726 Messrs. H. E. Ives and E. F. Kingsbury on the 



increases brightness flicker. It follows from this theory 

 that the point of setting in a flicker photometer for greatest 

 sensibility is that at which decrease of speed causes " colour 

 flicker," and change in the relative proportions of the two 

 colours causes " brightness flicker." Fig. 10 exhibits dia- 

 orammatically in a somewhat different way the same idea, 



Ear. 10. 



Conditions producing " colour flicker " and *' brightness flicker." The 

 distance between x and /3 represents the hue difference between suc- 

 cessive phases at various speeds. This hue difference becomes less for 

 any speed as either colour predominates, i. e. colour flicker is at a 

 maximum at the position of equal brightness, when brightness nicker is 

 a minimum. 



