certain limit they become unstable and tend to lose their
equilibria. There would result from this a commencement of
dissociation, with diminution of their potential energy and a
corresponding increase of their kinetic energy sufficient to launch
into space the products of intra-atomic disintegration.

It must not be forgotten that the atom being an enormous reservoir
of energy is by this very fact comparable with explosive bodies.
These last remain inert so long as their internal equilibria are
undisturbed. So soon as some cause or other modifies these, they
explode and smash everything around them after being themselves
broken to pieces.

Atoms, therefore, which grow old in consequence of the diminution
of a part of their intra-atomic energy gradually lose their
stability. A moment, then, arrives when this stability is so weak
that the matter disappears by a sort of explosion more or less
rapid. The bodies of the radium group offer an image of this
phenomenon -- a rather faint image, however, because the atoms of
this body have only reached a period of instability when the
dissociation is rather slow. It probably precedes another and more
rapid period of dissociation capable of producing their final
explosion. Bodies such as radium, thorium, etc., represent, no
doubt, a state of old age at which all bodies must some day arrive,
and which they already begin to manifest in our universe, since all
matter is slightly radio-active. It would suffice for the
dissociation to be fairly general and fairly rapid for an explosion
to occur in a world where it was manifested.

These theoretical considerations find a solid support in the sudden