Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div147" type="section" level="1" n="80">
          <pb o="41" file="0079" n="89" rhead="on PERSPECTIVE."/>
        </div>
        <div xml:id="echoid-div148" type="section" level="1" n="81">
          <head xml:id="echoid-head87" xml:space="preserve">
            <emph style="sc">Problem</emph>
          VIII.</head>
          <p style="it">
            <s xml:id="echoid-s1089" xml:space="preserve">59. </s>
            <s xml:id="echoid-s1090" xml:space="preserve">To throw a Priſm or Cylinder into Perſpective,
              <lb/>
              <note position="right" xlink:label="note-0079-01" xlink:href="note-0079-01a" xml:space="preserve">Fig. 26.</note>
            both of them being Perpendicular to the Geometri-
              <lb/>
            cal Plane.</s>
            <s xml:id="echoid-s1091" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1092" xml:space="preserve">Let G H I L M N be the Baſe of the Priſm
              <lb/>
            in the Geometrical Plane, and the viſible Part
              <lb/>
            thereof upon the perſpective Plane, let be n g h i;
              <lb/>
            </s>
            <s xml:id="echoid-s1093" xml:space="preserve">then to compleat the Repreſentation of the
              <lb/>
            Priſm, draw Perpendiculars from the Points
              <lb/>
            n g h and i to the Baſe Line, whoſe Length let
              <lb/>
            be ſuch that they may repreſent
              <note symbol="*" position="right" xlink:label="note-0079-02" xlink:href="note-0079-02a" xml:space="preserve">55.</note>
            lars to the Geometrical Plane, equal to the
              <lb/>
            Height of the Priſm, and find the
              <note symbol="*" position="right" xlink:label="note-0079-03" xlink:href="note-0079-03a" xml:space="preserve">50.</note>
            of the other Angular Points of the upper Sur-
              <lb/>
            face of the Priſm, in confidering them as Points
              <lb/>
            elevated above the Geometrical Plane: </s>
            <s xml:id="echoid-s1094" xml:space="preserve">This
              <lb/>
            being done, if the Repreſentations of all the
              <lb/>
            ſaid Angular Points be joyn’d, the whole
              <lb/>
            Priſm will be thrown into Perſpective.</s>
            <s xml:id="echoid-s1095" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1096" xml:space="preserve">Now to throw a Cylinder into Perſpective,
              <lb/>
            the Repreſentation of its Baſe and upper Sur-
              <lb/>
            face muſt firſt be had, by finding the
              <note symbol="*" position="right" xlink:label="note-0079-04" xlink:href="note-0079-04a" xml:space="preserve">50.</note>
            ance of ſeveral Points of the Periphery of its
              <lb/>
            upper Surface, and then two Perpendiculars
              <lb/>
            muſt be ſo drawn to the Baſe Line, that they
              <lb/>
            may touch the Appearances of the two circular
              <lb/>
            Euds of the Cylinder, and the Appearance of
              <lb/>
            the Cylinder will be had. </s>
            <s xml:id="echoid-s1097" xml:space="preserve">But to avoid uſeleſs
              <lb/>
            Operations, the viſible Part of the Baſe of the
              <lb/>
            Cylinder may be thus determin’d. </s>
            <s xml:id="echoid-s1098" xml:space="preserve">Draw the
              <lb/>
            Line A S from the Point A to the Station Point S,
              <lb/>
            then this Line muſt be biſected in the Point R,
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            about which, as a Centre, and with the Radius
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            R A, the Circular Arc B A C, muſt be deſcrib’d
              <lb/>
            cutting the Baſe of the Cylinder in the </s>
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