The electric light : its history, production, and applications

Front matter

ISli

Moorish salon in the Continental Hotel lighted by the Jablochkoff candle.

THE

Book I. History Of Artificial Lighting

CHAPTER PAGE

I. Oils, candles, and gas . • -v . • • * • • 1

II. History of the electric light . •---».. . . * . 11

Book II. The Voltaic Arc

I. How the electric light is produced . . . . .27

II. Electrical units . . '*• ' " ' . .. . . . 37

III. The arc-lamp carbons . . » . . . .46

IV. Single-light regulators ....... 55

I. Regulators with electro-magnet . . . . .60

II. Solenoid regulators . • . : .... 67

V. Multiple light, or division, regulators » < . . . .71

I. Derived-current, or shunt-circuit, lamps . . 72

II. Differential lamps . . . . . .78

III. Automatic safety apparatus r 90

VI. The Jablochkoff candle . '. 98

VII. Lamps without mechanism . . . . . . 105

I. Lamps with converging carbons . . . . 105

II. Recent candles . 110

Book III. The Incandescent Light

I. History of incandescence . . . . . . .116

I. The debut of platinum . .' . . . . 116

II. The debut of carbon . . . . . .117

III. The Russian lamps . . . .' . . 119

II. Incandescence in the open air . . . . . .123

I. The Reynier lamp 123

II. The Werdermann lamp . ' . . . . .125

CONTENTS.

PAGE

III. The actual Reynier-Werdermann lamps . . . 128

IV. Installation of Keynier-Werdermann lamps . . . 132 V. Various lamps ....... 134

III. The sun lamp . . . . . . . .137

IV. The Edison lamp . . . . . . . 148

I. His first researches ...... 148

II. Platinum-wire lamps . . . . . 152

III. Lamps with paper carbon . . . . .156

IV. Bamboo-carbon lamps ..... 158 V. The lamps actually employed . . . . .164

V. The Swan, Lane-Fox, Maxim, and new lamps . . . 170

I. The Swan lamp . . . < . . .170

II. The Lane-Fox lamp . .... . 177

III. The Maxim lamp . . . . . . .179

VI. Measurement of incandescent lamps . . . . .182

VII. Conditions of efficiency in the incandescent lamp . . . 187

Book IV. Production Of Electric Currents

I. Hydro-electric batteries . . . . . . .196

Secondary or storage batteries .... 202

II. Thermo-electric batteries ....... 207

III. Electrical induction . . . . . . . 211

Ruhmkorff's coil . . . . . . .214

IV. Theoretical principles of machines . . . ' . . 217 V. The first magneto-electric machines ..... 232

I. Nollet.— Van Malderen.— Holmes .... 233

II. Siemens.— Wilde.— Ladd 236

VI. The Gramme machine ....... 240

Division machines (Machines d division) . . . 245

Octagonal machines ...... 248

Alternating-current machines ..... 248

Self-exciting machines ..... 250

Precursors of Gramme ...... 255

VII. The Siemens machines. — Ferranti and Gordon machines . . 257

VIII. Recent dynamo-electric machines ...... 266

I. Weston machine . . . . . .266

II. Maxim machine ....... 267

III. Edison machine . . . . . .273

IV. Transformations of the preceding machines . . . 279 V. Machines in which the cores of the armature coils play a preponderating role ...... 286

