How light and shadow fall on bodies: primitive and derivative shadow
Folio 1r opens Ms C with ray diagrams of light sources larger and smaller than the shadowed body
Folio 1r opens Leonardo's inquiry into light and shadow with a proposition that, among bodies of equal size and distance, the more brightly lit one appears to the eye nearer and larger. Three ray-traced diagrams then work out how illumination casts shadow onto a body: a light source larger than the shadowed body producing graded shadow; a luminous body larger than the shadowed one giving distinct primitive and derivative shadows lettered a c d b, e o f, r S; and a luminous body smaller than the shadowed one, lettered o z, x y, m n. A note observes that the upper and lower edges of the derivative shadow are less sharply defined than its lateral edge. The sheet bears the stamp of the Bibliothèque de l'Institut de France.
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The brighter of two equal bodies looks nearer and larger
Leonardo opens with a rule of perception: among bodies of equal size and equal distance from the eye, the one that is more strongly illuminated appears both closer and larger. The opening proposition ties apparent size and distance directly to the intensity of light falling on a body.
Light source larger than the shadowed body
The large upper diagram traces rays from a luminous source, at right, that is wider than the body it strikes, throwing hatched shadow across the field to the left. The caption identifies it as a light source larger than the shadowed body and points to the various gradations of shadow it produces.
Primitive and derivative shadow, light larger than body (a c d b, e o f, r S)
In this lettered construction a luminous body larger than the shadowed one yields both a primitive shadow on the body and a derivative shadow cast beyond it, marked a c d b, e o f, r S. Leonardo adds that the upper and lower extremities of the derivative shadow are less distinct than its lateral edge, because the light is taller than it is wide.
Primitive and derivative shadow, light smaller than body (o z, x y, m n)
The lowest diagram reverses the relation: the luminous body is smaller than the shadowed one, and the resulting primitive and derivative shadows are lettered o z, x y, m n. The rays fan out toward a small source at right while the cast shadow spreads across the screen.