52 Electric and Magnetic Science 



adopted is that of the one-fluid theory, in much the same form 

 as that of Aepinus. It was, as he tells us, discovered indepen- 

 dently, although he became acquainted with Aepinus' work 

 before the publication of his own paper. 



In this memoir Cavendish makes no assumption regarding 

 the law of force between electric charges, except that it is 

 " inversely as some less power of the distance than the cube " ; 

 but he evidently inclines to believe in the law of the inverse 

 square. Indeed, he shows it to be " likely, that if the electric 

 attraction or repulsion is inversely as the square of the distance, 

 almost all the redundant fluid in the body will be lodged close 

 to the surface, and there pressed close together, and the rest of 

 the body will be saturated"; which approximates closely to the 

 discovery made four years previously by Priestley. Cavendish 

 did, as a matter of fact, rediscover the inverse square law shortly 

 afterwards; but, indifferent to fame, he neglected to communicate 

 to others this and much other work of importance. The value of 

 his researches was not realized until the middle of the nineteenth 

 century, when William Thomson (Lord Kelvin) found in Caven- 

 dish's manuscripts the correct value for the ratio of the electric 

 charges carried by a circular disk and a sphere of the same radius 

 which had been placed in metallic connexion. Thomson urged 

 that the papers should be published ; which came to pass* in 

 1879, a hundred years from the date of the great discoveries 

 which they enshrined. It was then seen that Cavendish had 

 anticipated his successors in several of the ideas which will 

 presently be discussed amongst others, those of electrostatic 

 capacity and specific inductive capacity. 



In the published memoir of 1771 Cavendish worked out the 

 consequences of his fundamental hypothesis more completely 

 than Aepinus ; and, in fact, virtually introduced the notion of 

 electric potential, though, in the absence of any definite assump- 

 tion as to the law of force, it was impossible to develop this idea 

 to any great extent. 



* The Electrical Researches of the Hon. Henry Cavendish, edited by J. Clerk 

 Maxwell, 1879. 



