Photometry of Lights of Different Colours. 



847 



The enormous area of the visual acuity curve is at once 

 explainable as due to the chromatic aberration of the eye. 



Fig. 1. 



Simultaneously Obtained Spectral Luminosity Curves by four 

 Photo metric Methods. 



— ° visual Acuirr I 



* EQUAL/Tr OFBR/gHFNESS 



FLICKER 



. CRITICAL FREQUENCY 



"WHITE" COA/TWUOUS SPECTRUM 

 REFERENCE STANDARD 



It has been shown by Bell * and by Luckiesh f , in work 

 published since the first of these papers was written, that the 

 defining power of the eye is much greater for monochromatic 

 lio-ht than for complex light of the same hue. It may thus 



* L. Bell, Elec. World, vol.lvii. p. 1163 (1911). 

 t M. Luckiesh, Elec. World, vol. lviii. p. 450 (1911). 

 3K2 



