first stone of the new dock was laid ; and while carrying out the dockyard pier Smeaton first employed the diving-bell in building the foundations. The works when finished were found to answer remarkably well. The area of the harbour included 42 acres, the piers extended 1,310 feet into the sea, and the opening be- tween their heads was 200 feet wide. He is said to have been proud of the pretty little harbour which he constructed at Eye- mouth, as it was one that effectively suited its purpose, and cost but a small sum of money. It lies in the corner of a bay, opposite St. Abb’s Head, on the Berwickshire coast, and is nearly landlocked. The canals of Birmingham, the Ure, and Dublin were improved by his skill. His work at the Eddystone made him a great authority on lighthouses, and after the erection of two (on his plans) at Spurn Point, between the years 1771-6, Government consulted him respecting the dockyards at Ports- mouth and Plymouth. Professional business poured in upon him and he was ever ready “to supply a design of any new machine, from a ship’s pump to a turning-lathe or a steam- engine.” Water companies consulted him as to water-supply; agriculturists, as to the drainage of their lands ; pit-owners, as to the working of their mines ; and millers, in all matters of mill- work ; Jie erected no less than forty-three water-mills of various kinds, and many wind-mills. His Chacewater engine, of 150 horse-power, was the finest of its kind that had then been erected. In this field of invention he was certainly distanced by Watt, the superior merit of whose condensing-engine he frankly admitted. While thus finding extensive employment in the three kingdoms, Smeaton continued to reside at Austhorpe, where he had been born. The mechanical experiments of his boyhood had been conducted there in an outhouse given him by his father, and there, in maturer and wealthier years, he erected a mansion, with a workshop, a study, and observatory all in one, for his own use. The latter was in the form of a square tower. On the ground-floor stood his forge, on the first-floor his lathe, on the second his models ; the third was his study, where he drew his plans and wrote reports ; the fourth was a lumber-room, from whence a tunnelled staircase led to the roof, where a vane, which worked a dial in the ceiling, could inform him, by merely raising his eyes, which way the wind blew. One of his maxims was, “ Never let a file come where a hammer can go.” He was a frequent witness before committees in Parliament concerning bills for the erection of public works, and when in London his chief pleasure was to attend the meetings of the Eoyal Society. In all difficult professional matters his advice was almost FORTIFICATION. 287 invariably followed — a proof, not only of his eminence as an engineer, but of his judgment, caution, and integrity. But John Smeaton’s useful public life was drawing towards its close. In 1783 his health began to decline, and he retired from active business. His wife died in the following year, and his two daughters kept house for him at Austhorpe, where, after being stricken with paralysis, he died on the 28th of October, 1792, in Ills sixty-eighth year. He was laid among his forefathers in the old parish church at Whitekirk, where there is erected a monu- ment to his memory, and above it is placed a model of his greatest work, the Eddystone Lighthouse. FORTIFICATION.— V . BY AN OFFICER OF THE ROYAL ENGINEERS. CLOSED WORKS. The points to be attended to in the design of fortifications have already been alluded to ; but, in order to understand the relative merits or defects of the various forms of closed works usually met with, it will be best to consider in detail each of these primary conditions, and to omit from present consideration all permanent forts or fortresses. These latter are in themselves closed ivorks, but ate generally on such a large scale that they may with advantage be studied separately, as embodying the most approved theories of defence held by the military engineers of a particular nation or period. Conditions to be fulfilled by Closed Field-worhs . — In arranging the design of a closed work it will be necessary to determine — 1. The size necessary for the accommodation of any given force. 2. The shape that will be best adapted to the peculiarities of the ground, and to the special defensive objects in view. 3. The modifications of the trace that will be required to ensure a reciprocal defence between the various parts of the work. Size . — The size of a work depends not merely on the number of men and guns actually required for its defence at any particular moment, but also on whether the defence is intended to last for any length of time, and whether the garrison are to be entirely restricted to the possession of their works. In the latter case, provision must be made for the fighting space necessary for the men, guns, and the magazines, etc., belonging to them ; and there must also be sufficient room in the interior of the work either for an encampment, or for the construction of buildings to serve as barracks. It rarely happens that field-works are so completely isolated as to require accommodation of this kind for more than a small portion of their garrison, and the length of the sides or faces of a work are, therefore, usually calculated on the space required for the defenoe itself. For this purpose it is usual to allow 1 yard lineal of parapet per man, if it is to be defended by single rank, or per file (two men) if double rank are to be employed. A field-gun firing at right angles to a face requires a space of 5 yards lineal to work in ; and when a gun is placed at an angle, provided the angle is not very acute, 5 yards on either side of it must be allowed Under most circumstances, when the works are of moderately regular shape, the above rule will give ample interior space ; but should the shape of the ground necessitate the interior space being much cramped, it must be remembered that, exclusive of the space occupied by traverses, slopes, etc., a minimum of 1 5 superficial feet per man and 600 superficial feet per field-gun is requisite. The dimensions of the traverses must vary with the circum- stances of each case. On faces liable to enfilade or reverse fire they must be of considerable thickness, to intercept the enemy’s projectiles ; whereas when they are only intended to protoct from the splinters of shells bursting in the work, they need not exceed 6 or 8 feet in thickness. In addition to the number of troops required for the primary .defence of the parapet, a reserve should invariably be allowed for, who should be kept under cover close at hand, to replace casualties, and repel any temporary success that may be gained by the assaulting columns of the enemy. It may often be necessary to determine the requisite garrison for a work already existing ; in which case, deduct from the total length of crest-line the space occupied by the guns and each face, and estimate for the remaining parapet as if to be defended by double rank. The number so obtained will be the total infantry garrison, to which the requisite number of gunners for the service of the artillery must be added. Occasionally it may be necessary to construct closed field- works near the coast, containing batteries, where the heaviest artillery are to be employed; under these circumstances the dimensions already given must be largely exceeded. As muck as 20 feet lineal of parapet are required for working a heavy gun with a lateral range of 60°. These guns must be placed at intervals of 46 or 50 feet, and a traverse provided for every pair of guns ; in addition to which an ample allowance must be made for the space occupied by the magazines, shell-filling rooms, and other adjuncts necessary sor the service of modern heavy ordnance. Closed field-works have, on different occasions, been constructed of very varied sizeg, as will be seen from the following extract from a memorandum of Sir J. Jones on the celebrated lines of detached works thrown up at Torres Yedras, by order of the Duke of Wellington: — “The redoubts were made of every capacity, from that which — limited by want of space — was occu- pied by 50 men and 2 pieces of artillery, to another which waa occupied by 500 men and 6 guns.” It may, however, be safely affirmed that all small closed works are bad, and are incapable of maintaining a prolonged resistance to the powerful shell-fire of rifled artillery, unless a greater amount of protection is provided than is usually possible to obtain in the field. Not only does the fire directed against one side of the work necessarily take in reverse the opposite faces, and thus neces- sitate such a number of traverses as to seriously cramp the interior space, but the garrison, being crowded into a small area, must suffer fearfully from the effects of shells bursting among them. The small redoubts which defended the Danish positien of Diippel, in 1864 (Fig. 35), are examples of this, for it appears ( vide “Austrian Military Journal,” 1864) that on that occasion the fire of the Prussian artillery rendered the interior of the works so untenable that, at length, in order to obtain more cover, the troops were, to a great extent, temporarily withdrawn from them to a more secure position a short distance in rear, and that one redoubt (No. 5) was stormed by the Prussian troops before the Danes could re-enter their own work. Shape to suit the ground . — The object of a work may be either that of occupying a particular site, so as to thoroughly defend the approaches to it; or else — although capable of resisting attack on any side — it may be specially designed to bring a heavy fire to bear in certain directions only, its own front being protected by the fire of some collateral works. In the former case the outline or trace must adapt itself closely to the contour of the ground, while in the latter the longest lines of parapet must be those firing in the required direction, irrespective of whether the best possible close defence is thereby attained. Care must be taken in all cases that the main lines are, if possible, so traced as to be secure from enfilade. The combination of these principles is by no means easy when the ground to be occupied is irregular, and when there are commanding points within range which may be seized by the enemy ; the result being usually a compromise between what is theoretically perfect and what is defective but prac- ticable. As soon as a general idea of the outline of a work has been decided on so as to carry out the required objects, it then becomes necessary to fit the plan to the ground, so that all the approaches may be thoroughly defended by the fire from the work. In doing this it will often be necessary to modify both the plan and profile previously determined on. There are certain limits, depending on the slope of the ground, within which the crest-line may be advanced or retired from the top or crest contour of a hill without sacrificing the power of efficiently defending the slopes. As will be seen from Fig. 36, the greatest distance to which it can be retired from the crest will be that which causes the line of fire to graze the slope of the hill, while the minimum distance will be that which allows of the fire passing at such a height above it (3 feet) as shall render it impossible for a body of men to advance unseen. In 288 THE TECHNICAL EDUCATOR. this sketch it is, of course, assumed that the parapets are of the same height. An y further deviation from the crest-line of the hill will in- volve an alteration of height for the profile, unless it happens that the ground is so steep that, with a small amount of labour, it can be scarped or rendered inaccessible, in which case defence by direct fire is not wanted, and the distant flank fire of another work will suffice. Flanking Defence . — The provision of a really formidable flank- ing defence in field-works is always a problem difficult to solve satisfactorily. Their ditches are usually so narrow, and the time necessary for crossing them so short, that it is very desirable the flanking fire on the attack- ing troops should cover the ground in advance of the counterscarps as well as the ditch itself. To do this, the fire must proceed from the parapet, and an arrangement of ■trace becomes necessary that has many serious defects. The necessarily increased length of parapet involves more labour, and some of the faces become unavoidably liable to enfilade. Works in which the fire from the parapets of the flanks defends the ditch are called forts; and those in which there is no flank defence, or where the ditches are flanked by parapet called curtains. The combination of any two bastions and a curtain is termed a bastioned front ; and when a bastioned front is traced on each side of the polygon or imaginary figure containing the work, it is called a bastioned fort. In a properly-constructed bastion fort, when there has been suffi- cient time to complete the necessarily wide ditches, the reci- procal defence of the various parts of the work is good ; but, on the other hand, the bastions are liable to enfilade and reverse fire, and the length of parapet to be constructed and manned is so very considerable that the interior space would be too much cramped to render this trace advisable for any but large and important positions. To ensure efficient flank defence, without risk of the fire from the flanks striking the defenders of the opposite bastions, care must be taken that the angles of defence are never less than 90°. It has been found advisable to fix on certain proportions between the various lines of construction, in order to get the best defence possible ; and as these proportions are dependent on the size of the polygon on which the fronts are designed, it may be well to state in order the operations necessary to enable a student to draw the trace of a bastioned front (Fig. 39). Fig. 40. DEMI-BASTIONED FORT. a, a, a. Dead Ground in Ditches. Fig. 37. — STAR FORT. A, a, a. Undefended Ground in the Ditches. buildings in them, are termed redoubts. Forts are not so generally applicable to irregular sites as re- doubts, and require more time for their construction. There are two types of fort of regular form, viz., the star fort and the bastioned fort, although a modification of the latter is sometimes employed, called the demi-bastioned trace. This only partially at- tains the advantages of the bastioned sys- tem, as regards flank defence (Fig. 40). In order to obtain flank defence, the parapets of a star fort are traced so as to form a number of salient and re-entering angles, thus giving a star-shaped outline (Fig. 37). Star forts have many defects, of which the following are the chief. The length of parapet is excessive, in proportion to the area they enclose. All the faces are liable to enfilade and reverse fire, and a portion of each ditch near the re-entering angle is necessarily unseen, and therefore undefended by the fire from the parapets (Fig. 38). The amount of this undefended space in the ditch, or dead ground, as it is called, is estimated by multiplying the relief of the flank by the inclination of the line of fire, and is measured on plan from the crest-line, in the direction of the ditch. A bastion is a lunette connected with other works by lines of ; 1. Bisect the exte- rior side by a perpen- dicular line drawn in- wards ; and make this line l, \, or £ of the exterior, if the polygon of construction is a square, pentagon, or any larger figure. 2. Join the end of the perpendicular with the angles of the poly- gon, and produce these lines inwards. These are called the lines of defence. 3. Set off on each line of defence a dis- tance equal to 3 of the exterior side, measured from the angle of the polygon. This will give the faces of the bastions. 4. From the ends of the bastion faces draw the flanks, making angles of 95° with the opposite lines of defence. 5. From the points at which the flanks cut the lines of de- fence, draw a straight line connecting the inner extremities of the flanks. This will be the curtain. In order that the whole fire from one flank may defend those parts of the ditch unseen by the other, it is necessary that the lines of fire should cross at the centre of the curtain, and that the line of the counterscarp should not be traced parallel to the escarp, but be directed on to the shoulder angles of the bastions. As will be seen in the sketch (Fig. 40), this latter arrangement increases the width of the ditch considerably, and consequently involves much time and labour to execute. ANIMAL COMMERCIAL PRODUCTS. 289 ANIMAL COMMERCIAL PROD [JOTS.— XII. PRODUCTS OP THE CLASS PISCES ( continued ). the cod ( continued ). It is tho great quantity of cod and its allied kinds, had- dock (Morrhua agio finus), tusk ( Brosmus vulgaris), and ling ( Lotus mola), which gives to these fish their chief mercantile importance. In 1854, 3,523,269 individual fish of the cod and ling kind were caught, of which 1,385,699 were from the Orkney and Shetland Islands, and the remainder from the other fish- ing stations on our coasts. In 1857 the total amount of cod, ling, and had- dock taken by the fishermen of the United Kingdom was: Cured and dried, 104,668| cwt. ; cured in pickle, 4,393.] barrels; cured, dried, and ex- ported, 34,310 cwt. The greatest cod fishery in the world is on the banks of New- foundland. These banks are based on a large rocky shoal about 600 miles in length and 200 in breadth, being, in fact, the top of a vast submarine plateau, over which the ocean rolls. This plaoe is a great rendezvous for cod, which resort there to feed on the worms, which are plentiful in these sandy bottoms, and on account of its vicinity to the polar seas, whither they return to spawn. The cod are found here in such numbers that although maritime nations have for centuries worked indefati- gably at these fisheries, not the slightest preceptible diminution of their abundance has ever been noticed. The Newfoundland cod fisheries are carried on now principally by the French and Americans. The British interest in them has de- clined of late years very con- siderably, as we have trans- ferred the site of our opera- tions to the coast of Labra- dor, where 20,000 English sailors, with from 200 to 300 schooners, are annually em- ployed. The Americans fit out their vessels chiefly at Bos- ton, and thus from their vi- cinity to these fishing-grounds possess a great advantage over the English. Immense quantities of cod are sent by England, France, and Holland, partly salted and dried to Southern Europe, chiefly for consumption during Lent and the other fasts of the Roman Catholic Church. Turbot ( Rhombus maximus). — Taken on all our coasts. The English markets, however, are supplied chiefly with Dutch turbot, which is preferred ; these are caught on the sand-banks Ling between Holland and the eastern coast of England. The Dutch receive =680,000 per annum for supplying the London markets with turbot ; and the Norwegians =615,000 for about 1,000,000 Norwegian lobsters, used partly as sauce for turbot. Sole (Solea vulg mis), —The sole is common on the British 19 — Fol. I. THE FLOUNDER, SOLE, AND PLAICE. coasts, and in season from May to November. The principal fishing stations are on the south coast, from Sussex to Devon* shire, especially at Brixham and Torbay. Plaice, flounders, dabs, halibuts, etc., are all in great request in the market but can only be mentioned. Lamprey (. Petromyzon marinus ).— An eel-like cartilaginous fash, having a funnel-shaped mouth, surrounded by a circular suctorial lip, by means of which it adheres to stones (Greek petron, a rock ; and muzo, I suck) and to the bodies of those fish on which it feeds. Formerly the lamprey was considered a great delicacy, and one of our kings (Henry I.) is said to have died in conse- quence of eating too freely of it. Although not so much iat demand now, great numbers are still fur- nished from the North Sea, the Baltic, and the German rivers, where they abound. Lampreys reach this country packed in jars with vinegar, spices, and bay leaves. Common Sturgeon ( Acipenser sturio) belongs to the group o cartilaginous fishes. The body is elongated, spindle-form, and usually from five to six feet in length ; the head, which i? epressed and produced into a triangular snout, is covered witl rows of large tubercular bony plates. The sturgeon is abun- dant m the seas of Northern Europe, also in the Caspian, the ack Sea, and the Mediterranean, ascending the rivers in great numbers to spawn. Cavim e , which forms an important article of commerce, con. sists of the roe of different species of this fish, cleaned, washed with vinegar, salted, dried, and then com- pressed into small cakes, or packed in kegs. Russian caviare —brought from the Caspian and Black Seas — is usually consi. dered the best. Much caviare is also prepared on the shores of the Lower Danube. That furnished by the sterlet (Acipenser ru- thenus) is so superior that, according to Cuvier, it is re- served for the imperial court of Russia. Isinglass, another product from these fish, is prepared from their air-bladders. This substanoe owes its commercial value to its extremely delicate fibres, which operate mechanically in the clarification of white wines and malt liquors. It is also much employed in cookery. Russian isinglass is preferred to that from Hungary and Germany. PRODUCTS OP THE SUB-KINGDOM MOLLUSCA. Mollusca (Latin, mollis, soft). — Soft-bodied, invertebrated animals, devoid of an internal bony skeleton, having a gangli- ated nervous system, the ganglia, or knots of nervous matter, being irregularly dispersed in different parts of the body. They 290 THE TECHNICAL EDUCATOR. have a distinct pulmonary or branchial circulation, white or bluish blood, and in most cases a shell covering, in which the animal resides. This is secreted by the margin of a peculiar organ termed the mantle, or an external fold of the skin re- flected over the body. Many of the lowest and some of the highest of the Mollusca are naked, or a horny and testaceous rudiment of a shell is developed, but remains concealed beneath the substance of the mantle. When, however, the shell is so much enlarged that the contracted animal finds shelter within or beneath it, then the mollusk is termed: testaceous (Latin, testa, a shell). We shall confine our notes to the testaceous Mollusca, as commercially they are the most valuable. The following are the chief classes of the Mollusca : — 1. Cephalopoda, or head-footed (Greek, hephale, head, andpous, a foot), having the head well developed, protruding from the mantle, and furnished with tentacula, serving for the seizure of food and for crawling. Examples : nautilus and cuttle-fish. 2. Gasteropoda, or belly-footed (Greek, gaster, the belly, etc.), crawling by means of a broad muscular disc on the lower surface of the body, which serves as a substitute for legs. Examples : Helix hortensis, the garden snail ; Lymncea stagnalis, the pond snail ; and Inmax agrestis, the field slug. i 3. Pteropoda, or wing-footed (Greek, pteron, a wing, etc.), comprehending a few mollusks which have a natatory wing-like expansion on each side of the head. They are naked, or pro- vided with a delicate univalved shell. Example : Clio borealis. Most of the species of the class Pteropoda are fossil, but a great many are still found in existing seas, living near the surface. The Clio borealis forms the food of the whalebone whale. It is an inch long, uses its light shell as a boat, its wing-like fins as oars, and so navigates, in countless numbers, the tranquil surface of the Arctic seas. 4. Conchifera, or shell- carriers (Latin, concha, a shell, and fero, I carry), including all the bivalved mollusks not Brachio- pods. Examples : oyster, mussel, and pearl oyster. 5. Brachiopoda, or arm-footed (Greek, brachion, an arm, etc.). — Bivalves devoid of locomotive power, and attaching themselves to foreign bodies : they are furnished with two long ciliated arms developed from the sides of the mouth, which, by producing currents, bring food to the animal. Examples : Terebratula and Lingula. APPLIED MECHANICS.— VII. BY ROBERT STAWELL BALL, M.A., LL.D., Astronomer-Royal for Ireland. MACHINERY USED IN AGRICULTURE. MECHANICAL APPLIANCES USED IN PREPARING THE SOIL MACHINES USED FOB SOWING MACHINES USED IN REAPING. The application of machinery to the different branches of agriculture is of considerable antiquity. Not to mention the simple implements such as spades, rakes, etc., more complicated machines have been in use since the earliest times. A form of plough which was used by the ancient Romans is still employed in parts of France and Italy. The ploughs with which we are familiar are, in fact, to a certain extent on the type of the ancient instrument, but have received from time to time im- provements which the experience of successive generations of cultivators of the soil has suggested. The Romans were also accustomed to irrigate their land by artificial means when cir- cumstances were suitable, and this process is still recognised as one of the most scientific applications of capital to agri- culture. In this lesson, however, we propose rather to sketch the present condition of agricultural machinery than to trace its history in successive ages. There are other applications of science to agriculture besides those which relate to the em- ployment of machinery ; notably among these is the service rendered by chemistry in the analysis of soils and manures : with such matters we have nothing to do. This lesson is intended to describe the mechanical appliances employed, first, in the preparation of the soil ; secondly, in the putting in of the crop ; and, thirdly, in the gathering of the crop. Those who wish to pursue the subject further will find a considerable amount of information in Donaldson’s “British Agriculture,” a work to which I must acknowledge my obligations in the pre- paration of the present lesson. MECHANICAL APPLIANCES USED IN PREPARING THE SOIL. Land may suffer on the one hand from an excess of water, on the other hand from a deficiency in that fertilising liquid ; in either case mechanical appliances must be resorted to as a remedy. In the one case we must by drainage endeavour to remove the superfluity, in the other case by irrigation we can supply the water which is necessary. There is no occasion, however, to do more than mention these important operations here, as the various methods employed for carrying off surplus water from the soil by artificial means, and distributing ferti- lising currents over parched grass-lands, are fully described in the lessons in “ Agricultural Drainage and Irrigation ” given in this work. Drainage and irrigation are most necessary mechanical opera- tions in the treatment of the soil prior to its being actually broken up for the purposes of tillage. To this important subject we now proceed. The earth is a very weighty material, and the labour that is expended upon breaking it up consists in great part of the actual exertion of raising its weight through a small height and replacing it again. Thus the soil that covers an acre to the depth of four inches weighs from 600 to 700 tons, and if in the process of breaking up this mass has to be raised even to the height of a few inches and replaced again, the consumption of work is very considerable. But in addition to the mere weight of the soil, there is its tenacity also to be overcome. It is probable that in many soils, if not in most, the force requisite to overcome this exceeds that which is due to the weight of the soil alone. Thus in digging a garden with a spade, though the sharp edge of the spade divides the soil, yet the mass that is being removed has to be tom away from the lateral portions, and in tenacious soils, as every one knows, this resistance is very great. A spade is, in fact, a powerful lever of the first order. The power is applied by the hands at one end, the fulcrum is the upper portion of the spade where it is in contact with the surface of the soil, and the load is the mass of earth which is being removed. The leverage in such an implement is at least sevenfold or eightfold, and even with this mechanical advantage the operation of digging is one of great labour. On the large scale, the use of the spade is, of course, re- placed by the plough. We here abandon the principle of the lever a 3 a mechanical power, but we replace it by the wedge which we have already described. In reality the ploughshare is a wedge which inserts itself into the soil, and overcomes both the resistance of the weight of the soil and also that presented by its tenacity. It will bo well to mention the names which are applied technically to the different portions of a plough. We shall then consider the principles on which the action of the plough depends. The bottom of the plough is called the sole ; to the point of this is fixed the share; the beam projects in the front of the plough, and to it the oxen or horses are attached. Attached to the beam in a vertical position is the coulter; this cuts a vertical section in the ground ; while the point of the share, expanding into a fin, cuts a horizontal slice from the ground under it# The mould-board is placed behind the fin, and serves to raise up and remove the slice which has been cut by the coulter and share. These different portions of a plough will be seen from the illustration of a very improved form of plough (Fig. 3). The action of the plough is therefore threefold. First, the vertical cut by the coulter, then the horizontal cut by the share, and, finally, the turning over of the portion thus cut by the mould-board. Experience has done more in devising the form of the plough than direct application of science. The actual problem of finding the best possible form of plough would be a very difficult one, even if all the conditions of the question were known ; but owing to the varying conditions of soil, it is almost impossible to devise any very rigorous statement of the problem which the best construction of a plough would involve. We shall, however, give a short account of what is known as to the principles on which the plough acts. The accompanying figure (Fig. 1) is taken from the “ English Cyclopaedia,” in which an excellent account of the theory of the plough will be found. Let A B D c represent the slice of ground which is being re- APPLIED MECHANICS. 291 moved by the plough ; A c is the vertical cut which is made by the coulter ; c D the horizontal cut which is made by the share. The object of ploughing is to turn this sod up to the vertical position, D c ah, and then to tilt it over to the inclined position, d! 1/ a' c', so that the original surface, A b, is changed into the under surface, a' V ; the object of this is to kill the weeds or grass that may be on the surface by burying them, and at the same time to expose as much of the soil as possible to the action of the atmosphere. The problem, then, which the mould-board has to solve, is to effect this operation as uniformly and with as little waste of power as possible. This condition points out that the sur- face of the mould-board must be that of a screw, which might be produced by a line nine or ten inches long, which revolved uni- formly about an axis through an angle of 135°, while at the same time it travelled along the axis through a space of three or four feet. The portions of a plough are now generally made of cast- iron, and a very beautiful property of cast-iron is made use of in the point of the share. It is well known that cast-iron when poured into an iron mould becomes intensely hard. It is called chilled iron, and is used where or- dinary cast-iron would "be too soft. In casting the share, the lower surface of its point is in contact with iron ; the conse- quence is that the under surface of the share is of chilled iron, while the upper surface is of ordinary cast- iron. The effect is that the upper part of the point is worn away more rapidly than the under surface, and consequently the share always pre- sents a sharp edge. The actual draught required in drawing a plough is very variable; but it may, on the average, be taken at about three hundred- weight. This point is carefully attended to in comparative estimates of the merits of different forms of plough. It is ascertained by attaching a dynamometer to the plough, and applying the power of the horses to the dynamometer. It is usual now to employ, when the circumstances will admit of it, steam power for drawing ploughs, in place of the muscular power of ani- mals. To render this plan capable of economical adop- tion, a large area must re- quire to /be ploughed, and the land should be tolerably level. The steam - engine which gives motion to the ploughs is in one corner of the field, and its power is communicated by means of wire ropes, which passing over pulleys properly attached at the margin of the field, are fastened to the ploughs. One engine is thus enabled to work several ploughs simultaneously. Tiie next operation to which the land is subjected is that of harrowing This is of a very simple character; it consists merely m drawing a frame covered with spikes over the newly- Fig. 2. ploughed fields, for the purpose of breaking up the clods which the plough has turned up. Nothing further need be said of this process. * MACHINES USED FOR SOWING. In sowing, it is desirable that the seed be distributed with regularity over the surface, and in the quantity which expe- rience has found most desirable for each kind of seed. It is also necessary that the seed be depo- sited at precisely that depth in the soil at which it will be most favourably circumstanced for ger- mination. Now machinery, by the regularity and certainty of its action, is eminently adapted for the purpose of placing seed at the right depth and in proper quantity. It is not, therefore, merely as a labour-saving agent that sowing machines are useful ; they accom- plish the work with a perfection that it is not possible for labour unassisted by their means to attain. It is found that seeds sown in drills yield a crop more economically than when the seeds are sown broadcast. The machines which are employed in sowing are therefore adapted for depositing the seed in drills. These machines are themselves technically called drills, in consequence of the object for which they are employed. In Fig. 2 is shown what is called the N o r t humberland turnip drill, used, as its name ex- presses, for sow- ing turnip seed. It is a very perfect instrument of its kind, and a de- scription of it will embrace the prin- cipal features of all the better ma- chines of this class. We have borrowed this figure, and the ac- companying de- scription of it, from the “ English Cyclopedia.” This machine is adapted to introduce ground bones, or other manure of the same class, into the ground simultaneously with the seed. “ The body of the drill consists of two boxes, a and b, divided by a partition between them, and each again divided into two by another partition at right angles to the first. Into the box A is put the manure, into b the seed. Iron slides are fixed on each compartment to regu- late the supply of seed or manure. In the lower part of the box, and just before the opening, which is regu- lated by the slides, are two cylinders, one for the box A, and the other for b. On the cylinder in A are fixed shal- low cups with short stems which dip in the boxes, and carry a certain quantity ovef the cylinder as it turns, which falling in the funnels, K, K, is deposited in the furrows made by the coulters, H, H. The cylinder in the box B has projecting pieces of iron with a small cavity in each near the end, which takes up a very small quantity of seed, and dis- charges it in the same manner into the two funnels, K, k. On the axis of the wheel e is a toothed wheel, which turns a small wheel, d, on the axis of the cylinder in a, and thus turns 292 THE TECHNICAL EDUCATOR. another wheel, c, on the axis of the cylinder in b. As these two wheels move towards each other, the two cylinders turn in contrary directions, which is a convenience in turning the seed and the manure into the funnels at the same time. The wheel f may be lifted up by means of a lever G, and then the cylinders do not revolve. There are various other contrivances Ivhich cannot easily be explained without a more detailed figure of the different parts.” It is always difficult to convey an adequate idea of complicated machines by description : an examination of the machine itself, which is to be met with m any agricultural museum or show, will explain its action better than any description, however lengthy. machines used in heaping. We have seen how machinery aids in preparing the soil and sowing the seed : we have now to examine its utility in enabling the farmer to realise the fruits of his labour. Reaping-machines are of very modem construction ; they are eminently useful as labour-savers, and simultaneously with the rise in wages of agricultural labourers have reaping-machines come more and more into use. They vary very much in external appearance, but certain principles appear to be common to all the different forms. The blade of the reaping-machine consists of a series of notches, as shown in Fig. 4. These notches are sharpened Fig. 4. on their edges by grinding-stones of peculiar construction. . If we conceive two blades of this shape, one immediately overlying the other, and if the one be held fast and the other be made to oscillate backwards and forwards rapidly, we have the essential principle of a reaping-machine. These blades are carried a few inches above the surface of the ground, and one of them is made to oscillate by means of a mechanical connection with the wheels of the machine ; a series of arms force the straw into the notches, and it is immediately cut across by the moving edges, and the machine neatly deposits the corn which has been cut. We have in this lesson been able to give only the merest outline of the debt which modern agriculture owes to machinery. There are innumerable appliances into which we cannot enter. Thrashing and winnowing machines would form a suitable sequel to reaping-machines. We might also speak of machines for cutting down trees, for removing stumps of old trees from the ground, and machines for excavating earth. There are numerous machines in constant use in America with which we are not familiar here. There the high price of labour has rendered all labour-saving appliances of far greater economic importance than in older countries where the population bears a higher proportion to the capabilities of the soil for pro- duction. PRACTICAL PERSPECTIVE.— I. INTRODUCTION. The intimation that “these lessons are written to supply a want ” has become so hackneyed, that it is only repeated here because no other sentence would so well express their real purpose ; and it is hoped that by their publication a series of really elementary lessons will be given which will be useful not only to artisans and teachers, but to the public generally. The words used in the introduction to the lessons in “ Prac- tical Geometry applied to Linear Drawing” refer equally to these lessons : — “ The subject is not treated as a mathe- matical, but as a thoroughly practical one, and therefore no absolute system of reasoning is attempted ; still, it has been thought right to give some simple and familiar explanations of the properties of the various figures, and the principles upon which their constructions are based, as it must be obvious that the more tb.o mind comprehends of the relation of one line and form to another, the more will the eye appreciate beauty and refinement, and the more intelligently will the hand execute.” In pursuance of this plan, only just as much of the theory of Perspective is given as will enable the student to comprehend the subject ; and an endeavour is made, as the lessons advance, to show the application of the principles, and of the few rules laid down. The studies are very carefully graduated, commencing with the perspective projection of single points, and proceeding in succession to the consideration of lines, planes, and rectangular solids, in the foreground and in the distance, when parallel or at an angle to the picture. The course next takes up the delineation of polygons, prisms and pyramids, circles, cylinders, and arches. The examples are all clearly drawn, the working lines being shown ; the lettering is plain ; and the instructions as simple and brief as is consistent with the proper explanation of the subject. Exercises are added in order that the student may test whether he has fully comprehended what he has been taught, and whether he can vary the circumstances whilst applying the principles. This will counteract the tendency to copy the diagrams so often met with. These exercises will also be found most valuable to teachers, who are advised to write them on the black-board, causing each student in the class to take a different centre, points of dis- tance, scale, etc., whilst still working out the subject according to the other data given. The student is urged to work the figures contained in lessons in “ Practical Geometry applied to Linear Drawing ’ either before, or concurrently with Perspective, as he will otherwise find himself constantly in the awkward position of being unable to construct the geometrical form which he is endeavouring to put into perspective. It will also be of advantage to him to study “Projection” either previously to, or at the same time with, these lessons, as he will then be able to observe the changes of form caused by the parallel lines of the one system and the convergent lines of the other, whilst the knowledge of developments will enable him to understand the true forms oi the surfaces which become so much altered by Perspective. All the studies are based upon the actual experience gained during nearly twenty years’ teaching, in which the inquiries of students, their difficulties, and the errors into which they are most liable to fall, have been most carefully noted ; and it is therefore hoped that these lessons may do the work at which they aim efficiently, so that the term “ Perspective,” instead of being uttered with dread, as a mysterious art known only to a few, may become as familiar as a household word to the many, and thus, by a knowledge of its principles, our students may be enabled, not simply to work out the lessons with their instruments, but to sketch with rapidity and correctness, whether from the object or from memory. When Perspective is thus understood, it becomes indeed the grammar of a universal language. PRACTICAL PERSPECTIVE. Perspective is that branch of “Projection” which teaches the mode of drawing objects, etc., as they appear to the eye of the spectator in whatever position he may be placed. This appearance will, of course, be altered by (1) the distance of the object from the spectator, and (2) its position. The moment we open our eyes a flood of light enters, and the rays which pass from the surfaces of every object are thus con- veyed by the eye to the brain. As these rays pass from the entire surrounding space through the small opening called the pupil of the eye, they are said to “ converge,”* and thus form what is called the “ visual angle. Of course, the angle at which the outer rays meet depends ^on the size of the aperture in the eye of different persons. For perspective purposes, however, an average angle has been generally adopted — namely, that of GO 0 ; for experience has shown that the majority of persons can see, let us say, a line, A b (Fig. 1), when the distances from a to c (the station of tho spectator) and from b to c are equal to the length of the line ; and it will be seen that an equilateral triangle is . thus formed, the angles of which, as has already been shown in “ Practical Geometry applied to Linear Drawing, ” are all 60 . But the rays do not proceed from a single line, thus forming a plane triangle, but from the entire surrounding space. The Converge .— To incline together, so as ultimately to meet in a point. PRACTICAL PERSPECTIVE. 29S triangle abc is thus, as it were, rotated on the central line C d, and a cone (that is, a solid triangular body having a circle for its base) is formed. The line c d, or axis on which the triangle has been rotated, is called the central or principal visual ray. It will be clear, then, that since the base of this cone (Fig. 2) comprehends all that can be seen when looking straight forward, our entire picture must be contained within it. The apex, c, of the cone is called the station-point, as being the other. Now let threads attached to the angles of the cube pass through small holes in the plane in straight lines to the eye. Then if these holes are joined by lines, the exact per- spective appearance will be obtained. Now it is easily understood that this centre of vision will be moved as we turn round, and hence some objects will gradually be removed from our view, whilst others become visible ; but so long as we do not stand on higher or lower ground, the height of our eye will remain the same. the station of the spectator, or the point of sight, since it is the point from whence the sight is obtained, The opposite end of the central ray is the centre of the base of the cone of rays, and is therefore called the centre of vision* The surface on which we draw is called the picture-plane. It is supposed to be transparent, and (as a rule) to be placed vertically between the spectator and the object ; the rays passing from the object through this plane give the apparent form. Thus, let a plane stand on its edge on a table, and let a cube be placed on one side of it, the eye of the spectator being on * As, however, in looking forward from the point of station, the point c (the one end of the central ray) is immediately in front of the centre of the circle, the point has generally been termed the “ point of sight.” The horizontal line is a line drawn through the centre of vision in a horizontal position, as its name implies. It shows the height of the eye of the spectator in relation to the objects drawn. This is shown in Fig. 3. Here c is the centre of vision, and h l the horizontal line. The cube lettered a is above the level of the eye • of the spec- tator, and h is below. Thus the under surface of a and the upper surface of h are seen. Both are on the left of the spectator, and thus the right side of each is visible. The cubes c and d are similarly placed as to the horizontal line, but being on the right of the spectator, their left side is presented to view. The cube e is above and / below the horizontal line, and thus the bottom of the one and the top of the other is seen ; but as 294 THE TECHNICAL EDUCATOB. they are immediately above and below the centre of vision, neither side is visible. Again, the cube g is on the left and h is on the right of the spectator, but both are on a level with the centre of vision, and therefore only the side of each is seen, but neither top nor bottom ; whilst in fc, which is immediately opposite to the eye of the spectator, none of the sides, excepting that which forms the front, are visible. It is necessary, however, to fix in a definite manner the positions of the lines which represent the distant edges of the objects, for it will be evident, on referring to the cube b, that if these were placed at sc, the object would appear a long balk of timber instead of a cube. The correct proportion is, however, obtained by means of points, of which we shall now speak. The points of distance represent the distance of the eye from the picture. To illustrate this, let us now turn to Pig. 4. Here A b c is the cone of rays standing on its base. Now, as the picture- plane forms a part of that base, it will be clear that the length of the axis, or central ray, c d, represents the distance of the eye (situate at the apex of the cone) from the picture, and it is now required to lay this length down on our paper. It has been said that the cone adopted for the purposes of perspective has its slanting side equal to the diameter of its base. Therefore any section taken through the axis would be an equilateral triangle, as E c F. Now, if we imagine this equilateral trianglo rotated on the line E F, first on the one side and then on the other, we shall obtain G and H, which will be the points of distance, for i> G and D h will be equal to D c, the altitude of the triangle or axis of the cone, which is necessarily the distance of the spectator from the picture. Fig. 5 is the plan of this cone. Having drawn the picture-plane, abed, and the base of the cone surrounding it, draw the perpendicular line E F. From E and F, with radius E F, describe arcs cutting each other in G and H, which will be the points of distance. To show at once the use of these points, draw the square e, and from its angles draw lines to D (representing rays of light passing to the apex of the cone). Now from the point f of the cube set off what you know to be the real width of the distant side (which in this case will be equal to the width of the front, the object being a cube), namely, / g. From g draw a line to G, which, cutting / r> in h, will give the point at which the distant edge of the cube is to be drawn. This figure may be slightly in advance of the student’s present knowledge, and is merely introduced here so that the purpose of the points of distance may as soon as possible be made evident. The steps leading to this subject will, however, be clearly shown hereafter. The centre of vision, although the centre of the base of the cone of rays, need not necessarily be the centre of the picture, for although the picture-plane must be contained within the circle, it need not occupy the whole, but it must touch the cir- cumference at one point. To find the points of distance when the picture-plane, abed (Fig. 6), and the centre of vision, r>, are given — Through d draw the horizontal line. From d, with radius D a— that is, from the centre of vision to the most distant angle of the picture-plane — describe the base of the cone of rays. Draw E F through D, and with E F as radius, describe arcs cutting each other in G, H, which, as before, will be tho points of distance. The bottom line of the picture, c d, is called the picture- line: It is not always necessary to employ the whole of the picture- plane or base of the cone of rays ; it is, therefore, generally enough to state the height of the eye of the spectator, and his distance from the picture. This plan will now be adopted, as we shall be thus enabled to employ the whole space at our disposal in delineating the subject of the study. The centre of vision will throughout the lessons be called c, and the points of distance, p d. It may also be as well to remark that wherever it is necessary to speak of the horizontal line and refer to it by letters, the letters H l will always be used to denote it. TECHNICAL EDUCATION ON THE CONTINENT.— X. BY ELLIS A. DAVIDSON. THE GRAND DUCHY OF HESSE. THE POLYTECHNIC SCHOOL AT DARMSTADT. During many years past there had existed in Darmstadt, under the names of Higher Trade Schools and the Technical School, institutions for the promulgation of Technical Education. They were tolerably successful and were well attended, and many men, who have since become celebrated as professors, engineers, architects, and public officers, proceeded from theso schools. The objects of both these institutions were precisely the same, but a complete education was not given in either ; and students had to proceed to various establishments, mostly in other places, to obtain instruction in higher or special studies. This, again, led to the establishment of other schools for various branches ; and thus a falling-off in the numbers in the two original schools took place. In 1868, however, the Legislature and the pro- moters of the separate schools united, and from this amalgamation the Polytechnic School at Darmstadt arose, as a High School for technical education adapted for persons of all grades of society and of every trade, admirably organised in every respect, and possessing a staff of nearly fifty professors and teachers, all men of the highest standing, working out a system well con- sidered and complete, in a manner which must have a lasting effect, not only on Germany, but possibly on Europe generally — we may say on the world ; for who can tell where the seeds sown by education may not be carried ? And when we see swamps drained, deserts watered, and canals made which unite sea to sea, and know that these are some of the works of Euro- pean engineers, we cannot but feel that the words spoken in the class-rooms are like so many rays of sunlight, which, though they may be buried in the mind of tho student for many long years, will rise again (even as the light of thousands of years ago is now evoked from the coal mine), perhaps in far-distant lands, to illumine aboriginal darkness, and to spread the laws of God (and is not science His law P) amongst the savage and ignorant. The Polytechnic School at Darmstadt, then, is a higher technical school, professing to give a complete course of instruction for the various branches of tho higher walks of industry, together with the required art-knowledge, accompanied, wherever possible, by actual practice. The studies are there- fore arranged to suit the necessities of the architect, engineer, machinist, practical chemist, manufacturer, pharmaceutist, agriculturist, land surveyor., and all others whose vocations are based on scientific principles ; whilst the general knowledge imparted is such as cannot fail to be eminently useful in every walk in life. The School is divided into the following departments : — 1. The General School. 2. The School of Practical Architecture. 3. The Engineering School. 4. The School of Mechanical Construction. 5. The School of Technical Chemistry. 6. The School of Agriculture. The studies in the general school comprise mathematics, and natural history in its widest sense, the courses being so arranged as to prepare pupils in every way for entering the higher departments of the institution, or any of the special classes they may subsequently select. The instruction in the Polytechnic Institute is given in the form of lectures, questions, repetition examinations, graphic and constructive practice, work in the laboratory, and excursions to various factories, building works, etc., whilst immense benefit arises from tho personal intercourse between the masters and pupils. The teachers are either members of the absolute school staff or persons called assistants, who lecture on or teach the practice of their particular vocation. An amount of practical skill is thus brought to bear, which others, however highly educated they might be, could not possess. The head of every department is, however, a professor holding a high University degree. Private persons also, who have made some particular branch of science or art their study, and have become celebrated in it, BUILDING CONSTRUCTION. 295 or who are the authors of some important invention, are from time to time invited to give lectures, and by this means the interest of the students is awakened, and their knowledge brought up to the state of science as developing around them. The appliances for carrying out the objects of the School are very complete, and include the museums, laboratories, and col- lections of the two original schools, the botanical garden, and fields for agricultural experiment. The models used for teaching projection, and those for illustrating the principles of mechanism, are admirable ; they will be described further on. The pupils have also the use of State museums of arts and manufactures, and of all similar collections. For admission to the lowest form of the general school, the candidates must be at least sixteen years of age. They must give proofs of their having reached the standard of instruction given in the upper classes of the “ Real ” schools of the country, and must be prepared to pass an examination as follows : — 1. Algebra as far as equations of the second degree, and an acquaintance with logarithms. 2. Plane geometry and the elements of solid geometry. 3. A good knowledge of the German language and style, shown in the composition of an essay on a given subject. 4. A knowledge of the great periods of general history, and of the leading events of those periods. 5. Exercises in linear and free-hand drawing. THE GENERAL SCHOOL. This department is organised to give a sound and practical education, not only to youths intending to enter the various trades, but also to the general public. The following is the course of studies :— First year : — General history and literature, the German lan- guage, mathematics, descriptive geometry, free-hand drawing, the French language, religion. The following studies are recommended : — The English lan- guage, zoology, systematic botany, gymnastics, vocal music, Latin. Second year General history, literature, and the German language, mathematics, especially analytical geometry of planes, descriptive geometry, free-hand drawing, experimental physics, mechanics, the French language. Studies recommended ; — 1 The English language, gymnastics, vocal music, Latin. SCHOOL OF PRACTICAL ARCHITECTURE. The course of studies agrees with the examinations in the Civil Service of the Grand Duchy of Hesse. The syllabus is arranged in two sections, corresponding with the examinations for higher or lower grades in the Civil Service. The courses are independent of each other. (a.) Lower Course (for students who are not preparing for the Civil Service): first year: — 1. Physics, acoustics, light, heat, galvanism, polarisation, optics. 2. Experimental chemistry. 3. Mineralogy and petrology. 4. Free-hand drawing, building materials, building construction (first course), ornamental draw- ing (first course), architectural drawing. Second year :— Practical geometry, free-hand drawing, the mathematical theories of building construction, architectural history (first course), science of architecture, building construc- tion (second course), ornamental drawing (second course), designing from given data (first course), streets and railways. Third year :— -Free-hand drawing, artistic perspective, archi- tectural history (second course), • building construction (third course), ornamental drawing, etc. (third course), designing from given data (second course), general instruction on mechanism. The students are recommended to give as much attention as possible to art generally, and to aim at the higher branches, with the view of elevating their mental grasp ; and by the study of the great works of ancient and modern times, and the scientific principles upon which they have been constructed, to qualify themselves for advancing in the field of intellect and professional skill. (b.) Upper Course (for students who are preparing for the Civil Service examinations) : first year : — Differential and inte- gral calculus, analytical geometry of spaces, physics (acoustics, light, heat, galvanism, optics, etc.), experimental chemistry, mineralogy, and petrology, free-hand drawing, building materials building construction (first course), architectural drawing. Second year: — Analytical mechanics, historic architecture, building specifications and cost, building construction (second course), ornamental drawing (first course), architectural designing from given data (first course), mechanical construction with details (first course). Third year : — Practical geometry, drawing from plants (first course, to assist in designing foliage in ornamentation), mathe- matical theory of architecture, historic architecture (second course), building construction (second course), ornamental draw- ing (second course), designing from given data (second course), foundations and bridges (first course). Fourth year : — Calculation of probabilities and method of least squares, higher geodesy, artistic perspective, the arrange- ment of dwellings for the people, designing from given data, bridge-building (second course), streets and railways, water- works, general mechanism, technology, lessons selected from the course of Technical Chemistry. The Engineering School, the School of Mechanical Construc- tion, the School of Technical Chemistry, and the School of Architecture, are all equally exhaustive as to their courses of requirements of the instruction, and all show the most careful consideration of the student, not merely to teach him just as little as will enable him to keep his head above water, but to enlighten his mind in every way, so that he may have spirit to think for himself and to strike out new paths. The models used in this school and in kindred institutions in most parts of the Duchy, for teaching Projection in all its branches, are exceedingly useful. A set adapted for the use of our Schools of Science, etc., and illustrating our lessons in “ Projection,” is in preparation. The models used for showing the various mechanical combinations are also very good. They are made principally of iron, painted and bright, and are of the average height of eighteen inches. Amongst them are the dif- ferent escapements, shafts for the transmission of motion at various angles, turbines, water-wheels, various systems of spur, cog, annular, crown, face, and bevil wheels, plummer blocks, square and elliptical wheels and cams, the various modes of coupling and disengaging shafts. Watt’s parallel motion, etc. All these are actual working models illustrating the lessons in the higher class text-books on Mechanism. Turning now from schools, let us devote brief space to the description of the Trade Association of the Grand Duchy of Hesse, the organisation of which took place between the years 1836 and 1838, under the auspices of, and by grant from, the Grand Duke. The object of this association is to watch over the progress and promote the interests of trade. The management is responsible directly to the Minister of the Interior, and has so successfully worked out the plans, that the number of mem- bers, which in 1836 was 794, has now reached about 3,500, each contributing an annual subscription. The means taken by this Union to accomplish their object are various — such as (1) the publication of newspapers and periodicals devoted entirely to trade, arts, and manufactures ; (2) an extensive lending library ; (3) the collection of models and trade products (the models in this museum consist of illustrations of the various methods of joining timber, stone-constructions, bridges, models of heating apparatus, illustrations of brickwork, escapements for watehes, English and foreign tools) ; (4) a collection of trade products, and (5) a fine collection of raw and manufactured trade products purchased from the Exhibition of all Nations held in London in 1851. The Association has also arranged and published an excellent set of models for teaching Projection, and some ex- ceedingly useful sets of technical drawing copies. It also orga- nises exhibitions of the productions of its members. Several local exhibitions have been held, and in exhibitions in other countries, notably in the Paris Exhibition of 1867, the exhibits have been such as to attract great attention, as showing the practical results of a well-applied system of Technical Education. BUILDING CONSTRUCTION.— X. arches ( continued ) Before, however, entering into the brick construction of the arch shown in Fig. 68, which was given in our last lesson on this subject in page 265, it is necessary to speak of the wooden supports temporarily employed in the construction of arches. 1 These will be fully described in other lessons ; still it is neces- 296 THE TECHNICAL EDUCATOE. sary incidentally to mention them'; for although they are really branches coming under the head of constructive car- pentry, yet it is important that their general purpose, prin- ciples, and application should be thoroughly understood by the bricklayer and mason. The temporary wooden constructions referred to are called “ centerings,” and consist of an assem- blage of timber beams so disposed as to form a strong frame ; the convex or outer frame being of the exact form of the intrados of the arch which is about to be erected. the arch which may take place, owing to the support being re- moved, may not be sudden ; for if the support were at once withdrawn, the arch might settle in one part more than in another, and the whole work might in consequence give way or be permanently injured. In Fig. 68 we find an exceedingly simple centering. The walls A B, c d having been raised, the centering is erected. This consists of five sticks of timber, e, f, g, h, i, kept in their places by the cross-struts j it. These posts would be placed These constructions are, of course, only intended for tem- porary use, and therefore the following objects should be kept in view by the designer : — 1 • To damage the timber as little as possible, so that it may be used again when required. Of course, this condition must yield to the necessity of the case ; but in all works proper economy (provided it do not degenerate into a “penny wise and pound foolish ’ ’ system) is an element which must never be neglected. 2. That the design of the centering must be such as to resist any strain which may cause alteration of form during the building of the arch ; and 3. That arrangements should be made that the centering can be eased or lowered gradually, in order that any settlement of at each face of the arch if it were a deep one, or even at closer distances if the arch were built over a very deep vault or passage. Cross-wise, resting on these uprights, are laid horizontals, the ends of which, l m n o p, are shown in the illustration ; and on these again planking is placed, on which the arch would be built. An important feature, however, is that mentioned under the third heading — namely, the arrangement which must be made so that the centering may be eased gradually before absolute removal. Fig. 68 shows the most simple method of doing this. It will be seen that each support rests on two wedges mutually opposed, as Q, r, etc. Now, it will be evident that by striking each in turn, the whole of the wooden structure will sink almost BUILDING CONSTRUCTION. 297 imperceptibly, and thus allow the arch to come to an equal settle- ment throughout, and then the whole framing may be removed. After the preceding observations on centering, we now return to the brickwork of the subject under consideration. It will be seen in Pig. 68 that the greater portion of the weight of the superstructure is borne by the upper arch, which is hence called the relieving arch. That this is necessary will be evident when it is remembered that all the support gained from the appa- rently broad straight arch was that derived from the arch of the width 6 T, or about one brick. The relieving arch, struck from the same centre as that to which the skew-backs of the straight arch converge, thus bears the main burden ; and its purpose is further en- hanced by a tension rod, u v — viz., a rod of iron passing from the intrados of the flat, to the extrados of the relieving arch, by reason of which the sinking of the former is ren- dered impossible, owing to its being suspended, as it were, from the latter. Fig. 69 represents a Gothic or pointed arch, constructed of bricks. Here another very simple form of centering is shown. It will be seen that the posts a and b are placed against the piers, and are kept sepa- rate by the cross-strut c, the force of which may be gradually diminished by striking the wedges at d. On these posts rests the true centering, whioh, it will be seen, is formed of pieces of timber placed in the manner called “ break- joint ” — that is, of two thicknesses of timber, so united that the joints of the one side, ef, are covered by the whole wood on the other; and this mould again is supported by, first, a cross-piece, g, at the springing, and then by cross-struts, h, i, which can be relieved or eased by the wedges at j and lc, as can also the center- ing by those at l and m. The several centres, or trusses, which maybe required for the depth of the arch, are united by timber laid cross-wise, the ends of which are shown at n and o, etc. The curves of the arch are, of course, struck from the im- posts, this being an equilateral arch. The intrados and extrados having there- fore been drawn, divide the latter ii\to the number of bricks required. Now the majority of the radii are drawn to the centres from which the arcs p, q are struck ; but it will be seen that if this system were continued, the entire mass of bricks forming the block r s t u would not be influenced by such con- vergence,, for the bricks would have to be cut so as to meet in the centre line, and would thus have no influence as a key- stone unless a heavy weight were placed over it to keep it down, without which the pressure on each side would tend to force it upward and out of its place. When, there- fore, these radii have reached about 50° on each side, and intersect in v, this point must be constituted a new centre, and all radii between s f and 5 u must be drawn to it. DRAWING FOR MASONS. Fig. 70 is an example of planking, brick footings, and stone piers, as adopted in the circular vaulting at the London Docks. The foundation consists, in the first place, of nine fir piles 9 inches square, disposed as in the plan (Fig. 71). On these rest, first, three fir-sleepers, also 9 inches Square, and across these fir -planking 6 inches thick, forming a plat- form 4 feet 10£ inches square. On this rests the mass of brickwork in five ranges, 11| inches high, consisting of four courses (Fig. 72). The foot- ings are 2} inches all round, thus making each range 4£ incheB smaller across than that on which it rests. The surface of the brick foundation at A is therefore 3 feet inches. The base of the pier, which stands on the brickwork, is of stone taken from Bramley Fall Quarry. This base is 3 feet square at the bottom, and 2 feet 4 inches at the top ; the angles are, however, splayed off, and the upper surface thus be- comes an octagon. The shaft, which is of granite, is octagonal, and is 2 feet wide at its lower end, but diminishes to 1 foot 10 J inches at 3 feet high. This may be said to be the springing- point of the arches. The section shows that of a four-centred arch, the centres C d 1 O of which are marked in the drawing. The pier widens out at the top, and is sur- mounted by a cap, or springing Btone, also from Bramley Fall Quarry. It has just been remarked that the upper surface of the base of the pier described above becomes an oc- tagon when the angles at the corners are splayed off. As a useful exercise in Geometry and Linear Drawing which bears immediately on this part of our subject, we will add two problems : (1) on the construction of a regular octagon on a given line, and (2) the in- scription of an octagon in a square. It is the second of these problems which is brought into practice in taking off the angles 298 THE TECHNICAL EDUCATOR. of the block, so that, when this is done, the upper surface may- present the form of a regular octagon. To construct a regular octagon on the given line a b (Fig. 73). — Produce A b on each side. Erect perpendiculars at A and B. From A and B, with radius A B, describe the quadrants c D and e f. Bisect these quadrants, then a g and b h -will be two more sides of the octagon. At h and g draw perpendi- culars, G I and H K, equal to A B. Draw G H and X K. Make the perpendiculars A and b equal to g h or i k — viz., A l and b M. Draw il, x m, and m K, which will complete the octagon. To inscribe an octagon in the square a b 'd c (Fig. 74). — Draw diagonals, A r> and c B, intersecting each other in o. From A, B, c, and D, with radius equal to A o, describe quadrants cutting the sides of the square in e, f, g, h, i, j, k, l. Join these points, and an octagon will be inscribed in the square. PROJECTION.— XIII. QUESTIONS EOR EXAMINATION ( continued ). 82. There is a solid cross, formed by a central cube of 1 inch side, on each face of which another similar cube is fixed. Give the plan and elevation when two vertical faces of the original cube are parallel to the vertical plane. 83. Draw the plan and elevation when of the two adjacent vertical sides of the original cube one'is at 60° and the other at 30° to the vertical plane. 84. Project this object when resting on one angle of the base of the lowest cube, which is inclined at 30° to the horizontal plane, the diagonal being parallel to the vertical plane. 85. A cone, the base of which is 4 inches and the altitude of which is 5 inches, is penetrated by a cylinder of 2 inches diameter. The axis of the cylinder intersects that of the cone at right angles, at 1 inch from the ground. Draw plan and elevation when axis of cylinder is parallel to vertical plane. 86. Project this object when the axis of the cylinder is at 60° to the vertical plane. 87. A cone of 3 inches diameter, the height of which is 3^, rests on a cube of 3 inches side. Give plan and elevation when sides of cube are 50° and 40° to vertical plane. 88. Project the front view of the group when the one dia- gonal of the base is parallel and the other at 35° to the horizontal plane. 89. There is a cube of 3 inches side, on which rests a cylinder of 2 inches diameter and 3 inches high. This supports a cone of 3 inches diameter and 21 inches high, the axes of all being coincident. Give the front elevation of the group, when resting in a plane inclined at 25°. The other conditions at pleasure. 90. There is a solid formed of two equal square pyramids of 2 inches base and 3 inches altitude, which are united by their bases. Draw the elevation and plan when the object rests on one of the triangular faces of one of the pyramids, the axis of the object being parallel to the vertical plane. 91. Give the projection of the object, when resting on one of the faces of one of the pyramids. The axis is at 45° to the vertical plane. 92. Draw the elevation and plan when the object rests on an edge of one of the pyramids, the axis being at 60° to the vertical plane. 93. Construct an isometrical scale of A of an inch to the foot. Show 20 feet. 94. Draw an isometrical projection of a plane square of 2 inches side. 95. Give an isometrical projection of a pavement consisting of squares of 1 foot side. Scale, § inch. Show 5 squares in width and 12 in length. 96. Draw an isometrical projection of a cube of 2 inches edge. 97. Draw the isometrical projection of a box 3 feet square and 2 feet high, made of wood 3 inches thick. Scale, 1 inch to the foot. 98. There is a block of stone, 6 feet square and 1 foot high ; on this rests another, of the same height and 4 feet square and on this again a third block, of the same height and 2 feet square, is placed, the centres of the three blocks being over each other. Give the isometrical view of the group. Scale ^ inch to the foot. 99. A cylinder of two inches diameter and 4 inches long lies so that its end is vertical. Give the isometrical projection. 100. There is a stool the top of which is a square of 12 inches side, the height 18 inches, and the thickness of the legs 2 inches (the other measurements at pleasure). Scale, 2 inches to a foot. Draw an isometrical view of this object. *** ft is obvious that no Key to the foregoing Exercises in Pro- jection can be given. Each proposition must be worked, out by means of drawing, and our space is too limited to do this even on a very small scale. AGRICULTURAL CHEMISTRY.— YI. BY CHARLES A. CAMERON, M.D., PH.D. CHAPTER YI. — ON THE IMPROVEMENT OE SOILS. We have shown in the last chapter that the fertility of soils is in general but little influenced by the arts of man. As a general rule, a bad soil always remains inferior to that which is naturally fertile. It is, however, possible to greatly improve the capabilities of inferior land ; and, as we have seen, fertile soils go out of condition where their cultivation is not properly attended to. Some soils are too light ; they do not. afford adequate mecha- nical support to the plant, and they do not retain sufficient moisture. On the other hand, there are clays so very adhesive, that it is almost impossible to render them sufficiently porous to allow that circulation of air and water through the soil, without which plants cannot be perfectly matured. It is evident that the act of commingling a light soil with a heavy clay would produce a mixture greatly superior to either when separate. A stiff clay may fail to produce good crops, whilst the light drifting sands — perchance not far distant — are scarcely clothed with any kind of vegetation. The combination of the two would in all probability produce a productive soil. This reason- ing is very sound in theory, and sometimes it admits of being practically applied; but occasionally the operation of mixing^ soils is found to be a most expensive one. When the two classes of soils are close to each other, it is very probable — nay, almost certain — that their admixture could, be economically effected. It is a much more common practice to improve light lands by the addition of sand or gravel to them ; but it is rather rarely that stiff clays are ameliorated by the addition to them of sand, though there appears to be no good reason why such should be the case. Bogs and peaty soils are often barren because they contain excessive amounts of organic matter ; they would consequently be greatly improved by the addition of marly clays. The defective ingredients of peaty soils — alumina and lime — are abundantly present in marly clays. Light lands are often greatly improved by folding sheep upon them. The tramping of the animals consolidates the soil, and their excreta enriches it' and renders it more coherent. Bulky fertilisers are best applied to stiff clays, and well-fermented and dense manures to light soils. Warping soils means to manure them with mud. The annual overflowing of the Nile covers the fields of Egypt with a fine mud, which possesses wonderful fertilising properties. In some parts of England, lands adjoining tidal rivers are periodically inundated during the influx of the tide, and the excess of water allowed to flow off with the ebbing waters of the river. In this way the surface of the land acquires a coating of silt or mud, often to the depth of several inches, and even feet. Herapath found that the quantity of phosphoric acid deposited by warping on the surface of a certain field amounted to 17,000 pounds, whilst from the same field a crop of wheat only abstracted 53 pounds of that compound. The beneficial action of quick or burnt lime on soils has been known from a very early period in the history of husbandry. The younger Pliny mentions that marl and lime were largely employed by the agriculturists of Gaul and Britain, and Theo- phrastus and Columella speak of lime as an article in common use amongst the farmers of their days. Limestone consists essentially of a compound termed calcic carbonate, which is composed of carbonic dioxide, oxygen, and the metal calcium. When heated very intensely, the carbonic dioxide flies off in a gaseous form, and the oxygen and calcium remain as a white earth, termed calcic oxide, or calcic anhy- dride. When water is poured on calcic anhydride (quick or TECHNICAL DRAWING. 299 caustic lime), the two substances unite and form calcic hydride (slaked lime, formerly termed hydrate of lime). During the alaking of lime heat is evolved, and the hard stone crumbles into a fine powder. If an excess of water be used, a semi-liquid results, termed cream or milk of lime, according to its con- sistency. In the soil lime acts chemically and physically, and it also contributes directly to the nutrition of plants. As a mere mechanical agent, it has proved most useful in rendering stiff clays less tenacious, and more porous and pervious. Many heavy clays, which can only be properly cultivated by great labour and expense, might be rendered friable, and easily workable, by a liberal application of lime. Dense, adhesive clays do not readily admit the permeation of air through them ; therefore any me- chanical agent — such, for example, as lime — which renders them more open, indirectly contributes to their chemical improve- ment, because the active circulation of air throughout the soil produces abundance of plant-food, as we have shown in a previous chapter. As lime, though not so dense as heavy clay, is more compact than sands, the latter are improved by a dressing of marl — a substance very rich in lime. In the case of clays and sands, no apprehension of injury from over-liming need be apprehended, provided that the lime be applied chiefly in the form of marl or chalk ; for enormous quantities of quicklime act corrosively upon vegetables and their seeds. The best wheat soils in Middle- sex contain 10 per cent, of calcic carbonate, and in many of the most fertile grass-lands in Ireland more than 20 per cent, of this substance exists ; whilst some of the soils of Somersetshire — famous for their cheese-producing capabilities — contain about 70 per cent, of lime compounds. In the use of lime as a mechanical agent'the chief point to consider is, Will it render the soil too light ? In the case of green crops there is little danger of the soil being too light ; but when oats and other cereals are cultivated, it sometimes happens that over-doses of lime are applied. In such oases — even if the soil be old lea or grass-land — the plants may braird satisfactorily, but they will hardly produce seeds, and will generally perish about June. The cereals require a moderately stiff soil to sustain their slender roots, and if such support be denied they rarely vegetate vigorously. Land rendered too porous by over-liming is improved by growing turnips on it, and allowing sheep to feed upon the crop in the field. The soil may also be con- solidated by means of heavy rollers passed over it. It is a curious fact, that land, injuriously affected by over-liming, may yet be in want of lime. This arises from the circumstance that lime sinks very rapidly from the upper 4 or 5 inches of surface-soil ; and although the whole soil may have been rendered too loose by former calcareous applications, yet the part of it from which the nutriment of the crop is chiefly derived may be deficient in lime. In cases of this kind, lime should be applied in the form of a heavy compost. Road-scrapings are often found a useful application to land suffering from the physical effect of over- liming, but which is in actual want of calcareous matter. The chemical action of lime upon soils is most important. Burnt lime, chalk, and marl combine with, and render innocuous, various hurtful acids which occasionally occur in soils, but more especially in undrained lands. Farmers well know that lime sweetens (to use their own term) their lands, and that it pro- duces on meadows and pastures sweet and nutritious herbage. Quicklime acts chemically upon some of the rocky parts of soils, and hastens their disintegration or decay ; in this way lime liberates a portion of the fertilising matter contained in the coarser portion of the soils. Every fertile soil contains a large amount of organic matter, formed chiefly from plants and parts of vegetables more or less decayed. During the decomposition of the organic matter (humus, or mould) its constituents enter into new combinations, and ultimately pass into their original mineral condition of carbonic dioxide, water, and ammonia, and earthy and saline matters. The perfect decay of organic matter only takes place when air is present ; and hence the more porous a soil is, the more quickly does its humus decay, because there is an abundant circulation of air in the soil. Quicklime also hastens the decom- position of organic matters, converting their nitrogen (combined with a portion of their oxygen) into nitric anhydride, which, uniting with lime, produces calcic nitrate (nitrate of lime) — a valuable source of nitrogen to plants. When soils contain an excessive proportion of organic matter, they are greatly bene- fited by an abundant application of lime. A single “ dressing ” of lime to an unproductive bog or peaty moss often produces a fine and spontaneous crop of white clover. Limestone, gravel, marls, and shell and coral sand owe their efficacy almost wholly to the calcic fcarbonate which they contain. They neutralise the sour liquids in undrained and boggy soils, and they supply lime to the crops. Shell and coral sands are well adapted to poor heathy lands ; limestone-gravel is an excellent agent in the reclamation of bogs. Marls and chalk have a wide application, and may be always used wherever the soil is deficient in lime. Limestone containing a small pro- portion of magnesia may be employed in agriculture ; but dolo- mite, or magnesian limestone, should not be used, for when burned and slaked its hydrate forms a hard mass instead of a powder. Quicklime exposed to the air absorbs — but very slowly the atmospheric carbonic dioxide, and in part becomes calcic carbo- nate — a compound which on the whole is not nearly so useful in agriculture as burnt lime. The sooner lime is used after it comes from the kiln the better ; and its conversion into calcic carbonate should be impeded by preserving it in large heaps. A thin layer of quicklime soon loses its caustic properties. The quantity of lime applied as a prime “ dressing ” per statute acre varies ; the longer the land has been without a liming, the greater is the quantity of lime which it requires. For medium and stiff soils 150 bushels are probably the minimum, and 300 bushels the maximum, quantity with which the best results may be effected. In the case of light lands lO or 80 bushels will in general suffice. Wet land requires more lime to produce a given effect than is necessary in the case of wet soils ; and here we have another instance of the many economical results of drainage. W hen the soil has been well limed it will, as a rule, be benefited by a moderate application of the earth once during each rotation of crops. The processes of “paring” and “burning,” at one time con- sidered to be in almost every case injurious, are now admitted by scientific agriculturists to be often very useful, when properly carried out. Good soils seldom contain more than 10 per cent, of organic matter; but bogs often include 95 per cent, (exclud- ing water) of partially decomposed vegetable matter, and only 5 per cent, of mineral matter. When bogs do not furnish fuel (turf or peat), or when that part of them which is generally used as fuel has been exhausted, their excess of organic matter is sometimes best got rid of by burning it. In general the com- bustion should be allowed to extend downwards to the depth of from 3 to 7 or 8 feet. The less mineral matter contained in the peat, the greater is the quantity necessary to be burned in order to obtain a sufficient quantity of ashes to mix with the unburned turf. Marshy land, and soils containing mosses and other weeds and / coarse herbage, are improved by burning their surface ; the weeds and their seeds arc-thereby destroyed, and their ashes in- crease the fertility of the soil. Burning is sometimes one of four processes employed in the reclamation of bogs ; the others being drainage, liming, and the application of sand or clay. A common defect of clays is their extreme plasticity and adhe- siveness. Their particles lie so closely together that air and water cannot freely circulate amongst them. If we subjected a piece of clay to intense heat, it would assume a glassy or slag-like condition ; but if we heated it moderately, it would only become a dry, porous, and friable mass. Now, by burning heaps of weed, cinders, or coal-dust on clays (selecting very dry weather for the operation), we can greatly improve their texture, and in- crease their productive capacity. After such an operation the air gains access to the interior of the soil, and prepares fiom its rocky particles the fine fertilising powder which, as we have already stated, is the chief source of the ash, or inorganic con- stituents, of plants. TECHNICAL DRAWING.— XIX. DRAWING FOR MACHINISTS AND ENGINEERS. MECHANICAL DRAWING. Fig. 202 is a drawing of a simple fly-wheel of a winch. Draw the circles A and B for the outer and inner edge of the rim. ... Divide the circle B into six equal parts, and draw the dia- meters c d, e h, G f, or radii c, E, F, D, H, G. 300 THE TECHNICAL EDUCATOE. Next draw the circles i and j, and also the circle i, the edge of the boss being bevelled. A portion of the inner circle, representing the end of the shaft, is then to be slightly flattened, and the key by which the wheel iB fastened is to be added. To find the points from which the arcs are to start from the straight lines, describe a circle passing through n o, cutting the sides of the other five arms in the required points. Similarly, the arms at their base are united by an arc, which, i in a subject as small as this, may be struck with any convenient Midway between the radii, on the circle i, Bet off the points X and L for the width of the inner ends of the arms. On each side of the radii set off on the circle b , g k, g l for the width of the arms at their outer end. Draw k & and L l, and repeat the process on each of the radii. The arms do not, however, meet the rim in a sharp point, but the straight lines are joined to the circle by means of a small arc, shown at N and o. These arcs are to be drawn as already shown in Pigs. 180 and 181. radius from some point on the line bisecting the angle. In a drawing on a larger scale, the arc would be drawn by the method shown in Fig. 200. These curves should not again form angles at the points where they meet the straight lines, which would be the case if drawn too flat, as in Fig. 203. The arcs should be so drawn that the curve merges imperceptibly into the straight lines, as shown by the dotted portion. From one of the points in which the radii cut the circle B, as e, set off the distance e p, e q. TECHNICAL DRAWING-. 301 From P and Q aet off the length p Q on the radii, and from p and Q, with radius p Q, describe arcs cutting each other in k, and from this the arc p q may be struck, representing the curve formed by the arm meeting the rim, which is rounded off to a semi-circular section at its inner and outer edges, as will be seen in the edge elevation (Fig. 204). This last is projected from Fi°\ 202, and should be drawn upon a centre line, whilst the centre line for the handle is drawn from the centre of the end of the handle. . Fig. 205 is a geometrical elevation of a V-threaded screw, as rendered in mechanical drawings in the general course of busi- ness. This is entirely a conventional method, generally used in the elevation of a cylinder such as would remain if the thread of the screw were turned completely off. This is called the inner cylinder. Again, the perpendiculars b and c give the elevation of a cylinder which would just contain the screw ; this is called the outer cylinder. Now set off on the central perpendicular a number of divisions equal to half the width of the thread — viz., f, g, h, i, j, etc. Through these points draw oblique parallel lines, taking care that their inclination is not too much to be inconsistent with the pitch of the screw, of which more will be said in another lesson. These oblique lines are to extend alternately across the inner Mechanical Drawing, for, in reality, the line which forms the thread of a screw is one which, in ascending, winds round a cylinder, and is termed the helix. The rapid method shown in this figure is, however, found so very useful that it is thought desirable to make the student acquainted with it in this place, in order that he may be able to draw subjects in which the screw may be introduced ; but the correct method of projecting \ screws will be worked out further on. Draw a central perpendicular, and at the base construct the rectangle representing the head of the screw, the curve at the bottom being struck from a point on the centre line. On each side of A set off half the diameter of the screw — viz., A b and a c, and draw perpendiculars from these points. Next set off from a, a d and A e, and erect perpendiculars from these points also. The perpendiculars d and e will give and the outer cylinders, and the angle of the thread is formed by joining their extremities. The mode of starting the screw at the head and of terminating it at the end, etc., will be understood from the example without further remarks. Figs. 206, 207. — The subject of this study is a hexagonal nut, i showing also the end of the screw and washer. Having drawn the plan (Fig. 206), project the circular washer from the diameter A b, and draw the horizontal c D (Fig. 207) at the proper height. It will be seen that the nut is a portion of a hexagonal prism. The full working out of the projection of prisms has been given in the lessons in “ Projection.” Next project the perpendiculars E e, ¥ f, G g, and H h from I the points E, f, g, and h on the plan. 302 THE TECHNICAL EDUCATOR. From i (Fig. 207), with radius I j, describe the arc f g, which will give the curved edge of the face of the nut, which is parallel with the vertical plane of projection. This arc, of course, is the same on each of the faces ; but does not appear so on the other two which stand at angles to the plane of projection. It is therefore necessary to find points through which to draw the curve as it appears. Divide one-half of the line F G in the plan — viz., F J — into any number of equal parts, as K, u, etc., and from these points erect perpendiculars, cutting the arc f j in k and l. Now divide the side represented by E f in the plan into double the number of parts marked on f j — viz., k', l', j', l", k", and from these points raise perpendiculars. Draw horizontals from j, l, k, cutting the perpendiculars, and through these intersections the curve is to be traced. In common practice it is usual, however, to draw this curve with the compasses, which may be executed in the following manner : — Draw a perpendicular from M in the plan to cut a horizontal drawn at j in h' ; then find a centre for a circle to pass through g, m', and h — viz., N. Then from n, with radius N g, an arc used as a rapidly-executed substitute for the curve e j' f can be drawn. The screw is to be drawn as shown in the last figure. Fig. 208 is a conventional representation of a square-threaded screw, as commonly used in practice. It must, however, be distinctly understood that this method, like that shown in Fig. 205, is only admissible in drawings on a small scale. The method of drawing this figure is, in the first instance, precisely similar to that employed in the V- threaded screw ; the oblique lines, however, are all drawn across the outer cylinder, and the alternate pairs united. SEATS OF INDUS THY. — V. By H. R. Fox Bourne. MANCHESTER AND ITS SUBURBS : THEIR MINOR INDUSTRIES. To the cotton manufacture of the Manchester district all its other trades are subordinate, yet many of these are very im- portant, and conduce greatly to the welfare of the locality and the whole country. Chief of these are the hardware trades by which suitable machinery is supplied for the working-up of cotton. Man- chester, indeed, vies with Birmingham in the more polished and delicate branches of iron manufacture. In its neighbourhood are some of the largest and most skilful machine-shops in the world, and the demand for tools, which has caused great tool- making establishments to be there set up, has at length made Manchester a centre of iron-trade with far-off regions and in all varieties of iron-ware. Manchester had, in 1860, 48 iron foun» dries and 63 machinists’ shops, giving employment to about 12,000 workpeople, while, some 60,000 persons were employed in its 95 cotton mills, and it had, besides, 13 silk mills, with about 2,000 labourers, and 16 small-ware mills, giving employ- ment to nearly as many. Those figures fairly indicate the relative value of the principal industries, not only of Manchester itself, but of all the district round about. Everywhere cotton is chief, but silk and wool are also worked up, and in greater proportion as we pass from Manchester in the direction of the woollen province of Yorkshire or the silken province of Derby- shire ; and everywhere engineers are at work constructing mills and tools for the textile manufactures. No better representative of this iron industry can be found than the Fairbairn Engineering Company in Ancoats. The veteran engineer whose name it bears was, indeed, to some extent the father of the whole trade. “ When I first entered this city,’’ he said of Manchester in 1816, “the whole of the machinery was executed by hand. There were neither planing, slotting, nor shaping machines, and, with the exception of very imperfect lathes and a few drills, the preparatory operations of construction were effected entirely by the hands of the work- men. Now everything is done by machine-tools, with a degree of accuracy which the unaided hand could never accomplish. The automaton, or self-acting machine-tool, has within itself an almost creative power — in fact, so great are its powers of adaptation that there is no operation of the human hand that it does not imitate.” In working out that change, Sir William Fairbairn himself did much. He had mastered his trade in London and elsewhere before — twenty-four years old — he settled in Manchester as a working millwright. In 1817 he entered into partnership with a shopmate, James Lillie, and they began a small business of then- own. Paying 12s. a week for a small shed, in which they set up a lathe of their own con- struction, they did various odd jobs until more important work came in their way. They had not long to wait for that. A large commission for mill-work from Adam Murray, a great cotton-spinner, was so well executed that other commissions became plentiful. Sir W. Fairbairn led the way in many of the improvements in mill-work and machine-making that have been effected during the last half century; and where he was not himself the inventor, he succeeded in giving full effect to the inventions of others. He came to be not only the chief en- gineer and machinist for the Manchester cotton industries, but a great iron-worker for all the world. He was one of the first to develop iron ship-building in 1829, and there are few branches of the iron trade in which he was not engaged. His help to the cotton-spinners, however, was sufficiently important. “In 1815,” he said, a few years ago, “the shafts of our cotton- mills were moving at 40 or 50 revolutions a minute, whereas at the present day we have as many as 300 and 350. The same number of revolutions are applicable, and now in use, for lace and silk. The extensive employment of wrought-iron for shafts and the slide-lathe has given wonderful facilities to the production of shafts for increased velocities, with reduced friction, by the transmission of great power through a com- paratively small section. In some of the more recent mills of my construction we have shafts only two and a-half inches in diameter conveying the power of a 40-horse engine.” It was by that sort of work — by making strong, yet light and slender iron do the duty formerly assigned to clumsy wood, and by carefully fitting all the parts together, so as to receive as much power and as little waste as possible — that Sir W. Fairbairn helped to bring about a revolution in all varieties of mill-work. The large establishment which still bears his name now com- prises five great divisions. There is a foundry and forge, provided with steam-hammers, for wrought-iron. There is a boiler-yard, with machinery for rivet-making, shearing, and punching, and a bridge-yard, with similar appliances ; there is a millwrights’ department, stocked with blacksmiths’ forges, turning, planing, and fitting shops ; and there is an engine department, able to produce steam-engines of every size and variety required. Establishments like that of the Fairbairn Engineering Com- pany abound in Manchester and all the adjoining districts. Some adhere more closely to Sir W. Fairbairn’s original project, and confine themselves to millwrights’ work. Others help the cotton-trade by other kinds of metal-handling. Here, a great factory is devoted to the construction of weavers’ tools. There, the work done is chiefly limited to the making of steam-engines. There, again, it may be, only the rough iron-work for railways is done. But everywhere the grand motive is the same— the increasing of facilities for bringing to the Manchester district its great stores of cotton-fibre ; for turning it, when there, into cloth ; and then for conveying it most promptly and easily to other parts. The extension of the silk-trade to the Manchester district owes its origin to the old habit of blending silk and cotton in one fabric. Macclesfield, seventeen miles south of Manchester, is the chief resort of silk-workers in this neighbourhood. Here the trade has been of very long standing. Although benefited in one direction, it has been damaged in another, by the spread of cotton-manufacture. The Macclesfield silk-trade was at its height between 1808 and 1825. In 1819 the first silk-mill in Manchester was set up by Mr. Vernon Hoyle, and in that year it was reckoned that the town contained about 1,000 weavers of mixed silk and cotton goods and 50 workers in pure silk. In 1832 it gave employment, in pure and mixed manufacture, to about 3,600 hands, while the total number of men and women concerned in the trade throughout the Manchester district was nearly 70,000. The number of other trades, more or less dependent on the cotton-manufacture, that have grown up in this great province, are legion. “ Amongst the textile fabrics,” says Mr. Harland, “ are those, single and mixed, of woollens, worsted, stuff, THE ELECTRIC TELEGRAPH. 303 flannel, etc., including blankets ; of linen, alone, or mixed with cotton, wool, or silk ; velvets, table-cloths, and damasks ; counterpanes and quilts ; nankeens, jeans, etc. ; crapes and bombazines, muslins and mousselines-de-laines, shawls and ■ mantles — in short, every kind and variety of textile fabric is manufactured in Manchester. Amongst more miscellaneous manufactures are those of hats and caps, umbrellas and para- sols, india-rubber, gutta-percha, and other waterproof and air- proof fabrics. In copper and brass are various manufactures, especially of rollers for calico-printers, boilers, steps, etc. ; in tin, all kinds of wares, including boxes and cases for enclosing goods for hot climates ; paper for writing, printing, and packing. In short — including the trades and handicrafts whose produce or productions are in demand everywhere, and those which may be termed the agencies between producer and consumer — there are from six to seven hundred varieties of occupation in Man- chester, supplying all the numerous wants of a high material civilisation.” Of all that, cotton is the chief cause ; but the cotton manufacture could not have attained its vast proportions in this district, but for the proximity of coal and iron with which to work it, and the presence of that perseverance and enterprise which characterises the population as a whole, and has enabled it to send out from its ranks so many men of eminence. Inventors and discoverers — a great number — have arisen in Manchester and its far-reaching suburbs ; notable merchants and manufacturers in yet greater number ; and not a few skilful statesmen, with Sir Robert Peel at their head. The eminent Scotch engineer who established the Fairbairn Engineering Company, was born in 1789. He was elected Pre- sident of the British Association in 1860, created a baronet in 1869, and died in 1874. He wrote some valuable works on mills and mill- work, and “ Iron, its History and Manufacture. THE ELECTRIC TELEGRAPH.— V. By J. M. Wigner, B.A. OTHER FAULTS — CONTACT — DEFECTIVE EARTH — LIGHTNING GUARDS MODE OF RENDERING SIGNALS INTELLIGIBLE — SINGLE NEEDLE INSTRUMENT CODE. Besides the faults to which we referred in our last paper, there are a few others of common occurrence, the effects of which must be explained in order that we may be able at once to detect them. Perhaps the most common of these is “ contact ” between two of the wires connecting any two stations. This is sometimes produced by damp weather enabling the current to escape along the surface of the insulators, and is then known as “weather contact.” More frequently, however, it arises from one of the wires becoming so slack as to touch against another, or else from some electrical connection being acci- dentally made between them. A fault of this kind is very easily recognised. The current leaves the transmitting station, deflecting the needle there as usual. At the fault, however (f, Fig. 19), three courses are open for it, and it accordingly divides between them. One portion continues to travel along its own wire, and deflects the needle at the receiving station, but less powerfully than usual, since much of the current has escaped another way ; a second portion passes by the place of contact, and returns along the second wire to the sending station, deflecting there the needle of the other circuit, but in the contrary direction ; the third portion travels along the same wire to the receiving station, deflecting the second needle there. These effects are more or less modified by the various resistances of the different circuits, still they are so obvious as at once to indicate the nature of the fault. Another cause of failure is “ defective earth’ at the receiving station. The communication with the earth-plate is in this case either broken or defective, and a portion of the current accordingly returns by other wires, deflecting their needles in the reverse direction to those in the regular circuit. This fault is liable to be mistaken for contact. The only other fault we shall refer to is demagnetisation of the needles or other injury to the instrument. The most common cause of such failure is that the lightning has struck the line in some part, and passing along it has injured the instrument. The fact of frequent injuries arising from this cause directed the attention of electricians to the discovery of some simple means of obviating the danger, and many efficient expedients have been introduced. Lightning in its effects is found closely to resemble frictional c D Fig. 20. electricity. If we have two pieces of wire, A and B (Fig. 20), connected together by a spiral of fine wire, D, and also having connected to them two pieces of wire ending in small balls (c) which nearly touch one another, any galvanic current will pass through the spiral, since it cannot leap across the break be- tween the two balls, however small it be. Frictional electricity would, however, at once take the more direct course, and leap over the small interval at c. This, then, is the principle on which most lightning conductors act, and Fig. 21, which repre- sents Breguet’s Lightning Discharger, shows us one mode in which this principle is put into practice. Two plates of metal cut at the ends into teeth resembling those of an ordinary saw are fixed to a wall, so close to one another that their teeth almost touch. The line-wire, l, is con- nected with the one of these seen on the left, and the current passes along the plate to the piece of metal a, and thence along a piece of fine wire, contained in a glass tube, to the screw b and the instrument. Another wire, J, leads from the right- hand plate to the earth, so that if the lightning strikes the line the electric fluid will dart from the points and travel on to the earth by this wire. Should this wire fail to carry off all the current, the thin wire in the glass tube is fused by it, and thus it is prevented entering the instrument-room and injuring the instruments there. The fine wire can, of course, be very easily replaced. The object of the handle seen attached to one plate is that during a storm it can, if required, be turned so as to afford a direct communication between the two plates, and thus cut the instruments for the time entirely out of the circuit. In some forms of lightning protector a thin wire, like that enclosed in the glass tube, is depended upon alone for protection, since any quantity of electricity like that produced by a flash of lightning would instantly melt this wire, and thus save the instruments. In the protector which we have explained pro- tection is afforded in both ways, and it is therefore doubly safe. Many other forms of lightning discharger are employed, but nearly all act in a similar way, and we need not, therefore, stay to explain the peculiar construction of each. We have thus seen the way in which the electric current is generated, the manner in which it is conducted from place to place, and the precautions which have to be taken to prevent its escape. We have also seen the nature of the more common interruptions in any electric circuit, and we must therefore pass on to that which is perhaps the most important point of all the manner in which an electric current may be made to pro- duce intelligible signals at a distant place, and the construction of the instruments that are employed for this purpose. An electric current is capable of producing many different effects, as we have already seen in our “ Lessons on Electricity’ in The Popular Educator. It will convert a bar of soft iron into a magnet, or cause a compass needle to point in a different direction ; it can be made to decompose water and various chemical substances, or to render a piece of fine wire red-hot, and to produce many other results. Many of these effects are capable of being employed as a means of transmitting our thoughts and messages, and in fact there are few of them that have not so been employed at different times and by various 301 THE TECHNICAL EDUCATOB. inventors. The number of instruments tliat have been intro- duced is, therefore, very large indeed, and there are many varieties which are still in constant use. The three effects of the current which have been by far most generally used in telegraphy are— 1. Its power of reversing a magnetised needle. 2. Its power of converting a bar of iron into a magnet. 3. Its power of decomposing various chemical substances. Perhaps the first is the most simple effect of all, and “needle instruments” which depend upon it are so extremely common that we will take these first, and endeavour fully to understand their con- struction and action. The broad principle on which they act was dis- covered by Oersted, and is simply this— that if an electric current be made to pass along a wire placed near a magnetised needle, that needle, instead of pointing to tho north, will point to one side of it ; and if the current bo made to pass along the wire in the reverse direction, the needle will point to the other side of the north. If, then, we have such a needle at the receiving station, and possess the means of sending at pleasure a positive or a negative current, we can cause this needle to be deflected to the right or left at pleasure, and from these two signals we can form a code by which any letter in the alphabet can be sent. In the needle instrument, as in all other kinds of instruments used in telegraphy for the transmission of messages, three distinct parts are necessary: these are (1) the transmitting instrument, (2) the receiving apparatus, and (3) the alarum. It might be thought that the last- named part is indispensable, but this is not the case, since the click of the needle might call the attention of the clerk in charge to the fact, that a message was coming. This is, however, very unsatis- factory, as an important message might be seriously delayed by the clerk not hearing this ; an alarum is therefore always employed. It consists of an ap- paratus by which the current is made to ring a bell in a manner that will here- after be described. It would, however, be very undesirable that this bell should continue to ring all the time that tho message is being received, and an arrange- ment is therefore made by which it may at pleasure be cut out of the circuit, a more direct path being then provided for the current. The usual plan is for the circuit, under ordinary circumstances, to be completed through the alarum. As soon as this rings, the clerk, by means of a switch, turns the current from the alarum to the instrument, and receives the message, taking care, when he has received it, to alter the switch again. The alarum is often put in tho same case as the instru- ment, but it is essentially a distinct thing. The general appearance of the single needle instrument is shown in Fig 22. In the centre of the dial-plate is seen the needle, the play of which is limited by means of two small pms placed one on each side. The handle in the lower part of the instrument is for the purpose of moving the transmitting apparatus, which is so arranged that when this handle is inclined to the right a current is transmitted along the line in such a direction that all the needles in the circuit are likewise deflected to the right, and when this handle is moved to the left a current “ the “verse direction, so that the needles are all deflected to the left. When a motion of the needle in either direction is spoken of, it should be remembered that it is the upper end of the needle that we mean. The mechanism in the interior of the instrument, by which ohe current may bo sent at will in either direction, will be explained in our next paper. We will hero assume that we have the power of sending at pleasure either a positive or a negative current. All the needles along the line of wire will accordingly act simultaneously, and be deflected in the same direction. Wo possess, then, two distinct signals — viz., an in- clination of the needle to the left or a similar inclination to the right. The lower end of the needle is so weighted that as soon as the current ceases it shall return to its original vertical position. From these two signs, then, we have to construct an alphabet, and this is not a very difficult task, since we can give two or more consecutive beats in either direction, or in alternate directions. No letter is found to require more than four such beats, and by carefully arranging the letters so that those most commonly employed are represented by the simplest signs, we are enabled to send mes- sages with an average of a little more than two inclinations for each letter. A trifling pause is made between each letter, and a somewhat longer one between the words ; but after a little practice it is easy to read off messages, even if some of these are omitted. The code of signals is, of course, purely arbitrary ; a standard one has, however, been settled on, and is now almost universally adopted, since great practical inconvenience is found to arise from the use of several independent codes. That originally introduced for the single needle instrument has now almost entirely given way to a universal one, based on that employed with the Morse instrument. This latter is seen on the face of the instrument shown in Fig. 22, and will easily be un- derstood from that. E and T being the letters in most general use, are represented by single beats of the needle to the left and right respectively. A, I, M, and N each require two beats, while all the rest of the alpha- bet require three or four. By a few examples we shall very easily learn the meanings of the marks on the instrument face. A is indicated by a beat to the left, immediately followed by one to the right ; B by one beat to the right and three to the left. Other letters are more complicated than these — F, for in- stance, requiring two to the left, one to the right, and then one more to the left. The signs appear at first to be somewhat difficult ; but a little practice soon re- moves this, and enables the operator to receive or transmit messages with con- siderable speed. In addition to these signs for letters there are several others which are fre- quently required, and hence are included in the code. When a word or message is understood, the receiver acknowledges ' by a single beat to the right ; if, on the other hand, he cannot decipher the move- ments of the needle, he gives a beat to the left, to signify “not understand.” Figures are all represented by five beats, as follows : \IJ// \\J// \\\//\\\\/\m Av& JA\\ I/A\ #v ////! 1 2 3 4 5 6 7 8 9 0 and as the signs succeed each other in a regular course they are easily remembered. The signs of punctuation are represented each by six distinct beats. Those for the comma and full stop are given on the dial-plate, and will be seen to be equivalent to the letters AAA and III respectively. A note of interrogation (?) is repre- sented by the signs for UD; inverted commas (“ ”), by those for A F ; a hyphen (-), by B A ; an apostrophe ( ’), by W G ; and parentheses ( ), by K K. In each of these cases the beats succeed one another without any pause, and the letters are merely given as an aid to memory. VEGETABLE COMMERCIAL PRODUCTS. 305 LEAVES AND FLAX VEGETABLE COMMERCIAL PRODUCTS.— X. INDUSTRIAL AND MEDICINAL PLANTS. I. TEXTILE PLANTS, OR PLANTS PROM WHICH WE DERIVE CLOTHING AND CORDAGE. TVs are indebted to the vegetable kingdom for clothing as well as food. At what time man first discovered the means of forming articles of clothing from the fibre of plants is not known, but the practice is very ancient. It was understood in the time of the Pharaohs, more than 1,600 years before Christ. Flax is thus alluded to in Genesis xli. 42 : — “ And Pharaoh took off his ring from his hand, and put it upon Joseph’s hand, and arrayed him in ves- tures of fine linen.” It is not improbable that flax was cultivated even in pre-historic periods. It formed both the garments and grave-clothes of the inhabitants of ancient Egypt ; for the micro- scope shows that the cere-cloth which envelopes the Egyptian mummies consists of the fibre of flax. Wc, therefore, place it first on our list of textile plants, as the one of which we have the oldest historic record. Common Flax ( Linum usitatissimum, L. ; natural order, Linacece). — This plant is a smooth fibrous-rooted annual, about two feet high, with sessile, alternate, lanceolate leaves and terminal blue flowers, in corymbose panicles. Ovary glo- bular, five-celled, each cell containing two smooth, oval, brown, and glossy seeds. Flax has a very remarkable geographical range, thriving in the temperate, sub-tropical, and even tropical regions. It is not only cultivated in the United King- dom, but in every part of Europe, in Egypt, and in India. Formerly every rural family in England cultivated as much flax as was required for domestic purposes ; now the spinning-wheel has been superseded, and both linen and cotton goods are manufactured by steam machinery in the greatest abundance, in every variety of pattern, and with much less time and labour. To obtain the fibrous or woody tissue of flax, the plants, after flowering, are first pulled up, dried in the sun, collected, and then soaked in water to destroy their green outer bark. This process is called water-retting, the word “ retting ” being a cor- ruption of rotting. The tough fibres of the stalks are thus set free, are again dried, and then scutched, or beaten with a heavy wooden instrument, which completes their separation. After this they are heckled, or drawn through the combing apparatus, next bleached, and, lastly, handed over to the spinner. From flax so prepared, coarse linen fabrics are manufactured ; but the flax must be heckled seve- ral times through much finer combs to render it fit for the manufacture of fine linen, lawn, or lace. Tow consists of the rough and broken fibres detached from the skeins during the combing process. Linen when scraped is termed lint, in which form it is very valuable to the surgeon as a dressing for wounds. i About 1,816,669 cwt. of flax, dressed and undressed, were imported into the United Kingdom in 1868, chiefly from Russia, Egypt, Turkey, Italy, Belgium, and Holland. We also raise flax largely ourselves, especially in Ireland, where it is one of the staple commodities. Hemp ( Cannabis sativa, L. ; natural order, TJrticacece ) . — The hemp-plant is a tall, roughish annual, with a stem from five to ten feet in height, and digitate leaves, with five to seven linear- lanceolate, coarsely-toothed leaflets. The flowers are green and inconspicuous, in compound racemes or panicles, and monoecious, that is, the stamens and pistils are in separate flowers on the same plant. The seed is produced in great abundance, and is used for feeding small birds. The fibres of the stem are much longer and stronger than those of flax, and when separated and prepared (in a manner very similar to that adopted with flax, and already described) constitute the hemp of commerce from 20— Yol. I. BUDS OF THE PLANT. THE HAIRY SEED OF THE COTTON PLANT. which sail-cloth, sacking, and every variety of cordage are manufactured. The hemp-plant is a native of Persia and of the northern parts of India, whence it has been introduced into Europe, where it is now extensively cultivated, especially in Russia. Like flax, hemp has a very extensive geographical range, growing in almost any country and climate. It thrives admirably in North America and in Africa, and is found both in a wild and cultivated state from Northern Russia to tropical India. When growing in warm countries the value of the hemp is much diminished, and another quality is deve- loped — it becomes powerfully narcotic, and its leaves, flowers, and stem become covered with a peculiar resinous secretion called chwrus in India. By the Arabs this resin is called hashash ; and during the Crusades, men intoxicated purposely with it, called hashasheens, used to rush into the camp of the Christians to murder and destroy, whence our word assassin is derived. Hemp is employed in other forms besides churrus as a narcotic. The whole herb, resinous exudation in- cluded, is dried and smoked under the name of gunyah or bhang, when the larger leaves and cap- sules only are employed. The Hindoos of British India, and the Bushmen of Southern Africa, smoke these preparations in rude pipes, as we do cigars and tobacco. These pipes are about three inches in length, and are usually made out of the tusk or canine tooth of some animal, perforated quite through, leaving only the enamel. The general effects of tropical hemp on the system, when smoked, are alleviation of pain, great increase of the appetite, and much mental cheerfulness. From experiments made with churrus, it would seem that the fakeers and other religious devotees of India are indebted to it for their ability to perform some of their wonderful feats. One of these experiments is thus described by Dr. O’Shaughnessy :* “At two p.m. a grain of the resin of hemp was given to a rheumatic patient ; at four p.m. he was very talkative, sang, called loudly for an extra supply of food, and declared himself in perfect health ; at six p.m. hCVas asleep ; at eight p.m. insensible, but breathing with perfect regularity, his pulse and skin natural, and the pupils freely contractile on the approach of light. Hap- pening by chance to lift up the patient’s arm, to my astonishment I found it remained in the posture in which I placed it. It required but a very brief exami- nation of the limbs to find that the patient had, by the influence of this narcotic, been thrown into that strange and most extraordi- nary of all nervous conditions, genuine catalepsy. We raised him to a sitting posture, and placed his arms and limbs in every imaginable attitude. A waxen figure could not be more pliant or more stationary in each position, no matter how contrary to the natural influence of gravity on the part : to all impressions he was meanwhile almost insen- sible.” Similar results were ob- tained from experiments on ani- mals. As soon as the influence of tho drug ceases, the patient recovers, without having received any injury from its effects. The narcotic hemp of warm climates was, owing to its pecu- liarities, thought to be another species, but it is now known only to be a variety, and is distinguished as Cannabis sativa, variety, Indica. The imports of hemp into the United Kingdom in 1868 were 1,042,320 cwt., chiefly from Russia, Hungary, Northern Italy, the Philippine Islands, and British India. The best Hun- garian hemp comes from the district of Peterwardein, under tho name of Sclavonian hemp. From Italy we receive, in small quantities, a remarkably fine variety, raised by spade culture, called “Italian garden hemp. ” * “Popular Economic Botany,” by T. C. Archer, page 153. SECTION OF SEED OF THE COTTON PLANT. 306 THE TECHNICAL EDUCATOR. In addition to sail-cloths and cordage, a coarse brown paper is mado from bemp. Oakum consists of tarry hemp, procured by 'untwisting old worn-out ship ropes, and is a most invaluable substance to the ship’s carpenter, who uses it as stuffing with which to stop any leakage in the vessel during the course of the voyage. Seams of timber-built ships are also caulked with oakum. Cotton "Wool (the woolly covering of the seeds of several species of Gossypium; natural order, Malvacem). — Much uncer- tainty prevails amongst the best botanists as to the number of species of Gossypium which furnish cotton. Linnseus has do- scribed live, Lamarck eight, Wildenow ten, and De Candolle admits of thirteen. The cotton of commerce, which consists of the hairs attached to the seeds, and is therefore cellular tissuo, appears to be derived mainly from three species, designated as the cotton herb ( Gossypium herbaceum, L.), the cotton shrub ( Gossypium Indicum), and the cotton tree ( Gossypium arbo- reum). 1. Cotton Herb ( Gossypium herbaceum, L.). — The greatest amount of cotton is derived from this species, which is sno best known and most widely spread. It is an annual, and cultivated in the United States, India, China, and many other countries. It grows from three to four feet in height, having sub-coi’G.ato, three to five-lobed, alternate leaves, and pale-yellow flowers resembling those of the mallow ; the stamens are monadelphous, or united into one bundle by their filaments, and the pistil has a three-celled ovary. After the plant has done flowering, a capsule is formed which is surrounded by the calvcine and involucral leaves. This capsule grows to about the size of a walnut in its husk, turns brown as it ripens, and then opens, displaying in its three-celled interior a snow-white or yellow down enveloping each of the three seeds lying in each cell ; altogether, nine cotton balls may be collected from each capsule, each ball with its enclosed seed being about the size of an ordinary grape. Chinese Nankin cotton is manufactured from a variety of this plant. The yellowish-brown colour of the nankin is not arti- ficially produced by dyeing, but is the natural colour of the cotton from which it is fabricated. 2. The Cotton Shrub ( Gossypium Indicum, LamaTck) . — The cotton shrub is cultivated in India. It closely resembles the former plant in many respects, but it grows from eight to twelve feet high ; its flowers change from white to red, and its capsules are ovoid. The cotton shrub is-cultivated in all countries whore the cotton herb is found. In the West Indies this plant lives from two to three years, in India and Egypt from six to ten ; and where the climate is excessively hot, it is usually very long-lived. 3. The Cotton Tree ( Gossypium arboreum). — The cotton tree inhabits India, China, Egypt, the coast of Africa, and some places in America. It grows from fifteen to twenty feet high, and its flowers are red. It yields a variety of cotton of a very fine, soft, silky nature, which is used by the Hindoos for making turbans. The cotton plant is usually cultivated in fields, and treated as an annual. It is grown from seed which is placed in the ground in holes, sufficiently wide apart to allow for the growth of the plant. The plants are carefully tended until they flower, which is usually eighty days from the time of sowing. The flowers, which are handsome, either yellow or red, and not unlike those of tho garden hollyhock, are succeeded by capsules, which, when ripe, open, and the cotton-covered seeds in their interior are immediately removed by the cultivator before the wind is able to scatter them. These cotton seeds are then sent to a mill, where by means of a peculiar apparatus called a gin, the cotton is separated from them ; they are then either kept for sowing again, or as material for the manufacture of oil, and oil-cake for cattle. Cotton comes to this country in packages called bales. The word bale is applicable to any kind of goods packed in cloth and corded with rope. The average weight of each bale is 336 lb. In 1866, 4,098,601 bales of cotton, weighing 12,295,803 cwt., were imported into the United Kingdom. The value of this cotton in the raw state was .