1857.] M. ChevreuVs Laws of Colour. 429 



Buffon followed Newton, and his researches had special reference 

 to wiiat M. Chevreul had called the "successive contrasts" of 

 colours. 



Father Scherffer, a monk, also wrote on the laws of colour. 

 Goethe, the poet, also brought his mind to bear upon the subject, 

 and studied it to a great extent. Count Runjford, about the end of 

 the eighteenth century, published several memoirs on the laws of 

 colours. He explained very satisfactorily the " successive " con- 

 trast, and arrived at some insight into the "simultaneous" one ; 

 still he did not lay down its real laws. 



Pi'ieur, Leblanc, Harris, and Field, were also writers of most 

 interesting works on this subject. The reason that they did not 

 arrive at the definite laws of colour was because they had not 

 divided those laws into successive, simultaneous, and mixed con- 

 trasts. These form the basis of the practical laws of colour, and 

 the honour of their discovery is due to M. Chevreul. 



The reason why a surface appears white or brilliant is, that a 

 large portion of the light which falls on its surface is reflected on 

 the retina, and in such a quantity as gives to the surface a brilliant 

 aspect ; whilst in plain white surfaces, the rays of light being diffused 

 in all directions, and a small portion only arriving to the eye, the 

 surface does not appear brilliant. The influence of colours on these 

 two kinds of surfaces is very different, as may be perceived by the 

 examples round the room, showing the influence of different 

 colours on gold ornaments. When rays of light, instead of being 

 reflected, are absorbed by a surface or substance it appears black ; 

 therefore white and black are not colours, as they are due to the 

 reflection or absorption of undecomposed light. It is easy to un- 

 derstand why a surface appears blue ; it is due to the property 

 which the surface has to reflect only blue rays, whilst it absorbs the 

 yellow and red rays ; and if a certain portion of light is reflected 

 with one of the cploured rays it will decrease its intensity ; thus red 

 rays with white ones produce pink. On the contrary, if a quantity 

 of undecomposed light is absorbed, black is produced, which, by 

 tarnishing the colour and making it appear darker, genei*ates dark 

 reds, blues, or yellows. The secondary colours are produced by 

 one of the primitive colours being absorbed and the two others 

 reflected ; for example, if red be absorbed, and blue and yellow 

 reflected, the surface appears green. There are two reasons why 

 a perfect blue, yellow, red, cannot be seen, &c. The first is, that 

 surfaces cannot entirely absorb one or two rays and reflect the 

 others. The second is, that when the retina receives the impression 

 of one colour, immediately its complementary colour is generated ; 

 thus, if a blue circle is placed on a perfectly grey surface, an orange 

 hue will be perceived round it ; if an orange circle, round it will 

 be noticed a bluish tint ; if a red circle, a green ; if a greenish 

 yellow circle, a violet ; if an orange yellow circle, an indigo ; and 

 so on. 



