H. XAGAOKA. 



b ô «-1 



n iyr m CQs(^ m -d) __ e iyjLcos~ y «>/' cos ('" a - £ ) 



where 



/' — V a2+ rt& cos "ô" + -^r 



a mn (/9+ S) + — sm f ß+ -77) 

 tg s = £ p ^- . 



a co.s 09+0)+ — cos f /9+ — J 



Thus the expression for the intensity of the diffracted light 

 becomes 



= n s (j°( r />)J(^) 2 



The position of dark lines due to such distribution of the openings 

 will be given by the roots of J e (Tp)=o. With perpendicular incidence, 

 the polar equation to the curve of zero intensity is 



J p + qcos — 



where p = a- + — - , q = ab, 



and h is a constant proportional to the roots of J°(yp)='o. 



By making a — o, we return to case II, which can therefore be 

 considered as a particular case of that discussed in III. 



