Gravesande, Willem Jacob 's
,
An essay on perspective
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An ESSAY
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ctive Plane; </
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<
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xml:space
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">and then (from the Station Point,
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thro’ the Extremities of the Perſpective Plane)
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he muſt draw right Lines; </
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<
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xml:space
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">which will limit the
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Space wherein the Figures muſt be placed; </
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<
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xml:space
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">ſince
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the Rays of Figures, without thoſe Lines coming
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towards the Eye, will not paſs thro’ the Perſpe-
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ctive Plane.</
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<
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">21. </
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<
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">The Figures being thus drawn on the Geo-
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metrical Plane, the next Thing is to find their Ap-
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pearance upon the Perſpective Plane. </
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<
s
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xml:space
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">Now,
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theſe Figures are made up of either ſtraight
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Lines, or crooked ones. </
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xml:space
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">To find the Repreſen-
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tation of a ſtraight Line, its Extremes need on-
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ly be ſought: </
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">And to have the Appearance of a
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crooked Line, ſeveral Points thereof need only
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be found. </
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<
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">Since all this is equally applicable
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to Figures, as well in the Geometrical Plane,
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as thoſe above it; </
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<
s
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">it follows, that the whole Bu-
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ſineſs of Perſpective conſiſts in only finding the
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Repreſentation of a Point.</
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<
s
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">And to find this Repreſentation in the follow-
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ing Problems, we only uſe certain Lines drawn
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in the Geometrical and Horizontal Planes;
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</
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">which, by their Interſection with the Baſe and
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Horizontal Lines, ſhew the manner of drawing
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new Lines upon the Perſpective Plane, which
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determine the propos’d Appearances. </
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">Now, it
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is plain, that in finding the ſaid Interſections, it
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is not neceſſary to place the Perſpective Plane
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perpendicular to the Geometrical and Horizontal
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Planes; </
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<
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">which would render the Work extream-
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ly laborious: </
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<
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xml:space
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">Whence the Perſpective and Hori-
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zontal Planes may be conſider’d as lying upon
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the Geometrical Plane, and ſo coinciding there-
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with.</
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<
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">The Perſpective Plane may lye upon the Geo-
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metrical Plane two ways; </
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Face reſpecting the Objects, or upon that </
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