Primitive and Derived Shadow; a Sun-Moon-Eye Diagram
The science of cast shadow and penumbra, with notes on percussion and an astronomical sighting
A multi-directional sheet of Leonardo's science of shadows, to be read partly upside down. He formulates rules relating the darkness and edge-blending of the derived (cast) shadow to its distance from the primitive (attached) shadow and from the light, and describes how a light larger than the body makes shadows intersect and reconverge as though from two separate lights. A separate passage defines the 'blow' (colpo) as an indivisible part of motion, bounding force in time and distance. A diagonal diagram aligns Sun, an 'eye in the world' and Moon, noting that the Sun appears to lie as much inside the moon as outside it. Further untranscribed writing fills the margins.
On this page
Darkness of the derived shadow depends on distance
The nearer the derived shadow is to the primitive, the darker it is and the less its edges blend with the surrounding light; the farther off, the more its edges mingle with the luminous borders. The farther the light is from the shadowy body, the more shadow-edge and light are mixed.
Powerful light sharpens shadows on dense bodies
The greater the diameter of the derived shadow compared with the primitive, the darker the primitive shadow. The more powerful the light striking dense bodies, the darker and more sharply divided from the light their shadows appear.
Intersection of shadows from a large light
A shadowy intersection occurs after which the divided shadows meet in two different convergences, as if from two separate lights. When luminous bodies exceed the shadowy bodies in size, the light acts as if divided and its shadows split after intersecting.
The blow as the boundary of motion
The rebound is the boundary of the blow, the blow the boundary of motion, and free motion the boundary of force, containing time and distance. Because the blow is an indivisible part of motion, bodies obey its nature before the motion begun, owing to the blow's infinite swiftness.
Sun, eye and moon aligned
A diagonal row of circles set among light rays is labelled Sun, Eye in the world, Moon, with the note that the Sun appears to the eye to be as much inside the moon as outside it.