134 



BARUS— ELLIPTIC INTERFERENCE 



[April 21, 



is the length of the prolongation of L' between the gratings we may 



write in succession 



(i) d = NDcosi 



(2) f=^cseci, 



( 3 ) o = ND sin / — c sec i, 



(4) tany = a/d, 



(5) C^=ND cost sec y, 



(6) b = csm(i^e — y). 



Fk;. 5. Diagram. 



cr 



To these should be added 



(7) dN/dc = t2ini/D. 



Hence after removing y and arranging 



nX = A^D {cos i sin (/ + 0) — sin / cos ( i -{- 0) — sin i] 



-\- csec i{i -\- cos {i -\- 6) ), 

 which reduces to 



or smce 



iK^^ND (sin 9 — sin /) -\-eseci(i + cos (i^6)), 



sin ■/ — sin ^ = X/D, 



