172 Sir Oliver Lodge on a Possible 



of light in the neighbourhood. (Compare Lord Kelvin, 

 Baltimore Lecture?, p. 465.) An electron might, in fact, 

 be a small region in which intrinsic circulation has ceased, 

 so that it possessed inertia only. 



The tension or reduction of: pressure set up in the neigh- 

 bourhood of such a centre of force could explain gravitational 

 attraction, and a change of rioiditv would also suffice to 

 explain the very minute reduction in the velocity of light. 

 The refractive index needed at any point is 1 -f 2yMlrc 2 , or 

 l + u 2 /c'\ where u is the velocity of free fall from infinity, 

 which is just what the light has done. The dielectric 

 constant would be modified so that K/K^ = 1 + 4:jM/rc 2 ; 

 the second term being Einstein's deflexion. It may be taken 

 as representing the deficiency of etherial circulation-energy 

 near a massive body, as compared with the unmodified 

 circulation-energy in free space. Just outside an electron 

 this deficiency is of the order 10~ 42 ; though just outside the 

 Sun it is of the order 10 -5 . 



This note is hardly germane to Dr. Silberstein's paper ; 

 so I may just add that the complication of introducing 

 compressibility, and not only compressibility but an enormous 

 gravitational compression, in order to evade rotationality in 

 a hypothetical ether dragged by moving masses — for absence 

 of velocity-potential is well known to complicate unduly 

 the theory of astronomical aberration — does not commend 

 itself to me. An incompressible ether, not viscous at all, 

 is far more simple ; and astronomical aberration then 

 follows, as easily as on the corpuscular theory, without any 

 ingenuity. 



But, as speculation in these unconquered regions is a 

 legitimate preliminary to exploration, 1 may say that I am 

 fully prepared, as Dr. Silberstein in one part of his paper 

 seems also prepared, to accept a gravitational influence on 

 the Ether's dielectric constant, and, therefore, on the square 

 of its index of refraction : though I should like to see this 

 done without postulating any increase of density in a 

 medium of which space is already completely full. It is 

 also highly desirable to avoid the frictional and thermal 

 considerations, accompanied by dissipation of energy, in- 

 separable from any sort of viscosity. These imperfections 

 are appropriate to a secondary or derived cosmic ingredient, 

 like matter; they are not appropriate to the fundamental 

 substance itself. 



If the ether has demonstrated anything, so far, it has 

 shown us, by its veiy elusive character and complete 



