108 PHYSICS OF ETHER 



after the model of a viscous solid would always contain the viscous 

 terms, so that even for the high time-rates of light-waves there would 

 be dissipation however small. Such a condition, it can be proven, 

 would give coloration to the remote members of the stellar system; 

 a fact inconsistent with observation. On the other hand, a soft vesic- 

 ular solid like gelatine may not necessarily contain the time-factor, 

 and yet be so soft that dislocation may occur even with constraints 

 of the order of aberration, but not of the square of that order. Such 

 an ether without a time of relaxation factor would fulfill completely 

 the conditions of a luminiferous ether, if, as Stokes tried to show, it 

 could be reconciled with the phenomena of aberration and the motions 

 of the heavenly bodies. The method of double refraction shows that 

 a solution of gelatine of one part in a thousand is rigid, while at the 

 same time it appears as mobile as water, and its rate of flow through 

 small tubes does not vary largely from the same. This experiment 

 illustrates very markedly Stokes's example. When such a solution 

 is continuously dislocated between two surfaces in relative motion, 

 the same double refraction is present, indicating that the stress is 

 still active during dislocation. Also a metal, like copper, shows a 

 similar stress while being strained beyond its elastic limit. If this 

 takes place by slip or dislocation throughout the mass which, though 

 irregular, may give a mean uniformity for sensible dimensions, such 

 a medium might serve as our model. Any deviation from perfect 

 regularity in molecular distribution and activity we might anticipate 

 would give such minute irregular dislocations at the limit of elas- 

 ticity. Such a medium would thus transmit completely any dis- 

 turbance within this strain limit. 



It is difficult, however, to conceive of the transmissions of a dis- 

 turbance across a surface of dislocation. For many ordinary media, 

 we should expect at such a surface total reflection. If we suppose 

 such a transmission of disturbance, its mode is not apparent, even if 

 we suppose a thin lamina in rotational motion which would diffuse 

 at least a portion, if not all, of the incident disturbance. Similar 

 difficulties would arise if we assume the ether a solid which becomes 

 fluid under stress and thus allows bodies to pass through it (as, for 

 example, through a block of ice, as Fitzgerald suggested). While 

 such solutions may seem highly artificial and do violence to our 

 convictions, the consequences of a quiescent ether may, when fully 

 developed and tested, demonstrate its impossibility and command 

 a more extended examination into the structural qualities of an all- 

 sufficient medium than the single case of an essentially vesicular 

 medium like jelly brought forward by Stokes and in a different form 

 as a contractile ether by Kelvin. The theory of Fresnel of a quies- 

 cent ether in space presupposes a change of its density proportional 

 to /i 2 within a ponderable medium, and a convection coefficient 



