372 



H. M. JOHNSON 



TABLE 9 

 Comparison of daily performance in light (P L ) and in darkness (P D ) 



* Excluded from average of individual's results by Chauvenet's criterion. 



The daily results obtained for the several subjects individually 

 are shown statistically in tables 4 to 9 inclusive. The small 

 number of observations made on some of the subjects is due to 

 their lack of availability; and the irregular rate of improvement 

 with practice, found in some cases, is due to unavoidable inter- 

 ruptions, most of which were occasioned by illness of the subjects. 



DISCUSSION 



The experiment shows that a minority of the subjects, and the 

 group as a whole, gave a better performance in the light than in 

 darkness. As the greatest portion of time and effort involved in 



