When we come to deal with a new problem we have really no right to show ourselves more exacting; yet there are found persons who refuse to admit the hypothesis of the atomic disaggregation of radium because they cannot have set before them a detailed plan of that complex whole known to us as an atom.

The most natural idea is perhaps the one suggested by comparison with those astronomical phenomena where our observation most readily allows us to comprehend the laws of motion.  It corresponds likewise to the tendency ever present in the mind of man, to compare the infinitely small with the infinitely great.  The atom may be regarded as a sort of solar system in which electrons in considerable numbers gravitate round the sun formed by the positive ion.  It may happen that certain of these electrons are no longer retained in their orbit by the electric attraction of the rest of the atom, and may be projected from it like a small planet or comet which escapes towards the stellar spaces.  The phenomena of the emission of light compels us to think that the corpuscles revolve round the nucleus with extreme velocities, or at the rate of thousands of billions of evolutions per second.  It is easy to conceive from this that, notwithstanding its lightness, an atom thus constituted may possess an enormous energy.[43]

[Footnote 43:  This view of the case has been made very clear by M. Gustave le Bon in L’Evolution de la Matiere (Paris, 1906).  See especially pp. 36-52, where the amount of the supposed intra-atomic energy is calculated.—­ED.]

Other authors imagine that the energy of the corpuscles is principally due to the extremely rapid rotations of those elements on their own axes.  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.