movement provoked by Röntgen's sensational experiments has a very
remote origin, it has, at least, been singularly quickened by the
favourable conditions created by the interest aroused in its
astonishing applications to radiography.

A lucky chance has thus hastened an evolution already taking place,
and theories previously outlined have received a singular development.
Without wishing to yield too much to what may be considered a whim of
fashion, we cannot, if we are to note in this book the stage actually
reached in the continuous march of physics, refrain from giving a
clearly preponderant place to the questions suggested by the study of
the new radiations. At the present time it is these questions which
move us the most; they have shown us unknown horizons, and towards the
fields recently opened to scientific activity the daily increasing
crowd of searchers rushes in rather disorderly fashion.

One of the most interesting consequences of the recent discoveries has
been to rehabilitate in the eyes of scholars, speculations relating to
the constitution of matter, and, in a more general way, metaphysical
problems. Philosophy has, of course, never been completely separated
from science; but in times past many physicists dissociated themselves
from studies which they looked upon as unreal word-squabbles, and
sometimes not unreasonably abstained from joining in discussions which
seemed to them idle and of rather puerile subtlety. They had seen the
ruin of most of the systems built up _a priori_ by daring
philosophers, and deemed it more prudent to listen to the advice given
by Kirchhoff and "to substitute the description of facts for a sham
explanation of nature."

It should however be remarked that these physicists somewhat deceived