e 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 electro-motive force, ascribed by Volta to the metals, when in
contact, 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.' When this argument, which he employed independently,
had clearly fixed itself in his mind, Faraday never cared to experiment
further on the source of electricity in the voltaic pile. The argument
appeared to him 'to remove the foundation itself of the contact theory,'
and he afterwards let it crumble down in peace.[1]

Footnote to Chapter 7

[1] To account for the electric current, which was really
the core of the whole discussion, Faraday demonstrated the
impotence of the Contact Theory as then enunciated and
defended. Still, it is certain that two different metals,
when brought into contact, charge themselves, the one with
positive and the other with negative electricity. I had the
pleasure of going over this ground with Kohlrausch in 1849,
and his experiments left no doubt upon my mind that the
contact electricity of Volta was a reality, though it could
produce no current. With one of the beautiful instruments
devised by himself, Sir William Thomson has rendered this
point capable of sure and easy demonstration; and he and
others now hold what may be called a contact theory, which,
while it takes into account the action of the metals, also
embraces the chemical phenomena of the circuit. Helmholtz,
I believe, was the first to give the contact theory this new
form, in his celebrated essay, Ueber die Erhaltung der
Kraft, p. 45.

Chapter 8.

Researches on frictional electricity: induction: conduction:
specific inductive capacity: theory of contiguous particles.

The burst of power which had filled the four preceding years with an
amount of experimental work unparalleled in the history of science
partially subsided in 1835, and the only scientific paper contributed
by Faraday in that year was a comparatively unimportant one, 'On an
improved Form of the Voltaic Battery.' He br