136 COLOR-BLINDNESS IN ITS RELATION TO 



the conclusion that the case was correctly judged. Besides these 

 cases described in detail, and illustrated by a number of interesting anec- 

 dotes, Wilson cites a great many others analogous, but only accidentally 

 encountered by our author, or mentioned to him by other persons, for 

 which he was indebted to the interest the question had excited in Eng- 

 land by his own initiatory steps. Wilson's data are not merely limited 

 to this kind of investigation. He also mentions the systematic researches, 

 (analogous in some measure to those of Seebeck,) which he undertook in 

 order to discover color-blind individuals, and by that means form some 

 idea of the frequency of colorblindness amongst the population. It is 

 to him, in fact, we owe the first efforts to establish regular statistics on 

 this subject, as it would be diflBcult to receive as such the cases collected 

 by Dalton. To attain this*end, Wilson examined at the same time a large 

 number of individuals belonging to the same class, such as soldiers, 

 students, police-agents, veterinary students, etc., and discovered in this 

 way 65 color-blind out of l,15i persons examined ; that is, 5.6 per 

 cent., or one color-blind out of every 17.7 persons. If desired that statis- 

 tics of this nature should render the service expected, it is plain that 

 there must be great strictness in the use of the methods of examination, 

 and especially in any case where a doubt of color-blindness exists. Here, 

 as in the classification of color-blindness in general, theory exercises 

 great influence. In this respect, it is very important that uniformity 

 should prevail, or at least that, at the time of the employment of the 

 different theories and methods, the limits should be well defined between 

 color-blindness on one hand, and, on the other, between the different 

 kinds of anomalies, and finally that the process should be so selected for 

 examination and classification that from any practical point of view 

 an accurate judgment could be formed of the result, and a classifica- 

 tion made of the different cases under any system whatsoever. It is only 

 by fulfilling these conditions that these statistical data can be useful; 

 and that they may have a real value, it is the more necessary that the 

 method should be so sure that no color-blind individual could escape 

 the experimenter. 



It is impossible to say that Wilson's statistics fulfill these requirements. 

 Wilson was not ignorant of Young's theory as restored by Helmholtz 

 and Maxwell. But this theory had not as yet begun to excercise a 

 general influence over the ideas of the nature of the anomalous percep- 

 tion of colors, thy methods employed in discovering it, and the manner 

 of classifying the different forms. Wilson's method and classification 

 therefore are deficient. His method consists in x>resenting to the 

 individuals to be examined pieces of colored paper, one after the 

 other, or a diagram in an illustrated work, and asking the names of 

 the colors. Those only who evince some hesitation in distinguishing 

 red, green, and brown are required to submit to Seebeck's proof, that is 

 to say, classifying according to their analogy, but without indicating by 

 name the pieces of colored paper, glass, or wool. From this it can be 



