Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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Perpendiculars f P, O H, muſt be let fall from
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the Points f and O, on the Baſe Line, and the
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Line P g drawn; </
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">then the Point V, wherein it
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cuts the Perpendicular O H, is the Point of Sight
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ſought, and the Parts O V, and V H determine
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the Height and Diſtance of the Eye.</
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V.</
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<
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">Let A be a Point in the Geometrical Plane,
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and a its Repreſentation in the perſpective Plane,
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it is requir’d to find the Appearance of the
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Point B.</
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,
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Without Compaſſes.</
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">Draw a Line from the Point B to the Eye O,
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and another from the Point E, wherein the
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ſaid Line continued, cuts the Baſe Line, to the
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Point A; </
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">then draw the Line E a, and where
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it cuts B O, is the Point b ſought.</
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<
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.</
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becauſe the Point a is the Repreſentation of A,
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the Line E a is that of E A. </
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Point B is in the Line E A, the Appearance of
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this Point will be likewiſe in E a, as alſo
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B O; </
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Lines E a, and B O.</
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">If the Point A be in the Line B O, or
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the Line B A be parallel, or a very little inclined
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to the Baſe Line, we cannot then uſe this </
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