Deep Wells, Particular Light, and the Shading of Mountains
Relief from a particular light; equal distant motions appear slower
This page of Book Five, headed QVINTA and numbered 231, completes the battle chapter and opens new ones, with a small pen diagram of an arc over upright bars on a base line. Wells grow darker with depth because their deepest part sees and is seen by less of the luminous air, while pavements are more lit between equal angles than the legs standing on them. A chapter on particular light argues it gives shadowed bodies better relief than universal light, as a sunlit stretch of country does against one shadowed by cloud. The section 'Of the shadows and brightnesses of mountains' then begins, followed by a chapter of common perspective stating that among equal motions the more distant from the eye appears slower, illustrated by the segments a to f, g to k, and l to m.
On this page
Why wells darken with depth
Wells grow darker the deeper they sink, because their deepest part sees and is seen by a lesser part of the luminous air than any other. Pavements of the same color as the men's and horses' legs are always more illuminated between equal angles than the legs themselves.
Particular light gives better relief
Particular light gives better relief to shadowed bodies than universal light, as shown by comparing a stretch of country lit by the sun with one shadowed by cloud, which is lit only by the universal light of the air.
Of the shadows and brightnesses of mountains
A new section opens, 'Of the shadows and brightnesses of mountains,' with the heading asking why distant mountains show their summits darker than their bases.
Common perspective: distant equal motion appears slower
Of things of equal motion, the one more distant from the eye appears slower, though in equal time it covers equal lengths at various distances, namely from a to f, from g to k, and from l to m. Velocity and length of motion appear in the same proportion as distance to distance.
Diagram of illumination between equal angles
A small pen diagram near the top of the page shows an arc drawn over upright bars on a base line, relating to the illumination of the legs and pavements between equal angles discussed in the text.