First. Of equal things, the more remote appears smaller.

The practice of perspective is divided into [two] parts, of which the first figures all the things seen by the eye at whatever distance; and this in itself shows all those things as the eye sees them diminished, and the man is not obliged to stand in one spot more than in another, provided the wall does not foreshorten it a second time.

a b c - d e - f g - h

But the second practice is a mixture of perspective made partly by art and partly by nature, and the work, made by its rules, has no part that is not mixed with natural perspective and with accidental perspective. By natural perspective I mean the flat wall on which such perspective is figured, which wall, although it be of parallel length and height, is constrained to diminish the remote parts more than its nearer parts. And this is proven by the first stated above, and its diminution is natural. And accidental perspective, that is, the one made by art, does the contrary in itself, because it increases upon the foreshortened wall the bodies that in themselves are equal, the more the eye is more direct and nearer to the wall, and the more the part of that wall where it is figured is more remote from the eye. And let this wall be d e, on which were figured 3 equal circles that are beyond that d e, that is, the circles a b c. Now you see that the eye h sees upon the rectilinear wall the sections of the larger images at the greater distances and smaller at the near ones.