applying to Light under the action of Magnetism. 475 



to the explanation of crystalline rotation of the plane of polari- 

 zation. But it does not agree with the phaenomena of glass, 

 &c. under magnetic action ; and for this case new equations 

 must be sought. 



The equations which I offer as competent to represent this 

 case are, 



d*Y d*Y „ dZ 



which are to be verified in the same manner as those applying 

 to the phaenomena of quartz, &c. 



Thus, in the first experiment, for Ray No. I., 



Y' = a . cos 

 Z' = a . sir 



2jt/ x\ a 4tt 2 /1\ 2 2tt/ x\ 



+ C _.«.cos-(^-j, 

 47r 2 . 2*7 x\ a 4w 9 /1\* . 2tt/ x\ 



The equations become 

 4jr 2 



r2 



-.a. cos- 



+ L> . — .a. sm 



T 



which agree in giving 



w 2 = 



i+f c 



2w 



For Ray No. II., 



Y<' = J.cosi? («-*-), 



and the equations become 



-C-5.cos T ^-^-), 

 2K2 



