294 Mr. William Sutherland on the 



give the value N = 9. Hence the velocity of light through 

 the water molecule appears to be one ninth of that through 

 free aether. But before we could ascribe any degree of 

 accuracy to this estimate we should need to be surer of the 

 value of x, whose measurement is attended with great experi- 

 mental difficulties. It is much to be desired that we had 

 similar measurements for other bodies than water, both liquid 

 and solid, to permit of other estimates of N, so as to see if it 

 is the same for all compound bodies, and also to decide be- 

 tween the theory here sketched and Fresnel's hypothesis, 

 that matter carries its own excess of aether with it, so that 

 x= (n 2 — l)/?i 2 , which in the case of water is *437, in excellent 

 agreement with Michelson and Morley's experimental number ; 

 but one such agreement is not sufficient to establish an 

 hypothesis founded on such artificial grounds. However, if 

 N = 9 then N — 1 = 8, and we have the electrical specific mole- 

 cular conductivity k = 68 + 2*2 (u — 8U). It is only a coinci- 

 dence that this agrees so exactly in form with Clausius's 

 calculation that the number of encounters experienced per 

 second by a molecule of volume U moving amongst a number 

 of others of volume U is greater than that experienced by an 

 ideal particle moving under the same circumstances in the 

 ratio u : u — 8U. Further experiment must elucidate the 

 subject-matter of these speculations. 



19. Suggested relation between the change in the volume of an 

 atom on combination and the change in its chemical energy. 

 — Returning to the idea that the dynic equivalent furnishes 

 a measure of the volume of its atom, we can get a suggestive 

 glimpse into the relation between the volume of an atom and 

 its chemical energy. Kundt has recently (Phil. Mag. July 

 1888) shown that the velocities of light through the metals 

 (uncombined) are as their electrical conductivities, being in 

 the case of silver, gold, and copper greater than through free 

 aether, and as in this case both n— 1 and N — 1 are negative, 

 we see that (n — l)u or (N — 1)U for the metals changes 

 greatly when the metals pass from the combined to the free 

 state. Now this is in strong contrast to the behaviour of the 

 non-metallic elements, which have been shown in the case of 

 0, N, C, S, P, CI, Br, and I to possess nearly the same values 

 of (n — l)u in the combined and free states, and the same may 

 perhaps be said of H. Again, in contrast to this approximate 

 inalterability of (w— Y)u for these non-metals we have the 

 fact, already pointed out, that the dynic equivalents of H, 0, 

 and N are much smaller in the free than the combined state. 

 If, then, the dynic equivalents give a measure of the volumes 



