126 ON THE RELATION OF OPTICS TO PAINTING. 



matters which, we can in reality only estimate in an un- 

 certain manner, such as the absolute intensities of light. 



That which is pleasant to the senses, the beneficial 

 but not exhausting fatigue of our nerves, the feeling 

 of comfort, corresponds in this case, as in others, to 

 those conditions which are most favourable for per- 

 ceiving the outer world, and which admit of the finest 

 discrimination and observation. 



It has been mentioned above that the discrimina- 

 tion of the finest shadows, and of the modelling which 

 they express, is the most delicate under a certain 

 mean brightness. I should like to direct your atten- 

 tion to another point which has great importance in 

 painting: I refer to our natural delight in colours, 

 which has undoubtedly a great influence upon our 

 pleasure in the works of the painter. In its simplest 

 expression, as pleasure in gaudy flowers, feathers, 

 stones, in fireworks, and Bengal lights, this inclination 

 has but little to do with man's sense of art ; it only ap- 

 pears as the natural pleasure of the perceptive organism 

 in the varying and multifarious excitation of its various 

 nerves, which is necessary for its healthy continuance 

 and productivity. But the thorough fitness in the con- 

 struction of living organisms, whatever their origin, 

 excludes the possibility that in the majority of healthy 

 individuals an instinct should be developed or main- 

 tain itself which did not serve some definite purpose.' 



