ON THE EELATION OF OPTICS TO PAINTING. 95 



fixed point of- view. It might seem to be an object 

 of pictorial skill to aim at producing, under the given 

 limitations, the same effect as is produced by the 

 object itself. / 



If we proceed to examine whether, and how far, 

 painting can satisfy such a condition, we come upon 

 difficulties before which we should perhaps shrink, if 

 we did not know that they had been already over- 

 come. 



Let us begin with the simplest case ; with the quan- 

 titative relations between luminous intensities. If the 

 artist is to imitate exactly the impression which the 

 object produces on our eye, he ought to be able to 

 dispose of brightness and darkness equal to that which 

 nature offers. But of this there can be no idea. Let 

 me give a case in point. Let there be, in a pic- 

 ture-gallery, a desert-scene, in which a procession of 

 Bedouins, shrouded in white, and of dark negroes, 

 marches under the burning sunshine; close to it a 

 bluish moonlight scene, where the moon is reflected in 

 the water, and groups of trees, and human forms, are 

 seen to be faintly indicated in the darkness. You 

 know from experience that both pictures, if they 

 are well done, can produce with surprising vividness 

 the representation of their objects; and yet, in both 

 pictures, the brightest parts are produced with the 

 same white-lead, which is but slightly altered by ad- 



