Reflect ed-D iff racted and Diffracted-Reflected Rays. 51 



The case 0>r in the present paper is not of much experi- 

 mental interest. We may therefore omit it here. For the 

 case of r>0 we shall have successively, and for the total 

 interferences RD, DR, equation (8), 



dX 

 dfju 



dr 



dn 



dfju 

 da 



X cos dO 



sin r— b sin dn^ 



tan r cos d6 



a 



sin r — b sin 



an 



ajx cos d0 

 sin r — b sin dn 



dd f _ p cos #(sin r — sin 0) dO 

 dn ~ cos 0'(sin r — b sin 0) dn ' 



and finally corresponding to equations (6), (7), (8), 



(ii) 



(12) 

 (13) 

 (14) 



dO' cos \(sin r — sin 0) 

 dn ~ 2e cos 0' b — sin r sin ^ ' 



• (15) 



<f#' cos \(sin r — sin 0) 



dn ~~ 2e cos #' 6 cos r cos -f a sin r tan r cos ' 



• (16) 



d#' cos \(sinr — sin 0) 





dn 2eco$ 0' 6(1— cos (r — 0) ) -fa sin r sin 0(1 — cot tan? 1 )' 



the last term in the denominator being corrective. Here 

 d0' jdn is the observed angular deviation of two consecutive 

 fr in fires. 



(") 





5. Normal Incidence or Diffraction, §c. 



For the case of normal incidence i—r = 0, the equations 

 corresponding to (6), (7), and (8) take a simplified form, and 

 are respectively 



d0Q eos# % . A ,„ ... 



r ,\sm#, . . . . (Id') 



dn 



d0l = 



dn 



mj = 



dn 



2be cos 

 1 



j X sin 0, 



2be cos 0' 

 cos X sin 



2be cos 0' 1 — cos# 



(16') 



(18') 



If 0' = 0=O for normal diffraction, which is particularly 



E 2 



