82 



ELECTRIC LIGHTING. 



inside as well as outside; but this machine produces alter- 

 nately reversed currents. 



Siemens' Machine. The machine of Siemens and 

 Hafner-Alteneck, represented in Fig. 22, which has in com- 

 parative experiments made in England furnished the best 

 results, is founded on nearly the same principle as that of 



FIG. 22. 



Gramme, although at first sight it appears to be merely a 

 modification of the elongated coil system of Siemens, that 

 we have already seen taken advantage of in the machines of 

 Wilde and of Ladd. In this new system the cylindrical coil 

 for receiving the induction is of large diameter, and is formed 

 of a revolving cylinder of copper, on which, parallel to its 

 axis, are wound a certain number of juxtaposed coils like the 

 coils of a galvanometer. These coils are connected for tension, 

 but metallic plates join with their connecting wire to a series; 

 of plates arranged round a drum of insulating substance, fixed. 



