242 KINETIC THEORIES OF GRAVITATION. 



• 

 verse; the first assertiug tins relation through immense distances, the 

 second exhibiting it only in very small spaces."* In what wa^' these 

 two great master-forces of nature, seemingly so unlike, and even antag- 

 onistic to each other, may possibly be connected in action or in principle, 

 is nowhere suggested ; but the character of the author forbids the sup- 

 position that the remark was hastily ventured, or conceived without 

 sober reflection. 



jS^o further reference however, to the subject of gravitation occurs in the 

 work, till toward its close. In the last " Lesson," Lame shows the neces- 

 sity 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 i^roducing pro- 

 gressive waves which will explain the optical phenomena of birefractive 

 bodies, or which could have led to the discovery of most of these phe- 

 nomena. Luminous waves then are i)roduced and propagated in trans- 

 parent bodies by the vibrations of an imponderable fluid, which is no 

 other than the aether." He determines analytically two systems of undu- 

 lation in the fether, of differing velocities ; one system radial, or normal 

 to the ellipsoidal surface of the wave, affecting the dilatation or conden- 

 sation 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.t 



Lame concludes his Lessons with some reflections on the internal con. 

 stitution of solid bodies, " It seems highly probable that the progress 

 of general physics will conduct one day to a j^rinciple 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 maj^ 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 

 sether."! 



"Since then the existence of the setherial fluid is incontestably demon- 

 strated by the propagation of light through celestial spaces, — by the 

 explanation (as simple as complete) of the condition of difiraction in the 

 theory of waves, — and as has been seen, — by the laws of double refrac- 

 tion, which prove with no less certitude the existence of an jether within 



* Lemons sur la Thcorie Maihemaiique de l'£lastk'ite des Corps SoVules. 8vo, Paris, ld52 

 Lesson i, p. 2. 

 + Loco citaf., Less, xsiv, sec. 131, pp. 327, 328. 

 t Loco ciiat., sec. 134, pp. 332, 333. 



