The eye, mirrors, and binocular double vision
Inverted images, a two-centred mirror, the eye as a circle of fire, and doubled sight.
This crowded sheet pursues the optics of the eye and of mirrors. Leonardo sets out the reasons why rays of light appear to the eye and appear inverted, and why an eye distorted by a finger sees itself as a circle of fire. He compares the inversion in a plane mirror to that in the eye, sketches a 'mirror of two centres', and explains binocular vision: only the central lines of the two eyes report a single object, while others make a thing appear double. A study of a transparent sphere closes the reasoning, noting where shadow is darkest and how every seen thing is known by the second objects around it. Some short marginal notes on the sheet lie outside the transcribed blocks.
On this page
Why the rays of light appear, and appear inverted
A heading above an eye-and-object diagram announces the theme: the reason why the rays of light appear to the eye, and why upside down, and how the rays are generated in the thickness of the eyelids.
The eye distorted by a finger sees a circle of fire
Below a second eye figure Leonardo notes why the eye, pressed out of shape with the finger, sees itself as what appears to be a circle of fire.
Mirror inversion and the eye (b a - d c)
If the mirror a c takes in the object a b it appears upside down, and so does c d; remove b from above and its image below the mirror at c is lost. The same happens to the eye: raising the upper lid causes the lower ray to be missing.
A mirror of two centres
A figure labelled Light and Eye is annotated that a mirror of two centres will produce these effects, linking the doubling geometry to a curved reflecting surface.
Binocular vision: central lines see single, others double
Only the central lines of the two eyes report a single object at b to the sense m; all the others show it doubled. Thus the thing n, seen by the eyes a c, seems to be two because it occupies two places, appearing at d and f.
Shadow in a transparent sphere; things known by their surroundings
In diaphanous spherical bodies the shadow is darker at the convex top than in the hollow, and darker within the ball's derivative shadow. Every seen thing is surrounded by secondary objects and is known by them; the farther the second thing lies from the first, the more the first fills the eye.