ON THE RELATION OF OPTICS TO PAINTING. 133 



pictures in which the aerial colour, the coloured re- 

 flection and shade, so variously alter the tint of each 

 single coloured surface when it is not perfectly smooth, 

 that it is hardly possible to give an indisputable de- 

 termination of its tint. In such cases, moreover, the 

 direct action of the colour upon the eye is only a 

 subordinate means ; for, on the other hand, the 

 prominent colours and lights must also serve for 

 directing the attention to the more important points 

 of the representation. Compared with these more 

 poetical and psychological elements of the representa- 

 tion, considerations as to the pleasing effect of the 

 colours are thrown into the background. Only in the 

 pure ornamentation on carpets, draperies, ribbons, or 

 architectonic surfaces is there free scope for pure 

 pleasure in the colours, and only there can it develop 

 itself according to its own laws. 



In pictures, too, there is not, as a general rule, 

 perfect equilibrium between the various colours, but 

 one of them preponderates to an extent which corre- 

 sponds to the dominant light. This is occasioned, in 

 the first case, by the truthful imitation of physical 

 circumstances. If the illumination is rich in yellow 

 light, yellow colours will appear brighter and more 

 brilliant than blue ones ; for yellow bodies are those 

 which preferably reflect yellow light ; while that of 

 blue is only feebly reflected, and is mainly absorbed. 



