,^^a*^t^ ..yO^ WRINKLES IN PRACTICAL NAVIGATION S. T. S. LECKY, MASTER MARINER, COMMANDER, R.N.R., F.R.A.S., F.R.Q.S., Eto. (LATE HIS MAJESTY'S INDIAN NAVY). Extra Master. Patsid in Steam, Compasi Adjxigtment, Ac Youngr/ Brother of the Trinity Bouse. Marine S^:perintendent of the Great Western Railway. Author of " The Danjer Angle and OJ-Shore Distance Tables," and of "Leckys General Utility TaJJas." NINETEENTH EDITION, REVISED AND ENLARGED W I L L I A M A L L I N G H A M , (NAUTICAL ASSISTANT, METEOROLOGICAL OFFICE). First Class Honours— Navigation. Prizeman— Political Economy Author of "A Manual of Marine Meteorology," " Weather Signs and how to read them; For ute at 6ea," Jitc. WITH 136 ILLUSTRATIONS AND PLATES, LONDON GEORGE PHILIP & SON, Ltd., 32 Fleet Street Liverpool: PHILIP, SON & NEPHEW, Ltd., 20 Cburch Streel ^Ai'I rights reseivedj I918 PUBLISHERS' NOTE. Ix issuing the Nineteenth Edition of " Wrinklea," the Publishers wish to draw attention to the fact that it contains numerous important alterations and additions, which it is believed will still further increase its value to practical Seamen. An entirely new Chapter (Part II. XVa), entitled " New Meteorological Measures for Old," has been included, together with four Appendices dealing with the following subjects: 1. Substitute for Horizon. 2. Gyroscopic Compa-sses. 3. The Moon an Auxiliary. 4. Chronometers: Use and Abuse. Ftbriiary, 11)17. PREFACE TO THE FIFTEENTH EDITION. For some years I was honoured with the close personal friend- ship of the late Captain Lecky, and, quite naturally, the future of " Wi-inkles" not infrequently came up for close consideration. All too soon, however, my friend and master was compelled by failing health to seek a respite from his labours under the sunnier sky of Las Palmas, and there death put a period to his adventurous career and strenuous life. A sterling seaman of the salt-water school, modern to his finger-tips, and a staunch friend — one always more willing to walk with Sir Knight than with Sir Priest — Captain Lecky's memory will long be cherished by seamen of every nation. His comprehensive intellect, his ripeness of judgment, his meditative mind, and his manly independence, are clearly displaj-ed in " Wrinldes," which was to him a labour of love, and concerning which he might rightly have written, in the words of Horace on a similar occasion, " non ovmis moriar : multaque pars mei vitubit Libitinam." It has devolved upon me to revise " Wrinkles" for this fifteenth edition, and in the task I have been greatly helped by a knowledge of Captain Lecky's methods and his aims with respect to the book. Something new and true has been added ; some of the chapters have been re- written, consequent on changes which could not have been foreseen by the author ; and neither time nor trouble has been spared to bring the book right up to date. It is therefore anticipated, with some degree of confidence, that " Wrinkles " will at least maintain the high repvitation it has held among the world's navigators ever since the First Edition brought out by Captain Lecky a quarter of a century aL'O. Sliould this belief be justified by results, the Fifteentli Edition of " Wrinkles" will serve not less than two purposes: It will continue to "awaken the interest of tlie student by making the subject attractive, and to train his intelligence by bringing before him whatever is striking, novel, and instructive " in the particular branches of the nautical profession with which it deals; and it will perpetuate the high navigational knowledge, and the capacity for taking pains, which were such marked features of the Author's life. WILIJAM Ar.LlNGIIAiL AvocA, Grove Park, Denmark Hm.i., LoNnoN, 1907. PKEFACE TO FIRST EDITIOJS. The particular aim of this treatise is to furnish seamen with thoroughly practical hints, such as are not found in the ordinary works ou Navigation ; or, if they do exist, are scattered through so many pages, and so smothered by their surroundings, as to require too much digging out — too many shells to be cracked before arriving at the kernel — a tedious process, which the practical mind recoils from: further, to indicate the shortest and most reliable methods, as well as the instruments and books necessary to enable the Navigator (amateur or professional) to conduct his vessel safely and expeditiously from port to port. The various nautical instruments are treated of separately, their peculiarities explained, and the errors to which they are liable pointed out, with the best means of remedying them, or of compensating their efi'octs. The volume contains but little that is claimed as strictly original : it is based upon life-long observation, matter gleaned from the works of men of repute, and information derived from intercourse with shipmates and the cloth generally. The mass of material at one's disposal renders its clear present- ment within a moderate compass somewhat, difficult, but great pains have been taken to select only the really essential problems, and, in view of those to whom the work is addressed, to choose the simplest possible language. If the style is thus more familiai than dignified, it is hoped tliat it may witli greater success attract the ear, and rivet the understanding of the nautical reader, thereby awakening and sustaining such an interest in the subject as will be most likely to create mental impressions of a lasting kind. Diagrams accompany many of the examples by way of illustratinjr and giving prominence to some of the more " important sim- plicities " of navigation, which are unhappily too ofteu disregarded by reason of their true significance not being understood and appreciated. To this end, also, a free use has been made of capitals, and certain words and sentences are rendered conspicuous by a change of type when it appears advantageous to do so. If occasionally the reader of quick appreliensiou is irritated by too great minutenes,s, he mu.st remember that as far as possible every imaginable question has to be anticipated, and that a single point left unexplained may render useless an otherwise careful description. Every .sailor knows what is meant by a " Wrinkle " ; some possess more tlian others, and in penning the following pages the writer has endeavoured to di.spiay his to the best advantage, and place them " cut and drieil " at the disposal of such membcre of the piofessiun as have had a less varied experience than him- self, and fewer facilities of acquiring an intimate knowledge of this branch of their liusiness. Methods have been selected which otier peculiar advantages in the matter of brevity of aoluiion. To seamen this is very impor- tant, as 1^11 know ; at the same time accuracy of Oie results has been kept in view, and care taken that the latter quality is not unduly sacrificed to the former. Rigorous exactness of working — so necessary- in the schoolroom — is but seldom required on board ship ; it is, therefore, only introduced in the proceas of rating chronometers, and one or two other iustance.s, where, from the nature of the question, one ia absolutely forced to deal with minute arithmetical quantities. Very many problems of interest to the scientific Navigator, as well as the discussion of many refinements of correction and reduction — which, neat as they may be in theory, are of little practical value — have been purposely omitted. On the other hand, an endeavour has been made to avoid the slovenly " Rule of thumb," " Rough and ready " principle which has given rise to the saying — somewhat unjust to a good class of seamen — " ii is near enough for a collier." These and other characteristics, it is hoped, may commeni tht work to the notice and approval of the profession. It must not he imagined that this book is written in any respect as a direct help to the Local Marine Board Examinations; there are plenty of excellent ones published fcir that express pur- pose. This has entirely to do, as its name indicates, with every- day navigation on board ship : the reader is supposed, indeed, to be in proud possession of his Master's certificate — if with blue seal so much the better; to have overcome the moonshine terrors of Decimal Arithmetic, and to have some slight knowledge of Plane Trigonometry. If, however, these pages should be read bj' one who has j-et to undergo the ordeal of examination, the writer trusts that the introduction behind the scenes, and the knowledge of first principlas thereby acquired, will teach him to think for himself, and be of service generally in enabling him to gain the coveted parchment. To the daring yachtsman, ambitious of personally undertakmg the conduct of his white- winged craft to distant parts of the world, and who has already acquired a certain groundwork of navigation, it is hoped that this Manual will present not a few advantages : it will be a sort of nautical finger-post at the junc- tion of many devious paths, which will point out to him the safest way to his destination ; and, whilst providing him with sound advice on most of the necessary points, will not distract his attention and waste his time on what, even to the professional, ma}' be regarded as superrtuous, or of questionahle importauca Under this last heading comes Marine Surveying — which is, consequently, excluded in toto as constituting a distinct study, and one wliich, in these exact daj-s, can scarcely be said to come within the province of merchant seamen, whatever it may have done in times gone by. If, however. Marine Surveying should be taken up by anyoue who has a natural taste for that sort of thing, with leisure and opportunity for indulging it, he should study such books as are devoted exclusively to it, since it is a subject more difTicult than many at first would suppose. • In one matter, more especially, the Author would crave the crracious forbearance of the Critic. He wishes it thoroughly understood that not in the least degree does lie claim for his present venture what is knov.-n as " literary merit." A lad who, at twelve or thirteen, ailopts the rough career of a sailor, when more fortunate ones of the same age are only just commencing their education, cannot reasonably be expected in after life to shine as a brilliant star in the literary firmamenL It is .scarcely consistent with the "eternal fitness of things" that he should. Our Gallic neighbours have a proverb which is in every way applicable — "Chacun son metier, et les vachcs sont bicn gard^;" which, when freely translated into the nautical langtiago of Britain, roads thus — "The Gunner to his linstock, the Steersman to the wheel, and the Cook to the foresheet" The book, therefore, is merely a friendly otl'er of help from one sailor to anotlier — nothing more. Sonie readei"s, no doubt, will make it their proud boast that they " clambered in tlirough the hawse-pipes," whilst others will have "entered by the cabin win- dows." To both the Author is not without hope his " Wrinkles'' may prove acceptable, and that, like a " Handy-Billy " clapped * Alioul ili> ni««l cninpUU Work is " UjJrDipmpliical Surojrlni:,' by C«|it W. Wlmrti'ii. RN It wti pulill>l<*tl l>]r John Murnj In l(il2. S«cond nllUon In liOS. on to the fall of a " Luft'-tackle Purchase," the present book may assist the more powerful ones iu pulling the Shipmaster through many of the navigational troubles by which he is often beset. In conclusion, should Experts complain that they do not find anything novel in this volume, the writer would merely remind them that it was not his intention that they should. The book has been prepared for comparatively 3'oung members of the pro- fession ; and one of the leading objects has been to elucidate in plain English some of those important elementary principles which the Savants have enveloped in such a haze of mystery as to render pursuit hopeless to any but a skilled mathematician. Comparatively few sailors are good mathematicians, and, in the writer's opinion, it is fortunate that such is the case ; for Nature rarely combines the mathematical talent of a Cambridge wrangler with that practical tact, observation of outward things, and readi- ness on an emergency, so essential to a successful sea Captain, who, curiously enough, is always expected to be as many-sided as the "Admirable Crichton'' — at once Sailor, Navigator, Parson, Lawyer, Doctor, and a host of things besides. The Author has only to add that he has done his best to secure accuracy in the printing of the book, and trusts that few errors of moment will be found to have crept in. He will at ail times be thankful to receive corrections and suggestions for the improve- ment of future editions. Squire Thor.ntox Stratford Lecky. LivERrooL, November 1S81. PREFACE TO THE NINTH EDITION. Ali.ao be praised ! " Wrinkles" has successfully withstood that most crucial of all tests — the test of Time. On every sea and in every manner of craft it has lieen afloat for better than twelve years, and luckily seems to have found favour with ' all sorts and conditions of men.' On board the schoolships Conway of the Mersey, and Worcester of the Thames, it has long been included among the prizes be- stowed upon the youthful lieroes of the moment. With infinite satisfaction it has recently come to mj' knowledge that even in H.M.S. Britannia it is not considered unworthy of a place at similar great festivals. For a book with no pretensions to mix in such goodly company, this is not bad ; on tiie contrary, it is very cheering, and has acted as a stimulus in the production of the present edition. In view of self-evident facts, it is not stepping over the mark to say that the popularity and wide circulation of "Wrinkles" has very considerably revolutionised the practice of navigation. This it lias accomplisheU more particularly by drawing attention to jioints of working detail not previously dealt with by the text-books, these having — as jnight be expected — invariably treated the subject from a purely academical point of view, and that a trifle ancient of its kind. Somolnxly very truthfully lays it down that 'The mastery of the ocean cannot be learnt upon the shore ' ; and so the many impeilimcnts to turning Theory into Pnicticc were not even so much as hinted at, it being perforce ignored by the various learned writers — mostly landsmen more accustomed to streets than straits, shops than ships (no disrespect intended) — that navigation iu the safe .seclusion of the study, aud navigation on board a storm-tossed and danger-Lieset ship, wore two vastly ditlerent things. In fact, tlio young commander, as soon as the pilot uttered his parting benediction," A pleasant voyage, Captain," and had slipped over the side into his dingy, was left to flounder about as best he could in a veritable sea of difBculties. The mission of " Wrinkles," written by one who has been through the mill in right good earnest, was to go to the rescue and ' stand by ' until such time as our young friend felt himself in every sense Master of the situation, and able to shift for himself. Eesponsibility is a word devoid of meaning to all save those who have to bear it. Do not most Mates think themselves smarter men than the Masters ? And yet Masters are all made from Mates ! ! What is accountable for the change ? Further, in the revision of works on Navigation, the produc- tion of new ones, perhaps also to some extent in the Board of Trade curriculum, and consequentially in the teaching of the 'Coaches,' "Wrinkles" has undeniably conduced to the discard- ing of 'played out' methods, and the substitution of others of greater liliahility and less ponderosity. Some of the most capable instructors have not been above taking hints from it, and even saying so; whilst sundry opticians in the marine line have been stirred up to modify certain of their instruments, and in several cases to devise others better adapted to the ' Navigation of the Period,' which has become uncommonly rapid — so rapid, that to ' Look slippery ' is now the all-pervading motto. The Victorian era may truly be said to form an eventful epoch in the progress of navigation, and no man knoweth the end. It is no longer the ' stand-off-shore-till-it-clears ' navigation of the two-foot rule order ; no more 'waiting for slants ' ; no 'ground- ing on beef bones. ' Growl you may, but go you must.' There used to be a fo'k'stle phrase very often heard during the reign of the old ' Black Ball liners,' viz., ' Liverpool on her stern and hound to go.' That was when every fellow who could handle pick, pan, and shovel — or at least thought he could — was in a state of frenzy to reach the Australian El Dorado : but in this later age of telephones, and telegraphs to the uttermost ends of the earth, craft of nearly every shape and colour — no matter where they hail from — are ' bound to go.' In fact, it is ' Rush ' all the time; or, as Jack puts it — ' No peace for the wicked' As with other branches of science, so also in the seafaring direction, the niarcli of events has brouglit about many improve- ments. There is a regular epidemic of inventions ; some good, •jome indifferent, and otliers so absolutely worthless as to be at Dnce relegated to the limbo of useless rubbish : but all bring grist to the mill of the patent agent, though not necessarily to the inventors. ' It is an ill wind,' &c. Out of the ruck we have now instruments of beautiful pre- cision, and much greater capabilities than heretofore. It would, however, be wrong to infer that thereby the duties of the navi- gator had been rendered less arduous, or that he was in any degree being coddled, or ' fed with a spoon ' ; on the contrary, the demands upon his energy, vigilance, nerve, and endurance, are greater than ever. These refined appliances — the outcome of the skill of the modern mechanician — are simply called into existence by the exigencies of rapid transit Without them, and without tlie right kind of men to use them, the speed, which costs so enormously, would in a measure be tlirown away. A ' 22- knotter, ' costing half a million sterling, and despite triple-cspan- bion engines, swallowing fully 20 tons of coal per hour, with perliajis 200 of u ' black scjuad,' and nearly as many hands in the victualling department, cannot afford to wander at large over the ocean d la Columbus. To do so would seriously interfere with the gilt on the gingerbread, and probably permit a leas speedy, though more skilful, rival to slip in first. Just fancy the discomfiture of the oue, the jubilation of the other, and how the 22-knot engineers would swear! The atmosphere of the mess- room would be perfectly blue with parliamentary language. lience the great need, in these highly-pitched competitive times, of the professional knowledge which will keep a vessel's stem pointed lUad straight for her destination during every singl-: minute oj night atid day. Owners, alive to this fact, are be- coming more and more particular in selecting men for command who can do it. It is the same on shore. There are drivers of goods trains, and drivers of express trains ; the latter are con- sidered the best men, and entitled to Wst pay, ajiti Otey get it No amount of ' cracking on ' or ' tiring up ' will compensate for bad courses, and eventually having to ' skirmish round ' for one's port in thick weather ; it is simply misdirected energy of an ex- pensive kind. On the vvliole, an impetus has been given to everytliing connected with this branch of the seaman's art, whether in the humble ' tramp,' the gorgeous ' greyhound,' or the persevering ' wind-jammer.' It behoves their respective skippers *io rise to the occasion and shew their mettle — not pot-metal. In the literature of navigation, ' Raper ' — probably because written by a seaman understanding seamen's wants — still holds the position of premier epitome. It has recently (1891) been revised in a very judicious manner by that Ancient Mariner and Cunning Pilot, Commander T. A. Hull, R.N., formerly Superin- tendent of Admiralty Charts. Beyond a few modern necessities, such as a chapter on compasses in iron vessels, the extension of the Traverse Table, and bringing it up to date generally, Captain Hull has shewn his good sense by 'leaving very well alone'; so, to tlie gratification of its devotees, ' Raper ' still remains ' Raper.' Not so with our quondam chum, ' John Norie.' It is no more the same venerated oracle which was conned to destruction in the days of one's apprenticeship, long long ago ; for ' Norie ' has been almost, if not entirely, rewritten by W. H. Rosser (18S9), so well known to London aspirants for Board of Trade parchment. Were it not for the title, one would hardly recognise its re-juvenated pages. Certainly re-modelling was needed, and the new ' Norie ' will no doubt continue as popular with a certain sot as it was in the now almost pre-historic times when the frigate-built India- men of Green, Wigram, Sraitli, and Dunbar, entered Blackwall docks in all their glory, with yards and gunports squared to a nicety, bunt-jiggers bowsed up for a harbour furl, stun'sail booms rigf'ed out to the mark, hammock-nettings neatly stowed, and a welcoming crowd of both sexes cheering and waving greetings from the pierheads. The sea then had a halo of romance about it, a blue- water flavour, which, alas, is now replaced by cast-iron and mild steel. The romance has been buried in the coal-bunkers. If one may judge by the differences here and there in the doctrines o.' tJie old and iiuw ' Norie,' its painstaking reviser has read " Wrinkles " to some jjurpase, aad hits takcu to heart at least some of its precepts. This tribute from a veteran teacher, silent though it be, is much appreciated. luinan's excellent Tables have been revised, re-arranj^ed. am. enlarged (1888). They are the only nautical ones in wliicli tiie log. sines, secants, tangents, &c., are given to every 15" of arc — no inconsiderable advantage to close workers. It is incompre- hensible that these fine tables are not better known in the merchant service. But the gem in its way is Xavigation and yautical Astrunvmi/. by Staff-Commander W. R Martin, of the Royal Naval College (1891). It goes without saying that this is a thoroughly safe guide, and has accordingly been adopted by the Admiralty as the orthodox text-book in the naval service ; indeed, it was written expressly for this purpose. The deadly dulness incidental to official text-books in general is, in this case, relieved by copiou.s notes and interesting historical references ; but the character of the book is mathematical to a degree somewhat over the heads of the pre.sent generation of merchant officers, who, with the ex- ception perhaps of certjiin Conivay and Worcester boys, and a few others with a natural bent that way, do not excel in thi pur.suit of ' the wily x.' This is unfortunate, but the remedy lies with the men themselves. Owing to proofs of ru1ftil)cing given, ' Martin' will be found specially useful for such as intend going in for " Honours." In addition to the recognised standards, a bewildering host of 'New aud Short Methods' have of late years passed through the printer's hands, some of them so good in themselves a.s almost to tempt one to backslide, and forsiikc his oKl love.s. But from this hereby I have been saved by being confronted with the fact that it would mar a loading feature of " Wrinkles" which 1 see every reason to stick to, uaniely, the retention of niethod.s which, by harmonising in their gcnenvl arrangements and characteristics, leail up to wich other, so that the one nuiy be a stepping stone to the next. At least such is the endeavour, so far as it i.s possible U» carry it out Bj' this system the mind is nut distracted by u I auiiiber of problems differing widely in detail, if not in priudple ; nor is the memory needlessly burthened. Not long since, an acquaintance, whilst discussing " Wrinkles," remarked — ' One of its chief merits lies not so much in what you have put into it, as in what yoic have kept out of it.' I'^xactly so! He too liad felt how the utility of a book might be jeopard- ised, if not destroyed, by offering to its readers more mental pabulum than they could conveniently digest, and more, indeed, These extensions and additions render the ' A iind B Tables Biniply invaluable, and immensely more complete Ut(cllar Savijation, Kos-ser followed suit with an abridged set for the same purpose, which tuuy lie taken as corroboration of their value. There is, however, a statement in Hossers edition of Norie's i'lpituiiic iliat these Tables were lusl put intu their )>resent form in Enwlanil, in 1882, in Rosser'-s Stellar Navigation ; but, in view of the above autlientic facts, this is evident!}- a mistake. Though actually published in July, 1883, Stdlar Navigation was not even entered at Stationers' Hall till the following December. Table I. of previous editions, for which I was indebted to Mr, A. C. Johnson in connection with his now well-known method, ha.s in this issue been superseded by Talile C. The two are on precisol)' the same basis, but mine has been computed to three places of decimals, the arrangement is different, and it has been extended to just three times the size of the other. These important altera- tions render the Table susceptible of an}' degree of accuracy the worker may feel justified in going to. In Johnson's deservedly popular method the object of his Table is to find the ' Longitude correction ' from thf Latitude and Azimuth, and for this purpose he evidently considei-s two places of decimals sufficient. Bxit in "Wrinkles" the introduction of the 'A and B Tables' permits of the Navigator suiting his own convenience as to whether he will follow the order laid down by Johnson as above, or, on the other hand, elect first to find the ' Longitude correction ' from Tables 'A and B,' and subsequently the Azimuth from Table C. The extension of the latter permits of this being done to the nearest quarter of a degree, which is close enough in all con- science. It will thus be seen that in the use of Johnson'.s method the Navigator lias 'two strings to his bow.' Sometimes one will be preferable, and sometimes the other. They will not fail to speak for themselves according to circumstances. Table D (Table II. of previous editions) has in all respects been treated similarly to C, and is therefore uniform with it. When, according to the nature of the work in hand, it suits to drop the third decimal in either of them, it can of course be done ; but there is no harm in having it ' ready for a call ' if required. I ike money, you may not want it at the moment, but it's handy to have it about you. Rather ! ! Should Tables be found to contain errors, they are naturally regarded with suspicion, and their value is materially lessened. xxii I'KKFACE. There need be no doubt as to the correctness of A B. C. aneeD advocated in ' Wrinkles,' the omission in previous editions of a chapter dovotetl to star-finding, has Icil to my being reproached with inconsistency. The reproiich is now removed and the book rniulo complete in this respect. In conclusion, the revision of ' Wrinkles ' lia.s liud my liest uttontion : everything in it has been considered and iv con- sidered, turned upside down, sliifted end for end, and examined micz-oscopically. Throughout, an endeavour has been made to awaken the interest of the student by making the subject attractive, and to train his intelligence by bringing before him ivhatever is novel, striking, and instructive in that particular branch of his j^'ofession to which this book is devoted. If pains can do it, tliis ought to be quite a glorified edition. I have been told more than once by the ' know-alls ' of the profession that ' Wrinkles ' contains nothing that is original. I meet this by referring them to my own disavowal in the preface to the first edition. In this one also there is the usual amount of Editorial scissors and paste. Many are my quotations from other books, but I liave tried my best to make due acknowledg- ment. This is not always so easy as it would appear, for in reading a large number of works upon any one subject, as I have done in the cour.se of my career, one's mind is sure to store up ideas without, at the time of reproducing them, being able to recollect the particular source from which they emanated. " As apothecaries we make new mixtures every day, pour out of one vessel into another ; and as those old Romans robbed all the cities of the world to set out their bad-sited Rome, we skim oflF the cream of other men's wits, pick the choice flowers of their till'd gardens to set out our own sterile plots As a good housewife, out of divers fleeces, weaves one piece of cloth, a bee gathers honey out of many flowers, and makes a new bundle of all." An officer, who at various times had purchased in all some live copies of " Wrinkles," explained to the Publishers that he never made a voyage (well, " hardly ever ") without having either to sell or give away his own. (N.B. — It is to be hoped he got ' sea price ' for them). Kind reader, sliould the book bo so fortunate as to meet with your approval, you cannot do better than I'ollow hi.s most ex- cellent example. S. T. S. L. Neyland, Fembkokeshire, AritiL, ls9-i. C O N r E N T S p.Airr I. C H A P T E p. I. NAITKAL LIliRAKV, ANl> INSTRUMENTS OK NAVIGATION. NeoeR^aiv I^vlk8 — List of Instruments ... P.iL'e I- 3 ClIAPTKI! H. TlIK MILE AND THE KNOT. Comparison of Milrs—Sliape of the Eartli Page 4— 10 I'H.M'TKI: III. TIIK .MAKINKKr! CoMl'ASS, AND IMPORTANT FACTS I'ONNECTEP WITH IT. PueilioD of Stanilard Coni|ia.s8— Coni)>aBS Cards — Im|K)rt4)nt Simpliiities— I'revi'utlMe acciilcnta — Tlie Steerinj; ComiKLss— Sjnii>:itliy with Sun — AitrHclion nl I,8nil — I.ii:Iitiiiiip and Irun VewHs How Sliipa are Lust. *« I'age 11-43 ClIAPTKR IV. THE MARINE CHRONOMKTElt Cable lAinjriludig- Care of ( 1,^ nonietiTs Luikinp Daii-er-"— l>ftily Rate? nnd Errom Piipe ■••• — 6ft ClIAl-TEK V. THE SEXTANT Striiglit Ti|m for Purrlinaom- Tinkerinfj P;ije 6fi— 7U ClUPTKK VI. rilK ARTIFICIAL AND SEA UORIZONS. A Firkle Mintreft' How U< clean Merniry— Tiie C.laM Koof- Selection ol 01*ervulii)ti S|Mit (leartotake on Sliore— IHsplurenieot of Sea Horizon -Nui iii.Tiemeiit of A M. and l'..M. niylitn. I'.iL'e ."^O !n'. Chapter TIL CHARTS. Mercator Charts— Chart and Map Projections — Admiralty Cliarts -Informa- tion convejed by a Chart — Rolled Charts an Abomination. PaL'e96— 111. Chapter VIII. THE P.\RALLEL RULER Horn Protractor and Straighteilge— Ivory and Boxwood Protractors. Page 112-116 Chapter IX. DIVIDERS. Spring Pen and Pencil Holder — Dividers for use with one hand. Pages 117, 118. Chapter X. THE PELORUS, WITH REMARKS ON AZIMUTHS. True Fore-and-Att Adju.stment— Azimuth Tables — Captain Weir's Azirautli Diagram — Apparent Time at Ship — Time Aziiiuith of the Sun, of the Stars, of tiie .Moon— Lecky's ABC and D Tables— Deviation by the Pe'.orus Page 119 13G. Chapter XL TOE STATION POINTER. Sextant Angles — Selection of Objects — Properties of the Circle — Good and Bad Fixes — The Goniograph — The Angle-Sextant — Coastal Navigation^ Fry's Fixing Factors Page 137— 16& Chaptkr XII. SOUNDING iMACHlNES AND LOGS. Basnett's — Lord Kelvin's Dejith Recorder- Cooper and Wigzella Sea Sounder— The Blue Pigeon— Submarine Sentry— The Common Log- Patent Logs— Ground Log— Electrical Logs— Tlie Dutchman's Log— Dead Reckoning — The Mariner's Creed Page 167— 187 Chapter XIII. THE MARINE BINOCULAR AND TELESCOPE Propertie,s of Light— The Power of the Telescope— Binoculars. Pase 188— 20a Chaf'Ter XIV. LORD KELVIN'S NAVIOATIONAL INSTRUMENTS. New form of Aziimitli and Steering Compass— The Cnrd of tlie Period- Table for Correotiiin of Quadnmtal Error — The Azimuth Mirror — An .•\(ljii3tal>!i' I)i llrctor ->f:iriiii' liiiii.iii'' Xn-dlc — Snuiidins Machine. Page 201 — 224. Chaptkr XV. THE MERCURIAL AND ANEROID BAROMETERS. Barometer ouly an .Atmosphere Weiu'lier — Defects of Aneroid. IVe 225— 23.T ClIM'TEIl XVI. OCE.\N METEOROLOGY Amerii-an Predictions— Sjiiciironous Weather Charts — Weather Puzzles- Ecoeutricities of Storm Progression — Tropical and Extra Tropical Cyclones — Buys- Ballot's Law— Indian Ocean Cyclones— Fitzroy's Weather Siyns. Page 234 -2C2. Chaptkr XVII. TIDES, CURRENTS, WAVE.S, AND BREAKERS. Bis Ben and liis two Chums -Great Eruption of Krakatoa— Tidal Waves- Mean Sea Level- Bores— Offing and Inshore Tides— Diunial Inequality — Meteorological Tides— Admiralty Tide Tables Page 2C3— 303. CnAPTKii XVIII. rOti AND FLOATING ICE. Coastwi-w Navigation— Detection of Ice— Exceptional Dimensions of Bergs —Loading in Fresh and Salt Water Pa^e 3urk« -Navigational Stars ... Page 324 -304. I coNTEN^TS. xxvii Chapter III. LATITUDE BY MKRIDIAN ALTITUDE. How Wrecks may occur— Regulation of Clocka at Sea — Star A[eriilian Alti- tudes Page 365— 378. Chaptkr IV. LATITUDE BY MERIDIAN ALTITUDE BELOW THE POLE. Circumpolar Stars- Azimuths — Diurnal Circle — How to calculate Meridian Altitude below the Tole Page 379-382. Ch.ipter V. LATITUDE BY THE NORTH STAR (POLARIS). Interesting Items— Nautical Almanac Method— When shall we lose our Pole Star? Page 383— 390. Chapter VI. LATITUDE BY EX-MERIDIAN OF THE SUN. Notes on Tables — The " New Navigatios " — Ex-Meridian Dodges. Page 391—395. Chapter VII. TIME. Equation of Time— First point of Aries— Mean and Sidereal Time — Crossing Meridian of 180°— Week-d.ay Symbols Page 396— 407. Chapter VIII. LATITUDE BY EX-MERIDIAN ALTITUDE OF A STAB Suitable Stars— Ex Meridian ?>. Meridian Altitudes— Star Ex-Meridians sub- Polo- Latitude by Pole Star Page 408— 419 Chapter IX. LECKY'S ABO TABLES. Rules for use of A and B— Azinuith by A B G Tables— Tables A and B— Table C Page 420— 451 CUAPTKR X. LONGITUDE BY CHRONOMETER. Sun the World's Timekeeper— Eclipses of Jupiter's Satellites, and Occulta- tions of Stars- Lunars and Chronometers— Sights taken on Prime Vertical XXviii CONTE.NTS. — Tfiivigation in High Liitituiles— Log Sine Square— Venus in Sun«hiiie- FiTcstallini; the Meridian Altitude— Short Equal Altitudes— Sun and burs Page 452 — 486 Chapter XI. SUMNER LINES. Circles of Equal Altitude — Sun's Position Projected on Chart— Circles of Position — Line of Bearing— Celestial and Terrestrial Cross Bearings. I'age 487- 500a Chapter XII. DOUBLE ALTrnJl)K.S. Use of Aziinutli Tables — Ros.sor'8 Arrangemeut — Johnson's Method— Ix>rd Kelvin's Sumner Tallies— John.son v. Sumner— Table C and I)aiiger Signal - (Japtain Parker's Analysis- Caution Page of Table C. Page 501 —527. ciiAPTKR xni. SI M U LTA N EO I ' S A LT I T U Li ES. How to ascertain Po-i^ition of Star at any given instant- Altitudes can be cal- culated —Croaa Bi'arini.'s of Stare Page 526— 535 Cll M'TKK XIV. SYSTEMATIC KKRORS IN AI,TITII>K, ANH HOW Tu TREAT THEM. Three Star Problem -Uses of a Drawing Board— Table D. Page 530-551. Chaptku XV. TO KIND THE KllKOR AND KATE OV A i IlllONOMETEU Equal Altitudes not recommended -Peisonal Equalinn— Artificial Horizon - Sextant fitting for St.irs- lUtin;; at Sea, on Shore -Stars lijwt and Weat— Page o-."2 -LC6 Chaptki! XVa. NEW METEOnOLOOICAL MKASIIJES FuU ul.l>. English ftrtui Conliiivntal Measures — More Unpaid Work for Onicers — Old and New Methods— Ikroinctvr and Thernioinoter Units ; British, Foreign — The Cenlimetro-Cirnuinie-Scciiiid Sy.stem — High Science vertut Practical Niivigation— Nece.«8ily for Siniplicily in Iiifuniintion—" Absolute " System of Units — Cunlpali^on of Scales ... ... I'oge 607— 677 CllAl-TER XVI. COMPASS ADJUSTMENT. Distinctive Colnuring— Magnetic Poles and Magnetic Equator — Hard Steel and Soft Iron — Eartli's Induced Magnetism — Magnetic Direction of Build- ing Slip — Semicircular Deviation — Admiralt)' Method — Preparations — Compensating Quadrantal Error— Sub-permanent and Induced Magnetism — Retained Magnetism — Adjustment in Suez Canal — Compons.ition of Heeling Error — Special Adjusting Marks — Coast Transit Marks — Com- pa-ss ReciirrI Form — Compass Co-elficients— Beall's Deviascope— Utility of Traverse Tables— Rundell's Proposal— Final Injunctions. Page 578— G43 Chapter XVII. SHAPING THE COURSE. Modes of Conversion — Earth's Magnetism Changing — Retained Magnetism- Great Circle Sailing — Use of Globes— Bergen's Epitome and Charts — Use of ABC and Burdwood's Tables in Great Circle Sailing — Versatility of the ABC Tables — Current Sailing — Leeway — Duncan's Triangular Sailing— Coal Consumption and Speed — Duties of a Master Mariner — Rules not hitherto given in Navigation — Consumption of Coal and Revolutions — Variability of Slip Page 644— 676. CH.A.PTER XVIII. THE DANGER ANGLE AND CORRECT DETERMIN.\TION OF DISTANCE FROM LAND. Distance of Sea Horizon — Four Point Bearing — Sextant Angles— Sextant the Seaman's sure Friend — Lecky's Ott'-Shore Distance Tables — Danger .\ngles, Vertical and Horizontal P.age 677— 702. Chapter XIX. COMPOSITION AND RESOLUTION OF FORCES AND VELOCITIES. Parallelogram of Forces iiiid Velocities -True Direction of AViud when Alloat —Diagrams shewing how Strains c.in be Calculated —Disposition of Anchors in a Gale Page 70.3— 711. Algebra Chaptkp. X.K. Appendix. Correcting Chronometer Rates— Thermal Error Tables— Heeling Error— Star- Telescope for Sextants— Three-point Problem — Sextant and Station Pointer- Definitions— Lunars versus Chronometers- Substitute for Horizon — Gyro- scopic Compasses— The iloon an Auxiliary— Chronometers : Use and Abuse Page 715—776. Nautical .Mmanac Elements used in previous pages Page 777 — 791. Trans- Atlantic and other Distances Page 701 — 795. Index Page 796. Reviews and Critiques Page S2O LIST OF ILLUSTRATIONS AND FLATKS. tAOK Datum Plane ------ 7 liadial Line Card - - - - - 15&1G Compass Card— North and South Line It- Compass Affected by Derricit - to fact 39 Sextant and Optical Law . - - - 67 Angles of Incidence and Rertoction 80 Refraction of Li','iit - - . 91 Map Prnjoctions - ... - - 100 & 101 Corapa.s8 Diagram .... 106 Parallel Ruler, Field's Iinjiroved - 112 Horn Protractor .... 111 & 116 Dividers ... lis Station Pointer .... 137 Fixing position liy 139 „ „ Method explained (Figs. 1—17) 141-164 Goniograph - ■ IM Angle-Sextant (Hughes's) 156 Priam, A - • 189 „ Dispersion of Rays 19.) Com|ias« Card. I/ird Kelvin's 204 1, ., ., Cap and jipann,' Point 20.') „ and Improved Rinnaclc-top 206 „ I>ord Kclvin'.H 212 Azimuth Mirror - L'l:. Adjustable Deflector, Lord Kelvin's • '.MU LIST OF ILLUSTRATIONS AND PLATKS. XXXI TAGB. Dippiii'' Needle .---.-. o^o SounJing Apparatus, Lord Kelvin's ..... 223 Atmosplierio. Pressure, Experiments illustrating - • • 226 & 227 Siphon • ..--.-.- 230 Isobaric Lines of the Ocean for February • - -to face 246 „ „ „ August • - - „ 246 Tidal Waves - • - to f.ict 20S, 270, 274, 287 „ Diagrams - - . . . . 272 Co-tidal Map of British Islands for day of New Moon - - to face 284 Tides in Strait of Magellan - - . - . ,,286 „ at Weymouth - • - - • - „ 290 „ „ Strait of Dover 294 Tidal Table, Stag Rock - • • - - -to face 299 Star Maps.— Little and Great Bears - - - ,, 345 Cassiopeia's Chair and Cygnus - - - „ . 346 „ „ and Pegasus - - „ 3 i7 Orion - - - - - - ,, 347 Leo and Corrus .... „ 347 Scorpio with Libra - - - - „ 348 Southern Cross with Centaurs ■ - • „ 348 Definition of Latitude ...... 367 Latitude by Stars ...... 376 & 377 ., Meridian ...... 