Angle of contingence to a circle; the eye and inverted vision
A geometric tangent construction and a note on the pupil
The upper fragment and lower sheet combine geometry and optics. Leonardo gives a compass construction for the 'angle of contingence' — the tangent to a circle n c f through given points — then turns to vision, sketching an eye lettered c A b amid lenses and half-moon shapes. His note reasons that if the pupil lay farther than the center required for the circle of light, everything seen would appear upside down.
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Constructing the angle of contingence to a circle
Given points a and b on the circle n c f, Leonardo draws the line b c from one point to the center, opens the compass to b c to strike the arc b g h, then draws the tangent b f touching the circle at f and raises the perpendicular c f to fix the true point of contact f.
The pupil, the circle of light, and inverted vision
In a note beside an eye lettered c A b, Leonardo reasons that if the things mirrored in the light and carried to the pupil found the pupil set farther than the center required for the circle of the light, all the things seen by the pupil would appear upside down.