Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div305" type="section" level="1" n="165">
          <pb o="84" file="0146" n="168" rhead="An ESSAY"/>
          <p>
            <s xml:id="echoid-s1937" xml:space="preserve">Let Z be the Geometrical Plane; </s>
            <s xml:id="echoid-s1938" xml:space="preserve">A the Seat
              <lb/>
              <note position="left" xlink:label="note-0146-01" xlink:href="note-0146-01a" xml:space="preserve">Fig. 57.</note>
            of the given Point; </s>
            <s xml:id="echoid-s1939" xml:space="preserve">and A B the Direction of
              <lb/>
            the Sun’s Rays.</s>
            <s xml:id="echoid-s1940" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div307" type="section" level="1" n="166">
          <head xml:id="echoid-head174" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1941" xml:space="preserve">Draw two right Lines, making a right Angle
              <lb/>
            with each other; </s>
            <s xml:id="echoid-s1942" xml:space="preserve">in one of which, aſſume P E,
              <lb/>
            equal to the Height of the given Point, above
              <lb/>
            the Geometrical Plane: </s>
            <s xml:id="echoid-s1943" xml:space="preserve">Then draw the Line
              <lb/>
            E C thro’ the Point E; </s>
            <s xml:id="echoid-s1944" xml:space="preserve">making an Angle with
              <lb/>
            C P, equal to the Sun’s Altitude; </s>
            <s xml:id="echoid-s1945" xml:space="preserve">and make A B
              <lb/>
            equal to C P. </s>
            <s xml:id="echoid-s1946" xml:space="preserve">Find the Appearance of the Point
              <lb/>
            B; </s>
            <s xml:id="echoid-s1947" xml:space="preserve">and the Repreſentation ſought, will be
              <lb/>
            had.</s>
            <s xml:id="echoid-s1948" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1949" xml:space="preserve">Note, This Operation, as likewiſe all the
              <lb/>
            others in this Chapter, regard all the Situations
              <lb/>
            of the perſpective Plane; </s>
            <s xml:id="echoid-s1950" xml:space="preserve">and is ſo evident, that
              <lb/>
            there is no need of demonſtrating it.</s>
            <s xml:id="echoid-s1951" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div308" type="section" level="1" n="167">
          <head xml:id="echoid-head175" xml:space="preserve">
            <emph style="sc">Proe</emph>
          . II.</head>
          <p style="it">
            <s xml:id="echoid-s1952" xml:space="preserve">104. </s>
            <s xml:id="echoid-s1953" xml:space="preserve">To find the Repreſentation of an elevated
              <lb/>
            Point, whoſe Appearance, as alſo that of its Seat, is
              <lb/>
            given, without uſing the Geometrical Plane.</s>
            <s xml:id="echoid-s1954" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1955" xml:space="preserve">Find F, the accidental Point of the
              <note position="left" xlink:label="note-0146-02" xlink:href="note-0146-02a" xml:space="preserve">Fig. 58.</note>
            Rays, and D, that of their Direction: </s>
            <s xml:id="echoid-s1956" xml:space="preserve">Then
              <lb/>
              <note symbol="*" position="left" xlink:label="note-0146-03" xlink:href="note-0146-03a" xml:space="preserve">68, 88,
                <lb/>
              98.</note>
            draw a Line from the Point D, through a, the
              <lb/>
            Perſpective of the Seat of the given Point; </s>
            <s xml:id="echoid-s1957" xml:space="preserve">and
              <lb/>
            another from F, through I, the Perſpective of
              <lb/>
            the given Point: </s>
            <s xml:id="echoid-s1958" xml:space="preserve">And then b, the Interſection
              <lb/>
            of the ſaid two Lines, will be the Point ſought;
              <lb/>
            </s>
            <s xml:id="echoid-s1959" xml:space="preserve">as is manifeſt.</s>
            <s xml:id="echoid-s1960" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div310" type="section" level="1" n="168">
          <head xml:id="echoid-head176" xml:space="preserve">
            <emph style="sc">Remarks</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1961" xml:space="preserve">
              <gap/>
            order to find the accidental Point of any
              <lb/>
              <gap/>
            ber of inclin’d Lines, we have </s>
          </p>
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