380 „ the Pole Star to face 384 Lost Time Problem 406 Time by Lunar Blcthoda ------ 461 Errors in Latitude, Methods of Correction - - - 479 — 481 Circles of Equal Altitude . . . to face 488, 490, 492, 497 P. & 0. ss. China . ... - to face 500a Circles of Double Altitude - - - - - „ 502 ,, „ „ Sumner Line - ■ - ■ 503 Errors in Altitude— Three-Star Problem - - to face 537, 538, 539 ....-- 539 Positions of Greatest Etl'cct (No. 1) and no Disturbance (No. 2) to face 585 Magnetic Experiment ---■■.. 587 XXXll LIST iiF ILI.USTKATKJNS AND IM.ATES. PAQB Magnet!:, How to place . .... to face 591 Ship's Hcml North M.A G. „ M4 East „ ..... „ f.35 North-Iijtst M.A.O. „ ''^ Ma^'ncti.sm, Exaiuj>Ic of difficult Comp-i-ss Adjustinont - „ 6'>0 Lines of Equal Magnetic Variation, 1912 - ■ • „ ''1'^ Dip, 1»)7 ■ - ., m; Horizontal Force, lOO: - - - „ 611 „ Vertical Force, 1907 ■ • - „ till Heeling Ernr -------„ •'>1- Ship'8 Head North .M. - • • - - - ., "US Current Sailing ...--.- (;(j3 Triangular Sailing - - • - 665 Distance by Four-Point Bearing .... 683, 084, 685 Sextant Angles for Distance - • - -to fact 688 Vertical Angles ...... 695, 696 I)angei Angle, Horizontal .---.- 698 Illustrated l>y Cork llarl-our - ■ • , Pacific. „ Indian Ocean. „ Indiuu Archipelago and China. The above list comprises only such books as are deemed absolutely necessary in this Steel and Steam Age, when cjuick- ness, coupled with safetj-, bulis so largely in the calculation of Ult profit and loss on a voj-age. Their cost would be about £10 — not a great expenditure when considered in connection with a Shipmaster's responsibilities ; and officers co-operating with either England or America are awarded copies of the Meteoro- logical Charts or the Pilot Charts without charge. Indeed the addition of a few more instructive works may suggest itself to some, and they will do well to obtain any, or all, of the under- uicntioiicd : — Eztit books 1. The ten Volumes of Chambers's Encyclopedia. (Excellent.) 2. Practical Seamanship. Todd and Whall. d Paasch's Illustrated Marino Encyclopedia. ( Exctllent.) 4. Popular Astronomy. Fiammarion and Gore. 5. Chambers's Matlicmatical Tables, by Pryde. 6. Practical Physics. Glazcbrook and Shaw. 7. Griilin's Nautical Series. Several volumes. 8. Any works, dealing with cither Navigation ur Nautical Astronomy, by II. B. Goodwin, A. C. Jolinsou, U. W. Littlehales, or II. S. Blackburne. !•. Know Your Own Ship. Walton. 10. Glossary of Navigation. J. B. Ilarbord. The navigator who desires to pass liis spare momenta, not only jilcaanntly but also proKtably, should invest in a copy of a work entitled Azimuth, by Lieut.-Commdr. (now Admiral) J. E. Craig, U.S.N., publislied by J. Wiley & Son."), New York (yity, U.S.A. A more attractive combination of mathematics ittid nautical astronomy is difficult to find. To complete his working outfit, every navigator should be a N«iHiMi regular subscriber to the yautical Magazinr, now jiublished in Mab.iuk' (lliusgow, and carefully read each month's number a-s soon as convenient after receipt. This organ of the Mercantile Marino not only atlbrds light and agreeable reailiug fur leisure NAUTICAL INSTRUMENTS. moments, but also helps to keep the mariner closely in touch with matters — theoretical or practical — pertaining to his pro- fession. Notices of alterations and additions in buoys and lights; the discovery of hitherto uncharted dangers; modifi- cations in shipping laws ; publication of the latest Admiralty Charts ; and similar items of importance to every seaman arc clearly set forth in the Nautical Magazine month by month. NAUTICAL INSTRUMENTS. To the master of any sea-going vessel other than a small coaster, the following nautical instruments are indispensable : — ust ot Compasses, chronometers, sextant, night-glasses, telescope, com- instrument! mon or patent log, hand and deep-sea leads, parallel rulers, dividers, charts, and mercurial barometer or aneroid — both it possible. Even the coaster must carry some of the above- mentioned instruments ; and, in deep-water vessels, an artificial horizon, pelorus, and a Station Pointer should be in evidence, station This last valuable instrument, until " Wrinkles" called attention Pointer, to its virtues, had seldom or never been met with outside survej'ing vessels of the Royal Navy. It is, however, now used freely in both War and Mercantile Navies. To vessels frequenting narrow waters and intricate channels the Station Pointer is most especially useful ; hence it should certainly be furnished to steamers trading to the Baltic, Mediterranean, Black Sea, East or West Indies, or China. The Radiograph _ ^. " -r^ Radiograpb is a cheap and fairly accurate substitute for the Station Pointer. It is proposed to treat of the above-mentioned instruments separately, devoting either a whole chapter or but a portion of one to each ; so that, like any other good workman, the navigator may become familiar with the tools of his trade. Nothing but persevering practice will make him an expert in their use. It will first, however, be convenient and in order to say some- thing about the size and shape of our planet, the seas of which the mariner has to traverse ; and to explain in what way the "knot" — his unit of speed thereon — has been arrived at, together with its precise relation to units of a like nature. CHAPTER II. THE MILE AND THE KNOT. Knights of the quarter-deck, as well as laymen, are frequently just a tride misty over this seemingly " knotty" subject A short chapter will serve to clear away the haze an^l unravel the tangle. There are three perfectly distinct kinds of miles — 1. The Statute mile. 2. The Geographical mile. 3. The Nautical or Sea mile. Nos. 2 and 3 are often improperly taken to be one and the same thing. The Statute mile is the English and American standard of itinerary measure, and was incidentally defined by an Act passed in the 35th year of the reign of " Good Queen Bess " to be ' 8 furlongs, of 40 perches of 164 feet each," = 5,280 feet This is a purely arbitrary measure, and has no connection with any scale in nature. The Geographical mile is based upon tiie size of the earth, it being the length of a minute of arc of the earth's equator, ami regarded as a fixed quantity in all longitudea Assuming the equatorial circunifcn'ncc to be 24,902'18 statute miles, =■ 131,483,510 Ic.t, and dividing by 21600 (SCO" x liO) we gel 1)0872 feet as the length of the Geographual vtiU. But the navigator is not much concerned with either of the foregoing. NVlien alluat he has only to deal with the yautical viiU, which ilepend.s fur its len^^'th upon the ifluijx as well as the size of the ^dobc In- .sails over. In a gciifral way we are accustomed to think of our oraii<:e-Rhap( d planet as a true sphere, but, if we go into clo.se det^iil, the fiattcniiig nt the poles and other irngiiliirities of shape will not allow themselves to lie slightin^jly pushed over as negligible quantitiea Uoat costly, refined, and protracted geodetic operations, under- taken by uiiiiiy countries during the past and present ct-ntury. IRREGULAR SHAPE OF THE EARTH. have settled within such exceedingly narrow bounds the size, weight, and precise figure of the globe, that it is only left to ' wranglers ' to wrangle pleasantly over a trifle of a few hundred feet or so in any direction. The polar flattening was long looked upon as the only departure from the true sphere, but the elaborate investigations of General A. R. Clarke, R.E., seem to show that the equator is not quite Equatorial irreproachable in its rotundity, the excess of its longer over its ''"'**' shorter diameter being not far from half a mile. General Schubert, of the Russian Survey, independently arrived at a somewhat similar conclusion. According to Clarke, the greater axis lies in 8° 15' west, and 171° 45' east of Greenwich, the lesser axis being at right angles to this.* The distortion of Earth's shape. the equatorial circumference is so small, comparatively, that its exact amount, and position of its vertices, are still under discus- sion and open to correction. Therefore, though a subject of interest to mathematicians of the higher order, for sailors it has no significance whatever. It is quite possible — indeed, probable — that no section of the earth is either a perfect circle or a perfect ellipse, even when minor or contour irregularities are neglected. For purposes of nursery illustration, therefore, the time-honoured orange makes a capital " object lesson," more especially since it can be offered as a prize to be devoured after the lecture. Most oranges, however, rather overdo the flattening of the polar regions : — for example. Polar flattea in a 15-inch globe made correctly to scale, the flattening would only amount to j^th of an inch, a quantity which could not be detected without actual callipering, so that in sea-going practice we need not distress ourselves about this little eccentricity on the part of Mother Earth. Practical Navigation is not an "exact science," and never will be. The earth's equatorial diameter may be taken at 7926-59 Eartbi size. statute miles, and its polar diameter at 789958 statute miles; the compression is therefore 2701 miles, or j^V^ «* ^he equatorial diameter. This is rather more than has hitherto been accepted, Sir George B. Airy (late Astronomer-Royal) having put the com- pression at 26-50 miles. If we reduce to inches the length of the * If confirmed, this discovery will no longer.pemiit of the earth being termed an " oblate spheroid ;" to be strictly correct, its designation henceforth would be an "ellipsoid," a geometrical figure having three rectangular axes of unequal lengths, its section in any ■lirection being an ellipse ; whereas an " oblate spheroid ■' gives a circular section if cut «t right angles to the axis of revolution. POLAR DIAMETER IN INCHES. polar axis as above, we get in round numbers 500,500,500 — a curious combination of figures, very easily remembered, and sutliciently near the truth for most purposes. Fqu»tori»i 'flie eartli's equatorial circumference has already \>een stated as 24,90218 statute miles; this, be it observed in passing, is tlie longest distance which can possibly be travelled in a direct line (Great Circle) over its surface. It i.s, however, the earth's 7Jie)")- dional circumference which is responsible for the length of the Mean length of uautical mile. Taking the arithmetical mean of diameters given nautical mile, qu previous page, this will be 24',859-7 statute miles, = 131,25!t,15G feet, and these, divided by 21, GOO, give 6076 8 feet as the mea- surement of the mean sea mile.* But why the qualification " mean " sea mile ? Because, as will presently be shown, the sea v.in.ibiiityin niile varies with the latitude. Its length at the equator is 6046 length. feet, increasini,' to 6109 feet at the poles. The difference is not appalling, and as ships on the high seas are not navigated to j'ards, it is clear that the variation in the length of the nautical mile is of no importance to the sailor, further than that if he " fancies himself," and wishes to be a cut above his fellows, he ought not only to be acquainted with the fact, but also capable of giving an intelligent explanation. We have already seen that a section of the earth in the plane of the meridian — instead of being a mathematically true circle — is somewhat oval (or elliptic) in shape. If the circiinifercnco of Oval iineciion. " ^''"" circle (a compass cani, for example) be divided into .'MO", everybodj' knows tliat the length of each degree, or rather the space between each degree, will bo the same to a hair's-brcath ; not so with the oval. As its radius of curvature is variable, in- creasing from the extremity of the mnjor axis to the extremity of the minor axis, and as in consequence of this the direction of the vertical will not go to the earth's centre, but meet at varying points, 80 on the earth's sxirface a degree of the meridian is fitund by geodetic measurement to increase from the equator to the poles. The nautical mile, therefore, varies slightly with the latitude, and it thus happens that liooks of reference assign to it values pretty much in accordance with the caprice of the writer and the idea . , pervading Ids mind at the moment ; for example, a favourite Quot homlnri. ' " . ' L,i MottDiiv notion is that the nautical mile should correspond to the latitude of the region most traversed bj- the Heets of commerce. Noric and others give the Adminiity nautical iniii' as 6,0S0 feet but a visit to the Hydrogmpher would probably lead to a repudia- tion on his part of tliat particular measure; indeed, it is dnnbtful if * 8re Appendii E THE LEGAL AND IDEAL METRE. tlie Admiralty lay claim to a naiitical mile of any fixed length. On page 37 of the .5th eJition of the Admiralty Manual of Scientific Enquiry — a work published by authority — the number of feet in a sea mile is given as 6075 ; and on another page the Table of Dip is stated to be calculated for a mile of 6060 feet. 6080 feet correspond to latitude 48°, and these figures — recommending themselves more particularly on account of round numbers — are adopted throughout " Wrinkles." The nautical mile is therefore 800 feet longer than the statute mile. For roughly converting nautical miles into statute miles, or Miie equiv«- vioe versa, it is useful to know that 13 nautical miles are near '*"**• about the equivalent of 15 statute miles; then by simple pro- portion you can find the equivalent of any other number. The easiest way to do this, when an Epitome is at hand, is to open the Traverse Tables at 30° ; then against the nautical miles in the Latitude column will be found the corresponding number of statute miles in the Distance column. Landsmen, and seafarers in some instances, confound the knot . , -^ with the nautical mile, and regard the word knot as used to '^ X* — - discriminate against the statute land mile. This idea is quite erroneous ! The knot is the world's unit of speed, the mile is the unit of length. One knot, two knots, etc., are speeds of one nautical mile, two nautical miles, etc., an hour. This definition should never be forgotten. Instead of our " yard," the French and other nations use the Metre. ' metre ' as their standard of length. It is assumed to be the ten-millionth part of the meridional quadrant, and was fixed by law at 89'870-432 inches, in accordance with what were then accepted as the dimensions of the earth. But taking the dimen- sions here given, the length of the metre should be S9'377786 inches. This last may be termed the ' ideal ' metre, in contra- Le?*' ""i distinction to the other or ' legal ' metre. '**"'• By way of finish it will be interesting to glance at one or two points in connection with those extensive national surveys already alluded to. But little reflection is needed to shew that where exactness is sought after, all measurements of the earth's surface — whether vertical or horizontal — must be referred to a common p^jo^ p|g„, datum plane. Looking at the figure, the question at once pre- I HIMALAYAN PARADOX. Oc««D depths. Ciavitatlonal titraction. Bailb't cntit, jtuiitf or sents itself : — At what distance from its centre are we to mensure the circuiuforence of the globe, or, iu other words, at what part is its diameter to be taken ? Is the circumference to be taken as the outer circle representing the summit of the higliest mountain (l^erest, 29,000 feet); or is the middle circle, representing the meav sea level, to be taken ; or la.stly, is it to be the inner circle, representing the profoundest depths of the ocean ?• It is evident a great deal depends upon the answer. Tliere can be no doubt that the Mean Sea Level is the natural and only reference plane that cjiu be employed for the purpose, lu measuring the " base line " of a survey, it is necessary that the altitude of every part of it above the level of the sea be deter- mined, in order that the measured length may be reduced to what it would have been had the measurement been made on the sur- face of the sea itself. At first sight it would seem as if there were no special difficulty in determining the mean sea level, but, as a matter of fact, all mea.surements of the earth's surface are very much hampered by its uncertainty. Observations seem to prove tiiiit the sea level does not coincide everywhere with the geo- metrical figure which mo.st closely represents the earth's surface, but may be raised or lowered here and tliere under the influence of local and abnormal attractions. Matter attracts matter, as ships in a calm are said to draw near to each other. So it hap- pens that the ab.solute height of lofty mountains above wan sea level is difiicult to arrive at on account of the permanent distor- tion of the neighbouring sea surface by the attractive firce ®f their own masses. Thus it has been calculated that the Himalayas ought to heap up the waters of the Bay of Bengal to the extent of 500 feet : but in reality they fail to do so, and it follows that what would be the undeniable action of the Himalayas, if of average density, must be counteracted by some occult influence. Science fortu- nately comes to the rescue. The ob.servations made at the various stations of the Indian Meridian Arc have brought to light a physical fact of the very highest importance and interest, namely, that the density of the strata of the earth's crust under and in the vicinity of the Himalayan Mountains, is less than that \inder the plains to the south, the deficiency increasing as the stations of oloervation approach the Himala^'as, and being a maximum when they arc situated on the range itself. Genornl • " -' . 1..... I, .....,,.. ^, , V. K... ,..,: ;,. |„ 12'<:!' N. It: '■ : s. ufl" 3it w. irl ..Horn St 4 O'i'J f>t .1 hi 18° IK. SI"'.: W 1,0- II S 1- i;. W. Iiill"ffi'S. 116* CO' r 110 niileii from tlie Kurils laUii.tt ihrre 1< 4,«ri5 ; 'ii.lly I»Ie«, 4.r.00 lallioma ; iicnr thr ijiilroiii's, 4,1, > MiiM.iin. iMji rvittmit, < i.- lallioiiii; >iij f'O inilti off tlit coMt o( r«ru, 4,li& htboiua. WANT OF RECTITUDE IN PLUMB-LINE. 9 Clarke shews that the form of the sea level along the Indian are departs hut slightly from that of the mean figure of the earth. As explained above, subterranean tenuity is the cause, and thus UMqu»i the non-appearance of the attraction which this gigantic range '**"'">'• ought to produce is satisfactorily accounted for. The Chilian Andes, from their greater nearness to the Pacific, have been computed to exert an influence on the sea level equal to 2,000 feet, but it is probable that in their case, also, this is, for the most part, nullified by want of solidity in the earth's crust; for what more likely than that, in the process of upheaval, sub- terranean voids have been left corresponding more or less to the elevations. Ben Nevis, which contains about a couple of cubic ^en Nevi» miles of matter, is said to produce in the neighbouring sea an elevation of three inches. Dr. A. Supan, in " Petermann's Mitteilungen," called attention to the fact that, according to the most recent measurements, particulars of which have lately been published, the old hypothesis, that there were important differences in the levels of the seas of Europe, is no longer tenable. The statistics given in the ".Bulletin Annuel de la Commission de Meteorologie du Departement des Pouches du Rhone" (1891), show that the mean level of the water at 38 stations in the Adriatic, Mediter- European ranean, Atlantic, English Channel, North Sea, and Baltic, differs in most cases but a few centimetres from that at Marseilles, so that, for practical purposes, it may be taken that the mean sea- level on all the coasts of Europe is much about the same. It will be .some years yet before this can be definitely settled. Meanwhile the conclusion cannot be avoided, that measurements of heights above the sea level as commonly stated, though fairly comparable one with another over a limited area, are subject to no little un- certainty if regarded as absolute quantities referred to the ideal sea level of the mean terrestrial ellipsoid. Now, for the same reason that mean sea level is not quite uni- form for all parts of the world, the plumb-line, u.sually considered a model of rectitude, does not hang truly vertical everywhere. Verticaiity of ' a J " plumb-line. This is the same as saying that the surface of the mercury in an artificial horizon is not truly level everywhere. Just consider the effect of this on the more delicate astronomical observations of a survey, and the knowledge and skill required to eliminate such errors. In mountainous countries, as near the Alps and in the Caucasus, deflections of the plumb-line have been noted to the extent of 29". VARIOUS KINDS OF LATITUDE Carious deflectioni. Various direc- tions of the plumb-line. Direction of earth's centre. termed the ■■ KtJuctJ Latitude. " Angle of thi TarllcnI." On the other hand, deflections have been observed in Hat countries ; for example, at certain stations in the vicinity of Moscow, within a distance of 16 miles the plumb-line varies 16' in such a manner as to indicate a vast deficiency of matter in the underlying strata ; but, luckily for the surveyor, these are exceptional case.s. Here is another nearer home. On the north coast of Banffshire, near the village of Portsoy, there is a spot at which the deflection amounts to 10", so that if that village were laid down on a map in a position to correspond with its Astro- nomical latitude, it would be 1,000 feet out of its proper place, since a second of arc ( ") about equals 1 00 feet on the earth's surface. Astronomical or Observed Latitude is the angular distance from the equator of the apparent zenith ; or it may be expressed a? the Declina- tion of' the apparent zenith. It is consequently dependent upon the directron of the plumb-line, since it is this latter which gives us the vertical point known as the zenith. Now, it has been shown that the plumb-line is subject to disturb- ance ; but when not di.sturbed, it coincides with the normal of the true ellipsoid, and, therefore, indicates the e in the external prolongation of a line from the earth's centre throogb the place of observation. IJut, properly speaking, this is the Reduced zenith. Geocentric Latitude, not mentioned hitherto, is the angle at the centre of the c.ii-lh subtended by the arc of the meridian between the place in question and the equator. It is therefore independent of the earth's shape. The (I'focentric is always less than the Geodetic Latitude, except at the equator and poles, where the two coincide. The maximum difference (ir Ai") is in Latitude 45°. As the Navigator ha.s only to deal with Astronomical Latitude, he need not worry over the.so fine distinctions. With the foregoing intricacies before the mind, one can have some slight inkling of the exceedingly delicnta and high-cla.s3 matheniiiticivl character of the observations atui ciilculations re- tjuiri'd in an extensive geodetic survey, such, for instance, a.s our own " Ordiuuice Survey," or the huge undertaking known as the " Great Trigonometrical Survey of India." Verily, brother, there are more things in lleaven and uu earth than are dreamt of in the simple philosophy of seamen ! ! CHAPTER III. THE MARINER'S COMPASS, AND IMPORTANT FACTS CONNECTED WITH IT. Curiously enough, until comparatively recently, ship-builders and ownei-s did not bestow on the compass the amount of con- Apathy of sideratiou which it undoubtedly merits. It is pre-eminently the instrument upon which the safety of the vessel depends, and justly ranks first in importance. It would be easier to disipense with the Chronometer, or even the Sextant, than with this in- valual)le guide. With a faulty compass, a straight course cannot be made. Formerly, when time was less an object than it is now, a bad landfall, or distance lost on the voyage through zigzagging over the ocean, was of no particular moment ; but in these days of keen competition, when the public look for the arrival of Rivalry in Trans- Atlantic and other mail steamers almost to the very hour, p^ss"eet. and the rival companies wage paper wars over the splitting of minutes in tne passages of their respective vessels, it is necessary that good navigating appliances should back up good shi^JS. Compasses for use on board ship are of two classes — the Stan- standard dard and the Steering Compass. Taking them in this order, the Compass. Standard first claims the reader's attention. To begin then, it is of the greatest importance that a spot placing of should be selected for the Standard compass where it would only ^^^''^ss^ be acted upon hy the general magnetic character of the skip, and not hy particular masses of iron in its immediate vicinity. To this some builders pay considerable attention, whilst others, un- fortun.itely, seem unaware of the necessity for such a precaution, Position taking it for granted that the compass adjuster can effect his ""P'"''*'"- object, quite irrespective of how the compass may be fenced in with iron. The Standard may not inaptly be termed the "Navigating compass." By it the course .should be set, and all bearings taken for ascertaining the ship's position. To this end, it must be SELF-CONTAINED BINNACLES. placed where an all-round •v\eiVi of the liorizon can be had, ex- cepting, of coui-se, when the masts or funnel intervene. In vessels of the larger class a special platform is erected, and in such cases the handrails and supports are of wood or brass. Unless, how- ever, the whole structure is tirndy and securely bolted down to the hull of the ship, it will be ceruin to vibrate in strong winds, or with much motion, and so destroy the steadiness of the card, rendering almost useless what may otherwise be a good compass. Boi Binoacie. The binnacle should be large enough and of such a shape as would permit of the adjusting magnets being placed inside, in- stead of on the deck. This is a neat and compact arrangement, and acce.ss to the interior can be had through a small door pro- vided with a good patent lock and key. To prevent tampering with the magnets, or the inside being made use of by quarter- masters as a handy stow-hole for odds and ends, this door should be religiously kept locked, and the key in the possession of the captain. Gray, of Liverpool, was about the first to bring out a binnacle emlxxlying this principle; or, to be more correct, it was a square stand or bo.\, upon which the binnacle proper was placed. To the late Lonl Kelvin is diie the credit of having brought into faslu(jn a really satisfactory form of binnacle ; and, with modi- tications, the bulk of compass-makers have followed suit The Kelvin One of tlie great advantages of the plan is that when it becomes Binnacle. neces-sary to remove the binnacle for any purpase— such as caulk- ing decks, &c., there is no occasion to disturb the magnets; whereas wiien they are nailed to the deck round about the bin- nacle, it will .sometimes happen that they are Uiken up by caulkers ignorant of the mischief tiiey are doing; and when replaced— as likely as not the magnets are shifted end for end, and put down at a greater or less distance from the conipa-ss than they occupied previously. Danger f.on. WIicu the Standard compass is improperly situated— as, for p.o«.,nityof example, on a narrow bridge, hemmed in by iron hand-rails. Hanked by boats' davits, awning-stanchions, ridge chains, stoke- hol.l ventilatoi-s of large size with moveable cowls, and probably not two feet from the iron sUnd of the engine-room telegraph, or twice that distance from the donkey boiler,- it is rather too much to expect that its behaviour will be satisfactory. No adjuster in the world could even ^re/tfrnZ tocompen.sate the errors of such a compa.s.s. He might cerUinly manage, by a liberal use of magiirt-s. to lick it into something like shape for the time TEMPTING PROVIDENCE. being ; but such an adjustment could not be depended upon for twelve hours after it was eti'ected, especially in a new vessel, and on a voyage to the southward the deviations would soon become 80 large as to be unmanageable. Compasses are not infrequently so badly placed that the Large errorj adjuster has to compensate errors amounting to eleven or twelve p°^,",""' points. The reader may imagine that the foregoing is an overdrawn picture, but if he will take the trouble to look around, he will not be long in finding how true its description is. Sometimes, too, it occurs in steamers that the end of a trysail-boom, when guyed amidships, comes within 18 inches or less of the compass. In this case, if the foot of the sail should be made to haul out with a traveller, on a massive iron jackstay — a very common mode of fitting now-a-days — it is clear the effect on the needle will entirely depend on the position of the boom, whether eased off to port or starboard, topped-up, or in the crutch. The writer was in one vessel where the wire toppinglifts of the main-boom came down within six feet or so of the Standard compass, and were proved to produce an effect of 5° when the boom was guyed over from one side to the other. Precaution, then, should be taken, that no iron subject to temporary removal, be within ten or twelve feet of the compass ; and the latter should stand at least 4 feet 6 inches above the deck, not only on Height of account of the beams, but to avoid the liability of being ^^^^^ ^^^^ influenced by any moveable article of iron on the deck next beloiv it. It is common enough, where the vessel is steered forward, to find a compass placed on the bridge just above the one in the wheelhouse.* In such cases it is imperative that the upper or bridge binnacle should be raised above the deck as much as One compass ° ........ anectmg possible, or the compensating magnets contained within it will another, aff'ect the other compass in the wheelhouse, and vice versa. If raising the binnacle on a wooden stool or solid block should render it inconveniently high, it is not a killing matter to build a suitable step — or even a couple of them — round about its base. The reciprocal action of one compass and its magnets upon another — more particularly in the position here referred to — is a thing very likely to be overlooked from the mere fact of the compasses not both being seen at one and the same time. ' See diagram facing page 39. 14 POSITION OF STANDARD COMPASS. Fitting out When fittiuy out a new sliip, it is not uncoiuinon for tlie '^' builder to consult the wishes of the future capUxin in the matter of compasses, &c. : if, however, the latter does not join the vessel till she is nearly finished and ready for delivery, it will be too late to expect much in the way of alteration, as builders, at all times averse to it, are particularly so wljen they ai"e just about to make Aittraiions in thc vcssel ovcr to her owiiei-s. But there is no reason why the poji ion. captain, if dissatisfied with the existing arrangements, should not himself endeavour to remedy them in the course of some subsequent voyage. It is an easy matter with a spare comjiass to make trial of various places about the decks, until one is hit upon comparatively free from the intluence of the ship's iron, and there the Standard should be rigged up. even if other important mutters have to give way for it. Neutral spoi It is wcU to know that in every vessel there is a "neutral ofihip. spot" wliere a compass would have little or no deviation ; but unfortunately, it may be found to exist in an impracticable position. Nevertheless it is worth looking for. There is only one caution neccssiiry — before finally screwing down the binnacle in the newly found neutral spot, be sure that it is really so l>y testing the deviation on two adjacent cardinal points, such as nurbli and east, as it may happen that a place has been hit upon wliere the coiup;iss will be tolerably correct on one point and VLiy much out on another. It is questiouable, however, whether this neutral spot would deserve the name in all latitudes. Tlie writer is led to the above remarks by haying noticed that Fluty oi the Staiidanl compa-ss of ships several j'ears old had been allowed tenure ^ lemaiu from the commencement in most unsuitablu positions, as if their captains considered, that once placed, there they should for ever remain. The following is a description of a Standard or Navigating compivss — honest and simple — whicli has stood the test of sevoraJ yeai-s' trial, and been found to fultil all the desirable conditions in a fair tlogree : — I r,uy, R.dui In point of size it is a compromise between the ju.stly lauded I ine c.,.1 Admiralty Standard compass and the gigantic ones wliich, until recently, were in u.so on board some of the Atlantic Mail Sto.imei-s. In Uie attempt to gain steailiness, and secure large margiiml divisions to steer by, the ciuds of these last-mentioned compasses sometimes attained the amazing diameter of 18 in. and 20 in. Thc card under description hua a diameter of 11 in., and is mounted similarly to the Admiralty one, on two pairs of CORRECT PRINCIPLE OF CARD. needles, respectively 8| and 6 inches in length, by half au inch in depth, and ^ of an inch in thickness. The longer pair occupy Position of the central position, the ends of each being 15' from the north °"='""- and south line, whilst the outer, or short needles, are each 45° from the same point, after the manner represented in Diagram No. 1. The needles, as will be seen, are secured to the card on Diagram 1. their edges in the usual way, are parallel to each other, and equi- distant. By this arrangement the advantages of a large card are secured without the drawback of long needles, which are objectionable for many reasons : the principal being that they are opposed to a perfect compensation of the compass by magnets, and that there is no practical gain of directive power, the latter being more than counterbalanced by the friction on the point of support, resulting from the increased weight. It follows from this last, that in all compasses the needles should be very thin, Short neediw and the brass or aluminium carriers as light as possible.* • There will be no loss of power consequeut on tbinuess, aa magnetism resides princi- pally in the surface. LECKY'S RADIAL-LINE STANDARD. Slufffishness. It may be lai'l down as a fundamental principle that the smaller the needles, the more correctly theif point; and the larger a card the more accurately it is read. When very large needles are used, sluggishness results, which the unwary navitrator is too apt to mistake for steadiness. Who has not seen a piece of marline or spun-yarn made fast to the compass bowl, and occasionally twitched by the man at the wheel to " keep the card alive," or, as it is termed in Jack's phraseology, " to keep the compass afloat." Independent of long needles, there arc many causes to which this state of affairs can be traced, and they will be referred to further on. Diarfram S. In •tetmihipi •hould b« irt la dtctcvt. It will be noticed, by reference to above diagram, that the upper surface of the card is of novel pattern. The outer rim is divided by radial lines into single degrees, every fifth and tenth being, for sake of clearness, marked stronger than the others. Now that the course — on board steamships at least — is very com- monly set in degrees, this, which might otherwise bo considered an objection, is no Ioniser on& Each quadrant is numbered by tens, from zero at north and south, up to 90* at east ami west EXPLANATION OF DETAILS. Tlie diameter of the central space, representing the usual points and half points, is 6'35 inches, and the length of the Stile or Shadow-pin mounted on the centre of the card is so proportioned Lectys eard (3"75 inches), that when the sun attains a greater elevation than "* "'" '* °^ 50°, its shadow will fall within the bufore-meutioned radial lines — showing at once, without reference to anything else, that the altitude is no longer favourable for observing azimuths. In this respect the compass is self-indicating. It is true that bearings of the heavenly bodies may be taken with other instruments up to altitudes of even G0° or upwards ; but to get a correct azimuth, when the body observed is so near the zenith, necessitates a much more refined instrument than the ordinary ship's compass. As a rule, except under great pressure, azimuths should not be taken at a higher altitude than 30° ; in fact, the nearer to the horizon, the better. To continue the description of this form of Standard compa.ss, — the glass cover of the bowl is of a curved form, struck with a radius of 6'5 inches, to allow room underneath for the play of the Shadow-pin ; and the bowl, of stout copper, is suspended by six strong iudia rubber supporters to an additional or inner brass ring. This last arrangement, now in tolerably common use, diminishes the shocks which would otherwise be communicated to the card by the jar of the engines and propeller, and by the pitching of the vessel in a heavy head-sea. These may be lessened still further by placing a light spiral spring in the socket of the pivot which sustains the card. In a well made compass of the oi'dinary pattei-n, the essenticUs Essentials of a are— that the pivot should be accurately centred in the bowl; eood compass, that is to say, that its point should be exactly in the intersection of the two diameters, passing through the centre of the gimbals, and in the same horizontal plane ; the upper edges of the needles should also lie in the same horizontal plane, or, if anything, an eighth of an inch lower. To avoid distortion from shrinking, the card should be mounted on its mica base before printing, other- wise the graduation of the marginal divisions is likely to be in error. The shadow-pin, if there is one, should not only be straight, but accurately centred on the card, and the general balance of the instrument so well preserved that the shadow-pin will stand truly vertical under all circumstances. The compass should be sensitive in smovth, and stead j in ruugh water. ji ni PORTA XT SIMPLICITIES, Hang or the Thc bowl, if inclined to list one way or the other, can be niude *""* ■ to hang horizontally by neatly serving the ginibal-ring with lead wire ; and in case the card itself should be a little out, some melted scaling wax sparingly dropped on the under side will spuudily restore its balance. The card, when poised on its support, should not be more than J of an inch below the upper edge of the bowl where the latter meets the glass cover, otherwise the sun would ret[uire to have considerable elevation before its shadow could strike down on it. Moreover, the higher the level of tlie card, the easier it is to take bearings directly by the eye. The pivot should have a finu point of hard steel or iridium, ground to fit the sapphire cup, and the magnetic axes of tiie needles must be strictly parallel to the north and south points of the card. Re»soiu for Beforc going further, it may be as well brielly to explain one mounting ^f j^ji^ j-eivsous why in modern compa-sses the needles are secured edge. to the card on their edge.s, instead of on their flats, as formerly. As just stilted, it is necessary, for obvious rea.sons, that the viagnetic axes of the needles should be parallel to the meridian line of the card. Now, when needles or steel bars are magnetized, it sometimes happens that the poles do not lie exactly in the cwiS <)/■ the fiyuye, but oblitjuely to it, vide diagram ; iu which ca.se, if NORTH AND •OUTH LINE OF. 00MPAB8 OAND. ..".