n - S r - b a. Of the eye. It is impossible, along a straight line, through an aperture smaller than the sides of the visual pyramid, for the eye to know well the thing placed beyond that aperture. Although the eyes a b have before them the aperture r S open opposite n, nonetheless n is not known, because the master pyramid cannot be led to that n.

c – r t – n m. Eye. The thing seen through an aperture smaller than the base of the visual pyramid will be seen along a transverse line, and the thing on the right will go to the left eye and cannot be seen by the two eyes at one time; and if it is seen, it will be ill understood. The eye n, agreeing with the eye m to form the angle of the visual pyramid over c, cannot pass through the aperture t r, whence it cannot know that n, whence the likeness of it is mirrored and given along a transverse line to the eye m.

Eye. The reverse pyramids of uncertain vision do not carry to the eye the true likeness of any figure; and I call them reverse because they make their base in the width of the object. How is it possible that the quantity of the likeness of the sun pass through the indivisible point of the primitive into the derivative pyramid? The sun is composed of a very great number of indivisible parts, and although the sun be corporeal, its powers are spiritual — that is, heat and splendour; and because no spiritual power has body, having no body, it does not occupy space; not occupying, it does not close the aperture, whence through that aperture the passage is permitted to each spirit at one and the same time.

i diamante g - K h - e c – a – b – f d. It is possible for the solar ray, reduced by a pyramid by the concave mirror to a point, to be doubled in heat and splendour, those rays in the derivative pyramid being cast back by a similar mirror at equal distance from the point.

a — n m — q p. Office of the eye. Even if a body is interposed between the eye and the object, it will not take from the eye the form of that object, although it be not transparent, provided that body be smaller than the space found between one pupil and the other. Let a be the object, p q the two eyes, m n the body interposed between the eyes and the object.

a - f d - c r. Of the eye. That body which is interposed between the object and the eyes, although it be smaller than the space between one pupil and the other, will nonetheless block the object from the eyes if it is found in such a part of the visual pyramid that with its extremities it spans the width of that pyramid. Let r c a be the visual pyramid, d f the place where the above-said pyramid is cut by the interposed body; d f is the body greater than the section of the pyramid.

n — b a — h t. Eye. If the body interposed between the eye and the object blocks one of the 2 sides of the visual pyramid, the seen body will appear of as much less brightness as it is seen by a smaller quantity of light. Let t h n be the pyramid, n h the cut side, a b the body that interposes itself and takes from the eye h the sight of the luminous object placed at n. And if the two eyes saw that light of one quality of brightness, the eye t sees it half more darkened; because the two eyes, working upon the luminous thing with equal office, equally refer the luminous thing to the sense; but if one eye brings to the sense a dark thing and the other a luminous one, the one mixes with the other, and the darkness will seem half less dark than before and the light half less bright than before; and this you will see by experience, interposing the finger between one of the eyes and the light.