of a Stream of Light passing through a Crystalline Plate. 87 

 whence writing n + \di - - for n, tbe equation becomes 



/ sin a i\ . 7 sin 3 i 



-H <fc+<Ji 3 ]' 263 ' 



sn 2 sn 



"where 



2 1_ 



C ~ - Ji, <* - ^ 



-^ 8 -c 8 . cos w, 

 If, (a--Z>-)(6 2 -c- 



'i, - ^ { aV + i ^-^(a 2 -6 2 ) (6 3 -c 2 ) 



L'jt us, in the first place, neglect the coefficient of n t then we 

 liavc 



sn 





V v V" 



+ [* r{ V4*^V<r-*>-ti'*g 







sini / f (6 4 aV) s , 6 4 + aV <2 \ siir q 



A / 1 ~r i T^ v T^T 7~T'> >>\ "o 7"o COS W ? ~ 



v V t46 3 (a 4 6 2 ) (/* c') l z J v- J 



iind the roots are (TT -}-/>), (T />), where 



Sln^ Bm 

 *_ +J% 



and writing for shortness 



P = (a'-W--^), Q = i(a 2 -6 2 



\\G have 



