A number of the acutest thinkers have, so far in vain, endeavoured to
grapple more closely with this fundamental problem of the philosophy of
nature, and to determine more exactly the nature of atoms as well as
their relation to the space-filling ether. And the idea steadily gains
ground that no such thing as empty space exists, and that everywhere the
primitive atoms of ponderable matter or heavy "mass" are separated from
each other by the homogeneous ether which extends throughout all space.
This extremely light and attenuated (if not imponderable) ether causes,
by its vibrations, all the phenomena of light and heat, electricity and
magnetism. We can imagine it either as a continuous substance occupying
the space between the mass-atoms, or as composed of separate particles;
in the latter case we might perhaps attribute to these ether-atoms an
inherent power of repulsion in contrast to the immanent attracting power
of the heavy mass-atoms, and the whole mechanism of cosmic life would
then be reducible to the attraction of the latter and the repulsion of
the former. We might also place the "vibrations of the cosmic ether"
alongside of the "operation of space in general," in the sense in which
these words are used by Professor Schlesinger.

At any rate, theoretical physics has in recent years made an advance of
fundamental importance and widest reach in our knowledge of nature, in
that it has come nearer to a knowledge of this cosmic ether, and has
forced the question of its essence, its structure, and its motion into
the foreground of monistic nature-philosophy. Only a few years ago the
cosmic ether was to the majority of scientists an imponderable something,
of which, strictly speaking, absolutely nothing was known, and which
could be admitted provisionally only as a precarious working hypothesis.
All this was changed when Heinrich Hertz (1888) demonstrated the nature
of electrical energy, by his beautiful experiments establishing the
conjecture of Faraday that light and heat, electricity and magnetism, are