Gravesande, Willem Jacob 's
,
An essay on perspective
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there; </
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<
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gure.</
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<
s
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xml:space
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">This being ſuppoſed, o f is parallel to e
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and conſequently the Triangle o f a is ſimilar
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to the Triangle a e A, and therefore we have this
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Proportion.</
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<
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</
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<
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<
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<
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<
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</
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">e a.
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</
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<
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cedent Figure, we ſhall have this,</
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">O A : </
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<
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<
s
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">Again, becauſe the Triangles O A L and O a G
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are ſimilar, we ſhall have</
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">O a : </
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">A L : </
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">a G.</
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<
s
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">And ſince the Triangle F E D and F a H are
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ſimilar;</
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<
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">And ſo if theſe three laſt Propoſitions be con-
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ſider’d, we ſhall have</
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">a G : </
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<
s
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">But D E was made equal to A L, and there-
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fore a G or a I is alſo equal to a H, which is
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qual to the Repreſentation ſought. </
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<
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to be demonſtrated.</
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<
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III.</
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Plane, raiſe the Perpendicular C B to the Baſe
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Line, equal to the Height of the Eye, in which
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take B L equal in length to twice the Perpen-
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dicular, whoſe Perſpective is requir’d. </
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