94 ON THE RELATION OF OPTICS TO PAINTING. 



II. SHADE. 



The circumstances which we have hitherto dis- 

 cussed indicate a profound difference, and one which is 

 exceedingly important for the perception of solid form, 

 between the visual image which our eyes give, when we 

 stand before objects, and that which the picture gives. 

 The choice of the objects to be represented in pictures 

 is thereby at once much restricted. Artists are well 

 aware that there is much which cannot be represented 

 by the means at their disposal. Part of their artistic 

 skill consists in the fact that by a suitable grouping, 

 position, and turn of the objects, by a suitable choice 

 of the point of view, and by the mode of lighting, 

 they learn to overcome the unfavourable conditions 

 which are imposed on them in this respect. 



It might at first sight appear that of the requisite 

 truth to nature of a picture, so much would remain 

 that, seen from the proper point of view, it would at 

 least produce the same distribution of light, colour, 

 and shadow in its field of view, and would produce in 

 the interior of the eye exactly the same image on the 

 retina as the object represented would do if we had it 

 actually before us, and looked at it from a definite, 



