nit of heat being the quantity of heat which would raise
1 lb. of water one degree Fahr. So that if a 1-lb. weight fell from a
height of 772 feet, an amount of heat is generated which would raise 1
lb. of water one degree Fahr.; and conversely, to lift 1 lb. 772 feet
high, one degree Fahr. of heat would be consumed.

Now if this law of thermodynamics is true, it must not only be true in
relation to terrestrial heat, or heat produced by artificial means on
our earth, but it must equally hold good in relation to the solar
system; and not only the solar system, but equally true throughout all
the systems of worlds that flood the universe. So that wherever we get
heat in the universe, in the solar system for example, there, according
to our first law of thermodynamics, we should have the capacity to do
work of some kind or other. That work may take either the form of
expanding a body, as the atmosphere of a planet for example, or it may
take a mechanical form, that is, actually moving a body by the increased
pressure due to aetherial heat waves generated by the sun. We have
already seen in Art. 64, on Radiant Heat, what a store of heat the sun
has. For thousands and millions of years the sun has been pouring forth
its heat rays into space, and yet its temperature does not seem to be
diminished. The great Carboniferous or coal period of past geological
times is an indication of the heat and light of the sun, which it must
have radiated out millions of years ago; and year by year, these
aetherial heat waves are still being poured forth by the sun on every
side into space, so that no matter where a planet may be in its orbit,
there it may be the recipient of these aetherial heat waves which break
upon its surface. Now if there be this quantity of heat existing in the
sun, and heat according to the first law of thermodynamics has a
mechanical value, which is that it can push or lift a body through
space, the question arises, as to what is the mechanical value of this
heat of the sun? Are we to suppose that if one unit of heat can lift 1
lb. 772 feet, the millions and millions of units of heat which are
constantly being poured out of the sun into space are doing no work at
all? Such an assumption is not only contrary to that simplicity which
governs our Philosophy, but is entirely opposed to experience, which is
the very foundation of all philosophical reasoning. If, therefore,
experience is to be any guide at all, we are compell