126 THEORY OF GALVANISM. 



end of the pile, in any assignable degree of force." 

 After an interval of fifteen years, and notwith- 

 standing the succession of brilliant discoveries that 

 have been made during this period, I am not aware 

 of any fact which is adverse to the above hypothe- 

 sis, or any phenomenon which it does not explain. 

 It mvist, however, be confessed that it entirely de- 

 pends upon the assumption of two postulates, for 

 which we have no other proof except the facility 

 with which they explain the phenomena ; yet they 

 are positions which are not in themselves improba- 

 ble, and which do not seem incompatible with our 

 ordinary conceptions on the subject. 



The pile A considerable part of the difficulty which has 

 electrical occurred in forming a theory of the pile, has, I 

 n"cinstnT.~ think, arisen from our not clearly discriminating 

 mem - between its effects in exciting common electricity, 

 and that modification of it which is called galva- 

 nism. I have endeavoured to point out in what 

 respect these two actions differ from each other; 

 and, imperfect as our knowledge is concerning the 

 cause, I conceive that there is an obvious difference 

 in the effect. Now it will appear that the pile, as 

 it is usually constructed, is both an electrical and 

 a galvanic instrument ; and that when we attempt 

 to form a theory of its action, we have two dis- 

 tinct sets of phenomena to explain. The power of 

 producing muscular contraction is an electrical ef- 

 fect, that of decomposing chemical bodies a galva- 

 nic effect ; while that of burning metallic leaves, or 

 igniting wires, probably partakes of both these ac- 



