4 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The red-green and blue-green junctions found for these eleven per- 

 sons are plotted as points in Figure 1 over the primary color sensation 

 curves, reduced to equal area, as given by Exner (Wien. Sitz. II, 111, 

 837). The arrows show the mean values adopted by Burch and agree 

 with Exner's junctions to a close approximation. The extreme points 

 at both junctions show a degree of variation in the sensation curves 

 which connotes slight abnormality easily detectable with a spectro- 

 scopic test. The average red-green junction was at w. 1. 5842 and the 

 blue green junction at w. 1. 4946. In Burch's earlier paper (loc. cit.) 

 in the examination of 70 persons, all of whom passed the Holmgren 

 wool test, still greater variations in the junction points appeared. 

 And these differences merge again into those shown by patients recog- 



400 



wave length 

 Figure 1. 



b00 



nized as color-blind by simple tests, so that while one may define an 

 average normal color-vision, from which large variations are rare, 

 it is clear that the relations of the color sensations are subject to con- 

 siderable variability. It is the purpose of this paper to classify such 

 variations with reference to their bearing on the general color sense 

 of the individual and to point out such of the more conspicuous ab- 

 normalities as have been detected in tests of color-sense. 



The facts will be stated in terms of the ordinary trichromatic theory 

 for the sake of simplicity. How far the observed facts regarding the 

 typical color-sensation curves may be complicated by aberrancies of 

 color perception referable to the cortex alone, and to what degree the 

 independent violet sensation postulated by Burch (loc. cit.) may be 



