ME. W. POLE ON COLOUE-BLINDNESS. 
329 
Now if I follow the Chevreul circle, starting from red, and going round, in the direction 
of a watch-hand, towards blue, in every division which I pass, the sensation of yellow 
becomes fainter and fainter, and at the same time the darkening shade becomes more 
and more powerful, until very soon the yellow disappears altogether, and nothing but a 
dark grey or perfectly colourless hue remains. This point is still within the limit of 
what may be called red ; and thus I arrive at the fact that there is a hue of red which, 
to me, is, as a colour, absolutely invisible. It is a well-defined crimson, not much 
differing from crimson-lake ; and its place on the circle is very near the division called 
“ red-violet,” probably the one marked 5 immediately beyond it ; and it is perfectly 
matched to my eye by the division 17 on the gamme of neutral grey. I can also imitate 
it by mixing about 3^ or 4 parts of carmine powder with 1 of ultramarine ; or on the 
colom'-top, 86 parts of carmine combined with 14 of ultramarine will about match a 
grey compound of 7 white and 93 black. 
This, to me, neutral hue of red is not contained in the spectrum, but lies among the 
hues which are wanting to connect the red and violet ends together, and make the image 
re-entrant. The red end conveys to me a decided sensation of yellow, and the violet end 
a decided sensation of blue. 
13. I can now easily fill up my description of that portion of the circular diagram 
lying between red-violet and yellow. The appearance to my eye of the whole of this, 
simply corresponds with that of the upper part of the yellow gamme, i. e. it presents a 
series of successive shades of yellow, commencing with the full colour, and gradually 
darkening down, by the abstraction of yellow and the addition of black, till it arrives at 
the colomdess limit before described. Thus, “ yellow-orange ” appears yellow slightly 
darkened; “red-orange” or scarlet, still more; carmine-red, again more; and red- violet 
or crimson is all darkness with no yellow at all. The gradations of hue visible to the 
normal eye, are to my vision represented by gradations of shade only, the element of red 
acting, not as a chromatic agent, but simply as a darkening power*. 
14. The appearance to me of the violet division of the diagram, or the part lying 
between blue and red-violet, is perfectly analogous to that of the part just described. 
The blue I see perfectly, but the various tints of violet are to me only darkened blue ; 
for example, the “ violet ” division of the Chevreul circle perfectly corresponds with 
No. 18 of the blue gamme, which is simply blue-f- black; and I can make by mixtures 
of powders, or by rotation of the coloured disks, combinations of blue and black which 
shall exactly match others of blue and red. And this of course may be expected to be 
so ; for since I have described the effect of pigmental red as only that of a darkening 
* This expression must of course be only understood as regards the effect obtained in the pigments ; 
what the intensity of direct light, of my red neutral hue, would be, I cannot say. It is probable that in 
regard to the degree of illumination generally, my sensations are normal. To an ordinary observer a crim- 
son pigment conveys much less light than a yellow one ; I appreciate the loss of light, but fail to see the 
accompanying effect of colour ; hence what may be to him redness and darkness combined, is to me dark- 
ness only. 