IX. Recent magneto-electric machines ...... 290

X. Efficiency of the dynamo ...... 298

XI. Measurements of dynamos and arc-lamps ..... 304

CONTENTS. xi

Book V. Distribution Of Electricity

CHAPTER PAGE

I. First mode of distribution . . . . . . 314

I. Electric conductors ...... 315

II. Disposition of electric wires for lighting the port of Havre 317

II. Conditions of a general distribution ..... 324

I. Regulators of the intensity of currents .... 326

II. Electric canalization of Edison .... 329

III. M. Gravier's system of electrical distribution . . . 333

IV. System of electrical distribution of M. Marcel Deprez . 338 V. Edison's method of regulation ..... 345

VI. Weston's method of regulation. — Brush regulator . . 350

III. Economy of conductors . . . . f . 354

I. Edison's multiple-series system of distribution 4 ... . 355

II. The secondary-generator system of distribution . . . 357

IV. Divisibility of the electric light . . . . 359 V. Electric meters . 363

Book VI. Applications Of The Electric Light

I. Electricity in light-houses . . .' . . . 371

II. The electric light in war and navigation ..... 388

I. Military and maritime applications from 1855 to 1877 . 388

II. Electric projectors of the French army .... 394

III. The electric light at sea . . . . . 399

III. The electric light in the theatre , 407

IV. Industrial applications . . . . t . . , 417

LIST OF ILLUSTEATIOIsrS.

FIG.

FRONTISPIECE — Moorish saloon of the Continental Hotel, lighted by Jablochkoff candles.

