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Let a b be the width of the light from a window, which falls on a
stick set up at one foot from a c [Footnote 6: bastone (stick).
The diagram has a sphere in place of a stick.]. And let a d be the
space where all the light from the window is visible. At c e that
part of the window which is between l b cannot be seen. In the
same way a m cannot be seen from d f and therefore in these two
portions the light begins to fail.
Shadow as produced by two lights of different size (180. 181).
1
80.
A body in light and shade placed between two equal lights side by
side will cast shadows in proportion to the [amount of] light. And
the shadows will be one darker than the other in proportion as one
light is nearer to the said body than the other on the opposite
side.
A body placed at an equal distance between two lights will cast two
shadows, one deeper than the other in proportion, as the light which
causes it is brighter than the other.
[Footnote: In the MS. the larger diagram is placed above the first
line; the smaller one between l. 4 & 5.]
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