Structure for the Ether. 171 



of wave-propagation comes out -J\/2 or "47 o£ the average 

 velocity of turbulent motion (see Phil. Mag. for October 

 1887, p. 350). In all investigations the two velocities 

 come out of the same order: and in FitzGerald's collected 

 papers, No. 53 and No. 91, the two velocities can be identical 

 tor a certain arrangement of turbulence (cf. pp. 259 & 256). 

 On [age -457, FitzGerald expresses his tentative opinion that 

 the hypothesis that " the ether is a turbulent liquid has great 

 possibilities underlying it." And, again, on p. 486, "there 

 seems very little more besides interpretation of symbols to 

 make a turbulent liquid a satisfactory explanation of the 

 structure of the ether/'' Some assurance of stability may 

 also be needed. 



Many things show that any granular structure which may 

 thus be possessed by the ether must be of a fineness incom- 

 parably minuter than any dimension associated with the 

 material units on which we can experiment. In fact, the 

 ether may quite well contain a linear dimension of the order 

 pQ-30 or X0~ 33 centim., and an energy of 10 30 or 10 33 ergs 

 per cubic centimetre (Phil. Mag., April 1907, p. 493). The 

 calm self-sufficient way in which it sustains all our stresses, 

 and transmits all our energies, shows that anything we can 

 impose upon ether is as far from perturbing it, or calling out 

 even second orders of small quantities, as the slight bias of 

 an ordinary draught of air is from perturbing the normal 

 motion of the molecules which compose it. A bullet in 

 air and an electron in ether can, however, attain perturbing 

 velocities ; and the fact is bound to be instructive when 

 increase of mass with speed is fully assimilated and its 

 mechanism understood. As said on p. 490 of the Phil. Mag. 

 for April 1907, retaining the meaning but slightly improving 

 the wording : The reason for the concentration of magnetic 

 intensity at the equator of an electron, moving with something 

 approaching the velocity of light, is that the flow associated 

 with and indeed constituting the magnetic field is then no 

 longer a small fraction of the intrinsic rotational velocity of 

 the ether itself (see also loc. cit. p. 494). 



To explain gravitational and other facts, we must assume 

 that the very formation or existence of an electron sets up a 

 radial strain or tension all round it, varying as the inverse 

 distance, and likewise reduces the circulatory energy in its 

 immediate neighbourhood ; not necessarily causing any 

 change of density, since electrostatic facts (notably the 

 Cavendish experiment) show the ether to be practically, and 

 probably actually, incompressible, but affecting its elastic 

 or dielectric constant in such a way as to modify the velocity 



