attracted, as happens for light in the phenomenon of astronomic aberration, so that the effective force is not directed along the straight joining the two bodies, but makes with this straight a small angle. This is a very special hypothesis, not well justified, and, in any case, entirely different from that of Lorentz. Laplace’s result proves nothing against the theory of Lorentz.
II
Comparison with Astronomic Observations
Can the preceding theories be reconciled with astronomic observations?
First of all, if we adopt them, the energy of the planetary motions will be constantly dissipated by the effect of the wave of acceleration. From this would result that the mean motions of the stars would constantly accelerate, as if these stars were moving in a resistant medium. But this effect is exceedingly slight, far too much so to be discerned by the most precise observations. The acceleration of the heavenly bodies is relatively slight, so that the effects of the wave of acceleration are negligible and the motion may be regarded as quasi-stationary. It is true that the effects of the wave of acceleration constantly accumulate, but this accumulation itself is so slow that thousands of years of observation would be necessary for it to become sensible. Let us therefore make the calculation considering the motion as quasi-stationary, and that under the three following hypotheses :
A. Admit the hypothesis of Abraham (electrons indeformable) and retain Newton’s law in its usual form;
B. Admit the hypothesis of Lorentz about the deformation of electrons and retain the usual Newton’s law;
C. Admit the hypothesis of Lorentz about electrons and modify Newton’s law as we have done in the preceding paragraph, so as to render it compatible with the principle of relativity.
It is in the motion of Mercury that the effect will be most sensible, since this planet has the greatest velocity. Tisserand formerly made an analogous calculation, admitting Weber’s law; I recall that Weber had sought to explain at the same time the
