Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div285" type="section" level="1" n="151">
          <p>
            <s xml:id="echoid-s1854" xml:space="preserve">
              <pb o="79" file="0141" n="163" rhead="on PERSPECTIVE."/>
            dicular is on one Side or other of the perſpective
              <lb/>
            Plane with reſpect to the Eye. </s>
            <s xml:id="echoid-s1855" xml:space="preserve">And the Line
              <lb/>
            paſſing through the Extremities of the ſaid Pa-
              <lb/>
            rallels, will determine the Repreſentation ſought,
              <lb/>
            by its interſecting the Line T a, as is evident by
              <lb/>
            what is demonſtrated.</s>
            <s xml:id="echoid-s1856" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div286" type="section" level="1" n="152">
          <head xml:id="echoid-head158" xml:space="preserve">
            <emph style="sc">Method</emph>
          III.</head>
          <p style="it">
            <s xml:id="echoid-s1857" xml:space="preserve">97. </s>
            <s xml:id="echoid-s1858" xml:space="preserve">To find the Repreſentation of ſeveral Perpen-
              <lb/>
            diculars equal in Length to ſome one, whoſe Per-
              <lb/>
            ſpective is already drawn.</s>
            <s xml:id="echoid-s1859" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1860" xml:space="preserve">Let H I, be the Perſpective of a Perpendicular
              <lb/>
              <note position="right" xlink:label="note-0141-01" xlink:href="note-0141-01a" xml:space="preserve">Fig. 52.</note>
            to the Geometrical or Perſpective Plane. </s>
            <s xml:id="echoid-s1861" xml:space="preserve">Now
              <lb/>
            about the accidental Point T, as a Center, and
              <lb/>
            with the Radius T H, deſcribe the circular Arc
              <lb/>
            H G, whoſe Chord let be equal to H I, and draw
              <lb/>
            the indefinite Line TGC, and let a and b, re-
              <lb/>
            preſent the Feet of the Perpendiculars, whoſe
              <lb/>
            Repreſentations are requir’d.</s>
            <s xml:id="echoid-s1862" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div288" type="section" level="1" n="153">
          <head xml:id="echoid-head159" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1863" xml:space="preserve">Deſcribe about the Center T, the Arcs b F E,
              <lb/>
            and a DC, paſſing through the Points a and b, and
              <lb/>
            draw the Lines T b and T a; </s>
            <s xml:id="echoid-s1864" xml:space="preserve">in each of which
              <lb/>
            aſſume b L equal to E F, and a X equal to C D;
              <lb/>
            </s>
            <s xml:id="echoid-s1865" xml:space="preserve">and the ſought Repreſentations will be had.</s>
            <s xml:id="echoid-s1866" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div289" type="section" level="1" n="154">
          <head xml:id="echoid-head160" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1867" xml:space="preserve">If H I, and a X repreſent Perpendiculars of
              <lb/>
            the ſame Length, it follows from the Demon-
              <lb/>
            ſtration of the precedent Method, that I H is to
              <lb/>
            H T, and a X to a T as the Difference of the
              <lb/>
            ſaid Perpendiculars, and Height of the Eye, </s>
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