328 
ME. W. POLE ON COLOUR-BLINDNESS. 
sensations I am capable of, most fully and completely, and form with each other the 
strongest contrast it is possible for me to conceive. 
I can, of course, never know whether my abstract sensations of these colours are the 
same as those of the normal-eyed; but this is of no moment, for we can only judge of 
our ideas by their manifestation ; and if I find that I can understand and agree in all 
that is said of blue and yellow by the world in general, and that they can also under- 
stand and agree in all that my impressions lead me to say about blue and yellow, I have 
a sufficient proof that I see these colours as others do. This experience is general among 
the colour-blind, who one and all identify blue and yellow as the colours about which 
they are most certain, and which they never run the slightest risk of confounding with 
each other. 
11. The fact next in importance is, that my ideas of the thhd primary colour', red, do 
not agree with those of the normal-eyed. 
The term red is so indefinite, in ordinary language, that 1 have had much trouble to 
find out by an example, what is usually considered the pure colour, free from yellorv 
on the one hand, or blue on the other. Many well-educated persons differ much on 
this point, and I have myself often detected considerable variation between examples 
of red which normal-eyed people have declared to correspond. I beheve, however, that 
the pigment carmine is usually understood to be the best artificial representation that 
can be had of the true unmixed colour. 
Now this red is by no means invisible to me ; it conveys a very marked sensation of 
colour, by which I am perfectly able to identify, in a great number of instances, bodies 
of this hue. If therefore my testimony ended here, there would be no reason for 
inferring that I am blind to red, or have much defect in my -sision regai’ding it. But 
when I examine more closely what I do really see in the cases referred to, I am obhged 
to come to the conclusion that the sensation I perceive is not one that I can identify 
separately, but is simply a modification of one of my other sensations, namely yelloiv. 
It is in fact yellow shaded with black or grey — a dark yellow. 
This I can prove to myself in several ways. First, I find that among the various tones 
in the gamme of yellow, there is one, namely that numbered 16, which perfectly matches, 
to my eye, the “ rouge” in the circle. Secondly, I can make very nearly this appearance 
of red to my eye, by mixing 1 part by measure of lampblack with 5 or 6 ^ of chrome- 
yellow powder, so as to darken it to the required tone. And thirdly, I can produce, on 
Mr. Maxwell’s colour-top, a tolerable match to the carmine card, by a combination of 
about 90 parts black with 10 parts chrome. 
12. It may be safely stated, therefore, that what is ordinarily called red, is distinctly 
visible to my colour-blind eye, not as an individual colour, but as a shade of yellow. 
'* These quantities are only given approximately to illustrate the fact ; they are very difficult to get accu- 
rately. The proportions hy mixing powders are very different to those required by rotation to produce the 
same hue ; and even when this has been tolerably arrived at, the quality of the pigments has much influence 
on the appearance of the match. 
