of Reflexion of Polarized Light, 



519 



This angle should, according to received ideas, coincide with 

 the polarizing angle, or its tangent should give the refractive 

 index; the tangent of 55° 1' is 1*4290, which is very different from 

 the refractive index found directly, which is 1*6229; but I have 

 repeatedly observed the refractive index found by reflexion differ 

 considerably from that found by refraction, and believe that the 

 law of Brewster is only approximate. 



In order to ascertain this point, I made the following experi- 

 ment on another rhomb of glass having the same refractive 

 index as that used in my former experiments. 



Table XII. • 

 Azimuth of polarizer =86°. Red sunlight. 



The refractive constants of tfiis rhomb were determined with 

 care, and found to be — 



Refractive index of extreme red . . . 

 Refractive index of extreme violet . . 

 Refractive index of red used in experiments 

 Dispersive power 



= 1-6190 

 = 1-6555 

 = 1-6230 

 = 0-0573 



The comparison of the values of <^ and j- from this table with 



the corresponding values in Table VIII. is satisfactory. 



The principal incidence is 54° 53', which agrees with the 

 values in Table XI., and confirms the deduction I have drawn 

 from that table. 



The observations contained in the preceding tables were made 

 during the course of the past summer, which was very favourable 

 for such a purpose. I have repeated the more important obser- 

 vations many times, and by using strong sunlight have always 

 succeeded in obtaining the same results. I consider that they 



