ON THE RELATION OF OPTICS TO PAINTING. 135 



tinct as the length of path increases which it has to 

 traverse, and that further, this coloration is more 

 pronounced as the background falls into shadow. 



In summing up once more these considerations, we 

 have first seen what limitations are imposed on truth 

 to Nature in artistic representation ; how the painter 

 links the principal means which nature furnishes of 

 recognising depths in the field of view, namely binocu- 

 lar vision, which indeed is even turned against him, 

 as it shows unmistakably the flatness of the picture ; 

 how therefore the painter must carefully select, partly 

 the perspective arrangement of his subject, its posi- 

 tion and its aspect, and partly the lighting and 

 shading, in order to give us a directly intelligible 

 image of its magnitude, its shape, and distance, and 

 how a truthful representation of aerial light is one of 

 the most important means of attaining the object. 



We then saw that even the scale of luminous 

 intensity, as met with in the objects, must be trans- 

 formed in the picture to one differing sometimes by a 

 hundredfold; how here, the colour of the object 

 cannot be simply represented by the pigment; that 

 indeed it is necessary to introduce important changes 

 in the distribution of light and dark, of yellowish and 

 of bluish tints. 



The artist cannot transcribe Nature; he must 



