THE ELECTBIC LIGHT 461 



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 subsequently so modified 

 his machine as to produce alternating currents. Such al- 

 ternating 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 magnetized, and 

 instantly evokes in its surrounding coil an induced cur- 

 rent 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 gath- 

 ered up and caused to flow in a common bed. The bob- 

 bins, in which the currents are induced, can be so in- 

 creased 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-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 one. 



