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© Veneranda Biblioteca Ambrosiana, Milan

Colonna destra. Figura colle lettere:

c-pnS-bd
Qui la similitudine di a b, passata al centro n, si volta in c d sotto sopra e l'ombra va diritta di a in c e da b in d e, passato S¹, si volterà sotto sopra in r t, e p sia ['l] lume.

Figura di occhio con:

n m

Se pigli le palpebre di sopra e colle dita le tiri in basso, i legni2 n m essendo scuri e campeggianti in campo chiaro e luminoso, ti parra' fare in contrario moto a quel del coperchio di sopra. E ques[t]o è perché, tocca[ndo] l'occhio le similitudine lontane, in simil lato pare si movino per altro moto contrario a questo. E ['n] la palla di vetro le cose mosse nel contatto di t v dimosteranno all'occhio (Figura colle lettere t v n) la verità del loro movimento e, passata la piramide n, faranno o appariranno di contrario moto e la palla del nostro occhio tutte le cose lontano rende al senso diritte e le da presso toccante se medesimo rende sotto sopra.

Figura colle lettere:

a b

L'occhio adunque vedendo le cose lontane diritte, e lo buso della popilla per la intersegazione delle spezie fatte in esso le volta sotto sopra, onde l'occhio le vede da lontano diritte e le da presso, toccante la piramide della intersegazione, appariscano di contrario moto.

Figura di occhio e oggetto colle lettere:

m S - n f

Colonna sinistra. Figura colla lettera:

Sperienzia come, non movendo la popilla de suo sito, le cose viste da quella pare moversi fori del suo loco.
Se riguarderai una cosa alquanto distante da te, la quale sia più bassa che l'occhio, e fermerai in quella le tue due popille e coll'una delle mani apri e tieni fermo il coperchio di sopra e coll'altra alzerai in alto il coperchio di sotto, sempre tenendo ferme le luce nella cosa riguardata, vederai essa cosa dividersi in due, e l'una sta ferma, l'altra si move in contrario moto a quello che fai fare col dito al coperchio di sotto.
Com'è falso l'openione di quegli che dicano questo accadere perché la luce esce fori di suo sito.
Se vuoi vedere come el sopra detto effetto non accade perché la luce si mova di suo sito, riguarda bene l'occhio d'un che s'adoperi in simile sperienza e considera ben lo spazio del bianco dell'occhio che si truova infra il disopra della luce e 'l coperchio di sopra dell'occhio, e in mentre che 'l riguardatore moverà il coperchio di sotto d'alto in basso, non vederai mai mutare lo spazio ch'è infra la luce e 'l coperchio di sopra. Adunque la luce non si muta di sito.
Come per le sopra dette cose si dimostra la popilla operare sotto sopra il suo vedere.

Figura colle lettere:

no - a - m - b
Se metti il dito in a b in modo tale che il razzo fatto nel coperchio di sotto non veda la piramide de' razzi fatti da m n, [m] [n] si mancherà all'occhio.

Right column. Figure with letters:

c - p n S - b d

Here the likeness of a b, having passed the centre n, turns upside down into c d; and the shadow goes straight from a to c and from b to d; and, having passed S, it will turn upside down into r t; and let p be the light.

Figure of an eye with:

n m

If you take the upper eyelids and with your fingers pull them downward, the sticks n m -- being dark and standing out against a bright, luminous field -- will seem to you to move in the contrary direction to that of the upper lid. And this is because, the eye touching the distant likenesses, they seem on the same side to move by another motion contrary to this. And in the glass ball, things moved at the contact of t v will show the eye (figure with letters t v n) the truth of their movement; and, the pyramid n having been passed, they will make, or appear to make, contrary motion. And the ball of our eye renders to the sense all distant things straight, and those near, touching itself, it renders upside down.

Figure with letters:

a b

The eye, then, seeing distant things straight -- and the hole of the pupil, by the intersection of the images made within it, turning them upside down -- whence the eye sees them straight from afar, and those near, touching the pyramid of the intersection, appear of contrary motion.

Figure of an eye and object with letters:

m S - n f

Left column. Figure with the letter:

Experiment showing how, without the pupil moving from its place, things seen by it appear to move out of their place. If you look at something somewhat distant from you, which is lower than the eye, and fix both your pupils on it, and with one of your hands open and hold still the upper lid, and with the other raise the lower lid, all the while keeping the eyes fixed on the thing regarded, you will see that thing divide into two: one stays still, the other moves in the contrary direction to that which you make the lower lid do with your finger. How false is the opinion of those who say this happens because the light goes out of its place. If you wish to see how the aforesaid effect does not happen because the light moves from its place, look closely at the eye of one who is performing such an experiment, and consider well the space of the white of the eye that lies between the top of the light and the upper lid of the eye; and while the observer moves the lower lid from top to bottom, you will never see the space between the light and the upper lid change. Therefore the light does not change its place. As, by the aforesaid things, is demonstrated the pupil to work its seeing upside down.

Figure with letters:

n o - a - m - b

If you put your finger at a b in such a way that the ray made at the lower lid does not see the pyramid of the rays made by m n, then m n will be missing to the eye.

How the eye turns images upside down through the pupil

Eyelid experiments, the pyramid of rays, and why near things appear inverted.

Optics & Light

Two columns of text with eye diagrams develop Leonardo's theory of vision as an inversion of images. He argues that the likeness of an object, passing the centre of the eye, turns upside down, so that distant things are seen straight while near things, touching the pyramid of intersection, appear reversed. Several passages describe hands-on experiments with the eyelids and pupil to show that apparent motion of a viewed object comes from the eye's workings, not from the light leaving its place. A transparent glass ball is used as a model of the eye's optics.

If you pull the upper eyelids down with your fingers, the dark rods n m against a bright field seem to move opposite to the lid. Leonardo uses a glass ball to argue that things touching the eye near the pyramid of intersection appear to move contrarily, while the ball of the eye renders distant things straight and near things, touching itself, upside down.

The hole of the pupil and the pyramid of intersection

The eye sees distant things straight, but the hole of the pupil, by the intersection of the images made within it, turns them upside down. Thus far-off things appear straight while near ones, touching the pyramid of the intersection, appear of contrary motion.

Fix the pupil, move the lower lid: the object splits in two

Fixing both pupils on a low, somewhat distant object while one hand holds the upper lid still and the other raises the lower lid makes the object divide in two, one part still and one moving contrary to the finger. Leonardo uses this to refute those who say the effect happens because the light leaves its place, noting that the white space between the pupil-light and the upper lid never changes; therefore the light does not move, and the pupil works its seeing upside down.

Blocking the pyramid of rays makes m n vanish (n o - a - m - b)

If you place your finger at a b so that the ray made at the lower lid cannot see the pyramid of rays from m n, then m n will be lost to the eye. A small figure labels the eye and object as m S - n f.

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

Colonna destra. Figura colle lettere:

Figura di occhio con:

Figura colle lettere:

Figura di occhio e oggetto colle lettere:

Colonna sinistra. Figura colla lettera:

Figura colle lettere:

Right column. Figure with letters:

Figure of an eye with:

Figure with letters:

Figure of an eye and object with letters:

Left column. Figure with the letter:

Figure with letters:

How the eye turns images upside down through the pupil

On this page

Images invert past the centre (c - p n S - b d)

Pulling the eyelid: rods seem to move in contrary motion

The hole of the pupil and the pyramid of intersection

Fix the pupil, move the lower lid: the object splits in two

Blocking the pyramid of rays makes m n vanish (n o - a - m - b)