£77,521,406, and its value, when manufactured into cotton fabrics, £232,564,218. Of these fabrics we exported to the value of £60,865,022, the remainder being retained for home consumption. In 1868 the quantity of raw cotton imported was 11,857,893 cwt. The substitution of the power-loom for the hand-loom has caused such an amount of prosperity to the cotton trade, that it is now one of the most important branches of our foreign commerce. In business, foreign cotton is separated into the following varieties : — North American or United States Cotton. — This is produced in the states of Georgia, South Carolina, Alabama, Mississippi, and Louisiana. The best American cotton, which is, in fact, the best known in the market, is the celebrated Sea-island cotton, which grows on a row of islands situated along the coast of Georgia. The principal ports for the exportation of United States cotton are Charleston, New Orleans, Mobile, and Savannah. South American Cotton. — This comes into the market from the Brazils, Guiana, Columbia, Venezuela, New Granada, and Peru. Almost all the West India islands, too, produce cotton, and indeed of a superior quality, preferable even to that obtained from the Brazils. African Cotton. — Excellent cotton is received from the French island of Bourbon ; Egyptian cotton has also greatly improved in quality recently, because the crops have been raised from American seed. The best African cotton is, however, grown in Algeria, and is remarkable for the beauty of its colour, the fine- ness of its silk, tho care taken in harvesting the crop, and tho good condition in which it appears in the market. The long silk cotton of Algeria partakes at the same time of the character of the long silk staple of Georgia, and the short cottons of Egypt, and approaches in quality the finest Louisiana variety . Algeria is capable — if the necessary encouragement is given — of producing the finest cotton in the world. East Indian Cotton. — This is very inferior to the North American, although British India, next to America, furnishes the largest quantity. The silk is very short, and not adapted to European machinery, which is framed for working the finer American long cotton. This cotton is raised chiefly for expor- tation to China. Recently a better staple has been produced in India from American seed, and already a considerable quantity has been exported to England. East Indian cotton comes in little bales, very strong'ly compressed and corded, which are carried on the backs of camels, or on wagons, to the Ganges, and there received into boats with capacious interiors ; theso descend the river, and take the cargo to European ships. Tho East Indian sorts known in commerce are the Bengal, Madras, Bombay, Surat, Siam, and Manilla cottons. Levant Cotton. — This includes all the cotton which is received from ports in European and Asiatic Turkey, as well as from tho Morea and the Archipelago. Like that from British India, it is of inferior quality. The principal sorts are the Smyrnian, Syrian, Cyprian, Macedonian, and Persian cottons. Most of the last is consumed in Persia, excepting some small quantities, which go to Russia rid Astraoan. OPTICAL INSTRUMENTS. — IV. BY SAMUEL HIGHLEY, E.G.S., ETC. SPECTACLES FOE THE PRESBYOPIC. In the normal or emmetropic eye the recession of the near- point commences about the tenth year, and progresses regu- larly with increasing age. At forty, it lies about 8 inches ; at fifty, at from 11 to 12 inches, and so on ; and no incon- venience is experienced from this recession till about the age of forty or forty-five. This change in the near-point is met with in all eyes, being also found in the healthy myopic and in the hypermetropic eyo, and is due to anomalies of accommodation ; while hypermetropia, myopia, and asligmatism are referable to anomalies of refraction (see Figs. 6 to 11, page 160). The question will be asked, When are we to consider an eye pres- byopic? Donders has established an arbitrary standard by which he considers we should regard presbyopia to have com- menced when the near-point is found to have receded farther than 8 inches. The hypermetropic eye is considered to become presbyopic so soon as, while using glasses which neutralise the hypermetropia, the near-point lies farther from tho eyo than 8 inches. This standard also holds good in regard to myopic eyes, when the distance of the near-point amounts to more than 8 inches, and it follows that only to slight degrees of myopia can presbyopia in the ordinary sense of the word belong; OPTICAL INSTRUMENTS. 807 where M = 4 it is almost impossible, even with total loss of the power of accommodation. In slight degrees of myopia, pres- byopia occurs much later than in the emmetropic eye. Herein the myopic (of to T \-) find a compensation for what they lose, in respect to vision of distant objects, and the advantage is not slight, to find that they can, up to the age of sixty or seventy, dispense with spectacles for the observance of such objects as come immediately under their eyes — an advantage never enjoyed by the emmetropic. Some persons flatter themselves that they enjoy this privilege when at fifty-five the near-point lies at only from 8 to 10 inches, and spectacles have not been found necessary ; such persons are proud of their sharp sight, and consider themselves a lucky exception to the laws of decay. Any suggestion as to their being near-sighted is answered in the negative, by a self- complacent smile. On trying them with Snellen’s distance-test, placed at 20 feet off, XX, XXX, or even XL, are not recognised, L or LX being the first easily distinguished, and not until they try concave glasses of 5 \ or ± can they recognise XXX or XX. Such are consequently myopic. On inquiry, it will generally be found that the parents presented the same peculiarities, when an inference may be drawn that the myopia is hereditary. But the far-point also begins to recede somewhat in the normal eye above the age of fifty ; so that it then becomes slightly hypermetropic (distant vision being improved by convex glasses), which at seventy or eighty may = i (that is, the patient can see distinctly at a distance with a convex glass of 24 inches focus). In such a case, the hypermetropia, which at first is only ac- quired {II. acquisita), may afterwards become absolute ; so that the person is not only unable to accommodate for divergent, but even for parallel rays. We must be careful not to confound that weakness of sight termed amblyopia with presbyopia, which might easily occur, as an amblyopic person also cannot see small objects distinctly, and convex lenses (by affording him larger retinal images) improve his vision. If the patient cannot with a suitable lens distinguish No. 1 of Jager at 8 inches distance, but only 4 or 6, or if he is obliged to hold the object nearer to his eye than is warranted by its size, then he is amblyopic. It may be laid down as a practical rule that the nearer we can approximate, by means of convex glasses, the vision and range of accommo- dation of a presbyopic eye to that of a normal one, the less is the impairment due to amblyopia, and vice versa. How are we to determine the degree of presbyopia, and correct the deficit of accommodative power P According to the old method, usually practised in opticians’ shops, the patient is tested by the “ tryers,” “ sight-suiters,” or “trial case,” which consists of a series of carefully worked convex lenses mounted in pairs in tortoiseshell spectacle-fronts which are clamped together at one end by a pivot that holds them in a box, which also forms a handle to be held by the patient, while each front in turn is placed before his eyes to find which focus enables him to read moderate-sized type at ordinary reading distance, the probable whereabouts of the power required being arrived at by some such guide as the following : — At 40 years of age convex lenses of 36 inches focal length will commonly be required; at 45 , 30 ; at 50 , 24 ; at 55 , 20 ; at 58 , 18 ; at 60 , 16 ; at 65 , 14 ; at 70 , 12 ; at 75* 10 ; at 80 , 9 ; at 85 , 8 ; at 90 , 7 ; at 100 , 6 — the three last deep lenses, 8, 7, 6, being rarely required, except for “ couched eyes.” After the patient has been once fitted it usually only becomes a matter of increasing the power of his spectacles by the glasses next higher in focal range, on his complaining that those he is then using are not sufficiently strong. The convex trial case includes the above-named series of I 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 24, 30, 36, and also 48 inches foci, the last being sagaciously and judiciously termed “pre- servers.” Such a rule-of-thumb method must, however, soon give place to the more exact system established in recent years by Continental oculists. According to Donders, the degree of presbyopia may be readily found, thus If p > 8" = 8 -f- n, presbyopia. Pr. = - 1 ; which simply means, we must deduct the (arbitrary) presbyopic near-point- (8 inches) from the absolute presbyopic near-point determined by trial. If we find a patient’s near-x>oint lies at 12 inches, the formula would stand thus — or supposing it to lie at 16 inches, it is j i — i_ p,. — j io 8 ia> x ' io - This also gives the focus of the convex lens, which would bring the near-point back again to (the arbitrary standard for the near-point) 8 inches. In the first case, the convex required would be 24 inches ; in the second case, 16 inches. In each case the difference between the two fractions expresses the deficit of accommodation the patient labours under. In the former case he would find himself, for distinct vision at 8 inches, minus such an amount of accommodation as is equivalent to a 24-inch convex lens, in the latter case to a 16-inch convex lens ; consequently, if to the first wo artificially supplied a 24-inch convex, and to the second a 16-inch convex, in each case we should correct his presbyopia ; and provided that the patient exerts all his natural accommodation (Jj and i respectively), ho would be able to read, etc., at 8 inches. Few persons, however, could sustain such a strain on the ciliary muscles for any length of time without fatigue (asthenopia) ; but as few persons wish to work for any length of time at so close a distance as 8 inches, a more convenient distance, such as 10, 11, or 12 inches, will answer without overtaxing the natural power of accommodation. The result of theory must, however, always be checked by trial, for it will often be found that strain may be avoided by supplying a weaker lens than the above formula indicates. The object to be attained in supplying a. presbyopic person usually with spectacles should be to reinforce his defective accommodation by convex lenses neither so strong as to super- sede his own remaining natural accommodation, nor so weak as to tax it further than it admits of. For such corrective trials a set of lenses of known focal length, in pairs, is required, together with a spectacle-frame, in which such lenses can be readily fitted and changed. Jager’s frame is the best, as the rings for supporting the glasses are movable, to admit of their distance being regulated, so that the patient can look through the centre of both glasses ; and, further, it allows of the centre of the pupils being noted. The set em- ployed on the Continent comprises 28 pairs of bi-convex lenses of 2, 21, 2\, 3, 3§, 4, 44, 5, 5i, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 28, 36, 40, 48, 60, 72, and 100 inches positive focal length, and 28 pair of bi-concave lenses of corresponding negative focal length, together with a set of glass prisms with refract- ing angles of 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 12°, 14°, 16°, 18°. These usually correspond to the Prussian inch, which differs but little from the English inch, but is less than the Parisian inch. In practice a reduction will rarely be necessary ; but it should be remembered that, as a large number of lenses sup- plied to opticians are of French manufacture, while the English scale is usually employed for measuring focal length, etc., the English inch is only equal to about 0'94 of the Parisian inch. It is evident care must be taken that the lenses used in the optician’s trial box also correspond to the French scale, and that his optometer is graduated to the same measure, unless he uses lenses worked to the English scale, when of course the English system must be adopted for “tryers ” and optometer. As it is well known that at first, while the amount of pres- byopic disturbance is but slight, glasses of ^ are usually sufficient, and also that in proportion as the time of life advances, and the range of accommodation steadily diminishes, stronger and stronger glasses are required, it was not un- natural that opticians and oculists should arrange glasses according to the time of life at which, on an average, they became necessary ; but as eyes differ too much to make ago alone the criterion in the choice of spectacles, with some amount of justice this old custom has been ridiculed; but as far as emmetropic eyes are concerned, the diminution of the range of accommodation being as a rule regular, the time of life may in general be taken as a guide, if the many circum- stances which modify the indications furnished by the time of life be not overlooked. 308 THE TECHNICAL EDUCATOR. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— Y. To inscribe four equal circles in a circle, each, touching two others and the containing circle (Fig. 48). other. From A, B, c, d, with radius of the circle, describe arcs cutting each other in E, p, G, h. Join these points, and a square will be described about the circle. Draw the diagonals e h and G F. Bisect the angle c f o, and produce the bisecting line until it cuts c d in i. From o, with radius o i, describe a circle cutting the lines A b and c d m j, k, and l. From these centres, with radius i c, describe the four required circles. To inscribe seven equal circles in a circle (Fig. 49). A Around the circumference of the circle set off the radius, thus dividing it into six equal parts in the points A, b, c, d, e, f, and draw the radii. Divide one of the radii, as o A, into three equal parts — viz., o <*, G H, H A. From O, with radius O G, describe the central circle. From o, with radius o h,. describe a circle which, cutting the radii, will give the points I, J, K, L, m. From these points, with radius o G, describe the six circles, each of which will touch the central circle, two others, and the containing circle. Similarly, a circle o G being given, to draw six equal circles to touch it and each other, divide the circumference of the given circle into six equal parts. Draw radii and produce them. From g set off G h, equal to g o. From o, with radius o h, describe a circle which, cutting the produced radii, will give, with h, the centres i, j, K, l, m of the six circles. Within a circle to inscribe any number of equal circles, each touching two others and the containing circle (Fig. 50). Divide the circle into equal sectors, corresponding to the required number of circles — viz., da, ab, b c, etc., and bisect the sectors by the lines E, F, G, etc. Produce any two of the radii, as A and b, and draw the tangent h i parallel to ab. Bisect one of the angles at the base of the isosceles triangle thus formed, and produce the bisecting line until it cuts o f in j. From o, with radius o J, describe a circle cutting each of the lines which bisect the sectors in l, m, n, k, etc. From these points, with radius j F, describe the required circles. By drawing p q parallel to A b, and bisecting the angle at the base of the triangle, the centre for another circle may be found ; and by continuing the process as before, another series of circles may be drawn. Application of the division of a circle in drawing a rack and trundle (Fig. 51). The circle A, on which the centres of the circles representing sections of the bars (or teeth of the trundle) are placed, is called the pitch circle; and the line on which are the points of contact between the teeth of the rack and those of the wheel, is called the pitch line. The pitch circle must be divided into parts equal to the given number of teeth, and spaces, b c, CD, etc., must be set off on the pitch circle, and similar lengths, ef(= b c), fg(= CD), etc., must be set off on the pitch line H i. The rest of the construction will be readily understood on reference to the figure. CHEMISTRY APPLIED TO THE ARTS. 309 Numerous studies in this branch of the subject will be given in the series of lessons on “ Technical Drawing.” The above (Fig. 52) is an example of the division of circles in drawing the plan and elevation of a column, and is intro- duced here in order to impress on students the necessity of acquiring the utmost accuracy in division of spaces. The circle forming the boundary of the plax is to be divided into a number of parts, corresponding to the required number of flutes — viz., 1, 2, 3, etc. ; half the width of the fillets is then to be set off on each side of these divisions, as a, b, etc., and semicircles drawn from the centres of the remaining spaces. The elevation of the column is projected by drawing perpen- diculars from the various points in the plan. For full details in the construction of elevations, plans, etc., see lessons in “Projection.” To divide a circle into any number of equal parts, having the same area (Fig. 53). Divide the diameter A b into the required number of equal parts, A C, C D, D E, E F, F B. From points a, a, midway between a c and f b, describe semicircles, f b and a c. From point e, describe the semicircle c E. From d, describe the semicircle f a. From b and b, midway between c D and e f, draw the semi- circles E A and D b. From c and F, draw the semicircles D A and E B, which will complete the figure. To divide a given circle into a given number of concentric rings and central circle having the same area (Fig. 54). Draw a radius a b, and on it describe a semicircle. Divide the radius A b into the number of equal parts corre- sponding with the number of rings, etc., required. From the points of division, 1, 2, 3, raise perpendiculars cutting the semicircle in 1', 2', 3'. Then from the point B as centre, with the radii Bl 7 , b2', b 3', draw circles passing through the points l 7 , 2 7 , 3'. The concentric circles passing through these points divide the area of a given circle into three concentric rings, c, D, E, and an inner circle, f, all having an equal area. The following figure is given as a study of geometrical draw- ing, showing an ellipse in which the curve is to be drawn by hand. Further studies, also to be drawn by hand, of a semi- elliptical arch, and an elliptical figure formed by arcs of circles, will be given in the next lesson. To draw an ellipse, the diameters A b and c D being given Place the diameters A B and C D at right angles to each other, intersecting in e. Find the foci F and f from c with radius equal to e a. Between e and f, mark off any number of points, as 1, 2, 3, 4, 5. (It is advisable that these points should be nearer together as they approach f.) From f, F, with radius 1 b, describe the arcs g, g, g, g. From f, f, with radius 1 A, describe the arcs H, H, H, h. The arcs h, h, h, h will intersect the arcs G, G, G, G it i, i, i, x, and these will be four points in the curve. Proceed to strike arcs from F F, first with 2 b, and then with 2 a ; and these intersecting will give four more points. When arcs have been struck with the lengths from all the points to A and b, the curve of the ellipse must be traced by hand through the intersections. CHEMISTRY APPLIED TO THE ARTS.— VI. BY GEORGE GLADSTONE, F.C.S. TANNING. Hides, in common with other animal substances, are liable to putrefaction ; and this action cannot readily be stopped, except by a process of drying, which renders the skin hard and stiff. 310 THE TECHNICAL EDUCATOR. or by that of tanning, in which the softness and pliancy, which are attributes of so much importance, can be retained. Hides and skins — the former term being applied to those of the heavier and larger animals, such as the rhinoceros, buffalo, ox, etc., and the latter to the smaller and lighter, such as the calf, sheep, goat, etc. — are in tanning converted into leather; an operation due to the affinity of tannic acid for the gelatine and albumen as well as the animal membrane contained in the raw article, which leads to the formation of a now compound that is not decomposed by the action of the atmosphere. The skin of all animals consists of two distinct parts — the epidermis, or scarf-skin, which forms a very thin layer in the exterior surface, and the cutis, or true skin, which lies below. It is with the latter that the tanner has to do. This is a fibrous substance largely composed of gelatine, whereas the other is of a horny character, and is not acted upon by the tannin. The affinity of the true skin for tannic acid may be easily tested, by making an aqueous solution of the latter, and then inserting in it a piece of skin of an ascertained weight, which will take it all up ; and the quantity of acid which had been dissolved in the water may then be calculated, by finding the increase in weight which the skin has attained during the operation. The raw articles are received into the tan-yard in very various conditions. The ox-hides and sheep-skins from the shambles are just in the state in which they came off the slaughtered animals ; those received from abroad have, how- evA, undergone some process to keep them from decomposition in the meantime ; they are generally either dried, in which case they have become almost rigid, or they are pickled in salt, in which case they retain much of their moistness and pliancy. The East India and Cape supplies are usually dry, and have the hair remaining upon them ; the wet, salted hides mostly come from South America. Before describing the course of treatment to which they are subjected, something must bo said of the various substances generally used as sources of tannin. The most familiar of these is oak bark, having until recently been much more exclusively used than now. It still continues to be tho only important article containing tannic acid which is obtained in any quantity in this country, though the bark and leaves of most trees contain more or less of this principle. The bark of young trees contains the largest per-contage, and the quantity is greater in spring than at other seasons ; but in this country neither of these considerations has much weight, the bark being of secondary importance to the timber, which improves with age, and is best when felled in the summer or autumn. These circumstances servo to account for the great variations in the quality of different parcels of bark, and show the import- ance of determining by chemical means the quantity of tannin they contain, which cannot be even approximately arrived at by the most experienced judges from the more appearance of the samples. Birch and willow bark are sometimes used in this country, but the former much more generally in Russia ; the agreeable and very permanent odour that distinguishes Russia leather being due to a peculiar oil contained in the bark of tho birch. The warmer climates supply a number of vegetable produc- tions rich in tannin, that are constantly attracting increased attention, and are destined to enter into still more general use, as the home supply of oak bark would not keep pace with the increase of the demand, wore the tanner dependent upon it alone. From tho shores of the Mediterranean two very impor- tant articles are received — sumach and valonia. The former consists of the leaves of the tree so called, which are dried and ground up ; the latter is the cup of a particular species of oak that grows extensively in Greece and Turkey, and which is remarkable for its very large acorns. From the tropics are obtained dividivi, myrobalans, and catechu, which are all rich in tannin. The first of these is the fruit-pod of a tree which grows in tropical South America ; the second is the dried fruit of one that is common in India ; and the last named (of which there are several varieties, known under the names of terra Japonica, cutch, and gambier), consists of the inspissated juice of certain trees which grow principally in the East Indies. These last are extremely rich in the important elements, being weight for weight about five times as effective in tanning as oak bark. Of late years the acacia trees, which abound in great variety in Australia, have been found to yield barks which are valuable in tanning, and considerable quantities of leather'are now made with tho aid of this material. The value of these different articles to the tanner is not, how- ever, to bo measured exactly by the proportion of tannin which they contain. The trade always looks for what is called “ bloom” upon the leather, and those substances which produce this effect best are consequently specially appreciated. The want of this quality in the different kinds of catechu detracts from the value which their richness in the tanning properties would otherwise assure to them ; while oak bark, valonia, and dividivi are distinguished for the beautiful bloom which they 1 impart. It is also worthy of note that some substances, which are themselves rich in tannic acid, are of no actual value for the manufacture of leather ; for though they will produce the chemical action necessary for this purpose, it is found in practice that the leather made with them is liable to decomposi- tion, so that it is wanting in its most important characteristic. Oak-galls, and all other excrescences which are not natural vegetable growths, have this defect ; and infusions of them are also very liable to another disadvantage — viz., a readiness to ferment, which results in the conversion of the tannic into gallic acid, the effect of which will be described presently. The usual processes for converting hides or skins into leather must now be described. If green hides (i.e., those fresh from the slaughterhouse) are to be operated upon, the first thing to be done is to cleanse them, by taking off all the particles of flesh, etc., which may be adhering to them ; and then, if they are not to be used at once, they must be pickled in salt to keep them sweet. Foreign hides, which have necessarily been either dried or salted, need a great deal of soaking in water to render them soft and porous ; so that a large supply of water is an essential requisite in a tan-yard ; and the water should be soft, as the earthy ingredients in hard waters are apt to form in- soluble compounds with the fatty matters in the skin, and so prevent the action of the tan. T-he next step is to take off the epidermis, and the hair with it. This is commonly done by liming, for which purpose the skins are steeped in vats containing a solution of quicklime in water, from three days to three weeks, according to tho nature of the article operated upon, the heaviest hides requiring the longest time. During this process the skins are handled, or turned over periodically, in order to keep the liquor stirred, and so prevent any unevenness of action upon them. Tho hides are then scraped with a long two-handled knife upon a beam ; the beam, as it is called, being a sloping bench with a curved surface, over which the hide is stretched during this operation. The sharp edge of the knife removes the epidermis and the hair at the same time. If the hide is then found to be uneven in thickness, it is turned over, and the inner side is subjected to a scraping and rubbing down until all inequalities are removed. The preparatory liming has unavoidably caused some of those insoluble compounds which have been already referred to as the result of using hard water ; and these must be got rid of before commencing the actual tanning process. For this purpose a “ bate,” or solution of dogs’ dung, is used, in which the hides are steeped for a week or ten days. The “ bate ” con- tains an ammoniacal chloride, the chlorine of which combines with the lime, forming a soluble compound that can be easily removed by washing. There are other modes of preparing for taking off the hair which have their advantages, especially in rendering the bating unnecessary. It may be done by producing a fermentation, for which purpose some milk, or a mixture of meal and water, is very effective. Another mode is technically called “ sweat- ing ; ” it is produced by piling the hides one over the other in a pit, when a considerable heat will be generated, and putrefac- tion will commence. This will be evidenced by the presence of an ammoniacal odour which will be evolved ; and care must then be taken to check the process immediately the hair has become loose, as a continuance of tho action would prove dele- terious to the quality of the hides. Exposing them to the action of steam in a steam-chest will produce the same loosen- ing effect upon the epidermis, and it is not attended with tho risk of injury, which is one of the objections against the sweat- ing process. The hair having been removed, and the bating (if necessary) PRINCIPLES OE DESIGN. 311 having been accomplished, the next step is to prepare the hide to receive the tan as readily as possible. This is called “raising,” the result being the distension of the cellular tissue of the skin, which facilitates the subsequent action of the tan. It may be done either by immersing the hides in a very weak aqueous solution of sulphuric acid, or of spent tan — the latter being considered the better, though the slower, process. We now come to the most important part of the whole opera- tion — the tanning, properly so called. This used to occupy a very long time, in some instances as much as two years ; but great attention has been paid to the shortening of its duration, and some plans have been devised by which it is possible to accomplish it in a fortnight or so. It is, however, found that a complete combination between the tannic acid and the gelatine is always a matter of time, an excess of the tannin being necessary in order to produce the required effect ; and if the operation be performed too rapidly, an inferior leather is sure to be the result. The old plan was to put the hides in pits between layers of ground bark, and leave them there for months, until the bark was considered spent, when the process would be repeated with fresh material, and so on until the hides were sufficiently tanned. It was afterwards found to be more expeditious to introduce tepid water into the pits for the purpose of drawing out the tannin from the bark. Now, an extract of bark, technically called “ooze,” is found to be still better. This may be made either with cold or warm water, and the strength of the solution can be regulated as may be desired. In the tan-yard a series of pits are arranged, with feed-pipes for supplying the ooze, and in these the hides are laid, and then the liquor introduced. The hides must, however, be handled or turned over twice a day at first, being returned into the same or the adjoining pit, the pits being so arranged that the first contains the weakest ooze, and so on up to the strongest or concentrated solution. When they are passed into the stronger ooze, the hides are handled only once a day, and subsequently only once a week or more, up to a month. From this circum- stance the pits containing the weakest solutions are called “handlers,” and those containing the stronger are termed “layers” and “bloomers;” a concentrated solution being finally used in order to give a bloom to the leather. Heavy hides require usually a period of about eight months to tan them properly with oak bark, and about double their weight of bark ; but if the other materials abeady named are used instead, a proportionately less quantity is required, and the time occupied is also somewhat shorter. After being finally taken out of the tan-pits the hides have to be carefully dried in a moderately warm chamber, and are usually rolled under heavy brass rollers in order to give them more compactness and a better surface, upon which their marketable value considerably depends. It. has been already stated, that the production of leather is due to the action of tannic acid upon the gelatine (of which skin is mainly composed), forming thereof an insoluble compound ; but tannic acid has, unfortunately, a great tendency to become oxidised and pass into gallic acid, which will not precipitate gelatine, and cannot, therefore, convert a raw hide into leather. It is therefore necessary that such precautions should be taken as will prevent this chemical change, though in many tan-yards a good deal of gallic acid is produced without its being objected to, as it has the property of swelling the hides, and so rendering them more permeable to the tan liquor ; however, the less in the strength of the latter is not compensated by the action of the gallic acid. An exposure to the air at an elevated tem- perature is a common cause of the oxidation of the tannic acid; and this action is particularly liable to take place when the vegetable fibre of bark or sumach is left in the solution, the fibre apparently acting the part of a ferment in such cases. Should fermentation have set in, it may readily be stopped by the use of alcohol, carbolic acid, or other similar substances. It will be seen from the foregoing that the tanning process is a singularly slow one, and though many plans have been sug- gested for shortening the time required, practical inconveniences have prevented their general application. The discovery of any simple means by which the operation could be materially expe- dited would confer a most signal benefit upon this large and increasing branch of trade. PRINCIPLES OF DESIGN.— IX. By Christopher Dresser, Ph.D., F.L.S., etc. AKT FURNITURE CHAIRS. Having considered those principles which are of primary im- portance to the ornamentist, we may commence our notice of the various manufactures, and consider the particular form of art that should be applied to each, and the special manner in which decorative principles should be considered as applicable to various materials, modes of working, and requirements of individual manufactures. We shall commence by a consideration of furniture, or cabinet work — first, because articles of furniture occupy a place of greater importance in a room than carpets, wall-papers, or, perhaps, than any other decorative works ; and, second, because we shall learn from a consideration of furniture those struc- tural principles which will be of value to us in considering the manner in which all art objects should be formed if they have solid, and not simply superficial, dimensions. In the present chapter I shall strive to impress the fact that design and ornamentation may be essentially different things, and that in considering the formation of works of furniture these should be regarded as separate and distinct. “ Design,” says Redgrave, “ has reference to the construction of any work both for use and beauty, and therefore includes its ornamentation also. Ornament is merely the decoration of a thing constructed.” The construction of furniture will form the chief theme of this chapter, for unless such works are properly constructed they cannot possibly be useful, and if not useful they would fail to answer the end for which they were contrived. But before commencing a consideration of the principles in- volved in the construction of works of furniture, let me sum- marise what is required in such worts if they are to assume the character of art-works. 1. The general form, or mass form, of all constructed works must be carefully considered. The aspect of the “ sky- blotch ” of an architectural edifice is very important, for as the day wanes the detail fades and parts become blended, till the members compose but one whole, which, when seen from the east, appears as a solid mass drawn in blackness on the glowing sky ; this is the sky-blotch. If the edifice en masse is pleasing, a great point is gained. Indeed, the general contour should have primary consideration. In like manner, the general form of all works of furniture should first be cared for, and every effort should be made at securing beauty of shape to the general mass. 2. After having cared for the general form, the manner in which the work shall be divided into primary and secondary parts must be considered with reference to the laws of propor- tion, as stated in my last article. 3. Detail and enrichment may now be considered ; but while these cannot be too excellent* they must still be subordinate in obtrusiveness to the general mass, or to the aspect of the work as a whole. 4. The material of which the object is formed must always be worked in the most natural and appropriate manner. 5. The most convenient or appropriate form for an object should always be chosen, for unless this has been done no reasonable hope can be entertained that the work will be satis- factory ; for the consideration of utility must in all cases pre- cede the consideration of beauty, as we saw in my last chapter. Having made these few. general remarks, we must pass to consider the structure of works of furniture. The material of which we form our furniture is wood. Wood has a “ grain,” and the strength of any particular piece largely depends upon the direction of its grain. It may be strong if its grain runs parallel with its length, or weaker if the grain crosses diagonally, or very weak if the grain crosses transversely. However strong the wood, it becomes comparatively much weaker if the grain cross the piece ; and however weak the wood, it becomes yet weaker if the grain is transverse. These considerations lead us to see that the grain of the wood must always be -parallel with its length whenever strength is required. For our guidance in the formation of works of furniture, I give the following short table of woods arranged as to their strength : — Iron-ivood, from Jamaica — very strong, bearing great lateral pressure. 312 THE TECHNICAL EDUCATOR Box of Illawarry, New South Wales — very strong, but not so strong as iron-wood. Mountain ash, New South Wales — about two-thirds the strength of iron-wood. Beech — nearly as strong as mountain ash. Mahogany, from New South Wales — not quite so strong as last. Black dog-wood of Jamaica — three-fourths as strong as the mahogany just named. Box-wood, Jamaica — not half as strong as the box of New South Wales. Cedar of Jamaica — half as strong as the mahogany of New South Wales.* Wood can be got of sufficient length to meet all the require- ments of furniture-making, yet we not unfrequently find the arch structurally introduced into such wooden objects while it is an absurdity so to do. The arch was a most ingenious inven- tion, as it affords a means of spanning a large space with small portions of material, as with small stones, and at the same time gives great strength. It is, therefore, of the utmost utility in constructing stone buildings; but in works of furniture, where we have no large space to span, and where wood is of the utmost length required, and is stronger than our requirements demand, the use of the arch becomes structu- rally foolish and absurd. The folly of this mode of structure becomes more apparent when we notice that a wooden arch is always formed of one or two pieces, and not of very small portions, and when we fur- ther consider that, in order to the formation of an arch, the wood must be cut across its grain throughout the greater portion of its length, whereby its strength is materially, decreased ; while if the arch were formed of small pieces of stone great strength would be secured. Nothing can be more absurd than the practice of imitating in one material a mode of construction which is only legitimate in the case of another material, and of failing to avail ourselves of the particular mode of utilising a material which secures a maximum of desirable results. While I protest against the arch when structural in furniture, I see no objection to it if used only as a source of beauty, and when so situated as to be free from strain or pressure ; but this matter I shall revert to when considering the formation of cabinets, when I shall illustrate my meaning more fully. One of the objects which we are frequently called upon to construct is a chair. The chair is, throughout Europe and America, considered as a necessity of every house. So largely used are chairs, that one firm at High-Wycombe employs 5,000 hands in making common cane-bottomed chairs alone, and yet we see but few chairs in the market which are well constructed. All chairs having curved frames — whether the curve is in the wood of the back, in the sides of the seat, or in the legs— are constructed on false principles. They are of necessity weak, and being weak are not useful. As they are formed by using wood in a manner which fails to utilise its qualities of strength, these chairs are offensive and absurd. It is true that, through being surrounded by such ill-formed objects from our earliest infancy, the eye often fails to be offended with such works as it would be were they new to it ; but this does not show that they are the less offensive and constructively wrong. Besides, when- * For full particulars on this subject see “ Catalogue of the Col- lection illustrating Construction and Building Material," in the South Kensington Museum. ever wood is cut across the grain, in order that we may get anything approaching the requisite strength, it has to be much thicker and more bulky than would be required were the wood cut with the grain ; hence such furniture is unnecessarily heavy and clumsy. Fig. 19 represents a chair which I have taken the liberty of borrowing from Mr. Eastlake’s work on household art.* This chair Mr. Eastlake gives as an illustration of good taste in the construction of furniture ; but I give it as an illustration of that which is essentially bad and wrong. Tho legs are weak, being cross-grained throughout, and the mode of uniting the upper and lower portions of the legs (the two semicircles) by a circular boss is defective in the highest degree. Were I sitting in such a chair, I should be afraid to lean to the right or the left, for fear of the chair giving way. Give me a Yorkshire rocking-chair, in preference to one of these, where I know of my insecurity, much as I hate them. A chair is a stool with a back-rest, and a stool is a board or plane elevated from the ground or floor by supports, the degree of elevation being determined by the length of the legs of the person for whom the seat is made, or by the degree of obliquity which the body and legs are desired to take when using the seat. If the seat is to support the body when in an erect sitting posture, about seventeen to eighteen inches will be found a convenient height for the average of persons ; but if the legs of the sitter are to take an oblique forward direction, then the seat may be lower. A stool may consist of a thick piece of wood and of three legs inserted into holes bored in this thick top. If these legs pass through the upper surface of the seat, and are properly wedged in, a useful yet clumsy seat results. In order that the top of the stool be thin and light, it will be neces- sary that the legs be connected by frames, and it will be well that they be connected twice, once at the top of each leg, so that the seat will rest upon this frame, and once at least two-thirds of the distance from the top.' The frame would now stand alone, and although the seat is formed of thin wood it would not crack, as it would be supported all round on the upper frame. A chair, I have said, is a stool with a back. There is not one chair out of fifty that we find with the back so attached to the seat as to give a maximum of strength. It is usual to make a back-leg and one side of tho back of the chair out of one piece of wood — that is, to continue the back -legs up above the seat, and cause them to become the sides of the chair-back. When this is done the wood is almost invariably curved so that the back-legs and the chair-back both incline outwards from the seat. There is no objection whatever to the sides of the back and the legs being formed of the one piece, but there is a great objection to either the supports of the back or the legs being formed of cross-grained wood, as much of their strength is thereby sacrificed. Our illustrations (Figs. 20—25) will give several modes of constructing chairs such as I think legiti- mate ; but I will ask the reader to think for himself upon the construction of a chair, and especially upon the proper means of giving due support to the back, until such time as I converse with him again in my next article. • * Tlie title of the work is “Hints on Household Art.” It is well worth reading, as much may be learned from it. I think Mr. Eastlake right in many views, yet wrong in others. I cannot help regarding him somewhat as an apostle of ugliness, as he appears to me to despise finish and refinement. 314 THE TECHNICAL EDUCATOR. CIVIL ENGINEERING. —IV. BY E. G. BARTHOLOMEW, C.E., M.S.E. ROADS — CANALS. The brief allusion we made in a former chapter to the excellent roads constructed by the Romans will indicate to the reader the fact that these, the most useful of all engineering works, are also amongst the earliest. No country can excel in com- merce or arts which is destitute of good roads ; and in colonising a new territory these are, or should be, the first points to which the engineer directs his attention ; for without some mode of conveniently transporting the products of agriculture or of science from one locality to another, no country can flourish. It is true that imperial Rome constructed her splendid high- ways rather with a view to the passage of her armies than to purposes of trade, but they were not the less available for more useful purposes either then or at the present time. A good road is of use just in the proportion in which it permits of the heaviest loads traversing it in all weathers, with the least expenditure of power. Hence, the two main points to be aimed at in the construction of a road are (1) that it shall be level, and (2) that it shall have an even surface. The first of these conditions can be attained only by a survey of the district through which the road is intended to pass. The desirability of a road being horizontal is too obvious a point to be enlarged upon ; at the same time, unnefcessary labour in excavating hills and in raising - causeways or embankments over valleys must be avoided. A very slight alteration or temporary deviation from the direction of the proposed route will often be the means of saving an immense amount of labour and expense, without materially increasing the distance, the longest road being frequently the shortest in point of time. Where an extended chain of hills crosses the proposed route, it may become necessary to carry it over the ridge ; but the gradient may be considerably diminished by cutting through the summit of the hill, and carrying the excavated soil into the adjoining valleys. Before deciding upon the exact point at which the ridge shall be cut, it will be desirable to examine the nature of the subsoil by frequent borings, as by this means rock may often be avoided. The duties of the civil engineer may be said to have ter- minated after he has determined on the course to be taken by the road, and calculated the extent of the cuttings and embank- ments requisite ; but it is absolutely necessary that he shall be practically acquainted with the nature of its construction, to enable him to check the operations of the contractor. In order that a road shall possess an oven surface, it must be composed of materials which will not readily yield to the traffic it will be subjected to. Durability, in all weathers, must be aimed at, and this is not always readily attainable. In a dry ■climate the difficulty is greatly diminished, but in so humid and changeable a climate as our own it is very much increased, whilst the passage of horses and vehicles aggravates the mis- chief. Hence the question how to construct durable roads in our large towns is one which can scarcely be said even now to be settled, seeing we are unable to pave the streets of even our most crowded cities with square blocks of stone, accurately fitted, as did the Romans. First, as to unpaved roads : — It must always be remembered that water, when not required, is the greatest enemy which the engineer has to contend with, and with roads it is no exception ; hence, no matter of what material the road bo constructed, it should be so formed as readily to throw off the rainfall. A moderately flat curve should be the figure given to the cross-section, the summit being in the centre of the road, and terminating at either side in a sunken channel to receive and carry off the water, which is far more injurious to the road when it is permitted to settle upon the surface. It then gradually soaks into the soil, rendering it soft and spongy, and the first vehicle which passes over it in this state produces an indent in which more water collects, and thus the mischief increases. On this account too much care cannot be bestowed upon the drainage. The nature of the material employed in constructing a road is of the first importance, but a difficulty frequently arises in procuring the most suitable kind of soil in the district which the road is to traverse, and the haulage of which from a dis- tance may involve an expenditure too great to be incurred. Telford stands forward prominently as a road engineer. The great road constructed by him in 1816-17, from Carlisle to Glasgow, may be taken as an excellent example of a country road. Its length is 93 miles ; it is 34 feet wide between the fences; but the central portion only, for a width of 18 feet, is metalled — that is, laid with broken stones ; the remaining portion on either side is gravelled. Its cost was .£1,000 per mile. The advantage of metalling a road lies in this, that the traffic itself assists to consolidate and harden the bottom. The metalling should consist of granite, broken with the hammer, by which the least quantity of the block is pulverised, and the stones retain the sharpness of their edges and angles, thus facilitating their entrance into the soil. The broken stone is spread in a layer over a subsoil, prepared to receive it either'by a rake or a pickaxe — the thickness of the layer being regulated according to the naturo of the bottom — the furrowing by the pickaxe being requisite to give a hold to the metalling. A light sprinkling of gravel is occasionally thrown over the metalling, which affords an easier footing for quadrupeds, and is in no way detrimental to the formation of the road. The process of metalling by spreading broken stones over the surface is called “macadamising,” after the name of the inventor, Macadam, and in this manner may be constructed excellent country roads, suitable, with proper attention, for all ordinary traffic. The bottom usually consists of broken stone or brick, rubble, burnt earth, bushes — anything, in fact, which by the action of moisture will not form mud. The character of the subsoil has much to do with the dura- bility of a road. If it be soft, broken granite, even thickly strewn, will prove a useless because an unendurable surface. This was found to be the case on the road under the Highgate Archway, where, owing to the soft and yielding nature of the subsoil, the only artificial surface which stood the wear and tear of the ordinary through traffic was a composition of gravel and Roman cement, in the proportion of 1 bushel of cement to 8 bushels of washed gravel and sand — the cost being about 2s. per square yard for a thickness of six inches. Many instances will occur in which the ordinary macadam- ised road will prove of no value — for example, in building a road across a bog or morass. In this case the plan adopted originally by Metcalf, in the last century, and subsequently by Stephenson, at Chat Moss, has been proved the most efficient. The yielding character of the bog would entirely absorb any soil thrown directly upon it; but by employing a floating medium, such as fagots, brushwood, or furze, and extending the width of the base considerably beyond what is required for the purposes of traffic, the soil may be made to rest upon the floating platform, and the road thus formed will efficiently bear up the weight of passing traffic. A macadamised road is of comparatively little use in a busv town. A through traffic is not nearly so injurious to a road as a traffic in which vehicles arc often turning — the pivot-wheel acting as a scoop, and producing an abrasion of the surface. The character of the surface of a road has, as may be sup- posed, much to do with the amount of friction existing in wheeled traffic. On a gravelled road the friction is 4 - 5 ; on an old flint road it is 2 - 0 ; a well-made pavement being reckoned as 1-0 — facts which at once settle the question of the desir- ability of maintaining a good surface on a road. It is an interesting fact, in connection with our subject, that the injury done to an ordinary macadamised road by four horses is three times as great as that done by four coach- wheels, but this proportion is considerably increased when the wheels are broad as in wagons. The fact that horses are so injurious to the surface of roads led to the effort, made many years since by Mr. Gurney, to introduce steam-p.ower upon common roads in lieu of horses. No ordinary macadamised road will withstand the traffic of the streets of large towns without the most continuous atten- tion, and a consequently large outlay. The more usual mode of meeting the difficulty is by a regular paving of stone, of which there are two kinds — the rubble and the ashler. A rubble is in reality an imperfectly constructed ' ashler pave- ment. The ashler causeway consists of hammer-dressed granite stones, from five to seven inches thick, eight to twelve inches long, and twelve inches deep. These stones are laid in regular order upon a foundation consisting of cement, sand, and gravel, which is allowed to set firm, the surface of this bottom being CIVIL ENGINEERING. 315 adjusted by suitable tools to the curve -which the cross-section of the finished road is intended to assume. After the surface- stones are arranged upon this bed, they are “ set ” by a copious discharge of thinly-mixed mortar being thrown over them, which settles down into the interstices between the stones and fixes them. The cost of a well-constructed ashler road varies from 7s. to 10s. per superficial yard. As compared with a macadamised road this is, of course, a high figure; but the difference is only in the first cost, and disappears when the item of maintenance is considered. In some instances a still more expensive kind of road is con- structed to meet special cases, as, for instance, the exceptionally heavy traffic between the Docks and the City of London, or over London Bridge, in which continuous lines of large granite blocks are laid end to end, with flush joints, thus forming a level stone tramway in the wheel-tracks. The blocks vary from 2^ feet to 10 feet long, are 18 inches wide, and 12 inches deep. Such a tramway so far reduces friction as to enable a single horse to draw a load exceeding ten tons at a rate of nearly four miles an hour, an advantage so obvious that, after the success of the experiment had been proved, it was proposed to lay a roadway of the same description between London, Liverpool, and Holy- head, upon which steam carriages might run. The idea was, however, rejected, as it was proved that, with all the care which could be bestowed upon such a road, the friction was still vastly in excess of that upon a smooth iron rail. A rubble pavement is one in which less care is bestowed upon the shaping and dressing of the stones ; hence there is less uniformity in their arrangement, and consequently wider interstices between them. The maintenance of a roadway is an important item of ex- pense. We have stated that a good ashler road costs much less to keep it in repair than a macadamised road, the main- tenance of the latter costing about 2s. lid. per superficial yard per annum ; but as macadamised roads cannot be entirely dis- pensed with, it is important to ascertain the best and the most economical method of keeping them in repair. The tendency of traffic is to wear down the surface from an erect curve to a level, or even to an inverted arch — the principal traffic being naturally confined to the centre of the road. This change of figure must be prevented, in order to keep up -the lateral drain- age ; the application of broken stone to all low parts must, therefore, never be neglected. The accumulation of mud must also be carefully avoided. A scraper is usually employed for the latter object, but this implement i3, without a doubt, the greatest enemy an ordinary road possesses. Even with the use of Bourne’s Multi-dental Scraper it is impossible to pre- vent the teeth from catching the projecting points of stone, the result of which is that the stone is dragged out of its bed, and a hole is formed. Nor does the mischief end there, for the surrounding stones, which were previously firmly wedged, be- come loose, and the solidity of the surface is impaired. The broom is the only thing that should be employed to remove loose mud from the surface, and this, if frequently applied before any large accumulation of soil has arisen, will always prove sufficient for the purpose ; for, besides doing its work with less injury to the road, it does it better than the scraper, entering more searchingly into the inequalities of the surface. It must be admitted that an ashler road, however excellent, is productive of great noise, and an uneasy vibration to the occupants of vehicles passing over it. For this reason, wooden blocks have, in several instances, been employed instead of stone ; and if this description of pavement could be made as durable, it has manifest advantages over the granite-paved surface. It is almost noiseless — too much so, indeed, for the safety of pedestrians — and the absence of jolting from stone to stone, combined with the yielding character of the surface, is productive of much less injury to the hoofs of the animals and to the springs of the carriages. An attempt has been made to render the surface of the wood more durable by studding it thickly with large-headed nails, but this course has not been successful. Knapp’s pavement consists of hollow iron blocks, divided into small compartments, filled with concrete to a level with the surface. Four of these blocks make one square yard. Asphalte has been recently employed in some of the busiest of the London thoroughfares. It forms an excellent surface, and an agreeable road, but its durability remains to be proved. Canals . — The advantages arising from a system of com- munication which, whilst extending over the interior of a country, is ar the same time connected more or less directly with the great highway of nations, the sea, are obvious. But there are other and equally apparent advantages in connection with water transit, advantages which are, however, particularly applicable to heavy goods. For instance, the tractive power of a wagon-horse upon a good road may be reckoned at 140 kilogrammes, whilst a single man is capable of drawing a load 350 times as great when floating upon water. Friction, in fact, is reduced almost to nil when the load is floating, providing the speed is inconsiderable ; indeed, the limit of weight to which a man is thus capable of imparting motion is not easily ascertained, but it appears to be bounded only by the vis inertia of the mass. The advantages, therefore, of canals as means of transport are evident, and vast sums of money have been expended upon their construction in this and other countries. There are, however, serious difficulties in the forma- tion of a canal, requiring considerable talent and forethought on the part of the engineer to overcome. The first point for consideration is whence to obtain the necessary water-supply. If the course of the canal were one continuous level throughout, communicating at either extremity with some large reservoir retaining a uniform level, there would be no further supply required than what was demanded by evaporation, or absorption by the soil ; but if the surface to be traversed is irregular, the introduction of lodes becomes neces- sary, and every barge which passes through a lock creates a demand upon the water supplied from the higher ground. The expense of employing pumps to return the water back to the higher level could not for a moment be entertained, except as an expedient during a limited period in dry weather; it is imperative, therefore, that an adequate supply of water should exist to provide for the loss arising from the emptying of the locks ; and the highest level of the canal should be so arranged as that it should receive at all times an equable and adequate supply of water from that source. Next in importance to the water-supply is the consideration of the course to be traversed by the canal. The commercial advantages arising from the contiguity of the canal to large towns must enter largely into the calculations of the engineer in his determination of this point ; but above all he must be guided by a consideration of the nature of the surface and sub- soil. If the subsoil be porous, consisting of sand or gravel, an undue loss of water will arise from absorption, to prevent which a large outlay must be incurred in puddling the channel with clay ; for this reason an absorbent soil should be avoided if possible. A matter of equal importance is the character of the surface ; every effort must be made by the engineer to prevent unnecessary excavation, and at the same time to limit as far as possible the number of lodes, those expensive and inconvenient but indispensable adjuncts to a canal, a further consideration of which we shall reserve for our next chapter. The engineer is much more restricted in his actions in pre- paring the plans for a canal than he is in laying out a road, or even a railway, because any deviation from an absolute level is inadmissible without the introduction of a lock. It is usual to lay out a canal in sections, the space intervening between lock and lock — and which therefore occupies the same level — being regarded as a section. The object of the engineer is, therefore, to make each section as long as possible, and as direct as the nature of the ground will admit. It is, of course, impossible to maintain one uniform level throughout ; but by judiciously avail- ing himself of the side of a hill, winding round its side, a»d selecting a short valley intervening between one hill and another, and spanning it by an aqueduct, and again skirting the side of another hill, and so on, the number of locks may bo. greatly re- duced. An apt illustration of the skill displayed by the engineer in the selection of the ground may be quoted in the case of the Monmouthshire Canal, which traverses very difficult ground, but which, winding round the side of the Blcrenge at the height of Several hundred feet above the valley of Crickhowell, enters the upper end of the valley in its course towards Brecon upon one continuous level throughout. In other instances — for example, the Rochdale Canal between Rochdale and Todmorden — the character of the ground neces- sitates the use of locks at very short intervals, involving a vast outlay in the first instance, and a great impediment to naviga- tion in the second. 316 THE TECHNICAL EDUCATOE. TECHNICAL DKAWING.— XX. DRAWING FOR MACHINISTS AND ENGINEERS. free-hand drawing ( continued ). Pig. 209 is a sketch of a common padlock, which affords a good subject for the practice of balancing curves. Having drawn a central perpendicular, and a horizontal line crossing it, set off the widths A B and a c ; then, having deter- mined on the distance ad, draw the curve on the left side — viz., B d — and balance it by the curve c d. Observe that these curves must not form a point at D, but must merge smoothly into each other. Pig. 210 shows the key of this padlock. Having drawn a central line, and another at right angles to it, draw the rectangle abcd. Set off e, f, g, h, and thus eight points will be obtained, through which the elliptical head of the key is to be drawn. It must, however, be understood, that this squaring out of curved forms is merely intended to assist the student in the most elementary stage, and must be discontinued as soon as possible. The barrel and remaining portions of the key are now to be drawn, and will easily be understood from the copy. Fig. 211 represents a small iron cramp. Now draw a horizontal line at E, and mark on it, on each side of the central line, a distance corresponding with E g. Produce this line, and continue the curve beyond b until it meets the straight line in F. The length from g to f and from B to F will then be equal, and thus a circle drawn from f, with the radius f g, would also include b. Now to draw circles by hand is, to almost all persons, a rather difficult task, but it may be rendered less so by drawing lines from the centre, and marking off on them the radius re- quired, as shown at f h. The curve may then be traced through the points thus obtained. The segments of circles on each side, then, having been drawn, and also the smaller circle representing the rivet, draw the upper portion of the padlock, the centre being at o ; and in this, too, the method shown above may be adopted. The keyhole, and plate surrounding it, can, it is hoped, be drawn without further instructions. Draw the perpendicular a, the horizontal b, and the perpen- j dicular a', at the required distance from A. | Now draw the horizontals CD, e f, g h, and I j, the ex- j tremity of i j being carried upward in a curve to K. Join c e and G k. From l set off l m, equal to l d, and also from L set off L n, equal to L F, and draw the semicircles d m j and f n h, which will complete this portion of the object. Having drawn the handle of the thumbscrew in the manner i shown in the callipers and padlock, draw the perpendiculars for the inner and outer angles of the thread of the screw. The method of drawing a screw in the simplest manner has been shown in Pig. 205. In the present study, however, the lines are to be drawn by hand instead of by the aid of the rule. No further separate studies of free-hand drawing will be given, as it is intended that the student should copy the rough sketches I and as many of the mechanical studies by hand as he can. TECHNICAL DRAWING. 317 mechanical DRAWING ( continued ). Fig. 212. — The subject of this lesson is a racket-wheel. This is a contrivance consisting of a wheel, with pins or teeth of a suitable form, which receives an intermittent circular motion from some vibrating piece. In this drawing, E is the rachet- vents the wheel from receding, whilst the click is moving over the teeth. The first step in drawing this figure is to trace the two circles between which the teeth are to be contained. These should be very lightly drawn, as no portion of either wheel, furnished with saw-like teeth. The driver is a click or paul, a, jointed at one end to a movable arm, b, which has a vibrating motion on the shaft c as a centre. As b moves towards the left hand it pushes the wheel before it through a certain space, and on its return the click, A, slides over the points of the teeth, and is ready again to push the wheel through the same space as before, being pressed against the taeth either by a spring or its own weight. A detent, d, pre- circle is to be used in the drawing ; but they are required to ensure uniformity in the teeth. Now, divide the outer circle into the number of parts re- quired for the teeth. There is no special reason why the outer circle should be divided rather than the inner ; it is merely that errors in division are more readily seen in large than in small circles. Where numerous divisions are required, some draughts- men draw a circle outside the one to be divided, and of a much 318 THE TECHNICAL EDUCATOR. larger radius ; on this they set off the required divisions, and from them draw lines to the centre ; these lines passing through the original circle, divide it without fraying the paper or other- wise injuring the clearness of the work. The outer circle then being divided, draw lines to the centre ; it will not be necessary to draw these radii the whole of the distance, but only between the two circles, to form the faces of the teeth, as shown at F S, H I, etc. Join the outer end of each line to the inner end of the next, as ii g, J i, etc. These lines will form the backs of the teeth. We now proceed to the arm, and for this the centre line must be drawn. Now it is necessary that, in copying a drawing, the exact inclination of such an arm or other part should be accu- rately given. To accomplish this, draw the diameter k L, measure from L on the circumference of the circle the length of the arc l m, and draw a line from the centre c through m. Then construct on your drawing an angle similar to lc M, and the line C M will give the inclination required. This method can be applied without reference to size, for it will be remem- bered that the number of degrees an angle contains is not altered by the length of the lines of which it is formed. Having then drawn the lino C M, set off on it the centre of the click, and complete the arm, setting off the widths on the circles at top and bottom. The straight sides are to be joined to the circles by small arcs, or by curves drawn by hand. The centres for the click and detent, and those from which their inner and outer curves are struck, are to be found in the same way. It will be seen that, owing to the form of teeth shown in this figure, the wheel can only be driven in one direction ; but in machines for cutting metal it is frequently necessary that it should work either one way or the other. Sir Joseph Whit- worth adopts in such cases the construction shown in Fig. 213, called Clement’s catch. Here the rachet-wheel has teeth, the ends of which are bounded by the circle, and the flanks of which are portions of the radii, whilst the click is so formed that it will either work as shown in the example, or may be turned over to act in the opposite direction. In drawing this figure, describe the circles for the inner and outer ends of the teeth; divide the outer circle into the re- quired number of equal parts, the teeth and spaces being equal ; draw the sides of the teeth by lines from the points of division to the centre, and join those lines which are to form teeth on the outer circle, and such as are to form spaces on the inner circle. The click is now to be drawn. Having fixed the centre, f, draw the line B c, which is radial to the circle. Bisect B c in r>, and the bisecting line D F will be the central line for the click ; the centres for the arcs forming the sides are shown at E and e'. Fig. 214 is a portion of the frame of a 'pump, and is here in- troduced as a study in joining circles, the whole of the external form being described by portions of three circles touching each other. Having drawn the base-line and perpendicular, B, mark on it the point A, and through it draw the horizontal c d. With radius a e, describe a semicircle. From B set off b f. From F, with radius F G, describe the arc g h. From F draw a line through G, cutting the line c d in I. From i, with radius I j, describe an arc, joining the semicircle to the arc last drawn. The rest of the drawing being obvious, it is hoped that, after this fundamental construction has been correctly done, the remaining portion will be accomplished without further instructions. COLOUR— VI. By Professor Church, Royal Agricultural College, Cirencester. ‘ COLOURS WITH WHITE, GREY, AND BLACK OCULAR MODIFI- CATIONS OF COLOUR — PERSISTENCE OF COLOUR-IMPRES- SIONS IRRADIATION — SUBJECTIVE COLOURS CONTACT AND SEPARATION OF COLOURS. We have seen, in the last lesson, that there are two kinds of contrast — the contrast produced by difference of tone and the contrast produced by difference of colour. We have also seen that these contrasts are produced under several conditions, and that they are modified through the mode in which they are per- ceived by the eye and impressed upon the mind. No sooner, in fact, are two colours so plaeed as to be seen at the same time or in quick succession, than they are apparently changed. The change may be one of tone only, of colour only, or of both tone and colour. Nor is it necessary, in such experiments, that two colours should be used : we may employ two tones of the same colour or a single tone of colour with white, grey, or black. We have already studied the apparent changes winch the primary and secondary colours mutually cause when placed in contiguity, and so may now proceed to state what modifying influences white, grey, and black respectively produce upon the most im- portant colours (see Figs. IX., X., and XI. in coloured plate). 1. Yellow. — Yellow with white is rendered darker, less luminous, and less prominent, and acquires a faint greenish hue. The lighter the tone of the yellow, the less pleasing is the combination. Yellow with grey is rendered darker, less luminous, and per- haps a trifle more orange. When the grey is of about the same intensity or tone as the yellow, the combination is not satis- factory ; but it becomes so when the grey is rather deep, the yellow then recovering brightness. Yellow with Hack is rendered lighter or paler, more luminous, and more prominent. The combination affords the most intense contrast next to that of white with black. The blackness of the black acquires a somewhat bluish-violet hue, which has a tendency to enrich it. 2. Orange. — Orange with white is rendered darker, and i perhaps a trifle more reddish. The contrast between orange i and white is much greater than that between yellow and white, and the combination is consequently more effective. Orange with grey, when the latter is pale, is darkened and reddened. With deep tones of grey, orange becomes more luminous. Orange with black becomes more luminous and yellower ; the contrast is next in intensity to that afforded by yellow with black. 3. Bed. — Bed with icliite becomes more intense and of a deeper tone. The combination, as to intensity of contrast, is similar to that of green with white ; being less decided than that of blue and violet with white, but more so than that of yellow and orange with white. Red with grey, where the latter is pale, becomes more intense, deeper, and occasionally acquires a slight bluish hue. Bed with black becomes more luminous and slightly yellower. 4. Violet.— Violet with white affords a contrast of very decided character, owing to the great difference of tone between a full violet and white. The violet is rendered deeper in tone in this combination. Violet with grey. — The distinctive colour of the violet makes j itself felt in this combination, which is a quiet and agreeable ; one. Violet with black affords an instance of the harmony of analogy rather than of contrast. The violet is enriched by its proximity with black ; but the latter thereby acquires a rusty hue, which takes away from its richness. 5. Blue. — Blue with white constitutes a pleasing combination. The contrast is very decided where the tone of blue is deep. The effect of white clouds in deepening the tone of the sky is a good example of one of the chief characteristics of this combination. j Blue with grey. — Grey enhances the tone and quality of blue, deepening it to a remarkable extent under certain circum- stances. Blue with black. — This combination resembles that of violet and black, but is less agreeable, especially where the blue is of a deep tone. Light shades of blue are rendered paler and more luminous by contiguity with black. 6. Green. — Green with white becomes more intense and of a deeper tone ; green is distinctly improved by the presence of white. Green with grey becomes deeper in tone. Green with black is rendered rather lighter in tone, and more brilliant; but the black suffers in purity, and becomes slightly tinged with a ruddy hue — the result of adding to the black, red, the complementary colour of the neighbouring green. From what has been said in the preceding paragraphs, it will TECHNICAL DRAWING. 319 have been seen that the effect of white upon a colour is to en- hance its quality and deepen its tone ; for white, presenting the maximum of luminosity itself, naturally lowers the apparent luminosity of coloured surface in contact with it. (We employ the term luminosity here in its common acceptation, not in its scientific sense as previously explained in Lesson I.) But the white is capable of enhancing the quality of a colour for a different reason (explained already when speaking of “ Simulta- neous Contrasts”). In virtue of this principle, the white, in contiguity with a colour, has a tendency to become tinctured with the complementary of that colour ; the presence of this trace of the complementary colour enhances the quality of the original colour itself, in obedience to the law of contrast : the same effect is observed, also, with grey and black when placed in contiguity with colours. This remarkable law of contrast, of which we are now speaking, may, indeed, in its widest terms and most general application, be summed up in the statement that two differing colours or differing tones tend, when placed together, to differ still' more. Light tones and colours become lighter, dark tones darker, complementary colours are mutually enhanced in distinct- ness ; and where a colour is present without its complementary, that complementary is, as it were, evolved, owing to extra sensibility of the eye for those colours which are not presented to it when it has been excited and fatigued by those at which it has been gazing. Before studying the more complex combina- tions of colours and their applications in the arts, it will be expe- dient to develop a little more fully some of those principles on which the “subjective” or “ ocular ” modifications of colours depend. To such phenomena we have just now, as well as on former occasions, briefly alluded ; but we are now in a position to extend and amplify our previous observations. The subjective modifications which colours suffer arise from at least three causes. First of all, we have the persistence of the impression on the retina of the eye.* The discharge of a Leyden jar gives a spark which is sensibly instantaneous, and yet the impression which it makes upon the eye endures a distinct fraction of a second. The spokes of a rapidly-revolving wheel are seen with perfect distinctness and perfectly separate if it be illuminated by an electric spark, although in an ordinary light they may present a shadowy surface, where all the elements of the wheel are blended together. Yet the apparent solidity of this surface may be proved to bo unreal by its approximative transparency to objects placed on the further side of it. These objects, if properly lighted, can be readily perceived through the shadowy surface previously described. Similarly with a series of flashes of electric sparks ; if these follow one another at intervals less than the period during which the impression of each spark remains upon the retina, the resultant effect will be that of a continuous light. A familiar example of this persistence of impressions upon the retina is to be found in the experiment of rapidly whirling a glowing stick or piece of red- hot charcoal ; a continuous circle of light being produced under these circumstances, if the rotation be sufficiently rapid. Now the effect of this peculiarity of the optical arrangements of the human eye is very marked in the case of colours ; but it does not take place exactly in the direction in which we might expect it. It would be imagined that if one of the eyes has been looking at a yellow disc or other yellow object it would perceive, \then directed upon a blue object, a mixture of yellow and blue, or a colour lying between them. However, under such circum- stances the blue object, so far from acquiring a greenish tinge, becomes rather tinctured with a violet hue. This effect is really one of subjective colour, as well as of persistent vision ; for the eye having seen a yellow object is partially blinded or paralysed, so far as that component of white is concerned; acquiring, on the other hand, greater sensitiveness to the per- ception of the complementary of yellow — that is, violet. White surfaces, or even coloured surfaces, which, of course, reflect much white light, will then have their violet or red and blue constituents brought into unusual prominence by the previous perception of yellow, and will be consequently tinctured with violet. As it is difficult to carry out mentally, from this prin- ** Illustrations of the remarkable effects produced by persistence of vision, and the imitation of this natural effect by various scientific toys, will be found in that portion of “Recreative Science” which appears in Yol. VI. of The Popular Educator. ciple, the whole scheme of alterations of colour effected by the peculiar kind of contrast just described, we shall here give a list of the principal colours as modified by the previous per- ception of others. Before doing so, it may be advisable to give our readers a method of proving for themselves that such modifications really occur. Close the right eye, and then look steadily with the left at a sheet of red paper. When the red paper appears dull, owing to the special sort of fatigue it induces in the eye, look im- mediately, still with the left eye, upon a sheet of violet paper. The violet paper receiving the complementary of red — namely, green — becomes much bluer. To verify this observation it is only necessary, after having closed the left eye, to open the right, and to look with it upon the sheet of violet paper. The violet will be perceived very differently now, and so far from being bluer than in reality, may actually appear modified in the contrary direction — becoming more red, instead of more blue. To be performed with successful and distinct results, such experiments as these require great care and frequent repetition. Moreover, different individuals have very different powers of appreciating colours and of recording their impressions. One eye, also, will often be found to differ from its fellow in many important particulars. Notwithstanding the delicacy and diffi- culty which may be experienced in determining the special relations of contrast (often called “mixed contrast”) now under consideration, they are of considerable importance in the practice of some kinds of decorative art. We now give our list of the modifications induced by mixed contrasts of colour. ' the eye has first seen and then loolcs at the latter colour will appear Yellow, orange. reddish -orange. Yellow, red, reddish-violet. Yellow, violet, bluish-violet. Yellow, blue. violet-blue." Yellow, green. bluish-green. Orange, yellow. greenish-yellsw. Orange, red, reddish-violet. Orange, violet, bluish-violet. Orange, blue, tinged with violet. Orange, green, bluish-green. Red, yellow. greenish-yellow. Red, orange. yellow. Red, violet, indigo-blue. Red, blue. greeuish-blue. Red, green. bluish-green. Violet, yellow. slightly greenish. Violet, orange, yellowish-orange. Violet, red. orange-red. Violet, blue. greenish-blue. Violet, green. yellowish-green. Blue, yellow. orange-yellow. Blue, orange. yellower. Blue, red. orange-red. Blue, violet. reddish-violet. Blue, green. yellowish-green. Green, yellow. orange-yellow. Green, orange. reddish-orange. Green, red. tinged with violet. Green, violet, reddish-violet. Grceu, blue, violet-blue. It must not be forgotten that the above modifications of colour, arising from mixed contrast, differ not only in intensity, but in persistence. The modification produced by the successive view of violet and yellow is stronger and more persistent than that produced by the successive view of blue and orange ; green is but slightly modified, and for a brief space of time only, by the previous view of red, and so on. And the above-described effects of contrast are influenced, to a great degree, by the difference of tone between the colours successively observed. A dark blue viewed after orange may actually appear somewhat greenish, when the normal modification would be precisely in the opposite direction — that is, towards violet ; yet this change occurs most conspicuously when the blue is of not too full a tone. Among the most important cases, constantly occurring in common life or artistic practice, of modifications of colours arising from per- sistence of the impressions made on the retina, we may cite the difficulty experienced by painters, from gazing too long at any bright coloured object, natural or artificial, of reproducing or 320 THE TECHNICAL EDUCATOR. matching its tone and hue. Again, we may allude to the well- known instance of the purchaser of coloured fabrics. If a series of bright yellow fabrics be displayed, and then some pieces of orange or red stuff, this latter is regarded as dull, and to have a crimson or even a violet tinge. Under such circumstances, the retina, fatigued by the sight of yellow, has a tendency to appreciate and perceive violet, its complementary, more dis- tinctly. Thus much of the yellow in the orange stuff is sup- pressed, and it appears redder than it really is ; red similarly acquires a violet tinge. Doubtless much of the weariness experienced by a long examination of the pictures in an exhibition ©f modern works of art is due to eye-fatigue, and the consequent ocular modifications of colour. The second subjective or ocular cause of apparent changes in the colours of objects is due to a defect of the organ of vision. The eye suffers from what in optical language is termed “ spheri- cal aberration” — a scattered light, of varying degrees of in- tensity, always surrounding the defined images of luminous and strongly illuminated objects upon the retina. The result of this nebulous border about such images is to increase their apparent size ; but it is nearly always imperceptible under the ordinary conditions of moderate illumination. When, however, we look at incandescent or glowing and luminous bodies, the effect is very striking. A piece of charcoal no thicker than one’s finger, if lighted at one end and plunged in oxygen, appears actually to swell as the combustion becomes more intense and the light brighter. A spiral of platinum wire heated to white- ness by a galvanic current not only has its diameter, so far as the wire, itself is concerned, enormously increased, but the separate turns of the spiral seem to approach and even to coalesce, if not originally too distant. The crescent of the moon appears, for the same reason, to belong to a much larger sphere than the dimmer mass of the satellite which it clasps. Much of the peculiar indefiniteness and mystery which impart considerable beauty to flames of different kinds, to strongly illuminated clouds and surfaces of water, and to the intense reflected lights of metallic ornaments, is due, in part at least, to irradiation, which, moreover, is one of the chief causes by which coloured margins are so frequently observed to surround coloured objects. A rim of greenish light may be observed round a red wafer placed on white paper, owing to the extension of the image of the red wafer beyond its geometrical image on the retina of the eye. Of course the rim is green, owing to the effect of simultaneous contrast. With a pure yellow, such as that of the spectrum, or that made by mixing green and red lights together, the rim of irradiate colour would be blue. This effect is roughly shown in Pig. III. of our coloured plate. The third ocular cause of the modification of colour has been already dwelt upon at some length, and in different places, in the present series of lessons : it is the production of subjective complementary colours. We may just allude to the phenomenon here, in order that this most important and fundamental fact may be thoroughly impressed upon the minds of our readers. Simply stated, the cause of the phenomenon may be traced to the impaired sensibility to light temporarily caused by the action of light upon the optic nerve. Not only is this true of white light, but of light of every colour. Not only does a moderately lighted room appear dark when we first enter it from broad sunshine, but, as we have before stated, the last piece of yellow or red cloth we look at will seem duller than the first, though they hare all been cut from the same roll. When light of any particular colour falls upon the eye, it becomes less sensitive to, and less appreciative of, that colour ; it is partially blinded to its perception. So, not only will a red wafer placed upon a sheet of white paper be surrounded by a rim of colour through irradiation, but that rim will be green ; and if the wafer be moved away, a green spot will occupy its former position. For the eye, by gazing at the red wafer, has had its sensibility to red light temporarily impaired, and so the white light received on that particular spot of the retina previously occupied by the red tinge of the wafer will have its red con- stituent virtually removed, and will produce the effect of the residual rays — namely, a green image, the complementary of the previous red one. Several other contrivances for producing subjective complementary colours have been devised. One of the most satisfactory of these is to view a surface of white, grey, or coloured paper, moderately illuminated, through an aperture 'n another sheet of paper of a different colour, and placed at a little distance above or before it. The lower surface, as seen through the aperture, will be tinged with the comple- mentary of the coloured surface above. So, also, the shadow of an object interposed in a beam of coloured light will, if received on a screen slightly illuminated with white light, appear to have assumed the colour complementary to that of the beam ; and, for the same reason, a beam of daylight finding its way into a room illuminated with yellowish light from candle-flames, will appear violet. The importance of this fact, as regards the proper treatment of shadows in painting, will have to be insisted on and illustrated farther on in the present course. We have now studied the mutual effects of many pairs of colours, the effects of white, grey, and black upon single colours, and the effect on a second colour of the previous perception of another. We have then passed to the causes, dependent upon the structure of the human eye, which modify the natural ap- pearance of coloured objects. We may fitly close this lesson with a few remarks on the uses which may be made of some of the facts and laws which have just been stated, confining our attention at present, however, to those effects of the apposition and separation of coloured spaces which are illustrated in our coloured plate. We have before stated that the yellow is the most forcible, luminous, and prominent of the primary colours. It will appear nearer to the eye than either red or blue. In Fig. IV. (coloured plate) a yellow leaf pattern is represented upon a ground par- tially red and partially blue. While there is no doubt of the prominence of the yellow, it will probably be allowed that the red ground appears nearer than the blue ; and if the blue had been of a purer and fuller tone still, the retiring effect which it possesses would have been still more perceptible. How far the retiring effect of blue is due to association or fancy, to our constant view of the sky and the hazy distance of a landscape, it is difficult to determine. But there can be no doubt that we are obliged, in decorative and pictorial art, to recognise the idea of distance conveyed by blue and bluish hues, and that such colours afford means of attaining effects of mystery, obscurity, hollowness, etc., which other hues do not furnish. Another association with the colour blue is that of coolness, just as red recalls the glowing warmth of a fire, and yellow the bright shining of the sun. Another feature of our diagram (Fig. IV.) is the distinctness of the sensation imparted by the three colours, yellow, red, and blue. If the red approaches the yellow rather more closely than the latter does the blue, it arises from the impossibility of representing by actual pigments these three colours. Figs. V. and VI. teach another fact relating to coloured spaces in contact. Often when we attempt to mix colours, our mixture is anything but successful. The difficulty of getting a good violet by adding blue and red together is well known. The result may be achieved in a different way. If lines or dots of red and blue be distributed suitably over a surface, the effect of violet will be produced — at all events, when the figure is held at some distance. One mode of accomplishing this result is seen in Fig. VI., where the distinction of the two colours is lost, and a mixed colour effect produced, in obedience to the laws of subjective colours already announced. In Fig. Vi the two colours retain their distinctness at ordinary small distances. When two colours of about the same intensity and tone, as the blue and yellowish or leaf-green in the central stripes of Figs.VII., and VIII., are in contact, there is a want of distinctness and purity about the margins of the contiguous colours, which renders the combination by no means a pleasing or favourite one. Yet a bright leaf-green is often seen in Nature against the deep blue of a summer sky, and no one dreams of quarrelling with this arrangement of colour. There are, however, delicate differences between the natural and artificial appositions of green and Mue. The green leaves of trees are full of minute variations of tone, structure, and form, and they are further helped to contrast with the more uniform blue beyond them by the reflected illumi- nation of some of the edges and the shading or darkening of others. The latter modification may be represented to us roughly in Fig. VIII. Here we see the enormous importance of white and of black, even in the narrowest lines and smallest quantities, in separating related colours. Such colours, difficult as they are to harmonise successfully under many ordinary con- ditions, afford by the aid of black or whito combinations of great delicacy and beauty. ANIMAL COMMERCIAL PRODUCTS. 321 ANIMAL COMMERCIAL PRODUCTS.— XIII. I. DYES. Some of the Mollusca furnish dyes and pigments. The Murex yields various shades of purple and crimson. The celebrated Tyrian purple was formerly obtained from Murex trunculus. The cuttle-fish (Sepia officinalis), which clouds the water by ejecting from its ink-bag a deep black fluid, thus effectually con- cealing itself, supplies the well-known pigment, sepia, of a deep brown-black colour ; and a calcareous spongy plate, found in the same fish, is used as a substitute for emery or sand-paper, and as a dentifrice. II. — SHELLS. The beautiful variety of form and colour in shells has in all ages attracted notice. Among savages shells are used for per- sonal adorn- ment, and made into domestic utensils, such as knives, spoons, drinking - cups, fish-hooks, and evenrazors. The wampum belts of some of the N orth American tribes are made of shells. A small species of white glossy shell, called cowry ( Cyprcea moneta, Figs.l, 2), abundant in the Asiatic and African shores, is used as money in small pay- ments in India and throughout extensive dis- tricts in Africa, 100 being equi- valent to one penny. The same cowries are converted into a glaze for earthen ware and an enamel for clock faces. Cyprcea cocci- nella (Fig. 3) is found in the English Chan- nel. The thin inner layers of a large flat bi- valve ( Placuna placenta) found in the Chinese sea, remarkable for their transparency and the absence of the nacreous or pearly layer within, are used by the Chinese for windows instead of glass. In Roman Catholic countries clam shells form recep- tacles for holy water ; while some, perfectly white, are cut up for arm-rings and other ornaments. The Voluta gravis, or chank shell of India, fished up by divers in the Gulf of Manaar on the north-west coast of Ceylon, is exported to India, where it is sawn into rings of various sizes, and worn on the arms, legs, fingers, and toes, by the Hindoos. The demand for these shells is caused by the religious rites of the Hindoos, and some choice specimens of them are valued at their weight in gold. The helmet shell ( Cassis , Fig. 4) supplies pieces large enough for umbrella handles, and the nacreous or inner layers of this shell, and other species, are exquisitely sculptured by Italian artists in imitation of antique cameos, and employed for rings, brooches, pins, bracelets, and other ornaments. The byssus, or fasciculus of shining semi-transparent horny or silky filaments, by which many kinds of bivalves attach them- selves to rocks, is in the large Pinna or wing-shell (Fig. 5) so much developed, that by the natives of Sicily it is manufactured into gloves, socks, caps, etc., of a beautiful brownish colour. These are valuable as objects of curiosity, but too expensive foj general use, the price of a pair of gloves being six shillings, an' that of a pair of stockings eleven shillings. The largo proportion of lime in shells renders them useful in making cement, and valuable as a fertiliser of the soil ; and for this reason shell-sand, the product of their natural crumbling on sea-shores, is. employed with advantage in im- proving heavy loams and clayey or peaty soils. Mixed with any soil deficient in lime, shell-sand exercises a beneficial influence. If we look at a shell we shall find it to con- sist of three layers, viz., one external and rough, a me- dium layer con- sisting of deli- cate super-im- posed laminas of polygonal prisms, and an internal and shining one called the nacre, which is com- posed of a series of extremely de- licate deposits, unequal in size and extent, and therefore imbri- cated in their position on each other, their margins pre- senting a series of lines with waved edges. These wrinkles, or furrows, which are of m i croscopic proximity and minuteness, de- compose the rays of light, and produce that beautiful iridescent play of colours visi- ble on the sur- face of the shell. It is this na- creous lustre _ which renders shells so capable of being applied to ornamental purposes, and gives to them their principal commercial importance. The brilliancy of the colours reflected depends on the thin- ness of the laminae of the nacre. Where the laminae are thick, a dull white appearance only is visible, as in the oyster. Some- times the external layers covering the nacre are rubbed off by natural causes, as in the case of shells which have been sub- jected to the roll of the waves on the sea-shore, where quantities may be found having the bright and iridescent nacreous surface exposed, but more or less injured ; generally, however, these outer layers are removed artificially with a knife, and the shell is polished. This nacreous layer is the well-known mother-of- pearl, and shells having it in the greatest abundance are called pearl shells, such as the sea-ears ( HaZiotis ) and a large species of top-shell ( Turbo marmoratus, L., Fig. 6). Mother-of-pearl, in consequence of its lamellar structure, admits of being split into laminae ; or it is cut, without being split, into square, angular, 21— Yol. I. 322 THE TECHNICAL EDUCATOB. or circular pieces, which are employed extensively in the arts, particularly in inlaid work and in the manufacture of knife and razor -handles, buttons, snuff-boxes, and toys. Cut into the form of leaves, flowers, and other devices, it forms a favourite material for ornamenting papier-mache — a name given to articles manufactured from paper pulp, which is moulded into varied forms, and rendered as hard as wood by being dried in an oven. The most valuable shelb in commerce are, however, those which form the nacre into t le fine, compact, concentric layers called pearls. These pearls are sometimes found free within the lobes of the mantle, but most frequently adhere to the nacreous coat of the shell. The species which produces the largest and most valuable pearls is the Pearl Oyster ( Meleagrina margaritifera, L., Figs. 7, 8). — -The most valuable pearl fisheries are those on the western coast of Ceylon; at the Bahrein Islands in the Gulf of Persia; at Tutico- reen, on the coast of Coromandel ; off St. Margarita, or Pearl Islands, in the West Indies ; in some places on the coast of Columbia; and in the Bay of Panama in the Pacific. Very large and beautiful pearls, too, are said to have been found recently on the peninsula of California. The fisheries in the Persian Gulf are the most valuable, giving employment to 4,000 boats and about 30,000 people, and yielding a revenue of more than 2,500,000 thalers .(,£375,000) a-year. The value of pearls depends upon their size, purity, and lustre. The best are spherical, free from spot or stain, and have a clear, bright, white or yellowish-white, or bluish colour, with a pe- culiar* lustre or iridescence. They vary in size — some not bigger than small shot, and others as large as a pea or bean. When pearls dwindle to the size of small shot, they are called seed-pearls, and are then of little value. “ A handsome necklace of Ceylon pearls, as large as peas, is worth from £170 to £300 ; and one of pearls the size of peppercorns may be had for £15. The largest and most valuable pearl of which we have any authentic account was purchased by Tavernier, at Catifa, in Arabia — a fishery famous in the days of Pliny — for the enormous sum of £10,000. It was pear-shaped, two inches in length, and half an inch in diameter, and is now the property of the Shah of Persia. The finest pearls generally pass under the name of “ Oriental pearls ;” and those with less lustre and beauty, even if they do come from the East Indies, are called “ Occidental pearls.” Pearls are most abundant in the pearl oyster, which appears to be subject to a disease, caused by the introduction of foreign bodies within the shell. A pearl, if cut through, will generally show a nucleus, formed by a grain of sand or some other foreign body, around which the nacreous matter has accumulated in concentric deposits, instead of being spread in the usually hori- zontal laminae on the inside of the shell. The value of pearls has been greatly depreciated in modern times through the successful imitation of them. The spurious glass and wax pearls now made in Paris, Venice, Nuremburg, and Bohemia have much diminished the trade in real pearls. The best imitations were first made by a French bead-maker named Jacquin. The water in which the fish called the bleak ( Cyprinus alburnus ) is washed, is filled with powdery particles, which shine with a pearly lustre. Jacquin noticed this ; he called this powder “essence of pearl,” or “essence d’ Orient,” and succeeded in covering the inside of glass beads with it, thus producing a most admirable spurious giass pearl. A con- siderable trade is done with spurious pearls on the coasts of Senegambia, Guinea, and Congo, and the adjacent islands, where they are indispensable goods for the transaction of business with the natives. NOTABLE INVENTIONS AND INVENTORS. VI.— THE MARINER’S COMPASS. BY JOHN TIMBS. The contrivance by which the magnet, in the very middle of a strip of iron, is still true to the distant pole, and remains a faithful guide to mariners, is the compass, before the inven- tion of which — “ Rude as their ships was navigation then. No useful compass or meridian known ; Coasting, they kept the land within their ken, And knew no north but when the Pole-star shone.” * See Pearls, “Dictionary of Commerce,” by J. R. McCulloch. Also “Journal of the Society of Arts,” No. 896, Vol. NVIII. If we hang up a magnet by a thread, or allow it to swim in quicksilver, or place it in a small bit of wood floating in water- it never comes to a state of rest until one end points to the north and the other to the south. The needle or index of a compass is a prismatic piece of tempered steel, which, by having been rubbed on a magnet, has acquired a magnetic power, and which, being placed on a pivot, is at liberty to turn in all directions. This accidental discovery of the property of a natural sub- stance rapidly influenced the fortunes of mankind. “ In the development of the commercial spirit of the Crusades, Providence is seen in its most manifest footsteps. Sitting upon the floods, it opens to new enterprises. The compass, twinkling on its card, was a beam from heaven ; that tiny magnet was given as a seigniory of earth and sky. Like a new revelation, the mysteries of an unknown world were unveiled; like a new illapse, the bold and noble were inspired to lead the way. Dias doubles the Cape of Storms ; De Gama finds his course to the East Indies ; Columbus treads the Bahamas ; and twelve years do not separate these discoveries.” The compass was the invention; the discovery which preceded it- — for there must be a discovery preceding every invention — was the finding of the natural magnet or loadstone ; and “ this did more for the supplying and increase of social commodities than those who built workhouses,” as said the grave philosopher, John Locke. The power of the loadstone to attract iron was known to the ancient Egyptians, who, however, did not apply it to any practical purpose. It is referred to by Aristotle and by Pliny, who tell us that ignorant persons called it quick-iron ; and in the Middle Ages it was believed to possess medicinal properties, as an alterative and cure for sore eyes. Tiger Island, at the mouth of the Canton river, in China, consists chiefly of magnetic ore, and mariners say that the needles of their compasses are much affected by their proximity to the island. Tradition extends the story to drawing the nails and iron bands from the planks of ships, and thus causing them to fall to pieces ; and it is remarkable that Chinese writers place the above magnetic island precisely in the region of the story of the voyages of Sindbad the sailor. At what period the polarity of the magnet, or its disposition to turn to the north and south poles of the earth, was first dis- covered is not known. The Chinese appear to have known it from a very remote date, and to have extended it through most of the leading countries of Asia ; the magnetic compass being used on land service prior to service at sea. Extracted from the Szuki of Szumathsian, a Chinese historian contemporary with the destruction of the Bactrian empire by Mithridates I., we find the following extraordinary relation : “ The Emperor Tchwingwang, 1,110 years before our own, presented to the ambassadors of Tong-king and Cochin-China, who dreaded the loss of their way back to their own country, five magnetic cars, which pointed out the south by means of the moving arm of a little figure covered with a vest of feathers ” “To each of these cars, too, a hodometer, marking the distance traversed by strokes of a bell, was attached, so as to establish a complete dead reckon- ing.” (Humboldt’s “ Cosmos.”) “A thousand years before our era, in the obscure age of Codrus, the Chinese had already mag- netic carriages, on which the movable arm of the figure of a man continually pointed to the south, as a guide to find the way across the boundless grass-plains of Tartary; nay, even in the third century of our era — therefore at least 700 years before the use of the mariner’s compass in the European seas — Chinese vessels navigated the Indian Ocean under the direction of magnetic needles pointing to the south.” Klaproth has collected from Chinese authorities many curious anecdotes of the use of those chariots. Under the Tsin dynasty they formed a part of every royal procession. Whatever was the position of the car, the hand of the prism always pointed to the south. When the emperor went in state, one of these cars headed the procession, and served to indicate the cardinal points. The magnetic wagons or cars were made as late as the fifteenth cen- tury ; several of them were carefully preserved in building the Buddhist monasteries, in fixing the points towards which the main sides of the edifice should be placed. Humboldt mentions the circumstance, that the magnetic land car used in China had attached to it a way measure. Over the trackless land, they were more certain of their course than the seaman of this age, who imperfectly ascertains the speed of his vessel by the log- TECHNICAL DRAWING. 323 line, is uncertain of his leeway, and has to correct all by the observation of the heavenly bodies for his latitude and for his longitude, the time by a watch showing the difference of noon at his place of observation and the part from which he started.” Thus writes Mr. Buckton to “ Notes and Queries,” 3rd Series, No. 257- adding : “ Mr. Seoresby (afterwards a clergyman) was the owner and master of a ship in the North whale-fishery from Liverpool. In a lecture delivered by him thirty-four years ago, he exhibited an important experiment, which does not appear to be generally known. He took a bar of iron two or three feet long, about one inch in diameter, and placing it in the direction of the magnetic meridian — that is, pointing to the north, at an angle of 40° or 50° with the horizon — he struck it a smart blow with a heavy hammer, by which from a simple bar of iron it became a magnet. Afterwards he placed the same iron bar in a direction at right angles to its former posi- tion, and striking it as before, its magnetism was thereby dis- charged, and it was proved to have none of the properties of a magnet. At the time I considered this a favourable illustration, although not so designed by Seoresby, of the magnetic theory of Euler, disclosed in his ‘Betters to a German Princess.’ ” The history of the compass in Europe has been much con- troverted. The twelfth century is assigned as the period of its introduction into Europe ; but it does not appear to have been then brought into common use for nautical purposes. Though passages of various dates speak explicitly of the use of the compass for land purposes, yet no mention of the magnet for navigation occurs, in any Chinese books that have come to the knowledge of Europeans, till the dynasty of Tsin, which lasted from the year 265 to 419 a.d. It is in the great dictionary, Roi-wen-you-fou ; and it is there stated that “ there were then iron ships directed to the south by the needle.” Sir John Davis contends that this passage rather refers to the magni- tude of their ships, and the extent of the voyages which they performed, than to the introduction of the needle into marine affairs. In the ninth century two Mahometan travellers are stated to have traded in ships to the Persian Gulf and the Red Sea, and though the compass is not mentioned, it is utterly im- probable that the Chinese should have known the directive property of the magnet, and have used it on land in thirty centuries, and yet not have employed it at sea. It was known on the Syrian coast before it had come into general use in Europe, as is obvious from a passage in a manu- script written in 1242, which thus describes the natural compass : “Wo have to notice, among the other properties of the magnet, that the captains who navigate the Syrian sea, when the night is so dark as to conceal from view the stars which might direct their course according to the position of the four cardinal points, take a basin full of water prepared for the purpose by placing it in the interior of the vessel ; they then drive a needle into a wooden peg or acorn-stalk, so as to form the shape of a cross, and throw it into the basin of water prepared for the purpose, on the surface of which it floats. They afterwards take a loadstone of a sufficient size to fill the palm of the hand, or even smaller, bring it to the surface of the water, give to the hands a rotatory motion towards the right, so that the needle turns to the water’s surface ; they then suddenly and quickly withdraw their hands, when the two points of the needle face north and south. They have given me ocular demonstration of this process during our sea-voyage from Syria to Alexandria in the year 650 of the Hegira.’ ’ When we consider the jealousy with which all knowledge was guarded by its possessors, espe- cially that of commercial value, we cannot but admit that the use of the compass must have been very common at a period when a passenger was initiated into the complete knowledge of the mode of magnetising the steel needle, as well as the mode of using it. About 1260, according to Dante’s teacher, the needle was highly useful at sea, but the navigators were prejudiced against its adoption ; for, says he, “ no master-mariner dares to use it, lest he should fall under the suspicion of being a magician ; nor would even the sailors venture themselves out to sea under his command, if he took with him an instrument which carries so great an appearance of being constructed under the influence of some infernal spirit.” Dante refers, in a simile, to “the needle which points to the star and Raymond Lully, in 1286, remarked that the seamen of his time employed “instruments of measurement, sea-charts, and the magnetic needle.” The earliest mention of the primitive mariner’s compass in English records is that in a work by Alexander Neckam (born about 1150), entitled “ Treatise on Things pertaining to Ships.” In the reign of Edward III. the magnet was known as the Sail- stone, or Adamant, and the compass was called the Sailing-needle, or Dial ; though it is long after this period that we first find the word compass. Chaucer, who died in 1400, mentions the com- pass, and the sailors reckoning thirty-two points of the horizon, which is the present division of the card. Dr. Gilbert, physician to Queen Elizabeth, and who bestowed much attention upon mag- netism, compared the earth to a great magnet ; and in our time Faraday said, “ The earth is a great magnet ; its power, accord- ing to Gauss, being equal to that which would be conferred if every cubic yard of it contained six one-pound magnets ; the sum of the force is, therefore, equal to 8,464,000,000,000,000,000,000 such magnets.” The use of the word compass had become familiar in the reign of Charles I., and Rowe, in his Play of “Jane Shore,” speaks of “the seaman’s compass.” Sir John Ross, during his last voyage in the Felix, when frozen in about 100 miles north of the magnetic pole, concen- trated the rays of the full moon on the magnetic needle, when he found it was five degrees attracted by it. A curious notion has been current, more especially on the shores of the Mediter- ranean, that if a magnetic rod be rubbed with an onion, or brought into contact with the emanations from that plant, the directive force will be diminished, while a compass thus treated will mislead the steersman. “ It is difficult,” says Humboldt, “ to conceive what could have given rise to so singular a popular error.” (“ Wonderful Inventions,” 1868.) TECHNICAL DRAWING.— XXI. DRAWING FOR MACHINISTS AND ENGINEERS. Fig. 215.— The subject of this lesson, based on a study in Pro- fessor Bradley’s excellent large work, is a dead-beat anchor escapement. The escapement wheel would carry the seconds hand of an astronomical clock. The pallets are shown in two positions, when the pendulum has vibrated through one arc. Draw the circles A and b, and divide A into the number of equal parts corresponding with the number of teeth required. From each of these points draw lines touching the circum- ference of the circle b, as shown by the lines c r> and E f. Draw the circle G, and with the radius divide it into six equal parts : the radii drawn from these will be the centre lines for the arms. Now from, the points of the teeth draw tangents to the circle G, as shown in tho lines H J and I K. The lines h j and I K will cut the lines C D, and the other faces of the teeth, in points l, m, etc., all of which will be situated on the circle, and thus c l will be the depth of the face of the teeth. The line H j, etc., will also give the upper part of the backs of the teeth, as h o, the length of which is fixed by the circle o. The remaining portion of the backs of the teeth are drawn as shown in another tooth. From p and Q, with any convenient radius, describe arcs cutting each other in r ; then from r describe the arc p q. The student is again reminded, that to find the centre from which any arc of a circle is struck, three points are to be marked on the arc, and the lines uniting them are to be bisected ; the intersection of the bisectors will then be the centre of the arc. On each side of s set off s t and s u, for the width of the arms at their upper end. Draw the circle v, and from w set off w x and w Y, for the width of the arms at their lower end. Draw t y and tj x for the edges of the arms ; but as these arms do not run as straight lines into the rim, but are connected by curves, the lines must only be fully drawn from t to y and from v, to x. The distance t T may be carried round to each of the arms by a circle. On this circle set off t t' equal to t t, and from t', with radius t t', draw the arcs connecting the edges of the arms with the inside of the rim. The arms are connected at the bottom by circles of any con- venient radius, as shown in the drawing at z and W. 324 THE TECHNICAL EDUCATOE. The anchor in its first position is an arc drawn from 1, whilst in its second position the arc is struck from 2. The remaining portion of the drawing is left to the student s knowledge ; and this plan will be constantly adopted, in order to release him as soon as possible from leading-strings, and by throwing him more and more on his own resources, give him It is unwise to set off points from each other, for if either one be at all inaccurate, the error is carried on throughout the work, whereas if all the distances are set off from a centre line, any error will be confined to any one point which may have been inaccurately measured. For the same reason the horizontal line G H is to be drawn, the opportunity for exercise of thought and ingenuity, with the conviction that each success will give confidence, and inspire him with the desire for further exertion. Fig. 216 is the front, and Fig. 217 is the side elevation of a crank, to draw which the student will require but few instruc- tions. The centre line, A b (Fig. 216), is to be drawn first, and a horizontal line having been drawn at A, the distances A c, A d, a e, a f are to be set off, and perpendiculars drawn from them. The distances of the other perpendiculars are to be set off from the centre line. This plan is to be universally adopted. and on each side of this half the widths of the end of the crank., the crank-pin, etc., are to be set off. In Fig. 217 the distance from centre to centre, A b, is to be first marked, and from these the different concentric circles are to be described. The lines c D and E f are next to be drawn near the circles at right angles to a b. On these the widths of the crank are to be marked, and the lines c E and D F are to be drawn. The subject will now be easily completed. Unless formed in one complete forging, the crank, however TECHNICAL DRAWING. 325 important in machinery, labours under the disadvantage of re- quiring the shaft to be divided, as shown at i and J in Fig. 216, unless when placed at the end ; and therefore, when a crank of a small throw is wanted, as in the mechanism for moving the slide-valves of a steam-engine, the eccentric may be substituted brass or gun-metal for the purpose of diminishing friction, is accurately fitted within projecting ledges, D, on the outer cir- cumference of the eccentric, so that the latter may revolve freely within it. This ring is connected by a rod, e, with a system of levers by which the valve is moved. for the crank. This will be further elucidated in another lesson. In the eccentric (represented on a larger scale in Fig. 218) a circular plate, A, is surrounded by a hoop, b, the plate being movable about the centre of motion at c. “The circular eccentric is simply a species of disc or pulley, fixed upon the crank-shaft, or other rotating axis of an engine, in such a manner that the centre or axis of the shaft c shall be at a given distance from the centre of the pulley. “ A ring or hoop, either formed entirely of, or lined with, “ It is evident that as the shaft to which the eccentric is fixed revolves, an alternating rectilinear motion will be im- pressed upon the rod, its amount being determined by the eccentricity, or distance between the centre of the shaft, c, and that of the exterior circle. “The throw of the eccentric is twice the eccentricity of c f, or it may be expressed as the diameter of the circle described by the point r. “The nature of the alternating motion generated by the 326 THE TECHNICAL EDHCATOE. circular eccentric is identical with that of the crank, which might in many cases be advantageously substituted for it.” — Le Blanc and Armengaud. In commencing to draw this example, describe the circles for the hoop, from the centre F. This hoop, which is made in two portions, united by bolts and nuts, is strengthened by flanges, G and g', the arcs of which are struck from the centres g and g' a little above and below the centre, F. The end of the shaft, C, and the circles surrounding it, are now to be drawn ; then the arm, and subsequently the web, H H. In order to guide the student in joining the curves, the centres of the arcs by which they are united are marked, and he is urged to work with the utmost care and accuracy so that the curves may flow gracefully into each other. The double nuts are next to be drawn. The fork of the rod is formed by three arcs. The arc I has its centre at i, and this is continued by an arc, K, turning in the opposite direction, drawn from fc. The inner arc, J, is struck from j. The rest of the figure will now be easily drawn without further instructions. Fig. 219. — This figure represents one of the ends of the valve- rod of a marine engine. The centres from which all the arcs are drawn are shown, and the whole object being of a very simple form, is left for the student to draw without further aid. TECHNICAL EDUCATION ON THE CONTINENT.— XI. BY ELLIS A. DAVIDSON. THE WORKING MEN’S UNION IN BERLIN — TECHNICAL EDUCATION IN FRANCE. We now turn to another class of institution, in the carrying out of which working men are associated for intellectual im- provement and social intercourse. The Berlin Working Men’s Union, which was established in 1843, attains its object by the following means : — Lectures, conversational lessons, vocal music, gymnastics, lending library, newspapers, social reunions (in which the wives and children of the members are associated). Whilst, however, endeavouring to contribute to the physical and moral welfare of the mem- bers, the main object of the Union— intellectual improvement — • is anxiously promoted, and this is accomplished by the diffusion of knowledge adapted to the requirements of the various trades, instruction in natural history, by practical lectures on technical art, by personal intercourse with men highly distinguished in the branches of industry on which they lecture, and by special classes for the study of technical drawing and modelling, and of the sciences on which the various trades are based. MEMBERS. The Union at the present moment numbers above 3,000 mem- bers, who pay a small monthly subscription. The Union does not reject persons who may not be working men ; still it has been found that at least nine-tenths of the members are of that class. This circumstance, and the years of travel incumbent upon every German artisan, bring about a frequent change of members ; and thus, although the average number on the books at any one period is 3,000, about 10,000 individuals will have been members at some time in the year. The number of per- sons who have been members of the Union during the previous Seven years is estimated at 60,000. CLUB-HOUSE. The Union, the operation of which was interrupted by the events of 1848, was reconstructed in 1859, and soon came into such active operation that it became necessary to erect a per- manent home for it. The building is large and commodious, containing an assembly or lecture room capable of accommodat- ing 2,000 persons, and thus, with the adjoining garden, oppor- tunities are afforded for recreation in winter or in summer. The class rooms, and those devoted' to conversation amongst the members, are all large and comfortable, and the apartments in the basement are devoted to domestic purposes. MEETINGS AND LECTURES. The meetings take place on four evenings of the week, and also on Sundays and holidays ; they are devoted to lessons, con- versation, lectures, etc., on the evenings of the week, and to social intercourse and choral music on Sundays. All the meet- ings, in fact, begin and close with part-singing. The subjects of the lectures, conversations, and discussions are various, ex- cluding only religion and politics. The lectures are all free to the members, and are given according to a previously published syllabus. From the annual reports of the years from 1861. to 1865, it appears that during that period 592 lectures were given (or about 118 lectures per year), the greater portion of which were devoted to subjects immediately connected with trade, manufactures, and natural history ; and here it is again neces- sary to point out that, in the broad system of German education, the term “ natural history ” does not merely mean the history of animals, but the science of every section of creation, and that “history” does not mean simply the history of Germany, but universal history ; so that the student, whilst reading of the events of any particular period in one country, reads also what was occurring in all other known parts of the world. This is a subject as yet very much neglected in our country. At the close of the lectures, the lecturers receive and reply to questions by the members, by which plan an immense amount of informa- tion is educed. TEACHING STAFF. As in the lectures, the utmost amount of instruction is im- parted in the classes by means of questions and answers, and by conversation with the teachers. The teaching staff is purely an honorary one, not any one of the professors accepting a salary, having taken the self-imposed duty in furtherance of the well-being of the working classes, who, as will be shown presently, avail themselves most grate- fully of the opportunities thus held out to them for receiving first-class instruction. The lecturers and teachers are men of the highest metropolitan — in fact, in some cases, European — repute, viz., professors of universities, medical men, architects, engineers, artists, officers of state, managers and proprietors of large works, etc. ; whilst the staff of about seventy teachers includes eight members of parliament and seven members of the town council ; and the Burgomaster of Berlin is one of the acting board of management. This co-operation of men of the highest position in the scientific, literary, and social circles with the working classes is one which must produce the best results, and which, we are happy to say, is becoming more general in this country than it formerly was. COURSE OF INSTRUCTION. The scheme of instruction is designed to improve the incom- plete education of members, and to give instruction adapted to tho particular requirements of each. The classes are well attended, the subjects of study being — writing and reading; arithmetic ; the German language, literature, composition, and correspondence ; free-hand and linear drawing ; geometry; book- keeping and exchanges ; commercial arithmetic ; book-keeping by double entry ; mechanical and architectural drawing ; prac- tical geometry and projection; vocal music; short-hand writing ; modelling ; the French language ; the English language ; pattern designing. The following figures show the attendance at some of the classes: — German reading and writing, 144; literature, 45; arithmetic, 60; mathematics, 20; drawing, 101; short-hand, 52; book-keeping, 42; French, 30; English, 15; gymnastics, 150. ARCHITECTURAL SCHOOL OF THE UNION. The earnest desire of a great body of the members for further systematic instruction in practical architecture led to the forma- tion of the School of Architecture, under the management of able professors and architects. In this school the students receive theoretical and practical instruction in architecture and the various trades which take their rise from that science. There are four courses of instruction, each extending over four months. The average number of students availing themselves of these advantages is 84. LIBRARY AND READING-ROOM. As may be supposed, the library is a most important feature in the institution, affording as it does means for instruction and amusement for the members and their families. Its contents have been acquired partly by gifts and partly by purchase : it is used by about 700 members in the winter and 500 in the summer. The library is open for the exchange of books two evenings in the week. The reading-room is open for the use of members on each evening in the week. The room is supplied BUILDING CONSTRUCTION. 327 with seventy papers and magazines — political, scientific, literary, artistic, religions, and technical — all of which are gratuitously presented by then* respective publishers. The room is very well attended, and is a source of great pleasure and instruction to the members. It may be interesting now to analyse the number of members, with a view to showing the classes of artisans who have at any time belonged to the Union during the years 1864 and 1865 : — Labourers . . . 633 Bakers .... 88 Barbers ... 52 Public Officers . 363 Coopers ... 44 Bookbinders . . 375 Book-printers . 132 Brush-makers . 44 Tilers .... 20 Turners . . . 217 Compositors and Printers . . 321 Dyers .... 62 Tanners ... 22 ‘Glaziers ... 59 Gold and Silver Workers . . 196 Belt-makers . .193 Glovers ... 60 Various Business Men. . . .1318 Tinmen . . . 301 Basket-makers . 85 Purriers, Hatters, and Cap-makers 123 Lacquerers . . 45 House and Deco- rative Painters 764 Fitters .... 215 Masons andBrick- layers . . . 606 Mechanics. . . 218 Millers .... 50 Needle-makers and Steel-workers . 60 Fringe-makers . 104 Saddlers . . . 195 Screen-makers . 11 Slaughterers . . 15 Locksmiths . . 680 Smiths. . . .273 Tailors .... 1118 Chimney-sweeps . 9 Shoemakers . . 776 Bope-makers . . 10 Frame-makers . 105 Stamp-cutters . 5 Students of Art and Literature 78 Cabinet-makers .2105 Potters ... 78 Watch-makers l . 87 Weavers . . . 1446 Joiners. . . . 388 Total in' Two Years . . 