Aerial Perspective: Bright Air, Whitened Horizon, Relief
Why lower air is brighter, the horizon looks whiter, and figures detach from their ground
Continuing the theory of aerial perspective, the page directs that in a range of mountains the lower parts be kept brighter than the heights, which show their true form and colour as they rise. Chapter [150] explains that thick low air catches more sunlight, so that toward the horizon the sky appears whiter and its colour is corrupted by dense vapours, while toward the sunrise the low air looks darker because fewer luminous rays pass through it. Chapter [151] adds that figures stand out best against grounds of contrasting light or dark colour at their edges. A further heading, [152] on depicting the sizes of painted things, opens at the foot of the page.
On this page
Mountains: lower parts brighter than the heights
In a range of mountains the lower parts should be kept brighter than the heights; the farther apart the hills, the brighter their lower parts, while the higher a form rises the more it shows the truth of its shape and colour.
Why thick low air whitens the horizon sky (chapter 150)
Thick air near the earth receives more sunlight than the thin air above because the rays meet more resistance. Where the sky ends at a low plain it is seen through this thicker, whiter air, so the horizon looks whiter than the zenith; looking toward the sunrise, the low air instead appears darker because fewer luminous rays pass through it.
Making figures stand out from their ground (chapter 151)
Figures appear most raised and detached when their grounds are of light or dark colours contrasting as much as possible at the figures' edges, with a diminution of brightness observed in the whites and of darkness in the dark colours.