Light and Shade: Shadow Cast on a Sphere, with Diagrams
Two small geometric figures proving how darkness imprints unequally on a spherical body
Continuing the demonstration begun on the facing page, the text shows how a shadowy body and a luminous body each embrace a sphere with a pyramid of rays (n a m and r c s), so that the point c, which faces the greatest darkness, is the darkest of all. Two small letter-labelled diagrams at the centre of the page illustrate the argument, one proving that the darkness e g f imprints itself unequally on the arc b a c. Two further chapters follow: a reminder to give the beginnings of light and shade to every part in relief, and a note that every surface takes on part of the colour of the objects facing it. A worked example of a sphere set among coloured objects then begins.
On this page
Pyramids of shadow and light embracing a sphere
The shadowy body embraces almost the whole object with its pyramid n a m, and opposite it the luminous body does the same with the pyramid r c s. The point c, which sees most of the opposing darkness, is therefore darker than any other part of the sphere.
Two diagrams: darkness imprinted unequally on the arc
Two small geometric figures at the centre of the page show a sphere gripped by crossing pyramids of rays. The second figure proves that the arc b a c sees all the darkness e g f, but that this darkness does not imprint with uniform quantity: a, seeing all of e f, is much darker than b, which sees only half (g).
Give the beginnings of light and shade to every relief
Every part of the body and every smallest particle that has some relief should be given the beginnings of its shadows and lights. Leonardo urges the painter to attend to this in modelling form.
Surfaces take on the colour of facing objects
Every part of a surface surrounding bodies transmutes into part of the colour of the thing set opposite it. The example begins: place a spherical body among various objects — sunlight on one side, an illuminated wall (green or another colour) opposite, and a red plane beneath.