14,152 The space at our disposal will not allow of our giving in these papers any further account of the means by which technical education is carried on in Germany ; yet all we have described is as a drop in the mighty ocean. The machinery is so vast, and its action so definite, that volumes could be written with- out exhausting the theme. We leave it, then, unwillingly but of necessity, in order to devote some attention to the TECHNICAL EDUCATION OF FEANCE. Our subject not permitting us to enter upon an investigation of the schools for primary instruction, or for the education of the blind, deaf and dumb, or idiots in France, we must pass over all the noble, institutions established for these, who have been called the disinherited of Nature. The improvement in the ordinary means of education pro- vided for children has been deemed by the friends of progress in France to be insufficient to meet the wants of the day. They felt it to be necessary that a great educational system, exten- sive, varied, and open to all those who wished to learn, should be made available to adults, offering the means of extending the elementary knowledge received in preparatory schools, and providing superior instruction suited to their peculiar avoca- tions. The ministerial orders suggesting lectures and evening schools for apprentices and grown-up people, responded to this double want. Private efforts had, it is true, in this instance preceded official decrees. Several societies had been organised in various places, to provide means for scientific instruction, for the benefit of town workmen. The Polytechnic Associa- tion, which dates from 1830, numbers now twenty-two different sections in Paris and its environs; whilst it has founded and endowed a much larger number in various departments, showing that individual enterprise. has not been idle. But the effect of an appeal from the Minister of Public Instruction to the intelli- gence of the country, caused the inauguration of such a vast educational movement, that from the 1st of January, 1864, to the 15th of December, 1866, the number of adult educational institutions was augmented from 5,623 to 28,546, and a spon- taneous accession of 600,000 voluntary pupils was thereby created. These institutions have adopted two different methods of instruction, each useful in its way : that of lectures to open the minds of the public, and to enlighten them in various important subjects, and that of absolute lessons for the purpose of affording accurate instruction adapted to the various walks of industry. The education of apprentices and adults, as has been shown in the various programmes already given, when it passes beyond the limits of elementary instruction, changes its character, enters into the arena of applied science and art, becomes, in fact, technical education. The recent introduction of the teaching of living languages, commercial geography, and political and industrial economy cannot fail to generalise and constitute for the working classes a superior system of educa- tion, by enabling them by the latter to understand and so be satisfied with laws and regulations, of the gist of which they would have otherwise have had no comprehension, and by the former to obtain information from the works published in foreign countries, or in visiting such to be enabled to com- municate with others, without the aid of interpreters, who, whilst they may translate the words, cannot translate the spirit, not having a practical knowledge of the subject. If we except some few departmental centres where public instruction is favourably endowed, the teaching of the applied arts is much better organised than that of the sciences. The practical and successful results achieved by the system of teach- ing adopted in the drawing and modelling schools, secured for France an honourable position at the London Exhibition in 1862, and this was confirmed by the work shown in the Paris Exhibi- tion in 1867. Paris, which has become so justly celebrated for the production of works of industrial art, has naturally put itself at the head of the movement. By the institution of a certificate of Master or Mistress of Arts as a reward for skilled teachers ; the introduction of drawing into the primary schools for girls and boys ; the re-organisation of the evening classes for male adults ; the opening of lay schools for female adults ; annual competitive examinations between classes of the same degree, and the renewal of models according to the rules of the most correct taste, a more enlightened and elevated object is given to instruction. These are great educational advances in which the municipality and the State both participate; and, further, the workmen of France have been, made to feel that the traditional fame of their country in industrial and ornamental art will not stand invulnerable against the competition brought about by the increased educational efforts made in other countries ; and that if they would hold then* own, they must make the strongest efforts with renewed vigour, or they will be compelled to relin- quish the palm of superiority. Already the admirable working of the English schools of art has produced an effect on designs and manufactures which is even now turning the pecuniary stream, which has until within recent years flowed to France, into the homes of the English designers and manufacturers ; and this healthy competition once established, the English have met with considerable success ; whilst they cannot but admit, and gratefully acknowledge, that the very men who are running in the race have helped them in every way. This refers to Ger- many as well as France, and it may not be out of place to men- tion here that every information as to systems, details, time tables, etc., of the educational institutions, specimens of the work done in each, copies of the books and examples used, and every possible personal assistance during visits, have been accorded to the writer of these papers by the authorities of the various institutions, and by the working men of all the countries whose educational institutions are herein described. BUILDING CONSTRUCTION.— XI. STONE AECHES — WOODWORK, ETC. The simplest form of arch — viz., the semicircular — may be considered as the half of a cylinder, and this knowledge will materially assist the student in projecting the different forms now required. The subject of cylinders, their sections and developments, having been fully treated in “Projection” (see Lessons IX. and X., pages 204, 235), it will only be necessary here to apply the principles there laid down. Let A B d c (Fig. 75) be the plan of a road to be crossed by a bridge, the arch of which is semi-circular. It must, however, at the outset, be explained, that an elliptical or any other form of arch would be projected in an exactly similar manner, the semi-circular being merely chosen in this case as simplest for the present purpose. Now if the arch were to cross the road at right angles to it3 sides, A b, c d, the elevation would be that drawn as at e f (Fig.' 76), and, of course, any section taken at right angles to the° sides would be of the same form, the arch being perfectly semi-circular. The development of the soffit — that is, the shape of the covering of the interior of the arch — would in that case be a parallelogram, whose width would be equal to the depth of the arch, and whose length would be equal to the curve forming the semicircle e f, and its plan would be the rectangle hike. 328 THE TECHNICAL EDUCATOR. But, in the present study, the arch crosses obliquely, its eleva- tion making- an angle of 60° with the side of the road, c r>. The plan of the bridge then becomes the rhomboid g h i j, instead of the rectangle h i k l. The construction necessary for the proper projection of the arch under these circumstances, so as to find its exact shape, is an application of the study given in lessons in “ Projection;” for it will be seen that the arch must be treated as a semi- cylinder, and the elevation as a section of it at an angle of 60°. Having drawn the elevation (Pig. 76) as it would be if it crossed at right angles to the roadway, and having divided it into its voussoirs, the joints of which converge to the centre, draw lines perpendicular to E F from the points E, N, o, p, q, k, s, f, meeting the line at which the arch really crosses in the of the arch (and here again the student is referred for ele- mentary information to the figures in “Projection” already mentioned). Produce the line L h indefinitely, and from the point h, which in Fig. 77 is coincident with e of Pig. 76, set off the lengths N, O, p, Q, r, s, e from the original elevation, in order to obtain the length of curve. But the student is reminded that this is only approximately correct, for it is measuring chords instead of arcs, and straight lines .are, of course, shorter than curves, •as a straight line is the shortest distance between any two points. In order, therefore, to approach as nearly as possible to the true length of a curve, it is desirable to divide it into numerous parts, by which the chords become shorter, and the difference between the curved and straight lines is lessened. points H, n, o, p, q, r, s, g (Fig. 77). At these points draw | lines perpendicular to h g. j Now the ground line G H (Pig. 77) corresponds with the I ground line E f (Pig. 76) ; it is only longer because it crosses obliquely, and thus the perpendiculars, in consequence of this lengthening of the whole line, will be further apart than they are in the original elevation. But although they will become further apart they will not be in any way altered in height ; therefore mark on the per- pendiculars n, o, p, q, r, s, the heights of the perpendiculars N, o, p, Q, R, s in the original elevation (Pig. 76), thus obtaining the points n' , o', p', q', r', s'. The curve drawn through these points will give the true form of the required elevation, and is the shape for the centering on which the arch would be built, and of the templet used in shaping the separate voussoirs. It will now be convenient, before too many lines crowd the paper, to work out the development of the underneath surface Divide, then, one of the spaces— viz., f s — into, say, four equal parts, and set these off from H on l h produced — viz., h h 7 . Now there are seven divisions in the intrados of the arch, and they are all equal ; therefore set off from h the distances n\ o', p', q', r 7 , s 7 , h 7 equal to F s. The length h h 7 is thus the length, of the curve. Prom N 7 , o', p 7 , Q 7 , r 7 , s 7 , H 7 erect perpendiculars, and intersect them by horizontals drawn from the points similarly lettered in the base line of the oblique elevation. Through the points thus obtained— viz., n" , o" , p", q" ,r" , s”, h" — draw the curve h h", and from them set off on the perpen- diculars the lengths h i. Connect these points by the curve i t, and the figure hit h" (Fig. 78) will be the development of i the soffit of the arch. To draw the outer edges of the voussoirs, proceed, precisely as before, to draw lines parallel to the axis of the cylinder, and at the points where such lines meet the base line of the oblique elevation, draw perpendiculars to G H. Mark on each of these BUILDING CONSTRUCTION. 329 the heights taken from the base line in the original elevation, and the rest will be seen from the diagram. Fig. 79 shows a simple projection of one of the voussoirs, the first on the left side. The face is, of course, drawn from the oblique elevation, the curve being struck from the templet already mentioned, which may for drawing purposes be cut out of a piece of veneer. If this is done, the student will easily be able to draw the portion of the curve required for each voussoir. one is divided into five stairs called winders, whilst the straight | stairs are called flyers. To draw the winders, produce the lines forming the edges of j the steps b and c, until they meet in A. Then from A, with radius A b, describe the quadrant connecting the lines d c an I a b. The same radius will also give the quadrant at the oppo- site end. From A with any radius describe the quadrant B, and divide it into five equal parts ; through these points draw lines converging to A, which will complete the plan of the winders. Scale 1 inch to a foot. Fig. 82 F'iz. 81 Scale 1* inch to a foot Produce the base and the slanting portion of the face until j they meet in w. This wedge form will then correspond with that in the oblique elevation produced to the centre. With the set-square of 30° draw the receding lines, and ft will be evident that the distant edges are parallel to those in the front. Fig. 80 gives the plan, and Fig. 81 the elevation, of a stone staircase, with detail to an enlarged scale. Draw the walls of the plan, and from the inside lines of these draw the lines a, b, c, d, and e, f, equal to length of the steps from end to end. Mark off on these the widths of the steps, and draw the lines which will be the plans of the edges d, g, \ li, c; b, i, j, 7c, l, to, n, o, p, q, r, s, t, u, v, w, a; e, x, y, f. The quarter- spaces will still be left in the corners, and of these the In the other corner there is really a quarter-space, and from this four steps rise, the last of which is the landing. It will be seen that the steps are built into the wall. This is shown by the dotted lines in the plan. The lowest one also rests on the ground, and this supports the length of the one above it, and so on in succession, the stairs fitting in to each other by a joint called a “joggle,” shown at a, b, and c in Fig. 82. It is necessary here to mention that the flat surface of a stair is called the tread, and the upright face is termed the rise. The slabs forming the passage seen in section in the elevation at x (Fig. 81) are joined as shown in Fig. 83. They, too, are built into the wall at their inner edge, and the passage is further supported by a cantaliver, not shown in this elevation. •330 THE TECHNICAL EDUCATOR. Fig. 84 shows the mode of describing the curtail, or lowest step, drawn to the scale of 1^ inch to the foot. Draw A B equal to the width of the visible portion of the tread of the step — namely, eleven inches by scale, an inch and a half being covered by the step above. Bisect A B in c, and divide C b into four equal parts. On the bisecting line c construct the square CDS I, the sides of which equal any one of these four parts. From c, with radius c b, describe the quadrant b g. From d, with radius D G, describe the quadrant G H ; and from e the quadrant H I, which will complete the spiral. From i draw a perpendicular, and make I j equal to i e. From j, with radius J I, describe the quadrant I K, and from K the straight end of the step will be drawn as shown in the general plan. The projection of the elevation of the steps is so simple that it will not require much explanation. Having projected from the plan the mere sections of the walls supposed to be cut through, draw any perpendicular, as c, and on it set off the heights of the rises. This height is, of course, regulated by the room at the disposal of the architect, and the height of the floor to be reached : in this case an average height of rise is taken — that of six inches. Letter each of these points to correspond exactly with the figuring of the edges of the steps on the plan. (It will be seen that, in order to avoid crowding, figures belonging to the winders are placed on the lines, instead of at their extremities.) Now from the points marked in the perpendicular in the elevation draw horizontals, and from the points at the ex- tremities of the edges of the steps in the plan draw perpen- diculars ; then the right angles formed by the intersections of the lines similarly lettered will be the end elevations of the stairs. All other guidance may be obtained by careful study of the diagrams. WOODWORK: DRAWING- TOR CARPENTERS AND JOINERS. JOINTS IN TIMBER. Before treating of what are usually termed joints, we must give some attention to the methods of uniting pieces of timber so as to increase their length, whilst achieving, as nearly as possible, the same amount «of strength which the timber would have if it consisted of one piece only. In writing on this subject, the author necessarily bases his observations on the principles laid down by such standard authorities as Tredgold, Robison, Thomas Young, Peter Nichol- son, etc. ; but he has also been guided in some degree by German and French practice. Some of the examples are culled from Continental sources, in order to give the student as extended a view of the subject as the limits of these lessons admit ; and to the information thus gleaned he has added the results of his own experience, extending over many years. The modes of joining timbers, so as to increase their length, are very numerous, and have most of them certain advantages when applied under particular circumstances. Some of the methods adopted are ingenious, but the simplest is generally the best. It will be clear that the method of joining shown in Fig. 85 must be the strongest that could possibly be adopted. Here two pieces of the same scantling* are laid over each other for a' certain length, and then either held together by iron bolts or by bands. The author prefers the latter, because, by boring holes through the timber, the fibres are divided, and the strength of the beam thereby diminished. This, it is hoped, will be made clear by the following diagram. Let us suppose ourselves looking down on a beam united as proposed, by placing the ends one over the other and bolting them together. Our view then would be that represented in Fig. 86. Fig. 87 shows the section of the lower timber on the line A b, as it would be if bored for bolts, and in this it will be seen that the fibres are totally severed at c and r>, and that the wood between the two bolt-holes cannot in any way contribute to the strength of the beam as far as its length is concerned, as it is only connected with it by its lateral cohesion. * Scantling . — The transverse dimensions of a piece of timber in breadth and thickness. Scantling is also the name of a piece of timber, as of quartering for a partition, or the rafter, pole-plate, or purlin of a roof. All quartering (the small timbers of which parti- tions are built) under five inches square is called scantling. This being understood, we return to the plan (Fig. 86), and here we shall see that, as the connection between the fibres at e and F has been severed by the bolts, the whole of the strip between them (shown in dotted lines) is rendered useless ; and as this occurs three times in the beam, the only parts left in their natural strength are those not pierced by the bolts ; and these are not fastened together at all. It is therefore necessary that iron plates should be placed over the parts to be joined, and by this means the whole may be held fir ml y together. Now the system proposed by the author for joining beams of great length is shown in the following diagrams. Figs. 88 and 89 show how a rebate is to be sunk in the one beam and a tongue left in the other. This form leaves a shoulder at c, against which the end d presses, thus affording security against compression from the ends, and preventing ail chance of the beams sliding over each other. Fig. 90 is a section showing the iron strap which forms three sides of a rectangle, the fourth being formed by a plate, which fits in the screws at the ends of the strap, and is secured by nuts. This allows of occasional tightening-up, if there should be any sagging owing to shrinking of the wood, etc. CHEMISTRY APPLIED TO THE ARTS.— VII. BY GEORGE GLADSTONE, E.C.S. SODA. Sodium (chemical symbol Na, from the Latin word Natrium), which is the metallic base of soda, is one of the commonest substances in Nature ; though it never occurs as a metal, because it immediately takes fire in the air, in consequence of its great affinity for the oxygen of the atmosphere. What is most generally known as soda is a compound with carbonic acid. Another most familiar combination is that with chlorine, forming the common table salt. A third, which is not uncommon in Nature, and which is also largely manufactured, is produced by sulphuric acid, forming sulphate of soda, or Glauber’s salts. The other preparations of soda are of minor importance. It is the carbonate of sodium (Na 2 C0 3 ) with which we are specially to concern ourselves, as it is manufactured on a very extensive scale, employing a large number of hands, and con- tributing greatly to the prosperity of certain districts in Eng- land and Scotland. The borders of the river Tyne, below Newcastle, may be considered the head-quarters of the manu- facture in England, though there are also some large works near Liverpool. In Scotland the principal establishments are situated in the neighbourhood of Glasgow. Great changes have taken place in this branch of trade, and many of the sources of supply whi,ch were much valued formerly are now comparatively neglected. The plants which thrive on the sea-beach used to be collected and burnt for this purpose, as their ash contains a considerable per-centage of soda ; and some kinds of sea-weed are also treated in the same way. In addition to the home supply from our own coasts, it used to be imported from France, Spain, the Canary Islands, and other places, under the name of barilla. It is now, however, made almost exclusively from other articles, very different in their character, and which can be obtained in almost unlimited quantities. Common salt, sulphur, limestone, and coal are now the principal ingredients; and all these are, fortunately, very abundant in Nature. The sulphur is by far the most expensive, as it has for the most part to be imported from abroad, but the sources from whence it is obtained are multiplying so rapidly that the manufacturers can depend upon a regular supply at a much more reasonable price than formerly. Until very recently, the sulphur used in this country came almost exclusively from Sicily, and the supply with difficulty kept pace with the in- creasing demand. This led to the substitution of pyrites, a mineral consisting of sulphuret of iron or copper, the price of which was so much lower as to be more economical. Pyrites are now brought in very large quantities from Ireland, Spain, Portugal, and Norway, to Newcastle, Liverpool, and Glasgow, in order to furnish the great chemical works at these places with this necessary ingredient. j Common salt (the chloride of sodium) is the article from CHEMISTEY APPLIED TO THE AETS. 331 which the soda of commerce is made. The first step is to convert it from a chloride to a sulphate. This may be done by roasting the salt in a furnace, along with sulphuric acid, by which means the chlorine is driven off and the sulphur takes its place. For this purpose a reverberatory furnace is used, fitted with shallow pans lined with lead, into which the salt and acid are put, and over which the fire from the furnace passes. The pans are charged with equal weights of salt and sulphuric acid of specific gravity 1'45, which are well mixed up by means of a rake, and then the door is closed and the furnace heated. About an hour’s roasting will suffice to convert the salt into the sulphate of soda, so that the same furnace will serve for several charges in the course of the day, turning out 91 tons of the sulphate to every 8 tons of salt. During this process the chlorine has been driven off, but the manufacturer cannot allow it to escape into the atmosphere by the chimney, because, in the first place, it is of value, and, in the second, it would be a serious nuisance to all his neighbours ; the gas, therefore, is made to pass through condensers — high chambers, through which a shower of water is continually falling; tho water absorbs the gas as it rises from below, and forms hydrochloric acid. The furnace is often arranged with a lofty chamber or tower between it and the condenser, in which limestone or baryta is placed, for the purpose of absorbing a part of the chlorine, and producing chloride of lime or barium, as the case maybe; the former being used as bleaching powder, and the latter as a white paint. By these various means scarcely any of the chlorine is lost, and the profits of the soda manufacturer are considerably enhanced. The sulphate of soda has now to be converted into the carbonate. For this purpose it is roasted with about an equal quantity by weight of carbonate of lime, and one-lialf its weight of coal, in a reverberatory furnace. These substances are generally broken up small, and well mixed together, and as soon as the furnace is heated to a bright red heat the charge is gradually introduced into the first compartment of the furnace. As soon as it has been sufficiently heated through, it is trans- ferred to the second, where it is subjected to a higher tempera- ture, and forms a soft doughy mass, which is kept well worked by means of long iron stirrers. During this process the mass evolves carbonic acid, and as soon as the gas has all passed off, and the contents of the furnace assume a tranquil liquid condi- tion, they are raked out of the furnace and allowed to cool. The substance which results from this treatment is commonly called ball soda. It will be seen from this description that a considerable amount of manual labour is necessary at this stage of the process ; and the success of the operation greatly depends upon the charge being well worked by the stirrers while it is in the furnace — very hot and laborious work. A very interesting arrangement is adopted in some of the best alkali works, in order to avoid tho stirring altogether. The furnace itself is made to rotate, and as it turns the ingredients become thoroughly and uniformly mixed. The part which receives the charge consists of a long iron drum, turning horizontally upon its axis — the flue passing through the two axes — and having a door in the circumference, which serves both for charging and discharging it, according as it is brought to the uppermost or lowermost part of its circuit. The charge passes in through a hopper, the aperture is closed, and the furnace is made to re- volve. When the roasting is complete, the door is opened, and the charge passes out into receivers placed below. The ball soda thus prepared consists of porous lumps, of a dirty grey colour, composed principally of carbonate of sodium, sulphide and carbonate of calcium, and carbon. This, when reduced to powder, is sold, and exported in considerable quan- tities, under the name of black ash. The balls will ‘fall to pieces of themselves by merely damping them with water and exposing them to a high temperature. Carbonate of sodium is very readily soluble in water at any temperature, though hot water will take up much more than cold. Advantage is taken of this circumstance in order to separate the carbonate of sodium from the other ingredients contained in the ash. A series of cisterns, each one at a slightly lower level than the preceding, are therefore filled with the black ash, and water is made to pass gradually through them, taking up more and more of the soda as it passes along, until it is fully saturated, and the ash is quite exhausted. It is generally found convenient to keep the water at a temperature of something over 100° Fahrenheit. Having thus obtained an aqueous solution, the water has to be evaporated, so as to separate the soda in a solid state. The evaporation of so large a bulk of water involves the expenditure of a great amount of heat, so that, as a matter of economy, the waste heat as it passes from the balling furnaces is ordinarily made to serve this purpose. Various forms of evaporating pans or troughs are used, and in some works the crystals as they form are raked out by manual labour, while in others machinery is adopted for this purpose. The soda thus obtained contains generally about 70 per cent, of carbonate, 15 per cent, of the hydrate, and 6 per cent, of the sulphate. In order to free the carbonate from the other compounds, the ash is again heated in a reverberatory furnace, with a little saw- dust or small coal. Care must be taken not to heat it so highly as to cause the ash to fuse, which would entirely defeat the object ; and during the process the ash must be kept well stirred. By this means the sulphur is driven off, and at the same time the excess of carbon, after having converted both the sulphate and caustic soda into the carbonate. If white alkali be required, the soda, after coming out of the carbonating furnaces, is again dissolved by means of steam, and then allowed to crystallise out on cooling. In this state soda is used in various manufactures, such as in soap-boiling and plate-glass making. For other purposes, however, it must be still further purified. To produce what are commonly known as soda crystals, the white alkali is again dissolved in boiling water, and then either filtered or transferred to iron tanks, where the liquor is left to settle for about twelve hours. If necessary, the latter opera- tion is repeated a second time, and a little lime is added, to assist in throwing down the remaining impurities. It is boiled until it attains a specific gravity of l - 3, and then left to stand until the temperature falls to 92° Fahrenheit, when it is run out into large cooling-pans to crystallise. Upon the surface of the liquor in these pans bars of wood are placed, which con- stitute a nucleus for the formation of the crystals. Attaching themselves in the first instance to the wood, they grow down- wards into the liquor, forming beautiful masses of large pointed crystals. In the course of from five to ten days, according to the season of the year, the liquor is exhausted as far as is possible by this means, and being drawn off, it is evaporated down, so as to preserve the residue, which forms an inferior white alkali. The soda crystals are almost pure carbonate of sodium, with ten equivalents of water of crystallisation (Na 2 C0 3 + 10H„O) ; or, in round numbers, about 37 per cent, of carbonate of sodium and 63 per cent, of water. This is as pure as it can be made in such large quantities as are required in commerce, and, accordingly, tho description of the manufac- ture of the carbonate of sodium stops at this point. Caustic soda is also made now on a considerable scale at the chemical works, as there is an increasing demand for it on the part of bleachers and soap-boilers. It is the hydrate of sodium (NaHO), and is made from the black ash, or soda ash, already described, by dissolving it in sufficient water to produce a liquor of a specific gravity of about IT, which is then put into a large vessel, and stirred actively while lime-water is being gradually added to it. After about half an hour it is left at rest, the decomposition having been completed ; and the lime, having taken up the carbonic acid of the soda, is gradually deposited in the condition of carbonate of lime at the bottom of the receiver. The soda liquors, being drawn off into boilers, are then concentrated, during the several stages of which process the sulphate, chloride, and other impurities crystallise out, and are removed by perforated ladles. The remaining liquor is finally boiled down until it is thoroughly concentrated, and is then left to cool, when it becomes solid. For some purposes the caustic soda is sold in the liquid state ; and in this case the boiling is stopped when the solution has been raised to a specific gravity of about 1'35, at which strength it retains its liquid condition on cooling. This is commonly called soaper’s lye. Bicarbonate of sodium, or the acid carbonate (NaHC0 3 ), may be prepared from the neutral carbonate already described, by filling a chamber with the soda crystals, and then passing carbonic acid gas through it. The gas may be generated by decomposing chalk or limestone (carbonate of lime) with 332 THE TECHNICAL EDUCATOR. hydrochloric acid, the chlorine combining with the lime and freeing the carbonic acid. In the course of ten to fourteen days’ exposure to the action of this gas, the soda crystals will have taken up a second equivalent of carbonic acid, and thus have become a bicarbonate. It will be seen, by a comparison of the chemical formulae, that the relative proportion of the carbonic acid to the soda is double that given above for the carbonate of sodium. The - bicarbonate is then gently heated for the purpose of drying it, and ground to a fine powder. Care must be taken not to make it too hot, or the carbonic acid will be driven off again, and it will be reduced to a carbonate. Soda-works must always be situated in places where salt, sulphur, limestone, and coal can be obtained on favourable terms, and also where there is plenty of waste land for depositing the refuse. The quantity of this is so great that large mounds of it are always to be seen in the neighbourhood of the works, and it would be greatly to the advantage of the trade if a means of utilising it could be found. The pyrites, now so largely used, consist of the sulphurets of iron and copper, and the latter metal is frequently in sufficient quantity to be worth extracting. Copper- works are accordingly rising side by side with the soda-works, and are usually carried on in conjunction with the latter, no less than 7,600 tons of copper having been made in 1869 from the pyrites used in the manufacture of soda. This represents one-eighth of the whole quantity of copper smelted annually in this country, and fur- nishes one instance amongst many of how one industry reacts upon another. PRACTICAL PERSPECTIVE— II. Fig. 7. — The object of this illustration is to show that all lines which in Nature are at right angles to the plane of the picture must in the drawing converge to the centre of vision. But little argument will be required to convince the student of this. He will have noticed how the metals on a railway seem to meet in the distance, and how the two sides of the pavement of a long street converge : he can, in fact, scarcely cast his eye around without being impressed with this fact. Fig. 8. — It will be clear then, that as a line which is at right angles to the plane of the picture is drawn to the centre of vision, any point which moves away from us, in a straight line from the foreground to the distance, will travel in such a line. The student who has followed the course laid down in other lessons in this work, will have learnt how to construct scales of different proportions ; but to others it will be necessary to explain, that as but few objects are drawn of their real size, a method is adopted by which their different parts, etc., shall be kept in a certain proportion to those of the object itself ; this is called “ drawing to a given scale.” Thus, if it is said that an object is drawn to the scale of “ 1 inch to the foot,” it is meant that whatever is 1 foot long in the object is represented by 1 inch in the drawing, and thus the representation will be one-twelfth of the real size. Now in Fig. 8 the scale adopted is f of an inch to the foot. The eye of the spectator is supposed to be 5 feet above the ground, and 11 feet distant from the picture. To represent this — Draw the picture-line, p L, and the horizontal line, H L, at 5 feet (that is, § of an inch) above it. Place the centre of vision, c, anywhere (in this case) on the horizontal line. The spectator is to be 11 feet distant; therefore set off 11 feet on each side of c, and the points of distance, p d, will be thus obtained. Now let it be required to find the perspective position of a pointy which is 9 feet on the left side of the spectator, and 2 feet back ; or as it is called, 2 feet within the picture. Whenever a point in the distance is tc be found, it is neces- sary, in the first instance, to ascertain its exact place in the foreground ; thus, having drawn the perpendicular, c A, set off from A, 9 feet along the picture-line ; then a' is the position of the point at 9 feet on the left of the spectator; but as yet- it is in the foreground, not back in the picture. Now it will be clear, that as this point moves directly back- ward, it will travel in a line at right angles to the picture-line, and that stfch a line will vanish in the centre of vision. Therefore, from a' draw a line to c, which will be the perspec- tive representation of a line running directly backward into the distance. But it is required that the point in question shall be not only 9 feet on the left or the spectator, but 2 feet within the picture. To find its position, then, set off 2 feet on the right ®f a' — viz., point 2 ; and .rom 2 draw a line to the point of distance, p D. Then 2' will be the required position of the point — viz., 9 feet on the left of th j spectator, and 2 feet within the picture. Now let it be required to find the perspective position of a point which is 9 feet on the left of the spectator and four feet within the picture, This is simply the same point, which is supposed to have travelled 2 feet farther back ; therefore, from a' set off point 4 (that is, two feet added to the former 2), and draw a line from 4 to the point of distance ; then 4' will be the perspective position of the point. Proceed in the same manner to find the position of the same point when it has travelled 6 and 8 feet backward, and thus obtain points 6' and 8'. Fig. 9. — Now let it be required to find the position and appa- rent height of a perpendicular, the real height of which is 12 feet, when it stands at 9 feet on the right of the spectator, and 2 feet within the picture. At b, 9 feet on the right of A, draw a perpendicular, b d, 12 feet high by scale ; and from the top and bottom of it draw lines to the centre of vision. This would represent a wall or plane extending from the foreground into the distance. Now it is clear that the required perpendicular will be some- where in this plane ; the question is, where ? This is solved by the application of the last study. Set off from B 2 feet along the picture-line — -viz., point 2 ; from 2 draw a line to the point of distance, and this line, cutting b c in 2', will give the position of the line. At 2' draw a perpendicular meeting the hue d c, and this will be the line required — which, it will be observed, has diminished, because it is a little distance back in the picture. Proceed in the same manner to find the position of the same perpendicular when it is at 4, 6, and 8 feet within the picture. Exercise 1, The height of the spectator is 6 feet, the scale being | of an inch to the foot ; the distance of the eye is 13 feet. Find the positions of the following points : — (1.) 11 feet on the right of the spectator, and 3 feet within the picture. (2.) 8 feet on the right of the spectator, and 6 feet within the picture. (3.) 10 feet on the left of the spectator, and 7 feet within the picture. (4.) 3 feet on the left of the spectator, and 12 feet within the picture. Exercise 2. The spectator is 5 feet high, and 15 feet distant from the picture. Find the position and perspective heights ef the following perpen- diculars : — (1.) 8 feet on the left of the spectator, 10 feet high, and 3 feet within the picture. (2.) 12 feet on the left of the spectator, 11 feet high, and 6 feet within the picture. (3.) 13 feet on the right of the spectator, 12 feet high, and 10 feet within the picture. (4.) 11 feet on the right of the spectator, 4 feet high, and 8 feet within the picture. Now this study will show the method of solving a question which has often been given in examinations — namely, that of finding the position of a bird flying at a certain distance from the spectator, and at a given height. Let us suppose the measurements to be these : — Distance on right of spectator, 9 feet; height from ground, 12 feet; distance back in the picture, 20 feet. Now it will be clear to the student that if a bird flying held in its talons a line with a weight at its end, such line would be a true perpendicular to the ground, the bird being at its upper extremity, and thus the whole question resolves itself into this : Put into perspective a perpendicular 9 feet on the right of the spectator, 12 feet high, and 2 feet within the picture. To do this we simply return to Fig. 9. Here we have already drawn a perpendicular, b b, at 9 feet on PRACTICAL PERSPECTIVE. 333 the right of the spectator, and 12 feet high, and we have drawn lines from its extremities to c. It now only remains to set off 20 feet along the picture-line from b, namely, b 20, and from 20 draw a line to the point of distance. This will give the point 6, which is the position of the perpendicular to be drawn on b to meet d c in c. Then c is the position of the bird, as required. Fig. 10. — It is not necessary in every case to show both the points of distance ; thus, as in this study— a line on the right side of the spectator — we can dispense with the left-hand point of distance. Here the height of the eye of the spectator is 6 feet (| scale), and his distance 16 feet. The subject of this study is a line which lies at right angles to the plane of the picture, at 12 feet on the right of the spec- tator, and 4 feet back in the picture, the length of the line itself being 6 feet. From A, the point immediately under the centre of vision, set off 12 feet, namely, to b, and draw a line to C. From b, towards A, set off 4 feet, namely, to c', and draw a line to the point of distance. This will give the point c. From c' set off 6 feet on the picture-line, namely, to d, and draw a line from r> to the point of distance, cutting b c in d. Join c d, and this will represent the line in the perspective position required. Exercise 3. The height of the spectator is 5 feet, and his distance 15 feet (scale, 5 inch to the foot). Give the perspective projections of the following lines, lying at right angles to the picture-plane : — (1.) 7 feet long, at 10 feet on the left of the spectator, and 2 feet within the picture. (2.) 9 feet long, 6 feet on the left of the spectator, and 4 feet within the picture. (3.) 1C feet long, 7 feet on the right of the spectator, and 6 feet within the picture. (4. ) 8 feet long, 6 feet on the right of the spectator, and 2 feet within the picture. Fig. 11. — The scale in this study is | of an inch to the foot. The height of the spectator is 6 feet, the distance 16 feet. Here a line, b c', 8 feet long, lies in the immediate fore- ground, the end b being 6 feet on the left of the spectator. It is required to put this line into perspective when lying at 2, 5, and 7 feet within the picture. From b and o' draw lines to the centre of vision, and as the line b c' is to travel backward, but remain parallel to the pic- ture-line, it must, however it may change position, be contained | ; between these two lines. Now from b mark off b 2, b 5, and b 7, representing the distances at which the line is to be placed, From each of these points draw lines to the point of distance, cutting B c in 2', 5', and 7'. From these points draw lines parallel to c' b, and contained between b c and c' c. These will be the perspective represen- tations of the line c' b at the distances of 2, 5, and 7 feet within the picture. Exercise 4. Scale \ inch to the foot. Height of the spectator, 6 feet ; and his distance, 15 feet. Put into perspective a line 6 feet long, when lying parallel to the picture-plane, at the following distances : — - (1.) When one end is at 3 feet on the left of the spectator, and the line is 4 feet within the picture. (2.) When one end is at 4 feet on the right of the spectator, and the line is at 10 feet back. Fig. 12 shows three squares, (1), (2), (3), lying flat on the ground, their front and back lines being parallel to the plane of the picture, and their sides at right angles to it. Here the eye of the spectator is 5 feet above the ground (or picture) line, and the distance is 11 feet (g scale). The sides of the squares are 4 feet, c' and D are 5 feet on the left and right of the spectatsr, whilst F G is immediately in front. Having drawn lines from b, c' ; F, G ; and d, e to the centre of vision, between which the squares must be contained, the next question is how to find the place for the back line of each. The general method of fijiding the position of a horizontal line at any given distance has been shown in the last figure, and this could be applied in the present study — namely, by setting off from o' the distance c, equal to the length of the required side of the square, and drawing from c a line to the point of distance. This would be the method to be pursued for any rectangle ; but for a square an easier method can be found, by which the trouble of marking the point c can be saved — namely, by draw- ing a line from c' to the point of distance, which, by cutting b c in d, will give a point immediately opposite to c', and a hori- zontal line drawn from this point will complete the figure. This is again shown in Fig. 12 (2), (3). It is not really neces- sary in (2) to draw a line to each of the points of distance, but in early studies it is best to do so as an additional test of accuracy. Exercise 5. Scale | inch to the foot. Height of spectator, 6 feet ; and distance of spectator, 16 feet. 334 THE TECHNICAL EDUCATOE. Put into perspective three squares lying flat on the ground with their front and distant edges parallel to the plane of the picture. (1. ) 3 feet side, immediately in front of the spectator and in the foreground. (2. ) 4 feet side, at 5 feet on the left of the spectator, and 8 feet within the picture. (3.) 2' 6" (2 feet 6 inches) side when lying at 6 feet on the right of the spectator, and 9 feet within the picture. For Fig. 13, the height and distance of the spectator are the same as in the last figure (Fig. 12). Fig. 13 (1) is a square of 4 feet side, standing on one of its edges, its surface being parallel to the picture-plane, and its nearest angle, b, being 5 feet on the left of the spectator. As there will be no difficulty in constructing this original square, a' b d c', we can therefore at once proceed to find its position and size when removed 11 feet within the picture. From A' and b draw lines to the centre of vision. From b set off on the picture-line the length b' (11 feet), and from that point draw a line to the point of distance, cutting b c in b. At b draw the horizontal line b a, which will be the base of the square at the required distance. Now, knowing the figure to be a square parallel to the plane of the picture, we could easily complete this study by constructing a square on a b, as in Fig. 13 (2). But this method would apply to a square only, and if any other parallelogram were required, we should have to obtain the size by the following process : — At a and b erect perpendiculars of any height (temporarily). Draw lines from the upper angles c' and D of the square or other parallelogram to the centre of the picture; then these, cutting the distant perpendiculars, will give the points c, d ; and these joined will complete the square at the required distance. Exercise 6. Scale, | inch to the foot; height of spectator, 6 feet; distance 18 feet. Put into perspective a square of 9 feet side, when standing with its surface parallel to the picture-plane. (1.) When in the foreground, at 7 feet on the left of the spectator. (2.) When at 5 feet on the left of the spectator, and 10 feet within the picture. Fig. 13 (3). — In this study the square is rotated on the line a" c," so that its surface is at right angles to the picture-plane. Having erected the perpendicular a' 1 c", at (say) 9 feet on the right of the spectator, draw lines from its extremes to the centre jpf vision. From a" mark off on the picture-line the length a" b' ^qual to the side of the square ; and from b! draw a line to the point of distance. This, cutting the line a" c in b", will give the point for the distant edge b" d" of the square. Fig. 13 (4) is the same figure removed to 15 feet within the picture. As the working is shown, and as the method is similar to what has already been done, it is hoped that the student will be able to obtain the required result without further instructions. Exercise 7. Scale £ inch to the foot ; height of spectator, 5 feet ; distance, 15 feet. Put into perspective the squares, the dimensions of which are given below, when standing at the stated distances ; the plane (or surface) of the square to be in every case at right angles to the picture-plane. (1.) 3 feet side, at 2 feet on the left of the spectator. (2.) 8 feet side, at 7 feet on the left of the spectator, and 6 feet within the picture. (3.) 4 feet side, at 3 feet on the right of the spectator, and 2 feet within the picture. (4.) 7 feet side, at 9 feet on the right of the spectator, and 6 feet within the picture. WEAPONS OF WAR— VI. BY AN OFFICER OF THE ROYAL ARTILLERY. BREECH-LOADING SMALL ARMS (continued). In a former paper we have treated of the transition from muzzle- loading to breech-loading rifles for military use, and have shown how this was accomplished in our own service, by the simple and satisfactory expedient of fitting the Enfield rifle with an arrangement which admitted of its being loaded at the breech, and providing it with a suitable and ingenious breech-loading cartridge. The combination gives us an arm about equal to the old Enfield rifle in shooting power, but more destructive, in consequence of the employment of a hollow bullet, and capable of greatly increased rapidity of fire. But it was clear that we had not here the final and complete solution of the question. The shooting power of the old Enfield is not of a sufficiently high character to satisfy the requirements of the present age. Since 1853, when this weapon was introduced, vast strides have been made in arms of precision ; and the Enfield rifle is now unable to hold its own against the small-bore rifles which surpass it in accuracy, range, flatness of trajectory, penetrative power, and other valuable qualities. So also with regard to the breech action : many minds have been at work on this question for several years, and the result is that there exist several breech mechanisms which are as superior to the Snider as the small- bore rifle is superior to the large bore. Therefore, it became a recognised necessity for the military authorities to look beyond their converted Snider-Enfields to a new arm for future manufacture. It would occupy too much space if we were to attempt to describe the steps and experi- ments which have finally resulted in the adoption of a composite arm — the Martini-Henry rifle. This arm has the form of barrel designed by Mr. Alexander Henry, of Edinburgh — viz., a poly- gonal barrel, the angles of which are broken by ribs which create re-entering angles, the inscribing circle tangential to the ribs being described with the same radius as the inscribing circle tangential to the plane sides. The twist of rifling is 1 turn in 22 inches. The calibre is -45 inch. Admirable results have been obtained with these bar.rels, which are now very generally adopted by military rifle-makers, who fit on to them different breech-actions, according to their fancy. The initial velocity of the rifle, with a charge of 85 grains, is about 1,365 feet per second, against 1,250 for the Snider; this, taken in conjunction with the fact that the bullets are of the same weight (480 grains), but that the Henry bullet is of less diameter than that of the Snider, results in a considerably flatter trajectory on the part of the Henry bullet, in greater range and in greater accuracy. Also, the Henry bullet is less affected by wind. What breech-action should be fitted to this barrel to render it a perfect arm ? This question has given rise to immense dis- cussion and to innumerable experiments. Mr. Henry himself had a breech-action of great merit, which some persons thought it would be well to employ. But the question was directed to be settled experimentally, and the result of the experiments was that the Henry breech mechanism had to yield the palm to a mechanism designed by Mr. Martini, a naturalised Swiss subject. This action is best described by the drawings given in page 336. The action consists, as will be observed, of a falling block, hinged upon a pin which passes through its rear end, the recoil being taken by the iron framework at the back. Inside this block is situated the striker, by means of which the cartridge is exploded, and the strong spiral spring by means of which the striker is actuated. The block is raised and lowered by a lever, which in the act of lowering the block also compresses the spring, thereby bringing the rifle to full cock; and the front end of the block striking smartly upon the bent lever, the extractor ejects the empty cartridge. When the fresh cartridge has been introduced, the block is returned to its place by the return movement of the lever, and the arm is ready for firing •, or, if it be not desired to fire it immediately, there is a small safety-bolt, easily manipulated by the fore-finger and thumb, which serves to lock the arm and prevent it from going off. Also, the gun is provided with an “indicator” at the side, to show when it is cocked. The indicator, being attached to the “tumbler,” moves with it and parallel to it; and as the arm cannot be cocked unless the tumbler be in a certain position, the indicator shows infallibly its condition. The tests which the Martini-Henry breech-action has under- gone have been extraordinarily severe, although scarcely more so than the criticism to which it has been subjected. This criticism has, however, had this good effect : if it has some- what interfered with the early adoption of this arm, by ren- dering necessary continued trials, it has, through these trials, fully established the extraordinary merits of the breech-action. At first the objection was urged that, although one or two show specimens, prepared specially for trial, might succeed in satisfy- ing such tests as the Committee were able to impose, the arms, if placed in the hands of the troops, would certainly break down. To meet this, 200 Martini-Henry rifles were issued to the troops, who for about a year and a half had them under WEAPONS OE WAB. 335 trial. The result of these trials, carried on in all climates, from India to Canada, in all weathers, and under all sorts of circumstances, has been to elicit most favourable reports of the arm. Then it was urged that at any rate the arrangements of the breech were mechanically defective ; that no mechanical engineer could have any doubt on this point ; that a mechanism radically unmechanical could not continue to give reliable and satisfactory results. Accordingly, the evidence was taken of three very eminent mechanical engineers — Professor Pole, Mr. Nasmyth, and Mr. Woods. These gentlemen, instead of pro- nouncing a condemnation of the mechanism, declared that it is an excellent piece of work, and passed high encomiums on its simplicity, strength, and efficiency. The criticism that as the recoil is taken by the breech axis pin, that pin must neces- sarily wear away or break in time, they met by the statement that the recoil is not taken by the pin at all, but by the socket behind the block, whence it is transmitted through- out the whole system of the rifle, the weight of which is thus brought to resist it; and this statement they supported by reference to a very simple experiment, in which the block axis pin had been replaced by one. of lead, on which no mark of any recoil was perceptible. In another instance the gun was worked perfectly without any pin at all. The spiral spring has been a prominent point of attack. It has constituted, so to speak, the citadel of the system, and against it all the main efforts of the opponents of the arm have been directed. One inventor of a rival breech-action based his claim mainly on the substitution in his system of a flat for a spiral spring. This objection the mechanical engineers met very decidedly. For the purpose for which it is required in this gun — viz., to cause a striker to impinge directly upon the percussion-cap of a breech-loading cartridge — they greatly preferred the spiral to the flat spring. It is far cheaper — as a halfpenny to sixteen-pence — it admits of a far more compact arrangement of parts ; it is, notwithstanding all that has been said to the contrary, quite as reliable as a flat spring — a point which they supported by quoting various well-known applications of spiral springs ; it is quite as easy to make of uniform quality in large quantities ; and as for the statement that the spiral spring gives more of a push than a blow, one witness showed mathematically that the blow which is struck by the spiral spring in the Martini-Henry is really a quicker, smarter blow than is struck by the hammer of the Snider. As to the merits generally of the spiral spring — the point which inventors of other systems have declared to be fatal to the Martini — all the mechanical witnesses agreed in pronouncing it thoroughly mechanical, sound, and reliable. Then it has been objected that the divided stock is weaker than the ordinary gun-stock. Not so, say the engineers ; it is rather stronger ; and if desired it can be made stronger still. Nor is this mere theory. They appealed to the results of an experiment which was carried out at Enfield in their presence to test this point. And so, before the independent testimony of thoroughly competent, indeed, distinguished witnesses, the criticisms which have been freely indulged in by those who have rifles of their own which they would prefer to see intro- duced, have melted away. Whether the criticism will therefore cease it is not easy to say; probably it will not. But the readers of these papers at any rate will have the assurance that the future arm of the British soldier, whatever may be said about it, has undergone tests and trials to which no other weapon was ever submitted ; that it has passed one ordeal after another not merely satisfactorily, but triumphantly — the ordeal of the rigorous trials which were instituted by Lieut.-Colonel Fletcher’s Committee, the ordeal of knocking about and hand- ling by the troops, the ordeal of two public trials at Wimbledon, where the arm carried off the greater part of the more impor- tant breech-loading prizes ; the ordeal of public criticism ; finally, the ordeal of a minute scrutiny at the hands of professional mechanics. If an arm can stand all this, and come out un- scathed, as the Martini-Henry has done, it is surely a fit arm to put into the hands of our troops. This, then, is the future weapon of the British soldier — the Martini breech allied to the Henry barrel. The cartridge to be used with this arm is the Boxer, but of a form different from that in use with the Snider. The first cartridges made for the Martini were very long, the small diameter of the barrel and the large charge of powder render- ing necessary this length so long as the cylindrical form of cartridge was retained. To this cartridge objections were made on account of its length. Accordingly the form was modified, the substantial features of the Boxer construction being re- tained. In the modified cartridge the body is enlarged in dia- meter, and tapered down at the fore-part to the diameter of the bullet. The outline of the cartridge is thus that of a long- necked bottle, whence the name by which it is frequently known, the “ bottle-neck ” cartridge. A drawing of this “short- chamber ” cartridge, as it is officially designated, shows the details of the construction, and it will be observed, on a com- parison of this drawing with that given in a former paper (page 272) of the Boxer cartridge for the Snider, that the construction of the two cartridges is practically the same. There is the thin coil-case, the iron disc base, the strengthening cup, the papier- mache wad by which the parts are held together, the cap and anvil arrangement for ignition. But the fore-part of the cartridge is different ; the mode of lubricating is different ; the bullet (which is Mr. Henry’s) is different; the cartridge is not covered with paper; and the base is strengthened by means of the insertion of a piece of tin between the folds of the brass, thereby obviating the necessity for additional strengthening cups. A few words may be said with regard to the bullet and lubrication. The bullet is solid, with the exception of a shallow cavity in the base, into which the folds of the paper which envelops the bullet are inserted. At its back end, the bullet is of the same diameter as the bore, viz., ’45 inches. It tapers slightly, until at the shoulder the diameter is only '439 inches. In a former paper it has been explained that the main feature of the bullet for the original muzzle-loading Minie and Enfield rifles consisted in the arrange- ment by which the bullet was expanded into the rifling, by the explosion of the charge acting upon an iron cup, or a wooden plug in a hollow at the base. Thus the bullet entered the rifle fitting loosely, and left it fitting tightly. In a breech-loader, however, there is no necessity for having a bullet which will enter the barrel easily, as it is, generally introduced into a chamber at the breech end, and may be made in the first in- stance of the full requisite diameter. We have seen, however, that Colonel Boxer in his bullet for the Snider did retain the plug expansion, with a view partly to getting the requisite length of bullet in a large-bore rifle without any undue in- crease of weight. But in the Henry rifle no such device is necessary, and Mr. Henry therefore made his bullet of the full diameter of - 45 inch, depending upon such slight enlargement as the bullet received by the opposition of its own inertia to the shock of discharge, to take up the rifling. The action of Mr. Henry’s bullet therefore depends upon what is known as the “ overtaking ” principle, the back end of the bullet slightly overtaking the fore end, owing to the inertia of the mass in front, and thereby setting up, and expanding the bullet into the grooves. The lubrication of this rifle is effected by means of a cylin- drical wad of pure bees’-wax, placed behind the bullet, and en- closed in discs of jute cardboard, to prevent it from striking either to the bullet or to the powder. This wad was originally made solid, but it was found not to act perfectly in very cold weather, and it was therefore thickened and hollowed out in front, thus giving more space for the powder to act through, and less work for it to do. The wad is squeezed between the exploded powder charge and the bullet, and just as the bullet is set up and enlarged, so the wax wad is set up and enlarged, although of course to a far greater extent, and as it is driven through the bore, lubricating it effectually. It remains now only for us to say a few words with regard to the powers of the Martini-Henry rifle, using the ammunition above described. The accuracy of shooting of the arm is re- markably great. The following facts extracted from official records are satisfactory upon this point. At 300 yards, the mean radial deviation of 20 shots fired from a fixed rest, has been as good as '47 feet ; at 500 yards, '79 feet ; at 800 yards, 1’29 feet; at 1,000 yards, 2T9 feet; at 1,200 yards, 2 - 28 feet. Perhaps these figures will scarcely convey to all our readers the impression which they would make upon the mind of any one who is familiar with the mode of estimating “ figures of merit” in rifle-shooting, namely, to find out by calculation the centre of each group of 20 shots, and to find the mean distances of these shots from this centre. Obviously, the smaller this distance, the smaller the limits of the group, and the more ac- 336 THE TECHNICAL EDUCATOE. curate the shooting. When a trial was recently made between the Snider, the Chassepot, and the Martini-Henry, the following results were obtained : — Martini-Henry. Snider, Chassepot. 500 yds. .... '315 feet. 1'47 feet. 2'77 feet. 800 „ 1'57 „ 3 '78 „ 5'22 „ 1,000 3'66 „ 8 '34 „ 13 '08 „ Putting this into a popular form of expression, it means that, if we take the Martini-Henry as a standard, as equal to 100, we have the following comparison — At 500 yds. At 800 yds. At 1,000 yds. Snider = 55'4 41'5 43'9. Chassepot = 29'4 30'0 28'0. Or, expressing it moro roughly still, we have the following tabular comparison of the performances of the rifles, namely: — At 500 yds. At 800 yds. At 1,000 yds. Martini-Henry to Snider, as about 2 to 1 2| to 1 2| to 1. Chassepot, ,’, ,, ,, 3 to 1 3 to 1 3 to 1. Let us now turn to the trajectory of the arm. It is obvious it will be observed that the Chassepot bullet has a slightly higher initial velocity than the Martini-Henry, but the bullet being lighter (380 against 480 grains) it has less power to over- come the resistance of the air, and therefore soon loses this higTi velocity. At 150 yards from the muzzle, or even at a less distance, the Martini-Henry bullet will be travelling with a velocity equal to that of the Chassepot, and from that point forward the latter will gradually be losing in the race. The effect of this high velocity, combined with a good weight and a small diameter, is to give the Martini-Henry bullet great penetrative power, as well as that low trajectory which has been spoken of. It has been found by experiment that the bullet will penetrate as follows : — 14| half-inch elm planks at 100 yards ; 3 three-inch fir balks dry, in addition to 1 wet, at the same distance ; 1 plate of - 261 inch iron at 200 yards ; 4 thicknesses of 3-inch rope at 350 yards ; a gabion filled with clay earth at 25 yards ; a sap roller at 25 yards ; a sand-bag at 100 yards. While the normal accuracy of the Martini-Henry rifle is far Fig. 7. BOXER-HENRY CARTRIDGE, ELEVATION. Fig. 8. BOXER-HENRY CARTRIDGE, SECTION. Fig. 9. SECTION OP BREECH OP MARTINI-HENRY RIPLE, OPEN. Fig. 10. SECTION OF BREECH OF MARTINI-HENRY RIFLE, CLOSED. Hefs, to Letters in Figs.— Pig. 9, 10 :— a, barrel; b, body of breecli -acti on ; c, block; d, main-spring; e, striker; f, block axis pin; g, stop nut ; h, extractor ; i, extractor axis pin ; j, pin for barrel stud-hole ; k, trigger and rest spring screw ; l, cleaning rod ; m, fore-part of stock; n, tumbler ; o, lever ; p, lever and tumbler axis pin ; Q, trigger-plate and guard ; r, trigger; s, tumbler rest ; t, trigger axis pin ; v, trigger and rest spring ; v, hind part of stock ; w, stock-bolt ; x, stock-bolt washer ; y, lever catch-spring ; z, lever catch-block and pin; a, locking bolt ; 5, locking bolt thumb-piece; c, thumb-piece screw ; d, locking bolt-spring. that the flatter an arm shoots— in other words, the lower its trajectory is — the more ground will the bullet cover in its flight. The greatest height of the trajectory of the Snider is 1T9 feet in 500 yards ; of the Martini-Henry only 8'9 feet. The practical effect of this is that, supposing two men to be firing, lying on the ground, and aiming at the feet of a body of troops 500 yards distant, a body of infantry might safely cross the Snider range anywhere between 92 and 438 yards, the bullets flying over their heads, while in only from 139 to 396 yards would they be safe in the Martini-Henry range ; and as for cavalry, while on the Snider range from 138 up to 400 yards they would be safe, there would on the Martini-Henry range be no spot which a cavalry soldier could pass in safety. Beyond 500 yards the advantage of the Martini-Henry rifle in respect of trajectory would be increasingly greater. The next point is initial velocity — : the velocity, that is to say, at which the bullet leaves the muzzle. This is as follows : — Martini-Henry 1,365 feet per second. Chassepot . u ..... . 1,391 „ Snider . . » 1,262 „ ! greater than that of the Chassepot and Snider, and enormously superior to that of the needle-gun, which is by far the worst arm of the four, the Martini-Henry bullet is less affected by wind — a great advantage to the marksman. The cartridge is stronger and better than that of the Chassepot. The rapidity of fire is more than double : thus, at an official trial — The Chassepot fired 20 rounds in 1 minute 42 seconds. The Martini-Henry „ 0 „ 48 „ Thus in seven points — namely, (1) increased strength and safety of ammunition, (2) greater accuracy, (3) longer range, (4) flatter trajectory, (5) higher penetrative power, (6) greater safety, strength and simplicity of construction, (7) increased rapidity of fire — the Martini-Henry is much superior to the Chassepot. It is also, although in a less degree, superior to the Snider on most of these points. Such is the weapon with which the British soldier will in future be armed. This brings to a close our remarks on Small Arms. In our next article we shall pass to the subject of Great Guns, which we propose to treat in an equally exhaustive manner. VEGETABLE COMMERCIAL PRODUCTS. 337 VEGETABLE COMMERCIAL PRODUCTS.— XI. TEXTILE PLANTS, OR PLANTS PROM! WHICH WE DERIVE clothing and cordage ( continued ). The value of cotton in commerce depends on the length and strength of the silk or staple. Cottons may be divided into the long silk and short silk. The United States generally furnish the short silks in the greatest quantity, with the exception of one sort, known as the Georgia long silk, or Sea-island cotton, of which the production elsewhere is very limited. Cotton threads are numbered from 1 to 300, according to the degree of fineness to which they are spun. In weaving, the cross threads or woof are shot by the machine across or at right angles to threads extending longitudinally, called the warp. Long silk cotton is generally spun into the threads for the warp, and the short silk is used for the woof. The chief seats of the cotton manufacture in the United Kingdom are Manchester, Bury, Oldham, and Glasgow. Most of the many thousands of cotton-mills give employment to from 50 to even 1,500 hands, presenting the most perfect order in every department. All these persons are employed by means of the fine white silky hairs with which the Creator has clothed ported to Europe. The yarn on reaching this country is manufactured into ropes, door-mats, and floor-mattings, which are far more durable than those made from bristles. In India, coir-fibre is very generally used for ship-cordage and fishing-nets. In 1850 about 10,661 tons were imported into London and Liverpool, chiefly from Ceylon and Bombay. Carludovica Palmata, L. and P. (natural order, Pandanecs), — This species of screw pine is terrestrial, and bears fan-shaped glabrous leaves from six to fourteen feet long, and four feet in breadth. It ranges from 10° N. to 2° S. latitude on the Ameri- can continent. Panama hats, which are distinguished from all others by con- sisting of a single piece, as well as by their durability and flexi- bility, are so named because they are shipped through Panama, though a large proportion are manufactured in Guayaquil, Ecuador. The finest hats are made in South America with fibre of the unexpanded leaf, called “ torquilla,” from which are also made very fine hammocks. The leaves are gathered before they unfold, all the ribs and coarser veins are removed, and the rest, without being separated from the base of the leaf, is reduced to shreds. After having been exposed to the sun for a day, and tied into a knot, the the seed ot the cotton plant, in order to effect its dispersion, straw is immersed into boiling water until it becomes white; it and which the ingenuity and skill of man now manufactures ; is then hung up in a shady place, and subsequently bleached for into clothing for many millions of the human race. Jute, or Gunny Fibre, is the produce of Cor chorus capsularis, L. (natural order, Tiliacece), an annual, growing from twelve to fourteen feet high. The fibre which is contained in the bark is generally about eight feet in length, and is obtained by treatment . very similar to that adopted with the flax and hemp plants. Jute fibre is fine, and has a remark- able satiny lustre, so that it is sometimes mixed with the silk in the fabrication of cheap satins, and is very difficult to detect in the goods. It3 chief use, however, is for making coarse canvas, or gunny, as it is called in India. Rice, oil-seeds, dye- stuffs, cotton, and sugar, are all sent to us from India in gunny bags or bales. When wet, jute fibre quickly rots, so that it is not adapted for the manufacture of either sail-cloth or cordage ; but notwithstanding this, it is often mixed with'hemp for the latter. The quantity imported in 1868 was 2,182,521 cwt. New Zealand Flax ( Phormium tenax, Forst. ; natural order, Liliacea}). — A coarse growing plant, with long narrow leaves, the slender fibres of which glisten like silk, and are white as snow. Its flowers are of a brownish-red colour, and not at all ornamental. This plant inhabits the marshes of New Zealand, but grows well in any soil ; and in mild climates, such as the south of France, winters in the open air. It affords a fibre of great strength, stronger than hemp, which is extracted by maceration, drying, and heckling, as in the case of the other products. Good ropes can be made from the coarser, and very fine linen from the finer fibres. The quantities imported are at present inconsiderable, owing to the circumstance that the strength of the fibre is injured by maceration. No machinery has yet been contrived which can approach or even imitate the dexterity of the native women in separating the fibre from the coarser parts. New Zealand flax fibre will not bear a cross strain, and therefore cannot be tied into a knot without breaking. Coir-fibre ( Cocos nucifera, L. ; natural order, Palmacece ). — This fibre is obtained from the outer husk of the cocoa-nut. It is strorger than hemp, and more capable of withstanding the action of water. It is separated from the husk by beating, and then cleaned by heckling in the usual manner. The coir-fibre thus procured is spun by the natives of India and Ceylon into yarns of different length and thickness, which are largely ex- 22— Vol. I. LEAF OF THE CASTOR-OIL TREE. two or three days. The straw (paja) is now ready for use, and in this state is sent to different places, where the Indians manu- facture from it hats, hammocks, and those beautiful cigar-cases which cost as much as five and six pounds a-piece. The plaiting of the hat is done on a block, which is placed upon the knees ; it is commenced at the crown and finished at the brim. Accord- ing to the quality of the hats, more or less time is occupied in their completion : the coarser ones may be finished in two or three days, while the finest take as many months. The average export from Guayaquil has been in the past six years from 15,000 to 16,000 dozens annually, the price vary- ing from 2 to 130 dollars, ac- cording to fineness. Lately the leaves or raw material have been in demand for export, the average quantity shipped beirg about 200 to 250 ewt. annually. These hats are also made in Yeraguas, Western Panama. Costa Rica, and New Granada. The petioles of the leaf are made into baskets, called petucas, the fibre being variously dyed. Manilla Hemp ( Musa textilis, Tournef. ; natural order, Musacem ) produces a woody fibre, which is used in India in the manufacture of fine muslins ; the most exquisite textile fabrics and the elegant Manilla hats are manufactured from it. II. — OLEAGINOUS PLANTS, OR PLANTS OILS. YIELDING VALUABLE Oil is of the greatest importance in the arts. It is extensively used for burning in lamps, for diminishing friction in machinery, for making candles and soaps, in the manufacture of paints and varnishes, and in wool-dressing — five gallons of olive, rapeseed, or other oils being used in the preparation of 6very pack of wool — also as an article of food, and as medicine. Oils are dis- tinguished into two kinds : fixed or fat oils — which are obtained by pressure from the fruits or seeds of plants — and essential oils. The fixed oils burn with a clear white light, and boil at a high temperature, about 600 c F. ; most are liquid at the ordi- nary temperature, but cocoa-nut and palm oils are solid at 50° or 60° F. All the fixed oils are nearly inodorous, and lighter than water. The volatile or essential oils give off vapour at the temperature of boiling water when mixed with water, or under 320° F. by themselves. The following are a few of the most important plants which yield the oils of commerce : — 338 THE TECHNICAL EDUCATOR. (a) FIXED OILS. Palm Oil is principally produced from the fruit of Elais Ouineensis, L., a native of the western coast of Africa. The fruit is about the size of an olive, of a yellow colour, three- fourths of which consist of a yellow oily pulp. This fruit is crushed and the oil extracted from the albumen by boiling in water. Palm oil is used in England principally in the manu- facture of yellow soap, but with the Africans it is an article of food. A generation ago large tracts of country on the western coast of Africa were covered by the oil palm, then little cared for ; now a large foreign demand for palm oil has sprung up, and with it property in these trees ; and this oil trade has stopped the slave trade on the Gold coast, where it once flou- rished, and at the mouth of the Niger. The average imports of palm oil into Liverpool alone have been for several years past upwards of 18,000 tons, giving employment to 30,000 people. In 1868 the palm oil imported into the United Kingdom amounted to 960,059 cwt. Industry and a desire of accumulating pro- perty are at last manifest amongst the African population, and everywhere are now to be seen on this coast the germs of a nascent civilisation. Cocoa-nut Oil is obtained from the albumen of the kernels of the cocoa-nut ( Cocos nucifera, L.) ; it is principally used for making cocoa-stearine for candles. In Trinidad and Demerara it is used by the coolie labourers as we employ butter. The imports in 1868 were 194,752 tons, almost the whole of which came from Manilla and Ceylon. Castok-oil Plant ( Bicinus communis, L.; natural order, Euphorbiacece). — This plant, in temperate climates, is a large herbaceous annual, with palmate peltate leaves, and monoecious flowers in terminal panicles, the lower male, the upper female. The capsules are prickly, globose, three-celled, with one seed in each cell. The seeds are ovate, shining, of a grey colour, mar- bled with black. The form of the leaf is shown in the pre- ceding page. The castor-oil plant is a native of India, Africa, and the West Indies. In warm climates it acquires a woody stem, and becomes a tree, rising in India often to a height of thirty feet. Nevertheless, it is still the same plant, and not entitled to be considered as a distinct species, although a woody perennial ; the leaves and flowers are unaltered, and the seed, if sown in temperate climates, produces herbaceous plants in every respect the same as those in common cultivation. Castor oil is obtained by expression from the seeds, without heat, hence it is called “cold-drawn castor oil.” The seeds, sewn up in horsehair bags, are crushed by the action of heavy iron beaters, and the oil, as it oozes out, is caught in troughs and conveyed to receivers, whence it is bottled for use. Castor oil is brought over from the East Indies in small tin cases, closely soldered, and packed in boxes, weighing about 2 cwt. each. In 1853, 23,597 cwt. were imported into the United Kingdom. Castor oil is much used in medicine, as a mild and certain purgative. Olive Oil ( Olea Europcea, L. ; natural order, Oleacem ). — The olive-tree is a small evergreen, much branched, and covered with a greyish bark. The olive itself is a drupe or stone fruit, with a fleshy covering, about the size, shape, and colour of a damson. When ripe this fleshy covering contains an abundance of olive oil, which it yields by expression. The olive is indigenous to Palestine, Greece, and the slopes of the Atlas Mountains in Africa. It is now widely diffused in Europe, and is cultivated with great success in Italy, Spain, the south of France, Naples, Sicily, Southern Illyria, Lombardy, and Dalmatia. The olives are gathered when nearly ripe, and the oil is drawn from them by presses and mills, care being taken to set the mill- Btones so wide apart that they will not crush the nut of the fruit. The pulp is then subjected to a gentle pressure, in bags made of rushes, and the best or virgin oil flows first. A second oil, of inferior quality, but fit for table use, is obtained by mois- tening with water the residuum, breaking the nuts, and increasing the pressure ; lastly, more water is added, and the residuum is again re-pressed, the product being an impure oil, fit only for soap-making or for burning. Spanish or Castile soap is made by mixing olive oil and soda ; and soft soap, by mixing fat, or fixed oil, with potash. The marc of olives, as the residuum is called after the oil has been expressed, is valuable either as manure or as food for cattle. The virgin oil is called Florence oil, and is imported in flasks surrounded' by a network formed of the leaves of a monocoty- ledonous plant. It is used at the table under the name of salad oil. Gallipoli oil forms the largest portion of the olive oil brought to England ; it is imported in casks. Olive oil is largely used in this country in dressing woollen goods, and for machinery. In 1868, 17,585 tuns of this oil were imported into the United Kingdom. Rapeseed, the seed of Brassica napus, L. ; natural order, CrucifercB. — This plant grows wild in many parts of England, and is cultivated extensively in this country, in France, and in Germany, for the sake of the oil procured from its seeds. Rape oil is more suitable than any other oil for the lubrication of machinery, and is now much used for locomotives, marine engines, and for burning in lamps. A single locomotive consumes from 90 to 100 gallons of oil annually. The consumption of oil by the London and North-Western Railway Company alone is every year 40,000 gallons. Good English rapeseed yields an oil very superior to that obtained from foreign rape; nevertheless, in 1868, we imported 356,884 quarters of rapeseed, and about 300 tuns of the oil in 1851, chiefly from France and Germany. Linseed, the seed of Linum usitatissimum, L. ; natural order, LinacecB. — We have already described this plant, under the name of flax. Flax seed or linseed yields a most valuable oil, known as linseed oil, largely employed in the arts, especially in painting and in the manufacture of printers’ ink. It becomes solid on exposure to the action of the air, or, in other words, is one of the drying oils. This article is always imported in the form of seed. In 1868 the imports into Great Britain were 635,528 quarters, principally from the East Indies and Russia. Smaller quantities come from Prussia, Germany, Egypt, and America. SesaMe ( Sesamum orientale, L. ; natural order, Pedalmccce), — This is a small showy annual, indigenous to India, and to the whole of Southern Asia, from Japan and China to the shores of the Mediterranean. In these countries it is much cultivated, and the oil, yielded in abundance by the seed, is used for dressing food, and as a common lamp-oil. In the East, this oil has some considerable repute as a softener and beautifier of the skin, and as an application to furfuraceous eruptions. Sesame oil is without odour, and does not easily become rancid. It is frequently used for the adulteration of balsams and Volatile oils. Large quantities of the seed are brought to this country from the East Indies and Egypt. We have now noticed the principal vegetable fixed oils. There are several other oil-producing plants in the market, but not much in demand at present. The following are deserving of notice: — Croton Oil (Croton tiglium, Lam.). This oil is a valuable and most powerful purgative, capable in over-doses of destroying life, and only administered one drop at a time, in cases where it is of the utmost importance to make a speedy impression on the bowels, and where the patient has difficulty in swallowing. It is also valuable as a counter-irritant. Croton oil is obtained by expression from the seeds. The common hazel- nut ( Corylus Avellana, L.) yields an oil most valuable for the delicate machinery of watches, diminishing the friction of the pinions, the axles of the wheels, and other rapidly moving parts, which would otherwise wear injuriously, and speedily become disordered. The oil of almonds also is employed for the same purpose. Other oils are obtained from cotton seed, ground nut, carthamus seed, etc. SEATS OF INDUSTRY.— YI. By W. Webstek. LOWELL AND ROUEN. LOWELL. Lowell is the principal centre of cotton manufacture in the United States, and hence is frequently described as “ the Man- chester of America.” The story of its foundation and progress forms one of the most interesting and encouraging chapters in the history of modern industry. It owes its name, its origin, and its prosperity exclusively to industrial enterprise, and is remarkable even among the towns of the New World for the rapidity of its growth. The site occupied by the busy and thriving town of Lowell possesses few natural advantages, and even the water power on which its prosperity depends had, to a great extent, to be SEATS OF INDUSTRY. 339 created. In 1792 a company, incorporated under the name of the Locks and Canals Company, obtained powers to construct a canal for the purpose of navigation round the Pawtucket falls in the Merrimack river, and it was many years after the completion of this work before it was seen that this canal could be utilised for manufacturing purposes. It was in 1821 that the project of establishing a cotton manufactory at Lowell took a practical shape. In that year several gentlemen purchased about 400 acres of ground, now forming the heart of Lowell, and built a factory and dwelling-houses for the operatives. This body of industrial pioneers was subsequently incorporated as the Merri- mack Company, which is still in existence, and is the largest of the manufacturing establishments in Lowell. Since it was originally constructed, the canal has been greatly extended, and in 1847 it was entirely rebuilt. The main canal is one mile and a half in length, sixty feet wide, and of a depth admitting the passage of vessels drawing eight feet of water. It is fed from a dam erected at the head of the Pawtucket falls, and its waters are distributed by means of numerous channels branching off in various directions, and discharging into the Merrimack and Concord rivers. This canal is said to be capable of supply- ing 1,250 cubic feet of water per second, or fifty mills with twenty-five cubic feet per second for each. In 1826 Lowell was incorporated, the name bestowed upon it being a recognition of the services rendered to the American community by Francis C. Lowell, a Boston manufacturer who had been largely instrumental in introducing cotton manufac- ture into the United States. The history of the town from this date is composed, for the most part, of the rise and progress of a dozen companies or “ corporations ” for the manufacture of cotton cloth. According to the published statistics for the year 1870, these companies own fifty mills containing 12,940 looms and 526,710 spindles, and give employment to 14,898 persons, consisting of 6,035 males and 8,863 females. The aggregate capital stock invested in the manufacturing com- panies of Lowell is returned at 13,650,000 dols., and the weekly product at 2,240,000 yards of cotton goods, 21,667 yards of woollen goods, 35,000 yards of carpeting, 2,500 shawls, and 10,900 dozens of hosiery. The raw material consumed during the same year amounted to 612,000 pounds of cotton, and 97,000 pounds of clean wool per week. From a table in the New American Encyclopaedia, we gather that there were twelve manufacturing companies in Lowell in 1860, with an aggregate invested capital estimated at 13,000,000 dols., employ- ing 12,507 operatives, working up 805,770 pounds of cotton, and 91,000 pounds of clean wool per week; and producing 2,463,000 yards of cotton goods, 44,000 yards of woollen goods, 25,000 yards of carpeting, and about 50 rugs per week. A com- parison of these figures shows that there has been but little increase in the trade during the intervening decade. There has, however, been a slight augmentation of the population, which in 1860 numbered 36,827, and in 1870 had risen to 40,937. The taxable property of Lowell for the latter year was valued at 25,000,000 dols. Eight of the manufacturing companies in Lowell, including the Merrimack, are devoted entirely to the manufacture of cotton goods. One of the others produces carpets, rugs, and pantaloon stuffs, in addi- tion to cotton-cloths ; and another manufactures broad-cloths, doe-skins, cassimeres, and shawls. The Lowell Machine Shop, which was incorporated in 1845, has a capital of 600,000 dols., and employs 550 operatives in the manufacture of cotton machinery, locomotives, etc. ; consuming 3,000 tons of wrought and cast iron per annum. The Lowell Bleaching Company, which dates from 1832, has a capital of 300,000 dols., and employs about 270 persons in dyeing some 15,000,000 yards, and bleaching other 8,000,000 yards of cloth per annum. The mode of life of the operatives in Lowell is peculiar. When this spot was selected as the site of a cotton manufac- tory there were no dwelling-houses in the vicinity to accom- modate the workmen, and the proprietors of the mills had accordingly to supply the want. The system then inaugurated is still maintained. Each of the manufacturing companies owns from twenty to thirty dwelling-houses, which are leased at a nominal rent to responsible persons as boarding-houses for the workpeople employed at the several mills. Some of these boarding-houses are barracks, capable of accommodating from forty to fifty inmates. The sexes are lodged in separate dwell- ings, and only persons employed by the company to which the house belongs are eligible as boarders. The companies also support an hospital, for the benefit of their operatives. All workpeople who are able to pay for the use of the hospital, however, are required to do so, and the employers of those who cannot afford to pay are charged with the cost of their treatment. Besides the large manufacturing companies, there are in Lowell several enterprising private firms engaged in various manufactures. A few years ago it was estimated that the aggregate capital invested in mills and machinery by individual proprietors amounted to 400,000 dols., and that they gave employment to upwards of 1,500 persons. There are in Lowell six banks of issue and three savings- banks. The amount of the deposits in the latter was recently returned at 2,605,148 dols., and the number of depositors at 12,192. After deducting the cost of board, the average weekly wages of the female workers is said to be 2 dols., and that of the males 4 dols. 80 cents. There are two loan and fund associations, and three insurance companies in Lowell. The provision made for the religious and secular education of the inhabitants of this manufacturing town probably furpishes even a more remarkable proof of their general prosperity than the statistics of the savings-banks. There are no fewer than twenty churches in Lowell, or one for every 2,000 of the population. Seven of these are Congregational, three Baptist, three Methodist, three Eoman Catholic, two Universalist, one Episcopalian, and one Freewill Baptist. Besides one high school, eight grammar schools, and three intermediate schools, Lowell possesses fifty-one schools for primary instruction, the aggregate of scholars at the latter being 9,599, and the average daily attendance 5,450. There are several libraries in the town s the principal being the Mechanics’ Association Library, which contains upwards of 6,000 volumes. During the past forty years, newspapers have been started in Lowell at the rate of about one per annum, and four of them are still continued. Lowell is the third shire town of Middlesex, Massachusetts, and is situated on the Merrimack, near the mouth of the Concord, about five-and-twenty miles distant from Boston in a north-westerly direction. It is connected with Boston by the Boston and Lowell Bailroad, and with various points to the north by means of several lines of railway. The local government consists of a mayor, eight aldermen, and twenty- four councillors. KOUEN. The ancient city of Rouei:, the Rolhomagus of the Romans, one of the chief seats of manufacture and trade in France, presents a striking contrast to the modern town of Lowell. If the history of the latter is unusually monotonous and un- eventful, even as compared with other towns in the New World, that of the former is certainly more rich in stirring associations than the generality of the manufacturing towns of Europe. The occupation of Rouen by a body of German troops, towards the end of 1870, is assuredly the most important occurrence that has taken place there within the memory of the oldest inhabitant, but it can hardly be classed among the great events in the history of the city. Since it was seized by Rollo and his followers in 842 and made the capital of the Norsemen in France, in conformity with a treaty wrenched from Charles the Bold, Rouen has changed hands several times. It was the residence of the Dukes of Normandy till the year 1066, when Duke William made his successful invasion of England, and brought his court over to London ; and it continued to be the capital of Normandy and the seat of the government of that province while it was in the possession of the Conqueror’s successors, up to the time of Richard Cocur de Lion. In 1204 Rouen was besieged by King Philip Augustus, and annexed to France along with the greater part of the duchy of Normandy. This monarch left his mark on Rouen, for it was he who built the celebrated cathedral of St. Ouen, one of the grandest specimens of Gothic architecture in Europe, and by far the most interesting of the many fine Gothic churches the city can boast. Among the numerous-relics preserved in the five- and-twenty richly-carved chapels of this cathedral, is the heart of Richard Coeur de Lion. But Rouen again passed into the possession of the English in the first half of the fifteenth century ; and it was during their occupancy that the heroic Jeanne Dare (commonly but improperly written d’Arc) was burned alive as a witch in the public square where her statue 340 THE TECHNICAL EDUCATOE. now stands, and which, has since been called in memory of her, Place de la Pucelle. After being thirty years under the power of the English, Eouen was re-captured by the French in 1449. Next to Lyons, Rouen is the most important manufacturing town in France. The principal branches of industry cultivated in the city are cotton manufactures, including checked and striped cottons, commonly known as Rouenneries, nankeens, dimity, lace, cotton velvets, shawls, etc. It also contains ex- tensive manufactories for the production of hosiery, mixed si-lk and wool fabrics, blankets, flannels, hats, cordage, cotton and linen yarns, shot, steel, lead, chemicals, paper, etc. It is also noted for its sugar refineries and potteries ; and ship-building and machine-making are prosecuted with great success. The trade of Rouen has reached considerable proportions. In years when France is favoured with a superabundant harvest, large quantities of flour of a high quality are exported ; and there is a constant trade in wine, sugar, and other French products, as well as in goods manufactured in the city. Rouen is the capital of the department of the Lower Seine, and is situated on the river Seine at a point eighty-seven miles west from Paris, and seventy miles from the sea, including the windings of the river. Vessels of 200 tons burden can be loaded at the handsome quays which have been constructed on the banks of the riyer. The streets of the city are narrow, and the houses for the most part are built of wood. Among the most important public buildings may be mentioned the Palace of Justice, the theatre, and the Hotel de Ville. The latter includes a public library, containing 40,000 volumes, and a splendid collection of paintings. There are several literary and scientific institutions and societies, and a large number of good schools established in the city. Rouen is the seat of various judicial and administrative authorities, and especially of a Tribunal of Commerce. In 1862 the population numbered 94,679, and is believed to amount at present to about 100,000. APPLIED MECHANICS.— YIII. BY ROBERT STAWELL BALL, A.H., LL.D., Astronomer-Royal for Ireland. THE MECHANICAL PRINCIPLES OF BRIDGES : THE GIRDER-THE WOODEN BRIDGE-THE ARCH. Bridges are of very varied form and construction. A tred which has fallen across a stream is, perhaps, the simplest bridge, and from this natural bridge up to such superb structures as span the Menai Straits, every conceivable intermediate link is to be found. In the present lesson we shall first consider the most simple type of bridge — that of a single beam or girder — and afterwards examine some more complicated constructions of this class. THE GIRDER. What is known in Mechanics as a girder will be understood from the accompanying figure. Let P Q (Fig. 1) be a beam, whether of wood, or cast-iron, or wrought-iron. This beam is supported at its extremities by A and b, and from its centre a weight is suspended. Now this weight, if not too large for the strength of the beam, is supported, and the beam is said to be strained transversely. Instead of having one weight attached to the beam, several weights might be suspended from it in different places, as in Fig. 2 ; or, finally, as in Fig. 3, the beam may be secured by having one end, p, firmly embedded in masonry or some secure support, and have a weight, w, sus- pended from the other end, q. In all these cases, when a beam is strained by a force or forces tending to break it across transversely, the beam is called a girder. We shall first examine the simple case of a beam supported at each end, and bearing a weight in the middle (Fig. 1). When a weight is attached, the beam is seen to bend down a little in the centre; as the weight is increased the curvature increases, until, when the weight reaches a certain amount, the beam breaks. It will be important for us to determine how the magnitude of the load which will break the beam is connected with its dimensions of length, breadth, and depth. It is manifest that the longer a beam be, the weaker it is, provided its section remain the same. It is easy to prove, in fact, both from theory and from experiment, that the breaking-load of a beam varies inversely as its length. Thus, for example, a beam of wood six inches square and twenty feet long is only half as strong as a beam six inches square and ten feet long. The effect of the section of a beam upon its strength is also to be ascertained without much difficulty. It is well known that a beam whose section is not square is stronger when placed edgewise than when placed flatwise. By actual trial, it will be found that if two perfectly similar and equal beams be taken, and that one beam be broken edgewise and the other be broken flatwise, the load necessary in the former case is to the load necessary in the latter case in the proportion of the depth of the beam to its breadth. From this law, and that which refers to the length, we shall be able to deduce an expression for the breaking-load of any beam of any material, provided that its section be rect- angular and constant. It is a well-known rule among practical men that a beam of cast-iron, one foot long and one square inch in section, is broken by a load of one ton : let us deduce from this result the expres- sion for the breaking-load of any beam of cast-iron which is l inches long, b inches broad, and d inches deep. p /Hk D C E ilk t A B 6 6 0 Fig. 2. A beam whose section was one square inch and whose length was l inches would require a load determined by the following proportion : — I : 12 ” 1 ton : answer. This proportion follows at once, from the law that the breaking- weight is inversely as the length : we infer, then, that for a bar l inches long and one inch square the breaking- strain is 12 -y ton3. The beam that we have supposed is b inches broad ; it is there- fore the same as b beams, each one inch broad, and d inches deep, standing side by side. Hence, the strength of the beam is b times the strength of a beam l inches long, d inches deep, and one inch broad, standing edgewise. By the second law, a beam one inch broad and d inches deep is d times as strong as a beam d inches broad and one inch deep ; and hence the original beam is b X d times as strong as a beam d inches broad and one inch deep. But a beam d inches broad and one inch deep is d times as strong as a beam of the same length which is one inch square. This is evident, for we may manifestly conceive that d beams, one inch square, placed side by side are identical in strength with the solid beam which APPLIED MECHANICS. 341 would be formed by making them cohere together. This would not, however, be true of beams placed one over the other. We infer, therefore, finally, that the beam l inches long, b inches broad, and d inches deep is bdxd—bd 2 times as strong as a beam of the same length and one inch square; but we have already seen the strength of the latter to be 12 — tons, • L and therefore the breaking strength of the entire beam is — 12bd 2 — ^ — tons. This may be expressed in the following manner : — area of section x depth 12 ; -rr — ■ length. All the magnitudes are to be expressed in inches, and the answer will be in tons. Example. — To find the breaking-strain of a cast-iron beam twenty feet long, six inches deep, and two inches broad. The area of section is 6 x 2 = 12 inches. and therefore the answer is 12 x 6 12 24 q = 3'6 tons. The expression we have here deduced for cast-iron holds also for other substances, the only difference being that the numerical co-efficient, which is 12 for cast iron, must be re- placed by one appropriate to the particular material of which the beam is composed. Thus, in the case of a beam of pine, the breaking-load, ex- pressed in pounds, is given by the expression — „„ area of section x depth 5.000 length “ ‘ For example, a piece of pine, ten feet long and six inches square, has a breaking strain of 36 x 6 6.000 = 10,800 pounds. In general, the strength of any beam is represented by area of section x depth ® length The values of s for certain substances are given in tables which will be found in treatises on Applied Mechanics. We have hitherto only discussed the case of Fig. 1, in which the load is applied at the centre of the beam. We have now to consider the case of Fig. 2, where the load, instead of being applied at one point, is distributed over several. A beam in this condition is always able to bear more than when the load is applied entirely at the centre. The most important case which occurs in practice is where the load is distributed uniformly along the beam ; as, for example, when a beam, supported at each end, has to sustain the weight of a wall of masonry. In such a case as this every inch of the length of the beam has the same pressure to support. To break a beam by a load applied in this manner requires twice as much weight as when applied at the centre only, and therefore the preceding expression will be applicable if the values of s be doubled. In large beams the weight of the beam itself forms often a large portion of the load which it has to support, and this pressure is, of course, distributed along the length of the beam. In fact, the dimensions of the largest beams are limited by the ’ consideration that, beyond a certain span, it is impossible to construct a beam which should sustain its own weight. In Figs. 1 and 2 we have supposed that the ends of the beam are free, and when the beam is loaded the ends curl up slightly. If, however, the ends of the beams be firmly secured by being embedded in masonry, as the end p of the beam in Fig. 3, the strength of the beam is greatly increased, and it will be found that nearly double the load is now necessary to break it than was before required. The beam of Fig. 3, in which the weight is suspended at one end while the other is fixed, is only one-fourth the strength of a similar beam supported at each end and laden in the centre, in the manner represented in Fig. 1. THE WOODEN BRIDGE. We shall now examine a few of the simple mechanical prin- ciples that are employed in the construction of a timber or iron bridge. The subject is here divested of the complexity which belongs to it in practice, and for information on which reference must be made to actual engineering works. This lesson is rather to be regarded as an illustration of mechanical principles than as a treatise on the building of bridges, which would, of course, be wholly out of place here, and is a difficult subject. It will be found both easy and instructive to verify experi- mentally the principles that are here laid down ; the apparatus necessary for this is simple and inexpensive. A number of slips of pine half an inch square, and of various lengths, from one foot to four feet, form the only materials necessary for the bridges which will be described in this lesson. These miniature wooden beams are to be fastened together in any positions that may be desired by means of cramps, such as that shown in Fig. 4, and which can be procured in any tool-shop ; they should open to about two inches, as sometimes three beams must be fastened by the same cramp. The use of these cramps dispenses with the necessity of any other fastenings, for it will be found that the slips thus fastened together will bear a very great strain, amounting to 100 pounds or more, without slipping. Thus, with the greatest facility, bridges and other structures may be built up, and actually loaded with considerable weights, 14 pounds, 28 pounds, 56 pounds, etc., to test their strength. Possessing a few dozen of these slips of wood, and a corresponding number of cramps, many varieties of simple bridges may be tested, the same slips re-appearing in different combinations ; and the apparatus may also be used for constructing models of roofs, and many other pieces of frame- work which will suggest themselves to the in- quiring student. It will probably be found surprising what efficient joints are produced by the compression of the wood in the cramp ; but, in cases of very great strains, the danger of slipping will be lessened by interposing two small pieces of sand-paper, back to back, between the surfaces of wood in contact. A few larger cramps will often be found useful for securing the important joints more firmly than is pos- sible with the small cramps; the bruising of the slips may be diminished if necessary by the interposition of small slips of card-board between the iron and the wood. Let us suppose that it is desired to make a foot-bridge from one support, A, to another, B (Fig. 5). The most simple way of doing it, if the distance be not great, is to lay a plank of suffi- cient strength across, with its ends on each support ; and for a short distance no method can be more efficient. To consider the strength of such a bridge, we must remember what has been already proved, that the load being the same, the weakness of the bridge increases proportionally to its length, and hence we see that the longer is the distance from A to B, the stronger must the planks be; but with an increase in the strength — that is, in the dimensions of the plank — there is a corresponding in- crease of its weight, and therefore an addition to the load which it has to sustain. When to this we add that there is, of course, a practical limitation to the magnitude of planks, we see at once that when the distance between A and b exceeds a certain amount, a bridge consisting of a single unsupported plank is a practical impossibility. It will be found that a slip of pine half an inch square, and resting on two supports, the distance between which is ten inches, would be broken by suspending a weight of about 80 pounds, more or less, according to the quality of the wood, at its middle point ; hence we should infer, and we can easily verify by experiment, that a rod of the same wood resting on two sup- ports forty inches distant, would be broken by a weight of about 20 pounds. We shall then examine the means by which a bridge consisting of a single plank can be strengthened. For convenience, we shall confine our attention to the rod of pine half an inch square and four feet long, being one of those witi which the experiments are made, and, of course, the observa tions will apply, mutatis mutandis, to every other case Let a b be a single beam, which is too long when unsupported Fig. 4. 342 THE TECHNICAL EDUCATOE. to form a safe bridge for the load which it has to carry. If, by means of a pedestal, it could be directly supported at the middle, at the point x, its strength would be doubled, because then it would be equivalent to one beam, A x, resting on the supports a and x, and to another, b x, resting on b and x ; and since the strength of a beam varies inversely as its length, each of these portions is twice as strong as the whole beam was before, and therefore the bridge will now support double the weight which it could carry originally. If three pedestals are applied, the length A B is divided into four parts ; each part is, therefore, four times as strong as the unsupported plank A b, and therefore the supported bridge is four times as strong as it was before the pedestals were applied to it. Whenever it is possible to have a number of pedestals under a bridge, they form the most suitable and efficient means of support, but in the majority of cases it will not be possible, and other means of support must be sought. If a rod of pine four feet long be supported at the ends A and B, it would sustain about 20 pounds hung at its middle. Let the points of trisection, p and Q, of this beam be taken. If these points could be firmly supported, we should then expect, accord- ing to the principles already explained, that the strength of the rod would be increased threefold. Now, if with the help of cramps another rod be fastened to A b at p, and to the support at c, and a second rod, Q r>, be similarly attached, the desired object is accomplished. It will be found on trial that the sustaining power of the bridge has been vastly increased, and it will also be noticed that, whereas before it yielded and bent under a slight load, it has now acquired considerable stiffness and rigidity. What is the reason of this P The point p could formerly be pressed down- wards a little without breaking the beam, and on the relaxation of the pressure it returned, of course, to the horizontal line. Let us suppose that it could be pressed down to p'. p p' is vertical, for the ends A and B being secured, p could not be pushed either towards A or B, but only vertically. In the triangle cpp' the angle c p' p is the greatest, and therefore c p is greater than c p'. Hence p cannot be depressed at all without coming nearer to C ; but when the rod c p is introduced, and firmly fastened both at C and P, it prevents P coming any nearer to C, and therefore p cannot move at all, provided the joint do not slip nor the pressure be sufficient to break c p. In fact, A p c may be looked upon as a triangle on the base A c ; and since, by Euclid I. 7, there cannot be two triangles on the same base and same side of it which have their conterminous sides equal, it follows that p cannot move when c p is applied, though the flexibility of the wood would have allowed it to do so previously. In precisely the same way it can be shown that Q is a fixed point. Hence the beam A b may be regarded as directly supported at p and q, and therefore the whole will be as strong as each of the three equal segments into which it is divided. Hence, by the principle already explained, the strength of the bridge is increased threefold. Actual experiment will be found to justify this reasoning. By placing a second four-feet rod parallel to A B, and distant from it by a few inches, and simi- larly supporting it by two other rods, and then laying a few short rods crossways over both beams to form a roadway, the bridge can be loaded with weights to test its strength. TPIE AB.CH. The simplest theory of the arch is that which is given by Dr. Hooke. A chain which is suspended from two points hangs downwards in a curve called the catenary, and each of its links is retained in equilibrium by the tension of the two adjacent links which counterbalance its weight. Precisely similar is the equilibrium of the stones which form an arch. Each of the stones is held in equilibrium by the pressure of the two adjacent stones, called voussoirs, and its own weight. The difference between the cases is, that while the equilibrium of the chain is unstable that of the arch is stable. NOTABLE INVENTIONS AND INVENTORS. VII.— THE MARINER’S COMPASS (concluded). BY JOHN TIMBS. We now resume the history of the compass. In 1280, when Marco Polo returned from his travels in Cathay, he is believed to have brought a knowledge of the compass, as well as other Chinese inventions, back to Europe with him ; but there is no known authority for this opinion that can lay claim to authen- ticity. It is certain, however, that before the close of the fifteenth century, when Vasco de Gama found his way round the Cape of Good Hope, the pilots of the Indian seas were expert in the use of sea-charts, the astrolabe, and the compass. We find the compass minutely described by Guyot de Provence, in his satire, “ Le Bible,” about the year 1190. Guyot, a minstrel by profession, had probably seen it in use during the Crusades, to one of which, most likely, he had previously attached himself. At all events, Cardinal de Vitry and Vincent de Beauvais, both Frenchmen, and both Crusaders, writing at a later period by a quarter or half a century than Guyot, speak of it as a great curiosity which they saw in the East, and we may infer that it was a thing almost unknown in Europe. There is not, hence, the slightest foundation for the belief that it was used by European seamen at so early a period, though there can be but little doubt that by the middle of the thirteenth century it had come into partial use, and into general knowledge ; since, in one of the songs of Gauthier d’Epinoir, is an allusion which no one would have made, had not his auditors been familiar with the magnetic needle. It was long contended that the inventor of the compass as a nautical instrument was Elavio Gioja, a native of Amalfi, near Naples; and the date given by the Italians is from 1300 to 1320. It is obvious, from what we have already said, that there is no foundation for this opinion. Before this assigned period, even the “ Tresor ” of Brunetto Latini (the master of the divine Dante) bears evidence that the compass was not a rarity. It is, how- ever, highly probable that Gioja greatly improved the compass, either by its mode of suspension, or by the attachment of the card to the needle itself, or in some other important particular. The French long laid claim to the discovery of the compass, or at least to the attachment of the card to the needle, from the circumstance of the north point being marked with the fleur-de-lis ; but there is no distinct evidence on this point, and Sir John Davis, with more probability, considers that the figure is an ornamental cross, originating in the devotion of an ignorant and superstitious age to the mere symbol. Besides, this ornament is not peculiar to the compass, but may be seen on the hour-hand of modern French clocks. Or, as Sir John ob- serves, “ as the compass undoubtedly came into Europe from the Arabs, the fleur-de-lis might possibly be a modification of the monasala or dart, the name by which the Arabs called the needle.” Still, the fleur-de-lis, as the ornament of the northern radius of the compass, is said to have been adopted by Gioja, the Neapolitan, because it was the device of the reigning King of Sicily at the time Gioja first employed the instrument in navigation. By whom the suspension now generally used was invented, is altogether unknown from any document or other evidence. We have already explained that a magnetic needle balanced on a pivot will,, subject to a correction for the variation of the magnet, point out the true direction of north and south. A card, bearing the points of the compass, and unalterably attached to any apparatus, such as a globe, will therefore afford the means of adjusting it north and south, if the centre of the card bo made the pivot of a magnetic needle. In the mariner’s compass, however, we affix the needle to the card, pointing it towards north and south, so that the card travels with the needle ; and if a pointer (fixed with respect to the ship) mark out the point on the edge of the card, which lies in the line drawn through the pivot parallel to the plane which symmetrically bisects the ship, the bearing of the ship’s head is shown by that part of the card to which the pointer directs for the time being. To ensure the horizontality of the compass-card, the cylindrical box in which it is enclosed is supported in a hoop at opposite points by pins projecting from it, so as to allow the box to revolve inside the hoop. This hoop is supported in the same manner on pivots, the line of which is at right angles to the first points ; so that by the rotation of the compass-box in the hoop, and of the hoop itself, the former can always form its position of equilibrium, which is NOTABLE INTENTIONS AND INVENTORS. 343 the horizontal position. The small oscillations of the apparatus I are immediately destroyed by the friction. The apparatus is then said to be supported on gimbles, or gimbals, allowed to have been the invention of an Englishman. The dip of the needle — that is, the angle which, when sup- ported on its centre of gravity, it makes with the plane of the horizon — was discovered by Robert Norman, of Wapping, in 1594. Next was discovered the variation of the compass; that is, that it did not point directly to the north, but some- what east of that point. To account for this it was supposed that the magnetic pole of the earth did not coincide with that of the axis on which the globe itself turned, and so it proved. The variation of the needle was known to a Chinese philo- sopher, who wrote about the year 1111. Columbus was sailing across the Atlantic Ocean, in his attempt to find a new world. On September 13, 1492, in the evening, being about two hundred leagues from the island of Ferro, Columbus first noticed the phe- nomenon : the variation was a little to the west at London. About nightfall, the needle, instead of pointing to the North star, varied about half a point, or between five and six degrees to the north-west, and still more on the following morning. Colum- bus was struck with the cir- cumstance, and he observed the variation to increase three days as he advanced. He at first made no mention of tho phenomenon, knowing how ready now his people were to take alarm ; but the pilots were filled with consternation. It seemed as if the very laws of Nature were changing as they advanced, and that they were entering another world subject to unknown influences. They apprehended that the compass was about to lose its mysterious virtues, and with- out this guide what was to become of them in a vast and trackless ocean ! Columbus now sought to allay their terrors. He told them that the direction of tho needle was not to the Polar star, but to some fixed and invisible point ; the variation was not caused, therefore, by any fallacy in tho compass, but by the move- ment of the North star itself, which, like the other heavenly bodies, had its changes and revolutions, and every day described a circle round the pole. The pilots had faith in Columbus, and believed him. His explanation, as the Copernican system was unknown, was plausible, and was believed ; and it showed Columbus’s readi- ness to meet the emergency. The phenomenon has now become familiar to us, but we are not so cognisant of its cause. “ It is,” says Washington Irving 0 “one of those mysteries of Nature open to daily observation and experiment, and apparently simple from their familiarity; but which, on investigation, make the human mind conscious of its limits, baffling the ex- perience of the practical, and humbling the pride of science.” The iron employed so extensively in modern vessels has created great, but generally unsuspected, deflections of the mag- netic needle from the position which, under the influence of terrestrial magnetism only, it would take in any given place and at any given time. Numerous vessels have been wrecked in consequence of this alone. In England, the errors of the compass from the action of iron have been corrected by placing near it powerful magnets, the action of which produces upon the needle equal effects, but opposite to those of the ship. The French employ a table of corrections, based upon minute observa- tion, and applicable to every indication of the compass affected. Nevertheless, fatal accidents are still attributable to the errors of the compass. One of the contrivances for diminishing this serious inconvenience is the correcting compass, which affords the means of taking the sun’s position, whereby the deviation may be corrected. Lightning alone exercises a decided influence on the needle, by reversing its points, so that north becomes south, and conversely. When a vessel is nearing land, the needle is said to be affected ; and certain rocks exercise a decided magnetic influence on the compass, volcanic rocks especially, but this influence is not felt on board ships. But the action of the iron forming the ship’s sides is far different;, nothing, not even the interposition of a thick non-magnetic body, will stop its influence. But the real danger proceeds from another source ; since the ship herself, under her weight of canvas, may increase the deviation of the needle. From experiments made on board an iron-built sailing vessel, pro- vided with iron rigging and lower yards of steel, and with two binnacle compasses on her poops, and a third placed between the mizen and main-masts, the lower part of which was all of iron, the deviations of the needle were respectively 56°, 24°, and 35°. It need scarcely be added that much experience may be gained by freighting an iron vessel only when she has been at sea for a considerable time, in order to ascertain how her compass behaves. The Rev. William Scoresby, whom we have already mentioned, published his various investigations of the influence of iron ships upon theijj compasses, and the requisite corrections. One of the most interesting of these we have described in the previous num- ber. In 1855 Dr. Scoresby communicated to the British Association a summary of his matured views and the evidence in their favour, in which he re- called attention to his plan of a compass aloft, which affords a simple and effective mode of ascertaining the direction of a ship’s course; and to exemplify this and other questions, Dr. Scoresby, in 1856, took a voy- age to Australia in the Royal Charter iron steam- ship. His theory proved correct. But the fatigue of the voyage to a man approaching seventy years of age was excessive, and, without doubt, accelerated his death. As a proof of his energy in the cause of science, it may be men- tioned that once in the course of this voyage, in a violent cy- clone, he ascended the mizen- rigging to judge of the height of the waves, which he calculated to be then thirty feet. He returned to England, and narrated his voyage to a large audience at Whitby ; but while preparing his journal for publication he died, leaving his widow to receive, as a memorial of his services, a chair formed from timber of the vessel in which he made his voyage to Australia. In reviewing the history of the compass, we are reminded of the remark of Sir John Herschel — that such inventions are not the creation of a few years, or a few generations. They pre- suppose long centuries of previous civilisation, and that, too, at the dawn of European history, when the declination of the needle was known. The following facts relative to tho construction of the mari- ner’s compass, the graduated card of which is shown in the annexed illustration, may prove interesting to the reader : — The shape of the needle is generally that of a long parallelogram, of which the width is very small in comparison with the length ; or that of an elongated lozenge. A hollow cone, generally of steel, but sometimes of agate, rises precisely in the centre of the needle to supply the means of balancing it on the fine point of the pin on which it works, and about which it may turn freely in any direction without the slightest hindrance from friction. The pin on which the needle works rises perpendicularly from the centre of a circular card, marked as in the illustration. The central portion of the card, lying within a graduated ring divided into 128 parts, is marked with a star of 32 rays, of 344 THE TECHNICAL EDUCATOR. which 16 are solid and 16 dotted. These rays mark the 32 points of the compass, the ray that marks the north point on the card being distinguished by a fleur-de-lis. The graduated ring already spoken of shows the division of each of the 32 points into quarter-points. In the ring or belt immediately without it is marked the reading of each point. In the narrow ring immediately without this is marked the numerical order of the points from north and south to east and west on either side ; and in the outermost ring is given the value of each point from north and south to east and west on either side in degrees and minutes, each point being equal to the l-32nd part of 360 degrees, or 11° 15'. ANIMAL COMMERCIAL PRODUCTS.— XIY. III. EDIBLE SPECIES. The preceding notice of the Mollusca would be incomplete without some reference to their value as a source of human food. Amongst the edible kinds we have the Oyster (Ostrea edulis). — Vast beds of this mollusk are planted and tended with great care. The oyster culture is carried on most extensively at Colchester and other places in England, and on the coasts of France. The oysters are laid in beds, in creeks near the shore, where in two or three years they grow to a con- siderable size, and improve in flavour. Between 14,000 and 15,000 bushels of Essex oysters are consumed in London annually. There are 200 vessels, of from twelve to fifty tons’ burden, manned by 400 or 500 men and boys, continually dredging for oysters on the Essex coast. Mussel ( Mytilus edulis). — This is another popular mollusk, not so digestible as the oyster, but nevertheless in considerable demand as human food, and largely employed as bait for whiting, haddocks, and cod. We have also the Cockle (Cafrdium edule ), Periwinkle (Littorina littorea), Whelk ( Buccinum undatum), and the Ormond Whelk ( Fusus antiquus), with which our markets are abundantly supplied. Others might be mentioned, but enough has been said to show that, whilst the shell of the mollusk is attractive and useful, the soft body of the creature that dwells within it is not less valuable. PRODUCTS OF THE SUB-KINGDOM ANNULOSA. Annulosa (Latin, annulus, a ring), a name given to the third great division of the animal kingdom. The body, in Annulosa generally, presents a symmetrical form, and consists of a series of rings or segments ; the nervous system is a double nervous thread, which extends along the body at its lower side, and is united at certain distances by double “ganglia,” as these nervous masses are termed — nerves being given off from these ganglionic masses. In the group Annuloida, the body is ringed and devoid of limbs, whilst in the Articulata it is composed of movable pieces, and the limbs are jointed. The Annulosa are divided into the following classes : — 1. Annelida (Latin, annulus, a little ring), animals having bodies soft and pliable, more or less cylindrical, and formed of a great number of small rings. Examples : earthworm and leech. 2. Crustacea (Latin, crusta, a hard covering), having an articulated, hard shelly case or covering, in which the softer parts of the body are contained. Examples : erabs, lobsters, etc. 3. Arachnida (Greek, arachne, a spider), having the head and thorax confluent with each other, and the body consequently consisting of only two segments, with eight legs, and smooth eyes. Examples : spider and scorpion. 