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XX
LIGHT AND ELECTRICITY
can better survey both regions. They are more extensive than
we had ever before thought. Optics is no longer restricted to
minute ether-waves a small fraction of a millimetre in length;
its dominion is extended to waves which are measured in
decimetres, metres, and kilometres. And in spite of this ex-
tension it merely appears, when examined from this point of
view, as a small appendage to the great domain of electricity.
We see that this latter has become a mighty kingdom. We
perceive electricity in a thousand places where we had no
proof of its existence before. In every flame, in every
luminous particle we see an electrical process. Even if a
body is not luminous, provided it radiates heat, it is a centre
of electric disturbances. Thus the domain of electricity
extends over the whole of nature. It even affects ourselves
closely we perceive that we actually possess an electrical
organ-the eye. These are the things that we see when we
look downwards from our high standpoint. Not less attractive
is the view when we look upwards towards the lofty peaks,
the highest pinnacles of science. We are at once confronted
with the question of direct actions-at-a-distance. Are there
such? Of the many in which we once believed there now
remains but one-gravitation. Is this too a deception?
The law according to which it acts makes us suspicious. In
another direction looms the question of the nature of electricity.
Viewed from this standpoint it is somewhat concealed behind
the more definite question of the nature of electric and mag-
netic forces in space.
Directly connected with these is the
great problem of the nature and properties of the ether
which fills space, of its structure, of its rest or motion, of its
finite or infinite extent. More and more we feel that this is
the all-important problem, and that the solution of it will not
only reveal to us the nature of what used to be called im-
ponderables, but also the nature of matter itself and of its
most essential properties-weight and inertia. The quint-
essence of ancient systems of physical science is preserved for
us in the assertion that all things have been fashioned out of
fire and water. Just at present physics is more inclined to
ask whether all things have not been fashioned out of the
ether? These are the ultimate problems of physical science,
the icy summits of its loftiest range. Shall we ever be per-