VARIOUS GENERATORS OF ELECTRIC LIGHT. 67 



kind of work required. Nevertheless, experience has shown 

 that in the use of the machine for the electric light, the best 

 results have been yielded with bundles containing eight insu- 

 lated wires, each i millimetre in diameter, 30 metres long, 

 and joined eight together. These wires are covered with 

 a layer of cotton impregnated with a solution of Judea bitu- 

 men in spirits of turpentine, or in benzine. This kind of 

 varnish has the advantage of .drying very quickly, and not 

 easily cracking ; it is besides very thin, so that it does not 

 materially increase the thickness of the different layers of 

 spires. 



According to the experiments of Jamin and Roger, the 

 electro-motive force of the current sent from a six-disc 

 Alliance machine, with the coils arranged for tension, and 

 with a velocity of rotation of 200 turns per minute, is equi- 

 valent to 226 Bunsen cells; but when the coils are arranged 

 for quantity the electro-motive force is equivalent to only 38 

 Bunsen cells. The resistance of the generator was equivalent 

 to that of 655 Bunsen cells in the first case, and to 1 8 in the 

 second case. The light yielded may be nearly represented 

 by that of 230 Carcel lamps, and the cost of the current pro- 

 ducing it would be, according to the calculations of Reynaud, 

 the inspector of lighthouses, i fr. 10 c. per hour. But since 

 these experiments were made great improvements have been 

 effected in the machines, and we shall presently give the 

 figures representing their performance and their cost ; here 

 we shall merely state as the net result that the ordinary 

 Alliance machines with four discs are able, with a speed of 400 

 turns per minute, to maintain 3 Jablochkoff electric candles. 

 Under exceptional circumstances this yield has even been 

 very much increased, and machines have been spoken of 

 capable of supplying 6 candles, but the ordinary machines 

 are far from giving such a result. 



Some time after the definite establishment of the machines 

 we are speaking of, Holmes, a former employe of the Alliance 

 Company, made in England machines of the same kind, 



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