The eye, the pupil, and images of the sun on the sea
Optics of vision, the sun's reflection on waves, perspective diminution, and a calculation
In the right column Leonardo reasons about vision: because the eye is small it can see only a small image of the sun; the visual power is infused with equal strength throughout the whole pupil (d-c-b-a); and species of things smaller than the eye do not converge pyramidally within it. He treats the visual angle — a grain of millet near the eye can hide a distant city — and how, when objects stand against the sky with nothing to compare them to, distance is judged only by the diminution of their outlines and color. The left column studies the sun on the horizon over the ocean, explaining how the many images of the sun scattered across the waves lie between equidistant lines and appear, wave by wave in the shape of a pine cone, at the bottom, side, and top. A short division (111; 7000; 2333 1/3; 3333) is worked in the margin, and further faint sketches and text are present across the stained sheet.
On this page
Why the small eye sees only a small image of the sun
Because the eye is small it cannot see the sun's image except small; were the eye equal to the sun it would see in flat water an image equal to the sun's true body, and an eye larger than the mirrored thing sees the image larger. The visual power is infused with equal strength through the whole pupil (d-c-b-a), so vision operates whole through the whole pupil and whole in every part of it.
The visual angle and the diminution of distant things
That thing is called larger which reaches the eye at a wider angle; thus a grain of millet near the eye (b-a) covers a whole city remote from it. Distance is judged by comparison with the diminished things around, or — against the sky, where no comparison exists — by the diminution of outlines and color, while luminous bodies could never be judged this way.
Images of the sun across the sea's waves
The many images of the sun on the waves seem to spread over a long distance yet lie within their lateral extremes, between equidistant lines; a parallel body set before the eye, perpendicular to the center of the world, occupies the near narrow part as much as the far wide part of the pyramid that shines on the water. Wave by wave, in the shape of a pine cone, the sun shows at the bottom, on the side, and at the top.
A marginal division
A calculation is set down in the margin: 111 over 7000, with the results 2333 1/3 and 3333.