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Codex Atlanticus — 0663 r

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© Veneranda Biblioteca Ambrosiana, Milan

Girato il foglio sul lato destro: Figura con:

f - e - b a - d c

Pruova come li occhiale aiuta a la vista. Siano li occhiali a b e li occhi c d, quali per essere invecchiati, bisogna che l'obbietto che soleano vedere in e con gran facilità e forte pieg[a]re 1) il loro assis dalla rettitudine de' nerbi ottici, la qual cosa per causa della vecchiezza viene tal potenzia di piegare a essere indebolita, onde non si po torcere sanza gran doglia d'essi occhi, sì che per necessità son constretti a fare più remoto l'obbietto, cioè da e a f, e lì poi lo vede meglio ma none alla minuta. Ora interponendo l'occhiale, l'obietto è ben conosciuto nella distanzia della gioventù, cioè in e, la qual cosa accade perché l'obbietto e passa all'occhio per vario mezzo, cioè raro e denso; raro per l'aria ch[e] [è] tra l'occhiale e l'obbietto, e [den]so si è per la grossezza del vetro d[elli] occhiali, onde la rettitudine ... [si] piega nella grossezza del vetro [e] [tor]ce la linia a d in modo, ch[e] [ve]dendo la cosa in e, esso la vede come in² f per comodità di non piegare l'assis dell'occhio da' sua nervi ottici, e per vicinità la vede e conosce meglio in e che in f, e massime le cose minute.

The sheet turned onto its right side. Figure with:

f - e - b a - d c

Proof of how spectacles aid the sight. Let the spectacles be a b and the eyes c d, which, being grown old, need the object that they used to see at e with great ease to strongly bend 1) their axis from the straightness of the optic nerves; and because, by reason of old age, this power of bending has become weakened, it cannot be turned without great pain of those eyes, so that of necessity they are constrained to set the object farther off, that is from e to f, and there they then see it better, but not in fine detail. Now, interposing the spectacle, the object is well known at the distance of youth, that is at e; and this happens because the object e passes to the eye through a varied medium, that is rare and dense: rare through the air that is between the spectacle and the object, and dense through the thickness of the glass of the spectacles, whence the straightness ... bends in the thickness of the glass and twists the line a d in such a way that, seeing the thing at e, it sees it as if at 2) f, for the convenience of not bending the axis of the eye from its optic nerves; and by nearness it sees and knows it better at e than at f, and especially small things.

Flowering Plant, and How Spectacles Restore Aged Sight

A tall blossoming stem, with a note on lenses correcting the failing eye

Botany Optics & Light

The sheet is dominated by a large finished drawing of a tall flowering plant, its stem crowded with star-shaped blossoms from base to tip. In the lower right corner a small lettered diagram accompanies a note on optics, explaining why aged eyes must hold an object farther off to see it and how a spectacle lens, by passing the image through rare air and dense glass, restores the near sight of youth. The optics text is written to be read with the sheet turned on its right side.

On this page

Study of a tall flowering plant

A carefully drawn stem rises the full height of the sheet, densely set with clustered, star-shaped flowers and long pointed leaves that curl outward. The drawing is a botanical study of the plant's habit rather than an illustration of the accompanying optical text.

Why spectacles let the old eye see up close

With the eyes marked c d and the spectacles a b, the note explains that an aged eye can no longer bend its axis from the straight optic nerves without pain, so it must push the object farther off, from e to f, seeing it better but not in fine detail. Interposing the lens lets the object be known again at the near distance of youth, at e, because the image passes through a varied medium, rare through the air and dense through the thickness of the glass, which twists the line a d so that the thing seen at e appears as if at f, and by nearness small things are known better.

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