SELIG HECHT 



123 



university trained. Most of them were teachers; the rest were pro- 

 fessional people acquainted with scientific matters. They were all 

 interested in the experiments, and did all they could to follow instruc- 

 tions in the method of making observations. 



The nature of the data which I secured with these people is well 

 illustrated in Fig. 2, which gives the results of two experiments on 

 the same subject made four days apart. Each point represents a 

 single reading with one eye in the manner described. The ordinates 



• Leffec/e „ , 



o Riohteue 



A Leffeus ^ , 



-^ 



^ 



o zoo Aoo 600 800 /ooo /zoo 



duration of darh adaptation — seconds 



Fig. 2. Results of two experiments made 4 days apart with the same subject. 

 The points are single readings as explained in the insert. 



record the illumination emitted by the red cross when it just becomes 

 visible. The data are not corrected for changes in the pupil area. 

 The figure shows very clearly that the experiments were conducted 

 under conditions that give reproducible results. I made a number 

 of these dupHcate sets on several individuals, and all show the same 

 degree of coincidence in the position of the points. 



In the results as a whole there is a certain amount of variation 

 from individual to individual. One subject may be consistently 



