Gravesande, Willem Jacob 's
,
An essay on perspective
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on PERSPECTIVE.
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Point in reſpect to each other, in the before ſup-
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poſed Plane. </
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<
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xml:space
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">Therefore the Line o F anſwers
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@kewiſe to the Line in the ſaid Plane imagined
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to be parallel to the propoſed Lines; </
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<
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xml:space
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ſequently the Point F, is that wherein the
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ſaid Parallel meets the Perſpective Plane; </
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<
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therefore it is the accidental Point ſought.</
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<
s
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">Note, Iſ the accidental Point T of Perpendi-
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culars to the Geometrical Plane be found, the
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Operation of this Problem may be ſhorten’d, in
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drawing the Line T D, which will neceſſarily
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paſs thro’ the Point N, and then the Point o will
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be found by the Interſection of the Arc O o,
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and a Semi-circle, whoſe Diameter is T D.</
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<
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VI.</
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">To find the Perſpective of one or more Lines
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inclin’d to the Geometrical Plane.</
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<
s
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">Let A be the Foot of a Line inclin’d to the
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Geometrical Plane, and a its Repreſentation.
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according to the Manner lay’d down for
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Perſpective Plane when ſuppoſed perpendicular,
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the Length A B of the Direction of the propoſed
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Line. </
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<
s
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">This being done, find the Point X the
<
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ſpective of a Point above the Geometrical Plane
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by the Length of P E; </
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<
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Perſpective ſought.</
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<
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II.</
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of inclined Lines, and their Directions.</
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<
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">Let AB be the Direction of an inclin’d Line; </
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<
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the Accidental Point of the Directions, & </
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