If the object is the mountain here figured, and the light is at the
point _a_, I say that from _b d_ and also from _c f_ there will be
no light but from reflected rays. And this results from the fact
that rays of light can only act in straight lines; and the same is
the case with the secondary or reflected rays.
204.
The edges of the derived shadow are defined by the hues of the
illuminated objects surrounding the luminous body which produces the
shadow.
On reverberation.
205.