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fall upon it. The spot which receives the rays at the widest angle
and by darkened rays will be most in the dark; a will be twice as
dark as b, because it originates from twice as large a base at an
equal distance. A spot is most illuminated when a large number of
luminous rays fall upon it. d is the beginning of the shadow d f,
and tinges c but a little; d e is half of the shadow d f and
gives a deeper tone where it is cast at b than at f. And the
whole shaded space e gives its tone to the spot a. [Footnote:
The diagram here referred to is on Pl. XLI, No. 2.]
2
01.
A n will be darker than c r in proportion to the number of times
that a b goes into c d.
2
02.
The shadow cast by an object on a plane will be smaller in
proportion as that object is lighted by feebler rays. Let d e be
the object and d c the plane surface; the number of times that d
e will go into f g gives the proportion of light at f h to d
c. The ray of light will be weaker in proportion to its distance
from the hole through which it falls.
FIFTH BOOK ON LIGHT AND SHADE.
161
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