experiment was again repeated in another form with similar results.
Rumford in dealing with the results of his experiments said: "It appears
to me to be extremely difficult, if not quite impossible, to form any
distinct idea of anything capable of being excited and communicated, in
the manner the Heat was excited and communicated, in these experiments,
except it be Motion."

Only a year later, Davy gave to the world some results of experiments
which he had performed, by which he had arrived at a similar conclusion
to that of Rumford, viz. that "Heat is motion of some kind." His
experiment consisted of rubbing two pieces of ice together, and by so
doing showed the ice could be melted. He then caused two pieces of metal
to be rubbed together, keeping them surrounded by ice, and still he
found that the two pieces of metal when rubbed together, produced heat,
and melted the ice. He therefore rightly concluded that heat was
produced by friction, and of the experiment adds: "A motion or vibration
of the corpuscles of bodies must necessarily be generated by friction.
Therefore we may reasonably conclude that this motion or vibration is
Heat. Heat then may be defined as a peculiar motion, probably a
vibration of the corpuscles of bodies tending to separate them. It may
with propriety be called a repulsive motion. Now bodies exist in
different states, and those states depend upon the action of the
attractive and of the repulsive powers on their corpuscles, or in other
words, on their different quantities of repulsion and attraction." It
was not, however, till 1812 that Davy confidently stated that "The
immediate cause of the phenomena of Heat is motion, and the laws of its
communication are precisely the same as the laws of the communication of
motion."

The question therefore confronts us, if heat be motion, what is the
particular character of that motion? Is it a vibratory motion as Davy
suggested, or is it similar to the undulatory wave motion of light? I
need hardly point out, that we have evidence in favour of the hypothesis
that light is due to some form of periodic wave motion in the Aether,
the hypothesis being that known as the undulatory theory. We have also
similar evidence in favour of the hypothesis, that heat is also due to
some form of motion of the same aetherial medium. Indeed, it can be
shown that heat possesses all the properties of light, and is subject to
the same laws, with the exception that it cannot aff