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[Footnote: In the diagrams A stands for celo (sky), B for
cadela (candle).]
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69.
ALL BODIES, IN PROPORTION AS THEY ARE NEARER TO, OR FARTHER FROM
THE
SOURCE OF LIGHT, WILL PRODUCE LONGER OR SHORTER DERIVED
SHADOWS.
Among bodies of equal size, that one which is illuminated by the
largest light will have the shortest shadow. Experiment confirms
this proposition. Thus the body m n is surrounded by a larger
amount of light than the body p q, as is shown above. Let us say
that v c a b d x is the sky, the source of light, and that s t
is a window by which the luminous rays enter, and so m n and p q
are bodies in light and shade as exposed to this light; m n will
have a small derived shadow, because its original shadow will be
small; and the derivative light will be large, again, because the
original light c d will be large and p q will have more derived
shadow because its original shadow will be larger, and its derived
light will be smaller than that of the body m n because that
portion of the hemisphere a b which illuminates it is smaller than
the hemisphere c d which illuminates the body m n.
[Footnote: The diagram, given on Pl. IV, No. 2, stands in the
original between lines 2 and 7, while the text of lines 3 to 6 is
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