218 



ELECTRIC CONDENSERS. 



their free ends and carried by insulating handles, 

 outer coat should be touched first. Why ? 



The 



356. The Leyclen Jar with Movable Coats. This 

 piece of apparatus is represented by Fig. 155. The three parts being 

 placed together in proper order, B within A and C within B, the 

 jar is charged in the usual manner. The inner coat C is then 

 removed with a glass rod and touched with the hand to discharge it 

 fully. B is then lifted out from A and the outer coat fully dis- 

 charged. The three parts are then put together again and found to 

 be able to give nearly as strong a spark as at first. This seems to 

 indicate that the charge rests upon the sur- 

 faces of the glass rather than upon the sur- 

 faces of the coats. If when the charged jar is 



in pieces, the thumb be placed on the outer 

 surface of the glass and the forefinger of the 

 same hand on the inner surface, a very slight 

 shock is perceptible. The oppositely charged 

 glass molecules that come into actual contact 

 with thumb and finger respectively are dis- 

 charged. By changing the position of the 

 thumb and finger, successive little shocks 

 may be felt as successive portions of the 

 inner and outer surfaces of the glass are dis- 

 charged. The inner coat furnishes a means 

 for the simultaneous discharge of the inner 

 layer of glass molecules ; the outer coat does 

 the same for the outer layer of glass mole- 

 cules. Thus all or nearly all of the electrified ^ 

 glass molecules may be discharged simul- f 

 taneously instead of successively. P 



357. The Leyden Battery. The effect that may 

 be produced with a Leyden jar depends upon its size and 

 the thinness of the glass. But a large jar is expensive and 

 requires great care; thin glass is liable to perforation by 

 the condensed and strongly attracting electricities of its 

 two coats. To obviate both of these difficulties a collection 

 of jars is used. When their outer coats are in electric com- 

 munication, which may be secured by placing them in a 



