126 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XVII.) 
bable or philosophic cause assigned for the assumed action ; or reason given why 
one or other of the consequent effects above mentioned should not take place : and, 
as I have again and again said, I do not know of a single fact, or case of contact 
current, on which, in the absence of such probable cause, the theory can rest. 
2071. The contact theory assumes, in fact, that a force which is able to overcome 
powerful resistance, as for instance that of the conductors, good or bad, through 
which the current passes, and that again of the electrolytic action where bodies are 
decomposed by it, can arise out of nothing. That, without any change in the acting 
matter or the consumption of any generating force, a current can be produced which 
shall go on for ever against a constant resistance, or only be stopped, as in the voltaic 
trough, by the ruins which its exertion has heaped up in its own course. This would 
indeed be a creation of power, and is like no other force in nature. We have many 
processes by which the form of the power may be so changed that an apparent con- 
version of one into another takes place. So we can change chemical force into the 
electric current, or the current into chemical force. The beautiful experiments of 
Seebeck and Peltier show the convertibility of heat and electricity ; and others by 
CErsted and myself show the convertibility of electricity and magnetism. But in 
no cases, not even those of the Gymnotus and Torpedo (1790.), is there a pure crea- 
tion of force; a production of power without a corresponding exhaustion of something 
to supply it*. 
2072. It should ever be remembered that the chemical theory sets out with a power, 
the existence of which is pre-pro ved, and then follows its variations, rarely assuming 
anything which is not supported by some corresponding simple chemical fact. The 
contact theory sets out with an assumption, to which it adds others as the cases 
require, until at last the contact force, instead of being the firm unchangeable thing 
at first supposed by Volta, is as variable as chemical force itself. 
2073. Were it otherwise than it is, and were the contact theory true, then, as it 
appears to me, the equality of cause and effect must be denied (2069.). Then would 
* (Note, March 29, 1840.) — I regret that I was not before aware of most important evidence for this phi- 
losophical argument, consisting of the opinion of Dr. Roget, given in his Treatise on Galvanism in the Library 
of Useful Knowledge, the date of which is January 1829. Dr. Roget is, upon the facts of the science, a sup- 
porter of the chemical theory of excitation ; but the striking passage I desire now to refer to, is the following, 
at § 113. of the article Galvanism. Speaking of the voltaic theory of contact, he says, “Were any further 
reasoning necessary to overthrow it, a forcible argument might be drawn from the following consideration. If 
there could exist a power having the property ascribed to it by the hypothesis, namely, that of giving continual 
impulse to a fluid in one constant direction, without being exhausted by its own action, it would differ essen- 
tially from all the other known powers in nature. All the powers and sources of motion, with the operation of 
which we are acquainted, when producing their peculiar effects, are expended in the same proportion as those 
effects are produced ; and hence arises the impossibility of obtaining by their agency a perpetual effect ; or, in 
other words, a perpetual motion. But the electromotive force ascribed by Volta to the metals when in con- 
tact, is a force which, as long as a free course is allowed to the electricity it sets in motion, is never expended, 
and continues to be excited with undiminished power, in the production of a never-ceasing effect. Against 
the truth of such a supposition, the probabilities are all but infinite.” — Roget. 
