^H! NHH 
 
' REESE LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 Deceived Jfoa^zh- > **9 / 9OO 
 
 No. J 8 (o % *7 . Clots No. 
 
MODERN PRACTICE 
 
 ELECTRIC TELEGRAPH 
 
MODERN PRACTICE 
 
 OF THE 
 
 ELECTRIC TELEGRAPH 
 
 A TECHNICAL HANDBOOK 
 
 FOR 
 
 ELECTRICIANS, MANAGERS, AND OPERATORS 
 
 WITH 185 ILLUSTRATIONS 
 BY 
 
 FRANKLIN LEONARD POPE 
 
 PAST PRESIDENT OF THB AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS; MEMBER OF 
 THE INSTITUTION OF ELECTRICAL ENGINEERS (LONDON) 
 
 FIFTEENTH EDITION .REWRITTEN AND ENLARGED 
 
 OF THE 
 
 UNIVERSITY 
 
 NEW YORK 
 D. VAN NOSTRAND COMPANY 
 
 LONDON 
 
 SAMPSON, LOW, MARSTON & CO. 
 (LIMITED-) 
 
 1899 
 
COPYRIGHT, 1891 
 O. VAN NOSTRAND COMPANY 
 
 Braunworth, Munn & Barber, 
 
 Printers and Binders, 
 
 Brooklyn, N. Y. 
 
IN AFFECTIONATE REMEMBRANCI 
 OF MY FORMER CHIEF 
 
 ENGINEER OF 
 
 THE AMERICAN TELEGRAPH COMPANY, 1861-1864 
 
 UNDER WHOSE 
 
 ENLIGHTENED, PROGRESSIVE, AND LIBERAL ADMINISTRATION THE 
 
 METHODS OF MODERN SCIENCE WERE FIRST APPLIED TO 
 
 AMERICAN TELEGRAPHY 
 
MORSE (SAMUEL FINLEY BREESE), Inventor of the recording electro-magnetic 
 telegraph, born in Charlestown, Mass., April 27, 1791; graduated at Yale, 1810; 
 studied art in the Royal Academy of London, 1811-15, under Benjamin West. In 
 1829 he again visited Europe for further study of his profession, and while returning 
 home in 1832, on board the ship Sully, conceived and made drawings of his recording 
 telegraph (see J. D. REID : The Telegraph in America^ chapters vi., vii.). From 
 this time until his death he was unremittingly employed with his invention, passing 
 meantime through many vicissitudes of fortune, and some most painful experiences. 
 He was first professor of fine arts in the University of the City of New York, in one of 
 the rooms of which institution he set up in 1835 his first crude recording telegraphic ap- 
 paratus, now preserved in the cabinet of the Western Union Company in New York. 
 In 1837, Alfred Vail, a skillful mechanic and inventor, became his partner in the enter- 
 prise. Vail entirely reconstructed the apparatus, and embodied it in the practical 
 form in which it was first introduced to the commercial world. After a series of dis- 
 couragements that would have utterly disheartened most men, Morse, assisted by Vail, 
 established in 1844, under an appropriation from Congress, the first line between 
 Washington and Baltimore. On May 24 of that year, Morse put to the test the great 
 experiment on which his mind had been laboring for many anxious and weary years. 
 His triumph was complete. Honors and riches were showered upon him at home and 
 abroad. Professor Morse was a man of great simplicity of character, firm in his 
 friendships, and most persistent and exhaustive in all his undertakings. He wielded 
 the pen of a ready writer, and his genius, learning, and taste were illustrated by 
 numerous contributions to the press, evincing not only graceful rhetoric but elaborate 
 and well-sustained argument. On June 10, 1871, a bronze statue of Morse, erected by 
 the contributions of the thousands of telegraphic employees in America, was unveiled 
 with imposing ceremonies in Central Park, New York. He died in New York, 
 April 2, 1872. 
 
PREFACE. 
 
 A, MOST a quarter of a century has passed since the publication 
 of the first edition of this work. During that period, and 
 more especially during the past ten years, the progress which has 
 been made in the application of electricity to the industrial arts has 
 been literally unprecedented, while the extraordinary practical results 
 which have been attained have exerted a reflex action in stimulating 
 in an equal degree the advancement of electrical science ; an ad- 
 vancement which has not been without its influence upon the theory 
 and practice of the electric telegraph. This circumstance has at 
 length rendered necessary, not a mere revision of the original treatise, 
 but the preparation, in fact, of an entirely new work throughout. 
 
 To the intelligent and observant mind of youth, the art of teleg- 
 raphy possesses a singular fascination, and in many instances its 
 pursuit tends to excite a spirit of scientific inquiry, not only com- 
 mendable in itself, but valuable as establishing a sure foundation for 
 future success in broader fields of labor. It has been the aim of 
 the author to supply a knowledge, not only of the principles and 
 practice of telegraphy, but of the theory of electricity and the 
 methods of electrical measurement, which should be of the highest 
 possible value to every person entrusted with the care and manage- 
 ment of telegraphic apparatus. It has, however, been deemed advis- 
 able to somewhat restrict the scope of the work, and hence the auto- 
 matic, type-printing, synchronous, submarine, and other methods, 
 requiring on the part of the practitioners a special training apart 
 from a knowledge of the ordinary system, have been excluded. The 
 construction and maintenance of aerial, subterranean, and submarine 
 lines has also, by a natural process of evolution in the progress of 
 
viii . Preface. 
 
 the art, become a separate profession, and the subject can therefore 
 receive but brief notice in a work primarily designed for the guidance 
 and instruction of the practical operator. 
 
 In the treatment of the subject, the use of mathematics has been 
 rendered unnecessary by the free introduction of concrete examples, 
 illustrative of methods and processes of arithmetical computation 
 available in electrical investigations. From the many methods of 
 electrical measurement, as applied to the solution of practical prob- 
 lems, a selection has been made, embracing only those which have 
 proved to be most directly applicable to every-day work. 
 
 The numerous authorities which have been consulted in the prepa- 
 ration of the present treatise have been carefully indicated in the 
 foot-notes ; in many instances with the addition of the titles of pub- 
 lications which may profitably be consulted by the student desiring 
 to investigate more minutely some particular branch of the subject. 
 These references are intended to constitute, in some sense, a key to 
 the standard literature of electricity, although from the nature of the 
 case, by no means an exhaustive one. 
 
 It is hoped that the brief biographical notices of men who have 
 distinguished themselves in connection with electrical science will 
 be found to add something to the value of the work, especially as 
 the facts given are sometimes difficult of access to the ordinary 
 reader. 
 
 The author acknowledges with pleasure his indebtedness to many 
 friends for courtesies extended, especially to Professor Moses G. 
 Farmer of Eliot, Me., and Messrs. E. M. Barton, of the Western 
 Electric Company of Chicago, E. S. Greeley of New York, and 
 Edward Weston, of Newark, N. J. 
 
 EDGEWOOD FARM, ELIZABETH, N. J., 
 September z, 1891. 
 
CONTENTS. 
 
 CHAPTER I. 
 
 INTRODUCTORY. 
 
 FAD* 
 
 Fundamental Principles, i, 2, 3. Nature of Electricity, 4. Ele- 
 ments of Electric Telegraph, 5 I 
 
 CHAPTER II. 
 
 SOURCES OF ELECTRICITY. 
 
 Origin of Electricity, 6, 7. Voltaic Element, 8. Description of the 
 Typical Cell, 9, 10. Phenomena of Cell, n, 12, 13. Chemistry of 
 the Voltaic Effect, 14, 15. Gravity Cell, 16. Specific Gravity, 17. 
 Hydrometer, 18. Charging the Cell, 19, 20, 21. Copper and Zinc 
 Solutions, 22. Specific Gravities of Battery Solutions, 23. Instal- 
 lation of Gravity Cell, 24, 25. Modified Form of Copper Plate, 26, 
 27. Formation of Electric Circuit, 28, 29, 30. Nomenclature of 
 Electric Circuit, 31. Chemical Reactions arising in Closed Cir- 
 cuit, 32. Effect of Continued Action, 33, 34, 35. Rate of Con- 
 sumption of Material, 36. Maintenance of Cell, 37. Prevention 
 of Evaporation, 38, 39. Dismantling Cell, 40. Diffusion of Solu- 
 tion within Cell, 41, 42. Neutralizing Zinc Solution, 43. Waste 
 Products of Cell, 44, 45. Other Forms of Cell, 46, 47. Lockwood 
 Cell, 48. Daniell Cell, 49, 50. Maintenance of Daniell Cell, 51. 
 Renewal of Daniell Cell, 52. Intermingling of Solutions, 53, 54. 
 Choice of Battery Materials, 55, 56. General Directions for Care 
 of Cells, 57. Oxide of Copper Cell, 58. Setting Up and Maintain- 
 ing Oxide of Copper Cell, 59. Chemical Reactions of Oxide of 
 Copper Cell, 60. Grove and Bunsen Cells, 61. Wasteless Battery 
 Zinc, 6ia 3 
 
 CHAPTER III. 
 
 SOURCES OF ELECTRICITY. (Continued.} 
 
 Magneto-Electricity, 62. Magnetism, 63. Magnetic Needle, 64. 
 Phenomena of Magnetic Induction, 65. Polarity of Magnet, 66. 
 Horseshoe Magnet and Armature, 67. Magnetic Spectrum, 68. 
 Magnetic Field, 69. Lines of Magnetic Force, 70, 71. Attraction 
 and Repulsion, 72. Electric Current Produced by Magnetic Field, 
 73. 74- Transformation of Mechanical Power into Electricity and 
 
x Contents. 
 
 PAGE 
 
 Heat, 75. Direction of Induced Current, 76. Mutual Reactions 
 of Current and Magnet, 77. Summary of Magneto-Electric Phe- 
 nomena, 78. Dynamo-Electric Machine, 79. Theoretical Dynamo, 
 80, 81. Frictional Electricity, 82. Thermo-Electricity, 83 24 
 
 CHAPTER IV. 
 
 THEORY OF QUANTITATIVE ELECTRICAL MEASUREMENT. 
 
 Electric Current, 85. Manifestations of Current, 86. Importance of 
 Quantitative Measurement, 87. Fundamental Units of Mass, 
 Space, and Time, 88. Illustration of Absolute System of Measure- 
 ment, 89. Derivation of Electrical and Magnetic Units, 90. C. G. 
 S. Units of Force and Work, 91. Conservation of Force, 92. 
 Electric Field of Force, 93. Relation of Current Force to Mechan- 
 ical Force, 94. Galvanoscope and Galvanometer, 95. Tangent 
 Galvanometer, 96. Character of Electrical Measurements, 97. 
 Characteristics Capable of Measurement, 98. Apparatus for Meas- 
 urement, 99. Ammeter, Voltmeter, and Calorimeter, 100 35 
 
 CHAPTER V. 
 
 THE LAWS AND CONDITIONS OF ELECTRICAL ACTION. 
 
 Apparatus Required by Student, 101. Construction of Tangent Gal- 
 vanometer, 102, 103, 104, 105. Construction of Rheostat, 106. 
 Preparation for Experiments, 107. Effect of Varying Number of 
 Cells in Series, 108. Cells in Parallel Series, 109. Cells in Paral- 
 lel, no. Increasing Length of Conducting Circuit, in, 112, 113. 
 Conditions which Determine Quantity of Current, 114. Resist- 
 ance, 115. Conductors and Insulators, 116, 117. Specific Resist- 
 ance of Different Metals, 1170. Conditions Affecting Resistance, 
 118. Provisional Theory of Electricity, 119. Mechanical Ana- 
 logue of Electrical Action, 120. Conception of Potential and 
 Electromotive Force, 121. Practical Electric Units, 122. Ampere, 
 123. Coulomb, 123^. Volt, 124. Ohm, 125. Resistance of 
 Liquids, 126. Ohm's Law, 127. Joule's Law, 128, 129. Experi- 
 mental Proof of Ohm's Law, 130. Internal Resistance of Cell, 
 131. First Case, 132. Second Case, 133. Law of Joint Resist- 
 ances, 134, 135. Third Case, 136, 137, 138, 139. Branch or De- 
 rived Circuits, 140. Electric Potential, 141, 142. Illustration of 
 Fall of Potential, 143. Fall of Potential Proportionate to Resist- 
 ance, 144. Graphic Illustration of Electric Circuit, 145. Fall of 
 Potential in Non-homogeneous Circuit, 146. Electrostatic Capacity, 
 147. Farad, 148. Power, or Rate of Work, 149. Watt, 150. 
 Current Induction, 151. Electrical Dimensions of Voltaic Cell, 
 152. E. M. F. and Resistance of Cell, 153. Quantity and Cost 
 of Materials Consumed in Battery, 154, 155, 156. Production 
 of Electricity in Proportion to Material Consumed, 157. Con- 
 
Contents. xi 
 
 FACE 
 
 sumption of Material in Series of Cells, 158. Electrical Dimen- 
 sions of Edison-Lalande Cell, 159. Effect of Temperature upon 
 Resistance of Metallic Conductors, 160, 161. Effect of Tempera- 
 ture upon Resistance of Liquids, 162. Effect of Temperature upon 
 Resistance of Daniell Cell, 163, 164 45 
 
 CHAPTER VI. 
 
 THE LAWS OF ELECTRO-MAGNETISM. 
 
 Elements of Electro-Magnet, 166, 167. Polarity of Electro-Magnet 
 Determined by Direction of Current, 168. Lines of Force as a 
 Measure of Magnetic Field, 169, 170. Unit of Magnetism, 171. 
 Magneto-motive Force, 172. Effect of Iron in Helix, 173. Effect 
 of Magnetization upon Soft Iron, 174, 175. Magnetic Saturation, 
 176. Magnetization Proportional to Ampere-turns, 177. The 
 Magnetic Circuit, 178. Magnetic Permeability, 179. Law of Mag- 
 netic Circuit, 180. Determination of Magnetic Reluctance, 181. 
 Ratio of Attractive Force to Distance, 182. Construction of Tele- 
 graph Magnet, 183. Theoretical Proportions of Telegraph Mag- 
 net, 184. Effect of Position of Windings, 185. Helix of Coil, 
 186. Relation of Thickness and Length of Wire to Number of 
 Turns, 187. Dimensions and Resistances of Magnet Wires, 188. 
 Thickness of Spaces between Turns of Wire, 189. American 
 Standard Wire Gauge, 190. British Standard Wire Gauge, 191. 
 Instruments for Gauging Wire, 192. Adaptation of Magnets to 
 Working Currents, 193, 194. Spectrum of Electro-Magnet, 194. 
 Magnetic Hysteresis, 195. Induction of a Current upon Itself, 196. 
 Magnet Cores must not be Hardened, 197. Effect of Self-induc- 
 tion and Hysteresis in Telegraph Magnets, 198. Other Indirect 
 Causes of Retardation in Electro-Magnets, 199. Electro-Magnet 
 with Polarized Armature, 200, 201. Combinations of Permanent 
 and Electro-Magnets, 202 80 
 
 CHAPTER VII. 
 
 TELEGRAPHIC CIRCUITS. 
 
 Telegraphic Circuits, 203, 204, 205. Open and Closed Circuits, 206. 
 Drawings of Electric Apparatus, 207. Conventional Representa- 
 tions of Circuits and Apparatus, 208. The Earth as an Electrical 
 Conductor, 209. Ground Connection, 210. Advantages of the 
 Earth Circuit, 211. Open Circuit, 212. Closed Circuit, 213. 
 American Modification of Closed Circuit, 214. Comparative Ad- 
 vantages of Different Plans, 215. Position of Battery in Closed 
 Circuit, 216. General Considerations respecting Telegraphic Cir- 
 cuits, 217. Relation of Conductivity to Insulation Resistance, 218. 
 Effect of Imperfect Insulation, 219. Working Efficiency of Tele- 
 graphic Circuit, 220. Telegraphic Conductors, 221, Iron Wires, 
 
xii Contents. 
 
 PAGE 
 
 222. Office Wires, 223. Copper Line Wires, 224. Telegraphic 
 Line Insulators, 225. Defects of Glass Insulator, 226. Resistance 
 Influenced by Form of Insulator, 227. Hard Rubber Insulator, 
 228. Paraffin Insulator, 229. Porcelain Insulator, 230. Defective 
 Insulation of American Lines, 231, 232, 233. Distribution of Po- 
 tentials in Telegraphic Circuits, 234. Potential in Perfectly Insu- 
 lated Circuit, 235. Determination of Potential by Calculation, 
 236. Potentials within the Battery, 237, 238, 239, 240. Potentials 
 in Imperfectly Insulated Circuit, 241. Effect of Imperfect Insula- 
 tion upon Flow of Current, 242. Resistance and Current in Leaky 
 Lines, 243. Computation of Working Efficiency of Line, 244, 245. 
 Effect of Position of Fault, 246. Best Position of Batteries in 
 Circuit, 247. Intermingling of Currents on Different Lines, 248. 
 Remedy for Cross-Current, 249, 250. Value of Poles and Cross- 
 Arms as Insulators, 251. Tests of Resistance of Cross-Arms, 252. 
 Tests of Glass Insulators, 253. Importance of High Working 
 Efficiency, 254. Best Method of Improving Efficiency, 255, 256... 102 
 
 CHAPTER VIII. 
 
 EQUIPMENT OF AMERICAN TELEGRAPH LINES. 
 
 Apparatus Essential in Telegraphy, 257. Construction of Key, 258. 
 Modifications of Key, 259. Adjustment of Key, 260. Sounder, 
 261. Short Line Instrument, 262. Adjustment of Sounder, 263. 
 Pocket Apparatus, 264. Box Sounder, 265. Working by Relay 
 and Local Circuit, 266. Construction of Relay, 267. Adjustments 
 of Relay, 268. Register, 269, 270. Adjustments of Register, 271. 
 Causes of Defective Marking, 272. Ink-Writing Register, 273. 
 Circuits of American System, 274. Arrangements of Apparatus 
 at Way-Station, 275. Connections of Apparatus of Way-Station, 
 276. Manipulation of Switchboard, 277. Testing for Disconnec- 
 tion, 278. Reporting Result of Test, 279. Wedge Cut-Out, 280. 
 Multiple Wire Switchboard, 281. Multiple Spring-Jack, 282. Uni- 
 versal Switchboard, 283. Manipulation of Universal Switchboard, 
 284. Arrangement of Apparatus of Terminal Station, 285. Ter- 
 minal Switchboard, 286. Instrument Tables, 287. Lightning Ar- 
 rester, 288. Plate Arrester, 289. Safety Fuse, 290. Inspection 
 and Care of Arresters, 291. Repeater, 292. Manual and Automatic 
 Repeaters, 293. Button Repeater, 294. Wood's Repeater, 295. 
 Management of Button Repeater, 296. Milliken Automatic Re- 
 peater, 297. Management of Automatic Repeaters, 298. Dynamo- 
 Electric Generator, 299. Characteristics of Dynamo-Current, 300. 
 Electro-Magnetic Field, 301. Commutator, 302. Characteristics 
 of Dynamo, 303. Dynamo in Potential Series, 304. Positive 
 and Negative Dynamo Series, 305. Arrangement of Shunt Coils, 
 306. Capacity of Dynamo Generator, 306^. Multiple Telegraphy, 
 307. Differential Electro-Magnet, 308. Construction of Differen- 
 tial Magnet, 309. Single-Current Duplex, 310. Circuits of Single- 
 
Contents. xiii 
 
 PACK 
 
 Current Duplex, 311. Artificial Line, 312. Balancing Resistance, 
 313. Electrostatic Capacity of Line, 314. Electrostatic Accumu- 
 lation upon Insulated Conductor, 315. Effect of Currents of 
 Charge and Discharge, 316. Condenser, 317. Ground and Spark 
 Coils, 318. Double-Current Duplex, 319. Quadruplex, 320. 
 Principle of Diplex, 321, 322. Operation of Diplex, 323. Diplex 
 and Contraplex Combined, 324. Quadruplex worked by Dynamo- 
 Currents, 325. Distribution of Currents in Quadruplex Apparatus, 
 326, 327. Practical Management of Quadruplex, 328. Adjustment 
 of Apparatus, 329. Repeaters for Multiple Telegraph Systems, 
 329* 138 
 
 CHAPTER IX. 
 
 TESTING TELEGRAPH LINES. 
 
 Object of Tests, 330. Faults and Interruptions, 331. Testing for 
 Disconnection, 332, 333. Testing for Partial Disconnection, 334. 
 Testing for Escape, 335. Testing for Cross, 336. Principle of 
 Cross Test, 337, 338, 339. Testing by Quantitative Measurement, 
 340. Wheatstone Bridge, 341. Best Ratio of Electromotive Forces 
 and Resistances, 342. Principle of Wheatstone Bridge, 343. Act- 
 ual Construction of Bridge, 344. Galvanometer for Wheatstone 
 Bridge, 345. To Measure the Conductivity Resistance of a Tele- 
 graph Line, 346. Conductivity Resistance by Loop Method, 3463. 
 Earth Currents, 347. Measurement of Resistance of Ground 
 Plate at Distant Station, 348. Measurement of Insulation Resist- 
 ance of Line, 349. Location of Position of a Ground, 350. Loca- 
 tion of Position of an Escape, 351. Method of Double Measure- 
 ment, 352. Loop Test, 353. Varley's Loop Test. 354. To Locate 
 a Cross, 355, 356, 357. To Locate a Bad Joint or Abnormal Resist- 
 ance, 358. Measurement of very High Resistances, 359. Shunts 
 of Galvanometers, 360. Measurement by Deflections, 361. Meas- 
 urement of Resistance of Insulators, 362. Measurement of In- 
 ternal Resistance of Battery, 363, 364. Measurement of Resistance 
 of Galvanometer, 365. Differential Galvanometer, 366. Testing 
 for Insulation by Received Currents, 367. Use of Voltmeter and 
 Ammeter in Telegraphic Testing, 368. The Weston Ammeter 
 and Voltmeter, 369. Recording Tests of Conductivity and Insula- 
 tion, 370 190 
 
 CHAPTER X. 
 
 HINTS TO LEARNERS. 
 
 Formation of the Telegraphic Code, 371. The American Morse Code, 
 372. Learning the Code, 373. Handling the Key, 374. Element- 
 ary Principles of Code, 375. Preliminary Practice with the Key, 
 376. Exercises upon Code Characters, 377. Reading by Sound, 
 378, 379. A Parting Word, 380 216 
 
LIST OF TABLES. 
 
 PAGE 
 
 I. CHEMICAL ATOMIC WEIGHTS OF ELEMENTARY SUBSTANCES OP 
 
 BATTERIES 8 
 
 II. SPECIFIC GRAVITIES OF BATTERY SOLUTIONS 9 
 
 III. NATURAL TANGENTS FOR EVERY HALF DEGREE 55 
 
 CONDUCTORS AND INSULATORS IN RELATIVE ORDER 57 
 
 IV. SPECIFIC RESISTANCES OF VOLTAIC SOLUTIONS 63 
 
 V. RECIPROCALS OF NUMBERS FROM i TO 100 67 
 
 VI. SYNOPSIS OF PRACTICAL UNITS 73 
 
 VII. CHEMICAL EQUIVALENTS OF BATTERY MATERIALS. 75 
 
 VIII. DIMENSIONS AND PROPERTIES OF COPPER MAGNET WIRES 94 
 
 IX. SIZE, WEIGHT, AND RESISTANCE OF TELEGRAPH WIRES 112 
 
 X. RESISTANCES AND ESCAPE UPON LEAKY LINES OF VARIOUS 
 
 LENGTHS 129 
 
 XL FARMER'S TABLE FOR COMPUTING FLOW OF CURRENT IN LEAKY 
 
 LINES 137 
 
 THE MORSE TELEGRAPHIC CODE . 218 
 
MODERN PRACTICE 
 
 OF THE 
 
 ELECTRIC TELEGRAPH. 
 
 CHAPTER I. 
 
 INTRODUCTORY. 
 
 1. Fundamental Principles. The electric telegraph is an 
 apparatus by means of which physical effects may be instantaneously 
 produced in distant places. Such effects are technically termed 
 signals. 
 
 2. The art of electric telegraphy consists in the production, control, 
 and organization of electric signals. The signals employed in teleg- 
 raphy may be either visible or audible. Visible signals may be 
 either evanescent, as in the needle telegraph used in Great Britain, 
 and in some forms of apparatus employed in working long submarine 
 cables, or permanent ', as in the case of the Morse register, and in the 
 instruments used on submarine cables of comparatively moderate 
 length. Audible signals are produced by the sounder, and some 
 other less common forms of apparatus. 
 
 3. The signals which are utilized in electric telegraphy are 
 produced at a distant point as required by the agency of elec- 
 tricity. 
 
 4. Nature of Electricity. We do not as yet know ; perhaps 
 we never shall know with certainty, what the agent we call electricity 
 really is. Formerly it was assumed to be an imponderable fluid. 
 This hypothesis was suggested by Franklin. In later years it 
 gradually came to be regarded as one of the many different forms of 
 energy, or, in other words, as a peculiar affection of the particles of 
 ordinary matter. Recent scientific opinion shows a marked tendency 
 
2 Introductory. 
 
 toward the acceptance of the old hypothesis of a fluid, in a modi- 
 fied form. 1 
 
 This conception of the essential nature of electricity appears to be the 
 logical outgrowth of the opinions held, more or less definitely, by such phi- 
 losophers as Franklin, Cavendish, Faraday, Henry, Thomson, and, more 
 especially, Clerk-Maxwell. The theoretical side of the question is discussed 
 with great ability by Oliver J. Lodge, in his Modern Views of Electricity, 
 while its latest aspects are summarized in a valuable paper by Professor 
 William A. Anthony: "A Review of Modern Electrical Theories," Electrical 
 Engineer, ix. 43 ; Trans. Am. Inst. Elec. Eng., vii. 33. 
 
 For practical purposes, however, it is fortunately not in the least 
 necessary that we should know what electricity is, nor that we should 
 commit ourselves to any particular assumption as to its essential 
 nature. A thorough knowledge of the physical effects which it is 
 capable of producing under different conditions, and of the laws 
 which govern its action, are all that the practical electrician needs 
 to acquire. 
 
 5. Elements of the Electric Telegraph. An electric tele- 
 graph comprises four essential elements. These are as follows : 
 
 (i) Means for setting in action, or, as it is commonly termed, producing, 
 
 electricity, termed the generator. 
 (ii) Means for conducting the electricity from place to place, termed the 
 
 conductor or conducting circtiit. 
 
 (iii) Means for controlling the flow of electricity for the purpose of pro- 
 ducing signals, termed the transmitter. 
 (iv) Means for indicating or recording signals, termed the receiver. 
 
 1 Electricity and magnetism are not forms of energy ; neither are they forms of 
 matter. They may, perhaps, be provisionally defined as properties or conditions of 
 matter ; but whether this matter be the ordinary matter, or whether it be, on the other 
 hand, that all-pervading ether by which ordinary matter is everywhere surrounded, is 
 a question which has been under discussion, and which may now be fairly held to be 
 settled in favor of the latter view. DANIELL : Principles of Physics [zd ed.], 532. 
 
CHAPTER II. 
 
 SOURCES OF ELECTRICITY. 
 
 6. Origin of Electricity. Electricity, or, more properly, elec- 
 trical action, may be produced in several known ways. Although 
 electricity, whatever may be its origin, is demonstrably one and the 
 same thing, 1 it has nevertheless become customary to speak of it 
 conventionally, under different names, indicative of its origin. Thus, 
 we have, principally : 
 
 (a) CHEMICAL ELECTRICITY. 
 
 (b) MAGNETO-ELECTRICITY. 
 
 (c) FRICTIONAL ELECTRICITY. 
 
 (d) THERMO-ELECTRICITY. 
 
 There are other means of producing electrical manifestations, 
 which have as yet no practical utility for the purpose under consid- 
 eration, and need not be further considered here. Of those which 
 have been specifically mentioned, chemical and magneto-electricity only, 
 have proved by experience to be adapted to the requirements of 
 the art of telegraphy. 
 
 7. Chemical Electricity. The effects of electricity are most 
 conveniently studied in connection with that form which has its 
 origin in chemical decomposition, especially as it is by the agency 
 of chemical electricity that nearly all the telegraphic apparatus of 
 the world is operated, 
 
 8. The Voltaic Element. The electricity which is employed 
 in telegraphy is usually derived from one or more batteries, each of 
 which is composed of a greater or less number of cells connected 
 Together in a series. A single cell is termed a voltaic or galvanic 
 element. 
 
 9. Description of the Typical Cell. The active or actu- 
 ating parts of each element consist in practice of two dissimilar 
 
 metals, each of which is immersed in a different chemical solution. 
 
 
 
 1 This fact was first experimentally established by Faraday in 1832. His account 
 of this investigation is very instructive, and is given at length in his Experimental 
 Researches (third series), vol. i. pp. 76-109. 
 
 3 
 
Sources of Electricity. 
 
 The following will serve to explain the construction most usually 
 employed in telegraphy : 
 
 In Fig. i is represented a cylindrical glass jar, 7 in. in height, 
 6 in. in diameter, and weighing about 2.5 Ibs. 
 
 FIG. i. Separate parts of Gravity Cell. 
 
 At the right of this is a mass of zinc weighing about 3 Ibs., which 
 has been cast in an iron mould in the form represented. It is pro- 
 Tided with a hanger by means of which it may be suspended from 
 the upper edge of the jar, and also with a damp-screw by means of 
 which a metallic wire may be securely, but removably, attached to it. 
 
 At the left of the jar is seen a triple plate of thin rolled 
 copper, spread out laterally into the form shown, which is 
 designed to be placed in the bottom of the glass cell. Each 
 separate plate may be cut in the 
 form shown in Fig. 2, the three 
 being then united by a single 
 copper rivet at the middle, and 
 the free ends separated radi- 
 ally, as in Fig. i, before placing 
 in the jar. 
 
 A vertical copper wire is permanently riveted to the copper plate. 
 It must not be soldered. The wire is made long enough to extend 
 some 6 in. or 7 in. above the top of the jar. It passes loosely 
 through the bore of a small glass tube, the reason for which is here- 
 
 FIG. a. Section of Copper Plate. 
 
Phenomena of the Cell. 
 
 after explained (27). It is provided at its upper end with a brass clamp 
 termed the copper-connector. Instead of using a glass tube, it is quite 
 usual to substitute a piece of wire covered with a coating of gutta-percha, 
 india-rubber, or other flexible material impervious to the solution. 
 
 The particular form of copper-connector shown in the figure con- 
 sists of a short cylindrical piece of brass, perforated with a longi- 
 tudinal hole for receiving the ends of the wires, into which enter 
 transverse . thumb - screws for 
 
 
 FIG. 3. Copper-connector. 
 
 clamping the wire. A longitudi- 
 nal cross-section of this device 1= 
 is shown in Fig. 3. 
 
 10. Each element, when com- 
 plete, consists of the several parts described, assembled together in 
 the relation shown in Fig. 4, which also shows the jar filled with 
 water to within i in. of the top. Care must be observed, in hang- 
 ing the zinc, not to fracture the glass jar. 
 
 It is very essential that the water for charging a voltaic element 
 should be both pure and soft. Impure or hard water obstructs, and 
 sometimes altogether prevents, the proper action of the chemicals. 
 
 Clean rain-water, if it can 
 be procured, is best for the 
 purpose. 
 
 n. Phenomena of 
 the Cell. If a cell, hav- 
 ing been thus filled with 
 water, in which zinc and 
 copper plates are im- 
 mersed, as shown in Fig. 
 4, be permitted to stand 
 undisturbed for a consid- 
 erable time, a collection 
 of minute bubbles will be 
 observed clinging to the 
 surface of the zinc plate, 
 but no such effect will be 
 observed upon the copper. 
 These bubbles contain 
 hydrogen gas, and are the 
 result of a chemical reaction which takes place between the water 
 and the zinc. 
 
 12. Water is made up of two parts of hydrogen and one part of 
 oxygen, held together by chemical affinity. In the present case, a 
 
 FIG. 4. Gravity-cell ready for Service. 
 
6 Sources of Electricity. 
 
 certain portion of the oxygen of the water enters into chemical com- 
 bination with the metal, forming the compound termed oxide of zinc. 
 A thin coating of this oxide ultimately covers the surface of the zinc 
 plate, giving it a dull bluish gray color, and preventing further oxidi- 
 zation. At the same time the hydrogen which was associated with 
 the oxygen in the decomposed water, is set free, and collects in 
 bubbles which adhere to the surface of the zinc plate. When these 
 bubbles are detached they rise to the surface of the water and the 
 contained hydrogen escapes into the air. 2 
 
 13. This process of oxidization will be recognized as identical 
 with that which takes place in the rusting of iron when exposed to 
 the action of moisture. It is also the same, from a chemical point 
 of view, as the process of combustion or burning. No perceptible 
 effect is produced upon the copper, because the oxygen has less affin- 
 ity for this metal than it has for hydrogen, and hence has no tend- 
 ency to separate from the water. 
 
 14. Chemistry of the Voltaic Effect. If now a small quan- 
 tity of sulphuric acid were to be added to the water contained in the 
 jar, and at the same time the zinc and copper be joined together 
 by a metallic wire in the air outside the jar, a much more vigorous 
 chemical action will immediately set in. The dissolution of the 
 zinc in the liquid will go on with increased rapidity, attended with 
 the evolution of hydrogen in bubbles, not as before upon the surface 
 of the zinc, but upon the copper. 3 
 
 15. Although the chemical action in the case just supposed is 
 attended by the development of electricity, yet such an organization, 
 as a generator of electricity for telegraphic purposes, -would be of 
 little practical utility. The chemical action, though vigorous at first, 
 quickly falls off, and in a short time nearly or quite ceases. This 
 effect arises from the adherence of the liberated hydrogen to the sur- 
 
 3 In a chemical compound the qualities of the constituents are wholly merged in 
 those of the product, and this circumstance distinguishes a true compound from a 
 mechanical mixture in which the qualities of each ingredient are to a greater or less 
 extent preserved. . . . Chemical combinations always take place in certain 
 definite proportions, either by weight or measure. . . . The atomic theory sup- 
 poses that two atoms of hydrogen combine with one atom of oxygen to form a mole- 
 cule of water, and since each atom of oxygen weighs 16 times as much as an atom of 
 hydrogen, the two substances must combine in the proportion of 2 : 16, or i : 8. This 
 principle is known in chemistry as the law of definite proportion. COOKE : New Chem- 
 istry^ 104-8. 
 
 3 The chemical reaction is as follows : Sulphuric acid is composed of hydrogen 2 
 parts, sulphur i part, oxygen 4 parts ; in chemical notation (H SO). The sulphur 
 and oxygen unite with the zinc, forming sulphate of zinc, composed of zinc i part, 
 sulphur i part, and oxygen 4 parts (Zn SO 4 ), which remains in solution in the water, 
 while the hydrogen is set free at the copper plate. 
 
The Hydrometer. 
 
 face of the copper, preventing contact of the solution therewith. 
 This gas also reacts upon the sulphate of zinc (s. z.) which permeates 
 the solution, and causes its zinc constituent to be deposited upon the 
 copper. For these reasons it is necessary to dispose of the hydrogen 
 in such a way that interfering actions may be avoided. This is effected 
 in practice by immersing the copper and zinc in different solutions. 
 
 16. The Gravity Cell. In the voltaic element which has 
 been described and shown in Fig. 4, the two solutions are of un 
 equal densities, so that one can be made to 
 
 float, as it were, upon the other, in the 
 same manner that oil floats upon water. 
 Hence it has received the name of the 
 gravity cell. 
 
 17. Specific Gravity. The density or 
 weight of a given bulk of any liquid com- 
 pared with that of pure water is termed its 
 specific gravity (s. g. ) The s. g. of a liquid is 
 numerically expressed in decimals or mixed 
 numbers, pure water being taken as the 
 standard or unity. For example, the s. g. of 
 water being i.oo, that of linseed oil is 0.93, 
 while that of commercial sulphuric acid is 
 1.84, and of mercury 13.58. 
 
 18. The Hydrometer. The s. g. of 
 any liquid may be determined with sufficient 
 accuracy for ordinary purposes by means of 
 the hydrometer, shown in Fig. 5, which con- 
 sists of a hollow glass float, weighted below 
 with shot, and carrying a stem at the top 
 provided with a graduated scale. When the 
 hydrometer is made to float in any liquid, 
 the division of the scale at the surface de- 
 notes its s. . 4 
 
 
 FIG. 5. Baume's Hydrometer. 
 
 19- Charging the Cell. The glass jar shown in Fig. 4, which 
 
 * The arbitrary scale of the hydrometer commonly known as Baume's, is deter- 
 mined as follows : The point to which the instrument sinks in pure water is assumed 
 as o (zero), while 15 is at the point to which it sinks in a solution containing 15 parts 
 by weight of common salt in 85 parts of water. This space is divided into 15 equal 
 parts, and equivalent graduations are continued to any desired extent. The most 
 useful scale for testing the s. g. of battery solutions is one having a stem about 2 inches 
 long, graduated in degrees from 15 to 40. These degrees denote the percentage of 
 common salt in a solution ; but do not correspond exactly with the percentages in 
 battery solutions, as will appear from an examination of the tables in (23). 
 
8 Sources of Electricity. 
 
 is 7 in. high and 6 in. in diameter, is intended to contain 7 Ibs., or 0.84 
 U. S. gallons of liquid ; and this quantity, when the copper and zinc 
 plates are in place, will fill it to within about one-half inch of the top. 
 A smaller size of cell (6 in. x 5 in.), is also kept in stock by dealers. 
 
 20. To charge the cell, prepare separately a sufficient quantity of 
 the zinc and of the copper solutions. For the zinc solution, which 
 may be mixed in the jar, take for each cell : 
 
 Pure soft water, by weight, 91 oz. (i pints). 
 Crystallized sulphate of zinc (white vitriol), 10 oz. 
 
 Dissolve, and let the solution stand for some hours. The s. g. of 
 the solution should be i.io. 
 
 21. It is not absolutely necessary to make use of s. z. in setting 
 up the cell. If pure water be substituted for the solution directed 
 to be used in the last paragraph, and the circuit be closed between 
 its poles, which is technically termed short-circuiting the cell (14), 
 sufficient s. z. will be formed within a day or two to bring it into full 
 action. Many electricians are of the opinion that a cell started in 
 this way will remain in good condition for a longer time than if 
 charged with a mechanically-mixed zinc solution. 
 
 22. Copper and Zinc Solutions. For the copper solution, 
 take in another glass vessel, for each cell : 
 
 Pure soft water, by weight, 42 oz. (2^ pints). 
 Crystallized sulphate of zinc, 4 oz. 
 Crystallized sulphate of copper, 8 oz. 
 
 The following table will be found convenient for reference : 
 
 TABLE I. 
 
 CHEMICAL ATOMIC WEIGHTS OF ELEMENTARY SUBSTANCES OF 
 
 BATTERIES. 
 
 SUBSTANCE. 
 
 SYMBOL. 
 
 ATOMIC WEIGHT. 
 
 Copper 
 
 Cu 
 
 5"! A 
 
 Zinc 
 
 Zn 
 
 6^.2 
 
 Sulphur 
 
 s 
 
 32. 
 
 Oxvsren 
 
 o 
 
 16 o 
 
 Hydrogen 
 
 H 
 
 i .0 
 
 
 
 
 The chemical notation for crystallized sulphate of copper is (Cu. 
 It is composed of 
 
 Metallic Copper 25.4 per cent. 
 
 Sulphur 12.8 " 
 
 Oxygen 57.7 
 
 Hydrogen 4.0 " 
 
Specific Gravities of Battery Solutions. 
 
 The chemical notation of crystallized sulphate of zinc is (Zn SO* 7H 8 O). 
 It is composed of 
 
 Metallic Zinc 22.7 per cent. 
 
 Sulphur ii. i " 
 
 Oxygen 61.3 " 
 
 Hydrogen 4.9 ' ' 
 
 When dissolved, the s. c. solution will be of a beautiful dark blue 
 tint, and its s. g. will be 1.21. 
 
 23. Specific Gravities of Battery Solutions. The follow- 
 ing tables will aid in maintaining cells is good condition : 
 
 TABLE II. 
 
 SPECIFIC GRAVITIES OF BATTERY SOLUTIONS. 
 ZINC. 
 
 S. g. of solution at 
 77 Fab. 
 
 Reading by Baume 
 hydrometer. 
 
 Per cent of crystal- 
 lized s. z. in solution. 
 
 REMARKS. 
 
 .11 
 
 15 
 
 IS-? 
 
 Minimum density. 
 
 .12 
 
 16 
 
 16.8 
 
 
 13 
 
 17 
 
 17.9 
 
 
 135 
 
 18 
 
 18.9 
 
 
 .14 
 
 19 
 
 20.0 
 
 
 15 
 
 20 
 
 21. 1 
 
 Maximum density. 
 
 .16 
 
 21 
 
 22.3 
 
 
 17 
 
 22 
 
 23-4 
 
 
 .18 
 
 23 
 
 24.6 
 
 
 .19 
 
 24 
 
 2 5 .8 
 
 
 .20 
 
 25 
 
 26.9 
 
 
 .46 
 
 4 8 
 
 62.1 
 
 Saturation. 
 
 COPPER. 
 
 S. g. of solution at 
 72 Fah. 
 
 Reading by Baume 
 hydrometer. 
 
 Per cent, of crystal- 
 lized s. c. in solution. 
 
 REMARKS. 
 
 1.03 
 
 5 
 
 5-0 
 
 
 1.07 
 
 10 
 
 IO.O 
 
 
 I. II 
 
 15 
 
 15.4 
 
 Half saturation. 
 
 I-I5 
 
 20 
 
 21.2 
 
 
 1.20 
 
 25 
 
 27-5 
 
 
 1. 21 
 
 27 
 
 3O.O 
 
 Saturation. 
 
 24. Installation of the Gravity Cell. The copper and zinc 
 plates being put in their respective places in the jar (which will then 
 4>e about three-fourths full of s. z. solution), the heavier s. c. solution 
 
io Sources of Electricity. 
 
 may be introduced into the bottom by means of a f in. tube of glass 
 or rubber, having a small glass or rubber funnel inserted in its upper 
 end. The lower end of the tube must be central and very near the 
 bottom, and the s. c. must be poured in quite slowly, so as not to 
 agitate the mass and cause the two solutions to mingle. If this 
 operation is carefully performed, the lower part of the jar will now 
 be filled with s. c. solution, of a uniform deep blue color, to a point 
 a little above the top of the copper plate, being separated from the 
 transparent s. z. solution above by a sharply defined line of demarka- 
 tion. Care must now be taken that the cell is not moved about,, 
 shaken, or stirred by the careless removal of the zinc or copper 
 plates, as this would cause the two solutions to intermingle, a con- 
 dition which it is very necessary to avoid. For the same reason, it 
 is advisable to place each cell in the position which it is to perma- 
 nently occupy, before introducing the s. c. solution. The most 
 convenient place will be found to be a shelf about 48 in. from the 
 floor. An enclosed box affixed to a wall or frame, and having a 
 glass front hinged to open upward, is an excellent arrangement, as 
 the cells are then in sight, so that their condition may be observed 
 at all times, while at the same time they are protected from dirt,, 
 and in a great measure from evaporation and from extremes of 
 temperature. 5 
 
 25. Instead of mixing the s. c. solution in a separate vessel, it is a 
 common practice to fill the jar to within i inch of the top with the 
 s. z. solution, prepared as above directed, and then slowly drop in 
 8 oz. of s. c. crystals about the size of a hazel-nut, which will fall to- 
 the bottom and slowly dissolve. The only objection to this pro- 
 cedure is its liability to form a s. c. solution of unequal density in dif- 
 ferent parts, which is undesirable (26). When this plan is adopted, 
 care must be taken not to put in more than the prescribed quantity 
 of s. c., and particularly to see that no particle of it gets upon the 
 zinc plate. 
 
 26. Modified Form of the Copper Plate. A more advan- 
 tageous form for the copper plate than that which has been described, 
 
 6 Wooden, tin, or porcelain covers are sometimes fitted to the cells for excluding 
 dust and preventing evaporation, and serve a good purpose. Wooden covers should 
 not fit too closely ; there is danger that they may swell from moisture and fracture 
 the jars. 
 
 Great annoyance is sometimes caused by the apparently unaccountable breakage of 
 glass jars. The primary cause of this is poor material or imperfect annealing during 
 the process of manufacture ; the immediate cause is usually a sudden change of tem- 
 perature. A jar on a high shelf in a warm room in winter is sometimes cracked by the 
 current of cold air caused by opening an outer door. A little care will avoid such 
 accidents. 
 
Formation of the Electric Circuit. 1 1 
 
 particularly in case it is desired to maintain a current of moderate 
 quantity for a long time, is a ribbon of very thin rolled 
 copper, 48 in. long and J in. wide, coiled spirally like a 
 clock-spring, and laid flat in the bottom of the cell, the con- 
 ducting wire being riveted to the outer end as seen in Fig. 6. 
 An objection to the form of plate shown in Fig. 4, when 
 used under the conditions here mentioned, is that unless 
 carefully looked after, the s. c. solution will 
 become weaker at the top than at the bot- 
 tom of the copper, whereupon a closed cir- 
 cuit (30) is established, consisting of one 
 FIG. 6. Modification of Copper metal (the copper), and two dissimilar 
 liquids (the strong and the weak solu- 
 tion), setting up an action which is liable to attack and destroy the 
 upper portion of the plate, uselessly consuming material for which 
 no equivalent external current is rendered. 
 
 27. This action explains the necessity of enclosing the connecting 
 wire from the copper electrode of the gravity battery in a glass tube, 
 or covering it with gutta-percha or india-rubber, where it is exposed 
 to the action of the solution. If it were not protected it would soon 
 be destroyed by chemical action, and the circuit consequently inter- 
 rupted. 
 
 28. Formation of the Electric Circuit. The parts of the 
 cell being properly assembled together, and the solutions in their 
 respective places as directed in (24), the element is ready for service. 
 If now the zinc and copper plates be joined together in the air by a 
 metallic wire as before explained (14), a current of electricity, as it is 
 technically termed, will traverse the wire. It wilt traverse, moreover, 
 not only the wire, but also the metallic plates and solutions within 
 the voltaic element, the whole path forming what is termed a circuit 
 of electrical conductors, or briefly, an electric circuit. 
 
 29. The presence of an electric current in such a circuit may 
 be demonstrated in several different ways, as will be shown further 
 on (86). For the present we are only concerned to observe its 
 immediate effects upon the constituent parts of the voltaic element 
 which sets it in action. 
 
 30. The circuit of a voltaic element maybe diagrammatically rep- 
 resented by a closed ring as shown in Fig 7. It is composed of the 
 following parts : 
 
 (i.) The zinc plate. 
 (2.) The zinc solution. 
 (3.) The copper solution. 
 
 (4.) The copper plate. 
 
 (5.) The metallic connecting wire. 
 
12 
 
 Sources of Electricity. 
 
 POSITIVE 
 
 The four first named constitute the internal circuit, and the last 
 the external circuit. 
 
 Before the zinc and copper plates are united by the connecting 
 wire, the circuit is said to be open or broken, and the cell is said to be 
 
 on open circuit. When the 
 connection is established by 
 the wire, the circuit is said 
 to be made, completed, or 
 L POLE closed, the last mentioned 
 phrase being most usual. 
 In this case the cell is 
 spoken of as being on closed 
 circuit, which is another way 
 of saying that chemical ac- 
 tion is going on within it. 
 
 31. Nomenclature of 
 the Electric Circuit 
 In a voltaic cell, the zinc 
 
 FIG. 7. Diagram of Closed Voltaic Circuit 
 
 plate is termed the positive plate or element, and the copper the 
 negative plate or element. These terms are purely conventional 
 and arbitrary, and properly signify nothing beyond the antagonis- 
 tic or opposite electrical condition which exists. The general 
 term for these plates is electrodes, a term introduced by Faraday. 
 The air terminals of the electrodes, to which the conducting wires 
 are attached, are called the poles. It should be noted that the 
 copper plate of the element, although the negative electrode, is con- 
 nected with the positive pole, and in like manner the zinc or posi- 
 tive electrode is connected with the negative pole, because the current 
 is conventionally assumed to flow from the positive plate, through 
 the solution and out by the copper plate. The positive and negative 
 poles of every generator of electricity are respectively designated by 
 the conventional signs -f- and (plus and minus). The direction 
 of the electric current, for convenience of description, is conventionally 
 assumed, as above stated, to be through the solutions from the zinc 
 to the copper electrode, and thence through the connecting wire 
 from the copper to the zinc electrode. The assumed direction in 
 any wire is denoted by the conventional sign of an arrow pointing in 
 the direction of the negative pole. 
 
 32. Chemical Reactions Arising in the Closed Circuit. 
 The chemical reactions within the cell, when its external circuit is 
 closed, and its several constituent parts traversed by an electric cur- 
 rent, are as follows : 
 
Effect of Continued Action. 13 
 
 (i.) The oxygen of the s. z. solution (12) combines particle by 
 particle with the metal of the zinc plate, forming oxide of zinc. 
 
 (2.) The oxide of zinc, formed as above, combines with the sul- 
 phuric acid of the s. z. solution (14), and forms s. z., which is added 
 to the s. z. already present in the solution surrounding the zinc. 
 
 (3.) Oxygen combines with the s. c. and forms oxide of copper. 
 
 (4.) The copper in this oxide separates from the oxygen and is 
 deposited in a pure metallic form upon the copper plate. 
 
 At the surface of the zinc plate, the oxygen of the water contained 
 in the s. z. solution is separated from the hydrogen, while at the 
 surface of the copper plate this hydrogen combines with the oxygen 
 which is separated from the oxide of copper. 
 
 33. Effect of Continued Action. This action goes on with- 
 out cessation, provided the circuit remains closed, until some one of 
 the materials contained in the cell becomes exhausted. It will be 
 observed that as the action continues, the zinc plate is gradually dis- 
 solved, being oxidized, or in fact burned ; that the proportion of 
 sulphate in the s. z. solution constantly increases, rendering it more 
 dense and its s. g. greater ; that, on the contrary, the s. c. solution 
 grows less dense, and its s.g. diminishes ; and finally, that the copper 
 plate continually increases in weight, by the deposition upon its 
 surface of metallic copper abstracted from the copper solution in 
 which it is immersed. 
 
 34. As the weight of the s. z. solution, as indicated by its s.g., 
 gradually .increases, while on the contrary that of the s. c. solution 
 continually becomes less, it necessarily happens after the lapse of 
 a greater or less time, the former becomes heaviest, and consequently 
 descends to the bottom of the cell, forcing the s. c. solution to the 
 top, where it is brought into direct contact with the zinc plate, 
 depositing metallic copper thereon. This deposit interrupts the 
 normal chemical action of the cell to such an extent that the electric 
 current greatly diminishes, and ultimately ceases altogether. 
 
 35. By intelligent management this injurious action may be pre- 
 vented, or at least postponed for a long time. The frequent use of 
 the hydrometer .(18) is almost indispensable for this work, and a 
 knowledge of the condition of the cell is also greatly facilitated by 
 placing it in front of a window, so that its interior may be clearly 
 viewed by transmitted light ; or at all events, it should be provided, 
 if possible, with a white background. 
 
 36. Rate of Consumption of Material. The rapidity with 
 which the materials of the cell are consumed, and its active life short- 
 ened, depends almost entirely upon the amount of work done by it, 
 
14 Sources of Electricity. 
 
 or in other words, the quantity of electricity per unit of time which 
 it is required to furnish. This question, which is an exceedingly 
 important one, will be fully considered further on (154). 
 
 37. Maintenance of the Cell. The first sign of the exhaustion 
 of a cell generally appears in the s. c. solution. It is not practicable 
 to examine the condition of this solution by means of the hydrometer, 
 but fortunately the degree of intensity of its blue color furnishes an 
 infallible indication of its density. The strong blue tint of the 
 original solution will after a time begin to fade in the vicinity of the 
 upper edge of the copper plate, and the line of demarkation between 
 it and the zinc solution will become less and less distinct. When 
 this is seen to occur, additional s. c. must be supplied, either through 
 the tube in the form of a solution as directed heretofore (24), or by 
 dropping i oz. of crystals into the jar, being careful to observe the 
 precautions heretofore noted (25). It is much better not to make 
 use of finely powdered s. c. for this purpose, as this is liable to 
 cement itself into a hard insoluble mass at the bottom of the cell, 
 which defies all efforts to remove it without breaking the jar. The 
 s. z. solution should be tested by means of the hydrometer (18) at 
 least once a week while the cell is in constant action. The s. g. of 
 the solution, which at the outset was about i.io, will gradually in- 
 crease. When it reaches 1.15, as shown by the scale,, the solution 
 should be diluted with water. If the s. z. solution be permitted to 
 approach closely to its saturation point, 1.45, see table (23), not 
 only is the chemical action of the cell diminished, but a saline 
 deposit of white powder (crystallized sulphate of zinc) begins to form 
 upon the zinc, and upon the edge of the jar above the solution, and 
 by capillary attraction ultimately conveys the liquid over the edge to 
 the outside of the cell and creates a disagreeable nuisance. This 
 may be avoided by keeping the s. g. of the zinc solution below 1.20 
 and by occasionally wiping the inner edges of the jar with a cloth or 
 sponge saturated with cotton-seed or heavy paraffin oil. 
 
 38. Prevention of Evaporation. Sometimes a thin stratum 
 of one of the oils above mentioned is gently poured upon the top of 
 the zinc solution, after the cell has been set up as directed in (24), 
 a procedure which effectually prevents evaporation and the formation 
 of saline salts. Inasmuch, however, as the presence of the oil 
 renders the cleaning of the zinc plate, when necessary, a disagree- 
 able and inconvenient task, it is perhaps an open question whether 
 the practice is to be recommended. If it is at all possible to give 
 the cell proper attention from time to time as required, it is probably 
 better to dispense with all such expedients, but when such is not 
 
Prevention of Evaporation. 
 
 the case, it may be advisable and even necessary to make use of 
 them. 6 
 
 39. The best way to dilute the zinc solution is to use a tube of 
 rubber, glass, or lead, about 24 in. long, and -J- in. diameter, bent 
 into a siphon, or an inverted ||, one leg of which is considerably 
 longer than the other. Fill the siphon with water, stopping both 
 ends with the ringers, and after placing a wooden bucket or other 
 convenient receptacle in front of the cell, but at a considerable lower 
 level, dexterously insert the tube into the cell (at the same time re- 
 moving one finger), so that the inserted end will be near the center 
 of the jar and about |- in. above the copper plate, while the longer 
 end is directed toward the bucket. Now withdraw the other finsrer 
 
 O 
 
 from the lower end of the tube, and the solution will flow in a steady 
 
 stream into the bucket so long 
 
 as the short end of the tube 
 
 remains immersed (See Fig. 8). 
 
 Some prefer, instead of a 
 
 siphon, to use a large syringe, 
 
 sold by dealers, with a nozzle 
 
 at right angles to the barrel, 
 
 having a capacity of about 3 
 
 gills. This should be rinsed 
 
 out in warm -water each time 
 
 after it has been used. 
 
 After withdrawing about I 
 quart of the solution in this 
 way, which with the cell under 
 consideration will be about 2 
 in. of vertical depth, refill the 
 cell to its original depth, \ in. 
 from the top, with pure soft 
 water. In order not to stir 
 up the liquids, this may with 
 advantage be done with a 
 small sprinkling pot having a 
 fine rose at the end of its spout, or with due care, may be equally 
 well effected by holding a spoon or some such implement just at the 
 surface, so as to break and scatter the vertical force of the stream 
 as it is poured. 
 
 6 Another device which is sometimes resorted to for the purpose of preventing the 
 formation of salts upon the edge of the jar, is to invert the latter before using, and 
 dip it in a bath of melted paraffin contained in a shallow dish, to the depth of half an 
 inch or less, which forms, when cold, an adherent and repellent coating. 
 
 FIG. 8. Drawing off Zinc Solution. 
 
1 6 Sources of Electricity. 
 
 40. Dismantling the Cell. The above described operation, if 
 properly carried out, will practically restore the cell to its original work- 
 ing condition. The increasing deposit upon the copper plate will not 
 interfere with the proper action of the cell, and need not be dis- 
 turbed. The zinc plate, however, will gradually become covered 
 with a thick coating of dark brown oxide, which will adhere to it 
 with considerable tenacity. This must be removed from time to 
 time, especially when, by becoming of a reddish color, it shows 
 traces of deposited copper. Lift the zinc plate carefully from the 
 solution, and remove the crust which has formed upon the metal, by 
 means of a scraper of hard wood, or a stiff brush sold by dealers in 
 supplies for that purpose (a wire brush answers the purpose admira- 
 bly). Remove all the oxide clown to the surface of the metal, wash 
 the latter in clean water, and return to its place in the cell. If any 
 undissolved crystals of s. c. are found in the bottom of the jar, these 
 should be washed and used again. 
 
 The zinc should be cleaned 'at once after removal from the cell, 
 while still wet. If the cleaning has to be deferred, the zinc must be 
 placed in water for some time before commencing operations. Great 
 care must be taken to see that no water gets between the arm of the 
 zinc and the brass binding-screw, as this will cause a deposit of sul- 
 phate of zinc, which may entirely prevent the passage of the current 
 when the zinc is again put to use. 
 
 41. Diffusion of Solution within the Cell. An absolute 
 separation of the copper and zinc solutions in the voltaic cell cannot 
 be attained. Liquids of unlike density separated from each other 
 by gravity always tend to intermingle by a slow process of diffusion, 
 and thus ultimately to form one homogeneous solution. This ten- 
 dency may be reduced to a minimum by intelligent management and 
 proper attention to the requirements of the cell while in action, so as 
 to cause but little practical inconvenience. 
 
 42. The solutions manifest a much stronger tendency to mix when 
 the cell is on open than when on closed circuit. Hence, cells in 
 which the solutions are separated by gravity, and in fact all sulphate 
 of copper cells, give the most satisfactory results when used, as in 
 telegraphy, upon circuits which are closed the greater portion of the 
 time. 
 
 43- Neutralizing the Zinc Solution. When the cell is dis- 
 mounted and renewed, the s. z. should be drawn off with the siphon 
 and thrown into a wooden vessel, together with a few pieces of 
 metallic zinc, which will purify the liquid by reducing any metallic 
 copper which may be present in it. It should then be filtered or 
 
Waste Products of the Cell. 1 7 
 
 strained through cloth or sand, and afterward diluted with water 
 until its specific gravity is reduced to i.io. It is then in suitable 
 condition to be used in the renewed cell, instead of making a new 
 solution as directed in (20). 
 
 44. Waste Products of the Cell. Where a large number of 
 cells are in constant use, it is generally worth while to dry and pre- 
 serve the material thus removed from the zincs, commonly called 
 "battery mud," as it is rich in metallic zinc and copper, and will 
 usually be willingly purchased at a fair price by brass-founders. 
 When the copper plates have become heavily encrusted with metallic 
 deposits, they may with advantage be disposed of in the same way. 
 Electrotype or deposited copper, as this is termed, is much valued 
 in many of the industrial arts. 
 
 45. Copper plates which have been used in the battery, and which 
 are intended to be used again, should be kept in water; taking care 
 that the connecting wire, with its coating of gutta-percha or india- 
 rubber, is completely immersed. Zinc plates, on the contrary, must 
 be kept in a dry place, never in water. 
 
 46. Other Forms of the Cell. Much unprofitable ingenuity 
 has been displayed by inventors in varying the form, proportions and 
 relations of the elements of the sulphate-of-copper cell, in pursuit of 
 imaginary advantages. As a matter of fact, it has been found to be 
 almost wholly immaterial what the form and arrangement of the 
 parts may be, so long as the necessary general principles of action 
 are kept in view. The consumption of a given amount of zinc and sul- 
 phate of copper can never in any chemical combination, or under any 
 circumstances, evolve more than a definite and perfectly well ascertained 
 quantity of electricity, in a form available for use, although if the cell 
 be unskillfully proportioned or arranged, the quantity of electricity 
 evolved may be less than it should be (154). The principal differ- 
 ence between different forms is that some require less frequent atten- 
 tion than others ; but this advantage is sometimes gained at the 
 expense of other more valuable qualities. 
 
 47. Among the different practical voltaic cells which have been 
 employed in America to a greater or less extent, commonly known 
 by the names of their originators and designers, but involving 
 essentially the same principles as the one which has been de- 
 scribed, may be mentioned the Hill, 7 Callaud, 8 Minotto, 9 Thom- 
 
 7 L. BRADLEY in The Telegrapher, iii. 153 ; E. A. HILL in the same, iii. 201. 
 
 8 BLAVIER : Telegraphie Electrtque, i. 271 ; POPE : Modern Practice of the Electric 
 Telegraph (4th ed.), 106. 
 
 F. JENKIN : Electricity and Magnetism, 225. 
 
1 8 Sources of Electricity. 
 
 son, 10 etc., etc., for a particular description of which recourse may 
 be had to the publications indicated in the references. 
 
 48. The Lockwood Cell. This form of cell has been found 
 to give excellent results in cases in which a moderate but perfectly 
 uniform current is required without attention for a great length of 
 time. The jar is of extra depth (9 in.) and the copper plate consists 
 of two flat spirals of wire coiled like a clock-bell and laid in reverse 
 directions to each other, one beneath and the other at the top of a 
 mass of 5 Ibs. of s. c. in crystals, placed in the bottom of the jar. 
 The connecting wire is continuous with the lower spiral, while the 
 two spirals are united by a vertical rod or stout wire which is con- 
 nected to their inner ends. The action of the current traversing the 
 coils appears to act, in some manner not well ascertained, to oppose 
 the tendency of the s. c. solution to ascend in the jar and reach the 
 zinc plate. A series of these cells will maintain a current for a 
 year under favorable conditions. 
 
 49- The Daniell Cell. This is the original form of the sul- 
 phate of copper element. It was formerly much used in the tele- 
 graphic service, but has now been practically superseded by the 
 equally efficient and more economical gravity cell. As usually con- 
 structed, the Daniell cell consists of a jar of glass or earthenware F 
 (Fig. 9) 6 in. in diameter and 8 in. high. A thin sheet of copper G 
 is bent into a cylindrical form so as to fit loosely within the jar, and 
 to this is affixed a chamber provided with a perforated bottom, 
 designed to receive a supply of s. c. in crystals. A copper strip is 
 riveted to the plate G and provided with a clamp at its extremity, 
 adapted either to receive a conducting wire, or to connect to the zinc 
 plate of the next adjacent element, as the case may be. Within the 
 copper cylinder is a porous-cup (as it is technically termed), H, of 
 unglazed porcelain ware, 7 in. high and 2 in. diameter, within which 
 is placed a bar of cast zinc of the cross-section shown at X, or as 
 sometimes preferred, a hollow cylinder with a vertical slit in one 
 side, the latter form yielding a somewhat greater quantity of elec- 
 tricity, but being less convenient to clean. 
 
 50. The porous-cup H is filled with s. z. solution prepared as 
 directed in (20) and the jar outside the porous-cup with s. c. solution 
 of s. g. 1. 10. A quantity of the crystals may be placed in the per- 
 forated chamber attached to the copper plate, which gradually dis- 
 solve and thus maintain the solution at its proper density. Pure 
 water may be used in the porous cell as directed in (21) if pre- 
 ferred. 
 
 10 F. JENKIN : Electricity and Magnetism, 223. 
 
Maintenance of the Daniell Cell. 
 
 51. Maintenance of the Daniell Cell. This cell is main- 
 tained in substantially the same manner as the gravity. Unless a 
 very large volume of current is required, it will be found much more 
 
 FIG. 9. The Daniell Cell. 
 
 economical to feed the s. c. solution with small quantities of crystals, 
 placed in the chamber once in every two or three days, and keeping 
 the solution but half saturated (s. g. i.io) and uniform in color 
 throughout, by stirring it with a wooden or glass rod. The s. z. 
 solution should be maintained as nearly as possible at the same s. g. 
 as the copper solution. 
 
 52. Renewal of the Daniell Cell. When taken apart for 
 cleaning, more or less copper will usually be found deposited in 
 patches on the porous-cup. This deposit cannot be prevented, but 
 may be greatly diminished by suspending the zinc free from the bot- 
 tom or sides of the porous-cup, or even by placing a piece of glass in 
 the bottom of the cup for the zinc to stand on. It is also a good 
 plan, for the same reason, to saturate the bottom of the porous-cup 
 to the height of half an inch with melted paraffin or tallow before 
 putting it to use. The porous-cup ought to be replaced by a new 
 
2O Sources of Electricity. 
 
 one whenever as much as half of its surface has become encrusted 
 with metallic copper by continued use. If it becomes cracked it 
 should be replaced at once, or a great waste of material will ensue. 
 
 The porous-cup of an element intended only for occasional use, 
 may with advantage be made thicker and less porous in texture than 
 if intended to be kept continuously in action. 
 
 53. Intermingling of the Solutions. It should be observed 
 that at the best, a porous cell merely obstructs and does not prevent 
 the ultimate intermingling of the copper and zinc solutions. The 
 liquids will pass through the porous wall of the cup by virtue of a 
 singular property, common to all dissimilar liquids when separated 
 by a porous partition, 11 and will be found to exhibit a constant 
 tendency to rise in the outer cell and to disappear from the porous- 
 cup. This tendency is obviously assisted by the passage of the 
 current. 
 
 54. Porous-cups which have been used in a cell, must not be 
 allowed to become dry after being taken out, but should be kept in 
 water, otherwise the crystallization of the s. z. contained in the pores 
 will almost certainly break them. 
 
 55. Choice of Battery Materials. The s. c. and the metallic 
 zinc used for electrical purposes should be of good quality and free 
 from adulterations. Adulterated s. c. is very seldom met with in the 
 United States ; that sold by dealers in electrical supplies is almost 
 uniformly of good quality. The best commercial zinc usually con- 
 tains a small proportion of iron and lead. An analysis of spelter of 
 good quality for electrical purposes, gave : 
 
 Zinc 98.76 per cent. 
 
 Lead 1.18 
 
 Iron 0.06 
 
 56. The question of the effects of temperature upon the efficiency 
 of the voltaic cell is a very important one, and merits much more 
 consideration than it has hitherto received. The sulphate of copper 
 cell is especially sensitive in this particular, and should be carefully 
 guarded against cold. This subject is further considered in a subse- 
 quent chapter (162). 
 
 57- General Directions for the Care of Cells. The direc- 
 tions for the management of the sulphate of copper element may be 
 summarized as follows : 
 
 (i.) Place the cells in a clean, dry, and well lighted situation, not 
 exposed to dust nor to extremes of temperature. 
 
 "JOHNSON'S Univ. Cyclopedia, Art. Endosmose. 
 
