DISCOVERY OF CONTACT ELECTRIFICATION 443 



and the plate B so that B may be stopped in any position. When the 

 crank is turned B passes alternately in front of and parallel to A and 0. 

 The contacts are so arranged that when B is parallel to A it is joined to 

 earth and so charged oppositely to A. It is then revolved in front of C, 

 at which instant C is joined to earth and is charged by induction oppo- 



sitely to B and like A. As B again conies in front of A, A and C are 

 joined and B is earthed. B now receives by induction a greater 

 charge than before, since A has now received the greater part of C's 

 charge. By successive revolutions of B the charge may thus be built up 

 to any desired intensity upon A. 



Bennett performed many experiments with this doubler, and after 

 learning how to discharge it completely he tested the electrification 

 induced upon metal plates by being placed in contact with various sub- 

 stances, both solid and liquid. He concludes that different substances 

 ' : have a greater or less affinity with the electrical fluid," and he then 



