IN PRACTICAL ASTRONOMY, SPECTROSCOPICALLY EXAMINED. 797 
make yourself in a moment, “colour-blind,” at least in its most generally 
acknowledged and leading characteristics,—your memory enables you most 
securely to describe how you saw things in one condition, as compared with 
your feelings in the other. 
What then is the main outward observed fact, which we have to imitate, or 
realise on ourselves, in order to stand in the place of the orthodox “ colour- 
blindness” both of literature, and of a great part of mankind ? 
In the carefully prepared work of that most amiable and laborious of 
scientific enthusiasts, the late Dr GEorGE W11son, —he has abundantly described 
the various objective features of “colour-blindness ;” and considers the chief 
one to be, in one word, an inability to distinguish between red and green ; these 
being actually and notoriously two distinct members of the only three esteemed 
primary colours: and separated further an immense spectral distance from each 
other, whenever the intervening secondary colours, formed by their mixtures, 
are allowed to appear. Blue and green are easily distinguished by most of such 
persons,—but red and green they can see no difference in. 
As a symbol of that leading and most bizarre fact in “ colour-blindness,” 
the worthy Doctor had his book bound in ved cloth, and armed with a bright 
green label. And I can also add from my own long experience of a late and 
most esteemed friend in another part of the world, that though he could dis- 
tinguish smudgy, indistinct colours, including dull greens and impure reds, of 
almost any kind ; and though he could recognise an immense variety of tints, 
including dark shades, in Nature; and could esthetically enjoy their brighter 
beauties and also their more sombre chiaro-scuro effects and deeper shadows ; 
and had moreover almost inimitable accuracy of vision for sharp defining and 
micrometric mensuration,—yet if, on a luminous sunny morning, a green leaf 
was of avery brilliant, pronounced green, and a red flower, as of the pomegranate, 
was of a very staring and declared red,—he could not then see, understand or 
believe that there was a particle of colour difference between them ! 
Now this being the very example most easy of artificial realisation with our 
Di-chroic dark bottle; and as difference of degree in that said bottle, realises 
also the next most extensive fact amongst the “‘colour-blind,” viz., the inability 
to distinguish between red and black,—I presume that I have really got hold, 
at least in principle, of something like the general natural agency in the case of 
a large section of these individuals: viz., vision through a dark fluid in the eye, 
in some persons possibly verging to green, in others to blue, in others to brown, 
but in all of them necessarily di-chroic as to the spectrum. 
Hence I can now, whenever there is occasion, take my place amongst a 
considerable number of the colour-blind, as one of themselves; and yet acquainted 
with colours in the very same manner as those persons who protest that they 
are not blind. Wherefore from such a position of double perceptive gifts, I 
