38 Sir Johii Conroy. [May 15, 



Table I. Silver Film, with Light polarised in the Plane of Incidence. 



Table II. Silver Film, with Light polarised perpendicularly to the 

 Plane of Incidence. 



The principal incidences and the principal azimuths were deter- 

 mined in the manner described in " Proc. Roy. Soc.," vol. 31, p. 486, 

 and vol. 35, p. 32, and the means of two sets of eight observations 

 each are given below. 



The values of the principal azimuths are higher than any obtained 

 before in the course of these experiments, whilst those of the 

 principal incidences are nearly the same as those obtained with the 

 silver plate polished with rouge ("Proc. Roy. Soc.," vol. 31, p. 493), 

 but considerably in excess of the determinations previously made 

 with silver films. 



Table III. 



Principal incidence. Principal azimuth. 



38' 44 07' 



75 

 75 36 



43 40 



Mean . , .75 37 



43 53 



