178 COLOR-BLINDNESS IN ITS RELATION TO 



theory, but it has besides convinced us that the colored shadows are 

 not suitable for the discovery in the first instance of color-blindness. 

 This is the sauie case with Eagoua Sciua's method of representing com- 

 plementary colors; and also that of Kose, which, practically, strongly 

 resembles the preceding. 



After having named the processes which, according to our convic- 

 tions, are not suitable for the end in view, we must mention two other 

 methods which thoroughly supply us with the information wanted. 

 One is due to Seebeck; the other to Maxwell. They are both founded 

 on the comparison of colors, and do not assume either any knowledge 

 or any use of the names of colors, which is, we think, an essential 

 advantage.. 



Maxwell's method consists in representing two colors on a rotatory disk, 

 to be compared by the person under examination, the tints, degree of 

 "saturation," and intensity of light of which may be changed at will. 

 They can be modified, until, to the color-blind, they attain an absolute 

 resemblance. The chromatic sense is then judged by its dissimilarity to 

 that of the normal eye. It is in this that the force and accuracy of the 

 method consist. It shows us with certainty how the subject sees the 

 colors as compared with each other. The Youug-Helmholtz theory is 

 confirmed by Maxwell's method, as this shows us that, by the aid of 

 only two primitive colors, we can exhaust the whole chromatic scale of 

 the color-blind. 



Seebeck's method consists in making the individual to be examined 

 classify a number of colored objects according to their reciprocal resem- 

 blance or dissimilarity. In this way, we have at once a complete picture 

 of the person's chromatic sense. We learn what colors he distinguishes 

 and which he confounds. By this method, also, we can know how he 

 sees colors in their relations to each other. But, although these two 

 methods avc, perfectly rcliahle, they are not entirely suitable for a practi- 

 cal purpose, because they require much time and are very inconvenient, — 

 that of Maxwell for the examiner and that of Seebeck for the examined. 

 He who has examined a large number of color-blind by Maxwell's 

 method knows only too well how mucli time this investigation consumes, 

 in however incomplete a manner it is made. This arises from the extreme 

 affectation of precision by the color-blind. It is not difficult for one 

 with normal sight to point out two similar colors on the rotatory 

 disk, because the essential point is the resemblance in the tint of the 

 color. But the color-blind person who cannot perceive this tint re- 

 quires a complete resemblance in the intensity of light or in the degree 

 of "saturation," and in this lies the difficulty. His appreciation often 

 depends upon the addition of a minimum of white or black, which is to 

 him of the greatest importance, although the normal observer cannot per- 

 ceive any diiference. We may add that the method is very fatiguing 

 and inconvenient to the examiner, on account of the continual changes 

 made in the colors, and the incessant work that the rotation of the 



