e X rays are thought, as has been said
above, to contain neither negative nor positive particles, but to be
merely pulses in the ether.--ED.]

However this may be, the edifice thus constructed, being composed of
electrons in periodical motion, necessarily grows old. The electrons
become subject to accelerations which produce a radiation towards the
exterior of the atom; and certain of them may leave the body, while
the primitive stability is, in the end, no longer assured, and a new
arrangement tends to be formed. Matter thus seems to us to undergo
those transformations of which the radio-active bodies have given us
such remarkable examples.

We have already had, in fragments, these views on the constitution of
matter; a deeper study of the electron thus enables us to take up a
position from which we obtain a sharp, clear, and comprehensive grasp
of the whole and a glimpse of indefinite horizons.

It would be advantageous, however, in order to strengthen this
position, that a few objections which still menace it should be
removed. The instability of the electron is not yet sufficiently
demonstrated. How is it that its charge does not waste itself away,
and what bonds assure the permanence of its constitution?

On the other hand, the phenomena of gravitation remain a mystery.
Lorentz has endeavoured to build up a theory in which he explains
attraction by supposing that two charges of similar sign repel each
other in a slightly less degree than that in which two charges, equal
but of contrary sign, attract each other, the difference being,
however, according to the calculation, much too small to be directly
observed. He has also sought to explain gravitation by connecting it
with the pressures which may be produced on bodies by the vibratory
movements which form very penetrating rays. Recently M. Sutherland has
imagined that attraction is due to the difference of action in the
convection currents produced by the positive and negative corpuscles
which constitute the atoms of the stars, and are carried along by the
astronomical motions. But these hypotheses remain rather vague, and
many authors think, like M. Langevin, that gravitation must result
from some mode of activity of the ether totally different from the
electromagnetic mode.

CHAPTER XI

THE FUTURE OF PHYSICS

It would doubtless be exceedingly rash, and certainly very
presumptuous, to seek to predict the future which may be reserved for
physics.