HISTOEY OF ELECTKICITY. 



native of this supposition, or that of two fluids, to choose between, foi 

 the mathematical results of both hypotheses are the same. Wilcke, a 

 Swede, who had at first asserted and worked out the JEpinian theory 

 in its original form, afterwards inclined to the opinion of Symmer ; 

 and Coulomb, when, at a later period, he confirmed the theory by his 

 experiments and determined the law of force, did not hesitate to pre- 

 fer 8 the theory of two fluids, "because," he says, "it appears to me 

 contradictory to admit at the same time, in the particles of bodies, an 

 attractive force in the inverse ratio of the squares of the distances, 

 which is demonstrated- by universal gravitation, and a repulsive force 

 in the same inverse ratio of the squares of the distances ; a force 

 which would necessarily be infinitely great relatively to the action of 

 gravitation." We may add, that by forcing us upon this doctrine of 

 the universal repulsion of matter, the theory of a single fluid seems 

 quite to lose that superiority in the way of simplicity which had ori 

 ginally been its principal recommendation. 



The mathematical results of the supposition of vEpinus, which are, 

 as Coulomb observes, 7 the same as of that of the two fluids, were 

 traced by the author himself, in the work referred to, and shown to 

 agree, in a great number of cases, with the observed facts of electrical 

 induction, attraction, and repulsion. Apparently this work did not 

 make its way very rapidly through Europe ; for in 1771, Henry Ca- 

 vendish stated* the same hypothesis in a paper read before the Royal 

 Society ; which he prefaces by saying, "Since I first wrote the follow- 

 ing paper, I find that this way of accounting for the phenomena of 

 electricity is not new. ^Epinus, in his Tentamen Theorice Electric! tails 

 et Magnetising has made use of the same, or nearly the same hypothe- 

 sis that I have ; and the conclusions he draws from it agree nearly 

 with mine as far as he goes." 



The confirmation of the theory was, of course, to be found in the 

 agreement of its results with experiment ; and in particular, in the 

 facts of electrical induction, attraction, and repulsion, which suggested 

 the theory. yEpinus showed that such a confirmation appeared in a 

 number of the most obvious cases ; and to these, Cavendish added 

 others, which, though not obvious, were of such a nature that the 

 calculations, in general difficult or impossible, could in these instances 

 be easily performed ; as, for example, cases in which there are plates 

 or globes at the two extremities of a long wire. In all these cases of 



6 Jffm. Ac. P. 1788, p. G71. 7 Ac. P. 17S8, p. 672. 



e Phil. Trans. 1771, vol. Ixi. 



