OF TREES THAT ARE LIGHTED BY THE SUN AND BY THE ATMOSPHERE.
In trees that are illuminated [both] by the sun and the atmosphere and that have leaves of a dark colour, one side will be illuminated by the atmosphere [only] and in consequence of this light will tend to blueness, while on the other side they will be illuminated by the atmosphere and the sun; and the side which the eye sees illuminated by the sun will reflect light.
439.
OF DEPICTING A FOREST SCENE.
The trees and plants which are most thickly branched with slender branches ought to have less dark shadow than those trees and plants which, having broader leaves, will cast more shadow.
440.
ON PAINTING.
In the position of the eye which sees that portion of a tree illuminated which turns towards the light, one tree will never be seen to be illuminated equally with the other. To prove this, let the eye be c which sees the two trees b d which are illuminated by the sun a; I say that this eye c will not see the light in the same proportion to the shade, in one tree as in the other. Because, the tree which is nearest to the sun will display so much the stronger shadow than the more distant one, in proportion as one tree is nearer to the rays of the sun that converge to the eye than the other; &c.
You see that the eye c sees nothing of the tree d but shadow, while the same eye c sees thè tree b half in light and half in shade.
When a tree is seen from below, the eye sees the top of it as placed within the circle made by its boughs[23].