DiscovKny of coy tact electrification 441 



THE DISCOA'ERY OF CONTACT ELECTRIFICATION 



By Pkofessor FERNANDO SANFORD 



STANFORD UNIVERSITY 



THE discovery tliat the mere contact of two dissimilar metals causes 

 them to become oppositely electrified seems to be everywhere 

 attributed to Volta, though Nicholson in the first volume of his " Jour- 

 nal/' published in 1802, calls attention to the fact that both Bennett 

 and Cavallo, in England, had made experiments upon contact electrifica- 

 tion previous to its supposed discovery by Volta. The fundamental 

 experiment from which Volta made this discovery is said by Auerbach in 

 Winkelmann's "Handbuch der Physik" to have been announced by 

 Volta in 1795, in Gren's Neues Journal der Physik, Vol. II., p. 144. 

 The experiments which Volta, himself, seems to have regarded as funda- 

 mental in his theory of contact electrification were published in a post- 

 script to a letter to Gren in Volume IV. of the Neves Journal. These 

 experiments were not only the same in character, but were performed 

 in the same manner and by means of the same apparatus as experiments 

 which had been performed about ten years earlier by Bennett, and which 

 had been published in a book to which Volta was a subscriber. 



The actual discoverer of contact electrification seems to have been 

 the Eev. Abraham Bennett, curate of Wirksworth, Derbyshire, who is 

 known in the history of electricity as the inventor of the gold leaf elec- 

 troscope, which still bears his name, and of a multiplier for increasing 

 by induction the intensity of a given charge so as to render it measurable 

 by an electroscope. 



In 1789 Bennett published a small book entitled "New IJxperiments 

 on Electricity," in which he gives an account of many of his discoveries 

 and describes the construction of his electroscope and doubler, as well as 

 the mechanical improvements made in the latter by Dr. Erasmus Darwin 

 and William Nicholson. This book was published by subscription and 

 contains a list of 394 subscribers, including many of the best known 

 scientific men of the day, and among the rest, " Mr. Volta, Professor of 

 Nat. and Exp. Philosophy." Volta had then been for ten years a pro- 

 fessor in the University of Pavia, and had corresponded for some years 

 with English physicists, notably Priestley and Cavendish, and only two 

 years later was made a foreign member of the Eoyal Society. 



Section VII. of Bennett's book is devoted to "Experiments on the 

 Adhesive Electricity of Metals and Other Conducting Substances." In 

 performing these experiments Bennett made use of Nicholson's improve- 



