Why Bodies Facing the Window Squarely Cast Shorter Shadows
Foreshortening of the window, the axis of derived shadow, and colored shadows
Leonardo explains that a body set squarely before a window casts a shorter shadow because it sees the window in its true form, while oblique bodies see it foreshortened and thus receive less light. He then lays down a rule that the axis of every derived shadow lines up through six midpoints: of the derived shadow, the original shadow, the opaque body, the derived light, the window, and the part of sky that lights the body, naming each with letters y h, l h, l, l k, v and e. A final proposition opens the theme of colored shadows: a body smaller than its light throws derived shadows tinted with the color of their origin.
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The oblique body sees the window foreshortened and is less lit
A body squarely before the window's middle sees it in its true form and casts a short shadow; oblique bodies see it foreshortened, appearing small. The central body sees the hemisphere large (e f), the side ones small: q r sees a b, m n sees c d. Having more light, the central body is lit well below its center, so its shadow is shorter.
The six midpoints aligned on the axis of a derived shadow
Every midpoint of a derived shadow aligns with the midpoints of the original shadow, the opaque body, the derived light, the window, and the part of sky that lights the body. Here y h is the middle of the derived shadow, l h of the original shadow, l of the body, l k of the derived light, v of the window, and e the last middle of the original light.
A body smaller than its light casts color-tinted shadows
Leonardo states that every shadow made by an opaque body smaller than the original light will send forth derived shadows tinted with the color of their origin, introducing the doctrine of colored shadows developed on the following folio.