Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div187" type="section" level="1" n="99">
          <p>
            <s xml:id="echoid-s1321" xml:space="preserve">
              <pb o="55" file="0101" n="115" rhead="on PERSPECTIVE."/>
            making theſe Abbreviations, will be laid down
              <lb/>
            in the following Methods.</s>
            <s xml:id="echoid-s1322" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div189" type="section" level="1" n="100">
          <head xml:id="echoid-head106" xml:space="preserve">
            <emph style="sc">Method</emph>
          II.
            <lb/>
          70. By the accidental Point of inclin’d Lines.</head>
          <p>
            <s xml:id="echoid-s1323" xml:space="preserve">Thro’ F, the accidental Point of the inclin’d
              <lb/>
              <note position="right" xlink:label="note-0101-01" xlink:href="note-0101-01a" xml:space="preserve">Fig. 36.</note>
            parallel Lines, draw F H, parallel to the Baſe
              <lb/>
            Line, and equal to F G. </s>
            <s xml:id="echoid-s1324" xml:space="preserve">And let A be the
              <lb/>
            Point, wherein one of the inclin’d Lines meets
              <lb/>
            the Geometrical Plane.</s>
            <s xml:id="echoid-s1325" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div191" type="section" level="1" n="101">
          <head xml:id="echoid-head107" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1326" xml:space="preserve">Aſſume R Q in the Baſe Line, equal to the
              <lb/>
            inclin’d Line; </s>
            <s xml:id="echoid-s1327" xml:space="preserve">and draw Lines from the Points
              <lb/>
            R and Q, to the Point Z, taken at pleaſure in
              <lb/>
            the Horizontal Plane.</s>
            <s xml:id="echoid-s1328" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1329" xml:space="preserve">Thro’ a, the Perſpective of A, draw a N pa-
              <lb/>
            rallel to the Baſe Line; </s>
            <s xml:id="echoid-s1330" xml:space="preserve">in which aſſume a L,
              <lb/>
            equal to M N; </s>
            <s xml:id="echoid-s1331" xml:space="preserve">and draw a Line from the Point
              <lb/>
            a, to the Point F; </s>
            <s xml:id="echoid-s1332" xml:space="preserve">and from the Point L, draw
              <lb/>
            another to the Point H. </s>
            <s xml:id="echoid-s1333" xml:space="preserve">Then a T will be the
              <lb/>
            Perſpective ſought.</s>
            <s xml:id="echoid-s1334" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div192" type="section" level="1" n="102">
          <head xml:id="echoid-head108" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1335" xml:space="preserve">By the Nature of the accidental Point,
              <note symbol="*" position="right" xlink:label="note-0101-02" xlink:href="note-0101-02a" xml:space="preserve">14.</note>
            Perſpective ſought is a Part of the Line a F;
              <lb/>
            </s>
            <s xml:id="echoid-s1336" xml:space="preserve">and therefore, we are only to demonſtrate,
              <lb/>
            that the Extremity of the faid Perpendicular is in
              <lb/>
            the Line L H. </s>
            <s xml:id="echoid-s1337" xml:space="preserve">Which may be thus done.</s>
            <s xml:id="echoid-s1338" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1339" xml:space="preserve">Let us ſuppoſe a Line, A I, to paſs thro’ the
              <lb/>
            Point A, parallel to the Baſe Line, and equal to
              <lb/>
            the inclin’d Line. </s>
            <s xml:id="echoid-s1340" xml:space="preserve">It is then manifeſt ,
              <note symbol="*" position="right" xlink:label="note-0101-03" xlink:href="note-0101-03a" xml:space="preserve">56.</note>
            L is the Perſpective of I; </s>
            <s xml:id="echoid-s1341" xml:space="preserve">and conſequently,
              <lb/>
            L H is the Appearance of a Line
              <note symbol="*" position="right" xlink:label="note-0101-04" xlink:href="note-0101-04a" xml:space="preserve">@@</note>
            </s>
          </p>
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