The Oxide of Copper Cell. 
 
 21 
 
 (2.) Do not move, shake, or stir the cells after the s. c. solution 
 has been introduced into them. 
 
 (3.) Start each cell with s. z. solution at s.g. i.io (or 15 Baume), 
 and s. c. solution not below s.g. 1.20 (or 25 Baume). 
 
 (4.) Keep the s. c, solution of a strong blue color up to a point 
 just above the copper plate, by adding s. c. as fast as it is consumed 
 by the action of the current, but be careful never to put in too much 
 s. c. at one time. 
 
 (5.) Test the s.z. solution frequently with the hydrometer, and 
 when its s.g. reaches 1.15 (or 20 Baume), dilute with water to re- 
 duce it to i.io (15 Baume). 
 
 (6.) Wipe off with a greasy cloth any crystallized s. z. which forms 
 upon the edges of the jars. 
 
 (7.) Do not let the zinc become too heavily coated with brown 
 oxides. If the oxides tend to form into pendants, hanging below the 
 zinc, detach these at once with a bent wire ; they cause a great waste 
 of material. 
 
 (8.) It is an excellent plan to wrap the zinc neatly in linen paper 
 (the kind called parchment paper is best), securing the folded flaps 
 at the top with sealing-wax, and tying strongly with twine passed 
 several times around the whole. This expedient prevents particles 
 of zinc from falling on the copper, and 
 also aids the action of gravity in pre- 
 venting the too rapid upward diffusion 
 of the s. c. solution. 
 
 58. The Oxide of Copper Cell. 
 A voltaic combination in which the 
 metallic elements are amalgamated 
 zinc 12 and protoxide of copper (Cu O), 13 
 and the exciting agent a solution of 
 caustic potash ( K O ), has of late 
 found much favor in the telegraphic 
 service, under the name of the Edi- 
 son-Lalande cell. In the size designed 
 for this use, the glass contain ing-jar is 
 8 in. high, 6 in. in diameter, and 
 
 FIG. 10. Oxide Plate of Edison- 
 Lalande Cell. 
 
 12 Zinc which has been immersed in dilute sulphuric acid, and then coated with 
 mercury, is said to be amalgamated. This process renders the chemical action upon 
 the zinc more uniform and less wasteful in certain forms of voltaic elements. It is of 
 no advantage in the sulphate of copper element. 
 
 13 Protoxide of copper is obtained by roasting copper turnings. The product is then 
 ground to powder and compressed into solid masses, from which are cut plates of 
 suitable size for the cell. 
 
22 
 
 Sources of Electricity. 
 
 weighs 5.75 Ibs. It is provided with a porcelain cover, from which 
 are suspended two rectangular plates of rolled zinc, fitted with a 
 double clamp-screw for attaching the wire. A skeleton frame of 
 
 copper (Fig. 10) is fitted to clasp 
 two rectangular slabs containing i 
 Ib. of copper oxide, and is suspend- 
 ed from the porcelain cover be- 
 tween and facing the zinc plates. 
 To prevent possible contact, a fen- 
 der of hard rubber is inserted be- 
 tween the oxide plates, projecting 
 on each side. A transverse cop- 
 per bolt and nut clamps the whole 
 firmly together. Fig. n shows 
 the appearance of the cell when 
 mounted. 
 
 59. Setting Up and Main- 
 taining the Oxide of Copper 
 Cell. The solution for this cell 
 consists of i part by weight of caus- 
 tic potash dissolved in 3 parts pure 
 soft water (s. g. 1.33 ; 38 Baume), 
 
 with which the jar is to be filled to within i in. of the top. Caustic 
 potash, in sticks of a size just sufficient to make the proper solution, 
 are usually supplied by dealers. The solution should be stirred with 
 a wooden or glass rod while the potash is dissolving, otherwise the 
 evolution of heat may fracture the jar. Finally, a stratum of heavy 
 paraffin oil (s. g. 1.46 ; 48 Baume), about J in. deep, is poured upon 
 the solution to prevent evaporation. 
 
 The cell will ordinarily require no further attention until its mate- 
 rials are entirely consumed, when both the zinc and oxide plates, as 
 well as the solution, must be renewed. 
 
 60. Chemical Reactions of the Oxide of Copper Cell. 
 When the external circuit is closed, the oxygen of the water in the 
 solution, uniting with the zinc, forms oxide of zinc as in other cells. 
 This, combining with the potash in the solution, forms a soluble 
 double salt of zincate of potash, which is decomposed as rapidly as 
 it is formed. The hydrogen which is set free unites with the oxygen 
 of the protoxide of copper of the negative plate, and deposits metallic 
 copper. The reaction takes up i equivalent of zinc, i of potash, i 
 of protoxide of copper, and deposits i equivalent of metallic copper. 
 The wasteful local action in this cell is so small as to be practically 
 
 FIG. ii. Edison-Lalande Cell. 
 
The Grove and Bunsen Cells. 
 
 FIG. \\a. 
 d'Infreville's Wasteless Zinc 
 
 negligible, which is an important advantage. 14 The copper is de- 
 
 posited in a, pure form, suitable for industrial uses. 
 
 61. The Grove and Bunsen Cells. Other voltaic combina- 
 
 tions, formerly largely used in telegraphy but now obsolete, consist 
 
 of amalgamated zinc in dilute sulphuric acid, and platinum in nitric 
 
 acid known as the Grove, and carbon in bichromate of potash solu- 
 
 tion known as the Bunsen. 15 
 
 6ia. The Wasteless Battery Zinc. The unavoidable waste 
 
 of metal in the gravity cell (10) from the unconsumed part of each 
 
 zinc electrode which has to be thrown aside, sometimes amounts to 
 45 per cent, of the original weight. This 
 loss is avoided by the " wasteless " electrode 
 invented by G. dTnfreville, which is made 
 up of two or more similar sections^ each 
 formed of a hub with inclined radial arms 
 (see Fig. n#.) The hubs of the several sec- 
 tions are slightly coned, and fit snugly into 
 one another. Fig. \\b. shows an electrode 
 of three sections after having been some time 
 
 in use. When the lowermost section has 
 
 been nearly consumed, a new one is added 
 
 at the top, and in this way each is oxidized 
 
 in turn without waste. The coned form of 
 
 the hubs enables the sections to be put to- 
 
 gether in a perfectly secure manner by a 
 
 light blow. With this electrode, the resist- 
 
 ance (153) per Cell is reduced tO One-third Sectional view of Wasteless Zinc. 
 
 its former value, while much is gained in constancy. 
 
 A brass hanger or support accompanies the zinc, which grasps it 
 securely by an ingenious elastic friction. A plan view of this hanger 
 
 is shown in Fig. nc. A con- 
 necting wire of any thickness 
 may also be firmly clamped, as 
 
 FIG. 1I ,.-d'infreviiie- 5 Hanger. shown, between the branches of 
 
 the Y-shaped extremity of the hanger, the arms of which interlock 
 by their own elasticity so as to hold it securely. 
 
 14 F. DELALANDE and G. CHAPERON in L Electricien, vi. 98, 103 ; Electrical Review 
 ^London), xiii. 59, 102; xiv. 485; N. Y. Electrical Engineer, ix. 153. 
 
 1 * For description and directions for management of the Grove cell see Modem Practice 
 vfthe Electric Telegraph, 4th ed , 15 ; and for Bunsen bichromate cell, the same, p 17. 
 
 FIG. \\b. 
 
 OF THK 
 
 UNIVERSITY 
 
CHAPTER III 
 
 THE SOURCES OF ELECTRICITY. (Continued.) 
 
 62. Magneto-Electricity. Electricity which is evolved from 
 a magnet, by moving coils of wire within the sphere of its influence 
 by mechanical power, is called magneto or dynamo-electricity. The 
 distinction between the two is purely arbitrary and nominal, and has 
 reference only to the particular structure and organization of the 
 machines from which they are respectively derived. 
 
 63. Magnetism. It has been known from time immemorial that 
 certain natural ores of iron possessed the property of attracting iron 
 and steel, and that these metals were themselves capable, under 
 proper conditions, of being endowed with a like property. This 
 property, which is called magnetism, is also capable of being mani- 
 fested, though in a less marked degree, by certain other metals, 
 especially cobalt and nickel. Such a mass of magnetic ore is called a 
 natural magnet or lodestone. A mass of iron or steel to which 
 magnetic properties have been imparted by any known means, is 
 called an artificial magnet. Soft iron is capable of retaining magnetic 
 properties only during such time as it remains under the direct 
 influence of the magnetizing force, and under such conditions is said 
 to be a temporary magnet. Hardened iron or steel continues to 
 retain magnetic properties after the withdrawal of the magnetizing 
 force ; and hence a mass of hardened steel, when magnetized, is 
 called a permanent magnet. 1 
 
 64. The Magnetic Needle. A piece of hardened steel, which 
 has been permanently magnetized, possesses marked peculiarities. 
 When a straight bar of this kind, which is termed a bar-magnet, is 
 suspended freely by its center of gravity, it always tends to place 
 itself approximately north and south, usually in the direction of its 
 greatest length. The imaginary line in which it thus places itself 
 is termed the magnetic meridian. A small magnetic steel bar, when 
 
 1 For an exposition of the modern theories of magnetism, the student is referred to 
 the papers of D. E. Hughes, Proc. Royal Soc., 1879, p. 56; J. A. Ewing, Royal Soc., 
 1890; Elec. World, xvi. 241. A summary will be found in Kapp, Electric Trans- 
 mission of Energy, 16. The celebrated lecture of Prof. A. M. Mayer, The Earth a 
 Great Magnet, New Haven, 1872, presents the whole subject of magnetism in a most 
 admirable, popular way. 
 
 2 4 
 
Phenomena of Magnetic Induction. 
 
 suspended by a filament, as shown in Fig. 12, or upon a pivot, as 
 shown in Fig. 13, is called a magnetic needle. Such a needle, in con- 
 junction with a graduated dial, consti- 
 tutes the well-known magnetic compass. 
 65. Phenomena of Magnetic 
 Induction. When an artificial mag- 
 net is placed in the immediate neigh- 
 borhood of one or more pieces of iron, 
 or of a quantity of iron chips or filings, 
 these are instantly at- 
 tracted. They attach 
 
 themselves to the magnet, and will be found to adhere 
 with considerable force to its surface. At the same 
 time, a magnetic influence is exerted upon these bod- 
 ies by virtue of which they themselves become mag- 
 nets. The magnetism thus appearing in such bodies 
 is said to be induced \\\ them, and this process of im- 
 parting or developing magnetism is called 
 magnetic induction. Thus, in Fig. 14, NS 
 is a bar-magnet, k is an iron key which 
 is attracted and held suspended by it, 
 and ;/ is an iron nail, in turn held in the 
 same way by the key, which has itself become a magnet. The 
 
 original magnetizing body suffers no 
 
 loss of magnetism by this process. 
 66. Polarity of the Magnet. 
 
 If a bar-magnet be rolled in a mass 
 
 of filings or other small fragments of 
 
 iron, these will 
 
 be found to 
 
 assemble in 
 
 much irreater 
 
 FIG. 13, Magnetic Needle on Pivot. 
 
 Fm. 
 
 Suspended Magnetic 
 Needle. 
 
 FIG. 14. Attraction of Magnet. 
 
 quantity near each of the ends than toward the middle of 
 the bar, as shown in Fig. 15. This shows that the attractive 
 force of a magnet is at its maximum at two points situated 
 near the respective ends of the bar, and gradually diminishes toward 
 the center, where it disappears altogether. These two points of 
 maximum attraction are termed the poles of the magnet. The one 
 
26 
 
 Sources of Electricity. 
 
 ' ' ' ' ! ': ' ''!'., ''.. i: ;-;"'' ! i " : 
 
 FIG. 15, Attraction of Iron Filings by Bar- Magnet. 
 
 which points toward the north pole of the earth when the magnet 
 is suspended, is conventionally termed the boreal or north pole (71), 
 
 and the opposite one 
 the austral or south 
 pole* 
 
 The intermediate 
 point, where no at- 
 traction is manifest- 
 ed,, is called the neu- 
 tral line or equator of the magnet. Some magnets, termed multi- 
 polar magnets, have more than one set of poles. 
 
 The distance between the poles of a magnet is called its magnetic 
 length. In most bar-magnets it is about 0.83 of the total length. In 
 a horseshoe magnet (67) it is the shortest distance between the poles. 
 A magnet need not necessarily be magnetized in the direction of 
 its greatest length ; a bar may be magnetized transversely, or in fact 
 in any direction. When a magnet is broken into detached parts, 
 each fragment instantly becomes an independent 
 magnet, having a north and south pole. 
 
 67. Horseshoe Magnet and Arma- 
 ture 1 . Instead of being straight, as in Fig. 14, 
 it is more usual, as well as more convenient, 
 for the magnetic bar to be given a form re- 
 sembling the letter U as m Fig. 16. This 
 form is known as the horseshoe magnet. A soft 
 iron armature is usually fitted to the poles of 
 a horseshoe magnet. This is sometimes called 
 the keeper, because it aids in retaining or keeping 
 the magnetic qualities of the bar. In general 
 terms, any mass of iron or steel subjected to the 
 attraction of a magnet is considered to be an 
 armature. 
 
 A magnetic attraction has been experimentally 
 produced between a magnet and its armature as 
 high as i. ooo Ibs. per sq. in. of surface in con- 
 tact. 3 
 
 68. The Magnetic Spectrum. If a sheet of thin glass or 
 
 2 The north pole of a magnetic bar or needle, by convention, is usually painted blue> 
 and the south pole red. Sometimes they are respectively stamped with the letters N 
 and S, and sometimes a straight line or mark serves to designate the north pole. 
 
 3 EWING and Low : Phil. Trans. Royal Soc., 1889, A. 221 ; see also H. E. J. G- 
 Du Bois : Phil. Mag., April, 1890. 
 
 FIG. 16. Horseshoe 
 Magnet and Arma- 
 ture. 
 
The Magnetic Field. 
 
 27 
 
 card-board be laid upon a 
 bar-magnet, and its surface 
 sprinkled with iron filings 
 from a pepper-box, as in 
 Fig. 17, upon tapping the 
 sheet with a pencil or simi- 
 lar object, a remarkable 
 phenomenon will occur. 
 The particles of iron will 
 arrange themselves sym- 
 metrically in curiously FIG. 17 
 curved lines as shown in 
 Fig. 1 8, which is taken from a 
 
 
 
 FIG. 18. Spectrum of Bar-Magnet. 
 
 . Method of producing Magnetic Spectrum. 
 
 photograph. This is called the 
 magnetic spectrum. 
 
 69. The Mag- 
 netic Field. The 
 sphere of attraction 
 which surrounds a 
 magnet is termed the 
 magnetic field, and is 
 filled with what were 
 happily termed b\ 
 Faraday, lines of mag- 
 netic force. These 
 exist unseen in every 
 magnetic field, but 
 their presence and 
 direction may be 
 made evident by the 
 expedient which has 
 just been described. 
 Magnetic force in it- 
 self is absolutely in- 
 We only know of its existence 
 
 appreciable by any of our senses 
 by its effects upon matter. 
 
 Since the peculiarities of the magnetic field are due to the presence 
 of a force, the properties of such a field may be made known by 
 determining the strength and the direction of this force, or, as it is 
 usually expressed, the intensity of the field, and the direction of the 
 lines of force* 
 
 Force is any action which can be expressed simply by weight, and is distinguished 
 by a great variety of terms, such as attraction, repulsion, gravity, pressure, tension, 
 
28 
 
 Sources of Electricity. 
 
 FIG. 19. Lines of Force of liar- Magnet. 
 
 70. Lines of Magnetic Force. The invisible lines of mag 
 netic force radiate in every direction from each pole of the magnet. 
 They may be regarded as an inseparable part of it, which accompany 
 it wherever it goes. Perhaps their true nature may be more clearly 
 
 conceived by assuming them to set 
 out from one pole, say the north 
 pole, and after curving for a 
 greater or less distance through 
 space, to return again to the south 
 pole, as indicated by the arrows 
 in Fig. 19. A view of the spec- 
 trum of the magnetic field at one 
 pole of a bar-magnet, as seen 
 end-on, exhibits merely radial lines, as in Fig. 20. 
 
 71. If a small bar- 
 magnet or magnetic 
 needle be suspended 
 at any point within 
 the field of a larger 
 magnet, it will invari- 
 ably tend to place it- 
 self parallel to the 
 line of force which 
 passes through both 
 its poles, as shown in 
 Fig. 21. This exT 
 plains why the needle 
 of the magnetic com- 
 pass always points to 
 the north. The earth 
 itself is a great mag- 
 net, and is surrounded 
 by a field filled with 
 
 invisible lines of force which we term magnetic meridians. These 
 lines determine the position of the suspended magnetic needle. 
 Thus by exploring with such a needle, the direction of the lines of 
 force in any magnetic field may be discovered (94). 
 
 72. Attraction and Repulsion. The respective north poles 
 
 compression, cohesion, adhesion, resistance, inertia, strain, stress, strength, thrust, 
 load, squeeze, pull, push, etc., all of which can be measured or expressed by weight, 
 without regard to motion, time, power or work. J. W. NYSTROM : Elements of 
 Mechanics, p. 59. 
 
 FIG. 20. Spectrum of Magnet Pole End-on. 
 
Current Produced by a Magnetic Field. 29 
 
 of any two magnets repel each other, and so do the south poles ; but, 
 on the contrary, the north and the south pole of the same or differ- 
 
 FIG. 21. Position of Magnetic Needle in Field. J. A. 
 
 ent magnets mutually attract each other. Hence it follows that the 
 north pole of any magnet must have the same polarity as the south 
 pole of the earth, and in strictness ought to be termed the south 
 pole rather than the north (66). It is more properly termed the 
 north-seeking pole. 
 
 73. Electric Current 
 Produced by a Mag- 
 netic Field. If a con- 
 ducting wire in the form 
 of a closed loop or end- 
 less ring be moved within 
 a magnetic field, in any di- 
 rection whatsoever which 
 alters the number of lines 
 of force passing through 
 it, a current of electricity will appear in the wire. The same thing 
 will occur if the wire be stationary and the field be moved ; or if 
 the wire be stationary and the intensity or strength of the field be 
 increased or diminished, either between zero and maximum, or to 
 a lesser extent ; or if the wire be moved from one part of the field 
 to another part of different intensity. 5 
 
 FARADAY'S own account of this capital discovery of magneto-electricity the results 
 of which are likely to ultimately become of greater importance than any other ever 
 
 
 
 
 
 
 
 
 
 
 , >. 
 
 
 , v 
 
 
 (/~\\ 
 
 
 
 / 
 
 I \ 
 
 \1 _J 
 
 \\ 
 
 
 
 1 
 
 
 
 
 
 
 ' 1 
 
 
 / 
 
 / 
 
 T 
 
 v / 
 
 / 
 
 \ // 
 
 
 \^ 
 
 
 ^^/ 
 
 ^- 
 
 
 
 
 FIG, 22. Lines of Force not cut by Movement of Ring. 
 
Sources of Electricity. 
 
 74- Thus in Fig. 22, 6 let the parallel arrows be assumed to repre- 
 sent lines of 'force in a uniform magnetic field. If the closed ring 
 of wire be moved parallel to those lines, as indicated by the dotted 
 
 arrow, no electric current 
 will appear in the ring. 
 Or if the ring and the 
 lines of force, either or 
 both, be moved in a trans- 
 verse direction with ref- 
 erence to each other, with- 
 out altering the total num- 
 ber of lines enclosed, as 
 shown in Fig. 23, no cur- 
 rent will be generated in 
 
 FIG. 33. Movement of Translation in Uniform Field. 
 
 \V7 
 
 the ring. Fig. 24, on the 
 other hand, represents a 
 field which is not uniform, being stronger or more intense, or in 
 other words, having a greater number of lines of force, in some parts 
 than in others. Moreover, as shown by the arrow-heads, these lines 
 
 run in opposite directions in ^ 
 
 different parts of the field. 
 If, now, the ring be moved 
 from a place where the 
 lines of force are more 
 numerous to a place where 
 they are less numerous, as 
 from position i to position 
 2 in Fig. 24, a current will 
 be generated - } and if this 
 motion be continued, as in 
 position 3, to a place where 
 the lines run in an opposite 
 direction, the effect will be 
 similar in kind, but will be 
 even greater in amount. So, also, if the ring be moved in a uniform 
 field in such a manner that either the number or the direction, or 
 both, of the lines of force cut by it are varied, a current will be pro- 
 duced. This happens if the ring be turned round an axis at right 
 angles to the direction of the lines of force, as shown in Fig. 25. 
 
 achieved by man, with the possible exception of the discovery of the expansive power 
 of steam is given in his Experimental Researches, i. 7. See N. Y. Elect. Eng. , xiii. 27. 
 SILVANUS P. THOMPSON : Dynamo-Electric Machinery (2nd edition;, 12. 
 
 FIG. 24. Movement of Ring in Field of Varying 
 Intensit}*. 
 
Transformation of Mechanical Power. 3 r 
 
 This last described organization is very common in machines for 
 producing electricity from magnetism. 7 
 
 75. Transformation 
 of Mechanical Power 
 into Electricity and 
 Heat. In thus moving 
 a closed circuit or loop of 
 wire through a magnetic 
 field so as to cut across 
 the lines of force, a cer- 
 tain physical resistance is 
 encountered, and a corre- ^ 
 spending mechanical force 
 must be applied to over- 
 come it and effect the FlG ' 25 ' Circular Mov ^ e d nt f Ring in Uniorm 
 motion. The equivalent 
 
 of mechanical energy thus consumed reappears as electricity in the 
 closed ring, except that a certain portion, which is transformed into 
 heat, as will be hereafter more fully explained (87). 
 
 76. Direction of the Induced Current. It has been stated 
 (31), that what we call the direction of a voltaic current is con- 
 ventionally assumed to be from the positive pole of the cell through 
 the conducting wire to the negative pole ; and it will be obvious that 
 if the respective poles were interchanged, the current would traverse 
 the wire in the opposite direction. The direction of the current pro- 
 duced in a conductor by moving it with reference to the lines in a 
 field of force, called the magneto-electric current, depends upon the 
 direction in which the relative motion takes place. The law may be 
 stated as follows : 
 
 A decrease in the number of lines of force which pass through or 
 are cut by a closed circuit, produces a current round that circuit in 
 the positive direction ; while an increase in the number of lines of 
 force which pass through or are cut by such circuit, produces a cur- 
 rent around such circuit in the negative direction. 8 
 
 The positive direction of the lines of magnetic force which pass 
 through the loop of the circuit, is invariably associated with a posi- 
 tive direction of the current flowing round the conducting circuit, 
 
 7 This and the four following paragraphs explanatory of the mutual reactions of 
 the magnet, the magnetic field and the conductor, are abridged from a portion of 
 chapters ii. and iii. of SILVANUS P. THOMPSON'S admirable work on Dynamo- Electric 
 Machinery. 
 
 * SILVANUS P. THOMPSON : Elementary Lessons in Electricity aud Magnetism, 
 360- 
 
32 Sources of Electricity. 
 
 just as the forward thrust is with the right-handed rotation in the 
 operation of driving an ordinary right-handed screw. This will ap- 
 pear from an examination of the direction of the current in the 'ring 
 as shown by the arrows in Fig. 25. 
 
 77. Mutual Reactions of a Current and a Magnet. 
 The phenomena which have been described, like most physical phe- 
 nomena, are reversible; that is to say, a magnetic field may also be 
 created by the passage of an electric current through a wire con- 
 ductor, and, moreover, a mass of iron or steel situated in such a field 
 will become magnetic. This effect, which is called electro-magnetism 
 (86, </), lies at the foundation of electric telegraphy. 
 
 78. Summary of Magneto-Electric Phenomena. It ap- 
 pears, therefore, from the facts which have thus far been stated, 
 that: 
 
 (i.) An electric current is set up in a conductor, either by moving 
 a magnet near such a conductor, or by moving the conductor near a 
 magnet. 
 
 (ii.) The establishment and maintenance of a continuous electric 
 current in a conductor requires a continuous expenditure of energy, 
 or, in other words, consumption of power, in order to produce the 
 necessary motion. 
 
 (iii.) To induce currents in a conductor, there must be relative 
 motion between conductor and magnet, of such kind as to alter in 
 some manner the number of lines of force cut transversely by the 
 conductor. 
 
 (iv.) Other things being equal, the more powerful the magnetic 
 pole or magnetic field, the more powerful will be the electric current 
 generated. 
 
 (v.) The more rapid the relative motion of the two elements the 
 more powerful will be the current. 
 
 (vi.) The direction of the induced current depends upon the 
 direction of the motion of the wire with reference to the direction 
 of the lines of force in the field. 
 
 79. The Dynamo-Electric Machine. A dynamo-electric 
 machine, briefly termed a dynamo, in the general and most proper 
 sense of the term, embraces every machine capable of converting 
 the energy of mechanical motion into the energy of an electric cur- 
 rent, and it is in this sense that the term dynamo will hereafter be 
 used in this treatise. 
 
 80. The Theoretical Dynamo. The simplest conceivable 
 dynamo is illustrated in Fig. 26. It consists of a single rectangular 
 loop of wire, rotating in a uniform magnetic field maintained between 
 
Frictiona I Electricity. 
 
 33 
 
 the north and south poles of a large horseshoe magnet. If the loop 
 be first placed in* a vertical plane, as in the figure, the number of 
 lines of force passing through it will be a maximum, but as it is 
 turned by the crank into a horizontal position, the number of inter- 
 secting lines will obviously diminish to zero. On continuing the 
 rotation beyond this point, the lines begin again to thread through 
 the loop from the opposite side, so that there will be a negative or 
 reverse maximum when the loop has been turned through an angle 
 of 180", or half-way round. During the first half of the revolution, 
 therefore, a current will be induced in the loop in one direction, the 
 strength of which will increase gradually from zero to maximum and 
 then diminish again to zero. Upon passing the 180 position,, there 
 will begin an induction in the reverse sense, and a similar effect will 
 
 FIG 26. Theoretical Dynamo-Electric Machine. 
 
 again take place, resulting in the induction of a current in the loop 
 in the opposite direction, the operation being completed when the 
 loop has been carried through one complete revolution. 
 
 81. Further considerations, having reference to the construction 
 and mode of operation of the actual dynamo, may profitably be post- 
 poned until the student has become familiar with the fundamental 
 laws which govern the flow and distribution of electric currents, as 
 the reaction of these currents upon the machine which produces 
 them, though important, are somewhat complex, and in the absence 
 of such knowledge will be found difficult of comprehension (299). 
 
 82. Frictional Electricity. Frictional electricity, which is 
 one form of what is termed static electricity, finds no practical applica- 
 tion in telegraphy. Nevertheless, the phenomena of static electricity, 
 under certain conditions, manifest themselves in such a way as to 
 
34 Sources of Electricity. 
 
 interfere with the transmission and reception of telegraphic signals, 
 and hence it will become necessary, in connection with that subject, 
 to give the matter further consideration. (See Chapter VIII., 314.) 
 83. Thermo-Electricity. This name has been given to 
 electricity derived from the direct conversion of heat-energy. Its 
 application to telegraphy has thus far been purely tentative, and 
 does not require consideration here. 9 
 
 9 For an account of thermo-electric apparatus, and its experimental application to 
 telegraphy, consult LoCKWOOD : Electricity, Magnetism, and Electric Telegraphy, 
 chap. iii. p. 36. 
 
CHAPTER IV. 
 
 THEORY OF QUANTITATIVE ELECTRICAL 
 MEASUREMENT. 
 
 85. The Electric Current. It has been stated (28) that a 
 conducting wire uniting opposite poles of what, for convenience, we 
 call a generator of electricity, whether this be a voltaic cell (30) or a 
 magneto-electric apparatus (80), is endowed with certain peculiar prop- 
 erties, by reason of which we conventionally assume an electric cur- 
 rent to flow from the positive to the negative pole of such generator. 
 
 86. Manifestations of the Current. The existence of this 
 so-called electric current in the conjunctive wire is manifested in 
 several different ways, the most important of which are as follows: 
 
 (a) If the wire be dipped in iron 
 tilings, a mass of these will cluster 
 around it and apparently adhere to 
 it, appearing as in Fig. 27. 
 
 (fi) If the wire be placed in the 
 immediate vicinity of a freely suspended magnetic needle (64), the latter 
 will immediately tend to set itself 
 at right-angles thereto, as indicated 
 in Fig. 28. Moreover, the direction 
 in which the needle moves will indi- 
 cate the direction of the current (31). 
 (r) If the wire be placed parallel 
 to another wire, or to another por- 
 tion of the same wire which is also 
 conveying an electric current, repul- 
 sion or attraction will be manifested 
 between the two wires according as 
 the two currents flow in the same or 
 in opposite directions. 
 
 FIG. 27. Iron Filings held to Wire by 
 Magnetism. 
 
 FIG. 28. Deflection of Needle by Current. 
 
 (d) If the wire be wound spirally around a rod of soft iron, as in Fig. 29, 
 
 the iron will become a 
 magnet, and will con- 
 tinue to be magnetic so 
 long as it remains under 
 the influence of the cur- 
 rent, but upon the re- 
 moval of the wire or the cessation of the current, nearly every trace of 
 magnetism will disappear from the iron. 
 
 35 
 
 FIG. 29. Magnetization of Soft Iron by Current. 
 
Quantitative Electrical Measurement. 
 
 (e) If the wire be severed and its ends immersed in water, the water will be 
 decomposed, the oxygen appearing at one terminal and the hydrogen at the 
 other, as shown in Fig. 30. This action is termed electrolysis. 
 
 (/) If the severed ends of the wire be united by a very 
 thin wire of platinum, 3 in. or 4 in. long, and this be 
 placed in a vessel of alcohol, a thermometer will show the 
 liquid to become heated by the action of the current upon 
 the wire (see Fig. 31). 
 
 (g) If the ends of the severed wire be placed side by 
 side upon the tongue, a peculiar taste will be experienced; 
 and if the current be strong enough, it may be felt by the 
 fingers. This sensation is termed an electric shock. 
 
 87. Importance of Quantita- 
 tive Measurement. An accurate 
 knowledge of the phenomena and 
 
 FIG. 30. Electrolysis of Water. laws of electricity, as of everything 
 
 else in the world around us, depends 
 
 primarily upon measurement. 1 It is by measurement and comparison 
 alone that we are able 
 to understand electrical 
 phenomena. 
 
 88. Fundamental 
 Units of Mass, 
 Space, and Time. 
 The principle of the 
 
 1 In physical science, a first 
 essential step in the direction 
 of learning any subject, is to 
 find principles of numerical 
 reckoning, and methods of 
 practically measuring some 
 quality connected with it. I 
 often say that when you can 
 measure what you are speak- 
 ing about and express it in 
 numbers, you know something 
 about it ; but when you can- 
 not measure it, when you can- 
 not express it in numbers, your 
 knowledge is of a meagre and 
 unsatisfactory kind ; it may be 
 the beginning of knowledge, 
 but you have scarcely in your 
 thoughts advanced to the state 
 of science, whatever the mat- 
 ter may be. SIR WILLIAM 
 THOMSON : Popular Lectures 
 and Addresses, p. 73. 
 
 FIG. 31. Development of Heat by Electric Current. 
 
Absolute System of Measurement. 37 
 
 absolute measurement of electricity and magnetism is, as Thomson 
 remarks, " merely an extension of the astronomer's method of reck- 
 oning mass in terms of what we may call the universal gravitation 
 unit of matter, and of the reckoning of force adopted by astrono- 
 mers, in common with all workers in mathematical dynamics, accord- 
 ing to which the unit of force is that force which, acting on a unit of 
 mass for a unit of time, generates a velocity equal to the unit of velocity* 
 
 89. Illustration of the Absolute System of Measure- 
 ment. As a concrete example, suppose we take a pound weight 
 as our unit of mass, and allow it to drop through space for a period 
 of one second, our unit of time. This mass will always fall through 
 the same space during the unit of time, and at the end of that time 
 will be capable of striking with a certain determinate force, which is 
 obviously measurable by an equivalent weight, and which therefore 
 becomes our unit of force, while the distance through which the mass 
 falls in one second becomes our unit of spaced Such a system of 
 measurement being wholly independent of the physical properties 
 of any arbitrary material, is properly called an absolute system. 
 
 90. Derivation of Electrical and Magnetic Units. The 
 actual units used in the measurement of electricity and magnetism, 
 are founded upon the French or metric system of weights and 
 measures, which has been commercially, adopted by all the civilized 
 countries of the world except Great Britain and the United States, 
 and is in extensive use in the last named countries among scientific 
 men. In electro-magnetic measurement, therefore, the centimetre has 
 been adopted as the unit of space, thegrtm the unit of mass or weight, 
 and the mean solar second the unit of time. This is briefly denom- 
 inated the e.g. s. (centimetre-gram-second) system. 4 
 
 91. The C. G. S. Units of Force and Work. The act of 
 moving a weight of i gram through a space of i centimetre, during 
 the time of i second, requires a perfectly definite and measurable 
 
 * The units of space, mass, and time, have been selected by common consent to 
 ierve as fundamental units. Other units, for practical use, determined from these, 
 such for example as the unit of force, are termed derived units. 
 
 3 In making this general statement, the effect of the resistance offered by the air has 
 been neglected (this being, of course, greater for a less dense than for a more dense 
 body), as has also the fact that a given mass which weighs a pound, for example at 
 Washington, D. C., will weigh more than a pound at the north or south pole of the 
 earth, and less than a pound at Panama, or at the equator. This is due to the fact 
 that the earth is not a perfect sphere. 
 
 The centimetre is somewhat less than half an inch English measure ; i foot is very 
 nearly 30.5 centimetres ; i cubic centimetre of water weighs i gram ; i oz. is very nearly 
 28 grams ; i Ib. is 454 grams ; the 5-cent nickel of the 1873 U. S. coinage weighs 
 exactly 5 grams and has a diameter of 2 centimetres ; the silver dime weighs 2.5 grams. 
 
38 Quantitative Electrical Measurement. 
 
 amount of force, which is termed a dyne. The dyne, therefore, is 
 the unit of force in the c. g. s. system, and is defined as the force, 
 which acting upon a gram for a second, generates a velocity of a centi- 
 metre per seconds Any force may be stated to be equal to so many 
 dynes. A megadyne is equal to 1,000,000 dynes (123, note). 
 
 The erg is the unit of work in the c. g. s. system, and is the work 
 done by a force of i dyne acting through a distance of i centimetre, irre- 
 spective of the time occupied? 
 
 Now if a force of i dyne be applied to move a closed conducting 
 ring a distance of i centimetre through a uniform magnetic field (as, 
 for example, the magnetic field of the earth), in the manner explained 
 in (73), work is done; an electrical force is set up in that conductor 
 which would be the exact electrical equivalent of the mechanical force 
 of i dyne, were it not that some part of the original force is unavoid- 
 ably transformed into heat during the operation. Neglecting the 
 value of the heat-loss, this quantity of electricity is capable of doing 
 mechanical work equal to i erg, as, for instance, by forcibly deflect- 
 ing a magnetic needle (86, b) or by attracting the armature of a 
 magnet (86, d). 
 
 92. The Conservation of Force. This is one illustration of 
 the great principle of the indestructibility or, as it is commonly 
 called, the conservation of force? which is so important, that it has 
 been justly remarked that the whole of natural philosophy is merely 
 a commentary upon it. 8 
 
 It follows from this principle, that whenever a signal is produced 
 at any point by electrical action, a physical effect must be made to 
 take place, and this necessarily involves the expenditure of some 
 form of force at some other point. It may be the force of chemical 
 affinity in the voltaic cell ; or it may be the force of steam or of fall- 
 ing water, or of human muscles exerted upon a dynamo-electric 
 
 5 EVERETT : Units and Physical Constants, pp. 22, 167. 
 
 6 EVERETT : Units and Physical Constants, p. 167. 
 
 7 DANIELL : Principles of Physics, 7. 
 
 8 This doctrine teaches that the total amount of force in the universe is unalter- 
 able, and that it can neither be created nor destroyed. Force, however, may appear 
 in a variety of different forms, and is capable of being readily changed from one form 
 to another, but every such mutation is nevertheless rigidly subject to quantitative laws. 
 A given amount of one form of force produces a definite quantity of one or more other 
 forms of force and no more. Hence this law is sometimes called the equivalence of 
 forces. This important and interesting subject is well worthy of further study, and 
 among special works relating to its various aspects, the author ventures to specially 
 commend the following : TYNDALL : Heat as a Mode of Motion ; YOUMANS : The 
 Correlation and Conservation of Forces ; a collection of papers by Grove, Helmholtz, 
 Mayer, Faraday, and others; STEWART: On the Conservation of Energy ; and 
 SPE AGUE : Electricity, its Theory, Sources, and Applications. 
 
Electric Field of Force. 
 
 39 
 
 machine, but in every case, the force expended must be equal to 
 that which is utilized, plus that which is transformed into heat in the 
 course of the operation. Telegraphic signals are usually produced 
 by means of the attraction of an armature by an electro-magnet. 
 The initiation and maintenance of this attraction involves the consump- 
 tion in the battery of a perfectly definite and well ascertained quantity 
 of material, which can never be less than the full equivalent of the 
 mechanical work done, but must be somewhat more, and may pos- 
 sibly be very much more, for by unskillful arrangements an undue 
 proportion of the original force may be turned into heat and ren- 
 dered unavailable for the purpose in hand (154). 
 
 93. Electric Field of Force. If we take a magnetic needle, 
 which, as we have seen, tends to remain in the magnetic meridian, 
 and place parallel to it a wire, traversed, as shown in Fig. 28, by a 
 current in the direction of the arrows, the needle will seek to place 
 itself at right-angles to the wire (86, b\ but being under the influence 
 of two antagonistic forces, it will come finally to rest in an interme- 
 diate position. This experiment shows that a conductor, when con- 
 
 FIG. 32. Spectrum of Field Surrounding Conductor. 
 
 veying a current, is surrounded by a field-of-force of the same char- 
 acter as that which we have found to surround the magnet (69). To 
 determine the position and direction of the lines of force in this 
 field, we may adopt the same expedient as in the case of the magnet. 
 
40 Quantitative Electrical Measurement, 
 
 Pass the conducting wire at right-angles through a piece of glass or 
 card-board. If iron-filings be dusted into the field, they will 
 arrange themselves in concentric circles (Fig. 32), showing that the 
 .lines of force encircle the wire, instead of radiating outwardly from it as 
 they did in the case of the magnet. It is these lines of force which 
 act upon the needle and tend to set it at right-angles to the wire, for 
 when any concentric line passes through both poles of the needle, the 
 latter must set itself at right-angles to the radii of the circle (71). 
 
 94. Relation of Current Force to Mechanical Force. 
 The particular angular position of a needle under the influence of 
 a current must necessarily depend upon the ratio between the 
 strength of the magnetic field-of- force due to the current, and that of 
 the field-of-force due to the magnetism of the earth, which may be 
 regarded as sensibly constant in any particular locality. 
 
 That portion of the force of the earth's magnetism which acts to hold a 
 horizontal needle in the meridian is called its horizontal component (H). Its 
 value varies from a maximum at the magnetic equator to nothing at the 
 magnetic poles. Its locality of greatest intensity is in lat. o and long. 101 
 W., where it is equal to 0.3733 dynes. Following are some determinations 
 of its value by observers of the U. S. Coast and Geodetic Survey: 
 
 Washington, D. C /. 0.2026 dynes. 
 
 New York 0.1872 
 
 Eastport, Me 0.1573 " 
 
 Key West, Fla 0.3055 " 
 
 Cincinnati, 0.2111 " 
 
 San Francisco, Cal 0.2533 " 
 
 St. Paul Island, Alaska 0.2008 
 
 Toronto, Ont o. 1654 ' ' 
 
 City of Mexico o. 3429 ' ' 
 
 (Rep't U. S. C. & G. S., 1885 ; App. No. 6.) This report gives the value 
 of the horizontal intensity found in over 1,500 observations in various parts 
 of North America, reduced to the epoch of 1885. 
 
 The value of the horizontal intensity is subject in most places to a slow 
 annual variation. Along a line drawn from British Columbia to Florida, 
 the intensity is constant ; east of this line it shows an annual increase, and 
 west of the line an annual decrease. {Rep. U. S. C. &* G. S., 1885, p. 271, 
 and charts.] 9 
 
 As the strength of the field, due to the current, is always strictly 
 proportionate to the capacity of the current to produce other physical 
 effects, we have a means, not only of comparing the forces of diflfer- 
 
 9 The refined methods of determination used are fully described by C. A. SCHOTT 
 in App. 8 of the same for 1881. For an elementary explanation of these methods see 
 TROWBRIDGE : New Physics, p. 142. See also A. GRAY : Absolute Measurements in 
 Electricity and Magnetism, p. 5 ; F. E. NIPHER : Theory of Magnetic Measurements, 
 P- 46. 
 
Tkc Galvanoscope and the Galvanometer. 41 
 
 ent currents, but, by comparison with the earth's magnetism, of 
 determining the actual dynamic value of any current, in terms of the 
 fundamental units of space, mass, and time (91). 
 
 A unit magnetic pole weighing i gram, and free to move in a 
 horizontal plane, under the action of the earth's horizontal force, 
 would require, at the end of i second, a velocity equal to 202.6 
 centimetres per second, if the experiment were made in Washington, 
 D. C. (See p. 40.) 
 
 95. The Galvanoscope and the Galvanometer. A mag- 
 netic needle provided with a conductor through which a current may 
 be passed in order to deflect it from the meridian (86, /;), is called a 
 galvanoscope or detector. When to these is added a graduated scale 
 or dial, the instrument becomes a galvanometer. In order that the 
 angle of deflection of a needle under the influence of any current 
 shall bear a definite ratio to the value of such current, certain pre- 
 cautions in its mechanical construction are necessary to be observed. 
 It is essential that the field produced by the current should, like that 
 of the earth, be so large in comparison with the needle, that the 
 motion of the latter within it, when deflected, shall not appreciably 
 change its relation to the entire field. 
 
 96. Tangent Galvanometer. In this instrument the forego- 
 ing condition is fulfilled. In its most simple form, the tangent 
 
 FIG. 33. Needle in Circular Loop. 
 
 galvanometer consists of a single circular turn or loop formed in the 
 conducting wire ; in the center of the loop is suspended the needle, 
 which in length should not exceed -^ the diameter of the loop. 
 Such an organization is shown in Fig. 33, in which n s is the sus- 
 pended needle, and P N the looped conductor which surrounds it. 
 
42 Quantitative Electrical Measurement. 
 
 The 
 
 principle of action may be understood by reference to Fig. 34. 
 
 Let the magnetic needle n s be sus- 
 pended in the earth's magnetic 
 meridian N S. If now the con- 
 ducting wire or loop be placed in 
 the plane of N S, and we suppose 
 this wire to be traversed by a cur- 
 rent capable of producing a mag- 
 netic field precisely equal in strength 
 to that of the earth, the needle will 
 swing toward a position represented 
 by the line A B, at right angles (or 
 90) to the one originally occupied. 
 But the two antagonistic forces being 
 equal, the needle will come to rest 
 in a position half-way between N 
 and B, called the resultant. This 
 coincides with the line Ai, which 
 forms an angle of 45 with the zero 
 or o line N S. Now if we double 
 the strength of the current, and con- 
 sequently that of the field produced 
 by it, it will partially overpower the 
 earth's field, and the needle will as- 
 sume the position corresponding to 
 the line A2, which is an angle of 
 63^ nearly. If we again double 
 the strength of the current, we shall 
 increase the deflection to 76, repre- 
 sented by the line A4- In geomet- 
 rical language, the line N4 is termed 
 tangent to the arc or 
 quadrant N B of the 
 circle. The circle 
 being divided in- 
 to 360, the 
 tangent, as 
 found in a 
 computed 
 '. table of 
 S natural tan- 
 
 FIG. 34. Principle of Tangent Galvanometer. gents (see 
 
Character of Electrical Measurements. 43 
 
 page 55), will always be proportionate to the strength of the current 
 by which the corresponding deflection was caused. The actual con- 
 struction of this useful instrument will be described in detail else- 
 where (102). 
 
 97. Character of Electrical Measurements. The qualities 
 of an electric current by virtue of which, as we have seen, it is 
 enabled to exert force, to produce physical effects, or, in technical 
 language, to do work, are three in number, viz: (i) quantity, vari- 
 ously called volume, or strength of current; (2) potential, variously 
 called pressure, tension, and intensity, 10 and (3) duration, or time 
 occupied in doing the work. The value of the first two of these 
 properties, in the case of any particular current, is dependent not only 
 upon the circumstances of its origin, but upon the special character- 
 istics of the conductors which the current is compelled to traverse. 
 Hence there are two distinct classes of electrical measurements: 
 
 (1) those which are applied directly to electricity itself, either in a 
 static or in a dynamic condition, that is to say, as a stationary charge 
 or as a flowing current, and (2) those which are applied to the con- 
 ductor which a current is or may be compelled to traverse. 
 
 98. Characteristics Capable of Measurement. Electricity 
 itself, whether in a static or a dynamic condition, has but three 
 properties susceptible of quantitative measurement, viz : (i) quantity, 
 
 (2) potential, and (3) duration. Electric conductors have four quali- 
 ties which may affect the value of the currents which traverse them, 
 and which, in like manner, are susceptible of measurement, viz : 
 (4) magnitude (length, breadth, and thickness), (5) weight, or mass, 
 (6) temperature, and (7) conductivity, or the reciprocal of this, called 
 resistance. All these considerations must be taken into account in 
 performing any electrical measurement. 
 
 99. Apparatus for Measurement. A complete apparatus for 
 executing electrical measurements must therefore comprise : 
 
 (a) A meter for quantity of current. 
 
 (b) A meter ior potential of current. 
 
 (c) A chronometer for time. 
 
 (d) A scale for linear measure. 
 
 (e) A scale or balance for weight. 
 
 (f) A thermometer for temperature. 
 
 (g) A standard of electrical conductivity or resistance. 
 
 10 The French scientific writers have always been accustomed to use the term *'- 
 tensite in the sense in which we use the term quantity or volume. The frequent trans- 
 lation of this word by the English term " intensity," which has in fact a wholly differ- 
 ent signification, has been the cause of no little confusion in electrical literature. 
 
44 Quantitative Electrical Measurement. 
 
 Not all these instruments are required in making every measure- 
 ment, for one or more of the unknown conditions may be arbitrarily 
 assumed, or they may be determined from others which are known, 
 as we shall hereafter frequently have occasion to note. 
 
 100. The Ammeter, Voltameter, and Calorimeter. The 
 instrument for measuring quantity of current need not necessarily be 
 a galvanometer, although in telegraphic work this is used practically 
 to the exclusion of everything else. Currents may also be measured 
 by the attractive force of an electro-magnet (83,^), as in the instru- 
 ment called the ammeter, or by ascertaining the volume of gas 
 evolved in a unit of time (83,*?), in which case the instrument is called 
 a voltameter, or by measuring the heat developed in a unit of time 
 (83,/), in which case it is called a calorimeter. All these instruments 
 find frequent use in general electrical investigations, but are less 
 convenient than the galvanometer for measurements in connection 
 with telegraphy. 
 
CHAPTER V. 
 
 THE LAWS AND CONDITIONS OF ELECTRICAL ACTION. 
 
 101. Apparatus Required by the Student. The student 
 who desires to obtain a thorough knowledge, not only of the art of 
 telegraphy, but of the principles of physics and chemistry upon which 
 that art is based, is earnestly advised to supply himself, in the first 
 instance, with his own apparatus. The comparatively small cost of 
 the necessary outfit will be many times repaid in the value of the 
 clear and definite experimental knowledge which this means alone 
 will enable him to acquire. It is for many reasons advisable that 
 two students should work together, as experience has shown that the 
 study is rendered far more interesting, and that much more rapid 
 and intelligent progress may be made in this way. The following 
 list of apparatus and supplies will serve the requirements of two 
 students, the approximate cost of each item being given : 
 
 4 cells "crowfoot" battery complete, with 4 copper connect- 
 
 ors (9) $0.75 $3.00 
 
 2 keys (258) 1.75 3.50 
 
 2 5-ohm sounders (261) 2.25 4. 50 
 
 2 Ibs. No. 18 " burglar alarm " insulated copper wire 35 .70 
 
 2 feet f-in. rubber tubing for gravity cell (39) .30 
 
 i 2-in. glass funnel for gravity cell (39) .10 
 
 i hydrometer (18) .50 
 
 i battery brush (40) .25 
 
 i 6-in. permanent magnet (67) .60 
 
 5 Ibs. sulphate copper 10 .50 
 
 i box No. 2 office-wire staples .10 
 
 Total for two students $14.05 
 
 102. Construction of the Tangent Galvanometer. A 
 
 tangent galvanometer and rheostat are almost absolutely necessary 
 in the experimental investigation of electrical action, and hence it is 
 to be regretted that a sufficiently cheap but good apparatus of this 
 kind has never been made available for the use of students and ama- 
 teur electricians. It is nevertheless quite possible for an ingenious 
 person, somewhat accustomed to mechanical tools and processes, to 
 
46 Laws and Conditions of Electrical Action. 
 
 construct, at a trifling cost, apparatus sufficiently accurate for all 
 practical purposes. 
 
 The following directions for making a tangent galvanometer are 
 taken in part from S. R. BOTTONE'S Electrical Instrument Making for 
 Amateurs. 
 
 103. First a ring of hard wood C is accurately turned in a lathe, 
 of the form and dimensions shown in Figs. 35 and 36. The channel 
 
 FIG. 35. Elevation of Tangent Galvanometer. 
 
 in the edge of the ring must be of such depth that the bottom of it 
 will be exactly 6 in. in diameter and \ in. in breadth. Such a 
 channel will hold 38 turns (in 2 layers) of No. 22 "American 
 gauge " double cotton-covered copper wire. The coil will require 
 62 feet of wire, weighing about 2 oz., and costing about 25 cents. 
 The wire must be wound carefully and accurately in the groove or 
 channel (this may be best done in a lathe), and the ends brought 
 
Construction of the Tangent Galvanometer. 47 
 
 out through small holes in opposite sides of the ring and through the 
 base, as shown in Fig. 36. The ring and the wire, being first well 
 dried, should be thoroughly coated with shellac varnish. 
 
 Scale M actual size. 
 FK;. 36. Cross-section of Tangent Galvanometer. 
 
 The base B may be of hard wood, preferably turned, 7 in. in 
 diameter and i in. thick. It is supported upon 3 equidistant level- 
 ing screws / /, which may be common screw-eyes (preferably of brass, 
 though iron will answer), with the sharp tips filed off. 
 
 The ring C is fixed firmly in a vertical position upon the base B, 
 taking care that it is placed accurately at right angles therewith. A 
 recess may be cut in the base, the ring being let into it, and secured 
 by a clamping piece b of wood, made fast to the base B by two brass 
 screws s. 
 
 The magnetic needle, N S, Fig. 37, may be of a piece of watch- 
 spring i in. long and \ in. wide. Soften this by holding it in the 
 flame of a spirit-lamp until of a dull red color, and then allow it to 
 
48 Laws and Conditions of Electrical Action. 
 
 F Gk?vknometlr (Fuiisie. 
 
 cool slowly. Drill a hole exactly in the cen- 
 ter about fa in. in diameter, and file the ends 
 into the tapering form shown. Straighten 
 the needle with a hammer, and unless its 
 center of gravity corresponds with the center 
 of the hole, correct the error by filing the 
 heavy part away. Next harden the needle 
 by reheating it in the lamp-flame until nearly 
 red-hot, and dropping it into cold water. It 
 must then be magnetized, by rubbing each 
 half separately from the center to the end, 
 with a permanent magnet (67), being very care- 
 ful to rub one end with one pole of the mag- 
 net, and the other end with the opposite pole. 
 A jeweled center is then fitted to the hole 
 in the needle, 1 and secured with glue, or 
 better, with white or red lead used as a ce- 
 ment. It is not difficult for the amateur to 
 make a center out of glass, in case a jeweled 
 one cannot be procured, by holding a piece 
 of | in. glass tube in the spirit-lamp flame, 
 and pulling it apart lengthwise as soon as it 
 softens. In Fig. 38 this operation is illus- 
 trated at C. E is one of the two pieces, 
 which will be drawn out as shown, into a 
 thread-like extremity. Fuse this thin end in 
 the flame and a little globule will be formed, 
 the 
 
 closing the bore of 
 tube as at F. When cold 
 the tube can be broken 
 off by cutting a scratch at 
 the desired point with a 
 triangular file. This leaves 
 a center, G, adapted to 
 support the needle freely 
 upon a pivot as shown in 
 Fig. 13, page 25. 
 
 Having fixed the cen- 
 ter in the hole in the nee- 
 dle as directed, poise the 
 
 whole Upon the point Of FIG. 38. Method of making Glass Center. 
 
 i Needles fitted with jeweled centers are sold by E. Goldbacher, 98 Fulton St., N.Y. 
 
Construction of the Tangent Galvanometer. 49 
 
 a common sewing needle as a pivot, and if the magnetic needle is 
 found not to balance so as to lie in a laterally horizontal position, 
 adjust the center before the cement has firmly set. If one end 
 of the needle appears heavier than the other, load the light end 
 with a touch of melted sealing-wax, applied to the under 
 side. 
 
 Procure a fine straight straw, 3^ in. long, and make a transverse 
 hole through the middle of it with a large pin ; thrust the top of the 
 glass center carefully through this hole, so that the straw, which is 
 to serve as an index or pointer, will lie exactly at right-angles with 
 the magnetic needle (Fig. 37). Secure the straw to the glass center 
 with a mere trace of glue, and set it away to dry. 
 
 Make a dial of card-board like Fig. 39 (which shows one half of 
 it), one half being graduated in degrees and the other half divided 
 
 FIG. 39. Half of Card-board Dial of Tangent Galvanometer. 
 
 in tangents, upon the principle explained in (96). The outer circle 
 should be 3J- in. in diameter. Next cut out, in a lathe if possi- 
 ble, a circular hole 4 in. in diameter in a circular piece of hard 
 wood H, 5 in. diameter and i in. thick, and then enlarge this hole 
 T 3 g- in. all round with a shoulder \ in. deep, as shown in the cross- 
 section, Fig. 36. 
 
 Make a bridge-piece D of hard wood, i in. thick, and secure it to 
 the base by brass screws as shown in Fig. 35. This bridge-piece 
 should be just high enough so that the center of the magnetic needle 
 N S will come exactly in the geometrical center of the vertical ring 
 C containing the wire. The circular board G is secured to the 
 bridge-piece D with brass screws, the sewing-needle (point upward) 
 inserted into it for a pivot, and the card-board dial secured thereto 
 
50 Laws and Conditions of Electrical Action. 
 
 by small brass or copper tacks, in such position that when the 
 magnetic needle is in the plane of the vertical ring, the straw will 
 point to zero upon the scale at each end. The horizontal wooden 
 ring H is now laid upon the dial and fastened in place with brass 
 screws. A circular piece of glass g is cut to the right 
 size to lie upon the shoulder of the ring H, and may 
 be secured in place by an elastic ring r of stout brass 
 wire, cut to the right length, so that it may be sprung 
 into place over the glass, and within 
 the wooden ring, after the needle is 
 in place. 
 
 If pieces of mirror be let into the 
 dial, they will materially aid in mak- 
 ing accurate readings of the indica- 
 tions, as the index and its image 
 will then appear coincident only 
 when the eye is vertically over the 
 point observed. The error arising 
 from angular observations is termed 
 parallax. 
 
 The ends of the coil wire are car- 
 ried through holes into grooves cut 
 for the purpose on the under side 
 
 of the base, and thence to two binding-screws, P N (English pattern), 
 Fig. 35, which may be purchased for about 20 cts. each. These 
 should be placed in the plane of the vertical ring upon 
 opposite sides of the base, and the ends of the wires 
 carefully soldered to them underneath the base. 
 
 Binding-screws are brass clamps for conveniently 
 attaching connecting wires to electrical instruments. 
 They are made in many patterns, the most common 
 types being those shown in Figs. 40 and 41. In Fig. 
 40, the wire is inserted into the transverse hole and 
 clamped by turning the screw. This form is very 
 handy for ordinary purposes, but where a very good FIG. 42. 
 contact is essential, as in measuring apparatus, the 
 English pattern, Fig. 41, is preferable, the wire being 
 looped round the stem and clamped by the thumb-nut. 
 ing two or more wires, this pattern is sometimes made with more 
 than one nut, as in Fig. 42. 
 
 105. The accuracy of the above-described galvanometer will 
 
 FIG. 40. 
 
 Ordinary 
 
 Binding-Screw 
 
 FIG. 41. Binding- 
 Screw, English 
 Pattern. 
 
 Double 
 
 For attach- 
 
Construction of the Rheostat. 
 
 depend largely upon the care used in making it. The most impor- 
 tant point is to make sure that the centers of the vertical coil and 
 of the magnetic needle exactly coincide, and that the wire is accu- 
 rately and smoothly wound upon the vertical ring. It is pos- 
 sible for the amateur to construct an instrument which will do quite 
 as accurate work as those which are sold for $50 and upward by pro- 
 fessional instrument-makers (367). 
 
 106. Construction of the Rheostat. A convenient form 
 of rheostat for use with the tangent galvanometer is not beyond the 
 constructive skill of the amateur. Procure from a dealer a device 
 called a " peg pole-changer," 
 
 Fig. 43, with 4 pegs, which may 
 be had for about $3. This is 
 to be mounted upon the cover, 
 
 a 
 
 FIG. 43. Peg Pole-Changer and Peg. 
 
 FIG. 44. Rheostat and Box. 
 
 C, of a wooden box, B, which is removably fastened by screws, as 
 shown in Fig. 44. 
 
 Procure also from a dealer two lengths of double cotton-covered 
 German-silver resistance wire, as follows : 
 
 13 ft. of No. 18 (American gauge) 0403 in. diameter. 
 
 40 " " " 26 " 0159 in. " 
 
 Stretch each piece of wire out straight, double it in the middle of its 
 length, and wind smoothly upon a separate wooden spool, a com- 
 mon thread spool will do. Commence winding at the bight or loop 
 c, and wind double so that both ends of the wire will come on 
 the outside of the coil, as at d d. Fasten the filled spools to the 
 under side of the box cover, C, with long brass screws, as shown in 
 Fig. 44. 
 
 The ends of the wires on the spools must be uncovered by 
 scraping off the cotton envelope ; then carefully cleaned with 
 emery cloth, and soldered with rosin to stout brass wires ww, 
 
52 Laws and Conditions of Electrical Ac tic 
 
 c 
 
 v 
 
 e) 
 
 which are screwed into the brass plates supporting the binding- 
 screws, precisely as indicated in Fig. 45. The spare peg-hole seen 
 
 in Fig. 43 will provide for a third 
 coil of still higher resistance (indi- 
 cated in Fig. 45 in dotted lines at 
 the right), in case one should be 
 needed. 2 
 
 The thick wire coil, made as 
 above, will have an approximate 
 resistance of i ohm, and the thin- 
 ner one an approximate resistance 
 of 20 ohms (125). 
 
 107. Preparation for Ex- 
 periments. Having provided 
 himself with the necessary appli- 
 ances, the student is now prepared 
 to undertake an experimental investigation of the laws of the electric 
 current. Four gravity cells should be set up in accordance with 
 directions in Chapter II, using pure water as directed in (21) and 
 not s. z. solution. Arrange these in some convenient place, as on a 
 
 d 
 
 0~ 
 
 FIG. 45. Connections of Rheostat. 
 
 FIG. 46. Cells in Series with Tangent Galvanometer. 
 
 common kitchen table, and connect them with each other as in 
 diagram Fig. 46, the copper of one cell to the zinc of the next, and 
 
 2 These resistance-coils, before being mounted, may with advantage be dried for 
 several hours in a hot, but not too hot, oven, and when taken out should be instantly 
 immersed in a hot mixture in readiness for the purpose, composed of 10 parts by weight 
 of rosin and i part of white wax. Let the compound cool with the coils in it, remov- 
 ing the latter just before it sets. Heat them again, if necessary, enough to remove 
 the surplus material. 
 
Effect of Varying Number of Cells in Series. 53 
 
 the free copper and zinc terminals, by means of pieces of copper wire 
 about 3 ft. long, to the binding screws P N of the galvanometer. 
 The cells are now said to be arranged in series, both with each other 
 and with the galvanometer. At first, little or no effect will be ob- 
 servable upon the needle of the galvanometer ; but in the course of a 
 few hours a deflection may be observed, which will slowly increase. 
 Leave the apparatus alone, except to tap the galvanometer occasion- 
 ally with the finger to facilitate the movement of the needle, until it 
 indicates about 58, when the cells may be considered to be in good 
 working condition. 
 
 108. Effect of Varying Number of Cells in Series. Let 
 the student now carefully observe the effect produced upon the needle 
 of the galvanometer by varying in the number of cells in series with the 
 coil. The results will be found to be something like the following: 
 
 Cells in Series. 
 
 Deflection. 
 
 Tangent. 
 
 
 ^8 
 
 1. 60 
 
 
 
 57^ 
 
 i <;6 
 
 2 ... 
 
 e;64- 
 
 I ^O 
 
 I 
 
 531 
 
 I . v\ 
 
 
 
 
 As elsewhere stated (96), the effective strength or quantity of cur- 
 rent is always in the ratio of the tangents of the angles of deflection. 
 Hence we have, in the above experiment, the apparently paradoxical 
 result, which is nevertheless susceptible of rational explanation 
 (132), that under the conditions stated, quadrupling the number of 
 the cells in the circuit only increases the quantity of current in the 
 ratio of 135 to 160, or about 18 per cent. 
 
 109. Cells in Parallel Series. Next arrange the four cells 
 in 2 series, with 2 cells in each series, as in diagram, Fig. 47. Such 
 
 FIG. 47. Cells in Parallel Senes. 
 
 an arrangement is termed parallel series, or sometimes multiple series 
 This gives quite a different result. 
 
 2 series of 2 cells each. Deflection 6gf (tangent 2.70). 
 
 UNIVERSITY 
 
54 Laws and Conditions of Electrical Action. 
 
 no. Cells in Parallel. Finally, connect all the copper ter- 
 minals to one terminal of the galvanometer and all the zincs to the 
 other, as in Fig. 48. This is termed connecting in parallel, or mul- 
 tiple-arc. The result will be again different, as follows: 
 
 4 cells in parallel, deflection 73^ (tangent 3.38). 
 
 FIG. 48. Cells in Parallel. 
 
 in. Increasing Length of Conducting Circuit. Leaving 
 the cells and the galvanometer connected in the manner last de- 
 scribed, let the current next be made to pass also through the length 
 of the 2 Ibs. of No. 18 copper wire, which will be in linear measure 
 a little over 300 feet. The deflection of the needle will now fall 
 from 73 J to about 59 J (tangent 1.70). This experiment proves 
 that when the current is made to pass through the long copper wire, 
 under the conditions of the experiment, its quantity is diminished to 
 about one-half the original amount. 
 
 112. Next place the galvanometer in circuit with one cell, as we 
 did once before, and found the deflection to be 53^ (tangent 1.35). 
 Insert the long copper wire in circuit with the galvanometer and cell, 
 and we get a deflection of about 44 (tangent 0.965), showing that 
 the quantity of current has been diminished about one-third. 
 
 113. Leaving the long copper wire still in circuit with the galvan- 
 ometer, add another cell, making 2 in series. The deflection now 
 becomes about 51 (tangent 1.23), and by adding still another cell, 
 making 3, we get a deflection of 53^ (tangent 1.35), exactly 
 what we had with one cell when the copper wire was not included 
 in the circuit. 
 
 114. Conditions which Determine Quantity of Current. 
 From the last experiment we arrive at two fundamental facts re- 
 
Table of Tangents. 
 
 55 
 
 TABLE III. 
 TANGENTS FOR EVERY HALF DEGREE. 
 
 Deg. 
 
 o' 
 
 30' 
 
 Deg. o' 30' 
 
 Deg. 
 
 o' 
 
 30' 
 
 
 
 .0000 
 
 .0087 
 
 30 .5774 
 
 .5890 
 
 60 
 
 1.732 
 
 1.767 
 
 i 
 
 0175 
 
 .0262 
 
 31 
 
 .6009 
 
 .6128 
 
 61 
 
 1.804 
 
 1.842 
 
 2 
 
 0349 
 
 0437 
 
 32 
 
 .6249 
 
 .6371 
 
 62 
 
 1.881 
 
 1.921 
 
 3 
 
 .0524 
 
 .0612 
 
 33 
 
 .6494 
 
 .6619 
 
 63 
 
 1.963 
 
 2.0C6 
 
 4 
 
 .0699 
 
 .0787 
 
 34 
 
 6745 
 
 .6873 
 
 64 
 
 2.050 
 
 2.096 
 
 5 
 
 .0875 
 
 .0963 
 
 35 
 
 .7002 
 
 .7133 
 
 65 
 
 2.144 
 
 2.194 
 
 6 
 
 .1051 
 
 1139 
 
 36 
 
 .7265 
 
 .7400 
 
 66 
 
 2.246 
 
 2 3OO 
 
 7 
 
 .1228 
 
 1317 
 
 37 
 
 , 
 7536 
 
 .7673 
 
 67 
 
 2.356 
 
 2.414 
 
 8 
 
 .1405 
 
 1495 
 
 38 
 
 7813 
 
 7954 
 
 68 
 
 2.475 
 
 2-539 
 
 9 
 
 .1584 
 
 1673 
 
 39 
 
 .8098 
 
 .8243 
 
 69 
 
 2.605 
 
 2.675 
 
 10 
 
 .1763 
 
 1853 
 
 40 
 
 .8391 
 
 .8541 
 
 70 
 
 2.747 
 
 2.824 
 
 ii 
 
 .1944 
 
 2035 
 
 4i 
 
 .8693 
 
 .8847 
 
 7i 
 
 2.904 
 
 2.989 
 
 12 
 
 .2126 
 
 .2217 
 
 42 
 
 .9004 
 
 .9163 
 
 72 
 
 3.078 
 
 3.172 
 
 13 
 
 .2309 
 
 .2401 
 
 43 
 
 .9325 
 
 .9490 
 
 73 
 
 3.271 
 
 3.376 
 
 14 
 
 2493 
 
 .2586 
 
 44 
 
 .9657 
 
 .9827 
 
 74 
 
 3.487 
 
 3.606 
 
 15 
 
 .2679 
 
 2773 
 
 45 
 
 I.OOO 
 
 1.018 
 
 75 
 
 3.732 
 
 3.867 
 
 16 
 
 .2867 
 
 .2962 
 
 46 
 
 1-035 
 
 1.054 
 
 76 
 
 4.011 
 
 4.165 
 
 17 
 
 .3057 
 
 .3153 
 
 47 
 
 1.072 
 
 1.091 
 
 77 
 
 4.331 
 
 4.510 
 
 18 
 
 3249 
 
 .3346 
 
 48 
 
 I. Ill 
 
 1.130 
 
 78 
 
 4.705 
 
 4.9 J 5 
 
 19 
 
 3443 
 
 3541 
 
 49 
 
 1.150 
 
 1.171 
 
 79 
 
 5.145 
 
 5-395 
 
 20 
 
 .3640 
 
 3739 
 
 50 
 
 1.192 
 
 1.213 
 
 80 
 
 5.671 
 
 5.976 
 
 21 
 
 .3339 
 
 3939 
 
 5i 
 
 1.235 
 
 1-257 
 
 81 
 
 6.314 
 
 6.691 
 
 22 
 
 .4040 
 
 .4142 
 
 52 
 
 1.280 
 
 1.303 
 
 82 
 
 7.115 
 
 7-599 
 
 23 
 
 .4245 .4348 
 
 53 
 
 1.327 
 
 I-35I 
 
 83 
 
 8.144 
 
 8.777 
 
 24 
 
 4452 
 
 4557 
 
 54 
 
 1.376 
 
 1.402 
 
 84 
 
 9.514 
 
 10.39 
 
 25 
 
 .4663 
 
 .4770 
 
 55 
 
 1.428 
 
 L455 
 
 85 n-43 
 
 12.71 
 
 26 
 
 .4877 
 
 .4986 
 
 56 1.483 
 
 1.511 
 
 86 ; 14.30 
 
 16.35 
 
 27 
 
 5095 
 
 .5206 
 
 57 
 
 1.540 
 
 1-570 
 
 87 19.08 
 
 22.90 
 
 28 
 
 b3i7 
 
 5430 
 
 58 
 
 1. 600 
 
 1.632 
 
 88 28.64 
 
 38.19 
 
 29 
 
 5543 
 
 5658 
 
 59 1.664 1.698 
 
 89 j 57-29 
 
 114.6 
 
56 Laws and Conditions of Electrical Action. 
 
 specting the electric current, which are that its quantity may be 
 affected, -first, by varying the length of the conductor which it 
 traverses, and second, by varying the number of cells in series in the 
 battery from which the current is derived. 
 
