180 COLOR-BLINDNESS IN ITS RELATION TO 



most in this, that it does not require a special apparatus for preparing the 

 necessary tints for the examination; it assumes there will be a supply of 

 objects of different colors provided in advance. It agrees again with this 

 method in not allowing, as Maxwell's does, the person examined to remain 

 passive, and simply give his opinion of the resemblance or dissimilarity 

 of the shades indicated, but requires him to discriminate and select the 

 shades, and in consequence reveal by an act the nature of his chromatic 

 sense. But practically our method differs essentiall}' from Seebeck's. 

 His certainly gives, in a certain sense, more complete results than ours 

 by requiring the subject to thoroughly classify, in accordance with their 

 reciprocal resemblances and dissimilarities, the various differently col- 

 ored objects placed before him. A complete table of his whole system 

 of colors is the result of this. Our method, on the contrary, requires the 

 person examined to select, amongst a large number of variously colored 

 objects, those alone which resemble the sample shown him by the ex- 

 aminer. The difference is evident. Seebeck's method is, without any 

 doubt, preferable when the nature of the color-blindness iu the aggregate 

 is to be considered ; that is, so long as this is yet unknown. His method 

 then gives a more complete idea than ours of the nature of the color-blind- 

 ness. But for our actual purpose, the main question is to discover a 

 defect,with the entire nature of which we are acquainted in advance. 

 Our practical mission then is evidently to discover, if possible, some cer- 

 tain sign which will enable us to accomplish this end by the shortest pos- 

 sible route. If a siugle proof which would detect the color-blind as 

 certainly as if he revealed to us his entire system of colors were discovered, 

 this would undoubtedly be the method preferred to any other, as it would 

 accomplish the object much more quickly and easily. This is the case 

 with our method. We are far from denying, in general, the value of a 

 thorough examination, but we will say that it may sometimes be super- 

 fluous. Its practical advantage will not be very great, if at the cost of 

 a great loss of time, and it may even be prejudicial, if, under a multitude 

 of details, it conceal what is essential; in a word, prevents our "seeing 

 the city on account of the houses." All this may bo applied to Seebeck's 

 method, when the object in view is the one of which we are in 

 pursuit. Our method again endeavors to seize as rapidly as possible 

 one or two essential characteristics while neglecting all the others. A 

 single caudal feather of the peacock reveals whence it came; a single 

 flower or fruit, the plant whence it was plucked; and the genus man is 

 recognized if we can but see a face. It is only when the face is muti- 

 lated, the flowers, fruits, and caudal feather are defective, that iu certain 

 cases it is necessary to have recourse to other characteristics. Our 

 method rests upon these principles ; it also offers the same security as 

 Seebeck's. But, as regards the time necessary to accomplish the exami- 

 nation, it bears nearly the same relation to that of the learned German, 

 that a minute does to an hour. This may seem a very trifling matter 

 at the first glance, but is in reality of immense practical importance 



