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ness 1st, because it is the only clear and consecutive account of 

 that affection which has yet been given by a party affected, in pos- 

 session of a knowledge of what has yet been said and written on it 

 by others, and of the theories advanced to account for it, and who, 

 from general education and habits of mind, is in a position to discuss 

 his own case scientifically ; and 2ndly, for the reasons the author 

 himself alleges why such a person is really more favourably situated 

 for describing the phenomena of colour-blindness, than any normal- 

 eyed person can possibly be. It is obvious that on the very same 

 principle that the latter considers himself entitled to refer all his per- 

 ceptions of colour to three primary or elementary sensations 

 whether these three be red, blue, and yellow, as Mayer (followed in 

 this respect by the generality of those who have written on colours) 

 has done, or red, green, and violet, as suggested by Dr. Young, 

 reasoning onWollaston's account of the appearance of the spectrum 

 to his eyes on the very same principle is a person in Mr. Pole's 

 condition, or one of any other description of abnormal colour- vision, 

 quite equally entitled to be heard, when he declares that he refers his 

 sensations of colour to two primary elements, whose combination in 

 various proportions he recognizes, or thinks he recognizes, in all hues 

 presented to him, and which, if he pleases to call yellow and blue, no 

 one can gainsay him ; though, whether these terms express to him 

 the same sensations they suggest to us, or whether his sensation of 

 light with absence of colour corresponds to our white, is a question 

 which must for ever remain open (although I think it probable that 

 such is really the case). All we are entitled to require on receiving 

 such testimony is, that the party giving it should have undergone 

 that sort of education of the sight and judgment, especially with 

 reference to the prismatic decomposition of natural and artificial 

 colours, for want of which the generality of persons whose vision is 

 unimpeachably normal, appear to entertain very confused notions, 

 and are quite incapable of discussing the subject of colour in a 

 manner satisfactory to the photologist. 



It is as necessary to distinguish between our sensations of colour, 

 and the qualities of the light producing them, as it is to distinguish 

 between bitterness, sweetness, sourness, saltness, &c., and the che- 

 mical constitution of the several bodies which we call bitter, sweet, 

 &c. Whatever their views of prismatic analysis or composition 