 115. Resistance. What is true of the copper wire is also true 
 of all known substances, namely, that they oppose a certain and 
 definite resistance to the passage through them of an electric current, 
 and the quantity of current which passes, other things being equal, 
 is in every case inversely proportional to the resistance which it en- 
 counters in the circuit (127). In other words,, the greater the resist- 
 ance the less the quantity of current, and vice versa. 
 
 116. Conductors and Insulators. Although all bodies 
 offer more or less resistance to the passage of the electric current, 
 there is an enormous difference in the resisting capacity of different 
 substances. Those which offer comparatively little resistance are 
 called in a general sense conductors of electricity, while those that 
 offer great resistance are termed insulators. This distinction, like 
 that, for example, between heat and cold, is wholly relative and not 
 absolute. The most perfect known conductors offer some resistance 
 to the current, and the most perfect insulators known permit some 
 current to pass. But the actual difference in some instances is al- 
 most beyond the power of the mind to grasp. 
 
 It is difficult to find any comparison which will give a tolerably good idea 
 of the extraordinary difference between the electrical resistance of these two 
 materials (copper and gutta-percha). It is about as great as the difference 
 between the velocity of light and that of a body moving through one foot in 
 6700 years ; yet the measurements of the two quantities are daily made with 
 the same apparatus and the same standards of comparison. This fact is 
 well calculated to give an idea of the range of electrical measurements, and 
 the perfection to which the instruments employed have been brought. 
 FLEEMING JENKIN on Submarine Telegraphy, in North British Review* 
 December, 1866. 
 
 117. The division of bodies into the two classes of conductors 
 and insulators, though in a certain sense arbitrary, is very conven- 
 ient in practice. In telegraphy, the term conductor is applied to- 
 all substances which are used in any manner as a portion of the 
 conducting circuit, while on the other hand, the term insulator 
 is applied to all substances which are employed to confine the elec- 
 trical current to such conductors, by preventing its escape in unde- 
 sired directions. Following is a list of some of the substances so 
 used, arranged as nearly as possible in the order of their specific 
 conductivity : 
 
Specific Resistance of Different Metals. 57 
 
 CONDUCTORS. 
 
 INSULATORS. 
 
 I. Copper. 
 
 15. Metallic oxides. 
 
 2. Zinc. 
 
 16. Ice (dry). 
 
 3. Platinum. 
 
 17. Paper (dry). 
 
 4. Iron. 
 
 18. Wood (dry). 
 
 5. Nickel. 
 
 19. Earth (dry). 
 
 6. Tin. 
 
 20. Cotton. 
 
 7. Lead. 
 
 21. Glazed porcelain. 
 
 8. Mercury. 
 
 22. Silk. 
 
 9. Carbon. 
 
 23. Bitumen. 
 
 10. Acids. 
 
 24. Sulphur. 
 
 ii. Aqueous solutions of me- 
 
 25. Oxydi/ed oils. 
 
 tallic salts. 
 
 26. Balata 
 
 12. Water. 
 
 27. India-rubber. 
 
 13. Wood (moist). 
 
 28. Gutta-percha. 
 
 14. Earth (moist). 
 
 29. Shellac. 
 
 
 30. Paraffin. 
 
 
 31. Hard Rubber. 
 
 
 32. Glass. 
 
 
 33- Air. 
 
 The conducting power of all alloys or mixtures of different metals 
 is very much less than that of any one of the metals of which they 
 are composed. 2 The air is the most perfect non-conductor known, 
 even when charged to saturation with aqueous vapor, but it should 
 be remarked that when the moisture of such vapor is deposited 
 upon the surface of insulating supports, it may form a conducting 
 film of water. 
 
 1170. Specific Resistance of Different Metals. The re- 
 sistance referred to in (115^, is specific resistance, a quality which 
 depends, in some way not definitely understood, upon the internal 
 molecular structure of each particular substance. Thus an iron wire 
 of the same weight and thickness as the copper wire used in the 
 preceding experiments (in, 112) would offer nearly 6 times as much 
 resistance. 
 
 If the resistance of a pure copper wire of a certain length and 
 diameter is known, the resistance of other wires, of similar dimen- 
 sions but of other metals, may be found by the following rule : 
 
 For Brass, multiply copper resistance by 
 " German-silver " " " 
 
 " Iron " " " 
 
 Platinoid 
 " Platinum " " " 
 
 4-5 
 12.9 
 
 5-9 
 
 19-5 
 14.8 
 
 For Matthiessen's determinations of the specific resistance of metals and alloys, see 
 SPRAGUE : Electricity, etc., p. 282 ; see also BENOTT: Jour. Soc. Tel. Eng. iv. 112. 
 
58 Laws and Conditions of Electrical Action. 
 
 118. Conditions Affecting Resistance. In the case of a 
 body having a certain specific resistance, the actual measurable re- 
 sistance depends upon certain conditions, viz. : 
 
 (i) Temperature. The resistance of all metals increases with the tem- 
 perature. The converse of this is true of most liquids at temperatures 
 above the freezing point (162). 
 
 (ii) Length. The resistance of any body is in proportion to its length, 
 measured in the direction traversed by the current. 
 
 (iii) Cross-section. The resistance of any body is inversely in propor- 
 tion to its area of its cross-section. Doubling the cross-section halves the 
 resistance. 
 
 Every resistance capable of being measured, must necessarily be 
 equal to the resistance of a certain length of a standard conductor ; 
 therefore resistance may be expressed in terms of length. Thus a tele- 
 graph line made up of two or more sections of wire, of unequal 
 thickness or gauge, and so presenting a different resistance per mile 
 of length, may be expressed in terms of the resistance of a given 
 length of a standard wire : that is to say, the actual resistance of any 
 telegraph line must represent and be equal to the resistance of a 
 certain length of wire of the standard gauge. This length is called 
 the reduced length of the line. The convenience of this mode of re- 
 ducing resistance to terms of length in making tests and measure- 
 ments of lines will appear hereafter. 
 
 119. Provisional Theory of Electricity. Before under- 
 taking to analyze and explain the results which have been observed 
 in the foregoing experiments, it will be convenient for the student to 
 form some sort of a mental conception of the agency which produces 
 the phenomena observed. A distinguished electrical engineer has 
 remarked : 
 
 The student of electricity, in considering the various phenomena which 
 come under his notice, must of necessity form some theory in his mind as 
 to the nature of the element with which he has to deal ; and as philosophers 
 are not in accord as to its nature and the theory of its action, the choice 
 must to a novice be a difficult one. Without, therefore, in the least offering 
 any opinion on this point, I would advise him, until his ideas are more 
 matured, to regard electricity as a substance like water or gas, having a ver- 
 itable existence, and also easily converted into heat and, vice versa, in other 
 respects indestructible. LATIMER CLARK: Electrical Measurement, p. vii. 
 
 120. Mechanical Analogue of Electrical Action. Ac- 
 cording to this manner of looking at the question, we may regard a 
 voltaic cell or a dynamo-electric machine as a sort of pump, by 
 which positive electricity is pumped through an endless channel or 
 
Conception of Potential and Electromotive Force. 59 
 
 conduit, as water might be pumped through a pipe to the top of a 
 hill, and thence allowed to flow back in a definite channel to the 
 foot of the pump from whence it started. This illustration, if fixed 
 in the mind, will materially aid the student in forming a useful 
 mental conception of the character of the flow of electricity in a 
 circuit of conductors. 
 
 121. Conception of Potential and Electromotive Force. 
 When water is pumped to an elevation by the application of power 
 and then allowed to run back to its original level, it is capable of being 
 made to do work in the course of its descent by means of water-wheels 
 or otherwise, and it is obvious that the amount of work it is capable 
 of doing under these conditions depends upon three things: (i) 
 the height of the fall, (2) the quantity of water, and (3) the length 
 of time the effect continues. We may express the condition of 
 affairs by saying that the water which has been raised has a certain 
 potential energy \ which may be defined as capacity to do work, and for 
 brevity we may call it potential. We may, therefore, for present pur- 
 poses, regard electricity as a material fluid to which a certain poten- 
 tial has been given by the action of a battery or of a magneto- 
 electric machine (80), and which is therefore capable of doing 
 mechanical work, as is the case with the descending water. That 
 quality of a voltaic cell, or of a magneto or dynamo-electric machine, 
 by virtue of which it confers potential upon electricity is termed 
 electromotive force^ usually abbreviated to e. m. f. 
 
 122. Practical Electric Units. The units offeree and work, 
 and their relation to force of gravitation, have already been referred 
 to (91), and it has also been explained (94) that a definite quanti- 
 tive relation exists between mechanical force and the force of an 
 electric current. This fact enables us to base our practical units of 
 electrical measurement upon absolute units ; or in other words, our 
 practical units are derived from constants furnished by nature. The 
 relation or law connecting the two forces is as follows : 
 
 The force which a given current traversing a circular arc 
 exercises upon a magnetic pole of given strength situated at its center, 
 is equal to the strength of the pole multiplied by the strength of the 
 current and also by the length of the arc, and divided by the square 
 of the radius or semi-diameter ; that is to say, the distance from the 
 wire from the magnet pole. 
 
 The names which have been given to the practical electrical units 
 are derived from the names of philosophers of various nationalities 
 who have distinguished themselves by electrical discoveries and 
 investigations. 
 
60 Laws and Conditions of Electrical Action. 
 
 123. The Ampere. The unit of current is called the ampere. 8 
 It is equivalent in value to -fa of the absolute or c. g. s. unit of current 
 (91). The actual value of any current within the range of the instru- 
 ment may be determined from the indications of a properly con- 
 structed tangent galvanometer. This is' done by the aid of the 
 following rules : 
 
 (i; Given the number of turns and the mean radius of the coil of the tangent 
 galvanometer, the observed deflection, and the horizontal force of the earth's 
 magnetism at the place of observation (94), to find the current in amperes: 
 
 RULE. Multiply together the mean radius in inches, the tangent of the deflec- 
 tion, the horizontal magnetic intensity of ihe earth in dynes, and the reduction 
 factor 4.0425, and divide the product by the number of turns in the coil. The 
 quotient is the current in amperes. 
 
 Example. In a tangent galvanometer having a lo-in. coil wound in 6 turns, 
 and giving a deflection of 60 in Washington, D. C., in 1885, required the value 
 of the current. 
 
 Ans. 5 (in.) X 1.732 (tan. of 60) X .2026 (dynes) X 4.0425 (reduction 
 factor) -f- 6 (turns) 1.182 amperes. 4 
 
 (ii) Given the number of turns and mean radius of the coil, the value of the 
 current and the horizontal intensity, to find the deflection. 
 
 RULE. Multiply together the number of amperes and the number of turns, and 
 divide this product by the product of the mean radius in inches, the horizontal in- 
 tensity in dynes, and the rednction factor 4.0425. The quotient will be the t ingcnt 
 of the deflection. 
 
 Example. A current of 0.25 amperes was passed through the coil of the above 
 described galvanometer in New York. What -was the deflection ? 
 
 Ans. 0.25 (amperes) X 6 (turns) -*- [5 (in.) X 0.1872 (dynes) X 4.0425 
 (red. fac.)] in 0.3874 tangent of 21 nearly. 
 
 * AMPERE (ANDRE MARIE), an eminent French philosopher and mathematician, in 
 honor of whom the unit of current received its name ; born at Lyons, 1775. He 
 became inspector-general of the university (1808) ; professor in the Polytechnic School 
 (1809) ; and Member of the Institute (1814). Having' made important discoveries in 
 electro-magnetism, he published (1822) his Collection of Observations on Electro- 
 Dynamics, a remarkable work. " The vast field of physical science," says Arago, 
 41 perhaps never presented so brilliant a discovery, conceived, verified, and completed 
 with such rapidity." He subsequently published his Theory of Electro- Dynamic 
 Phenomena, Deduced from Experiments (1826). Died in Marseilles, 1836. 
 
 4 Each unit in the metric system has its decimal multiples and sub-multiples ; that 
 is to say, measures larger or smaller than the standard unit. These multiples and 
 sub-multiples are denoted by prefixes, derived from the Greek and Latin languages 
 respectively, placed before the names of the units, as follows : 
 
 PREFIX. SIGNIFICATION. | PREFIX. SIGNIFICATION. 
 
 Micro- means one millionth of a . ! Hecto- means hundred times a . 
 
 Milli- " one thousandth of a . Kilo- " thousand times a . 
 
 Centi- " one hundredth of a . Myria- " ten thousand times a . 
 
 Deci- " one tenth of a . Mega- " one million times a . 
 
 Deka- " ten times a . 
 
 Thus a millimetre is one-thousandth of a metre ; a milliampere is one-thousandth 
 of an ampere ; a megohm is one million ohms, etc., etc. 
 
Tkc Coulomb. The Volt. The Ohm. 61 
 
 (iii) Example. The earth's magnetism in Toronto, Ont., being the direct- 
 ing force of a galvanometer having a lo-in. coil, how many turns must be 
 put on it in order that a current of 0.96 amperes shall give a deflection of 60 ? 
 
 Ans. 6 turns. 
 
 From the above explanations and examples, it will he seen that a 
 standard galvanometer may be constructed, from which it is always 
 possible, knowing the force of the earth's magnetism, to determine 
 the value of any electric current in amperes. In some cases, tangent 
 galvanometers are graduated so that the amperes may be read di- 
 rectly without calculation. Such an instrument is called an ampere- 
 meter, or more commonly, an ammeter (369). 
 
 1233. The Coulomb. The quantity of current which traverses 
 a circuit in i second, when the strength of current is i ampere, is 
 termed a Coulomb. f> It is a unit which is of little or no practical 
 utility in ordinary telegraph work, or in fact for any other purpose, 
 and is referred to here only because it has been given a place in the 
 accepted system of electric units. 
 
 124. The Volt. The unit of electromotive force is called the 
 volt. 6 It closely approximates that of a single sulphate of copper 
 or gravity cell in good condition (24), so that in telegraphic work it 
 is usually accurate enough for practical purposes to estimate i cell 
 equals i volt. Accurately, i gravity cell has an e. m.f. of 1.07 volts. 
 This value is subject to slight variation from various causes. It is 
 not much influenced by temperature (153, note). 
 
 125. The Ohm. The unit of electrical resistance is called the 
 ohm. 7 It is equal to the resistance to a column of pure mercury, i 
 sq. millimetre in cross-section and 106 centimetres (more or less), in 
 length, 8 at a temperature of o Centigrade or 32 Fahrenheit. 
 
 5 COULOMB (CHARLES AUGUSTIN DE), a distinguished mathematician, born at 
 Angouleme, France, 1736. He is regarded as the founder of experimental physics in 
 France. The theory of electricity is largely indebted to the investigations of this phi- 
 losopher. Died, 1806. 
 
 6 VOLTA (ALESSANDRO), born at Como, Italy, 1745 ; was first professor of physics 
 at Como, and afterward in the University of Pavia, where he taught and studied for 
 30 years. In 1782, he invented the electrical condenser (317), and finally arrived at 
 the invention of the famous cell which bears his name (8), which he described in a let- 
 ter to Sir Joseph Banks in 1800. Summoned to Paris by Napoleon, he received the 
 gold medal of the Institute, of which he became a member in 1802. His works were 
 published in 9 volumes, in Florence, in 1816. Died, 1827. 
 
 7 OHM (GEORG SIMON), born at Erlangen, Bavaria, 1787 ; studied in his native 
 city ; was appointed (1817) professor of physics at the Jesuit college of Cologne, di- 
 rector of Polytechnic School at Nuremburg (1883), and professor (1849) at Munich, 
 where he died in 1874. He discovered the so-called Ohm's law (124), which he pub- 
 lished in 1827, and for which was awarded the Copley medal by the Royal Society of 
 London. 
 
 In 1861, the British Association for the Advancement of Science, at the suggestion 
 
62 Laws and Conditions of Electrical Action. 
 
 The resistances of various wires used as telegraphic conductors is 
 given in the tables, pp. 94, 112. 
 
 126. Resistance of Liquids. The resistance of liquids is 
 enormously greater than that of metallic substances. The relative 
 specific resistances of some of the voltaic solutions used in telegraphy 
 are as follows : 9 
 
 Pure copper (standard of comparison) i. 
 
 Pure rain water 40,653,723. 
 
 Water 12 parts, sulphuric acid i part 1,305,467. 
 
 Sulphate of copper i Ib. , water i gallon 18,450,000. 
 
 Saturated solution sulphate of zinc 17,330,000. 
 
 Table iv, on the next page, contains the results of more recent 
 determinations of the specific resistance of copper and zinc solutions 
 at various temperatures, computed from the experiments of Becker. 10 
 As the temperature rises, the resistance falls off. This effect is fur- 
 ther referred to in (164). 
 
 of Sir William Thomson, appointed a committee on electrical standards, which, after 
 a long series of experiments by eminent physicists, determined the value of the ohm to 
 be nearly that of a column of pure mercury 105 centimetres long and i square millim- 
 etre in cross-section, at temp. o centigrade, and officially caused resistance coils made 
 of wire of an alloy of platinum and silver to be issued as standards. Resistance coils 
 copied from these standards are known as B. A. units or ohms. More recent careful 
 determinations of Lord Rayleigh and many others have proved beyond doubt that the 
 B. A. unit or ohm is more than i per cent, too small. An attempt has accordingly 
 been made to substitute for the old standards new ones of the corrected value. In ac- 
 cordance with the recommendation of the International Congress of Electricians, held 
 in Paris in 1884, a legal ohm is denned to be a mercury column of the above section, 
 and 106 cm. in length. The exact ratio is : 
 
 i Legal ohm = 1.0112 B. A. ohm. 
 i B. A. ohm = 0.9889 legal ohm. 
 
 At the meeting of the British Association in September, 1890, it was recommended 
 that the value for the mercury column of 106.3 cm - be substituted for the 106 cm. of 
 the International Congress, and it is not unlikely that this value may ultimately be 
 adopted. 
 
 In Germany, the Siemens unit (known as the S. U.) is largely used, and many of 
 the older instruments now in use in the United States are adjusted to this standard. 
 It is designed to be equal to a column of mercury i metre long and i sq. mm. cross- 
 section at temp. o C. 
 
 i Siemens unit = 0.9540 B. A. ohm. 
 i B. A. ohm. = 1.0486 S. U. 
 
 MOSES G. FARMER : Shaffner's Telegraph Manual, 514. 
 
 10 F. JENKIN : Electricity and Magnetism, 259. The maximum conductivity of s. z. 
 solution is 23.5 per cent (s. g. 1.286) according to KOHLRAUSCH : Physical Measure- 
 ment, p. 326. For other tables of resistances of liquids, see SPRAGUE : Electricity, etc. 
 (2d ed.), 298; STEWART and GEE: Elementary Practical Physics, 219; NIAUDET : 
 Electric Batteries (Fishback's Translation), 255 ; PRESCOTT : Electricity and Elec. 
 Tel., 182. For method of measurement see F. KOHLRAUSCH : Jour. Soc. Tel. Eng. 
 xiii, 290. 
 
Ohms Law. 
 
 TABLE IV. 
 
 SPECIFIC RESISTANCES OF VOLTAIC SOLUTIONS. 
 SULPHATE OF COPPER. 
 
 Percentage 
 of salt in 
 Solution. 
 
 14 
 
 16 
 
 18 
 
 20 
 
 24 
 
 28 
 
 30 
 
 Centigrade. 
 
 8 
 
 12 
 
 16 
 
 45-7 
 36.3 
 31.2 
 
 43-7 
 34-9 
 30.0 
 
 41.9 
 
 33-5 
 28.9 
 
 40.2 
 32.2 
 27.9 
 
 37-1 
 29.9 
 26.1 
 
 34-2 
 27.9 
 24.6 
 
 32.9 
 27.0 
 24.0 
 
 Resistance of 
 i cubic centi- 
 
 20 
 24 
 
 28 
 
 28.5 
 26.9 
 24-7 
 
 27.5 
 25-9 
 23-4 
 
 26.5 
 24.8 
 
 22.1 
 
 25.6 
 23-9 
 
 21.0 
 
 24.1 
 
 22.2 
 
 18.8 
 
 22.7 
 20.7 
 16.9 
 
 22.2 
 2O. O 
 
 16.0 
 
 metre ex- 
 pressed in 
 ohms. 
 
 SULPHATE OF ZINC. 
 
 
 10 12 
 
 14 16 
 
 18 
 
 20 
 
 22 
 
 24 Centigrade. 
 
 96 grams in 100 \ 
 c. c. of solution. ) 
 
 22.7 
 
 21.4 
 
 20.2 
 
 19.2 
 
 18.1 
 
 I7.I 
 
 I6. 3 
 
 ! Resistance of i 
 
 
 
 
 
 
 
 
 
 cubic centi- 
 
 Same solution \ 
 
 
 
 
 
 
 
 
 metre expressed 
 
 with an equal > 
 
 
 
 21. 1 
 
 20.3 19.5 
 
 18.8 
 
 18.1 
 
 r 7-3. i n ohms. 
 
 volume of water. ) 
 
 
 
 
 
 
 
 
 i 
 
 127. Ohm's Law. The fundamental relation which exists in 
 every electric circuit between electromotive force, resistance and 
 current, is expressed by Ohm's law, which may be formulated in the 
 following propositions : 
 
 (i) In any electric circuit, the current is the quotient of the electromotive 
 force divided by the resistance ; hence the current in amperes maybe found 
 by dividing the e. m. f. in volts by the resistance in ohms. 
 
 (ii) In any electric circuit, the electromotive force is the product of the 
 current and the resistance ; hence the total e. m. f. in volts may be found by 
 multiplying together the current in amperes and the resistance in ohms. 
 
 (iii) In any electric circuit, the resistance is the quotient of the electro- 
 motive force divided by the current ; hence the resistance in ohms may be 
 found by dividing the e. m. f. in volts by the current in amperes. 
 
 128. Joule's Law. 11 The relation which exists between cur- 
 rent and mechanical work is expressed by Joule's law, which may 
 be formulated in the following propositions : 
 
 11 JOULE (JAMES PRESCOTT), born in Salford, England, 1818. A self-taught philos- 
 opher, distinguished for the extent, originality, and accuracy of his physical researches. 
 He ascertained in 1841, the law of the evolution of heat by the electric current (128), 
 and determined in 1850, the numerical ratio of equivalency between heat and mechan- 
 ical force (92). His discoveries, which are too numerous to permit more than general 
 
64 Laws and Conditions oj Electrical Action. 
 
 (iv) In any electric circuit, the rate of doing worK is the product of the 
 e. m. f. and the current ; hence the rate in which work is being done in 
 watts (150) may be found by multiplying together the e. m.f. in volts and the 
 current in amperes. 
 
 (v) In any electric circuit, the rate of doing work is the product of the 
 current multiplied into itself and into the resistance ; hence rate of working 
 in watts may also be found by multiplying together the resistance and the 
 square of the current in amperes. 
 
 129. The term work, as herein used, includes the work which 
 appears in the form of heat, as well as that which produces physical 
 motion. 
 
 130. Experimental Proof of Ohm's Law. The student is 
 now prepared to understand an explanation of the results which 
 
 have been referred to in the 
 preceding paragraphs (108 
 113). Referring to the dia- 
 gram, Fig. 49, we may trace 
 the circuit as follows : Begin- 
 ning at the copper or the posi- 
 tive pole of the battery, thence 
 through the 62 feet of copper 
 wire which forms the coil of 
 the galvanometer ; thence to 
 the zinc Z or negative pole of 
 the battery ; thence in succes- 
 sion through the s. z. solution 
 and the s. c. solution S to the 
 copper plate C of the first cell ; 
 thence to the zinc plate Z of 
 the next cell, and through the 
 
 solution to the copper, and so on through the series until the starting 
 point, the copper plate of the terminal cell, is reached. 
 
 131. Internal Resistance of the Cell. The solution in each 
 cell may be regarded as a liquid conductor of cylindrical form, having 
 a length of about 3 in. (the average distance between the copper and 
 zinc plates) and a cross-section of about 28 sq. in. When a cell is 
 in good working condition, the resistance of the contained liquids, at 
 ordinary temperatures, is about 4 ohms, and may be regarded as 
 
 mention here, have been intimately related to the remarkable theory of the correlation 
 of the physical forces (p. 38, note 8) which was developed by Mayer, Helmholtz, Seguin, 
 Faraday, and Grove. His researches in electro-magnetism, particularly in respect to 
 its application as a motive power, were extensive and important. Honors were con- 
 ferred on him by almost every learned society in the world. His scientific papers were 
 collected and published by the Physical Society of London in 1884. Died 1889. 
 
 FIG. 49, Diagram of Galvanometer and Battery 
 Circuit. 
 
Kic. 50. Cells in Series with 
 Galvanometer. 
 
 Internal Resistance of t/ic Cell. First Case. 65 
 
 approximately equivalent to that of 250 feet of copper wire of the 
 thickness of that in the coil of our galvanometer (103). The actual 
 resistance of the zinc and copper plates of each cell, being at most 
 but an insignificant fraction of i ohm, may in the present instance 
 be disregarded in our computations. 
 
 132. First Case. In the first ex- 
 ample, we begin with 4 cells in circuit in 
 a single series, as shown in Fig. 50. 
 
 This figure is a diagrammatical or con- 
 ventional illustration of precisely the same i 
 thing which is shown in Fig. 46. The I 
 zinc plate of each cell is represented by a 
 thick black line, and the copper by a thin 
 line. The symbol for the galvanometer 
 explains itself. In like manner, Fig. 51 
 corresponds to Fig. 47, and Fig. 52 to Fig. 
 48. In Figs. 51 and 52, a black dot at 
 
 the intersection of two wires indicates that they are electrically 
 united at the junction. This conventional representation of batteries, 
 galvanometers, circuits, and other appliances will be employed here- 
 after in this work (208). 
 
 In this case, each cell has an approximate e. m.f. of i volt (124), 
 this value depending not at all upon the size of the element, but 
 solely upon its chemical constitution. The aggregate .;#*./] of the 
 4 cells of the series is therefore 4 volts. The aggregate resistance 
 of the 4 cells is 16 ohms, and that of the galvanometer r ohm. We 
 may neglect also the inappreciable resistance of the short connecting 
 wires between the battery and the galvanometer, and call the sum 
 of the resistances in the circuit (battery and galvanometer) 17 ohms. 
 By Ohm's law (127, i), we divide the e. m.f. 4 (volts) by the resist- 
 ance 17 (ohms), and our quotient is 0.235 (amperes). 
 
 With 3 cells in -like manner, we have an e. m.f. of 3 volts, an 
 aggregate resistance of 13 ohms, and by Ohm's law a current of 
 0.230 amperes; and so in the remaining cases. Continuing this 
 method of procedure, we get results which may be tabulated as 
 follows : 
 
 Cells in Series. 
 
 Deflections. 
 
 Tangents. 
 
 E. M. F. 
 
 Resistance. 
 
 Current. 
 
 4 
 
 58 
 
 1. 60 
 
 4 
 
 17 
 
 0-235 
 
 3 
 
 57i 
 
 l. 5 6 
 
 3 
 
 13 
 
 0.230 
 
 2 
 
 5<* 
 
 1-50 
 
 2 
 
 9 
 
 0.222 
 
 I 
 
 53T 
 
 i-35 
 
 I 
 
 5 
 
 O.2OO 
 
66 Laws and Conditions of Electrical Action. 
 
 We find, therefore, that the tangents of the angles of deflection are 
 in proportion to the strength of the current in amperes, as computed 
 by Ohm's law from known electromotive forces and known resistances. 
 
 133. Second Case. Take 
 the next arrangement (109), in 
 which we have 2 series of cells 
 and 2 cells in each series, Fig. 
 51. The question now arises: 
 If the resistance of each cell is 
 4 ohms, what will be the resist- 
 ance of the group? It is less 
 than in the preceding case, as 
 Fig. 51. Cells in Parallel Series with Gal- the increased deflection of the 
 
 vanometer. ji i i i 
 
 needle shows, and as might 
 
 have been inferred from the fact that the current from each series of 
 cells does not now pass through the other series, nor encounter its 
 resistance. Neither is the e. m.f. of one series superimposed upon 
 that of the other series as before. A little reflection will make it 
 clear that the present arrangement is precisely equivalent to 2 cells 
 in series, each having copper and zinc plates of double the original 
 area. Hence we may consider the cross-section of the liquid con- 
 ductor to be doubled, while its length remains unaltered, from which 
 it follows that its resistance is but half what it was originally (118). 
 134. Law of Joint Resistances. The law determining the 
 resistance of any circuit which divides into two or more branches 
 which reunite at another point, is a general one, and applicable in 
 all such cases, whether of batteries or of conductors. The resist- 
 ance offered by two or more such branches is termed their joint 
 resistance, and is computed by the following rules : 
 
 RULE i. Add together the reciprocals of the individual resistances of all 
 the branches, and the reciprocal of the result will be the joint resistance of tJie 
 group. 
 
 The reciprocal of any number is the fraction obtained by dividing 
 unity (or i) by that number; and the reciprocal of any common 
 fraction, is that fraction itself inverted. Thus the reciprocal of 2 is 
 \ or 0.5 ; and conversely, the reciprocal of 0.5 or \ is 2. The recip- 
 rocal of J is f . A table of reciprocals is given on page 67. 
 
 In case there are only two branches, a simpler method of compu- 
 tation may be used : 
 
 RULE 2. Multiply together the individual resistances of the two branches, 
 and divide the product by their sum ; the quotient will be the joint resistance. 
 
Table of Reciprocals. 
 
 TABLE V. 
 RECIPROCALS OF NUMBERS FROM 1 TO 100. 
 
 No. 
 
 Rec. 
 
 No. Rec. 
 
 No. 
 
 Rec. 
 
 No. 
 
 Rec. 
 
 No. 
 
 Rec. 
 
 I 
 
 1. 000 
 
 21 .0467 
 
 41 
 
 .0244 
 
 61 
 
 .0164 
 
 81 
 
 .0123 
 
 2 
 
 .5000 
 
 22 .0454 
 
 42 
 
 .0238 
 
 62 
 
 .0161 
 
 82 
 
 .0122 
 
 3 
 
 3333 
 
 23 
 
 0434 
 
 43 
 
 .0232 
 
 63 
 
 .0159 
 
 83 
 
 .0120 
 
 *! 
 
 .2500 
 
 24 
 
 .0416 
 
 44 
 
 .0227 
 
 64 
 
 .0156 
 
 84 
 
 .0119 
 
 5 
 
 .2000 
 
 25 
 
 .0400 
 
 .45 
 
 .0222 
 
 65 
 
 .0154 
 
 85 
 
 .0118 
 
 6 
 
 .1667 
 
 26 
 
 .0385 
 
 46 
 
 .0217 
 
 66 
 
 .0151 
 
 86 
 
 .0116 
 
 7 
 
 .1428 
 
 27 
 
 .0370 
 
 47 
 
 .0213 
 
 67 
 
 .0149 
 
 87 
 
 .0115 
 
 8 
 
 .1250 
 
 28 
 
 0357 
 
 48 
 
 .0208 
 
 68 
 
 .0147 
 
 88 
 
 .0114 
 
 9 
 
 .mi 
 
 2 9 
 
 0344 
 
 49 
 
 .O2O4 
 
 69 
 
 .1045 
 
 89 
 
 .OII2 
 
 10 
 
 .1000 
 
 30 
 
 0333 
 
 50 
 
 .0200 
 
 70 
 
 .0143 
 
 9 
 
 .OIII 
 
 n 
 
 .0909 
 
 31 
 
 .0323 
 
 5i 
 
 .0196 
 
 7i 
 
 .0141 
 
 9 1 
 
 .OIIO 
 
 12 
 
 .0833 
 
 32 
 
 .0312 
 
 52 
 
 .0192 
 
 72 
 
 .0139 
 
 92 
 
 .0108 
 
 13 
 
 .0769 
 
 33 
 
 .0303 
 
 53 
 
 .0188 
 
 73 
 
 .0137 
 
 93 
 
 .0107 
 
 14 
 
 .0714 
 
 34 
 
 .0294 
 
 54 
 
 .0185 
 
 74 
 
 0135 
 
 94 
 
 .0106 
 
 15 
 
 .0667 
 
 35 
 
 .0286 
 
 55 
 
 .0182 
 
 75 
 
 0133 
 
 95 
 
 .0105 
 
 16 
 
 .0625 
 
 36 
 
 .0277 
 
 56 
 
 .0178 
 
 76 
 
 .0131 
 
 96 
 
 .0104 
 
 17 
 
 .0588 
 
 37 
 
 .0270 
 
 57 
 
 0175 
 
 77 
 
 .0130 
 
 97 
 
 .0103 
 
 18 
 
 0555 
 
 33 
 
 .0263 
 
 53 
 
 .OI72 
 
 78 
 
 .0128 
 
 98 
 
 .0102 
 
 19 
 
 .0526 
 
 39 
 
 .0256 
 
 59 
 
 .0169 
 
 79 
 
 .0126 
 
 99 
 
 .0101 
 
 20 
 
 .0500 
 
 40 
 
 .0250 
 
 60 
 
 .0166 
 
 80 
 
 .0125 
 
 100 
 
 .0100 
 
 Any sum multiplied by the reciprocal of a number is equal to the same 
 sum divided by the number corresponding to the reciprocal. In the table, 
 the reciprocals are those of whole numbers, but it is easy to extend their 
 use to decimals, or to mixed numbers, by shifting the decimal point ; thus, 
 the 
 
 Reciprocal of 390 = .00256 
 
 " 39 = -0256 
 
 3-9 = -256 
 
 39 2.56 
 
 " " .039 25.6 
 
68 Lazi's and Conditions of Electrical Action. 
 
 135. In the present case we have 2 branches, with' a resistance of 
 8 ohms in each branch. Hence we have 8x8 = 64; 8 + 8= 16; 
 64 -^- 1 6 = 4 ; add galvanometer i, and we have as total resistance 
 5. Dividing the e. m.f., 2, by this amount gives a current of 0.4 
 amperes. We have therefore : 
 
 Cells in parallel series. 
 
 Deflection. Tangent. 
 
 E. M. F. 
 
 2 
 
 Resistance. 
 
 Current. 
 
 4 
 
 6gf 2.70 
 
 5 
 
 0.4 
 
 136. Third Case. Next we have (no) the 
 4 copper terminals connected to one terminal of 
 the galvanometer and the 4 zincs to the other 
 terminal, as in Fig. 52. In this case, by the rule 
 (134), the reciprocal of 4 is 0.25 ; the sum of the 
 four reciprocals is therefore i, the reciprocal of 
 which is i, and this added to the galvanometer 
 resistance i, makes a total of 2, while the e. m. f. 
 is now reduced to i. Hence, we have in this 
 case: 
 
 Cells in . j) enec tion. Tangent. E. M. F. 
 
 Resistance.! Current. 
 
 
 
 73i 3-38 i 
 
 2 | 0.5 
 
 ohms. 
 
 ' 137. Passing next to the experiment in (108), 
 
 in which we found that having 3 cells in circuit 
 with the galvanometer, and 300 feet of a certain 
 gauge copper wire, the deflection apparently in- 
 dicated that we produced exactly the same current 
 in the circuit that we did with i cell when the cop- 
 per wire was not included. Let us see whether 
 Ohm's law accounts for the result. We find from 
 the copper wire table (p. 94) that the resistance 
 of the length of wire included is approximately 2 
 
 We have, therefore : 
 
 Fig. 52. Cells in Par- 
 allel with Galva- 
 nometer. 
 
 Resistance of 3 cells battery ; 12 ohms. 
 
 " " galvanometer i " 
 
 " " 300 feet copper wire 2 
 
 Total 15 ohms. 
 
 3 (volts) -T- 15 (ohms) = 0.2 (amperes). 
 
Branch or Derived Circuits, 69 
 
 In the other case we had : 
 
 Resistance of i cell 4 ohms. 
 
 " galvanometer i " 
 
 Total 5 ohms. 
 
 i (volt) -5- 5 (ohms) 0.2 (amperes). 
 
 138. Ohm's law is therefore confirmed in every particular by the 
 results of experiment, and observation, and we learn, moreover, the 
 important fact that the quantity of current traversing any given circuit 
 may be varied either by varying the electromotive force or by varying 
 the resistance. 
 
 139. We also learn from Ohm's law, as interpreted by the ex- 
 periments which have been made, that every portion of an undivided 
 or non-branching circuit is traversed by the same quantity, or number of 
 amperes^ of current at the same time, without reference to its relative 
 resistance. 
 
 140. Currents in Branch Circuits. When any circuit divides 
 into two or more branches a current traversing that circuit dis- 
 tributes itself between these branches inversely in proportion to 
 their respective resistances, or, what is the same thing, directly in 
 proportion to their several conductivities. The branches are also 
 termed shunts or derived circuits. Each such branch may be re- 
 garded as a shunt to all the other branches in parallel with it. 
 
 The word shunt is of English origin, and is derived from the 
 analogy of a railroad siding where trains pass each other, which in 
 that country is known as a shunt. 
 
 141. Electric Potential. Having thus gained some experi- 
 mental as well as theoretical knowledge of electromotive force (121), 
 resistance (115), and current (91), the student should next endeavor 
 to acquire a definite understanding of the meaning of the term 
 potential. The resemblance between the behavior of electricity and 
 that of a material fluid like water has already been pointed out (120). 
 Recurring to this analogy, if we assume a stream of water to be 
 flowing through a closed pipe, we know that as soon as the flow 
 has become steady, exactly the same number of gallons per 
 minute will pass through every cross-section of the pipe, whatever 
 may be the difference in its diameter at different points. This is 
 exactly analogous to that which occurs in the case of an electric 
 current (139)- 
 
 142. Although the quantity of water which passes must neces- 
 sarily be the same in every cross-section of the pipe, the pressure 
 
place in the electric conductor. 
 
 FIG. 53. Hydraulic Illustration of Electric 
 Potential. 
 
 70 Laws and Conditions of Electrical Action. 
 
 per square inch is by no means equal throughout, and this is true 
 whether the pipe is level and whether it is of uniform diameter or 
 otherwise. As we proceed along a horizontal pipe in the direction 
 of the flow, we observe the pressure becomes less and less as we go 
 farther away from the supplying reservoir. 
 
 143. Illustration of Fall of Potential. A like effect takes 
 
 A fall, technically termed a drop in 
 potential, occurs as we recede 
 from the source of electricity, 
 just as there is a fall of pressure 
 in the water-pipe. For example, 
 let Fig. 53 represent a vessel 
 ~ filled with water. 12 The tap at C 
 is closed, and the water stands 
 at the same level in all the verti- 
 cal tubes, showing that no differ- 
 ence of pressure exists, and 
 
 consequently there can be no current of flow in the liquid. But 
 when the tap at C is opened, as in Fig. 54, it will be observed that 
 the level in the several vertical tubes stands lower and lower as we 
 pass from A toward C. The 
 height of water in each tube in- 
 dicates the pressure which exists 
 at the point of its junction with 
 the tube B. This difference in 
 hydrostatic pressure between dif- 
 ferent points in the pipe produces 
 the flow of water which we call a 
 current. The original cause of 
 the flow is manifestly the force 
 
 which lifted the water in the first place to a point above the level of 
 the pipe B, and thus conferred upon it the pressure or potential 
 which it now has (121). Therefore we may say without error, that 
 electromotive force causes potential to exist. When resistance is re- 
 moved, a fall of potential occurs at some point, and this fall of poten- 
 tial gives rise to an electric current. Therefore the fact of the exist- 
 ence of an electric current is conclusive evidence of the existence of 
 a difference of potential between two different points in the circuit 
 through which the current flows. 
 
 1S This excellent illustration is from Professor ELROY M. AVERY'S Elements of Natu- 
 ral Philosophy, of which the chapter on electricity and magnetism has been separately 
 published by Sheldon & Co., New York. 
 
 FIG. 
 
 Hydraulic Illustration of Uniform 
 Fall of Potential. 
 
Graphic Illustration of the Electric Circuit. 71 
 
 FIG. 55. Hydraulic Illustration of Varying 
 Fall of Potential. 
 
 144. Fall of Potential Proportionate to Resistance. 
 
 The fall of potential between any two points in a circuit bears the 
 same ratio to the fall of potential in the whole circuit that the 
 resistance between those points 
 does to the total resistance of the 
 circuit. In other words, in the 
 whole or any portion of a circuit, 
 the fall of potential is always in 
 proportion to the resistance. In 
 Fig. 55, the horizontal pipe is in 
 two portions of different diame- 
 ters, and in this case it will be 
 observed that the fall of the 
 pressure is more rapid along the smaller than along the larger section. 
 
 145. Graphic Illustration of the Electric Circuit. We may 
 represent by a diagram all the essential characteristics of the electric 
 circuit in a manner first pointed out by Ohm in 1828. For example. 
 
 let the ring in Fig. 56 represent a conductor of 
 uniform resistance having a source of electricity at 
 the point A. The electricity from this point will 
 be diffused over both halves of the ring; the posi- 
 tive going toward a and the negative toward b, 
 both uniting at c. As the conductor is assumed to 
 be homogeneous, it follows that equal quantities of 
 electricity traverse all sections of the ring at the 
 Fig. 5 6. Geometrical same time (139). If we assume that the flow of 
 illustration of Ohm's the current from one crO ss-section of the ring to 
 
 another is due to the difference of potential which 
 exists between the two points (143), and that the quantity which 
 passes is proportional to this difference of potential (144), it follows 
 that the positive and negative currents, proceeding in opposite direc- 
 tions from A, must exhibit a decrease in potential the farther they 
 recede from the starting point. This decrease in potential may be 
 graphically represented in a diagram, the 
 analogy of which to the hydraulic ap- 
 paratus of Fig. 54 will be apparent upon 
 inspection and comparison. Suppose the 
 ring of Fig. 56 to be stretched out in a 
 straight line A A', Fig. 57. Let the 
 vertical line A B (technically termed an 
 ordinate) represent the positive potential 
 at A, and A' B' in like manner the nega- 
 
 B 
 
 B 
 
 Fig. 57. Illustration of Uniform 
 Fall of Potential. 
 
/ 2 Laws and Conditions of Electrical Action. 
 
 tive potential at A'; then the line B B' will denote the value of the 
 potential in all parts of the circuit by the correspondingly varying 
 lengths of the vertical ordinates at any point between Kc or c A'. 
 The quantity of the current is proportional to the steepness of the 
 fall. This may be considered also as a graphic representation of 
 Ohm's law (127). 
 
 146. Fall of Potential in a Non-homogeneous Circuit. 
 In practice, in the circuits employed in telegraphy, the conductor is 
 never homogeneous, but, like the water-pipe referred to in (144), is 
 
 made up of several conductors of varying 
 conductivity. To illustrate this condition 
 of things in a diagrammatic form, let the 
 conductor A A', Fig. 58, consist of two 
 portions having respectively different 
 cross-sections. If we assume the cross- 
 . section of A //, for example, to be greater 
 
 than that of //A' in the proportion of * to 
 Fig. 58. Illustration of Variable .*. ,. 
 
 Fall of Potential. 2; then if equal quantities of electricity 
 
 pass through all sections in equal times, 
 
 as stated in (139) and (141), the difference of potential between 
 the extremities of the thicker wire will be only two thirds what it 
 would be in the case of the thinner wire of equal length. Hence, 
 the fall or drop in potential will be less in the thick than in the thin 
 wire, as shown by the line Br, in Fig. 58. The greater therefore the 
 resistance of the conductor, the greater the fall of potential. This 
 result is expressed in the following law : 
 
 In any electric circuit, the fall of potential is directly as the specific 
 resistances (117) of the sei'eral conductors composing it, and inversely as 
 the area of their cross-sections. 
 
 The simplest circuit, therefore, when laid out in diagrammatic 
 form, exhibits a series of gradients expressing the potential of its 
 various parts. 
 
 147. Electrostatic Capacity. A body charged with elec- 
 tricity in a static condition, as, for example, a long submarine cable, 
 a condenser (317) or the well-known apparatus called the Leyden 
 jar, is said to be in a state of electrification. This effect is also ob- 
 servable upon well-insulated land lines of considerable length, and 
 is one which in certain special methods of telegraphy needs to be 
 taken into consideration, as will hereafter appear. The quantity of 
 static electricity (82) thus held by any conductor, or that which any 
 body is capable of containing, is termed its capacity. This is often 
 called also electrostatic capacity and inductive capacity. 
 
The Watt. 
 
 73 
 
 148. The Farad. The unit of capacity is called \hzfarad, but 
 the capacities required to be measured in telegraphy being usually 
 very small, they are more conveniently expressed in micro-farads (p. 60, 
 note 4). Further explanation of this subject is reserved until the 
 effects of static electricity upon telegraph lines require consideration. 
 
 149. Power, or Rate of Work. It has been stated elsewhere 
 (92) that every electric current is capable of doing a certain amount 
 of work. This definite amount of work may, however, obviously be 
 done in a greater or less length of time, that is to say, at a different 
 rate, and this rate of work is called power. 
 
 150. The Watt. The electric unit of power, or rate of working, 
 is called the watt.^ It equals i volt multiplied by i ampere, or 7 J^ 
 of a mechanical horse-power. In any circuit the power equals the 
 square of the current in amperes multiplied into the resistance in ohms. 
 
 TABLE VI. 
 SYNOPSIS OF PRACTICAL UNITS. 15 
 
 
 1 
 
 
 
 Value. 
 
 Unit. 
 
 B 
 
 Name. Derivation. 
 
 
 
 
 >, 
 c/2 
 
 
 C.G.S 
 
 Equivalent. 
 
 E. M. F 
 
 E 
 
 Volt Ampere x Ohm 
 
 I0 8 
 
 .926 standard Daniell cell. 
 
 Resistance. . 
 
 R 
 
 Ohm Volt-:- Ampere 
 
 I0 9 
 
 1.01367 B. A. Units (?). 
 
 Current 
 Quantity. . . . 
 Capacity. . . . 
 
 C 
 
 Q 
 
 K 
 
 Ampere ! Volt -4- Ohm 
 Coulomb Ampere per sec. 
 Farad. Coulomb-*- Volt 
 
 TO-' 
 io- ' 
 
 io-9 
 
 ( .0000105 gram of hydro- 
 ( gen liberated per second. 
 
 Power. . 
 
 P 
 
 Watt Volt x Ampere 
 
 1C 7 
 
 .0013405 or - |?r h. -power. 
 
 Work I 
 
 \V 
 
 \ Volt x Coulomb 
 
 I0 7 
 
 7373 foot-pounds. 
 
 Heat j 
 
 
 Joule "i . o ,^1 
 J ( Ampere* x Ohm 
 
 I0 7 
 
 .238 calorie. 
 
 13 FARADAY (MICHAEL), a distinguished chemist and natural philosopher ; born in 
 Newing'On, England, 1791. He received but little education, and while young was 
 apprenticed to a bookbinder. While working at this trade, a scientific book fell into 
 his hands, which he read with avidity, and was thus led to devote himself to the study 
 of electricity. In 1813 he obtained the appointment of chemical assistant under Sir 
 Humphry Davy at the Royal Institution. In 1821 he discovered magnetic rotation. In 
 1831 he began the publication of his Experimental Researches in Electricity, beginning 
 with the induction of electric currents (151) and the evolution of electricity from mag- 
 netism (73). Three years later he discivered the principle of definite electrolytic 
 action (154). His original papers, including a wide range of contributions to modern 
 science, are too numerous to mention in detail. In 1833 he was appointed professor of 
 chemistry in the Royal Institution, which chair he continued to hold until his death. 
 He was a member of many learned societies of Europe and America. Died 1867. 
 
 14 WATT (JAMES), an eminent mechanical engineer, born at Greenock, Scotland, 
 1736. Under his father he acquired a knowledge of mathematical instrument-making. 
 When nineteen years of age he went to London, but soon returned and settled at 
 Glasgow, where, under the patronage of the university, he subsequently immortalized 
 himself by the invention of the steam-engine. Died 1819. 
 
 14 MUNROE and JAMIESON'S Pocket-Book of Electrical Rules and Tables, p. 13*. 
 
74 Laws and Conditions of Electrical Action. 
 
 151. Current Induction. An electric current traversing a 
 conductor has a capacity of setting up or giving rise to a temporary 
 current in a neighboring conductor. This effect is called volta 
 induction, or, more commonly, current induction; and the temporary 
 current thus produced is called the induced or secondary current. 
 The originating current in such a case is termed the primary or 
 inducing current. This effect is sometimes observed to take place 
 between two long and well-insulated telegraph lines which are situ- 
 ated parallel and near together for a great distance. The flow of 
 the secondary or induced current is in a direction contrary to that 
 of the primary or inducing current. 
 
 152. Electrical Dimensions of the Voltaic Cell. The 
 practical value of any type of cell for a given purpose depends upon 
 what is known as its electrical dimensions, and upon its constancy. The 
 first property determines the quantity of electricity which it is capa- 
 ble of producing in a given time; the second property the length of 
 time it is capable of maintaining such action. 
 
 153. E. M. F. and Resistance of the Cell. The elec- 
 trical dimensions of a cell are stated in terms of its e. m. f. and its 
 internal resistance. The first depends upon its chemical reaction, 
 without reference to size, and the second is practically uninfluenced 
 by any considerations other than the conducting power of the solu- 
 tions (126), the area of their cross-section (131) and the tempera- 
 ture. 16 
 
 The duration of the cell depends upon the quantity of material it 
 contains and upon the energy of the chemical action within it. The 
 gravity cell, described in Chapter II., has an e. m. f. of 1.07 to 1.08 
 volts, and when in good condition an average resistance of 3 to 4 
 ohms. 
 
 154. Quantity and Cost of Materials Consumed in the 
 Battery. The subjoined table shows the theoretical consumption 
 and deposition of material in each gravity cell per ampere per 
 hour, in fractions of an avoirdupois pound, by the aid of which the 
 cost of producing any given current may be ascertained when the 
 price of materials is known. 17 
 
 " Heat increases the e. m.f. of a sulphate of copper cell ; it does so by affecting the 
 solubilities of the two salts and supplying externally the energy absorbed in solution. 
 Between 32 and 52 Fahr. there is a difference of .01 volt ; between 50 and 60 also .01, 
 and between 50 and 100 about .025. J. T. SPRAGUE : Electricity, etc. (2d Ed.), p. 141. 
 
 17 The electro-chemical equivalent of zinc is here taken as 0.00033696 grams per am- 
 pere per second, according to the determinations of Rayleigh and Kohlrausch. A 
 table of electro-chemical equivalents, calculated from Rayleigh's results, is given by 
 GEORGE B. PRESCOTT, Jr., Electrical Engineer, iv. 7. 
 
Quantity and Cost of Materials Consumed. 75 
 
 TABLE VII. 
 CHEMICAL EQUIVALENTS. 
 
 Material. 
 
 Atomic weight. 
 
 Lbs. per ampere hour. 
 
 Zinc consumed 
 
 64.0 
 
 .0026749 
 
 Sulphate of copper consumed. 
 Copper deposited . . . 
 
 249-5 
 6^.0 
 
 .O1O28IO 
 
 .OO25Q4Q 
 
 
 
 
 Experience shows that, owing in part to local action (57: 7), the 
 actual consumption of zinc is greater than the theoretical, while the 
 consumption of s. c. and the deposit of copper are found to approxi- 
 mate quite closely to theoretical requirements. The greater part of 
 the actual zinc-waste in practice is due to the unconsumed residue 
 of each zinc, which finally has to be thrown out. (6ia.) 
 
 155. The following examples show how this computation is made. 
 Suppose i gravity cell is employed to operate a certain telegraphic 
 instrument, whose magnetizing coil has a resistance of 3.7 ohms, 
 and is connected with the cell by 30 feet of No. 18 copper wire. 
 Required the theoretical cost per month of maintaining the cell, 
 when used from 8 a.m. to 8 p.m. every day. 
 
 Average resistance of cell (assumed or measured) 3 ohms. 
 
 Resistance of 30 ft. No. 18 copper wire (table, p. 94) 0.2 
 
 Resistance of coil of instrument 3.7 
 
 Total resistance of circuit 6.9 ohms. 
 
 Hence 1.07 volts (i53)-s-6.9 ohms=o.i55 amperes. 
 
 From the table (154) we have : 
 
 Sulph. cop. consumed.. .01028") 
 
 Zinc consumed 00267 ^ x . I55 ( amp . ) 
 
 f X 360 (hrs.) 
 Cop. deposited (deduct) . 00260 J 
 
 .5736 Ibs. at 10 cts. $0.057 
 .1490 Ibs. at 16 cts. .024 
 
 $0.081 
 .1451 Ibs. at 16 cts. ~ .023 
 
 $0.058 
 
 156. Again, suppose two telegraph lines supplied from one battery 
 of 100 cells, each line carrying a current of 25 milliamperes (123); 
 required the theoretical consumption per month of material, working 
 24 hours per day. 
 
 I 37.00 Ib. at 10 cts. rr $3.70 
 X .05 (amp.) j Q fa \^ at ,5 cts _. T> ^ 
 X 720 (hours) <( 
 
 X ioo cells. $5 ' 24 
 
 I 9.36 Ib. at 16 cts. 1.50 
 
 Sulph. cop. consumed. . .01028"^ 
 Zinc consumed 00267 
 
 Cop. deposited (deduct) .00260. 
 
76 Laws and Conditions of Electrical Action. 
 
 We find, therefore, that the theoretical net cost of materials con- 
 sumed in a battery under the conditions given, is less than 4 cts. per 
 cell per month. In practice, it is usually from 4 to 5 cts. 18 
 
 157. Production of Electricity in Proportion to Material 
 Consumed. An idea very common among amateur electricians is 
 that it may be possible to make some change in the proportions or 
 arrangement of the gravity battery by which its power may be in- 
 creased without a corresponding expenditure of material. This is a 
 fallacy. Electricity may in one sense be regarded as a constituent 
 of zinc, which is set free when that metal combines with oxygen, 19 and 
 hence the quantity of electricity evolved in a voltaic cell can never 
 exceed a certain ratio to the weight of zinc consumed. The invaria- 
 ble laws of chemical combination teach us, moreover, that the con- 
 sumption of s. c. and the deposition of copper must in all cases 
 maintain a fixed ratio to the consumption of zinc.* 
 
 158. Consumption of Material in a Series of Cells. 
 Admitting the consumption of material in each cell, when two or 
 more cells are in series, to be in proportion to the quantity of current 
 by which the series is traversed, it follows that the cost of material 
 (the external resistance remaining constant) must be as the square of 
 the number of cells in series, and not in the simple ratio of the num- 
 ber of cells. Thus if we increase the number of cells threefold, we 
 have three times as many cells and three times the quantity of cur- 
 rent traversing each cell, so that the consumption of material will 
 necessarily be ninefold. 
 
 159. Electrical Dimensions of the Edison-Lalande Cell. 
 This element has a comparatively low e. m. ". (0.70 to 0.75 volts), 
 
 "but on the other hand its internal resistance is very small, and its 
 local action almost inappreciable. Such a cell is well suited for tel- 
 egraphic work. The diagram Fig. 59, exhibits the results 01 a test of 
 4 large cells, maintained in action in series with an external resist- 
 ance of 0.8 ohms continuously for 108 hours. Such a current would 
 suffice to supply 10 or 12 telegraph lines at the same time. 
 
 1 60. Effect of Temperature upon the Resistance of 
 Metallic Conductors. It has been stated (118) that the resist- 
 ance of all conductors is affected by temperature. Unless otherwise 
 specified, the resistance of electrical conductors is customarily as- 
 sumed to be taken at 60 Fahr. 
 
 18 L. BRADLEY in The Telegrapher, iii, 53 ; F. L. POPE, in the same, vii, 345 ; 
 Scientific American (n. s.) ix, 184. 
 
 19 This suggest-on is due to Latimer Clark. See his Electrical Measurement, p. 168. 
 30 See note 2, p. 12 ; also (154). 
 
7 8 Laws and Conditions of Electrical Action. 
 
 161. According to Miiller, the percentage of increase in re- 
 sistance of some of the metals most employed in telegraphy between 
 o and 70 Fahr. is as follows : 
 
 Iron 8 per cent. 
 
 Copper 6.1 per cent. 
 
 Platinum 6 per cent. 
 
 The difference in the measured resistance of a telegraph line of 
 iron wire may therefore vary as much as 13 per cent, between the 
 extremes of summer and winter temperature in the northern portions 
 of the United States. The resistance of German-silver and plati- 
 num-silver alloys vary but little with temperature, and hence stand- 
 ard resistances are made from wires of these artificial metals. 
 
 162. Effect of Temperature upon Resistance of Liquids. 
 The liquid mass which acts as a conductor in a voltaic cell under- 
 goes considerable variation in resistance with changes of tempera- 
 ture. Of the different voltaic combinations in general use, the 
 sulphate of copper cell is most affected in this way. Hence in experi- 
 ments with this cell, it is important that the temperature be kept 
 constant, or that frequent measurements should be made of the in- 
 ternal resistance and allowance made therefor. 
 
 163. Effect of Temperature upon Resistance of Daniell 
 Cell. Three series of tests of the Daniell sulphate of copper cell 
 were made by Preece ; in the two first cases, the s. c. solution was 
 saturated at all temperatures, while the s. z. solution had the same 
 density throughout the period of observation, being saturated at 
 about 57 Fahr. In the third case both solutions remained satu- 
 rated at about 50 Fahr. The results are given in the diagram, 
 Fig. 590. The curve ABCDE corresponds to the case in which the 
 s. c. solution was saturated at all temperatures, while the s. z. solution 
 was of constant density. The curve abed corresponds to the case in 
 which both solutions remained unaltered in density. The direction 
 of the arrows indicates the order of the experiments. In the curve 
 ABCDE, the portion AB represents the result obtained by heating 
 the cell from about 52 to 211 Fahr. (near the boiling point of 
 water), and the portion BC that obtained while the same cell -,vas 
 being cooled from 211 to 35 Fahr., nearly the freezing point of 
 water. A similar explanation applies to the curve abcde. 
 
 164. These curves clearly show : 
 
 (a) That when the temperature of a Daniell cell is raised from 
 the freezing to the boiling point of water, the internal resistance of 
 the cell decreases, abruptly at first, but more gradually afterward, 
 falling from 2.12 to .66 ohms, or more than one-third. 
 
Effect of Temperature upon Battery Resistance. 79 
 
 (If) That when a cell which has been thus heated is cooled, the 
 resistance increases at a more rapid rate than it fell off while being 
 heated; in other words, the resistance of a Daniell cell, within the 
 range of temperature experimented upon, is smaller before it has 
 been heated to a high temperature than afterward, provided the 
 heating and cooling be not done too slowly. 
 
 X 
 
 60 
 
 TEMP. FAHRENHEIT 
 
 104 122 140 158 
 
 176 
 
 194 212 
 
 *l 
 
 c! 
 Vi 
 
 
 \ 
 
 
 
 
 \ 
 
 
 10 
 
 r.'O 
 
 80 
 
 90" 
 
 30 40 60 60 70 
 
 TEMP. CENTIGRADE 
 FIG. 59 a. Effect of Temperature upon Resistance of Voltaic Cell. PREECE. 
 
 100' 
 
 (c) That if the cell thus cooled down be left undisturbed at a 
 given temperature, the resistance of the cell slowly diminishes until 
 at last, at the end of a certain period (40 to 50 hours), it returns to 
 the value which it had before having been heated. 
 
 (//) That the resistance of a Daniell cell is considerably less 
 when the s. c. solution is more dense than when it is less dense, at 
 any temperature. 21 
 
 21 W. H. PREECE : Effect of Temperature on the e. m.f. and Resistance of Bait* 
 ries. Proc. Royal Soc. 1883 ; Lond. Electrician, x. 367. 
 
CHAPTER VI. 
 
 THE LAWS OF ELECTRO-MAGNETISM. 
 
 165. The Electro-Magnet, as improved by Henry, 1 forms the most 
 essential part of every telegraphic receiving instrument, and is the 
 instrumentality by means of which the energy of the electric current 
 is transformed into mechanical power, and is made to produce phys- 
 ical effects appreciable by the senses. 
 
 Nearly every fact of importance in connection with the phenomena 
 of electro-magnetism has been known to experimenters and observ- 
 ers for half a century, but the apparently anomalous and contradic- 
 
 i HENRY (JOSEPH), LL.D., born Albany, N. Y., 1799; educated in the common 
 schools of that city and in the Albany Academy, in which he became professor of 
 mathematics (1826), and almost immediately entered upon a course of experimental 
 investigation, during which he made numerous and important discoveries in elec- 
 tricity and magnetism. Although at this date the electro-magnet had become in a 
 certain sense known, from the researches of Sturgeon ( Transactions Soc. Arts, xliii. ; 
 Nov. 1825), it was but a philosophic toy, in which a feeble magnetic excitation was 
 produced by currents of small e. m. f. in a short circuit. Henry's first success was 
 the invention of the electro-magnet as we now know it, a horse-shoe of soft iron sur- 
 rounded by many turns of insulated copper wire arranged in concentric layers (186), 
 a construction which no subsequent invention has essentially modified. He next 
 demonstrated that the difficulty of exciting magnetic energy at a distance by an 
 electric current, which had led Barlow in 1824 to pronounce the idea of an electric 
 telegraph " chimerical," may be completely overcome by the use of a battery of a 
 sufficient number of cells, arranged in series (107), provided the electro-magnet be pro- 
 vided with a helix having a sufficient number of turns. It was the invention of 
 Henry's electro-magnet which first made the electric telegraph a commercial possi- 
 bility, and it is worthy of note that in an article published in 1831 (Amer. your. 
 Science, xix. 400), he pointed out the applicability of the long-coil magnet to this 
 purpose. During 1 the same year he constructed an apparatus for giving signals at 
 a distance, which was operated through more than a mile of wire carried around the 
 walls of a room in the Albany Academy. This apparatus embodied all the essential 
 principles of the practical telegraph of to-day. The signals were produced by the 
 polarized armature of an electro-magnet which was made to vibrate by reversal of the 
 current (201) and to strike a bell. In 1832 he discovered the induction of a current 
 in a coiled conductor upon itself (196). In 1832 he was elected professor of natural 
 philosophy in the College of New Jersey, at Princeton, and in 1846 first secretary of 
 the Smithsonian Institution in Washington, which honorable position he continued to 
 hotd until his death in 1878. His collected scientific papers have been published in 
 2 vols., Washington (1886). For many particulars of interest respecting the contribu- 
 tions of Henry to the invention of the electric telegraph, see Life and Work of Jo- 
 seph Henry^ by F. L. POPE, and "The American Inventors of the Telegraph," by 
 the same, in the Century Magazine, xxxv. 924 (April, 1888). It has recently become 
 known that he was the first to discover the phenomenon of magneto electricity (62). 
 See papers by MARY A. HKMKY, N. Y. Elect. Engineer, xiii. 27 etseq. 
 
 80 
 
Elements of the Electro-Magnet. 
 
 81 
 
 tory character of mrmy of the results obtained has been very puzzling 
 to the student. It was not until after the conception of the exist- 
 ence of a magnetic circuit (178), analogous in many of its proper- 
 ties to that of the electric circuit, originally due to Joule, 2 had been 
 definitely formulated in 1873 by Rowland, 3 and its truth confirmed 
 by the subsequent researches of Bonsanquet 4 and others, that it 
 became possible to suggest an adequate explanation for many of the 
 singular and apparently unaccountable facts which had been noticed 
 by investigators. 
 
 166. Elements of the Electro-Magnet. The electro-mag- 
 net may conveniently be regarded as comprising three distinct ele- 
 ments, the laws of each of which must be separately studied, 
 although they all enter into the general result. These elements are 
 (i) the wire, (2) the iron, and (3) the current. 
 
 167. It has been stated (85, d} that when a piece of soft iron is 
 spirally encircled by a conductor, it is rendered magnetic by the 
 passage of a current through this conductor. Such an organization 
 constitutes an electro -magnet in its elementary form. 
 
