48 COLOUR VISION 



The flicker curve was taken with Prof. W. Watson's flicker apparatus 

 used in conjunction with Sir Wm. Abney's apparatus. The conditions 

 were arc light with positive carbon horizontal, current 18 amps., 

 D line - - 1 metre candle, patch 1 sq. inch observed at a distance of 3 ft. 

 It will be noticed that the flicker maximum is less than the equality 

 of brightness maximum, and in the proportion 92'5 : 100, but Ives's 

 results (v. p. 96, Figs. 38, 39) show almost complete coincidence. 



The most striking confirmation of the general accuracy of these 

 methods is that the luminosity values thus found agree with their 

 periphery values. We shall see later (p. 67) that at the periphery of 

 the retina colours of moderate intensity cease to convey the impression 

 of colour and appear white, so that the periphery values are not com- 

 plicated by the intrusion of the colour factor. Polimanti 1 confirmed 

 this fact for the flicker method. 



1 Loc. cit. 



