in Singly arid Doubly Refracting Media. 335 



their distance from the position of equilibrium. We will assume 

 as more probable that it depends on both. Accordingly this 

 force also will certainly in part present itself as a deformation- 



d 2 p / 

 force E' -rr, but of course as a deformation-force of the cor- 

 poreal particles displaced by the vibrating aether. To this 

 will then be added a directly acting displacing force, which, 

 as it is proportional to the existing excursion, may be denoted 

 by K//, and of which it remains uncertain whether it proceeds 

 immediately from the pressure of the aether particles or is only 

 indirectly produced by the reaction of the corporeal particles. 

 It is self-evident that e is positive, while the sign of the rest of 

 the forces is at first undetermined. And since the course of 

 the dispersion is, as we have intimated, independent of the 

 state of the aggregate, the contents of W and K do not refer 

 to those forces which in solid bodies hold together their con- 

 stituent parts, but much rather, analogous to the behaviour of 

 vapours endowed with rotation-polarization, to the forces be- 

 tween the constituents of the molecules themselves, or, in fine, 

 to the reciprocal forces between the aethereal and corporeal 

 particles, inasmuch as they depend on the quality and form of 

 the latter. We should therefore have, for the motion of the 

 corporeal particles, 



m '%= w %^' a>) 



The only remaining difficulty consists in the treatment of 

 the functions E, E', K, which, as is acknowledged, must con- 

 tain implicitly the vibration-period or wave-length. Here the 

 plausible assumption presents itself, that the three preceding- 

 forces, conditioned by the presence of ponderable particles, 

 and flowing from their reciprocal action in equal degree with 

 the aether, are rigorously proportional to one another. Corre- 

 spondingly we will put 



E = «e, W = ue r , K=zu/c, . (2) 



where e, e f , k denote constants which are given with the qua- 

 lity of the molecular constitution (or the density), and « alone 

 depends on the motion (consequently on the dynamic condi- 

 tion) of the medium. Hence comes, definitively : — 



d 2 p , ,d 2 p 



,d 2 P ' ,<p P ' , 



