456 



DR WILLIAM POLE ON THE PRESENT STATE OF 



But there is one point in which the comparison is particularly useful, as the dichromic 

 patient is unable to formulate any opinion thereon ; that is, the nature of the white that 

 he sees. He can speak of his two colours as distinguished from white, and he knows 

 that his white will result from their equilibrated combination ; but how far his white 

 sensation may resemble or may differ from the normal one, he has no means of 

 judging. 



Here, therefore, the comparisons we have just gone through are most valuable, as they 

 prove, beyond a doubt, that the white sensation of dichromic vision is essentially the 

 same as that of the normal-eyed. And this vastly simplifies the consideration of the 

 dichromic phenomena ; for it shows that the two dichromic colours must be complemen- 

 tary, not only to the dichromic, but also to the normal eye. This fact is sufficient of 

 itself to disprove the explanation that one of three fundamental colours is absent, for 

 the other two cannot be complementary. 



That yellows and blues may be complementary within a considerable range is shown 

 by the following numbers. 



Complementary Colours according to Helmholtz. 





Wave Length. 



Wave Length 



Orange, 



6077 and Blue, 



489-7 



Gold-yellow, . 



585-3 and Blue, 



485-4 



Gold-yellow, . 



5739 and Blue, 



482-1 



Yellow, . 



567T and Indigo-blue, 



464-5 



Yellow, . 



564-4 and Indigo-blue, 



461-8 



Green-yellow, 



and Violet. 





Here is plenty of room for slight variations in both the colours ; for although they 

 may be broadly described as yellow and blue, there is reason to think that their exact 

 hues vary in different individuals, as will be mentioned hereafter. 



Conclusions and Opinions. 



Let us now consider the conclusions to be drawn from the whole evidence on this part 

 of the subject. 



In the first place, we have seen that the universal concurrent testimony of the colour- 

 blind, interpreted by the same rules that would guide normal-eyed people in judging of 

 each other, is that their two colour-sensations correspond, in every practical sense, with 

 those which the normal-eyed call yellow and blue. 



And secondly, in answer to the suggestion that their real subjective impressions may 

 be something different from what they take them to be, their testimony is confirmed by a 

 large accumulation of evidence obtained by direct comparison with the normal phenomena. 



