94 Dr. C. V. Burton on a 



being vacuous should be a large number or a small fraction. 

 The value — 20 — chosen for //, would make the phase-difference 

 of pressure-fluctuation of about the same order between the 

 surface and the centre of the sun as between the surface of 

 the sun and that of the earth, under maximum conditions. 



The somewhat vague grounds on which the value unity is 

 assigned to $ were indicated at the end of § 28. 



38. Some of the derived quantities in the table above may 

 now be considered. In the first place, take f, which repre- 

 sents the maximum deviation from its mean value of F the 

 "specific displacement" of atomic matter (§7). If the 

 primary disturbance is slight enough to be adequately repre- 

 sented by linear equations, we should expect on general 

 grounds that £ would be small, and the value for f derived 

 from our assumptions is 5'6 x 10 -5 , while the energy of the 

 primary disturbance per unit volume, under the same assump- 

 tions, appears as 1/(6 x 10 8 ) part of the constitutive energy of 

 the aether. 



39. For n, the frequency of the primary disturbance, 

 1-29 x 10 10 per second is found, leading to 2*19 x 10 27 cm. 

 per second, or over two thousand million light-years per 

 second, for TiT, the velocity of propagation of a compressional- 

 rarefactional disturbance through the aether. This would 

 amply suffice for the sensibly instantaneous character of 

 gravitational attraction. 



40. The bulk-modulus of elasticity of the aether, denoted 

 by k is, with our assumptions, represented by 4*78 x 10 6b 

 dynes per sq. cm., or 4*72 x 10 60 atmospheres. Comparing 

 this with the assumed constitutive energy of the aether 

 (10 ergs per c.c), which is taken to be the basis of dielec- 

 tric elasticity (the reciprocal of dielectric capacity) in free 

 sether, the comparison appears to be consistent with our 

 assumption that the bulk-modulus is enormously greater than 

 any other elastic modulus of the aether ; an assumption in 

 accordance with which the aether, in relation to compressional- 

 raref actional motions, has been treated as a fluid. 



Direct Effects of the Primary Disturbance. 



41. Considering next the motion of the aether constituting 

 the primary disturbance, and the directly resulting motion 

 of matter with respect to the aether, the question arises : 

 what phenomena, if any, would present themselves to our 

 observation if such motions were actually taking place ? 

 In the first place, bearing in mind § 12 above, it will be 

 evident that a bodily vibratory motion of the aether, of 



