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black, orange, yellow, brown, blue and violet. Crimson and pink 

 appear to have no relation to scarlet. 



Green is a most perplexing colour ; it is not only confounded with 

 red, but with black, white, or grey, orange, yellow, blue, violet 

 and brown. 



Violet is confounded with blue or grey; and orange with yellow. 



More difficulty is manifested with light or dark tones of compound 

 colours than with full ones. 



In explaining more accurately the real nature of the author's 

 vision of colours, he employs as standard examples of reference the 

 " Cercles Chromatiques," and " Gammes Chromatiques " of M . Che- 

 vreul (copies of which accompany the paper), the former giving 

 various gradations of hue, the latter, gradations of tone. He states 

 that his vision is perfectly dichromic, and shows the applicability to 

 it of the definition of this kind of vision given by Sir John Herschel, 

 which he believes has never hitherto been followed out so completely 

 as is necessary to explain the phenomena observed. 



Slue and yellow he sees perfectly well, and has no reason to doubt 

 that his sensations of these two colours are the same as those of the 

 normal-eyed. The third primary, red, is the one in regard to which 

 his vision is defective, but the study of the sensations produced by 

 this colour has been involved in some difficulty. Carmine, the arti- 

 ficial representative of what is usually considered pure red, presents 

 to the author's eye a very positive sensation, which he long supposed 

 to be a distinct colour ; but on examining it more closely, he found 

 it to be merely a dark shade of yellow, as he could match carmine 

 red perfectly with a mixture of yellow and black. There is, how- 

 ever, a variety of red, namely crimson, which is perfectly invisible, as 

 a colour, to his eyes, giving only a sensation of darkness ; and the 

 whole of the hues of red and orange between this and yellow present 

 only different shades of the latter colour ; the red element appearing 

 to act, not as a colouring agent, but simply as a darkening power. 

 The author has endeavoured to find the place of this, to him, neutral 

 or invisible hue of red on the spectrum, and believes that if it exists 

 there at all, it must be situated at one or both of the extreme ends, 

 a position which would appear to distinguish it as possessing some 

 peculiar property, and he offers a conjecture that this, and not car- 

 mine red, may perhaps be the true primary colour. 



