134 COLOR-BLINDNESS IN ITS RELATION TO 



tainty and inadmissibility of attempting to discover the nature of this 

 blindness by simply interrogating the color-blind as to the names of the 

 colored objects ; he was careful to note what mistakes they made in 

 comparing the colors, or, in other words, he ascertained between what 

 -colors, different to the normal eye, they found resemblances. Follow- 

 ing up this principle, he proceeded methodically to examine individuals; 

 he invited them to arrange, in the order of their resemblances to each 

 other, a number of colored objects, which in the beginning were in confu- 

 sion. He used principally paper, about three hundred pieces of differ- 

 ent colors, not, however, rejecting other materials, especially pieces of 

 colored glass. He objected to silk on account of its brilliancy, but rec- 

 ommended wool, although he does not appear himself to have preferred 

 to use it. It is not clear from Seebeck's writings whether, after each 

 examination, he preserved the order in which these pieces of paper were 

 arranged by the color-blind; but it is certain he compared the manner 

 of arranging them in different cases, and drew his own conclusions. 

 By this comparison, Seebeck succeeded in pointing out two classes of 

 specifically distinct color-blindness. Of the thirteen cases he examined, 

 eight belonged to the first and five to the second class. Moreover, ho 

 shows that in the two classes there is a great varietj^ of degrees of color- 

 blindness, and seeks further to prove the probable existence in the two 

 classes of a gradual transition to the normal sense of color. 



But Seebeck and his contemporaries, like their predecessors, could not 

 discover a satisfactory explanation of the defect in question, or practi- 

 cally see its relation to the normal sense of color. This is easily ex- 

 plained by the fact that at this time there was not the least plausible 

 system of a physiological doctrine of colors. Indeed, as early as the 

 beginning of our century, a useful and satisfactory theory had been 

 devised by Thomas Young, but it had been neglected or forgotten, as were 

 many of the other ideas of this extraordinary man, who was far in 

 advance of his age, and consequently not understood. The theory of the 

 three primitive colors, or fundamental perceptions,of Young, was rescued 

 from oblivion by Helmholtz about the year 1850, and also later, but inde- 

 pendently, by Maxwell. This theory has undoubtedly already exerted a 

 very happy influence over the physiological doctrine of colors in general, 

 as well as over thatof the anomaly in chromatic perception. In designat-' 

 ing this theory by the names of both scientists, we thereby simply ren- 

 der justice to the merit which accrues to Helmholtz for having revived 

 and applied it. Owing to this theory, the question of the nature of color- 

 blindness has been of late the object of strong and growing interest. The 

 number of cases, and also of treatises on the subject, have increased ver^' 

 considerably, and the study, undertaken by physiologists as well as by 

 ophthalmological practitioners, has not been confined to congenital color- 

 blindness and its different forms, but has also extended with much 

 earnestness over pathological diagnostics. It is onlj' about ten years 

 since that a new theory, that of four cardinal colors, succeeded in making 



