The London, Edinburgh and Dublin philosophical magazine and journal of science . to its bulk of ether that itis practically unmoved by the ethereal vibration; and forsimplicity at present we suppose the ether to move freelythrough the volume T, becoming denser without changing itsvelocity when it enters this fixed volume, and less densewhen it leaves. In §§ 41, 42, of Lecture XV. above, and inAppendix A, a definite supposition, attributing to ether noother property than elasticity as of an utterly homogeneousperfectly elastic solid, and the exercise of mutual force betweenitself and ponderable
The London, Edinburgh and Dublin philosophical magazine and journal of science . to its bulk of ether that itis practically unmoved by the ethereal vibration; and forsimplicity at present we suppose the ether to move freelythrough the volume T, becoming denser without changing itsvelocity when it enters this fixed volume, and less densewhen it leaves. In §§ 41, 42, of Lecture XV. above, and inAppendix A, a definite supposition, attributing to ether noother property than elasticity as of an utterly homogeneousperfectly elastic solid, and the exercise of mutual force betweenitself and ponderable matter occupying the same space, isexplained : according to which the ether within the atom will the Weights of Atoms. react upon moving ether outside just as it would if our presentconvenient temporary supposition of magically augmenteddensity within the volume of an absolutely fixed moleculewere realized in nature. For our present purpose, we niayif we please, following Rayleigh, do away altogether with theponderable molecule, and merely suppose T to be a denser Fig. portion of the ether. And if its greatest diameter is smallenough relatively to a wave-length, it will make no unnegli-gible difference whether we suppose the ether in T to havethe same rigidity as the surrounding free ether, or supposeit perfectly rigid as in §§ 1—46 of Lecture XIY. dealing witha rigid globe embedded in ether. § 64. Resolving the incident light into two componentshaving semi-ranges of vibration vr. p, in the plane of the paperand perpendicular to it ; consider first the component in theplane having vibrations symbolically indicated by the arrow-heads, and expressed by the following formula 27n>t a) sin where u is the velocity of light, and X the wave-length. Thegreater density of the ether within T gives a reactive force 290 Lord Kelvin on on the surrounding ether outside, in the line o£ the primaryvibration, and against the direction o£ its acceleration, ofwhich the magnitude i
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