Gravesande, Willem Jacob 's, An essay on perspective

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          <p>
            <s xml:id="echoid-s2306" xml:space="preserve">
              <pb o="105" file="0181" n="210" rhead="PERSPECTIVE."/>
            more conveniently go in at the Door in the Side
              <lb/>
            of the Machine.</s>
            <s xml:id="echoid-s2307" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2308" xml:space="preserve">6. </s>
            <s xml:id="echoid-s2309" xml:space="preserve">There are two Tin-Tubes bent at each End,
              <lb/>
            (one of which is repreſented in Fig. </s>
            <s xml:id="echoid-s2310" xml:space="preserve">76. </s>
            <s xml:id="echoid-s2311" xml:space="preserve">becauſe
              <lb/>
            they could not be ſhewn in the Figure of the
              <lb/>
            Machine) placed in the Furniture, near the
              <lb/>
            Back-ſide of the Machine, each having one End
              <lb/>
            without the Machine. </s>
            <s xml:id="echoid-s2312" xml:space="preserve">Theſe Tubes ſerve to give
              <lb/>
            Air to Perſons ſhut up in the Machine, yet ſo,
              <lb/>
            that no Light may enter through them.</s>
            <s xml:id="echoid-s2313" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2314" xml:space="preserve">7. </s>
            <s xml:id="echoid-s2315" xml:space="preserve">At the Places c, c, c, c, on the Out-ſide of
              <lb/>
            the Back-part of the Machine, are four Iron-Sta-
              <lb/>
            ples, in which ſlide two Wooden Rulers D E, D E,
              <lb/>
            about 3 Inches broad, having two other thin
              <lb/>
            Rulers going through holes made at their Tops, at
              <lb/>
            the Places D, D, to which thin Rulers the Board
              <lb/>
            F is fixed; </s>
            <s xml:id="echoid-s2316" xml:space="preserve">and ſo by this Means the ſaid Board
              <lb/>
            may be vertically moved backwards or for-
              <lb/>
            wards.</s>
            <s xml:id="echoid-s2317" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2318" xml:space="preserve">8. </s>
            <s xml:id="echoid-s2319" xml:space="preserve">On the Top of the Machine, there is a
              <lb/>
            Board about 15 Inches long, and 9 Inches broad,
              <lb/>
            having an hole PMOQ quite through it, about
              <lb/>
            9 or 10 Inches long, and four Inches broad.</s>
            <s xml:id="echoid-s2320" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2321" xml:space="preserve">9. </s>
            <s xml:id="echoid-s2322" xml:space="preserve">Upon the aforeſaid Board are fix’d two Dove-
              <lb/>
            tail’d Rulers, between which another Board ſlides
              <lb/>
            of the ſame Length as that, and whoſe breadth is
              <lb/>
            about 6 Inches. </s>
            <s xml:id="echoid-s2323" xml:space="preserve">In the middle of this ſecond
              <lb/>
            Board is a round Hole about three Inches Diame-
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            ter, hollowed into a female Screw, in which is
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            fitted a Cylinder about four Inches long, which
              <lb/>
            carries the Convex Glaſs; </s>
            <s xml:id="echoid-s2324" xml:space="preserve">Of which more here-
              <lb/>
            after.</s>
            <s xml:id="echoid-s2325" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2326" xml:space="preserve">10 The Figure X is a ſquare Box about 7 or
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            8 Inches broad, and 10 in height, which ſlides
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            upon the plain Board mentioned in Numb. </s>
            <s xml:id="echoid-s2327" xml:space="preserve">8. </s>
            <s xml:id="echoid-s2328" xml:space="preserve">the
              <lb/>
            Side B ſerving as a Door, is next to the fore-ſide
              <lb/>
            of the Machine, as it appears in the Figure; </s>
            <s xml:id="echoid-s2329" xml:space="preserve"/>
          </p>
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