 168. Polarity of Electro-Magnet Determined by Direc- 
 tion of Current. The position of the respective poles of an 
 electro-magnet is in 
 
 all cases determined 
 by the direction of the 
 magnetizing current. 
 It is usual to coil the 
 conducting wire, 
 coated or insulated , with nonconducting material, into what is 
 termed a right-handed helix, shown diagrammatically in Fig. 60, in 
 which the conventional direction of the current (31) is indicated bv 
 the arrows, while the respective north and south poles induced 
 thereby are designated by the letters N and S Thus, if the current 
 
 flows around the iron 
 in the direction of the 
 hands of a watch, the 
 north pole will be at 
 the distant end of the 
 
 FIG. 61. Electro-Magnet with Left-handed Helix. 
 
 iron. If the current 
 be made to flow in the opposite direction, as in Fig. 61, the polarity 
 
 2 Sturgeon's Annals, iv. 58. 
 
 a H. A. ROWLAND : On the Magnetic Permeability of Iron, Phil. Mag. (4th series), 
 xlvi. 140 ; also in the same, i, 257, 348. 
 
 4 R. H. M. BONSANQUET : On Magneto- Motive Force, Phil. Mag. (sth series), xv. 
 205 ; the same, On Electro-Magnets, Electrician ( ond.), xiv. 291, 351. 
 
 FIG. 60. Electro-Magnet with Right-handed Helix. 
 
82 The Laws of Electro- Magnetism. 
 
 of the iron is reversed, the north pole now being at the end where 
 the south pole was before, and vice versa. 
 
 169. Lines of Force as a Measure of the Magnetic 
 Field. It has been explained (93) that a conductor conveying an 
 electric current is surrounded by a field of magnetic force, and that 
 in such a field, the lines of force are concentric with the conductor. 
 These lines of force may be regarded as units, in terms of which 
 magnetism may be expressed and measured. 
 
 The direction and polarity of the magnetic force is indicated by 
 the direction and polarity of the lines, the total number of its lines 
 is a measure of the total quantity of magnetism, while the number 
 of them contained in a given unit of area, measured in a direction 
 perpendicular to their direction, is a measure of the intensity of 
 magnetism at that point. 
 
 This conception of magnetic force may, perhaps, be better understood if 
 compared to the force of gravity similarly represented. Imagine a heavy 
 body suspended in the air, and suppose every cubic inch of the material of 
 which the body is composed to weigh one pound. If an imaginary line be 
 drawn to the earth from the center of gravity of each cubic inch of the sus- 
 pended body, the direction of these lines would represent the direction of 
 the force of gravity ; their total number would represent the total force in 
 pounds ; while their density, or the number of lines per square inch area 
 (measured perpendicularly to their direction), would represent the intensity 
 of the force at that point. In precisely the same way as these lines repre- 
 sent the direction, amount, and intensity of the force of gravity in that body, 
 so do the lines of magnetic force represent the direction, amount, and inten- 
 sity of magnetism, except that in the latter there is no constant direction of 
 action such as the downward force of gravity, the lines of force acting in 
 both directions, as if trying to shorten their circuit, like a stretched rubber 
 ring. The lines do not exist as such, any more than they do in the analogy 
 of the force of gravity ; it is merely a convenient way of representing mag- 
 netism in order to facilitate the conception and computation of problems. 
 CARL HERING : Principles of Dynamo-Electric Machines, 18. 
 
 170. An accurate knowledge of the characteristics of magnetism 
 is of great importance in the designing and construction of dynamo- 
 electric machinery, and it fortunately happens that recent researches 
 in connection with this class of work have greatly enlarged our 
 practical knowledge of the laws and conditions of magnetic and 
 electro-magnetic action as applied to telegraphic and other apparatus 
 of like character. 
 
 Provided we are able to calculate the intensity of the magnetic 
 field which is produced by the influence of a known current, we 
 have the means of calculating also the intensity of magnetism in an 
 iron core placed within that field. When, however, the magnetiza- 
 
Unit of Magnetism. 83 
 
 tion approaches the limit of intensity which the soft iron is capable 
 of receiving, the actual magnetization always falls short of the theo- 
 retical magnetization as calculated by this rule. 
 
 171. Unit of Magnetism. It is customary to express intensity 
 of magnetism, or magnetic density, as it is sometimes termed, by the 
 number of lines of force per unit of cross sectional area, measured per- 
 pendicularly to their direction. The unit of magnetism is the equiv- 
 alent of a single one of these lines of force, and is that quantity of 
 magnetism which passes through one square centimetre of the cross- 
 section of a magnetic field whose intensity is unity. It has been 
 proposed to call the magnetic unit the gauss:' To illustrate, suppose 
 a circular loop of wire like that shown in Fig. 33, p. 41, having a 
 -diameter of 10 centimetres (3.9 in.), to be traversed by a current of 
 7.958 amperes. The quantity of magnetism passing through an area 
 of i sq. cm. at the center of the loop will be i unit. 6 A magnetic 
 field in which the number of parallel lines of force per unit area is 
 the same in every part is termed a field of uniform intensity, or 
 briefly, a uniform field, A good illustration of such a field is that of 
 the earth referred to in (94). The field inclosed within a circular 
 loop of wire like Fig. 33 is not uniform, but varies in different parts, 
 being most intense near the circumference and least in the center. 
 
 172. Magneto-Motive Force. Recurring again to the electric 
 conductor surrounded by concentric lines of force, as shown in Fig. 
 32, p. 39, it is n6t difficult to understand that if we coil such aconduc- 
 
 5 GAUSS (KARL FRIEDRICH), born in Brunswick, Germany, April 30, 1777. When 
 very young was distinguished for his mathematical attainments ; became Professor of 
 Astronomy and Director of the Observatory in Gottingen, 1807 ; was made, in 1816, 
 Court Councilor and in 1845 a Privy Councilor of Hanover; after 1821 made impor- 
 tant improvements in geodetic methods and instruments ; and after 1831 devoted much 
 attention to the study of terrestrial magnetism. In 1833, with the assistance of his 
 coadjutor, WILHELM EDUARD WEBER, Professor of Physics in the University of Got- 
 tingen, he constructed an electric telegraph more than a mile in length, extending 
 from the Physical Cabinet to the Observatory in that city. This telegraph was re- 
 markable as being the first in which magneto-electricity (73) was used ; for the inge- 
 nious but simple method employed of using a ray of light as an index of the movement 
 of the galvanometer needle (a plan long afterward adopted by Sir William Thomson 
 in his well-known mirror galvanometer) ; and last, though not least, as having had an 
 actual existence for several years ; for although at first intended for scientific purposes 
 only, it soon came to be employed as a means of ordinary correspondence as well. 
 (SABINE : The Electric Telegraph, p. 27.) Gauss died at Gottingen, 1855. 
 
 What is known among manufacturers of electrical machinery as the English unit 
 of magnetic induction was proposed by GISBERT KAPP (Jour. Tel. Eng., xv. 518). 
 The unit line of force adopted is equal to 6,000 c. g. s. lines, the sectional area of the 
 iron being taken in square inches. The English unit, therefore, is one of these as- 
 sumed lines per square inch, and is commonly termed a Kapp line. 
 
 i Kapp line per sq. in. 930 c. g. s. lines per sq. cm. 
 
 i English unit = 930 c. g. s. units of magnetic induction. 
 
84 The Laws of Electro-Magnetism. 
 
 tor into an elongated helix or spiral, technically termed a solenoid^ 
 Fig. 62, and cause the current to traverse it in the direction indicated 
 by the arrows, the lines offeree inclosed within the helix, being the 
 resultant of those of the separate turns, assume the form represented 
 
 FIG. 62. Direction of Lines of Force within a Solenoid. 
 
 in the figure. In the drawing, for convenience of illustration, only a 
 part of each line of force is shown, but it must be borne in mind that 
 every line is in fact endless, forming a complete magnetic closed cir- 
 cuit returning into itself, so that different lines can never under any 
 circumstances intersect each other. The value of the current in am- 
 peres being known, a corresponding field of definite intensity is set 
 up within the helix. The intensity, or, as Bonsanquet calls it, the 
 magneto-motive force of the field, may be readily calculated by the fol- 
 lowing : 
 
 RULE. Multiply the number of turns in the helix by the current in am- 
 peres and divide this product (ampere-turns) by the length of the helix in 
 centimetres ; multiply the quotient by 1.2566, and the product will be the 
 intensity expressed in lines of force per square centimetre, or if the length be 
 taken in inches, the multiplier 0.3132 will give the quotient in lines per square 
 inch. 
 
 FIG. 63. Lines of Force traversing Iron Bar within the Solenoid. 
 
 173. Effect of Iron in the Helix. If now a soft iron core be 
 placed within the same helix, as shown in Fig. 63, the intensity of 
 the field is materially increased, or in other words the number of lines- 
 
Effect of Magnetization upon Soft Iron. 85 
 
 of force per unit of cross-sectional area is greatly augmented. The 
 strength of field due to the presence of the coil and its contained 
 iron is termed magnetic induction. The difference between the num- 
 ber of lines per unit of area, with and without the iron, evidently gives 
 the value of the magneto-motive force due to the iron alone. This 
 difference may be stated roughly as about 100 to i for soft iron of 
 average good quality. 
 
 174. Effect of Magnetization upon Soft Iron. The 
 graphic diagram, Fig. 64, was plotted from a series of observations 
 made with a magnetometer - 7 upon a rod of unannealed iron 10 cm 
 (3.9 in.) long and 
 4.3 mm. (o. 169 in.) 
 in diameter, placed 
 within a helix of 
 135 turns. 8 The 
 values of the cur- 
 rent in ampere 
 turns are plotted 
 out upon the hori- 
 zontal, and those g 
 of the magnetic 
 forces upon the 
 vertical scale. The 
 resulting curve 
 takes the form 
 shown in the figure 
 by the line o B. 
 It will be seen to 
 consist of two 
 parts; one part 
 which rises at a more or less steep angle, and which for some -dis- 
 tance from its origin at o continues nearly straight to the point i, 
 and another part B 2, also nearly straight, but which is inclined at 
 a much less angle to the horizontal, these two parts being joined by 
 
 7 The magnetometer is an instrument for the measurement and comparison of 
 magnetic forces. It consists essentially of a magnet or needle delicately suspended 
 in the magnetic meridian, and provided with a pointer or index, usually in the form of 
 a ray of light reflected by a small mirror. By placing the stationary magnet whose 
 force is to be determined at a measured distance east or west of the suspended needle, 
 with one of its poles pointing directly toward it, it is easy, by observing the angle of 
 deflection of the needle, to measure the attractive force of the magnet pole. For a 
 simple apparatus and method of performing this operation see J. TROWBRIDGE : New 
 Physics, 131. 
 
 s KENNELLY and WILKINSON : Practical Notes for Electric Students, aao. 
 
 FIG. 64. Relation of Current to Magnetic Force. 
 
86 
 
 The Laws of Electro-Magnetism. 
 
 a curved portion i, 2. The first-mentioned part of the curve corre- 
 sponds to the state of things when the iron core is unsaturated ; the 
 latter part to the state when the core is more than half saturated ; 
 while the curved intermediate portion corresponds to the intermedi- 
 ate state during which the core is approaching saturation (177). In 
 the curve of results of an electro-magnet two effects are in reality 
 combined ; that of the magnetism of the iron core, and that of the 
 magnetic action of the coils through which the current is flowing ; 
 this joint effect is shown in the dotted line. It is easy to separate 
 these two values, for if the iron core be removed, and the magnetic 
 effect of the coils alone be observed, a new set of data are obtained 
 which, when plotted out, will yield the more gently sloping line 
 o C. From this line two conclusions may be drawn : it slopes at a 
 small angle, because (i) the magnetic effect of the coils is small 
 compared with that of the iron core. It is quite straight, because 
 (2) the magnetic effect of a coil (which of course is not capable of 
 saturation) is exactly proportional to the strength of the current by 
 which it is traversed, throughout the entire range of the experi- 
 ment. 
 
 175. The following series of determinations, made with a coil of 
 500 turns surrounding an iron core 10 cm. (4 in.) long and i cm. 
 (13-32 in.) in diameter, further illustrate this matter. The figures 
 in the last column are the values of the magnetic moment** as calcu- 
 lated from the deflections produced in a magnetometer. 10 
 
 Amperes. 
 
 Ampere-turns. 
 
 Magnetic Moment. 
 
 O.OO 
 
 
 
 128 
 
 O.22 
 
 no 
 
 1224 
 
 0-39 
 
 195 
 
 1920 
 
 0.98 
 
 49 
 
 4608 
 
 1-33 
 
 665 
 
 5924 
 
 3-65 
 
 1825 
 
 17472 
 
 4.6 
 
 2300 
 
 21088 
 
 9.2 
 
 4600 
 
 27875 
 
 9.4 
 
 4700 
 
 28750 
 
 The above values, when plotted out, will give curves similar in 
 form to those shown in Fig. 64. The values of magnetic moment 
 
 9 The magnetic moment of a magnet in c. g. s. measure is the product of the 
 strength of its magnetic pole in dynes (191) multiplied by the distance between its 
 poles in centimetres. The intensity of magnetization of a magnet is the ratio of its 
 magnetic moment to its volume. 
 
 10 SILVANUS P. THOMPSON : Dynamo- Electric Machinery, (2nd edition), 355. 
 
The Magnetic Circuit. 87 
 
 for telegraphic magnets, when plotted out in the same way. will fall 
 upon the lower half of the steep, straight portion of such a curve." 
 
 176. Magnetic Saturation. It will be seen, therefore, that 
 the proportion of ampere-turns to magnetic intensity, referred to in 
 (174), holds good only through a certain range of magnetic increase. 
 When the intensity has reached a certain point, the iron becomes, 
 from that point onward, less and less susceptible to further magneti- 
 zation, and though, strictly speaking, the point of absolute satura- 
 tion can never be reached, there is a practical limit which cannot be 
 exceeded. 1 - The approach of saturation is well exhibited in the 
 core curve in Fig. 64, which begins to deflect when the magnetizing 
 force reaches the vicinity of 500 ampere-turns. 
 
 The cores of the electro-magnets of modern telegraphic apparatus seldom 
 exceed 0.5 in. in diameter. It has been experimentally proved that the 
 approach of saturation in a core of this dimension is not reached with less 
 tuan about 500 ampere-turns, which is some 3 times the degree of magneti- 
 zation ordinarily employed in telegraph magnets used in local circuits, while 
 that employed in magnets used in main circuits is still less. 
 
 177. Magnetization Proportional to Ampere -turns. 
 
 An important principle in electro-magnetism is, that precisely the 
 same magnetic effect may be obtained from a few turns of wire and 
 a large volume of current as from a great number of turns and a 
 small current, provided only that the number of ampere-turns remains 
 the same. This necessarily follows from the fact that the same 
 amount of work is done in the wire 
 by the circuit in each case (92). -L/* 
 
 178. The Magnetic Circuit. 
 In the practical application of 
 the electro-magnet for telegraphic 
 and other like uses, it is not usual 
 to make it in the form of a straight 
 bar. Much better results are at- 
 tained by bending the bar into the 
 form of a |J> or "horseshoe," as 
 shown in Fig. 65, which enables an 
 
 armature to be applied to it in such 
 
 rr . . Fro, 65. Principle of Horseshoe Electro- 
 
 a manner as to form a complete Magnet. 
 
 11 For an experimental investigation of the relation between the diameter of the 
 core, the total magnetizing force of the coil, and the force of attraction, see paper by 
 E. L. FRENCH : Electrician and Elect. Eng., v. 445. 
 
 12 The limit of magnetization in good wrought-iron is about 125,000 (c. g. s.) 
 magnetic lines per sq. in., or 20,000 per sq. cm. S. P. THOMPSON : The Electromagnet, 
 32, 83; ibid., Dynamo-Electric Machinery (4th Ed.), 148, 149. 
 
88 The Laws of Electro-Magnetism* 
 
 magnetic circuit. Inasmuch as magnetism is now known to be a phe- 
 nomenon pertaining to the internal molecular structure of iron, the 
 preferable method of treating the subject is to look upon that metal 
 as a substance which is a good conductor of the magnetic lines of 
 force, or, as it is expressed in madern scientific language, possessing 
 a high degree of magnetic permeability.^ 
 
 179. Magnetic Permeability. This characteristic may be 
 best defined as a numerical co-efficient which expresses the ratio be- 
 tween the number of magnetic lines formed in a space containing 
 nothing but air, as in Fig. 62, and as denoted by the value of the line 
 o B in Fig. 64, and the number formed in a space filled with a given 
 quality of iron, as in Fig. 63, and as denoted by the value of the 
 dotted line in Fig. 64- 14 This ratio differs for different qualities of 
 iron, and hence we say that the permeability of the iron differs 
 accordingly. 
 
 The higher the co-efficient of permeability, the less, so to speak, 
 is the magnetic resistance, and the more suitable is the iron for the 
 purposes of an electro-magnet. On the other hand, the permeability 
 of air and of most substances other than iron is comparatively very 
 small. 
 
 180. Law of the Magnetic Circuit. In (172) the method 
 of calculating the magneto-motive force of a magnetic circuit has 
 been given. We have next to find the resistance which the magnetic 
 circuit offers to the passage of the lines of force, a property which 
 has appropriately been termed by Dr. O. J. Lodge magnetic reluc- 
 tance. The total magnetism of the circuit, called the magnetic flux, 
 will be the quotient of the magneto-motive force divided by the reluc- 
 tance. The similarity of the law of the magnetic circuit to the law 
 
 of the electric circuit, heretofore referred to 
 as Ohm's law (127), will be apparent upon 
 inspection. 
 
 181. Determination of Magnetic 
 Reluctance. If the magnetic circuit is 
 a simple closed ring of iron, the magnetic 
 reluctance may be calculated precisely in 
 the same manner that we calculate the re- 
 sistance of an electric circuit. The value of 
 the reluctance is directly in proportion to 
 
 FIG. 66. Lines of Force in End- . . J , 
 
 less iron Ring. the length of the iron, inversely as the area 
 
 " FARADAY : Exper. Res., iii. 426 ; Sir W. THOMSON : Papers on Electricity and 
 Magnetism, 484. 
 
 14 ROWLAND : Phil. Mag. (5th series), xlvi. 140. 
 
Ratio, of Attractive Force to Distance. 89 
 
 of its cross-section, and is also inversely proportional to its perme- 
 ability. But if, instead of a homogeneous ring of iron, the circuit 
 be made up of different parts, differing in their magnetic reluc- 
 tance, it becomes necessary to determine the reluctance of each 
 part separately, and then add them together, as in the case of an 
 electric circuit of like character (118). For example, Fig. 66 
 shows the lines of force in an endless iron ring. Fig. 67 is a 
 similar ring cut in two, leaving an air-gap 
 between the severed ends. It has been 
 stated that the permeability of air is far 
 less than that of iron (179). The reluc- 
 tance of the air-gaps to the magnetic lines 
 may be taken roughly at i oo times that of 
 a mass of soft iron of good quality of the 
 same form and dimensions. The case of 
 the divided ring of Fig. 67 is equivalent to 
 that of the horseshoe magnet and its arma- 
 
 -~ - , FIG. 67. Lines of Force Cross- 
 
 ture shown in Fig. 65, when the armature inK A ir-ga P in Magnetized Ring, 
 is a little way removed from the poles, and 
 
 is the condition which is constantly met within the operation of 
 ordinary telegraphic apparatus. The lines of force traverse the 
 armature in passing from one pole to the other. 
 
 182. Ratio of Attractive Force to Distance. It is stated 
 in many text-books that the attractive force exerted by an electro- 
 magnet upon its armature varies inversely as the square of the dis- 
 tance between them. This proposition, known as Coulomb's law, 
 would be true, if it were true that the magnetic forces are concen- 
 trated at a focal point in each pole, and that this disposition of it 
 remains unchanged by the movement of the parts in response to 
 the magnetic attraction. But in fact there is not, and from the 
 nature of the case cannot be, any one law which correctly expresses 
 this relation under all conditions. It necessarily differs with every 
 alteration in the form of magnet and armature, and with every 
 change in their positions with reference to each other. This is well 
 shown in experiments 1 "' made with an electro-magnet having a core 
 formed from a round bar 19 in. long and i in. thick, bent into a 
 horseshoe, with its poles 1.25 in. apart. The distance of the arma- 
 ture from the poles was determined by the interposition of sheets of 
 rolled brass .00416 in. thick, the required number of these sheets 
 for each experiment being strongly pressed together and soldered 
 at the edges. The following table gives the results in weights lifted, 
 
 15 DANIEL DAVIS, Jr.: Manual of Magnetism (i2th Ed., 1857), 152. 
 
9 o 
 
 The Laws of Electro-Magnetism. 
 
 with various thicknesses of brass sheets, numbered from i to 10, 
 interposed between the magnet and the armature : 
 
 Distance. 
 
 Weight Lifted, Grains. 
 
 Product 
 
 o 
 
 82,000 
 
 
 I 
 
 35,000 
 
 35,000 
 
 2 
 
 25,000 
 
 50,000 
 
 3 
 
 20,000 
 
 60,000 
 
 4 
 
 15.500 
 
 62,000 
 
 5 
 
 12,100 
 
 60,500 
 
 6 
 
 11,300 
 
 67,800 
 
 7 
 
 9,300 
 
 65,100 
 
 8 
 
 7,400 
 
 59,200 
 
 9 
 
 6,500 
 
 58,500 
 
 10 
 
 5,500 
 
 55,000 
 
 The corresponding curve is plotted in Fig. 68. The rapid increase 
 in the attractive force as the armature approaches the poles of the 
 magnet is shown in a striking manner. 
 
 DISTANCES. *f345678910 
 
 80,000 
 
 70,000 
 
 40,000 
 
 30,000 
 
 FIG. 68. Ratio of Decrease of Magnetic Attraction to Distance. 
 
Construction of Telegraph Magnets. 91 
 
 183. Construction of Telegraph Magnets. Fig. 69 is a 
 representation of an electro-magnet, such as is usually employed in 
 telegraphy. The drawing is the actual size and proportions of a 
 type of magnet largely used by some of the most successful Ameri- 
 can instrument-makers. The iron portion of the magnet, of the best 
 
 FIG. 69. Telegraphic Electro-MagnetFull Size. 
 
 Swedish, Norwegian, or Lowmoor soft iron, consists of the following 
 parts: (i) the core proper, which is cylindrical in form, and is the 
 part around which the wire is coiled : it is made in two parts, A A, 
 usually termed the legs or branches of the magnet; (2) a rectangu- 
 lar bar, B, which serves to unite the two parts of the core (which are 
 secured to it by screws), and is termed the yoke ; and (3) the arma- 
 ture C, which, as has been shown, is really part of the magnet, being 
 the movable portion by means of which the magnetic force is exerted. 
 
 184. Theoretical Proportions of Telegraph Magnet 
 The best theoretical proportions to secure the maximum magnetic 
 effect from a given quantity of current, has been found to be to make 
 the four parts of equal length, the yoke being of somewhat greater 
 cross-section than the cores, and the armature of equal cross-section, 
 but broader and thinner than the yoke. But inasmuch as quickness 
 of movement is one of the most important considerations in tele- 
 graphic apparatus, experience has demonstrated that these theoret- 
 ical proportions may be modified with practical advantage. 
 
 The dimensions and proportions of the iron cores of electro- 
 magnets have been the subject of numerous experiments in order to 
 determine the most favorable conditions in respect to the two quali- 
 ties essential in telegraphic instruments: (T) maximum attractive 
 
9- 
 
 Tke Laws of Electro-Magnetism. 
 
 force with a given current, and (2) quickness of action. These 
 properties are in their nature antagonistic, and hence it is necessary 
 in practice to sacrifice to a certain extent the first-named desidera- 
 tum in order to more completely secure the second. The results of 
 the investigations referred to have shown that the outer diameter of 
 the coils or helices ought to be three times that of the cylindrical 
 cores, and that the length of each coil or helix should be equal to 
 its diameter. These proportions are exemplified in Fig. 69, and 
 approximate closely to those most commonly used at the present 
 day in the United States. The magnetic intensity developed in the 
 iron, within certain limits elsewhere set forth (174), being propor- 
 tional to the quantity of current traversing the wire (measured in 
 amperes), and also to the number of convolutions or turns of the 
 wire, we may express the magnetism developed in the iron as a cer- 
 tain number of ampere-turns. 
 
 185. Effect of Position of Windings. It makes no appre- 
 ciable difference upon what portion of the core any particular turn is 
 wound, nor does the fact that some of the turns may be close to the 
 iron and others at a greater distance from it, appreciably modify the 
 result, within the limits of the dimensions of the magnets used in 
 telegraphy. 
 
 186. The Helix or Coil. Upon the cylindrical cores of the 
 magnet are fixed flanges or collars D D (Fig. 69), of hard rubber or 
 other like material, which, in connection with the cores, form spools 
 or bobbins upon which- the magnetizing coil is wound in superposed 
 concentric layers. The space E E, which is designed to contain the 
 wire, has its boundary indicated by a dotted line. 
 
 187. Relation of Thickness and Length of Wire to 
 Number of Turns. The length of any given wire which can be 
 
 FIG. 70 Illustration of the Law of Diametrical Squares. 
 
 wound within a space of given dimensions, such as the space E E, 
 Fig. 69, is inversely in proportion to the square of the diameter of 
 the wire. This will appear from the diagram Fig. 70, in which are 
 shown within a space i in. square, the outlines of i wire i in. diame- 
 
Relation of Thickness and Length of Wire. 93 
 
 ter, 4 wires \ in. diameter, and 16 wires J in. diameter, all of which 
 occupy precisely the same area of cross-section in the spool. The 
 number of turns which can be put within a given space is also in- 
 versely as the square of the diameter of the wire, measured to include 
 its insulating covering. 16 As the electrical resistance of a wire is 
 directly as its length and inversely as its sectional area or the square 
 of its diameter (118), it will be obvious that the number of turns in 
 the coil of any electro-magnet must have a direct and invariable 
 relation to its resistance, and hence the resistance of a coil may be 
 taken as a measure of the number of turns of wire it contains. This is 
 convenient in practice, inasmuch as the resistance is easily deter- 
 mined by proper apparatus, while it is not so easy to find the number 
 of turns in a coil after it has been wound. It is for this reason, and 
 not because the resistance in itself has anything to do with the mat- 
 ter, that it has become customary among telegraphists to classify 
 electro-magnets by reference to their measured resistances. 
 
 It is difficult to wind a mag- 
 net coil neatly and accurately 
 without the aid of machinery. 
 It may be done in a common 
 .lathe, but amateurs generally 
 will find it more convenient to 
 use one of the little machines 
 now made for the purpose, 
 such as that shown in Fig. 71. 
 The hub, which is seen lying 
 on the table, is screwed into 
 the end of the cylindrical core 
 upon which the coil is to be 
 wound, and its other end 
 screws on the spindle at the 
 top of the machine. The oper- 
 ation of winding is sufficiently 
 explained by the illustration." 
 
 188. Dimensions and Resistances of Magnet Wires. 
 
 The following table gives the properties of the different sizes of cop- 
 
 18 A very convenient rule for calculating the windings of the coils of two different 
 electro-magnets of the same type, but of different dimensions, is given by Sir William 
 Thomson, and is as follows: Similar iron cores similarly wound with lengths of wire 
 proportional to the squares of their linear dimensions will, when excited by equal cur- 
 rents, produce equal intensities of magnetic field at points similarly situated in with 
 respect to them. Professor Silvanus Thompson has also pointed out as a corollary that 
 similar electro-magnets of different dimensions must have ampere-turns proportional 
 to their linear dimensions, if they are to be magnetized up to an equal degree of 
 ;saturation. 
 
 " These machines are made by H. Anderson, Peekskill, N. Y. 
 
 FIG. 71. Machine for Winding Magnet-Helices, 
 
94 
 
 The Laws of Electro-Magnetism. 
 
 per wire most used for the helices of galvanometers and telegraphic 
 magnets. It is taken from one calculated by George B. Prescott, 
 Jr., on the basis of Dr. Matthiessen's standard, viz. : 
 
 i mile of pure copper wire of 
 
 n. 
 
 ohms at 59.9 Fahr. 18 
 
 TABLE VIII. 
 DIMENSIONS AND PROPERTIES OF COPPER MAGNET WIRES. 
 
 
 DIAMETER 
 MILS. 
 
 AREA. 
 
 WEIGHT AND 
 LENGTH. 
 
 RESISTANCE AT 75 FAHR. 
 
 5 o 
 
 
 
 
 
 AMERIO 
 GAUGE > 
 
 Bare 
 Wire. 
 
 Silk- 
 covered 
 Wire. 
 
 Circular 
 MilsM 
 
 iMiU 
 .001 in. 
 
 Square 
 in. 
 
 rf 2 x. 7 8 S 4 
 
 Lbs. 
 per 
 
 1000 
 Feet. 
 
 Feet 
 per Lb. 
 
 Ohms 
 per looo 
 Feet. 
 
 Feet 
 per Ohm. 
 
 Ohms 
 per Lb. 
 
 18 
 
 40.3 
 
 42.6 
 
 1624.3 
 
 1275.7 
 
 4.91 
 
 203.8 
 
 6.39 
 
 156.47 
 
 1.30 
 
 20 
 
 32.0 
 
 34-o 
 
 I02I.5 
 
 802.3 
 
 3.09 
 
 324.0 
 
 10.16 
 
 98.401 
 
 3.29 
 
 22 
 
 25-3 
 
 27-3 
 
 642.7 
 
 504.8 
 
 1.94 
 
 5I5.I 
 
 16.15 
 
 61.911 
 
 8.32 
 
 24 
 
 20.1 
 
 22.2 
 
 404.0 
 
 317.3 
 
 1.22 
 
 819.2 
 
 25.69 
 
 38.918 
 
 2I.O5 
 
 26 
 
 15-9 
 
 17.9 
 
 254-0 
 
 199-5 
 
 .77 
 
 1302.6 
 
 40.87 
 
 24.469 
 
 35.23 
 
 28 
 
 12.6 
 
 14.2 
 
 159-8 
 
 125.5 
 
 .48 
 
 2071.2 
 
 64.97 
 
 15-393 
 
 I34.56 
 
 30 
 
 10.0 
 
 II.6 
 
 100.5 
 
 78.9 
 
 30 
 
 3294.0 
 
 103.30 
 
 9.681 
 
 340.25 
 
 32 
 
 8.0 
 
 9.0 
 
 6 3 .2 
 
 49.6 
 
 .19 
 
 5236.6 
 
 164.26 
 
 6.088 
 
 860.33 
 
 34 
 
 6-3 
 
 7-3 
 
 39-7 
 
 31-2 
 
 .12 
 
 8328.3 
 
 261.23 
 
 3.828 
 
 2175.50 
 
 36 
 
 5-0 
 
 6.0 
 
 25.0 
 
 19.6 
 
 .08 
 
 13238.8 
 
 415.24 
 
 . 2.408 
 
 5497-40 
 
 The thickness of silk-covered wire is approximate only ; it varies somewhat with 
 different makers. 
 
 The figures in the table refer to a single covering of silk. For a 
 double-covered wire, add the difference between the figures in the 
 second and third columns to the figures in the third column. 
 
 189. Thickness of Spaces between Turns of Wire. 
 The thickness of a covered wire or of its covering cannot be cor- 
 rectly determined by the process of direct measurement by a gauge 
 (192), though it may be approximated by the careful use of such a 
 micrometer caliper as that shown in Fig. 73. The most accurate 
 method is to measure the longitudinal space occupied by a number 
 of turns when closely wound upon a mandril or small cylinder ; 
 divide this length by the number of turns, and from the quotient 
 subtract the diameter of the copper wire measured by the microm- 
 eter caliper, and divide the result by 2, which will give the thickness 
 of the covering. 19 
 
 18 Electrician and Elec. Eng., iv. 217. 
 
 19 Helices made of bare copper wire, accurately wound by machinery in such a 
 manner as to leave an air-space of i mil. (.001 in.) between each two adjacent turns, 
 and having the successive layers separated by thin paper, have been much used in the 
 United Slates with very satisfactory results. 
 
Instruments for Gauging Wire. 
 
 95 
 
 190. American Standard Wire Gauge. Great confusion 
 formerly existed, both in this and other countries, in respect to wire 
 gauges, designated as the custom is by progressive numbers, there 
 having been almost as many so-called standards as there were differ- 
 ent manufacturers. The Brown & Sharpe Manufacturing Co., of 
 Providence, R. I., some years since established a gauge in which the 
 actual thickness of wires designated by successive numbers is 
 made to diminish in a true geometrical progression. Under the 
 name of the American gauge^ this has now become the generally 
 accepted standard in this country among manufacturers of copper, 
 brass, and german-silver wires, and it is this gauge that has been 
 used in this work, unless otherwise specified. This standard has 
 not as yet been generally accepted by manufacturers of iron wires, 
 such as are used for telegraph lines. 
 
 191. British Standard Wire Gauge. In Great Britain a 
 uniform wire gauge has been 
 
 adopted by law, and is now 
 the only authorized standard 
 in that country for all kinds 
 of wire. The table on p. 
 112 covers the range of sizes 
 ordinarily employed in teleg- 
 graphy. 
 
 192. Instruments for 
 Gauging Wire. For 
 quickly determining the 
 gauge number of a wire, the 
 ring-gauge, Fig. 72, is very 
 convenient. It consists of 
 a circular steel plate, hav- 
 ing slots accurately cut in 
 its edge, these being num- 
 bered successively from 5 to 33, covering the range of sizes of wire 
 used in telegraph work. The smallest slot which any given wire 
 
 can be made to enter shows its 
 gauge number. Fig. 720 shows 
 another form of gauge conven- 
 ient for the pocket, in which the 
 point at which the wire lies in 
 
 FIG. 72,,. Pocket v-Gauge. the an le formed by the sides of 
 
 the slot shows the correspond- 
 ing number on the graduated scale by inspection. The little in- 
 
 FIG. 72. Wire Gauge Ring Pattern. 
 
 g NEW STANDARD WIRC a*U8C 
 
9 6 
 
 The Laws of Electro-Magnetism. 
 
 FIG. 73. Micrometer Caliper. 
 
 strument known as the micrometer caliper, shown of full size in 
 
 Fig- 73, is extremely accurate 
 and convenient. It will readily 
 determine the thickness not 
 only of wire, but of sheet-metal, 
 paper, or the like, from the 
 fraction of a mil up to 0.3 in. 
 
 193. Adaptation of Mag- 
 nets to Working Currents. 
 If we assume three electro- 
 magnets like that in Fig. 68, 
 having spools or bobbins of 
 
 equal capacity, and wind them with three different gauges of wire 
 (for the sake of illustration, say the three sizes shown in Fig. 69) ; 
 for each turn of a wire i in. in diameter we should have 4 turns of 
 the \ in. and 16 turns of the \ in. wire. Now, if we send a current 
 of i ampere through the thinner wire, one of 4 amperes through the 
 medium-sized wire, and one of 16 amperes through the thick wire, 
 we should find, in accordance with the principle stated in (176), 
 that the magnetic force would be precisely equal in each of the three 
 magnets. This would be true, notwithstanding the difference in 
 strength of current, and of thickness, length, and resistance in the 
 wire of the helix, because the number of ampere-turns is the same in 
 each case. We have : 
 
 Diameter of Wire. 
 
 No. of Turns. 
 
 Current. 
 
 Ampere-turns. 
 
 1. 00 
 
 I 
 
 16 
 
 16 
 
 50 
 25 
 
 4 
 16 
 
 4 
 
 I 
 
 16 
 16 
 
 A thorough understanding of this principle enables the elec- 
 trician to determine the winding of his electro-magnet so as to corre- 
 spond with the characteristics of the current by which it is intended 
 to be worked ; for it will be readily seen that to produce a given 
 intensity of the magnetic field, upon which all magnetic effects de- 
 pend, the number of turns in the coil must be in inverse proportion 
 to the number of amperes of current traversing the magnetizing coil. 
 
 194. Spectrum of the Electro-Magnet. The action of the 
 magnetic forces in such an electro-magnet as that delineated in Fig. 
 68 can best be studied by means of magnetic spectra, produced in 
 the manner described in (68). Fig. 74 shows the spectrum of such 
 a magnet, when the current through the coils is barelv sufficient to 
 
Magnetic Hysteresis. 
 
 97 
 
 support the weight of the armature. The manner in which the 
 magnetic circuit (177) is forced 
 to complete itself through the 
 air, in passing from one pole 
 of the magnet to the other, is 
 beautifully shown by the curv- 
 ing of the lines of force. When 
 a soft-iron armature is placed 
 in the field parallel to the polar 
 surfaces, as shown in Fig. 75, 
 the greater number of the lines 
 of force are deflected so as to 
 pass through the ar- . 
 
 mature ; and such 
 
 
 FIG. 74. Spectrum of Telegraph Magnet. Kennely and 
 Wilkinson. 
 
 being the case, the 
 armature itself nec- 
 essarily becomes a 
 magnet of opposite polarity, whereupon mutual attraction takes place 
 between the magnet and its armature in the direction of the lines of 
 force which pass between them, 
 just as if the lines were so 
 many stretched India-rubber 
 bands, and the force was due 
 to their contraction. When 
 the armature is brought into 
 actual contact with the magnet 
 so as to magnetically connect 
 its poles, it becomes virtually a 
 closed or endless core like Fig. 
 '66, and the external 
 lines of force in the jj" - 
 air disappear. 
 
 195. Magnetic 
 Hysteresis. When 
 a mass of soft iron, such as the core of an electro-magnet, becomes 
 enveloped in a magnetic field (169), an appreciable time elapses 
 before it acquires the maximum intensity of magnetization which the 
 field is capable of producing. On the other hand, when the iron is 
 withdrawn from the field, or, what is the same thing, the field is 
 withdrawn from the iron, the latter does not lose its magnetism in- 
 stantaneously ; the magnetism falls off progressively in the same 
 way in which it increased, and in almost every case some small 
 
 FIG. 75. Spectrum of Telegraph Magnet and Armature. 
 
98 The Laws of Electro-Magnetism. 
 
 quantity of magnetism will remain for some time, and possibly for- 
 ever, after the separation of the iron from the field. This is termed 
 remanent, or more commonly residual magnetism^ In some brands 
 of cold-blast charcoal iron, when carefully annealed, such as Norwe- 
 gian, Swedish, and Lowmoor iron, scarcely a trace of residual mag- 
 netism remains, and these irons are therefore preferred in the 
 manufacture of magnet cores. Experiment has also shown that the 
 shape of the core is no less important than its quality, and that 
 quickness of action and freedom from residual magnetism may be 
 best secured by making the cores as short as possible. These con- 
 ditions are sufficiently fulfilled for ordinary purposes in the propor- 
 tions of the magnet shown in Fig. 68, p. 91. 
 
 196. Induction of a Current upon Itself. It has been 
 stated (151) that an electric current traversing a conductor has the 
 capacity of inducing a temporary current in a neighboring con- 
 ductor. This phenomenon manifests itself in the coils of an 
 electro-magnet in such a way that its effects are added to those of 
 hysteresis (with which, however, they must not be confounded), so 
 as to still further delay the magnetization and demagnetization of 
 the iron core. These inductive effects make their appearance when 
 the inducing current is either increased or diminished, but not 
 
 while it remains steady. Fur- 
 ther, an increasing or diminish- 
 ing current not only induces a 
 current in neighboring conduct- 
 ors, as indicated in Fig. 76 (in 
 
 FIG. 76. Illustration of Current Induction be- ' v . 
 
 tween Parallel Wires. which the arrow shows the di- 
 
 rection of the inducing current 
 in the wire A, and of the induced current in 
 the wire B), but it may also exercise an in- 
 ductive action upon the conductor in which 
 it flows. In a wire coiled back upon itself, as 
 in Fig. 77, an increasing current, flowing in 
 the direction of the arrow between A and B, 
 tends to induce a current in the opposite di- 
 rection between C and D, which opposes the 
 original current and delays its increase. If. ^ 77 ^^oi Seif-m- 
 on the other hand, the current between A duction m Coiled Conductor. 
 
 20 This effect was carefully studied some years since by Professor J. A. Ewing, who 
 gave it the name of hysteresis, from a Greek word signifying " to lag behind," denning 
 it as the lagging behind of changes in magnetic intensity to changes in magnetizing 
 force. EWING : Researches in Magnetism, Philosophical Trans. Royal Soc., 1885. 
 
Causes of Retardation in Electro-Magnets. 99 
 
 and B is diminishing, it tends to induce a current between C and D 
 in the same direction as itself, and this prolongs the duration of the 
 original current by delaying its decrease. As the wire in the coil 
 of an electro-magnet is placed under the same conditions as the wire 
 in Fig. 77, it is clear that both the magnetization and the demag- 
 netization of its core will be retarded, first, by the self-induction of 
 the coil, and second, by the effects of hysteresis in the iron. Besides 
 this, the presence of the iron enormously increases the normal self- 
 induction, because the rising magnetization induces an opposing 
 e. m.f. in the wire, upon the principle explained in (78), for it will 
 obviously make no difference whether the field be created about 
 the wire, or whether it be moved thither from some other point in 
 space. The sum total of these effects is termed magnetic inertia. 
 
 197. Magnet Cores must not be Hardened. After the 
 core of a magnet has been annealed, it is very important that it 
 should be left black, and no attempt be made to brighten it up. If 
 it be filed, or touched ever so little with a cutting tool, it will be 
 slightly hardened, and will be certain to show traces of residual 
 magnetism (195) when put to service. For the same reason the 
 armature of an electro-magnet should never be permitted to hammer 
 upon its poles. 
 
 198. Effect of Self-induction and Hysteresis in Tele- 
 graph Magnets. A series of experiments conducted by an 
 officer of the U. S. Coast Survey has shown that the average period 
 of time required for a well-proportioned telegraph magnet to release 
 its armature, varies from 0.003 second, with maximum tension of 
 retracting spring, to 0.033 w i tn minimum tension. 21 The best work- 
 ing adjustment would be midway between these values, that is to 
 say, 0.015 second. 
 
 199. Other Indirect Causes of Retardation in Electro- 
 Magnets. It has been stated that the magnetism developed in a 
 given mass of iron depends solely upon two factors, the quantity of 
 current, and the number of turns of the conducting circuit around 
 the iron (176). It has furthermore been stated that the quantity oi 
 current traversing a circuit in turn depends solely upon the e. m.j 
 of the generator and the resistance of the conductor (127). But ex 
 periment shows that in respect to quickness of magnetization and 
 demagnetization, irrespective of absolute intensity of magnetism, il 
 makes a very great difference whether an exciting current of equal 
 quantity has been produced by a low e. m.f, acting through a small 
 resistance, or by a high e. m.f. acting through a proportionately 
 
 G. W. DEAN : Coast Survey Report, 1864, p. 211. 
 
100 
 
 The Laivs of Electro-Magnetism. 
 
 great resistance ; the magnetic actions in the latter case being far 
 more rapid than in the former. This effect is due to the greater re- 
 sistance, which in the latter case has to be overcome by the currents 
 of self-induction set up in the coils of the magnet, which, as we have 
 seen (196), tend, in proportion to their strength, to give rise to mag* 
 netic inertia, by delaying both the magnetization and demagnetiza- 
 tion of the iron core. The e. m. f. which tends to set up these 
 opposing currents is necessarily of equal value in either case, as it is 
 determined by the quantity of current in the coil and the intensity 
 of magnetism in the core : but the resistance the currents are obliged 
 to overcome is much greater in the second case than in the first, and 
 therefore the currents themselves are in fact very much weaker, and 
 their retarding effect is diminished in the same proportion. This fact 
 has an important bearing upon the working of fast-speed instruments. 
 
 200. Electro-Magnet with Polarized Armature. If the 
 armature, like the core of the magnet, is of soft iron, and placed 
 parallel to the polar surfaces, as in Figs. 69 and 75, the action is 
 simply one of attraction, irrespective of the polarity of the magnet, 
 and independent of the direction of the exciting current. Jf, how- 
 ever, the armature itself be a permanent magnet (63), the direction 
 in which it tends to move will depend upon the polarity of the elec- 
 tro-magnet, which in turn is determined by the direction of the ex- 
 citing current. 
 
 201. In illustration of this, let the electro-magnet of Fig. 78 be 
 provided with a polarized armature, consisting of a small permanent 
 magnet n s, which is pivoted at one end to the yoke of the electro- 
 magnet, while its opposite end is free to play back and forth between 
 
 Electro-Magnet with Polarized Armature. 
 
 the poles of the N S of the electro-magnet. When the current 
 passes in one direction, as, for example, in Fig. 78, the n pole of the 
 polarized armature is attracted by the unlike pole S of the electro- 
 magnet, and at the same time repelled by its similar pole ; but upon 
 
Permanent and Electro-Magnets. 101 
 
 the reversal of the direction of the exciting current, the polarity of 
 the electro-magnet is likewise reversed, and the polarized armature 
 is now attracted to the opposite side, as shown in Fig. 79. It is ob- 
 vious, therefore, that the direction of the movement of the polarized 
 armature depends solely upon the direction of the current, and not 
 upon its strength. There is, therefore, an important difference be- 
 tween the operation of a permanently magnetic or polarized arma- 
 ture and a non-polarized or neutral armature. 
 
 202. Combinations of Permanent and Electro-Magnets. 
 Various mechanical combinations of electro and permanent mag- 
 nets have been made, all of which involve essentially the same prin- 
 ciples as the simple apparatus figured above, and by which a like 
 effect is produced. The polarization is not necessarily confined to 
 the armature, as similar results may be obtained by constructing the 
 apparatus in various ways, provided that some one portion of it is 
 polarized and another portion non-polarized. This principle is of 
 special value in multiple telegraphy (321). 
 
CHAPTER VII. 
 
 TELEGRAPHIC CIRCUITS. 
 
 203. It has heretofore been explained (30) that an electric circuit 
 consists of an endless series or chain of conductors. That portion 
 of the circuit which is situated between the terminals or poles, and 
 within the generator, is called the internal circuit, and its resistance 
 is the internal resistance of the generator ; the chain of conductors 
 which joins the poles outside of the generator is called the external 
 circuit, and its resistance is the external resistance of the circuit. 
 
 204. The essential characteristics of every electric circuit are the 
 same, although such a circuit may vary in length from a few inches 
 to thousands of miles. It may be supplied with electricity from a 
 single source, or from two or more sources situated at different 
 points, and it may include a single receiving and transmitting instru- 
 ment, or a large number of such instruments situated at different 
 points along its course. But in every case, without regard to the 
 length of the circuit, the time actually occupied in the transmission 
 of the electric impulses, although not inappreciable, may be re- 
 garded, for all practical purposes of ordinary telegraphy, as instan- 
 taneous. 
 
 205. Telegraphic Circuits. A telegraphic circuit is made up 
 of the following parts : (i) the generators, either batteries or dynamo- 
 electric machines; (2) the line conductors; (3) the earth, which is 
 usually employed as a substitute for the return line wire from the 
 distant station ; and (4) the instruments for transmitting and receiv- 
 ing signals. 
 
 206. Open and Closed Circuits. There are two ways in 
 which a telegraphic circuit may be arranged for the transmission of 
 signals, (i) The generator may be kept normally in connection with 
 the line, thereby causing a constant current to traverse the circuit, 
 and signals may be transmitted by alternately breaking and closing 
 the circuit ; or (2) the generator may be normally disconnected from 
 the line, and signals may be transmitted by alternately inserting the 
 generator into and withdrawing it from the circuit, so as to cause a 
 current to flow for the desired period of time to form the signals. 
 
 102 
 
Drawings of Electric Apparatus. 103 
 
 The first is called, in a general way, the closed-circuit and the second 
 the open-circuit system. In other countries than North America one 
 or the other of the above-mentioned systems is almost invariably 
 employed, but the system in universal use in our own country, 
 although usually spoken of as a closed-circuit system, may more 
 properly be regarded as a compromise between the two, possessing 
 some of the characteristics of each. As in the true closed-circuit 
 system, the current constantly traverses the line when no work is be- 
 ing done, but signals are transmitted, not by interruptions of this 
 current, but by first interrupting it at the sending point, and then 
 transmitting the signals by closing the circuit at properly timed 
 intervals, thus permitting the current from the generator to trav- 
 erse the line and the receiving instrument, as in the open-circuit 
 system. 
 
 207. Drawings of Electric Apparatus. There are three 
 principal methods of representing organizations of electrical appa- 
 ratus : (i) by perspective drawings, (2) by geometrical drawings, and 
 (3) by diagrams. 
 
 Perspective drawings are ordinary pictorial illustrations. They 
 show the appearance of the apparatus, but, as a rule, are not well 
 adapted to convey to the mind a clear idea of its principle and mode 
 of operation. 
 
 Geometrical or working drawings consist of plans, elevations, or 
 sections, drawn to a scale, which may represent the whole or some 
 part of the apparatus. They usually exhibit all the constructional 
 details, whether essential to the operation of the apparatus or not, 
 and while indispensable to the workshop, are ordinarily of little use 
 for purposes of explanation. Figs. 35 and 36 (pp. 46, 47) are exam- 
 ples of-geometrical drawings. 
 
 Diagrams exhibit the apparatus, circuits, and connections, not in 
 their actual form and proportions, but in such a conventional manner 
 as will most clearly illustrate the principle of the apparatus and its 
 mode of operation. Diagrams ought not to be encumbered with 
 details which are merely constructional, and therefore unessential. 
 The advantages of a uniform and well-understood system for the 
 conventional representation of electrical apparatus and circuits will 
 be apparent. 
 
 208. Conventional Representations of Circuits and Ap- 
 paratus. In the following paragraphs are briefly described various 
 component parts of telegraphic circuits, with the symbolical repre- 
 sentations which, by general consent, have been adopted to represent 
 them, and the apparatus employed in connection with them. 
 
IO4 Telegraphic Circuits. 
 
 (1) A wire, either straight or curved, connecting two points in a circuit. 
 Main circuits may be in full, and local circuits in dotted lines, where such 
 distinction is desirable. 
 
 (2) An overhead or pole line. 
 
 (3) A submarine or subterranean line or cable. 
 
 (4) The point at which any branch circuit connection is made is indicated 
 by a round dot at the intersection. If two lines cross without being con- 
 nected, the dot is omitted. 
 
 (5) In order to more readily distinguish wires which cross each other with- 
 out electrical connection, it is usual to represent a loop in one of them at 
 ihe crossing point. 
 
 (6) The direction of the current, from positive to negative, is shown by 
 arrows. 
 
 (7) A waved line denotes an artificial resistance or rheostat in the circuit. 
 
 (8) An adjustable rheostat. 
 
 (9) A voltaic cell is indicated by two parallel lines, the thick line repre- 
 senting the zinc and the thin line the copper. 
 
 (10) The same figure arranged in the reverse way, as shown, denotes a 
 storage battery or accumulator. 
 
 (n) A dynamo-electric machine. 
 
 (12) A ground or earth plate. 
 
 (13) A common or non-polarized relay. 
 
 (14) A polarized relay. 
 
 (15) A sounder. 
 
 (16) A recording instrument or register. 
 
 (17) A galvanoscope or galvanometer. If a tangent galvanometer, it may 
 be represented as in Fig. 50, p. 65. 
 
 (18) A coil or loose bundle of wire, its use being indicated by a reference 
 letter. 
 
 (19) A common Morse key. 
 
 (20) A single-current or three-point key. 
 
 (21) A single-current transmitter. 
 
 (22) A double-current transmitter. 
 
 (23) A condenser. 
 
 (24) A lightning arrester. 
 
 (25) A pole-changing switch, in which the crosses indicate the insertion 
 of plugs. 
 
 (26) A universal switch, in which the crosses indicate points where con- 
 nections are formed by inserting plugs. 
 
 (27) A three-point switch. 
 
 209. The Earth as an Electrical Conductor. The earth, 
 being composed of a vast mass of inorganic material, mostly of a 
 porous character, and permeated throughout by water, forms an ex- 
 cellent conductor of electricity, and it is almost invariably employed 
 in this capacity as a part of every telegraphic circuit. While its 
 specific conductivity, as will appear from the table (p. 57), is much 
 lower than that of metallic substances, yet this is abundantly 
 compensated for by the enormous area of its cross-section. 
 
Representations of Circuits and Apparatus. 105 
 
 4, 5- 
 
 K 
 
 13- 
 
 1A/IM/V. 
 
 7- 
 
 i5- 
 
 16. 
 
 17- 
 
 _2j2j^- 
 
 18. 
 
 23- 
 
 A T A yA^ 
 
 24. 
 
 #^ 
 
 
 25- 
 
 , 
 
 
 ^ 
 
 
 ' ^ 
 
 , 
 
 
 x 
 
 ' 4 
 
 > I 
 
 26. 
 
 27. 
 
io6 Telegraphic Circuits. 
 
 Fig. 80 illustrates the principle of the earth circuit. The current 
 of the battery is assumed to pass through the earth from one end of 
 
 the line to the other, as indi- 
 cated by the arrow. 
 
 210. Ground Connec- 
 tion. The connection with 
 the earth is made by means 
 of ground-plates, which may 
 be of sheet copper -f$ in. 
 thick, and having an area of 
 
 FIG. 80. Diagram of Earth Circuit. 36 by 48 in. Plates of gal- 
 
 vanized iron are cheaper r 
 
 and are often used instead of copper ; they appear to answer the 
 purpose perfectly well. The ground-plates should be buried in 
 moist earth in a vertical position. In many cases an available 
 substitute may be found by attaching the terminal of the line, by 
 soldering or otherwise, to a pipe which forms a part of an exten- 
 sive network of gas or water conductors buried in the earth, the 
 large surface of which insures a most excellent conducting connec- 
 tion. It is advisable, wherever possible, to attach the wire to both 
 gas and water pipes. When the wires are thus connected to a pipe, 
 certain precautions are necessary to be observed, especially that of 
 soldering the wire to the pipe outside the meter. 
 
 The connecting wire which is soldered to the ground-plate 
 should be coated with insulating material, to prevent corrosion 
 of the wire by the electrolytic action which might otherwise take 
 place (27). 
 
 If circumstances render it necessary to bury a ground-plate in 
 badly-conducting soil, as, for instance, where it is rocky, sandy, or 
 gravelly, without sufficient moisture, a pit should be dug, and filled 
 with scrap tin or other waste metals laid in contact with the plate, 
 and the surface drainage and discharge from water pipes should be 
 led into it. 
 
 211. Advantages of the Earth Circuit. Several important 
 advantages arise from the use of the earth in telegraphy as a part of 
 the circuit. The entire cost of the return wire and its insulation is 
 saved, while at the same time the resistance of the circuit is reduced 
 nearly one-half. On the other hand, the inclusion of the earth mate- 
 rially increases the difficulty of maintaining an efficient condition of 
 insulation throughout the circuit (219). 
 
 The specific electrical resistance of the soil and of the strata of 
 the earth, due to the geological character of some regions, are some- 
 
The Open Circuit. 107 
 
 times such as to render it a matter of great difficulty to secure a 
 sufficiently good ground connection. 
 
 An instance was observed some years since by the author in which it was 
 impossible to secure a ground connection which would not offer an abnor- 
 mally great resistance to the flow of the current. This was in the anthracite 
 coal regions of Pennsylvania. Professor Moses G. Farmer informs him 
 that he has met with the same difficulty in some places in the mountainous 
 districts of New Hampshire and Vermont, on the lines between Boston and 
 Montreal. 
 
 212. The Open Circuit. A telegraph line arranged upon the 
 open-circuit plan is illustrated in Fig. 81. Two terminal stations 
 are shown, each having a battery, a transmitting key, and a receiving 
 instrument. The circuit of the line divides at each key into two 
 
 _t 
 
 T- 
 
 FIG. 81. Diagram of Open-Circuit System. 
 
 branches, of which only one can be closed at the same time. One 
 branch includes the battery only, and the other the receiving instru- 
 ment only. The latter branch is normally in connection with the 
 circuit of the line. If a signal is to be sent, the key is depressed by 
 the operator, so as to establish the connection of the line with the 
 battery, having first broken it with the instrument. A current from 
 the battery will now flow through the key and over the line in the 
 direction indicated by the arrows to the other station, where it passes 
 through the instrument contact of the key and through the receiving 
 instrument, avoiding the battery, and thence back through the ground- 
 plate and the intervening mass of earth to the opposite pole of the 
 battery at the sending station, thus completing the circuit. In this 
 arrangement, therefore, each station transmits signals by inserting 
 its own battery at timed intervals into a circuit of conductors which 
 is already complete. 
 
io8 
 
 Telegraphic Circuits. 
 
 213. The Closed Circuit. Fig. 82 illustrates the closed-cir- 
 cuit plan, properly so called. In this the cells of the battery or bat- 
 teries are always in the line, and the circuit passes normally through 
 
 FIG. 82. Diagram of Closed-Circuit System. 
 
 the rear or breaking contact of the keys, and through the receiving 
 instruments at both stations. By depressing the key at either station 
 (as shown at the right hand in Fig. 82), the current of the entire line 
 is interrupted, and a signal is simultaneously given upon both receiv- 
 ing instruments by the falling off of the armatures of the electro- 
 magnets of the receiving instruments. 
 
 214. American Modification of the Closed Circuit 
 Fig. 83 represents the American modification of the closed circuit, 
 
 FIG. 83. Diagram of American Modification of Closed-Circuit System. 
 
 which is the standard arrangement employed in the United States, 
 Canada, and Mexico. It differs from the last described in that the 
 circuit does not normally pass through the key at all, but through a 
 
Position of Battery in Closed Circuit. 109 
 
 switch or special circuit-closer beside it, which, as a matter of con- 
 venience, is in practice usually mounted upon the key, though shown 
 separately in the diagram, as it is sometimes arranged in fact. To 
 transmit a signal according to this plan, the circuit of the line is first 
 broken by opening the switch, and the signals are then made by de- 
 pressing the key so as to close the circuit at timed intervals upon its 
 front contact-point. As in the last case, the alternate opening and 
 closing of the circuit at one station affects alike the receiving instru- 
 ments at all stations. 
 
 215. Comparative Advantages of the Different Plans. 
 Each of the foregoing plans of organization of a telegraphic circuit 
 has certain peculiar advantages and disadvantages, which will be 
 further considered hereafter. It may, however, be stated here, that 
 one principal advantage of the closed-circuit systems is that a great 
 number of stations may be placed upon a single line without materially 
 interfering with each other, and may be equipped with the simplest 
 of apparatus, all the batteries being placed at the terminal stations, 
 where they can more conveniently receive skilled and sufficient 
 attention. 
 
 216. Position of Battery in Closed Circuit. While it is 
 usual in a closed-circuit system to place a battery at each end of the 
 line, as shown in Figs. 82 and 83, it is by no means an essential 
 requirement. Comparatively short lines of say 25 or even 50 miles 
 in length are often supplied with a battery only at one end, while 
 very long lines are occasionally provided with an intermediate bat- 
 tery midway between the terminal batteries. In rare instances a 
 battery is placed in the middle of the line only. The arrangement 
 shown in Figs. 82 and 83 is considered preferable to any other ? unless 
 for exceptional reasons which may apply to some particular case. 
 
 217. General Considerations respecting Telegraphic 
 Circuits. In all telegraphic circuits (with the exception of those 
 of direct working electro-chemical systems, which do not come within 
 the scope of this work), the object sought to be obtained is to pro- 
 duce signals at a distant station by alternately closing and breaking 
 the circuit at the home station, so as to alternately magnetize and 
 demagnetize the electro-magnet of the receiving instrument at the 
 distant station. It is therefore primarily essential that the current 
 traversing the coils of the distant electro-magnet should be of suf- 
 ficient quantity to cause the latter to attract its armature with cer- 
 tainty when the circuit is closed, while, on the other hand, it should 
 be insufficient to maintain the armature in proximity to the magnet 
 against the force of the antagonistic spring, or other retracting device, 
 
no 
 
 Telegraph ic Circu its. 
 
 when the circuit is broken. This result is most perfectly attained 
 when the maximum current going through the helix of the receiving 
 magnet is sufficient to cause the armature to be promptly attracted^ 
 and the minimum current is zero, or no current. But upon lines 
 of ordinary length, exposed to unavoidable atmospheric influences,, 
 these conditions are usually impossible of fulfillment. The more 
 nearly this ideal condition can be approximated to, the better are 
 the results. It can only be fully realized upon a line of which the 
 insulation is absolutely perfect. 
 
 218. Relation of Conductivity to Insulation Resistance^ 
 Practically the end aimed at in all telegraphic circuits should be to 
 make the resistance of the conductor as small as possible, and the 
 resistance of the insulation as great as possible. Therefore, in con- 
 structing a telegraph line, it is important to employ the best possi- 
 ble conductor which the necessary limitations of cost will permit, 
 and to prevent the escape of the current in undesired directions 
 by the use of the most efficient insulators. 
 
 219. Effect of Imperfect Insulation. The deleterious ef- 
 fects of imperfect insulation upon the operation of a telegraphic cir- 
 cuit will be understood by reference to Fig. 84, which represents 
 
 
 * 
 
 r 
 4 
 
 
 
 
 4 
 
 n 
 
 u i 
 
 I 
 
 1 
 
 i 
 
 I 
 
 
 
 i 
 
 A 
 
 t 
 + 
 
 
 1 
 
 1 
 
 1 
 
 i 
 
 mm 
 
 ~H 
 
 
 
 
 
 
 
 ! 
 
 FIG. 84. Effects of Imperfect Insulation. 
 
 two stations, A and B, connected by a telegraph line, the earth 
 being used as a return conductor. If we suppose the line to be 
 provided with a battery at station A only, the current from its posi- 
 tive pole flows along the line toward B, as indicated by the arrows, 
 but a small portion of this current escapes from the line through or 
 across the defective insulators at every successive support. These 
 currents of leakage find their way directly into the earth in the direc- 
 tion indicated by the arrows, returning to the negative pole of the 
 battery, at A, without going through the instrument at B at all. 
 Every imperfectly insulated point of support therefore constitutes 
 
Telegraphic Conductors. 1 1 1 
 
 a branch circuit (140), and causes the current to divide in pro- 
 portion to the total resistance of the support and its insulator as 
 compared with the joint resistance of that portion of the line and 
 the branch circuits beyond the point of division. It is evident 
 that the greater the resistance, jointly and severally, of the insula- 
 tors, and the less the resistance of the line conductor, the greater 
 will be the percentage of the total quantity of current entering the 
 line at A which will reach the instrument at B. But as some por- 
 tion of the total current must escape from the line at every point of 
 support, it will come to pass, unless the line be perfectly insulated, 
 that at some distance from the initial point, depending both upon the 
 conductivity and the insulation of the line, so large a proportion of 
 the current will have escaped from the line through the supports to 
 the earth, that the remainder will be insufficient to produce any 
 appreciable effect upon the receiving instrument. 
 
 220. Working Efficiency of Telegraphic Circuit. The 
 working efficiency of a telegraphic circuit is therefore determined by 
 the ratio between the resistance of the conductor and the resistance of the 
 insulator. If the total resistance of the conductor be divided by the 
 total resistance of the whole number of insulators that is to say, by 
 their joint resistance the quotient will represent fas. efficiency of the 
 circuit. The smaller this quotient, the higher the efficiency (243). 
 
 221. Telegraphic Conductors.- The wires used for tele- 
 graphic conductors are almost invariably either of iron or of copper. 
 Iron wires were formerly exclusively used for outside or aerial lines. 
 Since 1885 these have largely been superseded, in all new work, by 
 wires of hard copper. Copper wires are invariably employed for in- 
 terior work, which term comprises the wires within buildings and 
 about the apparatus. They are also employed for all subterranean 
 and submarine conductors. The table on page 112 gives the di- 
 mensions, weight, conductivity, resistance, etc., of the sizes of iron 
 and copper wires most generally employed as telegraphic con- 
 ductors. 
 
 222. Iron AAfires. Until within a few years the size of iron 
 wire most commonly employed in the United States has been that 
 known as No. 9, which probably still constitutes something like one- 
 half of the total mileage of the country. Nos. 8, 6, and 4 are larger 
 sizes which have come into use, especially since 1875. No. 4 is the 
 largest iron wire used in this country, and No. 10 is the smallest 
 used in the public telegraph service. These numbers refer to the 
 so-called Birmingham gauge, and not to the American (190). See 
 Fig- 85- 
 
112 
 
 Telegraphic Circuits. 
 
 TABLE IX. 
 SIZE, WEIGHT, AND RESISTANCE OF TELEGRAPH WIRES. 
 
 EXTRA BEST BEST GALVANIZED IRON. 
 
 (Washburn & Moen Manufacturing Company.) 
 
 GAUGE 
 No. 
 W.&M. 
 
 Diameter. 
 Mils. 
 
 Weight. 
 Lbs. per 
 Mile. 
 
 Resistance. 
 Ohms per 
 Mile 
 
 Feet 
 per Ib. 
 
 Tensile 
 Strength. 
 Lbs. 
 
 4 
 
 229 
 
 730 7. 
 
 
 7.23 
 
 
 1900 
 
 6 
 
 196 
 
 540 9-5 
 
 9-59 
 
 
 1500 
 
 8 
 
 165 
 
 380 
 
 13- 
 
 
 13.89 
 
 
 1 100 
 
 9 
 
 I5 1 
 
 320 
 
 15- 
 
 
 16.50 
 
 
 900 
 
 10 
 
 138 
 
 268 
 
 18. 
 
 
 19.70 
 
 
 700 
 
 ii 
 
 123 
 
 215 
 
 23- 
 
 
 24.65 
 
 
 550 
 
 12 
 
 108 
 
 164 
 
 32. 
 
 
 32.19 
 
 
 450 
 
 14 
 
 83 
 
 96 
 
 55- 
 
 
 55- 
 
 
 150 
 
 GALVANIZED IRON. 
 
 (British Post Office Specifications.) 
 
 GAUGE 
 No. 
 
 Diameter. 
 Mils. 
 
 Weight. 
 Lbs. per 
 Mile. 
 
 Resistance. 
 Ohms per 
 Mile. 
 
 Feet 
 per Ib. 
 
 Tensile 
 Strength. 
 Lbs. 
 
 .... 
 
 242 
 
 800 
 
 6.75 
 
 6.6 
 
 
 2620 
 
 .... 
 
 209 
 
 600 
 
 9- 
 
 
 8.8 
 
 
 1960 
 
 .... 
 
 181 
 
 450 
 
 12. 
 
 
 11.7 
 
 
 1460 
 
 
 
 171 
 
 400 
 
 13-5 
 
 
 13-2 
 
 
 1300 
 
 
 
 121 
 
 200 
 
 27. 
 
 
 26.4 
 
 
 655 
 
 HARD DRAWN COPPER. 
 
 (John A. Roebling's Sons Company.) 
 
 GAUGE 
 No. 
 
 Diameter. 
 Mils. 
 
 Weight. 
 Lbs. per 
 Mile. 
 
 Resistance. 
 Ohms per 
 Mile. 
 
 Feet 
 per Ib. 
 
 Tensile 
 Strength. 
 Lbs. 
 
 9 
 
 114-43 
 
 209 
 
 4-3 
 
 
 25.2 
 
 
 625 
 
 10 
 
 101.89 
 
 166 
 
 5-4 
 
 
 31-2 
 
 
 525 
 
 SOFT COPPER. 
 
