Iheory of the Flicker Photometer. . 725 



A . /- 



The maximum value for ^ is given by cos (cat — v / o>') = l, 



the minimum by cos (wt— v / ft )) = 0. 



Substituting various values of co the data plotted in fig. 9 

 are obtained, where as before a represents the phase in which 

 light A predominates ; fi that in which B predominates. 



Fig. 9. 







y^ 



'^^^^v 



/Just Nohceable-j^^ 



"^0yy 



/ Hue D/fferencjt^ 







I Jr^^r 





S ^^^ 



/ s/ oi = 





/ s^ ^^^~~^* 





1 5 



* I 8 







'Bo =0 





T^elati/e Intensify of T/luminihor} 



-from the two Cajr^recf //jhfs 

 or? photometer 



Diagrammatic representation of the variation of hue difference at suc- 

 cessive phases of alternation, as speed and relative intensity of A and 

 B are changed. Ordinates show relative quantities of A and B„ in 

 mixtures at a and 0, &c. a, 0, *', 0', Sec. are extreme hue differences 

 for various speeds. The higher the speed the less the hue differences. 

 As the intensity of either light is increased over the other, hue difference 

 in the successive phases decreases. 



From left to right the relative proportion of light A is 

 shown; from right to left that of B . Any pair of similarly 

 lettered curves represent the hue difference for a given speed 

 and for a given ratio of A to B . Thus at the left end 

 where A alone is present, the hue at botli maximum and 

 minimum is A ; at the right end it is B . At the middle 

 point occurs the greatest hue difference, decreasing in either 

 direction. Moreover, if the speed is increased the points a 

 and ft draw nearer to each other. For infinite speed the 

 two curves coalesce. Any change in the ratio of A to B 

 from that at the middle' part decreases the hue difference 

 between a and /3, and hence reduces colour flicker, but 



