A Treatise on Painting/Chapter 121
Chap. CXXI.—Of Objects that are lost to the Sight in Proportion to their Distance.
The first things that disappear, by being removed to some distance, are the outlines or boundaries of objects. The second, as they remove farther, are the shadows which divide contiguous bodies. The third are the thickness of legs and feet; and so in succession the small parts are lost to the sight, till nothing remains but a confused mass, without any distinct parts.