THE ELECTRIC LIGHT. 441 



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, simi- 

 lar to those yielded by the voltaic pile. M. Gramme 

 subsequently so modified his machine as to produce 

 alternating currents* Such alternating machines are 

 employed 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- 



