Polarization Flicker Photometer. 37& 



If this hue difference is the least perceptible one, then we 

 define the hue difference discrimination fraction by relation (7). 

 We shall use the symbol 8& for this fraction. It will be 

 noted that this definition is exactly parallel to the definition 

 of the brightness discrimination fraction, which is 



This will be symbolized by 8 B henceforth, to avoid 

 confusion. 



Applying now (6) and (7) to (5), we have that the hue 

 at one phase is 



n l ; 



£=<s. 



at the other phase it is 



H 2 = 2 



from which 



2 2 + e V2K X —e V 2^ 



In order to handle this expression we may, as a close 

 approximation, take Kj equal to K 2 , defining it in terms 



of the mean of the critical speeds of the two colours, C ° B & ? 

 by the relation ^ 



V2K_ V 



'°4 



(10) 



We get then finally 



,gS H = lo g 2_ x / 2 ^logf-, . . (11) 



