object] is of the nature of a luminous body; one conceals and the other reveals. They are always associated and inseparable from all objects. But shadow is a more powerful agent than light, for it can impede and entirely deprive bodies of their light, while light can never entirely expel shadow from a body, that is from an opaque body.
120.
Shadow is the diminution of light by the intervention of an opaque body. Shadow is the counterpart of the luminous rays which are cut off by an opaque body.
This is proved because the shadow cast is the same in shape and size as the luminous rays were which are transformed into a shadow.
121.
Shadow is the diminution alike of light and of darkness, and stands between darkness and light.
A shadow may be infinitely dark, and also of infinite degrees