Bodies Lit by a Single Window Cast Unequal Shadows
How the size of window-light seen by each body governs its derived shadow
Continuing from the window s t, Leonardo compares two bodies m n and p q set opposite the light: m n has the smaller derived shadow because it sees the larger part of the hemisphere c d, while p q, seeing only the smaller part a b, casts more shadow. He states a general rule that bodies scattered in a room lit by a single window cast shadows more or less short according to how directly they face it. A large diagram couples a semicircular window with three spheres whose shadow cones diverge according to their placement.
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The greater the hemisphere a body sees, the smaller its shadow
Through the window the luminous species enter, and m n, p q are the bodies opposite. m n has the lesser derived shadow because its original shadow is small and its derived light great, the original light c d being great; p q casts more, because that part of the hemisphere a b lighting it is smaller than the hemisphere c d that lights m n.
Bodies facing the window most directly cast the shortest shadow
Bodies scattered in a dwelling lit by a single window make their derived shadow more or less short according as they face the window. Among equal bodies at unequal distances from the aperture, the longer shadow belongs to the less-lit body, and the shadow 4 keeps to x y the proportion that n m and v k hold with s t and v x.
Diagram of a window arc with three shadow-casting spheres
A large geometric figure fills the lower page: a semicircular arc (the window) crossed by radiating construction lines above three small circles. Each circle throws a shaded shadow cone toward the base line, the flanking cones splaying outward while the central one falls straight down.