ON LIGHT. 



379 



each 54 37', and a ray p q, polarized in a plane 45 

 inclined to the pl'ane of the section a b c d intromitted 

 perpendicularly at tlie face a b, so as to be reflected inter- 

 nally at Q on the side a c, (in which case, the reflexion 

 being at an angle of incidence 54" 37' was total); and 



Fig. 16. 



again at R, at the same angle, on the opposite side d b, 

 it emerged from the face d c, along the line R s, circu- 

 larly polarized. In this case, the plane of reflexion 

 making an angle of 45, with that of original polariza- 

 tion, the reflected ray will consist of two equal 7'ays, 

 oi)positely polarized ; and of these the one in eadi act of 

 reflection has lost, in the other gained, an exact i6th of 

 an undulation, making an 8th difference at each reflexion, 

 or a quarter after both ; so as to emerge under all the 

 conditions of circular polarization. In consequence, 

 when analysed at its emergence by a tourmaline plate, 

 it is found to undergo no change of brightness on turning 

 the plate in its own plane, whereas the original ray, p Q, 



