p. LECOMTE DU NOUY 



759 



First Series of Experiments. — The observers were protected by 

 a curtain from all light, and waited until their eyes had become 

 quite sensitive before making the experiments. 8 minutes in ab- 

 solute darkness seemed to be sufficient for men. These first figures 

 will show the difference between the rapidity of adaptation of men 

 and women. Wave length 0.55 fj. (Tables III and IV). 



TABLE IV. 

 Women. 



Obviously, for women the differences are so great that a mean 

 value would have no significance at all. 



It was found that it took over 20 minutes for observers J, M, 

 and O to reach the same sensitivity as men, viz., less than 7 X 10"'. 

 As Langley does not give any precision concerning the time of adapta- 

 tion, we may compare his figures to the mean value found for men: 



ergs 

 sec. 



Langley (0.55 /x), 5.55 X 10- 



We found sHghtly larger figures: 



J ,0.7 

 0.4 

 pO.8 

 Jo.4 



5.85 X 10 



_9 !£E 

 sec. 



ergs 



5.1 X 10-9 i^ 

 sec. 



But after more than 20 minutes in the dark, the eye becomes more 

 sensitive still, and we obtained the following figures (Table V). 

 These figures are smaller than those given by Langley, but as he 

 did not state the length of time which the eyes of his experimenters 



