﻿common Light obliquely incident on parallel plates, 211 



which is the same as the value obtained for the relation of pola- 

 rized to natural light when a ray of common light is refracted 

 through the plates. 



Assuming a value of /Lt = l*5 for crown glass, we may form a 

 Table of the degrees of polarization for different angles of incidence. 



Table for /x = 1*5 (crown-glass). Angle of complete polariza- 

 tion = 56° 18' 36", log /*= '17609, log7 = '84510. 



0< 



10°. 



15°. 



20°. 



22° 30'. 



25°. 



30°. 



35°. 



40°. 



. p _ 

 n+jp 



For ^=1-513 



•0107 



•02443 



•04430 



•05683 



•07111 



•10498 



•14745 



•19845 



P _ 

 n+p 



•01103 



•02504 



•04540 



(•05813) 



•07267 



•1076 



•1509 



•2029 



Probable values for <«= 1*54. 















P - 

 n+p 



•0116 



•0263 



•0476 





•076 



;113 



•158 



•212 



0. 



45°. | 50°. 



55°. 



56°18'36" 



60°. 



65°. 



70°. 



72°. 



P _ 

 n+p 

 For /* = 1-513 



•25786 



•32383 



•39231 



•40984 



(For 



56° 32'); 



•4560 



•50530 



•5309 



•53305 



P _ 



•2635 



•3305 



•3999 



.-4204 



•4642 



•5139 



•5394 



(•5416) 



Probable values for /x — 1-54. 















. P - 1 -275 1 -344 



•415 





•481 



•531 



•556 





n+P 









From the Table, for the values of we see that for four 



n + p 



plates the proportion of polarized light in the beam which passes 



through the plate still goes on increasing when the incidence 



becomes greater than the angle for complete polarization, and 



that at about 72° it attains its greatest value, when there is 



about 53 per cent, of the light polarized. 



I have also formed a Table for yLt = l'513, of which the results 

 are given ; and from these we can derive close approximate values 

 for the proportions of polarized light for values of //, not differing 

 much from these values. 



The probable values for //, = 1*54 are given in the Table. 



If we employ the four plates as a depolarizer to determine the 

 proportion of polarized light in the incident beam by reducing 

 the light to its ordinary unpolarized state, then (as before ex- 

 plained) the proportion of polarized light in the incident beam will 

 be given, for any angle of complete depolarization, by the value of 



~— for that angle, 



n+p p 8 



