Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div247" type="section" level="1" n="129">
          <pb o="70" file="0126" n="145" rhead="An ESSAY"/>
          <p>
            <s xml:id="echoid-s1694" xml:space="preserve">Note, When V I and T a cut each other ve-
              <lb/>
            ry obliquely, recourſe muſt be had to the Obſer-
              <lb/>
            vation at the End of the aforegoing Method, or
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            the following Way may be uſed.</s>
            <s xml:id="echoid-s1695" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div249" type="section" level="1" n="130">
          <head xml:id="echoid-head136" xml:space="preserve">
            <emph style="sc">Method</emph>
          III.</head>
          <p>
            <s xml:id="echoid-s1696" xml:space="preserve">86. </s>
            <s xml:id="echoid-s1697" xml:space="preserve">Let T be the accidental Point of the Lines
              <lb/>
              <note position="left" xlink:label="note-0126-01" xlink:href="note-0126-01a" xml:space="preserve">Fig. 47.</note>
            perpendicular to the Geometrical Plane, thro’
              <lb/>
            which Point draw a parallel to the Baſe Line,
              <lb/>
            in which aſſume T R equal to O T of Fig. </s>
            <s xml:id="echoid-s1698" xml:space="preserve">44.</s>
            <s xml:id="echoid-s1699" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div251" type="section" level="1" n="131">
          <head xml:id="echoid-head137" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1700" xml:space="preserve">Aſſume D N ſomewhere in the Baſe Line, e-
              <lb/>
            qual to the propoſed Line, and draw the Lines
              <lb/>
            D F and N F to the Point F, taken at Pleaſure
              <lb/>
            in the Horizontal Line; </s>
            <s xml:id="echoid-s1701" xml:space="preserve">then through the Point
              <lb/>
            a, the Appearance of A, draw the parallel a H,
              <lb/>
            to the Baſe Line, in which aſſume a Q equal
              <lb/>
            to G H. </s>
            <s xml:id="echoid-s1702" xml:space="preserve">Then if the Lines T a, and R Q be
              <lb/>
            drawn, and continued, till they cut each other
              <lb/>
            in the Point X, a X will be the Appearance
              <lb/>
            ſought.</s>
            <s xml:id="echoid-s1703" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div252" type="section" level="1" n="132">
          <head xml:id="echoid-head138" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1704" xml:space="preserve">The Part a Q of the Line a H, is the
              <note symbol="*" position="left" xlink:label="note-0126-02" xlink:href="note-0126-02a" xml:space="preserve">56.</note>
            pearance of a Line proceeding from A in the
              <lb/>
            Geometrical Plane, and which is equal to the
              <lb/>
            propoſed Line, and parallel to the Baſe Line;
              <lb/>
            </s>
            <s xml:id="echoid-s1705" xml:space="preserve">and conſequently , the Line R Q paſſes
              <note symbol="*" position="left" xlink:label="note-0126-03" xlink:href="note-0126-03a" xml:space="preserve">20.</note>
            the Perſpective of the Extremity of the propo-
              <lb/>
            ſed Line: </s>
            <s xml:id="echoid-s1706" xml:space="preserve">And therefore X the Interſection of
              <lb/>
            R Q and T a, is the Appearance of the ſaid
              <lb/>
            Extremity.</s>
            <s xml:id="echoid-s1707" xml:space="preserve"/>
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