•o^t.'ic »mi Of I i ncu m o» xnDcc N oiointted on tiieir t1ut/3, the aliove condition could not be con- veniently fulfilled, but by mounting the needles on their edges it can. If the foregoing points arc con.scieutiously attended to in the manufacture of the instrument, it will be found to give gotid results, and prove steady in a seawa}'. This latter quality may be still further en.sured by attaching a flat circular baud of brass to the man/In of the wird, on its under side, something after the fa-shion of the fly-wheel ; its efl'uct is to increase the vibrational period of the needles by throwing the weight to the outer edge, ami in this manner it is a most valuable auxiliary in conferring steadine.ss on ti»e card. The dimensions of the bra.ss ring are, ,'^ of an ineli in width on thc flat, and j'g of an inch in thick- ness. Lord Kelvin hits ingeniously availed himself of this jiriu- AiXD UNCONSIDERED TRIFLES. 19 ciplc in his patent Standard compass, which lias proved such a wonderful success. With Lecky's radial-line compass, azimuths of the sun or moon can readily be taken by simply watching where the shadow falls on the radial lines of the card. If partially veiled by clouds, so as to cast no shadow, a little practice will enable anyone to take a direct eye-bearing of the sun (if not too high) with a probable error of less than a degree. Bearings of objects on the horizon, such as ships, land, or lights, can be obtained with the utmost accuracy, by getting the Shadow-pin, margin of the card, and object in the same straight line. The writer and his officers have over and over again observed azimuths of stars — taking 3 or 4 on Taking widely difterent bearings as a check. When worked out, the ^^"°""" *■" *' o ^ ^ bearings. results generally con-esponded within a degree, and never ex- ceeded two degrees, even when the vessel had considerable motion. See that the compass has not lateral end-play in the gimbals, which would jar the card, and cause it to oscillate every time the ship rolled. If the gimbals do not fit close up to the sides, insert a small piece of soft wood, but do not jam them or impede their action. See also that the freedom of the card is not interfered with by its edges touching the bowl ; this sometimes happens with a too- ueat-fitting card when expanded by damp. Test it by spinning the card on its supporting pivot. In taking azimuths by the shadow of the sun or moon, the stiie or extreme convenience of the Stile is at once demonstrated. In shadow-pia smooth water the reading on the card can easily be made to half a degree, or under; at less favourable times, the swing can be obser\ed and the mean taken. There is no stooping or manipu- lating of a refractory azimuth-ring and speculum, the use of which, when the bearing happens to be on the beam, is rendered additionally awkwai-d in compasses fitted with chain boxes ; nor does one's nose get smeared with oil and brickdust that may be left on the brasswork by a careless quartermaster or lamp- trimmer. In swinging ship for a deviation table, there is nothing to do but stand still, with book and pencil in hand, and, as the ship is steadied on the required point, note the reading of the shadow Swinging simultaneously with the hour and minute by watch, previously ^""'p- set to Apparent Time at Ship. In fact the observer is master of the situation without an effort. With this compass, swinging the ship completely round, steadying her on every other point, should not occupy more than 30 or 35 minutes. rREVENTIDI.E ACC/DEXTS, A\n Best UTUge- ment of Sh»dow-pln. Principle of azimuth loitnimentt. Some compasses are still fitted with a Shadow-pin, to sliip in a socket on the glass cover : but there are several serious objections to this arranuement. The pin, from its exposed position, is continually gettinjj bent; if removable, it gets lost; if left on, and the binnacle top be hurriedly shipped or unshipped, it is apt to get a knock, which will probably break the gla-"^, and oiuse no end of inconvenience. Again, it is seldom that the Shadow-pin is stepped exactly in the same vertical line as the centre of the card, which ought strictly to be the ca.se if a correct result is looked for ; the sun has to attain quite a considerable altitude before the shadow can po.ssil)ly fall on the card ; and finally, from the motion of the bowl and the card not Iteing always coincident, the shallow on the latter ranges about much more than it need do. On tlie other hand, when the Shadow-pin is mounted on the card itself, it does not suffer by handling; if made straigiit. it will remain so; it is protected from injury; it is more Ciusily centred ; and from its curved shape the glass cover is stronger. The correctne.s.s of all the various instruments used for taking azimuths depends, in the lii-st place, upon certain of their parts preserving either a true horizontal or verti&il position, so that, if the objection be inadc to a Shadow-pin on the card, that it may not always stand truly vertical, it must not bo forgotten that it applies with equal, if not greater, force to all the other uiodeji of observing: and it is this liability of instruments to deviate from their proper position, whether vertical or horizontal, that makes it advisable to take azimuths at low altitudes, whereby any errors due to this cause are reduced to a minimum. To test the balance of the card is a simple matter. Firat of all unship it and assure yourself that the shadow-pin stands e.\actly at right angles to its surface ; this can be done with an ordinary set-square. Next, replace the card and put on the gla.ss cover; then, standing at a couvunieut distance from the binnacle, and the helmet or top being removed, 8torcakage of the glivss top, owing to excessive expansion of the spirit. From neglect of this simple precaution the writer has .seen several litjuid compas.ses come to grief nnvst unexpectedly, causing much anno^'ance during the rest of the pius.sagi', and expen.sc at the end of it. This is the only kind of compa.ss which is suitable for boat work ; in all other descriptions the card swings so much as to bo u.seless.t An erroneous idea sometimes prevails, that, in an iron vessel .such a compass is less afl'ect-ed than those of the common pattern. This is really not the ca.se, nor do the makers wish to convey • Tiir* alcohol- fanillttrly knowu a< spirlU of wine— i» preferal)!* to wat«r, or ai7 otliar liquid, Iwcaui* It iloei wl fr«cie evaii at Tery low teui|>erature«. 1 In th* heal liquiil compaMM tha card ii of hard enamel, which permits of pun tpirita of win* btlng uted without dlacoloratlori, and renden frtciiog Impossible. These poloU can never be gained In the ordloarjr painted card. FACTS VERSUS FALLACIES. 13 s\icli an idea. As explained above, a card, when nearly afloat, is much more sensitive and obedient to the earth's directive force tliau the same one would be if suffered to rest its whole weight on the sustaining pivot, and that -is all. The writer cannot here do better than quote the late Mr. Towson's remarks on this subject. He says, on page 122, in his work entitled "Practical Information on the Deviation of the Compass for the use of Masters and Mates": — " In connexion with compass deviations, many practical men have vainly attempted to discover some substance or medium that impouiiiit ia would insulate the needle from the influence of the magnetism of intercept the ship's iron. Many imagined discoveries of this character have been patented, and have served both to waste the time and money of the patentees, and to distract the attention of the mariner from that class of study which alone can promote his safety in navi- gating an iron ship. It may be stated with confidence that thei-e is no available medium that can intercept magnetic influence. For two centuries, at least, every class of bodies has been sub- mitted to experiment, in order to discover a material capable of intercepting the influence of one magnet on another, not for the purpose of preventing deviation, but because the mechanic clearly perceives that if such a material were discovered, a motive power could be produced by various arrangements of permanent magnets and insulating bodies. But no one has succeeded in making this discovery. Should, however, the efforts, which for centui-ies have been unsuccessful, be realized, although a new motive power would thereby be available, it would be altogether valueless in connexion with the compas.ses of iron ships. The magnetism of the earth generally, the loadstone, soft iron, hard steel, or the electro-magnet, is all of the .same nature. If we shut off one, we sliut off all. "If, therefore, we could succeed in insulating the needle from the magnetism of the ship, we should by the same means intercept the magnetism of the earth, and thus the compass would be rendered absolutely useles.s. In the first place, then, the object sought for is not available; and, secondly, if such a medium did exist, it would be entirely valueless in connexion with the com- passes of iron ship.s." There is an ill-defined idea prevalent among the older school Popular erron of pilots and seamen that the compass is aflected (1) by fog; ileyi°"n'" (2) by strong winds of long duration in the same quarter; (3) by the phenomenon known as the Aurora Borealis in the northern, and Aurora Australia in the southern hemisphere; (4) by the ANTIQUE COMPASS LEGENDS. attraction of land — notably when of volcanic origin, and liy the pruxiniitj' of the vessel's keel to the bottom in the shallow waters of harbours, rivers, and estuaries ; (5) by thunderstorms. These are the causes principally blamed for abnormal deflectioiis of the needle ; whether justly or unjustly remains to be seen. The two first may be disposed of very shortly. It can be stated in the most positive manner that neither meclMnically nor magnetically does fog affect the compass in the slightest degree. There is no difference in the magnetic constitution of a needle which has the good luck to reside on shore as compared with one whose misfortune it is to be buffeted about at sea This l>eing admitted, we would have heard long ago if the doings of the needles in the basement of the Observatory at Greenwich had been at all erratic during togs, of which London can boast some very fine specimens. There is also a magnetic department at the National Physical Laboratory, near Richmond. In both these, the delicatel3'-suspended needles are so arranged that their slightest movement is automatically registered on sensitized paper — in fact, photographed. Nothing out of the common can therefore occur without being detected, also the precise time of its occur- rence. It is tlierefore ea.sy to trace connection between the beliaviour of the needles and any outside phenomena 8uppo.sed to intiiience them, as the latter are also registered, though in a ditri-rent manner. 'Pill' same thing, of course, applies in the ca.se of winds of long duration, such as the stifi'-necked ea.sterly " blows " that, in the spring of the year, used to drive scores of " homewanl bounders " into Queenstown and Falmouth, and to a lesser extent do .so still. Should tlie ve.ssel be of iron, the deviation due to wliat is de- scribed furtiier on as " Retjiiiiod " magnetism might Ihj tlie culprit, initsmuch as, after a long stretch on one tick, with head pri'tty innch in .same dirt'Ction, an iron vessel would have her ordinary magnetic chanicttr temporarily altered, .so that when a shift of wind permitted a change in the course — say from north to eiust — the deviation on the new coui-se would be found different U) wliat it hail Ixjen on ea.st previous to the setting in of tiie .spell ol contrary wind. This is prolwibly the origin of the belief, ami though indirectly it might as sliewu be siccountable, wind, 08 gxuJi, could not deflect the needle a single hairs-breadth. We will p:iss on to No. ;{, which is much more interesting. Aided l)y the phiit<>grfii)hie camera and spectroscope, substan- tial progress in solar physics hiw iieen made within the puat MAGNETIC SYMPATHY WITH SUN. twenty j-ears or so. Sun-spot observations have been system- atized, and it is now accepted tliat the mean period of their recurrence is eleven years, thousrh individual periods may depart from it considerably. For a long time it has been made evident that there is a decided connection between this period and that of terrestrial magnetic phenomena. That is to say, they are more frequent and more pronounced at times of maximum sun- spots. The records shew that magnetic storms, as they are termed, mostly occur when an exceptionally large spot is visible near the central meridian of the sun's disc, or about the time of Sun-jpot». some great change in a sun-spot. It has been established, also, that these magnetic distui-bances take place at the same absolute time over the entire earth. The spot-group on the sun February 5-17, 1892, was the largest photographed at Greenwich since 1873, in which year was commenced the Greenwich series of photos. Its presence was associated with a correspondingly large magnetic di'^turbance, which attained its maximum on February 13-14. It began on the loth, about 5'32 p.m., was at its best between midnight and Magnetic 2 A..M., and gradually died out about 4 o'clock the same evening, thus lasting nearly 2-i hours. It seriously disturbed the telegraph and telephone services throughout the world, and was attended by one of the most brilliant auroral displays seen of late years in this country. At Greenwich, the needle for recording the varia- tion was pulled out of the meridian line 1° and more. At Kew, the same occurred ; whilst at Potsdam, " enormous " fluctuations were noticed : changes of 2° in two minutes were recorded, and deflections of 1|° were observed. (Dear reader, please note that changes or vibrations of 2° were considered " enormous."). November of 1882 was marked by a disturbance falling but little short of the one just described. In investigating the relationship between large sun-spots and magnetic storms, it appears that one or more will usually occur during the life of any particularly noticeable .sun-spot; and a curious point — .so far unexplained — is that these disturbances are more common in spring and autumn than at other times : thus. Season of taking the Greenwich records for the last 50 years, disturbances "'"' *"''* are two or three times more frequent before and after the equi- noxes than at the solstices. A preliminary sudden movement is a common feature of mag- netic storms. It may be taken as a warning of the disturliance to follow in a lesser or greater number of hours, but sometimes the disturbance follows on at once. 26 A rjiOIiJS-LEMSTROirS EXPERIMENT. Amount or disturbance board ship. Aiiinulhs .liirlnn fog. Auroras and sun-spots are found to wax and wane together even in their smaller fluctuations, but the theory that they de- pended for their frequencj- on the influence and position of the planets had to be abandoned. Bej'ond question, the Aurora is an electrical phenomenon, something after the style of sheet light- ning. According to Lemstrom, who, by overspreading the top of Mount Oratunturi, in Northern Russia, with a network of insulated wires, succeeded in producing identical eflects, the Aurora is due to currents of po.sitive electricity illuminating tlie atmosphere in their passage to the earth. The vertex of the luminous arch is always found in the direction of the magnetic imridian, and as the display is known to occur simultaneously in hiiih hemispheres, it shows, as might be expected, a connection between the magnetic polos of the earth. It is abundantly proved that the very largest magnetic storms do not pull the most delicately balanced needles more than IJ" out of the magnetic meridian. How then about the rougher instrument of the mariner ? Further, the effect of these disturb- ances is more in the direction of causing small vibrations of the needle than in holding it over for a length of time to the right or left of the line of rest: in fact, a man might pass his life at sea, and not experience a steady pull of F. * Knough has been said to shew that auroral displays, magnetic storms, imd periods of solar activity, are each coincident with the other, and protluctive of magnetic disturbance ; but even in their most intense form the amount of such disturbanoe would seldom l)e appreciable on board ship, certainly never so great lus to approHch oven a ([uarter of a point Should, then, unusual deviation be jToved to exist during a time of fog, a long continuance of wind from one quarter, or during a display of the Aurora, the navigator may put these three "suspects" on one side, and look in some other direction for the cause. Anyone can test these matters for himself. In thick fiigs it ia often beautifully clear overhead and the water smooth, so that 'Time Azimuths' can readily be tiken of Sun, Moon, or Stars, which can be rejieated it/tr)- the fog luus cleared off": and these observations can be further compared with those t^vken on the sumr course a short time previous to the fog setting in. The same can be done with the Aurora, and all doubts set at rest In like manner, when passing clo.se to islands known to be magnetic — such as St Helena, Pantellaria, or the Salvages— a ."Jeries of ' Sm Appendix r. ATTRACTION OF LAND. careful azimutlis would do moi"e to convince the sceptic than any amount of " ink-slinging." Besides, wliy should any one parti- cular ship be selected for a manifestation of this kind, when thousands of others, under similar circumstances, had been al- lowed to go scot-free. It is altogether unreasonable, unless the magnetic demon is guilty of favouritism. The writer would wish it understood that the foregoing is strictly borne out in his own experience at sea. Whenever op- Author's own portunity offered, most careful experiments were made to confirm ^'^p"*"'^*' or disprove all such theories, and though many thousands of azimutlis have been taken by him in such parts of the world as he has visited, and at various hours of the night and day, in no single instance was anything abnormal detected which could not otherwise be satisfactorily explained. No. 4. The attraction of land, and the effect prodiLced by proximity of vessel's keel to the bottom. This comes under the heading of " Local Attraction " — a term Attraction o» which will be more fully explained in another place : suffice it to say here, that it has reference only to the effects on the compass of magnetic forces external to the ship in which such compass is placed. From time to time one hears extremely foolish accounts of wreck through the supposed attraction of land. The writer recollects one in particular, which, from his familiarity with the locality, made rather an impression. It was that of a fine large steamer stranded near Cape Santa Maria in the River Plate. " Fools step in where angels fear to tread," so some sage newspaper correspondent attributed her loss to the effect of an imaginary magnetic hill somewhere round about that neighbourhood. This gentleman had probably been reading the story of Sinhad the sinbad the Sailor, and how, on getting near one of these magnetic hills, its attraction was so powerful as to pull all the nails out of the ship's side, and down she went, plump O ! ! As a matter of fact, the steamer was lost through ignorance of the north-easterly current which invariably runs on that coast with great strength during a Pampero. Pretty much the same thing appeared in the Press when H.M.S. Serpent came to grief near Cape Fiuisterre in Nov. 1890, but it was clearly shewn in evidence at the court-martial, that even had there been any " Local attraction " thereabouts, its effect would have been to keep the vessel o^' shore. Magnetic laws do not permit of the supposition that visible land will disturb the compa.ss of a .ship at .sea, because the effect STIIAIT OF MAGELLAN. Distance Uw magnetism. Compaif vagarief PUaaant channels to oawlgate. of of a magnetic force diminishes in such exceedingly rapid propor- tion as the distance from it increases, that it would require a local centre of magnetic force of an amount absolutely unknown to iiftect a compass half a mile distant. It has never been dis- puted that masses of rock are sometimes intensely magnetic, and quite overpower the earth's magnetism when a compass is placed sufficiently near. There is nothing new in this. For example, in the account of the voyage of H.M.S. Beagle during the survey of Tierra del Fuego, about the year ISSO, it is mentioned that several times when the ' Kater's ' Stiindard compass was taken on shore to get bearings, the " Local Attraction " was so excessive that the card had no directive force whatever, and observations were impossible. On returning to the lieu/jle the effect dis- appeared, though the vessel was dose in with the same land. Tlie writer recollects full well that, during the time the western p.irt of the Strait of .Magellan had to be navigated with fear- fully imperfect charts, it was a regular thing to hear recounted, witli a face as long as the main to'bowline, how in such and such channels the coinpas.ses had "jumped " two points or .so, and liad nearly put them on shore. It was no use attempting to convince tiie narrator to the contrary. The.se "jumps " are never heard of now : the magnetic pliantom who delighted in the.se pi-ank-s has been exorcised by the modern surveys of Wharton and othei-s, whicli shew tliat the previous charts were frequently whole points in error. In the intricate channels leading from the Strait to the Gulf of Penas, the writer, during the six years he used them, found errors of 3 and i points to be quite common ; but azimutlis there-and-then alivaya exonerated the compas.s, though the land was sometimes not more distant tlum half tiie lengtli of tile v&sseL The distance travereed in the.se channels was about 350 miles, with neither lights, buoy.s, nor beacons: sometimes a dozen or more of islets would be pas.sed wliere >io>ie were .shewn on the chart; and .sometimes a number appeared on tiie chart which were invisibb- el-sewhere. It was a splendid place to tench one to keep his eyes open and liis wits nliout him. Tiie hiw which has hitlierto been found to hold good as regards " Local attraction " of magnetic rocks is, that north of the magnetic equator the north-serkimj end of the compivss needle is attracted towanls any centre of disturlianco ; .south of the magnetic ei|Uator it is repelle*!. Now, in the cjise of the Sei'}^nt, steering soutii, the edict, liail there been any (which was certainly not the case), would have been to cause easterly deviation, and, as an^ one B.ia.S. MEDA AND PENGUIN. i9 may see, easterly deviation would have taken her off shore, as already stated. So far so good, but in some unaccountable manner it has hitherto been overlooked that while a ship is such a distance from visible land as to be altogether beyond reach of possible magnetic influence, she may, in shallow water, be passing closely over fer- ruginous rocks capable of producing very decided magnetic effects on her compass. This, however, was not the Serpent's case, as h.m.s. the water only shoals near Cape Villano when close in to the ^"f""- coast. Some instructive cases of this kind have come to light within the past few years : one instance is furnished by observations of the Variation of the compass on the east coast of Madagascar. The normal lines of Variation for several miles southward from St. Mary's Isle should vary from about 11° W^. to 12' \V., but instead of this, the French men-of-war, which are frequently running up and down this part of the coast, find that the Varia- tion near the shore at St. Mary's Isle is only 6° or 7° W., the Bed of sea north end of the compass being repelled by the nature of the bottom. These results tally with observations made on shore in Madagascar, New Zealand, and other places. There is a similar area of magnetic disturbance in the Adriatic, which was examined at the request of the late Father Secchi, the astronomer ; but by far the biggest thing in this way was discovered near Cossack by H.M.'s surveying schooner Meda — McJa. a wooden vessel employed on the marine survey of the north- west coast of Australia, a part of the world which is known to be highly magnetic in places. In July of 1885, the Meda, in pass- ing at night, found a sudden deflection of two points in the neighbourhood of Bezout Island, but was unable to investigate the cause until the following September, and then only partially. But in 1890, H.M.S. Penguin, then carrying on the survey, was employed to look into the matter more fuUj^ It was supposed by the Meda's oSicers and others that the island of Bezout was accountable for the vagaries of the compass in that neighbour- hood, but Captain Creak, R.N., F.R.S., the then Admiralty Superintendent of Compasses, adjudged it to be a magnetic ridge under the sea, and this proved to be the correct view. On November •1th, 1890, the Penguin being at work in the neighbourhood, the magnetic elements were obtained on shore near Reader Head, but nothing remarkable was found either m Dip, Declination, or Force. On the 5th. the ship was swun2 discovery. 30 BED OF SEA MAGNETIC H M.S. twice when 3 to 6 miles from the shore. On the first occasion 'n^ini tliere wsis a very sh'ijht indication of unu.sual variation. Leaving experience. J a o Port Walcott on the usual track in the afternoon, when Bezout Island bore S. 79' W. (true), distant two miles, the north point of the compass was suddenly deflected two points to the west- ward, just as had happened to the Aleda, thouj,'h not quite on the same ground. The ship was immediately anchored, and some hours of the next day were spent in examining this an- chorage and locality generally ; the soundings gave 9 fathoms throughout. Observations were also made during this time on Bezout Island (the nearest visible land) of the absolute values of the three magnetic elements, but, notwithstanding the short distivnce separating the island from the ship, the results were nonnal. On board the Penguin, the instruments employed were the standard compass, situated 68 feet above the bottom of the sea, and a Fox dip-circle, about 6 feet higher. It was found that the centre of the disturbance was about 50 feet in diameter. Drift- ing slowly over it from N.W. to S.E. three or four times, the greatest disturbance of the Stiviidard compass was produced by a force repelling the north end of the needle : this amounted to 23° of deviation when on the N.W. side of the centre, and to 55° on the S.E. side. The ship was anchored for four hours, nearly over the centre of disturbance, the nortii-.sceking end of the compass needle re- Aoioiiiit o( (lip. miiining constantly repelled ils much as 50° to 55'. When e.vacthj over the centre, the observed dip was 83* S., the normal value for the general loculit}' being 50° S. The north-seeking end of the dip-needle was therefore repelled xiinvanls to the extent of 33', though at the .same time — from being vertically over the focus — the Standard compjiss shewed but little deviation. Those large values of 55° in the Declination (Variation), and 33' in the Inclination (Dip), were confined to a very small area, the values of the disturbanee in both elements t/ccreasni^ rapidly as the centre wius pa.ssed in any direction. The position of the I'cnyuin'a centre of disturbance was Bezout Island (beacon on summit), S. 79i W. (true), distant 214 miles, ami was 13 miles from the Meda's centre of disturbance. Re-e«*inm» A furtlicr, and, in some respects, even more detailed examina- ^'"^y tion was subseciuently made of this interestin}; locality with the following results; — Within the limits of an area four miles long north-cast and south-west, by two miles broad, with a depth of NEAR COSSACK, AUSTRALIA. 8 to 9 fathoms at low-water springs, and bottom of quartz-sand, and shells, the compass was disturbed from 1° at the outer limits to as much as 56° near the focus of the disturbing fox'ce. Over this focus the dip-needle shewed 81° 10' S., the noi-th-seeking end being thus repelled upwards 31°. The greatest range in deflec- tion of the Standard compass was 86°, viz., 50° to the east and 30' to the west, confirming the previous occasion's observations. This place happens to be on the line of No Variation. Such deflections of the compass are due to magnetic minerals in the bed of the sea under the ship, and luhen the water is shallow and the force strong, the compass may be temporarily deranged when passing over such a spot, but the area of disturbance will be small, unless there are many centres near together. Observa- tions prove that disturbance of the compass in a ship afloat is experienced only in a few places on the globe.* The excess of red R^ny of suck magnetism found near Cossack, as above detailed, is a most unusual occurrence, and need not give navigators the nightmare. It, however, teaches a lesson. Observe azimuths as often as possible. Half his time, the oflicer of the watch is walking to and fro the bridge doing absolutely nothing. Why should this be, when he might be usefully occupied — not with a scraper or a paint-brush, ' tramp ' fashion — but in contributing his quota towards the safe navigation of the ship ? The minor question of compass disturbance by proximity of the vessel's keel to the bottom in frequented harbours, rivers, and estuaries, need scarcely be touched upon ; not that it is impossible, as shewn above, but because there is no authentic instance of such a thing having happened. W hen iron vessels first came out, it was even conjectured that the anchor and chain cable, acting as media between the hull and ground, produced an efiect upon the ship's magnetism suSicient to cause deviation of the compass. There was an air of plausibility about this, but experiments have demolished it, so far at least as well known anchorages are concerned. It does not appear that it occurred to the Penguins oflicers to test this hypothesis in the locality of all others most likely to produce an efiect. 5. Here we have, beyond doubt, the most fertile source yet Thunder- alluded to of possible compass disturbance, and disturbance of a storms, more or less permanent character. Ordinarily, thunderstorms do not derange the compass, as has been proved over and over again ; but there are many well authenticated instances where, when iron vessels have been actually struck by lightning, their • Sec Appendii G. Iroo boUs never 32 LIGHTNING AND IRON VESSELS. magnetic character has beeu so completely altered as even to cause reversal of the pointing of the needle. Now, though tlie hull of an iron vessel may be, and has been, damaged. slruLck by lightning, there is no record of its ever having sustained damage — indeed, such a mishap would seem to be impossible. Iron is a good conductor, and water is still better; therefore, when struck by lightning, the hull gives the electric fluid a free passage to the surrounding sea, where it is at once harmlessly dissipated. Wood, on the contrary, is a non-conductor, and, by resisting the current, is made to suffer accordingly. Moral. — It is unwise to oppose anjlhiog or anybody stronger than yourself. Hence it is not uncommon to hear — even in iron vessels — of the wooden spires of masts, and, more rarely, other fittings of the same material, being rent and shattered like matchwood. Masts composed entirely of iron from truck to keel would "determine" the discharge at their highest points, and secure perfect immunity from damage. It is conceivable that an iron vessel might be witiiin the radius of a severe thunder-storm without being what is called " .struck " by lightning, owing to the vast conducting surface of tlie hull steadily, but, in most cases, invisibly, draining ofl' the ditlu.sed electricity in the circumambient air before it had time to concen- trate and develop into either of the energetic forms known as Vioi.ni forms Forkfd-lightning and Bull-lightning — the hull acting, in fact, as igiiiiinE ^^ ^^^^ ^£ electric safety-valve. This is probably the condition when corposants (St KImo's fire) are seen sitting on the ma.st- heads and yard-arni'^, and luminous Will-o'-the-wis]i-like appear- ances silently chase each otlicr down the wire rigging and funnel shrouds. As the matter has u really important bearing on safe naviga- tion, it will be dealt with at some length. Perhaps the mast .satisfactory ami convincing motle of treating it will be to narrate a few boni\-fide exjieriences. The one referring to the Hedgcmore was related to the writer, and sulweiiuently communicated to him on paper by her captain. When off Nantucket, on a passage from Liverpool to New York, the White Star steamer Gcrnuinic, CapUiin Kennl^dy, I'ncountored an electric storm of unusual strength and durntion. It came on at midnight, July 11th, 1SS4, and endeil at 8 u'clock Lithining the following morning. A very peculiar accompaniment w " S.S. SEDGEMORE. 33 the bridge. The lightning was from every quarter, forming a complete network of flashes. The illumination of the fog was so thorough and .sustained that the ship appeared to be in a con- tinuous blaze or halo of light. The soundings not agreeing with the reckoning, led Captain Kennedy to conclude that his com- passes were affected, and so it proved. At noon on the 12th, the true position was ascertained, and on shaping the course from Fire Island to Sandy Hook, the ship s.s. Germanu had to be kept W. by S. i S. by compass, instead of W. i N. as usual, thus shewing an error of two points due to the electric storm. The account goes on to say that the Standard compass was so much affected during the storm, that for some two or three hours it was perfectly useless, and dependence had to be placed on the wheel-house compass (Lord Kelvin's), though it also was affected. On the homeward passage it was found that the errors on easterly courses were the same as usual. Now the possible conclusion to be drawn from this last state- ment is, that in the interval the Germanic had recovered her normal magnetic character. It is a pity that the foregoing account is not more circum- stantial in details ; its scientific value is absolutely nil. The next case is much more circumstantial, and consequently of consider- able value : it is also moi*e recent. On March 28lh, 1S92, when crossing the Gulf Stream (lat. 38|° N., long. 67J° W.), homewards from Baltimore to Liverpool, The the (s.s.) Sedgemore encountered a strong north-east gale, with ^j^^i^^^t^^^ heavy rain, thunder, and lightning. Corposants were constantly hovering about the mastheads. At Ohr. 45m. A.M., durmg a squall, there was a loud report, sharp and defined like the firing of a cannon, with a concussion that shook the ship throughout : at the same moment she was enveloped in a fierce light that penetrated to every part. The masthead electric light — carried on the foreside of the ivooden fore topgallant mast — was destroyed, and the mast slightly charred all over. The copper wire conductors were also destroj'ed from the lamp downwards until they reached the iron mast, after which (lie;/ luere uninjured. The steering compasses in the fore and after wheel-houses were completely reversed : the ship's course at the time by the Reversal forward one was E. by S. After the ship had been struck, this °f '•"?'» compass shewed W. by N., and moved in the opposite direction to the ship's head ; for example, when the helm was ported and UM'LKA SA A T I.IGUTSL\G EXPERIEXCES Alteration Standard. Reveital of magnetic character. the ship's head came to the right, the compass appeared to say that she had gone ofl" to the left. Later on, when observations had been obtained, Captain Trencry tried to adjust this com- pass. First, the fore-and-aft magnets were reversed, but without the slightest effect. Tlieu these magnets were replaced in their former positions, and the 'tiiwartship magnet was reversed, when the card immediately spun round to east, working freely, but with the original deviation on this point increased considerably. Previous to the attempt to correct this compass, spare ones had been tried in the same binnacle, but the results in every case were exactly the same. The ' Kelvin ' Standard on the upper bridge was not reversed as the others were, but wiis rendered sluggish, and had largely increased deviations. The following Table shews the change for the points on which azimuths had been taken. Ship'a UuuL Uov. before. Dor. after. Sliipa UeaU. Dor. before. Dor. after. North 0' 22' E. E. by N. 2' W. - 10" W. N. byK - 0' 20' E. East i° \\. - l.VW. N.N.E. - 0' 15' E. E. by S. - 6' W. - 20° W. N.E. by N. 0" 10° R E.S.E. 8° ^v. - 23 W. N.E. :)' 6*E. S.E. by E. 10- W. - 2(>' W. N.E. by K 0° 0' S.E. 12" W. - 29° W. E.N.E. - V w. - .■>' \\. S.E. by S. - 14- W. - 31^ W. S.S.E. ■ 16° W. - 33' W. Looking at the column of "Dev. before," the writer can scarcelj' bring himself to believe that the errors reconisd as between North and E.N.E. were determined at the same time as those between East and S.S.E. Tiie latt«r look very like the result of " lietaiueii " magnetism, and if so, ought to have shewn a cor- responding but contrary error on North, &c., if belonging to the .same scries of ob.servation.s. Wlien the compasses were re-ailjusted in Liverpool, it was found neces-sary to reveree all the magnets of the SUvndard, and to add several othora. In the case of the Steering compass, the 'tiiwartship magnet was kept reversed as Capt Trenery had placeil it, but had to be moved much clo.ser to its work ; the other magnets remained in their original positions. Both compasses and adjusting magnets were found to be in gooeen obtained. The inventor was careful to explain that the procc.s.s must not be overdone, for fear of re-polarising in the opposite ilircction. Kvidently the idea was incapable of being civrried to a successful i.ssue, as it very quickly died a natural death. Poiition of I" n large ve.ssel where, to gain power, the wheel is of consider- SKtrint ahle diameter — say 7 feet or upwards — tuv steering compa.s.se8 are absolutely nece.ssary, each so placed, to starboard and port, that the hclnisinaii may have the compass directly in front of liiiii, no matter at which side of the wheel he may be sUinding. If there should iiappon to be but one compiuss, an error, due to )i!irallax, will be intrwluced in the course. L<.>oking at the com- piuis in an obli(|Ue direction causes an apparent change in the relative ptwitions of the lubber-line and the marginal divisions of ihe card — the greater the clearance between the edge of the curd STEERING COMPASS TROUBLES. and the compass bowl, the greater tlie error. Unless the helms- man can get the centre of the card and the lubber-point in one with his course, he is sure to steer to one side of it. Where, from the inconvenient closeness of a skylight, stanchion, or other deck fixture, a single midship compass is unavoidably placed veiy near to the wheel, or is so placed because the steersman's sight will not define the degrees at a greater distance, this error or parallactic Parallax a displacement of the lubber-line is aggravated, amounting fre- ^°"^" °' quently to a quarter of a point. Now, in a moderate day's run of say 300 miles, in thick weather, this becomes a serious con- sideration, as it affects the ship's position at the end of it to the tune of 15 miles. Hence the necessity for a compass directly facing the steersman, which should be as far distant from him as may be compatible with distinct vision; and to this end its diameter ought not, in the case of a spirit compass, to be less than eleven inches. If constructed, however, on the principle patented by Lord Kelvin, there would be a great advantage in increasing the size to fifteen or even sixteen inches.