Kinetic Theories of Gravitation/Lamé, 1852

Gabriel Lamé, a distinguished French geometer, and author of a very learned and valuable work on the laws of elasticity, embracing a profound mathematical discussion of the theory of vibrations in almost all its scientific aspects, has incidentally alluded to gravitation in such a manner as to deserve a notice here.

Of his more immediate theme he forcibly remarks: "Elasticity is the real origin or indispensable intermediary of all the more important physical phenomena of the universe. . . . In a word, the function of elasticity in nature is at least as important as that of universal gravitation. Indeed gravitation and elasticity should be considered as effects of the same cause, which correlate or connect all the material parts of the [242] universe; the first asserting this relation through immense distances, the second exhibiting it only in very small spaces." In what way these two great master-forces of nature, seemingly so unlike, and even antagonistic to each other, may possibly be connected in action or in principle, is nowhere suggested ; but the character of the author forbids the supposition that the remark was hastily ventured, or conceived without sober reflection.

No further reference however, to the subject of gravitation occurs in the work, till toward its close. In the last " Lesson," Lame shows the necessity for admitting a pervading tether. And considering the question whether ponderable matter is really the medium which vibrates and transmits light in transparent crystals, he decides: "There can no longer exist a doubt on this question ; for it clearly results from our analysis that ponderable matter alone is incapable of producing progressive waves which will explain the optical phenomena of birefractive bodies, or which could have led to the discovery of most of these phenomena. Luminous waves then are produced and propagated in transparent bodies by the vibrations of an imponderable fluid, which is no other than the aether." He determines analytically two systems of undulation in the fether, of differing velocities ; one system radial, or normal to the ellipsoidal surface of the wave, affecting the dilatation or condensation of the medium, and not concerned in optical phenomena; and the other system transverse to this in two sets, or in the direction of two tangents to the ellipsoidal wave, representing the phases of polarized light.

Lame concludes his Lessons with some reflections on the internal constitution of solid bodies, "It seems highly probable that the progress of general physics will conduct one day to a principle analogous to that of universal attraction, of which this itself shall prove only a corollary, and which may serve as the basis of a rational theory comprehending both mechanics — the celestial and the terrestrial. But to presuppose this unknown principle, or to infer the whole from one of its parts, is to retard — it may be for a long time — the epoch of its discovery." And speaking of the great desideratum, a rational science of molecular mechanics, he asks : "Is this an enigma forever insoluble? To this question must be answered yes, if the existence of ponderable matter only is to be admitted ; — no, if we admit also the existence of the aether."

"Since then the existence of the aetherial fluid is incontestably demonstrated by the propagation of light through celestial spaces, — by the explanation (as simple as complete) of the condition of diffraction in the theory of waves, — and as has been seen, — by the laws of double refraction, which prove with no less certitude the existence of an aether within [243] transparent bodies, wo know that ponderable matter is not alone in the universe; its particles swim as it were in a kind of fluid medium. If this fluid be not the unique cause of all the observed facts, it must at least modify them, diffuse their action, and complicate their laws. It is then no longer possible to attain a rational and complete explanation of the phenomena of physical nature, without recognizing the intervention of this agent, whose presence is so inevitable. It is scarcely to be doubted that in this intervention, sagaciously investigated, will be found the secret or the true cause of the effects which are attributed to heat, to electricity, to magnetism, to universal attraction, to cohesion, to chemical affinities ; for all these mysterious and incomprehensible agencies are at bottom but co-ordinating hypotheses, — useful without doubt to our existing ignorance, but which the progress of true science will complete by dethroning."

These passages are less notable for any precise hypothesis as to the cause of gravitation than for their earnest unformulated faith in the mechanical agencies of the tether as the fountain head of all force.

A very striking illustration of the author's realizing sense of the aetherial presence occurs in a memoir communicated by him to the Academy of Sciences about ten years before this time, or in 184:2; in which, discussing the difference between the determination by Gay-Lussac of the co-efficient of gaseous dilatation, and that made by Endberg and verified by Regnault twenty-five years later. Lame made the somewhat startling announcement that the observed difference indicated an increasing aetherpressure on terrestrial matter! "The difference between these results is explained by admitting that the pressure of the aether has undergone on the earth in a quarter of a century an augmentation equal to a pressure of eight or nine tenths of a millimetre of the mercurial column."