[From the Philosophical Magazine, Vol. xiv.] 



XVI. Account of Experiments on the Perception of Colour. 



To the Editors of the Philosophical Magazine and Journal. 



GENTLEMEN, 



THE experiments which I intend to describe were undertaken in order 

 to render more perfect the quantitative proof of the theory of three primary 

 colours. According to that theory, every sensation of colour in a perfect human 

 eye is distinguished by three, and only three, elementary qualities, so that in 

 mathematical language the quality of a colour may be expressed as a function 

 of three independent variables. There is very little evidence at present for 

 deciding the precise tints of the true primaries. I have ascertained that a 

 certain red is the sensation wanting in colour-blind eyes, but the mathematical 

 theory relates to the number, not to the nature of the primaries. If, with Sir 

 David Brewster, we assume red, blue, and yellow to be the primary colours, this 

 amounts to saying that every conceivable tint may be produced by adding 

 together so much red, so much yellow, and so much blue. This is perhaps the 

 best method of forming a provisional notion of the theory. It is evident that if 

 any colour could be found which could not be accurately defined as so much of 

 each of the three primaries, the theory would fall to the ground. Besides this, 

 the truth of the theory requires that every mathematical consequence of assuming 

 every colour to be the result of mixture of three primaries should also be true. 



I have made experiments on upwards of 100 different artificial colours, con- 

 sisting of the pigments used in the arts, and their mechanical mixtures. These 

 experiments were made primarily to trace the effects of mechanical mixture on 

 various coloured powders ; but they also afford evidence of the truth of the 

 theory, that all these various colours can be referred to three primaries. The 