1. Pincers for lamp . . . . . . . ' . .2

2. Bronze Roman lamp . ..- . « .

4. 5. Roman candelabra in carved bronze, bearing one or more lamps . 3

6. Quinquet's lamp hung upon a wall . . . ... 6

7. Lamp of the Carcel type, with moderator mechanism, and bottom oil-

8. Lamp of M. Tessie du Motay for production of the Drummond light . 10

9. Hawksbee experimenting with Otto von Guericke's electric machine, in

England . . . 12

10. Franklin making the experiment with a kite, to establish the identity of

lightning and electricity . . . - » . . . .14

11. Experiment of electrifying a woman, from an engraving of the eighteenth

12. The Abbe Nollet giving a lesson in electricity . . . . .19

13. Electrometer, after the design in the Encyclopaedia ... 20

14. The Avenue de 1'Opera in Paris lighted by Jablochkoff candles . . 26

15. The two poles of the voltaic arc . . ..... . 33

16. Draw-plate, with hydraulic press, for making artificial carbons . . 48

17. Curved nozzle draw-press of M. Napoli. (Vertical section.) . . 50

18. Cylinder for nourishment of the carbons under pressure, by M. Napoli's

19. Workshop of M. Napoli, showing the different operations of manufacturing

electric-light carbons . " «, ' * •. ' <• . . 52

20. 21, 22. Points of a pair of carbons, plain, and coated with metal . . 53

23. One-sided position of the carbons, for the purpose of causing the light to be

of greater intensity in one direction . ^^-^ , ... 56

24. Carbon-holder regulated by hand, for the production of^the electric light . 57

25. Primitive carbon-holder, for production of the electric light in a vacuum 57

26. Hand-regulator of M. Boudreaux, with vertical carbon-iolders, for magic

lanterns and other experiments with electric light . -„ ' .58

28. First regulator of the electric light of Foucault (1849) , . .62

29. Regulator of J. Duboscq . . . ^> • * ^ xiv LIST OF ILLUSTRATIONS.

FIG. PAGE

32. Archereau's regulator, type of solenoid regulators . . . .67

33. Gaiffe's regulator ........ 68

34. Jaspar's regulator ........ 69

35. F. Carre's regulator ....... 70

36. Serrin regulator modified for derived current by the Lontin company . 73

37. M. Gramme's derived-current regulator ..... 75

38. De Mersanne regulator . . . . . . .76

39. Section of the carbon-carrier of the De Mersanne regulator . . 76

40. The Wallace lamp 77

41. Siemens differential lamp ....... 79

44. Vertical section of the upper carbon-rod . . . . .83

45. Relation of the two carbon-rods to each other in the double lamp . 84

46. Brush double lamp ........ 84

47. A street of New York lighted by Brush lamps .... 85

48. Brush street-lamp . . . . . . . 86

50. Details of the mechanism of the Weston lamp . . . .88

51. Section of one of the differential magnets of the Weston lamp . . 88

52. Mechanism of the Weston lamp . . . . . .89

53. Vertical section of operating parts of the Weston lamp ... 90

54. Clutch of the Weston lamp 90

55. Mechanism of the Wood lamp . . . . . . 91

56. Diagram of the working parts of the Wood lamp . . . .92

57. Wood single lamp ........ 93

58. Gerard automatic cut-out . . . . . . .94

59. Safety-box of M. de Mersanne ...... 95

60. Diagram of Brush lamp connections and cut-out . . . .96

61. Weston automatic cut-out . . . . . . . 97

62. 63, 64. Jablochkoff candle 100

65. Sockets of Jablochkoff candles and switch for lighting the candles succes-

sively by hand ........ 102

66. The Hippodrome of Paris lighted by Jablochkoff candles . . . 104

68. Gerard lamp. General appearance . . . . . .108

69. Vertical section of Gerard lamp ...... 109

70. Wilde's candle. Four-candle holder . . . . . .111

72. A street in Newcastle lighted by the Swan incandescent lamp . .120

73. Incandescent lamp of Konn, in a closed vessel . . . . 122

74. Principle of incandescence ii the open air . . . . .124

75. Reynier incandescent lamp ; first arrangement with rotating electrode . 124

76. Magnified image o'^he incandescent portion of the Reynier lamp . . 125

77. Werdermann lamp ........ 126

78. Burner of the Reyrier lamp ....... 128

79. Reynier's incandescent lamp, with globe ..... 128

80. Chandelier of Weraermann lamps ...... 129

81. Reynier's latest form of incandescent lamp .... 130

82. Reynier automatic lighter ... ... 131

83. Arrangement of parts and electrical connection of the automatic lighter 131

LIST OF ILLUSTRATIONS. xv

FIG. PAGE

84. Reynier system of distribution . . . . . .132

85. Temporary regulator of Reynier, serving as a safety-lamp, in electric

installations . . . . . . . .133

86. Incandescent lamp, with rotating electrode, of M. Ducretet . . 134

87. Incandescent lamp of M. Ducretet ...... 134

88. Section of M. Ducretet's lamp 135

89. M. Clamond's" incandescent lamp . . . . . .135

90. Sawyer's incandescent lamp in an atmosphere of nitrogen . . 136

91. Vertical section of the lamp-soleil . . . . . 141

