80 



so small, that supposing it reduced to one- tenth of its illuminating 

 power by the suppression of the whole of its primary red constituent, 

 I cannot imagine that any gas-flame or fire-light would be visible 

 through it, or any other luminous body but the sun. 



Still it remains a fact, however explained, that the red rays of the 

 spectrum generally are to the colour-blind comparatively but feebly 

 luminous. Mr. Pole speaks of red in more places than one as "a 

 darkening power ;" and in the letter I have received from him in 

 reply to my query as to the visibility of light through the red glass 

 above mentioned, he insists strongly on its action as darkness. This, 

 however, can only be understood of the effects of red powders in 

 mixture, and not of red light ; and as, to our eyes, an intense blue 

 powder, such as prussian blue, has, besides its colorific effect, a vio- 

 lent darkening one (owing to its feeble luminosity), so, to the colour- 

 blind, red powders, when added to others, contribute but little light 

 in proportion to the bulk they occupy in the mixture, and therefore 

 exercise a darkening power by displacing others more luminous than 

 themselves. I think it therefore very probable that red appears to 

 the colour-blind as yellow-black does to the normal-eyed, or, in 

 other words, that our higher reds are seen by them as we see that 

 shade of brown which verges to yellow that of the faded leaf of the 

 tulip-tree for instance. Now it is worthy of remark, that it is very 

 difficult for the normal-eyed to become satisfied that the browns are 

 merely shades of orange and yellow. Brownness (such at least has 

 always been my own impression) is almost as much a distinct sensation 

 as greenness ; so that I am not at all surprised at the expression in 

 22, that the " sensation of red as a dark yellow is certainly very 

 distinct from full yellow," or that a colour-blind person should, after 

 long and careful investigation, arrive at the conclusion that red is 

 not to him a distinct colour. I find all this completely applicable 

 to my own perception of the colour brown. 



Mr. Pole ( 11) appears to lay great stress on the fact, that in a 

 closed colour circle in which red, yellow, and blue are so arranged 

 that each shall graduate into both the others, there occurs in the 

 space where red and blue graduate into each other, " a hue of red 

 which is to him absolutely insensible," and that this red corresponds 

 not to that colour which, under the name of carmine, offers to the 

 normal-eyed the beau-ideal of redness, but what they term " crim- 



