1879.] some Experiments on Metallic Reflexion. 245 



polarization of the reflected light show which ray is retarded by the 

 plate ; and, to confirm this, the light transmitted by the nicol and 

 plate was examined with an Iceland spar, cut to show the rings. 



The azimuths are reckoned as positive when measured from the 

 plane of incidence in the direction in which the hands of a watch 

 move, to a person supposed to be so placed as to receive the light, 

 whether incident or reflected, into his eye. 



Plane of polarization 

 of incident light. 



+ 45 



-45 



Quarter Undulation Plate at A. 



Principal Principal 

 incidence. azimuth. 



80 10 +36 05 



80 21 36 35 



80 14 35 25 



80 23 36 05 



80 14 -36 50 



79 50 34 55 



80 05 35 40 



80 27 35 25 



Mean 80 13 



35 52 



Plane of polarization 

 of incident light. 



Quarter Undulation Plate at B. 



Principal Principal 

 incidence. azimuth. 



+ 45 



■45 



71 12 -34 40 



71 03 35 25 



70 51 34 25 



71 02 34 30 



71 +37 30 



70 22 .. 36 35 



70 07 36 35 



70 22 37 55 



Mean... 70 45 



35 57 



Similar measurements were made when the gold plate was in water 

 and carbon bisulphide. The values of the incidences differed greatly 

 according as one or other of the neutral axes of the quarter undula- 

 tion plate was in the plane of incidence, the measurements being 

 about as concordant as those made with the gold plate in air; the 

 means of these determinations were taken as nearest the truth. 



Since the retardation of the ray polarized perpendicularly to the 



