Peaks that stay too dark; the painter's window test
Why the highest peak whitens less than it should, and how to judge a picture's viewing distance
Chapter 796 shows that mountain peaks equal in spacing and in difference of height do not diminish equally in color, because the highest peak is darker than it should be. Leonardo traces the sight-lines: peak o lies wholly in thick air and whitens strongly, while p and q are seen partly through thinner air, so q comes out brighter than o but still not as bright as its distance requires. Chapter 797, on the painter's deception in the size of trees and other bodies of the countryside, urges the painter or miniaturist to decide how far off the picture is to be viewed and to imagine a small opening, hole, or window at that distance through which the objects reach the eye. A small mountain diagram with sight-lines and letter-labels sits in the text.
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The highest peak o whitens more than lower peaks p and q (labels o, p, q, r, k, i, l)
Peak o lies wholly in thick air and whitens strongly; p is seen through less thick air along r a and thinner air along p r, so it whitens almost like o; q is seen through thick air along i a, then thinner k i, then thinner l k, so it is brighter than o but not as bright as its distance requires.
Chapter 797: the painter's deception in the size of trees and countryside
Leonardo tells the painter or miniaturist to judge how far from the eye the picture is to be seen, and to imagine at that distance a spiracle -- a hole or window -- through which the objects set before him reach his eye. This reveals how greatly distant things must be reduced in the painting.
Inset mountain diagram with layered air (labels o, p, q, r, k, i, l)
A small ruled drawing of a mountain range in profile is set into the text, with sight-lines from an eye passing through successive layers of air toward the peaks. The letters o, p, q, r, k, i, l mark the peaks and the points where the lines cross the layers of thick and thin air.