92. Lamp-soleil suspended, perspective view .... 143

93. Entrance to the passage Jouffroy, in Paris, lit by the lamp-soleil . . 146

94. Thomas A. Edison 149

95. Sketch of Edison's first lamp. (From his French patent.) . . . 152

96. Edison lamp with incandescent platinum spiral, provided with safety

apparatus. (French patent, 1879.) . . . . . 153

97. Edison's platinum-lamp, with regulator operated by expansion of heated

air 154

98. Edison lamp with Bristol-board carbon, according to his French patent

99. Edison's carbon-lamp with spiral filament. (American patent, January

27, 1880.) 158

100. Lamp with horse-shoe filament . . . . . .159

101, 102, 103, 104. The actual Edison lamps » 160

105. Edison lamp provided with regulator of intensity . . . 161

106. Carbon-rod rheostat of the regulator of intensity .... 161

107. Sixteen-candle lamp (three-quarter size) . . . . . 162

108. Crystal chandelier of Edison lamps, used at the Paris Exposition of Elec-

109. Edison lamp with shade . . . . . . .164

110. Jointed bracket for Edison lamp . . . . . . 165

111. Edison three-light chandelier . .... . . 166

112. Parlor in New York lighted with Edison lamps . . . .168

113. Edison mining-lamp . . . . . . .169

114. Swan incandescent lamp . . . . . .172

116. Under side of the foot of the lamp, showing the electrical connections . 174

118. Swan lamp in socket . .. . . .... 174

119. Philosophical instrument establishment of Mr. Swan, at Newcastle, light-

ed by his incandescent lamps . . . . . 175

121. Lane-Fox incandescent lamp . ..... 177

122. Section of Lane-Fox lamp . . _v . . . . 178

123. Maxim incandescent lamp. (Full size.) . . . . 179

124. Maxim incandescent lamp and socket. (Full size.) .... 180

125. The Bernstein lamp . . . . . . . 181

126. Wheatstone's bridge . ... . . . . 182

127. Bunsen photometer . . . . . . 183

128. Method of using the Bunsen photometer ..... 184

130. Reynier battery .... ,200 xvi LIST OF ILLUSTRATIONS.

FIG. PAGE

132. Small model of the circular form of the Reynier battery . . . 202

133. Thermo-electric pile of Clamond ...... 209

134. Experiment of Faraday with two bobbins ..... 212

135. Experiment of Faraday with a bobbin and magnet . . . 213

136. Ruhmkorff coils . . . . . . .216

137. The Ruins of the Coliseum at Rome illuminated by the electric light 219

138. Magneto-electric machine ....... 220

139. Separately excited dynamo ...... 220

140. Series dynamo 221

142. Faraday's apparatus ........ 224

143. Direct induction in the ring armature ..... 229

144. Indirect induction, or induction by magnetic reaction of the radiating

armature-cores. ........ 230

145. Magneto-electric machine of Pixii, 1832 ..... 232

146. Magneto-electric machine of Clarke ...... 233

147. Experiments in the projection of the electric light at London, on the

Thames, with a Brush lamp of six hundred carcels . . 235

148. Siemens armature 237

149. Cross-section of the Siemens armature ..... 237

150. Wilde's first dynamo-electric machine, with Siemens' magneto-electric

exciter 238

151. Gramme magneto-electric machine for the laboratory . . . 241

152. First form of Gramme dynamo machine for lighting . . . 242

153. Gramme machine. (Workshop-type.) . . . . . 243

155. Five-light Gramme machine ...... 246

156. Diagram of alternating-current Gramme machine .... 250

157. Self-exciting alternating-current Gramme machine . . . 251

159. Armature of the Wood machine ...... 252

160. Cross-section of the Wood armature ...... 253

161. Gramme machine as modified by Mr. Wood .... 254

162. Original model of the Pancinotti machine, exhibited at the Exposition of

Electricity at Paris, 1881 . . . . . . .256

163. Siemens continuous-current machine. (Vertical model.) . . 258

164. Mansion-House Square, London, lighted by Siemens' lamps . . 259

165. Diagram of the winding of the Heffner von Alteneck drum . . 261

166. Diagram of the connection of the coils ..... 261

167. Alternating-current machine of Heffner von Alteneck . . . 262

168. Diagram of armature and field coils of Ferranti machine . . . 263

169. Gordon alternating-current dynamo ..... 264

170. Weston dynamo 265

171. Weston armature 266

172. Core of Weston armature ....... 267

173. Toothed iron disk used in Weston armature .... 267

174. Maxim dynamo-electric machine for lighting, with double ring and two

commutators ........ 268

175. Maxim exciting-machine with automatic current regulator. (Front view.) 270

176. Maxim exciting-machine with current regulator. (Side view.) . 271

LIST OF ILLUSTRATIONS. xvii

FIG. PAGE

178. Edison steam dynamo . . . ' . . . . 275

179. Construction of the armature of the Edison steam dynamo . ' . 276

180. Art-gallery in New York lighted by Edison incandescent lamps . 278

181. Brush sixteen-light machine . * .» - ' . V . . . 280

