COLOUR-BLINDNESS. 
501 
darkest, and putting those tints together that are most alike. 
Professor Maxwell adds, ‘’‘’The intelligent testimony of the 
colour-blind may supply a sure foundation for the theory of 
vision.” 
Many other curious and interesting points in connection 
with the philosophical part of our inquiry might be entered 
upon did the space at command permit us to do so ; but 
enough has been said about light and colour to enable the 
reader to comprehend the more intricate part of the subject 
we are about to enter upon — namely, colour-blindness. As I 
have already said, the defect does not necessarily interfere 
with the integrity of the eye as an optical instrument. Indeed, 
in a case recorded by Dr. Wilson of a Mr. It , an en- 
graver, he counts himself not a sufferer, but a gainer by his 
colour-blindness. “ Thus, an engraver has two negative 
colours to deal with — black and white. Now, when I look at 
a picture, I see it only in white and black, or light and shade ; 
and any want of harmony in the colouring of a picture is 
immediately made manifest by a corresponding discord in the 
arrangement of the light and shade, or, as artists term it, the 
effect. I find, at times, many of my brother engravers in 
doubt how to translate certain colours of pictures which to me 
are matters of decided certainty and ease. Thus, to me it 
is valuable. I am totally unable to retain certain colours in 
my mind, nor able to give then* names when shown to me a 
second time. Sometimes I can see some reds and greens by 
lamplight. A few years ago I ventured to buy some green 
baize ; but unfortunately bought a very bright red, which was 
excessively painful to my eyes by lamplight, but agreeable 
enough by daylight. One of my brothers is equally defective, 
and my grandfather was very deficient in his knowledge of 
colours. My sight is natural, and rather powerful ; for I am 
able to see very minute objects without assistance from 
glasses, and I can also see very distinctly with but little light. 
With regard to the rainbow, or solar spectrum, I can see 
clearly there are different shades of colour, but I am unable to 
say which is the red. The violet and yellow are very clear 
and distinct.” 
Those who have compared a coloured drawing or oil painting 
with an engraving of it will appreciate the nature of the difficulty 
which Mr. R so easily surmounts. In heraldic engraving, 
for example, a system has long been followed of representing 
each colour by a separate set of marks. It comes, however, to be 
a very curious question whether this gentleman's version of a 
picture would satisfy one whose perception of colours was 
perfect. Professor Kelland and I)r. Wilson think it would 
not, as they have observed in the course of their inquiry that 
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