y 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. There is thus no such
thing as rest: from the planet to the ultimate particle, all things are
endlessly moving: and the mystic song of the Earth-Spirit in "Faust" is
recognized as the expression of the sublimest truth of science:--

"In Lebensfluthen, im Thatensturm,
Wall' ich auf und ab, webe hin und her,
Geburt und Grab,
Ein ewiges Meer,
Ein wechselnd Weben,
Ein gluehend Leben,
So schaff' ich am sausenden Webstuhl der Zeit,
Und wirke der Gottheit lebendiges Kleid."

In a discussion containing so much that is noble, however, we are sorry
to observe that Dr. Youmans is betrayed into using the current
expressions concerning an "ether" which is supposed to be the universal
vehicle for the transmission of molecular vibrations. We are told, that,
while "the vibrations of a sonorous body produce undulations in the
air," on the other hand, "the vibrations of atoms in a flame produce
undulations in the ether." We would by no means charge Dr. Youmans with
all the consequences naturally deducible from such a statement. We
believe that he uses the term "ether" simply to render himself more
intelligible to those who have been wont to make use of it to facilitate
their thinking. Such an object is highly praiseworthy, and is too often
left out of sight by those who write elementary works. But the good
service thus rendered is far more than counterbalanced by th