the Weights of Atoms. 



react upon moving ether outside just as it would if our present 

 convenient temporary supposition of magically augmented 

 density within the volume of an absolutely fixed molecule 

 were realized in nature. For our present purpose, we niay 

 if we please, following Rayleigh, do away altogether with the 

 ponderable molecule, and merely suppose T to be a denser 



Fig. 1. 



portion of the ether. And if its greatest diameter is small 

 enough relatively to a wave-length, it will make no unnegli- 

 gible difference whether we suppose the ether in T to have 

 the same rigidity as the surrounding free ether, or suppose 

 it perfectly rigid as in §§ 1 — 46 of Lecture XIY. dealing with 

 a rigid globe embedded in ether. 



§ 64. Resolving the incident light into two components 

 having semi-ranges of vibration vr. p, in the plane of the paper 

 and perpendicular to it ; consider first the component in the 

 plane 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. The 

 greater density of the ether within T gives a reactive force 



