Gravesande, Willem Jacob 's, An essay on perspective

Table of Notes

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          <p>
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            ctive Plane; </s>
            <s xml:id="echoid-s457" xml:space="preserve">and then (from the Station Point,
              <lb/>
            thro’ the Extremities of the Perſpective Plane)
              <lb/>
            he muſt draw right Lines; </s>
            <s xml:id="echoid-s458" xml:space="preserve">which will limit the
              <lb/>
            Space wherein the Figures muſt be placed; </s>
            <s xml:id="echoid-s459" xml:space="preserve">ſince
              <lb/>
            the Rays of Figures, without thoſe Lines coming
              <lb/>
            towards the Eye, will not paſs thro’ the Perſpe-
              <lb/>
            ctive Plane.</s>
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          <p>
            <s xml:id="echoid-s461" xml:space="preserve">21. </s>
            <s xml:id="echoid-s462" xml:space="preserve">The Figures being thus drawn on the Geo-
              <lb/>
            metrical Plane, the next Thing is to find their Ap-
              <lb/>
            pearance upon the Perſpective Plane. </s>
            <s xml:id="echoid-s463" xml:space="preserve">Now,
              <lb/>
            theſe Figures are made up of either ſtraight
              <lb/>
            Lines, or crooked ones. </s>
            <s xml:id="echoid-s464" xml:space="preserve">To find the Repreſen-
              <lb/>
            tation of a ſtraight Line, its Extremes need on-
              <lb/>
            ly be ſought: </s>
            <s xml:id="echoid-s465" xml:space="preserve">And to have the Appearance of a
              <lb/>
            crooked Line, ſeveral Points thereof need only
              <lb/>
            be found. </s>
            <s xml:id="echoid-s466" xml:space="preserve">Since all this is equally applicable
              <lb/>
            to Figures, as well in the Geometrical Plane,
              <lb/>
            as thoſe above it; </s>
            <s xml:id="echoid-s467" xml:space="preserve">it follows, that the whole Bu-
              <lb/>
            ſineſs of Perſpective conſiſts in only finding the
              <lb/>
            Repreſentation of a Point.</s>
            <s xml:id="echoid-s468" xml:space="preserve"/>
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          <p>
            <s xml:id="echoid-s469" xml:space="preserve">And to find this Repreſentation in the follow-
              <lb/>
            ing Problems, we only uſe certain Lines drawn
              <lb/>
            in the Geometrical and Horizontal Planes;
              <lb/>
            </s>
            <s xml:id="echoid-s470" xml:space="preserve">which, by their Interſection with the Baſe and
              <lb/>
            Horizontal Lines, ſhew the manner of drawing
              <lb/>
            new Lines upon the Perſpective Plane, which
              <lb/>
            determine the propos’d Appearances. </s>
            <s xml:id="echoid-s471" xml:space="preserve">Now, it
              <lb/>
            is plain, that in finding the ſaid Interſections, it
              <lb/>
            is not neceſſary to place the Perſpective Plane
              <lb/>
            perpendicular to the Geometrical and Horizontal
              <lb/>
            Planes; </s>
            <s xml:id="echoid-s472" xml:space="preserve">which would render the Work extream-
              <lb/>
            ly laborious: </s>
            <s xml:id="echoid-s473" xml:space="preserve">Whence the Perſpective and Hori-
              <lb/>
            zontal Planes may be conſider’d as lying upon
              <lb/>
            the Geometrical Plane, and ſo coinciding there-
              <lb/>
            with.</s>
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          <p>
            <s xml:id="echoid-s475" xml:space="preserve">The Perſpective Plane may lye upon the Geo-
              <lb/>
            metrical Plane two ways; </s>
            <s xml:id="echoid-s476" xml:space="preserve">viz. </s>
            <s xml:id="echoid-s477" xml:space="preserve">Either upon the
              <lb/>
            Face reſpecting the Objects, or upon that </s>
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