through Space occupied by Ether. 197 



§ 17. For example, let us take N= 4 x 10' 20 *; and, as 1 find 

 suits the cases of oxygen and argon, s=l*42 x 10~ 8 , which 



gives N ^-s 3 = "60 x 10 ~ 3 . The assemblage thus defined would, 



if condensed one-thousand-fold, have "6 of its whole volume 

 occupied by the atoms and "4 by undisturbed ether; which is 

 somewhat denser than the cubic arrangement of globes 



(space unoccupied =1— ^- = -4764), and less dense than the 



densest possible arrangement (space unoccupied = 1 — — ~ = 



•2595). Taking now N|s 3 = *60x 10" 3 in (16), we find for 



the refractive index of our assemblage 1*00019, which is 

 somewhat smaller than the refractive index of oxygen 

 (1*000273) . By taking for K a larger value than 100 in (11), 

 we could readily fit the formula to give, in an assemblage in 

 which "6 of the whole space is occupied by the atom, exactly 

 the refractive index of oxygen, nitrogen, or argon, or any 

 other gas. It is remarkable that according to the particular 

 assumptions specified in § 5, a density of ether in the centre 

 of the atom considerably greater than 100 times the density 

 of undisturbed ether is required to make the refractivity as 

 great as that of oxygen. There is, however, no difficulty in 

 admitting so great a condensation of ether by the atom, if we 

 are to regard our present problem as the basis of a physical 

 hypothesis worthy of consideration. 



§ 18. There is, however, one serious, perhaps insuperable, 

 difficulty to which I must refer in conclusion: the recon- 

 ciliation of our hypothesis with the result that ether in 

 the earth's atmosphere is motionless relatively to the earth, 

 seemingly proved by an admirable experiment designed by 

 Michelson, and carried out with most searching care to secur J 

 a trustworthy result, by himself and Morley f. 1 cannot 

 see any flaw either in the idea or in the execution of this 

 experiment. But a possibility of escaping from the conclusion 



* I am forced to take this very large number instead of Maxwell's 

 19xlO lti , as I have found it otherwise impossible to reconcile the known 

 viscosities and the known condensations of hydrogen, oxygen, and 



nitrogen with Maxwell's theoretical formula Ns 2 = — =- x^t ='3989 ,=:> 



where v is the Newtonian velocity of sound in the particular gas, and D 

 is its diffusivity, that is, its viscosity divided by its density. It must 

 be remembered that Avogadro's law makes N the same for all gases, 

 t Phil. Mag., December 1887. 



Phil. Mag. S. 5. Vol. 50. No- W&.Aug. 1900. P 



