from the Quantum Theory of Spectral Emission. 623 

 Supposing 



a-,/" = (a + /9)cos 3 0, 



£+,*• = ( a + /3)sin 2 0, 



we get 



dr = i 



[2i ^[74-/3- (a + ^sin'-^] 1 -^ 

 L Jo 



9 f*" d0 —1 



"- 7 Jo LOy+'«-(«-t-^)siii^"] 1 / a J 



~ (7 + /3) 1;2 K \2 ' V TT/?) J' 

 where E and K are the usual elliptic integrals, defined by 



B(w/2,*) = | 



Jo 



v /l_Psiir 



K(,r/2,*) = _=^ 



On the assumption that D is small, Ave have 



D(c 2 -A) 



^ 1 

 7= E + 



c» 



A D (c -A) 



Co 6C 2 



So that, expanding E and K and making necessary 

 approximations, we have finally 



dl ttD r _3A-j m 

 BD~ Ic^U 2 2 J' 



Also 



I =j'v/(c 2 -<r')-^ 2 ^ = »[«,•*-«,]. 



So that we have 



rioh , ro . 7r (2/y^L) 1 ' /0 2 N 



