700 COLOR-VISION AND COLOR-BLINDNESS. 



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

 Lyons manufacturer, which contains samples of two thousand different 

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

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

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

 age engine driver or fireman, and just as most of us would be igno- 

 rant of the names of the immense majority of the colors displayed on 

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

 especially in large towns where the opportunities of education by the 

 colors of flowers and insects are very limited, are ignorant of the names 

 of colors which persons of ordinary cultivation mention constantly in 

 their daily talk and expect their children to pick up and to understand 

 unconsciously. It is among ])eople thus ignorant that the officials of 

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

 ing their supposed color-blind persons, and these i)ersons who would 

 never have been i^ronouuced color-blind by an expert have been able, 

 as soon as they have paid a little attention to the observacion 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 :he sense of 

 hearing may be greatly improved by 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 employ as 

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

 1 have heard apparently sensible people use, with reference to such a 

 procedure, the phrase upon which Faraday was wont to ])our ridicule, 

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

 To be effectual, 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 much 

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

 which railway signals may present themselves. «This being done, the 

 examinee must be 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 ascertain, not whether he describes a 

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