* By placing the compass as far forward of the wheel as possible, it is less within the influence of the iron spindle, tiller, rudder- head, and stern-post, all of which in an iron vessel are powerfully iron fittings magnetic. If, however, as is frequently the case now, the after- wheelhouse should be constructed wholly of iron, with possibly an iron deck in addition, and steam steering gear, it seems certain that trustworthy compensation by magnets must be extremely difficult, and only to be accomplished after a lengthened investi- gation of the nature of the many forces acting on the compass. The same may be said of compasses in the conning towers and turrets of ironclads. In sailing vessels it is not uncommon to find an attempt made to remedy this liability to error, when steering with a single compass in the midship line, by having the binnacle containing it made to slide over from side to side as required ; but it is easy to sliding see that, even in a wooden ship, such an arrangement is far from B'""^"^'^' advi.sable, as the iron spindle of the wheel must aft'eet the compass in a different direction every time the latter is moved across. However, there is nothing like trial, and when the ship is in the graving dock, or at sea in a calm, with perfectly smooth water, the sliding binnacle can be tried in both positions ; but the result * Lord Kelvin has coustructed 15-inch steering compasses which have been found by the writer and others to give excellent results. IGNORANT MEN REQUIRE WATCHING. cannot be considered satisfactory unless the experiment is tned with the ship's head in different directions. sieim Now-a-days large steamers are steered by steam, one man, steeriiie \y\i\\ a miniature wheel about 30 inches in diameter, suflicing to control tlie movements of the vessel's head. In this case one compass is all that is necessary, as the lielmsman stands directly behind the wheel, the spindle and pedestal containing the con- nections being immediatel}' on the fore side.* It is necessary hei"e to saj' a few words touching the fittings, as, unless particularly specified, they are not always made of brass. In one large mail steamer commanded by the writer, the spindle of the wheel and vertical shafting communicating with the steam- steering engine were actually made of iron, though their ends came within seven inches of the compasa How the maker had the hardihood to venture on such a petty economy, involving such Concealed scrious conscqucnccs, it is difficult to say. The iron work alluded ''"" to was enclosed in a brass pedostiil, which would have concealed it most effectually; but fortunately', before the ship was delivered to her owners, the matter was discovered and reported to the builders, who insisted upon the maker .substituting a Ijrass spindle and 8 feet of braas shafting for the iron. One cannot therefore be too wide-awake in the.se things when looking after the finish of a new ship. Ill the Kaiiie vessel there was a large teak skylight, almo.st toucliing the wheelhouse on the fore side; and to prevent the leaves of the sk^dight warping with the heat of the .sun, one of Iron .liffener.. the forcmon causod three iron brackets, or stiffeners, to be screwed firmly on the under side of each leaf, and was ver^' much astonished when tuld that every time the skylight might be opened or shut, that the compas.s in the wheelhouse would be affected to the e.ttent of .several degrees. Nothing short of actual trial would convince him that .such would be the case — his argument being, that as the wiwdon bulkhead of the wheolliouse intervened, the iron brackets could not possibly disturb the compass. However, the question was set at rest soon after, when the compasses came down from the maker. The disturbance cau.sed by opening and sliutting the skylight amounted nearly to half a point, so the after iron brncketsS were removed, and brass ones suUstituted. In another largo steamer, also commanded liy the writer, the heels of the main hatch cargo wn aa the cocnicii'nt A, and, in a well made compas*, is due f«r the mcwt p.irt to a misplaced lubber-line. When the sign is 4-, the )ubl>er-lin« should be moTed to the right. Perlalion ship's head north - 12" Head south + 2* east - 24* „ west -f IS' - 36* +20" -^ 20* 4)- 16» A - 4* TESTING CARD FOR DEFECTS. afterwards put in almost at random by some one ignorant of the mischief which may accrue from their carelessness. It is surely an easy task to paint close up to the lubber-line with a small camel-hair brush ; and, to avoid mistakes in reshippiug tiie bowl, when temporarily removed from the binnacle for any purpose, there should be only one lubber-line. This will prevent the pos- sibility of reversal in the gimbals. Compass bowls are not unfre- More than 3 quently marked with four lubber-lines, but the use of the after L"t>ijer-Linei one is not manifest. It should be painted over at the earliest possible moment. Those at the side may facilitate beam bearings. The reader must not imagine that " Pole Compasses " are the only ones liable to this defect, which has been known to exist in " Standard Compasses," " Steering Compasses," and even " Navi- gating Compasses." When detected, cover over the faulty line with two coats of thick white paint, and, with a black lead pencil, rule it carefully in again, in its proper place. Avoid making the line gouty, or too thick. Compass errors arising from mechanical defects already referred to are not unfrequently attributed to deviation. Flaws, punctures, or roughness of the jewelled cap, blunted or broken pivot-points, excessive weight in ^ chanicai card and consequent insufficiency of the directive force, or the defacts. card not traversing freely in the bowl, are of the class of defects to be guarded against. If any of these exist, it can be detected by using a small magnet to pull the north point of the card a few degrees to the right or left — say a point — and noting where it will come again to rest when the magnet is withdrawn. Then in like manner pull the needle in the other direction, and if in both ca-ses the card comes to rest at the same half degree, the compass is free from any of the above-named defects. But should the card not come to rest at the same place, then the further apart the two resting places are from each other, the greater is the defect from which it arises. Though unknown currents sometimes wreck ships, it is more often a current of magnetism than a current of ivater. It should be borne in mind bj- owners and others that a perfect compass is not the only want of the navigator. In fact, too much cannot be done by adopting improved nautical instruments of all kinds, so as to lessen the constant risk incidental to such id arduous, responsible, and hazardous profession. CHAPTER IV. THE MARINE CHRONOMBTER. The ilays of navigating by a carpenter's two-foot rule iiave gone by, and accurate time-keeping chrononu^tei-s are a necessity of the " lightning age " in which we liva Without them the rapid ocean voyages, which are now of every-day occurrence, could not possibly be made, although the writer has heard it stated, in all si'riousness, by non-nautical men, that the ijuick transit, from pox't to port, of the present ocean-express steamers, obviates the neces- sity for carrying chronometers I ! ! Such an idea, of course, could only be entertained by men entirely ignorant of the principles and requirements of navigation, and is scarcely in accordance with the steady increase in the esbiblishment, all over the world, of Time-signals for the special use of shipping. It may be truly .said that when chronometers came in, lunars went out — concerning the latter, something will appear in sul>- sequent pages. (Jf late years not only has the clironoineter been perfected in a high degree, as a reliable timekeepir, but its price has been reduced so low, by excessive and unhealthj- competition, that to be without one, on any over-sea voyage, would Ikj con- sidered almost criminal negligence. In the principal ports, l>oth at homo and abroad, the process of rating is rendered quite simple by means of public time-signals. In .some places the exact time is given by gun-tire, and at others by the dropping of a ball, or the instantaneous collapse of aconiv No matter what may be the method employed, the result is tlie same, and he who is now ignorant of tlie error and performance of his chronometers, cannot jilrad want of facilities for deter- mining them. Till' iiliiiiist iinlversHl iiitniduction, both by lai^l uinl s.'n ul' ili. SUBMARINE CABLE LONGITUDES. 45 electric telegraph, has lately beeu much used for the better deter- mination of meridian distances.* In this work the American Government, since 1874, has taken American a most prominent part, and has rivalled this country in goinc^ expeditions, bej'ond its own domains to accomplish it. Under the direction of the Bureau of Navigation a selected party of trained officers of the U.S.N, has successfully carried unusually long chains of meridian distances, by the aid of the telegraph wire, to many important places iu various parts of the world. These have been adopted as fundamental points whereby to fix others. One of the first of these chains (1878-1879) embi-aced Green- wich — Lisbon — Madeii'a — St. Vincent — Pernambuco — Bahia — Rio de Janeiro — Monte Video — Buetios Ayres and Para, all of which stations were duly occupied by members of the party. Dr. Gould, Director of the Argentine National Observatory at Cordoba, had previously connected Buenos Ayres telegraphically with Cordoba, which, consequently, became the end of the chain. Strange to say, the longitude of the Observatory at Lisbon — Lisbon longi. though so near home — proved to be wrong more than 2', shewing how unreliable Lunars, Moon culminations, &c., were for this work, notwithstanding the manifold resources of a well equipped Observatory. The other places were not half this amount in error. In 1883-1884, another expedition, including most of the officers of the preceding one, carried a telegraphic chain from Vera Cruz through Guatemala — La Libertad — Salvador — Paita — Lima — Arica — Valparaiso and Cordoba, thus closing again upon the same terminal point, but by a totally different route. The two independent longitudes came out as follows : — H. M. S. Cordoba Observat/iry by eastern chain - - 4 16 48'190 W. Cordoba- western chain - 4 16 48-238 W. Extraordin.rj, " " result 1 1 Difierence - - - - 0048 The difference is barely the twentieth of a second, and when one considers the great length of each chain and the number of intermediate links, the result is little short of a miracle. No uncertainty can, however, attach to meridian distances made by comparing previously regulated Time-keepers by means of land or submarine telegraph lines, when effected by skilled observers, and with proper precautions. Another remarkable instance of accordance is shewn by the Trans- Atlantic longitude measurements of the United States Coast Survey, where three * When Sir G. B. Airy determined the Valentia-Greenwich distance he had thirty chronometers carried to and from tlie two stations more than twenty times. By the aid 01 the Pacific cable the San Francisco-Manila distance is found to be 7 hrs. 46 m. 18.761 sees. ; and the time signal traversed the 7 £17 nautical miles of the cable in 0.648 second*. Easier and more accurate I 46 rjiOM/SJiST PART TAKEN BY measurements between the meridian of Greenwich and that of the New York City Hall, made in different years and through different cables, differed by only one-hundredth of a second of time ! ! It should be mentioned that, previous to the expeditions re- corded as ending at Cordoba, the principal places in Central America, including Vera Cruz, had been connected tLlegraphically with Washington, so that the work of lSS3-8-i was but a con- tinuation to the southward of a chain which had been dropped for a time. In 1881 — 1882, more or less the same party of officers were employed fixing Yokohama — Nagasaki — Vladivostok — Shang- hai — Amoy — Hong-Kong — Manila — Cape St. Jame-^ — Singapore — Batavia, and Madras, lliis latter having been determined in 1876 — 1877, through Bombay, Aden, and Suez, by officers of the Great Trigonometrical Survey of India. Vladivostok hud been determined bj' Colonel Scharnhorst, in 1875, " By order of the Czar," and here we have the results of the two independent measurements : — H. M. B. Russian chain by way of Siberiii, in 1875 - - 8 47 SI'S! American chain by way of Madras, in 1881 - - 8 47 30"92 Difference one- third of a second - o 039 The Madras — Vladivostok chain was 6,450 miles in length ; the other, St. Petersburg — Vladivostok, of abotit the same length, was effected by land telegraphs, and was very mucli the more difficult of the two. Again in 1888-89-90, the American party carried out another chain between ports in Mexico, Central America, the West Indies, and on tiic north coast of South America. In all these American expeditions a specially designed combin- ation of the Transit-instrument and Zenith-telescope was used for the determination of Latitude and local time. Time stars were selected as near the Zenith as pos-sible, in case the Transit instru- ment should be ever so sligiitly out of the meridian. And for Latitude, from 10 to 20 pairs, north and south, were observed on each of three or four niglits, weather permitting, so that there was every guarantee of accuracy in the results. OUservations of the Transit of Venus in 1874, and again in 1882, materially contributed to a more exact knowledge of selected stations, wliicli until then had Iteen known only approximately. In Australia and Now Zealand the system of telegraphic deter- AMERICA IN LOXGITUDE WORK. iiiiiiatioiis is being rapidly carried on. Paris — Greenwich was re-determined in 1902 with all imaginable care and refinement ; so also was Montreal — Greenwich in 1892; in fact it may be asserted that there are now but few habitable spots on the globe of which the longitude is not known with abundant accuracy for navigational purposes.* Vessels destined for long voyages should carry not fewer than Three three chronometers. If there are only two, and one becomes in- chronometen accurate, it is impossible to decide which is in error, whereas, with the former number, and regular daily com'parlsons, a tolerably correct judgment may be formed as to the going of each. The only advantage, therefore, in carrying a second chronometer lies in the fact of having a stand-by in the case of accident to one of them — such as the breaking of the mainspring, or other part of the delicate mechanism. Chronometers should, if possible, be kept in a part of the vessel Much vibra- free from jars or much continuous vibration ; not in the after-end ''°° '"J""'"'"'- of a screw-steamer, nor in proximity to a steam-winch ; neither should it be permitted to roll heavy bales or cases along the deck in their vicinity. If, however, this last cannot be avoided, it would be well to remove the chronometers from their outer cases for the time being, and bed them on soft feather pillows. On no account should they be slung in hammocks or cots whilst at sea, as it has been found to cause great irregularity in their per- formance. In most steamers of modern build there is a chart-room on the upper deck, about the midships of the vessel, and this, for many reasons, is a good place. In the absence of a chart-room the Captain's own cabin is, of course, the next best place ; and in this case it is well (in steamers) to have a fourth chronometer in the second officer's room, as a hack-watch for general use among the Hack Watch officers. If knocked about (so to speak), it will probably not go 80 well as the others, but this is immaterial, as a comparison can be made at convenience with the standard instrument ; indeed it should be made every third or fourth day, and entered in a small book kept in the outer case of the hack-watch. Chronometers are sometimes improperly stowed in one of the drawers of an ordinary set intended originally for clothing, &c. This is a very bad practice. To give them fair play, thej' should How to stow have a special mahogany box (as nearly air-tight as po.ssible), chronometer, fitted with a strong glass top, and divided by partitions, according to the number carried — each compartment being lined with green baize, and stuffed with best curled hair. * Paris— Greenwich re-iietermination wa.s carried out by English and French observers. The result of the English showed that the longitude of Cassini's meridian is 9 m. 20.932 sees. E. of the Greenwich Transit Circle with a probable error of ^0.006 sees. 48 STOWAGE OF CHRONOMETERS. Details ol fittlor. Protect cases. The chronometers should be removed from their own outer boxes, and the upper part of the double lid of the inner case dis- pensed with by taking the screws out of the hinges, so that the face of the instrument may be seen through the glass wheic the rate paper is usually kept. Being duly deposited in their several receptacles, all three can be seen through the double gla-ss, and, as the opening of the lids for time-taking is rendered unnecessary, sudden fluctuations of temperature are thereby avoided. The only occasion upon which the case requires to be touched is in the morning, to wind and compare, which should be done with closed doo expected that a chronometer will continue its "shop rate" on a voyage oxtentling over, .sjiy four months, during which the tem- perature has ranged between 40 and bo Fahrenheit i Shop rat anrallabli TEMPERATURE AND HARTNUPS LAWS. 49 Mr. Arthur E. Nevins, in a paper read before the Literary and Philosophical Society of Liverpool, says : — " At present, chronometer makers allow no corrections upon Paper i>y the rate given for changes of temperature — and the universal *'^''ut b. . ,, ^ Novins. practice at sea is to allow one rate tor the voyage, whatever the temperature may be — apparently under the impression that an acknowledgment that such a correction is necessary, would be equivalent to acknowledging that the instrument was a defective one. The present method of compensating a marine chronometer is not absolutely perfect, but still leaves the rate of the watch subject to variations, owing to changes of temperature ; and it is the infinite variety in amount and direction of these changes of rate in different watches, which causes the instruments on board a ship to differ from each other in the way they so frequently do. ■' Every good watch is, however, always affected in the same way, and to the same amount, every time that it is exposed to the same temperature, and the changes in watches follow a fixed law; and knowing, from observation, how they perform in certain temperatures, it is possible to calculate in what way they will perform in any other temperature to which they may be exposed. This law was discovered by the father of the late Mr. Hartnup, Hartnup'n when Astronomer to the Mersey Docks and Harbour Board, as l*"' the result of testing upwards of two thousand watches which passed through his hands at the Liverpool Observatory — having been sent there by the makers to be tested and supplied with accurate rates. " Mr. Hartnup's laws are the following : — l8t. Every chronometer goes fa-stest {i.e., gain.s most or lo.ses least) in some certain temperature, which has to be calculated for each chronometer from the rates that it makes in three fixed temperatures ; the tem- peratures u.sed at the Bidston Observatory for testing watches being 55°, 70°, and 85° Fahrenheit during winter, and 65°, 75°, and 85° in summer. 2nd. As the temperature varies, either increasing or decreasing from that in which the watch goes fa.«test, the watch goes slower ; and its rate varies in the ratio of the square of the distance in degrees of tempera- ture, from its maximum gaining temperature. For example— if a watch goes fa.stest in temperature 75°, it will go slower as the temperature either rises above or falls below 75° ; and it will go slower by the same amount in any two temperatures that are the same distance from 76V one being above and the other below, as in 65° and 85°— one being 10° below and the other 10° above 75°. "The importance of a knowledge of these facts in using D JO SHEWING WHAT MAY IIAITES chronometcra is easily seen.* Supposing a ship bound to the southward lias tlirco chronometers, A, B, and G, and they are all sent to the same chronometer maker to be rated. He gives the ciiiooometerj pj,^^ wliicli thesc clirouometers have kept while in his shop at a misitadinj. mean temperature of, say 60°. We will further suppase that A goes fastest in 60°, B in 70°, and G in SO". As the ship gets into warmer weather in approaching the tropics, until she gets into a temperature of 80 or more, A gnuluaily goes slower and slower all the time ; iigoes faster until the temperature ri.ses to 70", and then commences to lose, going slower and slower as the tempera- ture iucreiises more and more ; and G goes faster all the time until it reaches 80', which is about as high a steady temperature lis will be attained for any length of time out at sea. " Now, for these three chrouometei-s to agree in showing the same longitude, it would be nece.ssai-y for them all to keep steadily to the rates given them in England, or wherever they have i)een rated ; but if they do not keep to these rates, the longitudes indicated by them will diH'er continually, and, by so doing, cause uncertainty and anxiety to the person using them. " There is another cjuse which may also occur, and which is really more importivnt than the one above mentioned. It may happen, especially if all the chronometers on board are by the same maker, that they all go fa.stest in about the same tempera- ture. Now, supposing that all these went fastest in, say 80°, and as in the above mentioned instance the rates of all of them were obtained in about 00° by the maker, they would all go steadily fluster than the rates given as the weather got warmer, and would therefore all continue to indicate nearly, or exactly, corre- sponding longitudes, and these longitudes would all be wrong; but in this case the person using them would feel confidence in his position, and perhaps come to harm unexpectedly." A.i%ioi»geo( Lord Kelvin, in his "Lecture on Navigation," published by William Collins, Sons & Co., Lonoard the .ship " Teniusserim," in Liverpool, December, 1873, for a voyage to Calcutta . The ship sailed from Liverpool on the 21st of January, liS74, and on her voyage the chronometer was subjected to variations of * Stainen, u * rule, u»c5 undue stress bein^f put upon the chain. Oases have occurred where, through fear of causing injury, the officer having charge of the clironometers has neglected to take the full number of turns, and tiie consequence has been that, after a time, the chronometer has run down ju.st before the usual time of winding. The winding index on the face should prevent sucli a mishap, nevertiielcss it luus occurred. A clironometer has to be turned " face down " to wind, and it must be e!i.sed btick handsomely when the operation is completed, and nut allowed to swing back with a jerk. This daily reversing of the watch is said to be a good thing, ivs it distributes the oil in the bearings. Furthei'more, chronometers should be wound punctually at the same liour every Jay, otherwise an unused part of the mainspring comes into action, which, if badh' adjusted, is almost certain to produce an irregularity in the rate : attention to this also keeps them running on the same part of the chain, which is important For similar reasons it has been found that eight-day chronometers do not preserve altogether the sime rate tln-oughout the entire week ; that is to say, that (though other conditions may be the same) their daily rate towards the end of the week will not agree with their daily rate at the conmiencement of it; notwithstanding which, the viean rates of two consecutive weeks may agree exactly. To prevent this effect, an eigiit-day chronometer should be wound every day, the same as tiie others. On account also of the lightness of the balance, eight-day chronometers do not go so well on board steamers which suffer much vibration from their machinery. If a chronometer should run down through neglect or other cause, on being wound up again it will probably not start till it hiLS been quickly, hut not violentli/, slued half round and back again. This is easily done by placing the instrument on the table iiud turning it horizontjiUy between the hands. When a chronometer has run down, do not immediately wind it up and move the hands to the proper time, but wait till the (Jroenwich Mean Time liy some other chronomet<.>r corresponds nearly with what the hands of the stopped one point to, then wind SOME CONSEQUENCES OF INATTENTION. ^3 it up, and start it at the right instant. It' this is neatly done, it is possible to set it going within a second or two of G.M.T. Altering the hands of a chronometer does not necessarily hurt the instrument, but it is not advisable for any but a skilled person to do it ; nor does it inevitably follow that, because a chronometer has been allowed to run down for a few hours, its rate will alter. Effect on after The writer's experience of half a dozen instances goes to show pe'^f"™*"'^*- that it will remain much as before. In such a delicate piece of mechanism, small and totally un- looked for causes will sometimes operate to derange the rate veiy considerably ; for example, too much side-play in the gimbals will side pUy in have this effect. A chronometer loosely hung may go with e''"''*'^- beautiful regularity in port, and astonish its owner by its after performance at sea ; therefore, when the vessel is rolling consider- ably, the chronometers should be watched to see that they do not go over in the gimbals with a jerk ; if they do, the gimbals must be tightened up until the jerk is no longer perceptible. On the other hand, do not jam the free movement of the instrument. Too little play is almost as bad as too much. The writer on one occasion found his favourite time-keeper very wild in its rate, and for a long time he was at a loss to account for it. However, one day, when the vessel was going along in a heavy beam sea, he noticed the lateral play in the gimbals, and at once concluded that therein lay the cause of the trouble, which proved to be the case. When this was remedied (a very simple matter for a man whose fingers are not all thumbs), the chronometer resumed its former good behaviour. On another occasion, whilst loading in the tiers at Peniambuco, Magnetisation the master of an iron barque, lying alongside, asked the writer to ° ^''"' step on board, and look at a chronometer which he complained of as going in a most erratic manner ever since the vessel's arrival in port. After due examination of the works with the magni- fying glass out of the sextant case, nothing could be discovered to account for the vagaries of the instrument. It was only when leaving the cabin that it occurred to the writer to ask what was in the square wooden box lying close against the chronometer complained of. The cat was let out of the bag when the master of the barque innocently explained that it was his Standai'd compass, which he had unshipped and placed below for greater security whilst in port. The powerful compass needles had by induction magnetized the steel portion of the balance, and ruined the going of the chronometer. Of late years another element of 54 LURKISG DAXGERS. danger has been added to the list in the ease of veasels lit by electricity. It is of the highest importance that the chronometers should be kept outside the radius of influence of the dynamos ; say, at least, 50 or 60 feet away from them. For the convenience of engineers and others employed about electric plant, pocket watches have been made with springs and balances of Palladium, or some alloy, and termed "non-magnetic watches." For similar reasons great care should he t-aken not to stow the Cire in select clironometcrs either close against an iron bulkhead, an iron ship's Ins place lor ^ '1 Chronometers, side, tho Upper or lower end of a vertical iron stanchion, or within 8 feet of compass compen.sating magnets. Nor should the chrono- meter case be screwed down to a table conUiining drawers which miabIy be too near to the adjusting magnets of the wheel- iiouse compass. As already stated, the mere fact of a bulkhead separating them won't stop tlie mi.'ichief in the slightest degree. AvoiiiiiJJcn Again, in many poop-decked steamers the Captjiin's cabin is "" at tlie fore-end of tiie poop, with windows looking out on the main deck, and mast likely the Chief Oflicer occupies a similarly situated one on the opposite side. Now, it very often happens in steamers of tho cliu^s alluded to, that to resist the etTects of the sea, tlio transverse bulkhead forming the fore-end of the poop is constructed of iron, and sheathed with wood, to give it a finish. Of course it is lined inside also, and so tho captain, unconscious of the mi.schicf likely to ensue, may stow his clironometer clase up against the concealed iron. Clironometcrs should be kept nwuy from iron alnmst na religiously ns compasses. Captain K. J. SImrpe, Hoard of Trade Surveyor, points out that a chronometer should not be within 70 ft. of a dynamo. A point to remember ! In mixlern vessels, where iron is fast superseding wood in cabin R-s well as in deck littings, it is .sumetimes exceedingly difficult to select a really good place for the time-keepers. Very often it is "A STITCH IN TIME," £c. " Hobson's choice ; " nevertheless these matters should receive full consideration, if the vessel is to go safely. From the foregoing causes alone, the " Shore-rate " and the " Sea-rate " will seldom agree. It is advisable, therefore, that when practicable, chrono- meters should be rated on board, in the positions they are intended to occupy during the voyage. As before remarked, there are many facilities, such as time-guns and time-balls, for effecting it. Chronometers, when received on boai-d previous to sailing, Kecessity foi should be compared with each other, and the respective errors "comparison . . . previous to and rates applied to each, to note if they agree in their Greenwich sailing. Mean Time. This may seem a very needless precaution, but the propriety of it has twice been made apparent to the writer ; and what has occurred to one may happen to others also. Suppose that this matter of comparing be neglected, and that there .should be only two chronometers on board ; suppose further, that a wrong original error has been given with one of them (say, to the extent of one minute), and that the vessel proceeds to sea with dirty weather, and perhaps is several days out before getting sights ; then, when the comparison is made, the navigator finds to his dismay that his chronometers differ from each other to the extent of a quarter of a degree of longitude. The Dead Reckon- ing cannot help him — indeed, if it were depended upon, it might just double the error. The only thing left to be done is to make some well-known point of land as soon as possible, take careful sights, and find out which chronometer is at fault. If you intend passing close to an island for this purpose, do not go on the side which will bring the land between you and the sun, or xvhere xvill your horizon he ? Always think beforehand of the necessities of the case. It so happened one fine day, when a friend was sailing for the instructive West Coast of Africa, that the writer went on board to wish him " good luck." Being left for a time to his own devices in the skipper's cabin, he thought he would keep his hand in by com- paring the chronometers which had just come on board. No sooner said than done : but to his amazement all three disagreed to the extent, not of seconds, but of minutes. Another try with the same result. This was getting serious, and the writer was getting flustered. Once more the rate papers were examined, and behold they had been placed in the wrong boxes ! ! When pro- perly sorted, the chronometers proved in agreement. As few merchant vessels carry more than three chronometers, 56 Sri.ITTING SECONDS. Chronometer JournlJ. How to compare with precision. that numlter will be adopted in treating of the proper mode of inakinw the daily comparisons. For brevity, the several instru- ments should be known by letters, instead of the maker's numbei-s. Tiie letter should be marked on a small slip of paper, and gummed conspicuou.sly on the outside of chronometer case. For example, when st^vnding facing them, the left-hand chronometer might be called A, the middle one B, and the right-hand one C — everything, when possible, being taken in its natural order or sequence. An excellent form of chronometer journal is appended, and reference to it will shew that three chronometers enable three ditl'urent compari-sons to be made — tlie last being a check upon the others ; for example, A is compared with B ; Jl with C ; and A with C. These compari.sons should not Vie made simultaneou.sly by three dift'erent observers, which is the common method on board ship ; a.s it is impossible by it to attain the necessary accuracy. All tlie compari.sons must be made by one individual, and a fortnight's practice, or at most a month's, will enable him to eliect this to the tenlh of a second. When we consider how small a portion of time is represented by such a minute division, it i.s not improbable that some may feel incredulous as to the practi- cability of estimating it correctly. But after the preliminary drill with the method about to be indicated, the doubters will be able to as.sure tiiemselves that not only is it not impossible, hut that with care it is sufficiently easy. Jn all observatories on shore, the astronomer and his assistants are in the constint habit of splitting " tentlis " with wonderful precision, and it may interest the reader to know that there are mechanical contrivances for diviiling a second of time even into oue thousand jxirls. As these do not enter into the practice of navigation, a description of them here would be out of place. To compare accurately, the operator, being tjuito alone, should clo.se both windows and doors, so as to exclude noise. Having opened the outer cases, he should make ready with book and pencil for the first comparison, by opening the inner case of A, wiiieli will allow its ticking to be distinctly heard, whilst // is regarded through its glass lid. It will be percoivetl by the reader that the operation is per- formed by the delicate relation.ship or sympathy existing lietween the eye and ear. A will lie heard, and B will l>e seen. Now, look steadily at A, and mentally count with it, assisting by a quirk ni'ition of the hand corresponding to every half-second heat Having got well into the swing or rhythm of the beats. (57) t^ t-* %o *o ^-\p vp \p vp + + + + <^ m ro Q -^^^ *o X> o o o o f*1 O ro i -= ^ " " - ^ - o OO •a « ' ' VO v\ ^ t^ sis m rt m N » ■o * d O o O o . 00 >o rj- .' t Tl- rr ' + + + >o TC o >»• H£P -g « o ^ s=£ 00 00 00 o o o o 00 ON O Q « ♦© o- ■3 (►.>- fe 2 58 COMi'AlUSON OF CHRONOMETERS. and decided to " stop," say, at GOs. (the even minute) ; remove the eye to B when A'» second-liand has got to 52s. or 53s., keeping the sound of each half -beat still in your eare, and the hand going with it. When you have arrived hy sound at GOs. (your chosen "stopping" point) the eye will enable you to decide upon the number of seconds and parts of a .second shewn by /). The other two comparisons will be made in a precisely similar manner. Of course in actual practice you note down beforehand the hour and even minute, by the open chronometer, at which you intend to " stop," or compare with the closed one ; also, note the hour of the latter, and when proficient, the minute can also be noted, leaving only the seconds und tenths for the comparison. The beginner, after a few trials by himself, will soon drop into the way of comparing with accuracy, and will congratulate himself upon being independent of outside aid, whenever he may wish to do so. A likely jug- Another plan haa been suggested, but as the writer has not '" °" tried it, he can only .say it .seems feasible. " Keep one hand free. At the beat of the second, or half-.second, touch the table with the tip of the little finger, and rapidly pass along the other tips to tiie thumb, as a pianist would in playing a scale in the natural key. When, by practice, this can be etFected in exactly half a second, then the touch of each finger will represent 01s." Having compared all three chronometei-s, .1 witii li. B with C, and A with G, accuracy of the result can, in a measure, be tested by comparing the interval between A and C, \Tith the sum or ditfereiice, as the case m.ay be, of the other two intervals, for e\M\\\>\yi—{i'ide Form of Chronovieter Journal) on ® May ISth we have Time l.v riiroii. A 'i »1 OOO « 2 12 39-4 Oliron. li 2 1.S 000 „ C 2 M 5-4 Chron. A 2 36 00-0 „ V 2 16 44-8 Here 18m. 20C.s. adiled to Oni. o-ld.s. gives li)ni. 15 2.s., eat half-seconds, it will mostly happen that the beats of the two instruments are not .synchronous, BEST MODE OF COMPARING. but one will fall after the other by a certain fraction of a beat, which will be prettj' nearly constant, and must be estimated by the ear. This estimate may be made within half a beat, or a quarter of a second, without difficulty ; but it requires much practice to estimate the fraction within 0"ls. with certainty. But if a mean time or Solar chronometer is compared with a Sidereal t°\" *"'' ^ * oidereal chronometer, their difference may be obtained with ease within chronometerj one-tiventieth of a second. Since Is. sidereal time is less than Is. mean time, the beats of the Sidereal chronometer will not remain at a constant fraction behind those of the Solar chronometer, but will graduallj' gain on them, so that at certain times they will be coincident. " Now, if the comparison be made at the time this coincidence occurs, there will be no fraction for the ear to estimate, and the difference of the two instruments at this time will be obtained exactly. The only error will be that which arises from judging the beats to be in coincidence when they are really separate by a small fraction, and it is found that the ear will easily distinguish the beats as not synchronous so long as they differ by as much as 0"05s. (half-a-tenth) ; consequently, the comparison is accu- rately obtained within that quantity. Indeed, with practice it is obtained within 0'03s. or even 002s. Now, since Is. sidereal time = 0"99727s. mean time, the Sidereal chronometer gains 0'00273s. on the Solar chronometer in Is. ; and therefore it gains 0'5s. in 183s., or very nearly 3m. ; hence, once every three minutes the two chronometers will beat together. When this is about to occur, the observer begins to count the seconds of one chronometer, while he directs his eye to the other ; when he no longer perceives any difference in the beats, he notes the corresponding half-seconds of the two insti'uments." It follows that when two Solar chronometers are to be com- pared, it will in general be most accurately done by comparing each with a Sidereal chronometer hy coincident beats, and after- wards reducing the comparisons. It is not likely that the ordinary navigator will possess a Sidereal chronometer, but the method is introduced here as likely to prove interesting, and to shew what can be done. It has been already stated that chronometers should be com- chrono.nete« pared daily, and with methodical regularity, and the proper entries Jooro^i- made in a book known as the Chronometer Journal* The writer * It is not uncommon to see the error of a clirouoraeter marked opposite each day, on the margin of the page for the month, in the Nautical Almanac. This, in the liATISG AT JirnSTO.y OBSERVATORY. has fur many years used the form given at page 57, and it is so self-explanatory that very little more is requisite. The " 2nd ditterence " is merely the difference between the quantities for any two consecutive days in tlie column headed " 1st ditterence." Thus, in the comparison of .1 with B, on May ISth the " 1st ditterence " is iSm. 20"Gs., and on May 19th is I8m. 25-is. ; the ditterence be- tween these two is 4"Ss., and, as the one chronometer is gaining and the other losing, it ought to be equal to the sum of their daii}' rates. As A's rate is -f- l'6s., and B's — 3"ls., the sum 4'7s. shows a dissimilarity of only one-tenth of a second. In tiie case of the " 2nd ditterence " of B and C = lla, as both the.se chronometers ai-e losing, it ought to be equal to the differ- ence of their daily rates, which happens exactly to be the case. Of course, if two chronometers were both gaining, the "2nd ditterence " would in like manner be equal to the difference of their daily rates. But when their rates are going in opposite directions, the amount in the " 2nd ditterence " column ought to be equal to their sum. By scrutinizing the journal day by day, a fair judgment may be formed of how the chronometers are behaving. In the event of the " 2nd diflference " not agreeing with the daily rates, a cixroful analysis of the comparisons and record of temperatures, combined with a consideration of the respective merits of the instruments, may enable one to form a pretty just estimate of the value and direction of the change. For instance, if A does not agree with B, nor yet with C, but if B and G run well together, the inference that A has gone wrong would be a reasonable one, especially if A happened to be an ohl ottender. In anj' case the navigator is put upon his guard, which is always something. • At the Hidston Observatory, near Liverpool, any master sailing out of tiie port can have his chronometer rated for temperature. Obtervatory. The time requisite is six weeks, and on leaving, a paper accom- panies the chronometer shewing its performance for every 5° of temperature lietween 45° and 95° ; so that if the recommendation Ix; attended to concerning the advi.sability of keeping a maximum and inininnnn thermometer in the case with the chronometers, and the rate altered to suit as uften as neci'.ssjtry, the navigator can make sure of his tireenwich tin»e within a few -seconds, after a lapse of some months.