THE ELECTRIC LIGHT. 439 



tinuous motion to such a bar as we have here described; 

 and for this purpose he bent it into a continuous ring, 

 which, by a suitable mechanism, he caused to rotate 

 rapidly close to the poles of a horse-shoe magnet. The 

 direction of the current varied with the motion and 

 with the character of the influencing pole. The result 

 was that the currents in the two semicircles of the coil 

 surrounding the ring flowed in opposite directions. But 

 it was easy, by the mechanical arrangement called a 

 commutator, to gather up the currents and cause them 

 to flow in the same direction. The first machines of 

 Gramme, therefore, furnished direct currents, similar 

 to those yielded by the voltaic pile. M. Gramme sub- 

 sequently so modified his machine as to produce alter- 

 nating currents. Such alternating machines are em- 

 ployed to produce the lights now exhibited on the 

 Holborn Viaduct and the Thames Embankment. 



Another machine of great alleged merit is that of 

 M. Lontin. It resembles in shape a toothed iron wheel, 

 the teeth being used as cores, round which are wound 

 coils of copper wire. The wheel is caused to rotate 

 between the opposite poles of powerful electro-magnets. 

 On passing each pole the core or tooth is strongly 

 magnetised, and instantly evokes in its surrounding 

 coil an induced current of corresponding strength. 

 The currents excited in approaching to and retreating 

 from a pole, and in passing different poles, move in 

 opposite directions, but by means of a commutator these 

 conflicting electric streams are gathered up and caused 

 to flow in a common bed. The bobbins, in which the 

 currents are induced, can be so increased in number 

 as to augment indefinitely the power of the machine. 

 To excite his electro-magnets, M. Lontin applies the 

 principle of Mr. Wilde. A small machine furnishes a 

 direct current, which is carried round the electro-mag- 



