Among objects in various degrees of shade, when the light proceeds
from a single source, there will be the same proportion in their
shadows as in the natural diminution of the light and the same must
be understood of the degrees of light.
157.
A single and distinct luminous body causes stronger relief in the
object than a diffused light; as may be seen by comparing one side
of a landscape illuminated by the sun, and one overshadowed by
clouds, and so illuminated only by the diffused light of the
atmosphere.