concerning the Constitution of Matter. 203 



15. It may be remarked that, according to the assumptions 

 of this paper, every motion in the universe is ultimately due 

 to stationary motion in a quasi-solid medium. This medium, 

 which extends through all known space, is supposed to be (at 

 least appreciably) perfect in its elastic properties, that is, free 

 from viscous yielding and internal friction ; and its ever 

 changing distribution of stress and strain is to be held 

 accountable for all observed phenomena. 



16. The subject of this paper being now explained, so far 

 as the vagueness of my own views will allow, the fundamental 

 proposition may be stated as follows : — 



A given portion of matter consists, not of any individual 

 portion of ethereal or other substance, but of modifications in the 

 structure or energy or other qualities of the aether, and when 

 matter moves it is merely these modifications of structure or of 

 energy or of other qualities which are transferred from one 

 portion of the azther to another. 



The strain-figure has here been almost exclusively con- 

 sidered, and we have seen 



(i) That provided the motion is slow compared with a 

 certain velocity V (§ 4), a strain-figure will encounter no 

 resistance in travelling through the aether, and will obey laws 

 of motion which include Newton's Laws as a particular case. 



(ii) That gravitative and inter-atomic forces may possibly 

 be supposed to arise from the stresses which accompany the 

 distribution of strain. 



(iii) That a collision between two single strain-figures 

 would not set them vibrating, so that an atom consisting of 

 strain-figures would have a finite number of degrees of free- 

 dom, as required by the dynamical theory of heat. 



(iv) That the size and nature of possible strain-figures, 

 and therefore also of possible atoms, would be limited by the 

 conditions of equilibrium, thus giving rise, perhaps, to a 

 discrete series. 



On the other hand, it is a special difficulty of my theory 

 that we require some assumption as to the superposition of 

 strain-figures to account for the fact that the mass of a 

 material body is equal to the sum of the masses of its con- 

 stituent particles. 



In conclusion, I have to thank Mr. G. H. Bryan for his 

 kindness in verifying some portions of the analysis, as well as 

 for a suggestion which has immensely lessened the labour of 

 calculation. 



Note added November 21. 

 In the discussion which followed this paper, Professoi 



P2 



