A Treatise on Painting/Chapter 324
Chap. CCCXXIV.—Of a Town seen through a thick Air.
The eye which, looking downwards, sees a town immersed in very thick air, will perceive the top of the buildings darker, but more distinct than the bottom. The tops detach against a light ground, because they are seen against the low and thick air which is beyond them. This is a consequence of what has been explained in the preceding chapter.