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distance from the object is greater, has its external lines
intersecting in the middle, between the light and the object. This
proposition is very evident and is confirmed by experience. For, if
a b is a window without any object interposed, the luminous
atmosphere to the right hand at a is seen to the left at d. And
the atmosphere at the left illuminates on the right at c, and the
lines intersect at the point m.
[
Footnote: A here stands for levante (East), B for ponente
West).]
(
1
40.
Every body in light and shade is situated between 2 pyramids one
dark and the other luminous, one is visible the other is not. But
this only happens when the light enters by a window. Supposing a b
to be the window and r the body in light and shade, the light to
the right hand z will pass the object to the left and go on to
p; the light to the left at k will pass to the right of the
object at i and go on to m and the two lines will intersect at
c and form a pyramid. Then again a b falls on the shaded body
at i g and forms a pyramid f i g. f will be dark because
the light a b can never fall there; i g c will be
illuminated because the light falls upon it.
Light and shadow with regard to the position of the eye (141--145).
122
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