Kinetic Theories of Gravitation/Saigey, 1866

The following presentation of the theme, though from a litterateur rather than a physicist is interesting as showing what may be called the percolation of ideas. In a series of essays contributed by Emile Saigey (under the nom de plume of "Edgar Saveney") to the Revue de Deux Mondes for November 1, November 15, and December 15, 1866, the writer proposed to give a popular exposition of "Modern Physics and Recent Views on the Unity of Natural Phenomena." After a brief sketch of the received correlation of forces, he proceeds : " What then is gravity? What is that mysterious force which causes two bodies to attract each other in the direct ratio of their masses and an inverse ratio of their distance ? Two bodies attract each other ! Then matter is not inert ! Is there not then an apparent contradiction between the two terms, matter and inertia ? . . . Now what light is this new theory going to throw upon the principle of gravity ! Here is the answer. A substance to which the name of aether has been given is diffused throughout the entire universe. It envelops bodies and penetrates into their interstices. The existence of this substance is deduced from a series of proofs, among which luminous phenomena hold the first rank, aether is composed of atoms which impinge upon each other and upon neighboring bodies. It forms in this way a universal medium which exerts a constant pressure upon the molecules of ordinary matter. ... It becomes evident that bodies do not owe their gravity to an intrinsic force, but to the pressure of the medium in which they are immersed. The motion of heavy bodies no longer appears to us other than as a transformation of the aetherial motions ; and gravity henceforth enters into that majestic unity to which we have conducted all physical forces. . . . Are there then strictly speaking, two kinds of matter ? We can hardly conceive it, now that we have resolved everything into motion. In what respect would these two kinds of matter differ ? Would not the one be subject to the same laws of motion as the other ? Can there be two systems of mechanics? Certainly not ; since there is but one law for motion, there can be but [261] a single essence tor matter, and the molecules of ordinary matter must appear to ns as aggregates of aetherial atoms."

In his concluding essay, M. Saigey thus expounds the aetherial action:

" Let us imagine the tether uniformly diffused throughout space. Its atoms endowed with motions of progression and rotation, strike each other in the manner mentioned. Let us now suppose that at some point within the medium there is a special and disturbing cause, as for example, a molecule having weight [inertia ?J and itself endowed with a vibratory motion. The disturbance goes on extending throughout the aetherial mass, and by reason of the nature of this medium is propagated in all directions. The atoms nearest to the heavy molecule will receive violent shocks ; they will be powerfully urged and their ranks will grow thin in the neighborhood of the center of disturbance, and the layer contiguous to the molecule will become less dense than the rest of the medium. The motor action continuing, this same effect becomes propagated from layer to layer throughout space. As a final result, the aether becomes arranged around the center of disturbance in concentric layers, the first of which and nearest to the molecule will be least dense, and they will go on indefinitely increasing in density. This condition of things might be easily represented and the figure traced : the molecule at the center, around it spheres of atoms, wide apart at first, then nearer and nearer to each other. Let us remark, in passing, that the difference in density of contiguous layers, like all effects which are propagated by concentric spheres, is inversely proportional to the surface of these spheres, that is to the square of their radii. [?] This established, suppose a second molecule to be situated at any point of this system. It will encounter on the side toward the first molecule, layers of aether less dense than upon the opposite side : pressed upon by the aether in all directions, it will however receive fewer shocks on the side toward the first molecule, and it will consequently tend to approach it. Such would seem to be the cause of gravity." The law of inverse squares does not appear to be well made out, although this is a point to which all kinetic theorists make ostentatious reference. The density of the tether, instead of following this ratio, should ex hypothesis, follow directly the opposite ratio ; or rather the ratio of increase directly as the distance ; — which is perhaps what was intended. Of the other five conditions it is quite unnecessary to speak.