this
assertion has latterly assumed would have assented, in a general way,
to its correctness. Their assent, however, was more poetic than
scientific, and they were by no means prepared to see a rigid
mechanical signification attached to their words. This, however, is
the peculiarity of modern conclusions: that there is no creative
energy whatever in the vegetable or animal organism, but that all the
power which we obtain from the muscles of man and animals, as much as
that which we develop by the combustion of wood or coal, has been
produced at the sun's expense. The sun is so much the colder that we
may have our fires; he is also so much the colder that we may have our
horse-racing and Alpine climbing. It is, for example, certain that
the sun has been chilled to an extent capable of being accurately
expressed in numbers, in order to furnish the power which lifted this
year a certain number of tourists from the vale of Chamouni to the
summit of Mont Blanc.

To most minds, however, the energy of light and heat presents itself
as a thing totally distinct from ordinary mechanical energy. Either
of them can nevertheless be derived from the other. Wood can be
raised by friction to the temperature of ignition; while by properly
striking a piece of iron a skilful blacksmith can cause it to glow.
Thus, by the rude agency of his hammer, he generates light and heat.
This action, if carried far enough, would produce the light and heat
of the sun. In fact, the sun's light and heat have actually been
referred to the fall of meteoric matter upon his surface; and whether
the sun is thus supported or not, it is perfectly certain that he
might be thus supported. Whether, moreover, the whilom molten
condition of our planet was, as supposed by eminent men, due to the
collision of cosmic masses or not, it is perfectly certain that the
molten condition might be thus brought about.

If, then, solar light and heat can be produced by the impact of dead
matter, and if from the light and heat thus produced we can derive the
energies which we have been accustomed to call _vital_, it indubitably
follows that vital energy may have a proximately mechanical origin.

In what sense, then, is the sun to be regarded as the origin of the
energy derivable from plants and animals? Let us try to give an
intelligible answer to this question. Water may be raised from the
sea-level to a high elevation, and then permitted to descend. In
descendin