… [ordinary man]; at the far edge of the plain that borders the sky it should be made at the height of that boundary where the flat earth meets the sky — save for the mountains, which are free.

[417] How small figures ought not, in reason, to be finished.
I say that if things appear of minute form, it comes about that the thing is far from the eye; and this being so, there must be much air between the eye and the thing, and the much air hinders the plain appearance of the form of those objects, so that the minute particles of those bodies become indiscernible and unrecognized. Therefore you, painter, will make the small figures merely suggested and not finished; and if you do otherwise, you will counterfeit the effects of nature, your mistress. The thing stays small because of the great distance between the eye and the thing; the great distance encloses within itself much air; the much air makes of itself a thick body, which hinders and takes from the eye the minute particles of the objects.

[418] What background the painter should use in his works.
Since by experience it is seen that all bodies are surrounded by shadow and light, I want you, painter, to arrange that the part which is illuminated end against a dark thing, and likewise that the shadowed part of the body end against a light thing. And this rule will give great help in bringing your figures into relief.

[419] Precept of painting.
c. Where the shadow borders the light, take heed where it is brighter or darker, and where it is more or less smoky (softened) to- …