200 E. 8. Ferry — Persistence of Vision. 



The form of this curve suggested the possibility of lumin- 

 osity bearing a reciprocal relation to duration of impression. 

 This idea was tested in two ways. First, one particular region 

 in the spectrum was chosen and its luminosity varied so as to 

 be equal to the luminosity of different parts of the normal 

 spectrum as given in Table III ; the duration of retinal 

 impression was then measured for these luminosities and gave 

 the following values : 



Table IY. 



Duration of impression for a single color having its luminosity varied so as to 

 equal the luminosities of different parts of the normal spectrum. 



Corresponding to Given duration of 



Relative luminosity. wave-length. impression in seconds. 



1-86 -435 -0333 



13-89 -480 -0227 



28-28 -510 -0200 



50-00 -540 -0161 



89-25 -570 -0143 



100-00 -589 -0138 



83-25 -615 -0143 



54-37 -645 -0161 



11-16 -6R4 -0192 



The luminosities taken in this table are the same as in the 

 normal spectrum that gave the values in the fifth column, 

 Table II. A comparison of the third column, Table IY, and 

 the fifth column, Table II, indicates that luminosity is the 

 important factor in persistence of vision. To farther test this 

 deduction, observations were made on the duration of impres- 

 sion for different colors of the normal spectrum, when each 

 color was brought to the same luminosity. If the above 

 deduction is valid, then if each color is brought to the same 

 absolute luminosity, the retinal persistence of each color will 

 give the same value. The values obtained are given below. 



Table Y. 

 Duration of impression when each spectral color is brought to the same 

 luminosity. 



Wave-length. Duration in seconds. 



•510 -0151 



•540 -0147 • 



■570 -0149 



•589 -0147 



•615 -0147 



•645 -0147 



Duration of Light Impressions on Color-Blind Eyes. 



As a still farther test of the theory that retinal persistence 

 is practically independent of color but depends principally 



