Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div200" type="section" level="1" n="105">
          <pb o="57" file="0105" n="120" rhead="on PERSPECTIVE."/>
          <p>
            <s xml:id="echoid-s1370" xml:space="preserve">The Operation of Prob. </s>
            <s xml:id="echoid-s1371" xml:space="preserve">VII. </s>
            <s xml:id="echoid-s1372" xml:space="preserve">muſt be uſed
              <lb/>
            here, but with this Difference (ſee Fig. </s>
            <s xml:id="echoid-s1373" xml:space="preserve">of the
              <lb/>
            ſaid Prob.) </s>
            <s xml:id="echoid-s1374" xml:space="preserve">that whereas a I in the ſaid Problem
              <lb/>
            is perpendicular to the Baſe Line, here it muſt
              <lb/>
            make an Angle with the Baſe Line, equal to the
              <lb/>
            Angle of Inclination of the given Lines.</s>
            <s xml:id="echoid-s1375" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1376" xml:space="preserve">For the Demonſtration of this, ſee n. </s>
            <s xml:id="echoid-s1377" xml:space="preserve">7, and 10.</s>
            <s xml:id="echoid-s1378" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div201" type="section" level="1" n="106">
          <head xml:id="echoid-head112" xml:space="preserve">
            <emph style="sc">Prob</emph>
          . XIV.</head>
          <p style="it">
            <s xml:id="echoid-s1379" xml:space="preserve">73. </s>
            <s xml:id="echoid-s1380" xml:space="preserve">To throw a Body into Perſpective, having
              <lb/>
            ſome one or all of its Sides inclined to the Geometri-
              <lb/>
            cal Plane.</s>
            <s xml:id="echoid-s1381" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1382" xml:space="preserve">The Appearances of the Lines forming the
              <lb/>
            Angles of the propoſed Body muſt be found: </s>
            <s xml:id="echoid-s1383" xml:space="preserve">And
              <lb/>
            this may be eaſily done by Prob. </s>
            <s xml:id="echoid-s1384" xml:space="preserve">10. </s>
            <s xml:id="echoid-s1385" xml:space="preserve">
              <note symbol="*" position="right" xlink:label="note-0105-01" xlink:href="note-0105-01a" xml:space="preserve">69.</note>
            takes in all the Caſes. </s>
            <s xml:id="echoid-s1386" xml:space="preserve">And in this Manner the
              <lb/>
            Appearance of a Pyramid, an inclined Priſm,
              <lb/>
            & </s>
            <s xml:id="echoid-s1387" xml:space="preserve">c. </s>
            <s xml:id="echoid-s1388" xml:space="preserve">may be found. </s>
            <s xml:id="echoid-s1389" xml:space="preserve">But nevertheleſs, it hap-
              <lb/>
            pens ſometimes, that the Operations of the pre-
              <lb/>
            cedent Problem may be abbreviated; </s>
            <s xml:id="echoid-s1390" xml:space="preserve">as when
              <lb/>
            the Extremity of ſeveral Lines are found in one
              <lb/>
            and the ſame Line, or when inclined Lines, that
              <lb/>
            have difficult accidental Points, interſect one
              <lb/>
            another, and ſo mutually determine each other.
              <lb/>
            </s>
            <s xml:id="echoid-s1391" xml:space="preserve">This will appear manifeſt by the following Ex-
              <lb/>
            amples.</s>
            <s xml:id="echoid-s1392" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div203" type="section" level="1" n="107">
          <head xml:id="echoid-head113" xml:space="preserve">
            <emph style="sc">Example</emph>
          I.</head>
          <p style="it">
            <s xml:id="echoid-s1393" xml:space="preserve">To throw ſeveral parallel Shores which ſtrengthen a
              <lb/>
            Wall, into Perſpective.</s>
            <s xml:id="echoid-s1394" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1395" xml:space="preserve">I ſuppoſe here that the Baſes of theſe Shores,
              <lb/>
              <note position="right" xlink:label="note-0105-02" xlink:href="note-0105-02a" xml:space="preserve">Fig. 38.</note>
            which are the Places where they meet the Sur-
              <lb/>
            face of the Ground, are all in a right Line, pa-
              <lb/>
            rallel to the Side of the Wall; </s>
            <s xml:id="echoid-s1396" xml:space="preserve">and then the
              <lb/>
            faid Shores may be thrown into Perſpective in
              <lb/>
            the following Manner: </s>
            <s xml:id="echoid-s1397" xml:space="preserve">Having firſt found
              <note symbol="*" position="right" xlink:label="note-0105-03" xlink:href="note-0105-03a" xml:space="preserve">68.</note>
            </s>
          </p>
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