128 Remarks on Railway and Marine Signals. 



" a soldier s red coat or a stick of red sealing-wax conveys 

 to me a very positive sensation of colour, by which I am 

 able to identify in a great number of instances bodies of 

 this hue. If, therefore, the investigation of any experiences 

 ended here, there would be no reason to consider me blind to 

 red. But when I examine more closely what I do see, 

 I am obliged to come to the conclusion that the sensa- 

 tion I perceive is not one that I can identify separately, 

 but is simply a modification of one of my other sensations. 

 It is, in fact, a yellow shaded with black or gray, a darkened 

 yellow, or what I may call yellow-brown. I find that all 

 the most common hues of red correspond to this description; 

 and in proportion as they are more scarlet or more tending 

 towards orange, the yellow I see is more vivid. The 

 explanation, I suppose, is that none of such reds are pure — 

 they are combinations of red with yellow, so that I see the 

 yellow element of the combination, while the true red 

 element of the combination is invisible to me as a colour, 

 and acts only as' a darkening shade." 



Dr. Wolfe, referring to colour-blindness, says : — " It may 

 well be asked, how is it possible for a colour-blind engine- 

 driver, for instance, to perform his duty for any length of 

 time without exposing his deficiency ? But the explanation 

 given by Holmgren is simple when we come to remember 

 that a colour-blind person may come to distinguish between 

 red, green, and white lanterns or flags, and even learn to call 

 them by their right names, whilst all the time it is not colour 

 which he sees; he only differentiates by the degree of intensity 

 of light." "In short, the colour-blind person supplements 

 his defective vision of colour by all secondary aids. He 

 trains himself to notice differences which escape most other 

 eyes; these differences serve him in lieu of colour. That is the 

 reason why collisions do not daily occur on railways and at 

 sea from mistakes made by colour-blind officials." 



When the conditions are unfavourable for the colour-blind 

 person supplementing his deficiency of sight by other means, 

 as in rain, mist, and some other states of the atmosphere, 

 the danger of making mistakes in the colours of signals 

 becomes very great. 



From the statistics quoted above, we cannot escape the 

 conclusion that there are on board of our steamships and on 

 our railways numerous instances of persons whose visual 

 deficiencies disqualify them for their important responsi- 

 bilities in regard to human life, for the tests hitherto 



