When a Shadow's Shape Follows Body or Light Source
Shadows resemble either the shadowing body or the luminous source that casts them
Leonardo states that the shapes of shadows often resemble the shadowing body that is their origin, and often the luminous body that is their cause. A first diagram of a light and a shadowing body of equal diameter shows that when source and body are alike, both the primary and the cast shadow keep their figure and size if the shadow falls between equal angles. A second diagram demonstrates that a long light makes the cast shadow of a round body wider and lower, and that a cast shadow can never match the shape of the shadowing body unless the source matches that body in figure and size.
On this page
A shadow resembles either the body or the source
The shapes of shadows often resemble the shadowing body that is their origin, and often the luminous body that is their cause. This principle governs the two diagrams that follow on the page.
Equal source and body preserve the shadow's shape
If the figure and size of the luminous body match those of the shadowing body, both the primary and derivative shadow keep the figure and size of those bodies when falling between equal angles. Otherwise the cast shadow at a distance can never resemble the shadowing body unless the source matches the illuminated body's shape.
A long light spreads a round body's shadow
A light of long figure makes the derivative shadow born of a round body wider and lower, even when struck between equal angles. It is impossible for the cast shadow to be similar to the shadowing body unless the light that causes it is similar in figure and size to that body.