56 Electric and Magnetic Science 



the names boreal and austral were assigned, were postulated by 

 the Hollander Anton Brugmans (5. 1732, d. 1789) and by 

 Wilcke. These fluids were supposed to have properties of 

 mutual attraction and repulsion similar to those possessed by 

 vitreous and resinous electricity. 



The writer who next claims our attention for his services 

 both to magnetism and to electricity is the French physicist, 

 Charles Augustin Coulomb* (ft. 1736, d. 1806). By aid of the 

 torsion-balance, which was independently invented by Michell 

 and himself, he verified in 1785 Priestley's fundamental law 

 that the repulsive force between two small globes charged with 

 the same kind of electricity is in the inverse ratio of the square 

 of the distance of their centres. In the second memoir he 

 extended this law to the attraction of opposite electricities. 



Coulomb did not accept the one-fluid theory of Franklin, 

 Aepinus, and Cavendish, but preferred a rival hypothesis which 

 had been proposed in 1759 by Kobert Symmer.f " My notion," 

 said Symmer, " is that the operations of electricity do not depend 

 upon one single positive power, according to the opinion generally 

 received; but upon two distinct, positive, and active powers, 

 which, by contrasting, and, as it were, counteracting each other, 

 produce the various phenomena of electricity ; and that, when a 

 body is said to be positively electrified, it is not simply that it is 

 possessed of a larger share of electric matter than in a natural 

 state ; nor, when it is said to be negatively electrified, of a less ; 

 but that, in the former case, it is possessed of a larger portion 

 of one of those active powers, and in the latter, of a larger 

 portion of the other ; while a body in its natural state remains 

 unelectrified, from an equal ballance of those two powers within 

 it." 



Coulomb developed this idea : " Whatever be the cause of 

 electricity," he says,J " we can explain all the phenomena by 



* Coulomb's First, Second, and Third Memoirs appear in Memoires de 1'Acad., 

 1785 ; the Fourth in 1786, the Fifth in 1787, the Sixth in 1788, and the Seventh 

 in 1789. 



t Phil. Trim*, li (1759), p. 371. j Sixth Memoir, p. 561. 