* Tlie Observatory temperature i-atea ulimatlou of loms |>eople, may b« "handy," ami In ■ Mnsc it ia lo-, bat on a long voyaf^ A properly kept " Journal " woiilJ look nioro «hlp-ihap« ami biftnesa-llke, quit* apart froiii tlir quution of utility. * S«r ApgifuJii A. temperature at Bidaton MAINTAINING POWER WHEN WINDING. 6i can be copied out on any of the left-liand pages of the journal, all of which are headed " Remarks," and ruled in faint blue lines. In the specimen page of the Journal just given, it will be noticed sue of that, for conciseness, it is only drawn up for four days ; but in Jo""»' ordering one similar, the printer should be instructed to make the page deep enough to contain a week's work ; also to leave an inch and a-half of space at the bottom for adding up and getting the viean of the "second differences" and temperatures, so as to adjust the rates in accordance with their indications. Whenever the errors and rates have been ascertainea afresh by observation, the proper entries corresponding to the given date should be made in red ink, so as to be easily found for reference. Red ink It will be found to simplif j' their application and facilitate calcu- *"*'■'"• lations generally, if the errors are all recorded as either fast or slow of G.M.T., and not some one way and some the other. The writer prefers to have them all slow, as addition is easier than subtraction. To avoid having, in certain cases, the errors in- conveniently large, the optician could be instructed to put them all slow, say anything between ten seconds and ten minutes, according to the direction of the rate. The winding and comparing ought to be invariably done by one person. The winding should be performed with care, and at the same speed on every occasion. This is important, because the maintaining power, which keeps the chronometer going while winding, varies, and, hence, if wound slowly, a chronometer may lose during the process. So long as this is regular, it does not affect the daily rate, as ascertained from observations at several day's interval; but if wound sometimes slowly and sometimes rapidly, error may be introduced. In large Mail Steamship Companies, the second officer is generally constituted the " Navi- gating officer," and, as such, has charge of the chronometers. It is his duty every morning to make fortnal report to the com- mander that they have been attended to. It would be easy to devise a plan suitable to any particular ship, whereby it would become impossible to neglect this important duty. In some men- of-war, the crew cannot be piped to their mid-day meal until the chronometers have been reported. In a merchant vessel it is winding and usual to wind them in the morning. But whatever the time fixed ^l^^^™^ upon, there should be a certain formality observed, which could Navigating not be omitted without sure and speedy detection.* • A card, with the words "Wind Chronometers" printed or written on it, might be laid on the captain's plate by the steward every morning at breakfast time. 62 WHAT SALTED HIDES CAN DO. Injury to ChroDomete throogb sprlngi rusting;. Causes likely to alter rate. Trlpi'inj.' These sensitive instiuiueiits cuuuot receive too much care, for it is perfectly wonderful what apparently insigniKcant causes will sometimes utl'ect them. Many years ago the writer owned two very valuable chronometers, which he highly prized, as their performance had been most satisfactoiy. On a passage home from the River Plate they both came to grief quite unexpectedly. Comparisons with a third time-keeper, kept in the second officer's room, and observations on shore at St. Vincent, shewed that they had taken up a prodigious losing rate, which grew day by day until on arrival at Liverpool it amounted to 20 and 25 seconds, l^.xaminatiou by the maker disclosed the annoying fact, that the springs and other steel portions of the works were thickly pitted with rust. Now, the Captain's room was situated directly over the main hold, which on that particular passage happened to be stowed full of salted hides. The coat of the mast, which came up through one corner of the cabin, had worked adrift on the side wiiich was hidden from view, and the only inference to be drawn was, that the salt steam from the hold had penetrated to the me- chanism, with tiie unfortunate result already mentioned. Though tlioroughly cleaned and " re-sprung " they never went so well again. Jolting in a railway train, or a conveyance of any description, is liable to alter the steady going of a chronometer. The (|uick jerk of a boat smartly propelled by oars is still more likely to prove injurious. If, therefore, a chronometer has to be taken from one place to another in a pulling boat, it should be held free in the hand by the leather straj), and the men ordered to pull out of stroke ; or, if the officer is afraid of being called a ' lubber,' and his boat's crew ' a pack of old women,' he can give the word to " pull easy." When carrying it by hand, avoid a rota- tory movement, a.s this would very easily stop it till a similar movement set it going again, and so on. When travelling by train, place it on a pile of overcojits or railway rugs, in such a position that it will not fall. The princijxil cause, liowevur, of a chronometer altering its rate when reasonable care has been taken of it, in clnunje of tern jie rat are. In connection with this subject of rough carriage, tiie reader should know that a chronometer is exposed to a variety of mis- haps which are very little understood except by " the trade," — Tor example, when the locking-spring of the escapement is too weak, it is possible for two teeth of the " 'scapo-wheel " (instead of only one) to pass the locking- pal let during a single vibi-ation M YSTTFICA TION. bj of the balance. This is called " tripping," and it is evident that in this way a chronometer may gain several seconds in a very Mechanical short space of time, to the complete mystification of whoever has p""'""'"'" to do with it, unless he happens to be posted in respect of this peculiarity. Tripping may occur also thi-ough a worn " 'scape-wheel," the pallet-stone being badly set, or the several parts not being relatively in good adjustment. On the other hand, should the locking-spring be too strong, the pallet will not get back sufficiently to release the " 'scape-wheel," and the chronometer will not go at all, or if it does condescend to do so, will only move by fits and starts. Of course the maker would never let an instrument leave his hands in .such a plight, but it is mentioned to shew the refinement of .skill which is necessary in the manufacture and adjustment of such delicate mechanism. Again — owing to the axis of the balance-wheel being but slender, a sudden jerk may bend it or break the extremely fine pivot- points, a misfortune which at once puts the chronometer " out of action " till the damage has been repaired. Before removing it from its outer case to carry it anywhere, a Necessity for chronometer should be stayed, otherwise the instrument is apt to chfonometerj capsize in the gimbals, and when the inner case is next opened, to previous to astonish the individual who has carried it by his finding the XII next to himself, instead of facing him on the far side as usual. Incredible as it may appear, the writer knew an officer, who, to his consternation, got a chronometer into this very same fix, and worse than all, neither knew how it happened, nor what to do to get it back into its original position. The poising of a chronometer in the gimbals has a very great Poising a influence on its i-ate. This can be tested on shore by staying the ^^"^"^^'1,"], chronometer and keeping the case on its side for three or four days with the XII up. Next try it with the III, VJ, and IX up, and it will be found that the rate in each case will be difierent to what it was when the chronometer had a horizontal position. The more expensive pocket watches are adjusted for an}' position, but marine chronometers are intended always to be kept strictly horizontal, with the face up. Experience has proved that chronometers, with the words " Auxiliary compensation " engraved upon their face, are not one whit better than those fitted with the ordinary balance. Without this knowledge, a purchaser of one of these instruments might Auxiliary fancy he was getting something " very special." Auxiliary bal- Comrcnsation 64 LUBlilCATING OIL. Cleanins: Chronometers. Chronometer Makers aotl Chronometct Sellers. aiiccs, and some of the more coinplic.itcd kinds — froin their fraf^ile and jointed construction — are .specially liable to injury by shock. On this ground, if no other, the writer prefers the ordinary lialance. A caution will do no harm to those who, because an instrument is gointr pretty well, allow many years to pass without havinj^ it cleaned. It should be borne in mind that wear and tear is con- stantly going on ; that the oil thickens, and eventually gets dried up ; and that when this liappens, the pivots of the moving parts must nece.ssjirily grind tliemselves away, and work differently to what is intended. Oil is one of the great difticulties in dealing with chronometers. No two makei-s are agreed as to tlie best oil for use. All confess to great difficult}'. Not only is it difficult to get good oil that will remain perfectly fluid for some consider- able time, but suitjible oil, even if once niado, cannot always be reproduced by the same processes. Not only dermits of halj a dcijree of llie arc being numbered and considered as a whole degree. Thus, in the sextant, what is really only an arc of GO', is divided into 120 equal parts, each of which docs duly as a degree. The Octant, The instrument commonly known as a Quailrant is improperly so called. Though it is capable of measuring angles up to 90', the arc only consists of the eighth part of a circle, and, in accord- ance with the rule adopted in the former case, it should be termed an Octant.* These term.s, being at present opposed to each other, port (except iimlcr havy repair) to permit of their clirouonictcra uiihows tlio nectiaiiy of trsliiif; the chronometers themselves, irrespective of the n.imea which they bear, llierv is a lot ot luck aliout it. * Tlie original quadrant dcTtacd by John Davis, on* of Kogland'a sterling aeitmcn, in K'SO, consisted of two arcs, which together made np 90 degree*, and waa therefore an actual quadrant, a< the name Implies. It was geuaialiy known to aeamen as the " back- staff," because the oUerter turned hit back to the sub vilau taVlug >n altitude, and il •a.« iupertedail by IladKy's quadraut In 1*31 better known j> Quadi PKINCIPLE OF THE SEXTANT. 67 are a source of confusion, and might be rectitied by ubolisliing tlie word Quadrant, and substituting Octant. Instruments capable of measuring angles up to 144° are in like manner termed Quintants. Qui„tanis Tlie optical principle upon which the Sextant is founded is thus announced : — " If a ray of light sutlers two successive reflections in the same statement o( plane by two plane mirrors, the angle between the first and last Optical Law • - 1 1 i» 1 • ), governing direction of the ray is twice the angle of the mirrors. sextant. The following illustration is taken from Herschel's Astronomy, page 117.* P Let Ali be the limb or graduated arc of a portion of a circle Demonstration 60' in extent, but divided into 120 equal pai-ts. On the radius ofiawofdouWe CB let a silvered plane glass D be fixed at right angles to the plane of the circle, and on the moveable radius CE let another such silvered glass G be fixed. , The horizon glass D is permanently fixed parallel to AC, and only one-half of it is silvered, the other half allowing objects to be seen tli rough it. The index gla.ss G is wholly silvered, and its plane is parallel to the length of the moveable radius GE, at the extremity {E) of which a vernier is placed to read off" the divisions of the limb. On the radius AG is set a telescope F, through which any object Q may be seen by direct raj's which pass through the unsilvered portion of the glass D, while another object P is seen through the same telescope by rays which, after reflection at C, have been * Putlished by Longmans & Co. Pecului 68 Ituy.l yi:liXlKU \yA6 lyVEMEli. thrown upon the silvered part of D, and arc thence directed by a second reflection into the telescope. The two iinajres so formed will botli be seen in tlie field of view at once, and by moving the radius CE, will (if the reflectors be truly perpendicular to the plane of the circle) meet and pass over witliout obliterating each other. The motion, however, is arrested wlien they meet, and at this point the angle included between the direction CP of one object, and FQ of the other, is twice the angle ICC A, included lietween the fixed and moveable radii CA, CE. Now the graduations of the limb being purposely made only hidf as distant as would correspond to degrees, the arc AE, when iLiul off as if the graduations were whole degrees, will in fact road double its real amount, and therefore the numbers so read ofl'will express, not the angle EC A, but its double, which is the ictual angle subtended by the objects.* Though epitomes mo.stly explain how to read the vernier, they iiiiman ejc. ucglect to explain the peculiarity in the human eye which gave origin to its invention. t The value of the vernier as a means of reading minute divisions depends upon the fact that, when they arc within a certain degree of closeness, the eye cannot separate a series of parallel lines lying side by side, there being a point for all vision where such lines appear to mix witii the ground upou which tiicy are drawn, and thus form a tint: therefore it would V>c 'liflicult to say, unless under extreme magnification, to which one of these lines the index arrow pointed. Further tiian thi.s, it would be quite impossible to graduate the arc of a sextant to the reijuired degi'ee of miuutenes.s. Taking a .sextant of 8-inch radius divided to 10', the space between each line on the arc would be equal to 00019 of an inch, and the lino it'ioif would aliiiust have to conforni to the geometriciil definition of " Icngtli without breadth," conditions, in cither case, clearly iin]iracticable. Now it is a recognised fact that so long ns the eye can see a single straight line dintincthj, it can detect any break in its con- tinuity. The divisions on the arc of an 8-inch .sextant arc easily discernible under tlie magnifier. In modern instruments each degree is divided by strokes into six equal parts, each stroke * It can Iw sasily deinoDitnted tlmt the kngle HCA, betWMU tcro o( the arc au cAlletl a " Nonius," from Peter Nouiua, who, about the middle of the 16th century, tint cnunciited it* |-i|>le and a|<|ilicatinn in a aomewbat laboured and orudo form, which was •Implifled by I'iiTre Vernier in 1631. bp.cing o( USEFUL PECULIARITY OF THE EYE. 69 therefore represents 10', and the space between each stroke — supposing the stroke to be infinitely tliin — is •0116 of an inch, spacing oi which is well within the j ower of a dividing engine. Under but "I'visions. weak magnification, this space, tiny as it is, appears jierfeclly clear and distinct. So far the arc. In tlie form known as the " extended " vernier, the divisions are nearly double tlie distance apart of those on the arc, and are therefore even more clear and distinct, so that, when any one of the vernier lines coincides exactly with a line on the arc, the fact is easily observable, and this particular line may be taken as giving the true value of the reading. The principle of the vernier is such that, in a well cut sextant, only one at a time of the vernier lines can possibly coincide with one on the arc ivhen the zero line or arrow of the vernier is itself out of coincidence. But when the zero line is in coincidence, then the terminal line of the vernier must also be in coincidence, or the sextant is badly cut. At such times as a line on the vernier coincides with one on the arc, all the others appear broken or discontinuous, becoming moi-e so in proportion to their distance right or left of the reading. In badly divided instruments it may happen that two or even Testing three lines of the vernier may appear in coincidence and puzzle '"■'"'"'• the observer as to which he should accept. Such a sextant is not worth having, except for rouse-about work, such as angles of land, &c. It is found that a line, as tine as it can be clearly seen, will appear broken in its end-to-end continuity with another equally fine lino, if at their point of meeting the lateral displace- ment should amount to a quarter of the thickness of either line. The vernier permits of this being readily carried out in practice, and affords a method of arriving at small readings which cannot be excelled. To obtain the full benefit of it, the divisions, both of arc and vernier, must be accurately spaced, and sharply, though finely, cut. Instruments for the determination of angular mea.sure are not all alike in their graduation, so on attempting to read off a new instrument it is first necessary to ascertain by inspection the law of that particular vernier. To explain the 'principle of the vernier would be altogether too tedious, even if successful. The navigator who takes a proper pride in liis work should Respective possess a first-class Sextant or Quintant, and a good Octant. Q^^jantare The latter is fully oiiual to everyday work in the broad ocean, — octant, for example, during the winter months in the North Atlantic. The delicate exactness of the other instrument is quite thrown STRAIGHT TIPS FOR C^xt i Seztaot away when one can only get tiying shots at the horizon, from the crest of a CO- feet wave. Showers of salt spray, with the chance of an occasional knock, certainly seem less suited to the sextant than to its hardier and more humble relative. Un the other hand, for tine weather use, for stars, lunars, ob- servations on shore with artificial horizon, and for fixing the ship's position in the neighbourhood of land by angles, the Quintant is undoubtedly the proper instrument Angles of the land fur " fixing " purposes are not required to seconds, nor even to minutes : ordinarily, it is sutlicient if the error does not exceed the sixth of a degree (10); the only reason, therefore, for mentioning the Quintant in this connection, is that occa.sionally vne or both of the angles may be so large as to be beyond the range of tlie Octant.* A good Quintant or Sextant costs money — and is worth it. Unless you are a fair judge of one, it is as ea.sy to be deceived in purchasing purcluksing a sextjiiit as in buying a horse. The market is glutted with sextants made fur sale. Every pawnbroker's window in a seaport town is half full of them. Some vendors even hold out the inducement in large type that their instruments are " free from error." If, indeed, by accident such should happen to l^ the case at the moment of purchase, it need not Iw a matter of spiculiitioii how long they will remain so. The thing is absurd, and might with equal Justice be said of a chronometer or a patent log. At the Al>erdeen meeting of the British As.sociation in ISS.*) (four years after this was written), tho late Mr. G. M, Whipple, R.Sc. F.R..\.8., the then Superintendent of Kew (3bscrvatorj', read a paper " On the Errors of First-class Sex- tants, as determined fmm the Recnnlsof the Veritication Depart- ment at the Kew Observatory."- He pointed out that the instruments were sometimes inferior, and it was generally i)b.served that though good sextants could be had il a proper price were paid for them, there was a large inimbiT of " cheap and na-sty " instruments in the niarket, and in fact tl'.at the traile had partly drifte "s '<» trust, you, in your turn, must treat it with some degree of intel- ligent consideration. 72 USE OF A NICOL'S PRISM. Vernier aart false readinE^ Telescopic power. " Interrupted Ihreail ' To test the arc, set the zero of the vernier very carefully iit various divisions along the arc, and then note if the left hand division of the vernier coincides exactly with one on the arc If the latter is correctly graduated, it should coincide in every instance. Cheap sextants won't stand this test. Examine the vernier, to see that its feather edge lies perfectly Hush with the face of the arc, othorwise, by a slight side move- ment of the eye to the right or left of a point exactly vertical to where the divisions " cut," a false reading is obtiuncd. This is very likely to occur at night, when reading ofl' by the light from a swinging lamp. An extended vernier, by which is meant a vernier whose divi- sions are twice the disUmce apart of those on the arc, is now considered to be " the correct thing," and is a great help to accurate reading. A steel tangent-.screw will not only last longer, but will work more evenly than a brass one. One of the eye-pieces of the inverting telescope should have a tolerably high magnifying power — say 14 or 15 dianiotei's, a.s contacts of the sun's limbs in ob.servations with the Artificial Horizon are easier made in proportion to the size of the suns. To do away with the annoying and error-producing glare so often witnessed on the .sea horizon, till the sun gets above 50" or so, Mr. T. Mackenzie, of the RM.S. Moselle, in.serted a Nicol's prism close up against the object-gla-ss side of the diaphragm of his inverting tele.scopc. This was so placed that when the tele- scope was screwed home in its collar, the polarising plane of the prism would be parallel to the plane of the sextant, and conse queiitl}' perpendicular to the plane of the horizon when making ob.servation.s. By this "'°" "^ " '^ Screens. correspond to the thickness of the glass. The coloured screens which screw on to the eye end of the telescopes should also bo neutral tint. The front and back faces of the index glass ought to be strictly Test for parallel to each other. This can be tested by placing the sextants j'^'^f "l''f ""^f on a table or other steady support, and looking obliquely into the face of mirror at the reflection of some distant object. The image should *''"°''* have sharp and well-defined edges. If they are at all blurred or indistinct, the glass is more or less prismatic. Another method of determining this is to examine the reflected image of a star with the index set to a reading of 120° or there- abouts. The index glass reflects from its outer as well as from its * \'i horizon in a manner similar to the foregoing, and the method is a Sea HorUon correct one; but it will not work on shore where the top of some straight and level object is employed to represent the horizon, unless the object so selected be at least half a mile distant. The index and horizon-glasses would subtend a sensible angle at the place of an object ivitkin that distance ; and, though the glasses should be parallel to each other, coincidence would not be estab- lished between the reflected and true images. Beware, therefore, of self-styled opticians who are occasionally to be seen at their shop doors adjusting sextants by the roof of the house opposite. In doing so they betray their own ignorance 76 liAPrn OX "TrxKEnrxG.' as well as their customer's confidence. Some one, with more humour tlian reverence, has suggested the word " Shoptician " as a fitting title for such men. Pcrliaps it is. Some officers liave an idea tliat a large Horizon-glass i."* an advantage, as it gives more ' field.' Tiiis is not the case. The amount of ' field ' is regulated by the Index-mirror, and so long a.s the Horizon-gla.ss reflects tiie whole of the Index-mirror it does all that is required. For astronomical purposes the mirrors in ordinary use are ample ; but for measurement of points along the coast it is an une WHAT YOU ARK TO DO, AND NOT TO DO. resilvored according to Belcher's method, as described in the Sailor's Pocket Book. Do not stow j'our sextant case in a drawer, or on an out-ol'-tlie- M"de »' stow way shelf, from which a sudden jerk of the vessel might send it c'fse" *" flying. Rather, get a brass band j\ of an inch thick, and f of an inch broad. Let it be bevelled to fit three sides of the box a little better than half way up. Cover this with coloured flannel or wash leather, and screw it to the bulkhead in such a manner that the sextant case can be dropped into it, and remain secure in any weather, and at the same time be handy for use. A square sextant case is in all respects an improvement on the old shape : it can be secured to the bulkhead pretty much in the same way as the other. Fit a brass handle on the keyhole side to carry it by. For convenience of reference, in case of a suspected mistake Mode of fitting in reading ofl", the lid of the sextant case should be fitted so that it will close with the index clamped at any part of the arc. Further, the I'eceptacles for the telescopes should be long enough to allow of them being put into the case when set at focus. This is uncommonly handy when you are in a hurr}^ In an extra receptacle you should keep a nice soft camel-hair brush, about the size of the tip of your little finger; it is most useful for brushing off dust, &c. Never put your sextant away without lightly wiping the glasses with a clean piece of fine soft chamois leather. Do not use j'our pocket handkerchief for this purpose. Moisture '"'I'" ^n' allowed to remain on the mirrors will soon imj)air the silvering, ^^j juff^, bj and render star observations difficult. The chamois leather damp should be washed with soap and water when requisite, and rubbed perfectly soft with the hand after being well dried. If pressure be applied to the glasses in cleaning them, their adjust- ment will be disturbed. So be careful. A little sweet oil and lamp-black occasionally smeared over the arc and lightly wiped off again, does good, and makes it easier to read. You may also, now and again, very sparingly oil the tangent screw, as well as the back of the arc, and the front of the vernier-plale, where in each case the spnngs traverse. Rub off the superfluous oil with another piece of chamois leather kept specially for the purpose. Do not let the two pieces come near each other, as oil or gi-easc would not suit the mirrors. When you send your sextant to an optician to have the glasses Arc not to u resilvei-ed, instruct him not to polish the arc. The ordmary p° " * • THE liEAVlSG MWliOSCOPE. compass-maker, thinking to please you, is sure to do this, to the great detriment of the instrument, unless you give him most positive instructions to the contrary. Before finally deciding to purchase an expensive sextant or quiutant, arrange with the maker to have it tested, and its errors determined and tabulated Instruments ^t, thc National Physical Laboratory. 'J"he fee is a trifling one can be tested — Only tive sliiilings, exclusive of carriage to and fro. An)' at Kew obser- ppj.jQjj ordering instruments from opticians may direct them to be previously forwarded there for veritication. Address — The Director, National Physical Laboratory, Teddington. In these pages it has been shewn how to test the minors, also the parallelism of the shades, but to test the centering errors is practically bej'ond the power of the navigaUir. If a man of iiitinite resolve, he may succeed, it is true, b}- vexing his soul lodea and cen- with a scrics of a-stronouiical observations of a painfully tedious tering errors character. JIuch better to pack the instrument otf to Kew, where, by a system of collimators, the centering errors are deter- mined for every Ld" of arc both quickly and accurately. Please note that 'centering error' and 'index error' are quite inde- pendent of each other. Each must be ap|died in accordance with its own sign + or — . A few more hints re sextant managemeni. In reading oH', whether by day or night, do not hold it sideways to the light Let the light come straight along the index-bar to the vernier ; and to tone down excessive glare, a moveable ground glass screen should be fitted in front of the vernier. Neglect of these things may cause an error in tiie reading of two or three minutes. Gary Electric lamp lijig ji nctit arrangement by which to read off at night : a small " dr^-cell battery actuates a tiny incandescent lamp. This latter fits into a socket in the carrier of the " reader," ami siiews a light for two minutes. The current must then be switched off for an equal time ; but in practice this is unnecessary, as reading olf will not occupy more than half that time, antl during the next oljser- vation the lamp is recovering its power. The cost is £'-i 10s. The reailing microscope is sometimes called tiie magnifier or " reader." Now, it is no use for the mathematician ami mcchani- cia4i to expiud their energies in the protluction of a refined instrument if the means of reading its indications are of an inferior character. It would obviously be labour lost. The strength of a chain is measured by the strength of its weakest link, '{"hcrofore it is to the magnifier we lo.'k to give us truth- fully the final result to which the various parts of the instrument have jointly contributeil. The nuignifior has a duty to perform. A NOVELTY IN QUINTANTS. In traversing the vernier it is important, for delicate readinj;, tliat its sweep slioukl have the same radius as the arc itself. To fulfil this condition, it is clear that it should rotate on the same centre as the index-bar. This is not possible in the ordinary sextant, but Messrs. Hughes, of Fenchurch Street, have brouglit out an ' improved Quintant' having the legs in fi'ont and the index and horizon glasses at the back, which easily permits of it. The ' reader ' itself is so arranged that its focus can be altered without danger of bending the carrier. The legs being in front ai-e a great convenience in setting down or taking up the instrument. The makers claim that, owing to the setting of the mirrors, and the index-bar having freer range, an unusually large angle can be measured. Here it may be said that after 140° the relation between the index and liorizon glasses in an ordinary sextant becomes such as to render observations impracticable. Messrs. Hughes achieve their object by placing the telescope holder close up under the index-mirror, and shifting the horizon-glass to the extreme end of the arc, so as to make the angle formed by the centre line passing through both mirrors, and that passing through the Horizon-glass and axis of the Telescope, as acute as possible. This instrument, therefore, is specially adapted to Artificial Horizon work and measurement of large angles gene- rally. It has many points to recommend it, and is altogether a revelation and a revolution in Quintants. To conclude the chapter. There is a proverb that " You should never lend to any one your horse, your gun, or your dog." It applies also to the sextant, ' only more so.' Bear it in mind, dear boy. CHAl'TER VI. TllK AUTIFICIAL AND SKA HORIZON& Tliere arc iiiaiiy varieties of the ArliKcial llorizon tor >liure use ; liut results, not to be surpassed for accuracy, are olitniiialilc with tlio ordinary kind, in wiiich a flat and shallow cast-irou troufjh, containing pure ([uicksilvcr, is protected from the wind by an angular glass roof. This form is not quite so compact and portable (or so expensive) as some others, but circumstances alter cases ; and the Navigator, unlike the explorer, has not, lor an indefinite period, to trudge along under the weight of his own gear wilh the thermometer at roasting temperature. Law upon 'p|,j, Artiticial Horizon is ba.sed upon the well known principle in Catoptri&s — that tlie angle of reflection is equal to the awjlc of incidence: in other words, if a ray of light strikes any plane reflecting surface at a definite angle, it leaves it at the same angle, thus : — vhkbltii This fundamental law cannot be too strongly impressed on Ihi mind, as its ap^)licability to everyday matters is continually cropping up. Opticians avail themselves of it in quite a variety of instruments. The .sextjint is partly based upon it, and it forms a leading feature in the science of lighthouse illumination. Sound waves and heat rays have this property in common, and in mechanics there is the same law precisely. Kvery billiard player understands it well a.s it is apiilioal)lo to the motion of the balls on the table. A FICKLE MISTRESS. The principle can be illustrated in the simplest possible manner Mechanical by driving one of the balls against the opposite cushion of the '""stration. billiard table, and rfoticing the direction of its motion on ap- proaching the cushion, and again on rebounding from it. If the ball be propelled from the bottom left-ha,nd pocket, so that it strikes the exact centre of the top cushion, it will return to the bottom right-hand pocket, always supposing that " side " has not been given to it. All schoolboys are practically familiar with it in the common game of hand-ball, although some of the younger ones may possibly never have heard of the above rule relating to it. The Artificial Horizon, in conjunction with the all important sextant, is of service for astronomical observations on shore when the sea horizon is not obtainable. Even if the sea horizon were Artificial pre- available, the artificial one possesses many advantages over it. horizon For example, the accuracy of all observations taken with the sea horizon depends, in the first place, upon a correct knowledge of the estimated or measured height of the observer's eye above the sea level, whereas with the Artificial Horizon it is quite immaterial what the height of the eye may be, as it does not enter into the after calculation. Secondly, owing to the uncertainty of the efi'ects of refi'action. Sea horizon the apparent position of the sea horizon can never be depended upon. It is found to be sometimes above its normal place, and at others below it. The rule seems to be, that when the sea is ivai'Vier than the air, the horizon appears beloiv its mean place ; and when the sea is colder than tlie air, the horizon appears above its mean place. The known capriciousness of terrestrial refraction irregularity has prevented the formation of a table of values in connection °' ''''^'^^'°'' with this subject. Celestial refraction also varies much, so that tlie tabular amount applied to the altitudes of heavenly bodies may not at the time be the actual value. It is important to arrive as nearly as possible at the correct thing, by using auxiliary Tables 32 and 33 of Raper's Epitome, to correct the mean refraction given in Table 31. An investigation of the Tables will shew that the refraction is greatest with a high barometer and low thermometer. Again, if the sea be at all rough, and the observer not much Sea Ho saw-edged the horizon, from which the mei'curial one is of course exempt. That eminent authority, the late Lieut. Raper, R.N.,* says, — PHECAUTWXS IN FILL 1X0 THE TRUUGll. Its 'tie for ntiinK Chrono- • mctcis " The image of a celestial object reflected from the surfivce of a fluid at rest, appears as much beloiu the true horizoutal line as tlie object itself appears above it ; the angular distmce measured between the object and its image is therefore double the altitude. An advantage resulting from this is that in halving the angle shewn by the instrument, xveludve at (lie same time all the errors of observation* The reflected image in the fluid is always less bright than tlie object, but, .is it is perfectly formed, and as the surface is truly horizontal, the Artificial Horizon, when it can be emi)loyed, is always to be preferred to the sea horizon." To the navigator, the Artificial Horizon is seldom of other value than to enable him to ascertain the error and rate of his chrono- ineter at ports abroad, where there are no time signals for the puii)ose. In its use there are many points to be attended to, all of which conduce materially to the desired accuracy of the result, Siie of Trough. ^l•\^^, trougli should not be less than 4 inches inside lengtli because the convexity of the mercury at the edges renders that part unfit for retiecting truly. Moreover, the surface of the central portion is necessarily foreshortened to the observer, ami becomes more so as the altitude of the object decreases. The trough should stand sufficiently high inside the roof to admit of the surface of the mercury being on a level with the lower edges of the glas-ses, otherwise one is needlessly deprived of the full power of the instrument — that is to say, its range for measuring angles is lessenetl. For the .sjime reason, and also to avoid all possibility of convexity of surface, do not be stingy with the quicksilver. Kill the trough as full as you conveniently can, anack yard of the Hi)spitil belonging to the Pacific Steam Navigation Company, .so that it wivs only during " the smooths" that sights couM be obUlined. For the sjinie reason, avoid the neighl>ourln.KKl of wuterfalls, mills, factories, foundries, ami shops of worknien g>nenilly. The ptLs.singof vehicles on a road maj'also have a disturbing infiuencc on the mercury. Fortunately this lluid. from its i;reat weight, very ([uickiy comes to rest afttu- being siiaken, therefore, .so long us the tremor is not actually continuous, one can generally manage * See pages (5S-r>&4. SELECTION OF OBSERVATION SPOT. 85 to secure good observations. Wind is a frequent source of quak- Ruffled ing mercury, and care sliould be taken to have the horizon trough "*"'"^' firmly phiced, and the roof bedded on sometliing soft, so that the wind cannot get under its lowe.r edgi;. A screen of canvas to windward is a good thing as a rule, but on some ground this causes such vibration of the earth as to be worse than the free blast of the wind.