 (Geo. B. Prescott, Jr.) 
 
 o ^ 
 3* 2 
 
 AREA. 
 
 WEIGHT AND- RESISTANCE AT FAHR . 
 LENGTH. 
 
 5 W %~ 
 
 
 
 
 
 I 
 
 WO C ^ 
 
 Circular 
 Mils. 
 
 Square 
 Inches. 
 
 Lbs. 
 per looo 
 Feet. 
 
 Feet hms 
 Per Ib. P p^ 
 
 Feet Ohms 
 Ohm perlb ' 
 
 10 101.9 
 
 10381 
 
 8153 
 
 3L37 
 
 31.38 I. 
 
 looo .0313 
 
 12 80.8 
 
 6260 
 
 5128 
 
 19-73 
 
 50.69 1.59 
 
 629 .0805 
 
 14 64.1 
 
 4107 
 
 3147 
 
 12.41 
 
 80.59 2.59 
 
 386 .208 
 
 16 50.8 
 
 2583 
 
 2029 
 
 7 .8l 
 
 128.14 4-02 
 
 249 -515 
 
 18 40.3 
 
 1624 
 
 1276 
 
 4.91 
 
 203.76 6.39 
 
 156 1.302 
 
 20 31.9 102 1 
 
 802 
 
 3-09 
 
 324.15 10.16 
 
 98 3.292 
 
Line and Office Wires. 
 
 1*3 
 
 12 
 
 In the construction of a telegraph line, the longer each bundle or 
 piece of wire is the better, so long as it does not exceed a weight 
 which is convenient for 
 the workmen to handle. 
 Great care should be taken 
 in making each joint, and 
 in any case, the fewer 
 joints the better. A loose 
 and poorly made joint 
 sometimes causes as much 
 resistance as 50 miles of 
 line. 
 
 Fig. 86 shows the com- 
 mon twist-joint most used 
 in the United States. The 
 ends of the wires are 
 wrapped tightly around 
 each other with the aid 
 of a hand-vise and pliers, 
 and are then soldered, to insure good metallic connection and to 
 exclude moisture. The usual number of posts or supports in the 
 United States is from 30 to 40 per mile. The smaller the number 
 of posts the less the leakage from imperfect insulation and the less 
 the cost. 
 
 FIG. 85. Iron Wires for Telegraph Lines Actual Size. 
 
 FIG. 86. Twist-Joint for Iron Wire. 
 
 223. Office \Vires. The copper wires used for interior wiring 
 should generally be of No. 16 American gauge or thicker, and well 
 covered with insulating material. If the location is perfectly dry 
 and the number of wires is not very great, a coating of cotton braid, 
 double, and saturated with paraffin or wax, answers very well. If 
 there is any danger of exposure to dampness, some of the higher 
 grades of insulated wire, most of which aie known by special trade 
 names, such as Kerite, Okonite, etc., are to be preferred. Specimens 
 of some of the most useful varieties of these office wires^ as they are 
 called, are illustrated in Fig. 87. The great number of varieties of 
 insulation now in the market offers a wide scope for selection, both 
 in quality and cost. 
 
Telegraphic Circuits. 
 
 BCD E F 
 
 Fig. 87. Insulated Conductors for Interior Construction. 
 
 Reference 
 Letter. 
 
 Birmingham 
 Gauge No. 
 
 Diameter of 
 Conductor. 
 Mils. 
 
 Material of 
 Insulation. 
 
 Outside 
 Diameter of Outer 
 Insulation. Covering. 
 Mils. : 
 
 A 
 
 16 
 
 65 
 
 Okonite 
 
 148 Braided 
 
 B 
 
 18 
 
 49 
 
 Kerite 
 
 120 
 
 None 
 
 C 
 
 18 
 
 49 
 
 " 
 
 165 
 
 Braided 
 
 D 
 
 18 
 
 49 
 
 " 
 
 1 20 
 
 Lead 
 
 E 
 
 20 
 
 35 
 
 Okonite 
 
 109 
 
 None 
 
 F 
 
 20 
 
 35 
 
 Kerite 
 
 95 
 
 None 
 
 G 
 
 20 
 
 35 
 
 ' ' 
 
 95 
 
 Lead 
 
 224. Copper Line W^ires. About the year 1880 it was dis- 
 covered that copper wire, drawn by a process which gave it greatly 
 increased tensile strength without materially impairing its conduct- 
 ing qualities, could be had in the market, and as a result many lines 
 have since been built with this wire, with the most satisfactory results. 
 At the prevailing prices of copper and iron, the cost of the copper 
 line is little if any more, all things considered, than that of an iron 
 line of equivalent conducting capacity ; while, if very great conduc- 
 tivity is desired, it is absolutely necessary to resort to copper, as an 
 
Telegraphic Line Insulators. 
 
 iron wire thicker than No. 4 is so heavy as to be almost unmanage- 
 able. 
 
 225. Telegraphic Line Insulators. Telegraphic lines are 
 carried through the country supported usually upon wooden posts, 
 but occasionally upon other structures, such as buildings, bridges, 
 etc. These supports are separated at intervals, varying on different 
 lines from 150 to 300 feet, or from 20 to 40 per statute mile. At 
 each point of support each wire is affixed to an insulator, the office 
 of which is to prevent, so far as possible, the escape of the current 
 from the line through the support to the earth, in its endeavor to re- 
 turn to the battery by the shortest route (219). Much ingenuity 
 has been expended, and, it must be confessed, with very unsatisfac- 
 tory results, to devise an insulator which shall be capable of per 
 manently maintaining its non-conduct- 
 ing properties during continued wet 
 
 weather. The insulator which is in 
 most general use in North America is 
 an inverted cup of pressed glass, mount- 
 ed upon an oak pin which forms its sup- 
 port, as in Fig. 87, the line being se- 
 cured to its side by a tie wire which lies 
 in a circumferential groove surrounding 
 the insulator. The ordinary glass in- 
 sulator is a device which has little to 
 recommend it except its cheapness. 
 Nevertheless, there is much to choose 
 between the different forms in which 
 the glass insulator is to be had. Two 
 models in common use are shown in 
 diametrical cross-section in Figs. 88 
 and 89. The figures are one-half the 
 actual size, and the measurements are 
 given in the drawings. 
 
 226. Defects of the Glass In- 
 sulator. The glass of which these 
 insulators are composed is a substance 
 which, as regards its body, is a suffi- 
 ciently good non-conductor under most 
 circumstances ; but unfortunately, in 
 
 rainy and damp weather, especially when the temperature of the 
 atmosphere is rising, its entire surface becomes coated with a con- 
 tinuous film of moisture. This watery film forms a conductor at 
 
 FIG. 87. Glass Insulator on Oak 
 Bracket. Model of 1865. 
 
n6 
 
 Telegraph ic Circu its. 
 
 FIG. 88. Western Union Old Insulator. 
 
 every support, which conveys a portion of the current from the con- 
 ductor to the supporting pin upon which the insulator is mounted, 
 
 from whence it finds its way 
 into the ground, or, still worse, 
 into some other parallel and 
 neighboring wire. Although 
 water is a comparatively poor 
 conductor (116), so that the 
 quantity of current which es- 
 capes at any one point is in- 
 considerable, yet, when we con- 
 sider that on a line 500 miles 
 long, there may be more than 
 20,000 such points of escape, 
 the aggregate loss becomes in 
 practice a most serious matter. 
 227. Resistance Influ- 
 enced by Form of Insu- 
 lator. Each insulator, there- 
 fore, must be regarded in wet 
 
 weather as a conductor, and, as such, is subject to the same law as 
 
 every other conductor ; that is, the resistance which it will oppose 
 
 to the escaping current is directly in proportion to the length of 
 
 the conducting film upon its 
 
 surface, and inversely as its 
 
 cross-section (118). Hence 
 
 the length of the insulating 
 
 surface, measured from the 
 
 point of contact of the wire 
 
 to the point of contact of the 
 
 supporting pin, must be as 
 
 great as possible. On the 
 
 other hand, it is obvious that 
 
 the smaller the diameter of 
 
 the insulator, both external 
 
 and internal, the narrower 
 
 will be the conducting film, 
 
 and the greater its resistance. 
 
 Tested by this rule, it will FIG. 89. Western Union Standard Insulator. 
 
 be seen that the pattern illus- 
 trated in Fig. 89 must be better than that shown in Fig. 88, as in the 
 first the actual linear distance from the conducting wire to the sup- 
 
Hard Rubber and Paraffin Insulators. i i 7 
 
 FIG. 90. Hard Rubber Insu- 
 lator. (Batchelder.) 
 
 porting pin (as shown by the heavy outline) measures 5.5 in., while 
 in the second it is only 4.3 in. It is true that the insulator, Fig. 88, is 
 somewhat smaller in diameter than the other, which is so far an advan- 
 tage ; but, on the other hand, a comparatively great part of the insu- 
 lating length of the latter is underneath, 
 where it is well protected from the direct 
 action of the falling rain. 
 
 228. The Hard-Rubber Insulator. 
 Another variety of line insulator more or 
 less in use is the hard-rubber, which con- 
 sists of a malleable iron hook for clamping 
 and holding the wire, covered with a mass 
 of vulcanized rubber, in cylindrical form, 
 with a thread cut upon its exterior, which 
 is screwed into a block, wooden arm, or 
 other convenient support, as shown in Fig. 
 90. The non-conducting properties of vulcanized rubber have been 
 found to deteriorate very rapidly on the surface by exposure to the 
 weather, and hence this form of insulator is now but little used 
 except for short lines in cities, for which it possesses some advan- 
 tages by reason of its small size, 
 light weight, and general con- 
 venience. 
 
 229. The Paraffin Insu- 
 lator. Fig. 91 is a sectional 
 view of the paraffin insulator, 
 which has been much used on 
 the railway telegraph lines of 
 the United States. An outer 
 cylindrical shell of cast-iron, 
 open at its lower end, has ce- 
 mented into it a narrow-necked 
 inverted bottle of blown glass, 
 within which again is cemented 
 an iron stem, carrying at its 
 lower end a hook for support- 
 ing and clamping the wire. 
 The surface of the cement, both 
 within and without the glass bottle, is coated with paraffin having 
 a melting-point of about 145 Fahr. The iron shell is inserted into 
 a hole bored in the under side of a cross-arm, which last is bolted 
 transversely to the upright post. 
 
 FIG. 91. Paraffin Insulator. (Brooks.) 
 
i8 
 
 Telegraphic Circuits. 
 
 230. The Porcelain Insulator. The insulator shown in Fig. 
 92 is made in great perfection in Germany, and is extensively used 
 in Europe, Asia, and South America, but not in the United States. 
 All things considered, it is perhaps the most efficient insulator now 
 
 known. The figure is 
 a sectional view of the 
 best form, known as 
 the double bell. The 
 material is a fine and 
 dense porcelain, per- 
 fectly non-porous, and 
 white in color. The 
 glaze covers the whole 
 internal and external 
 surface, and is of a 
 pure white color. The 
 thread is smoothly 
 formed and well-de- 
 fined. The supporting 
 bracket is of malleable 
 iron, having an upright 
 cylindrical stem, and 
 the socket is packed 
 
 with hemp and linseed oil when the insulator is put on. A straight 
 iron bolt with a shoulder is used with a cross-arm, secured by a 
 nut screwed on the under side of the arm. 
 
 231. Defective Insulation of American Lines. The most 
 serious defect in the construction of the telegraphs of the United 
 States is unquestionably the character of the insulation. Very few 
 of the lines exhibit any material improvement in this particular over 
 those constructed forty years ago. It is true that the working 
 efficiency of the more important lines has been greatly increased 
 during the period which has since elapsed, but the improvement is 
 due almost wholly to the use of conductors of lower resistance, and 
 to the substitution of powerful dynamo-electric machines in the large 
 terminal stations for the voltaic batteries formerly used. The effi- 
 ciency of the less important lines is no greater, and, in many 
 instances, not as great, as it was twenty years since. The insulators 
 almost universally employed, as pointed out in (227), are deficient 
 both in material and in design. In addition to their inherent defects, 
 there are usually a considerable proportion of cracked or broken 
 ones, which the most vigilant inspection cannot wholly prevent. The 
 
 FIG. 92. German Porcelain Insulator. 
 
Effects of Climate upon Insulation. 119 
 
 records of the Western Union Company show that about 6 per cent, 
 of the glass insulators on its lines require renewal yearly. 1 
 
 232. Effects of Climate' upon Insulation. The combined effect of dirt 
 and moisture upon the surface of insulators is very deleterious. Ordinary 
 insulators in this country are affected proportionally as the air becomes 
 charged with moisture. In the winter months this often occurs, and is 
 notably the case when the ground is covered with melting snow, and the 
 rain is from the south. Northeast storms begin with the wind from the 
 northeast. Usually the wind changes to the east and south, and finally it 
 clears up with the wind from the west and northwest. During the portion 
 of the storm when the wind is from the southeast and south, the air is charged 
 with moisture to its full capacity, or total saturation. It is during this time 
 that the ordinary glass insulator is most affected. When the storm is accom- 
 panied by the wind changing in the other direction, that is, from northeast to 
 north, and finally to northwest, the insulation is much less affected, because 
 the atmosphere is seldom charged to over 80 per cent, of full saturation. 
 DAVID BROOKS : The Telegrapher, xi. 73. 
 
 Mr. Brooks, who has devoted much attention to the investigation 
 of questions relating to the insulation of telegraph lines, has remarked 
 that in cities in which the fuel principally used is anthracite coal, the 
 gas which is formed and escapes into the atmosphere produces a 
 very deleterious effect upon the surface of glass insulators. He 
 found while during rain, insulators in the country, in regions free 
 from smoke, give a resistance of 60 to 100 megohms per insulator, 
 in the city under the same conditions of weather, the resistance falls 
 as low as 4 to 6 megohms per insulator. He instances a line in the 
 city of Pittsburgh, a locality formerly famous for the quantity of 
 bituminous coal-smoke which pervaded its atmosphere, where glass 
 insulators which had been exposed on the line less than two years 
 were so coated with soot that they gave a measured resistance of 
 less than i megohm per insulator. Moses G. Farmer, who is also 
 excellent authority in such matters, says : " I presume from long 
 experience and many careful tests, made in the worst weather, that 
 9 megohms will be above the average value of three-quarters of the 
 insulators used in this country, in the Middle and Northern States, 
 in long-continued heavy storms." 2 
 
 A very fair idea of the comparative efficiency of some of the different 
 insulators referred to in this chapter may be gathered from the report of 
 a test of five years duration, extending from March I, 1868, to March i, 1873. 
 The different varieties^of insulators were exposed in sets of 10, the mean 
 resistance of this number being taken in each test. The total number of 
 
 1 PRESCOTT : Electricity and the Electric Telegraph, 302. 
 3 The Telegrapher, \. 34. 
 
I2O 
 
 Telegraphic Circuits. 
 
 measurements, in rain, during this period was 93. The results were as 
 follows : 
 
 DESCRIPTION OF INSULATOR. 
 
 Resistance Resistance per Mile 
 per Insulator. of 40 Insulators. 
 Megohms. Ohms. 
 
 Mean. 
 
 Minimum.i Mean. 
 
 Minimum. 
 
 I. Western Union glass, 1865 
 tvDe (like Fitr 87) . 
 
 8-3 
 
 8.6 
 28.3 
 
 10,000. 
 
 14.6 
 
 24. 
 
 2.6 
 
 3- 
 
 19. 
 2,300. 
 
 6.4 
 
 3-5 
 
 207,500 
 
 215,000 
 
 707,500 
 2,500,000,000 
 
 365,000 
 600,000 
 
 65,000 
 
 75,000 
 
 475,000 
 
 57,777,777 
 
 160,000 
 87,500 
 
 2. Large Varley, brown stone- 
 ware with ebonite covered 
 pin (Knglish standard) 
 
 3. Berlin porcelain, double bell 
 (like Fig. 92) 
 4. Brooks' Paraffin (like Fig. 91). 
 5. Boston screw-glass (nearly 
 like Fig. 87, but with internal 
 screw-thread), exposed I year 
 6. Western Union glass, 1871 
 type (nearly like Fig. 88), ex- 
 posed i year 
 
 
 The tests were made by D. Brooks of Philadelphia. The Telegrapher : ix. 90. 
 
 234. Distribution of Potentials in Telegraphic Circuits. 
 
 The manner in which the varying potentials at points in an 
 electric circuit may be graphically delineated in accordance with 
 Ohm's law, has been explained in (145). The application of this 
 method of illustration to the specific conditions of a telegraphic 
 circuit is instructive, as it enables the student to form, as it were, 
 a mental picture of the electrical condition of every portion of the 
 line when in normal condition, or when affected by leakage arising 
 from faults and defective insulation. 
 
 In pointing out the application of this graphic method of repre- 
 sentation, to a telegraphic circuit, it will be convenient in the first 
 instance to assume the circuit to be perfectly insulated. 
 
 235. Potentials in Perfectly Insulated Circuit. If a bat- 
 tery of 100 gravity cells in series be connected to a perfectly insu- 
 lated line of say 100 miles in length, open at the distant end, as 
 shown in Fig. 93, the line will acquire a potential throughout its 
 entire length, of 100 volts, which is equal to the e. m. /. of the battery. 
 This will be the case, however great may be the length of the line. 
 
 236. If now the distant end of the line be connected to the earth, 
 as in Fig. 94, a positive current will traverse the line. This will 
 not affect the e. m. f. of the battery, which remains 100 volts as 
 
Potentials in Perfectly Insulated Circuit. 121 
 
 before, but the distribution of potentials will be changed in every 
 part of the circuit. The distant end of the line becomes o or zero, 
 being the same as the assumed potential of the earth with which it is 
 
 100 Cells 
 
 100 
 
 75 
 
 50 
 
 35 Miles 
 
 EARTH 
 
 F"ic. 93. Insulated Open Circuit. 
 
 directly connected, and from this point it rises gradually and uni- 
 formly along the line to the terminal or pole of the battery; at which 
 point, as we shall hereafter see, it will be something less than 100 
 volts. Having ascertained the actual potential at this or any other 
 
 HI 
 
 EARTH 
 
 cioo 
 D 
 
 75 
 
 FIG. 94. Circuit Grounded at Distant End. 
 
 EARTH 
 
 point on the line, it may readily be calculated for any other point, 
 for in a circuit of uniform resistance, the potential varies directly as 
 the distance from the zero end of the line (145). Thus if it is 
 known to be 80 volts at 100 miles, it must be 40 volts at 50 miles, 
 
 Positive and Negative Potentials in same Circuit. 
 
 20 volts at 25 miles, and so on, the different poten- 
 tials at different points being represented by the 
 sloping dotted line in Fig. 94. The potential which 
 has been referred to is positive, but the law is of course the same 
 with a negative potential, which is a potential less than that of the 
 
 <TEARTH 
 
122 Telegraphic Circuits. 
 
 earth. An example of this is given in Fig. 95, which represents 
 two parallel insulated lines each 100 miles in length, looped 
 together at the distant ends. The middle of the battery c z is 
 connected to the earth ; and this point, therefore, acquires a poten- 
 tial of zero. The upper half of the battery imparts a positive poten- 
 tial to the upper line, and its lower half a negative potential to 
 the lower line. The potential falls regularly from the c pole of the 
 battery to o, and rises regularly from the z pole of the battery to o. 
 If a wire were connected between the earth and any point along the 
 length of the upper line, a current would flow from the line to the 
 earth, the quantity of which, by Ohm's law, would be in proportion 
 to the potential at that point. If the wire were connected in the 
 same way to any point on the lower or negative line, a current would 
 in like manner flow from the earth to the line. In the illustration 
 given, it will be observed that there are two points of zero potential 
 where it changes from positive to negative, one in the middle of the 
 battery and the other at the point where the lines are looped. This 
 is the same as the distribution of potentials in Fig. 57, p. 71, and 
 illustrates the distribution on a telegraph line like that represented 
 in Figs. 82 and 83, p. 108, in which there is a closed circuit with 
 a battery at each end, these constituting electrically one battery 
 united with the earth at its centre precisely as in Fig. 95. Fig. 96 
 represents a line of 100 miles connected with a battery having an. 
 
 100 Cells 
 
 100 Miles 
 
 EARTH 
 
 FIG. 96. Measurement of Potential by Auxiliary Battery. 
 EARTH 
 
 e. m. f. of 100 volts, the distant end of the line being to earth. If" 
 the free pole of a second battery, with its similar pole to the earth, 
 be now connected at any point to this line through a galvanometer, 
 each battery will tend to send a current to the line. If the batteries 
 are of equal potential, and attached at the same point, the needle 
 will be deflected, say to the right. If now the number of cells 
 and consequently the e. m. f. of the second battery be gradually 
 diminished, a point will soon be reached at which no current will 
 traverse the galvanometer, and its needle will stand at zero. When 
 
Determination of Potential by Calculation. 123 
 
 this condition exists, the e. m.f. of the second battery is equivalent 
 to the potential of the line at the point of attachment. The e. m. f. 
 of the auxiliary battery will always be less than that of the principal 
 battery, even when connected quite close to it ; while as we recede 
 from the battery, the number of cells or the e. m. f. required to 
 maintain the needle at zero will gradually diminish, till, near the 
 remote end, even a single cell will suffice to send a current into the 
 line, because the potential at that point is approximately zero. 
 
 236. Determination of Potential by Calculation. The 
 diagram, Fig. 97, illustrates the manner in which the potential at 
 any point on a perfectly insulated line may be calculated, when the 
 
 t 
 
 c 
 
 FIG. 97. Calculation of Potential from e. m. f. of Battery. 
 
 e. m. f. of the battery is known. Let A B represent a battery of say 
 100 volts, and let B C be an insulated line of any length. Let the 
 line A B be drawn of such a length as to be in proportion to the 
 internal resistance of the battery (131), and let the length BC cor- 
 respond, in the same proportion, to the resistance of the line. Let 
 the height of the line A D represent the e. m.f. of the battery. The 
 height of the line B E will now represent the potential of the line at 
 its junction with the battery, while the height of a vertical line, or 
 ordinate, F G, will represent the potential at any other point, as, for 
 instance, F. The potential at any point in the line may be calcu- 
 lated by the following rule : 
 
 As the aggregate resistance of the line and battery is to the resist- 
 ance C F, measured from the distant end of the line, so is the e. m.f. 
 of the battery to the potential at a given point (as F) ; or, 
 
 A C : F C : : A D : F G. 
 
 237. Potentials within the Battery. The distribution of 
 potentials within the battery follows precisely the same law. Fig. 98 
 shows a battery of 4 cells connected to a line of infinite resistance 
 that is, having its distant end open. The potentials are indicated by 
 the upper dotted line, and are, under these conditions, equal to the 
 e. m.f. at each point. The potential rises approximately i volt at 
 each surface of contact between the zinc and the exciting solution, 
 
124 
 
 Telegraphic Circu its. 
 
 the aggregate potential being attained in the fourth cell of the 
 series. 
 
 238. Fig. 99 shows the same battery connected to a line having 
 
 3 
 
 ... 
 
 r 
 
 .1' Jb \\, L 
 
 \\, \\t \ 
 
 FIG. 98. Battery Potentials with Open Circuit. 
 
 EARTH 
 
 the same resistance as itself; that is, the resistances of the internal 
 and the external circuits of the battery (203) are equal. The poten- 
 tial at the end of the line, instead of being 4 volts, is now o, or zero. 
 
 EARTH EARTH 
 
 FIG. 99. Battery Potentials with Closed Circuit. 
 
 The potential at other points in the circuit, measured in volts, is 
 shown in the diagram by corresponding figures. It will be observed 
 that the potential falls in the liquid portion of each cell in proportion 
 to the resistance, in the same way that it does on the line. 
 
 2 39- Fig. 100 shows the. same battery short-circuited, that is, con- 
 nected at each end with the earth by a wire of no appreciable resist- 
 ance. The potential at both ends of the battery being now main- 
 
Potentials in Imperfectly Insulated Circuit. 125 
 
 tained at zero, the potential rises within each cell, as in the previous 
 examples, the maximum point of potential being at the contact of the 
 zinc plate of each cell with the liquid, irrespective of the number of 
 
 EARTH EARTH 
 
 FIG. 100. Potential in Battery on Short Circuit. 
 
 FIG. 101. Potential in Cell on 
 Short Circuit. 
 
 cells in the series. Within each cell the potential falls as before, in 
 proportion to the resistance of the liquid. 
 
 240. Fig. 101 shows a single cell, short-circuited by a wire a b, 
 which is supposed to be so thick and so connected to the earth as 
 to maintain both plates z c at a potential of zero. In this case the 
 difference of potential in the circuit exists only within the liquid, as 
 shown by the diagonal dotted line. In all these varied examples we 
 find the distribution of potentials conforming strictly to Ohm's law 
 as laid down and illustrated in Chapter V. of this work. 3 
 
 241. Potentials in Imperfectly Insulated Circuit. The 
 distribution of potentials in a perfectly insulated circuit has now 
 been explained, but, as a matter of fact, no telegraphic circuit is 
 ever perfectly insulated, and in wet and unfavorable weather the 
 
 FIG. 102. Distribution of Potential on Leaky Line. 
 
 insulation is usually so defective that the normal distribution of 
 potentials is materially modified. 
 
 9 For the illustrations and explanations of the distribution of potentials in tele- 
 graphic circuits given in the foregoing paragraphs (234 to 240), the author desires to 
 acknowledge his indebtedness to LATIMER CLARK'S Electrical Measurement^ pp. 
 14-23 ; one of the very best of the early works on practical telegraphy, but unfortu- 
 nately long since out of print. 
 
126 
 
 Telegraphic Circuits. 
 
 In Fig. 102, let A B represent a telegraphic line, connected at A 
 to the pole of a generator, the e. m. f. of which produces at that 
 point a potential represented by the perpendicular A F. If there is 
 situated at b an escape through an imperfect conductor of known 
 resistance, the fall of potential between F and b\ and between b' 
 and B, may be determined, provided the resistance of the line, A b 
 and b B is known, inasmuch as it will be in proportion to the resist- 
 ance (144). It will be observed that the fall of potential is greater 
 from A to b than from b to B. Fig. 103 shows the distribution with 
 
 fb / c 
 
 FIG. 103. Distribution of Potential on Leaky Line. 
 
 two such points of escape of equal resistance at b and c. Fig. 104, 
 in like manner, shows the distribution with five points of escape, bed 
 ef. In each of these cases, the line at B being in direct connection 
 with the earth, the potential at that point is zero. The difference of 
 potential between each two successive points of escape becomes less 
 and less as the distant extremity of the line is approached, and 
 hence it follows that the quantity or effective strength of current in 
 
 FIG. 104. Distribution of Potential on Leaky Lines 
 
 the line progressively decreases at each point, but that the decrease 
 becomes less and less rapid as the terminal station B is approached. 
 In an ordinary telegraph line the number of points of escape are 
 
Effect of Imperfect Insulation upon Current. 1 2 7 
 
 very numerous, being necessarily equal in number to the points of 
 support, and hence the line of potential, F B, becomes a polygon of 
 a corresponding number of sides, or in fact a regular curve. 
 
 In Fig. 104, therefore, if the potential at the initial point of the 
 line A is assumed at 100 volts, we might find, for example, at suc- 
 cessive points, &' c' d' e'f, the following potentials, with a perfectly 
 insulated and with a leaky line : 
 
 Potential at point. 
 
 Insulated Line. 
 Volts. 
 
 Leaky Line. 
 Volts. 
 
 A 
 
 100.00 
 
 100.00 
 
 b 
 
 83.34 
 
 81.8 
 
 c 
 
 66.68 
 
 64.5 
 
 d 
 
 50.00 
 
 47-8 
 
 e 
 
 33-33 
 
 31.6 
 
 f 
 
 16.66 
 
 15-7 
 
 B 
 
 o.oo o.o 
 
 The less the resistance of the leaks, or the greater the leakage at 
 each point, the more will the curve F B of potentials vary from the 
 normal straight line. 
 
 242. Effect of Imperfect Insulation upon Flow of Cur- 
 rent. The effect of imperfect insulation upon the line, whether 
 general or special, is to largely reduce the resistance of the line, and 
 proportionately increase the quantity of current drawn from the bat- 
 teries by the line, so that the latter are exhausted much more rapidly 
 when the weather is wet. Hence, in working on the closed circuit 
 plan (213, 214), the line current is strongest in wet weather, except 
 near the middle of the line ; but the variation or margin at any sta- 
 tion, when the key is alternately opened and closed at another sta- 
 tion, which constitutes the working efficiency of the line, is very much 
 diminished. This variation or difference of course determines the 
 available strength of signals. The effect of imperfect insulation 
 upon the transmission of the current to a distant station has been 
 referred to in (219). The various electrical characteristics of leaky 
 lines have been found capable of determination by mathematical 
 analysis. 
 
 Since, however good the insulator may be, some small portion of the cur- 
 rent escapes from the line over it down the post to the ground, it is mani- 
 fest that if the line be long, the posts many, and the insulators very poor, a 
 small portion only of the entering current may reach the far end of the line. 
 
 The law which governs this may be thus enunciated : If the current upon 
 the line near the battery be called the entering current, and that upon the 
 distant end near where it enters the ground be called the arriving current. 
 
128 Telegraphic Circuits. 
 
 then the distance to which any stated fraction of the entering current will 
 reach is proportioned directly to the square root of the conductivity of the 
 wires, to the square root of the insulating power of the insulator, and 
 inversely to the square root of the number of poles per mile used. MOSES 
 G. FARMER: See Report on Telegraphic Apparatus at Paris Exposition (1867), 
 by S. F. B. Morse, p. 69. 
 
 243. Resistance and Current in Leaky Lines. When 
 the average resistance of each insulator is known, it is easy to com- 
 pute the actual insulation of the line per mile, or other unit of length. 
 It is only necessary to divide the resistance of a single insulator by 
 the number of insulators, inasmuch as it is simply a case of joint 
 resistance (134). So also, when the resistance per mile of the con- 
 ductor, and the resistance per mile of the insulation are both known, 
 the apparent resistance of the conductor and of the insulation for 
 any length of line may be determined. As the mathematical com- 
 putations in this case are somewhat complex, a compilation of results 
 is given in convenient form for use, in Table X, p. 129. This table 
 shows the apparent conductivity and insulation resistance (as meas- 
 ured from the terminal station) of various lengths of leaky line, from 
 100 to 2,500 units. The table also gives the percentage of any given 
 entering current which will reach a terminal station located at vari- 
 ous distances along the line. Many problems arising in the working 
 of leaky lines may be conveniently solved by means of a table of this 
 kind. 4 
 
 In a well insulated line, the ratio of the conductivity to the insu- 
 lation resistance ought to be as low as i to 80,000. The table is 
 computed upon an assumed ratio of i to 10,000, which is probably 
 as much as can be relied on in rain with the most carefully con- 
 structed glass-insulated lines in our climate, and may be regarded as 
 fairly representative of the actual present practice. 
 
 244. Computation of Working Efficiency of Line. As an 
 example of the use of this table, suppose it be required to determine 
 the comparative working efficiencies of the open-circuit (Fig. ST, p. 
 107) and the closed-circuit system (Fig. 83, p. 108) on a line of 200 
 miles in length, with a conductor of 10 ohms resistance per mile, 
 supported upon 40 poles per mile, the wet-weather value of the insu- 
 lators being 4 megohms each, and the resistance of the instruments 
 
 4 The author desires to express his obligations to Professor Moses G. Farmer for 
 valued assistance in the preparation of this table. The formulas and methods of com- 
 putation are discussed in the following named works : J. GAVARRET : Telegraphie 
 Electrique, 376 ; E. E. BLAVIER : Telegraphic Electrique, ii. 447, 449 ; A. B. KEMPE : 
 On the Leakage of Submarine Cables; Jour. Soc. Tel. Eng., iv. 90 ; H. R. KEMPE: 
 Hand-book of Electrical Testing (3d ed.), 445. 
 
Resistances and Escape upon Leak** Lines. 129 
 
 TABLE X. 
 RESISTANCES AND ESCAPE UPON LEAKY LINES OK VARIOUS LENGTHS. 
 
 [The unit of this table is that length of any line of which the ratio of the con- 
 ductivity to the insulation resistance is as i : 10,000.] 
 
 True Conductivity 
 Resistance. 
 Line to Ground. 
 Units. 
 
 Apparent Conduc- 
 tivity Resistance. 
 Line to Ground. 
 Units. 
 
 Apparent Insulation 
 Resistance. 
 Line open. 
 Units. 
 
 Per cent, of Enter- 
 ing Current reaching 
 grounded end of Line 
 of Resistance as in first 
 Column. 
 
 100 
 
 99.6 
 
 10030 
 
 99-5 
 
 200 
 
 197.2 
 
 5060 
 
 98. 
 
 300 
 
 291. 
 
 3430 
 
 95-7 
 
 400 
 
 379-3 
 
 2630 
 
 92.5 
 
 500 
 
 461. 
 
 2160 
 
 88.7 
 
 600 
 
 535-6 
 
 1850 
 
 84.4 
 
 700 
 
 602. 5 
 
 1630 
 
 79-7 
 
 800 
 
 662. 
 
 1480 74-7 
 
 900 
 
 712. 
 
 1380 
 
 69.7 
 
 1OOO 
 
 760. 
 
 1300 
 
 64.8 
 
 1 100 
 
 798. 
 
 1250 
 
 59-9 
 
 J20O 
 
 830. 
 
 I2IO 
 
 55-2 
 
 1300 
 
 857 ; 
 
 1180 
 
 50-7 
 
 14OO 
 
 880. 
 
 1150 
 
 46.5 
 
 1500 
 
 900. 
 
 1130 
 
 42.5 
 
 I6OO 
 
 916. 
 
 1 1 10 
 
 38.8 
 
 I7OO 
 
 930. 
 
 1090 
 
 35-3 
 
 l800 
 
 942. 
 
 1070 
 
 32.2 
 
 IOXX) 
 
 950. 
 
 1060 
 
 29.2 
 
 2OOO 
 
 960. 
 
 1050 
 
 26.6 
 
 2IOO 
 
 967. 
 
 1040 
 
 24.1 
 
 22OO 
 
 974- 
 
 1030 
 
 21,9 
 
 23OO 
 
 979- 
 
 1024 
 
 19.9 
 
 24OO 
 
 983. 
 
 1018 
 
 16.8 
 
 2500 
 
 987- 
 
 1013 
 
 14.7 
 
 Infinite 
 
 1000. 
 
 1000 
 
 oo. 
 
130 Telegraphic Circuits. 
 
 ioo ohms each. This would give for the line the same ratio of con- 
 ductivity to insulation as that assumed in the table, viz: i : 10,000. 
 The true conductivity resistance of the line from A to B (Fig. 105) is 
 2000 ohms. Assume the keys to be closed at both stations, the 
 
 -*-... o 
 
 FIG. 105. Distribution of Potentials upon Leaky Line (Closed) 
 
 resistances of both instruments being alike, the e. m. f. of the two 
 batteries also equal, and the internal resistance of the batteries to be so 
 small, compared with that of the line, that it may be neglected. The 
 first half of the line, from A to o, will be positive, and the other half, 
 from o to B, negative. When sending to A, the key at B is alter- 
 nately open and closed. 
 
 When key at B is open, the entire length becomes positive, being 
 wholly charged from the positive pole of battery at A (Fig. 106). 
 
 IDW'I'h 
 
 FIG. 106. Distribution of Potentials upon I eaky Line (Open). 
 
 With both keys closed, if a galvanoscope were to be connected 
 between the point o and the earth, it would indicate no current, 
 because the potential at o is zero. Hence the quantity of current 
 going to line from the battery at A will be the same as if the line were 
 connected to the ground in the middle that is, at a point ioo miles from 
 A. Assuming the e. m.f. of the battery to be TOO volts, the quantity 
 of current entering the line at A, by Ohm's law, will be as follows : 
 
 With key closed at B : 
 
 Apparent resistance of ioo miles (1000 ohms) of 
 
 leaky line (as per Table X.) 760 ohms 
 
 Resistance of instrument at A ioo " 
 
 860 " 
 Quantity of current ioo (volts) -?- 860 (ohms) = .1163 (amperes). 
 
Effect of Position of Fault. 131 
 
 With key open at B : 
 
 Apparent resistance of 200 miles (2000 ohms) of 
 
 leaky line (Table X*.) 1050 ohms 
 
 Resistance of instrument at A 100 ' ' 
 
 1150 " 
 Quantity of current 100 (volts) -*- 1150 (ohms) = 0.087 (amperes). 
 
 Thus we have : 
 
 Current in line at A when B is closed 1 163 amperes. 
 
 Current in line at A when B is open 0870 " 
 
 Net efficiency of circuit 0293 " 
 
 Considering next the open-circuit plan, in which the instrument at 
 the sending station is cut out by the key while the signalling current 
 is entering the line : 
 
 With key closed at B : 
 
 Apparent resistance of 200 miles of leaky line + instru- 
 ment at A (100 ohms) = 2100 ohms 967 ohms 
 
 Quantity of current entering line 200 (volts) -f- 967 ohms 
 = 0.206 amperes. 
 
 By fourth column in Table X, 26.6 per cent, of this only will reach the 
 instrument at A : 
 
 26.6 per cent, of .206 is .0548. Hence : 
 
 Current in line at A when B is closed 0548 
 
 Current in line at A when B is open oooo 
 
 Net efficiency of circuit 548 
 
 245. This investigation shows that on a defectively insulated and 
 leaky line, a material advantage is gained by dispensing with the 
 battery at the receiving end of the line, and assembling it all at the 
 sending end. In the case under consideration the difference in effi- 
 ciency with the same line and instruments is as 548 to 293 in favor 
 of the open circuit plan. With the battery constantly on the line, a 
 computation may be made by the aid of the table, which will show 
 that it makes no difference in the working efficiency, whether the 
 battery be placed in equal amount at each terminal station, or 
 whether it be all assembled in the middle of the line. 5 
 
 246. Effect of Position of Fault. The detrimental effect of 
 a special defect in insulation or cause of escape, such as contact 
 with the branch of a tree or a wet roof, is greatest when it is situated 
 
 s CROMWELL F. VARLBY : Report on Lines of Western Union Telegraph Co. (Ms.), 
 1867. 
 
132 Telegraphic Circuits. 
 
 midway between the terminal stations of the line, assuming the bat- 
 teries and instruments to be alike at each end. 
 
 When the fault is nearer one. end of the'line, the station farthest 
 from it will receive the weakest signals, and the station nearest it the 
 strongest signals. 
 
 In increasing the battery power,, in order to work over a special 
 defect or fault in insulation, the addition should be made to the sta- 
 tion nearest the fault. 
 
 247. Best Position of Batteries in Circuit. If the insu- 
 lation of a line were perfect at all times, the position of the battery 
 in the line would be immaterial. As all lines are ordinarily subject 
 to more or less escape or leakage throughout their length, it is 
 obviously not advisable, except upon comparatively short lines, to 
 place all the battery at one end ; for in such case the signals will be 
 received with much more difficulty at the station where the battery is 
 situated, than at the opposite end of the line. The usual arrange- 
 ment of a battery at each end is altogether preferable. 
 
 248. Intermingling of Currents on Different Lines. The 
 escape of the current through the insulators, poles, and cross-arms 
 from one wire to another 'n wet -weather, known as cross-fire, is a 
 far more prolific cause of interference in the working of lines than 
 the mere leakage to ground. This effect is sometimes miscalled 
 induction. Weather-cross is perhaps a more appropriate term. 
 
 As electric currents always flow in greatest quantity in the direc- 
 tion of the least resistance, the tendency is for the currents to escape 
 from a long circuit into a short one, or from a wire of higher into 
 one of lower resistance. A simple escape to ground, if not too 
 serious, may be overcome by the judicious application of increased 
 battery-power ; but when transverse leakage or cross-fire exists 
 between different wires running upon the same line of poles, any 
 attempt to increase the battery, in order to improve the working of 
 one wire, produces a detrimental effect upon the working of all the 
 others parallel to it. Upon the occurrence of a sudden shower, the 
 effects of cross-fire are usually manifested sooner than the escape to 
 ground, because the horizontal cross-arms are wet and become par- 
 tial conductors sooner than the vertical pole. 
 
 249. Remedy for Cross-Current. This difficulty may be 
 overcome by attaching a ground wire to each pole, the upper end of 
 which is wrapped around the central portion of each arm. These 
 wires act to intercept the currents of leakage passing from one wire 
 to another, and to convey them to the earth. The battery may then 
 be increased as much as desired on any one wire without interfering 
 
Value of Poles and Cross-Arms as Insulators. 133 
 
 with the others. It is true that the pole, even when wet, has some 
 little value as an insulator, which is lost by this appliance, but the 
 gain in the other direction much more than compensates for it. 
 
 250. The results of defective insulation, in causing the mixture of 
 currents between different wires on the same line of posts, are much 
 more detrimental near the ends of the circuits than in the middle 
 portions ; and as the terminals of the lines are almost invariably in 
 large towns and cities where the insulation is usually much worse 
 than elsewhere (232), the evil is aggra- 
 vated accordingly. Much would be 
 
 gained, therefore, by applying ground- 
 wires to the poles even for a distance 
 of 25 miles out from each terminus. 
 
 251. Value of Poles and Cross- 
 Arms as Insulators. Tests made 
 many years since to determine the aver- 
 age resistance, in wet weather, of the 
 pin-and-glass insulator, the cross-arm, 
 and the pole respectively, gave some 
 interesting results. The tests were made 
 
 from New York to Philadelphia (99 miles), and to Boston (236 
 miles). The following, in connection with Fig. 107, will explain the 
 method employed : 
 
 Let a = the resistance of half the arm. 
 
 Let b = the average resistance of the insulator and supporting pin. 
 
 Let c = the resistance of the pole. 
 
 The following measurements were made : 
 
 (1) Resistance between No. I wire and the ground. 
 
 (2) Resistance between No. i and No. 2 wire. 
 
 The first gave a 4- b + c. 
 
 The second gave a + a 1 + b + b' , 
 
 Add together the ground tests of No. i and No. 2, gives 
 a + a 1 + b + b' 2 c. 
 
 By contact test a + a' + b + b' . 
 
 Subtract the latter from the former, and divide by 2 gives resistance of pole. 
 
 c 
 The mean of a number of tests gave for the per cent, value of : of 
 
 FIG. 107. Resistance of Insulators, 
 Poles, and Arms. 
 
 & -f b 
 
 the total insulation : 
 
 Maximum 22 
 
 Minimum n 
 
 Mean. . 15 
 
134 
 
 Telegraph ic Circu its. 
 
 The insulating power of the wet pole added to that of the insulator and 
 cross-arm was found to be as follows : 
 
 \7I 
 
 New York to New Haven.. 
 New York to Philadelphia., 
 Mean 
 
 15 to 22 per cent, 
 ii to 12 per cent. 
 15 per cent. 
 
 A test from New York to Boston between two wires, 
 a and b, placed one above the other, as in Fig. 108, on 
 insulators and brackets on opposite sides of the same 
 pole, gave the following mileage insulation : 
 
 Wire a to ground 3, 050 ohms per mile. 
 
 Wire b to ground 3, 700 " " " 
 
 Wire a to b through the pole 
 
 900 
 
 6,750 
 
 5,850 
 
 900 
 
 c = - = 450 ohms per mile. 
 
 FIG. 108. Resistance of 
 
 Vertical Pole. 
 
 _ . . ,. . r 
 
 From this it appears that the application of 
 ground-wires to the poles would reduce the total 
 insulation about 15 per cent., and weaken the signals perhaps 3 per 
 cent. ; but, on the other hand, it would eliminate disturbing currents 
 amounting to about 18 per cent, of the total strength of signals. 
 
 252. Tests of Resistance of Cross- Arms. The following 
 measurements were made of cross-arms taken down from pole-lines 
 in New York City. They show the insulation resistance per mile of 
 40 arms : 
 
 All four surfaces wet with sponge .................. 3, 120 ohms. 
 
 Soaked one day, left to dry one day, and then wet. . . 2,680 " 
 
 Painted three years since .......................... 6,150 " 
 
 Same washed ..................................... 9, 166 
 
 Very dry ............................... 11,00010330,000 " 
 
 Newly painted .................................... 7,214 " 
 
 Unpainted for many years ......................... 4,300 " 
 
 Same after having been well washed ................ 13,657 " 
 
 Dry .............................................. 80,000 " 
 
 Arms and pins together (wet) ...................... 3,686 '* 
 
 253. Tests of Glass Insulators. Measurements made of 
 dirty and soot-covered glass and pin insulators, taken down in New 
 York, resulted as follows : 
 
 Dipped in water once (per mile of 40) ................. 23,220 ohms. 
 
 Dipped in water 4 times (per mile of 40) ............... 56,400 
 
 New insulator and pins direct from supply department.. 66,600 " 
 
Best Method of Improving Efficiency. 135 
 
 These figures show in a striking manner the surface deterioration 
 of glass insulators by exposure to the smoke and dirt of a large city. 
 Cleaning them nearly tripled their insulating power. 5 
 
 254. Importance of High Working Efficiency. The 
 importance of maintaining in telegraph lines as high a ratio of insu- 
 lation to conductivity resistance as possible, is shown in a striking 
 manner by the figures given in Table X. For example, suppose it 
 were required to determine the effect of increasing the ratio of effi- 
 ciency of a given circuit from i : 10,000, the basis on which the table is 
 computed, to i : 20,000. This might be effected, either by doubling 
 the resistance of the insulators, or by halving the resistance of the 
 line ; that is, 8 megohm insulators might be used instead of 4, or wire 
 of 5 ohms per mile instead of 10, either of which would affect the 
 ratio in like manner. But the resistance of the line, referred to in 
 (242), taken in units of the first column of Table X, is now only 
 1,000 instead of 2,000, and the percentage of received currents is 
 therefore raised from 26.6 to 64.8. On a line of 250 miles, it would 
 be raised from 14.7 to 52.9; that is, more than 3^ times as much 
 current would be received at the end of the line. 
 
 255. Best Method of Improving Efficiency. A line of 
 400 miles of No. 9 iron wire of 15 ohms conductivity resistance per 
 mile, and carried upon glass insulators giving 4.5 megohms each in 
 very unfavorable weather, with 30 poles per mile, would have an effi- 
 ciency ratio (242) of i : 10,000, the same as that assumed in Table X. 
 The true conductivity of the line would be 6,000 ohms, and the per- 
 centage of the entering current which would reach the distant end 
 would be only 2.15. If a copper wire of 5 ohms per mile were sub- 
 stituted, without changing the insulation, the percentage of current 
 received would at once be increased from 2.15 to 26.6, or more 
 than 10 times as much, the efficiency ratio being now i : 30,000. 
 The cost of the respective wires for 400 miles would be approxi- 
 mately as follows : 
 
 71,120 Ibs. of hard copper wire, .20 cents $14,344 
 
 128,000 Ibs. of galv. iron- wire, .05 cents 6,400 
 
 Difference in cost $7,944 
 
 The same or a better result may be more advantageously reached 
 by improving the insulation. If, for example, instead of the 4.5 
 megohm glass insulators, the German porcelain insulators of Fig. 
 92, p. 118, were used, the minimum resistance of which, according 
 
 s CROMWELL F. VARLEY : Report on Lines of Western Union Telegraph Co. 
 (Ms.), 1867. 
 
136 
 
 Telegraphic Circuits. 
 
 to the test, p. 120, is 19 megohms, we may safely assume that the 
 insulation will be three times as high as with the glass. This will 
 give us, with the i5-ohm wire, an efficiency ratio per mile of 
 15 : 450,000 or i : 30.000, as before. 
 
 The comparative cost would then be approximately as follows : 
 
 12,000 German porcelain insulators (Fig. 92), .25 cents $3,ooo 
 
 12,000 Best glass and bracket (Fig. 88), .05 cents 600 
 
 $2,400 
 
 It appears, therefore, that the operative value of a long line in wet 
 weather may be increased as much by expending $2,400 in improv- 
 ing its insulation, as by expending $7,944 in improving its conduc- 
 tivity. On the other hand, it must be taken into consideration that 
 when the line is designed to be employed for multiple transmission, a 
 marked advantage results from high conductivity, altogether irre- 
 spective of the question of insulation efficiency. Several different 
 strengths or values of current, in this case, require to be distin- 
 guished from each other by the selective action of the receiving 
 instruments, and the certainty with which this can be effected 
 depends largely upon the maximum volume of current which the line 
 is capable of transmitting. The interference arising in fine weather 
 from static induction (314) is also relatively much less marked upon 
 lines of high conductivity. 
 
 256. The beneficial effects of improving the insulation on long cir- 
 cuits are forcibly exhibited in the following table, which contains the 
 results of computations made by Moses G. Farmer. 6 
 
 TABLE XI. 
 
 Distances in miles to which a stated percentage of entering current will reach, 
 on a line of 18 ohms conductivity resistance per mile, with insulators of various 
 resistances. 
 
 Per cent, of en- 
 tering current re- 
 ceived. 
 
 Insulation Resistance (Megohms per Insulator) 30 Insulators 
 per mile. 
 
 I 
 
 4 
 
 9 
 
 16 
 
 36 
 
 100 
 
 1000 
 
 1600 
 
 10% 
 25 
 50 
 75 
 90 
 
 125 
 89 
 58 
 36 
 22 
 
 258 
 178 
 116 
 73 
 45 
 
 386 
 267 
 174 
 109 
 67 
 
 5i6 
 356 
 232 
 146 
 9 
 
 774 
 534 
 348 
 219 
 
 T35 
 
 1290 
 890 
 
 580 
 365 
 
 235 
 
 4094 
 
 2837 
 1850 
 
 1161 
 766 
 
 5160 
 356o 
 2820 
 1460 
 900 
 
 6 The Telegrapher, v. 269. 
 
Best Method of Improving Line Efficiency. 137 
 
 These results seem scarcely credible to those who have accus- 
 tomed themselves to the belief that the defects of insulation on our 
 existing lines are unavoidable, and that the only available remedy is 
 the costly one of increased conductivity. Yet the correctness of the 
 theory is abundantly proved by the working of such a line, for exam- 
 ple, as the Atlantic Cable of 1866, which was 2,185 m il es in length ; 
 had a resistance of about 3.7 ohms per mile, a total of over 8,000 
 ohms ; and which worked well with an c. m. f. of 10 volts, because 
 of its high insulation. It is also a familiar fact that any good line 
 can be worked at full speed for a distance of more than 1,000 miles 
 in cold dry weather, when the leakage due to imperfect insulation is 
 almost imperceptible even with sensitive measuring instruments. 
 
CHAPTER VIII. 
 
 EQUIPMENT OF AMERICAN TELEGRAPH LINES. 
 
 257. Apparatus Essential in Telegraphy. It has been 
 stated that the art of electric telegraphy consists in the production, 
 control, and organization of electric signals, which may be either 
 visible or audible (2). The system of telegraphy now generally 
 used in America under the name of the " Morse," produces audible 
 signals at a distance by means of an instrument called a sounder, 
 which comprises an electro-magnet ; a vibrating armature ; and a 
 key consisting essentially of a lever and contact-points, whereby the 
 transmitting operator is enabled to interrupt and restore the circuit 
 with convenience and rapidity, for the purpose of forming the con- 
 ventional signals. 
 
 258. Construction of the Key. The key is made in many 
 different forms, not essentially differing in principle. Its essential 
 portions consist of the lever, the finger-knob, the spring, the switch or 
 circuit-closer and the base. The lever, which was formerly made of 
 cast brass, is now more usually punched from sheet steel, which 
 renders it not only stronger but of less weight and more easy to be 
 manipulated with rapidity. 
 
 A pattern of key much used is shown in Fig. 109. The lever A, 
 4 or 5 inches in length, slightly curved, is provided with trunnions 
 at G, which turn between adjustable set-screws D D. The lever has 
 a small vertical reciprocating movement upon its axis, limited in one 
 direction by the adjustable set-screw F, and in the other by a platinum 
 contact-point c inserted in a brass stud C, insulated from the frame M 
 of the key. The finger-knob or button B, usually of non-conducting 
 material, enables the key to be conveniently depressed at pleasure 
 by the finger of the operator. This action brings a platinum contact- 
 point d, inserted in the under side of the lever A, into contact with 
 the one above mentioned which forms a part of the anvil. 1 One of 
 
 1 Platinum is used for these and other contact-points in electrical apparatus, for the 
 reason that the infusible properties of this metal prevent it from being oxidized by the 
 electric spark, which tends to pass between separated conductors whenever the circuit 
 is broken. This spark, in the case of the key, is principally due to the inductive eft's- 
 
 138 
 
Modifications of the Key. 
 
 the circuit-wires P is clamped to the brass rod J by means of a 
 clamp-screw L underneath the table, this rod being in metallic con- 
 nection with the base. The other circuit-wire is attached by means 
 of another clamp-screw K to a similar brass rod I, connected with 
 the anvil, and insulated from the frame. When the key-lever A is 
 depressed, the circuit between the wires P and N is closed, precisely 
 as if the wires themselves had been brought into contact with each 
 other. 
 
 When the pressure of the finger is withdrawn, the adjustable 
 spring E beneath the lever A, restores the latter to its normal 
 
 . 109. Bunnell's Steel- Lever Key. 
 
 position. The upward pressure of this spring is adjusted by means 
 of a set-screw H. When the key is not in use, the main circuit is 
 closed by shoving the pivoted switch-lever S into a recess formed 
 between the lip of anvil C and the frame M, thus establishing an 
 electrical connection between the wires P and N, notwithstanding 
 the separation of the contact-points c and d. 
 
 259. Modifications of the Key. Of late years other forms 
 of keys have been much used, in which trunnions are dispensed with. 
 One of these is shown in Fig. no. The lever is secured to a rear- 
 
 charge of the electro-magnets in the circuit ; when there are a great number of these, 
 the spark sometimes becomes very troublesome (196). Iridium, another infusible 
 metal, is sometimes used instead of platinum. 
 
140 Equipment of ~1 nit rican Telegraph Lines. 
 
 wardly extending flat steel spring, the opposite end of which is firmly 
 fastened by screws to the base. An adjustable set-screw passes 
 through a hole in the center of the spring and its nut may be set to 
 
 FIG. no. Western Electric Key. 
 
 bear upon its upper surface, thus enabling its flexibility to be 
 regulated as desired. A second check-nut is capable of adjustment 
 to regulate the stroke, or extent of vertical vibration of the key-lever. 
 A modification which is applicable to all keys, consists in placing 
 two binding-screws, one of which is insulated, upon the top of the 
 base as in Fig. in, to which the wire connections are made, thus 
 avoiding the necessity of boring holes through the table, which is 
 sometimes objectionable. 
 
 FIG. in. Victor Key. 
 
 260. Adjustment of the Key. In adjusting a key for work, 
 the best result will usually be attained by giving the lever a small 
 movement with a moderate upward spring-pressure. Trunnion keys 
 should be carefully adjusted, so as to prevent unnecessary lateral 
 movement on the one hand, and unnecessary friction on the other. 
 
The Sounder. 
 
 141 
 
 A trunnionless key, working upon knife-edged bearings, now very 
 extensively used and known as the "Victor," is shown in Fig. nr. 
 By this device, friction and weight are reduced to a minimum, while 
 adjustment is rendered more convenient. In this and in the preced- 
 ing pattern of keys, the electrical contact being made through 
 continuous metal, is more perfect than is possible when trunnions 
 are used. 
 
 261. The Sounder. The essential parts of this instrument, 
 shown in outline in Fig. 112, are an electro-magnet E, usually about 
 
 FIG. 112. Elevation of Sounder. 
 
 the size and proportion of .that shown in Fig. 69, page 91, and an 
 armature A fixed transversely upon a brass lever B about 3 inches in 
 length, fitted with trunnions at C and mounted between transverse 
 set-screws in the same manner as the key. Two other set-screws D 
 and F form adjustable stops, which limit the vertical motion of the 
 lever in each direction. When the circuit is closed through the 
 electro-magnet, the armature is strongly attracted, and is thereby 
 made to strike forcibly against a sounding-post or bridge G through 
 which the vibration is imparted to the table upon which the instru- 
 ment is secured. When the magnetism disappears, the lever is 
 thrown against the upper stop F by the recoil of an adjustable spring 
 H. The operator interprets the signals by mentally noting the 
 difference in character between the sounds of the down-stroke and 
 the up-stroke, and by estimating the space of time intervening 
 between them, as will be hereinafter explained (378). Fig. 113 is a 
 common pattern of sounder, about two-thirds the actual size. The 
 helices of the electro-magnet are wound with insulated wire, the 
 thickness and convolutions of which depend upon the strength of 
 
142 Equipment of American Telegraph, Lines. 
 
 current with which the instrument is designed to be used. When 
 intended for direct working, in which case the sounder is actuated by 
 the current received over the line Irom the distant station, the helices 
 are wound with wire which may differ in gauge from number 22 to 32 
 and even 36 (see table, page 94) according to the length or resistance 
 of the circuit in which they are intended to be used. Ordinarily the 
 sounder is operated by a local battery, consisting of a single gravity 
 cell (Fig. 4, page 5), in which case its electro-magnet is wound with 
 number 24 wire to a resistance of about 4 ohms. 
 
 FIG. 113. Sounder. 
 
 262. Short Line Instrument. When the length of the line 
 on which the sounder is to be used does not exceed 40 or 50 miles, 
 a convenient and compact form of apparatus, consisting of a sounder 
 and key mounted on one base, with proper electrical connections as 
 shown in Fig. 114, and having its electro-magnet wound to a resist- 
 ance of 20 or 30 ohms, may be employed with advantage. 
 
 263. Adjustment of the Sounder. The adjustment of the 
 sounder may be best effected as follows: First, loosen the stop 
 D until the armature A rests directly upon the poles of the electro- 
 magnet. Second, set the trunnion-screws upon which the lever B 
 turns, as tightly as possible without in the least binding the axis. 
 This can be determined by lifting and letting fall the lever, having 
 
Pocket Apparatus. 
 
 previously slackened the spring H. It should drop freely when 
 released. Third, lay a piece of paper between the poles of the 
 magnet and the armature, and close the circuit through the magnet, 
 
 FIG. 114. Combination Sounder and Key. 
 
 so that the attraction exerted upon the armature will clamp ttv 
 paper. Fourth, adjust the screw-stop D, until the armature i* 
 raised just enough, to permit the paper to be drawn out without 
 friction. Fifth, adjust the stroke by means of the screw F. 
 
 FIG. 115 Pocket Sounder and Key. 
 
 Sixth, strain the retracting spring H until the character of the 
 sounds produced by the up and down strokes of the lever is satis- 
 factory. 
 
144 Equipment of American Telegraph Lines. 
 
 264. Pocket Apparatus. Fig. 115 represents a convenient, 
 compact, and exceedingly portable form of direct-working sounder, 
 having a key attached, so as to form a complete apparatus for send- 
 ing and receiving communications. The engraving is nearly the 
 actual size of the instrument, which, together with its case, weighs 
 but a few ounces, and can be readily carried in the coat-pocket. 
 
 265. Box Sounder. Fig. 116 shows still another combined key 
 and sounder, in which the electro-magnet is of standard dimensions, 
 and is enclosed within a wooden box, the resonance of which 
 materially increases the volume of sound made by the strokes 
 of armature-lever. This apparatus, being complete in itself, is 
 often found useful in the railway telegraph service, for establishing 
 
 KIG. 116. Combination Box Sounder and Key. 
 
 temporary communication at any point along the line in case of 
 accident. 
 
 266. Working by Relay and Local Circuit. When the 
 line is of considerable length and corresponding resistance (118), or 
 its insulation is defective, as is usually the case in practice (232), 
 the main line current may be too feeble or too variable to satis- 
 factorily operate the receiving instrument. This inconvenience is 
 avoided by making use of an intermediate receiving instrument 
 called the relay, which is included in the main circuit. Its 
 armature-lever has only to perform the function of opening and 
 closing the circuit of a local battery at the receiving station, by 
 which means the sounder can be made to produce any required vol- 
 ume of sound. 
 
 267. Construction of the Relay. The relay consists of an 
 electro-magnet, having its armature delicately poised, so as to be 
 free and capable of being acted upon by minimum magnetic attrac- 
 tion. Fig. 117 represents a design which is largely used. 
 
 Fig. 118 represents the working parts of a relay in outline. The 
 electro-magnet M has its soft iron cores, usually 2 in. long and 
 
Construction of the Relay. 
 
 H5 
 
 \\ in. diameter, sc^-wrd into a yoke Y, 2 in. long and } in. in thick- 
 ness. The standard resistance of the coils is about 150 ohms, and 
 the average number of convolutions of wire in the coils 8,500. The 
 
 FIG. 117. Western Union Relay. 
 
 usual magnetizing force is about 200 ampere-turns (176). The 
 front ends of the magnet are supported in a vertical metallic frame 
 F, the foot of which is firmly secured to a hard-wood base, by screws 
 
 r 
 
 FIG. 1 18. Elevation of Relay. 
 
 from beneath. Two circular openings are formed in this frame, 
 large enough to permit the helices to pass freely through without be- 
 ing fastened in any way. The yoke end of the magnet is supported at 
 
146 Equipment of American Telegraph Lines. 
 
 S by a right and left screw, or a straight screw with two check-nuts 
 passing through a brass pillar fixed upon the base. This device is 
 capable of imparting to the electro-magnet M a limited horizontal 
 advance or retrograde movement. The armature A in front of the 
 poles is fixed transversely to the upright lever B, the lower end of 
 which is mounted upon a steel arbor turning between two adjustable 
 set-screws, mounted upon standards H projecting from the lower part 
 of the frame F. The armature-lever and armature are permitted a 
 limited movement to-and-fro upon the axis, responsive in one direc- 
 tion to the attraction of the electro-magnet, and in the other the 
 retractile force of the spiral spring T. This motion is limited in one 
 direction by the adjustable screw-stop C, and in the other by a fixed 
 stop of non-conducting material placed within the slotted projection 
 D, through which the lever B passes freely, not touching anything 
 but the stops. The spring T is attached at one end to the lever B 
 by a hook, and at the other end to a thread which winds upon a 
 spindle V provided with a milled head. (See Fig. 117.) This 
 spindle is supported in a socket upon the end of a horizontal brass 
 rod, which slides through a pillar and may be fastened in any 
 required position by a check-screw. The object of this device is to 
 enable the tension of the spring T to be adjusted through a some- 
 what wide range, the necessity for which will be hereinafter ex- 
 plained. 
 
 The electrical connections of the relay are as follows : Upon the 
 base are four binding-screws for the attachment of wires. Only three 
 of these are visible in Fig. 117, the other being concealed by the 
 electro-magnet M. The insulated copper wires projecting from the 
 helices of the electro-magnet are seen to pass down through the 
 wooden base, underneath which they are connected to the two 
 right-hand binding-posts, so that current entering at one binding- 
 post, after traversing both helices of the electro-magnet, returns to 
 the other and passes on. 
 
 It has been explained that the function of the relay is simply to 
 break and close the independent local circuit in which the sounder 
 is included, whenever the main circuit is broken and closed, or in 
 other words, to repeat the signals of the main circuit into the local 
 circuit. To this end the armature-lever A is carefully insulated 
 from the frame F by a non-conducting bushing interposed between 
 the lever and the axis upon which it turns. A wire leads under- 
 neath the base from one binding-screw to the support of the arma- 
 ture. Another thin copper wire W, coiled into a spiral, connects 
 the armature-lever with its support, being attached to the former by 
 
Adjustments of the Relay. 147 
 
 a small screw seen in the figure just above the axis. When the 
 armature is attracted by the electro-magnet, a platinum contact- 
 point near the top of the lever B (Fig. 118) is brought in contact 
 with a corresponding platinum point which forms the tip of the 
 adjustable screw-stop C. The stop C is in electrical connection 
 with the brass frame F, and this is in turn connected with the ex- 
 treme left-hand terminal binding-post by a wire under the base. 
 Hence it necessarily follows that whenever the two platinum points 
 are brought in contact by the advance movement of the armature- 
 lever in response to the attraction of the electro-magnet, a connec- 
 tion will be formed between the two terminals completing the local 
 circuit through the sounder. 
 
 268. Adjustments of the Relay. The adjustments of the 
 relay are three in number : first, the stroke, or extent of the to-and-fro 
 movement of the armature ; second, the antagonistic action of the 
 retracting spring; and third, the distance between the armature and 
 the poles of the magnet. 
 
 The first-mentioned adjustment is effected by the front screw-stop 
 C, which is movable, the rear stop being fixed. The maximum sepa- 
 ration between the platinum contacts ought never to exceed ^ of an 
 inch, and in case the actuating current is weak, it should be made as 
 much less than this as possible. Under ordinary conditions this 
 adjustment, once properly made, seldom requires alteration. The 
 second adjustment particularly requires judgment and skill on the 
 part of the operator. When the attraction of the electro-magnet is 
 very strong, as is usually the case in wet weather (242), the armature 
 will not fall off promptly, and hence the tension of the spring must 
 be increased by turning the milled head, thus winding the thread and 
 straining the spring. The spring T must never be wound around the 
 spindle V. When the thread has all been taken up, the spindle 
 must be removed to a greater distance from the armature, by loosen- 
 ing the check-screw and sliding the rod upon which it is mounted 
 through the post to a sufficient distance and then clamping it again. 
 In extreme cases the tension cannot be sufficiently increased by this 
 means, and it then becomes necessary to resort to the third adjust- 
 ment, which consists in withdrawing the magnet by the screws, so as 
 to increase the distance between the poles of the electro-magnet and 
 the armature. 
 
 269. The Register. This apparatus for recording the signals, 
 was originally regarded as an essential part of the Morse system. 
 It is now but little used except at small stations and on railway lines. 
 It consists essentially of a pair of grooved rollers moved at a 
 
148 Equipment of American Telegraph Lines 
 
 uniform rate by a system of controlled clock-work driven by a weight 
 or spring. A long narrow strip or ribbon of paper, taken from a roll, 
 passes between adjustable guides, and thence between the grooved 
 rollers, the motion of which draws it along from right to left at a 
 uniform rate. An electro-magnet is provided with a lever similar to 
 that of the sounder (261), and armed at the extremity with a style or 
 point of hard steel, which works in a groove rn the upper roller. As 
 the strip of paper passes between the rollers, a raised line is 
 embossed upon the upper surface of the paper whenever the mark- 
 ing point is forced into the groove by the attraction of electro-mag- 
 net exerted upon the armature at its opposite end of the lever. A 
 retracting spring is provided with adjustments similar to those 
 described in connection with the sounder. The paper-guide is 
 capable of lateral adjustment, so that the same strip of paper may, 
 if desired, be used several times, each successive line of characters 
 lying parallel to, and in front of the preceding one. 
 