182. Cross-section of the Brush ring . . . . . . 281

183. Construction of the Brush ring . . . »•' . . 281

184. Brush armature, with its coils in position . , . . 282

185. Cross-section of Brush commutator . .- / . .-' . 283

186. Diagram of Brush dynamo • . . . . . . 284

187. Wallace-Farmer machine . . . . . ' v . 287

188. Armature of the Lontin continuous-current machine . . . 288

189. Drum-armature of the Biirgin machine ..... 290

190. Magneto-electric machine of M. de Meritens. (Light-house type.) . 292

191. Details of the De Meritens armature . . . . . .293

192. Diagram of the De Meritens armature coils . . . . 293

193. Magneto-electric machine of M. de Meritens. (Workshop-type.) . . 294

194. M. de Meritens's continuous-current magneto-electric machine . 295

195. Details of the ring of continuous-current machine of M. de Meritens . 296

196. Gravier's plumbago commutator-brushes . . . . 297

197. Plan of the electric-lighting system of the port of Havre . . . 318

198. Diagram of one of the circuits in the electric-lighting of the port of Havre 320

200. View of the port of Havre lighted by Jablochkoff candles. Face page 324

201. Lane-Fox's regulator of current intensity ..... 327

202. Diagram of Edison street-mains . . . •, . 328

203. Edison junction-box, with fusible safety-catch, for street-mains . . 329

204. Edison junction-box, with safety-catch, for connection of service-wires

205. Safety-plate with fusible cut-off, placed at points where the wires enter a

206. Lamp-socket with safety-catch . . . -. '•• '. 332

207. View from below of the lamp-base . . . ... 332

208. M. Gravier's system of electrical distribution at the Zawiercie works,

Poland . .. 334

209. M. Gravier's regulator . . . ... . 336

210. Rheometric regulator of M. Gravier . . . . . 337

211. Music-hall on the Place du Chateau-d'Eau, in Paris, lighted by Jabloch-

koff candles . . . . . . . .339

212. Marcel Deprez winding for constant electro-motive force . . 340

213. Marcel Deprez winding for constant current . . ,. . 341

214. Arrangement of dynamos for the distribution of electricity on the system

of M. Marcel Deprez ....... 342

215. Professor Perry's machine for constant electro-motive force . . 344

216. Professor Perry's machine for constant current ~ . . . 345

217. Edison dynamo with compound winding, for constant electro-motive

218. Diagram of the Edison automatic regulator . . . . 348

219. Edison automatic regulator . . . . . . . 349

220. Weston automatic regulator for arc-lighting . , . . . 351

221. Details of the Weston automatic regulator . i . . .352 xviii LIST OF ILLUSTRATIONS.

FHJ. PAGE

222. Brush automatic regulator ...... 353

223. Edison multiple-series distribution ...... 356

224. Edison multiple-series distribution applied to one generator . . 357

226. Edison meter, with registering apparatus * .... 366

228. Electric light-house of Planier, near Marseilles . . . , 379

229. Arrangement of the Planier electric light-house .... 381

230. Section of the upper story and lantern of the Planier light-house . 382

231. Fixed light electric light-house ...... 385

232. Factory of MM. Sautter and Lemonnier lighted by the electric light . 387

233. M. Menier's yacht, with electric projector, navigating the Marne by night 391

234. Mangin projector ........ 395

235. Mangin projector, with its accessories, mounted upon the field-wagon 397

236. Portable apparatus, with Brotherhood engine and Gramme machine, for

use with Mangin projector ..... Face page 398

237. The Surveillante lighting the island of Tabarka for the first descent of

the French troops upon Tunis ...... 400

238. Apparatus used in " The Prophet," to represent the sun . . 408

239. Apparatus for the production of the rainbow on the stage . . . 409

240. The rainbow in the opera of " Moses " . . . . . 410

241. Magic mirror for the production of lightning in the theatre . .411

242. Electric lamp for illuminating an actor in the play . . . 412

243. Electric lamp, with mirror, for lighting a particular point of the scene . 412

244. Scene in the opera of " Moses " . . . . . . 413

245. Luminous fountain ........ 414

246. Electric lighting of the fast-freight room of the Paris depot of the Paris,

Lyons, and Mediterranean Railroad. (Lontin system.) . . 422

247. Electric lighting of an open space ...... 425

248. Farm-work carried on by means of the electric light . . Face page 425

249. Electric lighting of the work on the Kehl bridge .... 426

250. Plate reflector 430

251. Lighting of the Boulevard des Italiens by the Million lamp . . 436

Chapter I. Oils, Candles, And Gas

To acquire a real comprehension of the true role of the electric light and the changes which it can introduce both in our habits and in the industrial world, it is necessary to give succinctly the history of lighting in general, and of electric lighting in particular.

