1879.] on the Electric Liyht. 15 



streams arc gathered up and caused ti) flow in a common bed. 

 The bobbins in whicli the currents are induced can be so augmented 

 in number as to augment indefinitely the power of the machine. A 

 series of toothed wheels, for example, may be fixed on the same 

 axle, each wheel and its bobbins rotating between their own pair of 

 electro-magnetic poles. In the larger machines of M. Lontin, the 

 ends of the iron teeth which constitute the cores face correspond- 

 ing helices and cores fixed to an exterior iron ring. In this dispo- 

 sition the bobbins of the rotating wheel are the electro-magnets, 

 while the bobbins attached to the ring are those from which the 

 induced currents are drawn. By couj)liug the bobbins together in 

 various ways they can be united so as to furnish a single current, or 

 to furnish a number of distinct currents which may be regarded as 

 fractions of the whole current. To excite his electro-magnets, M. 

 Lontin applies the principle of Mr. Wilde. A small machine 

 furnishes a direct current, which he carries round the electro-magnets 

 of a second and larger machine. Wilde's i)rinciple, 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 one. 



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

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

 inducing electro-magnets. The latter are excited by the method 

 discovered 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 large plates of carbon, 

 with bevelled edges, are placed one above the other. The electric 

 discharge passes from edge to edge, and shifts its position according 

 as the carbon is dissipated. The plates are kept at the proper 

 distance apart by an automatic electro-magnetic arrangement. The 

 duration of the light in this case far exceeds that obtainable 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, em- 

 ployed at the Liverpool Street Station of the Metropolitan Railway. 

 The Farmer- Wallace " quantity machine " pours forth a flood of 

 electricity of low tension. While unable to cross the interval neces- 

 sary for the production of a single electric light, it can fuse thick 

 copper wires. When the current is sent through a short bar of iridium, 

 this refractory metal emits a light of extraordinary splendour.* 



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 

 machine, employing permanent magnets as the exciters of the induced 



* The iridium light was shown by Mr. Lndd. It brilliantly illuminated the 

 theatre of the lloyal Institution. 



