130 THEORY OF GALVANISM. 



rest upon the best authority, those who have at- 

 tended to the subject of galvanism will be able to 

 judge. I shall not think it necessary to enter into 

 any formal refutation of his hypothesis, or of the 

 reasoning by which it is supported, as I do not 

 perceive that he has advanced any thing which has 

 not been already noticed, or that he has adduced 

 any new arguments, in addition to those that had 

 *V been brought forward by Volta himself. 



The opinions which are entertained by M. Haiiy 

 an d by M. Thenard, respecting the immediate 

 cause of the galvanic action, do not materially 

 differ from each other, or from that of M Biot. 

 Like him, they believe in the existence of the two 

 electric fluids, and suppose that when the relative 

 proportion of the two fluids in one body is de- 

 stroyed by the contact or approximation of the 

 metallic plates, the phenomena of galvanism may 

 be produced, so as to refer the whole to an un- 

 equal distribution of the vitreous and resinous 

 electricity. The greater energy of the apparatus 

 when acids or saline solutions are employed instead 

 of water, Thenard, like Volta; ascribes merely to 

 their superior conducting power, and agrees with 

 him also in regarding the chemical changes which 

 take place as not essential to its operation.* 



The last publication on the subject of galva- 

 ' nism which I shall have to notice, is the essay of 

 Mr. Donovan of Dublin, in which, besides many 



* Haiiy, Traite de Physique, ii. 1 to 58 j Thenard, Trait 

 de Chimie, i. 19. 



