Gravesande, Willem Jacob 's, An essay on perspective

Table of Notes

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          <pb o="86" file="0150" n="173" rhead="An ESSAY"/>
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        <div xml:id="echoid-div313" type="section" level="1" n="170">
          <head xml:id="echoid-head178" style="it" xml:space="preserve">Of the Shadows of a ſmall Light.</head>
          <head xml:id="echoid-head179" xml:space="preserve">
            <emph style="sc">Prob</emph>
          . IV.</head>
          <p style="it">
            <s xml:id="echoid-s1980" xml:space="preserve">107. </s>
            <s xml:id="echoid-s1981" xml:space="preserve">To find the Perſpective of the Shadow of a
              <lb/>
            Point, whoſe Seat, and Height, above the Geometri-
              <lb/>
            cal Plane is known.</s>
            <s xml:id="echoid-s1982" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1983" xml:space="preserve">Let Z be the Geometrical Plane, A the Seat
              <lb/>
              <note position="left" xlink:label="note-0150-01" xlink:href="note-0150-01a" xml:space="preserve">Fig. 59.</note>
            of the given Point; </s>
            <s xml:id="echoid-s1984" xml:space="preserve">and C that of the Light:
              <lb/>
            </s>
            <s xml:id="echoid-s1985" xml:space="preserve">Draw the indefinite Line C A B; </s>
            <s xml:id="echoid-s1986" xml:space="preserve">and about C,
              <lb/>
            as a Center, with a Semidiameter equal to the
              <lb/>
            Height of the Light above the Geometrical
              <lb/>
            Plane, deſcribe the Arc F: </s>
            <s xml:id="echoid-s1987" xml:space="preserve">Again, about the
              <lb/>
            Point A, with a Semidiameter equal to the
              <lb/>
            Height of the given Point, deſcribe the Arc E. </s>
            <s xml:id="echoid-s1988" xml:space="preserve">
              <lb/>
            This being done, draw the Line E F touching
              <lb/>
            the ſaid two Arcs, and cutting the Line C A in
              <lb/>
            B. </s>
            <s xml:id="echoid-s1989" xml:space="preserve">Then if the Perſpective of B be found, the
              <lb/>
            Perſpective of the Shadow of the Point will be
              <lb/>
            had.</s>
            <s xml:id="echoid-s1990" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div315" type="section" level="1" n="171">
          <head xml:id="echoid-head180" xml:space="preserve">
            <emph style="sc">Problem</emph>
          V.</head>
          <p style="it">
            <s xml:id="echoid-s1991" xml:space="preserve">108. </s>
            <s xml:id="echoid-s1992" xml:space="preserve">To find the Perſpective of the Shadow of an
              <lb/>
            elevated Point, the Repreſentation of which, as alſo
              <lb/>
            of its Seat being known, without uſing the Geometri-
              <lb/>
            cal Plane.</s>
            <s xml:id="echoid-s1993" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1994" xml:space="preserve">The Operation of Prob. </s>
            <s xml:id="echoid-s1995" xml:space="preserve">3. </s>
            <s xml:id="echoid-s1996" xml:space="preserve"> for Solar
              <note symbol="*" position="left" xlink:label="note-0150-02" xlink:href="note-0150-02a" xml:space="preserve">104.</note>
            dows muſt be uſed here, with this Difference;
              <lb/>
            </s>
            <s xml:id="echoid-s1997" xml:space="preserve">that inſtead of the accidental Point of the Sun’s
              <lb/>
            Rays, the Perſpective of the ſmall Sight muſt
              <lb/>
            be uſed; </s>
            <s xml:id="echoid-s1998" xml:space="preserve">and in the Room of the accidental
              <lb/>
            Points of the Directions of the ſaid Rays, the
              <lb/>
            Perſpective of the Seat of the Light muſt be
              <lb/>
            aſſumed.</s>
            <s xml:id="echoid-s1999" xml:space="preserve"/>
          </p>
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Impressum