and Stakes- Planch's sEther. 165 



aberration, i. e. <7=logs=10 , 2, we shall have at the surface 

 of the Sun, as already mentioned in a footnote, 



<r= log s = 10-2 ^lO 4 #31000, . . . (S) 



•which means, no doubt, :m enormous condensation *. The 

 •corresponding relative velocity of slipping v/v^ will, by (2), 

 ■be almost evanescent ; the drag will be almost complete. 



On the other hand, at the surface of a hydrogen atom, 

 assumed for the moment to be a homogeneous sphere (and 

 the only existing body), we shall have log s= 1*7 . 10" 34 , that 

 is to say, 



_ P 



= 1 + 1-7. 10" 



34 



P, 



indistinguishable from unity. Notice that for small a the 

 denominator in (2) reduces to J<x 3 + .^o" 4 + higher terms, so 

 that the relative slip becomes 



£=J(i-i-) w 



For such bodies, therefore, as a hydrogen atom, or in fact 



any other atom, the ratio in question will be exceedingly 



nearly equal its limiting value 3/2, which is well known to be 



the maximum relative slipping for a sphere moving in an 



incompressible liquid. In short, for such small bodies there 



will be practically no drag at all. The more so for electrons, 



if one wished to attribute to them gravitational properties. 



This behaviour will be important in connexion with some 



such electrodynamic theories of ponderable media, as is that 



proposed by Lorentz. which require a complete slip. But 



even a sphere of the mass of 1 kg. and the radius of 10 cm., 



for which a= 1'09 . 10 ~ 16 , will practically have no " grip upon 



the aether." This will readily be seen to account, among 



other things, for the negative results of Sir Oliver Lodge's 



ingenious experiments with the Ether machine, even if its 



whirling part were made much more massive. As a mere 



curiosity notice that even the Moon would have ouly a partial, 



weak grip .upon our rehabilitated aether. In fact, at the 



Moon's surface we should have o-=10'2 x 0-094 = 0'96, and 



v 

 therefore, by (2), -- =1*15, which differs only by 0'35 from 



00 



the full slip. Thus the Selenites would obtain with a 



* Such fantastically large condensations need not frighten us. They 

 can be reduced if Boyle's law is replaced by some other appropriate 

 form of relation between pressure and density. Boyle's law, which is 

 by no means necessary, is here used only, as the simplest one, for the 

 sake of illustration. 