 FIG. 119. European Pattern Register. 
 
 270. Fig. 119 shows one of the most modern forms of the regis- 
 ter, in which the clock-work is propelled by a coiled spring, instead 
 of by a weight, as in the instruments formerly made. The ma- 
 
Adjustments of the Register. 
 
 149 
 
 chinery is entirely enclosed in a brass case with plate-glass panels, so 
 as to exclude dust. The end of the strip of paper is inserted 
 through the guide and between the rollers while the clock-work of the 
 register is in motion. The rate of speed at which the paper moves 
 may be varied, within certain limits, by means of a governor acting 
 
 FIG. 120. Combination Victor Key, Relay, and European Register. 
 
 upon the retarding or controllling device of the clock-work. The 
 register, relay, and key, are sometimes combined upon a single base 
 with their necessary connections, as in Fig. 120. 
 
 271. Adjustments of the Register. The armature must be 
 so adjusted as not to come quite in contact with the poles of the 
 electro-magnet (262). After the set-screw which limits the move- 
 ments of the armature toward the electro-magnet has been properly 
 adjusted, the armature should be held down, either by closing the 
 local circuit through the electro-magnet or by the finger ; the register 
 is then started, allowing the paper to run, and the marking-point 
 adjusted, by turning its milled head until a continuous uniform line 
 is produced upon the upper surface of the paper, by the action of the 
 style between the groove and the roller. The embossed line should 
 not be made any deeper than to enable it to be distinctly seen when 
 
150 Equipment of American Telegraph Lines. 
 
 placed in a transverse light in front of a window. The final adjust- 
 ment is that of the set-screw which limits the movement of the 
 armature away from the electro-magnet, which should be so fixed 
 that the marking-point will just clear the paper when released by the 
 breaking of the circuit. 
 
 272. Causes of Defective Marking. Imperfect marks will 
 result if the style does not work accurately in the groove of the 
 upper roller. This defect is usually due to the working loose of the 
 screws which form the transverse bearings of the axis of the marking 
 lever, so as to permit too much lateral play, and may obviously be 
 remedied by proper adjustment (260). When such adjustment has 
 been effected it should be let alone. The unnecessary alteration of 
 the adjustment of the pen-lever is frequently the cause of much 
 trouble to inexperienced operators. 
 
 273. Ink- Writing Register. A form of register now much 
 used is shown in Fig. 121, in which the characters are marked upon 
 the upper surface of a narrow 
 
 strip of paper by means of a small 
 sharp - edged jockey - wheel, driven 
 by the clock-work and supplied with 
 ink by means of a felt roller sat- 
 urated with thick, oily ink, which 
 revolves in contact with it, being 
 
 FIG. 121. Ink- writing Register. 
 
 held thereto by a spring. A knife-edge on the end of the armature- 
 lever, lifts the slack of the paper into forcible contact with the 
 tinder edge of the revolving inked jockey-wheel, whenever the arma- 
 
Circiiits of the American System. 151 
 
 ture is attracted, and thus the characters are plainly recorded in 
 black ink. 
 
 274. Circuits of the American System. Telegraphic cir- 
 cuits in the United States and Canada are almost universally arranged 
 upon the modification of the closed-circuit system, shown in Fig. 83, 
 page 1 08. If an operator at any station desires to transmit a com- 
 munication, he first opens the switch of his key and interrupts the 
 flow of current throughout the line. This causes the armatures of all 
 the relays in the circuit to fall off. He then proceeds to manipulate 
 his key, by closing and breaking the circuit at accurately timed 
 intervals, so as to form the conventional characters of the telegraphic 
 code in the order required to spell out his communication. During 
 this operation, the armatures both of his own and of all the other 
 relays in the circuit, as well as those of the registers or sounders con- 
 nected therewith, will respond instantaneously to every movement of 
 the key, and consequently the communication may be copied from the 
 sounder or register by an operator either at any one station, or if 
 required, at all the stations simultaneously. As the receiving 
 instrument of the sending operator normally responds to every move- 
 ment of his key, it is evident that the receiving operator at any 
 station may interrupt him at any time, by opening his own key, 
 and thus breaking the circuit in another place. The sending oper- 
 ator instantly perceives such an interruption, by reason of the failure 
 of his relay and sounder to respond to the movements of his own 
 key. 
 
 275. Arrangement of Apparatus at a Way-Station. 
 The simplest complete combination of apparatus is that found at an 
 intermediate or way-station having but a single main wire. It com- 
 prises one set of instruments, viz : a key, sounder or register, relay, 
 local battery, switch, lightning arrester, and the wires connecting the 
 different parts of the apparatus. The manner in which these are 
 usually arranged and connected with each other, and with the line, 
 will be understood by reference to Fig. 122, which represents a com- 
 plete way-station. 
 
 The sounder, relay and key may be conveniently placed upon a 
 table about two feet by three in size. The sounder, or its equivalent 
 the register, is best placed in the middle of the length of the table, 
 having the key on the right and the relay on the left. The knob of 
 the key should be about 12 in. from the front edge of the table. 
 The switchboard is most usually placed in an upright position upon 
 the wall above the table, or in any convenient position. The switch- 
 board is not absolutely necessary, but it is a very convenient device 
 
152 Equipment of American Telegraph Lines. 
 
 for making the necessary changes in the connections of the wires. 
 In the form most commonly employed (see Fig. 131) a device is used 
 similar to that described in connection with the rheostat (Fig. 43, p. 
 
 TO NEW YORK 
 
 TO PHILADELPHIA 
 
 L 1 
 
 SWITCHBOARD 
 
 
 
 r i ^ 
 
 
 
 
 \ 
 
 i 
 
 x , ,'" I 
 
 .1 
 
 / 
 
 A A 
 
 1 ' 
 
 
 
 
 0-- 
 
 / i \-J\ 
 
 
 RELAY 
 
 
 SOUNDER 
 
 fr^ 
 
 
 
 
 O~ 
 
 
 TABLE 
 
 KEY 
 
 LOCAL BATTERY 
 
 FIG. 122. Diagram of Way-Station. 
 
 GROUND 
 
 51), a number of metallic pegs with insulating handles adapted to be- 
 inserted between the edges of thick plates of brass, between which 
 they form an electrical connection. 
 
 276. Connections of Apparatus of Way-Station. The 
 way-station in the diagram Fig. 122, may represent for instance, 
 Trenton, N. J.; L being the line-wire from New York to Trenton, 
 and L 1 , the line-wire from Trenton to Philadelphia. The line-wires 
 are extended into the station building by leading-in wires properly 
 insulated, which are connected with the binding screws i and 2 of" 
 
Manipulation of tkc Switchboard. 
 
 153 
 
 the switch. These binding screws aie mounted upon vertical me- 
 tallic bars secured to the wooden back-board v see Fig. 131). Of 
 the instrument wires i l leads from the binding screw 4 of the switch 
 to one of the terminal screws of the key. From the other terminal 
 screw of the key, the wire i extends to the first right-hand main 
 terminal of the relay; the other instrument wire / a unites the bind- 
 ing screw 5 of the switch to the second right-hand terminal of the 
 relay; a wire g leads from the binding screw 3 of the switch to the 
 ground (210). The wires of the local or office circuit are run as 
 follows : From the local battery, the wire e runs to the first left-hand 
 (local) terminal of the relay; the wire/runs from the second left- 
 hand (local) terminal of the relay to one terminal of the sounder or 
 register ; and finally the wire h runs from the remaining terminal of 
 the sounder or register to the other pole of the local battery. It 
 is quite immaterial which pole of the battery is connected to the 
 relay and which to the sounder. 
 
 277. Manipulation of the Switchboard. The various 
 changes which may be made upon the one-line switch for different 
 purposes are as follows : 
 
 (i.) To cut out the Apparatus. Insert pegs connecting i and 2 
 with 6, as in Fig. 123. The main-line current now passes from the 
 4- pole of the main battery at New York through the instrument at 
 that station, and thence over the line L to i, and through 6 to 2, 
 thence over the line L 1 , and through the apparatus at Philadelphia to 
 the pole of the main battery at that place, and thence to the 
 ground. The - - pole of the New York battery is also connected 
 with the ground, and therefore the circuit is complete. When thus 
 
 FIG. 123. 
 
 FIG. 124. 
 
 FIG. 125. 
 
 FIG. 126. 
 
 FIG. 127. 
 
 arranged, it will be seen that the ground wire g, and also the instru- 
 ment wires i 1 and / 3 at the way-station, are entirely disconnected 
 from the main line. 
 
 This is the manner in which the pegs of the switch should always 
 be arranged when the operator is absent from the office or during the 
 prevalence of a thunder-storm. 
 
 In some of the switches in use, the cut-out bar 6 is omitted 
 When this is the case, the holes on bar 5 should both be pegged, 
 
154 Equipment of American Telegraph Lines. 
 
 and the others left open (Fig. 124). The key (Fig. 122) should 
 also be opened, which serves to disconnect the wire i 1 ; i* being 
 open at the switch. This prevents lightning from injuring the 
 instruments. In thus cutting-out by means of one of the instrument 
 wires, the one which runs to the key should always be made use of, 
 not the one going to the relay. 
 
 (2.) To cut in the Apparatus. Insert pegs in 1-5 'and 2-4 (Fig. 
 125) or else in 1-4 and 2-5 (it is immaterial which, though the 
 former is most usual), and remove the pegs from 1-6 and 2-6, taking 
 care that the remainder of the holes are also open. It is better to 
 peg holes 1-5 and 2-4 before taking out 1-6 and 2-6, which can read- 
 ily be done if four pegs are provided, as then the circuit of the main 
 line need not be interrupted even for an instant. Care should 
 always be taken before "cutting in " the instruments to see that the 
 key-switch is closed. 
 
 If Nos. 1-5 and 2-5 are used for cutting out, close the key, insert 
 peg at 1-4, and afterwards remove peg from 1-5. 
 
 278. Testing for Disconnection. In case the line is broken, 
 or the circuit is open, as it is termed, it becomes necessary for the 
 way-station to test the circuit. This is done by grounding the line. 
 Suppose the line disconnected at some unknown point. Trenton 
 already has pegs in the holes 1-5, and 2-4 (Fig. 125), as in the ordi- 
 nary manner of working, but of course perceives no current. A 
 spare peg is placed in 1-6 (Fig. 126), the effect of which is to connect 
 the end of the New York line L with the earth wire g. This com- 
 pletes the circuit of the New York battery, but produces no effect on 
 the Trenton instrument, as the current does not pass through it. 
 The peg is then transferred from 1-6 to 2-6 (Fig. 127). The cir- 
 cuit of the New York battery is again completed as before, except 
 that it now includes the Trenton instrument, its course being from the 
 line wire L through the instruments as usual, and through the peg 2-6 
 to the wire g, and finally to the ground. Trenton now becomes a 
 terminal station, working with New York by means of the battery 
 at the latter place. 
 
 This result demonstrates to the operator at Trenton that the dis- 
 connection is between that place and Philadelphia. If, on the con- 
 trary, the circuit had been completed through the relay when the peg 
 was inserted in 6, it would have shown the break to have been in the 
 opposite direction. 
 
 It sometimes occurs that the circuit cannot be completed on either 
 side, and the line appears therefore to be interrupted in both direc- 
 tions. In that case the trouble is in all probability within the limits 
 
The Wedge Cut-Out. 
 
 155 
 
 FIG. 128. 
 
 Switch Wedge or 
 Plug. 
 
 of the way-station itself, usually in the instrument connections, which 
 should be carefully inspected. 
 
 279. Reporting Result of Test. If the operator at a way- 
 station finds by the above test that the line 
 
 is interrupted in a particular direction, it is 
 his duty to report the fact at once to the 
 terminal station in the opposite direction, 
 from which he should receive instructions 
 in regard to his proper method of pro- 
 cedure, so that the uninjured portion of 
 the line may be operated until the difficulty 
 is removed. 
 
 280. The Wedge Cut-Out. This 
 device is often used at way-stations instead 
 of the switch last described. It is termed a 
 
 plug, or more prop- 
 erly a wedge cut-out. 
 The i n s tr u m e n t 
 wires, z 1 and i 2 of 
 Fig. 122, are con- 
 nected to the opposite sides of a wedge, 
 as it is technically termed, which is shown, 
 full size, in Fig. 128. It consist's of two* 
 brass plates insulated from each other by a 
 thin plate of hard rubber, and provided with 
 a handle of the same material. The ends 
 of the line-wire are connected with the two 
 binding screws at the top of the baseboard 
 (Fig. 129). The right-hand binding screw 
 is connected, by a wire under the baseboard, 
 with an elastic brass strip. The upper end 
 of this strip is rigidly attached to the board, 
 while the lower end is armed with a brass 
 pin, which, by the elasticity of the strip, is 
 pressed firmly against a second pin, also 
 screwed to the board. The stationary pin 
 is attached by means of a wire to the other 
 binding screw, and is thus placed in con- 
 nection with the line-wire. This device is 
 termed the spring-jack. When the wedge, 
 carrying the flexible instrument wires, is inserted between the two 
 pins, it separates them, thereby breaking the circuit of the main 
 
 ;. 129 
 
 Spring-Jack and 
 Wedge. 
 
156 Equipment oj American Telegraph Lines. 
 
 line, but simultaneously opening a new path for the current through 
 the two parts of the wedge and the instruments. Thus the latter 
 may be inserted into or withdrawn without interrupting the main 
 circuit, by a single instantaneous movement. For many places 
 this is an exceedingly simple and effective arrangement. It is some- 
 times used for large stations, in combination with the peg-switch, 
 as will be hereafter shown (286). The wedge cut-out is usually pro- 
 vided with a lightning arrester and ground-wire connection, ar- 
 ranged with pegs, as in Fip". ^29, in much the same manner as the 
 switch in Fig. 122. 
 
 281. Multiple-Wire Switchboards. It very often happens 
 that different lines traversing the country in the same or in different 
 directions pass through the same way-station. The necessities of the 
 service sometimes require that there should be apparatus provided 
 for each line, but more frequently a smaller number of instruments is 
 sufficient, provided means are furnished by which any one of them 
 can be inserted into the circuit of any line at pleasure. 
 
 --. .. 
 
 FIG. 130. Multiple Spring-Jack. 
 
 282. Multiple Spring- Jack. The simplest way of providing 
 for this is to make use of a number of spring-jacks (Fig. 130) cor- 
 responding to the number of line wires, and placed side by side upon 
 the same baseboard. The wires for each separate set of instruments 
 terminate in a wedge, and by this means any instrument may be 
 placed in connection with any required line-wire at a moment's 
 notice, simply by inserting its wedge into the corresponding spring, 
 jack. 
 
 283. Universal Switchboard. The arrangement last de- 
 scribed makes no provision for interchanging the line-wires among 
 themselves a proceeding which is necessary, for instance, when 
 
Manipulation of the Universal Siuitchboard. 157 
 
 two or more lines running in the same general direction are each in- 
 terrupted, but at different points. By connecting the uninjured por- 
 tions of different lines with each other, it is often possible to "patch 
 up" one or more complete circuits for the transaction of business. 
 The wirt-s are interchanged or cross-connected, as it is termed, at the 
 different way-stations, in accordance with instructions given by the 
 official in charge of the circuits at the terminal station. In order 
 to conveniently ac- 
 
 complish 
 different 
 
 this, 
 wires 
 
 the 
 are 
 
 Ground 
 
 brought into a switch- 
 board of sufficient 
 capacity at each of 
 the principal way- 
 stations, and the nec- 
 essary changes are 
 made upon this with- 
 out any interference 
 with the lines them- 
 selves. 
 
 There are many 
 varieties of universal 
 switchboards, but all 
 are constructed upon 
 the same principle. 
 This will be under- 
 stood by reference to 
 Fig. 131, which rep- 
 resents a switch designed for a way-station having two line-wires, 
 lE iW, and 2E 2\V, and two instruments A and B. 
 
 284. Manipulation of the Universal Switchboard. The 
 various changes, other than those which have been explained in con- 
 nection with the single-wire switch (277), are made as follows: 
 
 (i.) Both lines connected straight, with both instruments in. Insert 
 pegs as in Fig. 132, leaving the remaining holes open. 
 
 (2.) Lines cross-connected or interchanged. In this case, it is re- 
 quired to connect No. i wire west with No. 2 wire east, and No. i 
 east with No. 2 west. Insert pegs as in Fig. 133, leaving the other 
 holes open. Both instruments A and B are now included in the 
 circuit. To leave instrument A out of the circuit, change the pegs 
 to the position shown in Fig. 134. Instrument B is cut out by 
 placing the pegs as shown in Fig. 135. In Fig. 136, the wires are 
 
 MHHHK-- ..... 
 
 Fig. 131. Two line Universal Switch. 
 
158 Equipment of American Telegraph Lines. 
 
 interchanged and both instruments cut out, a proceeding which is 
 sometimes necessary when a test is to be made. 
 
 E W E W 
 
 O O O 
 
 G O 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 EWE 
 
 O O O O 
 
 G O 
 
 'to 
 
 
 
 
 
 
 
 
 
 
 
 
 
 E 
 f 
 
 V 
 
 ) r 
 
 / E 
 
 ) r 
 
 . w 
 
 ) r 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 E W E W 
 
 O O O 
 
 G O 
 
 FIG. 132. 
 
 FIG. 133. 
 
 FIG. 134. 
 
 FIG. 135. 
 
 (3.) Lines grounded or put to earth. This may be done on either 
 No. i or No. 2 wire, east or west, by inserting pegs along the 
 ground wire bar G, as required, as in the single-wire switch (277). 
 
 (4.) Lines looped. It is sometimes required to loop two wires, as 
 it is termed, for making tests or other purposes. To loop i and 2 
 east, with instrument A in circuit, insert pegs as in Fig. 137 ; with- 
 out instrument A, insert pegs as in Fig. 138. Numbers i and 2 
 east may be looped in a corresponding manner. 
 
 f 
 1 
 
 -. V 
 3 C 
 
 Y 
 
 ^ ( 
 
 E V 
 
 l r 
 
 
 
 
 
 i? 
 
 
 
 
 C, 
 
 
 
 
 
 
 
 
 
 
 
 
 E W E 
 
 o o o o 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 : 
 
 
 
 
 E W E W 
 
 O O O O 
 
 u 
 
 ir\..\ 
 
 
 
 
 In 
 
 
 
 
 (U 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FIG. 136. 
 
 FIG. 137. 
 
 FIG. 138. 
 
 The foregoing explanation will sufficiently illustrate the principle 
 upon which the switch is manipulated. Switches are made to ac- 
 commodate any number of wires, from i to 50 or more. 
 
 285. Arrangement of the Apparatus at the Terminal 
 Station. The simplest possible arrangement at a terminal station 
 is similar to that shown in Fig. 122, but it is rare that such a station 
 does not contain more than one line-wire. More than one line en- 
 tering a terminal station renders it desirable to employ a switch sim- 
 ilar in construction to Fig. 131, but with its connections differently 
 arranged, for at a terminal station, provision must be made for con- 
 necting and disconnecting the main batteries as well as the instru- 
 ments. 
 
 286. Terminal Switchboards. Fig. 139 represents a switch- 
 board in a large American terminal station. In this switchboard 
 
Terminal Switchboards. 
 
 159 
 
 both the peg-switch and the wedge cut-out are employed. In the 
 largest class of terminal stations the switchboard is divided into a 
 number of sections, each section accommodating a certain portion of 
 the lines entering the office. The wires are usually distributed ac- 
 
 cording to the geographical location of the region with which they 
 connect. The lines running eastward, for example, are placed in 
 one section of the switch, and those running northward in another, 
 while still another section accommodates the local lines, etc., etc. 
 
160 Equipment of American Telegraph Lines. 
 
 The switchboard represented in the figure is provided with 50 
 vertical bars, to the lower ends of which the line-wires are connected. 
 Between each pair of upright bars is placed a row of metallic disks, 
 to which the battery terminals are connected. All the disks in each 
 separate horizontal row are electrically united at the back by hori- 
 zontal copper wires, the extreme left-hand disk having a distinguish- 
 ing number opposite it. The vertical bars are connected at pleasure 
 with the horizontal disks at any required point by the insertion of a 
 peg at the point of intersection. Immediately underneath the lower 
 end of the vertical bars are placed a corresponding number of spring- 
 jacks. Each main wire entering the switch passes first through one 
 of the spring-jacks, and thence to the corresponding bar. Each 
 spring-jack bears an ivory plate, upon which may be engraved the 
 designating number of the circuit to which it is attached. 
 
 The baseboard of the switch is of mahogany, cut in strips ,2 in. 
 wide by i in. thick, separated by a space of -J in., to prevent injury 
 to the brass-work by shrinkage. Each strip of mahogany supports 
 two vertical bars and one row of disks. The spring-jacks are held 
 in position by stout spiral wire springs attached to the back of the 
 switch. One row of horizontal disks is connected directly with the 
 earth. The lightning arresters are not combined with the switch, as 
 in the smaller stations, but are placed at the point where the wires 
 first enter the building. The instruments seen upon the shelf or 
 counter in front of the switch are used for testing. They are pro- 
 vided with flexible connections and wedges (280), so that they can 
 be thrown into the circuit of any desired line at a moment's notice. 
 
 287. Instrument Tables. In most large stations, the different 
 sets of apparatus are arranged in groups of four, upon tables about 4 
 by 6 feet, divided by two vertical intersecting screens into four sec- 
 tions, each accommodating a complete set of instruments, sounder, 
 relay, and key. A group of 4 pairs of instrument wires extends 
 from the switchboard to each table, and a second group of 4 pairs of 
 local wires extends from each table to the local batteries. The 
 wires are usually insulated with a double coating of gutta-percha, and 
 are then laid up in cables and bound with tarred tape. It was for- 
 merly the practice to group a number of local circuits together, 
 using a common return-wire for the group. Experience has shown 
 that this arrangement is objectionable, and that it is better to keep 
 all the circuits, main and local, of each line, distinct from those other 
 lines in the same station. 
 
 288. The Lightning Arrester. This is a term applied to all 
 devices employed in connection with telegraphic apparatus for pre- 
 
77/^ Plate Lightning Arrester. 161 
 
 venting danger of injury to the instruments and operators by atmos- 
 pheric electricity, and from the powerful currents employed in elec- 
 tric lighting, which sometimes find their way into telegraphic 
 conductors. Atmospheric electricity, being of enormous potential, 
 will take a short route through a poor conductor, or even through a 
 non-conductor, in preference to a longer one through a better con- 
 ductor, while the reverse is true in respect to the currents of com- 
 paratively great volume and low potential employed in telegraphy. 
 
 289. The Plate Lightning Arrester. A common form has a 
 flat brass plate connected with the ground wire. Other plates of brass 
 which rest upon this are electrically separated therefrom by thin 
 sheets of non-conducting ma- 
 terial, or by the air. Each 
 
 of the smaller plates is pro- 
 vided with one or more 
 binding screws for the at- 
 tachment of the line-wires. 
 Accumulations of atmos- 
 pheric electricity upon the 
 lines usually break through 
 
 the insulating material to FIG. 140. Plate Lightning Arrester. 
 
 the ground-plate, and are 
 
 thus discharged into the ground without injuring the apparatus. Fig. 
 140 shows one of the most common forms. The ground wire is con- 
 nected to the upper plate by the binding screw shown at the left, and 
 the line-wires through the smaller transverse plates beneath. The 
 confronting faces of the plates are surfaced with V-shaped grooves, 
 which have been found by experience to facilitate the discharge of 
 lightning. The lightning arrester is often combined with the switch- 
 board, examples of which construction may be seen in Figs. 127 and 
 
 131- 
 
 290. The Safety Fuse. Another very effectual means of pro- 
 tection consists in interposing 3 or 4 inches of the thinnest copper 
 wire which can be procured (say No. 36) in each circuit between the 
 line and the instrument. An abnormal current, whether arising from 
 atmospheric disturbances or from contact with electric lighting or 
 power circuits, instantly fuses the thin wire, interrupting the circuit, 
 and thus effectually protecting both the operators and the apparatus 
 This device, of course, requires careful attention, inasmuch as it is 
 necessary to replace the fuse-wire after the disturbance has ceased. 
 
 291. Inspection and Care of Arresters. Care should be 
 taken to keop lightning arresters, especially those of the plate pat- 
 
1 62 Equipment of American Telegraph Lines. 
 
 tern, free from dirt and moisture. Neglect of this precaution is 
 liable to cause serious interruption of communication. A discharge 
 of atmospheric electricity often forms a permanent connection be- 
 tween the line and ground plates. Hence, arresters should be fre- 
 quently taken apart and examined, and this should especially be 
 attended to immediately after a thunder-storm. 
 
 292. The Repeater. When the length of a telegraphic circuit 
 exceeds a certain limit, dependent upon the ratio of its insulation to 
 its conductivity resistance, the working margin (220) becomes so 
 small that satisfactory signals cannot be transmitted, even by the 
 aid of increased battery-power. This limit, under the existing con- 
 ditions of insulation, is much less in wet weather than in fine. 
 
 Under such conditions, it was formerly necessary to retransmit all 
 communications at some intermediate station, but this duty is now 
 usually performed by the repeater. This is simply an organized ap- 
 paratus, in which the sounder (or in some cases the relay), receiving 
 the signals through one circuit, opens and closes the circuit of an- 
 other line, in the manner that a relay opens and closes the local cir- 
 cuit of a sounder (261). The repeater is also used to connect one 
 or more branches with the main line, for the purpose of receiving 
 press-news, etc., simultaneously at widely separated points. Under 
 these conditions the stations in connection may correspond with 
 each other as readily as if all were upon the same circuit. By mak- 
 ing use of repeaters it is quite practicable to telegraph direct, when 
 required, between places situated at distance of several thousands of 
 miles apart. 
 
 293. Manual and Automatic Repeaters. The different 
 repeaters which have been devised are almost innumerable. They 
 may, however, be classified as manual and automatic. The manual 
 repeater is usually employed for temporary purposes, as it requires 
 the constant attendance of an operator to maintain the connections 
 of a switch, in accordance with the direction in which the communi- 
 cation is passing. At repeating stations where a permanent service 
 is maintained, the automatic repeater is employed, which requires 
 no supervision, other than that necessary to insure the apparatus 
 being kept in proper adjustment. 
 
 294. The Button Repeater. A form of manual repeater 
 much used is shown in diagram in Fig. 141. It is known as the 
 button repeater. The western main line, after traversing the coil of 
 the relay M 1 , passes through the contact-points of armature of 
 sounder S 2 (the movements of which are controlled by relay M 2 ) and 
 thence to main battery B 1 , the opposite pole of which is connected 
 
The Button Repeater. 
 
 163 
 
 to ground. In like manner the eastern line traverses the coil of 
 relay M 2 and the contact-points of sounder S 1 and to battery B 2 and 
 ground. It is necessary to provide, in addition, means for u cutting 
 out," or closing the circuit around the breaking-points of each 
 sounder, otherwise the apparatus will be inoperative. For example, 
 suppose the eastern line to be opened by the key of the operator. 
 This allows the armature of relay M 2 to fall off, opening sounder S 2 , 
 breaking the circuit of the western main wire at its contact-points. 
 This causes the armature of relay M 2 to fall off, followed by that of 
 sounder S 1 , and breaking the circuit of the western line also. The 
 
 operator of the eastern line cannot now close the circuit, because it 
 is still open in another place, viz., at the contact-points of sounder 
 S 1 . The switch shown at L, technically termed the button, removes 
 this difficulty, for when it is swung to the right it closes a spring- 
 contact C 1 , forming a connection between the contact-points of 
 sounder S 1 , enabling the operator of the eastern line to open and 
 close its circuit at pleasure, while his signals are repeated into the 
 western line by the action of the contact-points of sounder S 2 . The 
 switch or button shown at L in the diagram, consists of two pairs of 
 contacts C 1 and C 2 , normally closed by a spring action, one pair or 
 the other being separated as the handle L is moved to the right or 
 left. If the handle remains in the center, both sets of contacts are 
 
164 Equipment of American Telegraph Lines. 
 
 closed and the eastern and western lines are entirely independent 
 of each other. 
 
 295. Wood's Repeater. Another form of button repeater, 
 known as Wood's, is illustrated in Fig. 142. In addition to the 
 functions performed by the apparatus last described, means are here 
 provided for joining the two lines through in one circuit without re- 
 peating. The apparatus of the button is shown in full, with the 
 instruments and batteries, etc., in outline for convenience of expla- 
 nation. M 1 and M^ are the eastern and western relays, S 1 and S 2 
 the eastern and western sounders. The local connections are omitted 
 
 FIG. 142. Wood's Repeater. 
 
 o avoid multiplicity of lines, but are run as usual. The eastern 
 and western main batteries at E 2 and E 1 have opposite poles to 
 ground at the repeating station, so that when the lines are connected 
 through, the two batteries will coincide. The following results may 
 be obtained with this apparatus : 
 
 (i.) Two independent circuits. The lever L remains in the position 
 shown in the figure marked i, i, and the peg at 4 inserted. 
 
 (2.) A through circuit. The lever L as before, but the peg at 
 4 open, interrupting the ground connection between the batteries B 
 and B 1 . 
 
 (3.) Two independent circuits arranged for repeating. The peg at 
 4 is inserted. If lever L be placed in the position indicated by the 
 reference figures 2, 2, the eastern sounder repeats into the western 
 
The Milliken Automatic Repeater. 165 
 
 circuit. If the lever is shifted to 3, 3, the western sounder repeats 
 into the eastern circuit. 
 
 296. Management of Button Repeater. The duty of an 
 operator in charge of the button repeater is very simple. He has 
 only to keep the relays properly adjusted, and when he hears either 
 sounder fail to work in unison with the other, to instantly reverse 
 the position of the lever L. 
 
 FIG. 143. Milliken's Repeater. 
 
 297. The Milliken Automatic Repeater. This may be 
 considered the standard repeater of the United States, although 
 many others have obtained more or less acceptance. All automatic 
 repeaters embody one essential principle, which is this : The move- 
 ment of the lever of the relay or sounder on the receiving side of 
 the apparatus brings into action some device for bridging the con- 
 tact-points of the opposite sounder, before breaking the main circuit 
 on the second line. This is usually effected by some form of spring- 
 contact, although there are different ways in which s-uch a device 
 can be applied to produce the result sought for. The principle of 
 
1 66 Equipment of American Telegraph Lines. 
 
 the Milliken repeater is shown in Fig. 143. The main and local cir- 
 cuits are run precisely as in the button repeater (141). The auto- 
 matic device for closing the opposite circuit is applied to the contact- 
 lever of each of the relays ; for example, the relay M 1 has a supple- 
 mentary local magnet L 1 , the armature of which, falling off under the 
 action of its retracting spring, prevents the armature of relay M 1 from 
 likewise falling off, because its spring is adjusted to a stronger ten- 
 sion than the relay-spring. The local magnet L 1 is actuated by a 
 local circuit which is controlled by a contact-point on the lever of 
 the opposite sounder S 2 . When the sounder lever falls off, it first 
 breaks the supplementary local circuit, and holds down the armature 
 of the opposite relay, just before the main circuit through that relay 
 is broken. This postponement of the breaking of the main circuit 
 is effected by the spring-contact on the sounder lever. Hence in 
 this repeater, the apparatus on the east side remains quiet while the 
 western line is working and vice versa. The Milliken repeater is 
 provided with buttons, not shown in the figure, for cutting out the 
 contact-points, so that the two lines can be worked separately, as in 
 the case of the manual repeaters. 
 
 298. Management of Automatic Repeaters. In repeat- 
 ing signals from one circuit to another, the sounder-lever which car- 
 ries the contact-points has to move a certain distance, after the cir- 
 cuit of the first line is closed, before it can close the circuit of the 
 second line. This occupies a definite time, so that the duration of 
 the current or length of each signal sent forward, is shorter than that 
 received from the transmitting station. A second repeater shortens 
 the signals still more, so that ultimately the signals may fail altogether. 
 This may be partially remedied in practice by the skill of the send- 
 ing operator, who, in working through a repeater, should transmit 
 his signals moreyfrw/y, as it is termed, that is, increase the duration 
 of the key contact (374). It is also important that the sounder 
 levers should be permitted the least possible movement compatible 
 with the proper operation of the spring contact-points and with con- 
 venience in reading. The armatures of the supplementary local 
 magnets seldom need adjustment if the batteries are kept in good 
 condition. The adjustment of the relays is precisely the same as in 
 ordinary apparatus. The tension of the retracting springs of the 
 sounders, on the other hand, should be very moderate, just enough 
 to raise the armature when released. A repeater works most effi- 
 ciently when the signals have what is termed a " dragging " sound. 
 When interrupting the sender through a repeater, the receiving op- 
 erator should first hold his key open for two or three seconds. 
 
Characteristics of the Dynamo-Current. 167 
 
 299. The Dynamo-Electric Generator. In some large 
 telegraphic stations, where the number of lines to be supplied is very 
 great, dynamo-electric machines have been substituted for batteries 
 with highly satisfactory results. A minute description of the differ- 
 ent organizations of apparatus or plants which have been employed 
 does not properly fall within the scope of the present treatise, but 
 the following explanation may suffice to render the principles of 
 operation comprehensible. 
 
 300. Characteristics of the Dynamo-Current. The theo- 
 retical principle of the dynamo has been briefly set forth in a fore- 
 going chapter (80). From the explanation there given, it will be 
 understood that this machine, in its elementary form, produces a 
 series of waves or undulations of electromotive force of alternating 
 polarity. Beginning at zero, for example, the e. m. f. gradually in- 
 creases to a positive maximum ; then gradually falls to zero, then 
 rises again to maximum negative, then falls again to zero, and so on 
 indefinitely in the manner 
 
 graphically represented in j^ jg^ 
 
 *ig- 144. such a condi- ^ ^ 
 
 tion is obviously wholly FlG< I44 Alternating Currenl . 
 
 unsuited for the tele- 
 graphic service, which requires a normally continuous current, of 
 determinate polarity and of approximate uniform strength. The alter- 
 nate pulsations produced by the revolutions of the armature are there- 
 fore rectified by means of a device called a commutator, the effect 
 of which is to reverse every alternate wave, so as to transform the 
 alternating waves into a series of waves all positive or all negative, 
 as the case may be. If the armature be provided with two coils, 
 placed at right-angles with each other, so that one is in a position 
 of maximum at the same instant the other is in the position of mini- 
 mum action, and the two effects be combined, the result will be a 
 
 current which, although 
 
 - 4 * 3 * j* 
 
 FIG. 145. Rectified Alternating Current. B 7 Pacing a considerable 
 
 number of separate equi- 
 distant coils upon the armature, and superposing their effects, in 
 the manner indicated by the dotted outline at the left, it is prac- 
 ticable to obtain a current which is practically constant, and is 
 found to be perfectly well adapted for telegraphic purposes. For 
 this reason the rotating armature coils of the dynamos employed in 
 telegraphy are divided into a large number of sections, each coming 
 
1 68 Equipment of American Telegraph Lines. 
 
 successively into the position of maximum inductive action as the 
 armature is revolved. 
 
 301. The Electro-Magnetic Field. In the theoretical 
 dynamo hereinbefore described (80), the magnetic field in which 
 
 the armature coils revolve is formed 
 by permanent magnets. In prac- 
 tice, the far more powerful field 
 produced by electro-magnetism is 
 for many reasons preferable. The 
 electro-magnet which maintains the 
 field may be excited by a current 
 traversing a shunt or branch of 
 the armature circuit (140), in which 
 its helix is included, from which 
 circumstance such a machine is 
 termed a self-exciting dynamo, and 
 specifically a shunt-wound dynamo. 
 Fig. 146 is a theoretical diagram, 
 and Fig. 147 a perspective view 
 of a shunt-wound dynamo such as 
 is used in telegraphy. 2 
 
 302. The Commutator. In 
 the theoretical dynamo (Fig. 26, 
 p. 33), it will be observed that the 
 armature coils terminate in two 
 semi-cylindrical metallic segments 
 carried upon the shaft. Two sta- 
 tionary metallic collectors, termed 
 
 brushes, are made to rub upon the segments at opposite points of the 
 circle as they revolve, the whole apparatus being termed the com- 
 mutator. In Fig. 146 there are a considerable number of segments 
 corresponding to an equal number of armature sections, and two 
 brushes, which form respectively the positive and negative poles of 
 the dynamo-electric generator. The thick black line in Fig. 146 
 represents the exterior or work circuit. The shunt circuit for ex- 
 citing the field-magnet is shown by a thin line, the extremities of 
 which are likewise united to the respective terminals or brushes. 
 The direction in which the currents flow in both the main and shunt 
 circuits is denoted by arrows. 
 
 a This particular machine is known as the " Edison No. 2." It is run at a speed 
 of 1200 revolutions per minute, and has a capacity of about 40 amperes. The resist- 
 ance of the armature is about 0.1 ohm and of the field-magnet coil about 30 ohms. 
 
 FIG. 146. Circuits of Shunt Dynamo. 
 
Characteristics of the Dynamo. 169 
 
 303. Characteristics of the Dynamo. Each dynamo, when 
 driven at a definite and uniform speed, maintains a practically uni- 
 form difference of potential (143) between its terminals or brushes, 
 which is dependent upon the original construction of the machine. 
 This corresponds to the difference which is maintained between the 
 poles of a voltaic element, and is due to the e. m.f. of the machine, 
 or of the cell, as the case may be. The especial advantages of the 
 
 FIG. 147. Perspective View of Shunt- Wound Dynamo. 
 
 dynamo over the voltaic battery are: (i) its small internal resist 
 ance (131) and consequent capacity to feed a very large number of 
 separate lines without interference, and (2) its economy, both in 
 space occupied and in cost of maintenance, in case the number of 
 wires to be supplied is large. 
 
 304. Dynamos in Potential Series. In a large telegraph 
 station the different lines necessarily vary greatly in their length and 
 resistance, but it is nevertheless requisite that the same quantity of 
 current should be as nearly as possible supplied to each. This 
 renders it necessary that the electromotive forces applied to the re- 
 spective circuits should differ accordingly. This is effected through 
 the agency of a series of separate dynamos connected together upon 
 the same principle as a series of cells in a battery (132). In the 
 
170 Equipment of American Telegraph Lines. 
 
 Western Union telegraph station in New York, for example, there 
 are 5 independent dynamos connected in a series, as indicated in the 
 diagram, Fig. 148. These have potentials as follows : A", 70 volts ; 
 B, 70 volts ; C, 60 volts ; D, 60 volts ; E, 65 volts. One terminal of 
 dynamo A is connected to the ground, the wires i, 2, 3, 4, and 5 are 
 
 70 
 
 SWITCHBOARD 
 
 FIG. 148. Dynamos in Potential Series. 
 
 led to corresponding horizontal bars on the station switchboard, 
 from the point of connection between each two adjacent dynamos of 
 the series. These bars are respectively termed the first, second, 
 third, fourth, and fifth potentials. The voltage of each potential, 
 and the average resistance of the individual circuits fed therefrom, 
 are as follows : 
 
 No. of Potential. 
 
 Volts. 
 
 Average Resistance 
 per Line. 
 
 I 
 
 70 
 
 3000 
 
 2 
 
 140 
 
 3500 
 
 3 
 
 200 
 
 000 
 
 4 
 
 260 
 
 5000 
 
 5 
 
 325 
 
 5000 
 
 As the different lines are each connected to one of the vertical 
 bars on the switch (Fig. 139), of which there may be any number, it 
 will be easily understood how any line may be supplied with the 
 particular potential which it requires, simply by pegging it to the 
 appropriate horizontal bar upon the switchboard. 
 
 305. Positive and Negative Dynamo Series. As both 
 positive and negative potentials of the various voltages are required 
 in a large station, two separate series of dynamos are employed, sim- 
 ilar to that shown in Fig. 148, one having its positive and the other 
 its negative terminal to the switchboard and line. A third series, 
 
Multiple Telegraphy. 1 7 1 
 
 of similar arrangement and capacity, is also provided, which has re- 
 versing switches, so that it may be made to send either a positive or 
 negative current to line. This may be used at will as a substitute 
 for either of the two regular series in case of accident. Each series 
 of five machines is driven by a 15 horse-power steam-engine. 
 
 306. Arrangement of the Shunt Coils. It will be observed 
 that the last dynamo E in the series (Fig. 148) is necessarily called 
 upon to furnish less current to the lines than the others. The sur- 
 plus power of this machine is therefore utilized with advantage to 
 furnish current through a shunt or derived circuit, not only for excit- 
 ing its own field, but the fields of all the other machines in the series. 
 A branch or derived circuit is taken from each terminal of this ma- 
 chine, and the field coils of each of the five machines of the series are 
 connected across from one branch to the other in parallel, as shown 
 by the thin lines in Fig. 148, so that each receives an equal portion 
 of the branch current. 
 
 306 a. Capacity of the Dynamo Generator. A plant of the 
 capacity of that which has been described can be made to furnish 
 for supplying 1000 lines, and yet is so compact that it may be in- 
 stalled in a small room. 
 
 307. Multiple Telegraphy. Within thirty years from the first 
 establishment of the telegraph, the inconveniences arising from the 
 multiplication of wires on the principal commercial routes of the 
 United States proved so serious that it became urgently necessary 
 to adopt measures of relief. The effort to devise an effectual remedy 
 led to the invention of systems of multiple telegraphy, in which the 
 same conductor might be used for the transmission and reception of 
 more than one communication at the same time, either in the same 
 or in opposite directions. The most generally useful of these have 
 proved to be those which have been termed the diptex, which trans- 
 mits two messages in the same direction at the same time ; the con- 
 traplex, which transmits two messages in opposite directions at the 
 same time ; and the quadruple*, which is capable of transmitting two 
 messages in each direction at the same time. . The contraplex is 
 more generally known as the duplex. 
 
 The principle which is common to all these systems is a provision 
 whereby the receiving instrument at the home station, while free to 
 respond to the signals of the key at the distant station, shall not re- 
 spond to the signals of its associate key. 
 
 308. The Differential Electro-Magnet. It has been here- 
 tofore explained that the attractive force of the cores of an electro- 
 magnet depends upon the ampere-turns in its coil (176), that is to 
 
172 Equipment of American Telegraph Lines. 
 
 say, first, upon the number of turns in the magnetizing helix, and 
 second, upon the strength of current in amperes traversing the wire. 
 It has also been explained that the polarity of the core is determined 
 by the direction of the circulating current (168). It follows from 
 these two considerations, that if two currents of equal quantity are 
 simultaneously made to pass in opposite directions an equal number 
 of times around a magnet core, they will neutralize each other's 
 effect, and no magnetism can be developed in the core. An electro- 
 magnet of this kind is termed a differential magnet. 
 
 309. Construction of Differential Magnet. There are 
 several ways in which a differential magnet may be constructed, all 
 involving essentially the same principle. Two independent wires 
 must be provided for the two opposing currents. These may be 
 wound side by side throughout the whole length of the helix ; they 
 may be disposed in concentric independent helices ; one helix may 
 be wound on each of the legs of a U magnet, or, what is perhaps 
 most commonly done, the helices may be divided into sections by 
 equidistant non-conducting planes at right-angles to their axes, and 
 the alternate sections connected with the respective circuits. 
 
 310. The Single-Current Duplex. The most essential parts 
 of the apparatus of the single-current duplex are the transmitter^ the 
 
 FIG. 149. 
 
 EARTH 
 
 Single-Current Duplex. 
 
 differential relay, the rheostat, and the condenser. Fig. 149 is a dia- 
 gram of the apparatus at one of the 'two terminal stations. The 
 transmitter D is virtually a key, which instead of being actuated 
 directly by the ringer of the operator, receives its motion from the 
 armature of an electro-magnet S in the circuit of local battery L 1 , 
 which is closed and broken by an ordinary key K. The key-lever 
 
The Single-Current Duplex. 
 
 / o 
 
 D of the transmitter has a spring contact-lever N pivoted at n and 
 having a contact 9 which normally rests upon a fixed stop ft, from 
 which it is lifted by the contact each time the key K is depressed. 
 The differential magnet is shown at M, and is wound in either of 
 the ways heretofore referred to (309) with two wires, but otherwise 
 does not differ from the ordinary single-wire relay (267). The actual 
 construction of the transmitter is best seen in Fig. 150. The spring- 
 contact here shown differs in form, but not in principle, from that 
 
 FIG. 150. Single-Current Transmitter. 
 
 outlined in Fig. 149. The spring in this instrument is carried upon 
 the lever, upon a little insulating pedestal, and normally presses up- 
 ward against a stop affixed to the free end of the lever. 
 
 When the armature is attracted, the opposite end of the lever is 
 raised, and the free end of the spring touches the adjustable contact- 
 stop fixed above it in a standard. The object of this device, as will 
 be hereinafter seen, is to close one contact before breaking the other, 
 or in other words, to transfer a current from one branch of the cir- 
 cuit to another without interrupting it. 
 
 311. Circuits of the Single-Current Duplex. Tracing 
 the circuit of the line entering the station in Fig. 149, it will be seen 
 to first pass through one wire of the differential relay M, entering by 
 wire 3 and thence going by wire 2 to contact-lever n, and thence 
 through stop 9 and wire 6 to the earth. Hence currents entering 
 from the distant station will actuate relay M and sounder R, pre- 
 
174 Equipment of American Telegraph Lines. 
 
 cisely as in the open-circuit system ^212).* If now, at a time when 
 no current is coming from the distant station, transmitter-lever D be 
 depressed by the closing of key K, the terminal of main battery 
 B will be brought, at the point o, into contact with spring-lever N, 
 and will almost simultaneously lift it from point h. This in effect 
 transfers the in-coming line from the ground-wire 6 to the battery- 
 wire i, and hence a current will rlow through wires 2 and 3 and one 
 coil of the differential magnet m to the line, finding its way to the 
 ground at the distant station. But it will furthermore be observed 
 that a branch leaves the line at the point #, and leads by way of wire 
 4 through the opposing wire of the differential magnet M, and thence 
 by way of 5 directly to the earth at the home station. Now it is evi- 
 dent that the outgoing current from battery B must divide between 
 the two branches at the point a in the ratio of their respective resist- 
 ances (134), and if these be equal, the currents must necessarily be 
 equal (140). This equality of resistance is effected by inserting a 
 rheostat X 1 (106) of german-silver wire into the branch, so as to 
 make its resistance equal to that of the line. When this has been 
 done, it is evident that the outgoing currents, being equal and oppo- 
 site in their effects, can produce no magnetism in the relay M, and 
 hence the latter cannot respond in any way to the signals of its asso- 
 ciated key K. But this will not in the least interfere with its ca- 
 pacity to respond to the action of currents transmitted by the distant 
 key. In such case one wire of the relay will be traversed by the 
 current due to the conjoint or superposed action of both terminal 
 batteries, while its action is opposed in the other wire of the relay 
 only by the current of the home battery. The incoming current, 
 therefore, produces upon it precisely the same effect as if the current 
 of the home battery were not present. 
 
 312. The Artificial Line. The branch from the point a 
 through 4 and 5 to the earth at the home station, is termed the 
 artificial line, and the whole problem of contraplex, generally termed 
 duplex telegraphy, consists in simultaneously reproducing in the arti- 
 ficial line, as nearly as may be, all the electrical conditions of the 
 external or working line, and in causing them to act in an opposite 
 sense upon the home relay. There are two conditions in respect to 
 which the actual line is subject to continual variation, viz., as to its 
 resistance (115) and its electrostatic capacity (147). 
 
 313. Balancing the Resistance. The effect of imperfect 
 insulation upon the resistance of the line has already been referred 
 to (242). It is greatest in fine weather and least in wet and foggy 
 weather. The resistance of the artificial line is, however, very easily 
 
Electrostatic Capacity of tke Line. i 75 
 
 balanced ; that is, adjusted to correspond with that of the main line 
 by plugging or unplugging, as required, a series of graduated resist- 
 
 FIG, 151. [Resistance Coils of Artificial Line, 
 
 ance coils of german-silver wire, arranged, as shown in Fig. 151, 
 upon the principle explained in (106). 
 
 314. Electrostatic Capacity of the Line. In order that 
 the process of adjusting the electrostatic balance of the artificial line 
 may be understood, it is neces- 
 sary first to explain the nature l l 
 and origin of the corresponding 
 phenomenon as exhibited upon 
 the main line. 
 
 Whenever electrical generation oc- 
 curs, there always exists, besides a EARTH EARTH 
 source of generation at which the FlG . I52 . Recombination of Positive and 
 normal equilibrium is first disturbed, Negative Electricity, 
 (i) certain conditions which allow the 
 
 positive and negative electricity thus separated to recombine, or else (2) cer- 
 tain other conditions by which the electricity generated is accumulated on 
 two surfaces separated by a medium through which it either cannot recom- 
 bine, or (3) can only recombine less rapidly than the source can generate. 8 
 
 3 F. C. WEBB : Electrical Accumulation and Conduction (part i), p. 2. 
 
i/6 Equipment of American Telegraph Lines. 
 
 The first condition referred to exists in the case of a cell, or series 
 of cells, having the poles joined by a conductor of inappreciable re- 
 sistance (Fig. 152). The second condition exists in the case of an 
 insulated telegraph line of considerable length, connected to one 
 
 3 
 
 J 
 
 FH;. 153. Accumulation of Static Electricity upon 
 EARTH P en Line - 
 
 pole of a grounded battery and open at its distant end (Fig. 153). 
 The third condition exists when the line assumed in the last case, 
 instead of being open at the distant end, is there connected to the 
 earth, either directly or through an instrument or other appreciable 
 
 EARTH EARTH 
 
 FIG. 154. Accumulation of Electricity upon Line to Ground at Distant End. 
 
 resistance. This is the condition of a -duplex telegraphic circuit 
 (Fig- I54)- 4 
 
 These figures are identical with those which have heretofore been employed in 
 illustration of potential. The area inclosed between the base line and the line of po- 
 
Effect of Currents of Charge and Discharge. 1 77 
 
 315. Electrostatic Accumulation upon Insulated Con- 
 ductor. When, therefore, a quantity of electricity flows through a 
 long insulated line, the electricity which constitutes the initial por- 
 tion of the current, being prevented by the resistance of the circuit 
 from recombining instantaneously, is stored up or accumulated upon 
 the surface of the conductor. The quantity thus accumulated de- 
 pends upon the diameter and length, or, in other words, upon (i) 
 the superficial area of the conductor,, (2) its distance from the earth, 
 or other conductors in electrical connection with the earth, and (3) 
 
 . upon the character of the insulating medium which intervenes be- 
 tween it and the earth. Thus, in any long insulated circuit, a certain 
 portion of the current which would otherwise reach the distant sta- 
 tion and be available for producing signals, is abstracted and tied up 
 in the form of a static charge. If the line be very long and the dura- 
 tion of the current be very short, the static charge may absorb the 
 whole of it, so that no effect will be appreciable at the distant sta- 
 tion. As the static charge takes up the initial portion of every cur- 
 rent sent, the effect is the same as if its appearance at the distant 
 station were retarded or delayed, and hence the apparent velocity of 
 the current is lessened. The initial rush of current into the line, 
 sometimes called the current of charge, produces for an instant a 
 much more powerful magnetic effect upon the armature of the relay 
 than does the permanent current which continues to flow after the 
 conductor has been fully charged. The momentary effect thus pro- 
 duced upon the relay is termed by the operators the kick. It varies 
 in amount with the electrostatic capacity of the line ; the longer the 
 line and the more perfect its insulation, the higher its capacity to re- 
 ceive charge and the more the force manifested by the charging cur- 
 rent. 
 
 316. Effect of Currents of Charge and Discharge. It 
 will therefore be understood that when one wire of a differential re- 
 lay is connected, as in the duplex apparatus, with a long insulated 
 line having a considerable electrostatic capacity, while its other and 
 opposing wire is connected with an artificial line principally made up 
 of a rheostat destitute of electrostatic capacity, although the resist- 
 ances of the two branches may be exactly the same, the initial charg- 
 
 tential may be correctly taken to represent, the electrostatic charge in each case. A 
 consideration of Fig. 154 will show that when the line is to ground at the distant end, 
 as in duplex telegraphy, 75 per cent, of the aggregate charge of the line is accumu- 
 lated upon the first half of it, and only 25 per cent, upon the second half. Therefore 
 the currents of charge and discharge are three times as great at the battery end as at 
 the ground end. This is upon the assumption that there is no appreciable loss through 
 imperfect insulation. 
 
178 Equipment of American Telegraph Lines. 
 
 ing current in the main line will not be counteracted by a corre 
 spending opposite effect in the artificial line, and hence a momentary 
 false signal will be produced upon the home relay. So also, at the 
 termination of the signal, when the line is detached from the battery 
 and connected to earth at the home station, the electrostatic charge 
 accumulated upon the line instantly flows back to the ground through 
 the rear contact of the transmitter, passing through one wire only 
 of the differential relay, and another false signal is produced. These 
 false signals, occurring at the beginning and end of each true signal 
 sent out from the home station, if not eliminated, would mingle with 
 the received signals from the distant station, and utter confusion 
 would be the inevitable result. 
 
 317. The Condenser. This difficulty is overcome by connect- 
 ing to the artificial line a device termed a condenser, which consists 
 of a large number of sheets of tin-foil connected with the artificial 
 line, interleaved with an equal number connected with the earth, and 
 separated by sheets of insulating material, usually mica or paraffined 
 linen paper. By arranging these sheets in separate sections, with 
 proper electrical connections, a very large superficial area of tin-foil 
 is exposed to inductive action, the actual extent of which may be 
 varied at pleasure, so that the artificial line may be made to charge 
 and discharge itself at the same instant, and to the same extent, as 
 the main or actual line. The disturbing effects of the static charge 
 and discharge upon the differential relay may thus be wholly elim- 
 inated. 5 The condenser is inclosed in a wooden box and provided 
 with a peg switch, as shown in Fig. 155, so that its electrostatic ca- 
 pacity may be varied as required. 
 
 The manner in which the condenser is connected to the artificial 
 line and to the earth is indicated at C in Fig. 149. At the common 
 point 5, which is the terminal of the opposing or equating coil of the 
 differential relay, are attached the rheostat X 1 (the resistance of 
 which is maintained equal to that of the main line), and the con- 
 denser C (the electrostatic capacity of which is also kept equal to 
 that of the main line), which, by their joint action when properly 
 adjusted, insure a perfect working balance to the apparatus under all 
 conditions. 
 
 5 The credit of the idea of giving to the artificial line of the contraplex apparatus 
 an electrostatic capacity corresponding to that of the main line, is due to Joseph B. 
 Stearns, who successfully applied it on the lines of the Western Union Telegraph 
 Company leading out of New York, in 1872. By this admirable application of a scien- 
 tific principle, in a manner no less ingenious than simple, it is not too much to affirm 
 that the commercial value of the aggregate telegraphic property of the world was more 
 than doubled at a single stroke. 
 
The Ground and Spark Coils. 
 
 179 
 
 FiG. 155. Adjustable Condenser of Artificial Line. 
 
 318. The Ground and Spark Coils. It is necessary that 
 the apparatus at the home station should always present an equal 
 resistance to the currents coming from the distant station, so as not 
 to overthrow the balance of the distant relay. This is effected by 
 means of small rheostats X 1 and X 2 (Fig. 149), termed respectively 
 the ground-coil and the spark-cot?, the resistance of the former being 
 made equal to that of the latter, plus the internal resistance of the 
 battery, and that of the latter being sufficient to prevent the polariza- 
 tion of the battery when momentarily short-circuited at the transmitter. 
 
 FIG. 156. Double-Current Duplex. 
 
180 Equipment of American Telegraph Lines. 
 
 319. The Double-Current Duplex. The principle of this 
 apparatus will be understood by reference to Fig. 156. Double cur- 
 rent or reversing keys are employed at each end of the line, each of 
 which, when depressed, reverses the poles of its associated main 
 battery without interrupting the circuit, and of course without chang- 
 
 FIG. 157. Polar Relay 
 
 ing the total resistance. Polar relays are also used, the peculiarity 
 of which consists in the employment of polarized armatures, the 
 construction and use of which have been explained in (200). The 
 actual construction of the polar relay is shown in Fig. 157. 
 
 The permanent magnetism of a polarized armature causes it to 
 remain, by its own attraction, indifferently in contact with either 
 pole of the electro-magnet, when no current is passing through its 
 
The Double-Current Duplex. 
 
 181 
 
 coils. If, then, we assume this electro-magnet to be differentially 
 wound, and the armature normally at rest upon the rear contact so 
 as to leave the local circuit open, it is obvious that whether the cur- 
 rent sent out from the associated key be positive or negative, it can- 
 not in either case, owing to the differential action, develop any mag- 
 netism in the cores, nor alter the position of the armature. The 
 
 FIG. 158. Pole-Changing Transmitter. 
 
 differential winding therefore produces the same effect with the polar 
 as with the neutral relay. But at the distant station, the currents 
 received over the line traverse one wire of the relay only, and hence 
 the polarity of the core at that station is reversed each time the 
 sending key is depressed or raised. When the key is down, a posi- 
 tive current passes, and the armature closes the local circuit ; when 
 it is up, a negative current passes, and the local circuit is broken. 
 In other words, the signals are produced by changing the polarity of 
 
1 82 Equipment of American Telegraph Lines. 
 
 the current, and not by changing its strength from zero to maximum, 
 as in the single-current system. The actual construction of the 
 transmitter employed is shown in Fig. 158. 
 
 320. The Quadruplex. This apparatus may be regarded as a 
 combination of the single-current and double-current duplex systems, 
 adapted to be operated simultaneously in the same circuit. It has 
 been explained that the polar relay in the double-current duplex 
 (319) is actuated solely by changes in polarity, irrespective of 
 strength, and in the single-current duplex (310) solely by changes in 
 strength of current, irrespective of polarity. If then we place both 
 a polar and a neutral relay in series in the same circuit, as shown in 
 Fig. 159, it is evident that we may produce signals by moving the 
 armature of the polar relay to-and-fro by means of alternate positive 
 
 LINE 
 
 FIG. 159. The Diplex the Basis of the Quadruplex. 
 
 and negative currents, and in case these are not strong enough to 
 affect the armature of the neutral relay, no signals will be indicated 
 thereby. So also, if we maintain a constant polarity, and merely 
 open and close the circuit, we shall produce signals upon the neutral 
 but not upon the polar relay. 
 
 321. Principle of the Diplex. Fig. 159 is a diagram show- 
 ing a line having at one terminal station two keys, one single-cur- 
 rent and the other double-current or reversing. The battery is also 
 in two sections, one section B 2 having three times as many cells and 
 therefore three times as much e. m.f. as the other section B 1 . By 
 tracing the connections, it will be observed that both sections of the 
 battery are included in a loop, the terminals of which are reversed by 
 the depression of the key K 1 , but that the greater section B 2 of the 
 battery only comes into action when the other key K 2 is depressed. 
 
Operation of the Dip lex. 
 
 183 
 
 Thus it is obvious that the e. m. f. of the current going to line will 
 be four times as great when key K 1 is depressed as when it is at 
 rest, and that the key K 2 when depressed serves to reverse whatever 
 c. m. f. may be in circuit at the moment, whether of both sections 
 or only the smaller section of the battery. In brief, the key K 1 con- 
 trols the polarity of the outgoing current regardless of its e. m.f., 
 while key K 2 controls the e. m. f. of the outgoing current regardless 
 of its polarity. 
 
 322. Turning now to the receiving apparatus, we have in series, 
 at the receiving end of the same circuit, a polar relay R 1 and an 
 ordinary or neutral relay R~. If the armature-spring of the neutral 
 relay R 2 be adjusted to such a tension that it cannot respond to the 
 comparatively weak current of the battery B 1 , when unassisted by 
 the battery B 2 , it is obvious that signals may be sent by reversing 
 the smaller battery section by means of the key K 1 , which will act- 
 uate the polar relay R 1 , 
 
 but will produce no effect 
 whatever upon the relay 
 R 2 . On the other hand, 
 signals may be sent by the 
 key K 2 , each depression 
 of which throws upon the 
 line the additional e. m.f. 
 of the greater battery sec- 
 tion B 2 . The additional 
 strength of current which 
 now flows will actuate the 
 neutral relay R 2 , but will 
 produce no effect upon 
 the polar relay other than 
 to increase the pressure 
 of its armature against 
 whichever stop it may 
 chance to be in contact 
 with. But the polarized 
 armature, on the other FlG> l6o> 
 
 hand, will instantly re- 
 spond to each reversal, whether of the smaller or the larger current. 
 
 323. Operation of the Diplex. Suppose a signal is being 
 sent by the depression of key K 2 ; both sections of the battery are 
 in circuit on the line, causing the armature of the neutral relay R 2 
 to be attracted. If now another signal be sent by the depression 
 
 L/N 
 
 Receiving Sounder of Diplex. 
 
184 Equipment of American Telegraph Lines. 
 
 of the key K 1 , the full strength of the current traversing the neutral 
 relay R 2 will be rmersed. It is obvious that during this operation, 
 no matter how instantaneously the reversal may be effected, there 
 must be an interval during which no magnetism is manifested. The 
 actual result of this is found to be that the neutral relay lets go its 
 armature for an instant, and the spring begins to pull it away, but it 
 scarcely has time to move before the opposite magnetism seizes upon 
 it and restores it to its original position. This, if not guarded 
 against, causes a slight break in the signal, known as the dip, which 
 may nevertheless be eliminated by the aid of special devices. 
 
 One of the most efficient of these devices is that of an interme- 
 diate local relay interposed between the neutral main-line relay and 
 its associated sounder in the manner indicated in Fig. 160. When 
 the armature of the neutral relay R falls off, the sounder S is not 
 affected until it reaches its rear contact-point, when it closes the cir- 
 cuit of the local relay L, and the latter, also by its rear contact, 
 breaks the second local circuit. When the main-line is closed the 
 reverse action takes place. Thus the sounder can only be affected 
 by a full opening of the main circuit, which shall continue long 
 enough to permit the relay armature to reach in rear contact. A 
 
 FIG. 161. Short-core Neutral Relay for Quadruple*- 
 
 neutral relay having very short cores, as in Fig. 161, is for this 
 reason advantageous (195). 
 
 324. The Diplex and Contraplex Combined. Having an 
 apparatus of this kind, capable of transmitting two sets of signals in 
 the same direction at the same time without interference with each 
 
Quadruple* worked by Dynamo-Currents. 185 
 
 other, it is not difficult to understand that by applying a differential 
 winding to both relays, polar and neutral, and by including both in 
 the circuit of the main and artificial lines, precisely as in the case 
 of the single-current and polar duplexes (310, 319), it becomes per- 
 fectly practicable to transmit two sets of signals upon a line in each 
 direction at the same time,, and this is in fact precisely what is done 
 in the case of the quadruplex. 6 
 
 325. Quadruplex worked by Dynamo-Currents. The 
 quadruplex apparatus at the larger stations in the United States is 
 now frequently operated by dynamo-currents, and it is probable that 
 this method will in time become practically universal. 7 The organi- 
 zation of the apparatus has been slightly modified from that illus- 
 trated in Fig. 159, to better adapt it to the conditions under which 
 it is required to work. The principle will be understood by refer- 
 ence to Fig. 162. D 1 and D 2 represent two independent series of 
 dynamos, such as hereinbefore described (304), one having its posi- 
 tive and the other its negative pole to the line. K 1 is the pole- 
 changing transmitter and K 2 the single-current transmitter, which, 
 for simplicity, are shown in the diagram as keys, but which are in 
 practice operated by electro-magnets, local batteries, and independent 
 keys, as indicated in Fig. 149. When the apparatus is at rest, the 
 current from the negative dynamo D 3 traverses a resistance coil of 
 say 600 ohms (which is inserted to avoid danger of injury to the in- 
 struments in case of an accidental short circuit) to the rear contact 
 of the pole-changing key K 1 ; thence through wire i (in which is in- 
 cluded a rheostat of say 1200 ohms) to the point 2, where it divides 
 into three portions ; the first portion going to the line and distant 
 station, the second through the artificial line, including rheostat X, 
 to the earth, and the third through the wire 3, the normally closed 
 rear contact of the single-current key K 2 , and a rheostat of say 900 
 
 8 The method of diplex transmission here described, which forms the basis of the 
 commercial quadruplex system, was invented in 1873 by Thomas A. Edison (see U. S. 
 patent No. 162,633, A P r - 2 7 ^75)- He also devised the apparatus described in (323), 
 to overcome the principal obstacle in applying the method in quadruplex transmission. 
 
 7 The first successful application of the dynamo machine as a substitute for the 
 voltaic battery in commercial telegraphy was made in 1879 by Stephen D. Field of San 
 Francisco. (See his U. S. patents, Nos. 223,845, Jan. 27, 1880, and 243,698, July 5, 
 1881.) Detailefl descriptions of some of the more important dynamo plants have been 
 published as follows : Western Union, New York, Operator and Electrical World, 
 xiv. 225 ; same plant improved, W. MAVER, Jr., in Electrical World, xi. 67, 79 ; W. 
 U. plant, Pittsburgh, W. MAVER, Jr., ibid, xii. 195 ; W. U. plant, Chicago, ibid^ xv. 
 173; Postal Tel. Cable Co., N. Y., ibid, xii. 65 ; Postal T. C. Co., Boston, ibid, xvi. 
 313. The plant of fifteen dynamos in the Western Union N. Y. central station does 
 the work of more than 30,000 cells of gravity battery. 
 
1 86 Equipment of American Telegraph Lines. 
 
 ohms, to the earth. If for example, therefore, we assume the resist- 
 ance of the main and artificial line to be 3600 ohms each, it follows 
 from the law of distribution of currents in branch circuits (140), that 
 
 FIG. 162. Quadruple! Operated by Dynamo Currents. 
 
 two-thirds the current will return to earth through wires 3 and 4, one- 
 sixth will go to the main line, and one-sixth to the artificial line. 
 
 326. Distribution of Currents in Quadruplex Apparatus. 
 If now the key K 2 be depressed in order to send a signal, a direct 
 connection will be formed between key K 1 and the point 2 through 
 
Practical Management of the Quadruple*. 187 
 
 wires 5 and 3, shunting the i2oo-ohm coil in wire i. At the same 
 time the wire 4 will be opened, and the whole current will divide at 
 the point 2, half going to the main line and half to the artificial line. 
 It follows, therefore, that with the several resistances in the ratios 
 shown, the current sent to line by the key K 1 when key K 2 is de- 
 pressed will be three times as strong as when the latter is raised, 
 and this will be equally true whether the current sent by key K 1 be 
 positive or negative. 
 
