Galvanism, from Galvani (o Ohm. 77 



to conclude, though with our present quantity of facts we are 

 unable to explain the exact mode of operation, that the </ 

 oxydatioii of the zinc in the pile, and the chemical changes 

 connected with it, are somehow the cause of the electrical effects ^ 

 it produces." This principle of oxidation guided Davy in 

 designing many new types of pile, with elements chosen from 

 the whole range of the known metals. 



Davy's chemical theory of the pile was supported by 

 Wollaston* and by Nicholson,f the latter of whom urged that 

 the existence of piles in which only one metal is used (with more 

 than one kind of fluid) is fatal to any theory which places the 

 seat of the activity in the contact of dissimilar metals. 



Davy afterwards proposed J a theory of the voltaic pile 

 which combines ideas drawn from both the "contact" and 

 " chemical " explanations. Ho supposed that before the circuit 

 is closed, the copper and zinc disks in each contiguous pair 

 assume opposite electrostatic states, in consequence of inherent 

 "electrical energies" possessed by the metals; and when a > 

 communication is made between the extreme disks by a wire, 

 the opposite electricities annihilate each other, as in the dis- 

 charge of a Leyden jar. If the liquid (which Davy compared 

 to the glass of a Leyden jar) were incapable of decomposition, 

 the current would cease after this discharge. But the liquid in 

 the pile is composed of two elements which have inherent 

 attractions for electrified metallic surfaces : hence arises 

 chemical action, which removes from the disks the outermost 

 layers of molecules, whose energy is exhausted, and exposes 

 new metallic surfaces. The electrical energies of the copper and 

 zinc are consequently again exerted, and the process of electro- 

 motion continues. Thus the contact of metals is the cause 

 which disturbs the equilibrium, while the chemical changes 

 continually restore the conditions under which the contact 

 energy can be exerted. 



In this and other memoirs Davy asserted that chemical 



*Phil. Trans., 1801, p. 427. t Nicholson'* Journal, i (1802), p. 142. 



; Phil. Trans., 1807, p. 1. 



