Report of the Committee on Colour- Vision. 283 



The reasons on which the Committee have based these 

 recommendations are set forth in the following pages. 



The subject of colour-sense and its imperfections is one introductorj , 

 which is necessarily of great scientific interest ; but it also 

 has a practical importance, as it affects a definite propor- 

 tion of the men who are engaged in the two great indus- 

 tries of railway tralfic and of navigation. Amongst railway 

 men, at least, if not also amongst sailors, a suspicion 

 has been excited that the methods adopted for testing colour- 

 sense are not entirely trustworthy, and have had the effect of 

 excluding some individuals from employments, the duties of 

 which they were well qualified to discharge. On this ground 

 alone, if on no other, it has seemed advisable to the Committee 

 that the reasons for their recommendations should be so stated 

 as to be intelligible, as far as possible, to ail those who are 

 interested in the matter. 



Every colour, and among colours for convenience sake are 

 included black and white, can be defined by three qualities : — 1st, 

 its hue — thus we talk of red, green, violet; 2nd, its purity, or 

 the measure of its freedom from admixture with white — which is 

 expressed by such terms as "deep" or "pale;" and 3rd, its 

 brightness or luminosity — thus we say a colour is " bright," 

 or "dark." Two colours are identical only when they can 

 be defined as possessing the same three colour qualities, or 

 constants as they are called, and if they differ in any one 

 they are no longer the same. When two objects are compared 

 together for colour, the large majority of persons will agree as 

 to their identity or difference. Their verbal descriptions of the 

 difference may vary slightly, but practical tests show that 

 in reality they recognize the same variations, and hence their 

 vision is termed normal vision. There is, however, not an 

 inconsiderable minority, as will presently be shown, whose per- 

 ception of colour differs very widely from that of the majority, 

 and, for want of a better term, members of this minority are 

 called " colour-blind" By this term it is not intended to convey 

 the idea that there is absolute insensibility of vision, or even of 

 colour -vision, but merely that the ordinary distinction between 

 certain colours is defective The variations in the amount of 

 this deficiency in colour-perception are numerous, and when 

 small, are often exceedingly difficult to classify. 



We have to regard these deviations from normal vision more 

 from a practical than from a theoretical standpoint, and in 

 testing for them we have to take the broad view that the colour- 

 blindness which has to be detected is that which may be dan- 

 gerous to the public in the industries already mentioned. 



There are some few people who fail to distinguish blue Character of 

 from green, and others, equally few, who only see in mono- colour- 

 chrome, but the colour-blindness which is most common, and, blmdness - 

 therefore, most dangerous, is the so-called red-green blindness, 

 in which there is a failure to distinguish between red and 



