8 ON CONTRASTING THE COLOURS OF FLOWERS. 



relating to the contrast of colours, as given by M. Clievreul, in his 

 treatise De la hi du co7itraste sinmllane des couleurs. Tiiis eminent 

 philosopiier liaving been employed by the French Government to 

 ascertain the cause of a supposed deterioration of the dyes employed in 

 the national manufactures, satisfied himself that, in fact, no deterioration 

 whatever had taiien place; but that the want of biilliancy complained 

 of arose from loss of skill in the art of blending colours. Hence his 

 famous treatise, of which we propose to give a very sliort abstract. 



" Every ray of white light i-< composed of a certain number of red, 

 yellow, and blue rays combined in certain proportions. Red, yellow, 

 and blue are called simple colours ; other colours, being produced by 

 a combination of two or all of these, are called compound colours. 

 When white light falls upon any surface, it is either wholly absorbed 

 or wholly reflected, or partly absorbed and partly reflected by that 

 surface ; in the first case the surface looks black, in the second white, 

 and in the third it takes the colour of the reflected ray or rays. In the 

 last case it is evident that the effect of the absorbed and of the reflected 

 rays, if combined, would be the reproduction of white light. Now 

 this property possessed by rays of different colours, or in other words 

 by different colours, of producing, when combined in certain pro- 

 portions, white light, is expressed by saying that such rays or such 

 colours are complementary the one to the other. Thus we say, that — 



Red is complementary to green, and vice versa. 

 Orange , , to blue , , 



Greenish yellow , , to violet , , 



Indigo , , to orange yellow , , 



because red and green, orange and blue, greenish yellow and violet, 

 indigo and orange yellow, produce white light by their respective 

 combinations. 



" By the simultaneous contrast of colours, is meant the effect produced 

 on the eye by two different coloured bodies placed side by side ; by 

 contrast of tone, is meant the modification in depth or intensity of 

 colour ; and by contrast of colour, the modification in the optical 

 composition of each contrasted colour. 



" The first great point to remember with regard to this subject is, that 

 whenever the eye perceives at the same time two substances, differing 

 from each other in appearance, it sees them as dissimilar as possible, 

 both as regards their optical composition and the depth or tone of their 

 colour. 



" With respect to the tone or intensity of colour, it is univerally true 

 that, if two colours of different intensities, or if two portions of one 

 and the same colour differing only in intensity, be placed side by side, 

 the light colour appears lighter and the dark one darker by the con- 

 trast ; and the difference is greatest when the contrast is strongest, and 

 least where it is weakest ; or in other words, the diff'erence is greatest 

 about the line of contact, and grows less and less as Me recede there- 

 from. 



" As to contrast of colour, it is found by experiment, and it may also 

 be proved by a priori reasoning, that whenever the eye regards two or 