4. Insecta (Latin, in, into, and seco, I cut), including those animals having an insected or divided appearance of the body into three well-marked portions, called respectively the head, thorax, and abdomen. Six legs are articulated with the thorax. Examples : bee, moth, and beetle. In the first class, Annelida, we have one species of very con- siderable value in commerce, the Leech ( Hirudo medicinalis, L.). — This is an abranchiate red- blooded worm, provided with a circular disc or sucker, at either extremity of the body. The oval aperture or mouth is formed of three pairs of cartilaginous jaws, each armed with two rows of very fine teeth, and disposed in such a manner that they form three radii of a circle. This apparatus enables the leech so to penetrate the skin as to ensure a ready flow of blood without causing a dangerous wound. Leeches are usually found in pools and marshes, sometimes in England, but principally on the Con- tinent, especially in Portugal, the south of Prance, Germany, Hungary, and Russia. The greatest quantities come through Pesth and Vienna from Hungary. Most of the leeches used in England are imported from Hamburg, whither they are sent from the lakes of Pomerania and Brandenburg, and from the province of Posen in Prussia. Leeches are taken by men, who wade into the pools with naked legs, to which they fasten themselves. The men then leave the water, and remove them before their bites become injurious. Leeches are sent over in bags, or more frequently in small tubs, closed with stout canvas to allow a free passage of air. Each tub usually contains about 2,000 leeches. Some idea of the extensiveness of the leech trade may be obtained from a fact mentioned by Dr. Pereira, that, some years ago, “ four principal leech dealers in London imported on the average 600,000 leeches monthly, or 7.200,000 annually.” The annual consumption of leeches in Paris is estimated at 3,000,000, and that of the whole of France at 100,000,000. The second class, Crustacea, furnishes several species which are used as food — as crabs, lobsters, crayfish, prawns, and shrimps, so well known as to render description needless. Omitting the Arachnida, which are of no commercial value, we come to the fourth class, Insecta, which is pre-eminent over the others in the number of individuals, and in their beautiful forms, colours, and transformations. Its members are in the highest degree valuable to man, furnishing him with unlimited supplies of honey, wax, silk, and dyeing materials. The following are the most important insects, regarded from a commercial point of view. The Silkworm Moth ( Bombyx mori) belongs to the family Bombycidce, a section of the nocturnal lepidoptera or moths. It has short plumose antennae, a thick short body, stout legs, and white wings, with two or three dark lines stretching across them parallel to the margin. It lays its eggs, which are of a greyish tint, on the leaves of the mulberry tree ( Monos alha), upon which the larva feeds. These larvae form the cocoons from which the silk is procured. The eggs may be preserved a long time without deteriorating, provided they are kept free from damp, and not too many in the same packet. The eggs in this state are called by the silk cultivators “ seed.” The larva when first hatched are a quarter of an inch long and of a dark colour, and the first care after their birth is to separate them from their shells, and place them in hurdles where they may find appropriate food. For this purpose, a paper perforated with holes and covered with mulberry-leaves is spread over the basket in which the larvae are placed, and in passing through the holes to get at the mulberry-leaves, they free themselves from their shells. The silkworm lives in the larval state from six to eight weeks, during which time it moults or changes its skin four times, increasing in size and voracity with every moult, and when fully grown is about three inches in length. The caterpillar now stops eating, betakes itself to some con- venient spot where, after spinning a few threads in various directions, it suspends itself in the midst of them, and by con- tinually twisting its body, it gradually envelopes itself in a thick, silken, oval-shaped cocoon. The silk is a secretion of a pair of tubes called sericteria, which terminate in a prominent pore or spinneret on the under lip of the caterpillar. The two fine filaments from the sericteria are glued together by another secretion from a small gland, so that the apparently single silken thread proceeding from the caterpillar, which forms the cocoon, is in reality double. Whilst spinning the cocoon, which is usually completed in five days, the larva decreases in bulk, casts its skin, becomes torpid, and ultimately assumes the chrysalis form in the interior of the cocoon. The cocoons, when completed, are thrown into warm water, which dissolves the glutinous matter that causes the threads to adhere, and separates them. The end of the thread is then found, and placed upon a reel ; the silk is wound off the cocoon and formed into hanks. When this is carefully done, the silken thread obtained from a single cocoon is sometimes from 750 to 1,150 feet long, or of an average length of 300 yards. Twelve pounds of cocoons yield 1 pound of raw silk. About 1 ounce of silkworms’ eggs will produce 100 pounds of cocoons ; 16 pounds of mulberry leaves are food sufficient for the production of 1 pound of cocoons ; and each mulberry tree yields about 100 pounds of leaves. These data afford the reader the means of cal- ANIMAL COMMEECIAL PRODUCTS. 315 eulatmg the number of insects, eggs, trees, and leaves necessary for the production of 6,000,000 or 8,000,000 pounds of silk, the quantity that is annually consumed in the United Kingdom. The art of rearing 'silkworms, of unravelling the threads spun by them, and manufacturing those threads into articles of dress and ornament, seems to have been first practised by the Chinese. In China, Japan, and India, silk has formed, from time imme- morial, one of the chief objects of cultivation and manufacture. The silkworm moth and the mulberry tree are, in fact, both natives of China, and a great portion of our supplies of silk is still derived from that country. There was a time when silk, now so abundant, was valued in Kome at its weight in gold, and the Emperor Aurelian refused his empress a robe of it on account of its dearness. At the period when our ancestors were naked savages — 2,000 years ago — the Chinese peasantry, through Canton. The principal ports from which we receive East Indian silk are Calcutta and Bombay. The exports from these places amount to 10,000 cwt. annually. Anatolia and Syria produce much good silk, principally around Damascus and Beyrout ; this goes chiefly to Western Europe, rid Aleppo, Smyrna, and Constantinople. A great deal of Persian and Armenian silk is brought by caravans from Asia, by Bassora, Bagdad, Damascus, etc., to the ports of the Levant, and goes by the name of silk of the Levant. This name also includes all the silk produced in Turkey, the Morea, and in the Archipelago, and brought into commerce through Gallipoli and Salonica. As the breeding of silkworms only prospers in warm climates, silk culture is confined in Europe to Italy, the South of France, and Spain. There is also considerable silk cultivation on the south- ern slopes of the Alps, in Tyrol and Illyria, and within the last A SILKWORM- REARING ESTABLISHMENT. amounting in some provinces to millions in number, were clothed in silk. t From China the cultivation of silk extended to Hmdostan, and thence to Europe, in the reign of the Roman Emperor Jus- tinian, about the middle of the sixth century. From the sixth to the twelfth century the culture of silk was confined to Greece, particularly to the Peloponnesus, where it spread so much that this part of Greece derived its modem name, Morea (Latin, morus, a mulberry), from that circumstance. From Greece silk cultivation spread into Sicily, Italy, Spain, and finally France. The French commenced its culture in 1564, under the auspices of Henry IV., and the raising of raw silk and its manufacture ' now forms a very considerable proportion of the French trade. We have not space for further detail of the progress of the silk manufacture. At present the United Kingdom is supplied with the raw ma- terial for manufacture principally from China, the East Indies, the Levant, France, and Italy. Of Chinese silks the best come from the provinces of Nankin and Tsekiang in Eastern China. Silk of an inferior character is received from Southern China, twenty years successful attempts at silk culture have been made in Bavaria and Lower Austria. The quantity of raw silk imported into this country in 1865 was nearly 8,000,000 pounds, and the value of the same manu- factured was estimated at more than £1 7,600,000. Although the climate of England is too cold to enable us to rear the silk- worm, we are able to manufacture the silk. We have upwards of 300 silk manufactories, giving employment to 50,000 hands. The principal seats of the English silk manufacture are : — For broad silks, Spitalfields, Manchester, Macclesfield, Glasgow, Paisley, and Dublin ; for crapes, Norfolk, Suffolk, Essex, Middle- sex, and Somerset ; for handkerchiefs, Manchester, Macclesfield, Paisley, andGlasgow ; for ribands, Coventry ; for hosiery, Derby and for mixed goods, Norwich, Manchester, Paisley, and Dublin. The annual value of the goods manufactured is computed at .£10,000,000. The exports of British manufactured silks are chiefly to the United States and the colonies. We also ship silks extensively to South America, Germany, Belgium, and even India and France. Next to the silkworm moth the Honey Bee (Apis mellificai 346 THE TECHNICAL EDUCATOE. is the most useful insect to man. This insect belongs to the order Htjmenoptera (membrane-winged), an order characterised in most of the genera by the presence of a sting. The habits of the honey bee are replete with interest, arising from its social economy and from the separation of the individuals into three communities based on sexual modification, viz., the queens, or prolific females; the workers, or barren females; and the drones, or males. The hive bee or honey bee is distinguished from the other species of Apis by having the femora of the posterior pair of legs furnished with a smooth and concave plate on the outer surface, which, fringed with hair, forms a basket adapted for the conveyance of pollen. A) swarm of bees consists generally of about 6,000 individuals, of which about one-thirtieth part are males, the rest females, and of these one only is for the most part prolific, called the “ queen.” The body of the queen bee is longer, her colours brighter, and her head smaller than these parts in the other bees, and her sting is curved. The male bees or drones have no stings ; their body is shorter and thicker. The workers have a straight sting, but as their growth is ar- rested before the full development of all their organs, they are smaller than either the queen or the drones, and their colours are 'less bright. The honey bee in its natural state generally constructs its nest in hollow trees, but throughout Europe it is now rarely found except under domestication. The comb consists of beautiful hexagonal cells, placed end to end in such a manner that each cell is closed by three waxen plates, each of which also assists in completing one of the cells of the other side of the comb. The whole duty of the construc- tion of the comb and the care of the young devolves upon the workers, whose incessant activity has rendered them the symbol of industry. It is a remarkable fact that we derive the greater part of our knowledge of the economy and habits of the hive bee from the labours of a blind man. The elder Huber lost his sight when only seventeen years of age, but by means of glass hives, vari- ously constructed, he was enabled, through the aid of his wife, to become acquainted with all that was going on in them, and from her faithful recital of what she saw, together with the aid of an untiring investigator, M. Burnens, he amassed the material for his celebrated work. In the construction of the comb the bees take hold of each other, and suspending themselves in clusters, which consist of a series of festoons or garlands crossing in all directions, remain immovable for about twenty-four hours, during which time the wax is secreted in the form of thin plates from between the scales of their bodies. One of the bees makes its way to the roof of the hive, and detaching its plates of wax in succession from the abdomen with the hind legs, works them up with the tonguo into the matei-ial which forms the comb ; this bee is fol- lowed by others, which carry on the work. As soon as a few cells are thus prepared, the queen bee begins to exude her eggs. The first eggs develop into workers, the next produce the drones arid also the queens. The eggs are deposited in the cells, and in five days the maggot is hatched. The sole employ- ment of the queen bee is the laying of these eggs, and as only one is deposited in each cell, this occupies her almost inces- santly. The queen, when thus engaged, is accompanied by a guard of twelve workers, who clear the way before her, and feed her when exhausted, always with the utmost courtesy turning their faces towards her, and when , she rests from her labour approaching her with humility. She “lays workers’ eggs for eleven months, and afterwards those which produce drones. As soon as this change has taken place, the workers begin to construct royal cells, in which, without discontinuing to lay the drones’ eggs, the queen deposits, here and there, about once in three days, an egg which is destined to produce a queen. The workers eggs hatch in a few days, and produce little white maggots, which immediately open their mouths to be fed ; these the workers attend to with untiring assiduity. In six days each maggot fills up its cell, it is then roofed in by the workers, spins a silken copoon, and becomes a chrysalis, and on the twenty-first day it comes forth a perfect bee. The drones emerge on the twenty-fifth day, and the queens on the six- teenth.”* * “ Familiar Introduction to the Study of Insects.'’ By Edward Newman, F.L.S. BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS. VIII.— JAMES HORSBURGH, F.R.S. BY JAMES GRANT. James Horsbtjegh, the distinguished hydrographer, whose works and discoveries won for him the justly-merited title of “ The Nautical Oracle of the World,” was a native of the county of Eife, a district singularly prolific of illustrious Scotsmen, even from an early period. He was born on the 23rd of September, 1762, in the little town of Elie, which in those days was a place of some importance, as the massive and ancient mansions which stand near its beach remain to testify. As his parents were in humble rank, his education at the parish school was varied by labour in the fields ; but, like many of those who live upon the Fifeshire coast, being destined for a nautical life, his education was directed with that view. He acquired the elements of mathematical science, book-keeping, and the theoretical parts of navigation, and at the age of sixteen went to sea as a cabin-boy, being bound apprentice for three years. He served in various vessels, chiefly in the coal trade, and made many trips to Newcastle, Ostend, Holland, and Ham- burg. In May, 1780, a temporary interruption was put to these little voyages, by the vessel in which he served being fired upon and captured, when off Walcheren,by a French war-ship of twenty guns, the captain of which placed him and all his shipmates in prison at Dunkirk. After being liberated by an exchange of prisoners, he made a voyage to the West Indies, and another to Calcutta in 1784. There, by the influence of Mr. D. Briggs, an eminent shipbuilder, he was made third mate of the Nancy, bound for Bombay, and during the two subsequent years he continued trading along the coast of India. In May, 1786, he was first mate of the Atlas, wliich was bound from Batavia to Ceylon. In his then capacity, he was regulating the ship’s course by the charts at that time authorised and in use, when she was wrecked in the night on the lonely island of Diego Garcia. According to its bearings on the chart, Hors- burgh believed himself in the open sea, when the crash of his ship upon the rocks showed that he was trusting to a worthless guide ; and but for this event, and the impression it made upon his mind, he might have remained to the end a hardy, skilful, and enterprising mariner, but nothing more ; so “ the loss ftf this vessel was repaid a thousandfold, by the effects it pro- duced.” He learned the imperative necessity for having more correct maps of the Indian sea than the world then possessed, and he resolved to supply this want himself, by making, and committing to paper, his nautical observations. From the day the resolution was put in practice, he rapidly accumulated a store of notes on the bearings of the Indian coasts and isles, which served as the materials for his future works c*i hydro- graphy. . On his return to Bombay, where he arrived a penniless, poor, and shipwrecked sailor, he immediately looked out for another vessel, and soon shipped on board the Gunjana, a large India- man employed in the China -trade ; and for several years he sailed with her and the Anna ,, in the capacity of first mate, and made many voyages between Canton, Bombay, and Calcutta ; but he never forgot the resolution he had formed after his mis- fortune at Diego Garcia; and “ he was clever enough to see that the great objects in life are accomplished less by dexterity and address than by a strong and undeviating purpose.” His notes and observations had increased to a mass that only re- quired arrangement. By the most careful study he had perfected himself in the whole theory of navigation, especially that portion which bore on Oriental hydrography ; he had familiarised him- self with lunar observations ; and during the short intervals of his stay in harbour had taught himself the mechanical part of his future occupation by drawing and etching. During two of the voyages which he made to China by the Eastern route, he constructed three charts, one of the Strait of Macassar, between the isles of Borneo and Celebes; another of /the western coast of the Philippine Isles ; and a third, of the tract from Dampier’s Strait, through Pitt’s Passage, towards Batavia ; and all these were accompanied by practical sailing directions. These charts he presented to an old friend and shipmate, Thomas Bruce, then at Canton, where they were shown to several Indian captains, and to Colonel John Drummond (son of Viscount Stratliallan, who fell in the Prince’s cause at Culloden), then at the head of TECHNICAL DRAWING. 347 the English factory in Canton. By his influence they were published in London, under the patronage of the Court of Di- rectors of the East India Company, for the use of their ships. The Court also presented a letter of thanks to their author, together with a handsome sum of money, to enable him to pro- cure some nautical instruments of which he was much in want. When first mate of the Carron, he returned to Britain in 1796, and the excellent trim in which he kept that ship won him great praise from several naval men, while his scientific acquirements procured him the acquaintance of Sir Joseph Banks, Mr. Dalrymple, hydrographer to the East India Company, Dr. Maskelyne, the Astronomer Royal, and other men of science. He was now employed to convey troops to Porto Rico and Trinidad, after which he quitted the Carron, and in 1798 was made captain of the Anna, his old ship, and with her made many more voyages between China, Bengal, and London, his nautical notes being daily and nightly — even hourly — his peculiar care. From the 1st of April, 1802, to the middle of February, 1804, he kept a register every four hours of the rise and fall of the mercury in two marine barometers, and found “ that while it regularly ebbed and flowed twice during the twenty-four hours in the open sea, from latitude 20° N. to 26° S., it was diminished, and sometimes wholly obstructed, in rivers, harbours, and straits, owing to the neighbourhood of the land.” This important discovery he transmitted to the Royal Society, and it was published in their “ Philosophical Transactions” in 1805. At Bombay he became proprietor of a valuable astronomical clock belonging to one of the French vessels which had been sent in quest of the lost voyager, the un- fortunate La Perouse, and regulating his own chronometers by it, he was eiiabled to make many valuable observations on the satellites of Jupiter ; and these he forwarded to the Greenwich Observatory. About the same time he prepared a chart of the Strait of Allas, a dangerous channel through the Sunda chain of islands between Lombok and the west coast of Sumbawa ; and this and other surveys were immediately engraved for the use of seamen sailing in those seas. Captain Horsburgh was now urged to publish, for his own pecuniary benefit, the result of his observations and discoveries ; but the expense seemed too great for a mere master mariner, and might dissipate all his savings, then amounting to .£6,000. Returning to London in 1805, he published by subscription “ Directions for Sailing to and from the East Indies, China, New Holland, the Cape of Good Hope, and all adjacent ports,” the result of twenty-one years’ hard experience in the Southern and Eastern seas. So correct were some of the charts in this publication, that their very accuracy nearly marred their produc- tion ; for with such care and minuteness “ were the bearings of Bombay harbour laid down, that it was alleged they would teach an enemy to find the way in, without the aid of a pilot. It was no wonder, indeed, that these were so exact, for he had taken them with his own hands during whole weeks in which he had worked from morning till night, under the fire of a tropical sun.” In the same year of this publication occurred his marriage, by which he had a son and two daughters. In 1806 he was made a Fellow of the Royal Society, and four years afterwards was appointed, on the death of his friend Dalrymple, hydro- grapher to the East India Company, and he now devoted his whole energies to the construction of those charts which still continue to be the text and standard of our Eastern ocean navigation. In 1816 he published “An Atmospherical Register for indicating Storms at Sea,” together with a new edition of “Mackenzie’s Treatise on Marine Surveying.” In 1819 he published his “East India Pilot,” and contributed to the Royal Society a Paper on the “ Icebergs of the Southern Hemisphere.” In 1835 he published a “ Chart of the East Coast of China,” drawn from personal observation, having the names of all the localities in Chinese characters, and in English, translated by himself ; and this was his last work. For six-and-twenty years after the date of his appointment as hydrographer, he was indefatigable in the great cause of humanity, preparing and correcting charts — true to the vow he had made on that night when the Atlas perished on the rocks of Diego Garcia ; and to that cause he may be said to have fallen a martyr, for the long hours he spent in the cold, damp vaults of the India House, poring over and comparing scientific documents, maps, plans, and charts, . together with his enthusiasm in, and general close study of, the science of hydrography, broke down a constitution that was otherwise robust and hardy. His last labours were addressed to the publication of a new edition of his favourite work, “ Di- rections for Sailing to and from the East Indies, etc;” with many additional notes ; he had it all ready for the press, save the index, when Death laid his hand upon him ; and in his last illness he said to his friend and patron, Sir Charles Forbes, “ I would have died contented, had the blessed God been but pleased to allow me to see that book in print ; ’ ’ and his last words were about the disposal of his works, so that they might be made available for more extended usefulness, as guides for all ships at sea ; and to this charge the Directors of the East India Company honourably acceded, taking care in the mean- while that his children should benefit by the arrangement. On the 14th of May, 1836, he died of hydrothorax, in his seventy-fifth year; and a striking public acknowledgment of his great merit is contained in the report of shipwrecks (by a Select Committee of the House of Commons), which refers to the highly valuable labours of the East India Company’s maritime officers, and the “ zealous perseverance of their distinguished hydrographer, the late Captain Horsburgh, whose Directory and charts of the Eastern seas have been invaluable safeguards to life and to property in those regions.” It is pleasing to add that the lessons he received from his pious old father, before he lef f his native place in the humble post of a cabin-hoy, were never forgotten by him in all his subsequent career, as he “was ever distinguished by the virtues of gentleness, kindness, and charity; and even amidst his favourite and absorbing studies, the important subject of religion employed much of his thoughts.” He wrote several treatises in defence of church establishments, and a few months before his death he published a pamphlet on polemic theology, entitled “ A National Church Vindicated.” Such was the useful career of this distinguished merchant- mariner. TECHNICAL DRAWING.— XXII. DRAWING FOR MACHINISTS AND ENGINEERS. PROJECTION AND DEVELOPMENT. In this plate the projection and development of a cylinder, penetrated by two other cylinders at different angles, are shown. Fig. 220 is the elevation of the object, of which it is required to project the plan. Draw a horizontal line in the lower plane, and from A and B of the elevation drop perpendiculars meeting it in a', b' (Fig. 221) ; then the distance between these two points will be the entire length of the ground covered by the object. Now to find the width of the plan, draw the central line or axis in the elevation, c d, and from c and d draw perpendicu- lars passing through the line a' b' in c and d. The line c d is then the plan of the axis. At any part of the axis of the elevation describe a circle equal to the true section of the cylinder, and through its centre draw e f at right angles to c D. On each side of c and d in the plan set off the length of the radius of the circle, o d', o d" — viz., c c', c c", and d d', d d". Draw c' d' and c" d", which will give the width of the straight part of the cylinder. Now it must be remembered that the circle drawn at o repre- sents the section at right angles to the axis, which for the present purpose is supposed to be rotated on e f, and this will explain the following process : — • Divide the circle into any number of equal parts in the points k, i, d', g, m, etc. ; then the length of the line joining the points, as to n, which are opposite to each other, will represent the width of the cylinder at that part as it would be seen on looking down upon it. Therefore, through g, h, i, j, k, l, to, n draw lines parallel to the axis of the cylinder and cutting the end of the cylinder in to' n', g' h' , i! j', and k' V. From these points drop perpendiculars passing through the plan, and on them from the central line, a' b', set off the lengths of the lines drawn across the circle, measuring from the line e f; thus, g" h" and i" j" in the plan will be the same length as the lines g h and i j in the circle o, etc. Through these points the ellipse is to be drawn, which is the horizontal section of the cylinder at this angle, and here seen in plan. It is scarcely necessary to mention that the end on which 348 THE TECHNICAL EDUCATOR the cylinder rests — viz., A E — will be projected in precisely the same manner, and the same working lines will serve for the one end as well as for the other. Thus, from the points where the lines drawn through m, n, g, h, etc., in the circle o cut the line A E, drop perpen- diculars, which, being intersected by horizontals drawn from the points correspondingly lettered in the plan, will give the points through which the ellipse of the lower end is to be traced ; one-half of this being hidden when looking down upon the object, it is drawn in dots. It is now required to project the plan of the cylinder, aeij, which penetrates the original object, and it will at once be will give the ellipse representing the plan of the circular end, H i. The projection of the upright cylinder, by which the longest one is penetrated, and on which it rests, is obtained in the same manner, and it is believed that the student will be able to work this without instructions, observing that the plan in this case is a circle. We now proceed to show the method of finding the exact shape of the sections, or surfaces at which the cylinders touch each other at their penetration ; and as all are executed on the same principle, it will be sufficient to demonstrate the process on one section — that at o p. seen that the line l k, which is drawn at the widest part of this smaller cylinder, intersects D c at right angles in k; there- fore, from K drop a perpendicular which will cut c' d' and c" d" in k' k". From g drop a perpendicular cutting a' b' in g', and from the points where the lines drawn through m, n and g, h cut g k in the elevation, draw perpendiculars intersecting the corresponding horizontals in the plan, thus obtaining the points through which the junction curve, k" g' k', is to be drawn ; the portion J K is to be projected in the same manner. Now, again, from the points where the lines drawn through ra n, etc., in the elevation cut G K and J K, draw lines parallel to L k, cutting H i in several points, left unlettered to test the knowledge of the student. From these points perpendiculars are to be drawn intersecting the horizontals in the plan, which Fig. 222. — Draw the horizontal o' o" equal to the diameter of the cylinder. At o draw a perpendicular to P, equal to o P, in Fig. 220, and set off on it the lengths b and s — the dis- tance of the points at which the lines drawn through i j and k l cut o P — viz., e, s. Draw lines through k and s parallel to o' o" (Fig. 222), and make them equal to i j and k l in the circle o (Fig. 220). Through o , i, k, p, l, j, o" draw the half ellipse, which is the form of the section at o p in the elevation. Fig. 223 is the section at N o, and Fig. 224 is the section at G K and je. Fig. 225. — In order to develop the surface of this cylinder, draw a horizontal line, as x x, and a perpendicular, as m' b'. Now returning to the elevation, produce the line B e, and draw M A at right angles to it. TECHNICAL DRAWING. 349 It will be seen that this addition completes the lower end of the cylinder, as if that portion were embedded in the ground- plane ; thus the real length of the cylinder is proved to be the distance between m and B, and it will be clear that if the cylinder stood on m a, the height of each point in the section would be the length of the perpendiculars drawn from them ; but they would be further apart than they appear to be on the elevation, in which they seem to become closer as they recede from the centre line. Therefore, from jT (Fig. 225) set off the divisions k, i, d', g, to, e, and l, j, d" , h, n, e, measured from the section in Fig. 220. From each of these points erect perpendiculars. If the circle be large it is advisable to divide again, so as to obtain more perpendiculars, as shown on the left side of the figure, since by this means the difference between the arcs and the straight lines represented by the divisions is diminished. Now from m', in Fig. 225, mark off the length mb, taken from Fig. 220, and on each of the perpendiculars mark off the lengths of the lines correspondingly lettered in Fig. 220 — viz., measuring from A M in Fig. 220, and setting off the distances from the line s x in Fig. 225. Now through e, to, g, d, i, k, b', l, j, d, h, n, e, draw the curve for the top of the cylinder. From each of these points set off the uniform length, b e, all the lines in the elevation, parallel to b e being of the same length. The curve drawn through these points will be the form of the lower end of the cylinder. It will be seen that the lines of penetration, n o and o p (Fig. 220), cut through the parallel lines through i, j and k, l in r, s and u, s. Measure the distance of these points from A M, and set them off on the perpendiculars in Fig. 225, as already shown, and the curves formed in joining the points will be the shape of the aperture which would receive the cylinder on which the oblique one rests. The opening ok j is obtained in the same manner, and is drawn half on each side, the metal or covering of the cylinder being supposed to be cut open on the line e' A. Figs. 226 and 227 are the developments of the smaller cylinders, which, being obtained in the manner just explained, require no further comment.* MECHANICAL DRAWING (continued,). THE TEETH OE WHEELS. In order to transfer motion or force from one axis to another, wheels furnished with teeth are employed, and although the mathematical calculations connected with the forms, etc., of teeth do not come within the province of these lessons, the method by which those forms are to be drawn is a necessary and important part of our subject. If two circular plates, A and b (Fig. 228) were placed so that their edges touched each other, and one of them were rotated on its axis, it would communicate motion by “ rolling contact ” to the other ; but, of course, we could never expect very great force from such motion. Now the transmission of force is one of the conditions of machinery ; therefore such means are taken as shall enable the wheels, not only to communicate motion, but power as well. One moment’s reflection will convince the student, that if the edge of a penny be pressed against that of a farthing, whilst the latter is held between the finger and thumb, the farthing will only move round whilst it is being held very loosely, because the edges of both the discs are smooth. If, however, a half-crown and a sixpence be substituted for the former coins, the additional- friction caused by the milled edges will allow of the sixpence being moved by the half-crown when held much more tightly than the farthing ; in other words, the projections (or teeth) on the edges of the discs enable them to overcome greeter resistance than if they were smooth. It is clear, that although a (Fig. 228) would move b when their circumferences touched each other, yet if a weight at- tached to a cord were wrapped round the axle, as shown in the figure, resistance would be offered, and the edge of A would slide against that of b. Let, however, a pin be inserted at c in A, and another at D * For elementary instruction as to development of cylinders and their sections, the student is referred to lessons on “ Projection." in b, and it is easy to understand that as the one presses against the other during rotation, motion and force will be communicated . But these pins could not pass each other, because the points of the circles on which they are situated would gradually approach until they absolutely touched each other, as at e. The motion would therefore be stopped altogether, or the pins would be broken off. It is therefore necessary that between the teeth spaces should be cut which shall sink into the edge of the disc, as shown at F and G. Then as the teeth approach each other, the point of the one enters into the space next to the other, and thus the action is continued. The motions, then, of wheels are exactly the same as those of two circles rolling upon each other. The original circles which roll on each other are called the pitch-circles, and when the system consists of a wheel and rack (ct, circle rolling on a straight line), the line on which the circle rolls is called the pitch-line. The great effort of the engineer ‘in designing the teeth, is to enable the wheels to move with an accurately uniform motion : the various forms given, and the mode of constructing them, will form the subject of our study. . There are various kinds of wheels : the following are the most important : — Spur-wheels are such as have their teeth standing out directly from the edge. When the teeth are made of wood, and inserted separately into the rim, they are termed cogs, and the wheel is called a cog-wheel — a form much used in mill-work. A sketch of this kind of wheel will be given in a future lesson. Face-wheels have their cogs or pins placed perpendicularly to the face of the wheel. Crown-wheels have their teeth standing perpendicular to the rim, as if the teeth had been first cut on a straight strip, which had afterwards been bent round. Annular-wheels are such as have their teeth cut on the inside of the rim or ring. Bevel-wheels are portions of cones — the teeth being cut on the slanting surface : they are, in fact, spur-wheels, the teeth of which are on the conical side, instead of the edge. They convey motion when the axes are at angles to each other. When the cones are equal, they are called mitre-wheels. It is sometimes convenient that the axes of bevel-wheels should pass close to each other without intersecting ; the teeth have then a peculiar form, and the wheels are called skew- bevels. The curves generally used for the form of the teeth are the cycloid, the epicycloid, and the hypocycloid — the construction of which will be fully described in “Practical Geometry applied to Linear Drawing.” It will, therefore, only be necessary here to remind the student that the cycloid is traced by any point in a circle whilst rolling along in a straight line ; that the epicycloid is traced to a point in a circle rolling against the edge of another circle ; and the hypocycloid is the curve traced by any point in a circle rolling round the inner side of the circumference of another circle. The circle which forms the curve is called the generating circle. When the diameter of the generating circle is equal to the radius of the circle in which it rolls, the hypocycloid becomes a straight line ; this will be referred to hereafter. 350 THE TECHNICAL EDUCATOR. OPTICAL INSTRUMENTS.— Y. BY SAMUEL HIGHLEY, P.G.S SPECTACLES FOR THE PRESBYOPIC ( continued ). The following table, drawn up by Donders from carefully recorded statistics, may prove of service to tbe optician as a guide to what glasses are required at different ages in emme- tropia, with normal acuteness of vision, and accommodation for writing and for reading ordinary type : — a Age. Glasses Required. cl b In Present. E. c In Original. E.* Distance of Distinct Vision. R a Far Point. To Near Point. 48 l-60th l-60th Inches. 14 Inches. 60 Inches. 10 50 l-40th l-40th 14 40 12 55 l-30th l-28th 14 30 12 58 l-22nd l-20tli 13 22 12 60 1-lSth 1-I6th 13 18 12 62 l-14tk l-12th 13 14 12 65 l-13tli l-10tli 12 13 11 70 1-lOth l-7'5th 10 10 10 75 l-9tli 1-6 -5th 9 9 9 78 1-Sth l-5'5th 8 8 8 80 l-7th l-4'5th 7 7 7 We have said that presbyopia occurs not only in the emme- tropic eye (Fig. 6, page 160), but also in the hypermetropic (Fig. 8), and in the myopic (Fig. 10), that is, if we adopt Donders’ standard near-point at 8 inches. Thus, if with the convex glass which neutralises the hyperme- tropia (that is, renders the hypermetropic eye capable of uniting parallel and divergent rays upon the retina), the near-point lies at 12 inches, the patient is not only hypermetropic, but also presbyopic, and he will require two different pairs of convex spectacles — one pair to enable him to see from 12 inches to infinity, and another stronger pair, which will bring his near- point nearer than 12 inches. Or should the patient possess a myopia == L (hi s far-point lying at 16 inches from the eye), and we find his near-point lies at 12 inches ; then he is not only short-sighted, but long-sighted also. His myopia = v, his presbyopia (as shown above) = Jj. The opinion of oculists is divided as to the proper time ern- metropics should begin to use spectacles. On the one hand, it is asserted that the employment of convex glasses should be deferred as long as possible ; and to this prejudice the vanity ®f human nature is too ready to give support, the adoption of spectacles being in such cases regarded as an outward visible sign of an inward material decay — of the advent of age. But must it not bo regarded as folly to unnecessarily weary both eyes and. brain, in guessing, with much trouble, at letters, stitches in needlework, etc., which could be seen distinctly by the aid of spectacles? But, on the other hand, an opposite error of judgment pre- vails, viz., that, by recommending the early employment of weak spectacles, the power of vision may be preserved; hence such terms as “preservers,” “conservative spectacles,” m connection with which may be noted the introduction of amber glasses,” “ tinted spectacles ” (light yellow, pink, or blue glasses), et hoc genus omne. In connection with the latter, the following caution may be given — viz., that most per- sons are ready to employ them, on account of their agreeable, soothing influence ; but we must remember that coloured, even but slightly-tinted glasses, withhold from the retina the ordinary stimulus of white light, so that its sensibility is abnormally increased, and thus they create a permanent necessity for then- constant use. It need hardly be said that a more than normal sensibility in the retina is an inconvenience, which, moreover, predetermines to disease. The common sense of the question seems to be, that so long as the eye does not err, and remains free from fatigue in the work required of it, its own power is sufficient, and it is inexpedient to seek unnecessary assistance from convex glasses. On the contrary, as soon as the eye begins to feel teased by the every-day work required of it, the aid of the optician, or the advice of the oculist, should be sought. • This will he referred to under treatment of Hypermetropia acquisita. Another question arises. After commencing the use of spectacles, how often ought the sights to be changed ? The answer is : As slowly as possible ; for every advance is, as it were, a milestone passed on the road to virtual blindness — that is to say, were the rate of change too rapid, and the person lived to an advanced age, a point might be arrived at when the optician’s resources would be exhausted, and then the dimmed sight could no longer be aided, for the deepest lens would have been passed, and found to fail with increasing years. The proper course is to use the weakest spectacles that will give the desired assistance, only in the evening, and to keep these for day spectacles so soon as stronger glasses are re- quired for evening work ; and so with every change, the weaker glasses being used for day, the new and stronger glasses for the evening. Moreover, the weaker glasses should be used for writing, while the stronger are reserved for reading; for the reason that the wearer can see with them at a greater distance, and to avoid the bent position for writing which becomes a custom with the short-sighted — a position injurious to the eyes, as it tends to throw the blood to the head, and so congest them. And here it may be noted that should a person apply to his optician for an increase in the power of his glasses, at shorter intervals than is usual, and a rapid increase in his presbyopia is ready observed, this may be suspected as a premonitory symptom of “ glaucoma,” especially if a. greenish opacity behind the pupil is noticeable : in such case the person cannot be too quickly sent to the ophthalmic surgeon, for the threatened disease is of a formidable nature. Contrary to what might be expected, persons who are occupied almost the whole day in reading, writing, or other close work even such as that of watchmaking and engraving — who are obliged to employ a magnifier, or as microscopists, do not essen- tially injure their eyes, nor does their range of accommodation diminish scarcely, if at all, more rapidly than it does in sailors, agriculturists, and others, who, for the most part, look at dis- tant objects. At least, this holds good with emmetropics, and even those disposed to myopia; though much reading or writing tends to make them more short-sighted, yet such occupations have no influence on their range of accommodation. But there are morbid conditions which cause the range of accommodation, and sometimes also the amount of refraction, to diminish more rapidly than usual, such as general debility (the result of exhausting disease), premature old age, and glau- coma previously referred to. In all such cases, the optician should only supply spectacles under the guidance of the ophthal- mic surgeon. In many instances the optician will be called on to adapt glasses to meet the requirements of the calling of his customer. Some occupations, such as minute drawing, engraving, watch- work, minute anatomical dissections, and microscopical mount- ing, require the constant use of the magnifying glass. In other- work the eye, even with normal acuteness of vision, must at least be still accommodated for distances from 4 to 6 inches. In such cases convex glasses become a necessity, to render per- manent accommodation for such distances possible. In other cases, the work must be performed at definite distances, such as, in writing in large registers, reading in the pulpit or in the orchestra, in the use of certain musical instruments, etc. It is often desirable to bring the distance of distinct vision to 18 inches, or 2 feet; so weaker glasses are necessary where, in the former cases, stronger ones would be required than would be given for reading or writing. Guided by sound principles and practical experience, the optician soon finds what spectacles meet the special requirements of each case. THE STEAM-ENGINE.— Y. STEAM-PIPES — -THE CYLINDER PRINCIPLE OP ALTERNATE MOTION THE PISTON AND ROD — PACKING OP THE PISTON. Having now mastered the mysteries of the boiler and its various appendages, we must turn our attention to the mechanism and construction of the engine itself. This, as we have explained, may be, and often is, entirely separate from the boiler, yet with- out it the engine is of no use. The boiler may be regarded as the part of the machinery where the power is generated, and the THE STEAM-ENGINE. 351 engine as that portion where this power is brought under control and made to accomplish the ends we desire. In locomotives and portable engines the two are usually com- bined, the various parts of the engine being securely fastened to the boiler itself or the framework which supports it ; but this is done merely as a matter of convenience. In large manu- factories, where much machinery is employed, the boilers are almost universally separate, and often at a distance from the engines to which they supply steam; and this is the most general plan. There are usually several boilers placed close together, and they may be employed either singly or together ; so that in case of any one requiring repair, steam may still be generated in the rest, and no stoppage of the machinery is caused. Several engines are often driven from one set of boilers. In many cases, indeed, a small engine is attached to the machine it is to drive, and is made a part of it, and a small steam-pipe is then connected to it. This is often found to answer better than driving the machine from the ordinary shafting, and has, besides, another advantage — viz., that if flexible steam-piping be employed, the machine may easily be shifted from place to place without altering the connections. In the case of pumps, this is frequently found to be a very great convenience. Cranes, centrifugal drying machines, and various other small machines, are frequently thus fitted with an engine of their own. It will, however, be much better to defer the consideration of these special engines for the present, and first of all to inquire carefully into the construction and action of the various parts of some simple form of engine ; and, having done this, the various modifications introduced will then be far more easily understood. We will therefore inquire in this way into the principle of the most common form of engine, such as may frequently be seen in any large factory, and is known as a “ low-pressure beam engine.” Various lines of shafting run along the different floors of the building, all of which are set in motion from the engine. All the various machines are then driven from this shafting, pulleys or sheaves being fixed at various intervals along it, over which straps pass to the different driving-pulleys of the machines. In the boiler we have a continual production of steam at a high pressure, which will find its way mto the air as .soon as any escape is provided for it. The first thing, then, is to conduct this steam to the engine. For this purpose a pipe starts from inside the boiler, and passes through it and on to the engine. The mouth of this pipe is usually placed in the upper part of the steam-chest, or, failing this, as near the top of the boiler as possible, so as to guard against the fine spray, which is produced by the rapid ebullition, entering the pipe with the steam, and being deposited in it or in the various parts of the engine. Much care is required in arranging for this, as otherwise excessive condensation of water, technically called “priming,” will be produced, causing much inconvenience and loss of power. Wrought-iron piping is usually employed for the passage of the steam, and it should -be of sufficient diameter not to impede the passage of the steam, since that would cause a material diminution in the pressure. This piping has to be very carefully made, and tested for strength. At the ends of each piece are flanges with bolt-holes drilled through them, and their faces are turned so as to be nearly true. When two pieces are to be joined together, some hemp packing, well smeared with red lead, is laid spirally on one face, the other is then brought up against it, bolts are passed through the holes, and the nuts are firmly screwed on (Fig. 21). The joint thus produced will last in- definitely, and if carefully made is perfectly steam-tight. Other kinds of packing are sometimes employed in place of hemp and red lead. When the engine is at any distance from the boilers, and the steam has therefore to travel along many feet of piping, there is a considerable loss of heat by radiation from the pipe. To guard against this it is nearly always packed with straw, or covered with wood, felt, or some other non-conducting mate- rial. Very frequently this “lagging” brings up the size of the pipe to that of the face-plates, so that they are hidden, and the pipe appears to be of uniform size throughout. The steam- pipe usually leads direct to the cylinder, and it always has a valve in it near this point, by means of which the steam can be shut off when we wish to stop the engine. Besides this, there is a valve placed just where the pipe leaves the boiler, so as to shut off steam there in case of any injury to the first valve or the pipe ; and in addition to these there is usually a “ throttle- valve ” in the pipe, which is moved by the governor balls, and serves to regulate the supply of steam in accordance with the requirements of the engine, as will be fully shown hereafter. The amount of force existing in the steam will, by a moment’s consideration, be seen to be very great indeed. As already explained, a cubic inch of water when converted into steam occupies at the pressure of the air very nearly a cubic foot— that is, it expands 1,700 times. In doing this, it has to overcome the pressure of the air, and therefore exerts a pressure • m. t Jj t. equivalent to raising a weight of 15 pounds to a height of 1,700 inches. This will be more clearly seen if we imagine our cubic inch of water to be placed at the bottom of a tube of indefinite length, having a sectional area of exactly one inch, and to have above it a piston, fitting the tube air-tight, but supposed to be without weight, and to move without friction (Fig. 22). Now the air presses with a force of 15 pounds on a square inch, and as this is the j L - - . area of our tube, we may regard the water as pressed Pig. 22. upon by a single weight of 15 pounds. Now let the water be gradually converted into steam, the piston will rise till it attains an elevation of 1,700 inches, or 142 feet nearly, all the time resisting the pressure of the air, which is equivalent to lifting a weight of 15 pounds. This, then, is the work accom- plished by the evaporation of one cubic inch of water — 15 pounds raised 142 feet, or 142 x 15, that is 2,130 pounds raised one foot high. To remember this we may express it in the following statement, which can easily be borne in mind : — The force produced by the evaporation of a cubic inch of water is sufficient to raise a weight of nearly one ton to a height of one foot. Only a small portion of this force is utilised in any engine at present constructed ; but we must now see how this portion is utilised' in the ordinary forms. Various plans for driving machinery by means of this force have been suggested and tried : some have let the steam, as it issues from a jet, strike against a set of vanes, and thus impart motion to them ; others have suggested the employment of a wheel similar in construc- tion to that used in the water turbine ; but the only plan that has come into use has been the employment of a cylinder with a piston moving up and down in it. The cylinder consists of a strong cast-iron tube of large dimen- sions and of considerable thickness. Its size varies with the power of the engine ; but it is usually about half as long again as its diameter. Its interior surface is bored or turned with great care, so as to be perfectly cylindrical and of uniform diameter throughout; it should also be free from flaws. Covers or caps are firmly bolted on to each end, the joints being- packed so a3 to be perfectly steam-tight, and suitable apertures are made near the end to provide for the ingress and egress of the steam. As it has to withstand the pressure of the steam and the jarring of the piston, this cylinder must be firmly and strongly made. Inside this there is a piston which can move up or down, but fits steam-tight. It is likewise composed of metal, and is virtually a disc of considerable thickness firmly attached to the piston-rod, which moves through an opening provided for it in the upper cover. We can now understand, by reference to Fig. 23, the manner in which this piston is driven by the steam. Let us first of all suppose that the piston is of considerable weight, and is nearly at the bottom of the cylinder, which 352 THE TECHNICAL EDUCATOR. is so arranged that it cannot quite rest in contact with it. The steam from. the steam-pipe is now allowed to enter the lower end of the cylinder, through the port E. Its pressure at once overcomes the weight of A and the pressure of the air on its upper surface, and raises it to the top of the cylinder, the air which previously occupied that space being driven out through d. If now the steam be shut off, and the pipe removed, or, simpler still, if a second opening be provided, the weight of the piston will drive out the steam into the air, and force the piston down again to the bottom. The steam may then be re-admitted, and the piston will be driven up again as before, and in this way an alternating move- ment of the piston-rod is obtained, which may easily be con- verted into one of rotation. This, then, is the simple principle of the engine, and, as will at once be seen, the chief difficulty here would be to provide some means for making the lower part of the cylinder communicate alternately with the steam- pipe and with the air. This may, however, be easily accom- plished by means of a two-way cock, as shown in Figs. 24 and 25. In each figure c represents the pipe communicating with the lower part of the cylinder, and s the steam-pipe, while A is open to the air. The passage through the plug of the cock is curved, as seen in the section, and when in the position shown in Fig. 24, a direct path is opened for the steam to pass into the cylinder, while all communication with the air is cut off. When the piston reaches the top, the tap is turned one-fourth of a revolution, to the position shown in Fig. 25 ; the steam is thus cut off, and that already in the cylinder can escape through A into the air. In this, which is the simplest form of engine, there are many important defects which have subsequently been to a greater or less extent overcome. The pressure of the air, it c c will be observed, obstructs materially the upward progress of the piston, since it presses on every square inch of its surface with a pressure of fifteen pounds. It does not, however, aid in driving it down, since when the piston is descending, both sides are equally exposed to its pressure. There is, therefore, in this way a very great loss of power. This is almost entirely avoided when a condenser is used. The steam then, instead of issuing into the air, is allowed to pass into an exhausted vessel, in which it is condensed into water, and a vacuum thereby pro- duced. The pressure of the air then impedes the ascent of the piston as much as before ; but, since there is a vacuum in the lower end of the cylinder, it aids the descent in almost the same degree, and thus, on the whole, there is little loss. Another disadvantage of this form of engine is, that its action is very uneven. The piston is driven by the force of the steam to the upper end of the cylinder, while the return is accomplished merely by its own weight, or any weight with which it may be loaded. In some cases, however, this is not nearly so great a drawback as in others. In a pumping-engine, for example, the whole strain is when the pump-rods are being raised, their own weight being suffi- cient to carry them down again. A single-acting engine is, therefore, employed for this purpose ; the piston is, however, usually forced from the top to the bottom of the cylinder, the pump-rods being attached to the other end of the beam, so that the water is raised while the piston is descending. In a future paper we shall introduce an illustration of this engine, and enter into the details of its construction. If we return now to our original cylinder (Fig. 23), we shall easily see that, if by any means we cause the steam to enter alternately at the upper and lower ports — the other port, in either case, being in communication with the air — we can make a double-acting engine, the piston being now driven in each direction, instead of in one only as in the former case. By using a four- way cock this may easily be done, and we shall thus have a model showing the principle of the double-acting engine. The student will from this understand the principle on which the steam-engine acts, and we can therefore turn our attention now to the construction of the piston and piston-rod, and the manner in which the supply of the steam to either end of the cylinder is regulated. The piston is usually made either .of cast-iron or brass, the latter being preferred, as it is lighter and does not so easily break. Bound the edge of the disc a deep groove was formerly turned, which was com- pletely filled with well-lubricated packing. The piston was then made in pieces, and the top disc attached to the rest by screws. By tightening these the packing was compressed and forced against the sides of the cylinder, so that the steam could not pass ; at the same time the undue wear of the piston or cylinder was prevented. Fig. 26 will explain this mode of construction. In practice, however, it is found that pistons packed in this way are far from durable, and much inconvenience is often caused by their getting out of order. They have, therefore, almost entirely given place to those which maintain steam- tight contact without packing, and are known as metallic pistons. In these there is a very great variety in the mode of construction, though the principle on which they all act is essentially the same. The groove round the piston, instead of being curved, is rectangular in section, and contains, in place of the hemp, two or more packing rings, which are usually made of brass. These are flat rings, having the same external diameter as the piston ; they are made in several segments, the ends sometimes being tongued and grooved to keep them in position. The joints in each ring are so arranged as to be intermediate to those in the others. Strong steel springs are then placed in the piston, in such a way as constantly to force the segments of these discs outwards, and the result is that they press against the interior of the cylinder, and become gradually worn, so as exactly to fit it, and as the pressure is uniform and the surfaces well lubri- cated, there is not much wear or friction. In Fig. 27 we have a cross-section of a piston of this kind. There are two packing rings, each of which is divided into two segments, as shown. Inside these is a thin steel ring, and then come the springs, of which there are five. These are made of strong steel, and may be tightened by the screws, which are seen behind them. Pistons packed in this manner are found to last a long time without showing signs of wear, and may usually be easily re- paired. The points required in any form of packing are perfect contact at all parts, so that no steam may piass by, and, on the other hand, not so strong a pressure against the sides as need- lessly to increase the friction ; and this medium may easily be obtained by properly adjusting the screws. The piston-rod is frequently made with a flat disc firmly welded to its end. The piston then has a hole drilled through it to admit the rod, and its base is countersunk, to make room for the disc. When it is slipped on the rod, and is in its place, a pin .is put through the piston edgeways, and holds both firmly together. In other forms the lower end of the rod is made somewhat larger and tapering, so that when in its place it fits firmly, and, as in the former case, is kept from slipping by a pin driven ! through both, as shown at A in Fig. 26. In locomotive pistons, and other cases, where the diameter is | comparatively small, the piston and its rod are not unfrequently ! made in one piece, and all fear of their becoming loosened by j the alternating pressure is thus avoided. OPTICAL INSTRUMENTS. 353 OPTICAL INSTRUMENTS.— YI. BT SAMUEL HIGHLEY, F.G.S., ETC. SPECTACLES FOE THE MYOPIC. In selecting spectacles for the myopic, great care is necessary, as, on account of the morbidly distended condition of the eye- ball, and of the tendency to get worse, unsuitable glasses might prove very dangerous. In some cases the myopia is so slight, that persons are not aware (as previously stated) that they are really short-sighted. On directing them to look at the distance- test, a decided improvement in their sight is admitted, on their trying slight concave glasses of 60 or 50 inches focus. The detection of myopia, as a rule, is not difficult. It might be confounded with that weak- ness of sight termed amblyopia, for amblyopic persons, in order to obtain larger retinal images, hold small objects very near to the eye. How can we distin- guish. whether the patient is myopic or amblyopic ? If he cannot (like short-sighted persons) distinguish very small objects, or if concave glasses, through diminishing the size of the retinal image too much, impair rather than improve his sight ; and, further, if he can see test type No. II. at five inches’ distance, and can see type double that size at twice that distance ; then In determining the range of accommodation in the myopic eye by Von Groefe’s optometer, as previously described, we found in the case stated that the amount of 1 A = - number six- teen of Jiiger Now, what glasses would be required to enable the patient to see distant objects P By the 6-inch convex of the optometer we have change 1 his eye into a very myopic one — in fact, into a myopia of | ; for we should have to place a concave of 5 inches focus before the convex of 6 inches focus to enable it to see a distant object, for this concave lens would render parallel rays as divergent as if they came from 5 inches distance. In order to find thv proper concave glass for dis- tance, we deduct concave 5 from convex 6 — 1 1 _ 1 6 5 ~ 30 * Hence the suitable concave glass will be No. 30. We have thus theoretically found the proper glass ; but, on account of the convergence of the optic axes preventing the eyes from accommodating themselves for the far-point (only attainable when we look at distant objects with parallel opti>, axes), we should probably find in practice that this would prove rent he is amblyopic, for in this case the retinal images increase in proportion to the size of the print, and all the weak-sighted require is large retinal images ; whereas in myopia it is dif- ferent, for although the short-sighted see large type further than small, the proportion between the distance and size of the print is far less. If, with a suitable concave lens, a person complaining of short-sighted- ness can read type of the size shown in the words “number eighteen ’ ’ in this page, and the words “ number sixteen of Jager,” at the same distance as the normal eye — viz., 20 feet — then he is simply myopic. If, however, with the most carefully selected glasses he can only read the word “Trent” in this page at the distance of 20 feet, then it is a case of myopia complicated with amblyopia, and the less the concave glasses correct, the greater is the degree of co-existing amblyopia, and vice versd. We must be careful not to jump to the conclusion, that because a person cannot see well at a distance, he must of necessity be myopic ; for he may be hypermetropic, in which case convex, and not concave lenses will be required to render distant objects clearly discernible. In extreme cases of myopia, due to lengthening of the eye- ball, sclerotico-choroiditis posterior is almost always present, and, according to Von Groefe, if the far-point lies nearer than 5 inches from the eye (the myopia being greater than §), then sclerotico-choroiditis posterior is present, and this dangerous complication requires medical treatment. 23— Vol. I. too strong ; for it is a rule that we should give the weakest concave spectacles with which the patient can see clearly and distinctly at a distance, so that he may only make use of a minimum of his power of accommodation, and not have to strain it unduly when observing near objects ; for we must remember that he will but seldom have to look for any length of time at a distance, but at near and dis- tant objects alternately. We therefore let him look at the distance-test at 20ft. distance, and find that he can distin- guish it perfectly. We now alternately place very weak concave and convex glasses before the spectacles, and note their effect. If the convex improves his vision, the spec- tacles theoretically selected are too strong, and we must give glasses of lower number. Should the concave improve vision, the selected glasses are too weak. But if neither convex nor concave effect any improve- ment, the spectacles that theory indicated suit exactly. By thus assisting myopes in seeing distant objects we change their eyes into normal ones, for we enable them to bring parallel rays to a focus upon the retina (see d, Fig. 2, page 111). We can also advantageously assist the myopic in seeing things at a short distance, such as reading a sermon, lecture, music, etc., at a few feet distance : as, for instance, a person wishing to see music, while playing on a musical instrument, say at 2 feet distance. Say, for objects at an infinite distance he is using concave spectacles of 12 inches focus. As his myopia equals about X V, then — - number eighteen 351 THE TECHNICAL EDUCATOR. 1 i_ _ 1 12 + 24 “ ~ 24 ’ Hence concave 24 will enable him to read music at 2 feet distance. It is, however, a much debated question whether short-sighted persons should be allowed to wear spectacles for reading, writing, etc. ; but Donders, one of the greatest autho- rities on the treatment of defective vision by means of spec- tacles, considers on physiological and ’pathological grounds that their use is advisable, except under circumstances presently to be named — that their employment is to be strongly recom- mended. In the first instance it is advisable to give the patient weaker glasses for reading than for distant objects; but if his accommodation be good, it is better, ’at a later period, to give him spectacles that will completely neutralise his myopia. In the same way, as in the 'previous case, we have to determine what glasses will meet the requirements of a short-sighted person who wishes to read at a distance of 12 inches. If his myopia = i, then — _ 1 JL _ _ 1 G + 12 ~ 12 5 and wo give him No. 12 concaves. For the reason previously given, somewhat weaker glasses are desirable. We should warn such patients against bringing a book close to the eyes, on feeling fatigued from reading. Instead of putting it down, they bring it nearer to the eyes, in order to obtain greater retinal images, and thus strain and tax their power of accommodation too much ; and if this is made a practice, it will increase their short-sightedness. Again, the same person should be supplied with weaker glasses for writing, if there be a tendency to congestion of the head, so that the injurious results of a stooping position may be avoided. When a myopic person complains of fatigue, and that after reading without glasses for a short time the letters become con- fused, blurred, and appear to run into one another, with pain in and around the orbit (Asthenopia-— see Diplopia, page 160), then the use of suitable concaves for near objects is indicated. This kind of weakness of sight is especially felt after reading, writing, etc., in a gloomy place or by artificial light ; and to ease the fatigue, the person so affected involuntarily rubs his hands over his forehead and eyelids. After a few minutes’ rest he once more sees distinctly, but the same annoyance again occurs, only more rapidly than before. The longer the rest given, the longer can work be continued. As a rule, however, it will (according to the experience of Donders) be found that hypermetropia is at the bottom of this affection, and then convex (not concave) lenses must be employed in the ultimate cure. Asthenopia proceeds from fatigue of the muscular system of accommodation. Myopes should further be warned against anything that tends to produce strong convergence, or writing, or making rectilinear drawings on a horizontal surface, to which end a high and greatly inclined desk should be used ; and they should bo ad- vised to read with the book in the hand. Emmetropic and hypermetropic do not suffer injury as quickly as myopic eyes from the use of unsuitable glasses. It is better to use glasses that are rather too weak, or no glasses, than such as are too strong, for strong glasses make hypermetropic eyes myopic, and myopic eyes hypermetropic. As a rule, it is much less injurious to produce a certain degree of myopia than of hypermetropia, as in the latter case much is required of the accommodative power : so in myopia we must beware of glasses that are too strong ; in hypermetropia, those that are too weak. But we must recollect that every rule has its exceptions, and all the circumstances connected with each particular case, which can exercise an in- fluence on the choice of spectacles, must be duly considered. Myopia is most prevalent in civilised countries, and, as a rule, in their most cultivated ranks ; and while, on the one hand, it is often hereditary, on the other, its foundation is too often laid in schools — more particularly boarding-schools, where by bad lights the pupils read bad print in the evening, or write with pale ink — and so developed in early life. The causes which give rise to myopia are still more favourable to its further development. A near-sighted eye is not a sound eye ; its defect is not dependent upon a simple anomaly of refraction, but upon anatomical and pathological causes, which may be progressive in character, and so constitute a true disease of the eye. The higher the degree of the myopia, the less is it likely to remain stationary. In youth almost every myopia is progressive, and is then often accompanied with symptoms of irritation. This is the critical period of the myopic eye. If the myopia does not increase too much, it may become stationary, and may even decrease in advanced age ; if developed in a high degree, it is subsequently difficult to set bounds to it — it may become tempo- rarily progressive or permanently progressive. Every progressive myopia is threatening with respect to the future ; so that by the age of fifty or sixty, if not much earlier, the power of vision may irrevocably be lost, either through separation of the retina from the choroid, from effusion of blood, or from atrophy and degeneration of the yellow spot. On the advent of myopia in youth, all promoting causes should be carefully avoided, and its rate of progress carefully watched by the oculist. SPECTACLES FOE THE HYPEBMETEOPIC. In myopia, through the state of refraction being too great, or the optic axis being too long (see Fig. 10, page 160), parallel rays are brought to a focus before the retina when the eye is in a state of rest ; in hypermetropia we have just the reverse of this (see Fig. 8, page 160), and through the refractive power- being too low, parallel rays are brought to a focus behind the retina, which defect we correct by means of a concave lens suited to the degree of hypermetropia, so as to give the slightly divergent, almost parallel rays, emanating from distant objects, a convergent direction, and bring them to a focus on the retina. In some cases stronger spectacles may be required for.neai- objects also. We need not feel surprise that hypermetropics are often not aware that they see distant objects worse than other people, whereas they would soon discover any deficiency of sight that would affect their capacity in reading and writing. A hypermetropic patient usually complains that after he has been reading or writing for some time the letters become ill- defined, and appear to run into each other, while at a distance, he says, he can see perfectly. The other usual indications of this defect have been previously given. All hypermetropics with a fair amount of accommodation habitually expend a portion of this, to compensate more or less for the deficient refractive power of the eye. The function of accommodation, which by normal eyes is only employed for near objects, is thus by hypermetropic eyes partially, or even nearly exclusively, used for distant ones, which accounts for such persons fre- quently being unaware of this defect, as previously stated. The proper corrective convex glass can only be found by trial on the distance-test. We may thus determine the manifest, and then by degrees ascertain and correct the latent hypermetropia ; but as the most efficient method of determining this is by completely paralysing the power of voluntary accommodation by the application of a strong solution of atropine, it is palpable that this defect, when once diagnosed, must pass out of the hands of the optician into those of the ophthalmic surgeon. The patient’s power of neutralising his hypermetropia being thus destroyed, his vision will be found to be materially deteriorated, but may again be restored by a convex glass of higher power than that required previous to the paralysis of accommodation. SPECTACLES FOE EYES OF DIFFEBENT FOCI. As a rule, there is, in all respects, great symmetry between the right and the left eye ; but occasionally there is to be found a great difference between the refractive power of the two eyes. We should, therefore, always test each eye separately as to its acuteness of vision, range of accommodation, and state of re- fraction. All imaginable combinations of refraction occur : with emmetropia in one eye there may be myopia or hypermetropia in the other; hypermetropia or myopia may occur in very different degrees in the two eyes ; or the one eye may be myopic, the other hypermetropic. When astigmatism occurs in one eye only, as a rule it will be found that in other respects harmony of refraction exists on both sides ; that is, with hypermetropia on one side, the astigmatism in the other will be hypermetropic ; with myopia in the right, there will be myopic astigmatism in the left; with emmetropia, the astigmatism is mixed. With difference of refraction we may find binocular vision — vision with each of the eyes alternately — or constant exclusion of the one eye. When binocular vision is present, at any distance, our aim must bo to maintain this, and, if possible, to extend it over a BUILDING CONSTRUCTION. 355 greater region. In the choice of glasses, where a difference of refraction between the two eyes exists, we allow the eye with least acute vision to remain subordinate to the stronger one, for which we supply the weaker glass, should it be advisable to give lenses of different foci. It is a popular belief that when two eyes differ, as a matter of course glasses of different foci must be necessary ; but in practice this by no means follows, for it is only when extreme difference between the refractive power of two eyes exists that such a course is advisable. When there is only a moderate amount of difference between the refractive power of two eyes, we may give similar glasses for both eyes ; and as the relation between the two eyes, to which the person has grower accus- tomed, remains unchanged, he is satisfied. If we adopted the opposite course, though we make the range of accommodation for both eyes more equal, the magnitude of the images in each would be different, and the result unsatisfactory. With hypermetropes, when there is imperfect acuteness of vision, it may be advantageous to produce, by means of glasses of different foci, nearly accurate images on the two retinas, by whose co-operation the power of distinguishing is thus, in many instances, really increased. In rare cases, when the difference between the two eyes is great, and binocular vision is absent, the person may believe himself blind in one eye, especially if that eye be so very short- sighted that objects must be brought unnaturally near to it before they can be recognised — so close, indeed, that the fact of its not being deficient in vision may only be discovered when accidentally some object has been brought close to that eye. In such cases, while one eye may require a lens of 20 inches focus, the other may only be suited with a concave of 2 inches. The most suitable glasses must be determined by careful trial. ASTIGMATISM. In astigmatism the refractive power of the eye differs in diffe- rent meridians of the cornea. It is a defect that is not remediable by the ordinary spherical lenses, but by segments of cylinders, which refract only transversely to their axes. This defect is usually tested for by means of lines ruled at different inclina- tions to each other, such as are given in Snellen’s test types, and noting which of such lines are recognised simultaneously ; or by the binocular method of M. Javal, whose test-plates consist of two similar circles, one being divided by radii corre- sponding to tho hours on a watch-face, with intermediate shorter radii corresponding to the half-hours ; the other being marked with the hour numbers corresponding to the longer radii of its fellow. These are placed so that their centres correspond to the distance between the pupils of the eyes, and are viewed through two lenses, say of 3 inches foci. This test-plate is withdrawn gradually, till all tho lines become dim and disappear, excepting one in each disc. Then, beginning with the lowest power, a set of cylindrical concaves are brought before tho eyes one after the other, with their axes perpendicular to the radius that has remained discernible, till the glass is found which makes all the radii equally black. The meridian of astigmatism, together with the number and position of the correcting glass, is thus determined. The circles cannot be discerned unless the visual lines are parallel and the head straight. The relative position of the visual lines being a fixed one, this sufficiently guards against any change of accommodation. The patient may state what line he really sees by aid of the hour numbers, as these are not seen by the same eye that notes the radii. This also affords a constant test of binocular vision. Astigmatism may also be tested by Stokes’s “ astigmatic lens.” This consists of two cylindrical lenses, the one plano-convex l of i ; the other plano-concave V - i. The first is fastened into a broad metal ring, the second into a ring that works within the other, to allow of these lenses rotating axially past each other, with their plane surfaces face to face. The outer ring is graduated, and an index-point is engraved on the edge of the inner ring. When the index points to zero or 180°, the axes of the two cylindrical lenses are parallel, and the combina- tion equals a concavo-convex cylindrical lens, with equal radius of curvature of the two planes, who^e action is about — 0. If the index points to 90° or 270°, the axes of the cylindrical lenses stand perpendicular to one another, and the system has its maximum of astigmatic action, so that by rotating from 0 to 90° the astigmatism ascends from 0 to To save calculation, different degrees of astigmatism are given directly upon the engraved scale. The instrument is set to the degree of astig- matism suspected * in the patient, and it is then rotated before the eye while it is fixed upon the distance-test. If improve- ment be observed in a particular position, the action of the instrument may be increased or diminished until the maximum of distinctness is obtained. • The absolute correction of astig- matism indicated by this instrument requires great care, and pertains to the domain of the ophthalmic surgeon rather than to that of the optician, who, however, must carry out the optical remedy the surgeon prescribes for the determined degree of astigmatism. BUILDING CONSTRUCTION.— XII. JOINTS IN TIMBER (continued). Another excellent method of joining beams of timber is that often adopted by ship-carpenters, called “fishing” the beam; and this is used, not only in original construction, but constantly in repairs. This system consists in placing the two beams end to end, and clasping them between two similar pieees, then either bolt- ing or strapping all three together. In Fig. 91 both these methods are shown. If strapping be adopted, it will be neces- sary to scarf the side pieces to the middle pieces, to prevent any chance of the middle pieces being drawn out. Scarfing timber will be presently spoken of. This system was used by M. Perronet for the tiebeams, or stretchers, by which he connected the opposite feet of a centre on which an arch was being built, and which, giving- way under the load, had pushed aside one of the piers above four inches. Six of such beams not only withstood a strain of 1,800 tons, but by wedging behind them, he brought the feet of the truss 2 \ inches nearer together. These stretchers were 14 inches by 11, of sound oak, and could have withstood three times that strain. M. Perronet, however, fearing that the great length of the bolts employed to connect the beams of these stretchers would expose them to tho risk of bending, scarfed the two side pieces into the middle piece. The scarfing was of the triangular kind, called “ Trait de Jupiter” (which will be described in connection with Fig. 98)-, each “ jag” being only 1 inch deep, whilst the faces were 2 feet long, and the bolts passed through close to the angles. Of course, the methods here described are open to the objec- tion that they increase the width of tho beam at the juncture, and that they lraA r e a clumsy appearance. This must bo ad- mitted ; but it is equally certain that they are the strongest systems, and should in every case be used where absolute stability is of more importance than the appearance. Tho method of joining next in simplicity is that called “ scarf- ing,” which may be of the rectangular or oblique kind. Tho former is shown in Fig. 92. It consists in “halving” the pieces on to each other, and bolting them together. Now it will be clear that, when bolted together, the wood • will only be half as strong as it was before being cut, as half its thickness has been cut away, and therefore the widths a b and c d represent all the strength remaining in the beam ; and even this is injured by the bolt-holes, as already referred to. This is in some degree remedied by affixing iron plates at A and b. But although the beam thus formed might be available for columns, or other vertical purposes, it will be seen that if ex- posed to cross strain it is liable to give way ; for the iron plates, being of but small section, are liable to bend under the weight, whilst the bolts, too, might bend or tear out ; and against any forces which might tend to draw the pieces apart no greater resistance is offered. The author therefore proposes— 1. That the parts which are to be halved together should be left several inches longer than required for the mere joint, the surplus portion of each to be formed into a dovetail, to be sunk into the thick part of the other, as at A (Fig. 93). If this is done at both ends, a great protection against the parts being drawn asunder is provided. 2. That instead of bolts, coupling-boxes be employed at each end to cover the joints, as at b. These boxes to consist of a bottom and sides, the latter having flanges to which the top is bolted. This will give perfect strength to that which was previously the weakest part. Two or three bands around tho THE TECHNICAL EDUCATOR. 3cG middle part will complete tlie joining, and these may be slightly countersunk into the sides of beams, by which means the parts will be still more surely prevented sliding over each other, whilst they will not be materially injured by*the small quantity of wood taken away in that part. By this system the size of the beam is only increased by the mere thickness of the iron- work, which may be easily covered by a cornice or other joiner’s work, should the situation require it. Pig. 94 is an example of the oblique system of scarfing, and here again it will be seen that, if considered as two pieces of wood joined, it has as a tie but half the strength of an entire piece, supposing that the bolts, which are the only connections, are fast in their holes. The ends of this scarf require strengthen- ing by plate3, and a bolt is required through the middle of the Pig. 96 differs from Pig. 95 only in having three keys. The principle and longitudinal strength are the same. The long scarf of Fig. 96 tightened by three keys enables it to resist a bending much better. None of these scarfed tie-beams can have more than one- third of the strength of an entire piece, unless with the assist- ance of iron plates ; for if the key be made thinner than one- third it will have less than one-third of the fibres to pull by. Pig. 98 is the elevation, and Pig. 99 the plan of the French scarf before alluded to, called “ Trait de Jupiter,” which differs from the method shown in Fig. 97 only in the key being placed at right angles to the slanting line of the scarf, instead of parallel to the line of the beam, as in Pig. 97. The advantage of this method is supposed to be that, when the key in Fig. 97 scarf. This form of scarf is not adapted for the office of a pillar, because the pieces, by sliding on each other, are apt to splinter off the tongue which confines their ends at A and b. Figs. 95, 96, 97, and 98 exhibit forms of scarfing which are -very generally approved, for either ties or posts. The keys re- presented at A in each are not absolutely necessary, for the pieces might simply meet square at those points. This form without the key needs no bolts, though they strengthen it to some extent, due allowance being made for the division of the fibres before alluded to ; but if worked very true and close, and -with square abutments, will hold together, and will resist bend- ing in any direction. But the key is a great and ingenious improvement, and will force the parts together with perfect tightness ; care being taken not to produce constant internal strain on the parts by overdriving the key. The forms of Figs. 95 and 96 are by far the best, because the tongue cf Fig. 97 (a) is so much more easily splintered off by the strain or by the key than the square wood at b in the other two figures. is driven in, it is liable to split off the piece B, as the force acts in the direction of the fibre ; whilst in Fig. 98 the pressure of the key tends rather to press the fibres together than to separate them. But, on the other hand, it seems evident that as the object of the key is to push the parts away from the centre, so as to force them tightly against the tongue b, the stress coming in the slanting direction, shown at b, is by far more likely to splinter the tongue off than when coming in the parallel direction shown at a in Fig. 97. Both the French and the English methods are sometimes worked with several keys, and in both the ends of the beams are generally cut to a sally, as shown in the plan (Fig. 99), which prevents the beam bending in a side direction ; and this may be further strengthened by the addition of an iron plate, shown at C. When girders are extended beyond a certain length, they are liable to bend under their own weight. They thus require sup- port, which it is not always possible to give by means of columns or posts. It therefore becomes necessary that the strengthening should be independent of any other support than CHEMISTRY APPLIED TO THE ARTS. 357 that which can be connected to, or contained by, the girder itself. This method is called “ trussing.” On this subject the writer takes the authority of Mr. Peter Nicholson, who says, “An excellent method to prevent the sagging (or drooping) without the assistance of uprights from the ground or floor below, is to make the beam in two equal lengths, and insert a truss, so that when the two pieces are bolted together the truss may be included between them, they forming its tie.” To prevent any bad effects from shrinking, the truss-posts are generally constructed of iron, screwed and nutted at the ends ; and to give a firmer abutment the braces are let in with grooves into the sides of each flitch. The abutments at the ends are also made of iron, and either screwed and nutted at each of the ends, and bolted through the thickness of both pieces, with a broad part in the middle that the braces may abut upon the whole dimensions of their section ; or the abutments are made in the form of an inverted wedge at the bottom, and rise cylindrically to the top, where they are screwed and nutted. These modes may either be constructed with one king-bolt in the middle (Fig. 100, a), or with a truss-bolt at one-third of the length from each end (Fig. 101, b and c). When there are two such bolts, they include a straining-place, d, in the middle. It is obvious that the higher the girder the less will the parts be affected by the stress, and consequently there will be the less risk of their giving way under heavy weights, or through long bearings. Mr. Nicholson says that the rods inserted may be “either of oak, or of cast or wrought iron. The latter material is, how- ever, very seldom used.” As this statement does not, however, give any reasons for the employment of either wrought or cast iron, a few observations on this subject are deemed necessary, especially as the immense improvements in the manufacture of iron have caused it to be so much more generally used than formerly, especially as the beams just described are almost entirely superseded by rolled or cast-iron girders. It is necessary to the present purpose to state, however briefly, that cast iron is crystalline in its structure (that is, it is formed of separate particles which have settled into their position whilst the molten metal was cooling) ; whilst wrought iron is fibrous (that is, the particles have been, whilst in a soft condition caused by heat, hammered or rolled together, so that they are of a long instead of a crystalline form, and their adhe- sion is thus increased). Malleable iron is therefore able to bear longitudinal strain (that is, the force which would tend to pull the ends apart) better than cast iron ; whilst the latter is best adapted to bear vertical pressure, as in a column, without bend- ing or giving way. In brief, cast iron bears compression, and malleable iron tension ; and, to speak familiarly, if the student wishes to know under what circumstances cast or wrought iron ought to be employed, let him ask the question, “ Could a rope be used ? ” Now if any weight had to be supported from below, it is clear that a rope could not be used, and hence columns to bear a roof would be made of cast iron ; but when the two feet, A, b (Fig. 102), of the iron rafters of a rail- way station have to be tied together, so as to prevent their spreading out, a rope would (though, of course, A I F J B no t permanently) answer the Fig. 102. purpose, and therefore mal- leable iron would be best adapted. For it is clear that the weight of the roof would have the tendency to push the ends A and B outward, and that, if cast iron were employed, it would be in a state of tension which it is not calculated to bear ; wrought iron is therefore best calculated to resist this strain. The rafters c and d, meeting in e, butt against each other, and as the weight of the roof is acting as pressure, the rafters are under a trans- verse stress as well as under a thrust, and here, too, iron would be used. From the shoe in which they meet, and which acts as the keystone of ah arch, a rod (e f) can be suspended to bear up the tie-rod A B. Here, again, a rope would do ; so that this rod must be of malleable iron. The point E being thus firmly held up, may be used as an abutment for “ struts,” F H and f g, and as these would have to bear the pressure of the roof, cast iron would be used ; whilst from G and H rods of wrought iron might again be employed to draw up the tie-rod at I and j. Returning now to Fig. 100, it will be evident that the pressure of the beam will be at A, and that the weight at that point would have the tendency to press downward. The trusses B and C therefore act as an arch, of which the king-bolt, A, acts as the keystone. The trusses b and c are therefore under com- pression, and cast iron or pieces of oak may be used. The same remarks apply to the form of truss applied in Fig. 101, where it will be seen there is, as it were, an arch formed within the girder. Where, however, it is not absolutely required that the trussing should be within the girder, far greater strength may be given by adopting the system the simplest form of which is given in Fig. 103. Here the weight of the beam is suspended from its ends, at which cast-iron shoes are placed, through which tension rods are bolted. These act on an iron support in the Fig. 104. middle of the length, and as the nuts are screwed up at A and b, the tendency is evidently to raise the central cast- ing, and so afford support to the beam. Girders of this form are used to support floors of upper rooms of warehouses, etc., or in schools where, for instance, the girls’ department is over that for the boys ; also in the now generally adopted system of scaffolding where travelling cranes traverse the work in pro- gress. In such cases where the girders on which the trams- are placed for the cranes are of great length, two supports,, united by tension rods, are used. Fig. 104 shows a section of a girder built up of wood and iron, and is called a flitch girder. An iron plate is inserted between the two planks, and iron bolts pass through all three ; . this is found convenient for the architraves of shop fronts, from, the convenience with which the casing, cornice, etc., can be-- attached to it. Beams of this kind also are now almost wholly ' superseded by rolled or cast-iron girders. CHEMISTRY APPLIED TO THE ARTS.— VIII. BY GEOKGE GLADSTONE, F.C.S. SOAP-BOILING. Soap is a term applied to various compounds, but it is only ' with those included under its more familiar acceptation that it is proposed to deal in this article. Such soaps are formed by the action of soda or potash upon fats or oils. Both animal and vegetable oils will serve the purpose of the soap- boiler, though some of them possess peculiar properties which render them specially suitable for certain purposes. It will be convenient to divide them into three classes — the hard, the soft, and the marine soaps. The first of these includes a great variety, from the common, yellow up to the fancy toilet soaps. The alkali used in making hard soaps is soda, and it must be in its caustic state. If the hydrate of sodium, described in the previous article, be used, the alkali is already in the con- dition required ; but if it be supplied in the form of the neutral carbonate, the soap-boiler has to make it caustic by digesting it- with lime. The fats or oils which may be used are very various. Tallow,, olive, palm, and cocoa-nut oils are all extensively used. In addition to these natural oils, oleic acid deserves mention as a waste product of the candle manufactories, but which is of value to the soap-boiler. Rosin is also an important con- stituent of the yellow soaps. All these, with the exception ef the last, which has an altogether different chemical composi- tion, contain stearic or margaric acids, and the hardness of the soap produced is greatly dependent upon the proportion of these acids. The firmness of a soap is . a matter of some importance, as one deficient in that respect is more wasteful. Another important ingredient in soap, especially to the manu- facturer, is water. As a mere matter of profit, of course, it is his object to make it take up as much as possible; but , though a certain quantity be necessary, it is not wise to push the dilution too far, as the reputation of the maker would thereby suffer. A really firm and apparently good soap can be made, nearly three -fourths of which shall consist of water ; but the consumer would very soon find out that its cleansing power was very small, and would not be likely to lay in a 358 THE TECHNICAL EDUCATOR. second stock of it. The hard soaps generally contain from 15 to 30 per cent, of water. The first step in the process of making soap is to boil the fat or oil with caustic lye in large caldrons. These are j generally made of iron, and in the best establishments they are heated by steam, being at once more economical and more easily regulated. The steam-pipes are sometimes so arranged that the heat may either be applied externally, or that the steam itself may be forced through the contents of the cal- dron, in which latter case it not only fulfils its function of heating, but also stirs up the ingredients in a most effectual manner. The boiling-pans are generally made large enough to hold twenty-fire to thirty tons of soap at a time. The fat and alkali are thus b piled together until no grease is any longer seen floating on the surface, but the two have combined together and formed a milky kind of liquid of a neutral character, the acid of the fat having counterbalanced the alkali of the lye. According as the solution is acid or otherwise, more or les3 of the other ingredient is added, until the cauldron is nearly full, and the proper proportions have been nicely adjusted. Common salt is then thrown in, which readily combines with the water, but not with soap — as any one who has tried to wash in sea-water with common soap will know— the result being that the soap separates in curds, which float upon the surface of the saline liquid, the residue going by the name of spent lyes. The spent lyes being drawn off, the saponaceous matter is again boiled up with fresh lye, and, if necessary, some more fat, taking care this time to have an excess of alkali in the solution. Salt is then again added to separate the soap from the liquid, after which the boiling is continued for some hours, in order to perfect the union of the soda with the fat. The soap is then ready to be skimmed off, and transferred to the frames in which it solidifies on cooling. It is then cut into bars and dried, and is ready for sale. The frames are made with movable sides and a porous bottom, so that any lye which may be mixed with the curds shall drain away, and when solidified the frames are removed, and the block of soap is cut by wires, first horizontally into slabs, and then vertically into bars. In England the frames are all of uniform size, so that a block of soap measures exactly 15 inches wide, by 45 inches long, and 45 inches high. The above description of the process will serve for a hard soap made exclusively from tallow ; but for various reasons it is often found desirable to use a mixture of fats or oils, or even of rosin. Castor oil possesses the advantage of readily saponifying, and forming a very hard product, which will take up a large per-centage of water. Cocoa-nut oil has the same characteristic ; but it has other specialities, which will be con- sidered presently, when speaking of marine soap. Palm oil is suitable for toilet soaps, an admixture of it communicating a rather agreeable perfume. It may be used to advantage to the extent of 75 per cent, of palm oil to 25 per cent, of tallow. Rosin will not make a hard soap by itself, as it has too great an affinity for water — so much, indeed, that after having been dried it will become liquid on exposure to the air. It makes, however, a very good compound, either with tallow or palm oil, if limited to about 15 per cent. In no case should it-exceed 30 per cent. The rosin should be saponified separately from the fat, and then added to the other after the last boiling described above, continuing the boiling for some time after- wards, until the two preparations have thoroughly combined. Rosin being cheaper than the other substances, the yellow soap thus made has an advantage in price, while for ordinary washing purposes the slight smell peculiar to rosin is not an objection. It, moreover, makes an excellent lather, and is a strong, useful soap. Oleic acid is very readily saponified, and requires much less boiling than the other substances already mentioned. It may bo used either alone, or with tallow or rosin. It makes a good soap, firm, and not affected by the weather. Olive oil is largely used in the south of Europe instead of j tallow, the shores of the Mediterranean being the native soil of the olive. In this country, however, it cannot compete in price j with the other articles above named. Considerable stress is often laid upon having mottled or marbled soaps, and not altogether without reason, because it is not so easy to givo them this appearance when containing a large proportion of water. Twenty per cent, may be taken as about an ordinary per-centage in the mottled descriptions. The salts of iron or copper (especially the former) are most generally adopted to produce this effect, which is due to their natural tendency to separate more or less from the mass of soap with which they are mixed, as it cools. If the cooling proceeds rapidly, sufficient time is not allowed for the inter- change of the particles, and the soap will present a uniform hue of the colour characteristic of the metallic salt employed. If it is cooled gradually, veins and patches, of a bluish colour in the case of iron, will afterwards be found to extend through- out the mass, which will turn to a reddish colour by the oxidation of the iron on subsequent exposure to the air. It is the conversion of the sulphate into the 'oxide which furnishes the red mottling of the Castile soap on the exterior surface, while it is of a bluish-black within. If the soap were too watery, the colouring substances would, by their superior weight, find their way to the bottom of the boiling-pan, and the effect desired would be entirely lost. Fancy soaps, which are made in great variety for the toilet, are usually scented with some aromatic oils. For this branch of the trade the ordinary commercial soaps are used, after undergoing a process of refinement, or a soap is specially made for the purpose from almond oil, or the like. Much taste is shown by the best London makers in the selection and combi- nation of the perfumes, which, along with the colouring matters, such as vermilion, yellow ochre, aniline, etc., are usually boiled up with the soap. To facilitate this operation, as a well-dried soap does not readily melt, it is usually cut up into fine shavings, and after boiling is well worked under rollers until it presents a uniform appearance. If the soap is intended to be highly scented, or very expensive perfumes are to be employed, the cold process is adopted, as much of the strength of the scent is lost by boiling. In this case the soap is shredded as before, and the perfume and colouring matters well amalga- mated with it by being worked in a mortar with a pestle. It is then divided into lumps, and roughly moulded with the hand into something of the shape it is finally to assume. After being left on a raek to dry for about a week, it is pressed into a mould, which imparts to the cake the form and device which may be required, and when taken out the edges are trimmed and the surface polished with the hand. Transparent soaps are prepared by taking an ordinary hard soap and dissolving it in hot alcohol, after having stored it for the purpose of driving off all the water. Soap being completely soluble in this medium, any extraneous matters which it may contain can be readily separated by filtration, care being taken to keep the solution hot during the process. The alcohol is then evaporated out of the filtrate, and on cooling it hardens into a transparent soap. These soaps are coloured, according to fancy, with vegetable colours dissolved in alcohol. This branch of the trade is little practised in England, in consequence of the heavy duty on spirits, which prevents the home manu- facturer from competing with those on the Continent. Soft soaps are made in this country with either potash or soda and the drying oils, the most familiar of which are those extracted from hempseed, rape, and linseed. These oils are deficient in stearine, and on that account are not available for hard soaps. On the Continent potash is much more frequently employed as the alkali instead of soda, potash being compara- tively cheap in those countries where wood abounds ; but it has such an affinity for water that even when combined with tallow or the non-drying oils, it will not make a firm soap such as will retain its character in a moist atmosphere. In this manufacture the non-drying oils, or sometimes the fish oils or tallow, are boiled up with a solution of potash, not too strong, until they form a thick sticky fluid, when a stronger lye is added and the boiling continued until it becomes quite clear and slimy. The compound has now to be tested carefully, to see whether there is a proper proportion between the fatty acid and the alkali ; because an excess cf either the one or the other will become evident on cooling. Having adjusted this properly, the heating is continued, in order to drive off the superfluous water, and the process is accelerated by keeping it constantly stirred. As the evaporation of the water progresses, the substance in the pan becomes thicker, and the froth on the surface diminishes, until the soap settles down in a thick mass at the bottom. The heat is then withdrawn, and when the TECHNICAL DE AWING-. 359 contents of the pan have cooled down they are scooped out and put into casks. Soft soaps, according to quality, contain from 40 to 50 per cent, of water. Sometimes they present the appearance of a clear yellowish jelly interspersed with small grains, which is produced by the addition of a little tallow, the less soluble constituents of which collect in small granules. At other times they present a uniform green colour, which is a natural result if the soap has been made from hempseed oil, but which is often produced artificially by the admixture of indigo in a yellow soaji. Both the colour and the granulation are mere fancies in the trade, and have no other necessary connection with the manufacture. With the drying oils, soft soaps may bo made with soda; other fats and oils besides those already named may be used with a mixture of soda and potash, in which the latter pre- dominates. The hard soaps should be as nearly as possible neutral ; but ■the soft cannot bo separated from the lye by the addition of salt, as in the former, so that they always retain an excess of alkali. They are principally used for scouring manufactured goods in the bleaching and dyeing works, and will be found mentioned in Lessons I. to IV. of this series, which treat of such operations. Marine soap is made of cocoa-nut oil. Whilst a very small quantity of salt will separate the curds produced by the sapo- nification of any other oil, it has no effect upon this. A very strong brine is necessary for the purpose ; but that is found to be unsuitable in practice, as the brine takes up the water at the same time, and leaves so hard a curd as to be unmanage- able. It has such a tendency to harden under any circum- stances that the oil is boiled with the very strongest caustic soda lye, care being taken that the alkali be not in excess, in which case the use of salt can be altogether dispensed with. The operation is facilitated by the replacement of some of the soda by potash. A cocoa-nut soap made with soda will hold upwards of 70 per cent, of water, and still be so firm as to deceive the uninitiated; however, it is, of course, proportionately weak in its cleansing properties. Its resistance to the effect of a weak solution of salt indicates its value on shipboard, other soaps being absolutely useless for washing in sea- water. Incredible as it may appear, flints, sand, or pipe-clay may •enter pretty largely into the composition of soaps, both hard •and soft, and that without injury to their useful properties. The silica contained in them is reduced to a soluble state by being melted in a reverberatory furnace with caustic soda or potash, then ground fine, and lastly boiled in an aqueous solution of the alkali, the result of which is that the silica forms a transparent gelatinous mass, sometimes known by the name of soluble glass. When the soap has been thoroughly boiled, the silicate of soda is mixed with it in the pan, and the compound is then transferred to the frames to cool and harden. As in the other processes, potash is only used when a soft soap is intended to be made. These soaps are cheaper than those made exclusively from oils and fats, while at the same time they fulfil their purpose very satisfactorily. TECHNICAL DRAWING.— XXIII. THE TEETH OP WHEELS. Pig. 229 . — To trace a cycloid* by mechanical means. Fasten a rail of wood, or any straight edge, to a board. Take a circular piece of wood, cut a small notch at any point in the edge (as at a), and fix a small knob or button in the centre (b). The point of a pencil held in the notch, whilst rolling the disc along the straight edge by means of the knob, will describe a cycloid. In order to prevent the disc slipping as it rolls along, it is advisablo to glue a narrow strip of sand-paper round the edge of both disc and rail. If, instead of a straight pieco of wood, a circle or arc be employed, the curve traced by the pencil will bo an epicycloid ; * The cycloid was invented by Galileo, an eminent mathematician and natural philosopher. He was born in Pisa in 1564, and died in 1642. if the inner side of a hoop be used, the curve will be the hypocycloid. Now if the same generating circle bo made to roll on the outside of a circle, and again on the inside, both curves starting from the same point, the portion inside the circle (the hypo- cycloid) will give the curve for the flank of the tooth, and the cycloid on the outside will give the face or point of the tooth. This will bo clearly understood when put into practice, and for this purpose the attention of the student is directed to Fig. 230. In this figure A and B are the centres from which the pitch- circles a' a" and b' b" are struck. These circles touch each other at C. Now if the epicycloid C D be drawn from C, then a portion of it, C F, will be the face or point of the tooth ; and, again, if by means of the same generating circle a hypocycloid, E C, be traced from the same point, the portion C G will be the flank of the tooth. Of course, if similar curves are drawn from H, in the reverse direction, the opposite side of the tooth will bo described. The length comprised by a tooth and a space is called a pitch. ^ This is, of course, equal to the distance from the centre line of one tooth to that of the next one. The following data are those generally adopted by mill- wrights and engineers : — Supposing the “ pitch ” to bo divided into 15 equal parts ; that is to say— Height of tooth outside the pitch-circle 51 parts. Depth of tooth within the pitch-cireloj 61 ,, Thus the total height of the tooth is 12 „ Width of tooth 7 j> Width of space between the teeth 8 ,, Some engineers, however, adopt the following proportions, and they arc, therefore, used occasionally in the examples : — Tho pitch divided into Width of space Width of tooth Depth of flank Height of face 11 parts, o it ” ir >> 4 8 ” ;< 3 J> Although teeth are designed and the patterns for them are made on the scientific principles shown, it is usual in most drawings to consider the curves as portions of circles, which may be drawn with such approximate correctness as to be sufficiently accurate for general purposes of drawings — the length of a pitch being, as a rule, taken as the radius. Tho face of the tooth, A e (Fig. 231), is struck with this radius (the pitch), and the flank, A D, is struck from C, the centres being in the pitch-line b. Now it will be noticed that the flank of the tooth under con- sideration bends inward about the middle, between A and V. This may be avoided by employing a circle of centres that is, a circle a little outside the pitch- circle — and although using the pitch as the radius, fixing the centres on this additional circle, Thus, place the steel point of the bow compass at F on the additional circle, but strike the flank from G. It will be seen that by these means the evil alluded to is avoided : the tooth thus becomes broader at the base, and con- sequently stronger. It will be found that when the diameter of the generating circle is equal to the radius of the circle in which it rolls, the hypocycloid is converted into a straight line ; therefore, when 360 THE TECHNICAL EDUCATOR. the one wheel is of half the diameter of the other with which it is geared, the flanks of the teeth, instead of being curves, are straight lines tending towards the centre, and they are hence called radial teeth. Two such are shown in Fig. 232. As teeth so formed are, however, necessarily narrower at the Draw the pitch-circles, touching each other in t. From t set off a pitch on each of the pitch-circles — viz., t A and T b. Join a and B. Bisect A b by the line c, and produce it. From A draw the radius A D. bottom than on the pitch-circle, they would be weaker at that j From b draw the radius b b. part, the radial flanks are not drawn quite down to the root, i At A draw a line at right angles to A D, cutting the bisecting but are turned off by small quadrants, by which means they ] line C in f. are materially strengthened : this is shown at A in Fig. 232, j At b draw a line at right angles to B e, cutting the bisecting and will be further illustrated in future examples. In order : line c in s. to strengthen the teeth, flanges are sometimes cast on one or From the centres of the circles to which these tangents are SU l e8 - . drawn, draw circles through f and G, and these will be the .rig*. 233. To draw radial teeth to gear with each other . circles of centres for the faces of the teeth. TECHNICAL DRAWING. 361 Now set off tlie pitches around the pitch-circles, and divide them into teeth and spaces. In the present example the tooth is taken at {j and the space at of the pitch, the height out- side the pitch-circle being | and within the pitch-circle g of the pitch. The radial flanks are now to be drawn, and turned towards the bottom by means of arcs, as directed in Fig. 232. Fig. 234 is inserted to remind the student of one of the methods of dividing a line proportionately to another. In this figure let A b represent the length of the pitch, which Draw the circles in the way which has frequently been shown for the root and points of the teeth. From f, with radius F A, describe the arc A h, which will be the face of the tooth ; and with this radius, and from the same circle of centres, the faces of all the rest of the teeth of the large wheel are to be struck. The faces of the teeth of the smaller wheel are to be struck with the radius G b. it is desired to divide in the proportion of five- elevenths and six-elevenths. Draw any line, c D, parallel to A b, and set off upon it eleven spaces. These may be any length. Draw lines, d b and c A, uniting the ends of the two lines, and meeting in e. From the point marked 6 draw a line to E, which will divide A B in F in the desired proportion. 362 THE TECHNICAL EDUCATOR TECHNICAL EDUCATION ON THE CONTINENT.— XII. BY E. A. DAVIDSON. FRANCE (continued)— METHOD OF TEACHING DRAWING. Primary instruction developing itself in adult classes gives to tlie apprentice and artisan elementary notions of science, which they can apply in their various occupations. Secondary special instruction further develops these germs, and increases in use as the artisan learns the application of science to the work on which he is engaged. But we would have it very clearly understood that we do not mean to imply that technical education can ever do away with apprenticeship. The variety of work which a lad sees going on around him in a workshop — the adaptation of machinery and tools — the broad way in which work is “cut out” and arranged — the division of labour, and above all, the curb which is put on during the years when he is passing from boyhood to man- hood, and the- tie by which he is held to regular occupation — all render a term of apprenticeship of the utmost importance to a youth. Technical education, then, is meant to assist, not to supersede apprenticeship, by giving a youth a knowledge of scientific principles, the application of which he learns practically in the workshop. Instruction of this kind had been going on in Prance long before it was really known as such. The Government, in order to meet the varied national wants, long since organised various establishments where professional apprenticeships were carried out practically. The schools of agriculture and the farm schools, the schools of arts and manufactures, the naval school, etc., are established for technical education of the most approved kind. Private enterprise did more, and an inquiry has made known the useful creations of industrial societies, of large companies, of chiefs of works, of heads of institutions, and of congregational establishments, which have, in the opposite parts of the country, realised the apprenticeships of various industries with much success. But in the face of the ever- increasing mass of wants, legislature became necessary to encourage and regulate the technical education which has now become general. Before mentioning any special systems of actual education, we must refer to one of the means employed, without which ■education cannot be carried on — namely, the diffusion of books. The colportage — that is, the sale of books by hawking, or other- wise than in shops — can neither diffuse them in sufficient num- bers, give adequate extension to circulation, nor place them in all hands. Its business is trade, not education, and even managed as it is, it cannot furnish sufficient guarantee for regularity or continuousness of delivery. The establishment of libraries in all the communes of France, lending or hiring out books, placing them within the reach of all, was a necessary means to be taken in the promulgation of education. Set on foot by the Minister of Public Instruction, established in the communal schools, kept by the schoolmaster, the scholars’ libraries were the first established. There are now about 8,000 libraries, which lend out 500,000 books per annum. But the ministerial action was not enough to endow 4,000 communes with libraries, and public spirit came in aid with remarkable alacrity. A great number of free societies have been formed for this special object, some including a whole province, others a department, and the rest purely local in their action. Many in Paris have striven to organise for themselves centres of action, from which to operate on the country around, either in giving their assistance in the formation of libraries, or in making known and encouraging good books, or by influencing hhe colportage. Whatever may have been the extent of their operations or the mode of their action, they have all assisted in maintaining a healthy agitation which has already borne good fruit. Not only have thousands been induced to read who never before touched a book except by accident, but publishers having thus a large market opened to them, and authors finding a public always ready for their works, have prepared them specially for the object to be attained ; the former, by more economic arrangements, nave endeavoured to reach the perfec- tion of cheapness ; whilst the latter comprehend that, in order to reach the soul of a whole nation, literature must separate itself from elaborations of style, and be pure and broad in its principles ; that in order to teach the million, the writer must not from the summit of an eminence declare the advantages of the olevated position to those who have only imperfect means of attaining it, but that, placing his foot on the lowest step of the ladder, he must take his less favoured brethren by the hand, and say, “Let me lead you up that he who would write for working men, must throw his whole heart into his work — must write clearly, simply, and, above all, honestly. It is obviously impossible, in a series of papers such as these, to give detailed accounts of each of the great schools for technical instruction in France ; the mere mention of all would occupy the remainder of the space at our disposal. One of those in which the industrial work is of an excellent and practical character, is the Ecole Municipale de Dessin Industriel at St. Quentin. We were shown an admirable drilling machine, ornamental wrought- iron gates, a spiral staircase in wood and another in iron, a crab, various doorways with panelled doors, a carved wooden pulpit, etc., all the actual hand-work of the students, and in most cases the working drawings from which the articles had been made were exhibited. In the Ecole Professionelle de Mulhouse, the mechanical works carried on are on an exten- sive scale. The tendency of the studies seems to be in the direction of mechanism, the works produced being principally of that character ; amongst these are vices, screw-hammers, lathes, various other tools and mechanical appliances, models of machines, all executed with the utmost accuracy and in the most workmanlike manner, all showing the knowledge of the principles involved in the construction. Again, in the Ecole Imperiale d’Arts et Metiers, at Chalons, the system of practical application of science is admirably carried out, and the students are taught pattern-making in wood. We saw the pattern for a bevel wheel six feet in diameter, also spur, face, cog, band, and fly-wheels ; but it must not be supposed that the works of the students are limited to wood, or even to mechanical subjects. Their work in both cast and wrought iron is admir- able in character — plummer blocks, hangers, cams, etc. — whilst in their artistic department they produce bronzes of whole figures, such as Napoleon, Britannia, Apollo, etc., in which the modelling and casting are equally good. Perhaps, however, the greatest triumph of work based upon scientific drawing was a large group of objects shown in the Paris Exhibition in 1867. It was labelled “ Models made by the Chiefs of the School Workshops, from the drawings of the students, designed for practical instruction in mechanical draw- ing.” These models consist of various apparatus, appliances, mechanical movements, tools, etc., and can be used therefore not only in teaching mechanical drawing (all being constructed to correct scales), but also in illustration of lessons on processes, physics, etc. Amongst them is a furnace which may be divided to show the vertical section ; engines of various kinds, a forge, etc. etc. Thus is the labour well directed; and it must be encouraging to students to work from models designed and partly made by others — it must tend to give them confidence in the system, and in their teachers, without which education cannot be carried on with energy or success. We must pass by (for the reasons already stated) the Ecole Speciale de Cluny, the professional schools at Ivry-sur-Seine, and at Vincennes (all of which carry on a system of technical education of the most practical character), and give a description of the system of teaching drawing to children and adults, which is largely carried out on the Continent, especially in primary and secondary schools in France. It will not, it is hoped, be deemed out of place here to devote thus much attention to this subject, when it is remembered that drawing is one of the most important elements in technical education,, that it constitutes the language of form by which men of every nation can communicate with each other, and that therefore the methods by which it can bo best taught must be worthy of serious consideration. It must be remembered that, until within very recent date, the subject of drawing has been treated in most countries as a branch of education of a lower character than any other; the instruction consisting for the most part in giving the student a copy, which he was expected to imitate, to measure the lines, ta shade where his example was shaded, and to colour where he saw colour in the copy. Many excellent systems gradually dawned, and have been adopted in Germany and other countries ; none, however, seem PRACTICAL PERSPECTIVE. 363 so well adapted to the wants of absolute beginners as the one originated and admirably carried out in the system about to be described. Many previous courses of drawing, though learnedly conceived and well executed, failed to attain the results in- tended, especially in regard to public instruction. It is clear that when the pupils in a large class have each a different copy, it becomes impossible for the teacher to do more than give to each a passing word as to the execution. He has not time to explain principles, whilst the work of the student is reduced to a merely servile process of copying, the results being obtained in the best way he can ; sometimes, in fact, beginning at the end, and filling in the constructive lines after- wards. The writer has often seen students who have been working perspective or projection from a printed diagram, where they know the form of the object, draw it first, and put in the lines of which they do not know the reason or purpose afterwards ! Further, in giving students a finished drawing to copy, they do not learn the principles upon which the representation lias been constructed ; and experience lias shown that many who can copy a drawing with exactitude and neatness, are utterly unable to produce even a fair representation from the object itself. Of course the success in teaching drawing to the young must, in a great degree, depend on the general cultivation of their intellectual faculties ; but, again, if this subject be well taught, it may bo made a useful handmaid to all other educa- tion, since its applications are so varied and its results so interesting. To accomplish these results, however, experience has shown that in classes of either children or adults, the following condi- tions are necessary 1. That the master’s lessons should be simultaneously given to all pupils in a class or section, and that for this purpose the subject must be drawn on a large scale. 2. That from the explanations given by the^ teacher, the pupils should be led by observation and realisation to the object itself, for which purpose well-made and well-selected models should form a part of the course. 3. That in the first year of the course the teaching, being intended for children whoso ages vary from ten to twelve years, should be of a character so elementary and simple as to be adapted to their capacity, but still bo the basis of the higher . instruction to which it forms the introduction. 4. That in the second year, a technical tendency should be given to the instruction, agreeing either with the industries of the locality, or with the career for which the pupil is intended ; where this is not ascertained, a general knowledge of architec- ture, mechanism, etc., to be given. 5. That the means employed should, whilst engaging the pupils, aid the teacher in his instruction, and furnish him with all that can render the study attractive and pleasant to the pupils. It is evident that a course fulfilling these conditions must be profitable, since it calls for the exercise of intelligence, observa- tion, and thought, whilst it produces that legitimate satisfac- tion which must result from the exercise of the intellectual faculties. How much latent intelligence, how much mental power, would have been awakened in the working men of a past period, had such light been thrown over the instruction of their child- hood ! Whereas the intellect was thrown back on itself, be- cause it was not cultivated in a manner favourable to its develop- ment. The appliances for carrying out this system are : — - 1. A very largo set of diagrams, so that the pupils may see at a glance the whole subject they are to draw, and to enable the master to give the necessary simultaneous instruction, in which he also, if able, uses the blackboard for drawing rapidly any detail which may seem to require further development. To aid the teacher in his explanations, he is furnished with books with corresponding illustrations, serving, in fact, as well- worked out notes of the lesson. 2. Solid models of a good size of the subjects to be drawn, which the students can handle and examine, and so see the reason of lines in the drawing. 3. A separate book for each pupil, in which the subject of the diagram is given, in order to lead to quiet individual study at the class or at home. The illustrations are for the most part rough sketches, figured as to sizes, which the student is required to work out on a given scale. Now the results of such a system must be, that it accustoms the pupils to consider the relations between the dimensions of a subject, and teaches them the method of representing it by means of properly disposed lines, and in a given proportion as to size. It creates in them a desire to inquire into the construc- tion of the object, a knowledge of which in all its bearings enables them the better to delineate it from points of view other than the one which for the time engages them ; it accus- toms them from the beginning to make practical and useful drawings, such as will be understood by all persons engaged in the various branches of industry; and, further, it affords them the satisfaction of having really by their own efforts made a drawing, instead of having merely copied one. The whole of this system, together with others which have been found in every respect most successful on the Continent, will be carefully worked out in the Technical Educator. PRACTICAL PERSPECTIVE.