ELECTRIC LIGHT, EDISON'S. 



sufficiently exhausting the air in the glass 

 chamber. By the present process it could be 

 reduced to but little over one millionth of an 

 atmosphere. 



The inventor thought that he had elaborated 

 a lamp which embodied the best principles, and 

 which was sure to prove a commercial success. 

 He had introduced improvements in the elec- 

 tric machine by which the equivalent of about 

 90 per cent, of the power expended was re- 

 turned in electricity. When he was nearly 

 ready to give the lamp in this form to the 

 world, he began, led partly by accident, to ex- 

 periment with carbon, with results which in- 

 duced him to alter his whole system and adopt 

 a carbon instead of a metallic burner. A 

 prominent cause for the failure of carbon burn- 

 ers had been the impossibility of obtaining a 

 form of carbon sufficiently pure in substance 

 and homogeneous and even in texture. Edi- 

 son was encouraged to try new forms from 

 obtaining a remarkably brilliant light in the 

 vacuum by the incandescence of a piece of 

 calcined cotton thread. He placed in the glass 

 a thread of ordinary sewing-cotton, which had 

 been placed in a groove between two blocks 

 of iron and charred by long exposure in a fur- 

 nace, exhausted the air, and sealed the tube. 

 He then turned on the electrical current, and 

 increased it until the most intense incandes- 

 cence was obtained before the slight filament 

 broke. Examining then the fragments under the 

 microscope, he found that the fragile substance 

 had hardened under the excessive heat, and 

 that its surface had become smooth and glossy. 

 This led him into a long series of experiments 

 with carbon. After carbonizing and testing a 

 great variety of fibrous substances, he found 

 that paper yielded the most satisfactory results. 

 The burner on which he finally settled was 

 made from Bristol cardboard in the form of a 

 tiny horseshoe. Strips about two inches long 

 and an eighth of an inch wide, curved in the 

 shape of an elongated horseshoe, are struck 

 from a sheet of cardboard, and a number of 

 them laid one upon another, with pieces of 

 tissue-paper between, in an iron mold ; this 

 is tightly closed and placed in an oven, which 

 is gradually raised to a temperature of 600 ; 

 the mold is next placed in a furnace and al- 

 lowed to come to a white heat, and then re- 

 moved and left to cool. The carbonized paper 

 horseshoe (F) is then taken out with the utmost 

 care, mounted in a diminutive glass globe, and 

 connected with the wires. The air is then 

 pumped out and the glass hermetically closed. 

 The form of the lamp is a small bulb-shaped 

 glass vacuum (A), globular above, with an 

 elongated end resting upon a standard (B), 

 through which the wires leading to and from 

 the generator pass, connecting with thin plati- 

 num wires (E, E') which penetrate the thick 

 end of the glass ; to these the carbon burner is 

 attached by clasps made from the same metal 

 (G, G'). No regulating apparatus is attached 

 to the lamp, as the current can be regulated 



at the central station where the electricity is 

 generated. 



The inventor has developed a method by 

 which the currents can be cut off from any of 

 the lamps and the lights extinguished, without 



affecting the supply of electricity to those 

 which are left burning. He proposes to sup- 

 ply the electricity in cities for lighting the 

 houses and public places, from stations in which 

 a number of electric machines adequate for 

 supplying an area of about a third of a square 

 mile are driven by one or two powerful steam- 

 engines. Each generator is capable of supply- 

 ing about fifty burners. The wires conducting 

 the electricity from the central station into the 

 houses can be led through the gas mains and 

 pipes, and the burners attached to ordinary 

 gas-fixtures with little labor and expense. The 

 amount of electricity supplied in each house- 

 hold is measured and recorded by an ingenious 

 but simple device. The electrometer, which 

 like a gas-meter may be placed in any part of 

 a house and connected with any number of 

 burners, consists of an electrolytic cell and a 

 small coil of wire. The passage of electricity 

 causes the deposit on a small plate in the 

 electrolytic cell of particles of copper. The 

 weight of this deposit indicates the amount of 

 electricity which has passed through the meter 

 during any period. The apparatus takes up 

 about half the space of an ordinary gas-meter. 



