264 
THEORY OF GALVANISM. 
some distinguished electricians, who have attempted to explain 
it in different ways. 
theor^^hat S To account for the effect of the interposed fluids, Mr. Cuth- 
the electro- bertson has suggested a theory which is both ingenious and 
sisted* 1 by the sufficiently 1 feasible*. With Volta he assumes the electromo- 
change of ox- tive change in the metals to be the first in the order of pheno- 
mena. And when (he observes) the copper has given, and the 
zinc has received, all the electricity, which their mutual powers 
require, if any menstruum be presented, which is capable of 
effecting a change in the metallic property of the two bodies, 
a change in their electrical states must, at the same time, hap- 
pen. But as the alteration of metallic property is only super- 
ficial, the charge of electrical condition will also be only at the 
surface 3 and the interior part of the zinc plate, retaining its 
property of resistance, th£ electric fluid, evolved at its surface, 
will necessarily be propelled forwards, thiough the menstruum, 
to the next copper plate of the series. This, however, can only 
happen in a progressive manner, because the fluid is but an im- 
perfect conductor, a condition indispensable to the maintenance 
of any galvanic intensity. 
Difficulty. The explanation of Mr. Cuthbertson is, unquestionably, a 
valuable supplement to the theory of Volta, inasmuch as it 
takes into account the efficiency of chemical menstrua. These, 
consistently with his view, will evolve electricity the more 
freely, in proportion as they destroy more rapidly the metallic 
property of the plates of zinc. The hypothesis, how r ever, is 
defective, because it fails to account for some of the pheno- 
mena ; — why, for example, the action of the menstruum is 
chiefly, if not entirely, exerted in oxidizing and dissolving the 
zinc plates 3 and why the evolution of hydrogen gas, or of 
nitrous gas, occurs chiefly at the copper surfaces. 
Fabroni’s hy- An hypothesis, originally suggested by Fabroni, and reversing 
pothesis, that those which have been already stated, has been adopted by 
causes the elec- several eminent philosophers in our own country. It assumes 
tricity, the oxidation of the metals composing galvanic arrangements 
* Nicholson’s Journal, 8vo. ii. 287. 
to 
