Perspective is demonstrative reason, by which experience confirms that all things send their images to the eye along pyramidal lines. By pyramidal lines, I mean those that start from the superficial edges of bodies and lead through distant convergence to a single point, which point, in this case, I shall demonstrate to be in the eye, the universal judge of all bodies.

I shall call the point that which cannot be divided into any parts.  Therefore, since this point located in the vision is indivisible, no1 body is seen by the eye unless it is greater than this point.  Being thus,2 the lines that come from the body to the point must necessarily be3 pyramidal; and if anyone wanted to prove that the visual virtue did not consist in this point4 and, indeed, that it were not5 that black point you see in the middle of the pupil, to these one could respond that6 a small thing such as a grain of millet or panic-seed, or another similar thing, could never diminish over any distance, nor could something greater than this point ever be seen entirely, as appears in the proof below.7

a b - c d - e f

[II]

Let a be the visual virtue, let b e be the concourse8 of the lines coming to the eye; let c d9 be the grains of millet within this concourse. By reason, you see that these will never diminish through distance, and body m n cannot be entirely comprehended by those.10 Therefore, it is necessary to admit that the eye has within itself one single and indivisible point, at which all the tips of the pyramids starting from the bodies come together, as appears here below.

Let a b be the eye, whose center contains the previously named point. If line e f  has to enter, as an image, through such a small hole in the eye, it must be admitted that the greater11 thing cannot enter into the lesser, unless that diminishes; and since it does diminish, it is necessary that a pyramid occurs.