We shall have to abandon the idea so instinctively dear to us that matter is the most stable thing in the universe, and to admit, on the contrary, that all bodies whatever are a kind of explosive decomposing with extreme slowness.

There is in this, whatever may have been said, nothing contrary to any of the principles on which the science of energetics rests; but an hypothesis of this nature carries with it consequences which ought in the highest degree to interest the philosopher, and we all know with what alluring boldness M.Gustave Le Bon has developed all these consequences in his work on the evolution of matter.[45] [Footnote 44: This is the main contention of M.Gustave Le Bon in his work last quoted .-- ED.] [Footnote 45: See last note .-- ED.] There is hardly a physicist who does not at the present day adopt in one shape or another the ballistic hypothesis.

All new facts are 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.