38 On the Hypothesei of Galvanism. [Jan. 



withstanding the contact of the water, is in the state of + and — 

 with respect to each other, C 2 being 95°, Z 2 must be 20° more, 

 or 115°.* But this hypothesis is liable to all the objections that 

 were urged against the last, while at the same time it assumes 

 another principle, which has not been proved, that water has not 

 the power of transmitting electricity with sufficient ease or rapidity 

 to prevent its accumulation in any part of the apparatus : and even 

 were we to admit of this retardation, and of the necessity of a 

 certain length uf time intervening hefore the equilibrium could be 

 established, yet this would take place at length, and then the effect 

 of the pile would cease. But we do not find this to be the case : 

 the action goes on without diminution, until either the fluid is 

 exhausted, or the surface of the zinc covered with oxide. We may 

 also remark, both with respect to thia and the last modification of 

 the electrical hypothesis, that as all the electricity must ultimately 

 be derived from ihe first copper plate, it ought to be soon exhausted. 

 There is no source from which the copper plate can receive electri- 

 city ab extra, and it Is continually transmitting it to the zinc, yet 

 the power of the copper In giving out electricity is never dimi- 

 nished. The electrical liypoiliesis, in all its modifications, is defec- 

 tive in making no provision for the continued generation of electri- 

 city ; for, as has already been remarked, the action between each 

 pair of metals is merely a change in the distribution of what they 

 before possessed, not an addition of any new electricity. 



Sir H. Davy, although originally an advocate for the chemical 

 hypothesis, was afterwards induced fo alter his opinion respecting 

 it, and to rank himself among the followers of Volta;+ yet it will 

 be found that the ideas which he entertains upon the subject are 

 very far from being the natural deduction from Volta's doctrine, 

 and tiiat he has added lo the original hypothesis a new and very 

 important principle. He agrees wilh Volta in considering the 

 action of the metals upon each other as the first step in the process; 

 but the effect of the fluid in restoring the equilibrium is supposed 

 to depend, not upon its conducting power, but upon the different 



» This modification of the hjpothesis Is tliat which is ado])ted by some of the 

 French vNriters, and also by Volta himself in his letter to Gren. Dr. Ikiiry seems 

 to regard Ihe hypothos-is nearly in the same point of view ; see Elem. Chim. i. 249. 



+ Sir H. I>avy assigns the following as tlic reason why he renounced the chemi- 

 cal and adopted the electrical hypothesis. Because iie could not refer to any che- 

 mical j)rinci|)les the exchange of electricity wJiich the metals experience by con- 

 tact ; becau-c i)i a pile formed of acid, zinc, and copper, the side of the zinc 

 next the acid is positive, but if a pile be formed of zinc, water, and acid, the 

 surface of the zinc next the acid is negative, the fame chemical change thus pro- 

 ducing a ditferent electrical clTect ; and lastly, because many ciiemical changes 

 are not attended with electrical phenomena. («) The remarks that have been 

 made will alTord a reply to the first of these objections; the second will he an- 

 swered when the chrmral. hypothesis is ^rtailed ; and as lo Ihe third, it may be 

 remarked, that the ciiemical hypothesis does not render it neceswry for us lo 

 suppose that electricity is concerned in all chimiral changes, noi" if it were so, 

 that we should always be able to detect its presence. 



(a) Phil. Trans. 1807, ^ 10. 



