It is already more than half a century since Count
Rumford demonstrated the immaterial nature of heat, and Young
established the undulatory theory of light,--ideas which had germinated
two hundred years ago in the lofty minds of Huygens and Hooke. Since
then have been discovered the polarization and interference of heat, the
triple constitution of the solar ray, the identity of magnetism and
electricity, the polar nature of chemical affinity, the optical
polarities of crystals, and the interaction of magnetism and light.
Since then the once meagre and fragmentary science of physics has become
one of the grandest and richest departments of human thought; and the
illustrious names of Helmholtz, Joule, and Mayer, of Grove, Faraday, and
Tyndall, may be fitly named beside those of the leading thinkers of past
ages. The physical forces are no longer to be looked upon as inscrutable
material entities,--forms of matter imponderable, and therefore
inconceivable; but they have been shown to be diverse, but
interchangeable modes of molecular motion, omnipresent, ceaselessly
active. The wondrous phenomena of light, heat, and electricity are seen
to be due to the rhythmical vibration of atoms.
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