A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
Among Bodies of equal Obscurity, Bigness, Figure, and Distance from the Eye, that will appear the smallest, which is seen on the Whitest Ground, or in the most luminous place: this may be observed in looking at a Tree, stripp'd of its Leaves, and illumined by the Sun, on the side opposite to that, whereon you look; for in that case, those Branches of the Tree, which face the Sun, will be diminished to that Degree, as almost to become invisible: And the same thing will be found in holding out a Pike, or other long Pole, straight between the Eye, and the Sun.
Parallel Bodies, placed upright, and seen in a Fog, will appear larger towards the Top, than near the Bottom: the reason is, that the Foggy Air, being penetrated by the Rays of the Sun, will appear by so much the Whiter, as it is the lower.
Bodies seen at a distance, appear ill proportioned: this happens, because the brighter parts send their Images to the Eye, stronger and more sensible, than those emitted from the obscurer parts; and I once observed, in looking at a Woman, who was dress'd in Mourning, that her Head which was covered with a White Hood, appeared twice as large as her Shoulders which were Black.