ch is incomplete, by something unfelt and
unseen which is necessary to its completeness, men of genius have in
part discerned, not only the nature of light and heat, but also,
through them, the general relationship of natural phenomena. The
working power of Nature consists of actual or potential motion, of
which all its phenomena are but special forms. This motion manifests
itself in tangible and in intangible matter, being incessantly
transferred from the one to the other, and incessantly transformed by
the change. It is as real in the waves of the aether as in the waves
of the sea; the latter--derived as they are from winds, which in their
turn are derived from the sun--are, indeed, nothing more than the
heaped-up motion of the aether waves. It is the calorific waves
emitted by the sun which heat our air, produce our winds, and hence
agitate our ocean. And whether they break in foam upon the shore, or
rub silently against the ocean's bed, or subside by the mutual
friction of their own parts, the sea waves, which cannot subside
without producing heat, finally resolve themselves into waves of
aether, thus regenerating the motion from which their temporary
existence was derived. This connection is typical. Nature is not an
aggregate of independent parts, but an organic whole. If you open a
piano and sing into it, a certain string will respond. Change the
pitch of our voice; the first string ceases to vibrate, but another
replies. Change again the pitch; the first two strings are silent,
while another resounds. Thus is sentient man acted on by Nature, the
optic, the auditory, and other nerves of the human body being so many
strings differently tuned, and responsive to different forms of the
universal power.

********************

III ON RADIANT HEAT IN RELATION TO THE COLOUR AND CHEMICAL
CONSTITUTION OF BODIES.

[Footnote: A discourse delivered in the Royal Institution of Great
Britain, Jan. 19, 1866.]

ONE of the most important functions of physical science, considered as
a discipline of the mind, is to enable us by means of the sensible
processes of Nature to apprehend the insensible. The sensible
processes give direction to the line of thought; but this once given,
the length of the line is not limited by the boundaries of the senses.
Indeed, the domain of the senses, in Nature, is almost infinitely
small in comparison with the vast region accessible to thought which
lies beyond them. From a few obse