﻿its Polarization and Colour. 



117 



the green of the sky is to be accounted for in this way I am not 

 able to say. Some, I believe, consider it to be entirely a contrast 

 effect. 



Appendix. 



Within a space T, small in all its dimensions against X, and 

 situated at the origin of coordinates, let a force parallel to Z, 

 and, so far as it depends upon the time, expressed by a simple 

 circular function, act on the medium. If £, ??, f denote the dis- 

 placements parallel to the axes at the point ocyz, and 



dx dy dz ' 



3 -"*+«*-*> § 





• (A)* 



d 2 d 2 d 2 

 where V stands for -j- 2 + 712 +T1 ^ ^ ancl ** are constants 



depending on the nature of the medium supposed to be isotropic. 

 For the luminiferous aether, Green has shown that a is to be 

 regarded as indefinitely great f. 



To represent the periodic force, write for Z, Ze int . Similar 

 transformations will then apply to f , ??, £, and 8 ; so that on 

 substitution in (A) and dividing out the common factor e int , 

 there results 





2—, 



■ = 0. 



(B) 



(6 2 v+/i 2 )r+(« 2 -^ 2 ) 



dS 

 dz 



-Z. 



Writing 



d?_ drj__ & 

 dy dx~™ s '' 



* Thomson and Tait's ' Natural Philosophy/ p, 530. 

 + Camb. Phil. Trans vol. vii 



