Greater light, greater shadow; death of the derivative shadow
Large sky-light casts a large shadow, universal light destroys it, and the simple shadow of first darkness
Continuing the treatise on cast shadow, Leonardo shows that a greater quantity of light produces a greater derivative shadow: a small light a b makes small shadows c g e and d f h, while the universal light of the sky (n m) casts large shadows r t x and o s u, each portion of sky projecting its opposite shadow. He adds that the derivative shadow is entirely destroyed under universal light, yet grows most powerful under a small, intensely bright particular light. A final paragraph defines the simple shadow of first darkness, using a sphere g set in a concavity b c e f lit by a particular light a. Two pen diagrams — a small light and an arc of sky, and the sphere in its concavity — accompany the text.
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Greater light yields a greater shadow (a b; n m sky)
A derivative shadow is larger the greater the quantity of light that casts it. A small light a b makes the small shadows c g e and d f h; but the universal light of the sky, n m, makes the large shadows r t x and o s u, since the sky-part p n casts shadow r t x and the sky-part l m casts the opposite shadow o s u.
Death and highest power of the derivative shadow
Under universal light the derivative shadow is entirely destroyed. Conversely, under particular lights it grows most powerful the smaller the sensible quantity of the light and the more potent its brightness.
The simple shadow of first darkness (sphere g, concavity b c e f)
The simple shadow can be seen by no reflected light and is only augmented by an opposite shadow. Leonardo sets sphere g in the concavity b c e f under the particular light a, which strikes at b, reflects to d, and rebounds by a second reflection onto g, gathering part of the simple shadow in the angle e.
Diagrams of the sky-arc and the sphere in its concavity
Two pen figures are set among the text: an upper pair showing a small light with hatched shadows and, below it, a wide arc representing the sky (n m) casting broad shadows; and a lower figure of a sphere g resting in a hatched concavity lit by a particular light a, illustrating the simple shadow.