Concave mirror from a circle-segment: equal angles
A 1/14 to 1/16 arc makes a good mirror; incidence equals reflection (a n b, b m c)
A geometrical optics study of a concave mirror. Leonardo notes that a segment of about one fourteenth, or if preferred one sixteenth, of the circle makes a quite good mirror, and asserts the equality of the angles a n b and b m c, and of the paired tangent angles o r and S u, because the line h o lies as far from the central line i g as the line K r. A dense fan of rays is drawn converging on the curved mirror at the left. A separate calculation multiplies 34 by 8 to give 272, and further untranscribed text runs across the sheet.
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A good mirror from 1/14 to 1/16 of the circle
A segment of one fourteenth, or if you wish one sixteenth, of the circle will make a very good mirror. The remark ties the curvature of a workable concave mirror to a small fraction of a full circle's arc.
Equality of the reflection angles
It is proved that the angles a n b and b m c are equal, and likewise the tangent pairs o r and S u among themselves, because the line h o is as far from the central line i g as is the line K r.
Rays converging on the curved mirror
A dense fan of straight lines is drawn converging on the curved reflecting surface at the left, mapping how rays strike the mirror and meet toward a focus.
34 times 8 makes 272
A short multiplication set at the right works 34 by 8 to give 272, a calculation apart from the mirror construction.