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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).
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63.
The derived shadow can never resemble the body from which it
proceeds unless the light is of the same form and size as the body
causing the shadow.
The derived shadow cannot be of the same form as the primary shadow
unless it is intercepted by a plane parallel to it.
1
64.
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