334 
ME. W. POLE ON COLOTJE-BLINDNESS. 
But by equation (I.), 
49 Ult. + 31 Y. = 51 Blk. + 29 A\Ti. ; 
20 Y. + 51 Blk. + 17 Wh. = 88 Em. gr. ; 
or, which is the same thing, 
23 Y. + 58 Blk. + 19 Wh. = 100 Em. gr., 
which is equation (IX.). 
I have in this way tested the whole of the equations both by theory and observation, 
and the correspondence of the two is very satisfactory. 
20. I may now point out how easily and perfectly the simple fact of dichi-omic 
vision may be made to explain all the phenomena, or as I have called them symptoms, 
collected in art. 7, and which appear, when considered alone, so anomalous and con- 
tradictory. 
A. See art. 10. 
B. The explanation of the appearance of the spectrum is precisely analogous to that 
of the colour-circle. The division between the yellow and blue colours I believe to be 
about half-way between the lines b and F of Feaunhofee. 
C, N. The neutral hues of red and green appear grey. 
D, E, F, G, O, P, S, T. Since certain hues of both red and green, as weU as aU kinds 
of orange and brown, appear shades of yellow, these five colours are confounded with 
each other. Eed and green are the two most common colour’s in nature, and as the 
hues of both most frequently met with, lie on the yellow side of the neutral, the 
mistaking of red and green is such a universal symptom of colour-blindness as to consti- 
tute the “ shibboleth” of the disorder. Bright grass-green and scarlet may be taken as 
perhaps the most common representatives of the two colours, and these, to me at least, 
present almost the same identical shade of yellow. 
H. The red which is confounded 'with blue is always crimson, or its light tint pink, 
never any of the scarlet or orange varieties ; and it is obvious that any of the red hues 
on the blue side of the neutral will be seen by the colour-blind only as blue. "W ith 
regard to pinks, it would appear that diluted or thinly applied crimson dyes give 
generally a bluer impression than the full colours. For example, taking the gamine 
of red- violet, and comparing it with that of grey, I find that No. 8 of the former ufiU 
perfectly match No. 10 of the latter, i. e. No. 8 of the crimson scale is to me neutral 
and colourless. But all above 8, i. e. all the fuller tones, decidedly incline to yellow, 
and all below, i. e. all lighter tints, as decidedly to blue ; so that, seemg Nos. 2 or 3 alone, 
I should have no hesitation in calling them blue, though of a very dull and imperfect 
kind. And it must be observed that the blue for which the colour-blind mistake crimson 
and pink, is always described by them as dirty and faded ; never so decided as to stand 
comparison with the pure colour, even diluted. I am told that the circumstance of 
certain coloured substances appearing to change in hue when reduced in thickness or 
diluted, is one familiar to the normal-eyed. 
