When a Body Nears a Smaller Light, Its Shadow Grows
If the luminous body is smaller than the object, closeness enlarges the shadowed part
Leonardo states the rule that when a luminous body is smaller than the body it illuminates, the shadow on that body grows as it is brought nearer the light. He proves it with a diagram in which the point-light a strikes two positions of a spherical object, and the straight rays embrace less of the sphere as it approaches, leaving more of it in shadow. The page closes by opening the converse proposition: which body, on nearing the light, instead diminishes its shadowed part.
On this page
A shadow enlarges when the light is smaller than the illuminated body
When the luminous body a is smaller than the shadowed body, its straight rays a n and a m embrace only part r s g and leave r l g in shadow. Bringing the sphere nearer the light to position d p e o, the rays a b and a c touch it at d and e, and the line d e divides its lit part from a shadow larger than before. Because the rays are straight, they separate from the middle of the body the more, the nearer it stands to the light.
Diagram of two sphere positions struck by rays from point a
At the center of the page two circles are drawn, joined by rays converging on a point at the left labelled a, the small luminous body. The nearer circle is the object drawn closer to the light, the farther circle its earlier, more distant position, illustrating how the shadow cone widens as the sphere approaches.