On trees.

What outlines the plants show when remote, against the air that becomes their background.

a b c

The outlines that the branchings of trees make against the illuminated air take on, the more remote they are, a figure tending toward the spherical; and the nearer they are, the more they show themselves removed from such sphericity. As with the first tree, which, being near the eye, shows the true figure of its branching; this is almost diminished at b, and wholly lost at c, where not only are the branches of that plant not seen, but the whole plant is recognized only with great difficulty.

Every shadowy body, of whatever figure it may be, appears at a long distance to be spherical. And this arises because, if it is a square body, at a very short distance its angles are lost, and a little further off the smaller sides that remain are lost as well; and so, before the whole is lost, the parts are lost, being smaller than the whole. Just as a man, in this same effect, loses first his legs, arms and head before his trunk; then he loses first the extremes of the length before those of the breadth; and when these are made equal, it would be square if the angles remained, but since they do not remain, it is round.

A square reduced to an octagon and almost to a circle.