Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div271" type="section" level="1" n="142">
          <pb o="75" file="0135" n="156" rhead="on PERSPECTIVE."/>
        </div>
        <div xml:id="echoid-div273" type="section" level="1" n="143">
          <head xml:id="echoid-head149" xml:space="preserve">CHAP. VI.</head>
          <p style="it">
            <s xml:id="echoid-s1775" xml:space="preserve">Of throwing Figures into Perſpective, when
              <lb/>
            the Perſpective Plane is conſider’d as being
              <lb/>
            parallel to the Geometrical Plane.</s>
            <s xml:id="echoid-s1776" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div274" type="section" level="1" n="144">
          <head xml:id="echoid-head150" xml:space="preserve">
            <emph style="sc">Prob</emph>
          . I.</head>
          <p style="it">
            <s xml:id="echoid-s1777" xml:space="preserve">92. </s>
            <s xml:id="echoid-s1778" xml:space="preserve">To find the Perſpective of a Figure, which
              <lb/>
            is in the Geometrical Plane.</s>
            <s xml:id="echoid-s1779" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1780" xml:space="preserve">When the perſpective Plane is parallel to the
              <lb/>
            Horizon, we commonly conſider it, as being
              <lb/>
            it ſelf the Geometrical Plane, in which Caſe,
              <lb/>
            the Problem is fully reſolved: </s>
            <s xml:id="echoid-s1781" xml:space="preserve">But when it
              <lb/>
            happens, that another Geometrical Plane is
              <lb/>
            ſuppoſed, either above or below the perſpective
              <lb/>
            Plane, upon which the Figures upon the Geo-
              <lb/>
            metrical Plane are requir’d to be drawn; </s>
            <s xml:id="echoid-s1782" xml:space="preserve">we
              <lb/>
            muſt draw geometrically thereon, Figures ſimi-
              <lb/>
            lar to thoſe in the Geometrical Plane; </s>
            <s xml:id="echoid-s1783" xml:space="preserve">ſo that
              <lb/>
            the Lines on the perſpective Plane, be to their
              <lb/>
            correſpondent ones on the Geometrical Plane,
              <lb/>
            as the Eye’s Diſtance from the perſpective Plane,
              <lb/>
            is to its Diſtance from the Geometrical Plane.</s>
            <s xml:id="echoid-s1784" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1785" xml:space="preserve">The Demonſtration of this is evident from
              <lb/>
            n. </s>
            <s xml:id="echoid-s1786" xml:space="preserve">8, and 9.</s>
            <s xml:id="echoid-s1787" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div275" type="section" level="1" n="145">
          <head xml:id="echoid-head151" xml:space="preserve">
            <emph style="sc">Prob</emph>
          . II.</head>
          <p style="it">
            <s xml:id="echoid-s1788" xml:space="preserve">93. </s>
            <s xml:id="echoid-s1789" xml:space="preserve">To find the Perſpective of a Line, perpen-
              <lb/>
            dicular to the Geometrical Plane.</s>
            <s xml:id="echoid-s1790" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1791" xml:space="preserve">Draw the Line O S, in which aſſume O R e-
              <lb/>
              <note position="right" xlink:label="note-0135-01" xlink:href="note-0135-01a" xml:space="preserve">Fig. 50.</note>
            qual to the Eye’s Diſtance from the </s>
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