AN INTERRUPTED MEDIUM. 537 



2Y-a_ 2b . 



7-Y : ~ST6 



2 (Mr) - (l-*)'' 7 " 7 ^ t-r + ra(a-tfT*))=0 (4.) 



(5.) 

 >s0<(7-y)=0 . (6.) 



and IV. . .......... (7.) 



From (1.) and (5.), 



/i 6 ,. 

 = - Z 



a a ,. . 



*-!> ('-*> 



From (2.) and (3.), * 7 + Y = o 



= 

 From (6-), 7-Y = - 



* 



a j .a 



COS J w I* 



a + b i*-r> 



-A ^2 - r^: nearly 

 4 a o i cos <p 



2 a b i cos 2 <_ 



_ a a ,. \ _ a ' i r 



^ ~ 2 + 2 a 6 cos 2 < ^ ~ 2 "*" 2 6 cos 2 </> 



_ a 6 . , a ir 



~ 2 2 a b i cos 2 d> 2 2 z cos 2 ^> 



^-s a (f + r) (o + 6) r O 



IV. gives 



2ab i cos 2 



(o + b) cos <i> -. a ~ra - j- ., j 



r z+r abt* cos * , , N sin- O) 4 z . 



-J- 7 -TTJ-. r T (1 *V - I y = 



(a + o) (z r) cos <p a + 6 

 2 a b i cos 2 ^) 



or a bicos* (b a (i r) H ' 5-3 (1 s) x-%- T (' /) =0 



cos 2 < ^cos-'cpa + d^ 



a b cos 4 



