204 



K <S. Ferry — Persistence of Vision. 



regions of the spectrum, that the curves of retinal persistence 

 of the dichroic and the normal eye will be of the same form. 



This appears to make the evidence conclusive that color is at 

 most a slight factor in retinal persistence, and that luminosity 

 is the all-important function. 



V3S 150 IK m 3/(5 liO 350 570 190 t'O tip HO t7C 190 



Duration of Impression of Green-blind Eye. 



The law previously derived connecting duration of impres- 

 sion and luminosity of lights of the same color can now be 

 made general and independent of color. This approximate 

 empirical law can now be expressed in the concise form — dura- 

 tion of retinal impression is inversely proportional to the 

 logarithm of the luminosity, or in the form of the equation 



D 



1 



Jc • loc I 



It is interesting to note the similarity of this with Fechner's 

 law* connecting the intensity of stimulus and the sensation 



* Revision der Hauptpunkte der Psychophysik (Leipsig). p. 184. 



