234 



THE ROYAL SOCIETY OF CANADA 



Figure 5 



2 aWc.s uf Data. 



In Tables VII to XIV "a" indicates the angle between the planes 

 of the nieols for each observation; "Cos^a" the intensity of the light 

 upon which the observation was made. In Tables IX and XI "Least 

 perceptible decrement" is the amount by which the intensity of the 

 light "Cos^a" was diminished in effecting a change in the sensation 



