OX THE KELATION OF OPTICS TO PAINTING-. 83 



jections, that is, perspective drawings which represent 

 a view taken from an infinite distance, give in many 

 cases a particularly favourable view of the object, 

 although they correspond to a point of sight which 

 does not in reality occur. Here the pictures of both 

 eyes for such an object are the same. 



You will notice that in these respects there is a 

 primary incongruity, and one which cannot be got 

 over, between the aspect of a picture and the aspect 

 of reality. This incongruity may be lessened, but 

 never entirely overcome. Owing to the imperfect 

 action of binocular vision, the most important natural 

 means is lost of enabling the observer to estimate 

 the depth of objects represented in the picture. The 

 painter possesses a series of subordinate means, partly 

 of limited applicability, and partly of slight effect, 

 of expressing various distances by depth. It is not 

 unimportant to become acquainted with these elements, 

 as arising out of theoretical considerations ; for in the 

 practice of the art of painting they have manifestly 

 exercised great influence on the arrangement, selec- 

 tion, and mode of illumination of the objects repre- 

 sented. The distinctness of what is represented is 

 indeed of subordinate importance when considered in 

 reference to the ideal aims of art ; it must not however 

 be depreciated, for it is the first condition by which 

 the observer attains an intelligibility of expres- 



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