and StoJces-Planck's ^jEther. 167 



s = 1 (or log s — 0) to the actual value of the condensation. 

 Thus the condensation formula (6) becomes 



(t^--diog* = n, ..... (8) 



where XI has been written for the total gravitational potential 

 at the place under consideration. For constant t» (Boyle's 

 law), and for a single spherical body, the previous formula 

 (3) reappears. 



It will be kept in mind that although the aether is assumed 

 to behave in this way (say, like a gas) with respect to slow 

 processes, it can still propagate rapid transversal light- 

 disturbances as if it were an elastic solid (like the famous 

 cobbler's wax of Lord Kelvin) ; but it will be best to think 

 of light as of electromagnetic disturbances. The normal 

 velocity c of propagating them is another property of the 

 aether, independent of that which is represented by t», and 

 subjected only to slight variations with condensation, as will 

 appear presently. The ratio of f to c will be of importance, 

 but as to the longitudinal waves themselves, they are of no 

 physical interest for the present and, on the other hand, are 

 not likely to become a nuisance. For it is not in our power 

 to produce them to any relevant extent, and even if they are 

 generated and maintained by some gigantic natural pro- 

 cesses, their only effect would be to alter very slightly, here 

 and there, the normal velocity of light-propagation. 



If we wish to form an idea of the numerical value of V, 

 or at least of its upper limit, for the case of Boyle's law, say, 

 it is enough to take the value of a given above for the Sun, 

 and to remember that Mjc i = l'5 km., and, in round figures, 



R = 7.10 5 km. Then the result will be - =S'2 . lO" 6 , that is 



to say, t> equal to about 2*5 km. per second *. This is quoted 

 by the way only. But the ratio of these two velocities will 

 be seen to acquire a particular interest in connexion with 

 the recent astronomical discovery. 



6. Let c, as before, stand for the propagation velocity of 

 light in uncondensed aether, i.e. in absence of, or far away 

 from, gravitating masses, and let c be the light velocity at a 

 place where the aether has undergone a condensation s. The 

 question is : How are we to correlate c' with s ? In other 

 words : On what are we to base the optical behaviour of the 

 aether modified by a condensation ? The only reasonable 



* If so. then the condensational disturbances' due to the Earth and 

 other planets, whose velocities exceed fc, will be confined to conical 

 regions as in Mach'a famous experiments. 



