to conclude, though with our present quantity of facts we are unable to explain the exact mode of operation, that the oxydation 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[1] and by Nicholson,[2] 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[3] 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 discharge 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 electromotion continues. Thus the contact of metals is the cause which disturbs the equilibrium, while the chemical changes of continually restore the conditions under which the contact energy can be exerted.
In this and other memoirs Davy asserted that chemical