— III. Fig. 14 is a representation of the interior of a hall, having a floor covered with square slabs of alternate white and black. This view is not drawn to any particular scale. Having drawn the general outline or rectangle, fixed the centre of the picture, and drawn the horizontal line, the points of distance must next be marked. These (as in the present illustration) need not be on the paper, but may be on the board or table on which you are drawing. From the four angles of the figure draw lines to the centre of vision, which will give the lines of junction between the floor and ceiling and the walls. Now this hall is supposed to be twice as long as it is wide. The floor thus consists of tv:o squares. Therefore, from A and b draw lines to the points of distance. These will give the points C and D. Join c and D, and this will complete one square of the floor. Again, from c and D draw lines to tho points of distance, and these will give the points E and F. Draw e f, then a e f b will be the perspective representation of the floor. From E and F draw perpendiculars, cutting tho upper edges of the wall in G and H. Draw the lines G H, which will complete the view of the in- terior. The windows and doors are necessarily omitted in this study. Now divide the line A b into the number of parts correspond- ing with the number of slabs to be placed on the floor, and from these points draw lines to the centre of vision. It will be seen that these lines, 1, 2, 3, 4, 5, 6, will pass through the diagonals A D and b C, and also through C F and D E. Thus lines 1 and 6 will cut the diagonals in a and b. Through these points draw a horizontal line, which will give the front row of squares. Lines 2 and 5 will cut the diagonals in c d. Through these points draw another horizontal line, which will give the second row of squares. Lines 3 and 4 will cut the diagonals in e and/. Through e and /, therefore, draw a horizontal line, which will give the third row of squares. By continuing this method, the entire surface of the floor will be covered with squares, each diminished in size or altered in form according to its position. The system of working by scale having been shown in several of the earlier studies, it will not be necessary to our purpose to give the measurements in every case ; but it will be evident that all the principles of perspective here laid down can be equally well applied, whatever may be the relative size of the objects or the height of the spectator. All measurements in the future figures are therefore assumed, leaving it to the student to work them to any scale he may think proper. Fig. 15. — In this study it is required to put into per- spective a square, the surface of which is at right angles to the plane of the picture, and which is divided into nine equal squares. Having drawn the picture-line and horizontal line, and having 364 THE TECHNICAL EDUCATOR. fixed the centre of the picture and the points of distance, set off from A the length A a', representing the distance of the front edge of the square on the left of the spectator. Make a' b equal to the height of the required square, and from a ' and b draw lines to the centre of the picture. From a' set off on the picture-line a' d equal to A B. From d draw a line to the point of distance, cutting a c in d'. At d' erect a perpendicular, cutting b c in c'. Then a' b c' d' is the perspective representation of the square placed at a', at right angles to the picture-plane. Divide a' b into three equal parts by the points e, f. From E and f draw lines to the centre of the picture, cutting c' d' in g and H. These lines will divide the squares horizontally into three equal strips. Divide the length a' d into three equal parts by the points i, j. From i and j draw lines to the point of distance, cutting a'd' in i', j'. At i' and j' erect perpendiculars, cutting B c' in k and L. These will divide the perspec- tive view of the square verti- cally into three strips, and these will become gradually narrower as they recede, although repre- senting spaces of equal width. Another method of dividing the square would be to draw diagonals. Then the lines e and F, cutting these, would give the points through which the lines T, j' should -pass. This method is only of use, however, where the figure to be divided is a square, whilst the method shown is equally applicable to any parallelogram. Fig. 16. — This is an applica- tion of the foregoing figure, and represents a wooden case divided into compartments. Having marked the point M, represent ing the distance of the front of the object from a, draw the parallelogram m n o p, which shows the depth of the side of the case. Draw the perspective view of the front of the case as in the last lesson ; then, instead of di- viding it into three equal parts, as in the line a ' b in the pre- vious figure, set off upon the line corresponding with a' b the spaces representing the thickness of the wood of which the carcase of the case and the shelves are made, and draw lines from these points to the centre of the picture. Next set off within the space on the picture-line which repre- sents the real width of the lower edge of the case the thick- ness of the sides of carcase, the upright partitions, and the distances between them. From these points draw lines to the point of distance, which, cutting m c, will give the points at which vertical lines are to be drawn. In this study the case is represented as square ; but the method of working would be the same, whatever might be the proportion of the breadth to the height. The horizontal lines showing the junction of the sides of the compartments will complete the object. Exercise 8. There is a case of shelves against a wall : the case is 8 feet high and 4 feet wide ; it has three shelves placed so as to divide the case into four equal spaces. The wood of which the case and shelves are made is 1 inch thick ; scale, 1 inch to the foot. The height of the spec- tator is 5 feet 6 inches, and his distance 15 feet. The front of the object is to he parallel to the picture-plane, at 6 feet on the left of the spectator. Exercise 9. Give a perspective view of the same object when at 10 feet on the light of the spectator, and 8 feet within the picture, when its front is at right angles to the picture-plane. Height of spectator, distance, etc., the same as in the last exercise. Fig. 17. — In this study only a portion of the picture-plane is used ; the centre of the picture being placed at one side, and the point of distance at the other. The subject of the study is a cube, placed first in the fore- ground, and then at different distances within the picture. The length from A to B represents the distance of the cube to the left of the spectator, and b c' is the length of its edge. From c' and b draw lines to the centre of the picture ; and, as shown in Fig. 13 (1), the cube, as it moves backwards at right angles to the picture-plane, will travel in this track. From b set off d, equal to the side of the cube, and draw a line to the point of distance. This line drawn from d will cut b c in d'; and a horizontal line from d' to cut C c' in c" will give the distant edge of the ground-plan of the cube. It will next be advisable to draw the perspective views of the ground-plans of the two other views of the cube. From d set off D e, equal to the distance between the back of the first cube and the front of the second. Draw a line from e to the point of distance, which, cutting B C in e', will give the position of the second cube ; and a horizontal line drawn from E', cutting c' C in e", will be the front edge of the plan. It will thus be seen that e' e" represents c' b when it has re- ceded to the given distance. Now a line drawn from e to the point of distance, cutting o' c in F, would be a diagonal of the square base of the cube. Therefore a horizontal line drawn from it would give F f', and complete the plan. But, as already remarked in the former figure, this method would apply to the square only ; and there- fore another method is shown — viz., set off on the picture-line from E the real length of the distant side, whatever that may be. The point f is outside the present figure ; but the lino drawn from it to the point of distance will be seen to cut b c in f', which gives the position of the back line of the plan. The third plan is to be drawn in a similar manner — viz., by setting off from the last point B on the picture-line the distanco of the next cube and the width of its side, and drawing lines to the point of distance, cutting b c in a' and h. Then, as in the previous case, horizontal lines will give the front and back edges of the plan required. Now on c' b construct a square, representing the front of the first cube ; and from the two upper angles, I and j, draw lines to the centre of the picture. On e' e" and a a' erect perpendiculars, and these will be cut by i c and J c at the required height. Horizontals being then drawn at the points where the perpendiculars are cut off, will complete the fronts of the two distant cubes. The perpendiculars d', f', and H will give the distant edge of the side of each cube, and the position of the rest of the lines to complete the transparent appearance of the objects will bo readily understood from the diagram. Exercise 10. Scale, J inch to the foot. Height of spectator 1 , 6 feet ; distance, 15 feet. (1.) Put into perspective a cube of 4 feet edge, when its front is parallel to the picture-plane, at 6 feet on the left of the spectator, and 5 feet within the picture. (2.) Put into perspective a cubical figure 2 feet square at base, and 9 feet high, when at 8 feet on the right of the spectator, and 10 feet within the picture. Fig. 18 is a cubical figure, or block of stone, which is much higher than the eye of the spectator ; and for this reason tiro top, of course, cannot be seen. In order, however, to account PRACTICAL PERSPECTIVE. 365 for this appear- ance, the object is drawn as if transparent, and thus the upper surface of the bottom and the under surface of the top become visible. The student is re- commended to work all his figures in this way, as the in- terior lines act as a check on the exterior ones, and many inaccuracies are often thus dis- covered. In order that the student may test his present know- ledge of the method of working pursued, those figures are not lettered ; but all the working lines are clearly shown, and the construc- tion will now be described. The base of the block is a square, and it is placed on the left side of the spectator, at a dis- tance which may be assumed, or which would be named in the ques- tion to be worked. Whatever this distance may be, set it off on the picture - line from the point imme- diately under the centre of the pic- ture ; and from this point again set off the width of the square base. From both the la st - mentioned points draw lines to the centre of the picture; then from the first one set off the real length of the distant side of the base, and draw a line to the point of distance ; this will cut the line drawn from the end of the front of the base to the centre of the picture, and will give the point at which the hori- zontal line forming the back edge of the plan is to be drawn. 366 THE TECHNICAL EDUCATOR. Now draw the front elevation of the block of such height as may be required, and from both the upper angles draw lines to the centre of the picture. The distant perpendicular is then to be drawn from the back angle of the base, and the interior lines will then follow in their places. Fig. 19. — This figure will afford further practice in placing objects in the distance, and the principle having already been fully explained in relation to the figures, it will merely be neces- sary to pass rapidly through the directions for working this study. Having drawn the plan as in Fig. 18, mark off on the picture- line the distance between the columns ; draw lines from these points to the point of distance, and these, cutting the line drawn from the end of the front edge of the base, will give the positions for the bases of the distant columns. From these plans erect perpendiculars, which will be termi- nated by the lines drawn from the upper angles of the object in the foreground to the centre of the picture, and these being connected by horizontal lines will complete the view. NOTABLE INVENTIONS AND INVENTORS. Fill.— POTTERY AND PORCELAIN ( continued ). BY JOHN TIMBS. The essential ingredients of pottery and porcelain are silica and alumina. Pottery is opaque, while porcelain is translucent. Wares of either kind are soft and hard, distinctions which relate as well to the composition of the ware as to the tempera- ture at which it is made solid. Common bricks and earthen- ware vessels, pipkins, pans, and similar articles, are soft ; while fire-bricks and crockery are hard. Soft pottery consists of silica, alumina, and lime, and admits of being scratched with a knife or file. Stoneware is composed of silica, alumina, and baryta, and may be regarded as a coarse kind of porcelain. Hard porcelain contains more of alumina and less of silica than the soft ; it is baked at a stronger heat, and is more dense. Soft porcelain contains more silica than the hard, and is also combined with alkaline fluxes, so that it may easily be scratched, and it is less able to resist a strong heat. Clay is so generally diffused, and is of such plastic nature, that articles made of it may be said to belong to every people and to all times. The first drinking-vessels were, doubtless, sun-baked, and consequently very destructible ; and it was not until the action of fire was discovered that permanence could be given to these articles. The sun-dried bricks of Egypt, Assyria, and Babylonia have, however, been preserved to the present day, and “ not only afford testimony to the truth of Scripture by their composition of straw and clay, but also, by the hieroglyphics impressed upon them, transmit the names of a series of kings, and testify the existence of edifices, all know- ledge of which, except for these relics, would have utterly perished. Those of Assyria and Babylon, in addition to the same information, have, by their cuneiform inscriptions, which mention the localities of the edifices for which they were made, afforded the means of tracing the sites of ancient Mesopotamia and Assyria, with an accuracy unattainable by any other means. When the brick was ornamented, as in Assyria, with glazed representations, this apparently insignificant but imperishable object has confirmed the inscriptions of the walls of Babylon, which critical scepticism had denounced as fabulous. The Roman bricks have also borne their testimony to history. A large number of these present a series of the names of consuls of imperial Rome; while others show that the proud nobility of the Eternal City partly derived their revenues from the kilns of their Campanian and Sabine farms ” (Birch’s “Ancient Pottery”). Among the Assyrians and Babylonians, clay was used as a material for writing on. The traveller Layard dis- covered in the palace of Sennacherib a whole library of clay books, consisting of histories, deeds, almanacks, spelling-books, vocabularies, inventories, horoscopes, receipts, letters, etc. About 2,000 of these clay books of the Assyrians have been discovered : they are in the form of tablets, cylinders, and hexagonal prisms of terra-cotta. . The potter’s wheel, to give symmetry of shape to clay vessels, is represented on the Egyptian sculptures ; it is mentioned in Holy Scripture, and was in use at an early period in Assyria. [ The very oldest wares of Greece bear marks of having been | turned upon the wheel. The art of firing the ware is also of j the highest antiquity. Remains of baked earthenware are common in Egypt in the tombs of the first dynasties ; and the oldest bricks and tablets of Assyria and Babylon, and remains I of Hellenic pottery, bear evidence of having passed through the | fire. As the clay is by this process rendered porous, and in- capable of holding liquids, glaze must have been early em- ployed ; and numerous fragments testify to tho use of enamels amongst the Egyptians and Assyrians, and glazing among the ancient Greeks and Romans. With respect to form, the Greek vases, by their beauty and simplicity, have become models for various kinds of earthenware ; while the application of painting to wares has transmitted to us much information respecting the mythology, manners, customs, and literature of ancient Greece. Even the Roman lamps and red ware illustrate in their orna- ments many customs, manners, and historical events. The largest vessels of clay formed by the Greeks were the casks, one of which — and not a tub — was used by Diogenes for a residence when he begged Alexander to stand out of the sun- shine. These casks were too big ro be formed on a wheel, and so required great skill in making. The ancient pottery has its distinctions of time and place, as between the rude urns of the early Britons and the more carefully finished specimens of their Roman conquerors. The. simple, unglazed earthenware of Greece contrasts with the more elaborate Etruscan forms, the finest of which, however, aro probably by Greek artists ; and the red and black potteries of India contrast with the black and white potteries of North America, the latter being interspersed with bivalve shells. Among the ruins of Central America have been found specimens of pottery considerably in advance of the arts assigned to the ruins, namely, 1000 B.c. These specimens had been formed without the assistance of the potter’s wheel ; but they are well baked, the ornaments are in different colours, and they are coated with a fine vitreous glaze, such as was unknown in Europe until about the ninth century. Porcelain is of modern introduction into Europe, but it was known in China more than a century before the Christian era. The Chinese improved their art during four or five centuries, and then, supposing themselves to have attained perfection, they allowed it to remain stationary. So completely was the manufacture identified with that nation, that, on the introduc- tion of porcelain into Europe by the Portuguese in 1518, it received the name of “china,” which it still partially retains. The Chinese continued to supply us with porcelain during many years. It was supposed that the fire-clay, or kaoline, used in its production was peculiar to China, and that it was, con- sequently, hopeless to attempt to manufacture porcelain in Europe. While the Chinese were improving their manufacture, the art of making decorative pottery became lost in Europe. It was revived by the Mahometan invaders of Spain, whoso tiles of enamelled earthenware are to be seen in the Moorish buildings of Seville, Toledo, Granada, and the Alhambra. They are of a pale clay, “ the surface of which is coated over with a white opaque enamel, upon which the elaborate designs are executed in colours.” The Spaniards acquired from the Moors the art of manufacturing enamelled tiles, and they still continue to be made in Valencia. The Hispano-Arabic pottery (as it is called from being adorned with Arabic inscriptions) is the prototype of the Italian majolica, the enamelled ware of Italy, dating from the twelfth century. It is related that a pirate king of Majorca, about the year 1115, was besieged in his stronghold by an army from Pisa, and being vanquished, the expedition returned to Italy laden with spoil, among which were a number of plates of Moorish pottery. They were not imitated until the four- teenth century, when specimens of majolica — so called from the island of Majorca — were produced ; they resemble the Moorish examples in having arabesque patterns in yellow and green upon a blue ground. About the year 1451 the manufacture had become celebrated at Pesaro, the birthplace of Lucia della Robbia, who is regarded by some as the inventor of this ware. His Madonnas, Scripture subjects, figures, and architectural sub- jects are referred to by Mr. Marryat as “ by far the finest works of art ever executed in pottery.” The manufacture of majolica flourished during two centuries, under the patronage of tho ANIMAL COMMERCIAL PRODUCTS. 367 house of UTbino, when the most eminent artists furnished designs. There is a tradition that Raffaelle was so employed, whence majolica sometimes passes as “ Raffaelle ware.” The most celebrated dates twenty years after the death of Raffaelle, but his scholars used his drawings in composing designs for the finest specimens. The manufacture attained its greatest celebrity between 1540 and 1560 ; the art then began to de- cline, and the introduction of porcelain — properly so called — helped to complete its downfall. Here we may mention that of late years, majolica, in England especially, has brought “ fabu- lous prices.” The Bernal collection, dispersed in 1855, con- tained about 400 pieces of majolica ware, which cost Mr. Bernal less than .£1,000, but realised at the sale £7,000 ! Majolica prospered in France under the name of faience, supposed to be derived from the village of Faience, in the depart- ment of Var, which, as early as the sixth century, was cele- brated for glazed pottery. The faience manufacture flourished under the patronage of Catherine de Medici and her kinsman Louis Gonzaga ; the latter established Italian artists, who pro- duced enamelled pottery from native materials. This declined, but in the eighteenth century it recovered, and became cele- brated for the brilliancy of a dark-blue enamel, with white patterns, upon a common ware. But the pottery peculiar to France is “ Palissy ware,” whose inventor had considerable diffi- culty in bringing his ware to perfection, though after sixteen years’ labour he succeeded. His rustic pottery became the fashion of the day ; his style is quaint and singular, his figures are chaste in form, the ornaments and subjects — historical, mythological, and allegorical — are in relief and coloured. His natural objects, except certain leaves, were moulded from Nature. His shells are from the Paris basin, his fish from the Seine, the reptiles and plants from the environs of Paris ; the colours are unusually bright, and mostly confined to yellow, blue, and grey. He is “ a great master of the power and effect of neutral tints.” A favourite subject with him was a flat basin, or dish, representing the bottom of the sea, covered with fishes, shells, sea-weed, pebbles, snakes, etc. France is also celebrated for its ware known as “Renais- sance,” or fine faience of Henri II., of which there are only twenty-seven pieces extant. The manufactory is conjectured to have been at Thouars, in Touraine. The material is fine white pipeclay, seen through a thin, transparent, yellow varnish ; the patterns arc engraved on the paste, the hollow being filled up with coloured paste, so as to resemble fine inlaying or chiselled silver work in niello. A single candlestick of this costly ware was sold some years ago for £220. Holland, from its extensive trade with Japan, was induced to imitate Japanese porcelain. The chief seat of the manufacture was Delft, and the ware was known and ‘esteemed in the six- teenth century by its fantastic design, good colour, and beautiful enamel. The Japanese origin was seen in the monstrous animals, the three-ringed bottle, the tall shapeless beaker, and the large circular dish, which were long regarded in Europe as favourite' ornaments ; while the common articles were so generally distri- buted as to obtain the name of “ Delft ware,”' — in Dutch, plaled. These, however, have been supplanted, even in Holland itself, by the superior manufactures of England, and the improvements introduced by Wedgwood in the making of pottery. About two hundred and forty years ago, some Dutch potters established themselves in Lambeth ; and, by degrees, a little colony was fixed in that village, possessed of about twenty manufactories, in which were made the glazed pottery and tiles consumed in London and other parts of the country. Here they continued to flourish till they were mostly superseded by the potteries of Staffordshire. In England, the first manufactory of fine earthenware is said to have been erected in the reign of Elizabeth, at Stratford- le-Bow. This has long disappeared. The specimens pre- served are remarkable for their lightness. The well-known Shakespeare jug — said to have belonged to our great dramatic poet — is a good specimen of Elizabethan pottery. It is of cream- coloured ware, divided lengthwise into compartments, each con- taining a mythological subject in high relief and of considerable merit. Fac-similes of this jug are made at Worcester. The Elizabethan pottery nearly approaches in hardness that of fine stoneware ; it is dingy white, with quaint figures and foliage in relief. The Staffordshire potteries came into note in this reign ; some of the earliest specimens are butter-pots of native brick- earth, glazed with powdered lead-ore, dusted on while the ware was in a green state. In 1854 a manufactory of earthenware was established at Fulham, specimens of which are still valued by collectors as “ Fulham ware,” consisting of white gorges or pitchers, marbled porcelain vessels, statues, and figures. About the time of the Revolution, ale-jugs of native marl, ornamented with figures of white pipeclay, were introduced. During the reigns of Anne and George I., an improved ware was made of sand and pipeclay, coloured with oxide of copper and manganese, forming the well- known “agate-ware” and “ tortoiseshell- ware,” conferring on the pottery tho character of a hard paste, which was subse- quently so much improved by Wedgwood, and introduced under the name of “ queen’s-ware,” by permission of Queen Charlotte. Previous to this period the upper classes of Great Britain ob- tained their porcelain from China ; while the great bulk of the earthenware in domestic use was supplied by France, Germany, and Holland. To compete with these formidable rivals, Wedg- wood, with persistent genius, employed the native materials which surrounded him in Staffordshire. He became a practical chemist, and improved the composition, glaze, and colour of his ware ; and he invited Flaxman, the sculptor, and other eminent artists to furnish him with designs. Among Wedgwood’s in- ventions are a terra-cotta resembling porphyry ; basalt, or black ware, which would strike sparks like a flint ; white por- celain, with properties similar to basalt ; bamboo or cane- coloured biscuit, jasper ; also a porcelain biscuit little inferior to agate in hardness, and used for pestles and mortars in the laboratories of chemists. He also imparted to hard pottery the vivid colours and brilliant glaze of porcelain. He repro- duced with very great success some of the finest works of anti- quity ; ho copied the Barberini or Portland vase, and, after executing fifty copies, destroyed tho mould. His finest produc- tions took rank with the choicest works of Dresden and Sevres. He greatly improved stoneware, which France manufactured before tho sixteenth century ; and, in England, Dutch and German workmen were engaged in its manufacture at an early period. The mode of glazing by common salt enabled the stone- ware manufacturers to compete successfully with delft and soft- paste fabrics. Next, a very fine unglazed stoneware, with raised ornaments, known as “red Japan ware,” was made in England, after the failure of many previous attempts. It appears that two brothers from Nuremberg discovered, near Burslem, a bed of fine red clay, which they worked at a small factory erected on the bed itself. They endeavoured to conceal their discovery and their mode of working, but the process soon became known. Their ware was fine in material and sharp in execution, the ornaments being formed in copper moulds. ANIMAL COMMERCIAL PRODUCTS.— XV. products of the sub-kingdom annulosa ( continued ). As for nearly a year the queen bee does not lay any eggs des- tined to become queens, if any evil befall her during that time the hive is left without a queen. Her loss or death stops the work of the hive, and, unless another queen is provided, the bees either join another hive or perish from inanition. After about two days, however, the bees generally decide to provide them- selves with a queen, and this state of anarchy subsides. A few of the workers repair to the cells in which their eggs are de- posited, three of these cells are made into one, a single egg being allowed to remain in it. When this egg is hatched, the maggot is fed with a peculiar nutritive food, called “royal beo bread,” which is only given to maggots destined to produce queens. Work is now resumed over the whole hive, and goes on as briskly as before ; on the sixteenth day the egg produces a queen, whose appearance is hailed with delight, and who at once assumes sovereignty over the hive. If the old queen should survive, and the young queens emerge from the eggs last deposited by the old queen under ordinary circumstances, the workers do not allow them instant liberty, as severe battles would take place between them and the reign- ing queen ; they are therefore kept prisoners in the cell, and fed through a small hole which is made in the ceiling of their cell, through which these captive queens thrust their tongues and receive their food from the workers. In this state of con- finement tho young queen bee utters a low complaining note, 368 THE TECHNICAL EDUCATOE. which has been compared to singing. When the old queen finds one of these captives, she uses every effort to tear open the cell and destroy her rival ; the workers prevent this, pulling her away by the legs and wings. After repeated attempts to pene- trate the cells and destroy her royal progeny, the old queen be- comes infuriated, communicates her agitation to a portion of her subjects, who, together with her, rush out of the hive and seek a new home. The queen and accompanying swarm gene- rally fly to some neighbouring resting-place, are observed by the owner, captured, placed in a new hive, and a new colony is at once commenced. The labourers that remain pay particular at- tention to the young imprisoned queens, and these, as they are freed from con- finement, succes- sively lead off fresh swarms, if the hive be not enlarged. Each swarm contains not only the re- cently - hatched young bees, but also a portion of the old inhabi- tants. After the hive has sent off three or four swarms, there are not enough bees leftto guard the royal cells. The young queens conse- quently escape, two or three at a time ; a battle ensues amongst them, and the strongest re- mains queen of the hive, after destroying all the royal larvae and pupae that remain. According to Huber there are two varieties of working bees. The nurse-bees, which continue in the hive, whose office is to build the comb and feed the larvae ; and the collect- ing bees, which fly abroad and bring back to the hive the pollen and honey which they collect. This pollen is formed into little pellets, and packed on the hind legs in the receptacle formed there for this object. Honey is also swal- lowed by the bee, which passes into the crop, where it accumu- lates as in a reservoir, and on the return of the bee to the hive is poured into a honey cell. When a pollen-laden bee arrives at the hive, she puts her two hind legs into a cell, and brushes off the pellets with the intermediate pair. These pellets are kneaded into a paste at the bottom of the cell. The softened kneaded pollen thus packed away is called “bee-bread.” Besides honey and pollen, bees collect a gum-resin called by Pliny propolis, principally from the balsamic buds of the horse-chestnut, birch, and poplar. This is used in closing up crevices in their hives, and in strengthening the margins of the cells of the comb. Honey and Wax are two valuable commercial articles for which we are indebted to the labours of the hive bee. Bees’ -wax is prepared by melting the comb in boiling water after the honey THE COCHINEAL INSECT (COCCUS CACTI) has been removed; the melted wax is then strained and cast into cakes, which have a pale-yellow colour and a pleasant odour. White bees’ -wax is formed by exposing the yellow wax in thin slices or ribands to light, air, and moisture, and then re-melting and forming it into cakes. Wax candles are made by suspend- ing the wicks upon a hoop over a caldron of melted wax, which is successively poured over them from a ladle till they have ac- quired the proper size, so that the candle consists of a series of layers of wax ; the upper end is then shaped and the lower cut off. Wax is also much used in taking casts or moulds, and as an ingredient in cerates and ointments. It is of great value in anatomy in representing normal or diseased structures. Most of our anatomical museums have instructive pre- parations made of this substance. In addition to the large amount of wax, the annual produce of our own hives, c ons id erable quantities are received from Canada. Africa also sends us heavy supplies. About 300.000 lb. are annually shipped from Madras. Alto- gether we use every year in this country about 500 tons of wax, valued at .£2 00,00 0. Above 2,000,000 lb. of honey are annually import- ed into the Uni- ted Kingdom, in addition to that obtained from our own bee- hives. Co chi n e a l (Coccus cacti ). — This valuable insect was first introduced into Europe in 1523 from Mexico. It belongs to the order Hemip ter a , or half - winged insects. The culture of the cochineal insect has ex- tended from the New to the Old World, and it is now produced in India, Java, Algiers, and many parts of Europe. The cochineal insect is small, rugose, and of a deep mulberry colour. It feeds on several species of cacti. These insects are scraped from the plants into bags, killed by boiling water, and then dried in the sun. Those are preferred which are plump, of a silvery appearance, and which yield when rubbed to powder a brilliant crimson. It is estimated that 70,000 of these minute insects are necessary to make a single pound of cochineal. In 1868 we imported 35,375 cwt. of cochineal, valued at .£588, 691. The red colouring matters known by the names of carmine and lake are made from cochineal. Cochineal is used for dyeing scarlet, and is employed chiefly for woollen goods. The dye is obtained by fixing the colouring matter of the insect by a mor- dant of alumina qnd oxide of tin, and exalting the colour by the action of super-tartrate of potash. THE ELECTRIC TELEGRAPH. ;;G9 THE ELECTRIC TELEGRAPH.— YI. By J. M. Wigneb, B.A. CONSTRUCTION OF SINGLE-NEEDLE INSTRUMENTS — THE COMMUTATOR T*IE COIL SWITCHES SWISS COM- MUTATOR-MODE OF JOINING UP CIRCUIT. Besides the regular signals we have already enumerated, there are always a few others to denote various special things ; but, ns these do not form part of the universal code, and are occa- sionally varied, we need not insert them here, but may pass on at once to explain in detail the mechanism of the instrument itself. This will easily be understood by reference to Pig. 23, which represents a back view of the interior of a single-needle tele- graph instrument, the outer case being entirely removed. No alarum is shown here, that being frequently contained in a separate case ; sometimes, however, for the sake of convenience, it is placed in the upper portion of the instrument-case, and even then it is quite distinct from the rest of it. At the back of the base-board are seen four binding-screws, by which the in- strument is joined in circuit with the batteries and the line. The wires leading from the positive and nega- tive terminals of the battery are con- nected with two of these, marked re- spectively c and z. The terminal l is connected with the line - wire, and E with the earth- plate. The handle seen on the face of the instrument is se- curely fastened to the cylinder, a b, of the commutator. This is made of some hard, dry wood, usually box, and is supported in front by the dial- pl ate, through which its axis passes, and at the back by the sup- port D. In the figure it is shown in the position it occupies when the handle is pressed to the right, so as to send a beat in that direction. The barrel, or cylinder, has a metal ring at each end (a and 6) ; these are perfectly insulated from one another by the dry wood between them. A brass spring, c, presses against the front one of these rings, and thus this end of the cylinder is in constant connection with the binding-screw z, through the medium of this spring and the brass strip leading from it. The other end of the cylinder is in metallic communication with the axle at that end of the cylinder, and thus, through the medium of the strip d and the spring which rises from it, with the binding-screw C. It will thus be seen that, by means of these springs, the two ends of the cylinder become virtually the two poles of the battery. Two short pegs of stout wire are inserted in the metal rings of the cylinder — one in the under side of the front ring, and the other on the upper side of the back ring. These are so placed as to be in the same plane as the handle in front. From e a strip of brass passes along the base, parallel with the cylinder, and is connected to a brass spring, k, so arranged that when the cylinder is inclined in that direction the pin e shall come in contact with the spring and raise it. A stout piece of brass, i, is likewise connected with the strip, and this serves as a stop for the pin in a to strike against. On the other side of the instrument is a similar spring, /, and 24— Yol. I. stop, but these are connected with the binding-screw g. The springs k and /, when not raised by the pin e, rest against the ends of a short piece of brass fastened to the support n, and thus are in metallic communication with one another. This, then, is the transmitting part of the apparatus, and above the commutator is seen the coil A, which is essentially the receiving portion. In its construction this is very similar to the “ detector ” referred to in page 255, being merely a delicate galvanometer, with the needle placed vertically. Two small cases are made of thin wood or pasteboard, allowing just sufficient room for the needle to swing freely within them. They are then carefully wound round with very fine copper wire covered with silk, so as to insulate the successive layers. Considerable care is required in winding these coils, as if the wires in the different layers run at all crosswise much of the power is lost. Both coils are wound in the same direction, and the ends are then connected, so as to make one continuous circuit round both. The reason for having two separate coils is that it renders it much more easy to put the needle in its place, one end of the axis being sup- ported in the bear- ing seen behind the coils, while the other turns in a small hole in the bridge seen on the dial face. The con- struction of the needle is shown in Fig. 24, where A i3 the magnetised needle which is within the coil, and B that seen on the face of the instru- ment. The latter is usually unmag- netised, and serves merely as a pointer. In some instru- ments, however, both are magne- tised, the poles being reversed so as to render the combination asta- tic. In either case the lower end is slightly weighted, so as to cause the needle to resume its vertical position immediately the current is interrupted. The needles are held in their places by means of small nuts on each side of them, screws being cut on the axis at the places where they are. The ends of the coil are connected to the binding screws g and h, the latter being in communication with L by means of a brass strip. We are now in a position to trace the course of the current through the instrument, and in doing so shall understand clearly the purpose served by the different springs and strips of which we have been speaking. First of all, we will suppose that a distant station is sending a message. In this case the batteries of the receiving station are not required, the only thing necessary being a direct path by which the current, as it arrives, may pass round the coils and on to the earth-plate. This we shall see is the case when the handle is vertical. The current arrives by the line-wire, and reaches l ; it then travels along the strip to h, traverses the coil, returning to g ; from this it passes up the strip /, across the piece of wire against which this rests to k , and thence to E and the earth- plate. In this way the line-wire and the earth-plate are virtually connected directly to the ends of the coil, and for a simple receiving apparatus this is all that we need- Now let us trace the course of the current when we send a message. Let us imagine the handle to be turned to the right, as shown in the illustration. The pin e first of all raises the 370 THE TECHNICAL EDUCATOR. spring / off the support against which it leans, the other pin then comes in contact with i. The current now passes from C, along d, to the axis of the commutator, thence, by e and /, to the screw g. It then passes round the coils, and returns to h, whence it goes from l along the line-wire, round the ceil of the instrument at the further end, and back, by the earth, to E. The circuit is then completed by the stop i, the cylinder a, and the spring c. When the cylinder is turned in the other direction, the course of the current is from c, by d, e, lc, to the earth-plate, returning from L, by h, g, a, and c, to z, so that now it passes round the coil in the reverse direction, and accordingly deflects the needle to the left instead of to the right. When the instrument is not a terminal one, but in the middle of a circuit, l is usually connected with the line-wire on one side, and e on the other. A switch is, however, connected with the instrument, so that earth may be put on at either side at pleasure, and the instrument on that side is thus cut altogether out of the circuit. Many different forms of switches are often employed for purposes similar to the above, and it is well, therefore, just to explain the principle on which they act. In Fig. 25 we have a figure of an ordinary peg switch, suitable for the case referred to. Three plates of brass are fixed upon a board in the manner there shown. One of these is placed in connection with the earth-plate, the other two with L and e respectively. If, then, we want to receive a message from l, we can cut off all stations on the other side by inserting a brass peg in the opening a, which will make a direct communication between e and the earth-plate. In a similar way we can cut off the stations on the other side by inserting the peg in c; while if it be necessary at any time to cut our own instrument altogether out of circuit, without interfering with other stations on the same line, we can easily do so by inserting the peg in b. In each case a much shorter path is provided for the current, and as it always travels along that which offers least resistance, it takes this in preference to the route through the instrument. When any instrument is by any such contrivance cut off from the rest, it is said to be “ short circuited,” and an arrangement of this kind is very frequently employed. It not unfrequently happens that there are several different circuits between which communications are at times required to be made, and in this case the number or shape of the brass plates is altered so as to meet the special circumstances. Another contrivance frequently employed for the same purpose is known as the “lever-switch,” and will be under- stood from Fig. 26. The line-wire is connected to a binding- screw on a strip of brass, B. A second strip, c, turns on a pivot at the end of this, and can at pleasure be made to rest on the springs or studs, A, i, and E, which are connected re- spectively with the alarum, the instrument, and the earth-plate, or any other pieces of apparatus. The current may therefore be made to take either of these courses as may be desired, and the number of pegs may bo increased if needed. This switch is not so much employed as the peg-switch already described, since the number of combinations that can be effected by means of it is much more limited ; it is, however, simple in construction, and less liable to be left wrong by accident. In Fig. 27 we have a diagram showing the simplest form of short circuit that we can employ. The two wires are brought to binding-screws affixed to the brass strips b and c, and from these other wires lead to the instrument. Another strip of brass is attached by a pivot to b, so that when it rests on c a direct passage is provided fbr the current from b to c, but when in the position shown the current must pass through the instrument. When there are several instruments in an office, and several different lines of telegraph starting from it, various arrange- ments of this kind are almost indispensable. Very frequently the different wires are brought to one part of the building, and connected there to a series of binding-screws, each of which is distinctly labelled. When there are several different circuits, which have at times to be connected, the “ Swiss Commutator,” or “ Universal Switch,” represented in Fig. 28, is found a very useful con- trivance. A flat slab of some hard, dry wood is taken, and strips of brass are inlaid on each side of it, those on the upper side running in the reverse direction to those on the lower. Holes are then drilled through these strips, as shown, and by inserting a spring brass peg in the proper one of these, a com- munication may be established between any one of the upper and any one of the lower circuits. Many other contrivances of this nature are often employed, but we need not stop to refer to them in detail. In our next lesson we shall describe a simpler form of com- mutator that is now adopted on many lines ; but it will be best first to explain the method of joining up any circuit, that is, of making the proper connections with the batteries and line-wires. We will suppose that we have two stations with instruments, batteries, and line-wires all complete, and we want to establish the communication between them. First of all, let each clerk connect the binding-screws L and E of his own instrument by meaus of a loop of wire, unless, as is frequently the case, there is an arrangement in the instru- ment for doing this by a short circuit. The battery wires are now connected to c and z respectively; sometimes there is a difficulty in determining which is the proper wire for each screw, but this is easily obviated. We have merely to connect one wire to each screw, and then turn the handle in front of the instrument. If the connections are rightly made, the needle will move in the same direction as the handle is inclined. Should it move in the contrary direction, we at once know the wires are wrong, and have simply to reverse them. The loop of wire is now taken off, and the line and earth wires joined on ; the operator at the other end then sends a few deflections to the right, and we at once see if the wires have been rightly connected, and if they have not we reverse them. In this way all the connections are sure to be right ; the main point to remember is that we first of all make sure our own batteries are rightly connected, and then afterwards see to the line-wires. Bearing this in mind will frequently save considerable trouble and loss of time. BIOGRAPHICAL SKETCHES OE EMINENT INVENTORS AND MANUFACTURERS. IX.— GEOKGE STEPHENSON. BY JAMES GRANT. George Stephenson, the engineer (father of the constructor of those vast works, the High Level Bridge across the Tyne, the Britannia Tubular Bridge, and that mightier work of art, the bridge across the St. Lawrence), was the second son of Robert Stephenson and his wife Mabel, and was born on the 9th of June, 1781, in a humble clay-floored cottage in the colliery village of Wylam, eight miles from Newcastle. There were five other children, whose lot was the heritage of toil, and all had to toil hard, for the wages of their father wore small, as his occupation was that of fireman to a coal-pit engine. George was in his eighth year when his father was employed in a colliery at Dewley Burn, where the situation of a herd-boy enabled him to earn twopence per diem to aid the half-starved family. From being a herd, the boy was promoted to lead horses when ploughing, to hoe turnips, and do other farm work, which raised his earnings to fourpence daily ; yet his taste lay not in agri- culture, but among those grimy pits where he had first seen the light, and he obtained employment as a gin-horse driver at the colliery of Black Callerton, two miles distant from his father’s cottage, and in his fourteenth year he thought that he had attained the height of his ambition, when he earned a shilling per day as assistant fireman to his father at Dewley Burn. On this pit being worked out, the workmen and apparatus were removed to another at Jolly’s Close, and thither went the Stephensons, to become the occupants of a cottage composed of one apart- ment, in a humble street of similar dwellings, with mountains of slag behind, and a run of foul water in front. The total earnings of the whole family amounted to nearly £ 100 per annum ; they lived rent-free, and yet not a penny was ever spent on education or mental culture of any kind ; for the social ideas of the Northumbrian colliers were then low indeed. “ Let any one picture to himself the situation of a friendless lad totally uneducated, living in such a colliery village, and then try to conceive by what force of circumstances that lad was to attain eminence in wealth and station and as a benefactor to mankind ! ” BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS, ETC, 371 At the colliery of Throckley Bridge he was employed in attending to the furnace of one of the giant engines which cleared the pit of water, and then his wages were twelve shillings weekly, and there the lad seemed to be in his peculiar element ; he would scour and grease, polish and work among wheels and levers, pistons, pumps and cylinders, till he actually came to regard his engine with something akin to admiration and affection. It became a kind of hobby with him to take Tier ■ — for so he called it — to pieces, examine all the component parts, clean, and put them together again ; then a shout of pleasure would sometimes escape him when the steam was let on — when the great lever went down and brought up a volume of water that flowed away like a small river ; but his eighteenth year found him still ignorant of the alphabet ! The necessity for education began to impress him seriously now ; he could model miniature engines in clay, thus fixing the shapes and proportions in his memory ; but when he was told of others that he had never seen but could read of in books, he resolved that, cost what it might, he would go to school ; and after a few preliminary lessons, received from a poor teacher, named Robin Cowens, at the rate of threepence weekly, he began regularly to attend an evening school, kept by Andrew Robertson, a Scottish dominie in the village of Newburn, where he rapidly advanced in penmanship and arithmetic. The latter he studied with a slate while attending to the engine, thus utilising time ; and this was all the education he ever received. The year 1801 found him a workman at the Dolly-pit of Callerton ; but though wages were high, food was scarce and dear ; thus he was compelled to spend his evenings, not in study, but in making and mending shoes. In this branch of trade he became an expert cobbler, and “ if anything could have spurred him on, it was the desire to sole the shoes of his sweet- heart, pretty Fanny Henderson, and of these he is said to have made a capital job.” He studiously avoided all taverns or public-houses, and his sobriety, industry, and energy had ere long their reward. His savings enabled him to furnish a small house at Willington Ballast Quay, on the Tyne ; and there he brought home Fanny as his wife on the 28th of November, 1802. From mending shoes, he now betook him to the repair of timepieces, and was known among his neighbours by the sobri- quet of “the clock-doctor.” On the 16th of December, 1803, was born his only son, Robert, who lived to attain the head of his profession as a railway engineer. In the following year he lost his young wife, to whom he was deeply attached, and the blow was all the heavier that his son was still an infant. He was then employed as a brakesman of the coal-lifting machinery at Killingworth, where he won the reputation of being a skilful and trustworthy workman. Being invited to superintend an engine near Montrose, in Scotland, he left his child in charge of a neighbour’s wife, and set out for the scene of his new employment, two hundred miles distant. This journey he performed on foot, carrying a wallet ; but after some quarrelling with his Scotch employers, he left them, to trudge back in the same humble fashion — his total earnings being =£28, which enabled him to succour his father, who was then aged and blind, and whom, with his old mother, he contrived to place in a comfortable cottage near Newcastle. The year 1807 saw him drawn as a private of militia, and every shilling he had saved was spent in procuring a substi- tute ; a loss which exasperated him so much, that for a time he conceived the idea of emigrating to America. Amid all his struggles and pecuniary difficulties at this dark period of his life, it is to his honour that he never failed in providing for the wants of his aged parents, and for his child that education, of which he had so sorely felt the loss himself. Three years after his escaping the militia ballot, there occurred an opportunity for bringing his name prominently forward in his own locality. At Killingworth High Pit there was a badly-constructed steam-engine, which failed to do its work. Several engineers in succession had failed to put it right, and the proprietors were glad to let George Stephenson examine it. Though he had a great reputation for cleverness — nothing more — they never expected him to succeed. He took the entire engine to pieces, re-arranged it, and set it to work in the most effectual manner, to the mortification of those who had miscarried, and the satisfaction of the proprietors, who presented him with a gratuity of =810. This event placed him on the footing of a regular engineer, and as such he was consulted in all cases of defective pumping apparatus. The year 1812 saw him engaged in planning machinery for working pits and wheeling off coal ; and the collieries of Mountmoor, Killing- worth, Derwentcrook, South Moor, and others belonging to Lord Ravensworth and his partners, were all put under his care. Among those who had thought deeply for years of the proper application of steam to carriages was Stephenson, who, after many experiments, began to run a locomotive oh the Killing- worth Railway in July, 1814. This he named the “ Blucher,” in honour of the Prussian marshal. At best it was only a coal- drag, that drew eight wagons of thirty tons at tho rate of four miles an hour. It was full of defects, and clumsy ; but Stephen- son soon remedied all by giving the furnace more draught ; he sent the waste steam into the funnel, by which the power of the engine wa3 doubled, and ere long tripled. In the following year, having had his attention drawn to the disasters in mines by the explosion of fire-damp, he devised a safety-lamp, not unlike that invented about the same time by Sir Humphry Davy. Still planning improvements at Killingworth, Stephenson con- tinued to develop travelling by steam, and step by step the rail and the engine were brought to a comparatively perfect state, and he was enabled to send his son to study at the University of Edinburgh. The engineering of the Stockton and Darlington Railway was assigned him, and it became, in most respects, the model for general railway work. He was already a partner in a locomotive manufactory at Newcastle, and three of these were ordered by the new Company, whom Parliament had empowered to employ steam in the conveyance of pas- sengers and goods, in lieu of the old horse-tramways. The 27th of September, 1825, saw the opening of this, the first public railway ; when, at a given signal, the engine started, at the rate of twelve miles an hour, with 450 passengers, and ninety tons of coals and merchandise, and reached Darlington, a distance of 8f miles, in 65 minutes. When the Manchester and Liverpool Railway was before Parliament in the same year, Stephenson, in the face of strong opposition from interested antagonists, gave much valuable information respecting the practicability and safety of trains drawn by locomotives, though, as yet, he had no idea of a speed that exceeded twenty miles an hour ; but even this was so greatly doubted, that one of the members of the committee remarked, that “ the engineer who conceived such ideas was only fit for a lunatic asylum 1” Opposition crushed, and legal sanction given, the railway company set to work, and, with a salary of =£1,000 per annum, Stephenson was appointed their engineer, with instructions that . the line between Manchester and Liverpool was to be kept as straight as possible. In this great undertaking, the first novel series of engineering had to be undergone — viaducts were to be built, hills tunnelled, embankments formed from the debris of cuttings, and the four miles of dreary bog known as Chat Moss converted in a hard and firm way ere the line was completed ; and ,£500 was offered for the best locomotive that could be brought forward for competition in running by a certain day. Stephenson determined to compete ; and on the 8th of October, 1829, three engines were brought forward ; the “Rocket” by him, and two others by Hackworth and Messrs. Braithwaite and Ericson. The test assigned was to run a distance of thirty miles, at not less than ten miles per hour, along a two-mile level near Rainhill, with a load thrice the weight of the engine. One locomotive was disabled by the failure of the boiler-plates ; another attained fifteen miles an hour, but failed to accomplish the distance ; and the “Rocket” alone stood the test and won the prize, attaining a maximum speed of twenty-nine miles an hour. This day was somewhat of an epoch in engineering, as coke was burned instead of coal, and the coke and water were carried in a tender attached to the engine. On September 15, 1830, the line was opened, and a train of eight locomotives and twenty-eight carriages, with 600 passen- gers, started amid the applause of thousands, who assembled from all quarters ; but the day was not without a disaster. When at Parltfield, the train halted to replenish the water-tanks, and there Mr. Huskisson, M.P., was killed. Next day 130 passengers left Liverpool for Manchester, and by the close of the week six trains were running daily on the line, and the speed was soon increased to thirty-one miles in less than a* hour. No less than thirty stage coaches were thrown out of employment, and their 372 THE TECHNICAL EDUCATOR. 500 passengers were increased to 1,600. This line now forms a part of the vast system known as the London and North- Western Railway. Stephenson now occupied a high position indeed in the world of science. His skill was acknowledged ; his perseverance rewarded. In 1837 he removed to Tapton Hall, near Chester- field, and leaving his son Robert to perfect yet further the powers of the locomotive, when about sixty years of age he began to think of retiring from active professional life. But his career of usefulness was not yet over. He had to visit the Continent several times, to attend consultations on railways, and matters connected therewith ; and on one of those occa- sions, together with his friend Mr. Sopwith, he had an interview with Leopold, King of the Belgians. He always figured promi- nently at the opening of railways, and at the festival of the Trent Valley Line, he was compared by Sir Robert Peel to Julius Agricola, the maker of the Roman roads in Britain. “ When I look back t j the time when I first projected a loco- motive in this neighbourhood,” said he, in reply to Sir Robert’s eulogium, “ I cannot but feel astonished at the opinions which then prevailed. Even by the most celebrated engineers we were told that it would be impossible ever to establish rail- ways. Judgo, then, how proud must be the feelings of one who, foreseeing the result of railways, has risen from the lower ranks on their success ! ” The High Level Bridge across the Tyne at Newcastle, the Conway and Britannia tubular bridges in North Wales, and the mighty tubular bridge, nearly two miles long, across the St. Lawrence, at Montreal, are lasting monuments of tho vastness of his Bon’s genius. Skilful subordinates assisted him, and it is but fair to admit that to the Scotchman, Sir William Fairbairn, of Manchester, is generally imputed the first idea of tubular bridge building. In 1844 Robert Stephenson was returned to Parliament as member for Whitby. Four years after this, his father died on the 12th of August, 1848, in his sixty- seventh year. The close of his days was characteristic of the simplicity of his early life, for George Stephenson occupied himself with birds and dogs, and other domestic pets, and in rearing flowers and vegetables in his garden, which he worked with his own hands. Ho was fond of visiting the scenes of his youth, among the smoky and grimy collieries of Newcastle ; going to the places where of old he had worked as his father’s assistant at the furnaces, and whom he had seen toiling, shovel in hand, clothed in worn woollen rags, and little foreseeing the future of his son or grandson “as he wiped the perspiration from his brow with a bunch of coarse tow.” It was remarked of George Stephenson, that though frequently invited to the houses of the great and wealthy, he never forgot his own humble origin, nor shrunk from recognising, or if possible befriending, an old fellow-workman. He gave advice cheerfully to all who required it of him in their career as engineers, but he had a peculiar aversion for all such as appeared to him overdressed, or indulging in airs or vanity. “ I hope you will excuse me, young man,” said he one day to an applicant of this kind ; “ I am a very plain-spoken person, and I am sorry to see a nice-looking, and rather clever young man like you disfigured by that fine, but absurd waistcoat, and all those chains and fang-dangs. If I had troubled myself with such things when at your age, I should not have been where I am now.” Such was the chequered but brilliant career of George Stephenson. His son survived him only eleven years. He died in 1859, in his fifty-sixth year, and was honoured with a public funeral and a grave in Westminster Abbey. The life of George Stephenson is such as to afford encourage- ment to any man who seeks to get on in life, provided that he is possessed of sufficient earnestness of purpose and per- severance to proceed steadily towards the goal that he has in view. Filial love, economy, sobriety, and fixity of purpose were the cardinal points of the compass by which George Stephenson steered his course through life. To act as he did m the various relations and duties of life is within the. power of all, and although the result obtained may not be so great, we may be sure that it will prove a rich reward for the efforts made to attain it. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— VI. To construct a semi-elliptical arch, of ivliich a b is the span, and c d the height (Fig. 56). Divide c A and c B into any number of equal parts. Divide A e and b e into a corresponding number of equal parts. Number the parts as in the figure. Produce D c, and make c g equal to C D. From d draw lines to the points 1, 2, 3, 4, 5, in the lines e a and E B. From G draw lines through the points 1, 2, etc., in the line A b, and produce these lines until they cut those of corre- sponding numbers drawn from D to the points in the lines E A and F B. Thus — g 1 will cut D 1 in a . G 2 „ D 2 in b. G 3 „ D 3 in c. G 4 „ » 4 in d. G 5 5 in e. The curve is to be drawn through these intersections. Strictly speaking, no portion of an ellipse is a part of a circle, and the curve cannot therefore be drawn with compasses so as to be mathematically correct ; but there are many ways in which figures nearly approximating to ellipses may be drawn by arcs of circles ; and among these the following is given To construct an elliptical figure by means of two squares, ABDC, BDEF (Fig. 57). Draw diagonals in each of the squares, intersecting each other in G and H. From B, with radius B c, describe the arc c e. From d, with the same radius, describe the arc A f. From G, with radius G C, describe the arc c A. From H, with the same radius, describe the arc E F, which will complete the figure. THE SPIRAL. The spiral is a curve, which makes one or more revolutions round a fixed point, but does not return to itself. To construct a spiral of one revolution (Fig. 58). Describe a circle, using the widest limit of the spiral as a radius, as A xn. Divide the circle into any number of equal parts, as I to XII, and draw radii. Divide one of these radii, as A xn, into a corresponding number of equal parts, as 1 to 12. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING. 373 Prom the centre, with radius A 1, describe an arc cutting- the radius I in B. Prom. the centre, continue to describe arcs from points 2, 3, etc., cutting the corresponding radii u, hi, etc., in the points c, d, e, p, g, h, i, j, k, l. From xxi trace a curve passing through all these points, which will be an Archimedes’ spiral of one revolution •sir It will interest our students to learn that Archimedes, the most celebrated of ancient mathematicians, was born at Syra- cuse, B.c. 287. He cultivated particularly the branches of science relating to the areas of curves and sections of curved surfaces. He proved that the area of a circle is equal to half the rectangle contained by its circumference and radius, and showed how to approximate, as near as may be required, to the quadrature of a circle. The spiral was invented by Conon, but its properties having been demonstrated by Archimedes, it is in honour of him called by his name. To describe a spiral oj any number of revolutions — in this case three (Fig. 50). OT Divide the circle into any number of equal parts, as i to XII, and draw radii. Divide one of the radii, as A xxi, into a number of equal parts, a' b' c', corresponding with the required number of revolutions. Divide each of these into the same number of equal parts as there are radii— viz., 1 to 12. It will be evident that the figure consists of three separate spirals — one from xn to c', another from c' to b', and another from b' to a'. Commence, as in the former spiral of one revolution (Fig. 58), by drawing arcs from the points 1, 2, 3, etc., to the correspondingly numbered radii, thus obtaining the points marked with the largest capitals ; and the first revolution having been brought up to c', proceed in the same manner to draw arcs from the points 1, 2, 3, etc., contained between B' and c', cutting the corresponding radii in the points marked with the italic capitals, and draw the curve through these points, thus reaching b'. Proceed in the same manner to draw arcs from the points between b' and A', thus obtaining the points marked with the smallest capitals, and the spiral may then be brought up to the centre. To describe a spiral adapted for the volute of an Ionic column, by means of quadrants (Fig. 60). Divide the given height into eight equal parts. From 3 and 4, draw lines at right angles to A B. Between these two lines describe a circle (the eye of tlie volute), the centre being at a distance from A B equal to four of the divisions. Inscribe a square in this circle. Bisect the sides of this square, join the bisecting points, and thus a smaller square will be inscribed in it. Divide each of the semi-diagonals into three equal parts, join these points, and two more squares will be formed within the former one. The quadrants are drawn in rotation from the angles of each square, commencing at 1 with radius 1 c. The next is drawn from 2 with radius 2 D. The next ,, 3 ,, 3 e. The next ,, 4 ,, 4 f. The process is then continued from the inner squares. THE INVOLUTE (Fig. 61). If a pex-fectly flexible line is supposed to be wound round any curve, so as to coincide with it, and kept stretched as it is gradually unwound, the end of, or any point in the line will describe or trace another curve, called the involute of the curve — being in reality the opening out, or unrolling, of the periphery of the first curved surface. Thus, if a circular piece of wood were fastened on a board, and a string equal to the circumference fastened by one end to it and rolled round it, a pencil placed in a loop in the end of the string would, as the string is gradually unrolled, trace the involute. The circle (or other original curve) is called the evolute. 374 THE TECHNICAL EDUCATOR. ferenco of the circle unrolled, and the curve drawn through the extremities of the other tangents will be the involute. THE CYCLOID (Pig. 62). If a mark were to be made with chalk on the iron tire of a wheel at the exact spot where it touches the ground, the white mark, as the wheel rolls along a level road, would be observed to move in a peculiar form, which is called the “ cycloid ” curve ; whilst the centre of the nave of the wheel (i), although moving onward, would travel in a horizontal line, that is, it would keep exactly the same distance from the ground, however far the wheel might roll. „„ ° . , Fig. 62 . When the wheel is at b, its centre is at i, and the point A is at A 1. When the wheel has moved to c, the centre will be at n, and the point A will be at A 2. When the wheel has moved on to d, the centre will be at in, and the point A will be at a 3. When the wheel has moved on to e, the centre will be at iv, and the point A will be directly over it, viz., at A 4. When the wheel has moved on to f, the centre will be at v, and the point A will be at A 5. When the wheel has moved to G, the centre will be at vi, and the point A will be at A 6. When the wheel has moved on to h, the centre will be at vii, and the point A will be at A 7. It will thus be clearly seen that the wheel in moving from A 1 to A 7 has passed completely through one revolution, and therefore that the length of the line A 1, a 7 is equal to the circumference of the circle laid out on a straight line. The straight line on which the wheel rolls is called the director. The wheel is called the generating circle, and the point A is called the generator. To construct the involute of the circle A (Fig. 61). Divide the circle into any number of equal parts (1 to 12), and draw ra-lii. Draw lines (tangents) at right angles to these radii. On the tangent to radius No. 1, set off a space equal to one of the parts into which the circle is divided ; and on each of the tangents set off the number of parts corresponding to the number of the radius. Tangent No. 12 will then be the circmn- VEGETABLE COMMERCIAL PRODUCTS.— XII. (h) VOLATILE OR ESSENTIAL OILS. These oils occur in the stems, leaves, flowers, and fruits of most sweet-scented plants, whence they are obtained by distilla- tion. In this respect they differ from the oils already described, which are found only in the seed, obtained by expression from the same, and do not evaporate ; hence the latter have been called fixed oils. The difference between fixed and volatile oils is easily shown. A drop of any fixed oil — such as olive oil, for instance — leaves a stain on paper which is permanent; but a drop of any volatile or essential oil — as, for example, oil of berga- mot — makes a similar stain, which evaporates and disappears. To obtain essential oils, the leaves, flowers, or other parts of the plant are put into an apparatus for distillation. This always consists of a boiler in which the vapour is raised, and a con- denser in which it again becomes fluid. For distillation on a small scale, a common retort and receiver answer every purpose, care being taken to keep the receiver cool, by placing it in cold water. When the water boils, the steam passes through the retort into the condenser, where it is re-converted into water, the essential oil floating on its surface ; this is skimmed off, and afterwards purified by filtering. But the perfume of most flowers depends on the presence of a fragrant volatile or essential oil, peculiar to the plant. When, therefore, we obtain this oil, wo really get the essence of the plant, or the essential principle which makes it valuable ; and although the plant may be an annual, and perish, together with its fragrance, in a few weeks or months, yet, if we extract the oil, we can retain the essence of the plant as long as wo please. The following are the most important of the essential oils which occur in commerce : — Oil of Lavender, from Lavandula spicata, L.; natural order, Laliatce. — Large quantities are raised at Mitcham, in Surrey; but it is also imported from France and Germany. Oil of Thyme, from Thymus vulgaris, L. ; natural order, Laliatce. — This oil is distilled from all parts of the plant. It comes into this country from Hamburg and from the United States. It is used in scenting Windsor soap. Oil of Peppermint, from Mentha piperita, L. ; natural order, Laliatce. — Besides that raised and manufactured at home, we receive large quantities from Germany and the United States. Oil of Anise, from Pimpinella anisum, L. ; natural order, Unibelliferce. — This plant is a native of the Levant, whence a great deal of the anise of commerce is derived. It is also much cultivated in France, Naples, and Germany — particularly in Thuringia and Swabia. We receive considerable importations from Germany and the East Indies ; but those sorts coming from Spain, Apulia, and Malta, are considered in commerce to be the most valuable. Oil of Caraway, from Carum carui, L. ; natural order, Unibelliferce. — The best caraway oil comes from Malta, Naples, and Alicante in Spain. Small quantities are received from Germany. Much more, however, is home-manufactured and exported. Cinnamon, clove, cassia, and pimento yield essential oils, to which reference has already been made in treating of those species ; oil of bergamot, oil of lemons, and Neroli oil, or oil of orange flowers, have also been mentioned in connection with those fruits. Oil of Boses, Attar of Boses, or Otto of Boses, is distilled from the petals of Rosa centifolia, L., Rosa gallica, L., and numerous other species of rose. The attar of roses is pre- pared in Persia and other Asiatic countries ; but, with all the aids of science, the process still remains unknown to Europeans. Some idea of its costliness may be gathered from the fact that 100,000 roses must be distilled to yield 180 grains, or three drachms of pure attar. Five guineas have often been paid for one ounce of this essence. It is the favourite perfume of the civilised world, and in the East is a most essential luxury. In Cashmere the harvest of rose leaves is celebrated as the festival of the year. Its description is well known in the exquisite poetry of Moore. III. TINCTORIAL PLANTS, OR PLANTS FURNISHING VALUABLE DYES. The clothing which is furnished by the textile plants and the sheep’s wool would be of one dull uniform hue, if it were not for the valuable dyes furnished by the tinctorial plants. At first the colours of plants, when transferred to clothing, imparted VEGETABLE COMMERCIAL PRODUCTS. 37d only a temporary beauty ; for the art of fixing them, or uniting them permanently with the cloth, by means of mordants, was unknown ; but by experiments long and carefully conducted, Nature has been interrogated successfully, and we are now able to render these colours fast, or permanent, thus enriching our silken, woollen, linen, and cotton manufactures with an almost endless variety of beautifully-coloured designs. It is impossible to mention even the names of the numerous plants which furnish materials for the dyer. Only a few, and those the most common in the commercial world, can be noticed. All the parts of plants furnish these dyes ; sometimes it is the root, or the wood of the stem ; sometimes the leaves, flower, or fruit. Alkanet Root (Anchusa tinctoria, L. ; natural order, Bor a- ginacece). — A perennial herbaceous plant, with rough, oblong, lanceolate leaves, a stem about afoot in height, purplish flowers, and a long* woody root, with a deep red bark. It is a native of the Levant, and is much cultivated in Germany and the south of France, particularly about Montpellier, for the sake of the red colouring matter contained in the bark of the root, easily obtained by soaking the root in alcohol or oil. It is used for colouring ointments red, especially lip-salves ; it is also employed as a dye, to colour gun-stocks and furniture in imitation of rosewood. Alkanet root comes to this country in packages, weighing about two cwt. each, chiefly from Germany and France. About eight to ten tons are annually imported. Sumach ( Rhus Coriaria, L. ; natural order, Anacardiacece) . — The sumach of commerce is the crushed or ground leaves of this plant, imported from Sicily. This material is valuable for tanning light-coloured leather, and imparts a beautiful bright- coloured yellow dye to cottons, which is rendered permanent by proper mordants. In 1868 13,251 tons of sumach were im- ported into the United Kingdom. Arnotto ( Bixa orellana, L. ; natural order, Flacourtiacece) . — This is a small evergreen tree, indigenous to tropical America, and now cultivated in the East Indies. It is called Roucon by the French, and the Orleans tree by the Germans. The first South American settlers noticed the brilliant and showy colour obtained from its berries, on the bodies of the Indians, by whom it is called bixa or bija, and not only used it themselves, but speedily converted it into an article of commerce. The arnotto tree grows about twelve feet in height ; its leaves are smooth and heart-shaped, and its pink-coloured flowers are followed by oblong bristled pods, somewhat resembling those of the chestnut, at first rose-coloured, but changing as they ripen to dark-brown. On bursting open, these pods show in their interior a splendid crimson farina or pulp, in which are contained ten or twelve seeds, in colour somewhat resembling coral beads. The arnotto of commerce is prepared from this crimson pulp. By maceration in hot water the seeds are separated from the pulp, which is then made into balls or cakes of two or three pounds’ weight ; these, when dry, are wrapped up in large leaves, and packed in casks for exportation. Another kind — the roll arnotto — is of a much superior quality. It is a hard extract, and contains a much greater proportion of colouring matter. Good arnotto is of the colour of fire, bright within, soft to the touch, and dissolves entirely in water. It is used in Holland for colouring butter, and in Cheshire and Gloucestershire for dyeing cheese (under the name of cheese-colouring), to which it gives the required tinge, without imparting any unpleasant flavour or unwholesome quality. Flag or cake arnotto comes from the West Indies, especially from the island of St. Domingo or Hayti. Roll arnotto is principally brought from the Brazils. The rolls are small, not exceeding two or three ounces in weight. Arnotto is also used to dye silks and cottons, especially to form the colour called aurora. It is much to be regretted that the beautiful orange and gold-coloured dyes yielded by this plant are fugitive, and become discoloured in the sun. The bark of the arnotto tree makes good ropes, available in the West Indies for common plantation uses. The imports of roll and flag arnotto into the United Kingdom in 1863 were as follows : — - Roll, 761 cwt., value .£2,853 ; Flag, 2,507 cwt., value ,£10,111. Myrobalans (Terminalia chebula, L. ; natural order, Com - bretacece). — This dye is obtained from a small tree indigenous to British India, and closely allied to the myrtle. All the species of Terminalia have astringent properties. The fruit and galls of this tree are very astringent, and much valued both by dyers and tanners. The fruit is about the size of a date, pointed at the ends, and of a yellowish brown. The myrobalans of com- merce are probably derived from more than one species. With alum they give a durable yellow colour. Myrobalans are now an important item in our commerce with India. We receive them from Calcutta and Bombay. The average annual imports are about 1,200 tons. Safflower ( Carthamus tinctorius, L. ; natural order, Com - posites).- — This plant furnishes a beautiful rose colour, which is used for silks, cottons, and the manufacture of rouge. Safflower is an annual herbaceous plant, somewhat resembling a thistle, to which it is allied. The leaves are ovate-lanceolate, somewhat spinous, alternate, sessile ; flowers yellow. The safflower is a native of the Levant, and is cultivated in China, India, and in the south of Europe. The dye is obtained from the florets. These are gathered, pressed into little cakes, dried, and then packed in strong bales, weighing about 2 cwt. each. As found in commerce, these cakes consist of flaky masses of a red colour, intermixed with yellow filaments, the former tint being due to the corolla, and the latter to the stamens. The flowers thus contain two colouring principles, one yellow, soluble in water, and the other rose-red, called carthamine, or carthamic acid, soluble in alkaline solutions; this latter, when precipitated from its solution, dried, and mixed with finely pow- dered talc, constitutes rouge. It is the carthamic acid which renders the safflower valuable as a dye. The greater portion of the safflower imported into England comes from Persia, Egypt, and the East Indies. The imports in 1851 were nearly 600 tons. Logwood ( Kcematoxylon Campeachianum,Jj. ; natural order, Leguminosce) . — A middle-sized tree with a contorted trunk, rarely more than one foot and a half in diameter, covered with ash-coloured bark ; branches crooked, beset with sharp thorns ; leaves pinnate or somewhat bi-pinnate, with sub-cordate leaflets ; flowers yellow, in terminal racemes. This tree, indigenous to Central America, Mexico, and Cam- peachy, has been introduced into the West Indies, and is now naturalised there. The heart-wood is the part of the tree em- ployed ; the generic name refers to its blood-red colour. Log- wood is of very frequent use in the arts, as it forms the basis of many of the reds in printing calicoes, and is esteemed one of the best deep-red dyes. It is imported in logs, which are cut up into chips and ground to powder, for the use of dyers, hatters, and printers, in powerful mills constructed for that purpose. Logwood, when boiled, communicates its own dark- red colour to the water, and the addition of a few drops of acetic acid changes the colour to a bright red. Red ink is made in this way, a little alum being added to render the colour per- manent. If, instead of an acid, an alkali— such as soda or potash — be added, the colour changes to a dark blue or purple, and with a little management every shade of these colours may be obtained. Logwood is so hard and heavy as to sink in water. It is used chiefly for dyeing red, blue, and black. We import every year about 40,000 tons from South America, whence a great deal also goes to Spain, France, and Germany. The principal ports for the reception of logwood are London, Cadiz, Bordeaux, and Hamburg. Madder ( Rubia tinctoria, L. ; natural order, Rubiacece) . — A small, herbaceous, perennial, creeping plant; stems slender, quadrangular ; leaves four in a whorl ; flowers small ; fruit yellow ; berry double, one being abortive. Madder is cultivated in France, Southern Europe, and the Levant, where it is indigenous, for the sake of the valuablo red dye furnished by the root. The roots are dug up when the plant is about three years old, carefully dried, and packed into bags or bales for exportation. As found in commerce, madder- root is in long cylindrical pieces, about the thickness of a quill, and of a deep red or brown colour. If ground before exporta- tion, the powder is sent in very large casks. We get madder roots whole from India, Turkey, Greece, Spain, and France ; and ground from Holland and Germany. Powdered madder roou is a bright Turkey red, but, by the addition of suitable chemicals, every shade of red, purplish-brown, purple, lilac, and even a lively rose colour can be obtained from it. Madder root im- parts its red colour to water and alcohol. It is used as a basis for red dyes, as it affords a tint which, when properly fixed by appropriate mordants, is not affected by light or moisture. Scarcely a calico or muslin print is made without the aid of madder root, in some way or other, for forming the pattern. The imports of madder root into the United Kingdom in 1SG8 were 177,336 cwt. ; of madder, 128,242 cwt. 376 THE TECHNICAL EDUCATOE. PRINCIPLES OF DESIGN.— X. ART FURNITURE (continued). By Christopher Dresser, P1i.D.,*F.L.S., etc. In my last chapter I gave, in an axiomatic form, those principles which should guide us in the construction of works of furniture, and there endeavoured to impress the necessity of using wood in that manner which is most natural— that is, “working” it with the grain (the manner in which we can most easily work it), and in that way which shall secure the greatest amount of strength with the least expenditure of material. I again invite my readers to consider these matters, for they lie at the very root of the successful construction of furniture. If the legs of chairs, or their seat-frames, or the ends or backs of couches, are formed of wood cut across the grain, they must either be thick and clumsy, or weak ; but, besides this, the rightly con- stituted mind can only receive pleasure from the contemplation of works which are wisely formed. Daily contact with ill-shaped lake’s work on “ Household Furniture;” as shown in our illus- tration, it is a correctly formed work. Fig. 22 is an arm-chair in the Greek style, which I have designed. Fig. 26 is a lady’s chair in the Gothic style. Fig. 25, a lady’s chair in early Greek. These I have prepared to show different modes of structure ; if the legs are fitted to a frame (the seat-frame), as in the early Greek chair just alluded to, they should be very short, as in this instance, or they must be connected by a frame below the seat, as in Fig. 27. The best general structure is that in which the front legs pass to the level of the upper surface of the seat. lig. 27 is a copy of a chair shown by Messrs. Gillow and Co., of Oxford Street, in the last Paris International Exhibition. In many respects it is admirably constructed. The skeleton brackets holding the back to the seat are a very desirable ad- junct to light chairs; so are the brackets connecting the legs with the seat-frame, which strengthen the entire chair. The manner in which the upper rail of the back passes through the objects may have mere or less deadened our senses, so that we are not so readily offended by deformity and error as we might be ; yet, happily for us, directly we seek to separate truth from error, the beautiful from the deformed, reason assists the judg- ment, and we soon learn to feel when we are in the presence of the beautiful or in contact with the degraded. My illustrations, given some in this chapter and some in the last, in page 313, will show how I think chairs should be con- structed. Fig. 19 is essentially bad, although it has traditional sanction, hence I pass it over without further comment. Fig. 23 is in the manner of an Egyptian chair. It serves to show the careful way in which the Egyptians constructed their works. The curved rails against which the back would rest are the only parts which are not thoroughly correct and satisfac- tory in a wood structure. Were the curved back members metal, the curvature would be desirable and legitimate. The back of this chair has immense strength (the backs of some of our chairs are of the very weakest), and as a whole it is a seat which would, if well made, endure for centuries. Fig. 20 is a chair of my own designing, in which I have sought to give strength to the back by connecting its upper portion with a strong cross-rail of the frame. Fig. 21 is a cha.r slightly altered from one in Mr. East- side uprights and is “pinned” is good. The chief, and only important, fault in this chair is the bending of the back legs, involving their being cut against the grain of the wood. Fig. 28 is a chair from Mr. Talbert’s very excellent work on “ Gothic Furniture.” It shows an admirable method of sup- porting the back. Fig. 24 I have designed as a high-backed lounging chair. With the view of giving strength to the back, I have extended the seat, and arranged a support from this extension to the upper back-rail, and this extension of the seat I have supported by a fifth leg. There is no reason whatever why a chair should have four legs. If three would be better, or five, or any other number, let us use what would bo best. In my drawing, the stuffing of the back has been accidentally shown somewhat too rounded. This does not in any way in- terfere, however, with what I have in view — viz., the illustration of a particular structure or formation of chair. I have now given several illustrations of modes of forming chairs. I might have given many more, but it is not my duty to try and exhaust a subject. "What I have to do is simply to point out principles, and call attention to facts. It is the reader who must think for himself — first, of the principles and facts which I adduce ; secondly, of the illustrations which I give; thirdly, of other works which he may meet with ; and fourthly, of PRINCIPLES OP DESIGN. 377 further means of producing desirable and satisfactory results than those set forth in my illustrations. As it cannot be doubted that a well-constructed work, how- ever plain or simple it may be, gives satisfaction to those who behold it — while a work of the most elaborate character fails to satisfy if badly constructed — we shall give a few further illus- trations of structure for other articles of furniture besides chairs, which have become necessary to our mode of life. lateral pressure, but would not bear quite the same amount of pressure from above. The latter, however, could bear more weight than would ever be required of it, and would be the more durable piece of furniture. Fig. 31 gives a legitimate formation for a settee ; the cutting- out, or hollowing, of the sides of the legs is not carried to an extreme, but leaves a sufficiency of strong wood with an upright grain to resist all the pressure that would be placed on the Fig. 29 is one of my sketches for Greek furniture, designed for Moor Hall. It was formed of black wood. Here the frame of the seat; is first formed, and the legs are inserted beneath it, and. let into it, while the wood-work of the end of the couch stands upon it, being inserted into it. This appears to have been the general method with the Greeks of forming their fur- niture, yet it is not so correct structurally as Fig. 30, another of my sketches, where the end and the leg are formed of one piece J of wood. The first formation (that of Fig. 29) would bear any amount of pressure from above, but it is not well calculated for resisting lateral pressure ; while the latter would resist this seat, and the lower and upper thickened portions of the legs act as the brackets beneath the seat in Fig. 23. This illus- tration is also from Mr. Talbert’s work. Fig. 32 is a table slightly altered (structurally improved, I think) from one in Mr. Eastlake’s work. I see no objection to the legs leaning inwards at the top ; indeed, we have here a picturesque and useful table of legitimate formation. Fig. 33 is the end eleva- tion of a sideboard from Mr. Talbert’s work. Mark the sim- plicity of the structure. The leading or structural lines are straight and obvious. Although Mr. Talbert is not always right, yet his book is well worthy of the most careful cou- 378 THE TECHNICAL EDUCATOR. sideration and study ; and this I can truly say, that it compares favourably with all other works on furniture with which I am acquainted. The general want which we perceive in modern furniture is simplicity of structure and truthfulness of construction. If persons would but think out the easiest mode of constructing a work before they commence to design it, and would be content with this simplicity of structure, we should have very different furniture from what we have. Think first of what is wanted, then of the material at command. NOTABLE INVENTIONS AND INVENTORS. IX.— POTTERY AND PORCELAIN (continued). BY JOHN TIMBS. We now come to porcelain, first produced in China, Japan, and Mexico. Bottles of Chinese manufacture have been found in the tombs of Thebes ; one of them inscribed with the date between 1575 B.c. and 1289 b.c. Porcelain was common in the Chinese Empire 163 b.c., and in its greatest perfection 1000 a.d. The porcelain tower near Nankin was erected in 1400. This “ vitreous, precious stone pagoda” was first built about a.d. 200, and rebuilt A.D. 1400, when it occupied nineteen years in construction, and cost .£600, 000. It was of rune storeys, though commonly reported thirteen, as it was intended to be of this number. Its height was 261 feet, and diameter at the base 06 feet 10 inches. There were in it 150 bells, and 140 lamps. In 1856, Tien Wang, one of the rebel chiefs, wantonly blew up the pagoda with gunpowder, some say to spite another Wang ; others, because he declared it to be too old ! The fragments of this remarkable edifice were left on the spot, and were carried away by the curious. “ So much for monuments that have forgotten Their very record.” — Byron. Marco Polo describes the manufacture in China during the thirteenth century. When specimens found their way to Europe, the Portuguese were so struck with the resemblance between the texture of this fine ware, and that of the cowry- shells, or porcellana, as they were called, that they imagined the ware might be made of such shells, or of a composition resembling them, and named it accordingly. They imported numerous and splendid collections into Europe, where it was called “ china ” from the country which produced it. The Dutch next established a traffic with India and Japan, and Europe was long supplied with porcelain through Holland. The English next shared in the trade, through the East India Company. In Queen Anne’s reign china collections became a passion. Fokien now produced the pure white porcelain of China; Nankin the blue and white and pale buff porcelain ; and King-te-ching the old sea-green and crackle porcelain. The ancient crackle is so much esteemed in Japan that £300 has been paid for a single specimen. The Chinese call this ware snake porce- lain. The egg-shell porcelain is much prized in China; it is coloured citron-yellow for the exclusive use of the Emperor, and ruby for the use of the Imperial family. An inferior porcelain, known as Indian china, is made at Canton. Chinese porcelain is of beautiful material and delicate texture, brilliant colour, and puro glaze; but the forms and design are so hideous, that it has been said the vase of the humblest Greek potter of the best period has an aesthetic value far surpassing the most costly productions of the Celestial Empire. (“EncyclopcediaBritannica,” eighth edition.) The first successful imitation of Chinese porcelain produced in Europe was by Bottcher, an apothecary’s assistant, at Berlin ; but he was suspected of practising the black art, and so escaped to Dresden, where, under the patronage of the Elector of Saxony, Augustus II., he made some vessels much resembling Oriental porcelain, from a brown clay found near Meissen, with a reddish tint. To preserve his secret, the Elector sent him to the fortress of Konigstein, on the Elbe, where a laboratory was prepared for him. In 1707 he returned to Meissen.' Bottcher hitherto produced only a kind of red and white Btoneware, but in 1709 he succeeded in producing a white porcelain, which led Augustus to establish a manufactory at Meissen, and to appoint Bottcher the director. He employed the kaollne of Ane in the Erzebirge for his porcelain, the secret of which was kept for some time. This kaoline powder was con- veyed in sealed barrels, and all persons in the factory were sworn to secrecy. No visitor was admitted, the oath to the workmen was renewed every month, and when the King was allowed to enter the factory, a similar obligation was imposed on him. In each room was set up the motto, in large letters, “Be secret unto death.” At length, just before the death of Bottcher in 1719, a foreman escaped from the factory to Vienna, where he submitted to be bribed, and rival factories soon sprung up in different parts of Germany. Among the finest Meissen ware are groups from antique models, figures in lace dresses, flowers studied from Nature, and vases of honey- comb china. The first rival of Meissen was the porcelain factory of Vienna, established in 1720, but its porcelain holds a lower rank than that of Dresden or Berlin ; it is remarkable for its raised and gilded work, and reliefs of solid platinum and gold. Next, at Hochst, on the Nidda, arose a celebrated pottery, the director of which carried his recipes about with him, but of which he was plundered, and the secret sold ; hence originated the porce- lain factories of Switzerland, of the Lower Rhine, and even of Cassel and of Berlin. The Fiirstenburg works, in the Duchy of Brunswick, originated in a bribe offered by one of the dukes to a Hochst workman. The ware of the factory of Nymphenberg, in Bavaria, is much esteemed, many of the designs being from the celebrated picture-gallery of Munich. The porcelain factory of Berlin was not very successful until the fraudulent transfe- rence of the best of the workpeople and the materiel of the Meissen factory. The Berlin porcelain was but an imitation of the Dresden, but it yielded the King an annual revenue of 200,000 crowns. The Prince-Bishop of Fulda established a factory in a house adjoining the episcopal palace, but it failed through the dignitaries of the church claiming the privilege of carrying off specimens without paying for them. The porcelain factories of Thuringia originated about 1758, when the son of a chemist experimented on some sand which he had bought of an old woman, and obtained by its means a porcelain-like sub- stance, which led to the erection of a factory at Sitzerode, sanc- tioned by the Prince of Schwartzburg. The abundance of fuel supplied by the forests of Thuringia led to the erection of several other factories, all which produced porcelain still prized by collectors. A factory established by the Empress Elizabeth, in 1756, near St. Petersburg, still produces good porcelain from native materials. Denmark has also a factory at Copenhagen, and Zurich one in Switzerland. Meanwhile, England had been striving in the porcelain manu- facture. The Bow works, closed in 1762, have been already mentioned. The mark is a crescent or how ; it is scarce, but never fine. This and the Chelsea were soft wares, made from a mixture of white clay, white sand from Alum Bay, and pounded glass. The Chelsea works, in an old mansion by the Thames bank (of which we have seen a view upon a fine Chelsea vase) did not flourish until George II. imported workmen, models, and materials from Brunswick and Saxony. The best period of Chelsea porcelain was between 1750 and 1755, when such was the demand for it that dealers flocked to the works, and at the doors purchased pieces as soon as they were fired. A service sent as a royal present cost <£ 1,200. The finest works were in the style of the best German ; the colours fine and vivid, and the claret colour peculiar. At the Chelsea ovens, the celebrated Dr. Johnson, who had conceived the notion that he was possessed of a secret for making porcelain, obtained permission to have his compositions baked here, where he watched them day by day ; he was not allowed to enter the mixing-room, and roughly modelled his composition in a room by himself. He failed, for none of the articles he formed would bear the heat of firing. He conceived that one simple ingredient was sufficient to form the body of porcelain ; whereas, the manager of the factory declared that in the composition of the Chelsea paste no less than sixteen dif- ferent substances were blended together. The Chelsea works were discontinued in 1764, when the manufacture was removed to Derby, and the ware was called Chelsea-Derby. It has the mark of a D, crossed by an anchor ; it is very beautiful, but dear as silver. At the Bernal sale, in 1855, a pair of scalloped Chelsea vases, painted with birds, brought .£110 5s.; at Sir John Macdonald’s sale, in 1850, a pair of Chelsea cups and saucers brought .£36 15s ; and in 1870, from the Bulteel TECHNICAL DRAWING. 379 collection, were sold an old Chelsea vase and cover, and a pair of vases and cover, painted with medallions, on pedestals, for 355 guineas. Nearly opposite Chelsea were the Battersea enamel works, at York House, where Ravenet and others drew for Alderman Jansen, but the factory was soon closed. The Derby factory was established in 1750, and became most famous by the junction of the Chelsea artists already named. - Flaxman designed for the establishment. Mr. Marryat describes the Derby porcelain as being very transparent, of fine quality, and distinguished by a beautiful bright blue, the ground being generally plain; the white biscuit figures are said to equal those of Sevres. The Worcester works were established in 1751, by Dr. Wall and some others. They first imitated blue and white Nankin china ; they afterwards adopted the Sevres style, with the Dresden method of painting. At these works were first used the Cornish stone, or kaoline, discovered in 1768. The early productions of their proprietors, Messrs. Chamberlain, bring great prices. The works are now carried on with renewed success by Messrs. Kerr and Binns, who claim for Worcester the invention of transfer printing on porcelain, from copper- plates; the first specimen, a small mug, brings a very high price. The “ blue Worcester” ware is also deservedly in high repute. Shropshire has long been famous for its porcelain factories. In 1772, at Caughley, near Broseley, was established the fac- tory, chiefly for blue and white, and blue, white, and gold porce- lain, known as Salopian ware. At Coalport, earthenware is made similar to the Etrurian or M'edgwood ware, of which we have already spoken, and here are the works of Hose and Co., famous for their porcelain of rose ground, the nearest approach to rose de Barri. The Staffordshire works are concluded to be of Roman origin, evident remains of Roman potteries having been re- peatedly discovered at a considerable depth below the present surface. The county is unrivalled in amount of production of pottery. The Minton factory is famous for its imitation of old Sevres and its flower-painting, its enormous majolica vases, its Persian figures, and its hard porcelain for chemical pur- poses ; its crucibles and capsules have stood the severest tests, equal to German ware. Messrs. Copeland, at Stoke, are noted for their exquisite busts, manufactured from porcelain earth, and copied from the antique. Their flower-painting and gilding are very fine, and they have supplied 36,000 tiles or slabs for the ceilings of nine lofty and spacious domes in the Imperial library at Paris. Early in the present century good porcelain was made at Nantgarrow and Swansea ; it is also stated that the Bristol china, a white ware, formerly common in the west of England, was made in Wales, and sold in Bristol. At the Rockingham works, in 1837, was completed for 'William IV. a superb dessert ser- vice of 200 pieces of porcelain, painted with 700 subjects; it had occupied five years, and cost upwards of 3,000 guineas. Erom the same works we have seen a fac-simile of a small Roman jug, dug up at Caistor, in Lincolnshire, of which the ground colour was red, with raised ornamentation of fern leaves of darker red. France, though possessing taste, skill, and science, was Unable to compete with other nations for want of a suitable raw material. A cunning Jesuit in China forwarded to France specimens of the earths used in the composition of Chinese porcelain, by which Reaumur, the celebrated chemist, dis- covered the true nature of porcelain to be a semi-vitrified com- pound, in which one portion becomes infusible at the greatest heat to which it can be exposed ; while the other portion vitrifies at that heat, and enveloping the infusible part, produces that smooth, compact, and shining texture, as well as transparency, which are distinctive of true porcelain. All that was then wanting for the perfect imitation was the discovery of materials similar to those received from China, the search for which was speedily successful. The first establishment was formed in the Castle of Vincennes, whence, in 1756, it was transferred to Sevres. In 1760, Louis XV., at the solicitation of Madame de Pompadour, bought up the establishment. The factory became celebrated for its soft porcelain, or pate tendre; but the great object was to produce the hard porcelain, which had rendered Saxony the envy of Europe. Then kaoline was not known in France, nor was its presence suspected until, about 1768, the wife of a surgeon, near Limoges, noticed there a white unctuous earth, which she tried to use as an economical substitute iu her house for soap. Her husband showed a portion of the earth to an apothecary at Bordeaux, who, being aware of the search making for kaoline, sent a specimen of the Limoges earth to the chemist Macquer, who at once recognised it as the desired kaoline. He then established the manufacture of hard porcelain at Sevres, in 1769; but such was the difficulty in suiting the colours to the less absorbent material that soft porcelain continued to be made until the year 1804. The pate tendi e was not considered as real porcelain ; it was of complicated and expensive composition, and liable to collapse during the firing. Mr. Marryat speaks of it as “remarkable for its creamy and pearly softness of colour, the beauty of its paintings, and its depth of glaze.” The ware for common use was painted with flowers, in patterns, or medallions ; that for royal use had grounds of bleu de red, blue turquoise, jonquill or yellow, green, and a lively pink, the rose du Barri. Some specimens were painted with landscapes, flowers, birds, boys, and Cupids, in medallions, and others with subjects after Watteau ; and the jewelled cups, with the bleu de roi ground, were celebrated. In form the Sevres china is not equal to the Dresden. Such was its profuseness of decoration that a law was passed in 1766, and renewed in 1784, limiting the use of gold in the decoration of porcelain at the royal manufactory at Sevres, which accounts for the rarity of the old French gilded porcelain. This being a royal establishment, all Sevres porcelain had on its under- surface an initial mark in blue, surmounted with the French crown. TECHNICAL DRAWING.— XXIV. DRAWING NOR MACHINISTS AND ENGINEERS. toothed wheels ( continued ) Fig. 235. — System composed of a rack driving a pinion. Hero the curves of the faces of the teeth in the rack are portions of a cycloid generated by the circle A, the diameter of which is half that of the pitch-circle B, rolling on the pitch- line CD. In commencing this study, draw the pitch-line, and a per- pendicular, on which set off the centre of the pitch-circle and the generating circle. Draw both of these circles, the tangent point being at T. Set off the length of the pitch along the rack and on the pitch-circle, and proceed to divide each pitch into a tooth and a space. Now describe the cycloid wliicli is to give the face of the teeth of the rack. If the drawing be large, or one from which a “pattern” is to be made, this cycloid may be cut in thin wood so as to form a templet (described in a previous lesson), and with this the faces of the teeth of the rack may be de- scribed ; but for general use in smaller drawings the curve may bo an arc of a circle, the radius of which is the length of the pitch, as shown at g h. The flanks of the teeth of the rack are perpendiculars, and are strengthened by being joined by quadrants to the line parallel to the pitch-line, which forms the root of the teeth. The curve of the faces of the teeth of the pinion are portions of the involute of the pitch-circle. For a full description of the nature of this curve, and the method of describing it, the student is referred to Lesson VI. in “ Practical Geometry applied to Linear Drawing.” . Fig. 236 will remind the student of the general principles of its construction. Let A b be a portion of the circle from which the curve is to be evolved, divided into a number of equal parts ; as, 1, 2, 3, 4, 5, 6. At these points draw radii, and draw tangents to each. . From the points of tangent set off on these lines divisions corresponding to the figure from which each is drawn. Thus, on tangent 1 set off one of the divisions, from tangent No. 2 set off two, and so on, and through the points so obtained the involute is to be drawn. Here, again, for general purposes in drawing, the arc of a circle is substituted for the true curve, and it will be seen that the arc struck with a radius equal to a pitch corresponds nearly (though not perfectly) with the curve shown at B (Fig. 236). 380 THE TECHNICAL EDUCATOR. The flanks of the teeth are radial, turned off into the inner circle by small arcs. The remaining portion of the pinion will be easily completed without further explanation. The space at H, as the student will no doubt know, is the lcey-bed, in which a key is placed to fasten the pinion on the journal or end of the shaft. being taken as equal, the radius of the pins is therefore one quarter of the pitch. The spaces in the pinion are struck with the same radius. The curve of the faces of the teeth is, as has already been said, a portion of the epicycloid; but an arc drawn from A, the middle of a pitch, so nearly coincides with the curve b c, which "37- In the system here shown, the pinion drives a wheel with, pins instead of teeth, and the face of the tooth of the c river is a portion of the epicycloid curve generated by a circle of half the circumference of the wheel. In copying this example, the pitch-circles of driver and follower having been described, and the pitches having been set off on each, the circles representing the pins are to be drawn. The spaces and diameter of the pins in this instance 1 is the curve properly constructed, that in drawings it is usually substituted for it. The following important remarks on the teeth of wheels are made by Professor Goodeve : — “ It will be proved, when we treat of rolling curves, that the surface of one tooth must always slide upon that of another in contact with it, except at the moment when the point of con- tact is passing the line of centres. TECHNICAL DKAWING. 381 “ This matter should be well understood. The teeth are per- petually rubbing and grinding against each other ; we cannot prevent their doing so ; our rules only enable us so to shape the acting surfaces, that the pitch-circles shall roll upon each other. “ Nothing has been said about the teeth rolling upon each other. It is the pitch-circles that roll ; the teeth themselves slide and rub during every part of the action which takes place out of the line of centres. “ Since, then, the friction of the teeth is unavoidable, it only remains to reduce it as much as possible, which will be effected by keeping the arc of action of two teeth within reasonable limits. “ Generally, the friction before a tooth passes the line of centres is more injurious than that which occurs after the tooth has passed the same line. The difference between drawing a walking-stick along the ground after you, and pushing it before you, is given by Mr. Denison as an illustration of the difference between the friction before and after the line of measurements are, however, marked on each part, and the student is to take these from his scale. He is advised to vork Fig. 238 (which is a rough hand-sketch of a small copying-press) to a scale of not less than § of an inch to an inch. To make this scale, draw a straight line, and on it set off a number of divisions of § of an inch each. Mark the beginning of the line o, the first division 1 , the second 2 , and so on ; these divisions will then represent inches. This plan is better than measuring direct from the foot-rule, as it avoids the neces- sity of calculating how many inches so many times § make, by which errors often occur. Now divide one of the above spaces into eighths for mea- suring the fractional parts of inches. The scale being thus prepared, draw the base-line, A b, and the central perpendicular, c r>. Next mark off 9" on each side of c — viz., c e and c f — tho length of the base being 18". Draw perpendiculars indefinitely high at E and e ; mark off on one of these If inch — viz., e g. It is not necessary to rr^ri centres ; but this difference is less appreciable when the arc of contact is not excessive.” MECHANICAL DRAWING FROM ROUGH SKETCHES. In the previous figures the student has been allowed to copy the examples by measurement, or to increase their sizes as ho may think proper. By such means, however, only practice in copying ready- made drawings is obtained, and such practice must only be taken as tho means to the end — certainly not as the result to be attained ; for a draughtsman who can but copy is, indeed, little better than a machine ; being merely capable of measuring accu- rately and drawing fine lines, most of the latter result being due to his instruments, he thus becomes, in the true sense of the term, a “ mechanical draughtsman.” It is to avoid this that the course here laid down blends mental study with manual practice, and in the present section an endeavour is made to afford the student practice in working from rough sketches, such as are made in an off-hand manner by the engineer, and entrusted to the occupants of the drawing- office to work out. These sketches, though approximately correct in general pro- portions, are not drawn to any absolute scale ; the student must not, therefore, trust to measuring from them. The true j measure this height on both perpendiculars, for by placing the T-square against G, the line G H will give the height of F H. On each side of the centre line now set off 7", and erect tho perpendiculars i and j for the centre lines for the standards ; the width from centre to centre being 14". On each side of i and j set off J k, draw the lines K, L (and corresponding lines on the opposite side), and draw the hori- zontal M N at 6|" above G h. Now draw the horizontal o p at 5.1" above G h, and q r at 31" above it; the width of o P is 2 5 -", and of qr 21". The arches are then to be drawn from centres on the perpen- dicular, c. The iron lid, s T, is, in the present view, at If" above G H ; it is §" thick. On it is a boss §" thick, to which a flange runs from each corner, and on this boss is a box § ' high, in which the end of the screw works. From this box, the screw, which is 1" in diameter, is 7-g-" long. At 1" above this draw u v, the central horizontal, for tho handle. The boss in the middle of the handle is 2" high and 3" diameter. The length from end to end of the handle is 174". The screw is to be drawn in straight lines, as shown in previous examples. The nuts, etc., will be easily understood without further instructions. 382 THE TECHNICAL EDUCATOE. ANIMAL COMMERCIAL PRODUCTS.— XYI. PEODUCTS OF SUB-KINGDOM ANNULOSA ( continued ). Blister Fly ( Cantliaris vesicatoria). — A small coleopterous insect about three-fourths of an inch long, of a nauseous odour and a brilliant golden-green colour. These insects secrete in their bodies a principle which has the power of vesicating or blistering the human skin when applied. For this purpose the beetle is reduced to powder, which, mixed with ointment or lard, is spread thinly upon a piece of leather, and then applied to the part intended to be blistered. The blister fly is found on a variety of shrubs in Spain, Italy, France, etc. It has been taken occasionally in England, but it is much more abundant in Spain ; and although we now receive it principally from Astra- can and Sicily, it still retains its usual commercial name of Spanish fly. In some years as many as twelve tons of these insects have been shipped from Sicily. Some idea of the im- mense number destroyed to form that amount may be obtained from the fact that fifty of them scarcely weigh a drachm. Lac Insect ( Coccus lacca). — The habits and economy of this insect are much the same as those of the cochineal. The lac insect attaches itself to the bark of trees abounding in milky juice — Such as the Ficus Indica or Indian fig, and the Ficus religiosa or Banyan fig — punctures the bark, and causes an exudation of the milky juice ; this eventually surrounds the lac insect, her eggs, and larva, producing an irregular resinous- looking brown mass on the branch, which it encircles. The commercial varieties of lac are stick lac, which is the substance in its natural state investing the small twigs of the tree ; seed lac, the same substanco broken off in small pieces from the twigs; and shell lac, consisting of the substance melted and formed into thin cakes. Seed lac and shell lac are the resin left after the dye has been extracted from the stick lac. Lac dye and lac lake are two preparations of the colouring matter of stick lac, imported in small cubic cakes from the East Indies. The colouring matter of these dyes much resembles cochineal, for which it is largely substituted. Upwards of 1,000,000 lb. are annually imported from Bengal, and 3,000,000 lb. of shell lac ; nearly one-half of it, however, is again exported to Italy, Germany, and other parts of the Continent. Lac is mainly consumed in the manufacture of dye stuffs, sealing-wax, and of certain varnishes and lacquers. Bed sealing- wax has its colour communicated by vermilion ; white sealing- wax is made with bleached gum lac ; black sealing-wax is a mixture of shell lac and ivory black ; and blue sealing-wax is made by colouring the shell lac with smalt or verditer. To make golden sealing-wax, powdered yellow mica is mixed with the shell lac. PEODUCTS OF THE SUB-KINGDOM EADIATA. Radiata (Latin, radius, a ray) is the fourth primary division of . the animal kingdom, and includes all those animals which have a radiated disposition of the organs of locomotion and in- ternal viscera around a common centre, whence the term radi- ated animals. Their nervous system and instincts are reduced almost to a nullity ; all are indolent and slow of movement, while many of them are rooted and fixed. They have been sub- divided into the following classes : — 1. Echinodermata (Greek, echinos, a hedgehog, and derma, the skin), or spiny-skinned animals. Examples : asterias or sea-star, and the common echinus or sea-egg. 2. Acalephce, or jelly-fishes, called also sea-nettles, because leaving, when touched, a disagreeable sensation, like the sting of a nettle. These have an extremely soft, gelatinous structure, and float and swim in the water by alternate contractions and dilatations of the body. 3. Polypi, or animals having a fleshy cylindrical hollow body, the mouth of which is surrounded by numerous arms or tenta- culm, and commonly fixed by one end. Examples : hydra or water polyp and the coral polyps. Of the above classes of radiated animals, the last only is of commercial importance ; it furnishes us with the Red Coral ( Corallium rubrum, L.). — This is a marine pro- duction, formed by numerous polyps in union with each other, called a polypidom. Becently taken, coral is covered with one continuous living membrane, in which are the polyp cells. These polyps produce the coral, a branched tree-like structure, beau- tifully red, and very hard, and for this reason much sought after for ornamental purposes. In places where good coral is obtained it forms an important article of commerce. It is abundant in various parts of the Mediterranean Sea. It occurs in the Bed Sea, the Persian Gulf, and on the coasts of Spain, France, Corsica, Sardinia, and Sicily. Very fine coral is found between Tunis and Algiers, off the coast of Barbary, where the French and Italians carry on the coral fisheries. Other species of the genus have from time to time been dredged off Madeira and the Sandwich Isles. Coral always grows perpendicularly on the surface of the rock to which it attaches itself, in whatever position the rock may be placed, and from eight to twelve inches in height. Coral requires from eight to ten years to arrive at its full growth. It is dredged up from depths varying from 10 to 1,100 fathoms. Its value depends on its size, solidity, and the depth and brilliancy of its colour. Some of the corals in the market are worth from eight to ten guineas an ounce, whilst other kinds will not fetch one shilling a pound. PEODUCTS OF THE SUB-KINGDOM PEOTOZOA. Protozoa, or first animals (Greek, protos, first, and zoon, an animal). Examples: Infusoria, or animal culm developed in vegetable infusions and sponges. Sponge ( Spongia officinalis, L.). — This organism is now ac- knowledged by naturalists as belonging to the animal world. A piece of sponge shows on its surface an indefinite number of minute holes, amongst which there are larger openings scattered. When alive and in the water, currents of water are seen to enter the smaller openings, which, after passing through the body of the sponge, are ejected out of the larger orifices. Nutri- tive matter is conveyed by these currents into the body of the sponge, and faecal matter is at the same time removed. A coating of living gelatinous matter is spread all over the fibres of the sponge, in consistence like the white of an egg. This runs away freely from the sponge when the latter is taken out of the water. Nothing then remains visible but the sponge, which is, in fact, the horny skeleton or structure formed by the labours of the animals constituting the gelatinous coating. Sponges occur in all seas, from the equator to the poles, but they attain their greatest size and perfection in the tropics. They grow on anything which will serve them as a point of attachment. Several kinds of sponge come into the market, but the most valuable, and those also most in general use, are called Turkey and West India sponges. The former is considered to be the best. The tubes and orifices of the Turkey sponge are smaller than those of the West India variety ; it is also more durable, and less easily torn. The Turkey sponge is obtained from the Mediterranean, where it grows on rocks and stones at the bottom of the sea in masses from the size of an egg to that of a man’s head. Our supplies are received from Cyprus and Candia, from the shores of Anatolia, and from several islands of the Grecian Archipelago, especially from the small island of Symis or Syme, whose inhabitants are said to be the best divers. The coast of Syria furnishes the finest toilette sponges, valued at from 35s. to 40s. per pound; ordinary sponge costing only 10s. per pound. Inferior sponge, with a large-holed texture, called horse sponge, comes from the coasts cf Barbary, Tunis, and Algiers. The annual importation into the United Kingdom amounts to between 200,000 and 300,000 pounds, valued at <£80,000. The coarser sponges come principally from America. Very large ones are obtained from the Bahama banks and the coast of Florida. The property which sponge possesses, of absorbing water into its tubes and retaining it until squeezed out, renders it valuable for all purposes involving washing and cleansing. PRACTICAL PERSPECTIYE. — IV. Fig. 20. — The subject of this lesson is a cross, made of square timber, or stone. The picture-line, height of spectator centre, and points of distance having been fixed at pleasure, From A set off A b, representing the distance of the per- pendicular of the cross on the left of the spectator, and beyond this mark off c', so that B c' may equal the thickness of the material of which the cross is supposed to be made. Draw the perpendiculars c' E and b d, and join them by the horizontal e d. PRACTICAL PERSPECTIVE. 383 At the required height from the picture-line draw the hori- zontal line G I. Make I T and g' g equal to c' b. At g and I erect perpen- diculars, also equal to c' B. Draw f f' and h h', and these will complete the front elevation of the cross. Now from the angles B, D, G, H, I, and i' draw lines to the centre of the picture. From b set off b j equal to c' B. From j draw a line to the point of distance, cutting B c in K. At k erect a perpendicular, cutting i' c in l, and meeting D G in sr. Through L draw a horizontal line, cutting I c in N, and G C in o. At n erect a perpendicular, meeting H C in p, which will complete the perspective view of the cross when standing in the immediate foreground, on the left of the spectator, its elevation being parallel to the plane of the picture. Fig. 21.— In this study the cross is represented as rotated, so that the elevation is at right angles to the plane of the picture. The attention of the student is called to the fact that whilst in the former view the foot of the cross was on the picture-line, it is not so in the present study. A moment’s reflection will show that the upright must recede from the foreground in order From j mark off j K, equal to j b, and from K draw a line to the centre of the picture. Draw b' k ' parallel to j k, which will be the bottom line of the upright of the cross. At k' draw a perpendicular, meeting a horizontal drawn from D in M. On k erect a perpendicular, K s', and a line drawn from s' to the centre of the picture should pass through M. Draw horizontal lines from H and I, cutting k s' in p and H. Strengthen p n, and the square h i n p will be the end of the cross-arm. From N draw a line to the centre of the picture, cutting k 7 m? in L. Draw i' L, which will give the junction of the arm with the upright ; a horizontal line from G will then complete the view. Strengthen the lines required in the projection itself, in order that the object may stand clearly out. Fig. 22. — The object of this study is to show the method of putting steps into perspective. The four steps are contained within the square A b g d. Having drawn this square, and divided it into the required number of squares (that is, provided the steps are squares , to allow of the projection of the arm, the end of which touches the picture-plane. Now let us suppose the first cross to be moved along the picture-plane until the point J is at J of Fig. 21. If, then, on this point J we erect the perpendicular j S, and rotate the rect- angle J s R Q' on this, as a door on its hinges, we shall obtain the figure in which the cross will be contained. Having erected the perpendicular j s, draw a line from each of these points to the centre of the picture. Mark off from J the length j q (Fig. 20), and from Q draw a line to the point of distance, cutting j c in q'. Draw q' r, which will complete the perspective representa- tion of the rectangle containing the cross, when its plane is at right angles to the plane of the picture. On j s set off i and H, equal to the height and thickness of the arms. On the picture-line set off from j the length of the arms j B and c' Q, thus leaving between them the width of the upright of the cross. In the present study these are all equal, but of course this is not necessarily the case. From B and c' draw lines to the point of distance, cutting J Q' in b', c' ; at these points erect the perpendiculars b' d and O E. From H and I draw lines to the centre of the picture, and draw F g, which will complete the perspective view of the elevation of the cross. It now remains to give the appearance of solidity to this representation. otherwise the containing figure must be an oblong formed of the required number of steps of the desired proportions), strengthen such of the lines as are required to form the angles of the steps— viz, b i, i f, f e, e g, g h, h i', i' j, j d. From each of these points draw a line to the centre of the picture. From b set off on the picture-line b k, equal to the real length of the front of the steps. From K draw a line to the point of distance, cutting B C in k'. At k' draw the perpendicular k' i'', and from i'' draw the horizontal i" f'; continue the perpendiculars and horizontals, f', e', g', h', i', j', and r>', which will complete the figure. Fig. 23. — The subject of this lesson is the same block of steps, turned so that their length is parallel to the picture-plane. From A, the point immediately under the centre of the picture, set off A b, the distance of the object on the right of the spectator. At b erect a perpendicular, b c', equal to the height of the containing square or parallelogram. From b and c' draw lines to the centre of the picture. From B set off B a', equal to the base of the containing square or rectangle. From a' draw a line to the point of distance, catting b c in a''. At a" draw the perpendicular a" d ; then u c' n A" is the perspective representation of the containing figure. On b c' set off the divisions corresponding with the number and height of the steps — viz., 1, 2, 3, and from these points 384 THE TECHNICAL EDUCATOR. draw lines to the centre of the picture. On B a' set off the divisions corresponding with the number and width of the treads of the steps — viz., 1, 2, 3. From 1, 2, 3 draw lines to the point of distance, cutting B a" in 1' 2' 3'. At 1' 2' 3' erect perpendiculars, and these cutting the lines drawn from 1 2 3 (in the line B c') to the centre of the picture will give the angles of the steps e, f, g, h, i, j, and will thus Exercise 11. There is a stone cross, the perpendicular of which up to the arm is 7 feet ; this perpendicular is at base 1 foot square. The arm, which is 1 foot square, rests pn the perpendicular, and stands out 2 feet on each side ; above this arm the perpendicular is continued so as to make the total height of the cross 10 feet. The scale is 4 inch to the foot, the height of the spectator is 5 feet, the distance 12 feet. (1.) Put this cross into perspective when standing in the fore- ground at 8 feet on the left of the spectator. complete the perspective view of the end of the block of steps, j (2.) Put the same subject into perspective, at the same distance From B set off b K, equal to the real length of the front of i oa left of spectator, but standing 10 feet back in the picture, the steps Exercise 12. Now from r (on the line b c') draw a horizontal, and from K 1 ° f s P ectator > and distance the same as iu draw a perpendicular. These, intersecting in i', will give the , pre ™“ p^t the cross into perspective when standing at 9 feet on the front of the first step. . | right of the spectator, its face being at right angles to the From i' draw a line to the centre of the picture, and from e picture-plane, draw a horizontal to intersect it in e'. . (2.) Put the same cross into perspective when standing at 0 feet At e' erect a perpendicular, and from r draw a horizontal to intersect it in f'. From f' draw a line to the centre of the picture, and inter- sect it by a horizontal drawn from G, thus obtaining the point g'. From o' draw a perpendicular, and from h draw a horizontal to intersect it in h'. From h' draw a line to the centre of the picture, and a hori- zontal from I to intersect it in i'. At i' erect a perpendicular, and intersect it in j' by a hori- zontal drawn from J. From j' draw a lino to the centre of the picture, and intersect it in d' by a line from D, which will complete the study. ou the right of the spectator, and 8 feet within the picture, its face being at right angles to the picture-plane. Exercise 13. The scale is $ inch to the foot, the height of the spectator is 6 feet, and his distance 15 feet. There is a flight of 6 stone steps ; the rise is 6 inches and the tread 9 inches, and the length of the steps 6 feet by scale. (1.) Put this block of steps into perspective when placed at 7 feet on the left of the spectator, the end elevation being parallel to the picture-plane. (2.) Put into perspective the same block of steps when standing so that their long edges are parallel with the picture-plane, the end elevation being at 5 feet on the right of the spectator. CIVIL ENGINEERING. 