374 H. M. JOHNSON 



G. P. L., the astronomer (table 9); and also by comparison of 

 the latest stage of performance of subject L. S. (table 7) with 

 the preceding stages. 



As to the dependence of the dynamogenic value of light on 

 wave-length, intensity, or on the distribution of either or both: 

 it would certainly seem that the question is open and important. 

 The present writer feels, however, that the work-method is not 

 the most appropriate one to its solution. The direct measure- 

 ment of thresholds or of the time required for perception or for 

 discrimination under the conditions which one may wish to com- 

 pare permits of the accumulation of an enormously greater num- 

 ber of measurements in the same period of time than can be 

 obtained by the work-method. As the effects sought can not 

 be readily isolated from those of other agencies, they can best be 

 demonstrated by methods the results of which accumulate rap- 

 idly and lend themselves to statistical treatment. 



In conclusion, I wish to acknowledge indebtedness to Dr. 

 Buford J. Johnson for a critical examination of this report in 

 manuscript; and for suggestions which materially improved the 

 last section. This of course does not imply that she assents to 

 the entire passage. 



