ed to come to the
conclusion that the heat poured forth into space does do work on the
bodies, as comets, meteors, planets, upon which the aetherial heat waves
fall. The problem is, what is the character of the work done? I have
already indicated part of the work, viz. in the expansion of the
atmosphere of the planets. Then there is also the reception of the heat
by the animal and vegetable life of the planet, but these do not account
for all the motive power of the aetherial waves, which break upon the
planet or its atmospheres.

The true solution of the first law of thermodynamics, in its relation to
the solar system, seems to me to be found in the fact already stated in
Art. 63, viz. that heat is a repulsive motion, and the law of
thermodynamics confirms that statement, and shows that the work done on
a planet by the aetherial heat waves is that of pushing it, or urging it
by their very energy and motion away from their controlling centre, the
sun. This would practically amount to a repulsive force which had its
home in the sun, and this conception would bring our Philosophy into
harmony with our experience, which teaches us that wherever there is
heat there is the capacity of doing work, the amount of work being
proportionate to the heat generated and consumed.

ART. 68. _Second Law of Thermodynamics._--This law was enunciated by
Sadi Carnot in 1824, when he wrote an essay on the Motive Power of Heat.
Previous to the time of Carnot no definite relation seems to have been
suggested between work and heat; Carnot, however, discovered what were
those general laws which govern the relation between heat and work. In
arriving at his conclusion, he based his results on the truth of the
principle of the conservation of energy already referred to (Art. 52).

Carnot started his reasoning on the assumption that heat was matter, and
therefore indestructible. The two great truths in relation to heat and
work, enunciated by Carnot, are known as, first, a Cycle of operations;
and, secondly, what he termed a Reversible Cycle. In order to be able to
reason upon the work done by a heat-engine, say a steam-engine for
example, Carnot stated we must imagine a cycle of operations, by which,
at the end of such operations, the steam or water is brought back to
exactly the same state in which it was at its start. He calls this a
cycle of operations, and of it he says, that only at the conclusion of
the cycle are we entitled to reason upo