196 



E. S. Ferry — Persistence of Vision. 



The values given in this table as well as in all the succeeding 

 tables are not averages of a number of observations, but are 

 the values of a single set of readings. The third and fourth 

 columns are the values obtained by two observers who had 

 only used the apparatus for about an hour, and are hence less 

 reliable than the values in the second column which have been 

 many times repeated. The curve platted from the values in 

 the second column is shown in fig. 1, curve 8. 



<*30 4?0 WO V90 



330 330 370 390 6/0 630 650 670 690 



Duration of Impression of normal eye for different colors and different inten- 

 sities. 



The fact was noticed with some surprise that on different 

 days the observations were nearly identical, if the eyes had not 

 been strained or made more than normally sensitive by re- 



