Gravesande, Willem Jacob 's, An essay on perspective

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              <pb o="26" file="0052" n="56" rhead="An ESSAY"/>
            from the Eye O upon the Baſe Line, the Appear-
              <lb/>
            ances of all Lines paſſing through S, will be
              <lb/>
            perpendicular to the Baſe Line; </s>
            <s xml:id="echoid-s709" xml:space="preserve">but the ſaid
              <lb/>
            Point S is the Station Point. </s>
            <s xml:id="echoid-s710" xml:space="preserve">Whence, &</s>
            <s xml:id="echoid-s711" xml:space="preserve">c.</s>
            <s xml:id="echoid-s712" xml:space="preserve"/>
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        <div xml:id="echoid-div93" type="section" level="1" n="53">
          <head xml:id="echoid-head55" xml:space="preserve">
            <emph style="sc">Problem</emph>
          II.</head>
          <p style="it">
            <s xml:id="echoid-s713" xml:space="preserve">42. </s>
            <s xml:id="echoid-s714" xml:space="preserve">To throw a Line in the Geometrical Plane
              <lb/>
            into Perſpective.</s>
            <s xml:id="echoid-s715" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s716" xml:space="preserve">It has been ſhewn , that to have the
              <note symbol="*" position="left" xlink:label="note-0052-01" xlink:href="note-0052-01a" xml:space="preserve">21.</note>
            ſentation of a right Line, the Perſpective of
              <lb/>
            the Extremes of the ſaid Line, need only be
              <lb/>
            found; </s>
            <s xml:id="echoid-s717" xml:space="preserve">and although it is difficult to find
              <note symbol="*" position="left" xlink:label="note-0052-02" xlink:href="note-0052-02a" xml:space="preserve">22.</note>
            Repreſentation of two Points, nevertheleſs I
              <lb/>
            ſhall ſhew here how to find more eaſy the Re-
              <lb/>
            preſentation of a Line in ſome Caſes.</s>
            <s xml:id="echoid-s718" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s719" xml:space="preserve">1. </s>
            <s xml:id="echoid-s720" xml:space="preserve">Let A B be a Line parallel to the Baſe
              <lb/>
              <note position="left" xlink:label="note-0052-03" xlink:href="note-0052-03a" xml:space="preserve">Fig. 13.</note>
            Line: </s>
            <s xml:id="echoid-s721" xml:space="preserve">To draw the Repreſentation of which,
              <lb/>
            having firſt found the Point a the Appearance
              <lb/>
            of A, one of the Ends of the given Line; </s>
            <s xml:id="echoid-s722" xml:space="preserve">af-
              <lb/>
            terwards through that Appearance, draw a Pa-
              <lb/>
            rallel to the Baſe Line; </s>
            <s xml:id="echoid-s723" xml:space="preserve">then the Line B O,
              <lb/>
            drawn from B to the Eye O, will cut the ſaid
              <lb/>
            parallel in the Point b, and b a will be the Re-
              <lb/>
            preſentation ſought.</s>
            <s xml:id="echoid-s724" xml:space="preserve"/>
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          <p>
            <s xml:id="echoid-s725" xml:space="preserve">43. </s>
            <s xml:id="echoid-s726" xml:space="preserve">2. </s>
            <s xml:id="echoid-s727" xml:space="preserve">Let C G be a Line, which continued
              <lb/>
            out, cuts the baſe Line in E. </s>
            <s xml:id="echoid-s728" xml:space="preserve">Now to draw the
              <lb/>
            Appearance thereof; </s>
            <s xml:id="echoid-s729" xml:space="preserve">through the Eye O, draw a
              <lb/>
            Line parallel thereto, cutting the Horizontal
              <lb/>
            Line in D, and joyn the Points E and D, by
              <lb/>
            the Line E D, which cut in the Points c and g,
              <lb/>
            by Lines drawn from C and G to the Eye; </s>
            <s xml:id="echoid-s730" xml:space="preserve">then
              <lb/>
            the Part c g of the Line E D, is the Appearance
              <lb/>
            ſought.</s>
            <s xml:id="echoid-s731" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div96" type="section" level="1" n="54">
          <head xml:id="echoid-head56" xml:space="preserve">
            <emph style="sc">Remark</emph>
          .</head>
          <p>
            <s xml:id="echoid-s732" xml:space="preserve">If the Lines G O and C O cut E D very ob-
              <lb/>
            liquely, and ſo their Interſection cannot be </s>
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