ll. He records observations on the
heat generated in water agitated by the pulping engine of a paper
manufactory, and calculates the equivalent of that heat in
horse-power. He compares chemical combination with mechanical
combination--the union of atoms with the union of falling bodies with
the earth. He calculates the velocity with which a body starting at
an infinite distance would strike the earth's surface, and finds that
the heat generated by its collision would raise an equal weight of
water 17,356' C. in temperature. He then determines the thermal
effect which would be produced by the earth itself falling into the
sun. So that here, in 1845, we have the germ of that meteoric theory
of the sun's heat which Mayer developed with such extraordinary
ability three years afterwards. He also points to the almost
exclusive efficacy of the sun's heat in producing mechanical motions
upon the earth, winding up with the profound remark, that the heat
developed by friction in the wheels of our wind and water mills comes
from the sun in the form of vibratory motion; while the heat produced
by mills driven by tidal action is generated at the expense of the
earth's axial rotation.

Having thus, with firm step, passed through the powers of inorganic
nature, his next object is to bring his principles to bear upon the
phenomena of vegetable and animal life. Wood and coal can burn;
whence come their heat, and the work producible by that heat? From
the immeasurable reservoir of the sun. Nature has proposed to herself
the task of storing up the light which streams earthward from the sun,
and of casting into a permanent form the most fugitive of all powers.
To this end she has overspread the earth with organisms which, while
living, take in the solar light, and by its consumption generate
forces of another kind. These organisms are plants. The vegetable
world, indeed, constitutes the instrument whereby the wave-motion of
the sun is changed into the rigid form of chemical tension, and thus
prepared for future use. With this prevision, as shall subsequently
be shown, the existence of the human race itself is inseparably
connected. It is to be observed that Mayer's utterances are far from
being anticipated by vague statements regarding the 'stimulus' of
light, or regarding coal as 'bottled sunlight.' He first saw the full
meaning of De Saussure's observation as to the reducing power of the
solar rays, and gave that observati