the notebooks of Leonardo DaVinci
Definition of the nature of shadows (119--122).
119.
WHAT LIGHT AND SHADOW ARE.
Shadow is the absence of light, merely the obstruction of the
luminous rays by an opaque body. Shadow is of the nature of
darkness. Light [on an 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.
119.
WHAT LIGHT AND SHADOW ARE.
Shadow is the absence of light, merely the obstruction of the
luminous rays by an opaque body. Shadow is of the nature of
darkness. Light [on an 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.