122 



THE NATURE OF FOVEAL DARK ADAPTATION 



An observation is never verified immediately. Once the subject 

 has announced that he sees the red cross, the lamp is at once turned 

 off. If an observation is questioned either by the subject or by the 

 experimenter, it is repeated later after a fresh light adaptation, and 

 the subject is unaware of its repetition. The practice of verifying 

 a reading within a second or so involves a number of fresh sources 



TABLE I. 

 Record of a Single Experiment on Dark Adaptation of Fovea. 

 Subject, M.G. 9 



Horizontal lines between measurements indicate a period of 5 minutes 

 light adaptation. 



of error such as retinal fatigue and refractory period which are bound 

 to influence the final result (cf. Cobb, 1919, p. 437). I, therefore, 

 consistently avoided such a method. 



IV. 



1, After several preliminary experim^ents, I made a final set of 

 m.easurements with fifteen subjects. Of these, eight were men and 

 seven women. Their ages varied between 28 and 35 years. They 

 were all of more than ordinary intelligence, all but one having been 



