306 How do the Colour-blind See the different Colours ? [Jan. 13, 



mental colours, it may be said that his red is not quite identical with 

 the common spectral red of the normal-eyed (something like cinnabar) , 

 but rather a clearer red, having a shade of carmine, about the same as 

 the red towards the end of the subjective spectrum of the normal-eyed. 

 His other fundamental colour, green, is also a clear green that for the 

 normal eye has a shade of blue in it. 



The two principal colours in the spectrum for the red-blind are as to 

 their fundamental tone yellow and blue. This yellow commences a 

 little later, reckoned from the end, than the red of the normal-eyed 

 (about Fraunhofer's line C), and stretches over the rest of the red, 

 orange, yellow, yellowish- green, and ends in the blue-green (between 

 Fraunhofer's lines b and F, nearer to the latter), where a narrow, 

 neutral, colourless belt forms the limit against the other principal 

 colour, blue, which stretches through the remaining part of the spec- 

 trum, corresponding with our cyan-blue, indigo, and violet. At this end 

 there is no " shortening." The red-blind person's confusing of pigment- 

 colours {green and yellow, orange and red, purple and blue and violet 

 red and blue-green and grey) is equally well explained by this. 



All this, as we see, is objectively taken in perfect accordance with 

 the Young- Helmholtz theory. Regarded from a subjective point of 

 view, we should perhaps have expected green instead of yellow as one 

 of the fundamental colours. But that yellow, and not green, is 

 that colour (as I have already for some time supposed, vide Upsala 

 " Lakareforenings Forhandlingar," vol. vii, 1871, p. 119, and " Cen- 

 tralblatt f. d. med. Wissenschaften," 1872, p. 826) does not shake 

 the basis of that theory, as is shown by Fick (" Zur Theorie der 

 Farbenblindheit," 1873) and by myself (" Om Fargblindhetens 

 Theori," 1878). Besides, the tone of the red-blind person's first 

 fundamental colour is not perfectly golden-yellow, but seems for the 

 normal eye to have a shade of greenish-yellow, perhaps best defined 

 as citron-yellow in the lighter, and as olive-green in the darker, shades. 

 His other fundamental colour does not seem to be purely cyan-blue or 

 indigo, but is rather a blue with a perceptible shade of violet. It 

 might be called indigo-violet. 



Perfect clearness in the theory will not perhaps be gained until we 

 shall have had opportunity of studying more cases of different kinds 

 and degrees, and especially a case of typical perfect green-blindness. 



Still the path is opened, and a more definite starting-point has been 

 found for the treatment of the theoretical problem of colour-blindness, 

 of which it is my intention to speak more explicitly in my larger work 

 on the same subject. 



