444 ON THE THEORY OP COMPOUND COLOURS. 



of these equations with my own, are given at "D," "W," and "Y." The 

 difference of these positions from those of "d," "w," and "y," shews the amount 

 of discrepancy between observation and theory. 



It will be observed that D is situated near V (vermilion), but that a line 

 from D to W cuts UV at C near to V. D is therefore a red colour, not 

 scarlet, but further from yellow. It may be called crimson, and may be imitated 

 by a mixture of 86 vermilion and 14 ultramarine. This compound colour will be 

 of the same hue as D ; but since C lies between D and W, C must be 

 regarded as D diluted with a certain amount of white ; and therefore D must 

 be imagined to be like C in hue, but without the intermixture of white which 

 is unavoidable in actual pigments, and which reduces the purity of the tint. 



Lines drawn from D through "W" and "Y," the colour-blind positions of 

 white and yellow, pass through W and Y, their positions in ordinary vision. 

 The reason why they do not coincide with W and Y, is that the white and 

 yellow papers are much brighter than the colours corresponding to the points 

 W and Y of the triangle V, U, G; and therefore lines from D, which represent 

 them in intensity as well as in quality, must be longer than DW and DY in 

 the proportion of their brightness. 



