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Bibliothèque de l'Institut de France, Paris

[I]

In the visual virtue, the species do not converge to strike at a single point. And if you would have it that they passed through such a point, it would be necessary to admit1 that intersection occurs, which, of its nature, turns everything upside down that is seen. Therefore, as we see upright only, there is no intersection at all. And this is also proved in the following manner: Take a wisp of straw and put it before your eye at the distance of half a braccio, and examine it there. Then if you push it forward, the farther you make it go away, the more it diminishes, until it goes to nothing. And if you draw it from that half braccio toward the eye, the closer you bring it, the more it will diminish.2 And if you touch your eye with it, you will lose it entirely because of its diminution. If the eye saw with a point, this could not happen; indeed, the closer you brought it, the more it would grow.

Optical diagram, showing visual lines extending beyond a small, spherical object to a concave background. Points along the surface of the eye, marking the limits and center of the pupil, are labeled a, b, c, and d. The upper and lower portions of the spherical object are labeled i and k. Lines interior to the eyeball are labeled r and o, which cross each other and meet the back of the eye at points m and n. Points along the concave background are labeled e, f, g, and h. Continuations of the visual lines beyond the concave background, and their labels, are canceled by broad, irregular strokes.3

[II]

From a to d is the entire power of the eyesight. i k is a spherical body smaller than the pupil. Half a b of the pupil4 sees behind the body at points e through g. The other half of the pupil sees space f h behind the body; therefore, the pupil sees what is beyond the body or straw i k.

[III]

And by this, it is proved that the eye does not see through a point, but that a point is created in the middle of the pupil by the convergence of the pyramids, which does not belong to the office of the visual virtue. The body mentioned above will produce an obscurity at location e h, like fog, and this is because there is a part of the pupil that cannot see g h. Similarly, c d cannot see space e f, and the point in the middle does not see space f g.

[IV]

The visual virtue can be in the body in the middle, o r, or it can be in triangle m n, farther back. No, because pyramid m n, which extends outside of the spherical body, would refer all species upside down behind itself.

The eye does not see through a single point (pupil a-d, body i k, crossings m n)

In the visual virtue, the species do not converge to strike at a single point. And if you would have it that they passed through such a point, it would be necessary to admit that intersection occurs, which, of its nature, turns everything upside down that is seen. Therefore, as we see upright only, there is no intersection at all. And this is also proved in the following manner: Take a wisp of straw and put it before your eye at the distance of half a braccio, and examine it there. Then if you push it forward, the farther you make it go away, the more it diminishes, until it goes to nothing. And if you draw it from that half braccio toward the eye, the closer you bring it, the more it will diminish. And if you touch your eye with it, you will lose it entirely because of its diminution. If the eye saw with a point, this could not happen; indeed, the closer you brought it, the more it would grow. Optical diagram, showing visual lines extending beyond a small, spherical object to a concave background. Points along the surface of the eye, marking the limits and center of the pupil, are labeled a, b, c, and d. The upper and lower portions of the spherical object are labeled i and k. Lines interior to the eyeball are labeled r and o, which cross each other and meet the back of the eye at points m and n. Points along the concave background are labeled e, f, g, and h. Continuations of the visual lines beyond the concave background, and their labels, are canceled by broad, irregular strokes. From a to d is the entire power of the eyesight. i k is a spherical body smaller than the pupil. Half a b of the pupil sees behind the body at points e through g. The other half of the pupil sees space f h behind the body; therefore, the pupil sees what is beyond the body or straw i k. And by this, it is proved that the eye does not see through a point, but that a point is created in the middle of the pupil by the convergence of the pyramids, which does not belong to the office of the visual virtue. The body mentioned above will produce an obscurity at location e h, like fog, and this is because there is a part of the pupil that cannot see g h. Similarly, c d cannot see space e f, and the point in the middle does not see space f g. The visual virtue can be in the body in the middle, o r, or it can be in triangle m n, farther back. No, because pyramid m n, which extends outside of the spherical body, would refer all species upside down behind itself.

The eye does not see through a single point

A vision diagram (pupil a-d, body i k, crossings m n) arguing there is no single point of intersection in sight.

Optics & Light

Leonardo argues that vision does not converge on a single point inside the eye, for a true intersection would turn every image upside down, whereas we see things upright. He proves it with a wisp of straw held before the eye: pushed away or brought right up to the eye it only shrinks and at last vanishes, never growing as it would if the eye saw through a point. A lettered diagram lays out the pupil (a, b, c, d), a small spherical body i k smaller than the pupil, and the interior lines r and o crossing to meet the back of the eye at m and n, showing how each half of the pupil sees past the little body to the background e, f, g, h.

The point in the middle of the pupil, formed by the convergence of the pyramids, does not belong to the office of sight. The visual power may lie in the middle body o r, but not in the farther triangle m n, for the pyramid m n extending beyond the sphere would refer all species upside down behind itself.

Reader's Edition — described with AI from the e-Leo transcription.

The eye does not see through a single point (pupil a-d, body i k, crossings m n)

The eye does not see through a single point

On this page

Why the eye cannot see through a single point

The straw experiment: an object only shrinks toward the eye

The pupil (a b c d) sees past a small body (i k) to the background (e f g h)

Where the visual power lies (o r, or triangle m n)