The Sun's Image in Curved Mirrors; Defining Half-Obliquity
Convex and concave reflection of the sun, with two quarter-circle diagrams
Optical and geometrical notes accompanied by two quarter-circle diagrams in the right margin. The upper text observes that the image of the sun grows in a convex mirror as the viewer draws away from it, and begins a parallel account for the concave mirror that the transcription leaves unfinished. The diagrams define 'half-obliquity' as the line bisecting a right angle, standing equally distant from the horizontal (equigiacent) line and the perpendicular, with points lettered a e b - c - d and a companion figure c - a - b. The sun-and-mirror passage breaks off mid-sentence in the source.
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How the sun's reflected image changes in convex and concave mirrors
The image of the sun in a convex mirror grows as one draws away from the mirror, and diminishes as the solar body itself recedes. Leonardo begins to state the corresponding behaviour for the concave mirror and the cause of the effect, but the transcription of this passage is left incomplete.
Half-obliquity as the bisector of a right angle in the quarter-circle
In the quarter-circle lettered a e b - c - d, the point c falls at the third of the horizontal (equigiacent) line. Half-obliquity is defined as the straight line arising at the right angle and standing equally distant from the line of equality (equigiacent) and the perpendicular, which together compose that right angle.
Companion figure relabelled c - a - b
A second, analogous figure repeats the construction with its points lettered c - a - b. It serves as a companion to the quarter-circle above, illustrating the same geometry of obliquity.