ON THE RELATION OF OPTICS TO PAINTING. 123 



in order to obtain strong relief ; or he may dimmish 

 them, with Fra Angelico and his modern imitators, in 

 order to soften earthly shadows in the representation 

 of sacred objects. Like the Dutch school, he may 

 represent the varying light of the atmosphere, now 

 bright and sunny, and now pale, or warm and cold, 

 and thereby evoke in the observer moods which 

 depend on the illumination and on the state of the 

 weather; or by means of undisturbed air he may 

 cause his figures to stand out objectively clear as it 

 were, and uninfluenced by subjective impressions. By 

 this means, great variety is attained in what artists call 

 8 style ' or ' treatment,' and indeed in their purely pic- 

 torial elements. 



