Gravesande, Willem Jacob 's, An essay on perspective

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        <div xml:id="echoid-div338" type="section" level="1" n="183">
          <p>
            <s xml:id="echoid-s2101" xml:space="preserve">
              <pb o="93" file="0163" n="189" rhead="on PERSPECTIVE."/>
            the Eye, and above it, when the ſaid Plane is in-
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            clined towards the Objects. </s>
            <s xml:id="echoid-s2102" xml:space="preserve">Obſerve likewiſe,
              <lb/>
            that F f of Fig. </s>
            <s xml:id="echoid-s2103" xml:space="preserve">60. </s>
            <s xml:id="echoid-s2104" xml:space="preserve">muſt here be aſſumed e-
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            qual to R S, and the Line Tt, Fig. </s>
            <s xml:id="echoid-s2105" xml:space="preserve">61. </s>
            <s xml:id="echoid-s2106" xml:space="preserve">muſt
              <lb/>
            be here a Part of the Line Z C continued, and
              <lb/>
            made equal to R S.</s>
            <s xml:id="echoid-s2107" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div340" type="section" level="1" n="184">
          <head xml:id="echoid-head197" style="it" xml:space="preserve">III. When the Perſpective Plane is Parallel or
            <lb/>
          Horizontal.</head>
          <head xml:id="echoid-head198" xml:space="preserve">
            <emph style="sc">Prob</emph>
          . V.</head>
          <p style="it">
            <s xml:id="echoid-s2108" xml:space="preserve">117. </s>
            <s xml:id="echoid-s2109" xml:space="preserve">To throw Figures which are in the Geometri-
              <lb/>
            cal Plane into Perſpective.</s>
            <s xml:id="echoid-s2110" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2111" xml:space="preserve">Draw the Line C F at Pleaſure, in which aſ-
              <lb/>
              <note position="right" xlink:label="note-0163-01" xlink:href="note-0163-01a" xml:space="preserve">Fig. 63.</note>
            ſume the Point I, and make I H and I G, equal
              <lb/>
            to the Eye’s Diſtance from the perſpective
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            Plane: </s>
            <s xml:id="echoid-s2112" xml:space="preserve">Moreover, make I C, and I F equal to
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            the Eye’s Diſtance from the Geometrical Plane,
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            or at the leaſt, let I G and I H, be to I F and I C,
              <lb/>
            as the Eye’s Diſtance from the perſpective Plane,
              <lb/>
            is to its Diſtance from the Geometrical Plane.
              <lb/>
            </s>
            <s xml:id="echoid-s2113" xml:space="preserve">This being done, raiſe two Perpendiculars to
              <lb/>
            the Line C F, in the Points G and H, and take
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            two Rulers, each of which has two equal Threads
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            ſo faſten’d to them, that the Diſtance P Q, and
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            N M be equal: </s>
            <s xml:id="echoid-s2114" xml:space="preserve">Then about F and C as Centers,
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            with the Semidiameters M N or P Q, deſcribe
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            two Arcs cutting the Perpendiculars raiſed at the
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            Points G and H, in the Points C and D, and fix
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            the Extremities of the two Threads of one Ruler,
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            in the Points C and D, and the Threads of the
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            other, in the Points F and E.</s>
            <s xml:id="echoid-s2115" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div342" type="section" level="1" n="185">
          <head xml:id="echoid-head199" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s2116" xml:space="preserve">Let Z be the Geometrical Plane, and A a
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            Point of the given Figures. </s>
            <s xml:id="echoid-s2117" xml:space="preserve">Move the </s>
          </p>
        </div>
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    </echo>
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