385 CIVIL ENGINEERING.— V. BY E. G. BARTHOLOMEW, C.E., M.S.E. CANALS ( continued ). The engineer having decided upon the most desirable course to be taken by the canal — the centre line having been staked out — next proceeds to lay out the centres of cutting for the various sections. These points will best be understood and explained by the help of diagrams. In excavating for the bed of a canal it is very seldom necessary to dig out soil equal to the capacity of the intended channel, be- cause, in al- most every case, the soil which is ex- cavated can be utilised on the spot, by being depo- sited upon one or both sides of the excavation, and, by pro- perly puddling and solidifying it, making it form the upper por- tions of the bed or the banks. Thus, frequently, nearly half the labour and expense is saved. To accomplish this, however, it will be necessary to deter- mine what shall be the depth and capacity of the excavation, so that, when the soil taken out is banked upon its margins, the completed channel shall have the capacity and dimensions it is intended the canal shall have. Now, it is with the view of deter- mining this point that the “centre of cutting” is required. Our space prevents our entering fully into the rules requisite for determining the position of this point, which will vary greatly according to circumstances, and principally according to the direction, slope, or angle of the original surface of the ground, relative to a line standing vertically in the centre of the channel. Let abcd (Tig. 4) represent the surface of the ground, and let the first condition of the surface be that of a hori- zontal plain. This line will then be at right angles to L l', the line standing vertically in the centre of the channel. In this case the dotted line abed, in which lies the centre of cutting, will occupy such a position as that the area of the quadrangle b cc'b' shall be equal to the sum of the areas of the quadrangles a efb + c gh d, in which ef and gh are the towing-paths on the sides of the channel f g d b', the small grip or ditch at a and d being formed to carry off the drainage from the banks. The enormous advantages which result from the adoption of this plan become apparent from an examination of the diagram. It will there be seen that only the lower and narrower portion of the channel has really to be excavated, the upper and wider part being built up, as it were, of the excavated soil. Fig. 5. The second condition we have to consider is, when the surface- line of the ground abcd (Fig. 5) is not at right angles with the vertical line l i/. In this case it may not be necessary to disturb the ground at all upon the upper side of the slope, except to excavate for the towing-path ef, and the drain at B. The line abed through the centre of cutting will, in this instance, be determined upon by the consideration that the whole of the excavated soil can be utilised upon the lower side of the channel only ; the capacity, therefore, of the figure I yb'dx must equal that of the figure x g h c, y x being in the line of the ground level. ef and g h being the towing-paths, and / b' d y the channel of the canal. It will be necessary to give one rule only for ob- taining the centre of cut- ting. Take a case of oblique cutting — i.e., where the canal has to be formed on the side of a hill, the inside and outside slopes being parallel, and one bank only required : — Let abcd (Fig. 6) be the sec- tion of the intended canal, and c D E G F that of the bank, the slopes a b and e f being parallel. To find the centre of cutting, continue the lines bc,de to G and A ; draw the perpendicu- lars c to, d n, and the diagonals A g, to n, intersecting at p ; through p p ^ draw the pa- ' 7 / " rallel s p t, and bisect it in o; then o will be the centre of cut- ting, and if anyline,HOF, be drawn through this point, cutting the slopes A b, e g produced, hbcio will always be equal to w D e F ; and the total breadth of the canal and bank (a d -f- n g) will be to the breadth of the bank added to the base of the slope (»g+uc), as the depth of the canal from its surface is to the depth below the centre of cut- ting. This point o will also be the centre of cut and cover, for a line staked out at the level of the ground above the point o will show the middle of tho land required for the canal. Cases maj arise, how. ever, in which the excavated earth cannot be utilised. The soil may be entirely unsuited for the formation of the banks, and must be removed. Ir such a cast the channel will have to be altogether excavated below the ground-level. Sometimes, as, for instance, in passing through towns, retaining walls have to be built, so that less breadth of land shall be required. In conveying canals over roads, or across ravines, it may be necessary to construct aqueducts of masonry, or troughs of iron. A handsome bridge of five arches, built of hard sandstone, conveys the Lancaster and Kendal Canal over the river Lune at a height of 62 feet above the water. This aqueduct is 600 feet long. The next point for our consideration is the lock. This inge- nious arrangement is intended to overcome the difficulties Fig. 4. Fig. 6. 3b6 THE TECHNICAL EDUCATOE. attendant upon conveying a canal over unlevel ground, so that the navigation shall he continuous. There are other contrivances besides the lock for attaining this object ; but for ordinary purposes the lock is the most desirable. Before the invention of the lock, inclined planes were made use of for enabling the barges to pass from one level to another, and it was only in 1460 that locks were first employed upon canals. They were used in the Canal of Martezana, in Italy. A lock consists of a portion of the canal fitted at each end with folding doors or gates, which when closed prevent the passage of the water through them, except when a valve or sluice, which is constructed in them, is opened. By means of these gates and valves the water in the intermediate portion can be brought to the same level with that either in the upper or lower section of the canal, and ■ a barge enclosed between them will descend with the descent of the water from the upper to the lower section, or will ascend with the rise of the water from the lower to the upper section. The upper gates are called the sluice- gates, and the lower the flood-gates. The area of the lock should never be allowed to exceed what is actually required for the savigation, because every time a lock is emptied the enclosed mass of water descends to a lower level, and causes, by so much, a demand upon the source of supply at the higher levels. It is therefore desirable to reduce this mass of water as much as possible. The difference of level upon the opposite ends of one lock should be kept, as nearly as possible, to 8 feet. If more than this, the strain caused by the water-pressure becomes excessive, and it is better to subdivide the height by a second lock. The depth of a lock must be such that a barge navigating the lower section can float freely into it when the sluice-gates are closed and the flood-gates open, and the height of the flood- gates must be such that when closed, and the water admitted into the lock from the upper level, it shall not overflow them. The position of a lock is just at the termination of a level where the ground begins to fall. It is for every reason desirable to construct a lock of masonry, so that the wash of the water, caused by opening the sluices, shall not augment its capacity. Sometimes, when the traffic is heavy, as upon the Regent's Canal, in London, the locks are made double — that is, side by side, separated by a strong pier of masonry — and a flood-gate or valve is placed in this pier, by which communication can be made between the two locks. By this arrangement a saving of water is frequently effected, as, instead of allowing an entire lockful of water to pass into the lower section, half of it can be passed into the adjoining lock, should that happen to be empty at the time. Great care is needed in constructing the retaining walls and piers of locks. As a rule, the thickness of a wall intended to support the lateral pressure of water should not be less than half the height of the water which presses against it. The surface of the masonry should be set in cement, and the bonding should be arranged so as best to withstand the thrust of the closed gates. The gates of locks are usually constructed of timber, although in some instances they are of iron. If of timber, they consist of two strong upright posts, the inner being called th 9 quoin , or hanging post, and the outer the mitre, or shutting post. These are framed together with several horizontal rails or cross-bars, and the whole consolidated by braces closely laid, and placed either vertically or diagonally, the dip ' of the diagonal being downwards C \ from the hanging — — - A post. By this means the stress is trans- ferred to that post. The valves or sluices are small doors sliding vertically over orifices left in the frame- work of the gate, and usually raised and lowered by a rack and pinion worked from above. The hanging of the gates demands great care. They must be made to fit so accurately both at the sides and middle, as that very little, if any, water can percolate through when they are closed. Their lower centre moves in an iron plate leaded into the stone-work, while the upper is supported by a strap keyed or bolted to attachments let into the upper courses of masonry. The strap, by the action of the keys or bolts, can be altered in its position, to allow for wear in the centre, and for other purposes, such as the ready unhinging of the gate for repairs. In Fig. 7 is shown a plan of the ordinary arrangement of hanging ; c being the centre of the gate g, S the strap passing round the centre, and p the iron plate let into the masonry. As it would be impracticable to allow the gates to rest upon the ground, owing to the friction which would result, and as, nevertheless, any space which existed under the gates when closed would be the cause of considerable leakage, when the level of the water is higher on the resisting side, their bases are made to close against a timber sill, called a mitre sill, the angle of which must agree accurately with that at which the gates are intended to remain when shut. This sill is partly embedded into the masonry on the bottom of the lock, and is framed as shown in Fig. 8. The arrows indicate the direction of thrust. The piece ab runs transversely across the lock, the ends being worked into the side walls under the hollow quoins. The angle acb, which, as we have stated, must correspond with the angle at which the gates stand when shut, varies according to the views held by engineers. It must certainly vary with the size of the gates — that is, with the pressure of the water. The larger the gates the more acute the angle should be. The reason for this is obvious: since if the gates are small, the pressure of water, being less, would scarcely ensure the efficient closing of the gates, if the angle be too acute ; whereas if the gates are large, the great pressure of water would act injuriously against the bearings of the gates, if the gates closed at too obtuse an angle. The nearest approach to a rule we can lay down is, that when the head of water is from 5 feet to 9 feet, the length of the king-post K (Fig. 8) shall be one-fifth of the length of the opening of the lock; if the head be less than 5 feet, the king-post may be one-sixth of the opening. Owing to the fact that the flood-gates are sometimes partly submerged, and sometimes entirely out of the water, their weight will vary. Long levers are therefore fixed to them, to facilitate opening and shutting them, at the same time being made very heavy to balance them. If the gates are very large and very heavy, the balance levers are dispensed with, and the gates are furnished with small iron wheels, upon which they rest, and which run on iron rails curved to the arc they describe. The gates are in this case opened and closed by means of chains attached to them. SEATS OF INDUSTRY.— VII. GLASGOW. — I. BY WILLIAM WATT WEBSTEB. Glasgow is by far the largest town in Scotland, and in point of wealth and population ranks third among the cities of the United Kingdom. It is at once one of the most ancient and one of the most flourishing centres of commercial and manu- facturing enterprise in Britain. All the principal phases through which trade and manufactures have passed since the dawn of the modern industrial era are illustrated in the story of this city. Entering early on a commercial and manufac- turing career, Glasgow has steadily maintained the foremost place among the industrial towns of Scotland ; and every great discovery or improvement in the methods of production and transit has, quickly after its introduction, been made to con- tribute to its prosperity. The spot now occupied by Glasgow was the site of a Roman station, and the remains of a Roman camp are still to be seen at a place called “ Camphill,” two miles to the south of the city. Glasgow formed part of the province of Yalentia, which was bounded on the north by the wall of Antoninus, that er- SEATS OF INDUSTRY. 387 tended from the Frith of Forth to the Frith of Clyde, and it is believed that it continued in the possession of the Romans till about the year 426, or shortly before the time when they finally abandoned the island. There is a tradition that the site on which the cathedral of Glasgow stands was consecrated as a burying-ground by St. Ninian of Galloway, as early as the beginning of the fifth century ; and historians are agreed that a religious house or see was established there by St. Mungo, or, as he was also styled, St. Kentigern, about the year 560. The city, undoubtedly, had its origin in a religious establishment, and St. Mungo is its reputed founder. Several fathers of the Roman Catholic Church have recounted the fabulous achieve- ments of this holy ecclesiastic, and those portions of the legendary story of his life which explain the arms and motto of the city with which his name has been associated for so many centuries may fitly find a place in this paper. The arms of Glasgow consist of a tree, with a bird perched in its boughs ; on one side is a salmon with a ring in its mouth, and on the other a bell. The tree is said to commemorate a miracle which St. Kentigern performed at Culross, when he broke a frozen bough from a hazel, and kindled it into flame by simply making the sign of the cross over it. Regarding the ring and the fish, an equally extraordinary story is told in the monkish legends. The queen of Cadyow having lost a ring presented to her by her lord, who threatened to put her to death if it could not be found, went to St. Kentigern in great distress, and besought him to put forth his supernatural power to recover the missing jewel. After he had concluded his devotions, the saint went forth to walk along the banks of the river Clyde, as his custom was, and seeing the fishermen plying their vocation, he asked them to bring him the first fish that was caught. It is hardly necessary to add that the ring was found in the mouth of the fish, and that the lady was saved from the fate which threatened her. The bell is the effigy of a famous bell that St. Kentigern brought from Rome, which was preserved in Glasgow till the Reformation, if not to a more recent period. There is no miraculous story associated with the bell. It is otherwise, how- ever, with the motto : — “ Let Glasgow flourish by the preaching of the word. ’ ’ Having incurred the hostility of the heathen chief of Cumbria, St. Kentigern was compelled to fly from the newly- organised settlement at Glasgow, and seek refuge in Wales, where he abode for some years, and founded the bishopric still called after his disciple, St. Asaph. When his enemy died, the holy man returned to the scene of his former labours, and was welcomed back by a great crowd. Beginning to preach the Gospel to the thronging multitude, St. Kentigern soon found that it was impossible, owing to the flatness of the ground, to make himself heard, except by those in his immediate neigh- bourhood. This acoustic defect, however, was soon remedied ; for, lo ! on a sudden, the plain on which he stood was trans- formed into a hillock, from whence he was both seen and heard. According to the legends, St. Kentigern received the name of Mungo from his spiritual father St. Servan, the Culdee of the Inch of Lochleven, whose favourite disciple he was ; and the word Mungo or Mungah signifies in the Norwegian language “ dear friend.” For five hundred years after the death of St. Mungo, which occurred in 601, the history of Glasgow is almost a blank. The people who inhabited the valley of the Clyde are believed to have acquired a certain degree of civilisation from being brought into close contact with the Romans, and the “ Kingdom of Strathclyde,” which was founded after the departure of the Romans, was intact at the time when Bede, the historian, died in 734. One of the princes of the Strath- clyde dynasty conferred a grant of lands on the religious house which St. Mungo established ; but the fraternity were robbed and maltreated, alternately by Piets, Scots, Saxons, and Danes. In 1115, David, Prince of Cumberland, repaired the devastations of St. Mungo’s settlement; and in 1129, four years subsequent to his accession to the throne of Scotland, this pious and munificent sovereign appointed his preceptor, John, commonly called Achaius, to be bishop of the see. A few years later the pile was rebuilt, and on its consecration David I., in addition to his previous gifts, conferred on the community of St. Mungo the valuable lands of Partick, which are now in the possession of the University of Glasgow. The liberality which this sovereign displayed towards the Church gained him the title of Saint, and caused one of his successors on the throne, James V., to grumble that he had been “ane sair sanct for the croon.” There are no means of determining- whether Glasgow had at this period attained the dimensions of a town, but the nucleus round which the city has gathered and grown was now formed. The claim of King David I. to be considered the re-founder of the city, is at least as good as that by which St. Mungo holds the title of founder. In 1181 the building erected by David I. was replaced by the present pile ; and in 1190, King William the Lion raised Glasgow to the dignity of a royal burgh, with the privilege of an annual fair, which is still held. For the next century and a half, however, Glasgow remained a small town of some fifteen hundred inhabi- tants. The first bridge across the Clyde was built by Bishop Rae, about the year 1345; and in 1451 Bishop Turnbull, on the authority of a bull obtained from Pope Nicholas V., established the University. But although the latter exercised almost as important an influence on the early fortunes of the city as the erection of the cathedral, yet as late as 1550 Glasgow was only the eleventh among the towns of Scotland. Commercial enterprise began to manifest itself in Glasgow at a comparatively early period. John M‘Ure, alias Campbell, “Clerk to the Registration of Seisins and other Evidents for the District of Glasgow,” published a history of the city in 1736, when he was in his seventy-ninth year, from which we learn that “ the first promoter and propagator ” of the trade of the place was William Elphinstone, a cadet of the noble family of that name, and father of Bishop Elphinstone, the founder of King’s College and University at Aberdeen. This trading- worthy acquired wealth and fame about the year 1420, by curing salmon and herrings, and exporting them to France and other Continental countries, bringing back brandy, wine, and salt in exchange. M‘Ure mentions as the “ second promoter and propagator ” of trade, Archibald Lyon, a younger son of Lord Glamis, who was brought to Glasgow near the close of | the fifteenth century by Archbishop Dunbar, and who be- came a great merchant, and “ undertook great adventures and voyages in trading to Polapd, France, and Holland.” The success of this high-born merchant is attested by the extent of the possessions he acquired in and around Glasgow. In the inventory of his wealth the following items occur :■ — “ A great lodging for himself and family upon the south side of the Gallowgate Street ; four closes of houses and forty-four shops, high and low, on the south side of the Gallowgate ; and a part of the left side of the Saltmarket.” But the foreign trade of Glasgow at this time must have been trifling, although about the year 1600 the prosperity of the foreign merchants excited the jealousy of the tradesmen, who wished to share the ad- vantages enjoyed by the former; and the disputes between them led to the establishment of a guildery in 1605, for regulating and maintaining the limits of trade and commerce, having at its head a dean, who was to be “ a merchant, a merchant sailor, and a merchant venturer.” The effect of the regulations in- stituted by this guildery was, that none but guild brethren were in future permitted to trade or traffic in Glasgow. An interesting account of Glasgow half a century later is to be found in a report on the revenue from the excise and customs of Scotland, dated 1651. “ With the exception of the coliginers,” says Commissioner Tucker, “ all the inhabitants are traders : some to Ireland, with small smiddy coals, in open boats from four to ten tons, from whence they bring hoops, rungs, barrel- staves, meal, oats, and butter ; some to France, with plaiding, coals, and herrings, from whence the return is salt, pepper, raisins, and prunes ; some to Norway for timber. There have likewise been some who have ventured as far as Barbadoes. .... The mercantile genius of the people is strong, if they were not checked and kept under by the shallowness of the river, every day more and more increasing and filling up, so that no vessel of any burden can come up nearer the town than fourteen miles, where they must unload and send up their timber on rafts, and all other commodities by three or four tons of goods at a time, in small cobbles or boats, of three, four, or five, and none above six tons a boat. . . There are twelve vessels belonging to the port, none of which come up to the town — total 957 tons.” The most notable among the mer- chants of Glasgow from 1651 to 1707 were Walter Gibson and John Anderson. The former had dealings with France, Spain, Norway, and Virginia, and was the first merchant who brought iron to Glasgow, while the latter is celebrated as the first merchant who imported wine direct into the city. 388 THE TECHNICAL EDUCATOR. PRACTICAL PERSPECTIYE. — Y. FiG- 24. — The subject of this lesson is a cross, of a similar character to that shown in Figs. 20, 21; but in the present study the object is lying on the ground with the ends of its cross-arm parallel to the picture- plane. It will be remembered that Fig. 20 was shown to be con- tained in a rectangle, and this plan is again adopted in the present lesson. From a, the point immediately under the centre of the and G d will be the real length of the arms, and F G their width. From f and G draw lines to the centre of the picture, cutting d' e in h, i. F h i G is the plan of the arm. But the timbers of which the cross is made are of equal thickness, and therefore f g is not only the width of the arm but of the upright stem of the cross ; and further, the arms project horizontally from the stem, precisely as much as the stem projects above them, and the space cut out of the comer of the containing rectangle is therefore a square, the side of which is B F. Therefore, from F and G draw lines to the point picture, mark off A b equal to the distance of the top of the cross on the left of the spectator; and from b set off towards A .the distance b c', representing the entire height of the cross. From b and c' draw lines to the centre of the picture. From b set off b d, representing the width of the containing rectangle. Draw a line from D to the point of distance (the point of distance is not shown in this figure), which will cut the line drawn from b to the centre of the picture in d'. At T>' draw a horizontal line, cutting c c in e, which will complete the perspective representation of the rectangle when lying on the ground. Now between b and D set off the lengths B F, F G ; then B f of distance, cutting the line drawn from b to the centre cr the picture in j and K. Draw J l and K m, and these will complete the plan of the cross. Now on f G construct a square, fgho, which will be the elevation of the end of the aria From n and o draw lines to the centre of the picture. At i draw a perpendicular, cutting o c in p, and at p draw the horizontal p Q, which will complete the solid rendering of the arm. The line drawn from G to the centre of the picture cuts J L in b; at B. erect a perpendicular, cutting o 0 in S. At J and L erect perpendiculars. Through s draw a horizontal, meeting WEAPONS OP WAR. 889 the perpendiculars j and l in T and u. At K and M erect per- ; pendiculars. From T and u draw lines to the centre of the picture, cutting the perpendiculars K and M in V and w. Join v w by a horizontal, and this will complete the figure. Such lines as would be visible in the object are then to be strengthened. Fig. 25. — The subject of this lesson is a simple doorway, con- sisting of two uprights, and a horizontal resting across them. Having drawn the picture and horizontal line, and having fixed the centre of the picture and the point of distance,* mark off the distances a b, b c', c' D, and D e. These will give the positions of the uprights. From b set off b e, and from e set off e g. These spaces represent the length which the horizontal pro- jects beyond the uprights. These would not be absolutely necessary if the one figure in the foreground only were to be drawn, but as a distant figure is to be added, it is advisable that they should be marked at the present stage. Draw the perpendiculars B, c', D, E ; join H I and J k , and from the upper and lower extremities of the perpendiculars draw lines to the centre of the picture. From d set off D L equal to the width of the receding side of the upright, and from l draw a line to the point of distance, cutting the line D in M. At M draw a perpendicular, meeting Fig. 27. — In this figure the two objects are placed in a lino, so that their faces are at right angles to the picture-plane. Having fixed E as the distance of the objects on the left of the spectator, set off from it e l, equal to the breadth of the side of the object. This length is similar to L D in Fig. 25, which, seen perspectively, becomes d m. From F and l draw lines to the centre of the picture ; and it is in this track that the object travels as it recedes into the distance. From f mark off F b, c', d, e, g, as in the previous figure, and from each of these points, excepting f, draw lines tc the point of distance, intersecting f c in b', c, d ' e, and e. At F erect a perpendicular, and mark on it the heights Q and R. From Q and r draw lines to the centre of the picture. Now from b', c, d', and e erect perpendiculars to meet Q in H, I, J, and l', and another from e will give s t. At q R draw horizontals, and at L erect a perpendicular. This will give the square Q R v u, representing the end of the horizontal ; and from u draw a line to the centre of the picture. From b' draw a horizontal, cutting l c in o, and at h draw a horizontal, cutting u c in f. Join o p by a perpendicular. At d' draw a horizontal, cutting Lcinw. At J draw a hori- zontal, cutting uc in N. Join w n by a perpendicular, and this will complete the view of the object. j in N, which will complete the view of one of the uprights. Draw a horizontal line through m, cutting the line drawn from b to the centre of the picture in o ; also a horizontal line from n, cutting h in p. Then the perpendicular o P will complete the perspective projection of the second upright. Produce the horizontal H K, and terminate it by perpendi- culars from F and G, which will give the ends Q R, S T of the horizontal. From q and R draw lines to the centre of the picture. Produce n p to meet Q in u, and from u draw the perpendicular u v. Q R v u will be the view of the end of the horizontal, and the projection will then be finished. Fig. 26 represents the same object at a distance back in the picture. Draw lines from F and G to the centre of the picture, and having set off from b on the picture-line (at a point not shown in the figure) the distance which the figure is supposed to be from the picture-plane, draw a line from such point to the point of distance. (The position of this line shown in the figure is lettered w.) The line w, intersecting B in x, will give the required position. Through X draw a horizontal, and this, intersecting all the lines drawn from the points in the foreground, will give the places of the perpendiculars in the distance, and the rest of the con- struction will be readily understood from the diagram. * The student is advised to fix these at different distances from those in the figure. This will prevent his absolutely copying the diagrams. In commencing the second figure, set off from G the length G f', equal to the distance of the second object beyond the first. From f' set off b", and all the other points as in the first figure. From these points draw lines to the point of distance, inter- secting the line drawn from F to the centre of the picture, as in Fig. 25, and from these raise perpendiculars. Then the lines drawn from Q, R, tr, v to the centre of the picture will give the necessary points and lines for the horizontal, and so com- plete the figure. WEAPONS OF WAR.— VII. BT AN OFFICER OF THE ROYAL ARTILLERY. GREAT GUNS AND THEIR PROJECTILES. We now enter upon another stage of our subject. We have dealt hitherto with hand-weapons — weapons to be wielded by individual combatants, and comprised within the term “ small - arms.” We have traced, however imperfectly, the gradual development of weapons of this sort, through the stages of swords, spears, and pikes, of arrows, javelins, and missile weapons, up to the Needle-gun, the Chassepot, the Snider, and the Martini-Henry. We must now turn to great guns, and consider the principal types of cannon in use in this and foreign countries. The same principles which have governed the successive developments of small arms have applied to cannon, with some 399 THE TECHNICAL EDUCATOR. modifications or additions. The power of being able to reach your enemy at a continually increasing distance, of being able to strike him with greater and greater certainty, of being able to do him more and more harm, and of accomplishing all this with the minimum of inconvenience and difficulty to oneself — this is the problem which for several centuries the artillerist has set himself to solve ; and these conditions may be said to apply to all classes of ordnance, heavy and light. But the con- ditions imposed in the two cases are very different. In the case of the light gun, the object generally is to destroy men ; in the case of the heavy gun, although the ultimate object is to carry destruction and dismay among the personnel of your enemy, that object can generally only be attained through the destruction of his materiel. Again, while there is practically hardly any limit to the size of the heavy gun, except the endur- ance of the weapon itself, the field-gun has to be of a weight no greater than will permit of its easy and rapid transport on a campaign, and from one part of a field to another. Lieut. Hime, R.A., in an interesting paper on Field Artillery, in the “ Proceedings of the Royal Artillery Institution,” observes that “motion is the essential difference between the two great branches of the artillery service, being as necessarily included in the conception of field artillery, as it is necessarily excluded from the notion of garrison artillery. The latt 3r is the artillery of rest, the former is the artillery of motion; and an immovable field artillery is a contradiction in terms.” Marshal Marmont used to say,“ Le premier merite de l’artillerie, apres la bravourie des canoniers et la justesse du tir, c’est la mobilite.” It would seem that this proposition might be fitly reversed — for no amount of gallantry, no amount of accuracy, would compensate for an absence of mobility. Gustavus Adolphus, at any rate, acted upon this principle, for, as Lieut. Hime tells us, he resolved at the commencement of the Thirty Years’ War to increase the mobility of his field artillery “ at all hazards,” and he actually took the extraordinary step of introducing leather guns of great mobility, but of inferior accuracy as compared with the iron guns then in vogue. These leather guns did good service before they dropped into disuse. Therefore, it is important to insist upon this fundamental distinction between field and garrison (or naval) artillery — the necessary mobility of the former. But it would not do to divide artillery into two great groups, separated by a hard and fast line. On the contrary — while in the one direction field artillery shades off into mountain artil- lery, and garrison artillery developes into the monster turret guns, which are moved on huge turn-tables within the cupola or turret — the two classes of field and garrison meet on common ground, and almost imperceptibly shade off one into the other in guns of position and siege guns. If we were required to classify artillery at all, we should adopt some such distribution as the following : — 1. Mountain guns. „ , f (a) Horse artillery. 2. Field guns j (h { Fleld artiUery< 3. Guns of position. 4. Siege guns. 5. Garrison and broadside guns. G. Turret guns. Most of these classes admit of further subdivision — for there are mortars, howitzers, carronades, shell-guns, and guns proper ; there are also smooth-bore and rifled guns. It is evident, therefore, that an exhaustive treatment of every detail of this large subject is impossible within the limits of the present series of papers. We shall therefore not attempt to deal with each sub-division or class of weapons in detail, but will take the more salient points of the different systems in the order in which they occur to us. Until some twelve years ago nearly all artillery consisted of smooth-bores. Rifled guns of great variety and ingenuity of design have been prepared by sanguine inventors, and many of them have been experimented with. But the guns of the English service, like those of other nations, remained smooth- bores. It may be supposed that it is unnecessary to speak of smooth-bores now — that their day has gone by so completely as to invest them with no other than an antiquarian interest. This is not the case ; it must take many years before smooth- bores disappear from our service ; for some purposes — as for the flank defence of ditches, where range and accuracy are of no importance, while a high velocity of projectile is of very great importance — smooth-bores will probably always be retained. Again, at this moment there does not exist a single rifled mortar in the British service ; while the Americans scarcely use any other than smooth-bore guns, even for their first-class arma- ments. So that, although the day of rifled guns dawned some dozen years ago, that of smooth-bores has not yet set. A smooth-bore gun is merely a hollow tube of iron, or steel, or bronze, or other suitable material, intended to project a spherical projectile. The expression “ smooth-bore ” has refer- ence, of course, to the unrifled condition of the bore. The largest smooth-bore gun in the British service prior to 1858 was the 68-pounder, so-called because the solid spherical shot which was discharged from it weighed 68 pounds. The gun itself weighed 95 cwt., # and it fired a charge of 16 pounds of powder. It is interesting to compare this, the biggest English gun of 1858, f with the biggest English gun of 1871. The latter is a 700-pounder, its weight is 35 tons, or 700 cwt., or more than ten times that of the 68-pounder. The charge of the 35-ton gun will be 113 lb. or 120 lb of powder. Before we come to speak more particularly of the 35-ton gun, we have a great deal of ground to cover. But it seemed interesting to show by this con- trast the strides which have been made in twelve years. All the heavy English smooth-bore guns were made of cast-iron — about as bad a material as could well be employed for ordnance, because of its comparatively low resisting power and its liability to yield suddenly, and without warning when it did yield, and thus to cause what artillerymen most dread — an explosive burst. However, for firing the comparatively low charges then in vogue, the cast-iron was fairly suitable. It is true that the annals of our artillery are darkened by the record of many disasters due to the bursting of these guns ; but it is probable that, had it not been for the introduction of rifled artillery, and the new conditions imposed upon the gunmaker, cast-iron would have continued to be employed for several years to come. Where great lightness was required — as for field-guns — bronze or “ gun-metal ” was employed. Bronze is an alloy of copper and tin in the proportion of about 11 to 1. The ad- vantages of this material are its lightness, its non-liability to explosive rupture, its value as old metal when the gun is worn out, and the facilities of production. On the other hand, the soft- ness of bronze has always constituted an objection to its use for artillery; this softness was apt to cause the guns to become bulged and unserviceable with long-continued firing, and “ drooping at the muzzle ” was a complaint to which bronze guns were considered to have been especially liable. The smooth-bore field-guns of the British service were gene- rally 9-pounder guns and 24-pounder howitzers for field batteries, and 6-pounder guns and 12-pounder howitzers for horse artillery. The howitzers differed from the guns in throwing heavier pro- jectiles with greatly reduced charges. While the relation of the charge to the projectiles in the guns was about as 1 to 3 1 or 4, in the howitzers the relation was about as 1 to 9 or 10. This reduction of charge enabled the howitzers, although firing far heavier projectiles, to be made thinner and shorter than other guns, which they thus did not exceed in weight — the 9-pounder gun and the 24-pounder howitzer weighing each about 13 cwt., the 6-pounder gun and 12-pounder howitzer weighing each about 6 cwt. The mode of carrying these pieces, as well as that of carrying and mounting guns generally, will be treated in a separate paper. Between the field-guns and the 68-pounder before mentioned, there were a number of guns intended for a variety of purposes. The designation of these guns was as follows : — 56-pounder, 42-pounder, 32-pounder, 24-pounder, 18-pounder, and 12-pounder. The 56-pounder and 42-pounder are fast becoming obsolete, but the other guns still exist in the service in considerable numbers. The whole of these guns were made of a weight and strength which permitted of the use of solid shot or shell, with relatively heavy charges of powder. There were, however, guns intended specially for projecting shell with low charges ; these were the 10-inch and 8-inch shell-guns and howitzers. I There were also * There were some of 112 cwt. f A few 150-pounder and 100-pounder smooth-bore guns were subse- quently introduced. % The number of inches whence these guns have their designation, refers to the diameter of the bore. WEAPONS OF WAE. 391 pieces designed for projecting either shell or shot with very j low charges; these were called carronades. The charges for shell-guns and howitzers varied from about £th to ^th the weight of the heaviest projectile ; the charges for all carronades being fixed at about ith the weight of the shot. Originally shells were not projected from guns and howitzers at all ; they were thrown from mortars. A mortar is a short piece for throwing shells at an angle of 45° into an enemy’s position; and for the bombardment of a town, or any large area, this “vertical fire,” as it is called, is terribly effective. Indeed, it would be terribly effective against all positions, if sufficient accuracy could be obtained to insure hitting the object aimed at. But the comparative inaccuracy of vertical fire — the shell describing a roundabout path to arrive at its object, and being therefore for a longer time under disturbing influences than the shell from a gun — has hitherto constituted a formidable objection to its extended use. It will be easily understood that the effect of a shell falling on to the deck of a ship would be tremendous ; but a ship, especially a ship in motion, presents such a small and difficult object for attack, as to entail an immense waste of ammunition in trying to hit it. The same objection does not apply to the employment of mortars against large entrenched positions, towns, etc. Attempts are now being made to introduce rifled mortars, by which the irregularities of vertical fire may be, if not removed, at least diminished, while in range and general power such pieces would be vastly more effective than smooth- bore mortars. An interesting development of mortar-fire was suggested by Mr. Mallet, C.E., in 1858. Mr. Mallet proposed to throw enormous shells, 36 inches in diameter, weighing 2,481 lb., and containing each a bursting charge of 480 lb. (equal to nearly five barrels) of powder. Thus, the total weight of each shell filled was about 1| tons. Mr. Mallet also pro- posed a mortar of suitable proportions to project these monster shells. The proposition attracted a good deal of attention, and by Lord Palmerston’s order two of the mortars and a number of the shells were supplied by Mr. Mallet for experiment. Both mortars and shells may be seen by visitors to Woolwich Arsenal, where they form objects of curiosity and interest. Mortars are designated by their calibres in inches. There are five sizes in the British service — viz., 13-inch, 10-inch, 8-inch, 5 (,-inch, and 4|-inch. *We see, then, that there existed smooth-bore ordnance suit- able for throwing projectiles of all sorts, and of delivering a “ horizontal ” or a “ vertical ” fire ; that these pieces were made of cast-iron, except those intended for field-guns, which, on account mainly of their greater lightness, were made of bronze. But a gun, after all, is only a means to the end. It is an instru- ment merely for throwing projectiles, with more or less of range and accuracy, more or less of destructive effect. We will therefore pass to the projectiles which were used with these pieces, before going on to state in what manner the range and accuracy of the smooth-bore guns has been improved upon, and how artillery has attained to the pitch of destructive power which it has now reached. We will therefore proceed to treat of the different classes of projectiles which are fired from smoothbore guns. With the exception of such projectiles as were intended to break up at the muzzle and produce an immediate scattering effect, or projectiles which, like the ground light ball, were not required to have any special accuracy, the projectiles thrown from smooth-bore guns were all spherical, that form being the one which naturally, in the absence of rifling, could be thrown with more certainty and accuracy, and to a greater distance than any other. The two main classes of projectiles are shot and shell. There is a third class of incendiary and miscellaneous projectiles which must not pass unnoticed. The varieties of each class are much more numerous than persons generally suppose. Thus, the word “shot” generally conveys but one impression to the mind of the non-professional. It almost inevitably suggests the solid “ round shot ” of iron. But, in addition to round shot, there are solid steel shot, and solid chilled iron shot, hollow shot, case-shot, and grape-shot. The solid shot is the simplest and most primitive form of projectile, the object with which it is employed being, of course, to kill or disable an enemy, or to batter down or penetrate his defences. When defences were of brick and stone, or wood, or when troops fought in the open, it sufficed to make the shot of cast-iron ; but when armour-plated defences came into vogue, it was necessary to use some other material. Accordingly, steel shot were introduced for use with the larger smooth-bore guns, with which some of our ships were still armed. The great cost of steel, however, and the success which had attended the employ- ment of the famous Palliser “chilled” projectiles (of which more particular mention will be made hereafter), induced the authorities to give a trial to some solid spherical “ chilled ” iron projectiles, some of which still exist.* The chilled spherical projectiles were far from satisfactory. Their form was unsuitable to the brittle material, but it was thought that they were somewhat more effective than ordinary cast- iron, and they were not more expensive. The fact is, that no spherical shot are very effective against thick armour-plates — at least, any effect which may be accomplished can only be obtained at a disproportionate expenditure of power, and then only at very short ranges. No smooth-bore gun can compare with a rifled gun for penetration ; because with the rifled pro- jectile, if the weight of shot be equal to that of the sphere, the diameter will be less, and if the diameter be equal, the weight will be more ; and we thus have either less work to do, and equal power to do it, or equal work to do, and more power to do it. To this must be added that the pointed form of head is far more favourable to penetration than is the hemi- spherical surface with which the spherical shot strikes the plate. Hollow shot were used by the navy against wooden ships at short ranges, in order to produce a greater splintering effect, and to carry more fragments into the vessel. They could not be used effectively at long ranges on account of their lightness. Of late years empty shells have been used as hollow shot when required ; but at one time hollow shot constituted a separate projectile. An application of small solid shot, weighing 1 lb. each, must not be omitted. They are thrown sometimes from a mortar, in charges of one hundred shot. The shot are piled loose in the mortar over the powder, a piece of wood being placed between the powder and shot; and against -crowds of men huddled together, or a fleet of small boats, these pierrier + charges of pound-shot are very useful. Case-shot is used for firing at troops in masses at short ranges. They consist of cylindrical iron cases, filled with balls. The case is broken by the dis- charge, and its contents are driven forward in a conical shower to a distance of from 300 to 400 yards from the muzzle of the gun. When cavalry are charging home, or when troops present themselves within the range indicated, case-shot are terribly effective, and many a gallant charge has been checked, and many a gallant column thrown into disorder and panic by a well-directed discharge of these destructive missiles. Grape-shot is intended for use on much the same sort of occasions as would be selected for the use of case, except that, being made up with heavier balls, its range is somewhat greater. It was also useful for cutting and destroying the rigging of ships in naval actions. Originally, grape consisted of a canvas bag filled with balls, piled round an iron spindle through the centre of the bag, the bag being drawn together between the balls, or “quilted” by a strong line. In this form the grape somewhat resembled a bunch of grapes — whence its name. For several years the quilted grape has been super- seded by grape of a pattern known as the Caffin grape. This pattern consists of four horizontal iron plates, connected by a spindle through the centre, and having three tiers of shot arranged between the plates. The advantages of this pattern are, that it is less perishable than the old-fashioned grape, the bag and cord of which were liablo to rot and fall to pieces ; that it is more portable, as it can be carried in pieces, and put together when required ; and that the parts are interchangeable. During the past two or three years the manufacture of grape has ceased, it being considered that case-shot will answer all the purpose. This completes the list of shot for smooth-bore guns. We will give in our next lesson descriptions of the various sheila, and other projectiles used with this class of ordnance. * We reserve for the present such remarks as suggest themselves in connection with chilled projectiles, until we come to speak of the Palliser shot and shell. t From the French word pierre, a stone — from a number of stones having been in early days fired in this way instead of shot. S92 THE TECHNICAL EDUCATOR. TECHNICAL DR AWING.— XX V. DRAWING FROM rough sketches ( continued ). PIG. 239 is half the elevation, and Fig. 240 is a vertical section of an equilibrium valve. Valves of this description are used in engines of large dimensions, such as those used for pumping tn Cornwall. In these valves a large extent of opening for the passage of steam is given with very little traverse, whilst very little power is required to work the valve. In the example here shown, A is the fixed seat, made of cast- iron or brass, which forms a part of, or is secured to, the valve- chamber. B is a bell-shaped valve-piece, also of brass, moved by a rod, c. The contact of the valve with its seat takes place at two places, a and b, which are formed into accurate conical surfaces, the one, a, being internal, and the other, b, external. When the valve is closed, these surfaces coincide with similar ones on the seat, and when it is lifted, as shown in Fig. 240, two annular openings are simultaneously formed ; thus giving a double ingress or egress, as the case may be, to tho steam, which enters at, or issues through, the upper opening, a, through the central part, D, formed in the valve-piece, B. It is hoped that these measurements having been given the student will be enabled to complete the figure, and also to draw the section. The two drawings may be placed next to each other, as in our example, in which case all the vertical measurements for the exterior of the section may be projected by simply carrying out the horizontal lines. Or the section may be placed under the elevation, in which case the measurements for the widths will be o'btained by drawing perpendiculars from the widths as set off in the elevation. These two examples should be drawn to the scale of £ an inch to an inch. projection AND penetrations ( continued ). It is now deemed desirable to give the student another course of lessons in projection, and for this purpose the first subject- selected is a bent cylinder. _ Fig. 241. — Let ab,cd represent a quarter of a cylindrical ring, the centre of which is at O. Now if this quarter-round were cut across the middle by a plane radiating directly from the centre — viz., o o' — and the upper half were rotated on a pivot at E, the cylinder would take the bent form represented in the figure, for D would be moved to d', and B to b'. The rod or spindle, c, of the valve, B, is fixed to a centre-eye cast in one with the valve-piece, and connected to it by four arms, two of which are shown at c c. Of the other two, which are at right angles to these, one is hidden by the rod c, and the other has been cut off by the plane of section. The seat is similarly formed with four arms, or deep feathers having an angular ring at the base, the top edge of which is bevelled and ground to fit the lower edge of the valve b, and when lifted, forms the opening shown at b. The student will do well to draw the whole of the elevation (Fig. 239), of which only half is given in the plate ; but as the object is perfectly symmetrical, there will be but little difficulty In doing this. Having drawn the centre line, x x, set off on each side 4|" for the width of the fixed seat, A, erect perpendiculars, and make the seat 1" high. The chamfered edge of the fixed seat is f high. It will be seen that no measurement is given for the space above it, because this is variable, being the aperture shown at b, which would be increased if the valve-chamber, b, were raised further, or would be closed altogether when b descends; the depth," however, of the bevelled edge of B is J-. Next follows a vertical rim, and from this the widest part of the valve-chamber starts by means of a portion of a quadrant of 1" radius, the width of the chamber being 3|" in the upper part, and 4^ in the middle, the height of the wider portion being 3§", and of the narrow, B, 1 i ", the arms rising to a central boss inch higher. Fig. 242. — The plan of this object is very readily obtained, for it will be clear that a c rests on a circle, and that b' d’ being the diameter of a circle equal and parallel to A c, and seen under precisely similar circumstances, will bo represented in plan by the circle d" b”. The diameters f g and H i being connected by the lines F H and G I, the plan will be completed” It is, however, necessary to add the plan of the section at J K. Now it is evident that this section is really a circle of pre- cisely the same diameter as the other two, therefore a perpen- dicular drawn from e will cut g I and f h in l M, which will be the diameter. But the section is not horizontal, and therefore its plan is not a circle, but an ellipse, of which the short diameter is the line N o, obtained by drawing perpendiculars from J and K. To find additional points in the ellipse, divide one of the circles into any number of equal parts, as p, p, q, q, and carry up perpendiculars to cut the elevation in the points lettered p/ X>', Q' c 1- From o' describe arcs through these points, cutting the section-line j k in p", q". From these points draw perpendiculars, and from P, p, q, q in the circle draw horizontals intersecting them in p'", q'", p'" , q"\ I he one half of the ellipse is to be traced through the points, and the other half is to be obtained in a precisely similar manner. To find the curves caused by a cylinder penetrating a sphere, the centre of the sphere not being situated in the axis of the cylinder. TECHNICAL DRAWING. 393 Let A B (Fig. 243) be the plan, and a' b' (Fig. 244) the elevation of the cylinder ; and let c D be the plan, and c' d' the elevation of the sphere. Draw the tangent e f, which will be the plan of the vertical circle which would touch the cylinder ; in other words, if a knife were passed through the sphere close to the cylinder, it From H (Fig. 243) draw a perpendicular cutting the diameter of the sphere in the elevation in h', then with radius o h' describe the required circle. The plan H I of this circle shows that it is cut through by the cylinder in j and K. Therefore, from j and K draw perpendiculars cutting the 7~17 0r " 1 — u- V 71 . i ' \ i i J / \ ;\ o ! U J\ i \ Y\ T A \! \ : z \ 1' o CM & 3 is an inverted cylinder in which a piston moves ; this piston is attached to APPLIED MECHANICS. the rod E, which passes through a stuffing-box in the usual \uanner. To the end of the piston the hammer-head, E F F, is attached. As the piston rises and falls the hammer-head moves up and down between the vertical guides. The piston-rod is attached to the hammer by an elastic packing of wood, the object being to protect the piston- rod from the effect of the blows which the hammer delivers. The hammer in Nasmyth’s original invention is allowed to fall by its own weight ; the only object of the steam is to raise it. It is, therefore, only necessary to provide for the admission of steam to the lower part of the cylinder when the hammer is to be raised, and to allow it to escape when the hammer is to fall. In order, however, to control the action of the hammer with facility, and to render it self-acting when necessary, several very ingenious contrivances have been introduced, a description of which will be necessary. At the bottom of the cylinder is a slide-valve, included in the box j. When in one position this valve ad- mits steam to the bottom of the cylinder, and when it is moved to the other position it opens com- munication between the bottom of the cylinder and the external air. The rod which moves this slide is shown at il; the other end of this rod contains a piston which slides in the cylinder m. This cylinder is called the steam-spring ; 411 the cylinder is placed in communication with the air, and the supply of steam is stopped ; the consequence of this is that the hammer falls and delivers a blow upon the mass placed on the anvil, the magnitude of which depends both upon the weight of the hammer and the distance through which it falls. Near the top of the cylinder are a number of holes. These holes dis- charge a twofold duty ; in the first place, they enable the air to escape from the upper part of the cylinder when the re-admitted steam forces the piston Upwards. When the piston attains a certain height ' it closes these holes, and then a cushion of air is interposed between the piston and the top of the cylinder, to prevent a collision. The most beautiful part of the mechanism of a steam-hammer con- sists in the contrivances by which it becomes self-acting, so as to deliver any number of blows of any required intensity. The arrangements by which this is accomplished will be understood from the figure. The problem required may be thus stated. After a blow has been delivered, the machine must re-admit steam to the cylinder, and then, when the hammer has been raised a certain height, the valve must be closed. Two right and left vertical screws of equal pitch are shown at it f ; these screws are connected by two equal pinions, so that when the screw P is turned by the handle Q attached to Fig. 3. — THE STEAM HAMMER. it is always provided with steam in its upper part by a pipe which leads from j. Thus the constant effect of the steam is to keep the rod l and the slide-valve attached to it pressed down, and thus to keep the hammer raised. In order, therefore, to allow the hammer to fall, the rod L L must be forced upwards against the steam in the spring M. This can be done by depressing the rod p p, which is under the control of the Workman in charge of the machine. When the valve is raised, the bevelled wheels, the two screws are turned with equal velo- cities in opposite directions, and thus the nuts are made to move parallel to each other with equal velocities. The bevelled wheel upon p slides upon it, but is prevented from turning round upon it by a feather ; this is to enable the screw p p to be depressed without altering the position of the bevelled wheel. The nuts upon the screws carry the lever o o, at the extremity of which a small roller, o, is placed; now, by turning the handle at Q, the 412 THE TECHNICAL EDUCATOE. roller o can be placed at any height along the guide3 between which the hammer-head moves. When the hammer in its ascent encounters this roller, it forces it upwards ; this de- presses the end of the bent lever which turns on a fulcrum on the screw tr, depresses p p, and closes the steam-valve. With this arrangement alone, however, the hammer could not fall to the anvil, for the moment it began to descend the action of the steam spring would open the valve, and restore the levers to their original position. An arrangement has, therefore, to be provided by which the rod D must be held up against the steam spring during the descent of the hammer. There is an enlargement upon the screw-shaft p, a little below the bevelled wheel, and there is a small trigger which, when the screw is forced downwards, drops upon the narrow portion of the shaft, and detains the screw in its depressed condition. It follows, therefore, that when the hammer has raised o, the steam-valve is permanently shut until the trigger is drawn back. An in- genious arrangement enables the hammer itself to disengage the trigger the moment the blow is struck. A piece called the latch, x, is attached to the hammer head ; it is usually kept in position by a Spring, but when the de- scent of the hammer is suddenly checked by the delivery of the blow, the inertia of the latch x carries it forward, and the end of the latch kicks against a piece, ss. The piece s s is capable of moving like one side of a parallel ruler ; it transmits the pressure to a piece v, which then pushes back the trigger w, and allows the ascent of the screw p. In this way the hammer will deliver blow after blow, and the action is at once arrested by the attendant raising the handle at v ; the hammer then oscillates backwards and forwards, giving time for the adjustment of the work. The actual form of the steam-hammer when in use is shown in Fig. 4. In the manufacture of wrought iron and steel, the rolling- mills are of not less utility than the steam-hammer. The ordinary bar and rod iron, which is used for such multitudes of purposes, is produced by rolling ; and heavier masses, such as iron plates, railway lines, or armour-plating for ships, are also manufactured by the rolls. We shall commence our description of the rolling-mills by a brief account of the manner in which railway bars are made from Bessemer steel. The Bessemer steel, after having been cast in large ingots from the “ converter,” soon solidify ; as soon as they are set, though still brilliantly white-hot, the ingots are seized by hydraulic cranes, raised from their moulds, and carried off to the rolling- mills. The ingots are in the form of parallelopipeds, very unlike the railway bars into which they are to be converted. These ingots are seized between a pair of rollers driven by very powerful engines ; the rollers compress the ingot and elongate it ; it is then passed again and again through the rollers, and gra- dually becomes a long bar. In the rollers are grooves, which are of the proper form to give shape to the bar ; it is sent through these grooves, and finally, after passing through a series of them, it is a complete railway line. It is then, while still retaining a great deal of the original heat which it had as an ingot, carried to a saw-mill, which cuts off the ends, thus making the bar neatly finished, and of the proper length. We condense the following account of the rolling of iron from Fair bairn’s work upon iron : — “ There are different kinds of rolling-mills used in the iron manufacture, and they vary considerably in their dimensions, according to the work they have to perform. The first through which puddled iron is passed are called the puddling rolls ; there are others for roughing down, which vary from 4 feet to 5 feet long, and are about 18 inches in diameter; those for merchant bars, about 2 feet 6 inches to 3 feet long, and 18 inches in diameter, are in constant use. The boiler-plate and black sheet-iron rolls are generally of large dimensions ; some of them, for large plates, are upwards of 6 feet long and 18 to 20 inches in diameter. These require a powerful engine, and the momen- tum of a large fly - wheel, to carry the plate through the rollers ; and not unfre- quently, when thin wide plates have to be rolled, the two combined prove unequal to the task, and the result is the plates cool and stick fast in the middle. The greatest care is necessary in rolling plates of this kind, as any neglect of the speed of the engine or the setting of the rolls results in the breakage of the latter, on the one hand, or bringing the former to a complete standstill on the other. “ The speed of the different kinds of rolling-mills varies ac- cording to the work they have to perform. Those for merchant bars make from 60 to 70 revolutions per minute, whilst those of large size, for boder-plate, are reduced to 28 or 30 ; others, such as the finishing and guide rollers, run at from 120 to 400 revolutions per minute. In Staffordshire, where some of the finer kinds of iron are prepared for the manufacture of wire, the rollers are generally made of cast-steel, and run at a high velocity. Such is the ductility of this description of iron, that in passing through a succession of rollers it will have elongated to ten or fifteen times its original length, and when completely finished will have assumed the form of a strong wire, a quarter to three-eighths of an inch in diameter, and 40 to 50 feet in length. “ A high temperature is an indispensable condition of success in rolling. The experience of the workman enables him to judge from the appearance of the furnace when the pile is at a welding heat, so that when compressed in the rolls the particles will unite. Sometimes it is necessary to give a fine polish or skin to the iron as it leaves the rolls, but this can only be done when the iron cools down to a dark-red colour, and by the practised eye of an intelligent workman.” Fig. 4. — STEAM FOEGING WITH NASMYTH’S HAMMEE. THE TECHNICAL EDUCATOR: &ti (EnqjclopffMa OF TECHNICAL EDUCATION. V O L U M E II. CASSELL PETTER & GALPIN: LONDON, PARIS & NEW YORK. INDEX TO CONTEXTS PAGE AGRICULTURAL CHEMISTRY: On Manuring and Natural Manures ... 6 Nitrogenous Manures . 115 Phosphatic Manures . . 197 On Sewage Manures . . 350 AGRICULTURAL DRAINAGE AND IRRIGATION : Watering Land by Artificial Means . . . .22 Sewage Irrigation . . 51 APPLIED MECHANICS: The Shearing Machine and Punching Machine . . 18 The Turning Lathe and the Slide Rest . . .60 The Planing Machine . 90 The Drilling Machine . 108 Machinery used in the Manufacture of Sugar . 108 Plour Mills . . 146, 187 Machines for Raising Water 187, 223 Maehines used in Sawing Timber .... 268 Machinery used in the Spinning of Cotton 321, 337 BIOGRAPHICAL SKETCHES OE EMINENT INVENTORS AND MANUFACTURERS : Galilei Galileo . 54 Charles Hutton 94 General Dudd Dudley 98 James Watt 138 Henry Bell 210 Benjamin Huntsman . 250 Thomas Bewick . , 282 John Roebuck . 302 James Ferguson 314 Sir Joseph Banks 326 M. de Reaumur . 362 Roger Bacon 411 BRICK AND TILE MAKING : Terra Cotta, Bricks, and Tiles . 157, 205, 266, 346 BUILDERS’ QUANTITIES AND MEASUREMENTS : Introduction — Squaring Di- mensions Abstracting — Bringing into Bill — Excavating — Well- 366 sinking .... 374 BUILDING CONSTRUCTION : J oints in Timber ( continued ) — Construction of Floors 5 Of Roofs generally 36, 100, 136 Roofs — Arched Ribs— Par- titions — Fire-proof Con- struction 167 Staircases .... 199 CHEMISTRY APPLIED THE ARTS: TO Candle-making . 74 Lucifer Matches 150 PAGE I Sulphuric Acid . . . 182 Alum .... 214 Glass-making . . . 396 CHEMISTRY OF THE FINE ARTS : Introduction — Grinding and Washing Pigments — Ancient and Modern Pigments — Relation of Chemistry to Art — White Pigments — White Lead — Zinc White — Whiting — Gypsum— Baryta White 408 CIVIL ENGINEERING: Canals ( continued ) . 44, 102 Docks . 161, 270, 309, 382 COLOUR : Complex Colour Combina- tions — Harmonies of Analogy — Harmonies of Contrast — Harmonies of Seriation — Harmonies of Change .... 14 Cautions as to the True Primary Colours and Chromatic Equivalents — Modification of Colour by Illumination — Dif- fused Daylight — Light of the Sky and Clouds — Sunlight — A Dominant Coloured Light — Arti- ficial Lights— Two Lights 75 Surface and Structure modify Colour — Colours of Metals — Damascening and Plating— Enamelling on Gold and Silver — . Lacquering — Colours of Gems— Coloured Marbles 122 Coloured Glass— Colours of Pottery and Porcelain — Mineral Pigments — Co- lours of Plants, Flowers, Woods, and Vegetable Fibres— Colours of Ani- mals and AnimalProducts 235 Bright’s Bells -r- Polarised Magnet — Various Kinds of Chemical Telegraphs — Bain’s — Bakeweli’s Copy- ing Telegraph — Caselli’s Pan-Telegraph . . 159 Bonelli’sPrinting Telegraph — Alphabetical Instru- ments — Breguet’s — Wheatstone’s Universal 193 House’s Printing Telegraph — Hughes’s Instrument- Instruments used at Present Time in this Country — Arrangements at Central Offices— Con- clusion .... 234 FARMING AND FARMING ECONOMY : Introduction . . . 130 Preparatory Work in Soils — Drainage — Clay Burn- ing — Liming — Subsoil and Trench Ploughing . 170 Mitigation of Physical Con- dition of Soils — Manures — Farm - yard Manure, Guano, Superphosphates, etc. .... 229 Rotation of Crops . . 261 Treatment of Fallows— Bare Fallowing — Root- crop and Green Fallows — Preparation of Land . 330 Management of Root-crops 373 FISH CULTURE: Origin of Fish Culture- Salmon Breeding — Rear- ing Troughs, etc. . . 353 FORTIFICATION : Flank Defence for Redoubts 129 GREAT MANUFACTURES OF LITTLE THINGS: Steel Pens . . .371 Buttons .... 389 LATHE, THE: DESIGN, PRINCIPLES OF : Decorative Design . . 24 Surface Decoration — Deco. ration of Ceilings . 56, 87 Wall Decorations . 119, 151 Carpets . 191, 248, 280, 312 Woven Fabrics generally . 312 Hangings .... 327 Pottery and Hollow Vessels 342, 375 ELECTRIC TELEGRAPH, THE: The Morse Printing Tele- graph — Ringing Key — Code — The Receiving In- strument — Arrangement of Instrument Room . 46 The Relay— Automatic Tele- graphs — Wheatstone's — Bain’s .... Ill Introduction — Principle of the Lathe — Simple Elementary Forms of Lathe .... 367 Lathe with Fly-wheel above — Lathe with Fly-wheel below — Modern Hand Turner’s Lathe . . 404 MINING AND QUARRYING: Distribution of the most useful Mineral Products — Nature of Beds and Lodes — ' Importance of Study of Geology . . 1 Coal : Importance of Coal — An- nual Consumption— Ex- tent of Supply— Geogra- phical Distribution . 33 PAGE Different Kinds of Coal — Analysis — Heating Power — Illuminating Power — Boring for Coal — Tools employed in boring for Coal .... 78 Winning — By Level — By Sinking — Choice of Lo- cality — Sinking the Shaft — Form and Fittings — Underground Plan of Mine — Post and Stall, and Long Wall Systems 97 Ventilation — -Fire Damp — Choke Damp — Davy Lamp — Blind Pits — The Pit’s Mouth — Sponta- neous Combustion . . 143 Coke — Advautagesof Coking — Different Qualities of Coke — Various Processes for Coking— Waste Gases —Patent Fuel . . 188 Iron : General Diffusion of the Ore — Principal Centres of Works — Different Kinds of Ore — Assaying — Analysis . . . 203 Manufacture of Pig Iron — Extent of Trade — Blast Furnaces— Description — Size — Calcination of Ores .... 219 Mode of Smelting Ore — The Fuel — The Flux — Temperature of the Fur- nace — Different Qualities of Pig Iron — Iron Found- ing .... 255 Refining — Form of Refinery — Process — Quality of Finer’s Metal — Puddling — The Furnace — Process — Quality of Puddled Ball . . . .273 Siemens’ Regenerative Gas Furnace — Bessemer Pro- cess of Puddling — Pig Boiling — The Forge — Machines for Squeezing and Hammering the Pud- dled Ball . . .296 Boiling — Puddled Bar — Finishing — Properties of Iron — Galvanised Iron- Effect of Tin and Copper — Natural and Artificial Salta of Iron — Their Uses . . . -319 Steel : Distinction between Steel and Iron — Cementation- Blister Steel — Shear Steel — Cast Steel— Tempering — Case-hardening — Cast- ing Steel or Iron — Pud- dled Steel . . .356 iv INDEX TO CONTENTS. PAGE MUSEUMS : THEIR CON- STRUCTION, ARRANGE- MENT, AND MANAGEMENT: The Aim of International, National, Local, nn.fAJu.u. j: ig. — COMPLETE. Fig. 5.— SECTION OF GROUND LIGHT BALL. projectile’s velocity was very great, and the loss to the enemy was considerable. It then occurred to General Shrapnel that if he were to fill these shells with musket and carbine balls, reducing the bursting charge to a minimum, consistent with the opening of the shell, and increas- ing the firing charge to a maximum, he would be able to pro- duce a still more de- structive fire. In this change wo note the distinctive differ- ence, which cannot be too clearly ap- preciated, between common and Shrap- nel shell — viz., the difference, that while the former depends upon the explosive effect of its own charge, the latter de- pends upon or derives its effect from the charge of the gun. A high velocity is not necessary in the first case ; it is essen- tial in the second. A first case; it is not only not essential, but absolutely prejudicial in the second. The original Shrapnel shell, as designed by General Shrapnel, was, m fact, a thin . common shell filled with bullets instead of powder, and having only so much powder in among the balls as would suffice to open the shell. The object of making the shell as thin as possible was, first, that it might contain as many balls as possible ; secondly, that a very small bursting charge might open it. These projectiles were first introduced about the year 1803, and were used at the battle of Yimiera in 1808, and at other actions during the Peninsular war, with an effect to which the French, against whom they were fired, bear ample though unwilling testimony. The action of the shell is as follows : — It leaves the gun like any other spherical projectile, travelling to the point at which the time-fuse has been set to explode it — which should be a short distance in front of the object aimed at. When it arrives at this point, if the action of the fuse be satisfactory, the shell will be opened, and the bullets and fragments will “ continue their forward course with a communicated velocity equal to that of the shell at the moment of fracture, and describing, as WEAPONS OP WAR. 9 they slightly disperse, ‘ a curved cone, the apex of which is at the point of explosion.’ ” The Shrapnel shell thus acts as case or grape at distances beyond those at which case and grape can be effectively employed. The Shrapnel shell has practically the effect of carrying forward the muzzle of the gun to within such a distance of the enemy as will enable a case- fire to be delivered. Actually the muzzle of the gun is, of course, not advanced ; but practically this is what happens, for the breaking up of the projectile, which with case occurs at the muzzle, is postponed until the projectile arrives within a short distance of the enemy. Indeed, when Shrapnel shell were first introduced, they were called by a name which exactly describes them — “ spherical case shot.” The present name was not adopted until many years afterwards, as a compliment to the inventor. Since the first in- troduction of Shrapnel shell, some important improvements and modifications have been adopted. It was found that the shells some- times were broken up by the shock of discharge, due to the friction of the powder between the balls. To obviate this it was necessary to sepa- rate the powder from the balls, and this was done by introducing into the existing store of Shrapnel a tin cylinder, which occupied the centre of the shell, and contained the bursting charge. These shells were known as “improved Shrapnel,” and they have only recently disap- peared from the service. When new shells had to be made, General (then Captain) Boxer, It. A., proposed a different arrangement. He pro- posed to separate the bursting charge from the bullets by enclosing it in a small chamber formed on one side of the shell, by the insertion of a wrought-iron plate or “diaphragm.” The accompanying drawings (Figs. 1 and 2) show the construc- tion of the “diaphragm Shrapnel shell.” The advantage of placing the bursting charge at one side, in- stead of in the centre, was that it avoided the excessive disper- sion of the balls at the moment of rupture. But in order to ensure the proper opening of the shell, it was necessary to provide it with internal grooves, or “lines of least resistance,” down which the powder would act. The powder is introduced into the chamber through a small loading -hole, and the fuse com- municates with the powder in this chamber through a small fire-hole in the brass socket. To prevent the bullets from conglomerating under the shock of discharge, they are made of hardened lead, and have coal-dust shaken in between them. Such is the diaphragm Shrapnel shell for smooth-bore guns. We shall see hereafter how General Boxer has suc- cessfully applied the principles of this construction to the Shrapnel shell for rifled ordnance. It will be observed that the shell in our drawing is fitted with a w ood bottom, riveted on. All shells are fitted with one of these bottoms,, or “sabots.” They serve the double purpose of presenting the right side of the shell — i.e., the side away from the fuse — to the charge, and slightly diminishing “ windage ” (the spam between the shell and bore), and thus reducing the escape of gas and the tendency of the projectiles to ria- chet along the bore. With bronze guns, it was necessary to pro- vide the shot, as well as the shell, with these bottoms, because otherwise a bounding movement of the shot became established, to the speedy destruction of the gun, and to the almost imme- diate destruction of all accuracy of i\re. The method of attach- ment adopted for these bottoms— an expanding copper rivet — is simple and ingenious, and a great improvement on the plan formerly adopted — namely, “ strapping ” on the bottom with tin “ straps.” We have now treated of shot and shell. There remains a third class of projectiles to speak of — incendiary projectiles. Of these there are six — viz., red-hot shot, Martin’s shell, ground light balls, parachute light balls, and smoke balls. Bed-hot shot are merely ordinary cast-iron shot heated to a “ wafer ” red heat and fired, with reduced charges, against wooden shipping or any combustible material. It is necessary to fire them with reduced charges, because the expansion of the shot, by reducing the windage, increases the strain upon the gun, and because red-hot shot are required to lodge in the object fired at, and not to pass through it. These projectiles were used with great effect, and on a large scale, at the siege of Gibraltar. Martin’s shells have, in a great measure, re- placed red-hot shot; although both descriptions of projectiles have lost their original value, in consequence of the substitution of armour- plated for wooden vessels. Martin’s shell, so called after its inventor, a civilian, consists of a thin spherical cast-iron shell , with an interior lining of loam ; shortly before use the shell is filled with molten iron. In order to ensure the breaking-up of the shell on striking an ob- ject, the sides are made thinner than the top and bottom. The loam lining, being a good non-conductor, serves the double purpose of keeping the iron in the interior hot and the ex- ternal shell cool for a longer time than would be possible if there were no such lining. The shell is intended to be fired against an inflammable object — such as a wooden ship. The shock of concussion breaks the shell, and the molten contents are scattered about, setting fire to everything combustible upon which they may fall. These shells were con- sidered by the committee which introduced them to possess greater incendiary power than red-hot shot. On the other hand, there is a certain amount of trouble and inconvenience involved in the preparation of the liquid iron. But when these difficulties are surmounted, and when the shell are used under favourable circumstances, they have been proved to be very formidable instruments of destruc- tion. Carcasses are thick iron shells, filled with a combustible composition, and having three holes for this composi- tion to burn out of. The composition consists of a mixture of saltpetre, sulphur, rosin, sulphide of antimony, turpentine, and tallow. It burns with great violence for from three to twelve minutes, according to the size of the carcass, which varies from the 12-pounder to the 13-inch. Car- casses are thrown into an enemy’s works, to set fire to his houses* stores, etc. etc. The composition becomes ignited at each vent by the flash of discharge, and continues burning after the carcass has fallen until it is expended. So violently does the composition burn, that it is almost impossible to extinguish it. It will even burn under water. The best mode of dealing with a carcass is to endeavour to roll it away from all inflammable material, and to smother it with earth. The ground light ball (Figs. 3, 4, 5) is another projectile of this class. It is, however, useful rather for illuminating than for in- cendiary purposes. It consists of an oblong skeleton iron frame, covered with stout canvas and filled with an inflammable composi- tion, consisting of saltpetre, sulphur, rosin, and linseed oil. The projectile has four or five vents, according to its size, from which the composition burns, for from nine to sixteen minutes. Fig. 6. — PARACHUTE IN ACTION. Fig. 7. — SECTION OF PARACHUTE LIGHT BALL, WITH FUSE. 10 THE TECHNICAL EDUCATOR. according to the size. These ground light balls are thrown from mortars at night into an enemy’s work, to discover his working parties ; and they are also serviceable, in the absence of carcasses, as incendiary projectiles. They are, however, open to some serious objections. In the first place, an oblong pro- jectile is not suitable for firing out of a smooth-bore gun ; neither range nor accuracy can be obtained with it. Again, if they fall short of the object, their smoke makes a sort of screen. If they fall into a ditch or on to muddy ground they are smothered ; and if they do fall in the right place, they can be very easily covered over with earth, and so rendered useless as lights. Even when not extinguished, the composition is of so dull a nature that its illuminating power is very small, while the area illuminated by a projectile on the ground is necessarily re- stricted, even under the most favourable circumstances. A good many of the foregoing objections, if not all, were met by General Boxer in his ingenious Parachute Light Ball. It consists of a thin wrought-iron shell, containing two half-shells of wrought iron (Fig. 7), the lower of which contains a brilliantly burning composition of saltpetre, sulphur, and red orpiment, and the upper a calico parachute, the lower part of which is attached by chains to the composition hemisphere. The shell, fitted with a fuse, is fired from a mortar. The fuse is timed to explode a small bursting charge when the shell attains its maximum elevation over the area or object required to be illuminated. On the explosion of the bursting charge, the outer shell is opened, and the two inner hemispheres begin falling. The lower hemisphere, which contains the composition, being the heavier, falls more rapidly than the other, which has, indeed, received a momentary impulse by the action of the bursting charge in the opposite direction. This jerk, and the more rapid falling of the composition hemisphere, causes the calico parachute to be pulled out and expanded (Fig. 6), and it then floats the composition hemisphere slowly down over the object to be illuminated, the composition burning brightly out of a hole at the bottom of the hemisphere, for from one to three minutes, according to size. In addition to overcoming all the difficulties and objections enumerated above as belonging to the ground light ball, the parachute light ball possesses the advantages of being serviceable at sea, or to illuminate an ■enemy’s fleet, which the ground light ball necessarily cannot be. It can also be fired from a very light and handy mortar. This construction of projectile has been very effectively employed for firework purposes. The Smoke Ball hardly needs any mention. It is merely a paper shell filled with a composition of gunpowder, saltpetre, coal, pitch, and tallow, which when ignited emits a dense and suffocating smoke, which is stated to be useful in expelling an enemy from mines, and in concealing one’s own operations. These projectiles have also served a peaceful use in the Arctic regions, where they were employed for signalling purposes — the long column of black smoke standing out prominently against the white background of these snow-clad regions. This completes the list of projectiles for smooth-bore guns, if we except the Manby shot, for saving lives from shipwreck, and which is not to be considered a weapon of war. We will now pass forward to another section of our subject. SEATS OF INDUSTRY.- VIII. BY WILLIAM WATT WEBSTER. GLASGOW.— II. With the establishment of the Union, which at the time was believed by the people of Scotland to be a great national catastrophe, a great impetus was given to the trade of Glas- gow ; and this event also marks an important era in the manu- facturing history of the city. Up to this period the foreign trade of Glasgow had been almost altogether restricted to the continent of Europe ; it was now extended to the colonies. When this trade was first entered upon, the Glasgow merchants had no suitable ships of their own, and were therefore obliged to charter vessels belonging to other ports. The nature and “canny” system of the trade engaged in may be gathered from the following description taken from Gibson’s “ History of Glasgow : ” — “ A supercargo went out with every vessel, who bartered his goods for tobacco, until such time as he had either Bold all his goods, or procured as much tobacco as was suffi- cient to load his vessel. He then returned immediately, and if any of his goods remained unsold he brought them home with him.” In a very short time Glasgow became the prin- cipal centre of the tobacco trade in Great Britain, and the Virginia merchants, or “tobacco lords,” as they were called, became notorious for their wealth and pride. A curious story is told of the first venture made by Glasgow mer- chants in the tobacco trade. In order to keep down expense, the captain of the ship sent out was appointed to act as supercargo. “ This person,” says the old merchant who has recorded the event, “ although a shrewd man, knew nothing of accounts ; and, when, on his return, he was asked by his employers for a statement of how the adventure had turned out, told them he could give them none, but there were its proceeds ; and threw down upon the table a large hoggar — that is, a stocking — stuffed to the top with coin. The venture had been a profitable one ; and his employers conceived that if an uneducated, untrained person had been so successful, their gains would have been still greater had a person versed in accounts been sent with it. Under this impression, they im- mediately dispatched a second adventure with a supercargo, highly recommended for a knowledge of accounts, who produced to them a beautifully-made-out statement of his transactions, but no hoggar.” It is estimated that more than one-half of the disposable capital of the city was embarked in the tobacco trade, from about 1735 till the declaration of American Inde- pendence in 1776. A notion of the extent of this trade in its best days may be formed from the statistics for the year 1772, which show that out of 90,000 hhds. of tobacco imported into Great Britain, Glasgow alone imported 49,000 hhds. The year preceding the American War of Independence — which closed for ever the tobacco monopoly which Glasgow up to that time had enjoyed — was still more remarkable, for there were imported into the Clyde in that year no less than 57,143 hhds. of tobacco, which were the property of forty-two merchants. When the tobacco trade collapsed, the Virginia merchants turned their attention to the West Indies, and soon transformed themselves into “West India lords.” Sugar cultivation in the West Indies and the introduction of cotton manufactures had opened out new paths to opulence. It was at this period that the cotton trade of Glasgow com- menced. Very shortly after the cultivation of cotton was introduced into the Southern States of the American Union, agents of Glasgow houses were established at Charlestown and New Orleans, in order to facilitate the interchange of American cotton and British manufactures. This trade was prosecuted with extraordinary vigour, and “ cotton lords ” soon came to take the place of the “tobacco lords” of a bygone day. It was also at this date that cotton manufacture was begun in Scotland, the first cotton-mill being built at Rothesay in 1778, by an English company; but before many years passed it was bought by Mr. David Dale, a Glasgow merchant, who became one of the most extensive cotton manufacturers in the country. The second cotton-mill built in Scotland was at Dovecot Hall, on the banks of the Leven, in Renfrewshire, and it soon proved so remunerative that it was enlarged, and five other mills were built in the vicinity. Among the earliest factories in Lanarkshire may be mentioned the celebrated New Lanark Mills, erected by Mr. David Dale, in 1785, in which Sir R. Arkwright had a share. Spinning operations were commenced in this mill in 1786, and two years later another mill was built, which was destroyed by fire before it had been completed, but was rebuilt in the following year. Subsequently two other mills were erected in the neighbourhood. From the first, Glasgow was the centre of cotton manufacturing enterprise in Scotland ; and nearly the whole of the cotton goods that have been made in that country have been manufactured either by or for firms belonging to that city. Within fifty years of the time when the first cotton factory was erected in Scotland, Glasgow was the centre of about 100 cotton-mills, and before the lapse of another decade the number of cotton-mills in Scotland had nearly doubled. The increase in the imports of cotton into Glasgow during this period was, as a matter of course, propor- tioned to the increase in the number of mills. Thus the quantity of cotton imported into the Clyde in the year 1775 was 508 bales, or 137,160 lb. ; in 1790 it was 6,500 bales, or 1,757,504 1b.; in 1812, 43,000 bales; in 1824, 54,708; and in 1834 the quantity had risen to 95,763 bales. The latter SEATS OF INDUSTRY. 11 figures represent a fifth of the cotton imported into Britain in 1834, and it is estimated that at least three-fourths of the whole quantity imported into the Clyde, or 71,777 bales, were worked up by Glasgow manufacturers. But before the introduction of cotton, the manufacturers of Glasgow and Paisley had acquired a high reputation for the excellence of the linen fabrics they produced. Linens, lawns, and cambrics were, indeed, the staple manufacture of Glasgow till after the close of the American War. The first tape-factory in Britain was established at Glasgow by Mr. Alexander Harvey, in 1732. This enterprising citizen abducted two inkle-looms, and an experienced workman from Haarlem, at the risk of his life ; and it was the Dutchman he brought oyer to this country who first initiated the manufacturers of Man- chester into the mysteries of tape-making. As might have been expected, the cotton cloths manufactured at Glasgow when the fibre began to be used, and for some time afterwards, were of the coarsest description. A handkerchief formed of linen warp and cotton weft, which went by the name of a “blunk,” was the chief article produced. It was not very long, however, before the Glasgow manufacturers attempted and succeeded in turning out a finer quality of cloth. About the year 1784, Mr. James Monteith manufactured a web of muslin from some “bird-nest” Indian yarn, and presented a dress made out of this fabric to Queen Charlotte. It was at this time that the cotton-spinning machinery of Hargreave and Arkwright was introduced into England, and as this machinery produced thread sufficiently fine for muslins, and as muslins were a pro- fitable branch of manufacture, the Glasgow manufacturers lost no time in adopting it. In a very few years Glasgow had a large trade in plain and printed muslins, and Paisley became celebrated for fancy muslins. These goods soon came into competition with the productions of the Indian looms, for as early as the year 1793 it is stated in a report of the East India Company, on the subject of cotton manufacture in this country, that “ every shop offers British muslins for sale equal in ap- pearance and of more elegant patterns than those of India, for one-fourth, or, perhaps, more than one-third less in price.” Under the date 1785, the following passage occurs in “Macpher- son’s Annals of Commerce:” — “The manufacture of calicoes, which was begun in Lancashire in 1772, was now pretty generally established in several parts of England and Scotland. The manufacture of muslin was begun in England in 1781, and was rapidly increased. In the year 1783 there were above a thousand looms set up in Glasgow for the production of the most beneficial article, in which the skill and labour of the mechanic raised the raw material to twenty times the value it was when imported.” The spinning of cashmere yarn has been carried on at Glasgow since 1831, and merino yarn has boon produced there since 1833. It is well known that it was at Glasgow that James Watt made his first model of the steam-engine, and it was at Port- Glasgow that the Comet was built, the vessel that first de- monstrated to Europe the practicability of steam navigation. The first steam-engine applied to the spinning of cotton in Glasgow was erected at Springfield, on the south side of the Clyde, in 1792. In the following year two power-looms were fitted up in the city by Mr. James Louis Robertson, and for a time were driven by a Newfoundland dog walking in a drum. In 1793, 40 power-looms were at work at Milton ; and by 1801 Mr. John Monteith had 200 looms in operation at Pollockshaws, near Glasgow. Steam now began to be generally applied, and the number of power-loom factories increased with astonishing rapidity. In 1850 the number of spindles employed in cotton- spinning connected with and dependent on Glasgow amounted to 1,683,093 ; and the cotton consumed reached a total of 45,000,000.1b., or 120,000 bales ; while the power -looms num- bered 23,564, producing a daily average of 625,000 yards of cloth. Pour years later there were from 26,000 to 27,000 power-looms in the Glasgow district, and the product was con- sequently proportionately increased. A return made to Parlia- ment in 1862 shows that there were in Glasgow and its dependencies in the previous year 163 factories, with 1,915,398 spindles, 30,110 looms, giving employment to 41,237 persons. Since that year the number of factories has decreased, but the amount of production has risen notwithstanding. In 1861 the number of yards of cotton cloth exported from the Clyde was 150,754,631 ; in 1867, 206,394,756 yards were exported. During the Civil War in America, the trade was, of course, in a state of stagnation, but it rapidly recovered from the blow. The great cotton manufacturing district of which Glasgow is the centre comprises New Lanark, Paisley, the Water of Leven, Kilbrachan, Johnston, Lochwinnock, Rothesay, and Old Kil- patrick. The Stanley Mills, near Perth, and the Deanstoun Mills near Doune, are also two outlying and very extensive cotton factories belonging to Glasgow, which were planted in these remote localities on account of the plentiful supply of water- power and labour. A few years ago, Mr. J. M'Donald, of Messrs. D. and J. M'Donald and Co., the eminent firm of sewed muslin manufacturers in Glasgow, stated before a committee of the House of Commons that their house employed upwards of 20.000 persons in Ireland, and that the amount of wages paid to them exceeded .£3,000 per week, or about .£160, 000 per annum. There are upwards of thirty-five other sewed muslin manufacturers in the city — several as extensive as the Messrs. M'Donald — and it is estimated that they give employment to about 148,000 Irishwomen, who receive .£1, 184, 000 per annum in wages. The shirtmakers of Glasgow also employ about 30.000 Irishwomen in shirt-making. The next most important branch of trade in Glasgow is the iron trade. Forty years ago there were only sixteen smelting furnaces in the vicinity of Glasgow, with an average out-put of 2,500 tons of pig-iron each. The manufacture of malleable iron is of recent date in Scotland, and no reliable record of the quantity produced was kept till the year 1845, when it amounted to 35,000 tons. In 1854 the quantity of malleable iron pro- duced was 125,000 tons, and of pig-iron 750,000 tons. This trade has been greatly extended since the period to which these figures refer. The most eminent of the “iron lords ” of Glasgow are the Messrs. Baird, of Gartsherrie. This firm owns 42 blast-furnaces, employing 9,000 men and boys, and producing about 300,000 tons of pig-iron per annum, or about one-fourth of all the pig-iron made in Scotland. At the Gartsherrie branch of their establishment, the Messrs. Baird employ 3,200 men and boys, and make 100,000 tons of pig-iron per annum ; the daily consumption of coal being upwards of 1,000 tons. Nine- teen-twentieths of the coal used at this work is taken from mines within half a mile of the furnaces. For forty years the coals used at Gartsherrie were got from a mine close to the furnaces ; and the iron-stone was for many years found in the immediate neighbourhood, but has now to be brought distances varying from two to twenty miles. A complete system of rail- way communication has been constructed for its conveyance, and the Monkland Canal is also used for the same purpose. The fame of the iron ship-builders and marine engine-makers of Glasgow has for many years been the boast of her citizens. These trades have of recent years expanded to extraordinary proportions, and have materially contributed to the prosperity of the city. Large numbers of ocean and river steamers are yearly launched on the Clyde, and some of the finest steamships in the world have been constructed in the neighbourhood of Glasgow. The increase in the trade of the port is as remark- able as any element in the prosperity of the city, and has been dependent on the extensive improvements which have been effected on the river. About fifty years ago the depth of the Clyde opposite Glasgow was barely five feet ; now it is fully twenty, and ships of the largest size can load and unload at the quays. The length of quay-wall in the harbour is about 14,000 feet. No account of Glasgow would be complete that took no notice of the chemical works of the Messrs. Tennant, which are the largest in the world, and comprise sixteen acres of ground under roof. The principal chimney-stalk at these works is 435 feet from the ground, and 450 feet from the foundation. This gigantic column has been surpassed, however, by a “stalk” erected a few years ago in its neighbourhood, which rises to an altitude of 468 feet from the foundation, and is composed of a million and a half of bricks. The principal water supply of Glasgow is obtained from Loch Katrine (a distance of forty miles), and this undertaking cost the city upwards of .£900,000. Glasgow owes no inconsiderable portion of its importance as a trading and manufacturing centre to its position in the middle of a district rich in coal and iron, the two principal factors of modern history. According to calculations made by Dr. Strang, Glasgow and its suburbs contained 446,639 inhabitants in 1861; and it is believed that the population is now considerably over half a million. 12 THE TECHNICAL EDUCATOR. TECHNICAL DR AWING.— XXVII. THE PROJECTION OP SCREWS (continued). Fig. 255 is the plan and Fig. 256 is the elevation of a square- threaded screw, the working of which the student will under- stand, the system being the same as in the last study. The points of the double helix on the inner cylinder are projected in the same manner, and therefore no further instruc- tions will be needed. Fig. 257 is the plan and Fig. 258 is the sectional elevation of the nut of this screw ; the last is projected from the plan (Fig. 257), and the heights are carried on from the elevation of Fig. The thread and the space are equal, and the depth of the groove is the same as the width of the thread. Having projected the first curve, which is the upper line of the thread, and having carried this helix up as far as may be required, set off the width of the thread on the perpendiculars below each of the points through which the curve has been drawn. Through the points thus obtained the lower curve of the thread may be drawn. 256, the reverse curves, as before, being used. Templets for this figure may be used as in the former case. Screws may have one, two, three, or even more threads,, according to the velocity which their action may be required to produce. A double-threaded screw is one in which the pitch of any individual helix includes two threads ; a three-threaded screw is one in which three threads are embraced, and so on. Fig. 259. — This figure represents a pair of spur-wheels in TECHNICAL DRAWING. 13 gear. The radius of the larger wheel, with 42 teeth, is 15J", and that of the smaller, with 24, is 9". Having drawn the pitch-circles, and having set off the pitches and divided them into teeth and spaces, as already shown, draw the circles for the points and roots of the teeth ; then the faces of the teeth (which in design and practice are epicycloidal. but i these will be the centre lines for the arms. Next draw the boss, central aperture for the shaft, and the key -bed ; then on each side of the six central lines set off, first, half the thickness of the central ridge or flange of the arms, and then the web, by which these are strengthened. It will be seen that the lines of the web do not run straight which in drawings are approximately rendered by arcs struck with a radius equal to the pitch), and finally the flanks which are radial, but which are turned off into the circle of roots by arcs, are to be drawn. The smaller wheel is a mere disc with teeth ; the larger one has six arms. Draw the circle representing the rim of the wheel, about as deep as the distance from the pitch-circle to the root of the teeth. Divide this circle into six equal parts, and draw radii : into the boss, or into the part supporting the rim, but turn off in each case by arcs, as already shown. It will be observed that when wheels are in gear there arc three teeth of each engaged, one tooth of each wheel touching in the pitch-line, one pair just parting, and one coming gradually into full action. In this example the central flange of the arms and the rim, instead of running by arcs into each other, are both bevelled so as to accomplish the same end — viz., easy delivery in moulding.. 14 THE TECHNICAL EDUCATOR. VEGETABLE COMMERCIAL PRODUCTS, xv. . dye plants ( continued .) Orchella Weeds ( Il-occcllct tinctovia , R, fucifovwiis, and R. hypomecha, L. ; natural order, Lichenes ). — These lichens, which constitute the orchils of commerce, are of an ash-grey colour, having a thallus much branched, flattened, and mealy in appearance, from one inch and a half to two inches in length. The blue dye known under the name of archil or orchil is pre- pared from these plants, which grow on all the rocky coasts and islands of the Mediterranean, and also in the Canary Islands, Madagascar, Cape of Good Hope, and South America. The colour yielded is not in itself a fast one, but it so greatly improves others that orchil is regarded as indispensable by the dyers. The imports into this country are about 600 tons per annum. The Tartar Lichen (Lecanora iartarca, L.), indigenous to Sweden, Norway, and England, answers the same purpose. Litmus paper, so much used by chemists as a test for acids and alkalies, is prepared from the blue dye furnished by this lichen. Whole cargoes of it are annually brought from Sweden to Hol- land, where its dye, called cudbear, is the most skilfully prepared, and therefore called Hutch blue. IV. PLANTS FURNISHING VALUABLE BUILDING AND FURNI- TURE WOODS. The cultivation of wood is now carried on in several countries in Europe, where the population is considerable and the natural forests have disappeared; above all, Germany is to be dis- tinguished for forest culture. But most wood, especially for ship-building, is still procured from those countries where the natural forests remain — viz., from Russia, Norway, Sweden, Canada, and the United States. In Germany, vast quantities of wood are annually floated down the rivers Rhine, Maine, Neckar, Weser, and Elbe, from the still productive woods of Thuringia, the Hartz, Eichtel, and Erz mountains, and the Black Forest. Russia exports a considerable amount of wood to England and the south of Europe, from St. Petersburg, Riga, Archangel, and from the Russian ports of Odessa and Cherson' on the Black Sea. Much timber is also exported to the south of Europe from Drontheim, Bergen, and Christiana, on the coast of Norway ; from Gottenberg, a port in Sweden ; and from Dantzic, Konigsberg, and Stettin, Prussian seaports on the Baltic. American timber is exported to the United Kingdom chiefly from Canada via Quebec, which is a great depot for wood. The importation in 1867 of timber and wood was: — Not sawn or split, 1,211,042 loads; sawn or split, 2,177,549 loads ; and staves, 62,625 loads. Of forest productions the following deserve to be mentioned as sources of considerable trade : — Mahogany ( Swietenia mahogoni, L. ; natural order, Cedre- lacece ) occupies the highest rank amongst the furniture woods. This is one of the loftiest and most gigantic trees of the tropics. It is indigenous to the West Indies and Central America. The mahogany tree is cut down in April and May, which is the height of the dry season ; it is then squared by the adze, the branches being lopped off ; and about the middle of June, when the rivers are swollen by the rains, the logs are placed on trucks and drawn by bullocks to the water-side ; there they are launched into the river, formed into rafts, and so floated down the stream to the vessels awaiting their arrival. Spanish mahogany is imported from Cuba, St. Domingo, and the Spanish Main, in logs twenty-six inches square and ten feet long.. Honduras mahogany is usually lighter than the Spanish, and is imported in logs four feet square and eighteen feet long. Mahogany is chiefly valued for its colour, firmness, and durability, and the beautiful polish which it is capable of receiving. On account of these and other excellent qualities, it is particularly suitable for ship-building. Mahogany is light and buoyant, free from dry rot, and does not warp ; it also suffers less from the action of shot than any other wood ; since shot, when re- ceived by it, generally remains fast in the wood without split- ting it. Mahogany is extensively used in the manufacture of the best articles of domestic furniture, fancy and ornamental wood-work, cabinet-making and veneering ; in fact, there are, comparatively speaking, but few persons who lave not this wood constantly before their eyes, in some form or other of useful home furni- ture. The quantity of mahogany imported into the United Kingdom in 1866 was 53,458 tons. Ebony (Diospyros ebenus, L. ; natural order, Ebenacem). This tree is a native of the Mauritius. As soon as felled the timber is immersed in water from six to eighteen months ; it is then taken out, and the two ends are secured from splitting by iron rings and wedges. Mauritius ebony is imported in round sticks, like scaffold poles, about fourteen inches in diameter. It is much used for inlaying and turnery. COLOUR.— IX. By Professor Church, Royal Agricultural College, Cirencester. COMPLEX COLOUR-COMBINATIONS — HARMONIES OF ANALOGY HARMONIES OF CONTRAST HARMONIES OF SEBIATION — HARMONIES OF CHANGE. Hitherto our studies of colours have been confined almost entirely to those which are considered elementary and those which are compounded with equivalents of their constituent primaries. \Ve have only alluded once and again to the existence and use of the vast series of mixed hues. It is, however, chiefly in the employment of these colours that the higher chromatic developments, constituting the poetry of colour, are mani- fested. The obvious assortments of the primary and secondary colours, with their contrasts, resemblances, and harmonies, are not difficult to understand ; but it requires a well-trained eye to discern the subtle differences and concords of composition in which several mixed hues preponderate, and a well-cultivated imagination to appreciate and to pursue their intricate delights. Here, where aid from descriptions is most desirable, it is most difficult. Endeavours to reproduce the more recondite har- monies of hues by mechanical processes are never wholly suc- cessful, and usually are even less useful than accurate verbal descriptions combined with references to natural examples. An illustration strikes us as we write. Many an observant student of Nature must have noticed the triple combination of hues presented by an old beech or elm tree as seen against the sky or clouds in early spring. We have the yellowish grey-green of the moss and lichen-grown trunk and branches standing out relieved against the dull grey of the shifting and variable clouds beyond ; and this tender green of the moss and grey of the cloud arc not flat or uniform, as they too often appear in our imitations of them, but fluctuating with a hundred varia- tions of texture, quality, and tone. A few dead leaves per- chance remain, suggesting, if not completing, by their brown or russet hues, the balance of colour, which just needed such idea of warmth and ruddiness as they convey. But let us regard a little more minutely, a little longer, this natural combination of hues, which we commend, with count- less others in the world around us, to every student of deco- rative art ; let us see whether it does not possess other elements of beauty than those which we have recorded. Yes; if we look a little closer we shall doubtless see some delicate portion of nearly pure primary or secondary colour, some stray fragment of brightness — perchance an early flower or insect — just as the ancient pines of the unbroken American forest have been de- scribed as bearded with hoary lichens, yet touched with grace by the violets at their feet. So, too, there will be observed in the outermost twigs of our tree that hopeful thickening by myriads of leaf-buds, neither purple-russet nor clove-brown, nor any colour which we can definitely fix, but very beautiful in themselves and promising the verdure of summer. Deep hollows of shade, and the brightness of light will be seen too, yet sparingly, and so, like the simpler colours, made the more precious. From this example, of which nothing but the original work of a master in the art of painting could convey an ade- quate notion, most important deductions may be drawn. It will help us to realise, in a thoughtful, artistic way, the value of temperance in colour, as well as of balance and distribution. It will lead us to introduce, among our blues and reds and yellows, some of those rarer tints which we cannot exactly name, but which the watchful student of Nature may see trembling on the leaves of the willow, or paving the autumnal paths of the forest, or shining at eventide from the cloudy but splendid pavilions of the sun. It behoves us now, passing from this somewhat pictorial COLOUR. 15 treatment of the obscure subject of the complex combinations of mixed hues and colours, to attempt the description and classification of harmonies of colour. It is usual to divide harmonies of colour into two classes — those of analogy and those of contrast. Having already de- scribed the conditions under which assortments of colours become more or less harmonious, we need here do little more than illustrate by an example or two the several kinds of har- mony of contrast here referred to. But it must be remembered that the distinction of harmonies into two classes is rather arbitrary. Some difference always exists between any two colours and any two tones, so that collocation, whether agree- able or otherwise, inevitably includes the element of contrast. Harmonies differ in degree or in complexity, but not in kind, so far as contrast is concerned. The ordinary harmonies of analogy pass by insensible degrees into distinct undoubted harmonies of contrast. We here cite M. Chevreul’s classification of har- monies, a classification which has been adopted by most writers on colour : — I. — HARMONIES OF ANALOGY. 1. The Harmony of Analogy of Scale. — This harmony is essentially the harmony of a series, or the harmony of grada- tion. It is produced by the simultaneous view of several tones of the same scale, and is obtained in varying degrees of per- fection according to the number of the tones present and the intervals between them. When the tones are not easily sepa- rable by the eye, and run into one another, then the effect commonly called “ shading ” is produced. 2. The Harmony of Analogy of Tones. — When two or more tones of the same depth, or nearly the same depth, but belong- ing to different but neighbouring or related scales, are viewed together, the harmony of tone is produced. Many such assort- ments, however, are displeasing to the educated eye unless they be so selected as to fall into a series with a gradually increasing quantity of some one of their colour-elements, when they may be ranged in the third kind of harmonies of analogy — 3. The Harmony of a Dominant Colour. — This harmony is produced by viewing a landscape, a bouquet of flowers, or any contrasted colour - assortment, through a piece of glass so slightly tinctured with a colour as not to obliterate but merely to modify the natural colours of the arrangement or com- position. II. — HARMONIES OF CONTRAST. 1. The harmony of contrast of scale is produced by the simultaneous view of two very distant tones of the same scale. 2. The harmony of contrast of tones is produced by the simultaneous view of two or more tones of different depths, belonging to neighbouring or related scales. 3. The harmony of contrast of colours is produced by the simultaneous view of colours belonging to very distant scales, and assorted in accordance with the laws of contrast. This kind of contrast includes also those cases in which the effect is still further increased by differences of tone as well as of colour. It must be confessed that the above classification of colour- harmonies is forced and imperfect ; for every harmony depends to a greater or less extent upon contrast, either of tone or of colour, or of both ; and our harmonies of analogy will be found to be derived from the milder and less startling kinds of con- trast. Two ruling ideas will, however, be apparent in colour- arrangements, and upon the recognition of these ideas we may, perhaps, found a more satisfactory classification of colour-har- monies than that of Chevreul. These two fundamental ideas are those of seriation and change. Of the first we have an example in the assortment yellow, orange, red ; of the latter in the assortment yellow, red, blue. Seriation or succession corre- sponds in some measure to the scales, and change to the chords, of musical composition. Seriation may be succession of tones or of colours, or of both ; but in all cases the idea of a series, of steps, of orderly succession, with the presence of a pervading and dominant element, is the leading feature of the arrange- ment. In harmonies of change, on the other hand, an element common to all the members or a majority of the members is wanting ; nor is there any distinct idea of orderly succession or of development in those harmonies which convey very dis- tinctly the notion of change, more or less abrupt. Between harmonies of seriation and harmonies of change there are numberless connecting links, so that the one kind may imper- ceptibly slide into the latter. For beyond the regulating prin- ciples of balance, distribution, appropriateness, harmony, etc., no rigid rules, as of cast-iron, need trammel the imagination of the colourist, and so no precisely-defined classes can be arranged to receive all the possible harmonies of assorted colours and hues. What further remarks we have to make with reference to this subject we now proceed to give under the two heads of harmonies of series and harmonies of change. Seriation, succession, development, sequence, gradation, or shading include many cases of the harmony of analogy, and are of two kinds. The tones of a scale succeeding one another in regular order furnish one example of shading ; another is seen in a series of assorted colours so arranged as to convey the notion of a gradual increase of some quality in the series. The gradual development of the full leaf-green of a plant in the spring furnishes an example of gradation, not only of tones but of colours. A greenish-yellow passes into yellowish-green, this into green, and this finally acquires both depth and a greater proportion of blue. Leaves in autumn may often be observed to reverse this order, passing through various tones and hues of russet, red, orange, and yellow. The open country continually offers illustrations of the two kinds of gradation we have named, and the landscape painter, apprehending the value of this fact, is enabled to realise the relations to each other of the different parts of the view spread before him, both as regards gradation of tone and gradation of colour. In the near objects constituting the foreground he notices the exten- sive range of the scales both of tone and colour, and the pre- ponderance of those hues which imply the notions of brightness and warmth. In the middle distance the range of tones and colours is more abridged ; while the far distance is commonly distinguished by retiring and cold colours, with a very limited range of scale as well as of colour. From these natural examples of gradation we may take many hints useful in applying colour to decorative purposes. Supposing we wish to conventionalise a compound leaf according to the principles laid down in the “Principles of Design,” we may do so not only so far as its details and form are concerned, but also in reference to its colour. Fig. 15 represents such a conventional colour arrangement — an arrangement the key to which is to be found in a natural sequence of colours often occurring in plants. What is called a harmony of analogy runs through the series of colours in Fig. 15. The four colours there assumed to be present resemble in kind and in order those found in the spec- trum of the sun to lie between the yellow and the green. The arrangement of the series conveys the idea of an increasing brightness and warmth as we descend from the pure green terminal leaflet to the smallest pair of leaflets close to the leaf- stalk. Fig. 16 represents the same series of colours in a diagrammatic way, but inverted, and furnishes us with a scien- tific analysis of the effects observed. The full green is repre- sented, in accordance with the common theory, at the base of Fig. 16 as containing eight parts of blue and three of yellow. The yellowish-green comes next, with one-third less blue and the same amount of yellow as before. The greenish-yellow contains only one-third the amount of blue of the original green. Then we reach the pure yellow, which is to be regarded as the common element of the series, bringing all its members into relation. In our next illustration (Fig. 17) the range of colour is more extensive. The series is not for general use in decorative assortments, but there are several useful lessons to be drawn from it and applied in practice. The contrasts between con- tiguous colours in the present example are much more startling than in Fig. 15, the intervals are larger, while the harmony is one which must be said to lie between those of analogy and those of contrast. The element of serial succession or de- velopment is weak here, that of change very apparent. The gradation in the assortment depends upon the increasing brightness of the colours as we ascend, and upon the link which connects each group of three neighbouring colours together — the presence of a common element. We arrive at this result by interposing a secondary between its constituent primaries all through its arrangement. Thus orange is placed between yellow and red, which latter is succeeded by violet, the compound of red and blue. Blue follows, and after this green ; then wo should re-commence the series by returning to the yellow with which it began. The analysis cf the colour- 16 THE TECHNICAL EDUCATOK. Green. Yellow Fig. 15. series in Fig. 17 is represented roughly in Fig. 18, where the thin lines represent yellow, a thicker line red, and the thickest line blue. Where two lines overlap, a compound colour appears. We may, however, learn something more from Fig. 17 than is here put down. The greater development of the stalks and leaflets towards the base, with the gradually increasing pointed character of the latter towards the summit, helps to carry out the idea of series suggested by the succession of the colours. If in some minor details, such as the larger size of the second pair of leaflets, we find a break Green, in the symmetry of the series, this is just the common feature YeUoxmsh,- of vegetable and animal growths by which they are in part dis- tinguished from the mathemati- cally accurate, but less interest- ing products of mere mechanism ; for very often the poetry, the mystery, of beautiful organic forms lies hid in such seeming exceptions to law. We must not fail to notice that there exist several methods of more completely harmonising the contrasted colours of such a series as that shown in Figs. 17 and 18. In copying the former figure in colours for the sake of the instruction this exercise affords, we recommend our readers to try the following generally applicable methods of bringing greater unity into such a series 1. An outline and veining of black, common to all tlie leaflets. 2. An outline and veining of gold, common to all the leaflets. 3. The addition of grey to the whole of the colours used, the largest proportion being added to the green, the least to the yellow. 4. Instead of making the secondary colours by mixture, introduce their constituent primaries by dots placed side by side. Splendid examples of such gradations of colour as those we have been describing are to be found in numerous specimens of decorative art and manufacture in the fabrics of India,* the silks of Damascus, the faience of Persia, the lacquer-ware of Japan, and the porcelain of China. To take a single example, we may refer our readers to the peculiar but beautiful selection and sequence of colours upon such plates of the so-called “ Persian ware ” as may be seen in the Ceramic Gallery at South Kensington. The particular variety of this ware which we have now in view is known as “Damas,” “Lindus,” or more generally “Rhodian.” The range of colours is limited except so far as one series is concerned — the series beginning with green, and passing through turquoise blue, to a pure deep cobalt, and thence to a lilac hue. The most conspicuous of the remaining colours is a dull brick- red, opaque and much raised in relief above the others. A chocolate- brown, and a black or grey like that of Indian-ink complete the list, except that now and then a specimen of the ware is found with a little yellow on it. On a ground of creamy white, conventionalised forms derived from the hyacinth, the tulip, and a few other plants occur. The leaves are filled in with a copper-green, some flowers are of deep blue touched with turquoise, others of a lilac hue. On some specimens no other colours are found than these four, yet these establish so lovely a series that it is doubtful whether the specimens which exhibit these colours only are not equal or even superior to the others. The colours of the plants rc- * See, for the important lessons to be drawn from the study of Oriental fabrics, Dr. Dresser’s seventh paper on “ Principles of Design” (Yol. I., page 230). Fig. 16. 3 £ 0 2A_ 3 3 * 3 W g V * 3 ^ presented probably suggested, in cases like the present one, some of the predominant harmonies in which the dull red, with its yellowish tincture, balances the cooler blues and greens, while the Indian-ink colour, in light circles and delicate spirals of smoke-grey, tones down the whole composition, and actually brightens and purifies its dominant series of colours. We ought not to fail to notice a most precious quality of these Persian wares — that fluctuation of colour, that absence of mechanical hardness of outline and uniformity of tone which distinguishes human handiwork of the thoughtful kind from the perfectly correct and thoroughly insipid work of a machine. But we must not linger any more over our illustrations of the harmonies of series or relation, but conclude our present lesson with a word or two on the “ har- monies of change.” Harmonies in which the se- quence or relationship of the constituent colours is indistinct or absent include most varieties of the harmonies of contrast. The change of tone or colour in them may vary greatly in abrupt- ness : in the more complex assortments of this class it is very difficult to attain anything like an agreeable unity, for if there be many startling changes or contrasts, the effect becomes tiresome and spotty. The har- monies of change become more agreeable the more closely the rules of judicious distribution and balance of colour and tone are followed. The free use of separating lines of white, grey, gold, or black is often indispensable. The value of reduced tones of colour, and of the mixed and tertiary hues to modify the crudeness of a startling contrast, is very remarkable. But we have already described at considerable length, in Lessons V., YI., and VII., the principles upon which harmonious contrasts depend, and so here simply confine our attention to two illustra- tive examples derived from the floral world. We might turn to the splendid family of the orchids, with their quaint forms and complex systems of colour, or we might choose one of the Malvacece, such as the Abutilon megapo- tamicum — a plant in which the green of the leaves offers a violent contrast with the red of the swollen calyces, and the five bright yellow petals of the corolla contrast again very forcibly with the violet hue of the central branch of clustered stamens — a startling assort- ment, but very rich in effect, when completed by the opening of the flower. In this example, besides the mere notion of con- trast, we have the idea of re- petition which resembles that of seriation ; red contrasting with its complementary, green, and yellow with its complementary, violet, both the complementaries having, therefore, the third ele- ment, blue, in them. But every flower presenting three different colours may serve to illustrate the harmony of contrast, and we need not go far for an example. Even the quiet violet with its minute orange-tinted eye, the faint green bases of its petals and their own chief hue, somewhere between blue and red, affords a colour-assortment of the kind under discussion, the balance of which is in a measure completed when the leaves of the plant are included in the series. Similar studies of other plants should be made ; it will surprise many persons to discover what a world of instruction, as well as of enjoyment, is to be derived from what we may call the chromatic analysis of flowers. The next subjects to be discussed are the modifications of colour arising from methods of illumination and differences of structure and surface. Yellow Bed. Blue — Yellow Orange. Bed. Violet. Blue. Green. Fig. 18. THE STEAM-EXGIN E. 17 THE STEAM-ENGINE.