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written on its left side. In the reproduction of this diagram the
letter v at the outer right-hand end has been omitted.]
1
70.
The shadow m bears the same proportion to the shadow n as the
line b c to the line f c.
1
71.
OF PAINTING.
Of different shadows of equal strength that which is nearest the eye
will seem the least strong.
Why is the shadow e a b in the first grade of strength, b c in
the second; c d in the third? The reason is that as from e a b
the sky is nowhere visible, it gets no light whatever from the sky,
and so has no direct [primary] light. b c faces the portion of the
sky f g and is illuminated by it. c d faces the sky at h k. c
d, being exposed to a larger extent of sky than b c, it is
reasonable that it should be more lighted. And thus, up to a certain
distance, the wall a d will grow lighter for the reasons here
given, until the darkness of the room overpowers the light from the
window.
139
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