On the eye. The species of the objects diffused in the air facing them are all in all that air and all in every part of it. It is proved. The reception of objects. All that air sees the object facing it, which is seen by that same object. It is proved by the third proposition of this work, which says: all visions made in one and the same quality of air are straight lines. Therefore, it being possible to draw a straight line from the eye to each part of the air seen by that eye, that vision is rectilinear. It is also proved by that which Aristotle says: every natural action is done in the shortest way possible, etc. Therefore vision will be made by the shortest line, that is, a straight line. On the species of objects diffused through the air. Objects have their species diffused in all the air seen by those objects, which species are all in all the aforesaid air and all in every part of it.

Second.

Labels: a b c d e - o p - r v - S - n m - x - t h. The edges of bodies are little known, because such edges are made of surfaces reduced to lines, which, being indivisible, are imperceptible.

First.

Labels: a n x g m b - e o p f - c q S t v r d.

How the eye does not know the edge of any body.

Labels: S r t - a b - c p - n m - d e f g h. The eye will never be capable of perceiving the true edge that the figures of any body standing out in a remote place have. It is proved: let the pupil of the eye be a b, let c p be the body set before the eye, of which the upper extreme c is marked, and let n m be the field in which that extreme must be seen by the eye. I say that the extreme of that body will not be known in what part of the field it terminates; this is proved with the help of the third proposition of this work, which says: the visual faculty is not in a point, as the perspective painters would have it, but is all in all the pupil, where the species of objects penetrate, and is within the eye in a greater space than the pupil; but the images are the more known the nearer they are to the centre of that faculty in the said space, and the less so the more remote from that centre. Therefore if the faculty a b takes the extreme of the object c, the central line of the visual faculty r sees c in the part of the field f, and the upper extreme of that faculty, S, sees c in the field h, and the lowest part sees c in the field d, and so it goes scattering through the whole field d h; and for this reason the extreme is not known to the eye, because the sense of the visual faculty is diffused through all that faculty, which offers to the estimative faculty a confused termination of that extreme c, so much the more or less as it is nearer to or more remote from the central line, and so much the more or less as c is more remote from or near to the eye.

Continues what is missing below. But the edges of drawn things (because they are joined to the field on which they were figured) are not subject to the said defect; and for this reason paintings near the eye must be figured with edges less distinct than the edges of remote things; and this you will recognize perceptibly by judging the upper edge of an object brought close to the eye and then moved away.