...are surrounded by shadows which are toward the middle of the scene, because they are shaded by the figures interposed between them and the light; and those are shaded on one side only which are interposed between the light and the scene, because where it does not see the light it sees the scene, and represents there the darkness of that scene, and where it does not see the scene it sees the splendour of the light, and represents there its brightness.

The secondary point is that the sowing, or distribution, of the figures be apportioned according to the case in which you wish the scene to be. Third, that the figures be, with readiness, intent upon their particular business.

[484] a. On the relief of figures remote from the eye. That opaque body will show itself to be of less relief which is farther from the eye; and this happens because the air interposed between the eye and that opaque body, being a thing brighter than the shadow of such a body, corrupts that shadow and lightens it, and takes from it the power of its darkness, which is the cause of making it lose its relief.

[485] On the edges of illuminated limbs. The edge of that illuminated limb will appear darker which is seen against a lighter ground, and likewise that will appear lighter which is seen against a darker ground; and if such an edge be flat and seen against a light ground similar to its own brightness, then such an edge will be imperceptible.

[486] c. On edges. The edges of second things will never be known as...