* For " Equal Altitudes," a spot free from disturbance is absolutely necessary, or, from inability to secure observations corresponding in altitude with those taken in the forenoon, the whole daj's work may be lost — to say nothing of the annoyance of the thing. Again, a place open to the public is objectionable, from the number of idle curiosity-mongers who are sure to surround the partj^ and, without intending it, make themselves very disagree- able by ignorantly getting in the way, &c. Supposing a spot suitable in all these particulars has been found, there yet remains an important consideration. If you are going to observe in the afternoon as well as the forenoon, due regard must be had to what the sun's bearing will be at the first named time, so that when wanted in the afternoon it may not be rendered invisible by houses, trees, hills, or other obstructions. This being seen to, get ready for work by filling the trough as before mentioned, and place it nearly in a line with the object to be observed ; but slightly in the direction that the How to place object is moving, so as to avoid having to slue the trough in ^"j^^i^""^ azimuth before the completion of the entire set. To make delicate observations depending so much upon eye and nerve, it is necessary to he comfortable in body. About the Position of -1 il J i observer. easiest position for the observer is, to sit down on tlie ground at the proper distance from the horizon, and to have the back well supported by a rough box filled with sand or stones, or a chair steadied by someone else sitting on it. One cannot be comfortable, however, even on a bed of rose.s, if half stung to death by mosquitoes; so in countries where these ^Jl"^'^"^^;^^ plagues exist, and night observations are retjuired, it will be necessary to give a wide berth to swampy localities, which are sure to be infested by armies of them, especially if the air be still : indeed, for this reason it is preferable to court a breeze instead of shutting it out. * Experiments made at Greenwich Observatory proved that tremors in the mercury were caused by passing trains up to a distance of one mile at least. There is no doubt a great deal depends upon the character of the ^ound. ITEMS TO BE REMEMBERED. Telescope screens pre- ferable to IndKi or horizon screens. Care as to which limb is observed. Sandflies are j'et worse, as nothing will get rid of them; even sailors, who are a long-suftering class, and learn to put up with most things, are not proof against their aHectioiiate attentions, and many an otherwise favourable opportunity of getting stars has been spoilt by these diabolical insects. Should it be intended to observe tiie sun, turn down temporarily the necessary horizon and index-screens ; and, being phiccd so that his image can be seen reflected from the centre of tlie mercury in tlie trougii, direct the sextant to the sun, and bring it down until it more or less covers the image in the mercury, then quickly turn ijack the hinged screens — the}* are no longer needed — in witli tlie telescope, and screw on to its eye-piece a suitable screen, light enough to give a well-defined image of the sun, and yet not too bright to dazzle and fatigue the eye. Beginners are very apt to use too bright suns, and in consequence the effect known as " irradiation," spoils the sharpness of the limbs.* Look to your t;iiigent-.screw to see that it is not at the wrong end of its run, which of course would depend upon whether the sun might l>e rising or falling, otherwise j'ou might find youi-self " two blocks" in tlie middle of a set. t By this time the images will be near the point of separation. Tell your assistant with the chronometer U) "look out," and at the actual moment of contact of tlie limbs call out " stop." t In the morning, for lourr limbs the suns will separate, and for upper limbs will clase. The contrary is the case in the afternoon, and this is irrespective of the kind of telescope employed, whether direct or inxertimj Attention to this rule will prevent any confusion as to which limb was ob.served. Observe upper and lower limbs alternately without unclumping the vernier : this neutnvlizes the efiect of irradiation, and gives less work to do in reading of!', besides being advantageous in giving practice with both opening and closing suns, and not having it all one way in the forenoon and another in the afternoon. It is unwise to make the sets too long, as doing so wearies both eye and hand, and the oUservations sutler accordingly, especially in hot climates, where the necessity of observing in the full glare of the sun makes it a trying operation. * " Irmdialinn" is an. optical illtisinn in virtue of which white objccia, or those of a very brilliant colour, when srrn 0:1 a dark Kruund, look lar);<'r than they really are. t This defect hat been obviated by Messrs. Ileith 1- Co. by the use of their Stmpcr l*nratH» ontlless ljinj;enl-#crew. { When nbsecvini;. never "make contact" yourself by movinK tlic tani;cut-Krew, but overlap or o|ien the inisges, as the case may be, clamp Krurely, and walch for tin- exact ihst.int uf eonlact. I'se Ihe telescope with greatest magnifying |io«er, as it mueli facilitates corn-i't cnnt.nts. ADVICE AS TO GLASS SHADES. 87 III " equal altitudes," take care that corresponding observations A.M. and P.M. are made of the same limbs. Ascertain index error immediately before and after sights, using any of the eye-piece shades u'hich were emjdoyed for the altitudes. In observing with the Artificial Horizon, it is preferable, for Eye-piece many reasons, to use the screens fitted to the eye-piece of the ^^^'^"^^ telescope instead <-)f the hinged ones on the sextant. A couple, and sometimes three, of different degrees of shade are to be found in every decent sextant case, and their advantage over the others will be apparent to the reader who has studied attentively the chapter on the Sextant : — for example, the brilliancy of the sun varies as clouds pass over, and although to meet the contingency you have to change the shades, no inherent error is introduced by doing so, a happy circumstance, and very different to the result obtained by the use of the Index and Horizon Screens, which latter, however, must of necessity be used with the Sea Horizon. Before commencing work, equalize the brightness of the two Correct images by raising or lowering the telescope by the large milled p°^'*">» '°' headed screw provided for thepurpose. This will bring the axis of the telescope almost in line with the edge of the silvered part of the horizon-glass, which is the best position for observing, and there it must remain all through the performance. No matter, then, what particular depth of shade you may afterwards be compelled to use for the eye-piece, the two images will preserve the same relative tint.* It may assist to give an example of finding the ti'ue from the observed altitude. \l 24/7/1875, on shore at Arica, in latitude 18° 28' 00" S., and longitude 70° 20' 25" W., observed the following angles between the upper limb of the sun reflected from the index-glass of the sextant, and the lower limb as reflected in the artificial horizon. I.E. -f 50". • In best sext.ints it is now usual to fit an eye-jiiece with a revolving di.sc containing 3 or 4 screens of various intensities, so that a .shift from one to the other i* only the work of an instant. Tliis arrangement is made to suit each of the telescopes. Tlie disc contains a clear aperture as well as the coloured screens, so that it can be screwed on before com- mencing to observe, and no time is lost. 88 GKAJi TO TAKE OX SU03E. No. ot'Ubs. ; 56° 40' 30' 56 24 20 56 14 10 56 04 10 55 56 30 5)281 19 40 Mean 56 15 5(j Index Errur + 5ii 2)50 16 4(i 28 08 2.3 Rffnictiou— Parallax — 1 3K 28 06 45 Scini-diainetcr — 16 47 Tnic Alt. 27° 50' 68' It will be noticed tlnii Dip is not allowed, also that the angles were dimin- ishing, shewing it to have been altcrnoon, in which case 0>ei"S upper linib) the ob.'crvcd limbs were teparating. For an ex- ample of stars, ue page 559. Observme Kccollect thilt, iis the Artiticinl Hm-izou mvis doiMe the actual power 01 ArtI- *=* ficui Horizon, altitude, you cannot with tlie ordinary Sextant ob-serve higlier altitude.s tlian G0° or G2° ; indeed, so hiijli an altitude is not to be recomiueuded, for though the ordinary ijuintant will measure 135° or thereabouts, the image will not be sharply de6ued when reflected from the Index-mirror at such a large angle, unless the glass be more than usually good. To save di.sappoiutment, it is well to ascertiiin beforehand what is the lowest altitude your Artificial Horizon will permit you to take ; — this is seldom under 18°, which gives you a range in altitude of about 40^ The im- proved Quintant of Messrs. Hughes & Son will measure angles correctly up to at least 140°. Requiiiitjto When going on .shore for sights, take with you a couple of takeonihore. cluiirs (unle.ss you think you can borrow them), one for the chronometer, and tlie other for the time-keeper, and to .support your own back as before mentioned. Take also pencil and note- book, chamois leather, a couple of towels to spread on the ground under the instruments, and, in hot wi'uther, an umhrdla to keep tlie chronovietcr cool. You cannot help exposing your sexbint when ohservimj, but that is no reiuson why yim should do so when not observing. Recollect that the metal is amenable to the law of expansion and contraction, and that oii.servations made under opposite conditions of heat and cold cannot be expected to agrea This is one of sevenil reasons why the writer prefers st^ira See page .').'j{ For night work, dispen.se with the umiirella, and sub- .stitute a couple of buH'.s-eyc l.imp.s— ime for the chronometer, and the ittlirr for reading i>H'b\-. HEIGHT OF EYE AND SEA HORIZON. Sg Don't forget tlie wash-basin or some substitute, unless you have a hirge reserve stock of quicksilver. Caution the lamp-men neither to flash the light in j^our eyes nor to throw it anywhere near the Artificial Horizon. A good arrangement is that in which the assistant is seated in the obseiwer's back -supporting chair, with the chronometer immediately facing him on the other, so that the light necessar}' for taking the time need not interfere with anything else. For this sort of expedition, select handy men who have some guviption. Think over and make all your preparations well ia advance, so as to avoid hurry-scurry and confusion when the time for action comes. Compare chronometers before leaving the ship, and again on your return on board. Many Artificial Horizons have been invented for use on board Artificial ship in times of ios, or for taking stars at night, when the natural Horizons <<" horizon is very ill-defined, but none of them can be considered a success ; and unless a man has plenty of money, and can afford to amuse himself with such toys, they are just as well left alone. THE SEA HORIZON. Visible hori.on Every seaman knows that by going aloft in clear weather his range of view is extended, and that on account of the earth's curvature the visible horizon recedes from him the higher he goes. In like manner, by descending towards the surface of the water his range of view is lessened, and the horizon approaches him. Advantage can be taken of this to get observations in foggy Observations weather. By sitting in the bottom of a small boat in smooth weather, water, or on the lowest step of the accommodation ladder, the eye will be about two feet above the sea level, at which height the horizon is little more than a mile and a quarter distant, so that unless the fog is verj'^ dense, serviceable observations are (juite possible. The writer, on three different occasions, when at anchor off the River Plate, during fog, has been enabled to ascertain the ship's position in the way described, and after verifying it by the lead, has proceeded up to llonte Video without seeing land. Of course the vessel was onlj^ allowed to go at slow speed, and the deep-sea and hand-leads were kept constantly going, as well as the ground- log, — the latter will be treated of by-and-by. Every navigator ought to ascertain, before leaving dock, the Height of eye height of his eye above the load water-line corresponding to his ,g^g, position on the bridge, upper, and main deck, and consequent distance of the visible horizon as seen from each of these places. DISPLACEilEXT OF SEA HORIZON. Where to observe from in cltar weather. Where to observe from Fore And back In fine clear weatlier take your observations from the highest convenient place, say the hndge. The reasons for this are that an error in tlie dip causes an error of the same amount in the alti- tude; and the dip changes most rapidly the less the elevation above the sea level. For a height of eye of 10 feet the dip is 3', and for 40 feet it is only 6' {vide Table 30 of Raper's Epitome). Raper stiys : — " If the altitmle be observed above the deck, as in the top for instance, the horizon will appear better defined, and the variations of the dip by the ship's motion will be less sensible ; also the difference of temperature of the sea and air appear to affect the pliice of tlie visible horizon less a-s the ob.server is more elevated. Hence it would appear that altitudes should be taken from aloft when convenient." In thick or misty weather take your obseifatioiis from as low a 2'ioint as possible, and in all cases apply the correction for height of the eye corresponding to what it is known to lie at the spot where the observation was taken. Reference has already been made to the uncertainty in the place of the sea horizon, due to the unetiual temperature of the air and water. This displacement of the horizon sometimes occui-s to a most serious extent, and unfortunately on board sliip there are no means of detecting it by obaervations of the sun, unless, indeed, its altitude should happen to be above 60', when, with a good Quintant, it can be taken /roHi opposite sides of the horizon, by which mean.s, if the dis]>lucement slmuld be equcd all round, the error due to this cause will be eliminated by taking the mean of the observations. Tiiis error in the place of the sea horizon is commonly found on the edge of soundings, and at the mouths of large rivers, and in tiie latter case is caused by the unequal temperature of the mingling currents of fresh and salt water. It exists in a marked degree in the Gulf Stream and its vicinity. The writer once found the latitude by an excellent meridian altitude of the sun to be as much as 14' in error. The time was mid-winter — the day a clear and clouiUcss one — the sea smooth, and the horizon clean-cuL Five observers at noon agreed within the usual minute or half-minute of arc; ncvcrthcle.ss, on making FiOng Island (U.S.A.) in less than two hours aflerward.s, tin- iatituile was found wrong tt) the amount stjvtoil. Many such civses have come under tlie writer's notice, but this imo aloiir Im citi'd on nrcount of the magnituelow it, although from the effects of refraction it was still visible. This the officer could not and would not believe. He aptly enough quoted the saying, " Seeing is believing, and feeling i.s the naked truth." However, he was convinced some few minutes later by a very familiar experiment. Being firmly seated in front of an empty wash-hand basin, so that the brass plug at the bottom was quite invisible, the basin was about half filled with water from a can, when, without moving his head, he at once, to his great astonishment, saw the plug. On letting the water run off[ the plug again disappeared. horizon whilst yet Experime with basil The figure repieseuts a portion of the earth surrounded by the atmosphere, the density of which, as shewn by tlie increasing nearness uf the circles, becomes greater as the surface is approached. Tlie ray of light proceeding from tlie star S is successively bent or refracted at the points abed efy, and finally comes to the eye of the observer at in the direction gO, naturally causing him to imagine the star to be situated in the heavens at S'. It was then explained to him that air, in common with all transparent media, possesses the power of bending rays of light out of their straight course. A ray of light from a celestial body, entering oui' atmosphere Explanation of refraction. PAIiALLAX rUZZLE PROBLF.yr. Parallax the victor. obliquely, is more and more bent down or curved as it approaches the earth, so that when it finally enters the eye, it does so in a direction different to what it had in traversinnj space. The denser the air is, the Gjreater the effect produced; con- sequently, there is more refraction near the surface of the earth than at several miles above it, where the air is thinner. Water is a much Vietter reflecting medium than air. Every sailor is familiar with the bent appearance of an oar-blade in clear smooth water, thoufjh ho may not know the cause. Literallj- speaking, then, refraction enables us " to see round corner-s." Now it might be supposed that what has just been said about the .sun and the horizon, also holds good for the moon. A little knowledge is dangerous, and the /taZ/-rtedged navigator, in his conceit, would be certain to say — "Uf course it does ! ! Why not ? Where is the difference ? " Frum the very much greater nearness of the moon it has a large parallax — quite exceptionally .so (isee page 323) — and this more than counteracts the etlLct of refraction. Recollect that the true altitude of a botly is calculated as if seen from the centre of the earth, with the rational horizon as zero. Now the mean hori- zontal parallax of the moon is 57', and the mean refraction at the horizon is 34' ; the difference is 23' in favour of parallax, so when the moon's lower limb appears to be touching the horizon it is really 23 above it. The navigator is left to puzzle over the difference (if any) in these two cases. If /it/i-fledged, he will have no difficulty in deciding whether they " run on all fours." See, then, how even the evidence of our own eyes, upon which wc place such implicit faith, is liable to deceive us. As refraction causes a celestial body to appear higher than it reallj* is, it nmst alwa^'s be Buhtractcd from the observed altitude. As parallax causes a celestial object to appear lower than it really is, it must always be added to the observed altitude. Reference to Table 31 of Raper will shew that refraction is greatest near tin- horizon, and vani>hes when the object is in the zenith. This i.s the case also with diurnal parallax.* DISAGREEMENT BETWEEN FORENOON AND AFTERNOON SIGHTS. The question is constantly asked, Can you tell me why it is I cjin so .seldom get my forenoon and afternoon sigiits to agree ? The explanation is simple enough, and as the subject is worthy of * Tlie qualiller "diiimal" ii ttldora UMil ocept wlieu it is iiFcea'Uiry to ili>tiiit;ui»li bs- twcon tliit kind of pamllax and the annual iiarnllai ol ilie liicci ^lnr'. whiih it liiie to the eartirn orbital motion. {St* page ajO.j \UN-AGREEMEN'r OF A.M. AND P.M. SIGHTS. 93 beiiifj carefully (joue into, an attempt will be made to render it clear. To simplify matters, the reader will be good enougli to suppose himself in a vessel at anchor, in the month of December, some few miles south-eastward of Monte Video, and that his chronometers are exactly correct, and his position known to a nicety by cross bearings of Flores Island and the Cerro. Next, let us suppose that, owing to abnormal refraction, the Elevation or horizon is depressed, say three minutes of arc, and remains in that ^^p"'"^'"" "' I: ' J ' Sea hori2on. condition all day. Let sights be taken at six o'clock in the morning, and again at six in the evening. From the horizon being unduly depressed, these altitudes will be too great by 3 minutes of arc, and when worked out will in each case give too small an hour angle, with the result that the a.m. sights will place the ship 4' of longitude eastward of her true position, and the p.m. sights will place her an equal amount westtuard of her true position, introducing thereby a discrepancy of 8 ' of longitude between the morning and afternoon sights — though the sights themselves have been most carefully taken, and the ship has not shifted her position in the least. To pursue the matter yet further. If the sights were worked with the incorrect latitude obtained from the meridian altitude, still greater error would result. The latitude, from having been worked with an altitude too great by 8', would itself be in error that amount. Now by working the a.m. sights with too northerly a latitude. Error due tc the resulting longitude is thrown U' still further to the eastward j^correct a a '■ 1 • 1 latitude. — and in like manner, with the P.M. sights, the resulting longitude is thrown 1|' still further to the westward. It follows that an apparently trivial error of 3' in the position of the sea horizon can very easily introduce a discrepancy of IV in the longitude as shown by a.m. and p.m. sights. Ca,ses, sufficiently common, could be selected, depending upon latitude, declination and hour angle, where an error of 3' in the place of the horizon would cause the a.m. and P.M. longitude to dlHl-r as much as 15' or IG'. From the foregoing we see that discrepancy between forenoon and afternoon sights can arise from the latitude used being slightly incorrect ; al.so f rom abnormal refraction, from the course Error in and distance in the interval not being altogether what it was 5°"^" ^"'^ supposed to be, and from badly centered and graduated arcs, as well as other imperfections in cheap sextants. A RED SEA EXPERtENCE, Popular fal- lacy concern- Int afternoon si£hts. Abnormal refraction in Red Sea and Persian Gulf. When these causes all happen to conspire together (whicli must sometimes be the case), there may be a very great discrep- ancy between the A.M. and p.m. observations. Moreover, the navigator is apt to lose sight of the fact that he has Ciirried on his longitude by dead reckoning for (3 hours, say from !3 o'cloth of them directly in the track of steamers piussing up and down. Tiie distance between them is such, that if one group should be pa.s8cd about sight time in the morning, the other group will be pa.s.>(ed aU)ut sight time in the afternooat ' To Ivi'i'p \ip till' ti.i'litioiin of the m-i, 9oini< fvw incu am .■.till iu the batiit o; " iiiakiug the KUD over llio I'oroj'artl" aj loou a» "one bull " ii itruck ; wbicli ii«rba|M — acconliug to tlio amount of " iiortliiii); " in the grog — luu a teudoncjr to render them a little uncertain in their n)oTenirnt.i Inter on in the cl.iy. Itut there is aUsoIutely no cvi>lcnoe to shew that ateady " Old Sol" thinks ha h.vi earne miles. AND THE MORAL IT CONVEYS. 95 It w;V5 found on the outward passage, when sights were taken in the raoruiiig oft' the Zeba_yir group, that they were apparently Singular marked too far west on tlie chart ; and when similar observations seeming dis were made in the afternoon, the Hanish group appeared to be ^^^^^^"^^ '" shewn too far east on the cliart. This was a serious business, longitude, as the relative bearing of the two groups of islands was thereby materially altered. The question, moreover, was one independent of the con-ectness of the chronometers, as the islands were shewn relatively to be out of place some 7 or 8 miles. After a very careful discu.ssion of all the data in connection with the subject (including observations on previous voyages by other observers), the writer came to the conclusion, that in all probability the altitudes of the sun had been vitiated by excessive refraction. To test this, on the passage home, sights were again taken off" the Hanish Islands, luhich this time happened to he imssed in the morning, and similar observations made off" the Zebayir Islands, which were passed in the afternoon, thus reversing the conditions of the outward voyage. The result fully justified the writer's expectations, as the Hanish group were now shewn too far west on the chart, and the Zebaj-ir Islands too far east, while on the outward pa.ssage just the opposite had been the case. So that all this bother and uncertainty as to the relative position of two important groups of islands was unmistakably proved to be due in part, if not wholly, to errors of observation, arising from excessive refraction. In 1895 special attention was paid to Red Sea refraction by Lieutenant W. A. Marshall, U.S.N., of the U.S.S. Detroit, and this observer came to the conclusion that the effect of excessive refraction when taking the sun in the Red Sea is a more probable cause of departure from the beaten steamer track than cross currents. With the exception of meridian altitude, the Detroit was navigated solely by means of early twilight, dawn, and night stars. In an article signed Meteor (William Allingham) in the Nautical Magazine for Jul}^, 1895, attention was called to this matter, and the opinion expressed that masters will do well to be on their guard against either source of error. In the September number appeai'ed an article liy Captain W. H. Hood, a conuiiander of the highest repute, confirming this view. Either excessive refraction, cross currents, or both combined, led to the discovery of the Avocet Rock in the Red Sea by the loss of two steamers upon it. Lieut. Koss and Ensign Thun-Hohenstein, of the Austrian Navy, conducting observations near Pola for finding the variation in the dip of the horizon, observed on a quiet day MEIiCATOli'S CHAJiT CONSTRUCTIOy. Great caution a rise of tlie apparent horizon above its computed position of 8' 47" at a heiglit of 50 feet, ami of 9 23 at a liei£;ht of 3o feet necessary in above Watcr. lEatioo. These things point strongly to the necessity for great caution in the navigation of a 8hi|). Nothing " slapdash " should be allowed in connection with it, nor too much taken for granted \Vho can tell how many wrecks might be traced to this cause which at the time were ignorantl)' set down to some extraordinary 'jump" of the compasses, or some unlooked for current? Seamen would do well to give tliis important subject the attention it merits. CHAPTER Vll. en A UTS. A few words concerning the nature of Charts, and the difficulty of their construction, will prove both interesting and instructive to the seaman ; in any case, it is only right that he should know something about one of the most important of the tools with which he has to work. When we attempt to represent any considerable portion of the earth's surface on paper, we are at once met hy the formidable difficulty caused by its curved form. A little reflection w ill Difiicuity oi convince anyone tliat it is impossible to make a spherical surface Chart con- like that of our globe coincide cxactlv with a tint surface such ttruction. i » c as a slieet of paper. If an orange be cut in two, the inside scraped out of either hair, and an attempt then made to flatten the cup-shaped rind on the table, what would liappen ? It is certain that in so doing the edges would give way and tear up nearly to the centre, showing the impossibility of performing the feat with a non-elastic suUstance. It is obvious, therefore, that no representation of the earth on a flat sheet of paper, such as a chart, can exhibit all its parts in their true magnitudes and relative positions. In the construction of charts, it consequently becomes necessary to adopt such a method of laying down the places, which it is intended to depict, as will best fulfil the particular purpo.se for which they may bo required. The various methods adopted for this purjiose are called prujectiuns. Among them may be eiiume- MERCATOE'S CHART CONSTRUCTION. rated the Orthographic, Stereographic, Polycouic, Gnoinonic, and chatt Mercator. Of all these, the one commonly used by the seaman p™)^"'""^ is Mercator. It takes its name from the inventor, Gerard Kaufl'man, commonly known as Mercator (this being the Latin of his surname), who originated the idea about the year 1556; but the true principles of the projection — or, more properly speaking, construction — were not demonstrated till half a century later, b}^ Mr. Edward Wright, of Caius College, Cambridge. For other purposes than those of navigation, a Mercator chart The Mercatw is likely to be extremely misleading ; the meridians are all Chart drawn as straight lines perpendicular to the Equator, and at equal distances from eacl) other. The parallels of latitude, also, are represented by straight lines parallel to the Equatoi", and also, like it, at right angles to the meridians. The scale of latitude and distance at either side, instead of being unvarying, increases with the latitude until at the pole it becomes infinite. Hence in making measurements you cannot apply the dividers to any part of the margin at random. Altogether an extraordinary produc- tion when compared with the globe as we know it. Now, on the actual globe, the degrees of latitude are (practically speaking) equal to each other,but the degrees of longitude diminish as they recede from the equator, and converge to a point at the Varying Poles. For example : on the Equator a degree of longitude ^j'^ree^s of contains 60 nautical miles, in the latitude of London it contains longitude. 37i miles, in the latitude of 65" North (say at Archangel, in Russia) it contains but 25^ miles, and so goes on lessening in the higher latitudes, until at the North Pole it has no value whatever — which is equal to saying, that there longitude has no existence. An observer at the North Pole, let him face round as he may, could only look true South. There is no direction of east or west, by which to convey the idea of longitude, and the sun when visible would always be on the meridian. Since in the Mercator construction the meridians, as already stated, are equidistant in every part, and the degrees of longitude are everj-where made equal to their dimen.sions on the Equator; it becomes necessary, in order to preserve a due proportion between them and the degrees of latitude, to increase the length of the latter in a corresponding ratio. From the true proportions being preserved throughout between the meridians and the parallels, the shapes of the objects delineated on the chart are in every part Earths surface correct. But as the Icnqths of the degrees both of latitude and '^'<"''«<* '" ^ , , ° the Mercator longitude, at a distance from the Equator, are enormously ex- projection. .•1 PARADOX. aggerated, the sizes of the objects in those parts of the chart are increased accordingly : so that the whole map, if it comprises many degrees of latitude on one side of the Equator, gives a most inaccurate notion of the relative magnitudes of its northern and southern parts. For instance, looking at the Admiralty General Chart of the .ppe'a'ancet. North Atlantic, No. 2059, there will be found in Ungava Bay, on the north coast of Labrador, an island named Akpatok ; and to the southward of Cuba, in the Caribbean Sea, will be found the well-known island of Jamaica. Anyone looking at the chart, and unacquainted with the facts detailed above, would undoubtedly think these two islands were exactly of the same length, and would be conlirmed in this impression by actual measurement with dividers. But, following out the rule governing measure- ments on a Mercator Chart, whereby it becomes necessary to measure the dimensions of each object in its own parallel of latitude, it will astonish the uninitiated to find that the i.sland of Akpatok is G5 miles in length, while that of Jamaica is 130 miles, or exactly double. This e.xample will put the wary navigator on his guard not to trust to appearances without first thoroughly understanding the priiiciples which govern them. This defect in the Mercator Chart does not in any way detract from its utility for nautical purposes. Utility o, Its great advantage to the sailor consists in the fact that — Ist, Mercaiori the .sliip's course between any two places, however remote, is n«'ut'ic»r represented by a straight line ; 2ud, Uiis line malcet the same angle purpoiei iffitfi each meridian. Therefore, to find the true course (or rhumb line) on the chart from any one point to any other, it is only necessary to connect them by a straight pencil line, and mcjisure its angle with any one of the meridians which it crosses. This may be accomplished with a common horn protractor; or, us is more usually done, by transferring with a pair of parallel rulci-s the direction of the aforesaid line to the nearest true compass diagram, and so at once read off the coui-sc or bearing in points and quarter points. If this coui-se can be carefully preserved, the port bound to will in due time be reached. In the chapter on Great Circle Sailing it will be demonstrated that, in following up this sulject, there are other important matters to be taken into consideration by the man who wishes to subscribe himself, " Youi-s truly, A Master Mariner." This construction of Mercator is not exact in very high lati- tudes, because cross- bearings of several dL-stant visible objects CHART FOR POLAR NAVIGATIUX. which are in fact the same as Great Circle courses, are projected Mercators on the chart as straight lines, when they are in reality curves ; '-''"' '"«"<:' .... . 1° very high therefore their intersections will not agree ; or, three objects seen latitudes, in range will not, when projected in their true places on the chart, lie in a straight line. For this reason a Mercator Chart would not be suitable for Polar navigation. Indeed they could not be drawn by the dnxughtsman, since, according to the principles of the construction, the poles are at an infinite distance, and could not be shewn on paper. For unusually high latitudes the Gnomonic projection is employed. It assumes the e^'e to be at the centre of the earth, and any straight line di'awn on such a chart represents the arc of a Great Circle. Its use is limited to small circular areas such as the Polar regions. Near the boundaries there is a certain amount of distortion, but round about the centre of the chart it may be said that nature is correctly represented. From the foregoing it will be apparent that a Mercator Chart gives a very incorrect representation of the earth's surface ; but, of all the known projections, it is tlie one best adapted to the wants of the seaman, and has therefore, with the exception just given, been universally adopted for his guidance. To treat at any length of the other projections of the sphere — more especially the Gnomonic — would be to encroach on the province of the surveyor and of tlie map-maker, which is not the intention of this work.* For harbour plans the earth is considered Harbour a plane, and no account whatever is taken of its curvature, which would be quite inappreciable within the confined limits of such a survey. In the Orthographic Projection the eye is assumed to be at an infinite distance from the object, so that all hnes drawn to it may be regarded as parallel. If, then, from every point on the surface of the sphere, lines be drawn perpendicular to the plane of a circle passing through its centre, their points of intersection with this plane will be an Orthographic projection. It is obvious that eqital parts upon the surface of the sphere are seldom represented ore the plane by parts either equal or similar, since they diminish progressively from the centre to the circumference. The central portions of the map are shewn nearly in their true proportions, but the more distant parts are greatly distorted in form and diminished in size. This is exactly the reverse to what happens in the Stereo'jraphic Projection, where the central parts are unduly contracted as compared with the outlying ones. The Orthographic — except for certain astronomical purposes — is seldom used. • The Gnomonic is very clearly described in the late Admiral Wharton's Hijira- ra with a corn broom. The innate love of fairplay— sn strong a characteristic of Britons— will capsite any attempt to •' Boycott " the book, and inileeal the call for yet another edition in so short a time shews that the gentry in question may as well accept defeat and throw up the sponge, hot gri mat grl. HOW TO INTERPRET A CHART. 