Distance, a Sphere's Shadow, and the Darkest Shade
Past the light's own distance the eye can never fully lose a sphere's shadow
This page of Book Five argues that when the eye is farther from a shadowed sphere than the light illuminating it, no position around the sphere can wholly hide its shadow: as the eye circles at a constant distance, the shadow lost on one side is regained on the other. Here b n c is the shadowed body and a the luminous body, and the eye sees the whole shadow b d c e. A further chapter states that a body lit by the light of greatest splendor casts the darkest shadows, contrasting point a lit by the sun with point b lit by the sun-lit air. Two small diagrams of lit spheres accompany the text, which also bears a running head and folio number.
On this page
The eye can never fully lose a sphere's shadow
When the eye is farther from the shadowed sphere than the light that illuminates it, no position can wholly deprive it of the body's shadow. With b n c the shadowed body and a the light, the eye sees the whole shadow b d c e; moving in a circle at the same distance, whatever shadow it loses on one side it gains on the other.
The brightest light casts the darkest shadow
The body illuminated by the light of greatest splendor will cast shadows of the greatest darkness. The point a is illuminated by the sun, while the point b is illuminated by the air that the sun has lit, and their contrast follows the proportion of the sun's light to that of the air.