KNOWLEDGE AND OPINION IN REGARD TO COLOUR-BLINDNESS. 457 



Then, what is there to oppose to all this ? What is there to lead to the belief that 

 the subjective warm sensation is not yellow, but red or green ? Absolutely not a fact of 

 any kind ! Nothing but a peculiar inference drawn empirically from a certain theory, 

 which, though commanding the greatest respect in regard to colour-vision generally, does 

 not in the least necessitate the form of application to colour-blindness under which this 

 inference has been drawn. 



While the evidence was confined to the statements of the colour-blind, it made but 

 little impression ; but since it has been so strikingly confirmed by the normal compari- 

 sons, it has become so cogent that the old explanation may be said to be, on the Continent 

 at least, generally abandoned. And even the staunch adherents of Young's theory 

 now fully admit the yellow and blue colours, urging that they may be consistently 

 explained in other ways. In proof of this, the opinions of several authorities, such 

 as Holmgren, Fick, and Von Kries, have been already quoted, and a few more may 

 be added here. 



Kuster and Kries, 1879, said, " It is in nowise proved that the two components 

 of the colour-blind correspond exactly, or even approximately, to those of the normal- 

 eyed. 



Professor Donders, 1881, distinctly and strongly supported the yellow and blue 

 colours.* 



In 1883 Dr Konig, a pupil of Helmholtz, published a distinct repudiation of the 

 old explanation, which he repeated in 1886 in a Paper to the British Association at 

 Birmingham. See " Data," AC. 



Other examples might be found, but, as a fit climax to them, it may be mentioned 

 that Von Helmholtz himself has, apparently in deference to the overwhelming mass of 

 evidence, now modified his views, and no longer insists on the applicability of the 

 original explanation of colour-blindness, which has caused all the difficulty. Further 

 explanations of his views will be given hereafter. 



In the face, therefore, of this general concurrence of opinion on the Continent, where 

 the subject has been chiefly studied and argued, the occasional adherence, in England, 

 to the older doctrine, must be considered exceptional, and will doubtless soon give place 

 to the better established views. 



And it must be a great satisfaction to the colour-blind patient to find that, after so 

 many years of struggling against the refusal of the theorists to receive his testimony, the 

 simple evidence of his senses has at last been allowed to prevail. 



* See abstract of his views given by myself in the Phil. Mag. for November 1892. 



VOL. XXXVII. PART II. (NO. 22). 4 A 



