doubt with faith in the principle of continuity. But it does seem
to me needful, before we conclude that radiated energy is
absolutely and forever wasted, that we should find out what
becomes of it. What we call radiant heat is simply transverse
wave-motion, propagated with enormous velocity through an ocean
of subtle ethereal matter which bathes the atoms of all visible
or palpable bodies and fills the whole of space, extending beyond
the remotest star which the telescope can reach. Whether there
are any bounds at all to this ethereal ocean, or whether it is as
infinite as space itself, we cannot surmise. If it be limited,
the possible dispersion of radiant energy is limited by its
extent. Heat and light cannot travel through emptiness. If the
ether is bounded by surrounding emptiness, then a ray of heat, on
arriving at this limiting emptiness, would be reflected back as
surely as a ball is sent back when thrown against a solid wall.
If this be the case, it will not affect our conclusions
concerning such a tiny region of space as is occupied by the
solar system, but it will seriously modify Sir William Thomson's
suggestion as to the fate of the universe as a whole. The
radiance thrown away by the sun is indeed lost so far as the
future of our system is concerned, but not a single unit of it is
lost from the universe. Sooner or later, reflected back in all
directions, it must do work in one quarter or another, so that
ultimate stagnation be comes impossible. It is true that no such
return of radiant energy has been detected in our corner of the
world; but we have not yet so far disentangled all the
force-relations of the universe that we are entitled to regard
such a return as impossible. This is one way of escape from the
consummation of things depicted by our authors. Another way of
escape is equally available, if we suppose that while the ether