ON THE RELATION OF OPTICS TO PAINTING. 75 



seems to predominate more particularly in painting, 

 and this is the reason why I have chosen painting as 

 the subject of my present lecture. 



The more immediate object of the painter is to 

 produce in us by his palette a lively visual impression 

 of the objects which he has endeavoured to represent. 

 The aim, in a certain sense, is to produce a kind of 

 optical illusion ; not indeed that, like the birds who 

 pecked at the painted grapes of Apelles, we are to sup- 

 pose we have present the real objects themselves, and 

 not a picture ; but in so far that the artistic represen- 

 tation produces in us a conception of their objects as 

 vivid and as powerful as if we had them actually before 

 us. The study of what are called illusions of the senses 

 is however a very prominent and important part of 

 the physiology of the senses ; for just those cases in 

 which external impressions evoke conceptions which 

 are not in accordance with reality are particularly in- 

 structive for discovering the laws of those means and 

 processes by which normal perceptions originate. We 

 must look upon artists as persons whose observation 

 of sensuous impressions is particularly vivid and accu- 

 rate, and whose memory for these images is particu- 

 larly true. That which long tradition has handed 

 down to the men most gifted in this respect, and 

 that which they have found by innumerable experi- 

 ments in the most varied directions, as regards means, 



