<36 



ELECTRIC LIGHTING. 



i centimetre. For the sake of perfect uniformity of thick- 

 ness at their polar extremities, and also for readiness of ad- 

 justment, they are provided with soft iron poles. Each plate 

 is magnetized by the ordinary process, and the bundle should 

 support three times its own weight. This magnetization is, 

 moreover, improved rather than otherwise by the action of 

 the machine. 



FIG 16. 



The bobbins have undergone many alterations; at the 

 present time they are formed of iron tubes split longitudinally, 

 and have brass caps also divided in order to diminish disad- 

 vantageous induction. They are 10 centimetres long and 4 

 centimetres in diameter, and there are two tubes one within 

 the other. 



The length and action of the wires of these bobbins should 

 depend, as will be readily understood, on the resistance of 

 the external circuit, on the number of bobbins, and on the 



