Matter thus seems to us to undergo those transformations of which the radio-active bodies have given us such remarkable examples.
We have already had, in fragments, these views on the constitution of matter; a deeper study of the electron thus enables us to take up a position from which we obtain a sharp, clear, and comprehensive grasp of the whole and a glimpse of indefinite horizons.
It would be advantageous, however, in order to strengthen this position, that a few objections which still menace it should be removed.

The instability of the electron is not yet sufficiently demonstrated.

How is it that its charge does not waste itself away, and what bonds assure the permanence of its constitution?
On the other hand, the phenomena of gravitation remain a mystery.
Lorentz has endeavoured to build up a theory in which he explains attraction by supposing that two charges of similar sign repel each other in a slightly less degree than that in which two charges, equal but of contrary sign, attract each other, the difference being, however, according to the calculation, much too small to be directly observed.

He has also sought to explain gravitation by connecting it with the pressures which may be produced on bodies by the vibratory movements which form very penetrating rays.

Recently M.Sutherland has imagined that attraction is due to the difference of action in the convection currents produced by the positive and negative corpuscles which constitute the atoms of the stars, and are carried along by the astronomical motions.