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 reph;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 contrary, 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 Rev. Abraham Bennett, while the discovery of the variation of the phenomenon with temperature is due to Tiberius Cavallo.
