Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div363" type="section" level="1" n="196">
          <p style="it">
            <s xml:id="echoid-s2268" xml:space="preserve">
              <pb o="103" file="0179" n="208" rhead="on PERSPECTIVE."/>
            Mirrours muſt not be plac’d within the Machine; </s>
            <s xml:id="echoid-s2269" xml:space="preserve">for
              <lb/>
            in ſuch a cloſe Place, ones Breath will ſully them; </s>
            <s xml:id="echoid-s2270" xml:space="preserve">but
              <lb/>
            not the Convex Glaſs, becauſe it is encloſed in a
              <lb/>
            Tube.</s>
            <s xml:id="echoid-s2271" xml:space="preserve"/>
          </p>
          <figure number="72">
            <image file="0179-01" xlink:href="http://echo.mpiwg-berlin.mpg.de/zogilib?fn=/permanent/library/xxxxxxxx/figures/0179-01"/>
          </figure>
        </div>
        <div xml:id="echoid-div364" type="section" level="1" n="197">
          <head xml:id="echoid-head214" style="it" xml:space="preserve">The Uſe of the
            <emph style="sc">Camera</emph>
            <emph style="sc">Obscura</emph>
            <lb/>
          in Deſigning.</head>
          <head xml:id="echoid-head215" xml:space="preserve">
            <emph style="sc">Definition</emph>
          .</head>
          <p style="it">
            <s xml:id="echoid-s2272" xml:space="preserve">1. </s>
            <s xml:id="echoid-s2273" xml:space="preserve">ACamera Obſcura is any dark Place, in which
              <lb/>
            outward Objects expoſed to Broad-Day-light,
              <lb/>
            are repreſented upon Paper, or any other white
              <lb/>
            Body.</s>
            <s xml:id="echoid-s2274" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2275" xml:space="preserve">The Way to repreſent Objects in the Camera
              <lb/>
            Obſcura, is to make a ſinall Hole in that ſide
              <lb/>
            thereof next to the Objects, and place a Convex-
              <lb/>
            Glaſs therein, then if a Sheet of Paper be ex-
              <lb/>
            tended in the Focus of the ſaid Glaſs, the Objects
              <lb/>
            will appear inverted upon the Paper.</s>
            <s xml:id="echoid-s2276" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div365" type="section" level="1" n="198">
          <head xml:id="echoid-head216" xml:space="preserve">
            <emph style="sc">Theorem</emph>
          I.</head>
          <p style="it">
            <s xml:id="echoid-s2277" xml:space="preserve">2. </s>
            <s xml:id="echoid-s2278" xml:space="preserve">The Camera Obſcura gives the true Repreſen-
              <lb/>
            tation of Objects.</s>
            <s xml:id="echoid-s2279" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2280" xml:space="preserve">The Figures repreſented in the Camera Obſcura
              <lb/>
            are form’d (as is demonſtrated in Dioptricks)
              <lb/>
            by Rays which coming from all the Points of the
              <lb/>
            Objects, paſs through the Centre of the Glaſs:
              <lb/>
            </s>
            <s xml:id="echoid-s2281" xml:space="preserve">So that an Eye placed in the ſaid Centre, would
              <lb/>
            perceive the Objects by the ſaid Rays, which
              <lb/>
            conſequently by their Interſection with a Plane,
              <lb/>
            muſt give the true Repreſentation of the Objects. </s>
            <s xml:id="echoid-s2282" xml:space="preserve">
              <lb/>
            But the Pyramid which the ſaid Rays forms </s>
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