e
co-ordinated so happily by it, that it more and more satisfies our
minds; but it cannot be asserted that it forces itself on our
convictions with irresistible weight. Another point of view appeared
more plausible and simple at the outset, when there seemed reason to
consider the energy radiated by radioactive bodies as inexhaustible.
It was thought that the source of this energy was to be looked for
without the atom, and this idea may perfectly well he maintained at
the present day.

Radium on this hypothesis must be considered as a transformer
borrowing energy from the external medium and returning it in the form
of radiation. It is not impossible, even, to admit that the energy
which the atom of radium withdraws from the surrounding medium may
serve to keep up, not only the heat emitted and its complex radiation,
but also the dissociation, supposed to be endothermic, of this atom.
Such seems to be the idea of M. Debierne and also of M. Sagnac. It
does not seem to accord with the experiments that this borrowed energy
can be a part of the heat of the ambient medium; and, indeed, such a
phenomenon would be contrary to the principle of Carnot if we wished
(though we have seen how disputable is this extension) to extend this
principle to the phenomena which are produced in the very bosom of the
atom.

We may also address ourselves to a more noble form of energy, and ask
ourselves whether we are not, for the first time, in presence of a
transformation of gravitational energy. It may be singular, but it is
not absurd, to suppose that the unit of mass of radium is not attached
to the earth with the same intensity as an inert body. M. Sagnac has
commenced some experiments, as yet unpublished, in order to study the
laws of the fall of a fragment of radium. They are necessarily very
delicate, and the energetic and ingenious physicist has not yet
succeeded in finishing them.[46] Let us suppose that he succeeds in
demonstrating that the intensity of gravity is less for radium than
for the platinum or the copper of which the pendulums used to
illustrate the law of Newton are generally made; it would then be
possible still to think that the laws of universal attraction are
perfectly exact as regards the stars, and that ponderability is really
a particular case of universal attraction, while in the case of
radioactive bodies part of the gravitational energy is transformed in
the course of its evolution and appears in the form of