 327. A computation of the effects of the several resistances will 
 also show that when an arriving current reaches the point 2, the 
 resistance which it has to encounter in passing thence to the ground 
 is the same, whether the key K 2 be depressed or raised. When the 
 key is depressed, the resistance is only that of one or the other of 
 the 6oo-ohm coils between the key K 1 and the dynamos ; when 
 raised, it is the joint resistance of one coil of 600, plus the coil of 
 1200 (a total of 1800), in one branch, and the coil of 900 in the 
 other branch, the joint resistance of the two being 600, the same as 
 in the first instance. The relays R 1 and R 2 at each station, being 
 both differential, are not affected by outgoing currents, whatever may 
 be the strength or the polarity of such currents. 
 
 328. Practical Management of the Quadruplex. Skill 
 in the management of an apparatus of so much complexity as the 
 quadruplex can only be acquired by experience and careful study. 
 Only a few hints can be given here. 8 As a preliminary to these sug- 
 gestions, an. explanation of certain technical terms which have come 
 into use with the apparatus is necessary. 
 
 The " No. i side " of the apparatus comprises the pole-changing 
 transmitter, the polar relay, and their attachments. 
 
 The " No. 2 side " of the apparatus comprises the single-current 
 key, the neutral relay, and their attachments. 
 
 The tap-wire is the intermediate wire which divides the battery 
 into two unequal portions, usually termed respectively the long end 
 and the short end. (See Fig. 159.) 
 
 The resistance which is inserted to compensate for the internal 
 resistance of the battery is called the ground-coil. A resistance x, 
 Fig. 162, is also placed between the condenser and the differential 
 
 s A great amount of information of value respecting the history, theory, and prac- 
 tice of quadruplex telegraphy may be found in a series of articles by WILLIAM MAVER, 
 Jr., in Electrical World, xi. 254, 266, 280 ; and in a subsequent discussion by FRANCIS 
 W. JONES, ibid, xi. 290, 330, xii. 276; W. MAVER, Jr., ibid, xi. 305, xii. 231 ; CLAR- 
 ENCE L. HEALY, ibid, xi. 292 ; THOMAS HENNING, ibid^ xi. 330 ; H. W. PLUM, ibid, 
 xi. 316. See also F. W. JONES : The Quadruplex, Journal Am. Electrical Soc., i. 16 ; 
 F. L. POPE: Quadruplex Telegraphy, The Telegrapher, xi. 271. 
 
1 88 Equipment of American Telegraph Lines. 
 
 relays on long circuits, to retard the time occupied in the charge and 
 discharge of the condenser, in correspondence with that of the line. 
 
 The proportion between the long and the short end of the battery 
 varies in practice with the length of the line. On lines of 100 miles 
 or less the division is usually equal, or, as it is termed, 2 to i ; on a 
 line 350 or 400 miles, it may be with advantage as much as 4 to i. 
 
 329. Adjustment of the Apparatus. The following method 
 of procedure has been recommended by experienced operators, 
 though it is proper to say that some difference of opinion exists in 
 reference to the minor details of adjustment. 
 
 First. Instruct distant station to "ground." He will then put 
 the line to ground through his battery-compensation resistance or 
 ground-coil. Both stations should assure themselves that the resist- 
 ance of the ground-coil is equal to that of the battery. 
 
 Second. The line being to ground at both ends, proceed to centre 
 the armature of the polar relay. When centred, it should remain 
 indifferently in either an open or closed position of the local circuit 
 as placed by the finger. 
 
 Third. Switch in the home battery, and vary the rheostat resistance 
 in the artificial line until the polar relay can be again centred. If 
 disturbing effects from foreign currents are felt, it may not be pos- 
 sible to do this accurately. In such case, approximate it as nearly 
 as possible. 
 
 Fourth. Instruct the distant station to switch in his battery. This 
 may assist in adjusting the polar armature. 
 
 Fifth. Instruct distant station to close both keys, thus sending 
 full current to you. Close your No. 2 key ; send dots on your No. 
 i pole-changer, and alter the capacity of your condenser until its 
 effects on the home polar relay are eliminated. This condition is 
 termed the electrostatic balance. 
 
 Sixth. After both stations have thus balanced, test the correct- 
 ness of the adjustments as follows : 
 
 Instruct distant station to send dots on No. i and words on No. 
 2. While this is being done, alternately open and close both keys 
 at the home station. If both sets of signals from distant station 
 come distinctly under all circumstances, the balance is obviously cor- 
 rect. The same test should be repeated by the distant station, in 
 order to ensure an accurate working adjustment. 
 
 In the above test, if the sending on No. 2 side should fail to come 
 well, instruct distant station to hold No. i key open for a few 
 seconds, and then closed the same length of time. If the signals 
 come imperfectly in both cases, it indicates that the contact-points 
 
Repeaters for Multiple Telegraphy. 189 
 
 of the distant pole-changer require cleaning. A very fine flat file 
 is the proper tool to use for this purpose. 
 
 If the dots on No. i fail to come well at the same time with the 
 writing on No. 2, instruct distant station to alternately open and close 
 No. 2 key at intervals of a few seconds ; the trouble may usually be 
 traced to defective contacts upon the single-current transmitter, pro- 
 vided the balance has been properly attended to. 
 
 It should not be forgotten that a change of weather which is suffi- 
 cient to affect the insulation of the line, may necessitate a readjust- 
 ment, to a greater or less extent, of both the rheostat and condenser 
 balance of the quadruplex. Both the line resistance and the elec- 
 trostatic capacity are diminished by a defective state of insulation. 
 
 The difficulties which may arise in the operation of a quadruplex 
 apparatus are of such various character that it would be quite impos- 
 sible to enumerate them in detail. Those which have been referred 
 to are among those most liable to occur under ordinary circum- 
 stances. 
 
 3290. Repeaters for Multiple Telegraph Systems. Not- 
 withstanding the apparent complexity of the duplex and quadruplex 
 apparatus, the arrangement of repeaters in connection with them is a 
 very simple matter. It is only necessary to include the electro-mag- 
 net which works the transmitter of one line of communication in the 
 same local circuit with the receiving apparatus of another line of 
 communication. This facility of adaptation of repeating devices 
 gives great flexibility to the system, and enables it to be employed 
 for special service in a great variety of ways. Thus, for example, a 
 single wire might be used as a duplex between New York and Boston, 
 New York and Hartford, and Hartford and Boston. The local cir- 
 cuits of the transmitter and of the receiver in a main office may be 
 extended through several branch offices in the same city, and thus 
 all these branch offices may exchange messages directly, either with 
 a distant main station, or with any one of a similar group of branch 
 offices in the distant city. The limits of the present work will not 
 permit a detailed description of these various applications of the 
 system, with their numerous modifications, but the general principle 
 will be readily comprehended by those who have made themselves 
 familiar with the apparatus on which they are based. 
 
CHAPTER IX. 
 
 TESTING TELEGRAPHIC LINES. 
 
 330. Object of the Tests. Telegraphic lines, from their ex- 
 posed situation, are peculiarly subject to interferences and interrup- 
 tions from various causes, and hence one of the most important 
 duties of an operator is to familiarize himself with .the nature of 
 these disturbances, so that their locatibn may be quickly determined 
 and the proper measures taken for their removal. This is effected 
 by an experimental investigation, technically termed testing. Another 
 object in testing is to examine the electrical condition of the wires 
 at stated intervals, and thus detect incipient faults before they be- 
 come serious enough to cause interruption of the service. 
 
 331. Faults and Interruptions. The principal sources of 
 interruption may be classified as follows : 
 
 (0) Disconnection or Break. The continuity of the circuit is in- 
 terrupted. A break may give rise to three different conditions : 
 (i) When neither of the broken ends is in electrical connection with 
 the earth; in this case the circuit is wholly interrupted so that no 
 current can pass ; (2) when one end is in connection with the earth ; 
 in this case there is no current on the portion of the line which is 
 disconnected from the earth, but more or less on the other portion 
 and (3) when both ends are in connection with the earth, in 
 which case there will be more or less current on both sections of 
 the line. 
 
 (b) Partial Disconnection, or Resistance. This fault may arise 
 from unsoldered and rusty joints in the line-wire ; from loose connec- 
 tions in the offices, or about the instruments, switches, and batteries ; 
 or from a defective or insufficient contact between the earth-plate 
 and the earth. 
 
 (c) Escape. Leakage from the line to the ground arising from 
 defective insulation generally, or specifically from the line getting 
 into contact with trees, wet buildings, etc. When an escape is so 
 serious that it is impossible to work past it, it is called a dead ground. 
 
 (d) Cross. This term is used to denote a leakage or escape of 
 current from one wire into another. An absolute contact between 
 
Testing for Disconnection. 
 
 191 
 
 two or more wires, so tli.it current passes freely from one to the other, 
 is termed a metallic cross. Sometimes parallel wires on the same 
 supports swing to and fro in the wind, occasionally touching each 
 other, and causing an intermittent disturbance termed a swinging- 
 cross. When only a portion of the current passes from one wire to 
 the other, through defective insulation, wet cross-arms or the like, 
 the effect is termed cross-fire, or sometimes weather-cross (248). 
 
 A defect in a ground wire or plate which serves as a common ter- 
 minal for two or more lines, produces an effect similar to that of a 
 metallic cross. This difficulty not infrequently arises from the re- 
 moval of a meter in the line of a gas-pipe which is used as a ground 
 connection for the wires (210). 
 
 332. Testing for Disconnection. When the circuit of a line 
 operated on the American or closed-circuit system (214) is totally 
 
 OOt , < rOO = OO-x 
 
 i \ 1+ 
 
 FIG. 163. Test for Disconnection. 
 
 interrupted, the armature of every relay in the circuit will fall off. 
 In such case, the operator at each way-station should immediately 
 proceed to test the line by connecting his ground to the line, first on 
 one side, and then, if necessary, on the other, as has been explained 
 in a previous chapter (278). If either connection closes the line, the 
 interruption is on that side, for the circuit of the opposite terminal 
 battery is completed through the ground in place of the interrupted 
 wire. If the ground-wire gives no current on either side, it is most 
 probable that the trouble is in the testing-station, though it may be 
 that the ground connection is defective. Each operator should first 
 assure himself by a careful examination that the fault is not in or 
 about his own apparatus. 1 Having ascertained the direction in which 
 the difficulty lies, he should at once report the facts to the terminal 
 station at the opposite end of the line. 
 
 1 An easy and expeditious way of doing this is to open the key, and then slightly 
 moisten one finger of each hand and touch lightly the binding-screws by which the 
 line-wires enter the switch. If the break is within the office a current will be perceived 
 by the touch. 
 
192 Testing Telegraphic Lines. 
 
 Fig. 163 represents a line with four stations, A, B, C, and D. If, 
 for example, the line be interrupted by a break at JF t two operative 
 circuits may be formed by putting on the ground-wires at B and C, 
 as shown in the figure. A can work with B, and C with Z>, notwith- 
 standing the break between B and C. 
 
 333. Disconnection is usually caused either by the breaking of the 
 line-wire or else by the careless leaving open of the switch of a key. 
 Other less frequent causes are wires loose in their binding-screws (a 
 defect peculiarly liable to occur in railway-station offices, on account 
 of the continual vibration caused by the passage of trains), defective 
 switches, and breakage of the fine copper wire in and about the re- 
 lay. Sometimes the latter is burned in two just where it enters the 
 helix, by the action of lightning. 
 
 334. Testing for Partial Disconnection. It is somewhat 
 difficult to locate this fault by testing merely with a key and relay. 
 It is liable to be of an intermittent character, which by no means 
 tends to lessen the difficulty. In case of this or any intermittent 
 fault, the best plan is to cross-connect, where it can be done, by in- 
 terchanging the defective line with a good one at the terminal and 
 
 x r^x 
 
 FIG. 164. Test for Intermittent Fault 
 
 also at some other station, as in Fig. 164. If, for example, the fault 
 is at F on No. 2 wire ; by cross-connecting at A and also at B, as 
 shown, the fault will shift to No. i, showing it to be between the two 
 points where the wires were to have been interchanged. If it were 
 beyond B it would have remained on No. 2 circuit. In the latter 
 case, put the wires straight again at B, and cross-connect at C and 
 so on, station by station, until the fault shifts to No. i, which proves 
 it to be between the two last stations. 
 
 335. Testing for Escape. Call the stations up in rotation, 
 beginning with the most distant one, and instruct each one to open 
 his key for say ten seconds. When any station beyond the point of 
 escape is open, a weak current will nevertheless pass to line through 
 the home relay, the circuit being partially completed through the 
 ground by the fault. For example, in Fig. 165, assume that terminal 
 station A is testing. When the key is open at C or D a current will 
 
Testing for a Cross. \ 93 
 
 pass to ground through the point ot escape, which will disappear when 
 JB opens his key, showing the fault is between B and C. 
 
 If the escape is so serious as to be in- effect a ground, the operator 
 at a way-station can often ascertain in which direction from him the 
 
 r-00 
 
 B C 
 
 -oo * oo 
 
 f- 
 
 J. 1^^ 
 
 FIG. 165. Test for Escape. 
 
 fault is located, from the fact that it cuts off or perceptibly weakens 
 the current from the terminal battery in that direction, when tested 
 with the ground-wire by the aid of the sense of feeling in the finger 
 or tongue. 
 
 336. Testing for a Cross. In case a cross is suspected to 
 exist between two wires, as for example No. i and No. 2, instruct 
 the most distant station to open No. i, and send dots on No. 2 wire. 
 Then open No. 2 at your own station, and if the dots sent on No. 2 
 at the distant station are received on No. i, the wires obviously must 
 be crossed. Some care is necessary not to be deceived by cross-fire, 
 due merely to imperfect insulation, and not to actual contact between 
 the wires. If the wires are in actual contact, the dots or signals will 
 come nearly as strong on one wire as on the other. 
 
 Next, instruct the distant station to leave No. i open. Open it at 
 the home station also. No. 2 will now be free from interference, and 
 station^ maybe communicated with upon it without difficulty. Com- 
 mencing at the most distant station, call them in succession, and in- 
 struct each one in turn to send dots on No. 2. If the dots come 
 on both wires, the cross is between the home station and the sending 
 station, but if upon No. 2 only it is beyond the station sending. 
 Each operator along the line should be instructed, while sending dots 
 on one wire, to open the other wire, if practicable. 
 
 337- Principle of the Cross Test. Figures 166 and 167 will 
 explain the principle of this test. A two- wire line is represented 
 having four stations, A, B, C, and D. Assume the operator at A to 
 be testing for a cross which is located between B and C. In Fig. 
 1 66, No. i is open at station C and No. 2 is open at station A. If 
 C sends dots on No. 2 the current will pass over to No. i at the 
 
i 9 4 
 
 Testing Telegraphic Lines. 
 
 cross, as indicated by the arrows, and the dots will come on the No. i 
 instrument at A, showing that the cross is between A and C. In 
 case C is not able to open No. i, the result will evidently be the 
 same, provided it remains open at D. 
 
 FIG. 166. Test for Cross. 
 
 Now, if C closes both wires and B opens No. i, and writes dots 
 on No. 2, as in Fig. 167, B cannot work when No. 2 is open at A, 
 as both wires are open, one at A and the other at B. With both 
 wires closed at A, the dots which B sends on No. i will reach A on 
 No. 2, the current from F going over both the wires to the cross, 
 and from thence to A on No. 2 alone. Thus the cross is definitely 
 located between B and C. 
 
 FIG. 167. Test for Cross. 
 
 338. A convenient and expeditious method of testing for crosses, 
 in offices where there are a considerable number of wires, is for the 
 operator to station himself at the switch with a test instrument, as 
 shown in Fig. 139. When any station has been instructed to send 
 dots on some particular wire, the testing operator can detect them 
 by placing one finger upon the ground-wire and the other upon the 
 line-wire to be tested, or its corresponding bar upon the switch. In 
 wet weather, however, this method of testing is sometimes attended 
 with much uncertainty, as it is extremely difficult to distinguish by 
 this means between the effect of a metallic cross and those due to 
 the leakage from wire to wire through imperfect insulation. 
 
The Wheatstone Bridge. 195 
 
 339. When a cross is found to exist between two lines, the one 
 having the largest number of offices, or for other reasons the most 
 available for business, should be cleared. The remaining wire can 
 then be utilized for a considerable portion of its length, by instruct- 
 ing the stations nearest the cross in each direction to open the main- 
 line wire at the switch, on the side towards the cross ; ground the 
 other side, and ground the line in the other direction. This will 
 enable the second line to be utilized in two sections. 
 
 340. Testing by Quantitative Measurement. The tests 
 which have been thus far described are such as may be made by the 
 ordinary apparatus employed for the transmission of messages. 
 They serve merely to roughly indicate the nature of the difficulty 
 when it is serious enough to appreciably interfere with correspond- 
 ence, and to determine between which two neighboring stations it is 
 situated, but for accurate work more refined methods are necessary. 
 Galvanometers and rheostats are the most essential instruments em- 
 ployed for this purpose, and the results are deduced by computation 
 from actual measurements, made upon the principles which have 
 been explained in Chapter IV. 
 
 The measurements required are principally of two kinds : measure- 
 ments of resistance and measurements of quantity, or, as it is usually 
 termed, current. 
 
 341. The Wheatstone Bridge. This apparatus consists of 
 three sets of resistance coils, a galvanometer, a battery, one or more 
 keys, and the necessary connections.- Its principal use is to 
 measure resistances, which may be done by its means with great 
 convenience and accuracy, usually from o.oi ohm up to 1,000,000 
 ohms. The theoretical arrangement of the bridge is shown in Fig. 
 1 68. It consists of four resistances, a, b, d, and x, arranged in a 
 parallelogram, the galvanometer being connected across one trans- 
 verse diameter, and the battery across the other. When the values 
 of the four resistances are so adjusted in relation to each other that 
 the current from the battery produces no deflection upon the gal- 
 vanometer, it is certain that these several values must then bear a 
 
 1 This ingenious and useful system of electrical measurement was first described by 
 SAMUEL HUNTER CHRISTIE, in Phil. Trans. R. S., 1833, 95-142. Its importance re- 
 mained unappreciated until attention was directed to it by Professor CHARLES WHEAT- 
 STONE, in a lecture before the Royal Society in 1843, entitled " An account of several 
 new Instruments and Processes for determining the Constants of a Voltaic Circuit." 
 Phil. Trans. R. S., cxxxiii. 303-327. Although full credit was accorded to Christie by 
 Wheatstone for his admirable device, electricians have ever since persisted in calling it 
 the Wheatstone Bridge, and it seems probable that it will always continue to be 
 known by that name. 
 
Testing Telegraphic Lines. 
 
 determinate ratio to one another. This ratio may be expressed as 
 follows : 
 
 As a is to l>, so is d to x. 
 
 This ratio holds good, entirely irrespective of the magnitude of 
 
 any of the resist- 
 ances. In the actual 
 apparatus, therefore, 
 as used in practice, 
 two of the resistances 
 (a and b) are fixed, 
 and the third (d) ad- 
 justable, the fourth 
 (x) being that which 
 is to be determined. 
 342. Best Ratio 
 of Electromotive 
 
 FIG. 168. Principle of Wheatstone Bridge. 
 
 Forces and Resistances. In performing the operation of test- 
 ing, with equal resistances in the branches a and b of the bridge, the 
 most trustworthy determinations are reached by preserving a due re- 
 lation between the value of the e. m.f. employed, the branch resist- 
 ances a and b, and the unknown resistance x, which is to be meas- 
 ured. Hence when the unknown resistance is 
 
 Between I and 100 units, a and b should be 10 ohms each ; e. /./., i volt. 
 Between 100 and 1000, a and b should be 100 ohms each ; e. m. f., 10 volts 
 Between 1000 and 10,000, a and b should be 1000 ohms each ; c. ///. /., 100 
 volts. 
 
 343. Principle of the Wheatstone Bridge. This may be 
 most readily comprehended by considering that at every point where 
 
 100 
 
 75 
 
 50 
 
 25 
 
 120 
 
 FIG. 169. Fall of Potential in Arms of Bridge. 
 
 a circuit divides into two or more branches, the potential of each 
 branch must necessarily be the same. If, at any other point, any 
 two or more of these branches are again joined, the potentials must 
 again be the same. In the bridge, therefore, if we assume the po- 
 tential at the point where the current first divides to be say 100 volts, 
 
Principle of the IVheatstone Bridge. 197 
 
 and at the point where they meet again or are connected to the earth 
 to be o, let each circuit be assumed to be divided into 100 equal 
 spaces, as indicated in Fig. 169. If now a wire be connected across 
 from one of the branch circuits to the other, connecting the point 50 
 
 FIG. 170. Wheatstone Bridge Apparatus. 
 
 to 50 or 75 to 75, or, as shown in the figure, 25 to 25, or between 
 any other two points whatever having the same potential, no current 
 can flow from one point to the other through the wire, because there 
 exists no difference of potential between its ends ; but if, on the 
 other hand, the wire is connected between any two points of different 
 
198 
 
 Testing Telegraphic Lines. 
 
 potential, as, for example, from 50 to 25, a current will necessarily 
 flow through it (143), and a galvanometer placed in the wire will be 
 deflected. When, therefore, the needle is not deflected, the propor- 
 tionality referred to in (341) must always exist between the resist- 
 ances of the four sides of the bridge. 3 
 
 344. Actual Construction of the Bridge. One of the most 
 useful sets of coils for general purposes is that shown in Fig. 170, 
 
 and in outline, with diagram 
 of bridge connections, in Fig. 
 171. The various resistances 
 are arranged in the manner 
 hereinbefore described (341) ; 
 and in the diagram, Fig. 171, 
 as well as on the actual box. 
 the respective values of the 
 resistances are denoted by 
 numbers representing ohms. 
 The points marked INF.. or 
 " infinite," indicate a total 
 disconnection when the plug 
 is withdrawn. 
 
 In some of the more mod- 
 ern sets of apparatus, such 
 
 as that shown in Fig. 172, the galvanometer, rheostat, branch-coils, 
 contact-keys, and five cells of battery, with the necessary connections, 
 are all put up in a portable mahogany box, with lock and handle. A 
 lifter is provided for raising the needle from its pivot when the appa- 
 ratus is not in use. 
 
 345- Galvanometer for the Wheatstone Bridge. In se- 
 lecting a galvanometer for any particular purpose, one having a 
 few turns of thick wire, and small resistance, is most suitable for 
 measuring small resistances, while for long circuit or a great resist- 
 ance of any kind, a galvanometer of many turns of thin wire should 
 be selected. Fig. 173 shows an excellent type of galvanometer for 
 use in the bridge as well as for general purposes. It has an astatic 
 system of needles, 4 suspended by a delicate silk fibre, and is fitted 
 
 3 The above explanation has been adapted from LATIMER CLARK : Electrical 
 Measurement, p. 85. The student desiring to acquaint himself thoroughly with the 
 theory of the bridge may, with advantage, consult also F. JENKIN : Electricity and 
 Magnetism, p. 241 ; H. R. KEMPE : Handbook of Electrical Testing, p. 166 ; SILVANUS 
 THOMPSON : Elementary lessons on Electricity and Magnetism, p. 318. 
 
 4 An astatic system of needles consists of two needles suspended parallel to each 
 Other and near together, with their poles placed in contrary directions. One is a little 
 
 FIG. 171. Diagram of Bridge Connections. 
 
Galvanometer for the Wheats tone Bridge. 199 
 
 with a permanent magnet, called a directing magnet, by which the 
 needle can be brought to zero in any desired angular position of the 
 apparatus. 
 
 FIG. 172. Wheatstone Bridge Apparatus, with Galvanometer and Battery. 
 
 346. To Measure the Conductivity Resistance of a 
 Telegraph Line. Have the remote end of the line put to ground, 
 taking care that no relays are left in circuit. Connect the home end 
 
 stronger than the other, so that the pair has a very feeble tendency to place itself in 
 the magnetic meridian (86 6). Such a system is capable of being deflected by a very 
 weak current, and hence is used in th2 construction of the more delicate types of 
 galvanometers. 
 
2OO 
 
 Testing Telegraphic Lines. 
 
 FIG. 173. Astatic Galvanometer with Directing Magnet. 
 
 of the line to the terminal C, and the terminal E to the ground, as 
 in Fig. 174. Unplug from A B (b) and B C (a) each, a resistance 
 
 most nearly approx- 
 imating in value 
 that of the line to 
 be measured (342). 
 Usually this will be 
 1000 in each. Press 
 the right-hand or 
 battery-key B' and 
 remove plugs from 
 E A (d) until the 
 resistance un- 
 p lugged equals 
 roughly that which 
 is to be measured. 
 Then depress the 
 left-hand or galva- 
 nometer-key A', and 
 
 rearrange and adjust the plugs in E A (<i) until the key can be 
 repeatedly opened and closed without causing any movement of the 
 
 FIG. 174. 
 
 EARTH 
 Conductivity Test, 
 
Conductivity Resistance by Loop Method, 201 
 
 galvanometer-needle. 5 When this balance has been effected, the 
 resistance unplugged in E A is equal to the conductivity resistance 
 of the line under test. 
 
 346^. Conductivity Resistance by Loop Method. A more 
 accurate method of making conductivity tests, which is available 
 whenever there are three or more parallel wires available between 
 the same points, is the loop test. If we suppose the wires to be Nos. 
 i, 2, and 3, they are looped together in different combinations at the 
 distant station, and the resistances of the several loops taken in 
 succession, one end of the loop under test being connected to C and 
 the other to E, as in Fig. 171. For example, suppose the resistances 
 to measure as follows : 
 
 Resistance of I and 2, looped 6550 ohms. 
 
 " 2 and 3, " 6180 ' : 
 
 " i and 3, " 6830 " 
 
 Sum of all three 19560 " 
 
 As by this process the resistance of each wire has been taken 
 twice over, we divide the amount by 2 = 9780 ohms. 
 
 If we deduct from this result the total of each pair of looped wires 
 in succession, the remainder in each case must be the resistance of 
 the wire not in the loop. Thus : 
 
 9780 6180 = 3600 for No. i wire. 
 9780 6830 == 6830 for No. 2 wire. 
 9780 6550 = 3230 for No. 3 wire. 
 
 Conductivity tests may also be made with sufficient accuracy fo? 
 most purposes, and with great convenience and facility, by means of 
 a properly constructed voltmeter. See (369). 
 
 347. Earth Currents. In making conductivity tests with the 
 distant end of the line to ground (346), interference is sometimes 
 caused by earth currents, which flow through the wire, and aid or op- 
 pose the testing current, as the case may be. When these are toler- 
 ably steady and not too strong, their effect may be eliminated by 
 making measurements with both a positive and a negative current 
 and taking the mean of the two results. Sometimes, however, these 
 earth currents are so strong that an accurate measurement cannot be 
 made, and the loop method (3460) must be resorted to. 
 
 6 Care should be taken in all cases, when finally closing the circuit by the second 
 or galvanometer-key, to first make very short contacts or " taps," just enough to indi- 
 cate the direction of the deflection of the needle, until the coils are nearly adjusted to 
 a balance, otherwise much time will be needlessly lost by the oscillations of the needle. 
 
2O2 Testing Telegraphic Lines. 
 
 348. Measurement of Resistance of Ground Plate at 
 Distant Station. The principle of this measurement is the same 
 as that last described. Two lines are necessary ; the earth takes the 
 place of the third line. For example, suppose we have : 
 
 Resistance of No. I and No. 2, looped 6550 ohms. 
 
 " No. i and distant ground 3625 " 
 
 " " No. 2 and distant ground 2975 " 
 
 Half the sum of which is 6575, from which deduct loop resistance 
 of Nos. i and 2, gives 25 ohms as resistance of ground. The resist- 
 ance of a ground plate ought not to exceed 10 ohms. 
 
 349. Measurement of Insulation Resistance of a Line. 
 In making this test, the connections at the home station are the 
 same as in the conductivity test (346) ; the line is open or insulated 
 at the distant station, instead of being to ground. In most cases, 
 the insulation resistance will exceed the amount of resistance avail- 
 able in the E A side of the bridge. In this case the resistance in 
 A B (/>) must be made greater than that in B C (a). For example, 
 it may be 10 in B C and 100 or TOGO in A B. In this case, when 
 the balance has been obtained, the amount unplugged in E A (d) 
 must be multiplied by 10 or by 100, as the case may be, in order to 
 obtain the correct resistance. It will be observed that under these 
 conditions, the ratio of the resistances in the different parts of the 
 bridge remains unchanged. 
 
 350. Location of the Position of a Ground. When the 
 fault is a dead ground, which is not often the case, it is a very simple 
 matter to locate it. For example, if the line were 250 miles long, 
 and from previously recorded measurements its conductivity was 
 known to be 3250 ohms, or 13 ohms per mile, and the resistance 
 measured through the fault was 1287 ohms, then the distance from 
 the testing station would be 1287 -5- 13 = 99 miles. 
 
 351. Location of the Position of an Escape. This is 
 one of the most common cases which arise in practice. If no other 
 than the defective line is available for the measurement, the process 
 presents some difficulties, for the reason that the resistance of the 
 fault is usually variable. If we have, for example : 
 
 (1) Resistance of line in good order (from previous tests). . 4500 ohms. 
 
 (2) " with distant end open (measured) 35OO " 
 
 (3) " with distant end to ground (measured) 2700 
 
 Subtract (3) from (2) and also (3) from (i) ; multiply the two re- 
 mainders together and extract the square root of the product, and 
 
Varleys Loop Test. 203 
 
 finally subtract this result from (3). In the above case, this would 
 give the resistance of the conductor to the fault as 1500 ohms. 
 While this method is theoretically accurate, it will not do to depend 
 too much upon it in practice, for the reasons given. 
 
 352. Method of Double Measurement. Let two measure- 
 ments be made, one from each end, the opposite end of the line 
 being open. Suppose the fault the same as in the last case. By 
 records and measurements we have, 
 
 (1) Conductivity resistance of wire when good. . . . 4500 ohms. 
 
 (2) Resistance measured from A with B open 35oo " 
 
 (3) " B with A open 5000 
 
 To find the resistance from A to the fault. Subtract (3) from the 
 sum of (i) and (2), and divide the remainder by 2. 
 
 To find the resistance from B to the fault. Subtract (2) from the 
 sum of (i) and (3), and divide the remainder by 2. 
 
 The fault is 1500 ohms from A and 3000 ohms from B, which 
 may be reduced to miles as in (350). 
 
 353. The Loop Test. When a good wire is available between 
 the same points as the defective wire, this method may be made to 
 give extremely accurate results in the hands of a careful operator. 
 The arrangement of the connections, the method of making the 
 measurements, and the computation of the result are precisely the 
 same as in the method described for measuring a distant ground in 
 (346). If the resistance of the fault is considerable, care should 
 be taken to employ sufficient battery-power to get decided deflec- 
 tions on the galvanometer. The loop should be made at the nearest 
 station available beyond the fault. 
 
 354. Varley's Loop Test. The arrangement of connections 
 for this modification of 
 
 the loop test is shown in 
 Fig. 175. The defective 
 wire is looped with a good 
 wire, and terminal B is 
 
 connected to a grounded ] ^^Xftn^ -^ EARTH 
 
 battery. B C and A B are 
 the fixed resistances ; E A 
 is adjusted until equilib- 
 
 rium is reached. The FlG> , 7S . Principle of Varley's Loop Test. 
 
 actual connections are 
 
 shown in Fig. 176. The calculation is made as follows : 
 
 Suppose a line having a total conductivity resistance of 4500 
 
204 
 
 Testing Telegraphic Lines. 
 
 
 A B 
 
 
 
 j 
 
 
 D 
 
 g=> 
 
 
 A' 
 
 i ^ ^ 
 
 [ 
 
 
 ~ T B^ 
 
 I 
 
 E 
 
 EARTH 
 
 ohms looped with another line of the same resistance, we should 
 then have : 
 
 (1) Total resistance of loop 9000 ohms. 
 
 (2) Resistance in E A to balance, 6000 
 
 Subtract (2) from (i) and divide remainder by 2, gives number 
 of ohms between terminal E and the fault (in this case 1500), which 
 
 is reduced to miles in 
 the usual way (350). 
 
 The defective wire 
 must always be at- 
 tached to terminal E, 
 or the needle cannot 
 be made to balance. 
 Therefore, in case a 
 balance cannot be ob- 
 tained, the obvious 
 remedy is to reverse or 
 interchange the loop 
 connections with the 
 rheostat. 
 
 355. To Locate a 
 Cross. In case a 
 third good wire is not available, connect one of the crossed wires to 
 C and the other to E of the bridge. Make one measurement of the 
 loop through the cross with both lines open at nearest available sta- 
 tion beyond, and another with the same wires looped at that station. 
 If the two measurements are approximately the same, the number of 
 ohms in the loop divided by 2 and converted into miles will give the 
 distance of the cross from the testing station. If the lines are of 
 different length, owing to the routes being different, allowance must 
 be made for the fact ; also, if the wires are of different conductivities 
 per mile. 
 
 356. When the two measurements differ considerably, showing 
 that the cross offers more or less resistance, the above test would 
 give a result in excess of the real distance. In such case the follow- 
 ing procedure maybe adopted. In Fig. 177, suppose wires No. i 
 and No. 2 to be crossed at X. 
 
 By measurement from A B we get the following results, for ex- 
 ample : 
 
 (1) No. i from A to C (with No. 2 open at B and D) 3000 ohms. 
 
 (2) No. 2 and No. i from A to B through the cross at X. . . 4650 " 
 
 (3) No. 2 and No. i from B to C through the cross at X. . . 2650 " 
 
 IW*- 
 
 Varley's Loop Test. 
 
Shunts of Galvanometers. 205 
 
 Deducting (3) from the sum of (i) and (2) gives 5000, which 
 divided by 2 gives 2500 ohms, as resistance of No. i wire from A to 
 X. The distance on No. 2 wire may be found, if desired, in the 
 same way. 
 
 FIG. 177. Distance Test for Cross. 
 
 357. When a third wire in good order is available, the most con- 
 venient as well as the most accurate method of locating a cross, is 
 to ground either one or both ends of one of the crossed wires and 
 make the other crossed wire into a loop with the good wire. The 
 cross can then be treated as a ground, and located by one of the loop 
 tests heretofore given in (353) and (354). 
 
 358. To Locate a Bad Joint or Abnormal Resistance. 
 It sometimes happens that a line gives a much higher resistance 
 than it should do, according to computation or by previous measure- 
 ment. In such cases a bad joint may be suspected. To locate it, 
 instruct a station midway of the line to put on ground. Take a 
 measurement through first half of the line and this ground, the dis- 
 tant end being open. This will show whether the fault is in the sec- 
 tion measured or beyond. Repeat the test to another station in the 
 middle of the defective section, and so on until it has been fixed 
 between two sections. 
 
 359. Measurement of very High Resistances. The 
 highest resistance which can be measured by the Wheatstone Bridge 
 apparatus, described in (344), is i megohm, or 1,000,000 ohms. 
 This is a sufficient range to cover most of the requirements ordi- 
 narily met with in practical telegraphy, but in testing insulators, or 
 the insulation resistance of very short sections of out-of-door line, it 
 is often desirable to be able to determine much higher resistances. 
 The method of proportional deflections is usually resorted to in such 
 cases. A galvanometer having a coil of a large number of turns of 
 very thin wire and a delicately suspended needle (345) is most suit- 
 able for the purpose. 
 
 360. Shunts of Galvanometers. The galvanometers for 
 this work must be provided with shunts ; these are short coils of 
 .wire, arranged to be connected or bridged across the terminals of 
 the galvanometer, and are usually marked (to indicate their multi- 
 plying power) i- 10, i-ioo, and in very delicate instruments usually 
 i-iooo also. 
 
2O6 
 
 Testing Telegraphic Lines. 
 
 FIG. 178. Shunt Box for Galvanometer, 
 
 The first shunt coil has 1-9, the second 1-99, and the third 1-999 
 of the resistance of the galvanometer coil. They are made of cop- 
 per wire, that they may be affected by temperature in the same ratio 
 as the galvanometer coils. Fig. 178 shows an arrangement much 
 
 used, in which either of 
 three shunts may be thrown 
 into use at will by changing 
 the peg. 
 
 361. Measurement by 
 Deflections. This meth- 
 od is useful in making com- 
 parative tests of insulators. 
 In this case the internal re- 
 sistance of the testing bat- 
 tery is inappreciable in com- 
 parison with the resistance to be measured, and hence the force of 
 the current acting upon the needle may, without sensible error, be 
 regarded as proportionate to the e. m.f. of the battery. 
 
 First, connect the galvanometer G in circuit with a large known 
 resistance R (say 10,000 ohms) and a single cell E, whose e. m.f. is 
 known, as, for instance, a gravity cell (9). If the deflection exceeds 
 12, reduce it to a point below that figure by the ^ 
 
 use of the proper shunts. 6 The arrangement of 
 the connections for performing this operation, 
 which is termed taking the constant of the galva- 
 nometer, is illustrated in Fig. 179. Second, remove 
 the shunt and the resistance R, and having re- 
 placed the latter by the unknown resistance to be 
 measured, add a sufficient number of cells of the 
 same kind (in series) to produce a convenient 
 deflection, not exceeding 12, as before. The 
 result is found by simple rule of three, as in the 
 example given in the next paragraph. 
 
 362. Measurement of Resistance of In- 
 sulators. Mount a set of say 10 insulators, 
 I, Fig. 1 80, upon a suitable frame out of doors, 
 exposed to rain under the same conditions as if 
 in actual service. Bind a line-wire to the whole series, and connect 
 this with one terminal of the galvanometer G, the other terminal of 
 
 The reason for this procedure is, that above this point the angles of the deflec- 
 tions cease to be proportional to the strength of the currents producing them. (Com- 
 pare table of tangents, p. 55.) 
 
 FIG. 179. Taking 
 Constant. 
 
Measurement of Internal Resistance of Battery. 207 
 
 galvanometer to zinc pole of battery E, and the copper pole of bat- 
 tery to ground. Suppose that with the particular galvanometer 
 msed, the following results are obtained, the weather being very wet : 
 
 i cell through 10,000 ohms 41 J 
 
 i " " 10,000 " (with 10 shunt) 5 
 
 Constant of galvanometer (i cell through 10,000 ohms). . 50 
 
 10 cells through 10 insulators in parallel 10 
 
 Therefore, if i cell will give 50 through 10,000 ohms, as per constant, 10 
 cells will give 50 through 100,000 ohms : and will therefore give 10 
 through 500,000 ohms. 
 
 Hence the joint resistance of the 10 insulators is 500,000 ohms, 
 and their mean individual 
 resistance 5,000,000 ohms, ' 
 
 or 5 megohms, per insu- Q Q Q Q Q Q Q 
 
 lator. 
 
 363. Measurement of EG 
 the Internal Resist- - I 1 | l | i | i ! + /"T\ 
 
 ance of a Battery.-(i) ( 1 II I l|l|l|l|l lp\fj ^ 
 
 It follows from Ohm's law 
 
 (124) that when the total \^><^\ 
 
 resistance of any circuit, FlG . l8o . Test O f insulators, 
 
 embracing that of an in- 
 cluded battery and galvanometer, is doubled, the quantity of the cur- 
 rent flowing through it is halved ' ; and hence if the indications of the 
 galvanometer be proportional to the strength of current, its deflection 
 will also be halved. If a tangent galvanometer (96) of known re- 
 sistance is at hand, connect it with a plugged rheostat in the circuit 
 of the battery to be measured. Reduce the sensitiveness of the in- 
 strument by a shunt (360), if necessary, to bring the deflection as 
 near 60 as possible, and note the corresponding tangent of the 
 deflection as given in the table, p. 55. Unplug resistance until the 
 tangent of the deflection is halved, showing that the total resistance 
 has been doubled. Deduct the resistance of galvanometer and con- 
 nections from the added resistance ; the remainder is the resistance 
 of the battery. Do not forget that the shunt, when used, diminishes 
 the resistance of the galvanometer as a part of the measured circuit. 
 
 364. (2) If the resistance of the galvanometer is unknown, a 
 modification of the Wheatstone bridge may be used. Make the 
 connections as in Fig. 181. Connect the terminals B' and E by a 
 short, thick wire. The left (galvanometer) key is permanently de- 
 pressed. Touch the right-hand key and adjust resistance A E (d) 
 until the needle remains at rest (it will not be at zero). It is neces- 
 
208 
 
 Testing Telegraphic Lines. 
 
 N 
 
 B 
 
 1 \ 
 
 *4 1 j 
 
 j 13 
 
 sary to shunt the galvanometer in this test. If the resistance in 
 A B (a) is equal to that in A B (), the amount unplugged in A E 
 is equal to the resistance of the battery. In any case, by proportion, 
 
 A B is to A C as A E is to the 
 resistance of the battery. 
 
 The most accurate results 
 will be reached when A B is as 
 high and A C is as low as pos- 
 
 ., r i sible, but not so high as to 
 
 l\ carry A E beyond the range 
 
 of the rheostat. 
 
 365. Measurement of 
 Resistance of Galvanom- 
 eter. If, in the diagram, 
 Fig. 1 8 1, the battery and gal- 
 vanometer are made to change 
 FIG. 181. Resistance of Battery. places, the resistance of the 
 
 galvanometer may be deter- 
 mined in the same way. Make B C (a) not more than one-tenth of the 
 probable resistance of galvanometer, and make A B (b) not less than 
 ten times the same, but not so high as to carry A E beyond the range 
 of the rheostat The least possible value of B C with an ordinary 
 bridge set would be 10 ohms. A smaller resistance might be extem- 
 porized from a piece of wire, if necessary. 
 
 366. The Differential Galvanometer. This instrument is 
 primarily designed to show the difference in strength between two cur- 
 rents. The coil is wound throughout with two wires, equal in length, 
 resistance, and number of convolutions, so that the same current in 
 each will have a like effect upon the needle. The two wires are 
 sometimes formed into a tape by plaiting together the silk with which 
 they are covered. If, therefore, two equal currents traverse the 
 respective wires in opposite directions, the needle will not move. If 
 one current be stronger than the other, the needle will be moved by 
 the stronger current with a force due to the difference in the strength 
 of the two currents. This instrument was formerly much used to 
 measure resistances by comparing them with standard resistance 
 coils, but has now been practically superseded by the Wheatstone 
 bridge (341). 
 
 367. Testing for Insulation by Received Currents. 
 This system of testing offers many advantages over that hereinbefore 
 referred to (340) for the daily examination of telegraph lines. The 
 current from a testing battery, of a definite and approximately uni- 
 
Testing for Insulation by Received Currents. 209 
 
 form e. #/./., is sent at a stated time through the different lines, or 
 sections of lines, and the volume of current, as indicated by a tan- 
 gent galvanometer such as that shown in Fig. 182, or by an ammeter 
 (369) at the receiving end, is registered. It is evident that the 
 strength of the received current will be greater or less as the insula- 
 tion is better or worse, and hence if the e. m.f. of the battery be 
 constant, the volume of the received currents as observed from day 
 
 FIG. 182. Western Union Tangent Galvanometer. 
 
 to day will give an accurate knowledge of the condition of the lines. 
 The normal resistance of each line is known from the stated con- 
 ductivity tests, and so if the currents be sent from a battery of known 
 e. m. f. it is only necessary to divide the latter amount by the former 
 to know at once the maximum current which can possibly be received 
 through any wire. For example, if a battery of 50 cells be used on 
 a circuit of 2500 ohms, then 
 
 50 volts -f- 2500 ohms 0.02 ampere. 
 
 This may be regarded as the standard current of that circuit, and 
 the greater the leakage the greater will be the diminution of the cur- 
 rent below that standard. Tables may be made for convenient refer- 
 ence showing the normal current of each line. Special faults are of 
 
2io Testing Telegraphic Lines. 
 
 course investigated by the bridge apparatus (341) when their presence 
 has been revealed by the procedure above described. 
 
 368. Use of the Voltmeter and Ammeter in Tele- 
 graphic Testing. Since the general introduction of electricity 
 in lighting and power service, a new class of instruments for the 
 measurement respectively of potential and current, known as volt- 
 meters and ammeters, have been brought to great perfection, and are 
 now frequently employed with advantage in telegraphic work. Much 
 time is saved in making readings and computations, as a simple in- 
 spection of the indication of the pointer on the scale at once gives 
 the result in volts or amperes. The pointer comes to rest promptly, 
 so that a reading dan be made almost instantaneously. 
 
 369. The Weston Ammeter and Voltmeter. Fig. 183 
 shows Weston's portable type of direct-reading mil-ammeter, about 
 
 one-fourth its actual size. 
 It comprises a permanent 
 magnet, having a hollow 
 rectangular coil of alumin- 
 ium wire suspended within 
 its field upon jeweled piv- 
 ots, to which coil the pointer 
 is attached. Fig. 184 is a 
 full-sized view of the work- 
 ing parts of the instrument. 
 One of the most useful types 
 for telegraphic work has a 
 
 FIG. ,8 3 . Weston's Mil-ammeter. scale reading to i ampere, 
 
 with subdivisions of 10 mil- 
 amperes, which may be read by inspection to a single mil-ampere. 7 
 Another type, which is adapted to perform all the measurements 
 ordinarily required in a large telegraph station, is provided with 
 several scales ; one of a single volt, which may be read to .001 volt, 
 for determining the potential of a single cell ; another of o to 500 
 volts (which can be read to single volts or half volts), for taking the 
 potential of a large number of cells when connected in series in a 
 single battery ; another of i ampere (which can be read to mil- 
 amperes) for determining the strength of currents. Some are made 
 
 7 The construction of the voltmeter and ammeter are simLar, the difference being 
 in the length and thickness of the wire in the deflecting coil, which is made long, thin, 
 and of great resistance in the voltmeter, and comparatively short and thick and of 
 small resistance in the ammeter. Two or more coils of different lengths may be fitted 
 to the same instrument, as in a galvanometer, giving different grades of sensibility. 
 
The Weston Ammeter and Voltmeter. 211 
 
 with a coil of precisely 100 ohms resistance, giving a full scale 
 deflection with i volt. Such an instrument is very convenient for 
 measuring line resistances. For example, with 100 volts the resist- 
 ance in circuit required to bring the pointer to the upper division of 
 the scale would be 10,000 ohms, and hence by pointing off two 
 decimal places any resistance in ohms in the circuit may be deter- 
 mined by direct reading from the scale, in the same manner as volts. 
 
 FIG. 184. Mechanism of Weston's Direct-Reading Instrument 
 
 The Weston instruments are particularly well adapted for all cur- 
 rent measurements usually performed with a tangent galvanometer 
 (102). They are not only, for most purposes, more accurate, but 
 are far more convenient, as they may be placed in any position, and 
 are in no wise affected by the neighborhood of masses of iron or of 
 foreign electric currents. No time need be lost in leveling, adjust- 
 ing, or waiting for the needle to settle, while the convenience of 
 being able to read off the results directly without calculation is very 
 great. 
 
 Another and a very important advantage is, that the tests may be 
 made with the same current which is employed in the ordinary 
 operation of the circuit Tests for resistance, especially, not unfre- 
 quently give very fallacious results, when made, as is often the case, 
 
212 
 
 Testing Telegraphic Lines. 
 
 JS 
 
 i 
 
 
 
 , 
 
 1 
 
 & 
 
 A 
 ri 
 
 ! 
 
 
 a * 
 
 II 
 
 i 
 
 
 a 
 
 Ii 
 
 t 
 
 ; 
 
 15 
 O 
 
 O 
 
 
 
 
 is 
 
 i 
 
 <K 
 
 
 1 
 
 4 
 
 X 
 
 
 ^ 
 
 i. 
 
 w V 
 
 p 
 
 !i 
 
 
 
 
 
 in Ckt. 
 
 ii 
 
 
 >* 
 
 3 
 
 oi 
 
 
 
 1 
 
 as 
 
 | 
 
 S5 
 
 
 P< 
 
 a 
 
 
 
 I 
 
 I 
 
 a 
 
 
 
 
 t 
 
 <D 
 
 
 
 
 1 
 
 
 
 o 
 
 ^ 
 
 
 rH 
 PH 
 
 QS 
 
 <u 
 
 
 a 
 
 a 
 
 s* 
 
 i 
 
 1 
 
 
 a 
 
 ^ 
 
 
 BC 
 a 
 4J 
 
 CO 
 
 ^ 
 
 
 (D 
 
 p < 
 (D 
 
 00 
 
 
 3 
 
 i 
 
 
 H 
 
 f-4 
 
 
 
 1 
 
 2 
 
 1 
 
 
 JH 
 
 .2 
 
 
 
 ^ 
 
 a 
 
 a 
 
 * 
 
 1 
 
 
 PI 
 fi 
 
 
 
 s 
 
 OB 
 
 
 
 00 
 
 
 Jz; 
 
 
 rt 
 
 
 
 i^ 
 
 1! 
 
 
 fH 
 
 5 
 
 m 
 
 
 
 
 
 2 
 
 i 
 
 
 (D 
 
 fe 
 
 ^ 
 
 
 ^ 
 h 
 
 
 
 c. 
 
 c* 
 o 
 
 ^ 
 
 
 K 4 
 
 > 
 
 4J 
 
 '> 
 
 
 A 
 
 O 
 U 
 
 | 
 
 i 
 
 
 
 *J 
 
 o 
 
 D 
 13 
 
 
 S 
 
 i 
 
 
 
 U 
 
 U 
 
 <M 
 
 
 
 
 Station 
 
 '1 \.^< :,:\ 
 
 M 
 
 s^ 
 
 
 
 u; 
 
 0) 
 
 
 1' 
 
 Tor 111 1 n us. 
 
 
Recording Tests of Conductivity and Insulation. 2 1 3 
 
 
 ft 
 
 
 
 e " 
 
 sg 
 
 * 
 
 8 
 
 
 1 
 
 r 
 
 c 
 
 
 
 
 |i 
 
 
 3 
 
 
 
 
 s s 
 
 C 
 
 
 P 
 
 S 
 
 1 
 
 
 II 
 
 H 
 
 B" 
 
 in 
 
 9 
 
 r 
 
 
 
 5 
 
 
 
 SI 
 
 1 
 
 
 
 Is 
 
 
 
 
 | 
 
 8 
 8 
 
 
 
 t* 
 
 o 
 B 
 
 
 
 
 5" 
 
 1 
 
 
 
 = 
 
 1 
 
 
 
 
 4 
 
 
 
 
 ! 
 
 
 S H 
 
 h 
 
 
 >~ 
 
 < 
 
 
 p E 
 
 
 
 3g SI 
 ?BS ? 
 
 
 
 BT O 
 
 1-4 
 
 
 
 i 
 
 1 
 
 1 
 
 
 
 
 
 
 
 
 | 
 
 3" 
 
 o 
 
 
 
 '* 
 
 i 
 
 
 
 s 
 
 
 
 1 
 
 
 
 S" 
 
 
214 Testing Telegraphic Lines. 
 
 with a current of much lower potential than the actual working 
 current. 
 
 370. Recording Tests of Conductivity and Insulation. 
 The forms of returns for line tests adopted by the Western Union 
 Telegraph Company are given on pp. 212, 213. When the tangent in- 
 strument is used, the constant (361) is written in the upper right-hand 
 corner of the sheet. One horizontal line is appropriated to each 
 separate wire tested. The headings sufficiently explain entries to be 
 made in the several columns. When the tests are made by the bridge 
 apparatus, the results are entered directly in the resistance columns, 
 but if with the tangent instrument, these are computed and filled up 
 at the electrician's office in New York. The same observations ap- 
 ply to the insulation form. The record of the wet and dry bulb 
 thermometer is important, as it enables the percentage of moisture 
 in the air to be determined and its effect upon the different kinds 
 of insulation to be compared and studied. 
 
 By inspecting and comparing these sheets, as returned from the 
 various testing offices, the electrician's department is kept fully 
 informed of the electrical condition of the lines in all parts of the 
 country. The system of stated reports was instituted by Lefferts, 
 of the American Telegraph Company, in i863, 8 and has resulted in 
 a vast improvement in the efficiency of the service. 
 
 8 LEFFERTS (MARSHALL), born January 15, 1821, in Bedford, now part of Brook- 
 lyn, N. Y. In early life he was a civil engineer and was employed in laying out the 
 city of Brooklyn. Subsequently he became a successful merchant in New York City, 
 and a prominent militia officer. In 1849 his marked scientific tastes led him to be- 
 come interested in telegraphy. Entering into the new enterprise with the energy and 
 zeal which were among his most notable characteristics, he organized and became the 
 president and manager of a range of lines operating the Bain electro-chemical sys- 
 tem, extending from New York to Boston and Buffalo. Legal complications in con- 
 nection with patents eventually led to a consolidation of these lines with those con- 
 trolled by the Morse patentees, in consequence of which he resumed for a time his 
 manufacturing and mercantile business. In 1860 he was appointed engineer and exec- 
 utive manager of the American Telegraph Company, which under his administra- 
 tion became one of the most popular and successful telegraph organizations that ever 
 existed on this continent. He retained this position until the consolidation of the 
 American with the Western Union Telegraph Company in 1866, and subsequently 
 occupied a responsible post in the united service until 1871. At this date he was 
 elected president of the Gold and Stock Telegraph Company of New York, which po- 
 sition he held until his death. He possessed a most unusual organizing and executive 
 ability, and while a strict disciplinarian, it afforded him genuine pleasure to discover 
 and to reward meritorious service, even in the humblest capacity. His uniformly just 
 and considerate treatment of his employees, no less than his genial and kindly spirit, 
 insured the most loyal, enthusiastic, and diligent service from all. By a liberal system 
 of advancement to the intelligent, the skillful, and the deserving, the standard of 
 character and acquirements among the employees of the American Company was 
 elevated to an extent to which later times have afforded few parallels. As engineer of 
 
Recording 7 ^esis of Conductivity and Insula tiou. 215 
 
 this extensive organization, he labored unceasingly to place its service upon a perma- 
 nent foundation befitting its importance and its high mission. He was the first to 
 appreciate the importance of testing lines and apparatus, and it is to the standard ot 
 excellence which he established that the commencement of the era of scientific teleg- 
 raphy in America may be traced. Assuming in 1861 the administrative management 
 of a heterogeneous assemblage of poorly built and ill-arranged telegraphs, equipped 
 with a miscellaneous collection of apparatus of antiquated and unserviceable types, he 
 five years later turned over to the Western Union Company 30,000 miles of wire, 
 constituting perhaps the most complete, thoroughly organized, and efficient tele- 
 graphic system in the world. The influence of the reforms and improvements which 
 were instituted during his administration will continue to be felt in the American 
 telegraph service for all future time. He died suddenly, July 3, 1876, while on his 
 way, as commander of a military organization, to participate in the celebration of the 
 centennial anniversary of the Declaration of American Independence, in Philadelphia. 
 
CHAPTER X. 
 
 HINTS TO LEARNERS. 
 
 371. Formation of the Telegraphic Code. The code of 
 alphabetical and numerical signals employed in telegraphy, as devised 
 by Vail in 1837,! is made up of various combinations of a small 
 number of elements. In the so-called " Morse " code, as used in 
 America, there are seven of these elements, viz. : 
 
 (i) The dot; (2) theitasA; (3) \hzlongdash; (4) the ordinary 
 space; (5) the letter-space; (6) the word-space; and (7) the sentence- 
 space. It is important to remember that the value of the spaces in 
 the code is as great as that of the dots and dashes. A common 
 misconception exists in the minds of students that the telegraphic 
 code consists exclusively of dots and dashes. The foundation of 
 perfect telegraphic manipulation lies in the ability, which can only 
 be acquired by careful observation and training, to accurately divide 
 and subdivide time into intervals which are multiples of an arbitrary 
 unit. 
 
 1 VAIL (ALFRED), born at Speedwell, near Morristown, N. J., September 25, 1807. 
 In early life he became an apprentice in his father's Speedwell iron- works. After attain- 
 ing his majority, he pursued a course of study and graduated at the University of the 
 City of New York with the intention of entering the ministry, but in September, 1837, 
 chancing to witness one of the early experiments of Morse with his crude telegraphic 
 apparatus, his mind, naturally of a strongly scientific cast, was instantly fired with 
 enthusiasm at the future possibilities of this marvelous invention. He became wholly 
 absorbed in the enterprise, and persuaded his father, Stephen Vail, to furnish the 
 means required to perfect, develop, and introduce the electric telegraph. Among the 
 improvements in the apparatus and methods originated by himself, of the utmost prac- 
 tical value, were the register (269), which is to-day but little changed from the form 
 he gave it in 1844, and the "Morse" alphabetical code (372), now in universal use in 
 America. (See American Inventors of the Telegraph, Century Magazine, xxxv. 924, 
 April, 1888.) The efforts of Vail in overcoming the numerous practical difficulties 
 that beset the work of installing the pioneer telegraph line between Washington and 
 Baltimore in 1844, were indefatigable, and it is to his genius, patience, and untiring 
 diligence that the ultimate success of the enterprise was in no small measure due. 
 The last ten years of his life were passed by him in comparative retirement, engaged 
 in his favorite pursuits of science and literature. He died at Morristown, January 18, 
 1859- 
 
The American Morse Code. 
 
 217 
 
 372. The American Morse Code. The complete code as 
 now used in the United States and Canada, comprising letters, 
 numerals, punctuation, and other signs more or less used, is given 
 below : 
 
 I. ALPHABET AND NUMERALS. 
 
 A 
 
 B 
 C 
 D 
 E 
 F 
 G 
 H 
 I 
 
 J 
 
 K 
 
 L 
 
 M 
 
 N 
 O 
 P 
 
 Q 
 
 R 
 
 S 
 T 
 
 U 
 V 
 
 w 
 
 X 
 Y 
 Z 
 
 & 
 
 nrm 
 
 The arbitrary unit of time in this code, which, when written down, 
 becomes a unit of length, is technically termed the dot ; an unfortu- 
 nate name for this element, inasmuch as it conveys the idea of an 
 inappreciable lapse of time, or of the transmission of a current of 
 infinitely short duration. On the contrary, an appreciable time is 
 required for the production of signals by electricity (315); in the 
 magnetization of electro-magnets (195), and in the movement of 
 clock-work. The formation of a dot, therefore, necessarily involves 
 time. Assuming, therefore, that 
 
 (1) The dot is the unit of time, 
 
 (2) The dash is equal to 2 dots ; 
 
218 
 
 Hints to Learners. 
 II. PUNCTUATION, ETC. 
 
 Comma, , 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Semicolon, ; 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Colon, ; 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Colon Dash, : 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 
 
 Period,' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Interrogation, ? 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Exclamation, J 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Dash, 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Hyphen, 
 
 
 
 
 
 
 
 
 
 
 . 
 
 
 
 - 
 
 
 
 
 
 
 i 
 
 
 
 Pounds, 2 
 
 
 
 
 
 
 
 
 
 
 
 
 l 
 
 I 
 
 
 
 
 Shillings, 2 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Dollars, 2 $ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 Capitalized Letter, 3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Colon-Quotation, : " 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 Decimal Point, 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Paragraph, If 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Parenthesis 3 ( } 
 
 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 
 
 
 J. ell C 1 J LllCoiOy 1 i 
 
 Underline, 8 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 Quotation, 3 ** 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Quotation within Quotation, 8 u * 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 " 
 
 
 
 
 
 
 (3) The long dash is equal to 4 dots ; 
 
 (4) The ordinary space between the elements of a letter is equal to I dot ; 
 
 (5) The letter-space is equal to 2 dots ; 
 
 (6) The word-space is equal to 3 dots ; 
 
 (7) The sentence-space is equal to 6 dots. 
 
 3 To be used before the characters to which it refers. 
 
 3 To be used before and after the words to which it refers. 
 
Handling the Key, 219 
 
 The old rule in transmission was to make the dash equal to 3, and 
 the long dash to 6, dots. When the receiving was largely done by 
 recording instruments this was a most necessary requirement, for a 
 dot, and a dash equal to only 2 dots, might easily be mistaken for 
 each other in reading by sight, but now that receiving by sound has 
 become practically universal, this objection has lost its force, and by 
 shortening the dashes a material gain in rapidity of transmission is 
 effected without any corresponding disadvantage. 
 
 373. Learning the Code. The student should first thoroughly 
 commit to memory the groups of signs representing the letters of 
 the alphabet, the numerals, and the principal punctuation points, viz., 
 the/mW, the comma, and the point of interrogation. The remaining 
 characters can be learned afterwards, as they will be little needed by 
 the beginner. 
 
 374. Handling the Key. The most approved manner of 
 grasping the key, and one which has been employed by some of the 
 most successful, experienced and rapid American operators, is shown 
 
 FIG. 185. 
 
 in Fig. 185. Curve the fore-finger, but do not hold it rigid. Let the 
 thumb press slightly in an upward direction against the knob. Keep 
 the wrist well above the table. No better general 1 direction can be 
 given than that the key should be grasped, held, and controlled with 
 the same flexible but perfectly controlled muscular action of the fin- 
 gers, wrist, and fore-arm with which the skilled penman holds his pen. 
 Carefully avoid tapping upon the knob of the key ; the raising spring 
 should assist the upward motion of the key, but should never be 
 permitted to control it. 
 
 By constant drill, as hereinafter directed, the habit of making dots 
 with regularity, uniformity, and precision must first be acquired ; 
 then dashes, and lastly in order, group of clots and dashes, letters 
 and words. If possible for the student to obtain a register (269), 
 he should by all means employ it in his practice, for he will then be 
 more easily enabled to observe and correct the faults in his own 
 
22O Hints to Learners. 
 
 manipulation. In commencing, the habit should at once be acquired 
 of making the dots like short, firm dashes. The student should 
 learn to form the conventional characters accurately and perfectly ; 
 speed will come in good time, but only as the result of constant and 
 persistent practice, accompanied by a determination to excel. 
 
 375. Elementary Principles of the Code. As a basis for 
 practice, the code may be regarded as comprising six elementary 
 principles, viz. : 
 
 First principle. Associated dots. 
 
 I S H P 6 
 
 Second principle. Associated dashes. 
 
 Third principle. Isolated dots. 
 
 E 
 
 Fourth principle. Isolated dashes. 
 
 L or cipher. 
 
 Fifth principle. Dot followed by dash. 
 
 A 
 
 Sixth principle. Dash followed by dot. 
 
 N 
 
 376. Preliminary Practice with the Key. The student 
 should first practice upon the above elementary principles. 
 
 (1) Make dots with the key at uniform and regular intervals, 
 until they can be produced with the precision of a machine, and of 
 definite and uniform dimensions. The student will find this more 
 easy, if at first he times himself by the beats of a watch or a small 
 clock. 
 
 (2) Next, make dashes, first at the rate of about one per second, 
 which speed may be increased by degrees, as skill is acquired by 
 practice, to three per second. Make the space interval between suc- 
 cessive dashes as short as possible. If the upward movement which 
 forms the space be made full, it cannot be made too quickly. 
 
 (3) The third principle occurs but once, and needs no specific 
 directions. 
 
 (4) This principle will be found somewhat more difficult to exe- 
 cute. The usual tendency is to make T too long, and L too short. 
 Theoretically, the cipher is one-half longer than L, but in fact it is 
 always made the same, as the practice has been found to occasion 
 
Preliminary Practice with the Key. 221 
 
 no inconvenience. Occurring alone, or among other letters, it is 
 translated as L, but when found among figures is read as o. 
 
 (5) The fifth principle forms the letter A. The usual tendency is 
 to separate the two elements too much. 
 
 (6) The dash followed by a dot (N) is usually found to be some- 
 what difficult. Time the movement by pronouncing the word ninety, 
 sounding the first syllable fully. Guard especially against the usual 
 tendency to separate the elements by too great a space. 
 
 377. Exercises upon Code Characters. Having become 
 thoroughly familiar with the principles, the following exercises may 
 with advantage be taken up in order : 
 
 (1) E I S H P 6 
 
 These should be practiced repeatedly until the correct number of 
 dots in each character can be certainly made at every trial. A habit 
 once formed of making the wrong number, usually one or two too 
 many in the case of H, P, and 6, is almost impossible to eradicate. 
 Guard especially against the objectionable habit of shortening or 
 dipping the final dot, a vice which leads to innumerable and vexa- 
 tious errors and misreading of signals. 
 
 (2) T M 5 1[ 
 
 The faults to be particularly guarded against in this exercise are 
 shortening or elongating the terminal dash, and separating the suc- 
 cessive dashes by too great a space interval. 
 
 (3) _A_ _U_ _V_ _4_ 
 
 The usual tendency to allow too much space between the dot and 
 dash in the above letters may be overcome by forming them as by 
 an elongation of the final dot in I, S, H, and P. 
 
 (4) I A S U H V 
 
 Practice these characters in pairs, that the distinction between 
 them may be more firmly impressed upon the mind. 
 
 (5) N D B 8 
 
 The student who has mastered the sixth principle will find no 
 difficulty with the above characters. 
 
 (6) A F X , W i 
 
222 Hints to Learners. 
 
 (7) U Q 2 Period 3 
 
 These are similar to preceding exercises and present no new 
 difficulties. 
 
 (8) K J 9 ? 
 
 G 7 Exc. 
 
 J and K are usually considered the most difficult letters in the 
 code. Avoid the tendency to separate J by a space into double N, 
 and be careful that the dashes are of equal length. The numerals 7 
 and 9 require some care to ensure correct spacing. 
 
 (9) O R & C Z Y 
 
 These are termed the spaced letters, and the utmost care and dili- 
 gent practice are necessary in order to form them accurately. The 
 ability to transmit the spaced letters with absolute correctness is the test 
 of a strictly first-class sender. The space should be just enough in 
 excess of that ordinarily used between the elements of a letter to 
 enable the letters intended to be made to be distinguished with cer- 
 tainty from I, S, and H. The most usual tendency is to make the 
 space too great, even in some cases as great as the space between 
 letters. This is a most fruitful source of misapprehension and error, 
 and too much pains cannot be taken to acquire and maintain cor- 
 rect habits in this particular. 
 
 In transmitting words containing groups of two or more spaced 
 letters, careful operators are accustomed to slightly increase the 
 spacing between the successive letters of the group. 
 
 Practice in transmission from miscellaneous manuscript is strongly 
 recommended. The ability to read all kinds of copy ; good, bad, 
 and indifferent, correctly at sight, is a most valuable one, and is not 
 difficult to acquire by attention and experience. 
 
 If the principles here laid down be firmly adhered to, the learner 
 will find much reason for encouragement, not only at the rapidity 
 with which he will master what at first sight appears to be a very 
 difficult undertaking, but at the extreme accuracy with which he 
 will be able to manipulate his instrument after a fair amount of 
 practice. He must also carefully bear in mind that one of the most 
 universal faults among those attempting to learn the telegraphic art, 
 is that of going over a great deal of ground and learning nothing 
 thoroughly. 
 
