158 



WILLIAM L. DOLLEY, JR. 



TABLE ^-Concluded 



Vanessa than continuous light is in harmony with the results ob- 

 tained in experiments upon the human eye which have been de- 

 scribed previously. If McDougall and others are correct in their 

 contention that a given light acting for a given length of time 

 upon the human retina appears brighter than the same light act- 

 ing for a longer period, it is to be expected that intermittent 

 light of a certain flash-frequency will have a greater stimulating 

 efficiency upon the human eye than continuous light. This ex- 

 pectation is confirmed by the results of the investigations of von 

 Kries and Brlicke, who maintain that a disk upon which are 

 painted black and white sectors when rotated at a certain rate 

 appears brighter than when rotated at other more rapid rates. 

 This is also confirmed by the results obtained by Hyde and 



