Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div77" type="section" level="1" n="42">
          <p>
            <s xml:id="echoid-s660" xml:space="preserve">
              <pb o="23" file="0047" n="50" rhead="on PERSPECTIVE."/>
            Perpendiculars f P, O H, muſt be let fall from
              <lb/>
            the Points f and O, on the Baſe Line, and the
              <lb/>
            Line P g drawn; </s>
            <s xml:id="echoid-s661" xml:space="preserve">then the Point V, wherein it
              <lb/>
            cuts the Perpendicular O H, is the Point of Sight
              <lb/>
            ſought, and the Parts O V, and V H determine
              <lb/>
            the Height and Diſtance of the Eye.</s>
            <s xml:id="echoid-s662" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div78" type="section" level="1" n="43">
          <head xml:id="echoid-head45" xml:space="preserve">
            <emph style="sc">Method</emph>
          V.</head>
          <p style="it">
            <s xml:id="echoid-s663" xml:space="preserve">35. </s>
            <s xml:id="echoid-s664" xml:space="preserve">When the Appearance of a Point is known,</s>
          </p>
          <p>
            <s xml:id="echoid-s665" xml:space="preserve">Let A be a Point in the Geometrical Plane,
              <lb/>
              <note position="right" xlink:label="note-0047-01" xlink:href="note-0047-01a" xml:space="preserve">Fig. 11.</note>
            and a its Repreſentation in the perſpective Plane,
              <lb/>
            it is requir’d to find the Appearance of the
              <lb/>
            Point B.</s>
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          </p>
        </div>
        <div xml:id="echoid-div80" type="section" level="1" n="44">
          <head xml:id="echoid-head46" xml:space="preserve">
            <emph style="sc">Operation</emph>
          ,
            <lb/>
          Without Compaſſes.</head>
          <p>
            <s xml:id="echoid-s667" xml:space="preserve">Draw a Line from the Point B to the Eye O,
              <lb/>
            and another from the Point E, wherein the
              <lb/>
            ſaid Line continued, cuts the Baſe Line, to the
              <lb/>
            Point A; </s>
            <s xml:id="echoid-s668" xml:space="preserve">then draw the Line E a, and where
              <lb/>
            it cuts B O, is the Point b ſought.</s>
            <s xml:id="echoid-s669" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div81" type="section" level="1" n="45">
          <head xml:id="echoid-head47" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s670" xml:space="preserve">The Point E is its own Repreſentation; </s>
            <s xml:id="echoid-s671" xml:space="preserve">and
              <lb/>
            becauſe the Point a is the Repreſentation of A,
              <lb/>
            the Line E a is that of E A. </s>
            <s xml:id="echoid-s672" xml:space="preserve">Now ſince the
              <lb/>
            Point B is in the Line E A, the Appearance of
              <lb/>
            this Point will be likewiſe in E a, as alſo
              <note symbol="*" position="right" xlink:label="note-0047-02" xlink:href="note-0047-02a" xml:space="preserve">27.</note>
            B O; </s>
            <s xml:id="echoid-s673" xml:space="preserve">therefore it is in b the Interſection of the
              <lb/>
            Lines E a, and B O.</s>
            <s xml:id="echoid-s674" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div83" type="section" level="1" n="46">
          <head xml:id="echoid-head48" xml:space="preserve">
            <emph style="sc">Remark</emph>
          .</head>
          <p>
            <s xml:id="echoid-s675" xml:space="preserve">37. </s>
            <s xml:id="echoid-s676" xml:space="preserve">If the Point A be in the Line B O, or
              <lb/>
            the Line B A be parallel, or a very little inclined
              <lb/>
            to the Baſe Line, we cannot then uſe this </s>
          </p>
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