terminal, when separated from each other by a measurable space of air.

The memoir on the 'Electricity of the Voltaic Pile,' published in
1834, appears to have produced but little impression upon the
supporters of the contact theory. These indeed were men of too
great intellectual weight and insight lightly to take up, or lightly
to abandon a theory. Faraday therefore resumed the attack in a
paper, communicated to the Royal Society on the 6th of February,
1840. In this paper he hampered his antagonists by a crowd of
adverse experiments. He hung difficulty after difficulty about the
neck of the contact theory, until in its efforts to escape from his
assaults it so changed its character as to become a thing totally
different from the theory proposed by Volta. The more persistently
it was defended, however, the more clearly did it show itself to be
a congeries of devices, bearing the stamp of dialectic skill rather
than of natural truth.

In conclusion, Faraday brought to bear upon it an argument which,
had its full weight and purport been understood at the time, would
have instantly decided the controversy. 'The contact theory,'
he urged, 'assumed 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 shall 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