Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div87" type="section" level="1" n="49">
          <p>
            <s xml:id="echoid-s690" xml:space="preserve">
              <pb o="25" file="0051" n="55" rhead="on PERSPECTIVE."/>
            rence with the Geometrical Line; </s>
            <s xml:id="echoid-s691" xml:space="preserve">which would
              <lb/>
            come to the ſame thing.</s>
            <s xml:id="echoid-s692" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div89" type="section" level="1" n="50">
          <head xml:id="echoid-head52" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s693" xml:space="preserve">Firſt continue the Line E a, until it meets
              <lb/>
            the Horizontal Line in D, and draw a Line
              <lb/>
            from D to the Eye, and another through the Eye
              <lb/>
            parallel to the Baſe Line.</s>
            <s xml:id="echoid-s694" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s695" xml:space="preserve">Then the Parallels O M and F C are at the
              <lb/>
            ſame Diſtance from each other, as L D is from
              <lb/>
            E B; </s>
            <s xml:id="echoid-s696" xml:space="preserve">whence it follows, that F O is equal to E D,
              <lb/>
            and therefore O D is parallel to A F. </s>
            <s xml:id="echoid-s697" xml:space="preserve">Whence
              <note symbol="*" position="right" xlink:label="note-0051-01" xlink:href="note-0051-01a" xml:space="preserve">13:</note>
            the Appearance of E A, is a Part of E D. </s>
            <s xml:id="echoid-s698" xml:space="preserve">And
              <lb/>
            after the ſame Manner we prove, that the Re-
              <lb/>
            preſentation of B A is a Part of B a.</s>
            <s xml:id="echoid-s699" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div91" type="section" level="1" n="51">
          <head xml:id="echoid-head53" xml:space="preserve">
            <emph style="sc">Remarks</emph>
          .</head>
          <p>
            <s xml:id="echoid-s700" xml:space="preserve">40. </s>
            <s xml:id="echoid-s701" xml:space="preserve">When there are no Lines drawn, and we
              <lb/>
            would uſe this Method, the Horizontal Line
              <lb/>
            may be laid aſide; </s>
            <s xml:id="echoid-s702" xml:space="preserve">and then having firſt drawn
              <lb/>
            the Geometrical Line, whoſe Diſtance from
              <lb/>
            the Baſe Line is equal to the Length of the Ray,
              <lb/>
            we aſſume the Diſtance from the Eye to the
              <lb/>
            Geometrical Line, equal to the Height of the
              <lb/>
            Eye.</s>
            <s xml:id="echoid-s703" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s704" xml:space="preserve">Although this Method appears uſeleſs, as being
              <lb/>
            more difficult than the precedent ones, yet in
              <lb/>
            the Eighth Chapter we have ſhewn the Uſe that
              <lb/>
            may be drawn from it.</s>
            <s xml:id="echoid-s705" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div92" type="section" level="1" n="52">
          <head xml:id="echoid-head54" xml:space="preserve">
            <emph style="sc">Corollary</emph>
          .</head>
          <p>
            <s xml:id="echoid-s706" xml:space="preserve">41. </s>
            <s xml:id="echoid-s707" xml:space="preserve">It follows from this Demonſtration, that
              <lb/>
            the Appearances of Lines paſſing through the
              <lb/>
            Station Point, are all perpendicular to the Baſe
              <lb/>
            Line; </s>
            <s xml:id="echoid-s708" xml:space="preserve">for if the Perpendicular O S be let </s>
          </p>
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