103 nature of bottom, accurately marked at regular and small dis- tances, is a credit to human ingenuity and a testimony of man's intelligence. On the large scale Harbour plans, the practice is Harbour pian invariably followed of giving the exact latitude and longitude of some well defined spot, and from this any other position on the plan can be easily determined by means of two scales — one for latitude and distance, the other for longitude. This comes in handy for rating chronometers by sun or stars, and for other purposes. The Admiralty charts and plans also give the meridian upon which the longitude depends; consequently, should that meridian at any time be better determined, the correction can be applied without further trouble. The longitude scale of Harbour plans is made as follows : — Assume the latitude to be 50°, and the scaie of dist- scale of the plan to be 4 inches = 1' of latitude or distance. To *"'^*- the common log of 4 add the cosine of 50° ; the nat. number of the resulting log will be the number of inches = 1' of longitude, namely, 2'571. You can check this by the Traverse Tables (Raper, page 511). Against 400 will be found 257'1, — shift the decimal two places to the left and you have it. Knowing this, any fellow can make a scale for himself if necessary. The value of a chart must manifestly depend upon the accuracy of the survey on which it is based, and this becomes more im- portant the larger is the scale of the chart. To estimate this, the date of the survey, which is always given in the title of Admiralty sheets, is a good guide. Besides the changes that, in waters where sand or mud prevails, may have taken place since the date of the survey, the earlier surveys were mostly made under circumstances that precluded great accuracy of detail, and until a plan founded on such a survej' is tested, it should be regarded with caution. It may indeed be said that, except in well-frequented harbours and their approaches, no surveys yet made have been so minute in their examination of the bottom as to make it certain that all chart indica dangers have been found. The fulness or scantiness of the soundings is another method of estimating the completeness of a chart. When the soundings are sparse, or unevenly distributed, it may be taken for granted that the survey was not in great detail. Blank spaces among soundings mean that no soundings have been obtained in those spots. When the soundings round about are deep, it may with fairness be assumed that in the blanks the water is also deep ; but when they are shallow, or it can be seen from the rest of the chart that reefs or banks are present, such blanks sliould be regarded with suspicion. This is especially ly^FORMATIOy CONVEYED BY A CHART. When danger shew them- Diflcrem turveys. Cholc<< of object! for b«atlni:«. the case in coral regions and oft" rocky coasts, and it should he remembered that, in waters where rocks abound, it is always possible that a survey, however complete antl detailed, may have failed to find every small patch, as with the Avocet Hock in the Red Sea. A wide bertli should therefore be given to every rocky shore or patch, especially in smooth wafer. Witli a good high swell, dangerous places are sure to shew themselves, and a hand aloft at such times maj' save the ship. In dealing with charts, the following rule should he followfd : — Instead of considering a coast to be clear unless it is shewn to be foul, the contrary should be assumed. Except in plans ni harbours that have been surveyed in detail, the five-fathom line on mo.st Admiralty charts is to be considered as a caution or ' danger signal ' against unnecessarily approaching the shore or bank within tliat line, on account of the possibility of tiie existence of undi.scovered inequalities of the bottom, wiiich nothing hut an elaborate detailed sui-vey could reveal. In general surveys of coasts, or of little frequented anchorages, the necessities of navigation do not demand the great expenditure of time required for such a detjiiled survey. It is not contemplated that ships will approach tlie shore in such localities witliout taking special precaution.s. The ten-fathom line is, on rocky shores, another warning, especially for vessels of deep draught. Charts wiu*re bottom con- tour or fathom-lines are not marked must be especially regarded with caution, as it generally means that soundings were too scanty, and the bottom too uneven, to enable tiiem to be dnuvn with accuracy. Lsolated soundings, shoaler than surrounding deptiis, sliouid always be avoided — especially if ringed round — as there is no knowing how closely the spot may have been examined, and mountain tops are occa-sionally fond of just stopping short of tlu' surface, a-s if they were lying in wait for the unwary. In approaching land or tlangerous banks, regard nuist alwa\> be iiad to the sade of the chart used. A small error in laying down a position means only yards on a big scale chart, wiiereas on a small .scale tiie same amount of displacement means largi' fractions of a mile. For the same reason, near objects should bo u.sed for bearings in preference to objects further off, althougli the latter maj' l>e more prominent, as a small error in beiiring, or in laying it down on the chart, has a greater effect in mis- placing tiie position in proportion to the length of the line to bi' drawn. A DIFFICULTY IN CHART PRINTING. 105 To be properly fitted out, a ship slioulJ be provided not only with large-scale coast sheets, but with plans of harbours intended to be visited. It sometimes happens from press of work that chart corrtc- only the copper-plate of the larger scale chart of a particular ''°°''' locality can at once receive any extensive rearrangement of coast- line or soundings. This is an additional reason, besides the obvious one of its possessing fuller detail, why the largest scale available should always be used for navigating. The printing of charts is responsible for a source of inaccuracy little known to sailors. The paper used in the process has to be damped, or the impression would be too faint. On drying, dis- Distortion c( tortion takes place, from the inequalities in the paper and the p^p*"'- amount and irregularity of the original damping. It must not therefore be expected that very accurate series of angles to different points will always exactly agree when carefully plotted upon the chart, especially if the lines to objects be long. The larger the sheet, the greater the amount of this distortion; but it is never so great as to affect navigation. The chart onaker takes care not to damp his paper, but it is one of his troubles that the atmosphere insists upon doing it for him. For really accurate plotting of the large triangles of a survey, the sides should all be calculated in advance, and the chief points laid down at one sitting, whilst the liygrometric con- ditions are the same. Our variable climate makes this a rather difEcult matter in practice. It is now pretty generall}^ recognised that on ocean charts the compass roses should only indicate the true points. All other sheets should shew the correct magnetic points, half points, and compass quarter points. These diagrams cannot be too plain and free diaerair.;, from ornamental devices. Where possible, their diameter should be 3 inches, but never less than 2i. The latest Admiralty pattern of compass rose is as recent as 1st January, 1912, on ami after which date Tkue bearings will be introduced in all Admiralty publications as soon as practicable. Outside of, and clearl}- separated from, the magnetic compass and circle, which i.s graduated in points and degrees from 0° to 90° in each quadrant, the Admiralty now places a true compass graduated from 0* (True North) to 360°, nieasuted clock-wise. The bearings of leading and clearing marks on Admiralty Charts will be given both True and Magnetic ; and a note to that effect will be placed on the title of each chart. Thus— 298° (N. 5i° W. Mag.) is self explanatory. Similarly, on the bearing of, say. AMERICAN COMPASS-ROSE. S. 40* \V. true, witli variation 12* E.. this information will be indicated as 220' (S. 28* W. Maj,'.). The modern navigator will, in this way, be able to disperse with N., S., E., W., etc., when setting a course ; and simply confine himself to the number of degrees from N., measureo better to do away with the murjnflic degree circle altogether. If degrees are wanted, let them be trur, and. to enable them to be read easily, the diameter of the circle should be four inches. Then, with an inner mugnelic compiuss rose of three inches — quite big enough — OLD-FASmONED COMPASS-ROSES. should there would be an intervening blank of half an inch all round, which would conduce to clearness of expression, and prevent pos- sibility of confusion. On the other hand, should the argument in favour of the horn or other protractor be accepted, we come back to the simple viag- netic compass-rose shewing points and quarter-points without circles of any kind. No doubt each kind will have its advocates, but the writer believes in simplicity. The -magnetic bearing or course may be wanted in a hurry, and Compass di. if so, a compass-rose divided to quarter-points cannot be beaten brdeara°n"d as things go at present. Tlie determination of the true course is simple. , . alwaj's performed with deliberation, and in the chart-room, where the graduated rolling parallel ruler or other form of protractor is at hand. In any case, the present Admiralty diagram is a vast improve- ment on the sj'stem which used to be in vogue with " Blue-back " charts when the writer was a youngster. The manner then ip which compasses, true and magnetic, got mixed up and sprawled all over the shop was something wondrous to behold. The ar- rangement could not have been better calculated to give rise to mistakes at critical times — indeed, the writer has known it to do so. The vessel referred to got on the rocks a few miles to the eastward of Queenstown, but luckily bumped ott' again without springing a leak, though her bottom was dented in like an old tin pot. The skipper was on the bridge, using a chart with a Elaborate aia compass compared with which a spider's web was simplicity itself. ^"""^ As might be expected, he got confused with the jumble of lines, and ashore she went. The writer was on the after-wheelhouse at the time, and the first .bang sent him flying down on top of a pompous-looking passenger, who, no doubt, would remember the ' regrettable incident ' for quite a long time afterwards. Coming to the subject of " Blue-back " charts, a great draw- l>ack is the absence, in many instance;;, of the heights of mountain ranges, peaks, hills, islands, and lighthouses. These are all of great assistance in navigation, and no chart is complete without them. Lighthouse heights, when not on the chart, can, it is true, be got from the lighthouse-book, but it is more convenient to have them on the chart. Admiralty charts can be backed with " brown holland," which, Holland back- so far as the material is concerned, makes them last almost for s^^j"^^^*,'' ever ; but it increases the expense, and, seeing that some sheets >n special are continually having alterations made in them, according as the Trade Notice. 108 ffOir TO BACK CHARTS. banks and channels shift about, it is not advisable to resort to backing.* It gives them a dangerously permanent character. Except, perhaps, for tiie smaller class of vessels, wlicre the Captain buys his own charts, the unwieldy "blue-back" has had its day, and it is only a que.stion of " How long ? " until it is Scale of superseded by the cheaper and handier productions of the Admi- Biue-Backt. ralty. As a result of trying to make them suit all purposes, the scale of the blue charts is, in general, too large for ocean navigation, and not large enough for coast work. In case an Admiralty sheet should be destroyed by the cap- sizing of an ink bottle, the spilling of lamp oil, or any of the accidents which do happen, it is merely a loss of from one to five shillings; whereas, when its rival comes to grief, it cannot he replaced under from ten to fifteen shillings. Moreover, the extra coat of the latter offers temptation to keep it in use till completely out of date, and so marked and smudged as to be in many places illegible — a circumstance likely to lead to di.saster, if indeed it has Board oi not already done so. The Boai-d of Trade has lately become verj' particular on this point, and one of the official notices directs the attention of shipowners, and their servants and agents, to the nece.''sity of seeing that the charts taken or sent on board their v\nYi9. are correrteiT'^omx to the time of sailing. Acourtof imiuiry into the loss of the British sailing ship G. IK. U'o/^'counnented severely upon the fact that the navigating charts wlmc not acces- sible to the officers, and expressed an opinion " tlnit masters of sea-going ships should be compelled l>\' law to hMT.u the chart by which a vessel is being navigated accessible at all times for refer- ence by the navigating officers." This does not stand alone. With the Admiralty chart the sailor can see at a glance if he has the latest information. The year and the month of the various corrections are engraved at the foot ; should the cor- rection be large, the notntieing economi- cally (?) navigated near land by small scale charts, wiiich ainnot possibly shew coa.st dangers. Wliarton,* in alluding to the increasing necessity for large jcalc charts constructed from detailed surveys, says: — " A steamer works against time ; her ptiying capabilities largely depend on her getting quickly from port to port, and captains will take * Uydntrapkical Surveying, f»fe 63. UXDISCOVESED COAST DANGERS. every practicable short cut that offers, and sliave round capes and cutting ofi corners in a manner to be deprecated, but which will continue as '"'•""sia long as celerity is an object. A channel which a sailing vessel *'"^^''°" will worii through in perfect safety, from the obvious necessity of keeping a certain distance off shore, for fear of failintr wind, missing stays, &c., will be the scene of the wreck of many a steamer, from the invetei-ate love of shortening distances, and going too near to dangerous coasts only imperfectly surveyed. Better charts will not cure navigators of this pi-opensity, but will save many disasters by revealing unknown dangers near the land." The late Admiral Wharton might have added that this "short cut navigation " is not only due to fierce competition in trade, but unfortunately to an unwise rivalry among seamen themselves, and an utter disregard on their part of the maxim "Let every man steer by his own compass." Because Brown and Jones do certain things which look very like putting tlieir heads in tlie fire, Robinson — even against his better judgment — thinks he must do the same, and so the thing goes on till the weakest comes to the wall. Charts and Sailing Directories are as much part of the ship's Owners equipment as the Compass or the Lead, and should be provided ^j^^ chart* by the owner. When the captain has no longer to pay for them, he will keep a better stock, and not take his ship all over the world by one or two general charts, to the manifest risk of life and property. Mr. Henry Maclver, a Liverpool shipowner, so long ago as 1885, in a letter to the Times, pointed out inter alia that "reliable charts and chronometers are more conducive to safe navigation than lifebuoys, foghorns, and the other para- phernalia to which Board of Trade surveyors devote so much attention, and owners .should be compelled by law to furnish their vessels with all that may be required." Many shipowners, he said, " required their masters to provide both charts and chrono- meters, the latter have to economise by reason of small salaries, and accidents frequently happen in consequence." In Appendix (P) will be found the signs and abbreviations adopted in the Admiraltj^ charts. One more " wrinkle," though a simple one, for which the writer is indebted to Captain Matt. B. Walker, of South Shield.s. pencu>. Use hexagonal pencils ; they won't roll off the table like round ones, and are just as cheap. Common sense.* • Triangular pencils are still better calculated to remaiu where they are told. GHAl'TKR VIII. Field'! Improved Parallel Ruler How lo use It THE PARALLEL U U L E R. TIlis, in its coiniiionust form, is an instrument so very familiar to tlie seaman, and withal so simple in itself, that it may seem ratlier absurd to refer to it; nevertheless, there is something to be said even about the parallel ruler, and it may so happen that that something — or a portion of it — ma^' be new to the reader. The ordinar}' black ruler, with bnuss joints, is usuall\- employed to transfer the direction of a bearing or course to the nearest compass diagram on the chart, whereby to ascertain its name and valuo. Now, in ocean charts, where compjiss diagrams are very properly few and far between, a great deal of slipping and sliding, and trying back, as well as "smudging" of the chart, may be saved, and much greater accuracy ensured, by the use of a kindred instrument, known eis"Ciyptitin FirhVs Tmpmird PnroUi} Ruler." Apparently, at first sight, it only differs from the other in being made of boxwood instead of ebony ; but a closer inspection reveals that one ot its edges is divided into degrees, similar to the (J-inch ivory protractor found in most small cases of mathe- matical instruments ; the opposite edge is also divided, but in points, half-points, and quarter-points; these latter, however, arc never likely to be used, as the degree marked side of tlie ruler is preferable. The advantage derived froni this instrument is, that by laying it down on the course you wish to detcnnine, so that its centre imtrk ."hall Im on a meridian line, you at once read oil' the true cour.se on the divided edge, where it is cut bij the aforesaid meridian line. TEST FUR ROLLING PARALLEL RULER. 113 Few things can be neater or liaudier in practice, and it gives the course in degrees (and by estimation, to parts of a degree), with au accuracy but little short of that obtained by actual com- putation. The ruler is to be had in three sizes ; but the two sue of Ruier. smaller ones, from the minuteness of the angular divisions, are not to be recommended. The 2-4-inch ruler will be found vei-y convenient, and the marking clear and well defined. After it has been in use a little time, get it cleaned and French-polished. This is one of the manj- things wliich have been improved upon. The improvement consists in discarding the points on the lower improvement edge, and substituting the centre-mark of the depree divisions. Bv °" ^"'''' ^ . P ^ . . . ^ "^ improvement. this means the short radius is just double what it was before, and the divisions at the middle of the ruler are in consequence much plainer. You must take care to keep this new form from warping. When shut, the two parts must fit as closely together as they did when being graduated. Even better than the above is the graduated rolling parallel ruler. On shore this has been in use for ever so many years, but it is only of late that it has found its way on board ship. Of all the means for determining courses or laying off bearings this is about the quickest. Since only the rollers touch, it has the fur- ther advantage of not soiling the chart so much as the jointed ruler, which is in contact over its whole surface. To work truly, the rollers must be exactly of the same diameter ; this is easily Graduated tested before purchase. Carefully set the further edge of the •'""'"b ruler to the bottom marginal line of a chart ; run the ruler nearly up to the top, and draw a tine pencil line along hoth edges. (In passing, let it be noted that it requires a practised hand to rule a perfectly straight line ; the pencil must be held at exactly the same inclination throughout.) Now shift the ruler end for end, set the further edge to the bottom line as carefully as before, and roll up within an eighth of an inch or so of the top pencil line- Draw two more pencil lines along top and bottom edges re- spectively, and the thing is done. The eye will decide in a moment if the upper pair of lines are parallel, as tliey should be> if so, then the rollers are equal. Next examine the lower pair of lines; if parallel, then the two edges of the ruler are parallel, as they should be. A good instrument-maker will see to these matters for the sake of his own reputation; nevertheless, it is satisfactory to try for one's self. Of course the chart or paper must be laid on a flat surface. The mahogany top of a chart- table, when the wood is well seasoned and the ends strongly u Th« Horn Protractor. 114 UOIiS I'KOTRACTOH AND STRAIGHT-EDGE. clamped, should remain a.s flat as the day it left the joiner's bench. The gi-aduated rolling parallel ruler is, at prescut. a trillo more expensive than its brethren. The ordinarj' parullol ruler, or indeed a straight-edije of any kind, when u.sed in conjunction with a common semi-circular horn protractor, will give satisfjiction to the less fastidious. If j'ou have not a horn protractor, it can be procured for a shilling or two at any optician's. Do not get one with a less radius than 3^ or 4 inches, which is a good serviceable size. To use it, proceed as follows : — Having the chart on the table, with its north side from yim as u.sual, lay the straight-edge over the course you wi.sh to steer or determine, and place close against it (edge to edge) the horn protractor, sliding the latter along (its straight side being always in contact with the ruler) till its centre mark comes fair over any meridian line on the chart ; the e.xiict true course in degrees and half degrees will lie found at the circumference, where the latter is cut by the same meridian line, thus: — r -\' How to fit and 11 le It. In thi.s particular case it is N. 70' E. or S. 70' W. (true). Almost ever}' one going to sea abaft the mjust has a giniter's scale, which would answer fii-st-rato with the horn protractor in the manner just de.scribed; but if there should not be one, and the parallel ruler be broken or last, any lath or piece of wood, dressed straight with the carpenter's trying-plane, would do just as well. The horn protractor can, however, be rendered of eijual service wilhoid any kind of straight-edge, by the simplest possible con- trivance. Bore a tine needle-hule at its centre mark, and another about a (piarter of an inch or so below it ; through these two holes reeve a couple of feet of sowing cotton (silk is better), and knot one HORX PROTRACTOR AND STRING. "5 end ; keep the knot on the to}? side of the lower hole, so that it may not prevent the protractor from l^'ing flat on the chart, and bring the other end up through the puncture at the central point, and haul it tight. To ascertain a course or bearing, it is merely necessary to lay the iiorn protractor with its zero line on any convenient meridian, sliding it towards the north or south, so that the thread when stretched may lie exactly over the two positions on the chart between which it is required to know the course, thus : — In the diagram, A represents tlie knotted end of the thread ; B, the centre hole through which the thread conies up ; EF, the zero line of the protractor, laid exactly over GU, a meridian line; CD, two positions on the chart between which it is required to know the course ; the line ^J6'i)Z represents tl'.e thread. The true course (N. 80° E. or S. 80° W.) will be found at J, where the margin of the protractor is cut by the thread. The oblong ivory protractor already mentioned could be used in obiong ivory a precisely similar manner, but the horn one has the advantages '^'° "' '"'■ of transparency and larger marginal divisions. Both are divided from zero at E and F up to 90° at the middle line, and when usincr them in the manner indicated above, the course is in each case to be reckoned from North or South towards East or West, as the case may be. Hughes' Radiograph and Gust's xylonite ^^^^'^^f '"""' Station Pointer, in addition to their more legitimate uses, serve the purpose of a horn protractor. Owing to its tendency to buckle, the horn protractor should be kept between the pages of a heavy book when not in use. Xylonite (celluloid) is a better material tlian horn for transparent protractors. IViiUY ASI) BOXWOOD VltOriiACTOliS. and compasf cours^^ Deviation and local attraction As already explained in a previous chapter, the course hetween any two places on a Mercatoi- chart is the angle which a straijhl line connecting them mahea wiVi the meridian. Here seems a pood place to say a few words about Courses. So far, reference has merely been made to the tvit^ court^f. When the variation has been applied it becomes the magnetic course; and when the Deviation has been npplieil to this last, it becomes the compass coui-se, or the one which is to be actual!}' steered bv that particular compass for which the deviation has been allowed. The navigator will do well, then, to bear in mind that there are — 1st, the Ti-ue Course ; 2nd, the Magnetic Course ; and 3id, the Comi>ass Course. The t)-ue course is the angle which the ship's fore-and-aft line makes with the Geographical Meridian ; the magnetic course is the angle between the ship's fore-and-aft line and the Magnetic Meridian ; and the comjMss course is the angle which the fore-and-aft line of the ship makes with the direction of the Compass needle on l>oard. One word about Deviation. It is too often mixed up with Local Attraction, the two expressions being used indifferently to mean the same thing. This is wrong, as thej' arc entirely distinct The first named is due to causes within the ship herself, the latter, to outside influences. Remember this. For laying off courses as above, the writer had made to order an ivor}- protractor, 10 inches by 3 inches. This size admits of good large divisions, but it is expen.sive. A similar one in box- wood would cost less, and probably be practically as good. The only thing that can be .said against box-wood is its greater liability to chip at the edges.* Ebonite scales nnd protractors are found to answer well, though they expand and conti-nct .slightly with change of temperature, l>ut this extreme refinement is a thing apart from our .subject, and need not be considered. •A l>ox-»oo iMtlier, co.itiog p«ihai>i 2m. tid. CHAPTER IX. To give a "natty man" satisfaction in their use, dividers should be of good quality. The "points must be fine, and formed . of well tempered steel that cannot be bent or blunted. Above all, steei points the joint should be good, for if not, it will be provokinoflv difficult "'' •'°°°"' , , . 1 ,. ^ f woi king joints to set the legs to any required distance, on account of the spring and want of uniformitj' in their motion. A pair of dividers witli an indifferent joint, when being opened or closed, will move by fits and starts, and either go beyond the measurement required or stop short of it. The joint .should also be stiff enough in its action to hold the legs in any required position without fear of alteration when handled with ordinary care. These are the things which require to be tested when making a purchase. Instrument cases always contain a key for tightening up the joints of the dividers when they work slack. What are known as Hair Dividers give Hair Dividers very exact measurements, but for sea use they are too good, and too costly. It is convenient to have a small bracket fastened on to the Bracket (or bulkhead over the chart table, to contain two pairs of dividers — large and small. Screw a piece of poli.shed mahogany, S inches long by 3 inches broad, and f inch thick, flat against the bulk- head. About two-thirds of the distance from the bottom insert a couple of bi-ass eyes side by side. The dividers may be shipped into these, and their points rest on a f-in. ledge or shelf, forming a foot to the bracket. This shelf should have a moderately tliin piece of india-rubber let flush into its upper surface, as a bed to receive the points without injury when dropped hurriedly into their place. To a landsman all this may seem needless trouble, but the sailor knows the value of the maxim — " A place for every- thing, and everything in its place." Moreover, a ship roils and tumbles about in all directions — a house does not ; so that afloat it is absolutely necessary to have safe places of deposit for other things besides glass and crockery. SPIilAG r£.\ AXD PESCIL HOLDER. Pen and There is a very neat little American " dodge " for holding pens, pencil rack „Iiich Can be purcliased in Liverpool for a few pence, and is very useful. It consists of a spiral spring secured to a thin hack plate, and the whole is gilded, and looks iiuitc ornamental. The pen is held between any two parts of the spring. One of these ingenious little contrivances will contain four or live pens or pencils. It i.s secured to the bulkliead by a small screw at top and bottom. DIVIDERS FOR DSB WITH ONE HAND. When a .ship is rolling violently, and it becomes neces-sjiry to consult a chart, every seaman is aware of the difficulty ex- perienced in keeping the chart and parallel ruler on tlie talile with one hand, whilst with the other he is trying to manipulate the dividers. Some clever fellow, who has evidj.'ntly been pretty oftin in this ti.K, lias invented a pair of dividere/or use with one h'Uul, wliicli are wortliy of coming into general use. They were fii"st shown to the writer by the captain of a schooner-yacht on the Clyde, who claimed to be the inventor. Tlio diviik-rs are represented above, and it will he seen that they are opened by a pressure of the palm of tlie hand on the circular part, wliicii causes the legs to overlap eacli other and the points to separate. The closing movement is readily controlled by the thumb and forefinger, which, for this purpose, act against the palm pressure. A.s they are unpatented, they can bo onlend from any instrunient maker, and can lie made with any degree of finish " to suit t/if pockrt " of the purchaser. CHAPTER X. THE PELORUS, WITH REMARKS ON AZIMUTHS. This valuable instrument, the invention of Lieut. Friend, R.N., deserves more than a mere passing notice. Its utility is so great that every iron ship should be provided with one. The Pelorus is a dumb card — that is to say, a compass card Dumb card. without needles — made of brass, entirely unmagnetic, and not par- taking in any way of the character of a compass, except that its face shows the points and degrees in the usual manner. The card is something less than 7 inches in diameter, and is mounted on gimbals, which, in conjunction with a central balance-weight suspended from the under side of the instrument, enables it to preserve its horizontality, whatever the motion of the ship may be. The card revolves on an upright pivot like a " teetotum." This pivot also serves to carry the sight vanes, which can revolve upon it independently of the card, or can be secured to it at pleasure by a large railled-headed screw surmounting the pivot. One of the uprights of the sight vane is fitted with a thread, and Description has a hinged mirroi- or speculum at its base, and the other has a coloured eye-screen, which is made to slide up and down the bar at will. A fore-and-aft mark on the inner ring does duty as the lubber's point or ship's head, and another smaller milled-headed screw on the fore part enables the card to be clamped to this mark at any desired course without fear of shifting. The whole thing is so simple, that anyone looking at it can understand the arrangement in less than five minutes. The apfraratus is enclosed in a mahogany box some eleven inches square, and from which it is inseparable. The patent-right having long since expired, the instrument is now constructed to order by almost any compass maker at a cost cost. of about £3 10s. It is an improvement to have the card 9 inches in diameter. Having a Pelorufl, the first thing is to provide .suitable stands I20 STAXDS FOR PELORVS OX UPPER DECK. Stands for for it in various parts of the ship, so that it may be moved Peioniv from one to the other as may be found convenient Sometimes at one position a sail, the funnel, a mast, or an important passenger, may lie in the way of the body to be observed, in wliich case the Pclorus can be removed to anotiier spot where tlie view is unobstructed. It will be found advantageous to fit at least four such stands — oue on each side of the bridge, and a couple in the neighbourhood of the quarter-deck. A skylight, the top corner of a deck-house, or a meat safe, will answer the purpose very well. The sUinds on the bridge may be made in the form of a small table without legs, to bi-acket against the handrail. Some men go to the expense of a couple of turned teak-wood pedestals. The pliices selected need not be amidships — in fact, they are better when not so; but, wherever they may be, it is absolutel;/ Cire In piae- necessary that great pains sliould be taken to ensui'e the fore-and- '"' S""''' (J^Jl ii,jg QJ (f,c instrument being strictly parallel with tlie ship's keel. To effect this with certainty (the instrument being in its How to do it. intended position — say on the starboard or port side of the bridge), measure carefully the horizontal distance of its centre from tlie midship seam, and lay ott' this distmce on the ileck boUi at Ote boiv and stern eiul of the vessel. At each such place erect a batten, and see that it stands perfectly plumb ; tlie ship herself i.s, of course, supposed to be on an even beam ; then set the North point of the card (though, any other will do just as well) to the lubber line, and clamp it there by the small milled- headed screw at the fore side ; release the sight vane, if clamped, and turn it so that the centre mark at the base of the upright holding tiie thread may also coincide with the North point; place the box by eye approximately .square with the fore-anl«s. independent of everything else, since you can, if you are smart, use it ii-s tlie distant object. The sun's bearing will seldom alter 80 much in the minute or so required to shift the instrument quickly from one place to another, as to introduce any appreciable error ; but if extreme accuracy be required, it is an e;isy matter to get the exact chanije of bearing corresponding to the Latitude Declination, and Apparent Time from Burd wood's Tables. The Pclorus is handy for many purposes whicli will l>e referred to hereafter, but its chief use is to ascertain the Deviation of the compass, or to set the coui"se. Before going into the details of how this is to be done, it will perhaps be advisable to say some- thing about Azimuths. The general practice on board ship is L) oViserve an azimuth or bearing of the sun by compass, at the same time that the morning sights are tiiken : the sun's altiliule, as found by these sights, is used to find the true ai'.imuth. This is li round-about method, involving much needless labour, and should be abolislicd now that tables are published which give by simple inspection the required information. It will be made clear further on, tliat in an iron vessel the Deviation requires to be determined pretty frequently ; and to be constantly getting out one's sextant to " shoot the sun," and after- wards take the bearing, and then work up a lengthy problem, is not conducive to this end. Half the trouble and all the fuss may be avoided by using the method wherein the time, instead of tlie iiltitiulfl, is employed. This is called the method of " Time .Vzinniths;" therefore, when, according to common cust<-)m, an azimuth is taken along wit]i the morning sights, instead of labori- ously figuring out the sun's true bearing by the altitiule-azimidli problem, the hour angle (time from noon) found by the .sights can be employed to take out the true bearing direct by inspection. AZimXTH TABLES. Now that iron and steel have almost entirely superseded wood for shipbuilding, good Azimuth Tables are as necessary as tlie compass itself. In ISGO, StifF-Conunander Burdwood, ll.N., published a book entitled : " Sun's True Bearing, or Azimuth Tables," in which is given the siui's true bearing at intervals of i minutes for e»ich degree of latitude between (JO" and 30 in both hemisphere.s. In 1875, Captain Davis, RN., brought out an extension of these tables down to the Kquator, so tliat at the present time the sun's true bearing can bo taken out from those lx>oks for any latitude ADVANTAGES OF AZIMUTH TABLES. 123 between 00° north and 60° south, ami for any time between sun- rise and sunset excepting xvhen the altiude exceeds 60'. In 1896, Mr. H. B. Goodwin, M.A., R.N., published Azimuth Tables for the higher declinations (24° to 30°) between the parallels of 0' and 60\ There arc still, however, a few prejudiced enough to believe Time azimuth that the " old-fashioned plan," as they call it, is preferable to the p"'"^^^^ *-° 1 111 mi ^"- "'"""""S tables, as the latter, in their estimation, are liable to error. These are the men who insist upon their officers working up azimuths according to the " Epitome method." They forget, or do not know, that in all calculations the greater the number of figures employed, the greater the liability to error ; and surely trained computers are less likely to make mistakes than seamen, who, by nature of their calling, are not nearly so well versed in such work. During the long series of years since their publication, not half-a-dozen errors have been detected, and the Tables may now be looked upon as immaculate. By glancing the eye up and down the column, and across the page to the right and left, a mistake of any importance is detected in an instant by the want of harmony in the run of the leading figures. In working out any problem in navigation, one might just as well refuse to employ the ready-made tables of secants, sines, and tangents, 'and insist upon computing for one's self the necessary logarithms for each particular case. Burdwood, in his preface, says : — " Results exhibited in a tabular form have certain advantages. ^^^^^^ ^^^ In these tables, for example, the value of an error in either of the preference three elements used in the computation is seen at once, and hence the most desirable time for making the observations, so that an error in either the Apparent Time, Latitude, or Declination, shall produce the least error in the true bearing." To use these tables, it is necessary to know the Latitude and Declination each within half a degree, and the Apparent Time at Ship within, say, a couple of minutes ; but this latter depends upon circumstances, as reference to the tables will show that, under certain conditions, the sun's bearing will not alter one degree in an hour, and at other times it will alter a degree in three minutes. Herein, as Burdwood justly say.s, lies one of the great advantages of the tables. In nautical literature, the greatest amount of competition has been in connection with the most ready means for determining the Azimuth. The navigator has consequently his pick of UNPOPVLAniTY OF DIAGRAMS. Methods, Tables, and Dia£»rams sufficient in number to sink a ship. Excellent Azimuth Diagrams are occasionally given on the backs o£ the United States Pilot Charts with accompanying letterpress. CAPTAIN WEIR'S AZIMUTH DIAGRAM. Lord Kelvin, looking at it from a mathematician's point of view, considers it about the neatest thing of its kind ever pro- duced, and wonders that it had not suggested itself before — apparently a repetition of Columbus and the egg. The process of taking out the Azimuth — the Latitude, Declina- tion, and the Hour-Angle being given — is simple and quickly done. With ordinary care, the small error inseparable from the use of diagrams will not in most cases exceed half a degree, and this is not worth consideration ; but there are ca.ses involving the centre of the diagram where the lines run into confusion, in which the error might possibly amount to a degree or a little more. These cases being confined to low latitudes and large hour-angles, would not occur every day, and on certain routes would never occur at all, so that exception to the diagram cannot ju.stly be taken on this score. The writer, however, is not in love with mathematical dia- grams of any sort, and least of all with one for this particular purpose. Azimuths in well-conducted vessels are taken fre- quently, and where the same diagram is worked upon with pencil and ruler day after day by several otlicers, it soon gets played out. Officers' cabins are small ; their table, even supposing they have one, is smaller; and diagrams which require a good large table upon which to spread them out fiat and leave space at tlie margin for parallel rulei-s, do not find favour with the average merchant officer, who seldom liivs room enough for iiimself and kit. e.speciall3^ when two are billeted in a cabin measuring at mo.st G feet by 5. Whatever the cau.se, experience proves that, where it does not involve more time, the pn-ference is given to calcula- tion. Weir's diagrain is 30 by 21 inches, and should be kept Mat, not rolleil. APPAKENT TIME AT SHIP. Though the tiuding of the Apparent Time at Ship is a simple operation, yet few know the right way of doing it; therefore it is a.s well to give a couple of examplea It is premised that the longitude is known within a qujirter of a degree or so. DAILY HETTISG OF CLOVKii. 