Gravesande, Willem Jacob 's, An essay on perspective

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          <p>
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              <pb o="98" file="0172" n="200" rhead="An ESSAY"/>
            fore the before-mention’d Perſpective will be an
              <lb/>
            Hour-Line of a Dial, drawn upon the Plane
              <lb/>
            H L M I, and whoſe Style is G F.</s>
            <s xml:id="echoid-s2174" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2175" xml:space="preserve">The ſame may be demonſtrated of the Re-
              <lb/>
            preſentations of other Hour-Lines, which form
              <lb/>
            a Dial upon the Plane H L M I.</s>
            <s xml:id="echoid-s2176" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2177" xml:space="preserve">We now proceed to lay down the beſt way of
              <lb/>
            determining the ſaid Repreſentations.</s>
            <s xml:id="echoid-s2178" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div353" type="section" level="1" n="192">
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            <emph style="sc">Prob</emph>
          . I.</head>
          <head xml:id="echoid-head207" style="it" xml:space="preserve">122. To draw Vertical Dials.</head>
          <p>
            <s xml:id="echoid-s2179" xml:space="preserve">Draw the Line E O, thro’ E, the Foot of the
              <lb/>
              <note position="left" xlink:label="note-0172-01" xlink:href="note-0172-01a" xml:space="preserve">Fig. 66.</note>
            Style of the Horizontal Dial A B F D, equal
              <lb/>
            to the Length of the Style of the Dial to be
              <lb/>
            drawn, and making an Angle with the Meri-
              <lb/>
            dian C. </s>
            <s xml:id="echoid-s2180" xml:space="preserve">XII, equal to the Plane’s Declina-
              <lb/>
            tion.</s>
            <s xml:id="echoid-s2181" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2182" xml:space="preserve">This Angle muſt be aſſum’d towards the
              <lb/>
            Point D, when the Plane’s Declination is South-
              <lb/>
            Eaſt, as here; </s>
            <s xml:id="echoid-s2183" xml:space="preserve">towards F, when the Declination
              <lb/>
            is Weſtward; </s>
            <s xml:id="echoid-s2184" xml:space="preserve">towards A, when it is North-Eaſt-
              <lb/>
            wardly; </s>
            <s xml:id="echoid-s2185" xml:space="preserve">and towards B, when it is North Weſt-
              <lb/>
            wardly.</s>
            <s xml:id="echoid-s2186" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2187" xml:space="preserve">Now, thro’ the Extremity O of the ſaid Line,
              <lb/>
            draw the Line I H, perpendicular thereto; </s>
            <s xml:id="echoid-s2188" xml:space="preserve">and
              <lb/>
            the Line C P, thro’ the Center of the Dial, pa-
              <lb/>
            rallel, and equal to E O; </s>
            <s xml:id="echoid-s2189" xml:space="preserve">thro’ whoſe Extre-
              <lb/>
            mity, P, draw the Line P S, parallel to H I.</s>
            <s xml:id="echoid-s2190" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s2191" xml:space="preserve">Then, to make the Dial, draw the Line h i,
              <lb/>
              <note position="left" xlink:label="note-0172-02" xlink:href="note-0172-02a" xml:space="preserve">Fig. 67.</note>
            in which prick down the Diviſions of the
              <lb/>
            Line H I; </s>
            <s xml:id="echoid-s2192" xml:space="preserve">and in the Point o, (which is the
              <lb/>
            ſame as O) raiſe the Perpendicular o p, equal to
              <lb/>
            the Length of the Style of the Horizontal Dial
              <lb/>
            A B D F. </s>
            <s xml:id="echoid-s2193" xml:space="preserve">This being done; </s>
            <s xml:id="echoid-s2194" xml:space="preserve">draw a Parallel,
              <lb/>
            h i, thro’ the Extremity of this Perpendicular;
              <lb/>
            </s>
            <s xml:id="echoid-s2195" xml:space="preserve">on which, prick down the Diviſions of the </s>
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