Biographical Memoir of Henry CavendisJt. 219 



metals are more abundant toward the centre. Thus this new 

 experiment furnished quite new views with respect to the theory 

 of the earth. It appeared, at first, to disagree with those made 

 by Maskelyne in Scotland, in which the deviation, produced 

 by the vicinity of a mountain in the plumb-Une of his instru- 

 ments, made him infer a mean density of only four and a half 

 times that of water ; but it is asserted, that, after a more accu- 

 rate calculation of Maskelyne's experiments, their result was 

 found to come very near that obtained by Mr Cavendish. 



He was also one of the first who applied calculation to the 

 theory of electricity. His investigation was performed before 

 iEpinus's work on the same subject appeared, but it was not 

 communicated to the public until after. He set out upon the 

 same hypothesis, namely, that there is but one kind of electrical 

 matter, the molecules of which mutually repel each other, and 

 are attracted by other bodies ; but Mr Cavendish shews, that, 

 supposing this action to be exercised in a proportion less than 

 the inverse of the cube of the distance, it may be proved, 

 by means of Newton's theory respecting the attraction of a 

 sphere, that all the electrical matter of a body of that form 

 ought to come to its surface *. It is well known that our fellow 

 member the late M. Coulomb, afterwards demonstrated, by di- 

 rect experiments, that the action of electricity is exercised in 

 the reverse ratio of the square of the distance, and that he proved, 

 in a much more general manner, the necessity of this distribu- 

 tion at the surface of bodies, whatever their figure may be. 



When Walsh announced the analogy between the shock which 

 the torpedo gives, and that of the Leyden phial, it was objected 

 that the fish in question does not produce sparks. Mr Caven- 

 dish immediately endeavoured to explain the reason of this dif- 

 ference f. He even constructed, after the principle of his expla- 

 nation, a sort of artificial torpedo, which presented the same phe- 

 nomena when it was electrified. The true cause of animal elec- 

 tricity, however, escaped him ; and it was for M. Volta that it 

 was reserved to discover an apparatus calculated to engender 

 this wonderful fluid without intermission, and to electrify itself 

 incessantly, — an apparatus very probably analogous, in its es- 

 sence, to those with which nature has supplied the electrical 

 fishes. 



• Phil. Trans. 1771, p. ft48. t Ibid. 1776, p. 196. 



