...the space f-e; for which reason that object c remains transparent, according to the definition of transparency, behind which nothing is hidden — which cannot happen to one who sees the object with a single eye, an object larger than that eye; and this could not happen to an eye that sees objects much smaller than its pupil, as is shown in the margin. And from what has been said we can conclude our question: because a painted thing occupies all the space that it has behind it, and by no means is it possible to see any part of the field that lies within its circumferential line, behind it.

Which appears more in relief: the relief near the eye, or the relief remote from the eye.
That opaque body will show itself of greater relief which is nearer to the eye; and consequently the more remote will show itself of lesser relief, that is, less detached from its field. This is proved: let p be the front of the object p-h, which is nearer to the eye a than is n, the front of the object n-m; and the field d-f is that which ought to be seen behind the first two said objects by the eye a. Now we see the eye a, which beyond the object p-h sees all the field d-f, and does not see, behind the second object n-m, more than the part of the field d-g. Therefore we shall say that the proportion of the demonstration of the relief of the two objects to one another is as field is to field, that is, from the field d-g to the field d-f.