llowed the energies which were potential in
the vegetable, up to their local exhaustion in the animal. But in
1845 a new thought was forced upon him by his calculations. He then,
for the first time, drew attention to the astounding amount of heat
generated by gravity where the force has sufficient distance to act
through. He proved, as I have before stated, the heat of collision of
a body falling from an infinite distance to the earth, to be
sufficient to raise the temperature of a quantity of water, equal to
the falling body in weight, 17,356 deg.C. He also found, in 1845, that
the gravitating force between the earth and sun was competent to
generate an amount of heat equal to that obtainable from the
combustion of 6,000 times the weight of the earth of solid coal. With
the quickness of genius he saw that we had here a power sufficient to
produce the enormous temperature of the sun, and also to account for
the primal molten condition of our own planet. Mayer shows the utter
inadequacy of chemical forces, as we know them, to produce or maintain
the solar temperature. He shows that were the sun a lump of coal it
would be utterly consumed in 5,000 years. He shows the difficulties
attending the assumption that the sun is a cooling body; for,
supposing it to possess even the high specific heat of water, its
temperature would fall 15,000' in 5,000 years. He finally concludes
that the light and heat of the sun are maintained by the constant
impact of meteoric matter. I never ventured an opinion as to the
truth of this theory; that is a question which may still have to be
fought out. But I refer to it as an illustration of the force of
genius with which Mayer followed the mechanical theory of heat through
all its applications. Whether the meteoric theory be a matter of fact
or not, with him abides the honour of proving to demonstration that
the light and heat of suns and stars may be originated and maintained
by the collisions of cold planetary matter.

It is the man who with the scantiest data could accomplish all this in
six short years, and in, the hours snatched from the duties of an
arduous profession, that the Royal Society, in 1871, crowned with its
highest honour.

Comparing this brief history with that of the Copley Medalist of 1870,
the differentiating influence of 'environment,' on two minds of
similar natural cast and endowment, comes out in an instructive
manner. Withdrawn from mechanical appliances