— YII. By J. M. Wigneb, B.A. BEAM — PARALLEL MOTION— CRANK— FLY-WHEEL— ECCENTRIC. As we said in our last lesson, we shall first describe the con- struction of a condensing 1 beam-engine; and Fig. 32 represents a model showing very clearly the construction and action of the different parts of an engine of this kind. In an actual engine the arrangement of the condenser, hot-well, and pumps shown on the lower base is often very considerably modified, so as to suit the exigencies of the special case, but their action is not in any way altered by this change. A portion of the side of the cylinder is hero shown removed, so as to exhibit clearly the piston and slide-valve which we have already described. L represents the “working beam,” which is made very strong, and is usually of great weight. A pivot passes through its centre point, and turns in bearings supported by stout iron pillars, or, as is more commonly the case, firmly built into the masonry of the engine-house. This beam is carefully balanced, so that it may oscillate on its' bearings without a great amount of force being re- quired. The piston-rod, A, imparts motion to one end of this, and at first sight it might seem sufficient merely to fasten it by means of a pin or a common joint. We must remember, however, that the piston-rod has to move vertically up and down, and, as we shall easily see, the point of attachment to the beam moves in an arc, and does not, therefore, remain vertically over one spot. If, then, it was fast- ened in this way, the piston- rod would at once be bent, so that it would not act. The plan originally adopted to obviate this consisted in fixing an arc to the end of the beam, and attaching the rod to this by means of chains. This plan, however, was very clumsy, but the difficulty is fully met by the beautiful contrivance in- vented by Watt, and known as Watt’s Parallel Motion. The piston-rod here is jointed to a compound rod, D, the other end of which is jointed to the beam. A similar rod, also lettered D, is affixed to the beam a little way from the end, and a rod, E, is jointed to the end of these, so that a parallelogram is formed by the three rods and the portion of the beam between the pivots. The most important part of the arrangement is another rod, C, which is jointed at one end to a wall-plate attached to the building, or else, as in the figure, to a firm upright, B, affixed to some convenient part of the engine, and at the other end to one of the lower angles of the parallelogram. As will easily be seen, when the beam is nearly at the end of its oscillation, the pivots in it are nearer the centre line than when it is horizontal ; the rod c, however, at these times pulls the lower ends of r>, B in the other direction ; and thus, when the lengths of the rods are carefully adjusted, A moves up and down in a perfectly vertical line. To the other end of the beam the connecting-rod, I, is affixed, 1 which imparts motion to the driving-wheel of the engine. This is accomplished by means of a crank, K, affixed to the axle of the wheel V. The connecting-rod, i, is fastened to the end of k by a pin passing through both, and turning freely in one. When in the position represented, the end of the beam to which the connecting-rod is attached is rising, and it accordingly raises the end of K, and sets the wheel in rotation. As soon, 28-Vol. II. however, as the stroke of the piston is completed, and this end of the beam is at its highest point, the connecting-rod, I, and K will be in the same straight line, and it is clear that then any pressure, whether up or down, will merely be transferred to the axis of V and the bearings in which it turns, and cannot in any way tend to turn the wheel. At this point, indeed, the crank loses all its power, and ceases to act. This is apparently a great drawback, and at first sight we should suppose that it would cause the motion of the engine to be very irregular and uneven. The difficulty, however, is easily overcome. The wheel v is made with a very heavy rim, and this serves as a kind of reservoir of force. When the crank is in its most advantageous position, the tendency is to increase the speed of the engine; owing, however, to the weight of the fly-wheel, a very slight in- crease is produced, the power being as it were stored up in the form of momentum imparted to the wheel, and this momentum urges it past the “ dead-points ” as they are called, and thus renders the motion for all practical purposes quite uniform. It is manifestly a thing of considerable importance to have the weight of the fly-wheel so adjusted as to bear a due proportion to the power of the engine. If, on the one hand, it be too heavy there will be a needless addition to the load of the engine ; while if, on the other hand^ it be too light, the motion will not be uniform. The practical rule is that the power stored up in it should be about equal to that pro- duced by 6 half- strokes. Thus, if the steam exert a pressure of 1 ton on the piston, and the length of the stroke be 4 feet, the power thus generated is 6x4x1, or 30 tons. The weight and velocity of the wheel should therefore be so arranged that its momentum i3 about equal to this. If, then, the weight of the rim be 1 ton, its velo- city should be that which would be acquired by a body falling 24 feet ; if it weigh TJ- tons, it should be that acquired in falling 16 feet, and so on in proportion. The machinery to be set in motion is usually driven by a strap passing round the fly- wheel, and then round the driving pulley of the shafting. In some cases cog-wheels are employed in place of the straps to drive the first motion. z is the eccentric by which motion is imparted to the slide- valve. On the axis of the fly-wheel a circular disc of metal, e, is keyed in such a way that the axis does not pass through its centre, but considerably to one side of it. A ring of brass sur- rounds this, so affixed that the disc can turn freely inside it, but cannot slip out. The rods at the side of z are fastened to this ring, and thus as the axle rotates, carrying the disc with it, the ring is alternately moved to the right and to the left, and imparts this alternating movement to the eccentric. Behind the cylinder, and hidden by it, is a bent lever, one end of which is jointed to z, and the other to the valve-rod, m; and by means of this the alternate movement of z moves the slide-valve and regulates the supply of the steam. The steam-pipe is omitted in the figure, but it enters the valve-casing as in Fig. 31, and the exhaust leads to the con- denser o, seen under the cylinder, where the waste steam is condensed, and a vacuum thereby produced. In this way there is scarcely any resistance on the exhaust side of the piston, and the full pressure of the steam is communicated to the beam through the piston p and piston-rod. The description of the remaining portion of the steam-engine must be deferred to cur next lesson. 18 THE TECHNICAL EDUCATOR APPLIED MECHANICS.— X. BY ROBERT STAWELL BALL, M.A., LL.D., Astronomer-Royal for Ireland. THE SHEARING MACHINE AND PUNCHING MACHINE. In the last lesson we briefly described the most important tools used in the manufacture of wrought iron — namely, the steam- hammer and the rolling mills. In the present lesson we shall describe the other tools which are of the utmost utility in the subsequent treatment of wrought iron. The plates of iron which are produced by the rolling-mills are destined for various purposes. The best of them are employed for boilers ; others are used for making iron ships, iron girders, and multitudes of minor uses. The iron plates for which the punching and shearing machines are used vary in thickness from ordinary sheet-iron up to nearly an inch in thickness. The shearing machine, as its name indicates, is employed in trimming the edges of plates, and in cutting them, to the required sizes. The punching machine is employed for the purpose of making holes in the plates, by which they can be attached together with rivets. The usual form of rivet is shown in the annexed figure (Fig. 1). It consists of a cylindrical shaft, at- one end of which is a hemi- . spherical head. The rivet is heated red-hot, and is passed through holes in the plates which are to be united together. The workman then strikes the projecting cylindrical end with a hammer, while his assistant holds a heavy tool against the head to prevent the rivet being driven out by the blew. A second hemispherical head is thus formed on the pro- jecting end while the rivet remains red-hot, and as it cools, the contraction of the red-hot iron draws the plates together with prodigious force. The appearance two such plates present when riveted together is shown in Fig. 2. Since this is the universal method of attaching iron plates to each other, it follows that some convenient and rapid method of producing the necessary holes in the plates i 3 a matter of necessity. This will be evident if we remember that very many thousands of such rivets are used in the construction of an iron ship, and each rivet requires two, or sometimes a greater number of holes. To meet this want the punching machine has been devised. It is somewhat varied in form, to meet the exigencies of different manufactures, but it is substantially in all cases a combination of two distinct mechanical principles, the fly-wheel and the lever. The latter we have already considered, and it will now be necessary to give a descrip- tion of the former, and an account of the mechanical principles upon which its use de- pends. The fly-wheel is generally a cast-iron wheel, with a very massive rim. It is mounted on an axle, and has motion communicated to it by a steam-engine. The fly-wheel is strictly a reser- voir of power. It is a store into which the engine pours its energy, to be withdrawn, as occasion may require, by the machine which is in use. A little consideration will be necessary in order to understand the amount of work that a fly-wheel moving with a given velocity is capable of storing up. We have already explained in the lesson upon the hammer, that if a body whose mass contains to pounds be moving with a velocity v, the number of foot-pounds of work which have been employed to produce this velocity, and therefore the number of units of work that this body* will give out before it comes to rest, is — v 3 m — . 64 We shall now apply this result to determine the number of units of work in a revolving fly-wheel. Let n be the angular velocity of the fly-wheel. The angular velocity of a body is the number of angular units through which it turns in the unit of time. Thus, for example, if we say the angular velocity of a body is 3, what is meant is, that it turns through three times the angular unit in one Fig. 2. Fig. 1. second. Now it will be seen, by referring to the lessons in Trigonometry, that the angular unit is 206,265 seconds ; and therefore, when a body has an angular velocity of 3, it turns in one second through 206,265 x 3 seconds, and dividing this quantity by 60 X 60, we find the number of degrees through which the wheel will move in one second. It follows, from the definition of angular velocity, that if R be the radius of the wheel, the actual velocity, of any point on its circumference is nR. If the wheel be large, we may, without appreciable error, assume all points in its rim to be moving with the same velocity. Let to be the number of pounds in the rim. Then the mass to is moving with the velocity nR, and therefore the total quan- tity of work stored up in the wheel when revolving is — n’Ea m In order to give an application of this formula, we shall apply it to the following problem : — A fly-wheel twelve feet in diameter, whose rim weighs four tons, revolves four times in a minute. It is required to deter- mine the number of units of work which it contains. Since the wheel turns round once in fifteen seconds, its angular velocity is — Therefore the velocity of the rim is — 0G2 x 6 = 2-52. We have then a mass of four tons moving with a velocity of 2'52 feet per second. The quantity of work stored up is therefore — (2-52U 8980 x 1 = 889. 84 Hence 889 units of work must have been expended in order to get up this speed in the wheel, and a similar quantity will bo given out before the wheel can come to rest. It is usual, however, to give the fly-wheel a much higher velocity than in the example we have taken ; and the higher the velocity, the greater the quantity of work. This will be evident from the expression for the work, viz. — 64 * for this varies proportionally to n 2 — that is, to the square of the angular velocity. Hence, if we increase the speed of a wheel to double its amount, we quadruple the quantity of work that it contains. If the wheel we have been considering revolved twenty times in a minute instead of four times, the quantity would be increased 25-fold, and would become 25 x 889 units. The fly-wheel which is used in connection with a punching machine is small, but revolves with a very high velocity, and so is capable of holding a large store of work. Let us suppose a wheel of 2 feet in diameter, whose rim weighs 2 cwt., and revolves five times in a second. The angular velocity is therefore — 22 10 x — = 31-4. 7 Hence the quantity of work stored in the wheel is — ( 31 - 4)2 224 = 3451. This wheel is therefore capable of raising a load of 3,451 lb. through one foot before it comes to rest, or a pressure exceeding two tons must be exerted through one foot by machinery con- nected with this fly-wheel before it is brought to rest. We shall now be able to understand the use of a fly wheel in machinery which, like a shearing machine, has occasionally to overcome a very large resistance. The engine accumulates a vast store of its energy in the rapidly revolving fly-wheel. Before the machine which experiences the resistance is in action, the motion of the fly-wheel becomes accelerated. When the machine comes into action one of three things must happen ; the fly-wheel must be stopped, or the machine must be broken, or the resistance must be overcome. But TECHNICAL DBA WING. 19 the fly-wheel cannot be stopped until it has poured forth all the energy which it contains ; and, of course, the dimensions of the fly-wheel and its velocity are so proportioned that its store of energy shall be ample for the work. Nor can the machine be broken ; for machines of this class are always very massive, in consideration of the vast strains to which they are liable. It follows, therefore, that the resistance must be overcome. The general appearance of a shearing machine will be under- stood from Fig. 3, which is the representation of one of the simpler machines of this class. It consists of a long lever of the first order, A o B, which has its fulcrum at c, the centre about which it turns, while the power is applied at the end A, and the resistance is encountered at the end b. At the end A is a roller, which turns around an axis, and is a means of diminishing the friction, which would otherwise be inconvenient. The roller, d, is acted upon by a cam, f. This cam consists of a circular piece of iron, which is mounted excentrically at H. As the axle h revolves the cam gradually elevates the roller, and thus applies the power to the extremity of the lever. After the roller has reached its greatest height, the weight of the lever is sufficient to bring it down when, by the revolution of the cam, its descent is possible. In this way the continuous rotation of the cam gives a reciprocating movement to the lever. At the back of the cam is shown the fly-wheel, f'. This is mounted on the same axle, h. The engine, or other source of power, which gives motion to the axle, is not shown in the figure. At the end b of the lever is one jaw of the shears, K ; the other, l, is firmly attached to the stand. Whenever the roller d is raised, the jaws are closed, and the piece of iron or other body that lies between the jaws is severed. Let us suppose that a bar of wrought iron one square inch in section is required to be sheared across. It has been found, as the result of numerous careful experiments, that an average pressure of about 20 tons is necessary. It is very remarkable that this is about the same force as would be required to tear the bar across by extension ; a little consideration will, how- ever, point out why this should be so. In each case the same number of particles of iron have to be separated from each other. On the scale which we have used for the figure the mechanical advantage of the lever is about six-fold. Hence it will be necessary that the end A of the lever be pressed upwards with a force of about 3 tons, or a little more, in order to cut the bar across. We shall also be able to form an estimate of the number of units of work which will be absorbed from the fly-wheel in the operation of shearing. A pres- sure of 20 tons — that is, of 20 x 2,240 = 44,800 pounds — has to be exerted through a certain distance. It is not very easy to ascertain what that j distance is ; it must be less than one inch. This will be evident from Fig. 4. In this A B are the edges of the shears ; cu is the bar which is ex- posed to their action. Now it is evident that almost imme- diately after the cut of the shear commences the iron must be divided completely across ; hence the force has only to be exerted through a space which we may certainly assume does not exceed one quarter of the total thickness to be cut. The force of 44,800 pounds has, therefore, only to be exerted through the space of ^th part of a foot; consequently the total number of units of work is — — x 44,800 = 933. 48 Hence, for each operation of shearing, a number ©f units of work not exceeding 1,000 is abstracted from the energy stored up in the fly-wheel. The operation of punch- ing is in many respects analogous to that of shear- ing; in fact, punching con- sists in shearing cut a cylindrical piece from a plate of iron. The im- portant part of a punching machine will be understood from Fig. 5, in which ab is the plate of iron through which a hole is required to be made ; p is the punch, which is made of hardened steel; CD is the block, and e the recess into which the piece of metal is forced from the plate. The punch, p, is depressed, by means of a fly-wheel cam and lever, in a manner analogous to the shearing machine ; the quantity of work absorbed in punching a hole can also be, estimated in the manner already described. TECHNICAL DRAWING.— XX VIII. DRAWING FROM ROUGH SKETCHES (continued). In this lesson some further examples are given with the view of’ affording the student additional practice in setting cut work to a scale, instead of merely measuring the lines from copies. It is again, however, necessary to mention that these are rough sketches, such as might be given by the head-engineer (though these would in most cases be rougher still), or as might be taken from the object, to be afterwards made into correct drawings. The proportions are only, therefore, generally correct. The figures, not being drawn to any particular scale, must not be depended upon as copies; the subject is, therefore, to be worked according to the measurements marked upon them. - Fig. 260 is the head of a connecting-rod of a locomotive passenger engine. The construction of connecting-rods generally will be found in the lessons describing the details of an engine. It is only, therefore, necessary in this place to give the names of the parts and the method of drawing them. a is the rod-end ; b, the end of the axle ; c, the outside of the brasses ; D, inside of the brasses ; E, oil-cup ; F, cotter ; G, gib ; H H, set-screws to keep the cotter from moving. As usual in all objects which are symmetrical, a centre line should be first ruled. Starting, then, with the line a h, and this having been made 41" on each side of the centre line, the complete block forming the head of the connecting-rod is to be drawn. The arc at the top is struck from a centro situated at c, whilst its meeting with the sides of the block is rounded off by two smaller arcs struck from d, d. The lines forming the inside and outside of tho brasses are now to be drawn, and the axle-end, the centre of which is 7 4" from a b, and the radius of which is 2". The oil-cup, gib, cotter, and set-screw will new follow, and the line a b is to be united to the rod-end by arcs. This example should be drawn to the scale of 6 inches to the foot, or half real size. Fig. 261. — The subject of this lesson is a section of a stop- cock, drawn to about half the real size. A stop-cock is an arrangement by which gases or liquids are allowed to pass, or are at pleasure prevented passing, through pipes, or from any receptacle in which they may be contained. r lhey consist of A, the cock, b, the plug, and C, the handle, which in some cases forms the upper portion of tho plug, placed at right angles to its axis, and in ethers (as the present) is simply a lever pierced with an aperture of tire same shape at the top of the plug, which may be removed when desired. Stop-cocks are generally made of brass, composition metal, or cast iron. The cock is formed with or without flanges for attachment to different pipes, vessels, boilers, etc. Tho above example terminates in a screw working in a plate. In this view 20 THE TECHNICAL EDUCATOK. the tap is turned “ on,” so that the hole through which the liquid would pass is shown in dotted lines. The plug is conical, so as to fit better in its seat, the part which receives it being turned out so as to correspond with the conical surface. The plug is also kept in its place by a nut ' in the plan, the width of the point g h, taken from the development shown at the side of the elevation — viz., g' h‘ — and from these points draw lines to tho centre of the plan ; these radial lines extend- ing only between the circles d' and d’, as a' i and tij. Join rf and h' by means of arcs to k and l (the widths of the teeth already sot off), and from It and l draw as far as the circle e', the root of the teeth, passing through the pitch-circle of the upper end of the teeth in m n. Join m and n to i and,), and this will complete this portion of tho plan. It only remains now to project all the points of teeth, as g‘ h', on the line d (Fig. 266), by carrying up perpendiculars from the plan to meet the corresponding lines in the elevation. This is shown by dotted lines in the illustration. Tho arms and shaft are then to be added in plan and elevation. A scale- of feet and inches is appended to Figs. 265 and 266, from which the diagrams have been constructed, and which may be used by the learner to ascertain the relative dimensions of the different parts of the bevel-wheels as shown in the diagrams. His own drawing, however, should not be made from the scale that we have given, but from one of his own construction, the measurements in the diagrams being ascer- tained from our scale, and then made in his own drawing from his own scale. AGRICULTURAL DRAINAGE AND IRRIGATION.— YII. By Professor Wrigiitson, Royal Agricultural College, Cirencester. WATERING LAND BY ARTIFICIAL MEANS. That the practice of irrigating, or artificially watering land, has been practised from the most ancient times, there is no doubt. It would occupy more space than we can afford, as well as carry ns into questions which it is not our object to discuss, had we to give a detailed history of the art. It must, therefore, suffice to mention that in Egypt, where the annual overflow of the Nile early taught the lesson, in Persia, in Palestine, as well as in India and China, and later, in Homan agriculture, irrigation occupied an important place. In hot and arid countries, indeed, it is positively essential, while in the more temperate climates of Western Europe it is a valu- able means of increasing the productiveness of land. This practice outlived the fall of Homan civilisation, and under the direction of the monks of the Middle Ages was carried on with success. It is supposed by some authors to have been intro- duced by the Moors into Spain, and from thence to have been re-introduced into other parts of Southern Europe ; but more probably it lingered in England, as well as in parts of France, Spain, and Italy, from the time of the Homans, and as civilisa- tion progressed, and greater attention was devoted to the arts of agriculture, its extension would be secured. In Italy irrigation is carried out on a truly grand scale. The waters of the Po, the Adige, the Tagliamento, and all the minor streams are employed for this purpose, and there is no country which possesses a greater extent of rich water-meadow than Lombardy. The entire country, from Venice to Turin, has been spoken of as one great water-meadow, and yet irriga- tion is not there confined to grass lands, but is used in tho cultivation of rice, vines, and other crops. Public attention was first called to the importance of irriga- tion in this country by Robert Vaughan, who published a work in 1610, entitled so lengthily, that we only give the first few words: — “Most Improved and Long-experienced Water- works : containing the Manner of Summer and Winter Drowning of Meadow and Pasture,” etc. Among the earliest established water- meadows are those of Wiltshire and Hampshire, which were made between 1700 and 1710. These meadows were not, however, laid out upon the best principle, and subsequently underwent considerable improvement. In the latter part of last century the subject of irrigation was again taken up in a treatise by George Boswell, published in 1780, and a series of papers followed by the Rev. T. Wright, of Auld, in Northants, published from 1789 to 1810. Instances are also on record in which irrigation was used in the cultivation of corn as well as grass in two parishes of Forfarshire and Aberdeenshire ; but until very recently it was almost exclusively applied to grass in England, and the history of irrigation in Scotland dates from even a later time. In 1794-5 the Highland and Agricultural Society brought a practical irrigator from Gloucestershire, and several extensive proprietors set an example by forming irrigated meadows. The subject of irrigation is extensive, and when we remember its various phases, and the numerous questions connected with the soils and situations where it may be employed, the waters most suitable for the purpose, the grasses and other plants which it benefits most, and the general management of water- meadows and irrigation works, it will be seen that there is material for volumes. Add to this the important aspect of irrigation as connected with the utilisation of the sewage of our towns, and some idea will be obtained both of the importance and extent of the subject. In these pages we propose to touch briefly upon all the above points ; but especially upon the last, namely, the utilisation of sewage. With reference to the various kinds of irrigation, the water may be applied either upon the surface, or from beneath. Super- ficial irrigation may be natural, as in the proximity of rivers which periodically overflow their banks ; or artificial, by which is meant the conveying of water by channels so arranged as to distribute water evenly over the surface of land. The methods of doing this are controlled by the contour of the ground. In most cases the land is formed into beds or broad ridges, raised in the centre. The water is brought by a main “ carriage,” or ditch, and is allowed to flow into shallow trenches along the tops of the ridges. These trenches being full, overflow, and tho AGRICULTURAL DRAINAGE AND IRRIGATION. 23 water trickles down the sides of the ridges, finding its way into gutters provided for the purpose between the elevated “panes” or “ stetches.” The meadow is so laid out that while the carriage gutters on the tops of the ridges bring the water on to the meadow, the gutters in the hollows between the ridges serve to carry it off into the brook at a lower level. The accompanying figure will render this arrangement plain. a, dam across river; b, main carrier; c, watering' gutters; d, drain- ing gutters ; e, main draining gutter. Where the land has a uniform slope the “ catch- water ” system of irrigation may be followed. In catch-water meadows the water is allowed to flow on to the most elevated portion of the ground by means of a “ feeder,” and as it overflows, and seeks a lower level, it is again collected by a second feeder, which crosses the line of greatest declivity, and re-distributes it over a still lower tract. Thus the water finds its way across a succession of feeders, each of which is a new point from which it is distri- buted. In either of these two methods “ stops ” are used in order to control the flow of the water, these stops being com- posed of boards placed across the feeders, or of sods placed so as to block the passages, and cause the water to overflow at the particular point required. Water-meadows may be formed wherever there is a constant supply of water, in dry as well as moist seasons, where the water is not required for mills or other purposes, and where the water “ rights ” are clearly defined so as to allow of the appropriation of the stream for the purpose of irrigation. The clearer the water, the better for the purpose, and this at once marks a distinct difference between “ warping ” and irrigation. The former operation is in use in the extreme south-east of Yorkshire and north-east of Lincolnshire, in the proximity of the Humber. This and other rivers carry down vast quantities of mud from the interior of the country to the sea, the result being a deposition of alluvial material at their joint estuary. So considerable is this accumulation, that a long tongue of newly-formed land prolongs the south-east extremity of Yorkshire far into the ocean, and a lighthouse has been removed nearer to the sea three times within a very short historic period. This then is a case of natural warping, and by directing the flow of mud-charged waters on to lands adjacent to the river, the deposition is regulated according to the require- ments of man. The rise and fall of tides assist in this opera- tion, enabling successive floods of water to be poured over the portion of land embanked for warping. Thus, in a year, from one to three feet of soil of superior quality is accumulated. In irrigation, the presence of mud or other suspended matter in the water is not desirable, since the deposition of fine particles on the leaves of growing plants would interfere with their functions and retard their growth ; while substances in a state of solution are absorbed by the soil and the roots of plants, and minister to their wants. In an earlier paper we con- trasted the two operations of drainage and irrigation, and at this point it may be well once more to point out the true functions of water when used for the latter purpose. Stagnant water, the enemy against which the drainer strives, is a “ dog in the manger,” uselessly occupying the interstices of the earth, keeping out the air, and, by its evaporation, rendering the land cold. In irrigation, on the other hand, it is essential that the field should be in the first place cleared of stagnant water, either by natural or artificial means. It must be dry, or drained. Next, from time to time a sheet or layer of moving water is allowed to find its way over its surface, carrying with it nourishment for plants, in many cases a higher temperature, and dissolving and render- ing available the mineral wealth of the soil. Such, in few words, is the theory of irrigation. Let us now glance very briefly at the general management of such meadows. The water is allowed to flow over the surface in winter and in summer, and provision is made for this by a proper arrangement of sluices. According to Mr. George Stephenson, the meadow should be periodically watered from October to January. Each watering is continued for fifteen to twenty days without intermission, and at the expiration of each of these periods the ground should be made completely dry for five or six days, to give it air. Mr. Bravinder, of Cirencester, who has the most intimate knowledge of the working of these meadows, says they “produce (after the winter’s watering) an early and abundant supply of grass for ewes and lambs, and other stock, which is exceedingly useful in the spring. The custom is to consume the first crop by keeping sheep on the land till May, when other grass and green crops are ready to take the stock. The water is then turned on again, and subsequently a second crop is produced, and mown for hay about the latter end of June or beginning of July. The water is turned on a third time, and the aftermath which succeeds is fed off, which generally lasts till Christmas.” In all this, great care is requisite in keeping the water-course3 clear, and regulating the “ stops,” so as to cause the water to flow evenly over the entire surface. Again, in severe frosts the watering must be discontinued, as by persisting in allowing water to flow at such times the temperature of the ground will be injuriously lowered. Usually, in districts where water-meadows obtain, a considerable extent of them is committed to the care of an experienced man, who both keeps the channels in good order and regulates the supply of water. In conclusion we must briefly notice one of the most bold attempts at irrigation, under difficulties, ever attempted in this country. Mr. Campbell, of Buscat Park, Gloucestershire, con- ceived the idea of pumping water from the Thames (which skirts his property) to the highest point of his estate, and allowing it to fall from thence by gravity, and fertilise a large area of land. In order to carry out this scheme, a “ plant ” of no ordinary kind was required. A gigantic undei-- shot wheel was placed across the Thames, which is not a very formidable river at that point ; three powerful pumps, worked by the said wheel, were erected for the purpose of sending a constant stream of water by large iron piping up to a reservoir, or artificial lake, twenty-five acres in extent and sixty feet deep, scooped in the Oxford clay. Descending from this huge reservoir are delivery-pipes, carrying the fertilising fluid to those parts of the estate where it is required, and where it is further distributed over the surface. Some hundreds of acres have thus been irrigated, and splendid crops of Italian rye -grass have been the result, giving food to an immense number of sheep. Such is a very general sketch of the system of irrigation proposed, and, to a great extent, now in opera- tion at Buscat Park. It is a grand idea, carried out with immense energy and great expenditure of capital. Whether suitable to the climate of this country, or likely to be re- munerative, are questions which time alone can answer. In the case now under consideration the results obtained have been satisfactory, as exhibited in the production of heavy crops of Italian rye-grass, which would not have been nearly as good had it not been for the fertilising properties of the water which was thus boldly diverted from its original course, and turned over the land. It still remains, however, to be seen if the increased crops thus obtained will afford a sufficient return for the great outlay necessary in the first instance. 24 THE TECHNICAL EDUCATOR. PRINCIPLES OF DESIGN.— XII. Bf CHRISTOPHER DRESSER, PH.D., F.L.S., ETC. DECORATIVE DESIGN. Before we pass from a consideration of furniture and cabinet work generally, we must notice a few points to which we have as yet merely referred, or which we have left altogether un- noticed. Thus we have to consider upholstery as applied to works of furniture, the materials employed as coverings for seats, and the nature of picture-frames and curtain poles ; we must also notice certain general errors in furniture, strictly so called. When examining certain wardrobes and cabinets in the International Exhibition of 1862, I was forcibly impressed with the structural truth of one or two of these works. One especially commended itself to me as of a fine structural character, while of classic formation. Just as I was expressing my admiration, the exhibitor threw open the doors of his well- formed wardrobe to show me its internal fittings, when, fancy my feelings at beholding the first door bearing with it, as it opened, the two pilasters that I conceived to be the supports of the somewhat heavy cornice above, and the other door bearing away the third support, and thus leaving the superincumbent mass resting on the thin sides of the structure only, while they appeared altogether unable to perform the duty imposed upon them. “ Horrible ! horrible ! ” was all I could exclaim. Some of the most costly works of furniture shown by the French in the last Paris International Exhibition were not free from this defect ; and this is strange, for to the rightly constituted mind this one defect is of such a grave character as to neu- tralise whatever pleasure might otherwise be derived from con- templating the work. We see a man, a genius perhaps— a man having qualities that all must admire; but he has one great vice — one sin which easily besets him. While the man has excel- lent and estimable qualities, we yet avoid him, for we see not the excellences but the vice. It is so with such works of furni- ture as those of which we have been speaking, for their defects are such as impress us more powerfully than their excellences. Respecting these works of furniture, this should be said : they are more or less imitative of works of a debased art period — of a period in which structural truth was utterly dis- regarded — yet this is no reason why we should copy the defects of our ancestors. Infinitely worse than the works just spoken of, is falsely- constructed Gothic furniture, where the very truthfulness of structure is openly set before us. Not long since I was staying with a client whose house is of Gothic style. Being about to furnish drawings for the decorations of this mansion, I was carefully noting the character of the architecture and of the furniture, which latter had been designed and manufactured expressly for the house by a large Yorkshire firm of cabinet- makers. The structure of the furniture appeared just, the pro- portions tolerably good, the wood honest, and the inlays judicious ; but, can it be imagined, the whole was a mere series of frauds and shams — the cross-grain ends of what should be supports were attached to the fronts of drawers, pillars came away, and such falsity became apparent as I never before saw. How any person could possibly produce such furniture, be he ever so degraded, I cannot think. I have seen works that are bad, I have seen falsities in art, but I never before saw such falsity of structure and such uncalled-for deception as these works presented. The untrue is always offensive ; but when a special effort is made at causing a lie to appear as truth, a double sense of disappointment is experienced when the un- truthfulness is discovered. In his work on “ Household Taste,” to which we have before alluded, Mr. Eastlake objects, and I think very justly, to the character of an ordinary telescopic dining-table. He says : “ Among the dining-room appointments, the table is an article of furniture which stands greatly in need of reform. It is generally made of planks of polished oak or mahogany, laid upon an insecure framework of the same material, and sup- ported by four gouty legs, ornamented by the turner with mouldings which look like inverted cups and saucers piled upon an attic baluster. I call the framework insecure, because I am describing what is commonly called a ‘ telescope ’ table, or one which can be pulled out to twice its usual length, and, by the addition of extra leaves in its middle, accommodate twice the usual number of diners. Such a table cannot be soundly made in the same sense that ordinary furniture is sound ; it must depend for its support on some contrivance which is not con- sistent with the material of which it is made. Few people would like to sit on a chair the legs of which slid in and out, and were fastened at the required height by a pin ; there would be a sense of insecurity in the motion eminently unpleasant. You might put up with such an invention in camp, or on a sketching expedition, but to have it and use it under your own __ roof, instead of a strong and serviceable chair, would be ab- surd. Yet this is very muck what we do in the case of the modern dining-room table. When it is extended it looks weak and untidy at the sides ; when it is reduced to its shortest length the legs appear heavy and ill- prop ortione •. . It is always liable to get out of order, and from the very nature of its construction must be an inartistic object. Why should such a table be made at all P A dining-room is a room to dine in. Whether there are few or many people seated for that purpose, the table might well be kept of an uniform length, and if space is an object it is always possible to use in its stead two small tables, each on four legs. These might be placed end to end when dinner parties are given, and one of them would suffice for family use. A table of this kind might be solidly and stoutly framed, so as to last for ages, and become, as all furniture ought to become, an heirloom in the family. When a man builds himself a house on freehold land, he does not intend that it shall only last his lifetime ; he bequeaths it in sound condition to posterity. We ought to be ashamed of furniture which is continually being replaced ; at all events, we cannot possibly take any interest in such furniture. In former days, when the principles of good joinery were really understood, the legs of such a large table as that of the dining-room would have been made of a very different form from the lumpy, pear-shaped things of modern use.” In nearly all these remarks I agree with Mr. Eastlake, and especially in his remark that, owing to the very nature of its construction, a modern dining-table must be an inartistic object. No work can be satisfactory in which any portions of the true- supporting structure or frame are drawn apart ; and this occurs to a marked degree in this table, as is shown in Mr. Eastlake’s illustration, which we here copy (Fig. 36). Another falsity in furniture is veneering — a practice which should be wholly abandoned. Simple honesty is preferable to false show in all cases ; truthfulness in utterance is always to be desired. It was customary at one time to veneer almost every work of furniture, and even to place the grain of the veneer in a manner totally at variance with the true structure of the framework which it covered. This was a method of making works, which might in their unfinished state be satis- factory, appear when finished as most unsatisfactory objects. Since this time much progress has been made in a knowledge PRINCIPLES OF DESIGN. of truthful structure and of truthful expression, yet this method of giving a false surface by means of veneer is not wholly abandoned as despicable and false. A few months back I had occasion to visit a cabinet ware- house in Lancashire, and the owner called my attention to the fins grain of some old English oak, and remarked that certain pieces of fur- niture were of solid wood. Upon investi- gation, how- ever, I dis- covered that while the fur- niture in ques- tion was made throughout of oak, the bulk of the structure was of common wainscoting, and the surface was veneered with English oak. I confess that I would much rather have had the furniture with- out its false exterior, and daily my love for fine grain in wood gets less. I think that this arises from the fact that strong grain in wood takes from the unity of the work into which it is formed, and tends to break it up into parts, by rendering every mem- ber conspicu- ous. What is wanted in a work of furni- ture, before all other consider- ations, is a fine general form— a harmony of all parts — so that no one member usurp a primary place — and this it is almost impos- sible to achieve if a wood is employed hav- ing a strongly- marked grain. With us a room is considered as almost unfurnished if the windows are not hung with some kind of drapery. The original object of this drapery was that of keeping out a draught of air, which found its way through the imperfectly fitting windows ; and the antitype of our window-hangings was a simple curtain, formed of a material suitable to achieve the purpose sought. Such a curtain was legitimate and desirable, and would contrast strangely with the elaborate festooning and quadrupled cur- tains of our present windows. We daily see yards of valuable material, arranged in massive and absurd folds, shutting out that light which is necessary to our health and well-being ; and a pair of heavy stuff curtains and a pair of lace curtains to each window, each curtain consisting of sufficient material to more than cover the window of itself. An excess of drapery is always vulgar, and a little drapery usefully and judiciously employed is pleasant. Many win- dows that are well made, and thus keep out all currents of air, need no curtains. If the window mouldings are of an archi- tectural cha- racter, and are coloured much darker than the wall, so as to become an obvious frame to the window, and thus do for the window what a picture- frame does for a picture, no curtains will be required. I have recently had a wonder- fully striking illustration of this. Two ad- joining rooms are alike in their architec- ture : one is decorated, and has the win- dow casement of such colours as strongly contrast, while they are yet harmonious, with the wall. Before the room was deco- rated, and the windows were thus treated, a general light colour pre- vailed, both on the wood-work and on the walls of the room, and cur- tains were hung at the windows in the usual way. With the al- tered decora- tions, the win- dows became so effective that I at once saw the undesirability of re-hanging the curtains, and yet not one of all my friends has observed that there are no curtains to the windows ; while if the curtains are removed from the adjoining room, where the window-frames are as light as the walls, the first question asked is, “ Where are your curtains ? ” _ Curtains should be hung on a simple and obvious pole. All means of hiding this pole are foolish and useless. This pole need not be very thick, and is better formed of wood than of 26 THE TECHNICAL EDUCATOR. metal, for then the rings to which the curtains are attached pass along almost noiselessly. The ends of the pole may be of metal, but I prefer simple balls of wood. The pole may be grooved, and any little enrichments may be introduced into these grooves, providing the carving does not come to the sur- face, and thus touch the rings, which by their motion would injure it. Whatever is used in the way of enrichment should be of a simple character, for the height at which the curtain pole is placed would render very fine work altogether ineffective. As to upholstery, 1 would say, never indulge in an excess. A wood frame should appear in every work of furniture, as in the examples we have given. Sofas are now made as though they were feather beds ; they are so soft that you sink into them, and become uncomfortably warm by merelv resting upon them, and their gouty forms are relieved only by a few inches of wood, which appear as legs. Stuffing should be employed only as a means of rendering a properly constructed seat comfortably soft. If it goes beyond this it is vulgar and objectionable. Spring stuffing is not to be altogether com- mended ; a good old-fashioned hair seat is more desirable, as it will endure when springs have perished. As to the materials with which . seats may be covered I can say little, for they are 'many. Hair cloth, although very desirable, is altogether in- artistic in its effect. Nothing is better than leather for dining- room chairs ; Utrecht velvet, either plain or embossed, looks well on library chairs ; silk and satin damasks, rep, and many other fabrics are appropriate to drawing-room furniture, and upholsterers ® n< l a new three-coloured material, called tj-iU Wlnd30r i brocade,” manufactured by Messrs. Warde of Halifax, useful for such purposes. Chintz I am not fond of as a chair covering, and in a bath-room I would rather have chairs with plain wooden seats. than with cushions covered with tins glazed material. With a mere remark upon picture-frames I have done. Picture-frames are generally elaborately carved mouldings or are simple mouldings covered with putty ornaments, which’ whether carved or formed of putty, are overlaid with gold leal ; they are, indeed, highly ornamented gilt mouldings. I much prefer a well- formed, yet somewhat simple, black, polished moulding on the interior of which runs a gold bead. For prints and water-colours the annexed frame (Fig. 37) is all that can be desired. A fanciful yet good picture-frame was figured m the Building News of September 7tli, 1866, which wc now repeat (Fig. 38). VEGETABLE COMMERCIAL PRODUCTS. XVI. VALUABLE BUILDING AND FURNITURE WOODS ( Continued ). East Indian Ebony ( Balbergia latifolia, L . ; natural order, Leguminosoe). —The real raven-black ebony, one of the heaviest and haidest of all woods, and which in the fineness of its texture resembles ivory is derived from this tree, which is indigenous ^ S an i of T ^ylon, f ad is also found in Java, Sumatra, and the Manilla Islands.. This ebony is used for wind instru- ments and the keys of pianos. The alburnum, or sap-wood of both the mahogany and ebony trees, is white and valueless, and is chipped off with the adze before the logs are shipped. The indurated heart-wood of these trees is the only part of the stem fit for industrial and economic purposes. A great deal of ebony comes into commerce from the Cape of Good Hope, and arrives in England in sticks of about three to six ieet long, and two to four inches thick. h^ B r^ WO n B u- (Bm ' US sem P erviren s, R; natural order, Euphor- We®).— This is an evergreen shrub, a native of Southern and EU1 ’°? e ' Th ° wood 13 dense > compact, and admirably f °Vr d eng 7 aVe f and also for tlie formation of graduated loni and d f ^ - art- 115 1S im P° rted in pieces four feet dlameter from Smyrna, Constantinople, at' NSemW ® Ih ° finS SaW ' dust of this wood is sold nnSl NT. g ^ °i ther Places as P° unce . which dries writing quickly. The annual imports are between 3,000 and 4 000 tons (San i 'fr altm ’ L -Uata»i o,Z,sZ Maceas). This tree, which produces the beautifully perfumed mnch 1 ; W0 l < f 18 a . natl y e of India and China. Sandal- wood is much iued for entomological cabinets, as its fragrance is a pre- servative from insects. In China it is employed as incense and is manufactured into toys. The shavings and saw-dust of sandal-wood are valuable in perfumery. Lignum Vitas (Guiacum officinale, Plum. ; natural order Zygophyllacecz). This is the hardest and heaviest wood known It is of a dark olive colour, and cross-grained, the fibres running obliquely into one another, in a form somewhat resembling the letter X, so that it cannot be split with an axe, and is therefore divided by the saw. The tree is forty feet high, and four or five feet m circumference, with numerous knotted, much divided branches, abruptly pinnate leaves, and bright blue flowers. It grows in tropical America, especially in Jamaica, where it is very abundant, and whence our supplies are chiefly obtained. The timber of this tree is very valuable, where strength and durability are needed and weight is no object. Lignum vitm comes over in billets about three feet in length and a foot in diameter, and is chiefly used for ship-blocks and pulleys. It takes a fine polish, and turns well, and for this reason is used by turners for articles requiring a hard close-grained wood. Bird’s-eye Maple (Acer saccharinum, L. ; natural order Aceracece). This tree is a native of North America, where it grows from Canada to Georgia. In early spring it yields, when tapped, an immense quantity of sugar. The beautiful wood known, as bird’s-eye maple, so much admired in cabinet work is obtained from this species. American Cedar ( Cedrela odorata, L. ; natural order Cedrelacece), a native of the West Indies and Central America’. This tree furnishes the wood used for the boxes in which cigars are packed, and for the inside portions of furniture. Pencil Cedar (Juniperus Bermudiana; natural order, Conifer as). A North American tree, which furnishes the red wood for lead pencils. Lance-wood ( Duguetia Quitarensis, St. Hilary; natural order, Anonacece).— This tree furnishes lance-wood, which is used by coachmakers for the shafts of gigs and other vehicles where both strength and elasticity are required. We receive lance-wood from Cuba and Guiana, whence it comes in the form of poles, fifteen to twenty feet in length and six to seven inches in diameter. Rosewood ( Triptolemcea and Balbergia; natural order, Leguminosce). — Several undetermined species of these genera of trees furnish rosewood. We receive this wood from Brazil, in planks about twelve feet in length, flat on one side and rounded on the other, .each being evidently one-half of the stem, with the bark removed. Violet-wood and king-wood, which come to this country also from the Brazilian forests, are probably only other species of the same plant, as both resemble the rosewoods. They are in much smaller pieces, usually in round sticks four or five feet long and from two to six inches in diameter. The best rosewood comes from Eio de Janeiro, and has recently been ascertained to be chiefly the timber of Balbergia nigra. Rosewood is much used for library and drawing-room furniture, and is so named because, when fresh, it has the odour of a rose! The imports into England in 1863 were 2,120 tons. Black Walnut ( Juglans nigra, L. ; natural order, Juglan- dacea) . This is a large tree, indigenous to North America. Previous to the introduction of mahogany and rosewood, walnut was held in high estimation in the manufacture of costly furni- ture. It is still imported for furniture, although to a less extent than formerly, and is now chiefly employed in the manufacture of the stocks of all kinds of fire-arms. Snakewood (Piratinera Guianensis ; natural order, Avto- carpaceos). This is a very beautiful ornamental wood, of a rich chestnut-brown colour, mottled with cloudy amber-coloured spots, resembling the markings of serpents — a scarce wood, imported from South America in sticks, two or three inches in diameter, and five or six inches in length. When dry, snake- wood readily takes fire if rubbed against wood harder than itself, and is so used for obtaining fire by the native Indians. Satin Wood ( Sivietenia chloroxylon, L. ; natural order, Cedrelaceas) . This is a handsome, hard, yellow veneering wood occasionally imported from. India, the West Indies, and South America, in logs seven or eight inches square and ten feet in ength. It is used by cabinet-makers and upholsterers in inlay- mg work, and for picture-frames. The far greater proportion of our building timber consists of the wood of various coniferous trees, which we import from America, Northern Europe, and Switzerland. The deal used in VEGETABLE COMMERCIAL PRODUCTS. 27 carpentry is the wood of several species of pine and fir. Thus, white deal is furnished by the Norway spruce fir ( Abies excelsa, L.), and yellow deal by the Scotch fir (Pinus sylvestris, L.) ;■ the silver fir ( Abies picea, Link.) furnishes a whitish deal used for flooring. There are numerous others, as the American and European larches ( Larix Americana, Michx., and L. Eu- ropean, L.), and the hemlock spruce fir ( Abies Canadensis, Michx.), which are employed for ship and house building. We can only mention them, and we must now leave this branch of our sub- ject, as we have not space for further selection. The names only of the trees — European, Asiatic, African, American, and Australian — which yield valuable furniture and building mate- rials would form quite an extensive catalogue. V. PLANTS PRODUCING VALUABLE GUMS, RESINS, AND BALSAMS. The substances now to be considered are distinguished as follows : — Resins are the inspissated or thickened juices of plants, and are commonly associated with an essential oil ; they are in- soluble in water, but are dissolved by alcohol and essential oils. Gum Resins or Balsams are partly soluble in water, from the quantity of gum they contain. Gums are soluble in water, but not in alcohol. Balsam Fir ( Abies balsamifera, Michx. ; natural order, Conifer a). — This tree furnishes the Canada balsam so much used in mounting microscopic preparations of objects of natural history, as it not only preserves, but at the same time gives them transparency. This oleo-resinous flui^ is contained in blisters of the bark, which are punctured, and the balsam is then caught as it exudes. It is imported from America. India-rubber, Gum-elastic, or Caoutchouc, is the har- dened milky juice of many euphorbiaceous plants and others. That from the Brazils is the produce of Siphonia elastica (Rich.), a noble tree, growing to a height of sixty feet, with a light, stone- coloured bark. That collected in Central America, and now an important article of export all along the Atlantic seaboard, is obtained from Castilloa elastica. The Brazilian method of obtaining the caoutchouc, or india-rubber, is to spread the milky juice upon clay moulds, and dry it in the sun or in the smoke of a fire, which blackens it. The moulds are in the form of balls, bottles, and shoes. The juice is collected from incisions made in the stem, and is received into a cup of clay placed under the wound. It flows freely, to the extent of about four ounces daily from each tree. This juice is then smeared over the clay moulds in successive layers, which are dried separately, until a sufficient number havo accumulated to give a proper thickness ; the clay is then washed out, and the india-rubber is ready for the market. In Central America the juice is collected from incisions made in the stem, and is received into vessels. A tree four feet in diameter will yield twenty gallons of juice, each gallon pro- ducing two pounds of good dried rubber ; and an industrious man will collect twenty-five gallons a day. The milky juice is strained through a wire sieve, so as to exclude all impurities before it is transferred to barrels, in which the real manufacture of the rubber is performed. The best manner of converting the milk into rubber is by mixing with it the juice of a certain vine, termed by the natives achuca, which has the singular property of producing coagulation within the space of five minutes. About a pint of the infusion of the vine is well mixed with every gallon of the milk. This is done in a large tin pan, and the rubber separates as a soft mass from the brown liquid. This mass is then placed on a board, slightly pressed by hand, and rolled out with a piece of heavy wood. A great quantity of water is thus squeezed out, and the rubber, which has now as- sumed its elasticity, is made into flat round cakes a quarter of an inch thick, twenty inches in diameter, and perfectly white in colour. Hitherto the greater portion of the caoutchouc imported has been received from South America, but latterly a consider- able amount has come from Singapore, Assam, and other places in the East Indies. This is the product of the Ficus elastica, L. (natural order, Urticacece), or the famed banyan tree, so cele- brated for its pillared supports, “ whose daughters grow about the mother tree,” and which has furnished the motto “ Tot rami quot arbor es ” to the Royal Asiatic Society. But this product is nevertheless very inferior to that furnished by the Brazilian india-rubber tree. Caoutchouc is contained in the juices of many tropical trees, and in small quantities in many plants of temperate regions ; it seems to form an essential part of the milky juices which are characteristic of the Euphorbiaceoe, Apocynacece, and Urticacece. In 1864, 71,027 cwt. of caoutchouc were imported into the United Kingdom in the raw state — viz., from South America, 52,097 cwt., valued at =6389,576 ; and from the East Indies, 11,930 cwt., valued at .£113,069. The same year, our exports of caoutchouc to Europe and the United States were 29,107 cwt., valued at <£205,932. The total import for 1867 was 79,756 cwt. Gutta-percha ( Isonandra gutta, Hook. ; natural order, Euphia-biacece) . — This is a magnificent tree, sixty or seventy feet in height and from five to six feet in diameter, growing in the Malayan Archipelago. Gutta-percha is the inspissated juice of this tree, and is procured as follows : — The trees are felled, the bark removed, and the milky juice which is found between the bark and wood is collected and poured into a trough made from the stalk of the plantain-leaf. It quickly coagulates on exposure to the air, and is then kneaded into cakes for expor- tation. Gutta-percha is one of the most valuable vegetable pro- ductions ever discovered. It is in its natural state hard, rough, dry, opaque, tough, inflammable, and slightly soluble. On immersion in hot water it becomes softened and capable of being moulded into any figure, which it retains when cold ; a number of pieces, too, may be united so perfectly as to show no mark whatever of their junction. It is not elastic, but so tough that a thin slip, one-eighth of an inch in substance, will sustain a weight of forty-two pounds. A great variety of articles are made from gutta-percha, and, above all, cables for the convey- ance of the submarine telegraph, which, without this invaluable substance, could not have existed. The demand for gutta-percha is continually increasing, and it is certain that a process too destructive to the trees is adopted in the endeavour to furnish the requisite supply. In 1864 the gutta-percha imported amounted to 36,750 cwt. ; and, at the very lowest estimate, not fewer than 300,000 trees were destroyed to obtain that amount. A short time ago this tree was abundant on the island of Singapore ; now few if any other than small plants are to bo found there, all the largo trees having been felled. The range of its growth appears, however, to be considerable, as it doubtless extends over all the islands of the Malayan Archipelago. Tar (Pinus sylvestris, L. ; natural order, Coniferce). — Tar is an impure turpentine, viscid, and brown-black in colour, pro- cured by destructive distillation from the roots of various coni- ferous trees, particularly the above species. This process was known to the ancients, being described by Theophrastus, and is nearly the same now as in his time. A bank is chosen near a marsh or bog, as the roots of pines so situated always yield the greatest supplies of tar ; in this bank a conical cavity is formed, the sides of which are beaten down and rendered as firm as possible with heavy wooden mallets. A cast-iron pan is placed at the bottom of the hole or funnel, with a spout which projects through the side of the bank, and barrels are placed beneath this spout to collect the tar as it comes away. This cavity is then filled with the roots of the pine, which are cut and neatly packed so as to fill up the entire space, and the whole is covered over with turf and beaten down with the mallet or stamper. The roots in the inside of the cavity are then set on fire, and the tar, as it distils, runs down the sides into the iron pan, passing through the spout into the barrels, which, as fast as filled, are bunged, and are then ready for exportation. Tar is used chiefly by seamen, for preserving cordage and wood from the effects of the atmosphere. Nearly all our tar comes from Russia, Norway, and Sweden ; the United States, also, supply us with a considerable amount ; the forests between Bayonne and Bordeaux in France, the Black Forest, and the forest of Thuringia, in Germany, send large quantities into com- merce. In 1851, 24,000 tons were received into this country. Pitch is tar condensed or deprived of the more volatile parts by distillation. The tar is boiled in an open iron pot until all the volatile matters are driven off ; the residuum remaining is pitch. This is a black, solid, and glossy substance, very brittle when cold, but softening and becoming ductile when heated. That used in this country is mostly home manufactured. Pitch is frequently mixed with tar, and used for similar purposes, in ship-building, for caulking the seams of vessels, etc. 28 THE TECHNICAL EDUCATOR. PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING.— VII cycloid ( continued ). epicycloid, and hypocycloid curves are the exact curves forming the teeth of THE cycloid, drawing The involute, much used in wheels work- ing in racks or in gear with each other; and these will therefore be more fully worked out in the lessons on “Technical Drawing. ” The cycloid was invented by Galileo, an A. eminent ma- thematician and natural philosopher. He was born at Pisa in 1564, and died in 1642. To describe the cycloid. Draw the director A b, (Fig. 63), the generating circle C, and a line through the centre, called the line of centres, de, parallel to a b. Draw the diameter vi 6, and divide each half of the circle into any number of equal parts — viz., la, 2a, etc. On each side of point vi, set off the lengths va, iva, nia, etc., and v6, i v6, mb, etc., 1 equal in size and number to the divisions in the circle. From o, ia, na, ma, etc., erect perpendi- culars, cutting the line D E in i, ii, hi, etc. From each of these points describe circles equal to the ge- nerating cir- cles. From va set off on the circle of which v is the centre the length of the line vi 5a — viz., 56. Mark off the same length on the corresponding circle, from v6. From iva set off on the circle drawn from centre iv the length of the line vi 4a, and do the same on the correspond- ing circle from iv6. Proceed thus, setting off the lengths of the lines vi 3, 2, and 1, on the circles resting on the points numbered correspond- E F Pig. 66. B' G ingly (in Roman figures), and through the points marked on the various circles — viz., 16, 26, 36, etc. — rdraw the curve. THE EPICYCLOID AND HYPOCYCLOID. When a circle, instead of rolling along a straight line, rolls around the edge of another circle, any point in it will describe the curve known as the epi- cycloid (Fig. 64). To describe the epicycloid „ Draw the di- recting circle b c, and the generating circle d. From A, with radius A d, de- scribe the circle of cen- tres E F. Divide the generating circle into any number of equal parts, la, 2a, etc., and set off these lengths from vi on the directing circle c b — viz., the points marked i, ii, in, etc., in the larger Roman figures. From A draw lines through i, ii, hi, etc., cutting the circle e f in i, ii, iii, etc. (smaller Ro- man figures). From each of these points, as centres, de- scribe circles similar to the generating circle. From points v, iv, iii, ii, i, set off on the circles resting on them the lengths vi 5a, 4a, etc. ; and through the points thus ob- tained — viz., 16, 26, 36, etc. — the epicy- cloid is to be drawn. When the generating cir- cle rolls inside instead of out- side the direct- ing circle, the curve traced is the hypocycloid (Fig. 64). It is constructed in precisely the same manner as the epicy- cloid, excepting that the lengths VI 5a, etc., are set off from v, iv, iii, etc., inside instead of outside the directing circle ; and the points 5c, 4c, 3c, etc., are thus obtained. If the diameter of the generating circle were equal to the radius of the directing circle — that is, if vi 6 extended to A — 'a PRACTICAL GEOMETRY APPLIED TO LINEAR DRAWING, 29 point in the generating circle, instead of generating a curve, would trace a straight line. To construct a square equal in area to a given quadrilateral figure, a b c d (Pig. 65). Draw the diagonal A c, and bisect it by a perpendicular. From B and D draw lines parallel to A C, and cutting the perpendicular in e and f. Draw a line bisecting e f in o, and from A draw a line parallel to E F, and cutting this bisecting line in G. Find a mean proportional between o e and o G — viz., o h. Set off the length o H (the semi-diagonal) from o on e f and o g — viz., i, J, k. Join hijk, and the square will be equal to the quadrilateral figure A b c d. To construct a square which shall he equal in area to two other squares added together (Fig. 66). Place the two squares so that a side of the one, as A b, shall be at right angles to one side of the other, as B E. Draw the line A e. Now, according to Euclid (I. 47), * “ In any right-angled tri- angle, the square which is described upon the side subtending the right angle, is equal to the squares described upon the sides which contain the right angle.” And it will be seen that abe is a right-angled triangle, and that the squares abcd and befg are described upon the sides of it which contain the right angle ; and therefore the square aehi, which is described on (the hypothenuse) A E, which subtends the right angle, is equal to the sum of the two other squares. To construct a square equal in area to any member of squares added together (Fig. 67). This is done by merely carrying on the process shown in the last figure. Let it be required to construct a square, which shall be equal to the areas of the three squares of which A, B, and c are the respective sides. Place b at right angles to A, then the hypothenuse D would be the side of the square equal in area to the squares constructed on A and B. Place C at right angles to D, draw e f, and construct a square upon it ; then E F H G is equal to the. squares constructed on C and D, and * This preposition is said to have been discovered by Pythagoras, a disciple of Thales, who, after travelling in India and Egypt in pursuit of knowledge, settled in Tarentum, in Italy,' where he founded the celebrated Pythagorean school, 550 years b.c. therefore equal to the squares constructed on all three lines. Any number of squares may be thus added together. To divide a given triangle, a b c, into two equal parts by Oj line parallel to one of its sides (Fig. 68). Bisect one of the sides, as c B, in the point d, and erect the perpendicular D E equal to D c. From C, with radius c E, de- scribe an arc cutting c d in f. From f, draw F G parallel to A B, which will divide the triangle into two parts of equal area. To divide a triangle into two equal parts by a line perpendi- cular to one side (Fig. 68). From c, draw c h perpendicular to A B. Bisect A B in i. Find a mean proportional between B H and b i — viz., B j. From b, set off B K equal to b j, and the perpendicular K L will divide the triangle as required. To divide the space contained between the lines A b and c d into equal parts, by means of lines parallel to A B (Fig. 69). Draw the line E F perpendicular to A B, and set off on it equal lengths corresponding to the number of spaces into which A b c D is to be divided — viz., 1 to 8. These spaces may bo any size, but must be equal. From e, with radius E 8, describe an arc cutting c D in G. Draw E G. From E, with radius E 7, E 6, E 5, etc., describe arcs cutting E G in H, I, J, K, L, M, N. Draw lines parallel to A b through these points, and the space will be divided as required. To draw a circle of a given radius, which shadl touch another given circle and a straight line (Fig. 70). Let A be the given circle, B c the straight line, and d e the radius of the required circle. The question here is, to find a point which shall be the centre of a circle of a given radius, which shall touch the given circle and straight line. From O, the centre of the given circle, draw a radius and produce it. From the periphery of the circle, and on this radius, set oft F g, equal to D e. From o, with radius o G, describe an arc. At any point, as H, in B C, draw a perpendicular, H I, equal to D E. From I draw a line parallel to B c, cutting the arc drawn from o in J. From j, with the required radius, describe a circle, which (if the work has been accurately done) will touch the given circle and straight line. 30 THE TECHNICAL EDUCATOR. PRACTICAL PERSPECTIVE.— VI. Fig. 28 is a perspective view of a strong 1 table or bench, tbe edge of the top of which is “ flush ” with the legs and surrounding rail. Having drawn the picture line and horizontal line, and having fixed the centre of the picture and point of distance, place the point b (the nearest angle of the table) at the required distance on the left or right of the spectator. From b set off b c', equal to the complete length of the table, and from b and c' draw lines to the centre of the picture. On the other side of b set off b d, the width of the end of the table, and from d draw a line to the point of distance (not shown in this figure), cutting b c in d'. From d' draw a horizontal line, cutting c' c in e. The figure c' e d' b will then be the perspective view of the area covered by the table. From B and C' mark off on the picture line b g and c' F equal to the thickness of the legs, and from G and F draw lines to the centre of the picture, cutting d' e in g' and f'. Now on the other side mark off b H equal to b g, and from D set off the same width — viz., D J. From h and j draw lines to the point of distance, cutting b d' in h' and J'. From h' draw a horizontal line, cutting g g' in g", and cut- rise from k, but in the present study this is hidden by the leg G b. The student is, however, recommended, when he has worked the present study, and understands the principles laid down, to change the position, for it will be evident that if the object were placed farther left, the point K would become visible. For the fourth leg, the upper part of which is hidden by the top of the table, draw perpendiculars from the points h, l, f', and these will complete the object. The whole of the lines constituting the figure should now be thickened or inked. Fig. 29. — This study is merely another view of the last sub- ject, in which the end b o p d is parallel to the picture-plane. The working of this will be carried on in precisely the same manner as the last, with this exception, that in starting, the points B, h, J, d are marked on the picture-line, and lines drawn from them to the centre of the picture. Then the points G, F, c' are marked, and lines drawn to the points of distance, all' of which is the reverse of what was done in the last figure j and thus it will be seen that the figure bd(/i represents the plan of the table with its narrow end towards the spectator, whilst the long side is seen receding from the plane of the picture. The lines and points are lettered to correspond with those in the last view, so that the change of position may be clearly traced. It is not necessary to repeat the working. ting f f in i and c' E in c n . From j' draw a horizontal line, cutting a g' in K, and f f' in l and o' E in h. It will then be seen that at the corners of the original area the plans of the four feet are delineated — viz., c'fi c", gbh' a", m L f' e, k J d' g', and a complete ground-plan of the table is thus put into perspective. Now proceed with projecting the table itself, in the following manner : — At c' and B erect perpendiculars, make these the required height of the surface of the table, and draw the horizontal N o. From N and O draw lines to the centre of the picture. Draw a perpendicular at d', meeting o c in p. Draw the horizontal p Q, which will complete the block of the table. Draw the horizontal r for the lower edge of the plate of the table, and from the point where it meets the perpendicular B o draw a line to the centre. Now draw the perpendiculars F, g, A, and j', and the hori- zontal s, between f and g, for the framing of the table. This framing is mortised into the legs, and therefore the line must not be drawn across the lines f and g, which represent the edges of the legs ; but as it is necessary to find the correct position ot this framing on the perspective side, produce s lightly to the angle t. and from T draw a line to the centre of the picture.. Strengthen this line only between the points Uand v. Strengthen that portion of the horizontal j' k which lies between .r' asd the perpendicular h'. It will be easy to under- stand that the inner edge of the distant leg of the table would Exercise 14. Scale, J inch to the foot. Height of the spectator, 6 feet: distance. 18 feet. Put into perspective a cross made of stone 1 J foot square — total length of the upright, 12 feet ; length of the arm, 7J feet. The arm crosses the upright at 71 feet from the bottom of the upright. Draw a plain elevation of this cross, and then project a perspective view when lying on the ground, at 3 feet on the left of the spectator, in such a manner that the end of the arm is parallel to the picture- plane, and is in the immediate foreground. Exercise 15. Put into perspective the same cross when lying on the ground, so that the lower end of the upright is parallel to the x>icture-plane and 6 feet within the picture; all other measurements at pleasure. By this term — frequently used in examination papers — is meant that the student may fix his own dimensions, so long as he shows that he under- stands the working out of the principle. Exercise 16. Scale, height, and distance of spectator at pleasure. There are two blocks of stone, 2 feet square at their base, and 8 feet high. They stand 4 feet apart, and across the top of them rests a block, 8 feet long and 2 feet square at its ends — tbe faces of all three blocks being in one plane, that is, if a flat surface were plaocd against them, every part of the faces of all three blocks would toiteh it. Put into perspective this object, when the plane of it3 face is parallel to the picture-plane, and when it stands at 8 feet on the left of the spectator and 10 feet within the picture. PRACTICAL PERSPECTIVE. 31 Exercise 17. Put into perspective the same object when standing so that its face is at right angles to the picture-plane, at 9 feet on the right of the spectator, and 6 feet within the picture. Exercise 18. The height of the spectator is 6 feet, his distance 18 feet, the scale being 1 inch to the foot. Put into perspective the table which forms the subject of Pigs. 28 e, it will be clear that the apex of the pyramid will be some- where on the perpendicular raised on e. But this perpendicular lies within the picture, and therefore the true height of the pyramid will be somewhat diminished? therefore, draw a line from the centre of the picture, through e, and meeting the picture-line in F. F is therefore e brought to the foreground, and a perpen« dicular raised in F will represent the perpendicular e when it C and 29 when standing at 4 feet on the right of the spectator and 6 feet within the picture — the long side of the object to be parallel to the picture-plane. The dimensions of the table may be at pleasure. Exercise 19. Put into perspective the same object when its end is parallel to the picture-plane — at 7 feet on the left of the spectator, and 5 feet within the picture. The object of the next study is to teach the method of making perspective projections of pyramids. Fig. 30. — Let the length of the side of the base be repre- eented by AB; then, as has already been shown, the perspective view of the plan will be the figures a b c'' d. Now if the diagonals A c" and B D be drawn, intersecting in has travelled in a track at right angles to the picture until it reaches the picture-line ; and now these two lines are said to be in one plane, because if a wall extended from f to the centre of the picture, both these perpendiculars would be portions of the surface of such wall or plane ; and thus a line drawn on the plane from any point in the perpendicular F, parallel to the base-line of the plane, would pass through the perpendicular E. Now the plane supposed to stand on f C is at right angles to the picture ; and therefore F is drawn to the centre of the picture, and a line drawn from any part of the perpendicular F parallel to the ground-line must also vanish in the centre of the picture. Therefore, mark on the perpendicular f the real height of 32 THE TECHNICAL EDUCATOR. the pyramid — viz., F g. From G draw a line to the centre of the picture, cutting the perpendicular e in h, which is the perspective position of the apex. From A, b, c", and d draw lines to h, which will complete the figure. Fig. 31 shows the perspective projection of a pyramid when higher than the level of the spectator. Here the length of the side of the base is A B, and from A and B lines are drawn to the centre of the picture. Then from b a line drawn to the point of distance gives 1), the distant angle, and the horizontal D I completes the view from below of the base of the pyramid. In this there will thus already be one diagonal — viz., b d : draw the second, A x, intersecting b d in e, and at E erect a perpendi- ' K cular. From the centre of the picture draw a line through e, meeting A B in f . At F draw a perpendicular, and on it mark the real altitude of the pyramid — viz., F g. From G draw a line to the centre of the picture, cutting the perpendicular E in H. Then H is the position of the apex. Draw lines from A, B, I, and D to H, which will complete the projection. Exercise 20. The height of the spectator is C feet, and his distance 15 feet. Scale, | inch to the foot. Put into perspective a pyramid, the base of which is 6 feet square, and the altitude of which is 8 feet. The pyramid stands at 5 feet on the right of the spectator. Exercise 21. Put into perspective the same pyramid when standing at 4 feet on the right of the spectator, and at 8 feet within the picture. Exercise 22. The same picture and the same horizontal line, etc., to be used. Put into perspective a block, 9 feet high, and 4 feet square at base, with a pyramid 5 feet high resting on it, its edges corresponding with those of the upper end of the block. The object is to stand 5 feet on the left of the spectator. Fig. 33. Fig. 33. — In this figure the ob- ject represented is a structure con- sisting of four square piers sup- porting a pyramidical roof. It will at once be seen that this is a further development of the Fig. 32 will, it is believed, require scarcely any explanation. It represents merely a cubical figure placed on the right of the spectator, and on this rests a square pyramid. Having drawn the block, and rendered it as if transparent, draw diagonals either in the upper surface of the base, or in the under surface of the top, and through the intersection of the diagonals in either the one, the other, or both, draw a perpen- dicular. From the centre of the picture draw a line through the inter- section of the diagonals, cutting the picture-line, or the upper edge of the cubical figure. On this point raise a perpendicular, and set off on it the real height of the pyramid above the block on which it stands. From the point thus marked draw a line to the centre of the picture, which, cutting the perpendicular rising from the inter- section of the diagonals, will give the perspective height of the pyramid. I subject of the last study, the block being, as it were, hewn ! away, leaving only the piers standing at the angles. The position, height, and distance of the spectator having been fixed, mark the position and width of the base, and put the whole ground-plan into perspective, as already shown in the study in Fig. 28. On this plan erect the piers ; and the line carried round, uniting the outer edges of the tops of the piers, will form the base of the pyramid. Draw diagonals in the base, and at their intersection erect a perpendicular. From the centre of the picture draw a line passing through the intersection of the diagonals, and meeting the edge of the base of the pyramid. At this point draw a per- pendicular equal to the altitude of the pyramid, and from its extremity draw a line to the centre of the picture, cutting the distant perpendicular in a point, which will be the apex of the pyramid. To this point draw lines from the angles, and these | will complete the projection. MINING AND QUARRYING. 33 MINING AND QUARRYING. - By George Gladstone, F.C.S. COAL. -II. IMPORTANCE OF COAL — ANNUAL CONSUMPTION — EXTENT OF SUPPLY — GEOGRAPHICAL DISTRIBUTION. Coal is so essential in all mining and metallurgical processes, that it fitly takes the first place in the present series of articles. Fuel of one sort or another is of course to be found in every country under heaven ; but fuel of a sufficient heating power, and at a comparatively reasonable price, is one of the most important elements in the prosperity of a nation. Great Britain is singularly blest in this respect. The sup- plies are large. Some people may, perhaps, be disposed to think that this is not altogether an unmixed good ; for (whether fortunately or not to succeeding generations) the extent of the supply, and the convenient situation of many of the coal-fields to ports of shipment, naturally encourage exportation on a large scale to foreign parts. Both the home consumption and the export have indeed increased of late years with such rapid strides, that alarmists have been raising the cry of the early exhaustion of our coal-fields. This led to serious inquiry into the matter, and very different opinions were arrived at by those best qualified to judge. One geologist, writing in 1861, estimated the total available supply of the British coal-fields at 79,843,000,000 tons, which at the rate of consumption of 1859— viz., 72,000,000 tons — -would make it last 1,100 years. But the writer did not shut his eyes to the fact that the annual consumption was increasing at a A very complete and careful series of observations on the increase of temperature was made years ago at Dunkinfield Colliery (Cheshire), which favours the supporters of the lower level, as it was then found that the rate of increase was only equal to 1° Fahrenheit for every 84 feet from surface. The temperature at the great depth of 2,055 feet was only 75'5° F. It may be that some local circumstance favours the miner in this particular colliery; for it is not altogether borne out by similar investigations in other collieries, though they seem to indicate that the rate of progression in coal mines is scarcely so rapid as in others. At Wigan a temperature of 80° was re- corded at a depth of 1,800 feet, and at Monkwearmouth a similar rate of augmentation has been registered — viz., 1° F. to every 60 feet. It is not unreasonable to suppose that consider- able differences in temperature may be due to the nature of the rocks through which the shaft passes, so that it may hardly be right to compare a colliery in this respect with a Cornish tin mine; and for our present purpose we may fairly take 1° in 60 feet as our datum. 2. The thickness of workable coal in any coal-field is also, to some extent, a matter of opinion. It would be a simple affair if the coal were all in one seam, but that is not the order of Nature. In some coal-fields there are twenty seams or more ; it rarely happens that there are less than four or five. There is no regular rule that can be laid down as to the limit in respect of thickness at which a seam of coal ceases to be work- able. In some parts of the country much thinner seams are worked than at others ; and there can be no doubt that an important increase in the value of coal would lead to the work- Fig. 5. LOWER LEVELS OF THE BAREMOOR COLLIERY, SOUTH STAFFORDSHIRE. Scale, 1 inch = 1 7 6 feet. 1> the two-foot coal ; 2, the Broach coal ; 3, the Herring- coal ; 4, the Broach binds ironstones ; 5 , the thick coal ; 6, the Grains and Galibin ironstone ; 7, the first Heathen coal ; 8, black batt and fire-clay ; 9, the second Heathen coal ; 10, cake and white ironstones. rapid ratio, and he accordingly allowed in his calculations for an annual increase of 1,500,000 tons. The effect of this allowance was to reduce the 1,100 down to only 325 years ! The increase of 1,500,000 per annum was based upon the statistics of the previous five years ; but in 1867 the produc- tion was no less than 104,500,000 tons, representing an in- crease between 1859 and the latter date of no less than 4,500,000 tons per annum. In the face of such astounding facts as these, it seems almost futile to attempt an estimate of the probable duration of our coal-fields. One thing is certain, that every right-minded person must hail with gratitude every invention of modern science which tends to economise the con- sumption of fuel. The elements that have to be considered in the calculation of the. available supply are rather numerous. 1. The depth to which workings can be carried. 2. The thickness of workable coal in the various coal-fields. 3. Their area. 4. The extent to which they are already exhausted. 5. The probability of extending their area, or of opening up new fields. 1. In the previous paper it has been shown that in conse- quence of the natural increase of temperature a mine will be suffi- ciently hot. (viz. 80°) at a depth of 1,750 feet. But in order to got an available supply of 79,000,000,000 tons, it is calculated that coal-mining will have to be carried to a depth of 4,000 feet. This, of course, would be impossible without artificial con- trivances ; but, however shallow a coal mine may be, the venti- lation must be attended to for the purpose of carrying off the dangerous gases. The means of ventilation are therefore well understood by miners, and its effect in cooling the air of mines is well known ; so that with such improvements as may be made in the. course of years, we may fairly take 4,000 feet as a reasonable limit. Some persons anticipate the possibility of going down 5,000 feet, but the former figure will be adopted here. 29— Yol. II. ing of many thin seams which are now altogether neglected. Those only two feet thick have been worked before now in some districts, and probably the time will come when all such seams will be made use of, though on economical grounds that will not take place until the thicker seams are well nigh exhausted. Some seams, moreover, are very liable to change in this respect, so that the thickness observed in one working is no criterion for others even in the same neighbourhood. In Fig. 5, which repre- sents the lower levels of the Baremoor Colliery, in the South Staffordshire coal-field, an illustration is afforded of the great changes which occur in what is known there as the “ thick coal.” In the old pit marked A, the seam is 31 feet thick ; at the new one, b, only 9 feet ; while at the other end of the diagram, c, it is seen to be still thicker than at a. This cannot but be regarded as an extreme instance, for it is the thickest known seam in the British isles ; but it is no uncommon thing for one that is well worth working in one pit, to thin off so much as to be of no commercial value whatever in a neighbouring colliery. Until, therefore, every seam has been thoroughly explored throughout all the coal-fields of Britain, this element of uncer- tainty must attach to all calculations. 3. The area of the coal-fields may be taken at about 4,500 square miles ; but in many places coal is now worked beyond these limits, being overlaid by more recent strata; and if a depth of 4,000 feet be realised in practice, 1,000 square miles will probably have to be added to the previous figure. 4. The operations at some of the coal-fields are yet almost in their infancy, while others have seen their best days. For- merly the workings were carried on with less system and more wastefully than now, and some of those in the iron districts, such as the neighbourhood of Birmingham and Coalbrook Dale, have suffered very considerable exhaustion. Even in these there is still a large quantity of coal which can be saved by 34 THE TECHNICAL EDUCATOR. judicious working. It will be evident, however, that in forming any estimate of the quantities remaining, each coal-field must bo separately considered. 5. As to the probability of extending their area, and of opening up new fields, a considerable difference of opinion exists. This point can only be determined by actual borings. It has been found within the last few years that the superior strata in some parts of the midland counties are not so thick as had been supposed, and that the Carboniferous rocks are within a practicable depth, Nor is there any substantial reason why the workings should not be carried some little distance under the sea. Adopting, then, the data furnished by the Geological Survey, and taking only those seams which are 2 feet thick and upwards, and which do not exceed 4,000 feet in depth, Mr. Hull arrived at the calculation that 79,843,000,000 tons of coal still remained available. Since he made his estimate, however, the odd 843.000. 000 have been consumed. The various coal-fields lie in patches extending from Glouces- tershire and South Wales up to the extreme north of England ; and in Scotland on both sides of the Forth and Clyde, and in Ayrshire. In Ireland there is a wide extent of Carboniferous rocks, but the beds of coal are very uncertain, and are only worked to a very small extent. The South Wales coal-field covers an area of about 900 square miles, and the quantity of produce may be taken at about 16.000. 000.000 tons. Its commercial value is considerably en- hanced by its geographical position, having the Bristol Channel for its southern boundary, and by the fact of the coal seams being interstratified with bands of ironstone. The facilities for shipment of the coal at Swansea, Cardiff, Newport, and other ports, have led to a very large export trade ; and the presence of iron ores in such abundance has created an immense demand for coal in the smelting and puddling works, and rolling mills. A peculiar feature of this coal-field is that the character of the coal materially alters as you proceed downwards, and from east to west. The seams at the eastern extremity are more or less bituminous, the upper being more so than the lower ; in the middle of the coal-field they are semi-bituminous and anthracitic (the latter lowermost) ; and in the extreme west there is none but anthracite. The Yorkshire and Derbyshire coal-field, extending con- tinuously from Leeds through Sheffield, and nearly to Derby, is, including the coal-ground overlaid by more recent forma- tions, more extensive than the preceding, and will yield at least as much coal. The produce of this great inland district is almost entirely consumed at home. In this region some very excellent iron ores are obtained, from which the best iron in the kingdom is made. The coal underlying the Permian and Triassic rocks on the eastern side of this coal-field has been worked as yet to only a very small extent. The Newcastle field supplied London almost exclusively before the time of railways, "the coal since brought to London by rail being principally raised in the midland counties. A very large quantity is exported to foreign parts, owing to the facilities of shipment at Newcastle, Sunderland, Hartlepool, and other ports. Both in area and in produce this is decidedly less than either of the two preceding, though about the double of any of the rest in England and Wales. It contains several valuable seams, each having its special advantages. One produces a strong semi-bituminous coal, very suitable for furnaces ; another, the best quality of household coal ; a third, a good gas coal, yielding also a very excellent coke. There is still some 7,000,000,000 tons of coal available in this district, though it has been worked for a very long period. It is traversed by a great whin dyke, which crosses the country in an east and west direction, on a line with the Tyne valley, by which the strata on the south side of the dyke are thrown down no less than 540 feet; the eastern end of this dyke may be seen to advantage at Tynemouth, where it juts out into the sea immediately on the north side of the harbour. Contrary to the rule which prevails so generally in other parts of the country, there is but little ironstone to be obtained in this coal-field. The South Lancashire is the next in respect to size, and con- tains a very great thickness of workable coal ; but it is troubled with numerous faults on a large scale. At Wigan, the cannel, which is very valuable for gas works, is three feet thick ; but it gradually thins off in every direction from that point. The South Staffordshire has already been mentioned as illus- trative of the irregularity in the thickness of some seams. What goes by the name of the thick, or ten-yard coal, is, in fact, about a dozen different seams all united together. It generally runs about 30 feet thick ; but at Foxyard’s Colliery, near Dudley, it measures 39^ feet, including six thin partings of shale, the solid coal being equal to 36A feet. At this spot, owing to con- siderable upheavings of the strata, the coal crops out at the surface, and for about 100 yards in length it is worked as an open quarry, with a face of 40 feet in height. It is the only instance in this country of an open coal-working upon such a scale. This is in the centre of the “Black Country,” properly so called, a district almost wholly given up to the coal and iron trades. The consumption of coal at the iron works is now so great that, notwithstanding such a seam as this, the process of exhaustion is going on very rapidly, and there is scarcely 1.000. 000.000 tons now left available in this field. There is one seam here which bears the inelegant but appropriate name of “stinking coal;” it is altogether neglected, as it contains so much sulphur that the fumes from it, if used for domestic pur- poses, would be intolerable, and it is absolutely useless for making iron, a very small admixture of sulphur being most injurious to this metal. The less important coal-fields do not require separate notice. They are the North Staffordshire, the Bristol, the Forest of Dean, the Denbighshire, the Flintshire (which contains some very good cannel coal), and a few others. The Scotch are important in more respects than one. The Clyde and Ayrshire fields actually join at some points, and they are one in their principal features. They furnish a strong slow-burning “splint” coal, which is associated with the cele- brated black band ironstones, the splint being very suitable for the operations of the smelter. The notorious Boghead cannel also occurs in limited portions of this field ; it is the best cannel in the whole kingdom, and is highly valued, though the seam only averages about R feet thick. The Leshmahago coal basin lies a little further to the south. It is of limited area, but is likewise rich in cannel of very ex- cellent quality. The total area of the Scotch coal-fields exceeds 1,700 square miles, and the available produce may be estimated at about 25.000. 000.000 tons. In Ireland Carboniferous rocks occur ; but the coal is of no great value, and it is only worked to a small extent. The available quantity is too doubtful to justify its being included in the general total. At Kilkenny anthracite is the staple article. SEATS OF INDUSTRY.— IX. BY WILLIAM WATT WEBSTER. MULHAUSEN. Few manufacturing towns on the Continent of Europe have acquired a wider celebrity, or are better entitled to a place in a series of papers devoted to the description of the chief representative seats of industry, than the enterprising little town of Miilhausen, or Mulhouse, which was recently trans- ferred from France to Germany, along with the province of Alsace and the German-speaking portion of Lorraine.. For many years Miilhausen has taken rank as one of the principal centres of cotton manufacture in France, and its name has been associated with a variety of schemes for the amelioration of the condition of the working classes. Miilhausen is situated in a fertile and well-watered district about sixty-one miles S.S. W. of Strasburg, and twenty-seven miles south of Colmar. It is divided into two parts, called old and new Miilhausen. The old town is built on an irregular oval-shaped island formed by the river 111, which at this .point separates into several branches, and is crossed by four bridges. The houses are substantial, and the streets are well paved and cleanly kept, although winding and rather narrow. Among the principal buildings in old Miilhausen may be mentioned the Reformed and Roman Catholic Churches, the Hotel de Ville, and the College. The new town lies to the south-east of the old town, and extends from the right bank of the 111 to . the Rhone and Rhine canal, which here expands into a spacious basin. It is laid out in wide, regular streets, lined with a superior class of houses. Miilhausen is an important station SEATS OF INDUSTRY. on the Strasburg and Basle Railway. The list of the institu- tions established in the new town includes a Tribunal of Com- merce, a Consulting Chamber of Manufactures, a Conseil de Prud’hommes, an Industrial Society, and a Commercial College. In 1855 the population of Mulhausen numbered 28,715, and it is now estimated at about 45,000, the last census having shown that it (Contained 43,244 inhabitants. Lambert, the celebrated mathematician, was born in Mulhausen, and in the centre of one of the squares of the town which bears his name, a large column has been erected to his memory. The leading facts in what may be called the political history of the town, so far as they have been handed down to us, may be told in a few words. Mulhausen is said to have been known to the Romans under the name Ariabinvm ; but our knowledge of the pdace at that remote period is confined to the mere name, and long centuries subsequently elapsed of which we have no record. It is, however, certain that Mulhausen was a consider- able town in the thirteenth century, for it was erected into a free and imperial city by Rudolph of Hapsburg in 1273. The next event in the history of Mulhausen that merits notice was the adoption of the Reformed faith by the authorities and inhabitants of the town in the year 1523. For several centuries previous to 1798, Mulhausen was the capital of a small republic belonging to the Swiss Confederation ; but in that year it with- drew from the Federation, and, renouncing its independence, became incorporated with France, and its connection with that country continued up to 1871. The manufactures of Mulhausen were of little importance till after the middle of the last century and the introduction of I cotton-printing and muslin fabrics, which took place about the year 1745. Prior to that date the manufacture of woollen goods was almost the only industry of the place. But the pro- gress of cotton manufactures in the town was very rapid, and the cotton-prints and muslins of Mulhausen soon became noted for the pre-eminent excellence and unrivalled variety of their colours and patterns. In these respects the productions of the looms of Mulhausen challenge comparison even with the silk goods of Lyons ; and not a little of the prosperity which this town has so long enjoyed must be ascribed to the artistic merits of its fabrics. In the numerous mills and factories established at Mulhausen and its neighbourhood, there are, however, a variety of goods manufactured besides those we have mentioned. The silks woven there, and especially the flowered silks, are held in the highest estimation. A very superior quality of woollen and fine cambric goods is also manufactured in large quantities, and there are very extensive mills for the production of cotton and woollen stockings. Mulhausen has besides a reputation for damask and other linens, carpets, straw hats, stained paper, starch, parchment, chemical products, and the common qualities of leather, as well as morocco. Large iron- works have long been in operation in the town and vicinity, and locomotives and other descriptions of steam-engines are constructed in great numbers. The tanneries, bleach-fields, and dye - works of Mulhausen are very extensive, and its breweries and distilleries are held in high repute. There is a brisk trade carried on at Mulhausen, not only in the multi- farious articles manufactured in the district, but also in raw cotton, wine, brandy, corn, and other agricultural products. The cotton manufactures of Mulhausen were very injuriously affected by tho American Civil War of 1861-5, and it is to be feared that they have sustained another severe stroke by the events that have taken place in France since the 3rd of August, 1870. Before the Franco-Prussian war, however, the activity of the spinning-mills at this town had sensibly declined. The manufacturers of Mulhausen labour under the disadvantage of having to import their cotton by way of Havre or Marseilles, and the development of manufacturing enterprise in towns nearer the sea-board will doubtless tend to check, and may even eventually destroy, a large portion of the manufactures of the place. There are as yet few symptoms of decline. The manufacturers of Mulhausen have branch establishments in several parts of the Haut-Rhin and in the neighbouring depart- ments, and till quite recently at least the amount of goods manufactured and exported was on the increase. A consider- able proportion of the capital invested in manufacturing enter- prise in Alsace is derived from Switzerland, and it is said that many of the mills and factories are heavily mortgaged to resi- dents in Basle. 35 The work-people of Miilhausen did not always possess the many privileges they at present enjoy. About forty years ago the Socidte Industrielle, a body distinguished for its intelligence and patriotism, such as few manufacturing towns could hoast of, drew up the following account of the state of the operatives in Alsace : — “ They are allowed a quarter of an hour for break- fast and an hour for dinner, working for the most part from five o’clock in the morning till eight o’clock at night. Each family sleeps together in one room, which is either a cellar or a garret of the smallest dimensions. Their furniture i? wretched, often only a miserable shake-down bed to accommo date all the family. They are very ill-clothed, often need the aid of the Societe de bienfaisance, and are very dirty, especially in the spinning-mills. In the workshops obscene language and stories are often to be heard, which the children pick up with wonderful avidity, and repeat with a revolting zest.” The next two sentences of the Societe’s report need not be trans* lated. “ Beaucoup des ouvriers,” it continues, “ vivent eis concubinage. Ils appellent ces sortes d’unions manages d lot, Parisienne, et en ont fait un verb allemand parisiren.” In 1835 Mr. Andrew Ure, the author of the “ Philosophy of Cotton Manufacture,” visited Alsace while on a tour through the cotton factories of France and Belgium, and has left us an accoimt of his observations and reflections, from which we shall make a few extracts. “ Great misapprehensions,” he remarked, “ prevail concerning the physical and moral condition of the factory operatives abroad, especially in the fertile region of Alsace. They have been represented as being mostly Pro- testants, and in very comfortable circumstances. There can be no greater mistake. Among the multitude of factory pro- prietors in Alsace there is only one Protestant. The working classes are devotees of the Romish communion.” A little- further on in the same work occurs the following passage on the condition of the Mulhausen operatives : — “ If Sunday be a day of rest and tranquil pleasure to those who work in a moderate manner through the week, it is, on the contrary, a day of debauchery and orgies to those who, having been kept at labour beyond all reasonable bounds, take that occasion to riot in their liberty. Hence it is not uncommon here to see drunkards of from twelve to fifteen years of age. Their degree^ of instruction is very slender. All their physical, and in conse- quence all their intellectual, faculties are exhausted by toil. „ . Certain enlightened proprietors have established, at tliGir own expense, schools within their mills at Mulhausen, and especially M. Naegely. The cruel conduct of parents in sending their children at an almost infantine age to the factory, seldom fails to entail fearful retribution; for whenever the children discover the mercenary bargains of which they have been made the victims, they take The first opportunity of renouncing their filial engagements, and of abandoning their parents. And this alienation in the family, aggravated often by the brutality and ignorance of its head, is one of the main causes of the misery which prevails among multitudes of tho work-people. Tho operative spinners of Mulhausen are generally pale, and subject to chronic catarrhs, which degenerate often into phthisis. Tho piecers and card-tenters sometimes lose the first joint of their fingers. The weavers are often seized with chronic rheu- matism.” Such was the moral and physical condition of the vast- majority of the factory operatives in Alsace at the time when Mr. Ure visited them; but several of the mill proprietors in that district had already began to show consideration for the welfare of their work-people. It is pleasant to turn from tho dark picture suggested by, rather than delineated in, these extracts, to another passage in Mr. Ure’s notes of his tour, descriptive of the great manufacturing establishment of Messrs. Gros, Divillier, Roman and Co., at Wesserling, in one of the most beautiful valleys of the Vosges mountains. This is pro- nounced by Mr. Ure to be “the most picturesque, peaceful, and well-ordered manufactory ” he had ever seen, and he waxes quite eloquent in its praise. With the word-painting and tho landscape we are not at present concerned, and so we shall pass at once to the substantial and economical portions of Mr. Ure’s narrative. “The works of Wesserling,” he tells us, “ con- sist of cotton mills, power and hand weaving of calicoes and muslins, bleaching grounds, and print-works. The calico- printing was commenced as far back as the year 1760. Tho spinning mill, the loom shops, the bleach fields, and cylinder 36 THE TECHNICAL EDUCATOR. press rooms date from the year 1802. The establishment is placed at a distance of two leagues from all towns, and is the central point of nine villages, containing a population of from 12.000 to 14,000 souls. There is no other manufactory within a league of it. Feelings of philanthropy presided at the origin of Wesserling. The first founders had for one of their objects to give comfortable employment to the natives of the valley, and they have been rewarded by an invincible attachment on the part of their work-people. Most of them (the operatives) are proprietors of a house and a little land, which their families cultivate, and the whole of them have rights to the use of the pasture-common. Their chief agriculture is that of the potato and meadow-grounds, and they all possess cattle. They are Roman Catholics, while their masters are Protestants of the Genevese church ; but both live in the mutual charities of religion. The language of the country is still German as of old, and the temperament of the people is a little phlegmatic but docile. Their intelligence may be developed with a little pains, especially that of the female sex. The proprietors founded, sixteen years ago, a savings’ bank for the operatives, which pays five per cent., and they study to persuade the youths to deposit. The work-people have benefit societies managed by themselves ; but as the state of wages and employ- ment seldom varies, they do not suffer from the vicissitudes of trade. A skilful medical man attached to the establishment attends gratuitously the workers and their families. Each of the villages has one or two well-conducted schools, and at Wesserling itself there is an upper school, erected by the public authorities as the model seminary of the canton.” It is within the last twenty years that the most successful efforts to improve the circumstances and character of the work- ing classes of Mulhausen have been made. In the year 1853, the first Association for the erection of “cites ouvrieres,” or workmen’s towns, was founded at Mulhausen, with a capital of 300.000 francs, in sixty shares of 5,000 francs, or .£200 each. The State contributed 300,000 francs to assist the undertaking; the whole of which sum had to be laid out in streets, side-paths, sewer3, fountains, plantations, baths, wash-houses, and bakeries. In order to convey an idea of the immense benefit this association has conferred on the community of Mulhausen, it may be stated that it has built about 700 houses, affording accommodation to a population of some 5,000. These houses are of various descriptions and dimensions, some consisting only of a ground- floor, while others have a storey. They are planned to meet the requirements of health, comfort, and decency ; and each house has a garden attached to it. In a large number of cases, the working man is the proprietor of the house in which he resides. ' The method by which this is accomplished deserves to be de- tailed. A house with a ground-floor only costs 2,650 francs, or £1106, and a house with an upper floor costs from 3,300 to 3,400 francs. The Association sells its house to the workman at cost price, and the purchaser begins by a payment of 300 francs, or .£12, which is kept in reserve for the expenses of the contract, or is returned in the event of the purchaser being obliged to withdraw from the bargain, or unable to pay up the remainder of the price. When the last-mentioned contingency occurs, the Association repays to the purchaser the difference between his deposit and the claim it would have had against him if he had .-simply been a tenant. In all cases where a sale is agreed on, the purchaser is put in occupation, and by a payment of from 18 to 25 francs per month for a few years, according to the contract, he becomes the owner of the house. This monthly payment, it will be seen, is little more than an ordinary tenant would be charged as rent. When the Association merely lets its houses, it charges rent at the rate of 8 per cent, on the cost of the tenement ; but the shareholders are bound by their charter not to take more than 4 per cent, interest on their money, and any surplus revenue that may be got pays for insurance, taxes, and repairs. The “ cites ouvrieres ” of Mill- hausen have proved so beneficial that the scheme has been adopted in Paris, and in other French towns. With the im- provement in the material oondition of the work-people of Alsace effected by Associations for the construction of work- men’s towns and kindred movements, a corresponding moral advance has been made. But there is little of a distinctive -character about the trade unions, co-operative and friendly .societies of Mulhausen, and it is not necessary to describe them in the present article. The Franco-German war was a critical period in the history of the town, and it is to be hoped that the energy and enterprise which have so long distinguished its inhabitants will enable them to surmount the difficulties in which they were conse- quently involved. BUILDING CONSTRUCTION.— XV. OF ROOFS GENERALLY. The term roof seems derived from the Saxon word hrof, or, perhaps, a contraction of the German words Hier-auf (upon here), and, as is well known, means the cover or top of a build- ing, generally consisting of two sloping sides, though occasion- ally of other figures. The ancient Egyptians, Babylonians, Persians, as well as other Eastern nations, had their roofs quite flat. The Greeks appear to have been the first who made their roofs with a slant each way, from the middle to the edges. This was very gentle, the height from the ridge to the level of the walls not exceeding one-eighth or one-ninth of the span, as may be seen by many ancient temples now remaining. In Northern climates subject to heavy rains and falls of snow, the ridge must be very con- siderably elevated. In most old buildings in Britain, the equi- lateral triangle seems to have been considered the standard both in private and public edifices, and this pitch continued for several centuries till the disuse of what is called Gothic archi- tecture. The ridge was then made somewhat lower, the rafters being three-fourths of the breadth of the building. This was called the true pitch ; but subsequently the half-square seems to have been considered the true pitch. The heights of roofs were gradually depressed from the half square to one-third of the width, and from that to a fourth, which is now a very general standard, though they have even been executed much lower. There are some advantages in high-pitched roofs, as they dis- charge the rain with greater facility ; the snow continues a much shorter time on the surface ; and they are less liable to be stripped by heavy winds. Low roofs require large slates, and the utmost care in their execution ; but they have the advantage of being much cheaper, since they require timbers which are shorter and of less scant- ling. When executed with judgment, the roof is one of the principal ties to a building, as it binds the exterior walls to the interior and to the partitions, which act like strong counter- forts against them. Roofs are of various forms, according to the nature of the plan, and the law of horizontal and vertical sections. The most simple form of a roof is that which has only one row of timbers arranged in an inclined plane, which throws the roof entirely on one side ; this is called a “ lean-to ” or shed roof (Fig. 141). The most general roof for an oblong building consists of two rectangular planes of equal breadth, equally inclined, and ter- minating in a line parallel to the horizon. Consequently, its form is that of a triangular prism, each side being equally in- clined to the plane of the wall-head ; this is generally called a “ pent roof.” Fig. 142 is the end view, or “ gable,” and Fig. 143 is the plan of such a roof. When the plan is a trapezium, and the wall-heads properly levelled, the roof cannot be executed in plane surfaces, so as to terminate in a level ridge. The sides, therefore, instead of being planes, are made to wind in order to have the summit parallel to the horizon; but the most eligible method is to make the sides of the roof planes, enclosing a level space or flat, in the form of a triangle or trapezium, at the summit of the roof. Roofs flat on the top are said to be truncated. These are chiefly employed with the view to diminish the height, so as not to predominate over that of the walls. When all four sides of the roof are formed by inclined planes, it is called a “ hipped roof ” (Figs. 144 and 145), in which case two of the inclined sides — namely, those which slant from the long sides of the building — will be trapezoids, and the other two triangles. But if the building to be covered be square (Figs. 146 and 147), and all the slides slant equally, the roof will form a, square pyramid, for the projection and development of which see lessons in “ Projection.” BUILDING CONSTRUCTION. 37 A building having a hipped roof consists of a square prism, on which a triangular prism rests, but the ends of the prism are slanted off. When the planes of roofs, instead of being continued until they meet in a ridge, take another slant at a certain height, they are called “curb” or “Mansard” roofs (Fig. 148), from the name of their inventor, a great French architect* who lived in the sixteenth century. They are much employed in France, and are hence often called “ French roofs.” When the plan of the roof is a regular polygon, a circle, or an ellipse, the hori- zontal sections being all similar to the base, and the vertical section a portion of any curve, convex on the outside, the roof is called a dome. We will now enter more particularly into the construction of a roof, in order to explain the principles which guide the designer, and to give the names of the different timbers em- ployed. It has already been stated that a badly-designed roof may prove the ruin of an entire building by forcing the walls out- feet of the rafters together, they are mortised into a beam called the tie-beam, in such a manner that they cannot spread outward, and this is the first step towards the proper con- struction of a roof. Wall-plates have already been mentioned. They are timbers laid on the tops of the walls to prevent the roof-trusses pressing on one particular part, and to spread the pressure along the whole length. Resting on these, and crossing the entire width of the building, the long timber tie-beam is placed ; and the very manner of placing it is such that any weight pressing on it may bear downward and not out- ward, and thus it ties the walls together ; into this the rafters are mortised, in one or other of the methods already shown. The rafters are not allowed simply to meet at the top, but abut against the slanting part of an upright, called the king- post, the purpose of which must not be misunderstood. Casual observers might imagine that the king-post rests upon the tie-beam, and supports the rafters at their junction ; but it does no such thing, the rafters abutting against the tie-beam meeting at the top and forming a triangle, because the two- ward ; whereas, if constructed on correct principles, it will tend to tie them together, and so give firmness to the whole struc- ture ; and it has also been mentioned that the most generally adopted roof is that formed by two inclined planes ; but it will at once be seen that this must be very limited in its application, and could only be used with anything like safety where the walls are very strong so as to resist the pressure of the roof ; for it must be clear that the weight of the timbers and slates or tiles would tend to force the walls out of the perpendicular. This will be understood on referring to Fig. 149. Now when this force (w) came into action, it would spread the feet of the rafters outward, and therefore the obvious remedy is to tie them together. Thus a rope would, to a certain extent, answer the purpose ; but instead of tying the * Francis Mansard, an eminent French architect, horn at Paris in 1598, was the son of the King’s carpenter, and received those instruc- tions which led to his eminence as an architect from Gautier ; but for the high rank to which he attained in his profession he was indebted to the force of his own genius : he died in 1666. His nephew, Jules Hardouin, became a great favourite of Louis XIV., and was enabled under his patronage to realise a large fortune. Amongst his principal works were the Ch&teau de Clugny and the Palace of Versailles. He died suddenly at Marly in the year 1708. sides together are greater than the third (“ Euclid,” Book I. Prop. 20), and the third in this case is the tie-beam. Now, in the triangle A b g (Fig. 150), the weight d could be suspended; and as the two sides A and b meet in c, c becomes, as it were, the keystone of an arch, and firmly supports the weight D suspended from it. Thus then, in Fig. 151, the points A and b act as the abut- ments of an arch, and the head of the king-post, k, is the key- stone into which the upper ends of the principal rafters, p r, are mortised ; and thus, the more the keystone be pressed down, the firmer will the structure be. But the weight of the roof does not really press upon the keystone, but upon the rafters, and these again transfer their force to the tie-beam, t b. Now, at its ends, the tie-beam is well supported, but in most cases is liable to sag, or sink in the middle ; and if this were to occur, the ends of the rafters would be drawn inward, and with them the walls on which the wall-plates rest. The king-post is therefore a continuation of the keystone, and comes just down to, but does not rest upon, the tie-beam, which is therefore strapped up to the king-post by an iron band ; and thus, in- stead of the tie-beam supporting the king-post, the king-post supports the tie-beam, the middle port-ion of which is suspended from it. 38 THE TECHNICAL EDUCATOB. In order to tighten up the tie-beam, an opening is pierced through the upper ends of the iron strap, and through the king- post. Iron “ gibs ” are passed through this hole, and two iron wedges entering from the opposite sides are driven in. It will be evident that the effect of this will be to draw up the strap, and with it the tie-beam around which it is placed. Fig. 152 is a section showing the king-post, tie-beam, iron strap, gibs, and wedges, and Fig. 153 shows the front of the strap. All the parts referred to will be seen in their places in Fig. 151, in which are also shown struts, s, s, which, abutting on the foot of the king-post, support the principal rafters, p r, at a point between their upper and lower ends. If the width require that the beam should be further braced up, the struts S, S, then, instead of being mortised directly into the rafters, serve to support two posts smaller than the king-post, but of the same character, called queen-posts , Q. To these, again, the tie-beam is strapped up as in the former case. Against their feet struts abut, supporting the rafters ; and it will be seen that this system may be carried on as long as the nature of the materials would permit ; the whole truss resting on the wall- plates, w. Now it will be clear that such strong and heavy assemblages of timber as these roof-trusses need not necessarily be placed close together, being intended as the main supports of the whole covering of the building ; further framing is therefore necessary, in order that the intermediate spaces may be pro- perly and securely roofed over. This is done by throwing timbers at intervals across the trusses. These are called “purlins,” p, and are sometimes “notched” on the principal rafters, as at p, on the right side of the drawing, or rest against blocks, as shown at the corresponding point on the left side ; the latter is to be preferred, as the principal is not weakened by the removal of any part of the thickness. Thus a horizontal framework is created, and across these, at about a foot apart, smaller timbers called “common” rafters are placed, c k. These either abut on a timber called the pole-plate, p, rest- ing on the end of the tie-beam, outside the insertion of the foot of the principal rafters, or may be notched on to it, and passing by it, may form the eaves, or projecting part of the roof, under which a gutter may be placed. Across the common rafters strips of wood called “ battens ” are nailed, and to these the slates are attached; or, in cases where the inside of the roof is to be left visible, it is covered in with boards, to which the slates are nailed. The interior of these boards, and the timbers on which they rest, are then stained and varnished : and such roofs have a beautiful appearance, especially when the lines are such as to show the scientific principles upon which the whole is constructed. The open timber roof of the Middle Ages forms one of the most beautiful features of that period of architecture. They were, in the first instance, constructed on the most per- fectly correct principles of science. They were then, in some cases, elaborately carved and filled in with most exquisite tracery, or were painted. The construction was not concealed by ornament; but, on the contrary, the decoration served all the more to show the construction to advantage. And we can thus feel the truth of Mr. Brandon’s words : “ A timber roof of the fifteenth century, with its massive timbers elaborately wrought ; its rows of hammer-beams, terminating in beauti- fully - carved figures of angels ; its enriched panelling and traceried spandrils ; its exquisite bosses ; and, above all, its profusely-ornamented cornice, is truly as glorious a sight, as it is a grand triumph of the carpenter’s art. Such excellence, how- ever, was but very gradually accomplished.”* In some cases the heads of the queen-posts are kept apart by a horizontal timber (shown by a dotted line in Fig. 151) called the straining beam, which is strapped up to the king-post, which in such a roof-truss would not come down to the tie- beam. The subject of roofs in timber and iron is of such im- portance, and its elucidation requires such numerous illustra- tions, that a separate series of lessons will be devoted to it in The Technical Educator. The leading principles of the construction of roofs covering a span of great width are exemplified in the complex structures by which our large railway stations and termini are covered in, and which may be studied with advantage. * The whole subject of Gothic Architecture will he treated of here- after in this work in a separate series of lessons. VEGETABLE COMMERCIAL PRODUCTS. XVII. PLANTS PRODUCING VALUABLE GUMS, RESINS, AND BALSAMS (continued) . Turpentine Pine ( Pinus palustris, Wild., and Finns Tceda, L. ; natural order, Coniferce). — The importation of turpentine by other nations is not very considerable, since almost every country possesses trees from which it may be procured. England, however, is an exception, the demand for turpentine being much greater than the home supply. We receive nearly all our tur- pentine from the United States, and it is obtained from the above two species of Pinus. There are also in the market, Bordeaux turpentine, obtained from Pinus pineaster, Aiton; Strasburg turpentine, from Abies pedinata ; Venice turpentine, from Abies larix (Rich.), the common larch ; and Ohio turpen- tine, from the Pistacia terebinthus (L.), a tree indigenous to Cyprus. The process of collecting turpentine is in each case nearly the same. The bark of the trees being wounded, the turpen- tine trickles out in drops into boxes or other vessels placed so as to receive it. The incisions are made about the close of the month of March, and the turpentine continues to flow through- out the vegetative season, particularly during the summer months. Turpentine is imported in barrels, weighing from two to two and a-half cwt., and has the appearance and consistence of honey. Oil or spirits of turpentine is obtained by distillation from the raw turpentine ; this residue is the common resin or rosin of the shops. Spirits of turpentine, as a solvent of all resins, is much used in the preparation of paint and varnish ; and rosin in the manufacture of common soap, common sealing- wax, for the bows of violins, and for caulking ships. In 18G3, 27,343 tons of turpentine, valued at .£31,274, were imported into the United Kingdom, chiefly from North America. Gum-arabic (Acacia vera, Wild., and Acacia Arabica, Wild.; natural order, Leg uminosce).