in Singly and Doubly Refracting Media. 417 



the latter, analogous to what was obtained before, 



Z*=W\ > n - 1= -^A?> ' ' ' (18 > 

 L 2-1 



if we generalize as much as possible by introducing the symbol 

 of summation. 



8. The problem that now remains is, to express the 



values -,, — , = L 2 as functions of the variable molecular dis- 

 e 77 k! 



tance r ; while m! and m remain, as masses of cubic space, 

 independent of any orientation. 



It may first be asked, Which linear density of the corporeal 

 structure comes into consideration in relation to the resistance 

 to the vibrations of the aether ? that in the direction of the 

 giving- way of the corporeal particles, or that in the direction 

 of the ray, or that in a third direction perpendicular to the two 

 mentioned ? We shall unhesitatingly select the first. 



Further, e 1 and k! both depend generally, complementary to 

 each other, on the form, the chemical quality, and the forces 

 of the molecular combination. It hence appears probable that 

 every alteration "of density will affect the one quantity as well 

 as the other. In fact the result of my previous memoirs is, 



e f 

 that the quotient - = L 2 is not merely independent of the 



cubic density for gases and liquids, but also has an identical 

 value for the two or three principal indices of refraction of 

 anisotropic media. On the other hand, it is different for calc- 

 spar and aragonite notwithstanding their similar chemical 

 composition. We shall therefore regard our constant L 2 as 

 connected solely with the optico-chemical quality. 



The quotient -„ on the contrary, as the ratio of two quan- 

 tities belonging to one another, of deformation of the setter 

 and the corporeal particles, will necessarily change with the 

 molecular distance r of the latter. Now, since for r infinitely 

 great (which of course implies that mf = 0) nis equal to 1 and 

 an increase of n' is united with the diminution of r, there- 

 fore - will be inversely proportional, at least approximately, 



to some power of this distance. We select, for obvious reasons, 

 the first ; and if we thus put 



?4 < 19 > 



Phil. Mag. S. 5. Vol. 2. No. 13. Dec. 1876. 2 E 



