Degrees of shadow and light cast by a window on a body
Propositions on how much of a window each point of a shady body can see
The page continues Leonardo's analysis of the degrees of shadow and light produced when a window's light falls on a shadowy body, grading each place from the first to the last degree according to how much of the window (a d, b d, c d) it can see. Two lettered propositions follow: the part of a shadowy body seen by less light is less luminous, and light striking between equal angles holds the first degree of brightness, with light and shadow doing their work through pyramids. Faint construction lines run behind the text and the letter labels a through q are referenced throughout.
On this page
Degrees of shadow measured by how much of the window is seen
A triangle contains the first degree of shadow because the light a d does not reach it. The place x h is the second degree, seeing only a third of the window (c d); h e the third degree, seeing two thirds (b d); and e f the last degree of shadow, reached only by the window's faintest light at f.
The part seen by less light is less luminous [729]
Point m is the first degree of light, seeing the whole window a d along line a f; n the second (light b d), o the third (c d), p the penultimate, and q the last, which sees no part of the window. As much as c d enters into a d, so much darker is n r s than m, while the rest of the field stays without shadow.
Equal angles give the first degree of brightness [730]
Every light falling on shadowy bodies between equal angles holds the first degree of brightness; that which receives the less equal angles is darker, and light and shadow both perform their office by pyramid. The angle c holds the first degree of brightness.