Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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the Station Point, and A the Point wherein the
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Perpendicular meets the Geometrical Plane.</
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<
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,
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Without Compaſſes.</
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">Having firſt found the Perſpective a of
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">31.</
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Point A, draw the Line A S cutting the Baſe
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Line in E, through which Point E draw the
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Line Ea; </
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<
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xml:space
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">then from the Point B draw a Line
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B a to the Point a, cutting the Horizontal Line
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in F. </
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Point L, cutting E a in I; </
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<
s
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">and a I is the Repre-
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ſentation ſought.</
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<
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.</
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s
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">To prove this, let G N be a Perpendicular to
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the Baſe Line drawn from the Point G, wherein
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the ſaid Baſe Line is cut by the Line B F; </
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">alſo
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let G D be equal to the Perpendicular whoſe Ap-
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pearance is ſought, and a H parallel to the Baſe
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Line.</
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s
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">It is plain that the Perſpective of E A is
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E a: </
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">But E A paſſes through the Station Point;
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</
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s
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">and conſequently its Repreſentation is
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dicular to the Baſe Line; </
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<
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to prove, that a I is equal to a H.</
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lar; </
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s
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">But B M by Conſtruction is the double of B C;
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</
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">whence B F is alſo the double of B G, which,
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conſequently, is equal to G F.</
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ſimilar, therefore</
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