Reading by Sound. 223 
 
 378. Reading by Sound. This art can only be acquired by 
 constant and persevering practice, keeping in mind the principles 
 above given. The lever of the telegraphic sounder makes a sound 
 at each movement, the downward motion producing the heavier one. 
 The down-stroke indicates the commencement of a dot or a dash and 
 the up-stroke its termination. A dot makes as much sound as a 
 dash ; the only difference is in the length of time or interval which 
 elapses between the two successive sounds. Thus, if the recoil or 
 up-stroke were absent, it would be impossible to distinguish E, T, 
 and L from each other. 
 
 379. In learning to read by sound it is advisable for two persons 
 to practice together, taking turns at reading and writing, and each 
 correcting the faults of the other. The sounds of the code charac- 
 ters must first be learned separately, and then short words chosen, 
 which must be written very slowly and distinctly and well spaced, 
 the speed of manipulation being gradually increased as the student 
 becomes more proficient in reading. After becoming sufficiently 
 well versed in the art to read at the rate of twenty-five or thirty words 
 per minute, further practice may best be had in copying with a. pen 
 and ink (not with a pencil) from a sounder connected with a line 
 employed in transmitting ordinary commercial and railway messages, 
 in order that the student may familiarize himself with the technical 
 usages of the lines, and the minute details of actual telegraphic 
 business. 4 
 
 380. A Parting "Word. In conclusion, the student is warned 
 against falling into the common error, which is not confined to teleg- 
 raphy, of expecting great results from little labor. To become an 
 expert sending and receiving operator requires a vast amount of 
 time and patience, and the most unwearied application. Remember 
 that whatever is worth doing at all, is worth doing well. It is seldom 
 that a thoroughly competent operator cannot obtain immediate and 
 remunerative employment, and it is probable that such will continue 
 to be the case, however crowded the lower walks of the avocation 
 may hereafter become. 
 
 4 Full explanations respecting the methods, regulations, and forms usually employed 
 in the commercial, railway, and express service, in the forwarding and reception of 
 messages, train orders, reports, etc., and much other miscellaneous information of like 
 character useful to the student of telegraphy, may be found in the later editions of 
 Abernethy's Modern Service of Commercial and Railway Telegraphy. A little work 
 by T. J. Smith, on The Philosophy and Practice of Morse Telegraphy^ may also be 
 consulted with advantage. 
 
INDEX 
 
 ABERNETHY'S Commercial and Railway Te- \ 
 legraphy referred to, 223. 
 
 Absolute system of measurement, 37; con- 
 crete example of, 37. 
 
 Accumulator or storage battery, how shown 
 in diagram, 104. 
 
 Accumulation, electrostatic, upon insulated 
 conductor, 177. 
 
 Adjustment of key, 140 ; of quadruplex ap- 
 paratus, 188 ; of register, 148 ; of sounder, 
 142. 
 
 Air, non-conducting properties of, 57. 
 
 Alloys of metals, inferior conducting power 
 of, 57. 
 
 Alternating current, 167 ; rectification of, 
 167. 
 
 Amalgamation of zinc, 21. 
 
 American modification of closed-circuit sys- 
 tem, 108. 
 
 American lines, defective insulation of, 118. 
 
 American electrical society, journal of, refer- 
 ence to, 187. 
 
 American institute of electrical engineers, 
 extract from transactions of, 2. 
 
 American standard wire-gauge, 95. 
 
 Ammeter or amperemeter, the, 44, 61 ; use of 
 in telegraphic testing, 210 ; Weston's port- 
 able, 211 ; advantages of for testing, 211. 
 
 Ammeter, Weston's combined voltmeter and, 
 for telegraphic testing, 210. 
 
 Ampere, Andre Marie, biographical notice 
 of, 60. 
 
 Ampere, the unit of current, definition of, 
 60 ; value of, 60 ; determination of, 60. 
 
 Ampere-turns, 85 ; magnetization propor- 
 tional to, 87. 
 
 Amperemeter or ammeter, the, 61. 
 
 Anderson's machine for winding helices of 
 electro-magnets, 93. 
 
 Anthony, Wm. A., Review of Modern Elec- 
 trical Theories,, reference to, 2. 
 
 Apparatus, electric, drawings of, 103 ; tele- 
 graphic, conventional representations of, 
 103, 104. 
 
 Apparent resistance of line, 128 ; table of, 129. 
 
 Armature of magnet, 26 ; of electro-magnet, 
 91 ; polarized, 100. 
 
 Armature time of telegraph magnet deter- 
 mined, 99. 
 
 Artificial line of multiple telegraph, the, 174. 
 
 Artificial magnet defined, 24. 
 
 Astatic system of needles, 198 ; gal manom- 
 eter. 200. 
 
 Attraction and repulsion, magnetic, 28 ; mu- 
 tual, between electric conductors, 35. 
 
 Attraction, magnetic, ratio of to distance, 89. 
 
 Authors referred to : 
 Abernethy, J. P., 223. 
 Anthony, William A., 2. 
 Avery, Elroy M., 70. 
 Becker, C., 62. 
 
 Benoit, Rene, 57. 
 
 Bidwell, Shelford, 26. 
 
 Blavier, E. E., 17, 128. 
 
 Bonsanquet, R. H. M., 81. 
 
 Bottone, Selino R., 46. 
 
 Bradley, Leverett, 17, 76. 
 
 Brooks, David, 119, 120. 
 
 Cavendish, Henry, a. 
 
 Chaperon, G., 23. 
 
 Christie, Samuel Hunter, 195. 
 
 Clark, Latimer, 58, 76, 125, 198. 
 
 Clerk-Maxwell, James, 2. 
 
 Cooke, Josiah P., 6. 
 
 Daniell, Alfred. 2, 38. 
 
 Davis, Daniel, jr., 89. 
 
 Dean, G. W , 99. 
 
 Everett, J. D., 38. 
 
 Swing", J. A., 98. 
 
 Faraday, Michael, 2, 3, 29, 38, 73, M. 
 
 Farmer, Moses G., 62, 119, 128, 136. 
 
 Franklin, Benjamin, 2. 
 
 French, E. L., 87. 
 
 Gavarret, J., 128. 
 
 Gee, W. W. Haldane, 62. 
 
 Gray, Andrew, 40. 
 
 Grove, Sir William, 38. 
 
 Healy, Clarence L., 187. 
 
 Helmholtz, Herman L. F., 38. 
 
 Henning, Thomas, 187. 
 
 Henry, Joseph, 2, 80. 
 
 Hering, Carl, 82. 
 
 Hill, Edward A., 17. 
 
 Hughes, David .,24. 
 
 Jamieson, Andrew, 73. 
 
 Jenkin, Fleeming, 17, 18, 62, 19!. 
 
 Johnson, A. J., 20. 
 
 Jones, Francis W., 187. 
 
 Kapp, Gisbert, 24, 83. 
 
 Kempe, A. B M 128. 
 
 Kempe. H. R., 128, 198. 
 
 Kennelly. A. E., 85. 
 
 Kohlrausch, F., 62. 
 
 Lalande, de, F., 23. 
 
 Lockwood, Thomas D., 23, 34. 
 
 Lodge, Oliver J., 2, 88. 
 
 Maver, William, Jr., 185, 187. 
 
 Mayer, Alfred M., 24. 
 
 Mayer, Julius R., 38. 
 
 Morse, Samuel F. B., 128. 
 
 Munroe, John, 73. 
 
 Niaudet, Alfred, 62. 
 
 Nipher, Francis E., 40. 
 
 Nystrom, John W., 28. 
 
 Plum, H. W.. 187. 
 
 Pope, Franklin L , 17, 76, 80, 187. 
 
 Preece, William ll, 79. 
 
 Prescott, George B., 62. 
 
 Prescott, George B., Jr., 74, 94, ua. 
 
 Rowland, H. A., 81, 88. 
 
 Sabine, Robert, 83. 
 
 Schott, C. A., 40. 
 
 225 
 
226 
 
 Index. 
 
 Shaffuer, Tal P., 62. 
 Smith, T. Jarrard, 223. 
 Sprague, John T., 38, 57, 62, 74. 
 Stewart, Balfour, 38, 62. 
 Sturgeon, William, 80. 
 Thompson, Silvanus P., 31, 86, 87, 93, 198. 
 Thomson, Sir William, 2, 73, 88, 93. 
 Trowbridge, John, 40, 85. 
 Tyndall, John, 38. 
 Varley, Cromwell F., 131, 135. 
 Webb, F. C., 175. 
 Wheatstone, Sir Charles, 195. 
 Wilkinson, H. D., 85. 
 Youmans, Edward L., 38. 
 Automatic repeaters, management of, 166 ; 
 Milliken's, 165. 
 
 BAD JOINT ON LINE, m^hod of locating, 205. 
 
 Balancing of resistance in multiple telegraph, 
 174. 
 
 Bar magnet, 24. 
 
 Batteries, composed of number of cells, 3. 
 
 Battery, method of determining cost of main- 
 tenance of, 75 ; position of in closed-cir- 
 cuit system of telegraphy, 109 ; potentials 
 within, 123 ; best position for on leaky 
 line, 131, 132 ; internal resistance of, 
 methods of measuring, 207. 
 
 Battery materials, choice of, 20. 
 
 Battery solutions, table of specific gravities 
 of, 9. 
 
 Baume's hydrometer scale, 7. 
 
 Becker's experiments on resistances of 
 liquids, 62, 63. 
 
 Benoit on specific resistance of metals, refer- 
 ence to, 57. 
 
 Bichromate of potash cell, 23. 
 
 Bidwell, Shelford, on maximum magnetic at- 
 traction, 26. 
 
 Binding screws, different patterns of, 50. 
 
 Biographical notices : 
 
 Ampere, Andre Marie, 60. 
 
 Coulomb, Charles Augustin de, 61. 
 
 Faraday, Michael, 73. 
 
 Gauss, Karl Friednch, 83, 
 
 Henry, Joseph, 80. 
 
 Joule, James Prescott, 63. 
 
 Lefferts, Marshall, 214. 
 
 Morse, Samuel Finley Breese, vi. 
 
 Ohm, Georg Simon, 62. 
 
 Vail, Alfred, 216. 
 
 Volta, Alessandro, 61. 
 
 Watt, James, 73. 
 
 Blavier's Telegraphic Electrique, reference 
 to, 17, 128. 
 
 Bonsanquet, R. H. M., on magneto-motive 
 force, reference to, 81. 
 
 Boston screw-glass insulator, tests of effi- 
 ciency of, 120. 
 
 Bottone s Electrical I nstrument-making for 
 Amateurs, extracts from, 46. 
 
 Box sounder, 144 ; use of in railway service, 
 144. 
 
 Bradley, L., on Hill's gravity cell, 17. 
 
 Branch circuit connection, diagram of, 104. 
 
 Branch or derived circuits, 69 ; rule for joint 
 resistance of, 66. 
 
 Brass, specific resistance of, 57. 
 
 Break or disconnection, conditions arising 
 from, 190. 
 
 Breakage of battery jars, causes of, 10. 
 
 Bridge, Wheatstone's, 195 ; theoretical ar- 
 rangement of, 195 ; invented by Christie, 
 195; principle of illustrated, 196; best ra- 
 tio of electromotive forces and resistances 
 in, 196 ; actual construction of, 198 ; gal- 
 vanometer for. 198 ; methods of making 
 various tests with, 199-208. 
 
 British association ohm, determination of, 
 
 62, 63 ; value of, 62. 
 British standard wire-gauge, 95. 
 Brooks, David, on effects 01 climate upon 
 
 telegraphic insulation, 119; on effects ol 
 
 smoke in cities on insulation, 119 ; tests ot 
 
 various kinds of insulators by, 120. 
 Brooks's paraffin insulator, tests of efficiency 
 
 of, 120. 
 Brown & Sharpe M'f'g Co.'s American 
 
 standard wire-gauge, 95. 
 Brushes of dynamo-electric machine, 168. 
 Bunsen's nitric-acid cell, 23, 
 Button repeater, the, 162 ; management of, 
 
 165. 
 
 CABLE, submarine, diagram of, 104. 
 
 Caliper, micrometer, tor gauging wires, 96. 
 
 Callaud's cell, 17. 
 
 Calorimeter, the, 44. 
 
 Canada, closed circuit used in, 108. 
 
 Capacity, inductive or electrostatic, 72 ; defi- 
 nition of, 72 ; unit of, 73. 
 
 Cavendish's theory of electricity, 2. 
 
 Cell, gravity, maintenance of, 14 ; disman- 
 tling of, 16 ; best adapted to closed cir- 
 cuits, 16 ; waste products of, 17 ; electro- 
 motive force of, 74 ; resistance of, 74. 
 
 Cell, usual internal resistance of, 64 ; elec- 
 trical dimensions of, 74. 
 
 Cell, oxide of copper, 21. 
 
 Cell, sulphate of copper, effect of tempera- 
 ture upon resistance of, 78. 
 
 Cell, voltaic, Hill's, Callaud's, Minotto's, 
 Thomson's, 17 ; Lockwood's. 18 ; Dan- 
 iell's, 19 ; Edison-Lalande, 21 ; Grove's, 
 23 ; Bunsen's, 23 : rate of consumption of 
 material in, 13 ; effect of continued action 
 in, 13; various forms of, 17 ; general direc- 
 tions for care of, 20 ; how shown in dia- 
 gram, 104. 
 
 Centimetre, the unit of space, 37. 
 
 Centimetre-gram-second system of units, 37 ; 
 units of force and work, 37. 
 
 Chaperon, G., and F. de Lalande, on voltaic 
 batteries, 23. 
 
 Characters, code, exercises with, 220. 
 
 Charge, electrostatic, 177 ; current of, 177. 
 
 Chemical atomic weights of battery materials, 
 table of, 8. 
 
 Chemical electricity, 3. 
 
 Chemical equivalents, table of, 75. 
 
 Chemical law of definite proportion, 6. 
 
 Chemical reaction of voltaic cell, 6 ; in closed 
 circuit, 12. 
 
 Chemistry of voltaic effect, 6. 
 
 Circuit, conducting, effect of increasing the 
 length of, 54. 
 
 Circuit, closed, the, 12 ; chemical reactions 
 in, 12 ; theoretical diagram of, 12. 
 
 Circuit, distribution of potentials in when in- 
 sulated, 120. 
 
 Circuit, electric, constituent parts of, n; 
 formation of, n; nomenclature of, 12; 
 graphic illustration of. 71. 
 
 Circuit, external, the, 12 ; internal, the, 12. 
 
 Circuit, imperfectly insulated, distribution of 
 potem.als in, 125. 
 
 Circuit, magnetic, 80 ; conception of due to 
 Joule, 80. 
 
 Circuit, open or broken, the, 12. 
 
 Circuits, telegraphic, 102 ; open and closed, 
 102; diagram of, 104; essential character- 
 istics of, 102; general considerations re- 
 specting, 109; working efficiency of, in ; 
 distribution of potentials in, 120. 
 
 Circuits of American telegraphic system, ar- 
 rangement of, 151. 
 
Index. 
 
 227 
 
 Clamp-screw of gravity cell, 4. 
 
 Clark, Latimer, on Wheatstone's bridge, 
 196 ; provisional theory of electricity, 58. 
 
 Clark's Electrical Measurement, references 
 to, 125, 198 ; extract from, 58. 
 
 Clerk-Maxwell, theory pt electricity, 2. 
 
 Climate, effect of upon insulation, 118. 
 
 Clip, the, in diplex and quadruplex telegraph, 
 how obviated, 184. 
 
 Closed and open circuit systems of teleg- 
 raphy, comparative advantages of, 109. 
 
 Closed-circuit system of telegraphy, 102 ; 
 description of, 108 ; American modification 
 of, 108 ; position of battery in, 109. 
 
 Coast survey report, reference to, 99. 
 
 Cobalt, magnetic properties of, 24. 
 
 Code, telegraphic, formation of, 216 ; ele- 
 mentary principles of, 219. 
 
 Code, American Morse, 217, 218 ; alphabet 
 and numerals of, 218 ; punctuation, etc., 
 of, 218 ; best method of learning, 219 ; 
 exercises with, 220. 
 
 Coil or loose bundle of wire, how shown in 
 diagram, 104. 
 
 Combinations of permanent and electro-mag- 
 nets, 100. 
 
 Commutator of dynamo-electric machine, 
 function of, 167 ; construction of, 168. 
 
 Compass, magnetic, 25. 
 
 Condenser, construction of, 178 ; application 
 of to duplex telegraph, 178 ; first applied 
 by Stearns, 178 ; how shown in diagram, 
 104. 
 
 Conducting circuit, an element of the electric 
 telegraph, 2. 
 
 Conductivity resistance, relation of insula- 
 tion to, no ; of line, measurement of with 
 bridge, 199. 
 
 Conductors, insulated, for interior construc- 
 tion, 114; telegraphic, m. 
 
 Conductors and insulators, characteristics of, 
 56 ; tible of, 57. 
 
 Connecting wire in gravity battery, protec- 
 tion of, ii. 
 
 Conservation of force, principle of ex- 
 plained, 38. 
 
 Constancy, value of in voltaic cell, 74. 
 
 Constant of galvanometer, method of deter- 
 mining, 206. 
 
 Consumption of material in cell in relation to 
 electricity evolved, 17. 
 
 Contraplex and diplex methods, combination 
 of, 184. 
 
 Conventional representation of circuits and 
 apparatus, 103, 104, 105. 
 
 Cooke's New Chemistry, extract from, 6. 
 
 Copper, chemical equivalent of, 75. 
 
 Copper connector, of gravity cell, 5. 
 
 Copper plate, of gravity cell, 4 ; modifi- 
 cations of, 10 ; the negative element of, 12. 
 
 Copper line wires, 114 ; table of dimensions 
 and qualities of, 112. 
 
 Copper sulphate, chemical analysis of, 8. 
 
 Copper wire, bare, for magnet helices, 94 ; 
 hard drawn, table of sizes, weights, resist- 
 ances, etc., 112. 
 
 Core of electro-magnet, 91. 
 
 Core, diameter of in electro-magnet, force of 
 attraction affected by, 87 ; best proportions 
 for, 91. 
 
 Cost of materials consumed in battery, 74 ; 
 of battery maintenance, method of deter- 
 mining, 75. 
 
 Coulomb, Charles Augustin de, biographical 
 notice of, 61. 
 
 Coulomb, the unit of electrical quantity, defi- 
 nition of, 61. 
 
 Cross, definition of, 190 ; metallic, 191 ; 
 
 swing, ,191 ; weather, 191 ; method of test- 
 ing tor, 193 ; principle ot test for, 193. 
 
 Cross, on line, locating position of, 204. 
 
 Cross-arms, tests of insulating value of, 133, 
 134. 
 
 Cross-current, remedy for, 132. 
 
 Cross-tire, 191 ; explanation of cause ot, 132 j 
 remedy tor, 132. 
 
 Crossing of two wires, representation of in 
 diagram, 104. 
 
 Cross-section of body, effect of upon resist- 
 ance, 58. 
 
 Current, alternating, of dynamo-machine, 
 167. 
 
 Current, electric, formation of, n ; produced 
 by magnetic held, 29 ; manifestations of in 
 conductor, 35 ; effect of imperfect insula- 
 tion upon now of, 127 ; direction of, how 
 shown in diagram, $04. 
 
 Current lorce, relation of to mechanical force, 
 
 'to- 
 Current induction, 74. 
 
 Current, inducing or primary, 74 ; direction 
 of, 31. 
 
 Current, induced or secondary, 31, 74. 
 
 Current in leaky lines, 128; taDle tor com- 
 puting, 129. 
 
 Current of charge on insulated line, 177. 
 
 Current of dynamo-electric machine, charac- 
 teristics of, 167. 
 
 Current, relation of to magnetic force, 85 ; 
 self-induction of, 98 ; in coiled conductor, 
 98. 
 
 Currents, adaptation of electro-magnets to, 
 96 ; method of determining, 96 ; distribu- 
 tion of in quadruplex telegraph, 186. 
 
 Currents, earth, disturbing influence of on 
 conductivity tests, 201. 
 
 Currents of charge and discharge, effects of 
 on line, 177. 
 
 Currents, received, test of insulation by 
 means of, 208. 
 
 Curve, of ratio between magnetic attraction 
 and distance, 90 ; of electrical dimensions 
 in oxide of copper cell, 77 ; of resistance 
 as affected by temperature in Daniell's 
 cell, 79 ; of magnetization of soft iron, 
 85 ; of magnetic saturation, 85 ; of poten- 
 tials in electric circuits, 121, 123, 124; of 
 potential within battery, 125 ; of potential 
 on leaky line, 125, 126, 130. 
 
 Cut-out wedge, the, 155. 
 
 DANIELL'S Principles of Physics, extract 
 from, 2 ; reference to, 38. 
 
 Daniell's sulphate of copper cell, 18 ; main- 
 tenance of, 19 ; renewal of, 19. 
 
 Davis, Daniel, Jr., experiments on magnetic 
 attraction. 89, 90. 
 
 Davis's Manual of Magnetism, reference to, 
 89. 
 
 Dead ground, definition of, 190. 
 
 Dean, G. W., experiments of on self-induc- 
 tion and hysteresis in telegraph magnets, 
 
 QQ. 
 
 Deflections, proportional, measuring high re- 
 sistances by method of, 205. 
 
 De Lalande, F., and G. Chaperon, on voltaic 
 batteries, 23. 
 
 Density, magnetic, 83. 
 
 Derived and fundamental units, 37. 
 
 Derived or branch circuits, 69. 
 
 Detector or galvanpscope, 41. 
 
 Diagrams of electric apparatus, 103. 
 
 Differential, electro magnet, principle of, 171 ; 
 galvanometer, construction and use of, 
 208. 
 
 Diffusion of solution in gravity cell, 16. 
 
228 
 
 Index. 
 
 Dimensions, electrical, of voltaic cell, 74. 
 
 Diplex telegraphy, 171. 
 
 Diplex, principle of, 182 ; receiving appara- 
 tus of, 183 ; clip in, 184 ; short core relay 
 for, 184. 
 
 Diplex and contraplex, combination of, to 
 form quadruple*, 184. 
 
 Direction of electric current, purely a con- 
 ventional assumption, 12. 
 
 Disconnection or break, conditions arising 
 from, 190 ; testing for, 191 ; testing for at 
 way station, 154 ; causes of, 192. 
 
 Disconnection, partial, 190 ; testing for, 192. 
 
 Distance between magnet and armature, ef- 
 fect of upon attractive force, 89 ; experi- 
 mental determination of, and tabulated 
 results, 89, 90. 
 
 Dot, an element of telegraphic code, 216 ; the 
 unit of time and space in ditto, 217. 
 
 Double current duplex, apparatus of, 180. 
 
 Double current or reversing key, 180; how 
 shown in diagram, 104. 
 
 Double measurement, process of in line test- 
 ing, 203. 
 
 Drawings, of electric apparatus, 103 ; per- 
 spective, 103 ; geometrical, 103. 
 
 Duplex telegraphy, 171. 
 
 Duplex, single current, 172 ; apparatus of, 
 172 ; circuits of, 173 ; artificial line of, 173; 
 balancing of, 173 ; effect of currents of 
 charge and discharge in, 177 ; ground and 
 spark coils of, 179 ; double current, de- 
 scription of, 180. 
 
 Duration of cell, considerations affecting, 74. 
 
 Dynamo current, characteristics of, 167 ; ap- 
 plication of to quadruples telegraphy, 
 185, 186. 
 
 Dynamo-electricity defined, 24. 
 
 Dynamo-electric generator, employment of 
 in telegraphy, 167. 
 
 Dynamo-electric machine, the, 32 ; theory of 
 explained, 32 ; diagram of, 104 ; field of, 
 168 ; commutator of, 168 ; brushes of, 168 ; 
 characteristics of, 169 ; Edison's, 168 ; ar- 
 rangement of in potential series, 169; posi- 
 tive and negative series of, 170 ; capacity 
 of, 171 ; shunt coils of, arrangement of in 
 telegraphy, 171. 
 
 Dynamos, arrangement of in series in New 
 York station, 170. 
 
 Dyne, unit of force, definition of, 38. 
 
 EARTH, the, an electrical cpnductor, 104; 
 magnetism of, 40 ; field offeree due to, 40. 
 
 Earth circuit, principle of, 106 ; advantages 
 of, 106. 
 
 Earth or ground plate, how shown in dia- 
 gram, 104 ; precautions in fixing, 106. 
 
 Earth currents, disturbing influence of on 
 conductivity tests, 201 ; how eliminated, 
 
 201. 
 
 Edison, T. A., inventor of method of diplex 
 
 - transmission, 185. 
 
 Edison's dynamo-electric machine, 168, 169. 
 
 Edison-Lalande oxide of copper cell, 21 ; 
 electromotive force and resistance of, 76 ; 
 duration of, 76 ; chart of electrical dimen- 
 sions of, 77. 
 
 Effect of continued action on voltaic cell, 13. 
 
 Efficiency, working, of lines, importance of 
 high, 135 ; best method of improving, 135 ; 
 examples of advantageous results of, 135, 
 136; of telegraphic circuit, in ; computa- 
 tion of, 128. 
 
 Electric circuit, formation of, n ; graphic il- 
 lustration of, 71. 
 
 Electric current, manifestations of in con- 
 ductor, 35 ; produced by magnetic field, 29. 
 
 Electric field of force, 39. 
 
 Electrical action, laws and conditions of, 45 ; 
 
 mechanical analogue of, 58. 
 Electrical and magnetic units, derivation of, 
 
 Electrical and mechanical force, statement 
 of law connecting, 59. 
 
 Electrical Engineer (N . Y.), references to, 23, 
 74 ; extract from, 2. 
 
 Electrical measurement, quantitative, theory 
 of, 35 ; importance of, 36. 
 
 Electrical Re-view (London), reference to, 23. 
 
 Electrical II orld, relerence to, 185. 
 
 Electrician (London), reference to, 81. 
 
 Electrician and Electrical Engineer ^ refer- 
 ences to, 87, 94. 
 
 Electricity, chemical, 3 ; magneto, 24 ; dyn- 
 amo, 24 j t rictional, 33 ; static, 33 ; ther- 
 ruo, 34. 
 
 Electricity, theories of nature of, 2 ; origin 
 of, 3 ; sources of, 3 ; characteristics of capa- 
 ble of measurement, 43; apparatus re- 
 quired for measurement of, 43 ; provisional 
 theory of, 58 ; production ot in battery in 
 proportion to material consumed, 76. 
 
 Electricity and magnetism, essential nature 
 of, 2. 
 
 Electrification, 72. 
 
 Electro and permanent magnets, combina- 
 tions Of, 101. 
 
 Electro-chemical equivalent, of zinc, 74, 75 ; 
 of copper, 75 ; ot copper sulphate, 75. 
 
 Electrodes of cell defined, 12. 
 
 Electrolysis of liquids by electric current, 36. 
 
 Electro-magnet, the, 80 ; its modern form in- 
 vented by Henry, 80 ; polarity of deter- 
 mined by direction of current, 81 ; ele- 
 ments of, 81 ; adaptation of to working 
 currents, 96 ; spectrum of, 96, 97 ; indirect 
 causes of retardation in, 99 ; with polar- 
 ized armature, xop ; differential, principle 
 of, 171 ; construction of, 172. 
 
 Electro-magnetism, 32 ; laws of, 80. 
 
 Electromotive force, conception of, 59 ; of 
 ordinary gravity cell ? 74. 
 
 Electrostatic or inductive capacity, 72 ; of 
 line, 175. 
 
 Electrostatic accumulation upon insulated 
 conductor, 177. 
 
 Electrostatic balance of duplex telegraph, 
 178. 
 
 Elements of electric telegraph, 2 ; of electro- 
 magnet, 81. 
 
 Endcvmose, action of in voltaic cells, 20. 
 
 English unit of magnetic induction, 83. 
 
 Equator of magnet, 26. 
 
 Equipment of American telegraph lines, 138. 
 
 Equivalent, of mechanical energy, 31 ; elec- 
 trical and mechanical, definition of, 38. 
 
 Erg, unit of work, definition of, 38. 
 
 Escape or leakage on line, 190 ; testing for, 
 192; <n line, locating position of, 202; 
 ditto by double measurement, 203 ; by loop 
 test, 203. 
 
 European register, 148. 
 
 Evaporation in battery cells, prevention of, 
 10, 14. 
 
 Everett's Units and Physical Constants, refer- 
 ence to, 38. 
 
 Ewing's researches in magnetism, 98. 
 
 Exercises with code characters, 220, 221. 
 
 External circuit, the, defined, 12. 
 
 FALL OF POTENTIAL, illustrated, 70 ; propor- 
 tionate to fall of resistance along con- 
 ductor, 71. 
 
 Farad, the unit of electrostatic or inductiev 
 capacity, 73. 
 
Index. 
 
 229 
 
 Farad .y. Michael, biographical notice of, 73. 
 
 Faraday s theory of electricity, 2 ; discovery 
 of magneto-electricity, 29 ; Experimental 
 Researches^ references to, 3, 29 ; lines of 
 magnetic force, 27, 28. 
 
 Farmer, M. G., on resistances or' battery so- 
 lutions, 62 ; observations on earth circuit 
 as affected by character of soil, 107 ; on 
 effects of wet upon telegraphic insulation, 
 119 ; on working efficiency of telegraph 
 lines, 128; table of percentages of received 
 current on telegraph lines, 136. 
 
 Fault in line, effect of position of, 131. 
 
 Faults and interruptions, classification of, 
 190. 
 
 Field, electro-magnetic, of dynamo machine, 
 168. 
 
 Field, magnetic, the, 27. 
 
 Field, magnetic, lines of force a measure of, 
 82. 
 
 Field of force, electric, 39. 
 
 Field of magnetic force, properties of, how 
 determined, 27. 
 
 Field, Stephen D., inventor of application of 
 dynamo to telegraphy, 185. 
 
 Flux, magnetic, 88. 
 
 Force, conservation of, doctrine of, ex- 
 plained, 38. 
 
 Force, definition of, 27 ; lines of, a measure 
 of magnetic field, 82 ; relation of current 
 to mechanical, 40 ; unit of, defined, 37. 
 
 Formation of the electric circuit, n. 
 
 Franklin's theory of electricity, 2. 
 
 French, E. L., on electro-magnetic attrac- 
 tion, 87. 
 
 Frictional electricity, 33. 
 
 Fundamental and derived units, 37. 
 
 Fundamental units of mass, space and time, 
 36. 
 
 GALVANIC ELEMENT, the, 3. 
 
 Galvanized iron wire, table of sizes, weights 
 and resistances of, 112. 
 
 Galvanometer, the, 41 ; how shown in dia- 
 gram, 104 ; astatic, 200 : differential, con- 
 struction of, 208 ; for Wneatstone bridge, 
 198. 
 
 Galvanometer, tangent, 41, 209; construction 
 of, 41 ; use of in testing insulation by 
 received currents, 209 ; in experimental 
 investigations, 52 ; table of tangents for, 
 
 Galvanometer, taking constant of, 206 ; re- 
 sistance of, method of measuring, 208 ; ap- 
 plication of snunts to, 205. 
 
 Galvanoscope, the, 41 ; how shown in dia- 
 gram, 104. 
 
 Gap in magnetic circuit, effect of, 89. 
 
 Gas and water pipes used for ground con- 
 nections, 106. 
 
 Gauging wire,instruments for, 95. 
 
 Gauss, Karl Friedrich, biographical notice 
 of, 83. 
 
 Gauss, the proposed unit of magnetism, 83 ; 
 definition of, 83. 
 
 Gauss anJ Weber's electric telegraph, 83. 
 
 Gavarret's Telegraphic Eiectrique, reference 
 to, 128. 
 
 Generator, the, an element of electric tele- 
 graph, 2. 
 
 German-silver, specific resistance of, 57. 
 
 Glass insulator, the, 115; defects of, 115; 
 tests of, 120, 134. 
 
 Glass jar of battery cell, 4 ; breakage of, how 
 avoided, 10. 
 
 Gram, the unit of mass or weight, 37. 
 
 Gravity cell, description of, 4; installation of, 
 9 ; formula for preparing solutions for, 8. 
 
 Gray's Absolute Measurements in Electricity 
 and Magnetism, reference to, 40. 
 
 Ground or earth plate, how shown in dia- 
 gram, 104 ; at distant station, measuring 
 resistance of, 202 ; defective, effect ot, 191. 
 
 Ground connection, how made, 106 ; precau- 
 tions in making, 106. 
 
 Ground, on line, 190 ; locating position of, 
 202. 
 
 Ground and spark coils in duplex telegraph, 
 179. 
 
 Grove's nitric acid cell, 23. 
 
 HANGER OF GRAVITY BATTERY CELL, 4. 
 
 Hardening of magnet cores objectionable, 99, 
 
 Hard iron and steel, magnetic properties of, 
 24. 
 
 Hard-rubber insulator, the, 117. 
 
 Healy, Clarence L., on quadruplex teleg- 
 raphy, 187. 
 
 Heat, development of by electric current, 
 36; effect of upon e. m.f. of sulphate of 
 copper cell, 74. 
 
 Helices of electro-magnets, machine for 
 winding, 93 ; thickness of spaces between 
 wires of, 94 ; of bare copper wire, 94. 
 
 Helix, magnetic, effect of iron in, 84; effect 
 of position of windings in, 92 ; construc- 
 tion of, 92 ; relation of number of turns to 
 thickness and length of wire in, 92 ; num- 
 ber of turns in, measured by its resist- 
 ance, 93. 
 
 Henning, Thomas, on quadruplex telegraphy, 
 187. 
 
 Henry, Joseph, biographical notice of, 80. 
 
 Henry's theory of electricity, 2. 
 
 Hering, Carl, on lines of magnetic force, 82. 
 
 Her ing's Principles of Dynamo- Electric Ma- 
 chines, extract from, 82. 
 
 High resistances, methods of measuring, 305. 
 
 Hill, E. A., on the voltaic cell, 17. 
 
 Hill's cell, 17. 
 
 Hints to learners, 216. 
 
 Horizontal component of earth's magnetism, 
 defined, 40 ; value of in various parts ot 
 North America, 40. 
 
 Horseshoe, magnet, 26 electro-magnet, 87. 
 
 Hughes, Prof. D. E., theory of magnetism, 
 24. 
 
 Hydrogen, evolution of in voltaic cell, 5. 
 
 Hydrometer, the, description of, 7. 
 
 Hysteresis, magnetic, definition of, 97; effect 
 of on telegraph magnets, 99. 
 
 INDUCED OR SECONDARY CURRENT, 74; direc- 
 tion of, 31. 
 
 Inducing or primary current, 74. 
 
 Induction, current, 74 ; static, 175, 177; mag- 
 netic, phenomena of, 25 ; magnetic, cause 
 of, 85. 
 
 Induction of current upon itself. 98. 
 
 Inductive or electrostatic capacity, 72. 
 
 Inertia t magnetic, definition ot, 99. 
 
 Ink-writing register, 150. 
 
 Installation of gravity cell, 9. 
 
 Instrument tables, 160. 
 
 Insulating value of wet poles and cross-arms, 
 tests of, 133, 134. 
 
 Insulation, imperfect, effects of, no ; defec- 
 tive of American lines, 118 ; effects of cli- 
 mate upon, 118 ; effect of upon flow of 
 current, 127 ; Farmer's table of, 136. 
 
 Insulation resistance of line, measurement of, 
 202 ; relation of conductivity to, no. 
 
 Insulation, test of, by received currents, 208. 
 
 Insulator, glass, Western Union, old pattern, 
 116 ; new standard pattern, i r6 ; hard rub- 
 ber, 117; paraffin, 117 ; porcelain, 118. 
 
230 
 
 Index. 
 
 Insulators and conductors, characteristics ot, 
 56 ; comparative table of, 57. 
 
 Insulators, telegraphic line, 115; common 
 glass, 115 ; defects of, 115; resistance of 
 influenced by form, 116; comparison of 
 different forms ot, 116; tests of, 120, 134; 
 measurement of resistance of, 206 ; value 
 of wu poles and cross-arms considered as, 
 133. 
 
 Intensity, of magnetization defined, 86 ; of 
 magnetic field denned, 27. 
 
 Intermingling ot currents on telegraph lines, 
 132. 
 
 Internal circuit, the, defined, 12. 
 
 Internal resistance of battery, methods of 
 measuring, 207. 
 
 Interruptions and faults on telegraph lines, 
 classification of, 190. 
 
 Iron, magnetization of by electric current, 
 35 ; specific electrical resistance of, 57 ; ef- 
 fect of in magnetic helix, 84. 
 
 Iron filings held to conductor by magnetism, 
 
 Iron wires for lines, table of sizes, weights, 
 
 and resistances ol, 112 ; joints in, 113. 
 Iron and steel, magnetic properties of, 24. 
 
 JENKIN, FLEEMING, on conductors and insula- 
 tors, 56 ; on Wheatstone's bridge, 198. 
 
 Jenkin's Electricity and Magnetism, refer- 
 ences to, 17, 18, 62, 198. 
 
 Johnson's Universal Cyclopedia, reference to, 
 
 20. 
 
 Joint, detective, on line, method of locating, 
 205. 
 
 Joint, twist, for iron wires, 113; importance 
 of soldering. 113. 
 
 Joint resistance of branch circuits, rule for 
 determining, 66. 
 
 Jones, Francis W., on quadruplex teleg- 
 raphy, reference to, 187. 
 
 Joule, James Prescott, biographical notice 
 of, 63. 
 
 Joule's law, statement of, 63. 
 
 Joule's conception ot magnetic circuit, 81. 
 
 KAPP LINE, the, 83. 
 
 Kapp's Electric Transmission of Energy, 
 reference to, 24. 
 
 Kapp's unit of magnetic induction, 83 ; value 
 of, 83. 
 
 Kempe, A. B., on the leakage of submarine 
 cables, reference to, 128. 
 
 Kempe, H. R., Handbook of Electrical Test- 
 ing, references to, 128, 198 ; on Wheat- 
 stone's bridge, 198. 
 
 Kennelly and Wilkinson's/Vvz<r//cYi/ Notes for 
 Electric Students, reference to, 85. 
 
 Kerite insulation for office wires, 113, 114. 
 
 Key, construction of, 138 ; adjustment of, 
 140 ; platinum contacts of, 138 ; modifica- 
 tions of, 139 ; Western Electric pattern, 
 140; Victor pattern, 140; double-current 
 or reversing, 180 ; common Morse, how 
 shown in diagram, 104 ; three-point, how 
 shown in diagram, 104 ; method of hand- 
 ling, 219 ; preliminary practice with, 220. 
 
 Key and sounder, combination, 143 ; pocket, 
 
 1 44- 
 Key, relay, and register, combination of, 149. 
 
 Kick, due to electrostatic charge and dis- 
 charge, 177. 
 
 Kohlrausch's Physical Measurement, refer- 
 ence to, 62. 
 
 LAW OF MAGNETIC CIRCUIT, 88. 
 
 Law of electric current, Ohm's, 63 ; Joule's, 
 63. 
 
 Law connecting mechanical and electric 
 force, 59. 
 
 Learners, hints to, 216. 
 
 L" Electrician, reference to, 23. 
 
 Lefferts, Marshall, biographical notice of, 214. 
 
 Legal ohm, determination of, 63 ; value of, 63. 
 
 Length of body, effect of upon resistance, 58. 
 
 Letter space, an element of telegraphic code, 
 
 216. 
 
 j Lightning arrester, description of, 160; com- 
 bination of with switch, 156, 157; inspec- 
 tion and care of, 161 ; how shown in dia- 
 gram, 104. 
 
 j Line, computation of working efficiency of, 
 128 ; electrostatic capacity of, 175 ; over- 
 head, diagram of, 104 ; submarine or sub- 
 terranean, diagram of, 104 ; artificial, of 
 multiple telegraph, 174. 
 
 | Lines, leaky, resistance and current in, 128 ; 
 table for computing resistances and escapes 
 upon various lengths of, 129 ; best position 
 for battery on, 131, 132 ; effect of pos.tion 
 of fault in, 131. 
 
 Lines of magnetic force, conception of due to 
 Faraday, 27 ; rendered visible by iron 
 filings, 27. 
 
 Local circuit, working by relay and, 144. 
 
 Lockwood cell, description of,' 18. 
 
 Lockwood's Electricity, Magnetism, and 
 Electric Telegraphy, references to, 23, 34. 
 
 Lodestone or natural magnet, properties of, 
 24. 
 
 Lodge, Oliver J,, theory of electricity, 2. 
 
 Loop test for conductivity resistance, 201 ; 
 for position of escape, 203 ; Varley's mod- 
 ification of, 203. 
 
 MAGNET, bar, 24 ; horseshoe, 26 ; multipolar, 
 26 ; natural and artificial, 24 ; temporary 
 and permanent, 24. 
 
 Magnet, polarity of, 25 ; magnetic length of, 
 26 ; maximum attraction exerted by, 26. 
 
 Magnet, telegraph, best proportions for, 91 ; 
 details of construction of, 91. 
 
 Magnet wires, Prescott's table of dimensions 
 and resistances of, 93. 
 
 Magnetic attraction and repulsion, 28. 
 
 Magnetic circuit, conception of by Joule and 
 others, 81 ; formation of, 87 ; law of, 88. 
 
 Magnetic compass, the, 25. 
 
 Magnetic density, 83. 
 
 Magnetic field, the. 27 ; exploration of by sus- 
 pended needle, 28 ; of the earth, 40. 
 
 Magnetic flux, 88. 
 
 Magnetic force, relation of current to, 85. 
 
 Magnetic hysteresis, definition of, 97. 
 
 Magnetic induction, phenomena of, 25; cause 
 of, 85. 
 
 Magnetic inertia, definition of, 99. 
 
 Magnetic length of magnet, 26. 
 
 Magnetic meridian, the, 24, 28. 
 
 Magnetic moment, definition of, 86; experi- 
 mental determination of, 86 ; tabulated re- 
 sults of, 86. 
 
 Magnetic needle, the, 24. 
 
 Magnetic permeability, 88 ; definition of, 88. 
 
 Magnetic reluctance, 88; determination of, 
 88. 
 
 Magnetic resistance, 88. 
 
 Magnetic saturation, curve of, 85; definition 
 of, 87. 
 
 Magnetic spectrum, the, 26. 
 
 Magnetic and electrical units, derivation of, 
 
 characteristics 
 
 Magnetism, definition of, 
 of, 24 ; 
 of, 
 remanent or residual, 98. 
 
 r netism, definition ol, 24 ; characteristics 
 f, 24 ; unit of, 83 ; intensity of, 83 ; density 
 f , 83 ; lines of force a measure of, 82 ; 
 
Index. 
 
 Magnetism and electricity, essential nature 
 of, 2. 
 
 Magnetization, of one body by another, 25; 
 intensity of defined, 86 ; proportional to 
 ampere-turns, 87 ; maximum limit of in 
 soli iron, 87. 
 
 Magneto-electricity, 3 ; definition of, 24 ; 
 phenomena of, summarized, 32. 
 
 Magneto-motive torce, 81, 83; definition of, 
 83 ; method of computing, 84. 
 
 Magnetometer, construction and use of, 85. 
 
 Maintenance of voltaic cell, 14. 
 
 Manual and automatic repeaters, 162. 
 
 Manuscript copy, practice from recom- 
 mended, 222. 
 
 Materials consumed in battery, quantity and 
 cost of, 74. 
 
 Matthiessen on specific resistance of metals, 
 reference to, 57. 
 
 Maver, William, jr.. on dynamo telegraphy, 
 185 ; on quadruplex telegraphy, 187. 
 
 Maximum magnetic effect in electro-magnet, 
 best proportions for, 91. 
 
 Mayer's Eartk a Great Magnet, reference to, 
 24. 
 
 Measurement, absolute system of, 37; quan- 
 titative electrical, theory of, 35 ; impor- 
 tance of, 36; electrical, character of, 43 ; 
 practice of, 195. 
 
 Mechanical force, relation of to current force, 
 40. 
 
 Mechanical power, transformation of into 
 electricity and heat, 31. 
 
 Mechanical analogue of electrical action, 58. 
 
 Megadyne, definition of, 38. 
 
 Metallic cross, 191. 
 
 Metals, specific resistance of, 57. 
 
 Metric system, foundation of absolute sys- 
 tem of electrical and magnetic units, 37. 
 
 Mexico, closed circuit used in, 108. 
 
 Microfarad, the, 73. 
 
 Micrometer caliper for gauging wires, 96. 
 
 Milliken's automatic repeater, 165. 
 
 Minotto's cell, 17. 
 
 Modern Practice of Electric Telegraph (4th 
 ed.), reference to, 17, 23. 
 
 Moment, magnetic, definition of, 86. 
 
 Movement of conductor in magnetic field, 
 effects of, 30. 
 
 Muller, on increase of resistance of metals by 
 rise in temperature, 78. 
 
 Multiple series of cells, 53. 
 
 Multiple wire switchboard, 156. 
 
 Multiples of electrical units, 60. 
 
 Multipolar magnet, 26. 
 
 Munroe and Jamieson's Pocket-book of Rules 
 and Tables, reference to, 73. 
 
 Mutual reactions of current and magnet, 32, 
 
 NEEDLE, magnetic, deflected by current, 35. 
 
 Needles, astatic, system of, 198. 
 
 Negative plate or element of cell, 12. 
 
 Neutral line of magnet, 26. 
 
 Niaudet's Electric Batteries, reference to, 62. 
 
 Nickel, magnetic properties of, 24. 
 
 Nipher's Theory of Magnetic Measurements, 
 
 reference toj 40. 
 
 Nomenclature of electric circuit, 12. 
 North pole and south pole of magnet, 26. 
 North-seeking pole, the, 29. 
 North British Review, extract from, 56. 
 Nystrom, J. W., definition of force. 27. 
 Nystrom's Elements of Mechanics, extract 
 
 from, 27. 
 
 OFFICB WIRES, 113 ; table of dimensions of, 
 
 114. 
 Ohm, Georg Simon, biographical notice of, 61. 
 
 Ohm, the unit of electrical resistance, defini- 
 tion of, 61 ; value of, 61, 62, 63. 
 
 Ohm's law, statement of, 63 ; experimental 
 proof of, 64. 
 
 Oil, used to prevent evaporation in voltaic 
 cells, 14. 
 
 Okonite insulation for office wires, 113, 114. 
 
 Open circuit, in telegraphy, 102, 103 ; system 
 of telegraphy, description of, 107. 
 
 Open and closed circuit, comparative advan- 
 tages of, 109. 
 
 Operator and Electrical World, references 
 to, 185, 187. 
 
 Origin ot electricity. 3. 
 
 Oxide of copper cell, 21 ; maintenance of, 22 ; 
 chemical reaction, 22. 
 
 Oxide of zinc formed by action of voltaic 
 cell, 6. 
 
 PARAFFIN INSULATOR, the, 117. 
 
 Parallel arrangement of voltaic cells, 54. 
 
 Parallel series of cells, 53. 
 
 Paris exposition, Report on Telegraphic Ap- 
 paratus, extract from, 128. 
 
 Parting word, a, 223. 
 
 Permanent and temporary magnets, 24. 
 
 Permanent and electro-magnets, combina- 
 tions of, 10 1. 
 
 Permeability, magnetic, definition of, 88 ; of 
 iron, 81. 
 
 Phenomena, of voltaic cell, 5 ; of induction 
 upon telegraph lines, 177. 
 
 Philosophical Magazine, reference to, 81. 
 
 Philosophical Transactions of Royal Society, 
 references to, 26, 98. 
 
 Physiological effects of electric current, 36. 
 
 Platinoid, specific resistance of, 57. 
 
 Platinum, specific resistance of, 57. 
 
 Plum, H. W., on quadruplex telegraphy, 
 187. 
 
 Pocket telegraphic apparatus, 144. 
 
 Polar or polarized relay, 180 ; how shown in 
 diagram, 104. 
 
 Polarity of the magnet, 25 ; of electro-mag- 
 net determined by direction of current, 81. 
 
 Polarized armature, 100. 
 
 Pole changer, peg, construction of, 51. 
 
 Pole-changing transmitter in multiple teleg- 
 raphy, 181. 
 
 Poles of magnet, 25 ; of voltaic cell, 12. 
 
 Poles, tests of insulating value of when wet, 
 133, 134. 
 
 Pope, F. L., on quadruplex telegraphy, 187. 
 
 Porcelain insulator, the, 118 ; tests of, 120. 
 
 Porous cell, action of, 20. 
 
 Position, method of locating, of ground, 202 ; 
 of escape, 202 ; of cross, 204 ; of bad joint 
 or abnormal resistance, 205. 
 
 Positive plate or element of cell, 12. 
 
 Post-office, British, table of iron wires, 112 
 
 Potential, conception of. 59 ; of telegraph 
 line, determination of by calculation, 123 ; 
 of line, measurement of by auxiliary bat- 
 tery, 122. 
 
 Potential, electric, explanation of, 69 ; fall of 
 along conductor, illustration of, 70 ; pro- 
 portionate to resistance, 71 ; in perfectly 
 insulated circuit, distribution of, 120 ; in 
 imperfectly insulated circuit, 125; within 
 battery, 123. 
 
 Potential series, arrangement of dynamos in, 
 in telegraphy, 169. 
 
 Power or rate of work of electric current, 73. 
 
 Practical electric units, 59. 
 
 Practice, preliminary, with key, 220. 
 
 Preece, W. H., on effects of temperature on 
 sulphate of copper cell, 78, 79. 
 
 Prescott, Geo. B.. Jr., on electro-chemical 
 
232 
 
 Index. 
 
 equivalents, 74 ; table of properties of soft 
 copper wires, 112. 
 
 Prescott's Electricity and Electric Tele- 
 graph, reference to, 62. 
 
 Primary or inducing current, 74. 
 
 Properties and dimensions or copper magnet 
 wires. Prescott's table of, 94. 
 
 Proportional deflections, measuring high re- 
 sistances by method of, 205, 206 ; measur- 
 ing resistance of insulators by, 206. 
 
 QlMDRUPLEX TELEGRAPHY', 171 \ principle Of, 
 
 182 ; a combination of diplex and contra- 
 plex systems, 184; distribution of currents 
 in, 186 ; how worked by dynamo currents, 
 185; practical management of, 187; ad- 
 justment of apparatus of, 188 ; repeaters 
 for, 189. 
 
 Quantity, of current in circuit, conditions 
 which determine, 54 ; of material con- 
 sumed in battery, 74. 
 
 RAIN WATER, should be used in batteries, 5. 
 
 Rate, of consumption of material in voltaic 
 cell. 13; of work of electric current, how 
 found, 64 ; relation of to time, 73. 
 
 Reading by sound, 222. 
 
 Receiver, the, an element of the electric tele- 
 graph, 2. 
 
 Reciprocals, 66 ; table of, 67. 
 
 Reduced length of conductor, meaning of, 58. 
 
 Register, the, 147 ; construction of, 147 ; 
 European pattern of, 148 ; combination of 
 with key and relay, 149 ; adjustments of, 
 149 ; causes of defective marking in, 150 ; 
 ink-writing, 150 ; how shown in diagram, 
 104. 
 
 Relay, construction of, 144 : function of, 146 ; 
 adjustments of, 147 ; short core, for diplex 
 and quadruplex apparatus, 184 ; polar, or 
 polarized, 180 ; how shown in diagram, 
 104 ; common or non-polarized, how 
 shown in diagram, 104. 
 
 Relay and local circuit, working by, 144. 
 
 Relay, key, and register, combination of, 149. 
 
 Reluctance, magnetic, 88 : determination of, 
 88. 
 
 Remanent or residual magnetism, 98. 
 
 Repeater, the, 162 ; manual and automatic, 
 162- button, 162; Wood's, 164: Milli- 
 ken s, 165; for duplex, quadruplex, and 
 multiple systems, 189. 
 
 Residual or remanent magnetism, 98. 
 
 Resistance, electrical, explanation of, 56; 
 conditions affecting, 58 expressible in 
 terms of length, 58 ; artificial, how shown 
 in diagram, 104. 
 
 Resistance, of circuit, relation of to quantity 
 of current flowing in, 56 ; abnormal on 
 line, method of locating, 205 ; relation of 
 conductivity to insulation of line, no; ra- 
 tio of conductivity to insulation, minimum, 
 128. 
 
 Resistance, conductivity, of line, measure- 
 ment of with bridge, 199. 
 
 Resistance, insulation, of line, measurement 
 of, 202 ; of insulators, method of measur- 
 ing, 206 ; of various kinds of insulators, 
 1 20. 
 
 Resistance, joint, law of, 66 ; of a circuit, how 
 to determine. 66. 
 
 Resistance, specific, of different metals, 57 ; 
 of copper wires for electro-magnets, table 
 ot, 94 ; of galvanized iron, hard-drawn 
 and soft copper wires, Prescott's table of, 
 112 ; of metals emploved as conductors in 
 telegraphv, percentage of increase in by 
 rise of temperature, 78. 
 
 Resistance of liquids, Farmer's values of, 62; 
 Becker's ditto, 63 ; of sulphate of copper 
 solution, 62, 63 ; of sulphate of zinc solu- 
 tion, 62, 63 ; internal, of voltaic cell, 64 ; 
 of ordinary gravity cell, 74 ; of sulphate 
 of copper cell, effect of temperature upon, 
 78 : experiments of Preece on, 78 ; inter- 
 nal, of battery, methods of measuring, 207. 
 
 Resistance, very high, methods of measur- 
 ing, 205 ; of galvanometers, method of 
 measuring, 208; of helix, a measure of 
 number of turns in, 93; of leaky Hues, 
 
 128 ; table of, 129. 
 
 Resistance coils, construction of, 51. 
 
 Re istance, magnetic, 88. 
 
 Retardation in electro-magnets, indirect 
 causes of, 99. 
 
 Reversing or double-current key, 180. 
 
 Rheostat or artificial resistance, construction 
 of, 51 ; how shown in diagram, 104. 
 
 Ring gauge, for wire, 95. 
 
 Roebling, J. A., table of hard-drawn copper 
 wires, 112. 
 
 Rowland, H. A., On Magnetic Permeability 
 of Iron, 81. 
 
 Royal Society's Proceedings, references to, 24, 
 79- 
 
 SABINE'S Electric Telegraph, reference to, 83. 
 
 Safety-fuse, use of, 161. 
 
 Saturation, magnetic, definition of, 87; curve 
 of, 85 ; experimental investigation of, 86. 
 
 Schott, C. A., on determination of value of 
 horizontal component of earth's magnet- 
 ism, 40. 
 
 Second, the unit of time, 37. 
 
 Secondary or induced current, 74. 
 
 Self-exciting dynamo-electric machine, 163. 
 
 Self-induction, effect of on telegraph mag- 
 nets, 99. 
 
 Sentence space, an element of telegraphic 
 code, 216. 
 
 Series arrangement of voltaic cells, 52. 
 
 Series of cells, effect of varying number in, 
 53 ; consumption of material in, 76. 
 
 Shaffner's Telegraph Manual, reference to, 
 62. 
 
 Short-circuiting a cell, 8. 
 
 Short-line sounder, 142. 
 
 Shunt, definition and derivation of, 69. 
 
 Shunts, applied to galvanometer for measure- 
 ment of high resistances, 205 method of 
 using, 206. 
 
 Shunt-wound dynamo-electric machine, 168, 
 169. 
 
 Siemens' mercury unit, value of, 62. 
 
 Single-current duplex, the, 172. 
 
 Sizes of galvanized iron and copper wires, 
 table of, 112. 
 
 Soft iron, effect of magnetization upon, 85 ; 
 maximum limit of magnetization in, 87. 
 
 Soil, earth circuit affected by characteristics 
 of, 106, 107. 
 
 Sound, reading by, 222 ; methods of practice 
 in, 223. 
 
 Sounder, the, 141 ; adaptation of to short 
 lines, 142 ; adjustment of, 142; combina- 
 tion kev and, 143 ; pocket. 144 ; box, 144 ; 
 how shown in diagram, 104. 
 
 Sources of electricity, 3, 24. 
 
 Space, an element of telegraphic code, 216. 
 
 Spaced letters, formation of, 222. 
 
 Spaces, in helices of electro-magnets, thick- 
 ness of, 94. 
 
 Spark and ground coils in duplex telegraph, 
 179. 
 
 Specific gravity, explanation of, 7 ; of battery 
 solutions, table of, 9. 
 
Index. 
 
 233 
 
 Specific resistance of materials, 57 ; how de- 
 termined, 57. 
 
 Spectrum, magnetic, the, 26; of electro-mag- 
 net, 96. 
 
 Spelter tor battery zincs, analysis of, 20. 
 
 Sprague, J. T., on effect of heat on f. m.f. of 
 sulphate of copper cell, 74. 
 
 Sprague's Electricity, extract from, 74 ; ref- 
 erences to, 38, 57, 62. 
 
 Spring-jack and wedge cut-out, the, 155 ; mul- 
 tiple ditto. 156. 
 
 Static or Irictional electricity, 33. 
 
 Static charge of line, nature of, 177. 
 
 Stearns, Joseph B., his inventions in duplex 
 telegraphy, 178. 
 
 Stewart and Gee's Elementary Practical 
 Physics, reference to, 62. 
 
 Stewart's Conservation of Energy, reference 
 to, 38. 
 
 Storage battery or accumulator, how shown 
 in diagram, 104. 
 
 Student, apparatus required by, 45. 
 
 Sturgeons A nnals, reference to, 81. 
 
 Sub-multiples of electrical units, 60. 
 
 Sulphate of copper, chemical analysis of, 8 ; 
 chemical equivalent of, 75 ; solution, re- 
 sistance of, 62, 63. 
 
 Sulphate of zinc, chemical analysis of, 9 ; so- 
 lution, resistance of, 62, 63. 
 
 Swinging cross, 191. 
 
 Switch, universal, how shown in diagram, 104; 
 three-point, how shown in diagram, 104; 
 pole-changing, how shown in diagram, 
 
 Switchboard, multiple wire, 156 ; universal, 
 
 156; terminal, 158. 
 Switchboard for way-station, description of, 
 
 152 ; manipulation of, 153 ; testing by 
 
 means of, 154. 
 
 TANGENT GALVANOMETER, description of, 41 ; 
 principle of, 42 ; details of construction of, 
 45; Western Union pattern, 209; use of 
 in testing insulation by received currents, 
 209. 
 
 Tangents, natural, table of, 55. 
 
 Tapping upon key, importance of avoiding, 
 219. 
 
 Tap-wire, in quadruplex telegraph, 187. 
 
 Telegraph, electric, elements of, 2. 
 
 Telegraph lines, mutual current induction 
 between, 74 ; American, equipment of, 
 138. 
 
 Telegrapher, The, extracts from, 119, 120, 
 136; references to, 17, 187. 
 
 Telegraphic circuits, 102 ; distribution of po- 
 tentials in, 120. 
 
 Telegraphic code, formation of, 216 ; ele- 
 ments of, 216; a multiple of time, 216. 
 
 Telegraphic conductors, m. 
 
 Telegraphic magnet, theoretical proportions 
 of, 91 ; details of construction of, 91 ; 
 spectrum of, 97 : effects of self-induction 
 an<l hysteresis in, 99. 
 
 Telegraphy, multiple, 171 ; diplex, 171 ; con- 
 traplex, 171 ; quadruplex, 184. 
 
 Temperature, effect of, on action of voltaic 
 cell, 20, 78 ; on resistance of substances, 58 ; 
 effect of in increasing resistance of metals 
 employed as telegraphic conductors, 78. 
 
 Temporary and permanent magnets, 24. 
 
 Tensile strengths of galvanized iron, hard 
 and soft copper wires for telegraph lines, 
 table of, 112. 
 
 Terminal station, arrangement of apparatus 
 at, 158. 
 
 Terminal switchboard, 158. 
 
 "Testing telegraph lines, 190 ; for disconnec- 
 
 tion at way-station, 134 ; by quantitative 
 measurement, 195 ; character of measure- 
 ments in. 195. 
 
 Tests of telegraph lines, object of. 190 ; of 
 conductivity and insulation, recording of, 
 214. 
 
 Test-sheets, Western Union Company's 
 forms tor, 212, 213, 214. 
 
 Thermo-electricity, 3, 34. 
 
 Thompson, Silvanus P., on magnetic reac- 
 tions, 31 ; on Wheatstone's bridge, 198. 
 
 Thompson's Elementary Lessons in Elec- 
 tricity and Magnetism, reference to, 31, 
 198 ; Dynamo-Electric Machinery, refer- 
 ence to, 86. 
 
 Thomson, Sir William, on importance of 
 quantitative measurement in physical 
 science, 36; Popular Lectures and Ad- 
 dresses, extract from. 36. 
 
 Thomson's theory of electricity, 2 ; cell, 17 ; 
 rule for computing the windings of elec- 
 tro-magnets, 94. 
 
 Time, necessarily involved in formation of 
 dot, 217 ; telegraphic code a multiple of, 
 .216. 
 
 Transmitter, the, an element of the electric 
 telegraph, a. 
 
 Transmitter, pole changing, 181 ; single cur- 
 rent, 173 ; single and double, how shown 
 in diagram, 104. 
 
 Transverse magnetization, 26. 
 
 Trowbridge's New Physics, references to, 40, 
 85. 
 
 Twist-joint for iron wires, 113. 
 
 Tyndall, observations on conservation of 
 energy, 38. 
 
 TyndalPs Heat as a Mode of Motion, refer- 
 ence to, 38. 
 
 Typical voltaic cell, description of, 3. 
 
 U OR HORSESHOE MAGNET, 26. 
 
 Unit of magnetism, 83; of magnetic induc- 
 tion, Kapp's, 83 ; English, 83 
 
 Units, lundamental and derived, 37 ; elec- 
 trical, synoptical table of, 73 ; practical, 
 derived from natural constants, 59. 
 
 Universal switchboard, 156 ; manipulation of, 
 157' 
 
 U. S. Coast and Geodetic Survey, reference to 
 reports of, 40. 
 
 VAIL, ALFRED, biographical notice of, 216 ; 
 originator of the telegraphic register in its 
 present form, 216 ; of the alphabetical 
 code, 216. 
 
 Varley's insulator, tests of efficiency of, 120 ; 
 loop test for position ot escape on line, 
 203. 
 
 Varley's Report on Western Union Lines, 
 references to, 131, 135. 
 
 V-gauge for wire, 95. 
 
 Victor Key, 140. 
 
 Volt, the unit of electromotive force, defini- 
 tion of, 61 ; value of, 61. 
 
 Volta, Alessandro, biographical notice of, 
 61. 
 
 Volta induction, 74. 
 
 Voltaic cell, phenomena of, 5; directions for 
 charging, 7. 
 
 Voltaic effect, chemistry of, 6. 
 
 Voltaic element, the, 3. 
 
 Voltaic solutions. Becker's table of resist- 
 ances of, 63 ; Farmer's ditto, 62. 
 
 Voltameter, the, 44. 
 
 Voltmeter, use of in telegraphic testing. 210 ; 
 Weston's portable, 210- advantages of 
 for testing, 211 : Weston's combined am- 
 meter and, for telegraphic testing, 210, 211. 
 
234 
 
 Index. 
 
 WASHBURN & MOEN MVc Co.'s IRON WIRE 
 
 TABLE, 112. 
 
 Watt, James, biographical notice of, 73. 
 Watt, the unit of power or rate of work, 
 value of, 73 ; rule for determination of, 
 
 Way-station, arrangement of apparatus at, 
 151 ; connections ot, 152 ; manipulation of 
 switchboard in, 153 ; testing in, 154. 
 
 Weather- cross, term applied to escape be- 
 tween different wires, 132. 
 
 Webb, F. C., on electrostatic phenomena, 
 175. 
 
 Webb's Electrical Accumulation and Con- 
 duction, extract from, 175. 
 
 Weber, Eduard, 83. 
 
 Wedge or plug cut-out, the, 155. 
 
 Weights of iron and copper wires for tele- 
 graph lines, table of, 112. 
 
 Western Electric key, 140. 
 
 Western Union glass insulators, 116. 
 
 Western Union Telegraph Company's forms 
 for test sheets, 212, 213, 214. 
 
 Western Union telegraph station, New York, 
 arrangement ot dynamos in, 170. 
 
 Weston's voltmeters and ammeters for tele- 
 graphic testing, 210, 211. 
 
 Wheatstone bridge, the, 195. 
 
 Wilkinson, Kennelly and, 85. 
 
 Winding magnet helices, machine for, 93. 
 
 Windings ot helix, effect of position of, 92. 
 
 Windings of magnet coils, Sir Wm. Thom- 
 son's rule for computing, 94. 
 
 Wire-gauge, American standard, 95 ; British, 
 
 95. 
 Wire, instruments for gauging, 95, 96 ; in 
 
 helix, relation of length and thickness ot 
 
 to number of turns, 92. 
 Wires, copper, for line construction, 114; lor 
 
 magnets, dimensions and resistances of, 
 
 93 ; Prescott's table of, 94. 
 Wires, crossing 01, represented in diagram, 
 
 104. 
 Wires, iron, in ; table of sizes, weights, and 
 
 resistances of, 112; joints in, 113; dia- 
 gram of actual sizes of, 113. 
 Wood's repeater, 164. 
 Word-space, an element of telegraphic code, 
 
 216. 
 
 Work, electric, in circuit, 64. 
 Working efficiency of telegraph line, what it 
 
 depends on, 127. 
 
 YOKE, of electro-magnet, 91. 
 
 Youmans' Correlation and Conservation y 
 Forces, reference to, 38. 
 
 ZINC OF GRAVITY CELL, 4; process ot clean- 
 ing, 16; amalgamation of, 21. 
 
 Zinc, oxide of, formed by action of voltaic 
 cell, 6. 
 
 Zinc, electro-chemical equivalent of, 74, 75; 
 chemical analysis of, 9. 
 
 Zinc solution of gravity cell, neutralizatioB 
 of, 1 6. 
 
 Zinc plate of cell the positive element, 12. 
 
 Zinc, d'Infrcvillc's wasteless, 33. 
 
LIST OF WORKS 
 
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 ARNOLD, E. Armature Windings of Direct Current Dynamos. Extension and 
 
 application of a general winding rule. Translated from the original German 
 
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 445 
 
446 VAN NOSTRAND'S LIST OF WORKS 
 
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 Electric Lamps and Electric Lighting. 8vo, cloth. $3.00. 
 
OiV ELECTRICAL SCIEA'CE. 44 T 
 
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 HOUSTON, Prof. E. J. A Dictionary of Electrical Words, Terms, and Phrases. 
 
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 INCANDESCENT ELECTRIC LIGHTING. A Practical Description of the Edison 
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O.V ELECTRICAL SCIENCE 449 
 
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450 LIST OF IVOKKS O.Y ELECTRICAL SCIENCE. 
 
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