1881.] How do the Colour-blind See the different Colours ? 305 



fectly clear conception of the normal-eyed people's different colonrs, 

 and can tell his conception, by the aid of his other eye, for other 

 normal- sighted persons. His definitions are thus — in opposition to 

 persons colour-blind on both eyes — perfectly reliable. 



As words are always less reliable than actions (vide Frithiof 

 Holmgren : " De la Cecite des Couleurs dans ses Rapports avec les 

 Chemins de Fer et la Marine," p. 116), and a description in this case 

 is always inferior to a shown colour, I have in every instance let the 

 person in question point out an objective colour with his normal eye 

 for every one of his conceptions with his abnormal one. 



Indirectly we find in this way which qualities of perception are 

 wanting in the abnormal eye in comparison with the normal one. The 

 same result is directly arrived at by letting the colour-blind eye control 

 the subjective perception of the normal. 



It is my intention to explain the application of this principle in my 

 more detailed work on this subject, as well as the particulars of the 

 result. 



I will now only give the chief points of this result, which perhaps 

 is done in the shortest and easiest way by giving the details of the 

 colour-blind person's subjective spectrum. If w r e take the objective 

 solar spectrum for a starting point, and choose our own definition of 

 the different colours from the subjective spectrum of the normal eye, 

 we come to the following results : — 



As we have long supposed, for good reasons, a colour-blind person 

 sees only two colours in the spectrum. These are his two subjective 

 principal colours. 



The principal colours in the spectrum of a violet-blind person are, as 

 to their fundamental tone, red and green. Towards the red end his 

 spectrum has quite the same extension as that of a normal-eyed person, 

 and is thus, in comparison with the latter, " unshortened." Reckoned 

 from the red end, his first fundamental colour stretches over that part 

 of the spectrum which is generally seen as red, orange, and yellow. 

 First in the yellowish-green fa little on the other side of Fraunhofer's 

 line D) he sees a narrow, uncoloured ( u paper- white ") belt, from 

 which his other colour, green, commences, and is continued with at 

 first more and more saturated, and afterwards darker and darker 

 shades, over the place where we see green, greenish -blue, cyan-blue, and 

 indigo to the commencement of the violet, where his spectrum abso- 

 lutely ends with a sharp limit (about Fraunhofer's line G). His 

 spectrum is thus at this end considerably " shortened." The fact 

 that violet-blind persons confuse the pigment colours (such as green 

 and blue, purple and red, orange and yellow, violet and yellowish-green 

 and grey) is thus explained of itself. 



All this is in the main consistent with the Young- Helmholtz theory. 

 Respecting the tone of the violet-blind person's subjective funda- 



