Kinetic Theories of Gravitation/Leray, 1869

Within the last twenty years, probably more than a dozen " original " discoveries of the cause of gravitation have been announced to the French Academy of Sciences. Two brief essays of the same year may here be noticed. A Note by P. Leray, entitled a " New Theory of Gravitation," was presented to the Academy through M. Faye September 6, 1869.

" This new theory rests on the assumption of an aether — a fluid exceedingly rare and perfectly elastic — and on the two following principles : First, that in the free aether (that is, undisturbed by the presence of other bodies) there exist at every point equal currents crossing each other in all directions ; second, that in passing through bodies, the currents of the aether are retarded proportionally to the thickness traversed, and to the mean density of the path. It may be added, that the currents thus enfeebled, on passing again into the aether, recover but slowly their former force, and may be considered approximately — within the limits of our solar system — as preserving a constant value." This gravific fluid evidently does not differ essentially from that of Lesage. These simple hypotheses, says the writer, " conduct in effect to the same results as the law of universal attraction, without requiring any action at a distance ; and give moreover the key to many phenomena which this law does not explain."

Considering first, the case of an isolated body, it is evident that the currents, being equal in all directions, neutralize each other, effecting therefore no change of position in the isolated body ; although by the [270] vis viva absorbed from the aether, heat light and magnetism are produced in the body as shown in the stars. " This cause being permanent, explains without difficulty why the light and heat of the sun are constant "! A body in motion is of course retarded by the relative differential of the currents, although this retardation would be sensible only with very light bodies.

Considering secondly, the case of two bodies, (exterior to each other,) the currents enfeebled by traversing the bodies would impinge less strongly on the' mutually-facing sides of the two bodies than on their exterior sides, thus producing an approach by the difference of impulse. And lastly, in regard to weight, this is the result of the quantity of motion communicated to a body by the shocks of the aetherial atoms. The two facts of experience, that the weight of a body remains invariable whatever its position, and that all bodies fall with the same velocity in a vacuum, prove that ponderable atoms are spherical, having an equal superficial density in all directions, and that all ponderable atoms are alike, or that there is ultimately but a single elementary substance.