Fats and oleaginous materials were employed as a means of lighting by the most ancient peoples. But, even among the most civilized nations of antiquity, such as the Greeks and Romans, this mode of lighting had preserved nearly as barbarous a form as among the savage tribes. The lamp of a Roman emperor was not much pleasanter or less smoky than the torch of resinous wood with which the first known men lighted their abodes — those men whom history ignores, and whom geology has resuscitated during the last twenty-five years.

This lamp consisted simply of a vessel filled with oil, into which dipped a thick, twisted wick, formed of any fibrous material, wool, linen, cotton, etc. The end of this wick was raised so as to rest on the edge of the vessel, and it was there that the oil burned, creeping up through the wick by capillarity (Fig. 2).

Specimens of these apparatus can still be seen elsewhere than in museums. The peasants of other countries have preserved the classic lamp up to our days, perfecting a little the burner, or neck, to prevent the wick from falling back into the oil. As a regulator to advance this wick as fast as it was burned, the Roman matron, as well as the peasant's wife of to-day, had doubtless no better arrangement than a common hair-pin ; for the pincers and hook specially made for this purpose resembled one in shape, and were but little more convenient (Figs. 1 and 3).

This thick wick, or, we should rather say, this string of tow, does not permit the air to penetrate sufficiently to burn completely the carbon of the oil. The unburned carbon escapes in a nauseous smoke, which produces a choking sensation. But the smoke of ancient times must have been much worse than that of to-day, because the oil was very impure, and was often replaced by fats full of all kinds of impurities. We give here illustrations of the lamp which figures in the most poetical stories of Greece. We may see in it the elegant lamp which the imprudent Psyche over-

Fio. 1.— Pincers FIG. 2.— Bronze Koinan lamp. FIG. 3.— Hook

for lamp. for lamp.

turned upon Cupid on that fatal night when she yielded to the ill-fated desire of unveiling the incognito of her mysterious lover. We can understand the anger of the divine child, which, in the case of the little electric burner, would be inexplicable. In this last case, even if he were to be burned, he would need no perfumes to disinfect himself.

In the sumptuous palaces of imperial Rome, as well as in the hovel of the slave situated in the remotest fields, the system of lighting was everywhere the same. It was easy to substitute for coarse earthenware precious metals for making the lamp, to give ifc an elegant form, and support it on candelabra, richly sculptured (Figs. 4 and 5) and designed with skill ; but it is always the same lamp which we have to de-

OILS, CANDLES, AND GAS.

scribe — its luxurious appearance could not modify its organization in any essential.

Many savants to-day consider fire, as well as language, to be the great characteristic of humanity. It is singular that this primordial invention, which has made man the superior of all that is highest in nature, and has taken him out of the rank of animal, has been one of the last to be perfected. Yet this is precisely what has happened. The Roman lamp, scarcely superior to the utensils of the primitive savages, remained without a rival during the greater part of the middle ages.

FIGS. 4 aiid 5. — Eoman candelabra in carved bronze, bearing one or more lamps.

Only at the end of the twelfth century did the great novelty dawn upon England — a light-giving solid material to replace oil. This novelty had for name the " tallow-candle "! It was made of sheep' s fat, and of the well-known form which it has preserved to the present day. It may have seemed a dangerous invention, because it took a long time for its use to extend itself. It was in the reign of Charles V, at the end of the fourteenth century, that the French began to use it. I refer to the rich men of France ; it was as yet too great a luxury for the commonalty to indulge in.

