Lord Kelvin lately drew up on another model the plan of a radioactive atom capable of ejecting an electron with a considerable _vis viva_.

He supposes a spherical atom formed of concentric layers of positive and negative electricity disposed in such a way that its external action is null, and that, nevertheless, the force emanated from the centre may be repellent for certain values when the electron is within it.
The most prudent physicists and those most respectful to established principles may, without any scruples, admit the explanation of the radioactivity of radium by a dislocation of its molecular edifice.

The matter of which it is constituted evolves from an admittedly unstable initial state to another stable one.

It is, in a way, a slow allotropic transformation which takes place by means of a mechanism regarding which, in short, we have no more information than we have regarding other analogous transformations.

The only astonishment we can legitimately feel is derived from the thought that we are suddenly and deeply penetrating to the very heart of things.
But those persons who have a little more hardihood do not easily resist the temptation of forming daring generalisations.