Gravesande, Willem Jacob 's, An essay on perspective

Table of Notes

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          <p>
            <s xml:id="echoid-s1961" xml:space="preserve">
              <pb o="85" file="0149" n="172" rhead="on PERSPECTIVE."/>
            one of the Directions drawn upon the
              <note symbol="*" position="right" xlink:label="note-0149-01" xlink:href="note-0149-01a" xml:space="preserve">68, 88.</note>
            trical Plane; </s>
            <s xml:id="echoid-s1962" xml:space="preserve">but it is ſufficient here, that the
              <lb/>
            Angle the ſaid Directions make with the Baſe
              <lb/>
            Line, be only known: </s>
            <s xml:id="echoid-s1963" xml:space="preserve">And ſo, as the Problem
              <lb/>
            expreſſes it, the Geometrical Plane may be en-
              <lb/>
            tirely laid aſide.</s>
            <s xml:id="echoid-s1964" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1965" xml:space="preserve">105. </s>
            <s xml:id="echoid-s1966" xml:space="preserve">When the Perſpective Plane is parallel,
              <lb/>
            the Sun’s Rays will have no accidental Point;
              <lb/>
            </s>
            <s xml:id="echoid-s1967" xml:space="preserve">for their Repreſentations are then parallel; </s>
            <s xml:id="echoid-s1968" xml:space="preserve">in
              <lb/>
            which Caſe, one of the Parallels muſt be drawn
              <lb/>
            through the Point a, inſtead of the Line D a. </s>
            <s xml:id="echoid-s1969" xml:space="preserve">
              <lb/>
            Moreover, when the Perſpective Plane is perpen-
              <lb/>
            dicular, or inclin’d, and the Sun’s Rays are pa-
              <lb/>
            rallel thereto; </s>
            <s xml:id="echoid-s1970" xml:space="preserve">a Line muſt be drawn through the
              <lb/>
            Point a, parallel to the Baſe Line; </s>
            <s xml:id="echoid-s1971" xml:space="preserve">as likewiſe
              <lb/>
            another Line through the Point I, parallel to the
              <lb/>
            Sun’s Rays; </s>
            <s xml:id="echoid-s1972" xml:space="preserve">cutting the firſt Line in the Point
              <lb/>
            ſought.</s>
            <s xml:id="echoid-s1973" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div312" type="section" level="1" n="169">
          <head xml:id="echoid-head177" xml:space="preserve">
            <emph style="sc">Problem</emph>
          III.</head>
          <p style="it">
            <s xml:id="echoid-s1974" xml:space="preserve">106. </s>
            <s xml:id="echoid-s1975" xml:space="preserve">To find the Perſpective of the Shadow of an
              <lb/>
            elevated Point, when there is ſome Body hindring its
              <lb/>
            falling upon the Geometrical Plane.</s>
            <s xml:id="echoid-s1976" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1977" xml:space="preserve">The Perſpective of the Section of the Body
              <lb/>
            made by a Plane paſſing through the given Point
              <lb/>
            perpendicular to the Geometrical Plane, and pa-
              <lb/>
            rallel to the Sun’s Rays, muſt be found: </s>
            <s xml:id="echoid-s1978" xml:space="preserve">And then
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            the Interſection of the ſaid Perſpective, and a
              <lb/>
            Line drawn from the Appearance of the given
              <lb/>
            Point to the Repreſentation of its Shadow, is the
              <lb/>
            Repreſentation ſought.</s>
            <s xml:id="echoid-s1979" xml:space="preserve"/>
          </p>
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