in Singly and Doubly Refracting Media. 517 



Accordingly equations I., II., III. may ivell be accepted as 

 the fundamental law of the theory of dispersion. 



Further, for anisotropic media we have, correspondingly, 



and 



W3*$*2)+*©*--) 



+'{*.®*3+3)^.©*---) 



«-,(g + ....)} 



+«(a' I r+a>'+a'»r)=o, .... (viii.) 



at least so far as the individual molecular qualities are grouped 

 around similarly situated axes. 



Here the first equation refers to both ellipsoids (<£, E), the 

 second only to Pliicker's direct one (<£). 



And, lastly, as regards circularly polarizing media, the above 

 differential equations need only, in accordance with a remark 

 of MacCullagh's, a simple additional term in order to take in 

 these media also. If we imagine in them a wave following 

 the Z-axis, we shall have as highly probable 



r»(S-l)Wg + S) + «(if+S) 



and, in addition, the integral-equations 



£=»cob2*t (£-£), i?=±^sin27r(|-|) . (X.) 



Here the amplitude-ratio &': %,, and with it also the refrac- 

 tion-index n, appear as independent of the sign of rj : we get 



, 1 «D±GZ 

 n 2 -l = Zj 2 > 



(IX.) 



L 



