378 TITCHENER AND PYLE— ON THE AFTER-IMAGES [July 23, 



It does not seem necessary to print the full set of results, though 

 the data are at the disposal of anyone who may wish to consult 

 them. The net outcome of the enquiry, in Professor Baird's words, 

 is as follows : " In not a single instance did any stimulus give a 

 colored after-image at a retinal region where it gave an uncolored 

 image," i. e., where it was seen as black or gray. He proceeds : 

 " I have tried every variation of the conditions (with exclusion of 

 chromatic adaptation) '.vhidi my ingenuity could devise; and the 

 result is in every instance negative, so far as the contention of the 

 Misses Fernald, Thompson and Gordon is concerned." 



Criticism and Interpretation. 



1. The positive outcome of Tschermak's observations with the 

 glass wedge must, in our opinion, be explained by the prepossession 

 of the observer and the roughness of the method employed. Had 

 Tschermak been in doubt as regards the after-image, he would have 

 had recourse to a more refined instrument, as the Marbe color-mixer. 

 And had he adopted a better method, we cannot doubt, on our side, 

 that the outcome of his observations would have been negative. We 

 may, perhaps, venture to express the hope that he will now submit 

 his hypothesis to a stricter test. 



2. It is less easy to account for the peripheral results. The 

 experimcntum crucis, in positive regard, would seem to be the pro- 

 duction of a colored after-image, in the achromatically adapted eye, 

 at a point lying well beyond the limits of B-Y vision. It must be 

 remembered that in all liminal determinations an unnoticed varia- 

 tion in physical or physiological conditions, or in the conditions of 



