Page:Popular Science Monthly Volume 83.djvu/445

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THE discovery that 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 "Journal" published in 1802, calls attention to the fact that both Bennett and Cavallo, in England, had made experiments upon contact electrification 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 fundamental in his theory of contact electrification were published in a postscript to a letter to Gren in Volume IV. of the Neues 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 Rev. Abraham Bennett, curate of Wirksworth, Derbyshire, who is known in the history of electricity as the inventor of the gold leaf electroscope, 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 Experiments 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 professor 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 Royal 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-