

AC CUM ULA TORS. 1 3 



it and the conductor, simultaneously with the sparks 

 on the upper surface ; indicating that each surface re- 

 ceives the same amount of charge. 



But the potential on opposite surfaces will be oppo- 

 site. If the upper surface acquires positive potential, 

 by an increase of electricity, the same amount will be 

 repelled from the lower surface, making it negative. 

 But if the upper becomes negative by a decrease, 

 electricity, to the same amount, will be attracted to the 

 lower surface, making it positive. 



To prove that these charges are equal, let the tin- 

 foil strip be removed 

 after the plate has been 

 charged ; and a wire, 

 held by a piece of 

 india - rubber tube, to 

 insulate it, be bent so 

 that its ends come into 

 contact with the oppo- 

 site surfaces, as shown 



Fig. 19 The. Pane Discharged. 



in Fig. 19 : a flash and 



report will follow, and both surfaces, after the wire 

 has remained in contact for a few moments, will be 

 found completely discharged. 



Now, since the removal of the strip produced com- 

 plete insulation, perfect equilibrium could occur only 

 by the positive of one surface being exactly equal to 

 the negative of the other. 



Since induction varies inversely as the square of 

 the distance (page 47), it is evident that, if this factor 

 alone is considered, the amount of charge which can be 

 given will be in the inverse ratio of the thickness of 

 the glass, and hence greater on thin than on thick 



