'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 form of the power may be so changed, that an
apparent conversion of one into the other 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 Oersted and myself
show the convertibility of electricity and magnetism. But in no case,
not even in those of the Gymnotus and Torpedo, is there a pure creation
or a production of power without a corresponding exhaustion of something
to supply it.'

These words were published more than two years before either Mayer
printed his brief but celebrated essay on the Forces of Inorganic
Nature, or Mr. Joule published his first famous experiments on the
Mechanical Value of Heat. They illustrate the fact that before any great
scientific principle receives distinct enunciation by individuals,
it dwells more or less clearly in the general scientific mind. The
intellectual plateau is already high, and our discoverers are those who,
like peaks above the plateau, rise a little above the general level of
thought at the time.

But many years prior even to the foregoing utterance of Faraday, a
similar argument had been employed. I quote here with equal pleasure
and admiration the following passage written by Dr. Roget so far back as
1829. Speaking of the contact theory, he says:--'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 essentially
from all the known powers in nature. All the powers and sources of
motion with the operation of which we are acquainted, when producing
these peculiar effects, are expended in th