A Treatise on Painting/Chapter 204
Appearance
Chap. CCIV.—Of the Relief of Figures remote from the Eye.
Any opake body appears less relieved in proportion as it is farther distant from the eye; because the air, interposed between the eye and such body, being lighter than the shadow of it, it tarnishes and weakens that shadow, lessens its power, and consequently lessens also its relief.