DISCOVERY OF CONTACT ELECTRIFICATION 449 



contact. The result was now reversed; that is, the fixed plates were electrified 

 negatively, and tlie moveable one had positive electricity. 



Volta then varied the experiments, just as Bennett had done, by 

 applying the tin wire only to the movable plate and testing its charge, 

 and then to the fixed plate, and repeating the process. He then re- 

 ph;ced the movable brass plate of the doubler by a tin plate, and using 

 brass and tin wires for touching the plates, he found that he got a 

 charge by touching his brass plate with a tin wire and his tin plate 

 with a brass wire, but got no effect when he touched the plates with 

 wires of their own metal. He then says: 



We must therefore conclude that the contact of two metals of a different 

 kind with moist conductors, without the mutual contact of these metals themselves 

 (which is wanting in the sixth experiment, where brass is in contact with brass, 

 and tin with tin), produces nothing or almost nothing; and that, on the con- 

 trary, the mutual contact of the two metals of a different kind, which takes 

 place in the fifth experiment, produces the whole, or almost the whole, effect. 



The above considerations seem to make it certain that though Volta 

 was apparently the first to recognize the existence of a current in a 

 circuit composed of two metals and an electrolytic conductor, he has no 

 claim to be regarded as the first discoverer of contact electrification. 

 This honor should undoubtedly be accorded to the Eev. Abraham Ben- 

 nett, while the discovery of the variation of the phenomenon with tem- 

 perature is due to Tiberius Cavallo. 



VOL. Lxxxin. — 31. 



