SCOTOPIA OR TWILIC4HT VISION 



65 



and other luminosity curves. With 0'2 foot-candle of parafoveal 

 illumination the curve is the luminosity curve of the photopic eye. 



Fig. 22. " Extinction of light " curves for different degrees of light adaptation. Abscis- 

 sae, wave-lengths ; ordinates, logarithms of the intensities of the light. (Abney.) 



100 



60 



Fig. 23. " Persistency of light " curves corresponding to the " extinction of light " 

 curves for different degrees of light adaptation. Abscissae, wave-lengths ; ordinates, 

 reciprocals of extinction values. (Abney.) 



As the parafoveal illumination diminishes the curve shifts towards the 

 violet end, so that the scotopic curve for complete dark adaptation is 

 finally reached. 



p. c v. 5 



