700 COLOR-VISION AND C0L0R-BLINDNES«. 



country. 1 have lately seen a pattern card of colored silks issued by a 

 Lyons nianuliKitnror, wliich contains samples of two thousand dillerent 

 colors, each with its more or less appropriate name. There is licre a 

 larger color vocabulary than the entire vocabulary for the exj)ression 

 of all his knowledge and of all his ideas, which is possessed by an aver- 

 age engine driver or lireman, and just as niost of us wouhl he igno- 

 rant of the names of the immense majority of the (!olors displayed on 

 that card, so hundreds of men and boys among the laboring classes, 

 especially in large towns where the oj)portunities of education by the 

 colors of flowers and insects are very limit(Hl, are ignorant of the names 

 of colors wliicli persons of ordinary cultivation mention constantly in 

 their daily talk and expect their children to jiick up and to uuderstnud 

 unconsciously. It is among people thus ignorant that the olficials of 

 the board of trade and of railways have been most successful in find- 

 ing their supposed colorblind persons, and these persons who would 

 never have been pronounced color-blind by an expert have been able, 

 as soon as they have paid a little attention to the observation and 

 naming of color, to pass an official examination triumphantly. The 

 sense of color presents many analogies to that of hearing. Some peo- 

 ple can hear a higher or a lower note than others, the difference de- 

 pending upon structure, and being incapable of alteration. No one 

 who cannot hear a note of a certain pitch can ever be trained to do so; 

 but within the original auditory limits of each individual the sense of 

 hearing may be greatly improved bj'^ cultivation. In like manner a 

 person who is blind to red or green must remain so, but one whose 

 color sense is merely undeveloped by want of cultivation may have its 

 acuteness for fine differences very considerably increased. 



In order to test color- vision for railway and marine purposes, the first 

 suggestion which would occur to many people would be to emi)loy as 

 objects the flags and signal lanterns which are used in actual working. 

 1 have heard apparently sensible ])eople use, with reference to such a 

 procedure, the phrase upon which Faraday was wont to pour ridicule, 

 and to say that the fitness of the suggested method •' stands to reason." 

 To be etfectual, such a test must be applied in different states of atmos- 

 phere, with colored glasses of various tints, with various degrees of 

 illumination, and with the objects at various distances; so that mu(;h 

 time would be required in order to exhaust all the conditions under 

 which railway signals may i)resent themselves. This being done, the 

 examinee must bo either right or wrong each time. He has always an 

 even chance of being right; and it would be an insoluble problem to 

 discover how many correct answers were due to accident, or how many 

 incorrect ones might be attributed to nervousness or to confusion of 

 names. 



We must remember that what is required is to detect a color-blind 

 person against his will ; and to as(;ertain, not whether he describes a 

 given signal rightly or wrongly on a particular occasion, but whether 



