-Production of Circularly Polarized Light. 523 



the loss of light by absorption' is small and the dispersion 

 low. Equation (5) becomes 



where u= - K/AOK for the D. line, 

 r l*p03o 



and ,« , = cos 2\Jr, where yjr is the angle of the rhomb. 



Ench of the values of -^ is above the critical angle, which 

 is 41° 42' for uviol glass. Both at yfr = 74° 38''2 and 



' # g 777- 



-\fr = 42° 34'*8, we get relative retardation amounting to — 



for each reflexion, and the larger value is chosen since then 



A is practically independent of variations in \. For fused 



quartz, of refractive index 1*5533 for the D x line, the larger 



value of f is 75° 4'«5. . 



If we consider an interval comprising a range of X equal. 



to that between the C and F lines *, and call the increment 



or decrement in fi corresponding to it + da (//,< 1) we can 



make an estimate of the variation in A for any \ from the 



lir . 

 value -Q- which obtains for the Dj line. We have from (6), 



o 



dA= ^±.r - 1 r -- TT - . 2 , \ ,. U'.fr. (7) 



77T 1 . o , LL 2 . COS z \fr Sin 2 ^|r — u* COS^i/r f 



utan-^ Isin 2 ^ — " a . t r~ tj 



8 7 cos 2-\Jr 



Here ^=74° 38', 

 1 



for Dt line 



S fnr nviol . 



l '^L V for uviol glass. 



da =+0-00781 



C — F 



Substituting we find r/A =+0°'052. 



c — f 

 Therefore for four reflexions, the extreme phase-difference 

 for the — F interval considered above will be 



4. r/A =0°-208. 



C — F 



* The total interval, for which §A is calculated comprises an interval 

 A — \ on each side of the D t line, i. e. an interval of approximately 



1700 A.U. on each side. 



2 M 2 



