ON 



THE EELATION OP OPTICS 



TO 



PAINTING. 



Being the substance of a aeries of Lectures delivered in 

 Cologne, Berlin, and Bonn. 



I FEAR that the announcement of my intention to ad- 

 dress you on the subject of plastic art may have created 

 no little surprise among some of my hearers. For I 

 cannot doubt that many of you have had more fre- 

 quent opportunities of viewing works of art, and have 

 more thoroughly studied its historical aspects, than I can 

 lay claim to have done ; or indeed have had personal 

 experience in the actual practice of art, in which I am 

 entirely wanting. I have arrived at my artistic studies 

 by a path which is but little trod, that is, by the phy- 

 siology of the senses ; and in reference to those who 

 have a long acquaintance with, and who are quite at 

 home in the beautiful fields of art, I may compare 



