THEORY OF GALVANISM. 



from the zinc, through the menstruum, to the 

 next adjoining copper in the pile or trough." This 

 effect, however, can only happen in a progressive 

 manner, because the fluid is but an imperfect con- 

 ductor ; and to this he ascribes many of the pecu- 

 liar phenomena of the apparatus. Dr. Henry, 

 in a judicious essay, " On the Theories of the 

 Excitement of Galvanic Electricity "* observes, 

 that, " the explanation of Mr. Cuthbertson is un- 

 equivocally a valuable supplement to the theory of 

 Volta, inasmuch as it takes into account the effi- 

 ciency of chemical menstrua." But, as he farther 

 remarks, it is defective, because it does not ex- 

 plain why " the action of the menstruum is chiefly, 

 if not entirely, exerted in oxidizing and dissolving 

 the zinc plates, and why the evolution of hydrogen 

 gas, or of nitrous gas, occurs chiefly at the copper 

 surface." 



The an- The first attempt which I made to explain 

 tne chemical action of the pile, was written 

 about the same time with the above remarks of 

 Mr. Cuthbertson, and may be considered, in some 

 degree, as supplying the deficiency of his hypo- 

 thesis which is noticed by Dr. Henry. I pro- 

 ceeded upon the principle which was laid down by 

 Dr. Wollaston, that electricity is evolved by the 

 oxidation of metals ; and generalized it so far 

 as to conclude, that the electric fluid is always li- 

 berated when an oxidable substance is united to 

 oxygen. In addition to this principle, I proposed 



* Manchester Mem. 2d series, ii. 293. 



