336 



ELEMENTARY LESSONS ON [CHAP. vn. 



automatically set in motion by means of an electro- 

 magnet included in the circuit 

 whenever the resistance of the 

 arc becomes too great. Most 

 of these regulators or electric 

 lamps are so contrived that if 

 by any chance the arc goes 

 out, the mechanism brings the 

 carbons together for an instant 



Fig. 138. Fig. 139. 



and then separates them to the required distance. Fig. 



138 shows the regulator of Foucault as constructed by 

 Duboscq. 



373. Electric Candles. To obviate the expense 

 and complication of such regulators, electric candles have 

 been suggested by Jablochkoff, Wilde, and others. Fig. 



1 39 depicts Jablochkoff^ s candle, consisting of two parallel 



