THE ELECTRIC LIGHT. 565 



current, which is carried round the electro-magnets of a second and 

 larger machine. Wilde's principle, it may be added, is also applied on 

 the Thames Embankment and the Holborn Viaduct ; a small Gramme 

 machine being used in each case to excite the electro-magnets of the 

 large ones. 



The Farmer- Wallace machine is also an apparatus of great power. 

 It consists of a combination of bobbins for induced currents, and of in- 

 ducing electro-magnets, the latter being excited by the method discov- 

 ered by Siemens and Wheatstone. In the machines intended for the 

 production of the electric light, the electro-motive force is so great as 

 to permit of the introduction of several lights in the same circuit. A 

 peculiarly novel feature of the Farmer- Wallace system is the shape of 

 the carbons. Instead of rods two large plates of carbons with beveled 

 edges are employed, one above the other. The electric discharge passes 

 from edge to edge, and shifts its position according as the carbon is 

 dissipated. The duration of the light in this case far exceeds that ob- 

 tainable with rods. I have myself seen four of these lights in "the same 

 circuit in Mr. Ladd's workshop in the city, and they are now, I believe, 

 employed at the Liverpool Street Station of the Metropolitan Railway. 

 The Farmer- Wall ace " quantity machine " pours forth a flood of elec- 

 tricity of low tension. It is unable to cross the interval necessary for 

 the production of the electric light, but it can fuse thick copper wires. 

 When sent through a short bar of iridium, this refractory metal emits a 

 light of extraordinary sj^lendor.* 



The machine of M. de Meritens, which he has generously brought 

 over from Paris for our instruction, is the newest of all. In its con- 

 struction he falls back upon the principle of the magneto-electric ma- 

 chine, employing permanent magnets as the exciters of the induced 

 currents. Using the magnets of the Alliance Company, by a skillful 

 disposition of his bobbins, M. de Meritens produces with eight magnets 

 a light equal to that produced by forty magnets in the Alliance ma- 

 chines. While the space occupied is only one fifth, the cost is little 

 more than one fourth that of the latter. In the De Meritens machine 

 the commutator is abolished. The internal heat is hardly sensible, and 

 the absorption of power, in relation to the effects produced, is small. 

 With his larger machines M. de Meritens maintains a considerable num- 

 ber of lio-hts in the same circuit.'' 



o 



In relation to this subject inventors fall into two classes, the con- 

 trivers of regulators and the constructors of machines. M. Rapieff has 

 hitherto belonged to inventors of the first class, but I have reason to 



' The iridium light was shown by Mr. Ladd. It brilliantly illuminated the theatre of 

 the Koyal Institution. 



^ The small machine transforms one and a quarter horse-power into heat and light, 

 yielding about 1,900 candles ; the large machine transforms five horse-power, yielding 

 about 9,000 candles. 