125 Write down the error of chronometei-, prefixing the plus ( + ) to find sign it' it is slow, or the mhnis ( - ) sign if it is fast. Apparent Write down the Equation of Time taken from page II. of the and set Nautical Almanac, and correct it roughly for Greenwich Mean p°'=''*' "'*''^'' Time. If the precept at the head of the column says the Equation is to be subtracted from Mean Time, prefix the minus sign ; but if to be added, prefix the j^l^s sign. Turn the longitude into time, and if it is westerly, prefix the minus sign; if it is easterly, prefix the plus sign. If the three quantities should happen to have similar signs, add tliem together, and prefix the common sign ; but if the quantities should happen to have unlike signs, add those of similar sign together, and take the difference between their sum and the unlike quantity, prefixing the sign of the greater. This remainder will be the amount, which (to find Apparent Time at Ship) is either to be added to or subtracted from the chronometer time, according to its sign. Example : Jan. 16th, 1880, about 10 hours p.m., at Greenwich ; required to know the Apparent time at Ship, the longitude being 64° 38' West, and the error of the chronometer 4m. 22s. slow of Greenwich Mean Time. H. 51. s. Ijongitude, 64° 38' W - 4 18 32 ] Having like signs, add tliem Equation of time - 10 3 / together. - 4 23 35 I Having unlike signs, take the Error of chronometer + 4 22 ( difference. Chr. fastofApp. TimeatSliip - 4 24 13 Therefore, to find Apparent Time at Ship, it will merely be necessary to subtract 4h. 24m. 13s. from the time shown by chronometer. To set your watch or clock, fix upon a given Time, a minute or so in advance of what the chronometer actually shows, to enable you to prepare ; let the time by chronometer at which you intend to regulate your watch be lOh. 26m. 13s.; subtract from this 4h. 24m. 13s., and 6h. 2m. Os. will be the Apparent Time at Ship when the hands of the chronometer arrive at lOh. 2Gm. 13s. This matter of setting the wheelhouse and other clocks to Apparent Time at Ship is such an every-day necessity, that we will give one more example. In this ca.se the longitude is East, and the Equation of Time and chronometer error are both additive. 126 T/.Vh-AZlJifUn/S. Exam. 2 : September 24th, 1880, about 4 p.m. at Greenwich ; required to kuow the Apparent time at Ship, the longitude being 17" 40' East, and the chronometer 8m. 258. slow of Greenwich 'Mean Time. Longituao Y" 40- E +"l 1o 40 ^ Having like signs, »re .11 Equ.atioii of time + 8 16 >. = .jjn„» Error of cbronomiter + 8 25 j tddilivo. Clir. slow of App. Time at Ship + 1 27 21 Here we have Ih. 27iii. 2is. to be acMcil to tlie clironoiueter time ; 8o, to imike the even minute for the scutch, let us fix upon 3h. 54iu. 398. by chronometer; adding tlie above correction to this, we get oh. 22ni. Os. a-s tlie Apparent Time at Ship when the hands of the chronometer arrive at 3h. 54m. S9s. It will be noticed in both the.se examples that, in choosing tiie chronometer time at which to regulate the watch, the proper number of odd seconds has been allowed, so that the watch may be set to the even minute without tlie trouble of counting second.s, or of estimating them wlien there is no second-hand. The following example .shows the mode of ascertaining the deviation by using Burdwood's azimuth tables : — TIME-AZIMXJTHS OF THE SUN. Saturday, January ITtli, 1880, about 0"45 J'.m., the sun was observed to bear by Standard comjuLss S. 15° W., when a chronometer, which was 4 m. 23s. slow of Grecnwicii Mean Time, sliowed 5h. 29m. SOs. ; latitude by account, 40*" 12' North; longitude by account, 70° 60' West; \-ariation at place of ship, corrected for secular change, - 0A°. Here, be it undcrstodl, that E.xsterly variation or deviation is always represi'nti'd hf the plu8( + ) sign, and Westerly variation or deviation by the minus ( - ) sign. Time by chronomctor S li'J 30 Chronometer slow of Q. Me«n Tim* + 4 23 Greenwich Mean Time 5 33 5.'1 Corrected E<|ua. of Time, page 11., N.A. ... - 10 19 Declin.ilinn corrected for Cireenwich Mciin Time, 20° 46 South. Apparent Time at Greenwich S 23 34 Longitude in time ... - 4 43 20 Apparent Time at Ship 40 14 r.u. Open Burdwood at the nearest whole degree of latitude (40") having the declination of the contrary name; this will be found at page 109. In the right-hand margin .seek for Oh. 40m. p.m., ami under 21°, the nearest whole degree of declination, will be found the sun's true l>oaring 1C9A°, which, according to the precept at the foot of the left-hand page, is to lie reckoned from North tti West i APl'LICArWN OF VARIATION AND DEVIATION. la; The work now takes this form : — ®'s True bearing .-it Ob. 40iii. p. M. ... N. 169^° W. ISO" ®'s True bearing with name changed ) S. 10J° W for couveuience J q.o a. i i. .1 ■ u. V,iriatiou by chart " *^ Applied to the nght. -,,,,..,. „ ono \\j * '^'■' "hat it would be in a wooden ® 3 Magnetic hearing S. 20" W. , ship uninfluonced by iron i)'.i Bearing by compiss S. 15'' \V. r, . ,. , ,0 ( Because the mag. bearing is to tlie l^^^i"'"'" +» \ rijA* of the compass bearing. It will be noticed that in applyintjf the variation to the sun's '"'erpreta- true bearing, it is added (because Westerly), although the minus !|?" ^' • ( — j sign is prefixed. The minus ( — ) sign in this case is only s-eus. the navie of the variation, and does not mean that the quantity following it is to be subtracted. The deviation is + 5°, which means, in like manner, that its name is Easterly. In finding the tnagnetic bearing from the true bearing, stand in imagination at the centre of your compass-card, looking out- wards towards the margin, and upply westerly variation to the right, and Easterly to the left. To find the covipass course from the magnetic course, apply the deviation in exactly the same manner. TIME-AZIMTJTHS OF THE STARS. Although Burdwood's and Davis's Tables are termed " Tables Azimuth of the Sun's True Bearing or Azimuth, " they may, notwith- '^'''" "pp"" " _ •' *' cable also to standing, be made available for determining the true bearing of Moon and the moon, planets, and stars, when the declination of those stars. bodies ranges between 23° N. and 23° S. On next page is a table of the mean places of stars of the 1st and 2nd magnitude included within that range for January 1st, 1902. In 1897 the ABC and D tables (given further on) were so niiicli enlarged that separate publication became necessary. They now afl'ord a very ready means of determining the Azimuth not only of Sun, Moon, and Planets — whatever their declination — but of any of the 92 na\igational Stars they refer to, thus constituting a material advance on anything yet produced in the way of Azimuth Tables. But they go much further, for this publication also contains rules and examples for the speedy solution of about a dozen other problems of everyday use. • • ■■ Ucky's General Ulilily ADC and D Tables." London : G. Philip & Son, Ltd., 32 Fleet Street. E.O. Liverpool : Philip, Son & Nephew, Ltd., '.XJ Church Street STARS FOK liUUDWOOI) ASO DAVIS. Inter-tropical stars for Asimuth. Meaning of + and — signi. Star- Ailmutlii A'lvantagcsof Sur- Aaimothi ever m Namks. Right As V .lUAL AKU- Declinition. A.N.MUU Varii- a.s* H. H. t:. S. Q ' It •11 /SCetL (DenebKaitos) ... 38 40-25 + 3-01 18 31 27-81 S + 19-80 2-0 'o Arietis. (Hamel) 2 138-SO + 3-37 22 59 57 -12 N + 17-U 1 a Tauri. {Aldebaran) ...... 4 30 17-77 + 3-44 16 18 44-!)«N + 7-46 0-3 1-S (S Orionis. (Ri>iel) 5 9 49-66 5 31 14-43 + + 2-88 3-04 8 18 52-09 S 1 15 51 -30 8 + 4-35 1 Orionis. (Alnilam) + 2-51 2-2 'K Orionis 5 43 6-52 + 2-84 9 42 15-29 S + 1-47 Var.'o Orionis. (litlelyuesir) 5 40 51-97 + 3-25 7 -23 -JO -42 N + 0-89 2-0 \y Geininorurii. {Alhena)... 6 32 3 06 + 3-47 1 6 28 59 --'7 N - 2-84 - l'4a C.iiiis Maj. (Sirius) 6 40 49-67 + 2-64 16 34 52-55 S - 4-76 0'5 .a (Jaiiis Mill. (Procyon) ... 2 a llvdr.x. (Alphnrd) 7 34 1II-3S + 3-14 5 2S3;f-6lN - O-Wi 9-22 46-3-> + 2-9o 8 14 O-90 S - 15-48 \'i lo Leoiiis. iliegnhu) 10 3 9-21 + 3-20 12 26 41) -73 N - 1750 2-5 7' Lcoiiis. {.iljciba) 10 14 34-2.1 + 3-31 20-20 14-66N - 18-12 2-2 H Leoiiis. {Denebo/a) 11 44 3-71 + 3D6 15 7 11-70N - 20-12 1-2 a Virginis. iSpica) 13-20 174 + 315 10 .38 59-34 S - 18-87 a Boiitis, {A returns) 14 11 11-47 + 2-73 19 41 32-95N - 18-85 2-2 o Ophiiiolii. (Jias Alhajut) 17 ;<0 23-10 + 2-78 12 37 51 -96 N - 2-82 10 k Aquii.-c {AUair) 19 46 012 + 2-93 8 36 33-32N + 9-32 A word of cauiion respecting tlie applicutiou of the ' aunual variation ' of the Declination. In astronomy, North is represented by +, and South by — ; consetiuenti} , wiien the sign prefixed to the annual variation in the Nautical Almanac is + , it means that the change is in the direction of North, no matter what name the Declination may have. Thus if the Declination is North, the + sign makes it more so ; but if the Declination is South, the + sign diminishes it Similarly the — sign increases South Declina- tion and diminishes North Declination. This is a veritable pitfall for the unguardetl, more especially as this rule does not apply to certain tables given in some of tiie epitomes, in which tliese signs are used in their purely arithmetical sense of add and sub- tract. The above is Nautical Almanac style. It is perfectly wonderful how few men avail themselves of the stars on a fine night, to see how their compa-sse.s are behaving. This arises principally from an ill-dcfiiicd idea that any problem connected with the stixrs is much too ditlicult to be meddled with. Mow ditterent are the actual facts ! ! ..■l;i/Ha//(.!i of the stars, planets, and moon, are just as eivsily and as quickly tvorked up as aziviuths of the sun. The former passe.ss a decided advantage over the latter, inasmuch as a mistake in the working is at once detected if you observe a couple or three stars, since, having diflerent elements, the compu- tations are intlependent of each other. Whereas you may take 20 a/imuths by the sun, and even though all agree, they may HOUR ANGLES. every one be greatly in error, through having been inadvertently worked in each case with the wrong Latitude, or Dechnation, or Time. The greater the number of observations, the more the error would be confirmed, and though you might somewhat wonder at it, you would probably accept the result, and perhaps get led into danger. Now, with the stars the case is entirely different, as the one is a check upon the other. To find the hour angle or meridian distance of a star, a planet. To determmi, or the moon, you have merely, on taking the bearing, to note """'' *"*^'* time by the chronometer, and proceed as follows : — \st. To the time shewn by chronometer, apply its error for the day — the result will be Greenwich Mean Time, to which apply the longitude in time, adding it if the longitude be East, and subtracting it if the longitude be West; the result will be Mean Time at Ship. 2nd. Take from the Nautical Almanac (page II. for the month) the Sidereal Time (last column), and add to it the accelera- tion on Greenwich Mean Time, found in the table for the purpose on page 486 of the Nautical Almanac for 1895, or Table 23 of Raper's Epitome, or page 740 herein. 3 re?. Add together the Mean Time at Ship and the corrected Sidereal Time ; from the sum, increased if necessary by 24 hours, subtract the right ascension of the star; the remainder will be the star's hour angle West of the meridian. If the remainder be greater than 1 2 hours, take it from 24 to name Houi hours, and the result will be the hour angle East of the meridian. '^"^'^ ^^^' ""^ ° West. Should the remainder be more than 24 hours, reject 24 hours, and the result will be the hour angle West of the meridian.* This last part will seem somewhat confusing to the beginner, but it is nothing like so difficult as it looks. Moreover, should there be any doubt as to the amount of the hour angle, or its name, the question is easily settled by refei-ence to Raper's Table 27, where the apparent time is given at which the principal .stars pass the meridian. Knowing more or less the time at ship when you made the check against observation, and by Table 27 the approximate time on which the "'="»J'« ^^^^^ star will pass the meridian, you at once see whether the star is Angle. East or West of it. But, independently of this, in actual practice * To understaod this, independent of any printed rule, refer to diagram on page 380. 1 AZIMUTH OF SIBIUS. the observed compass bearing of the star will nearly always tell you which side it is, provided you apply to it the variation and approximate deviation. If still befogged, remember that the sextant will settle the matter : rising bodies are cast, and falling bodies west, of the meridian. The preceding rule for tindiug the star's hour angle applies also to the moon and other planets. Burdwood has a caution near the end of his preface, to thL« effect : — Left hand " With reference to the note at the foot of each page uf the azimuth tables, as the sun in the forenoon or a.m. is East of the colu Azimuth Tables never meridian, and in the afternoon or P.M. West of the meridian, in to be used but applying tjje note to indicate the bearing of a star, substitute East of the meridian for a.m., and ]Yest of the meridian for p.m." In taking from the tables the azimuth of a star, or the moon, its hour angle must always be taken from the right-hand column of the page, under the words " Apparent Time, P.M." The sub- joined examples will, it is hoped, show with what ease and certainty star, planet, and moon azimuths can be worked. Exaiiijili: 1. — About 10 P..M., Suturilay, Jauiiary 17th, 1880, ship beiiij; iu latitude 39° 20' N., and longitude 73" U' W., the star Sirius was observed to bear, by Standard compass, S. ISj" E., when a chronometer which was 4m. 34b. slow of G.M.T. showed 14h. 42ra. CIs. Vari.ition at ship's place, - 7". li. M. s. Time by chron 14 42 5 Declioation of Sirius, IGi" S. Error + 4 24 Open Burdwood at latitude 39°, cmtrary tuitnf to tlir dtdiiuilion {\Kiic 90), and with declination 16j° and hour angle Oh. •'•Siu. in thr riijhl-lfiiul culnmn, look fur the bearing bv interpola- tion, wliich will be found to !i i«ige, is to Wreud from Nortli to East, The rcmainiler of the work is its foilow.s :— G. M. time 14 46 29 Longitude in time -4 52 44 Mean Time at Ship 9 53 45 Sidereal Time from N. A 19 46 12 Acceleration for I4li. 4Uni. 29g. -<- 2 2(i R A. of the meridian 5 41 23 RA. of • Sirius « 30 54 • 's hour angle 23 01 29W. 24 00 00 ''« hour angle 68 31 E. True bciuing of • Sirius nt Oh. 58m. East of meridian K. 163^" E. 180° , , , .. .1 I. with unmeehangeil... S. lOj" E. Ex.mpleol Variation bv chart _ rt St4i-A 3 20 10 10 11 1-2 1-3 1-4 1-5 1-7 2-0 8 10 3 40 11 11 1-2 13 1-4 1-5 16 18 21 8 20 4 00 11 1-2 13 14 1-4 1-6 1-7 1-9 2" 2 8 00 4 20 12 12 1-3 1-4 1-5 1-6 1-8 2-0 2:t 7 40 4 40 1-2 1-3 1-4 15 1-5 1-7 1-9 21 2 4 7 20 6 00 1-2 1-3 14 1-5 I'O 1-7 1-9 SI 2 4 7 00 r. 20 1-3 1-8 1-4 15 16 1-8 1-9 2-2 2';"» 6 40 5 40 1-3 1-8 1-5 1-5 16 1-8 in 22 2."i 6 20 G 00 1-3 1-3 1-5 1-5 1-6 18 2 22 -•' 6 00 For the 12 houn lirfore the Mariilisn passage {abon the I*ole) the azimuth i* North au>l Kant, and for the It honrn after it i> N'orth and Wwt. The Itcoriogi are in degreri and leulhi, and the dadiiiatiuu 'ux> hceu ukcu *.% iS' i!>' N. Table 27 of Raper gives the time of meridian passage alx)\ c tiie I'olc, and from this the liour-angle am be estimated at any- time witli sufficient nearness. Though the bearing is given for AZIMUTH TABLES FOR ALL WORK. 133 latitude 60°, it is not advisable to employ it to the northward of latitude 45°, owing to the probability of errors of observation arising from so high an altitude. There are plenty of other stars to be had, and some of them brighter. Excepting Polaris, allusion has only as yet been made to those stars whose declinations range between 23° N. and 23° S., the limits of Burdwood and Davis ; but to confine the navigator to these alone would be to deprive him of the aid of some of the brightest stars in the heavens, and so Goodwin's Azivmith Tables for the Higher Declinations cover from 24° to 30°, both inclu.sive, between the parallels of latitude 0" and 60". This brings us to LECKY'S GENERAL UTILITY ABC and D TABLES.* To start with, let it be quite understood that the writer does Origin oi not claim to have originated the principle of these Tables ; that * *'' question is minutelj^ disposed of in the preface to the present edition. They merely bear his name to assist in distinguishing them from those with alphabetical prefixes published by other people. Reference to the preface will shew what he does claim. The use of the writer's Tables is explained in Part II., chapter IX. ; here it is enough to say that, by their aid, the azimuth of sun, moon, planet, or star can be taken out almost as quickly as from Burdwood or Davis, with this great advantage, that there is no restriction of hour-angle, nor practicallj^ of declination. To shew the conciseness of the method as well as its accuracy, the true bearing of the moon (Ex. 2) is worked out afresh by the ABC Tables. Data as before. Table A + "204 „ B - -191 „ C + -013 = S. 89i° W. Surely this method is simple enough, and concise enough, to please anybody ! ! The latitude, declination, and hour-angle being given, a reasonably smart man can work the azimuth in a Sharp is ti few seconds under a minute. In the case of ultra-zodiacal stars ""I''' J *"' ' _ i/uzci the it is not necessary to know the declination, as they are .specially motion, provided for in the lower portion of Table B. It is important to know that when their declination exceeds the observer's latitude, stars are more tlian ordinarily useful for azimuths if observed at their nearest approach to the Prime Vertical. t Their change of bearing is then exceedingly slow — sometimes not 15' in an hour — and the advantage is obvious. * Now greatly extended and publislied sep-irately. t When the heavenly body is on the Prime Vertical the following formnlse fill the bill, yin Az. = Sec. Lat. X cos. declin ; Sin Alt. = Sin. Lat. X cosec. decl. ; Cos. Hour-angle = tan. Lat. x cotan. declin, : vide page 468. 134 UEVlATlUiS DETECTING IS PRACTICE. DEVIATION BY THE PELORTTS. To revert to the Pelorua The following is the method to be pursued to tind by it the deviation of the compa.ss on any course which is being steered at the time : — Work up position by dead "o"""" reckoning from last observation; prick this ott'on the Variation chart, and note corresponding variation; coiTect this for the annual change by the chartlet at the north side of the sheet ; set your watch to Apparent Time at Ship as already instructed ; suppose it to be about 2 p.m. Then, to allow yourself sufficient time, ascertain the sun's true bearing a quarter of an hour or so in advance, say for ever}- four minutes between 216 and 224 P.M. Apply tiie variation taken from the chart in order to con- vert the true bearings into correct magnetic ones; write these latter with corresponding times down on a slip of paper, and you are ready to begin when the time comes. We will suppose there are several compasses in the ship t^'t is not an uncommon number), and that you wisli to ascertain the deviation of each by simultaneous observations. Of course you are provided with a whistle. Station a 'hand ' by each compass, with instructions to note the exact direction of the ship's liead when he hears the whistle.* The Pelorus being in its stand, unclamp the card, .so that it ma}' be free to revolve on its axis ; set the sight vane to the sun's " cor- rect magnetic " bearing, corresponding to the Apparent Time by watch, and secure it firmly to tlie card by the large milled-headed .screw on top. Tell your assistants to " look out," and the ship being nicely steadied on her course, move the card, with sight vanes attivched, to the right or left till you see the sun's image reflected in the speculum and bisected by the thread; then whistle, and continue to do so, .say for half a minute — so long as the sun is cut by the thread (of course it is understood that the card is not to be again moved after the first whistle). Now note the reading of the card opposite the lubber-line, and this will be the actual "correct magnetic " direction of the ship's head at the tinie the signal wius made. The compasses, if free from error, will in- dicate the .same thing. Should they not do so, the difl'erence be- tween the ship's head by Pelorus and the ship's head by compass will be the deviation of that particular compass on that particular coui-se. The rule to determine its name is this : — * All nHIctr without ii whittle la Ilka a aailor without * knife, and ercrx ona knowi what tb« latter It lika. FIRST PRINCIPLES OF OBSERVING. 135 If the " correct magnetic course " be to the left of the " compass Rules for course " (lookiuff outwards from the centre of the card), the devia- Ilf"'!"^ ^ '' Deviation tion IS westerly, but should it be to the right of the " compass course," the deviation is easterly. Westerly deviation throws a ship to the left of her course, and Deviation i.ai Easterly devnation throws her to the right. Exactly the same ^"'^''O"— '" •^ o »/ what respectff effect is produced by variation of the compass, and in this respect similar, the two are similar. One of the first things done by a lad going to sea is to learn how to "box the compass;" but the old sailor's method of doing this in points, J points, and ^ points, will soon be obsolete. The student of to-day, who takes a pride in his profession, will learn how to " box the compass " in degrees — that is to say, he will Boxing the learn to tell ofT-hand how many degrees correspond to any given ^"""p^^^ '" compass course reckoned in points or parts of a point. It should not take longer than an hour to master this important matter. To set a course by Pelorus, the operation is very similar to that setting course described above. Proceed as before, except that this time the ^^ P^iorus, card is to be clamped not only to the sight vanes, corresponding to the sun's bearing at the appointed time, but also to the lubber's point at the correct magnetic course you wish to steer ; thus, both the card and the sight vanes will be immovable. Under these circumstances you must starboard or port the helm until the thread bisects the sun's image in the speculum ; when carefully steadied in this direction, whistle as a signal to the helmsman and those looking out for the other compasses, that the vessel is on her course, and to " keep her steady as she goes." Among the many advantages this instrument possesses, it enables the deviation of any number of compasses to be found by one observation, and this deviation is quite independent of the error due to any possible displacement of the lubber-lines. The principle of the Pelorus is merely this, that it measures the Principle of horizontal angle between the sun (or other object) and the ship's ">* P'^'"""- head. Under certain simple conditions the unassisted eye can do the same thing, only somewhat less accurately. For example, at the instant of noon to an observer in the English Channel, the sun bears South (true). If now, the vessel is so manajuvred by her helm as to bring the sun on the port beam — say on a line with the bridge handrail, or the forward or after side of a dock-house, hatch-coaming, or skylight— it is certain tliat her head must be West (true): if the helm shouM be ported so as to bring the sun PFinnrrs is sot a compass. dead aft in a line with the masts, the ship's head must 1 >e North (true) : if the helm be still ported so as to bring the sun on the starboard beam, the ship's head must be East (true) : and lastly, if the sun be brought right ahead, the course must be South (true). In this way, in a small craft, the errors of the compaabes might be approximately determined on the four points named. In a ship there are many things which give true fore-and-aft lines, as well as thwartship ones, but the intermediate angles are wanting. The Pelorus supplies this deficiency, as it enables us to measure any angle between the beam and the fore-and-aft line : and tliis is the view which must be taken of it. You must divest youi'self of tlie inclination to consider it a comjMsa ; to repeat, it is merely an instrument for metvsuring the horizontal angle between any object and the ship's head. Dumb cards without odmbals give incoiTcct — sometimes very incorrect — results, and should on no account be emploj'ed. There are a number of instruments now before tlie public which profess to be " Compass correctors." It is not proposed to discuss their relative merits ; but presuming them to be right in principle, which in some cases is open to question, it would be letter if the}' were termed " Compass course correctors," or " Deviation detectors," as the former name is quite inapplicable. These instruments are most!}- complicated; and if by any chance they get a knock or a fall, it would be difficult to le-adjust them. Whereas the construction of the Pelorus, while correct in prin- ciple, is so extremely simple in detail, that any sea-going engineer, or a handy civrpenter, could "put it to rights" without much trouble. The Pelorus must not, from the similarity of names, l>e confounded with another invention, known as the Palinurus — so CJillcd after a famous old Greek pilot — nor with the Polaris, both of which are totally different instruments. The Pelorus will be again referred to when "Compass adjustment" comes to be treated on. CHAPTER Xr. THE STATION POINTER. This is an instrument that, until the publication of " Wrinkles," very few men in the merchant service were acquainted with eveji by name, and in the Navy it was seldom used, except by ofEcers of the surveying branch. When the great practical value of the instrument is considered, this statement seems almost incon- ceivable. In 1893 it was supplied to all war .ships, and is becoming quite popular in the better class of merchant vessels. Of the many methods for ascertaining a ship's position when in sight of a jxro^perhj surveyed coast, none can in any way compare for ease and precision with that in which the Station Pointer figures as the chief assistant of the Sextant. So very important an instrument deserves quite a long chapter, but it is easy reading to the end, and quite in keeping with a pipe or Manila cheroot, so light up aud settle down to it comfortably. The Station Pointer is composetl of a graduated circle of brass, having one fixed and two movable arms radiating from its centre. The movable arms turn in one plane round this centre, which is common to both, and where they pass outward under the circle have verniers attached, so that the angle either of them makes with the fixed leg, which lies between them aud constitutes the zero point of the circle, can be readil}' measured. They are made of different sizes, and more or less perfect in detail. All An instru. ment com- paratively unknown Station Painter doKrtbad. SFXTAXT AXGLES. of them liave clamping screws to set the movable legs to any required angle, and some, like a sextant, are fitted with tangent screws and reading microscopes. It is an exceedingly simple instrument to understand, and has no special adjustments or ilelicate mechanism to get out of order. Of course, like everything else, the Station Pointer must be used a few times before actual expertness can be hoped for. As before stated, its use when employed in connection with the sextant is to fix a ship's position on the chart by means of two horizontal angles subtended by three well-defined objects — such OS towers, lighthouses, churches, windmills, islets, capes, points, mountain peaks, hills, or other marks wliich may be found on the chart and dulj^ recognised. Every aspiring officer should be as quick with the sextant in observing horizontal angles as he generally is in observ- ing vertical ones — the sun's altitude, for mstanco. Strange to say, this is not the case. The majority of otiicers seem to be under the impression that the sextant can only be held in an up- and-down position, and never dream that it can just as easily be used on its thit to take horizontal angles. Clearly such men have never taken a " lunar distance," or they would know better. A sextant is useful to meiusure any kind of angle, whether hori- zontal, oblique, or vertical. It should unquestionably be a part of an officer's education to learn to handle liis sextant so as to observe as readily and as accurately one way as tlie other ; and to this end, therefore, during spare half-hours in harbour, or when sailing along a coast, let a couple or more officers tike their sextants on deck and measure simiUtaneoiLS horizontal angles, until by the agreement of rtsnlts it is known that proficiency is attained. In taking a horizontal angle between two objects, stand erect and perfectly at ease, poise tiie sextant lightly in the right hand, with its face up, anle always to look direct at the fainter object of the two, and reflect the brighter one to it ( 'on.seiiuently, whenever it happens that the fainter object is to the right hand, it may l>e nece.ssary to hold the sextant /(tc« down. There is absolutely no difficulty about this iiiaft>T that cannot l>e EXAMPLE FOR STATION-POINTER. 139 overcome by a very moderate amount of practice, and, in after years, the knowledge may prove of incalculable value. To exemplif}' the use of the Station-Pointer, let us imagine a vessel sailing along a weather shore beset with ofF-lying dangers, and desirous of hugging the coast to keep in smooth water, and gain her port, — say Holyhead, coming from Liverpool. Let the reader refer to Admiralty Chart 1170^. As soon as Point Lynas is passed, the captain will naturally Buoys doi get anxious about those bugbears to navigation, " the Coal " and "''*'''*• " Ethel " rocks. It is true they are buoyed, but strong running tides, gales of wind and heavy seas, are apt to drag the buoys from their proper positions, and so lure to disaster, as in the case (some years ago) of the S.S. " State of Louisiana " and the Hunter rock buoy, off Lame, on the Irish Coast. Besides, the compasses may be swinging so as to make bearings inaccurate. Possibly the vessel may be iron or steel, and the deviation uncertain, or some obstacles may be in the way of the object of which you wish to get the bearing. Whatever difficulty may present itself in getting an accurate " fix " by the usual methods, none at all exists with the Sextant and Station-Pointer. Select three objects on shore which you know are laid down on How to fii the chart ; for instance. Point Lynas Lighthouse, the East Mouse, p""""" ^^ and the Middle Mouse. Let an assistant measure with his sextant Pointer, the horizontal angle between the first two, whilst you at the same moment measure the angle between the East and Middle Mouse, noting the time by watch for sake of reference. Having read off" the sextants, take the Station-Pointer, and holding the legs from you, open out the left-hand one and set it to the left-hand angle, between Point Lynas and the East Mouse. In like manner set t4ie right-hand leg to the right-hand angle, between the East and Middle Mouse. Lay the instrument down on the chart, so that the feather-edge of the centre leg maj^ pass over the East Mouse, whilst the others pass respectively over Lynas and the West Mouse; thu.s. The centime of the instrument will then represent the exact position of the ship, and it may be pricked on the Chart through I40 SELECTIOS OF OBJECTS FOR ASGLES. the small hole for the purpose. The definite spots between which the angles are to be mea.sured must be settled beforelmnd. In the case of a lighthouse there would be no difficulty, as the middle line of the towi-r, or of the lantern, would naturally present itself. For small islets or rocks it is usual to tivke the estimated centre, and, if close enough, to select a conspicuous rock or patch of colour to be used in common. In the case of larger i.slands, the right or left extremes at the water line are usually suitable ; but where the rise and fall of tide is considerable, be careful not to select gradually shelving points or spits, which at low water may shew half-a-niile or so outside of what they do at high water. A glance at the chart should en.-xMe j-ou to avoid a blunder of this kind. As the vefvsel progresses Westward, fresh stations can be .selected. For example, when abrea.st of the Middle Mouse, use it and Lynas for the left-hand angle, and the Skerrie.s and Middle Mouse for the right-haml angle. As the "Coal" and " Ethel " rocks are approacheil, watch till the Middle Mou.se is in one with Lynas Lighthouse. When in transit, one angle between them and the beacon on the West Mouse will fix the ship's position with great accuracy, and .so on till the Skerries are rounded. Any one who takes the trouble mentally to follow this opera- tion as described above, will scarcely fail to see that it cannot be 8urpa.s.sed for ease and dispatch. Indeed, if there should be two assistants as angle-takers, whilst the 'chief manipulates the Station-Pointer in the chart-room, the vessel's position can be accurately laid down on the chart in from one to two minutes from the time the objects were pointed out between which the angles were to be taken. Any one doubtful has only to try to be convinced. To comprehend " the »vhy and the wherefore " of this method, which bj- some is called " The three-point problem," and by others " The problem of the two circles," it is necc.s.sary to consult Euclid, but only in a very quiet way.* The fir^t thing to understaml is that through aiiy three points, not in a straight line, a complete circle can always be draivn, and but one ; {vide Euclid, IV. 5). * Properljr apctking it ii a problem of tSrte circle*, since it includes the important one pi.uing through the two outfr pointi and |>osition o( obwrrer. This last circle ii really the key lo the whole position. In the figures only two are drawn, but the student would do well to take a tracing off them and describe the third circle for himieir. A LITTLE GEOMETRY IS USEFUL. Let A, B, aud C represent the points througli which the circle IS to be traced. Draw lines joining AB and BC. Take any extent in the dividers greater than half the line BG, and with one foot in C describe a short arc at D and E respec- tively ; with the same radius, and one foot in B, describe two xo find centr« other short arcs, cutting the former in D and E ; through Z> and °' » <^'''"='*- E draw a straight line. In a similar manner from A and B, respectively, describe two short arcs, cutting each other at F and G. Through F and G draw a straight line, which produced will meet the one through D and E at the point H. Then from H as a centre, at the distance of any one of the given points, as HB, describe a circle, and it will pa.ss through the other points A and G as required. The student would do well to solve a few cases, until satisfied in his own mind that, no matter how the points may be placed with respect to each other, a circle can always be drawn that will pass through all three. 2nd. Another geometrical peculiarity has to be confiidered aud understood. D Anywhere on the circumference of a circle, select two points, as A and B, and connect them with a straight line ; this line is termed the chord of the arc A DB. A DB is also one segment of PROPERTIES OF THE CIRCLE ASD the circle, and AFB is another. Euclid (III. 21) tells us that from any point in the circumference on the same side as AFB, the points A, B, will subtend the same angle. (Thus the angle Angle in the A GB {Fig. 2) Contains precisely the same number of deii^rees as .egment. j.jjg anc;le APB). This being the case, it is evident that the circumference AFB is the locus, or path, of a constant angle, which is termed " the angle in the segment A FB," and an observer getting this angle must be somewhere on the circum- ference AFB, the size of which depi'nds upon the angle observed. When the observed angle is acute, he is on an ai'c of a circle which is greater than a semi-circle ; when tlie angle is 90°, he is on a semi-circular arc ; and, when the angle is greater than 90°, he is on an arc less than a semi-circle. So far the work may not inaptly be compared to getting a " line of bearing"; but it is still necessary to fix the ship's place on this line — or, in other words, to cross this bearing with another, just in the same way as you would do with compass bearings, or as you might cut the known parallel of latitude on the chart with the North and South line of longitude, in order to definitely lay Co ordinaies off the ship's position. Latitude alone would not do so, nor would longitude; but the intersection of the one with the otlier indicates the precise position. For this purpose, therefore, let ua imagine another circle somewhat similar to the foregoing. L.. .C Fii/. S. v.. "" a What has been .said about the first, of course, holds good witli this one also — namely, that from any 2>oint in the circumference BKV, the points B, C,wiU subtend the same angle, whatever that maj' happen to be, according to the size of the segment. Now, if the angle subtended by A, B, \i\ Figure 2 were observed simul- taneously with the angle subtended bj- B, C, in Figure 3, the two lines of bearing will intersect each otiier, and give the place of the ship. A reference to F'igure 4, backed by a careful stu V. 7. " PROBLEM OF THE TWO CIRCLES.' '45 4. Tlic throe objects may lie in a curve, concave to the observer, so long as the latter is well outside the circle upon whose circumference the three objects are situated. In this case the ' fix ' will be good, notwithstanding the small angles. Fig. 8. \ If two of the objects be much nearer, as compared with the third, and seem, roughly speaking, about equidistant from, the observer, at whose position they subtend an angle ranging between 60° and 120°, whilst the angl? between the third and middle point is comparatively small, the selection is a good one. tiy- 9 6. Two of the objects may be in tiaiisit with the observer. If this sliould be the case, one angle between them and the thu-d is suffiaent. This is the best and simplest 'fix' of all. The single angle should not be less than 30».* * This can scarcely be included in the "problem of the two circles," but it is inserted here with the others for sake of convenience. 1 48 GOOD AND BAD "" FIXES.' Fig. 10. Two of tUe point! ID traotit. Case to b« guarded ftK«iDSt. An ImpoBsiblo III tliU case the ship's position is fixed on the circumference of tho segment A SB, hy producing the Hne liC until it cuts it at int ill the segment ASC; an