not think it has been suggested by
any scientist that the heat emitted and radiated by the sun is ever
returned in any way back to the sun from infinite space, whether by
reflection or by any other method. So far as I can learn, there are no
facts in connection with the solar system which would lead us to make
that assumption. On the contrary, experience and experiment teach us
that radiation implies loss of heat, and that the body, which so
radiates, ultimately becomes cold, unless its internal heat is kept up
by some means or other. So that the terms introduced by Carnot in the
second law of thermodynamics, viz. that of a Cycle of Operations and of
a Reversible Cycle, do not apply to the solar system, and the solar
system, viewed from the standpoint of a machine, with the sun as the
source of the heat, does not represent a perfect engine, that is, all
the heat is not used up in doing work, some of it being radiated out
into space. Wherever, however, the heat, that is the aetherial heat
waves generated by the sun, comes into contact with a planet, as
Mercury, Venus, or Jupiter, then, in accordance with Carnot's reasoning,
work is done. Carnot points out that, in order for work to be done, we
must have a source and a condenser, that is, two bodies at different
temperatures, a hot body and a cold one. Now these conditions of work
are satisfactorily fulfilled in the solar system, and as a result work
is performed. We have the sun with its huge fires, and its intensity of
heat, representing the source or the hot body, while every planet and
every meteor and comet, that come under its influence, represent the
cold body, and between the two work is always going on. That work is
represented by the repulsive power of heat, which I have already
indicated, so that, viewed from Carnot's standpoint with relation to the
motive power of heat, we find that there are in the solar system those
conditions which govern work, and by which, from a mechanical
standpoint, work is performed; further, that work takes the form of a
repulsive power on every planet or other body upon which the aetherial
heat waves fall. Therefore, from the second law of thermodynamics we
have another proof of this repulsive power of heat already indicated and
referred to in Art. 63.

ART. 69. _Identity of Heat and Light._--We have seen from the preceding
articles of this chapter, that heat is due to a periodic wave motion of
the Aether, and in the succeeding ch