Studies in Visited Sensation. 



469 



and white employed for continuous shading. In other words, their 

 physical luminosity was assigned in terms of the arbitrary scale. The 

 approximate means of forty observations are given in each case, the 

 variations from the mean ranging from + - 1 per cent, for full 

 blue to + - 3 per cent, for yellow. The following table gives these 

 approximate means — the brightness or sensation luminosity being 

 taken from the black-white curve through 12 per cent, mid-point, 

 which affords our scale of sensation. 



Physical Sensation 

 luminosity. luminosity. 



Full blue 9 per cent, white 44*0 per cent. 



Keel 18 „ „ 59-0 



Light blue 30 „ „ 71-0 



Orange 35 ,, ,, 74*5 ,, 



Yellow 72 „ „ 92-0 



The values so determined are indicated on the accompanying graphic 

 representation of the black-white curve. 