To our fathers it seemed a great step in advance — and for their epoch they were right — and they were contented with it for a long time. Le roi soleil had no other luminaries to light up at night the glories of Versailles, and the plays of Moliere, of Racine, and even those of Voltaire, were produced by the light of candles of six to the pound.

For a long time, also, those traveling through the streets of the cities were most happy to be guided on their way by the light of candles placed in the corners of the windows. Lanterns for public lighting date from the middle of the seventeenth century only ; and it is not until a hundred years later that we find them surmounted by a reflector, depriving the sky of their slender rays in order to cast them back upon the earth. It was then that they assumed the well-known name of reflectors (reverberes). Some among us, who have passed the critical time of youth, can remember them dangling from the altitude of a gallows-frame, whence they descended at the end of a cord, like a bucket into a well, when it was necessary to light or to extinguish them.

To-day the tallow-dip has developed into the candle. Thanks to the discovery of the composition of fatty bodies, made by Chevreul in 1811, it became possible to extract from tallow the best of its luminiferous components, stearic acid. M. Chevreul himself tried it in conjunction with Gay-Lussac, and the two took out in Paris a patent for the process, which, however, was never used, any more than the English patent taken out in London by Gray-Lussac under the name of Moses- Poole. We must not forget, however, that their method could not work in practice.

Another chemist, Cambaceres, took out four patents for the same object during the years 1825 and 1826. He was somewhat more fortunate than his illustrious competitors, and was the first to manufacture stearine-candles, undoubtedly very imperfect and very impure, as their yellow coloration plainly showed. These candles soiled the hands like the tallow-dips, smelled almost as bad, and burned in an inferior manner in spite of the perfecting of the wick. For these reasons their sale was very limited, and Cambaceres soon gave up the manufacture.

It was two young physicians, MM. de Milly and Matard, who took up the problem in 1829, and reached at last a satisfactory solution after two years of patient research. Thus it is in the year 1831 that the history of the manufacture of stearine-candles begins, and, as the first factory was situated near the Arc de Triomphe de 1'Etoile, they were named bougies de Vetoile (star- can dies), soon known throughout the world, which name they kept when the factory was moved away from that place.

More solid and better in appearance, as well as less greasy to the touch, and provided with a wick which needed no snuffing, because it burned itself up, burning without smoke or disagreeable odor, the stearine- candle preserved the form of the old tallow- dip, and, from the physical point of view, worked in the same manner. But it also gave more light. It is it which will hereafter be employed as a standard in comparing sources of light, a candle being taken as such standard which burns ten grammes of stearine per hour— unfortunately, a unit which varies greatly according to the greater or less purity of the stearine employed in commerce.

The " star- candles " then sold for three francs fifty centimes a kilogramme, so that the standard candle, burning ten grammes per hour, costs three and a half centimes for one hour's burning. On account of a lower price, it now costs little over two centimes. On the other hand, it is much dearer than the tallow-candle, which formerly did not bring half the price of the stearine- can die, and which to-day is worth far less, in the proportion of one franc twenty-five centimes to two francs ten centimes a kilogramme. It is true that a kilogramme of tallow gives only four fifths as much light as the same quantity of stearine. But, taking this difference into account, the expenses will be found not to exceed one centime and a half per hour and per unit of light ; that is to say, hardly three quarters of the cost of the stearine-candle for the same result.

Hence the new candle has only been an advance from the point of view of comfort and luxury, but not from the standpoint of economy. The same does not apply to another invention, which has transformed the conditions under which oil is employed — we speak of the modern lamp.

The end of the eighteenth century was marked by a discovery which produced upon the public as great an effect as that of the electric light to-day. This discovery, whose name now sounds even vulgar to us on account of its very popularity, is the Argand lamp. We shall now show how it has transformed the ancient Roman lamp.