252 Notes 



meaning, and particularly those terms which denote colours 

 that are known to be mixtures of others, as green, purple, and 

 orange. Neither the prismatic green nor the colour of any 

 known green body may, perhaps, combine with red so as to 

 make actually an accurate white, and yet the existence or 

 composition of such a green may not be impossible. The 

 philosophical reader will clearly perceive that no argument 

 of any weight can be drawn from considerations of this sort 

 against this theory of coloured shadows. 



23. Every one knows that red colours and yellow colours 

 mixed together, in different proportions, produce orange col- 

 ours of various kinds : also that reds and blues produce purples 

 and violets -, and, lastly, that blues and yellows produce greens 

 in great variety ; but it is not so generally known that green, 

 purple, and orange colours are, as it were, almost annihilated 

 by mixture, and much improved by contiguity with red, yel- 

 low, and blue colours respectively. 



The little diagram [Fig. 28] suggests all these things to 

 the memory, and a great many more of the same kind ; and, 

 therefore, must be extremely useful to the artist who is endeav- 

 ouring to produce certain effects by contrast, harmony, etc., 

 but it should always be carefully remembered that it contributes 

 nothing to the proof of any of the truths here advanced; the 

 proof rests upon the reasons given for each of them respect- 

 ively. 



