"The facts of chemical physics point to electrification being distributed in an atomic manner, so that an atom of electricity, say an electron, has the same claims to separate and permanent existence as an atom of matter. The fundamental question then is, how far the conception of separate isolated electrons, pervading the aether of free space, can provide an explanation of electrodynamic and optical phenomena. ...Whatever view one may entertain as to the presence of qualities other than electric in the atom, all are I think now-a-days agreed that the electron is there. And whatever view one may have as to the validity and sufficiency of an æther with simple rotational elasticity, the formal equations to which that theory leads for free space are just those equations of Maxwell which Hertz's experimental work has fully verified. The problem of electrodynamics is then that of the free æther, whose properties are represented analytically by these acknowledged equations, disturbed by the action of the electrons of material atoms moving about in it. The original Amperean electrodynamics, proceeding by consideration of elements of current, has not proved valid or sufficient in matters involving electric radiation, or even ordinary electrodynamic force. A most successful modification of it was that proposed by Weber in which elements of current were replaced, as the fundamental object of consideration, by moving electric particles which acted on each other at a distance according to a law of force involving their velocities. This theory was, however, shown long ago by Lord Kelvin and Professor von Helmholtz to be untenable on account of its violating the principles of the modern theory of energy; now, of course, direct action at a distance is altogether out of court. The present question is whether a theory of electrons which act on each other, not directly according to a law of force, but mediately by propagation of the effect across the intervening æther, suffices to avoid the discrepancies of earlier theories and give a consistent account of electrical and optical phenomena; and it is maintained that the answer is altogether in the affirmative."