Dr. W. Pole on Colour-Blindness, 441 



be absent without the defect having an influence on the other 

 two. 



Edmund Rose was the first to point out this difficulty in the 

 application of Young's theory, but he was, in my opinion, quite 

 wrong in inferring that this was fatal to the theory. The retina 

 is not a thing formed by human hands. It is not an instrument 

 with three strings, one of which is broken for the colour-blind. 

 It is a living instrument — gentium non factum — whose three differ- 

 ently-tuned strings have developed themselves in combination with 

 each other. If one is absent, then the tuning of both the others is 

 certainly not what it would have been under a regular develop- 

 ment of the whole. 



We have also to consider the subjective sensations of the colour- 

 blind. 



I presuppose that they see the ordinary daylight as the normal 

 eyes see it, i. e. neutral, colourless. Herschel, in his remarkable 

 letter to Dalton, says, " when your two colours are in equilibrium, 

 they form your white ; " and in the case of Mr. Pole also he says 

 he " is strongly disposed to believe that he (Mr. Pole) sees white 

 as we do." 



The reason why, according to my view, the white of the colour- 

 blind should correspond with that of the normal-eyed, lies deeper; 

 What the total light brings forth must necessarily be the manifes- 

 tation of the total process, and according to the nature of things 

 this is, in opposition to the partial process, neutral, or it would 

 become so, if it were not so already. Colour-blind people who 

 have due regard to their sensations, see in white no third colour, 

 but only the negation of the other two, something neutral. Mixed 

 with either of these, it leaves the colour unchanged, and only re- 

 duces the saturation. Nobody can believe that the white to the 

 Green-blind should be a purple, such as for the normal eye is 

 formed out of red and violet, aud no one has ever believed it. 



According to the assumption that the white light of the colour- 

 blind is neutral, colourless, I consider their fundamental colours as 

 complementary. 



In common with the declarations of intelligent colour-blind 

 persons, I have assumed that the Red-blind must have for their 

 warm colour a yellow, leaning towards green, and the Green-blind 

 a yellow leaning towards red ; and that blue or violet, as cold 

 colours, will correspond with these. And I consider these assump- 

 tions as already, to a certain extent, proved by the revelations of 

 one-eyed colour-blindness. 



In the lecture given at Cambridge, 1881, Donders repeats 

 this opinion : he says : — 



The warm and cold must be considered as complementary 

 colours ; to which of our sensations they correspond cannot well 

 be told, probably the cold colour is blue or violet, and the warm 

 one is yellow, approaching to red or green. 



