234 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V. 



Wittich's are mostly lower than 2', with the exception of dark blue, violet 

 and didsV green which are in the neighbourhood of 3' 26". Whereas our 

 chromatic thresholds are mostly above 2', with exceptions such as red 

 and orange which are at 55" and 48" respectively, i.e., quite low, just as 

 with Aubert's thresholds for these same. Our characteristic thresholds 

 are frequently as high as 4' and 5', especially in the case of blue and 

 violet and green, the same three colours by the way which had highest 

 colour thresholds in Yon Wittich's results. 



Of the cause of the discrepancies between our results and Von 

 Wittich's and Aubert's it is not difficult to form a feasible opinion from 

 the nature of the conditions under which all three sets of experimental 

 investigations were performed. When we remember the superior 

 accuracy of our measurement apparatus we would ceteris paribus 

 expect our threshold sizes to be somewhat smaller because of that fact. 

 And this may be the reason why our achromatic thresholds are for the 

 most part lower than theirs. But the explanation of the tendency of 

 our chromatic and characteristic thresholds to be higher must be differ- 

 ent from this. This seems very probably due in part to the fact that 

 our experiments required choice to be made among a larger number ot 

 colours than did Aubert. We used more colours which would have a 

 very effectual tendency to increase the difficulty of deciding which of 

 them any specimen under examination while yet in the doubtful region 

 near the threshold, might be. Accordingly, such an impediment would 

 beyond question, contribute to the raising of our characteristic thresh- 

 olds. However, this can only be an explanation in part, because, other- 

 wise, we would expect a certain proportionality between the relation of 

 the number of our colours and Von Wittich's and Aubert's, and the 

 relation of the corresponding chromatic and characteristic thresholds of 

 the respective investigations. But in fact we find no such regularity 

 of correspondence between the number of colours used and the increase 

 of the characteristic threshold size when we compare the results of 

 Aubert, Von Wittich and ourselves. For example, Aubert exploits 

 only a few colours, some four representative ordinary colour tones, and 

 some two other commercial colours such as brown, whereas Von Wittich 

 operated upon ten different colours, while we used ten also in our experi- 

 ments of this kind. Hence, the discrepancy between our chromatic and 

 characteristic thresholds and those of Von Wittich and Aubert cannot 

 be solely due to the numbers of colours among which distinction had to 

 be made, because we find our results prevalently higher than Von 

 Wittich's who employed the same number of colours as we did. And 

 we also find that neither our results nor Von Wittich's stand so much 



