ELECTRIC CHARGE AND THE CONDENSER. 



125 



of one dry cell acts upon the condenser, and the momentary flow 

 of current which charges the condenser produces a throw of the 

 ballistic galvanometer. The condenser can then be discharged 

 by touching the wire W to the point a. By touching the wire 

 W to the point c, the electromotive force 2E of two dry cells 



glass handle 



Fig. 83. 



acts upon the condenser, and the momentary flow of current 

 which charges the condenser produces a throw of the ballistic 

 galvanometer. The condenser may then be discharged as before. 

 By touching the wire W to the point d, the electromotive force 

 $E of three dry cells acts upon the condenser, and the momentary 

 flow of current which charges the condenser causes a throw of 

 the ballistic galvanometer; and so on. In this way the throws 

 of the ballistic galvanometer may be observed when the con- 

 denser is charged by an increasing series of voltages, , 2E, $E, 

 4-E, and so forth, and it is found that the throw of the ballistic 

 galvanometer becomes larger and larger in proportion to the 

 voltage. But the throw of the ballistic galvanometer is pro- 

 portional to the charge which is drawn out of one plate and forced 

 into the other plate of the condenser. Therefore the amount 

 of charge which is drawn out of one plate and forced into the 

 other plate of a condenser is proportional to the electromotive 

 force which acts upon the condenser. Therefore we may write: 



Q = CE (I) 



where Q is the quantity of charge which is drawn out of one 



