this it is made clear that the shadow is not produced by the angle of the derived shadow but only by the body casting the shadow; &c. If a spherical solid body is illuminated by a light of elongated form the shadow produced by the longest portion of this light will have less defined outlines than that which is produced by the breadth of the same light. And this is proved by what was said before, which is: That a shadow will have less defined outlines in proportion as the light which causes it is larger, and conversely, the outlines are clearer in proportion as it is smaller.
[Footnote: The two diagrams to this chapter are on Plate IV, No. 1.]
On the relation of derived and primary shadow (163-165).
163.
The derived shadow can never resemble the body from which it proceeds unless