ON THE RELATION OF OPTICS TO PAINTING. 129 



folds, on the contrary, the coloured surface reflects 

 against itself, and thereby makes its own colour more 

 saturated. A white surface, on the contrary, of great 

 brightness, produces a dazzling effect, and is thereby 

 insensitive to slight degrees of shade. Strong colours 

 thus, by the powerful irritation which they produce, 

 can enchain the eye of the observer, and yet be ex- 

 pressive for the slightest change of modelling or of 

 illumination ; that is, they are expressive in the 

 artistic sense. 



If, on the other hand, we coat too large surfaces, 

 they produce fatigue for the prominent colour, and a 

 diminution in sensitiveness towards it. This colour 

 then becomes more grey, and on all surfaces of a 

 different colour the complementary tint appears, espe- 

 cially on grey or black surfaces. Hence therefore 

 clothes, and more particularly curtains, which are of 

 too bright a single colour, produce an unsatisfactory 

 and fatiguing effect; the clothes have moreover the 

 disadvantage for the wearer that they cover face and 

 hands with the complementary colour. Blue produces 

 yellow, violet gives greenish yellow, bright purple 

 gives green, scarlet gives blue, and, conversely, yellow 

 gives blue, etc. There is another circumstance which 

 the artist has to consider, that colour is for him an 

 important means of attracting the attention of the 

 observer. To be able to do this he must be sparing in 



II. K 



