E. E. Wright — Measurement of Extinction Angles. 361 



Fig. 4. 



.4-0. 



88° 8T 9 0° 91° ^ 



Fig. 4. — Intensity curves for crystal plates at angular distances of 0', 15', 

 30', 45', and 1° from plane of polarizer, the analyzer being revolved about 



2~t 

 axis from 88° to 92' with plane of polarizer, sin- -=- (} ' — a') = K = 3/4. 



Curves calculated from the formula 



I 1= l/8 [4+cos2o + 3 cos 2 (q-26) ]. 

 As in fig. 3, the heavy curve indicates the relative intensity of emergent 

 light for different positions of the crystal plate (6 ranging from 88° to 92", 



or —2"" to +2°) under crossed nicols (0= -=-) and K=3/4. Calculated from 



a 



the formula 



I, = 3/8 (1 + cos 40) 



heavy curve indicates the relative light intensity under crossed nicols 

 (6='—) for different positions of the crystal plate (6 ranging from 88° to 92° 

 or —2"- to +2'') and K = 1. Calculated from the formula 2 Ij = 1 + cos 40. 



