Gravesande, Willem Jacob 's, An essay on perspective

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            and drawing a Line from the Point I to the
              <lb/>
            other Point of Diſtance; </s>
            <s xml:id="echoid-s538" xml:space="preserve">which, by its Inter-
              <lb/>
            ſection with E D, will give the Appearance of
              <lb/>
            the Point A.</s>
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        <div xml:id="echoid-div61" type="section" level="1" n="31">
          <head xml:id="echoid-head33" xml:space="preserve">
            <emph style="sc">Method</emph>
          II.</head>
          <p>
            <s xml:id="echoid-s540" xml:space="preserve">26. </s>
            <s xml:id="echoid-s541" xml:space="preserve">γ is the Horizontal Plane, X the Perſpe-
              <lb/>
            ctive Plane, Z the Geometrical Plane, O the Eye,
              <lb/>
            D C the Horizontal Line, B E the Baſe Line, and
              <lb/>
            A the given Point.</s>
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          <note position="left" xml:space="preserve">Fig. 8.</note>
        </div>
        <div xml:id="echoid-div62" type="section" level="1" n="32">
          <head xml:id="echoid-head34" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s543" xml:space="preserve">Draw a Line from the Point A, to the Eye O, cut-
              <lb/>
            ting the Baſe Line in the Point B, and the Horizon-
              <lb/>
            tal Line in the Point C: </s>
            <s xml:id="echoid-s544" xml:space="preserve">Then aſſume B E in the
              <lb/>
            Baſe Line, equal to B A; </s>
            <s xml:id="echoid-s545" xml:space="preserve">and C D in the Hori-
              <lb/>
            zontal Line, equal to C O; </s>
            <s xml:id="echoid-s546" xml:space="preserve">and join the Points
              <lb/>
            E and D, by a Line cutting the Line A O in
              <lb/>
            the Point a; </s>
            <s xml:id="echoid-s547" xml:space="preserve">which will be the Appearance
              <lb/>
            ſought.</s>
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        <div xml:id="echoid-div63" type="section" level="1" n="33">
          <head xml:id="echoid-head35" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s549" xml:space="preserve">27. </s>
            <s xml:id="echoid-s550" xml:space="preserve">The Triangle O D C in the Horizontal
              <lb/>
            Plane, is ſimilar to the Triangle A B E in the
              <lb/>
            Geometrical Plane; </s>
            <s xml:id="echoid-s551" xml:space="preserve">and conſequently A B is pa-
              <lb/>
            rallel to O C, and A E to O D. </s>
            <s xml:id="echoid-s552" xml:space="preserve">But the Appear-
              <lb/>
            ance of A muſt be in the Lines B C, and E D;</s>
            <s xml:id="echoid-s553" xml:space="preserve">
              <note symbol="*" position="left" xlink:label="note-0040-02" xlink:href="note-0040-02a" xml:space="preserve">
                <unsure/>
              13.</note>
            and therefore it will be in a, their Interſection.</s>
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        </div>
        <div xml:id="echoid-div65" type="section" level="1" n="34">
          <head xml:id="echoid-head36" xml:space="preserve">
            <emph style="sc">Remarks</emph>
          .</head>
          <p>
            <s xml:id="echoid-s555" xml:space="preserve">28. </s>
            <s xml:id="echoid-s556" xml:space="preserve">If the Place wherein the Eye ought to be in
              <lb/>
            the Horizontal Plane be not known, but the Point
              <lb/>
            of Sight is; </s>
            <s xml:id="echoid-s557" xml:space="preserve">then, to find the Place of the Eye,
              <lb/>
            a Perpendicular muſt be rais’d from the Point </s>
          </p>
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