SCOTOPIA OR TWILIGHT 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 



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. 0. V. 5 