— Gum-arabic is produced by these two trees, which grow in abundance in Arabia, and in Egypt on the banks of the Nile. It flows spontaneously from then- trunks and branches, in the form of a mucilage, which dries and hardens on exposure to the air. The more sickly the tree, and the hotter the weather, the more abundantly exudes the gum. It is very nutritious, and the Arabs who gather it almost live upon it during the harvest. The principal African and Arabian ports for the exportation of gum-arabic are Aden, Mokha, Suez, Cairo, and Alexandria. Gum-senegal, the product of Acacia Senegal (Wild.), is the best and dearest sort of Arabian gum. It is distinguishable from gum-arabic by its clearness, consisting of choice drops of tears, some as large as a pigeon’s egg, entirely white, and shining like glass. Gum-tragacanth, which is yielded by Astra- galus tragacantha, L., is also considerably in demand, and is one of the chief gums of commerce. We receive this gum from Greece and Asia Minor. The principal place for its exportation is Smyrna. These gums are chiefly used in the manufacture of silks, crapes, and muslins, to stiffen and glaze the fabric; they are employed also in calico-printing, to give consistence to the colours ; in medicine, painting, and in the manufacture of ink. The quantity imported in 1850 was 1,984 tons, of which 328 tons were gum-senegal. Gum-sandarach (Callitris quadrivalvis. Verst. ; natural order, Coniferce). — This tree is a native of Earbary, on the African coast. The Turks construct the ceilings and floors of their mosques of its wood, which is all but indestructible. The gum, which is much used in making fine varnishes, is imported to the extent of from twelve to fifteen tons annually. Gamboge (Hebradendron gambogioides, Grah. ; natural order, Clusiacece). — Gamboge is a gum-resin obtained from this tree, which grows wild on the Malabar and Ceylon coasts. In Ceylon gamboge is obtained by wounding the bark of the tree as soon as the flowers begin to appear. It appears in commerce in three forms — in solid rolls or cylinders, in hollow rolls or pipes, and in amorphous masses or cakes. Gamboge is imported from Ceylon, Siam, and Cochin-China. The best is the pipe-gamboge from Siam. Gamboge is employed a3 a water-colour or pigment by TECHNICAL 'DRAWING. 39' artists, also in medicine as a drastic purgative. Our imports were — in 1863, 388 cwt., valued at .£3,268; and in 1864, 42 owt., valued at .£520. Camphor Tree ( Laurus camphor a, L. ; natural order, Lau- racece). — The camphor tree is a native of China, Japan, Borneo, and the island of Formosa. Camphor — a gum-resin — is obtained as follows : — “The wood of the Laurus is cut into small pieces, and put, with plenty of water, into small iron boilers, which are cover ed with an earthen dome lined within with rice straw. As tlhe water boils the camphor rises with the steam, and attaclhes itself as a sublimate to the stalks, under the form of granulations of a grey colour. In this state it i3 picked off the straw, and packed up for exportation to Europe.” * Camphor is brought to this country in chests, drums, and casks — in small granular, friable masses, of a dirty-white or greyish colour. It is much used in museums and private col- lections of natural history, as a preservative of animal and vegetable bodies against the depredations of . insects. It is also used in medicine, in the composition of varnishes, and iq the manufacture of fire-works. The total amount annually received from China and Japan is about 466,000 pounds. Frankincense (Boswellia serrata, Roxburgh ; natural order, Amyridacece). — This is an odoriferous gum-resin, much used by the Homan Catholics in their churches. It was employed by the priests of ancient Egypt to conceal the unpleasant emana- tions arising from the sacrifices offered in their temples. It is imported from India and the Levant. Asafcetida ( Narthex asafcetida, Falconer; natural order, Z7m- belliferce). — This fetid gum-resin exudes from incisions made in the roots of the plant. It is first a milky juice, but when dried in the sun, acquires a mottled appearance and a pink colour. The plant is indigenous to the south of Persia, Afgha- nistan, and the Punjaub. Asafcetida usually comes over in casks and cases. It is much used in medicine as a valuable stimulant and anti-spasmodic, in eases of asthma and spasmodic COUgli. T I. the barks op commerce. Many varieties of bark are known in commerce, the chief of which are those used for medicinal purposes, such as the Peru- vian and Cascarilla barks ; and economic barks, employed in the arts and manufactures, such as the bark of the cork oak, and the valuable tanning bark of the common oak. MEDICINAL BARKS. Peruvian Bark (. Cinchona Condaminea, Humb. and Bonpl., etc.; natural order, Cinclionacece) . — Peruvian bark is the pro- duct of various species of Cinchona, a group of evergreen trees &nd shrubs growing on the slopes of the Andes in Peru and Bolivia, at elevations varying from 7,000 to 10,000 feet above the level of the sea. The medicinal properties of this bark are entirely owing to the presence of three alkaline and bitter principles — quinine, cinchonine, and quinidine — which are the most effective remedies known against intermittent and allied fevers. The Jesuit mis- sionaries were the first to discover and make known its value as a remedial agent, and for a long time they were the sole ven- dors of it, whence its name of “Jesuit’s Bark.” The generic name Cinchona was given to the plant because, in 1638, the Countess of Cinchona, wife of the Viceroy of Peru, was cured of intermittent fever by it3 use ; hence, also, the powdered bark was called Pulvis Comitissce, or Countess’s powder. There are, at the fewest, twelve species of Cinchona from which the Peruvian bark of commerce is derived. All these resemble each other in their general features ; having opposite leaves, which are shining, lanceolate, on short petioles, and email, tubular, and white or rose-coloured flowers, arranged in ample panicles at the extremities of the branches. The princi- pal varieties of Peruvian bark recognised in the Pharmacopoeia are the pale, the yellow, the red, and the crown bark. Pale or grey bark is obtained from Cinchona nitida and C. micrantha ; Loxa or crown bark, from C. Condaminea ; yellow or Calisaya bark is yielded by Cinchona Calisaya ; the source of the red bark is not yet ascertained. The pale bark contains most cinchonine, the yellow most quinine ; Loxa or crown bark, the largest proportion of quinidine ; the red yields the alkaloids in about equal proportions. • Ure's “Dictionary of Arts, Manufactures, and Minos." Vol. I. London, 1867. Peruvian bark come3 to us in the form- of quills or hollow cylinders, which vary in length and diameter, the longest seldom exceeding two feet — the diameter varying from a quarter of an inch to two inches. These quills are the bark of the smaller branches of the tree, which rolls up thus as it dries in the sun. Pale black arrives in quills only ; the Calisaya or yellow bark, and also the red bark, comes both in quills and flat pieces, which last are derived from the trunks, and reduced to this form by being alternately exposed to the sun and then subjected to pressure until perfectly dry. Peruvian bark is usually im- ported in packages, or serons, made of dried cow-hides. The annual imports into this country amount to between 80 and 90 tons. The cinchona plant has been introduced with every prospect of success into British India, where large plantations are now established in many of the hilly districts ; and more recently into Japan and the Mauritius. Cascarilla Bark (Croton Eleutheria ; natural order, Euphor- biacea). — This tree is a native of St. Domingo, the Antilles, and the Bahama Islands. Its bark is imported chiefly from Eleuthera, one of the Bahamas, and comes in small-sized quills and in chips. Cascarilla bark has strong aromatic and tonio properties, and is an excellent remedy in chills and fever, being occasionally employed as a substitute for cinchona. When burned it gives forth a sweet musky odour, and is often used iq fumigations. The amount annually received in this country is from ten to twelve tons. Cedron ( Simdba cedron, Aubl.; natural order, Simarubaccce). — The cedron is a small tree confined to the republic of New Granada, ranging from about the 5th to the 10th degree of north latitude. Every part of the plant, but especially the seed — owing to the presence of an alkaloid ( cedrine ) — is intensely bitter. On account of this principle, it is used extensively, and with considerable success, in cases of intermittent fever. But the chief reputation of the cedron rests upon its being con- sidered an efficacious antidote for the bites of snakes, scorpions, centipedes, and other noxious animals ; and so highly do the natives of the land in which it grows value it, that they will pay a large price for a single seed. Quassia Abiara, belonging to the same order as the cedron, is also a valuable febrifuge. VII. TANNING materials. In the bark of certain trees a peculiar light yellow glistening substance exists, called tannin, or tannic acid, which consists of small yellow crystals. This tannic acid has the power of com- bining with the gelatine in the skins of animals, and converting them into leather by forming a tannate of gelatine. The most valuable bark for this purpose is that of Oak (Quercus pedunculata ; natural order, Cupulifera ). — Indigenous to this country, and also much cultivated. We im- port large quantities of oak bark from Holland and Belgium. In 1852 we received 19,034 tons, whilst the home produce was 150,000 tons. Yalonia (Quercus cegilops). — Under this name the acorn-cupa of this species of oak are used ; although the tree is dwarf and shrubby, these cups are very large and much prized by tanners. Large quantities are imported from the Levant, chiefly viti Smyrna, not less than 29,396 tons having been received in 1866. Sometimes the acorns are gathered before they are fully formed ; they are then called camata, or camatina. In this state they are more valuable, but too expensive to bo largely employed. TECHNICAL D R A WIN G.— XXI X. DRAWING FOR MACHINISTS. ISOMETRICAL PROJECTION. The principles of isometrieal projection having already been given in previous lessons (Vol. I., page 267), it is not necessary to repeat them here ; it will be sufficient to remind the student that the square A c B D (Fig. 267) is represented in isometric projection by the lozenge a' c b d. From this figure it will be seen that the side d b of the square is at 45° to D E, whilst the side D h is at 30° to D E. The difference, then, between the triangle ,D E h and the triangle D E b is the triangle D b b, the angle !)DB being 15°, and d b b being 45°. It will therefore be plain that if the side of a cube be given, 40 THE TECHNICAL EDUCATOR. and we are required to find the side of the hexagon which would form the isometric projection of it, we need only take the length as the basis of a triangle, as r> b, at the one end con- struct an angle of 30° (that is, an angle similar to bd b), and at the other an angle of 45° (similar to the angle b b d). This triangle then, as said before, will represent the side of the cube and its isometric projection. The side d b of such triangle will be the required length of the side of the hexagon, and any divisions or parts marked on b D, as b /, may be transferred to b d by drawing a line from f parallel to b b, cutting b d in g ; then b g will have the same proportion to b d that b / has to b d. CONSTRUCTION OF AN ISOMETRICAL SCALE. Although the method of constructing the isometrical scale has been given in a former lesson (Vol. I., page 269), it is repeated here for the convenience of the student, to save the trouble of reference to another volume. Let it be required to construct an isometrical scale of — that is, 1 inch to the foot. Fig. 268. — Draw the line A b, and A c at an angle of 15° to it. It will be found convenient to draw an angle of 30° by means of your set-square, and to bisect this angle. From A set off any convenient number of inches to represent feet, as A d, d e, dividing any one of them into 12 equal parts, as D E. Now from e draw a line at 45°, cutting a c in f. From all the points of division, 1 to 12, draw lines parallel to e f, and these will give on a c the divisions contained between a and f, which will represent the twelfths of inches in the isometrical measurement. Fig. 269 is an isometric projection of a square case divided into compartments. Let a be the position of the nearest angle of the object to be projected. On each side of A draw a line with the set-square of 30° placed against the T-square. This will at once give the angle b a c (120 ) which will be formed in the isometrical projection by the meeting of two lines at right angles to each other. Now the measurements of this case are as follow : — General front elevation, 2' 1" square ; depth, 5" ; thickness of wood, 1" ; width of compartments, 7". On A erect a perpendicular. Make A d and ab 2' 1" by the isometric scale. Draw D e parallel to a b, and b e parallel to a d. This will complete the isometrical projection of a vertical square, which would be the left side (a) of the cube shown in Fig. 270. From d and e draw lines parallel to A c. On A c set off the depth of the case — viz., 5" — and erect a perpendicular cutting the lino drawn from D in F. From F draw a line parallel to D e, cutting the line drawn from E in g. This will complete the projection of the object treated as a block only. Now it will be clear that, as the thickness of the wood is to be 1 inch, and there are to be three compartments in width, and three in height, these will be 7 inches each ; therefore, along A B and A D, set off an inch for the thickness of the case, then a space for the compartment, an inch for the thickness of the board dividing the compartment, and so on. From these points lines drawn parallel to the sides of the figure will complete the projection of the front of the case. Now from each of the inner angles joining the planes of the sides of the compartments which would be visible, draw lines parallel to A c. From the points on A d, marking the thickness of the shelves, draw lines parallel to a c, cutting c f in h, i, etc. From these points draw lines parallel to A B ; these, cutting the lines already drawn from the inner angles of the compart- ments, will give the distant inner angles at which the per- pendiculars form the back edge of the upright divisions, and the projection will thus be completed. Fig. 271 is the isometric projection of a wooden stand for a machine. It is drawn to the same scale as the last, the dimensions being as follow Length, 3 feet ; breadth, 1' 10)" ; height, 2' 5, B c, will give the four points T, z, z', h', which joined, will be the required projection. It will be seen that the points T and h' have already been used for a previous purpose. • The points now used fall exactly on these ; this would be altered if the prism were of a different length. It will be evident that if the axle were required to be cylindrical, a circle could easily be projected in T z' h' z, as in the former portion of the figure. The points at which the prism penetrates the wheel are found by drawing lines from i', z', h', z parallel to A H, cutting the diagonals j h', h j', and its distant end is projected by producing these lines to cut the diagonals of the distant side of the cube. Fig. 274 is an isometrical projection of a trestle, the working of which, being simply an application of principles already ex- plained, is left to the knowledge and ingenuity of the student. NOTABLE INVENTIONS AND INVENTORS. XI.— THE COTTON MANUFACTURE. BY JOHN TIMBS. Cotton, named by the Arabs Kutu or Kutun, is a filamentous matter, produced from the surface of the seeds of the Gossypium plants, found wild in both the Old and New World. Herodotus and Arrian speak of the cotton-plant as indigenous in India, and the linen found in Peruvian tombs attests its having existed in that country long before it could possibly have been carried to America by Eastern intercourse. In fact, the wild American cotton-plants are specifically different from those of the Old World; but at the present day, the cotton of the West is cul- tivated in Asia and Africa, while that of the East has long since been introduced into the American plantations. Cotton has been wrought into garments for the people of India for 3,000 years. Humboldt states that it formed the only clothing of the natives of Mexico, and is one of the plants they most anciently cultivated. There is evidence of the existence of the cott@n-plant in America long before there was any direct communication between the civilised world and the two great portions of that continent ; and we have it positively stated that the Spaniards found calico common in the dresses of the inhabitants when they conquered Mexico. It must have been known to the ancient Egyptians, and Rosellini found some of the seeds in one of the monuments of Thebes. It is conjectured that fine Indian cottons were used in ancient Rome because there was a regular commercial intercourse established, through the medium of Egypt, between Rome and India, the chief part of which was on the coast of Malabar, where weaving was practised at the remotest period of which we have any record. Fine cottons were imported into Europe in Juvenal’s time, as they were ages before from India ; and from China, the country of the Seres, came silk, which the Romans believed to grow on trees. Virgil, in the “Georgies,” seems to allude to the cotton-plant and silk as follows : — “Of iEtliiop’s hoary trees and woolly wood. Let others tell ; and how the Seres spin Their fleecy forests in a slender twine." — Dryden’s Translation. The Germans, who in general avoid introducing into their language words of foreign origin, call cotton BaUmivolle, i.e. tree-wool. Cotton-wool was known in Spain in the twelfth century. It was imported by the Genoese and Venetians into England and the Netherlands in the beginning of the fourteenth century ; but the use to which it was applied, except for candle- wicks, is not known. In 1430 fustians were made, perhaps invented, in Flanders. In 1534, several ships from London and Bristol traded to the Levant, and imported, among other articles, cotton-wool. It might, therefore, be expected that at this time some cotton factories would have been established in England ; and this seems to be confirmed byLeland’s Itinerary , ni the reign of Henry VIII., stating that cottons were made at Bolton-le-Moors, in Lancashire, and in the neighbouring villages ; also by the mention, in an Act of Parliament passed in 1552 (Edward VI.), of Manchester, Lancashire, and Cheshire cottons. In the early stages of the trade, the raw cotton manufactured m Great Britain was chiefly the produce of the West Indies ; the finer sorts came from Surinam, the Brazils, and the Isle of Bourbon. The cotton from the last-named settlement commanded the highest price in the English market up to the end of the last century, when it was superseded by the Sea Island cotton, found in Georgia, Florida, and South Carolina. The cultivation of cotton in America made very little progress at first. In 1791, sixteen years after the first sample had been sent to England, the total import of American cotton at Liverpool was sixty-four bags. Two years later an American inventor, Mr. Whitney, discovered a very simple and expeditious method of separating the wool of the cotton-plant from the seed — a process which had previously been both tedious and expensive. Yet in 1784, when an American vessel arrived at Liverpool with eight bales of cotton on board, they were seized by the Custom House officers, who had never before seen cotton from that quarter, under the impression that they had been imported from some other country. In 1785 only five bags of American cotton were imported into Liverpool, and in the following year six bags. Such were the small beginnings of that imnfense trade which now gives employment to millions on both sides of the Atlantic; and which, according to the Abolition party, has been the main cause of the rapid increase of the wealth and influence of the slave power in the United States. The British colonies are capable of producing vast quanti- ties of cotton, and in our great colony of India the plant is indigenous. It has been computed that a piece of ground of the size of Yorkshire is sufficient to produce a quantity of cotton nearly double the annual consumption of England. The supply from the British possessions is greatly increasing, espe- cially ip India, in consequence of the construction of railways and canals ; whilst specimens of cotton cloth have been shown from the East and West Indies, and Australia, fully equal in. quality to the best from New Orleans. A field of American cotton at the gathering season, when the globes of snowy wodi are seen among the glossy dark-green leaves, is singularly beautiful ; and in the hottest countries, where the yellow blossom or flower and the ripened fruit are seen at the same time, the beauty of the plantation is still more remarkable. In the early stages of the culture in India it was described as very slovenly, as the seed was sown broadcast, and the plant neglected at every stage of its growth; which, together with the carelessness of the natives in gathering the cotton, in separating it from the seeds, and in packing it, made the Indian cotton very inferior to that of the United States. Nevertheless, the perfection to which the weaving of cotton had then been brought by the natives of many parts of India, notwithstanding their rude and imperfect implements, attests at once their patience and ingenuity. A peculiar combination of heat, light, and moisture is essential to the quality of cotton, the most favourable instance of which may be assumed to be the coast of Georgia and the Carolinas. In 1852 the value of the whole crop of American cotton imported into England was .£30, 000,000, equal to that of the British wheat crop. The economy of the cotton manufacture has been exemplified by modern instances, which strikingly carry conviction with them. Thus we read of the superiority obtained by the use of machinery compared with the laborious process of the Hindoo seated on the ground, with his legs in a hole, producing the most beautiful muslin ; whereas the cotton can be brought 10,000 miles, cleansed, spun, woven, dried, packed, and carried back again, and then sold in the provinces where it was first grown, at a less price than that of the cloth produced by the Indian weaver. We read also of the early stages of a pound of unmanufactured cotton, which came from the East Indies to London : from London it went to Manchester, where it was manufactured into yarn ; from Manchester it was sent to Paisley, where it was woven ; it was then sent to Ayrshire, where it was tamboured ; it came back to Paisley, where it was veined ; afterwards it was sent to Dumbarton, where it was hand-sewed, and again brought to Paisley ; whence it was sent to Renfrew to be bleached, and was returned to Paisley ; whence it was sent to Glasgow, and was finished; and from Glasgow it was sent per coach to London. The time occupied in bringing this article to market was three years, from its being packed in India till it arrived in cloth at the merebant’s ware- house in London. It must have been conveyed 5,000 miles by sea, and about 920 by land, and contributed to support not less than 150 persons, by which the value had been increased 2,000 NOTABLE INVENTIONS AND INVENTORS. 43 per cent. Well, indeed, may the steam-engine have been termed “ the cotton-spinner’s best friend.” The first spinning-machine on record was patented in 1738, by Louis Paul, with whom John Wyatt had connected himself in partnership, though the name of Wyatt appears only as a witness. This statement is founded solely on information fur- nished by Wyatt’s family ; and the late Mr. Robert Cole, the solicitor, proved that Louis Paul was the sole inventor of a machine for spinning cotton by rollers, and that Wyatt was a workman in Paul’s employ for weekly wages — as proved by patents and papers in Mr. Cole’s possession, including several hundred letters, mostly relating to cotton machinery. Paul had already patented a pinking-machine, by which he made considerable profit, and a deed extant proves that he received .£200 for allowing one person to use the machine. Paul’s spinning-machine patent, as we have said, is dated 1738. It was then requisite for an intending patentee to make an affi- davit that he was “ the first and sole inventor” of the machine about to be patented, and having obtained the patent he realised considerable sums by granting licences. The deed of May, 1739, is signed by John Wyatt, as attesting witness; and in it the machine is referred to “as invented by the said Louis Paul,” who covenants to fit it up. Dr. James, writing to Warren, a Birmingham bookseller, dated London, 17th of July, 1746, says, “Yesterday we called to see Mr. Paul’s machine, which gave us entire satisfaction, both in regard to the carding and the spinning. You- have nothing to do but to get a pur- chase for your grant. The sight of the thing is sufficient demonstration enough. I am certain that if Paul could begin with .£10,000 he must, or at least might, get more money in twenty years than the city of London is worth.” Wyatt had clearly advanced money to Paul at first, and he continued to do so, either as loans or for wages, until the total reached ,£200. In consequence of this debt, a mortgage deed was prepared between Paul and Wyatt, referring to 300 spindles for spinning, “according to the said invention of the said Louis Paul,” which were conveyed to Wyatt, his heirs, etc., to whom Paul covenanted, within six months, to “ give the same plan for working, etc., as he hath already gone by.” Paul further covenanted to give to Wyatt a plan of another machine which he had invented “ for the carding of wool, and other things for the use of the before-mentioned machine, or engine for spin- ning.” Subsequently, when in the Fleet Prison for debt, Wyatt wrote to Sir Leicester Hall, “ I am the person that was the principal agent in compiling the spinning engine.” Paul obtained a renewal of his patent, and tried to erect one of his machines in the Foundling Hospital, whereby, as he said, “ a number of mixed children, between five and fourteen years, might bo enabled to earn then- food and clothing.” Paul’s machine was ultimately abandoned, having been brought to no practical effect, although it was adduced many years afterwards as evidence against the originality of Arkwright’s invention. Tracing the means by which astonishing results have been effected, we find that in the year 1760, or soon after, James Hargreaves, an untaught weaver, living near Church, in Lanca- shire, began to devote his attention to the application of machinery to the preparation and spinning of raw cotton for weft. In the same year the Society of Arts offered a premium for the greatest improvement on the common spinning-wheel, and afterwards offered a premium of .£100 for the construction of a machine that would spin six threads of wool, cotton, flax, or silk, at the same time. Hargreaves first invented an im- proved method of carding the cotton, not very different from that nowin use; and in 1767 he invented the spinning- jenny, drawing several threads at once — at first containing eight spindles — made to revolve by bands from a horizontal wheel. The power of the spinning-jenny was soon increased to eighty spindles, when the saving of labour produced, such alarm amongst those persons employed in the old mode of spinning, that a party of them broke into Hargreaves’ house, and destroyed his machine. It was, however, again brought into use, when a second rising took place, and both carding and spinning machines Were destroyed, one result of which was that the manufacture Was, for a time, driven away from Lancashire to Nottingham. Hargreaves stated that he derived his idea of the jenny from seeing a hand-wheel with a single spindle overturned, when he remarked that the spindle, which was before horizontal, was then vertical ; and as it continued to revolve he drew the roving of wool towards him into a thread. He then conceived that if something could be applied to hold the rovings as the finger and thumb did, and that contrivance to travel backwards on wheels, six or eight, or even twelve threads, from as many spindles, might be spun at once. This was done, and suc- ceeded; but Hargreaves, driven by the mob, as we have described, to Nottingham, could not bear up against such ill- treatment, and there died in obscurity and distress. He had previously given the property of his machine to the Strutts, who thereon laid the foundation of their industrial success and opulence and a peerage. The cotton yarn produced by the common spinning-wheel and spinning-jenny could not, however, produce cotton yarn suffi- ciently strong to be used as warp, for which purpose linen yarn was employed ; and then another machine, the spinning- jenny, which took up what Hargreaves had begun, was invented by as humble an individual, Richard Arkwright, who was born at Preston in 1732, and being the youngest of a poor family of thirteen children, he received very little education. He was bred to the business of a barber, which he carried on in the town of Bolton, where remain two shops once occupied by him. He became a dealer in hair, which he collected through the country, and having dressed it, he sold it to the wig-makers. He possessed likewise a profitable secret method of dyeing hair. Up to this time the English cotton cloths (called calico, from Calicut, in India, the place of their production) had only the weft of cotton, the warp or longitudinal threads being of linen, it being impossible by any means then known to spin cotton with a sufficiently hard twist to be used as a warp. The raw materials were delivered by the master to cottagers living in the villages of the district, who both carded and spun the cotton, and wove the cloth. The demand for these cottons soon became so great, that although there were 50,000 spindles constantly at work in Lancashire alone, each occupying an individual spinner, they could not supply the quantity of thread required. To remedy this state of things, several ingenious individuals had thought of spinning by machinery, instead of by the one-thread wheel. Among these was Paul, whose machines have been described. A Mr. Robert Earnshaw, of Mottram, in Cheshire, in 1753 invented a machine to spin and weave cotton at one operation, which he showed to his neigh- bours and then destroyed, through tiro generous apprehension that he might deprive the poor of bread. Arkwright had now turned his attention to mechanics, and with one Kay, a clockmaker, who made him some wheels, they jointly devised a model of a machine for spinning cotton- threads; and next year, 1768, they erected this machine at Preston, in the parlour of the house adjoining the Free Grammar School ; but dreading the hostility of the Lancashire people to their attempt to introduce spinning by machinery, they removed to Nottingham. Here wanting capital, Arkwright took his model to Messrs. Need and Strutt, stocking-weavers at Not- tingham ; Mr. Strutt being a man of scientific attainments, was satisfied of the nature of the proposed machine, and he and his partner joined Arkwright in 1769, and took out a patent for the machine as its inventor. It is related that when Ark- wright applied to Mr. Strutt, his machine was much impeded by the fibres of the wool sticking to the roller, which defect Mr. Strutt engaged to remove on condition of participating in the profits of the result. They repaired to the mill, when Mr. Strutt, taking a lump of chalk out of his pocket, applied it to the roller, and the sticking was instantly prevented. A spinning-mill driven by horse-power was, at the same time, erected and filled with frames. In 1771 Arkwright and his partners established another mill at Cromford, in Derbyshire, the machinery to which was set in motion by a water-wheel ; and in 1775 he took out a second patent, with additions to his former one. This was a combination of the carding and spinning machinery with two pairs of rollers, the one re- volving faster than the other, which forms the peculiarity of the machine. The most important of Arkwright’s contrivances was his drawing out the cotton to a harder twisted thread, so as to be used for warp as well as weft. This was managed by a principle altogether novel. The cotton was first drawn from off the skewers by one pair of rollers made to move at a comparatively slow rate, and which formed it into threads of a first or coarser quality ; but at a little distance behind the first was placed a 44 THE TECHNICAL EDUCATOR. second pair of rollers — revolving’ three, four, or five times as fast — which took it up when it had passed through the others, the effect of which was to reduce the thread to a degree of fineness so many times greater than that which it originally had. The first pair of rollers might be regarded as the feeders of the second, which could receive no more than the others sent to them, and that again could be no more than these others themselves took up from the skewers. As the second pair of rollers, therefore, revolved, we will say five times for every revolution of the first pair — -or, which is the same thing, re- quired for their consumption in a given time five times the length of thread that the first did — they could obviously obtain so much length by drawing out the common portion of cotton into thread of five times the original fineness. Nothing could be more beautiful or more effective than this contrivance, which, with an additional provision for giving the proper twist to the thread, constitutes the water-frame, or throstle, so called from its being originally moved by water-power. Such, in principle, were the two great inventions that effected an entire change in the manufacture of cotton, wool, and flax. The idea of spinning by rollers Arkwright accidentally de- rived from seeing a red-hot bar elongated by being made to pass between two rollers ; and though there is no mechanical analogy between that operation and the process of spinning, it is not difficult to imagine that by reflecting upon it, and placing the subject in different points of view, Arkwright might be led to this invention, which he specially claimed as his own. Of other machines which he included in his patents, he was rather the improver than the inventor ; and the original spinning-machine for coarse thread, the spinning-jenny, Arkwright admitted to have been first conceived by Hargreaves. Previous to this time no establishment of a similar nature had existed, none at least to which the same system of management was applicable, and it strongly marks the judgment and mental powers of Arkwright, that although the details of manufacturing or commercial business were altogether new to him, he at once introduced a system into his works which has since been uni- versally adopted by others, and which, in all its main features, has remained unaltered to the present time. In the year 1775 he completed a series of machinery so various and complicated, yet so admirably combined and well adapted to produce the intended effect in its most perfect form, as to excite the astonishment and admiration of every one capable of appre- ciating the ingenuity displayed and the difficulties overcome. At the expiration of the partnership of Strutt and Arkwright they separated. Arkwright went on by himself at Cromford, and the Strutts for themselves at Belper. A fierce spirit of detrac- tion strangely represented that Arkwright stole the invention of another ; but Mr. William Strutt, who was a competent judge on such subjects, attested that Arkwright was a skilled me- chanic, and. quite equal to such an invention. He did not, however, enjoy the rights of his ingenuity without opposition alike from. the manufacturers, and the spinners, and the weavers. His factories were attacked, his patents were invaded, and the merit of his being an original inventor denied. Circumstantial accounts of this system of injustice are to be found in the histories of the cotton manufacture, but cannot be quoted in this sketch. The “Encyclopaedia Britannica ” has this con- clusion : “We have access to know that some of Mr. Arkwright’s most intimate friends never had the slightest doubt as to the originality of his inventions, and some could speak from their own . personal knowledge, and their testimony was uniform and consistent,” and such became the opinion of the principal manu- facturers of Manchester. “ If,” says the “ Penny Cyclopedia,” “the evidence be fully weighed upon which it has been attempted to convict Arkwright of the serious charge of pirating other men s ideas, we think it will rest upon very slight grounds, while the proofs which he exhibited of possessing talents of the very highest order in the management of the vast concerns in which he was afterwards engaged, are unquestionable.” It was not, however, until after the lapse of five years from their erection, that from the works at Cromford any profit was realised ; but from that time wealth flowed in abundantly. The establishments were greatly extended, and new ones were formed, and success continued to flow, notwithstanding Ark- wright’s patent had been cancelled by law. Meanwhile, he had almost built the town of Cromford, and lived in patriarchal prosperity amidst the scenes of industry where he raised up his own fortune. He served as High Sheriff of Derbyshire in 1786, and received knighthood from King George III. But his health failed, and he died in 1792, in the sixtieth year of his age, leaving a fortune little short of half a million, besides having presented each of his ten children with .£20, 000. No man ever better deserved this good fortune, or had a stronger claim on the respect and gratitude of prosperity. His inven- tions opened a new and boundless field of employment, and while they have conferred infinitely more benefit on his native country than she could have derived from the absolute domi- nions of Mexico and Peru, they have been universally produc- tive of wealth and enjoyment. The power which gave motion to the rollers and spindles of Arkwright and his fellow-inventors was supplied at first by falls ’of water, when manufacturers of necessity planted their establishments in districts where water-power was readily obtained, however inconvenient these situations might be in other respects. Watt’s improvements in the steam-engine, however, supplied them with what they wanted, at a higher price certainly, but at any place and at any time they chose. As soon as steam-engines were used to drive the machinery, factories might be set up in towns, made independent of drought or flood, and wrought by a motive power whose energies could be adapted with the utmost nicety to the work required. Steam-engines were accordingly employed in turning the rollers and other machines used in spinning the cotton, as early as 1785, and the inventions of Watt and Arkwright, when thus combined, gave an impulse to the manufacture, which neither of them by itself could have produced. To show the advantages that have resulted from this combination of intellect, industry, and capital, it may be said that the quantity of cotton introduced into this country was under 5,000,000 pounds when the inven- tions of Arkwright were projected; in 1868 it was 11,857,893 cwt. CIVIL ENGINEERING.— VI. BY E. G. BARTHOLOMEW, C.E., M.S.E. CANALS ( continued ). The loss of water in a canal is variable, and at some periods excessive. We have already pointed out the necessity of pro- viding for this loss by effecting a communication between the summit level of the canal and some invariable source of supply. This point is of paramount importance, and demands a still closer notice. Supposing the supply to be drawn from a river, it is usual to construct a weir across it, and after damming up the stream, to admit a portion into the canal. Thus whilst the level of that portion of the river above the weir will vary very slightly under the influence of drought or rain- fall, the amount admitted into the canal will be proportionally constant. Under all circumstances of supply, however, it is imperative to provide a carefully constructed outlet for any excess of water arising from floods ; the position of this outlet will, of course, be in the same section of the canal with the supply. The character of the water admitted to the canal is a matter of importance. If derived from a turbid source it should, if practicable, be passed through filtering beds, or reservoirs, in which any suspended matter may be allowed to settle. This plan will permit of a much longer period elapsing before the water need be drawn off the canal for cleansing the channel, for under all circumstances an accumulation or deposit of mud in the bed will arise, and unless a system of sluicing— a plan adopted to a great extent in Italy — be employed, the water must be occasionally drawn off ; and as from necessity all navigation has to be stopped during this period, every means should be adopted to obtain 'pure water to supply the loss. The course of the canal, which we have stated must be guided by commercial as well as engineering considerations, needs a few words of consideration. It is not always possible, owing to the nature of the ground, to lead the main channel of a canal through a town. If such is the case, an offshoot or branch leading to some convenient locality in the town, and terminating with a wharf, must be constructed. A certain proportion must be allowed to exist between the size of the locks and the interval between them. The reason for this is that a lock full of water drawn off from any interval above it for the purposes of navigation shall not lower the | water in that interval excessively, that is, so that a loaded CIVIL ENGINEERING. 45 Fig. 12. barge could not float. As a matter of course, the dimensions of the channel of a canal are in terms of the barges which navi- gate it. Thus if we suppose the maximum draught of any boat = d, its extreme breadth = b, and its extreme length, including the rudder, — L, it is usual to allow the depth of water (d') to be d -f- 1'5 feet, in which d usually equals 5 feet; the width at the surface is usually 3(b + 3d') = 40 feet ; and the width of the bottom 3b = 25 feet. The width of the channel becomes greatly narrowed as it approaches the lock, where the width is the least. A lock need never exceed the breadth of a barge by more than 1 foot or B + 1 foot. Again, the length of the lock should not exceed l -f- 1 foot, and the depth d + 1* feet. An ordinary canal lock is 75 feet long, 8 feet broad, and 5 feet in depth over the mitre-sill. Now the least length allow- able between locks should be such that 12 inches of depth over and above what a loaded barge will draw shall, when the barge is en- closed in the lock and the water drawn off, never lower the water in the interval above more than 6 inches. Hence when the chambers of the lock are large and the canal narrow, a greater dis- tance must be arranged between the locks. The Saone and the Loire are united by the canal of Briare, navi- gable to ships of small bur- den; hence the respective di- mensions are larger than those given above. The locks are 110 feet long and 17 feet wide, giving a super- ficial area of 1,870 feet. If the fall be 6 feet 4 inches, 11,843 cubic feet will be drawn from the upper section; if 8 feet 6 inches, 15,859 cubic feet; if 10 feet 6 inches, 19,635 cubic feet. The canal being 48 feet wide at 3 feet below the ordinary level of the water, the length of the interval to the next lock should be 446 feet, so that the fall of 6 feet 4 inches in the lock should not lower the water in the interval more than 6 inches. It must, however, be 607 feet when the locks are 8 feet 6 inches of fall, and 755 feet when the fall is 10 feet 6 inches. The importance of attending to these points will be seen from supposing a caso where the reverse has occurred from necessity or oversight. If two locks, having a fall of 8 feet 6 inches, were only separated by 160 feet, the water drawn from the interval for the purpose of mounting the boat would lower it nearly 26 inches, and there would not remain sufficient to keep it afloat; consequently it would be necessary to draw a lockfull from the upper interval, and then a second to cause it to rise, whilst only Fig. 11 one would be required if the locks were at a sufficient distance. In many instances canals have been cut to connect two tidal rivers. There is in such a case no difficulty in obtaining the water for the navigation, a3 the whole channel may be re-filled at every tide up to the level of that tide. In this case, however, the entire channel must have a much larger capacity, as com- pared with that of the locks, than is required in other cases, because, as the supply is only obtainable at stated intervals, sufficient must be admitted at these periods to compensate for the whole loss arising from the navigation during the interval. Hence the canal becomes its own reservoir. The form of the chambers of locks should be a paral- lelogram; it is the most con- venient, and expends the least quantity of water. In the canal of Languedoc the form is oval, but the greater loss of water expended more than coun- terbalances the advantage of greater strength obtained by the curved wall. The walls of a lock should not be perpendicular outside. The pressure of water being proportionate to the height of the column, the walls must have the greatest width at their base, and narrow gradually to- wards their summit. In- side, the wall may be per- pendicular, ex- cept at the bottom, where they may have the same curve as the sides of the boats. The walls should not be less than 4 feet 3 inches thick at the level of the water, and should have th roughout them a lining of bricks set in cement to prevent filtration of the water. The openings of the lock are gra- dually widened, after leaving the mitre-sills, by what are tefmed shoulders of defence facing the higher level, and discharging walls facing the lower level. The continuations of these are termed wing walls and return walls. The whole of these are built of one continuous piece of masonry upon each side of the lock respectively, and have for their object the prevention of the water passing round and behind the chamber-walls, and the resistance necessary to withstand the thrust of the gates when under the influence of the water-pressure. In Fig. 9 we give an elevation of the usual form of a lock-chamber contiguous to the gate. The finished masonry extends from A to D, from which points the shoulders spring, diverging right and left. The position of the anchors which support the collars or hanging-pieces of the gates, as shown at Fig. 7 (Vol. L, page 386), is allowed for during the building of the side walla by the 46 THE TECHNICAL EDUCATOR. insertion of solid blocks of stone. The platform of the lock is a point requiring great care in construction. It has to receive the shock of the water when admitted by the opening of the sluice, and is very difficult to keep in repair. It is usually formed of timber laid upon a foundation of piles, with a layer of masonry beneath it. The ends may with advantage be worked into the masonry of the side walls. Where it is possible to obtain them, large flagstones are preferable for the surface of the platform. The timbers forming the gates of locks will vary in size according to the dimensions of the opening, and their respective depths below the water-level, the lower rails having to support a greater pressure than those above. The weight of water sup- ported by each horizontal rail will be found by multiplying their length, the interval from one to the other (usually 38 inches from centre to centre), the height of the water above the centre of the rail, and the product by 62 lb. (the weight of a cubic foot of water), the last product of these measures giving the number of pounds which the rails ought to support throughout their whole length. For small gates the timbers or rails may be from 4 to 5 inches square, and for larger, from 7 to 8 inches ; the latter being sufficient for a fall of 10 ft. 6 in., with a width of 17 feet between the hanging posts, six rails being put in the height. Whilst on the one hand it is desirable to have an excess of strength above the calculated requirement, it is on the other hand undesirable to make this excess excessive, as so much more weight is injurious to the supporting collar and the masonry to which it is attached. The diagonal direction of the braces may be dispensed with by the substitution of a bar of iron placed diagonally from the supporting collar to the lower end of the shutting-post. The escape of water through the gates must in every way be guarded against. It is very difficult, indeed almost impossible, to prevent its escape through the joint of the shutting-posts, because of the difficulty of making them touch throughout their own length. To obviate this they should be cut in a circular form, one concave and one convex ; the cur- vature should be with a radius of about 12 feet. The rails are mortised into the uprights, and are further strengthened by strong angle irons and T-pieceg. The sluice is ordinarily an opening, o (Fig. 10), left ip the framing of the gate, and closed by a paddle, p, working vertically in guides G, g, and raised or lowered by an iron bar, b, termi- nating at the top in a rack, r, actuated by a pinion, w, and handle, h. In Fig. 11 is shown another kind of sluice, in which the paddle, p, moves laterally, being fixed to the short end of a lever, l, heavily weighted at the lower or paddle end. The movement is given by a rack and pinion working nearly hori- zontally. The idea of this arrangement is that when no water is pressing against the paddle, the weight at the bottom draws it over the aperture, and when drawn back by the toothed gear it will remain back until the water-pressure ceases through a level having been obtained. In some cases screws are employed to raise the paddles (Fig. 12). This plan is adopted at Dunkirk. There are, as we have intimated in a former chapter, other modes of raising or lowering the barges from one level to another besides locks. The “ lift” is a plan adopted upon the Grand Western Canal, and has certain advan- tages over the lock. These lifts are 46 feet high, and consist of two chambers, having a piece of masonry between them. Each chamber contains a timber cradle, in which the .boat is placed which requires to be raised or lowered. When on a level with the canal the cradle allows the beat to swim into it by raising a water-tight gate at the end. The two cradles, when full of water, or when containing a boat, balance each other, being suspended by strong chains, which pass over iron wheels placed above the level. An additional 2 inches of water in the cradle not containing a barge is sufficient to raise the barge in the other. The barges using these lifts weigh 8 tons, and occupy 3 minutes in passifig up or down the 46 feet, and only 2 tons of water are consumed in the operation, whereas 3 tons would be expended for boats of this tonnage in the ordinary way. If an inclined plane is employed to raise or lower the boats, they are floated upon a sledge, which is drawn up by a steam- engine. Notwithstanding the obvious advantages of conveying heavy merchandise by water, it is remarkable that scarcely any atten- tion was paid to the subject in this country until about the middle of the sixteenth century, when it was proposed to render the Isis and the Avon navigable, and then -to unite the two streams by a canal 3 miles long. The first canal of importance was the Duke of Bridgewater’s, between Worsley and Man- chester, executed by Brindley. Several remarkable instances of bold and successf ul engineering occur upon this canal, espe- cially the aqueduct over the Irwell at Barton, consisting of three semi-circular arches, the centre arch being 63 feet span and 39 feet over the r;vor. Since the year 1776 no less than 2,400 miles of canal have been made in Great Britain. One of the most celebrated is the Caledonian Canal, uniting Fort William with Inverness. The entire distance between these points is upwards of 100 miles, but in consequence of the natural position of the chain of Lochs Ness, Oich, Lochy, Eil, and Linnhe running in an almost right line in a direction from north-east to south- west, only 21 miles of canal were requisite to render the entire line navigable for vessels drawing 15 feet. The breadth of the canal and enlargements of the locks is 122 feet at top, and 50 feet at bottom, and the depth 20 feet. The slope of the sides is as 2 of height to 3 of breadth, and is continued to within 2 feet of the water-level, the bank being 6 feet wide. Throughout the entire canal there are 23 locks, each being 40 feet wide and 172 feet long. Somewhat to the south of the northern entrance an enlargement of the canal to 162 yards of breadth for 967 yards of length constitutes a floating dock for repairs and other pur- poses of 32 acres. Loch Ness, the most northernly of the chain, has a level 32 feet, above the canal, to which vessels are raised by the four Muirtown locks, each 180 feet long, and 40 feet broad. The addition of Loch Ness gives at once a natural addition of 22 miles to the navigation. At its south-west extremity five more locks raise the navigation 40 feet higher to Loch Oich. The waters of Loch Lochy are 10 feet higher than those of Loch Oich, and are reached by the intervention of a single lock. This loch forms the summit of the canal, which then descends 64 feet to Loch Eil by eight locks. The whole of these eight connected locks are formed of solid masonry 1,500 feet long. The foundations of the embankment at Clachna- charry are in mud, which is so "soft that an iron rod could be thrust down 55 feet with ease. The mode in which the lock at this point was constructed is so instructive that we give it. The immense depth of mud precluded the use of a coffer-dam ; an iron railway was accordingly laid down, on which the heavy clay found close by was carted, and the two banks of the canal were formed by “tipping” as far as where the depth of water at an ordinary neap tide was 20 feet, and when the site of the intended lock was approached, the banks were united into one mass. The weight of the clay compressed the soft mud, and squeezed out the water. Upon this mound of clay a quantity of stone was laid, and allowed to remain for six months, by which time the mound had sunk 11 feet, and become consolidated. The pit for the lock was then excavated out of the consolidated clay, and the water kept down by a steam-engine of nine-horse power. At the bottom of the excavation rubble stone masonry was laid with hydraulic mortar to the thickness of 2 feet in the middle of the chamber, increasing to 5 feet on each side, and upon this an inverted arch of masonry was struck, and the side walls built. The entire cost of the canal was .£982, 359, and the quantity of Baltic timber expended upon the works was so great that the price rose from 2s. 6d. to 7s. per cubic foot during the time occupied in its construction. . THE ELECTRIC TELEGRAPH.— VIII. THE MOUSE PRINTING TELEGRAPH — RINGING-KEY — CODE— THE RECEIVING INSTRUMENT ARRANGEMENT OP IN- STRUMENT-ROOM. The telegraph instruments we have already described are those that transmit their signals by the property which the electric current possesses of reversing the poles of a magnetised needle. We must now consider the next class of instruments — 'namely, those in which the power of the current to convert a bar of soft iron into a temporary magnet is turned to account. As we saw in our lessons in “ Electricity ” in The Popular Educator, we have only to take a rod of iron, and wind some insulated wire many times round it, and then, by sending a current along the wire, we at once convert the rod into a powerful magnet. This magnetic power continues as long as the current passes, but THE ELECTRIC TELEGRAPH. 47 ceases as soon as it is in any way interrupted. Now it is pretty clear that we may in several ways avail ourselves of this power in the transmission of messages, since it is perfectly immaterial at what part of the circuit the current is interrupted. The telegraph instrument which, next to the needle instru- ment, has come into most general use, is one of this class, and is known as the “ Morse Instrument,” after Professor Morse, by whom it was invented. This instrument is found in practice to answer extremely well ; it may, in fact, be in most respects re- garded aa the best instrument known for general use, being simple in its construction and action, and not liable easily to get out of order. One great advantage that it possesses over the needle instrument is that it prints or embosses its own message on a strip of paper, and thus leaves a permanent record ; whereas, in those already described, the operator must observe the very transient signals, and at once write them down or dictate them to another clerk. If a word or letter be dropped, the sender must be interrupted and made to repeat ; while in the Morse the whole message is printed, and the receiving clerk can then carefully read and transcribe it at leisure. The original strip may also be preserved for reference if necessary ; and, in addition to this, the fact that the transmitting clerk knows that he is actually printing his message, and that thus any mistake will at once be brought home to him, tends to render him much more careful. The peculiar click of this instrument will be familiar to many travellers, as it may very frequently be heard at work in the booking offices of railway stations. The “ transmitter,” or, as it is usually called, the “ ringing- key,” of this instrument is much simpler in its construction than that required for a needle instrument, since the current has only to be sent in one direction. All that is required is an arrange- Fig. 34. ment by which the circuit can be interrupted, and a battery current made to pass along it at pleasure. All this is easily effected by the instrument shown in Fig. 34. The base is made of some hard, dry wood, usually mahogany, and a stout brass rod is mounted on an axle fixed to this ; a handle, b, being affixed to one end of it, and an adjusting screw, c, to the other. One battery wire, p, is connected to a binding- screw, which communicates with a small anvil placed under B, and is usually tipped with platinum ; the other battery wire is joined to the earth-plate, l is the line-wire, which it will be observed communicates through a binding-screw with the rod B c. Above the small anvil is a short piece of wire which comes into contact with it when B is pressed down, and thus causes the current to pass from p to E, and on to the distant station. A spring, however, keeps this point away from the anvil when the instrument is at rest. The screw c presses on another plate or anvil at the other end, from which a wire, A, leads to the receiving apparatus and on to earth. The reason of this is that the wire L is used for the transmission of messages in either direction. When, therefore, the key is at rest, as shown, any current arriving by L passes through c and A to the receiving portion of the apparatus, and there makes the required signals. When, however, we want to send a message, and press down the key for that purpose, our own receiver is cut out of circuit, and the current only goes through the distant instrument. One inconvenience sometimes arises from this arrangement. If the line-wire were in any place broken or injured, no current would pass, and the operator might continue to send the mes- sage, supposing all was right, for as the current does not pass through his own instrument, he would not know that the circuit was broken. The receiver, too, might want to interrupt him, but with this arrangement would be unable to do so. A small galvanometer is therefore always placed in the course of the line-wire, and the constant currents sent cause the needle of this to keep continually oscillating. If now the distant operator wishes to interrupt, he merely presses down his key, so as to remove the screw c from its anvil, and thiis break the circuit. No current will now pass, and the sender, perceiving that his galvanometer has ceased to vibrate, will at once wait and hear what the distant station has to say. It will thus be seen that this small galvanometer is a very important part of the apparatus. The sketch in Fig. 35 will render clear the manner in which the different pieces of apparatus are joined in circuit in the way we have been explaining. For the sake of simplicity, we have here represented the key as consisting of a bar of metal, tho centre of which is in connection with the line-wire, while the ends may communicate with the battery, b, or the instrument. m ; and by referring to the illustration of key already given, it will be seen that this is essentially the case. G, G represent the galvanometers placed in the circuit of the line-wire, and E, E the earth-plates. Tho receiving part of the instrument is much more compli- cated in its construction. The message is printed on a strip of paper about half an inch wide, a long roll of which is placed on a drum supported above the body of the instrument. _ Tho end of this riband passes between two rollers, which are pet in motion by means of clockwork, the driving power being in some cases derived from a spring contained within a barrel, and in other cases from a weight. A fan is attached to some portion of the clockwork, so as to render the motion of the paper uniform. This part of the apparatus does not require further description here, and almost every maker adopts some special form of con- struction peculiar to himself. The electrical portion of the instrument is that which more especially concerns us, and this is remarkably simple in its make and action. The line-wire is connected to a binding-screw attached to the base of the instrument, and from this the current- passes round the coils which surround two iron rods placed side by side. In Fig. 36 we have a view of the essential parts of the apparatus. A is one polo of the electro-magnet, and b its keeper, which is fastened to the lever B d. This oscillates with very little friction on pivotB at c, and its play is limited by the arm, I, attached to it, and the set-screws, G G. The end of A is usually covered with a piece of thin paper or a layer of varnish. as otherwise a little magnetism often re- mains in it, causing the keeper B to remain in contact after the current has ceased. A spiral spring, capable of adjust- ment by the milled head h, is fastened to the end of the lever remote from the magnet, and when the current is not passing holds the keeper as far away from the magnet as the set-screws, G G, will allow. r> is the style, or pen, and is so placed that it is opposite a groove in the roller e. The paper riband is drawn between e and F As soon now as a current is transmitted along the line-wire, and passes round A, it converts it into a magnet, and over- coming the spring at n, presses the style D against the roller, and thus embosses or indents the paper strip. If this strip be in motion we shall evidently have a continuous line traced along it so long as the current passes, and when we 48 THE TECHNICAL EDUCATOR. interrupt the current there will be a corresponding blank. We might in this way send strokes of various lengths, but this would be found inconvenient, since the paper does not always travel at exactly the same rate. Only two signs, therefore, are employed— a dot, which is produced by sending a very brief current, and a dash, which is made by keeping the key pressed down for an instant. Sometimes, instead of a blunt point at d, we have a wheel with a narrow edge, which is in contact at one side with an ink roller. In this way the marks are inked on the paper strip, instead of being embossed. We have, then, nere, as in the case of the needle instrument, two distinct signs— the dot and the dash— and by a judicious combination of these we can send any letter in the alphabet we choose. The very same code is employed as that used with the single-needle instrument; in fact, the code used for that is merely the Morse code translated, an inclination of the needle to the left being considered the equivalent of a dot, and one to the right representing the dash. We append, however, the full code of the Morse, which is now adopted in nearly all countries. great. We give as an example a specimen of a strip as re- ceived, the equivalent letters being placed under each sign. The main difficulty in transmitting messages with this instru- ment is found in arranging the spaces properly ; and to meet this Professor Morse introduced a transmitting plate, in which each letter was represented by strips of ivory and brass inlaid m a board. Any letter could then be sent by merely drawing a metal style connected with the line-wire over the sign on the plate, but this never came into general use. The full construc- tion of the receiving apparatus, and the general arrangement of the instruments in the office, will easily be understood by re. ference to Fig. 37, which shows the interior of an instrument, room completely fitted. Fig. 37. — INTERIOR OF AN INSTRUMENT-ROOM. The letters of the alphabet are thus represented : — A . — A (so) . _ B _ ... C D E . F . ._. G H .... I .. K L M N O (ce) — T E S ... T — U U (ue) V w . X Y Z Ch The following code is adopted to represent figures 3 . 4 ..... 5 6 ... 7 Tn this code, as will be seen, no letter requires more than four signs, while figures are all represented by five. The stops can easily be learnt from the needle-code in Lesson V. Spaces about equivalent in length to the dash are left between each letter, those separating the words are about three times as In the instrument here shown, the set-screws which govern the play of the lever are placed at the end of the lever instead of on an arm attached to it, as seen in Fig. 36, but they act in the same way. The course of the paper strip can now be traced as it leaves the upper drum, passes between the rollers, and, after being embossed, is wound on to the second drum to the left. Both these are so made that one side will tako off, and allow the disc of riband to be removed or replaced. The clock- work is contained within the brass case of the instrument, the key by which it is wound up being seen. p is the battery-wire just disconnected from the ringing-key, behind which is the galvanometer. To the left of this is a switch, by which the current as it enters may be directed at pleasure to the alarum or the instrument, or, in the case of an intermediate station, be made to pass straight on. The wire L is that which communicates with the line, while t is connected to the earth-plate. The alarum is seen behind the drum on which the riband is coiled. The only other point to whicn we need refer is the small lever seen at the base of the receiving instrument : by means of this the clockwork can be started or stopped at pleasure. It would not do for the paper to be continually unwinding ; the clockwork is therefore stopped by means of this lever. As soon as the alarum rings to indicate that a message is coming, the clerk alters the switch, so as to direct the current to the instrument. He then gives a signal to show he is attending, and starts the clockwork. The riband then commences to unwind, and is embossed with the message which he can afterwards transcribe, THE STEAM-ENGINE. 40 THE STEAM-ENGINE.— VIII. By J. M. Wignee, B.A. CONDENSER — AIR-PUMP — FORCE-PUMP — GOVERNOR BALLS — THROTTLE-VALVE HORSE-POWER WATT’S INDICATOR. In non-condensing engines the steam, after having done duty in raising or depressing the piston, is allowed to escape by the exhaust direct into the air. The consequence of this is that the full pressure of the air is exerted against the opposite side of the piston to that on which the steam is acting, and all this pressure has to be overcome before the piston can be moved. In the condensing engine which we are now describing this source of waste is almost obviated. The cylinder here is nearly void of air, so that if we can in any way condense the steam that fills the cylinder after it has accomplished its work in driving the piston to the end, we shall have a vacuum into which the piston may return, and shall thus avoid all loss of power from this cause. This object is accomplished by means of the condenser, which is another of the many great improvements in the engine that are due to the genius of James Watt. In the earliest engines the plan adopted was to cool the cylinder by the application of cold water to its exterior surface. This plan was very slow, and caused a great loss of heat, as tho cylinder became so cold that a portion of the fresh steam as it entered was expended in raising its temperature again, and in so doing became condensed on its inner surface. The next improvement consisted in injecting a jet of water into tho cylinder, and in this way the condensation was effected much more rapidly, but still there was much waste of heat. At last Watt introduced tho separate condenser, which has been found to answer remark- ably well, and to effect a verv great saving. The condenser is represented at o (see Fig. 32, page 17), and consists of a large air-tight vessel communicating with the exhaust by means of the pipe seen under the valve facing. A small force-pump, R, worked by a rod, h, jointed to the work- ing beam, raises cold water from a cistern or well, and forces it along the pipe, t, into the con- denser. The inner end of this pipe is fitted with a rose, so that the water is scattered in a fine shower, and thus condenses the steam very rapidly, so that a considerable degree of exhaustion is maintained. A pressure gauge is usually affixed to the condenser, so as to indicate readily the exact degree of condensation produced. By the use of this arrangement the condensation is practi- cally instantaneous, and there is no delay in commencing the alternate stroke. The injected water added to that produced by tho condensation of the steam accumulates in the condenser, and would soon impede its action were no means provided for removing it, and any air which may find its way in with it. An air-pump, m, is therefore placed by its side, and motion is im- parted to it by means of the pump-rod, f, which is affixed to one rod of the parallel motion. A pipe, closed by a valve opening outwards, leads from tho lower erd of the condenser to this pump, and along this the condensed water and the air pass, and are delivered into the hot cistern, n. The air, of course, bubbles up through the water and escapes. The s:eam when it leaves the cylinder has still a large amount of heat stored up in it, and this raises the temperature of the injected water, so that the water in n is quite hot. It is used, therefore, to feed the boiler, into which it is injected by the pump, Q, along the feed-pipe, s. As much of the heat in the steam is latent, a large amount of water is required to condense it. If the condensing water has a temperature of about 60° while the temperature when condensed is 100° or 120°, nearly twenty pounds of water will be required to one pound of steam. This is, of course, very much more than is required for feeding the boiler; aud hence, in many engines, arrangements are made by which a portion of the condensed water leaves the condenser 30 — vol. ir. Fig. 33. at a temperature very little below the boiling-point, and with this the boiler is fed. The more usual plan, however, is for the feed-water to have a temperature of about 120°. Various other kinds of condensers are often employed in place of that already described. In steam vessels “ surface condensers ” are commonly adopted. In these the steam i3 made to pass through a series of brass or copper tubes, on the exterior of which the cold water plays, and thus condenses the steam. In other cases the positions are reversed, the water being made to pass through the tubes while the steam is condensed upon their external surfaces, and this plan appears to meet with more general approval. In this kind of condenser it is well to let the circulation be as rapid as possible, and the more rapid it is the less the area of condensing surface that will be necessary to ensure efficiency. The usual proportion allowed is from twelve to eighteen square feet for each nominal horse-power of the engine, but with a rapid circulation less than this will suffice. There must, however, be no delay in the condensation, or else a resistance will be offered to the movement of the piston. The supply of the water and steam should be so arranged that the steam as it enters the condenser is first exposed to the action of the heated water just leaving it. In this way the cold water entering meets the steam when its condensation is nearly completed. Condensers of this kind answer very well, but it is not often found necessary to employ them except in the case of marine engines. Wo have now referred to the various parts of the engine that are 3hown in Fig. 32 : there is, however, one important part omitted there. In most cases it gill l lll i lilll l S is an important thing to main- tain a nearly uniform rate of motion. Without some regula- tor, however, this cannot be attained ; the pressure of steam in the boilers often varies con- siderably from time to time ; the load of the engine is also sub- ject to constant fluctuations ; and in a large factory some of the machines are frequently stopped for a time, and others again are set to work. The tendency of all these alterations is to produce great variations and irregularities in the speed of the engine, and cause thereby much inconvenience. The manner in which the speed is usually regulated is by means of a throttle-valve, acted upon by governor balls, as seen in Fig. 33. This valve consists of a metal disc, g, placed in the steam-pipe ; it is mounted on an axis passing through it edge- ways, so that when it is horizontal the passage of the steam is not materially affected, but as it is inclined the passage becomes more and more closed. In some convenient part of the engine is placed a vertical axis, H I, mounted on pivots at each end, and driven by an endless band passing round tho driving pulley A, and also round the axis of the fly-wheel or some similar part. On this axis are jointed two bent levers, c B, C B, each of which carries at its lower end a heavy metal ball, b. Above c c is a loose collar, d, supported by two rods, K K, hinged to the other ends of the levers, and moved by them. A groove in this collar holds two pins in the crutch of the lever, d E f, and thus moves the throttle-valve, G. If now the load of the engine be diminished, or from any other cause the speed increase, the balls at once, by centrifugal force, fly further apart. In so doing they raise the upper ends of the bent levers, and with them the collar d. The result of this is that the end, F, of the lever is depressed and the valve partially closed, and the supply of steam being in this way diminished, the speed of the engine is at once reduced. If on the other hand the engine moves more slowly, the governor balls fall, and thus open the throttle- valve to a greater extent. In this way the speed is maintained very nearly at a uniform rate. In some engines now made, the governor balls, instead of working a throttle-valve, are con- nected with a second slide-valve, and thus alter the period of the stroke at which the steam is cut off, and in this way regu- late the speed. A regulator of the kind already described is that most gene- 50 THE TECHNICAL EDUCATOR. rally used. Its action is, however, far from perfect, as it takes some little time for the engine to recover its rate of speed after a sudden variation in the load. Many alterations have been suggested : in some of these the governor balls are retained, but the construction of the valve is very materially modified, so as to render it much more sensitive. In one form, which has been found to answer well, a double spindle valve is used in place of the disc, two valves being mounted on the same spindle, so that a trifling movement of this materially alters the rate at which the steam is allowed to pass. Before passing on to notice the construction of other kinds of engines, it will be well to explain the manner in which the power of an engine is described. In reading any books or papers relative to engines we constantly find the term “ horse- power,” the engine being said to have so many horse-power. Now it is important for us clearly to understand what is meant by this expression, especially as it is often somewhat vaguely employed, being in some cases used to denote “nominal” power, and in others “ actual ” power. The latter, of course, varies with the pressure of the steam employed, but the former is an arbitrary term expressive of the size of the engine, and may generally be taken as expressing the actual power when the steam has a working pressure of 7 pounds to the inch in the case of a low-pressure engine, and 21 pounds in the case of a high- pressure engine. The actual steam pressure usually exceeds this, and as a result the actual power of any engine is usually much in excess of the nominal. The term “ horse-power ” was originally an arbitrary standard taken to express the work capable of being, under ordinary circumstances, performed by a horse, and is now used as ex- pressive of a force capable of raising 33,000 pounds to the height of one foot in the space of a minute. The actual horse- power of any engine may therefore be easily calculated. By means of an “ indicator” or gauge the actual pressure in the cylinder is ascertained, and from this a deduction of 1 .^ pounds is made to allow for loss by friction, imperfect vacuum in the condenser, and similar causes. We then ascertain the area of the piston in square inches, and multiplying this by the working pressure obtained, as just explained, we find the total pressure on the piston. Now multiply the number of strokes performed in a minute by the actual length of each, and we shall thus learn the space traversed by the piston in feet. Multiplying this by the total pressure, and dividing by 33,000, we have the actual horse- power. The rule for calculating this should be carefully remembered, as it is often required, and it may be simply expressed in the following form : — Prom the pressure of the steam, expressed in pounds per square inch, deduct pounds for loss, and multiply the area of the piston in square inches by the remainder ; then multiply this amount by the space travelled by the piston per minute ex- pressed in feet, and divide by 33,000 ; the quotient will be the actual horse-power. An example will render this perfectly plain. Let us suppose an engine whose piston has an area of 200 square inches, and the length of whose stroke is two feet. Further, let it make sixty complete strokes or double movements of the piston per minute, and let the pressure of the steam be twelve pounds per square inch. What is its actual power ? The pressure exerted on the piston by steam in this case is 200 x 10 J, or 2,100 lb., and the space travelled over by the piston in each minute is 120 X 2, or 240 feet. The work ac- complished, therefore, is 2,100 X 240 = 504,000 foot-pounds, and the horse-power, therefore, is 504,000 or a 0Ter 15 . jf 33,000 in any of these cases the vacuum in the condenser is imperfect, there is a corresponding pressure opposed to that of the steam, and this must be allowed for in calculating the power. The nominal power is, as we have said, an arbitrary expres- sion, and is nearly always considerably below the actual power, being often as low as from a fourth to an eighth of it. The formula usually employed for calculating this is known as the Admiralty rule, and is as follows, -^-L, where d is the 6000 diameter of the piston expressed in inches, and v the velocity of the piston expressed in feet per minute. We can now apply this rule to the case just given, but must first ascertain the diameter of the piston, and since its area is 200 square inches, this is about 16 inches. The formula - therefore becomes 16 X 16 X 240 = *?-— = 10 J nearly. 6000 600 This, then, is tho nominal horse-power of the engine. The same term is frequently applied to a boiler as expressive of its size and capabilities ; but it is very evident that in this case its meaning is somewhat different. An engine of one horse-power will, as we have seen, exert a force equivalent to raising 33,000 lb. a foot high per minute. In an hour, therefore, it would raise nearly 2,000,000 lb. to the same height. Now we have seen that the evaporation of a cubic inch of water exerts a force equivalent to raising a ton a foot high; to raise the 2,000,000 lb., therefore, will require the evaporation of nearly 1,000 cubic inches of water. A con- siderable portion of the force thus produced is, however, employed in moving the engine itself, and wasted or lost in various other ways, so that a much larger quantity of water must be evaporated by the boiler to accomplish the amount of work required. Allowing for all these sources of waste, engineers calculate that as a general rule a boiler should evaporate one cubic foot of vater per hour for each horse-power of the engine. This is therefore taken as the standard ; and thus, when a boiler of 50 horse-power is spoken of, we at once understand that one is meant which is, under ordinary circumstances, capable of evapo- rating fifty cubic feet of water per hour. There is a small but very important piece of apparatus that is frequently attached to one end of the cylinder of an engine, and known as the “indicator,” to which we must here refer. The pressure of the steam in the cylinder is often very different from that in the boiler, as the size of the steam- pipes and ports considerably modify it. We require, therefore, in order to tell accurately the power of the engine, some means of ascer- taining the pressure in the cylinder during the stroke. The vacuum in the condenser may likewise become imperfect, owing to the air-pump being out of order, or from some other cause, and we want in some way to be apprised of the fact. Both these ends are accomplished by means of the indicator, which fs shown in Pig. 34. It consists of a brass cylinder, a, some ten or twelve inches long, and about two inches internal diameter ; it is very truly turned inside, and has a solid piston or plunger, b, fitting inaccurately. To the upper extremity of the piston-rod a pencil, g, is firmly fixed, so as to record on a card suitably placed the movements of the piston. At the lower end a screw is cut, by which it is usually affixed to the upper end of the cylinder, a stop-cock, e, being placed so as to cut off the com- munication when it is not required to use the instrument ; a spiral spring is fixed to the piston, b, and at the upper end to a ring or fastening, c, fixed in a suitable position ; this is so arranged that when the spring is in its normal state, the piston is about the middle of the cylinder. The spring can, however, be compressed or extended. A card, f, is mounted in a frame placed above the indicator, and made to move backwards and forwards with the motion of the piston. This is usually accomplished by a cord passing round a pulley, and fastened to some convenient part of the engine. This cord pulls the card one way, and as soon as the motion of the piston is reversed, a spring or weight brings it back to its original position. When the stop-cock, e, is closed, the pencil is at rest, and a horizontal line is therefore traced on the card as it moves to and fro ; but as soon as the steam is allowed to enter the indicator, the pencil moves up and down, and a figure is traced on the card which indicates to an experienced eye the action of the engine. Let e be turned on just as the steam is admitted to the upper end of the cylinder, the piston b will be immediately forced up, and trace an almost vertical line ; the full pressure is not, however, instantly attained, and hence the line continues for agricultural drainage and irrigation. 5 a little way to slope upwards. If the steam is cut off at a | third, or any other portion of the stroke, the line immediately tends downwards, and by its rapid fall indicates the decreasing pressure, until the piston arrives at the lower end of the cylinder. The upper end is now put into communication with the con- denser, and if the vacuum there bo good, it will be indicated by a sudden, fall in the curve. The pressure of the air being allowed to act freely on the upper side of the piston, it will by this be depressed below the normal line, the spring being I extended by the pressure, and the lower the piston sinks the more perfect does it show the vacuum to be. It is compara- tively easy to graduate the card so as to show at a glance the exact pressure, and also the degree of vacuum in the condenser ; and the further these extremes are removed from one another, the greater is the power of the engine. We may, in fact, obtain a general idea of its action from the area of the figure traced on the card ; for the larger this is, and the more closely approaching to a parallelogram, the more perfect is the action of the engine. Apart from showing in this way the power, the indicator diagram is of very great service in showing the action of the valves. If, at the extreme right of the figure, the line descends but slowly, it clearly shows that the communication with the exhaust is made too slowly, or else that condensation does not proceed with sufficient rapidity. The more vertical the line is here, the better is the action of the condenser. The ascending stroke at the other end of the card should likewise be nearly vertical; but to an experienced engineer each corner of the diagram will indicate some peculiarity in the action of the “lap” or “lead” of the valve, and thus enable him at once to point out and rectify any defects. We can, however, only just point out the broad principle of this very valuable piece of mechanism, and for full details must refer the student to some of the various works that inquire fully into the indicator and the indicator diagram. AGRICULTURAL DRAINAGE AND IRRIGATION.— YIIL By Professor Wkightson, Royal Agricultural College, Cirencester. SEWAGE IRRIGATION. The sewage question is interesting and important from two aspects : first, because it touches the sanitary condition of the country; and, secondly, as an agricultural problem. The pollu- tion of our rivers has been the first and most distressing effect of a large population and a defective sewage system ; and the loss of an immense mass of valuable fertilising material has been the second, although less urgently pressing, inducement to action. Hence the sewage question claims attention alike from town and country; and it is not surprising that every intelli- gent person throughout the kingdom should be more or less interested by it. The problem is simplified by the admirable manner in which the agricultural requirements meet those of a more purely sanitary character. If the rivers cry out against an influx of filth, the land calls as loudly for material to restore its waning fertility ; hence, both the land and water are grateful when sewage is diverted from the rivers and poured over the fields. Time is required to show how far such a system can be generally and successfully applied. The soil possesses a won- derful deodorising and decolorising power, and filthy water, after having passed through a layer or filter of earth, comes forth more or less purified. Soil has also been shown, of late years, to be capable of removing some of the most important elements of fertility from solution, and holding them until they are required as plant-food. This power is not yet fully under- stood, but it is supposed to resemble that possessed by woollen cloth for fixing colouring matter used in dyeing, or the power by which charcoal acts in purifying sugar. Hence, soil is well calculated both to render sewage innocuous, and to conserve its valuable fertilising qualities. The only questions are : How far these powers possessed by soils are likely to be persistent in any particular case ? how far the produce of such land will continue to be wholesome ? and how far the sewage will continue to flow from the area devoted to it as a pure stream ? We are thus introduced to the subject of “sewage irrigation,” offering, as it does, a simple solution to an important national question. Divert the streams of sewage from their course towards the neighbouring river; construct a series of water-meadows, or fields for cultivation, laid out upon a similar principle, and allow the fertilising flood to expand over their surface ; let the purified water again be collected by ditches and discharged into the river at a lower level. Such is the simple plan proposed, and in many cases carried out with success, up to the present time. Before entering more into detail with reference to cases in which this principle has been adopted, I shall point out the advantages it presents over rival systems for utilising sewage. It deals with sewage as it is. There seems to be little reason for expecting that the population of this country will abandon the water-closet. Earth and ashes may in country places be advantageously substituted for water, as lias been shown by the Eev. H. Moule, but such a plan is not likely to meet with favour in towns, and appears impracticable for such gigantic centres of population as London, Birmingham, and Liverpool. If it be granted that water will continue to be the vehicle for carrying away urban excreta, then we have irrigation as the sole means by which it can be advantageously applied. Schemes have indeed been proposed by which the valuable matter contained in sewage, as well as the deleterious and offensive matter asso- ciated with it, should be precipitated, collected, dried, and used as a manure, while the water, freed from its impurities, should then flow harmlessly on its course. Feasible as such a proposal may at first sight appear, it is beset with difficulty. The value of sewage does not depend upon its filthiness, but upon certain ingredients which occur in very small quantities. • Bobbed of these, the sewage water would be valueless, and any system of sewage utilisation, on the principle of precipitation, must pro- vide that these valuable ingredients be arrested in the precipi- tated mass. This, however, is a difficulty which appears insur- mountable. First, because these valuable ingredients — ammonia and potash — are exceedingly loth to quit their soluble condition under any circumstances, and especially when mingled with such a mass of water as in town sewage. The consequence is that, precipitate as you like, or with what you please, the ammonia and potash will flow away in the “purified” water, and the remaining mass, whether it be named ABC or X Y Z, will be of small fertilising value. From these considerations it is evident that as yet no plan based upon the principle of precipita- tion is likely to suoceed, and that irrigation is the only alter- native. We have, then, to do with an immense mass of sewage, the character of which we must very briefly consider. Sewage consists of the entire water-supply of our towns after it has been used for domestic purposes, of the excreta of man and animals, of the rainfall of the town area, and of earthy matter washed and worn from the streets. It contains valuable ferti- lising matter in an extremely dilute condition. This can be demonstrated by analysis, and many eminent chemists having examined town sewage at various times, have given us a toler- ably accurate idea of its composition. Phosphoric acid, nitro- gen, and potash, are the three principal ingredients of agricul- tural importance. These substances can be purchased in the form of guano, “superphosphates,” potash salts, and other manures ; and since these substances are marketable, an esti- mate can readily be formed as to the cheapest rate at which they may be obtained. Thus, it may be shown that ammonia may be purchased in the form of some manorial substance at the rate of, say, £60 per ton. Hence, a commercial value may be attached to the three substances above mentioned, and by finding the proportion in which they exist in town sewage, an estimate may be formed as to its value. It is needless here to enter further into detail, and it is sufficient to state that the value of sewage calculated upon purely chemical grounds is l'8d. per ton, varying, of course, according to season and other con- ditions. The result of sewage irrigation agrees closely with this estimate, being more usually below than above it. Thus, in the case of Rugby, where the effects of sewage were closely watched by a Eoyal Commission, the Commission lost money upon the sewage, contracted for at Id. per ton. On the Barking Creek farm the result of sewage application was approximately that 100 tons of sewage yielded 1 ton of grass, and if this were worth 10s., then 100 tons yielded 10s., or at the rate of l - 2d.per ton. It is only fair to state that Mr. Mechi, who converts the whole of his farm manure into the liquid form, obtains very 52 THE TECHNICAL EDUCATOR. superior results to those just given ; but it must be remembered that Mr. Mechi has perfect control over the composition of the liquid manure used at Tiptree, which is, probably, frequently more concentrated than town sewage. Also, at Tiptree the liquid dressing is applied when it is required ; whereas in the utilisation of town sewage it is necessary to pour the water over the land at all seasons, whether required or not. We have, then, to do with a substanco of trifling value per ton, although of high value when wo reflect upon its immense quantity. The question is therefore as follows : How is a substance valued at from Id. to 2d. per ton to be economically applied to the land ? How can we carry such a worthless material for miles into the country, and apply it for purposes of cultivation P The answer is simplo. It cannot bo applied advantageously where any appreciable cost per ton must be incurred. Pumps, expensive pipes, and business expenses, are serious difficulties in sewage application, and success will probably only ensue where gravity is the sole force for conveying the sewage to its destination. The estimated value of sewage depends upon chemical analysis, and upon results obtained at Rugby and elsewhere from its use. Both methods, however, fail in precision : the first, because the value of the water as an essential element in the development of plants is not considered; and the second, because the sewage has never been applied under conditions calculated to bring out its maximum effects. Could the use of sewage be restricted to seasons of the year when water is most needed, and could it then be applied to plants capable of making the greatest use of it, results far superior to any yet recorded might be obtained. It is, indeed, probable that the success attending liquid manuring at Tiptree and elsewhere may be thus accounted for, as in such cases thorough control can be exercised. In dealing with the drainage of a large town, storing the sewage cannot be contemplated. At the same time much may be done towards its profitable application by so dividing the fields over which it flows, that crops may be grown requiring it at different periods. This has been done with success at Barking Creek farm, where rye-grass, cereals, flax, mangold, strawberries, etc., are very successfully cultivated with tho aid of sewage. I shall now mention a few cases in which the drainage of towns has been used for irrigating land. Edinburgh offers one of the oldest examples. There the sewage is allowed to flow over a tract of about 300 acres, with good results per acre, but the amount realised per ton of sewage is difficult to estimate, on account of the vast mass of water employed. The produce per acre per annum is from <£20 to £30 worth of grass, sold to the cow-keepers of the city. The quality of the land is exceedingly poor, being little better than sand, a fact which has given countenance to the scheme of the Essex Reclamation Company for pouring the sewage of North London over the Maplin Sands. It is worthy of remark, that immense as is the mass of water used per acre in the case of the Edinburgh meadows, any attempt to enlarge the area of irrigated surface has been attended with a diminished yield over the remainder. Another curious fact is, that although sewage is capable of raising large crops of grass, the fertility of the soil does not appear to be increased. This fact has been pointed out by Messrs. Lawes and Gilbert, in their experiments at Rugby, where land, which had produced large crops under the influence of sewage, imme- diately fell back to its old standard of productiveness when the supply of sewage was withdrawn. The authorities just named made a series of experiments upon the use of sewage in the neighbourhood of Rugby. They employed the large quan- tities of 3,000, 6,000, and 9,000 tons of sewage per acre respec- tively, upon contiguous plots, and found that each additional quantity was followed by an increase of crop, although the amount of grass per 100 tons of sewage used was less in the case of the heavy dressing. This, taken in connection with a similar result obtained at Edinburgh, is interesting, as showing the large amounts of this material which may be advantageously applied to land. Further, at Rugby it was found that although a large quantity of grass was grown, the quality of the herbage suffered under the system of sewage irrigation. The utilisation of the Croydon sewage has very often been cjtod as a successful enterprise. In this instance, sanitary con- siderations have been the chief inducement to action, and the writer will never forget one proof that, from this point of view the success has been most complete. On a hot day in July he arrived at Beddington, and was kindly received by Mr. Marriage, the lessee of the irrigated land. Among other refresh- ment, two bottles were placed upon the table, the one contain- ing a wine, the other a colourless fluid (not whisky), which was neither more nor less than purified sewage. It appears that visitors to the irrigated fields are given the choice between wine and a sample of purified sewage, in order that they may thus test the complete success of the process used. The appearance of the liquid and the absence of smell betokened the removal of all unwholesome matter. The sewaged fiolds at Croydon yielded a rent of £5 per acre to the lessors in 1868, but the old lease was then just falling in. Italian rye-grass was the crop exclusively grown, and this required frequent renewal, as in a year or two its place was usurped by “ water-grass.” Frequent re-sowings have also been found necessary at Barking Creek farm. During the dry season of 1868 I was informed that the irrigated lands at Boddington suffered from the drought, although supplied with an almost unlimited amount of water. Here the sewage alternately spreads over fields, and is collected by ditches three times in succession, after which it flows into the river. The exit of the stream of purified sewage is perio- dically inspected, and the condition of the water reported upon. In the foregoing remarks upon sewage irrigation the subject has been treated very generally. The mass of published statis- tical information is exceedingly large, and in order to enter into details much more space would be necessary than is here allotted to the subject. The object of the writer has therefore been to introduce as many interesting facts as possible in con- nection with a subject which, in the preceding short essay, has been little more than outlined. PRACTICAL PERSPECTIVE.— YU. Hitherto all the planes and objects delineated have been supposed to be so placed that some of their lines are parallel, and others at right angles to the plane of the picture. We now enter upon the system by which perspective pro- jections are made when the sides of the plane or object recede from the picture at angles other than right angles. Reverting to Fig. 4 (Vol. I., page 293), it will be remembered that the triangle E c f was supposed to be laid down so that the points G and h were obtained on the horizontal line ; and these represented the true distance of the spectator from the picture. In the system now under consideration, a similar triangle, A c b, standing on the line a b, is supposed to be laid down below or above the horizontal line ; and this will give the point i, the station-point of the spectator. The line id is then called the line of direction, as indicating the direction of the central ray, or axis of the cone of rays. With this brief introduction, it will, it is hoped, be found possible for the student to follow the lessons. These are most carefully graduated, not merely according to theory, but from absolute practice in teaching. We will therefore at once pro- ceed to Fig. 34. — Here, having drawn the picture-line and the hori- zontal line, and having fixed the centre of the picture and the line of direction, the length of which is determined by the distance of the spectator from the picture, draw a horizontal line at s. Thus far for the height and distance of the spectator. The next question is this— What angles do the sides of the object make with the picture-plane ? This must, of course, depend on the plan given in Fig. 35, Here e f is the base-line, or line on which the picture-plane is to stand ; and the square abdc is the plan of the plane to be put into perspective. From this it will be seen that the angle pab is one of 40°, and the angle e a c one of 50°, with the plane of the picture. Returning now to Fig. 34, and having drawn a line at s parallel to the picture-line, on each side of the point s construct angles corresponding with the angles which the lines of the plan make with the line e f — viz., G s h and isj. In this case these angles are known to be 50° and 40° ; but as a rule, if a plan be given, the angles at the station-point may be constructed similar to those of the plan by the method shown in Fig. 18 of “ Prac- tical Geometry applied to Linear Drawing” (Vol. I., page 124). Produce the lines s H and s j until they meet the horizontal lino; and these points of meeting are called the vanishing PBACTICAL PEESPECTIYE. 53 points for these lines. Call the one v p 1 (vanishing point No. 1), and the other v p 2. From V P 1, with radius vpI to s, describe an arc, cutting the horizontal line. Call this intersection m p 1 (measuring point No. 1). From v p 2, with radius v p 2 to s, describe an arc, outting the horizontal line in mp2 (measuring point N». 2). Now it will be remembered that when in former studies a line was supposed to be receding from the picture-plane at right angles to it, and it was required to cut off a certain portion of that line, or to mark a particular point upon it, the real length 1 to be cut off was marked on the picture-line, and a line was drawn to the point of distance , intersecting the original line in The reason why these points are called measuring points will be understood when their use in measuring is seen as we proceed. All the points necessary for our present purpose having been fixed, we can now proceed with our perspective projection. Having fixed that the angle A of the plan shall be at a' on the pictur3-line, draw a line from a' to each of the vanishing . points. a point required. In the present system of perspective, the measuring points are used for this purpose, as will bo seen by the following process : — From a' set off on the picture-line the length a' b’ and A' o', equal to ab and A c, the sides of the plan. From b' draw a line to the measuring point belonging to the vanishing point to which the line which is to be cut off is drawn. Thus the fine we are now considering is drawn from a' to V P 1 1 therefore, THE TECHNICAL EDUCATOK. from b' draw a lino to mpI, which cutting the lino a'vpI, gives the intersection b, which is the point required ; and a' b is the perspective representation of the line ab of the plan when receding at 40° from the picture. Similarly, draw a line from a' to V p 2 ; and from c' draw a lino to M P 2, cutting a' Y p 2 in c. Then, as in the former case, A' c is the perspective representation of the line A c of the plan. It is here necessary to bear in mind a short rule — viz., all lines which in the object are 'parallel to each other vanish in the same point. Now, on referring to the plan, it will be seen that the line B d is parallel to A c, and that the line c D i3 parallel to A b. Therefore, in the perspective projection, these lines will vanish in the same points. From b draw a line to v p 2, and from c draw a line to v p 1. These lines intersecting in d (which corresponds with d in the plan) will give A ' b dc as the perspective representation of the plane abdc when placed at tho angles of 40° and 50° to the picture-plane. Let us take Fig. 35, however, to be not a single plane , but the plan of a cube, the faces of which are at the stated angles to the picture-plane. Then, having projected the plan already shown, erect a per- pendicular at a' — viz., a' k. This perpendicular is to be the real height of the foremost edge of the object, whatever that may be. But as in this case a cube is the subject of the study, tho edgo a'k will of course be equal to any one of the edges of tho plan — viz., A b, a c, b d, or c d. New the upper edges of the cube are parallel to the lower ones, and therefore they will vanish to the same points. Therefore from k draw lines to both vanishing points. From b and c draw perpendiculars cutting the lines drawn from k in L and M. From L and m draw lines to vpI and v p 2, and these, inter- secting in N, will complete the representation of the cube. It will prevent the student experiencing much disappointment in his results if ho bears in mind that when the angle on each side of tho station-point has been constructed, the space con- tained between these two angles should correspond with the angle of the object itself ; thus, when an angle of 50° has been constructed on the one side of s, and an angle of 40° on the other, then the angle JSH remaining between them should be tho angle of tho object, which in tho present instance is a right angle. It is also necessary to point out when a rectangular object, such a3 a cube, stands at equal angles to the picture-plane — that is, when it recedes on each side at 45° — the points of distance become the vanishing points. Fig. 36. — In this figure the rule, that “ all lines which in tho object are parallel to each other vanish in tho same point,” is plainly illustrated. Here the subject is a square, divided into smaller squares by lii)C3 parallel to the sides. Having drawn the picture-lino, horizontal line, and line of direction, find the vanishing points and measuring points, as in tho former case ; it has already been stated that the station- point may be taken below or abovo the horizontal line. The latter is chosen in the present study. The angle A of the plan (Fig. 37) being fixed at a', draw lines to the vanishing points. From a' set off a'b' and a' c' equal to the sides of the square, and from these points draw lines to the measuring points, which, cutting the lines drawn to the vanishing points, will give tho points b and c, completing the perspective view of the ex- ternal square. Set off on the picture-line between A' and b' and a' and c' the paints T, 2'. 3', corresponding with those similarly figured in the plan. From 1, 2, 3 draw lines to the measuring points, cutting A' b and a' c, and from such intersections draw lines to the vanishing points, which, crossing each other, will divide the square as required, and will thus complete the perspective repre- sentation of tho original figure. Fig. 38. — This is another adaptation of the same study, and gives the principles on which windows, doors, etc., in buildings standing at an angle to the picture, are drawn. The height of the spectator and the distance having been fixed, let us suppose that tho angle at which the plane is to be represented i3 that shown at s — viz., fs a. Produce s G until it cuts the horizontal line in vp. From v P, with radius to s, describe an arc, cutting tho horizontal line in M p. Draw A B, the vertical edge of the plane to be drawn, and from its extremities draw lines to the vanishing points. From A set off A c equal to the width of the plane, and draw a line to the measuring point, which, cutting A V p in c, will give the plane for the distant vertical side c b. Now on A B set off the required points of division, e and D, and from these draw lines to the vanishing point, which will divide the plane into three strips, which, if it were parallel to the plane of the picture, would be horizontally placed. Between A and c set off the points 1, 2, representing the widths into which the plane is divided vertically, and from these points draw lines to the measuring point, cutting a c in 1,2; on these erect perpendiculars, which will complete the figure. BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS AND MANUFACTURERS. X.- GALILEI GALILEO. BY JAMES GRANT. Galilei Galileo, the inventor of the telescope — one of the most distinguished of Italian philosophers — was born in the city of Pisa, about the year 1564. His father, a Florentine noble, had him educated for the profession of medicine ; but a love for geometry inspired him, and to this study he turned all the powers of his mind. The writings of Archimedes and Euclid he mastered without the aid of a tutor ; and so great were his acquirements, that in his twenty-fifth year ho was appointed by Cosmo II., then Grand Duke of Tuscany, to the mathematical chair in Pisa. Before three years were passed he had to quit that city, his sturdy opposition to the philosophy of Aristotle having gained him many enemies ; so he accepted the professorship of mathematics in the then famous University of Padua, where for eighteen years his name adorned it, and he succeeded in developing a high taste for the physical sciences. Galileo had distinguished himself by no discovery (a few minor contrivances excepted) till he attained his forty-fifth year. This was in 1609, when he produced a telescope; and perhaps no invention that science has presented to mankind is so boundless in its influence, and so extraordinary in its nature, as that long glass by which distant objects are viewed clearly. It chanced that in 1609 — the same year in which Kepler pub- lished his “ Commentary on Mars ' ’ — Galileo was in Venice, when, in the course of conversation, he heard it stated that “ a Dutchman, named Jansen, had constructed and presented to Maurice, Prince of Nassau, an instrument through which he saw distant objects magnified and rendered so distinct that they seemed close to the observer.” Struck by this story, which a few believed and many discredited, the mind of Galileo became filled with the importance of such an instrument ; and so thoroughly had he already studied the entire science of lenses, that he not only discovered the principle of their application in a shifting tube, but was speedily able to make a telescope for his own use. To the uninstructed mind the power of seeing clearly objects at a vast distance brought close and nigh apparently, must seem miraculous ; and hence it was that the Arabs, whom the officers of Colonel Malcolm’s force in Persia permitted to. look through their telescopes, fled in terror, exclaiming, “ You are magicians ! Now we see how you take towns ; that thing, be they ever so far off, brings them as close as you like.” It was an invention valuable alike for peace and war ; but to have been the first astronomer in whose hands so valuable a gift was placed, was an eminence to which Galileo owed all his reputation and future persecution. As soon as his telescope was complete he applied it to the stars of the firmament, and on the night of the 7th of January, 1610, when first he used it, he saw close to Jupiter three little bright stars, hitherto unseen by human eye, lying in a line parallel to the ecliptic, two to the east and one to the west of the planet. Then a great emotion of enthusiasm is said to have filled his heart ; but regarding them as merely ordinary stars, he never thought of estimating their distances. But on the night of the 8th of January, when again regarding Jupiter, he BIOGRAPHICAL SKETCHES OF EMINENT INVENTORS, ETC. 55 was surprised to see all tlie three stars to the west of the planet. It was requisite that the motion of Jupiter should be direct to produce this effect, whereas it was distinctly retrograde. On the 10th he could distinguish only two stars to the east of the planet, the motion of which he was quite unable to explain. He ascribed the change to the stars themselves, and on the night of the 11th he no longer doubted that he had discovered three planets that revolved round Jupiter ; and on the 13th he saw, for the first time, the greater planet’s fourth satellite. This discovery cast a new light on the entire celestial system. Hitherto it had been believed that while this earth was the only planet favoured with the existence of a moon, it was of necessity the only one in the universe that was habitable, and as such occupied pre-eminence in being the centre of the system ; but the discovery of four moons revolving round a much nobler planet than ours, deprived the old argument of all force, and established a new analogy to it and the other heavenly bodies. In 1610 Galileo, in his “ Sidereal Messenger,” announced his great astronomical discovery to the then very limited world of science. Kepler perused it with the deepest interest ; for while it confirmed and extended his own brilliant discoveries, it dis- pelled the old illusions of past philosophy; and in the “ Disserta- tion ” which he published on the discovery of the learned Pisan, he expressed a hope that similar satellites might be traced around Mars and Saturn. Galileo next applied his wonderful glass to the study of Venus, and in 1610 discovered in the phases of that planet the forms of waxing and waning peculiar to the moon. He next detected the spots on the face of the sun, ascribing them to the rotation of the central luminary ; and on the surface of our moon he saw her valleys in shadow, her mountains in light, and determined the curious fact of her balance or trepidation in the firmament, in virtue of which parts of her shining disc occasionally appear and disappear. It was while thus occupied in his native city of Pisa— to which he had been recalled by the Grand Duke Cosmo, ever his generous patron, that he might pursue his astronomical studies — that the fame of his discoveries spread over all Europe, and many learned men, who had been obstinate adherents of more ancient systems, felt themselves compelled to acknowledge the truth of the new. But Galileo, though ambitious of propa- gating the new truths which he wished to establish as to the working of the solar system, had mistaken the general disposi- tion of mankind, and the narrow prejudices of the age in which he lived. “ That same system of the heavenly bodies which had been discovered by the humble ecclesiastic Nicholas Copernicus, which had been patronised by the kindness of a bishop, published at the expense of a cardinal, and which the Pope himself had sanctioned by the warmest reception, was, after the lapse of a hundred years, doomed to the most violent opposition as subversive to the Christian faith. On no former occasion had the human mind exhibited such a fatal relapse into intolerance.” So the clergy became the most bitter oppo- nents of Galileo, and were resolved to persecute him even unto death, if possible, becoming for the time thorough barriers to the progress of science. Thus in the year 1615, in consequence of complaints laid before the Holy Inquisition, Galileo was summoned to Home, that he might answer for the foul heretical opinions he had promulgated verbally and in writing. He was charged with “ maintaining as true the false doctrines held by many, that the sun was immovable in the centre of the world, and that the earth revolved with a diurnal motion ; with having certain disciples to whom he taught this false doctrine ; with keeping up a correspondence on the subject with several German mathe- maticians ; with having published letters on the solar spots, in which he explained the same false doctrine as true ; and with having glossed over with a false interpretation those passages of the Scripture which were urged against it.” In February, 1616, the consideration of these charges came before a meeting of the Holy Office, and the court avowing their desire tc deal gently with the prisoner, issued the following decree : — “ That his Eminence Cardinal Bcllarmin should enjoin Galileo to renounce entirely the above cited false and heretical opinions ; that on his refusal to do so he should be commanded by the Commissary of the Inquisition to abandon the said doctrine, and to cease to teach and defend it ; and that if he did not obey this command he should be thrown into prison.” Galileo appeared before Cardinal Bellarmin on the 26th of the same month, and after receiving from him some gentle admonitions, the Commissary, in pursuance of remit made' to him, commanded the astronomer, in presence of a notary and certain witnesses, to abstain altogether from the diffusion of his erroneous opinions, as it was now unlawful for him to teach them in any way whatever, either orally or in writing. To these absurd injunctions Galileo was compelled to promise obedience, and was passed through the perilous gates of the Inquisition. To the influence of the Grand Duke Cosmo, and many other Tuscans of high rank, the mildness of this sentence must be ascribed. Nor was the Papal Court itself without many high ecclesiastics who took a deep interest in the trial of one who was by most men considered as the pride of Italy. How- ever, so great was the dread of the officials of tho Holy Office that he might not be deterred by threats from propagating his obnoxious doctrines concerning the motion of the earth round tho sun and so forth, that a stern decree was issued denouncing them as false, contrary to the writings of the Fathers, and prohibiting the sale of every book in which they should be maintained. Beturned now to the Tuscan capital, Galileo resumed his studies with undiminished ardour ; but his recantation was so formal and without reservation, that prudence might have restrained him from bringing them unnecessarily before tho world, and, more than all, his clerical persecutors. No decree had been issued against liis telescope, his scientific discoveries, or the free exorcise of his genius. He was simply forbidden to teach a doctrine deemed injurious to implicit belief in the Scrip- tures, and to the Christian faith. Moreover, he was liable to the authority of a court which possessed tho power of torture and of death by fire within its jurisdiction. But his enthusiasm in the cause of science was irrepressible, and rendered him fearless as to consequences. Thus, before six years were past, he began to compose his “Cosmical System; or, Dialogues on the Two Greatest Systems of the World — -the Ptolemean and the Copernican,” a work, the concealed object of which was to establish the very opinions he had promised, under threats, to abandon. Three speakers, Sagrado, Salviatus, and Simplicius, debate on the merits of those systems, and thus Galileo hoped that by this indirect mode of diffusion he might get the better of the Holy Office. So the work was printed at Florence in 1632. A year elapsed before the Fathers of the Holy Office gave any indication of an attempt to open their prosecution again. Nor, to do them justice, did they seem to care for doing so, until they saw that those tenets, to them so obnoxious, were spreading fast, in consequence of the publication of the imaginary dialogues. A careful examination soon proved the work to be a deliberate violation of the injunctions laid upon Galileo, whom they summoned once more before their tribunal in 1633, and tho poor old man, now in his seventieth year, was compelled to travel from Arcetri to Borne, at a time when the appliances for locomotion were not what they are now ; and on his arrival he was committed immediately, like a criminal, to the chambers of the Fiscal of the Inquisition. The friendship and influence of the Grand Duke obtained a change for him, and. he was permitted to reside in the palace of the Tuscan ambas- sador during the two months over which his trial extended. Examined on oath before that dread and mysterious tribunal, he candidly acknowledged that he was the author of the Dia- logues, and that he had composed them in such a manner that the arguments in favour of the Copernican system, though given as partly false, were yet managed in such a mode that they were more likely to confirm than overthrow its doctrines ; but that this error, which was not intentional, arose from the natural desire of making an ingenious defence of false propositions and of opinions that had the semblance of probability. Such was his simple confession. For defence he could pro- duce only the certificate of Cardinal Bellarmin, which omitted all allusion to the non-teaching of the Copernican doctrines. This was deemed by the “Holy Inquisition to be but an a ggrava- tion of the crime, and they proceeded to pronounce a sentence, or rather, under terror of death, to extort a confession perhaps one of the most memorable in the history of the human heart. After solemnly invoking the name of our Saviour, they de- clared that Galilei Galileo had become a heretic by believing in a doctrine contrary to the Scripture, “ that the sun was tho 56 THE TECHNICAL EDUCATOR. centre of the earth’s orbit, and did not move from east to west ; and by defending, as probable, the opinion that the earth moved, and was not the centre of the world, and that he — the said Galileo — -had thus incurred all the censures and penalties enacted by the Church against such offences ; but that he should be absolved from these penalties, provided he abjured and cursed all the errors and heresies contained in the formulae of the Church, which should be submitted to him ; that he should be condemned to the prison of the Inquisition during pleasure, and that during the three following years he should recite the seven penitential psalms.” Seven cardinals subscribed this astonishing sentence on the 22nd of June, 1633. Then Galileo, worn with age, weary of the mental torture to which he had been subjected, and weakened by the influences around him, signed an abjuration, alike humiliating to himself, and degrading to philosophy. In his old age, with hair and beard as white as snow, bent on his knees, with his right hand resting on the New Testament, Galileo avowed that he abandoned, “ as false and heretical, the doctrine of the earth’s motion, and of the sun’s immobility, and pledged himself to denounce to the Holy Office any other person who was suspected of such heresy.” It seemed as if the hand of Fate was over the unhappy Galileo now. Freed from the Inquisition and all its terrors, he only returned home to find calamity there, for his favourite daughter had been seized with an illness which soon ended in death. Intense melancholy, hernia, palpitation of the heart, and a perfect loss of appetite now fell upon himself, all of which was believed by his enemies to be the curse of God upon him as a heretic ; and though he prayed for leave, impoverished though he was, to visit Florence in search of medical advice, it was refused him by the Holy Office, which had special super- vision of his movements. The Pope, however, took mercy upon him, and in 1638 he was permitted to visit the Tuscan capital, in care of his friend Padre Castelli and a familiar of the Inqui- sition, an indulgence soon withdrawn, and he was ordered to return to Arcetri. His eyesight had now begun to fail him, and in the year 1637 he became stone-blind. Even the Inquisitors now had mercy on the patriarch of science, aged, blind, bereaved, impoverished, and crushed in spirit. They permitted him to have the society of his friends, who now thronged about him to express their admiration and sympathy. Among those who came thus were the reigning Grand Duke of Tuscany, Pierre Gassendi, the great French philosopher and mathematician, John Milton, the author of “Paradise Lost,” Diodati, and many more. His sense of hearing soon followed his sight ; but the brilliant faculties of his mind remained unim- paired ; and it was while occupied in experiments, and in con- sidering the force of percussion, that a fever and palpitation of the heart fell upon him, and he expired on the 8th of January PRINCIPLES OF DESIGN.— XIII. BY CHRISTOPHER DRESSER, PH.D., F.L.S., ETC. Having considered furniture, the formation of which requires a knowledge of construction, or of what we may term structural art, we pass on to notioe principles involved in the decoration of surfaces, or in “ surface decoration,” as it is usually called, f Under this head, we commence by considering how rooms ii should be decorated ; yet, in so doing, we are met at the very outset with a great difficulty, as the nature of the decoration of a room should be determined by the character of its architecture. My difficulty rests here. How am I to tell you what is the just decoration for a room, when the suitability of the decoration is often dependent upon even structural and ornamental details ; and when, in all cases, the character of the decoration should be in harmony with the character of the architecture ? Broadly, if a building is in the Gothic style, all that it contains in the way of decoration, and of furniture also, should be Gothic. If the building is Greek, the decorations and furniture should be Greek. If the building is Italian, all its decorations and furni- ture should be Italian, and so on. But there are further requirements. Each term that I have now used, as expressive of a style of architecture, is more or less generic in character, and is therefore too broad for general use. What is usually termed Gothic architecture, is a group of styles having common origin and resemblances, known to the architect as the Semi-Norman or Transition style, which occurred in the twelfth century under Henry II. (it was at this time that the pointed arch was first employed). The Early English, which was developed in the end of the twelfth and early part of the thirteenth century, under Richard I., John, and Henry III. ; the Decorated, which occurred at the end of the thirteenth, and early portion of the fourteenth century, under Edward I., Edward II., and Edward III. ; tho Perpen- dicular, which occurred at the latter part of the fourteenth, and through the greater portion of the fifteenth century, under Richard II., Henry IV., V. and VI., Edward IV. and V., and Richard III. ; and, lastly, the Tudor, which occurred at tho end of the fifteenth, and the beginning of the sixteenth century, under Henry VII. and Henry VIII. All these styles are pro- perly spoken of as one, and are expressed by the one term — Gothic. It is so also, to an extent, with the Greek, Roman, and Italian styles, for each of these appear in various modifications of character, but into such details we will not enter y it must suffice to notice that the character of the decoration must be not only broadly in the style of the architecture of that building which it is intended to beautify, but it must be similar in nature to the ornament produced at precisely the same date as the architecture which has been employed for the building. It must not be supposed that I am an advocate of repro- ducing works, or even styles of architecture, such as were created in times gone by, for I am not. The peoples of past ages care- fully sought to ascertain their wants — the wants resulting from climate — the wants resulting from the nature of their religion — the wants resulting from social arrangements — the wants im- posed by the building material at command. We, on the contrary, look at a hundred old buildings, and without consider- ing our wants, as differing from those of our forefathers, take a bit from one and a bit from another, or we reproduce one almost as it stands, and thus we bungle on, instead of ever seeking to raise such buildings as are in all respects suited to our modem requirements. Things are, however, much better in this respect than they were. Bold men are dealing with the Gothic style in its various forms. Scott, Burgess, Street, and many others, are venturing to alter it ; and thus, while it is losing old charac- teristics, and is acquiring new elements, it is already assuming a character which has nobility of expression, truthfulness ef structure, and suitability to our special. requirements. In time to come, further changes will doubtless be made ; and thus the style which arose as an imitation of the past, will have become new, through constantly departing from the original type, and as constantly adopting new elements. I have said that the decoration of a building should be brought about by the employment of such ornament as was, in time past, associated with the particular form of architecture employed in the building to be decorated, if a precisely similar form of architecture previously existed. Let not the ornament, however, be a mere servile imitation of what has gone before, but let the designer study the ornament of bygone ages till he understands and feels its spirit, and then let him strive to produce new forms and new combinations in the spirit of the ornament of the past. This must also be carefully noted — that the ornament of a particular period does not consist merely of the forms employed in the architecture, drawn in colour on the wall, or the ceiling, as the case may be. The particular form of ornament used i: