Gravesande, Willem Jacob 's, An essay on perspective

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          <p>
            <s xml:id="echoid-s1178" xml:space="preserve">
              <pb o="47" file="0089" n="101" rhead="on PERSPECTIVE."/>
            take the Part 2 s, equal to the Height of the Eye
              <lb/>
            above the Point 2, which is in the Baſe of the
              <lb/>
            Column; </s>
            <s xml:id="echoid-s1179" xml:space="preserve">likewiſe aſſume s a in the ſaid Line
              <lb/>
            equal to S A of the precedent Figure, and from the
              <lb/>
            Point a draw to a s the indefinite Perpendicular
              <lb/>
            a Y. </s>
            <s xml:id="echoid-s1180" xml:space="preserve">Theſe General Preparations being made,
              <lb/>
            take at Pleaſure the ſmall equal Parts 6 i and 69
              <lb/>
            in the Line s a; </s>
            <s xml:id="echoid-s1181" xml:space="preserve">draw the Lines i h and 9 m Pa-
              <lb/>
            rallel to 63 z, and from the Point h draw the Line
              <lb/>
            h 3 4, thro’ the Center 3 of the Semicircle h m;
              <lb/>
            </s>
            <s xml:id="echoid-s1182" xml:space="preserve">aſſume a 5 in a Y equal to i 4, and draw the Line
              <lb/>
            5 s cutting i b in g, and 9 m in q. </s>
            <s xml:id="echoid-s1183" xml:space="preserve">And, (in Figure
              <lb/>
            32.) </s>
            <s xml:id="echoid-s1184" xml:space="preserve">about the Point A, as a Center, with the
              <lb/>
            Radius i h or 9 m, which are equal, deſcribe the
              <lb/>
            Circle F L M H, cutting the Arc B A C in the
              <lb/>
            Points D and E; </s>
            <s xml:id="echoid-s1185" xml:space="preserve">then draw the Line D E cut-
              <lb/>
            ting the Line A S in I; </s>
            <s xml:id="echoid-s1186" xml:space="preserve">aſſume I G equal to i g,
              <lb/>
            and I Q equal to 9 q; </s>
            <s xml:id="echoid-s1187" xml:space="preserve">and thro’ the Points Q and
              <lb/>
            G, draw F H and L M, parallel to the Line E D,
              <lb/>
            cutting the Circle D M E F in the Points L,
              <lb/>
            M, F, and H. </s>
            <s xml:id="echoid-s1188" xml:space="preserve">Now if the Repreſentations of Four
              <lb/>
            Points, whereof L M F and H, are the Seats, and
              <lb/>
            the two firſt of which is equal to 29, and of the
              <lb/>
            two others 2 i, be found*; </s>
            <s xml:id="echoid-s1189" xml:space="preserve">the Repreſentation
              <lb/>
            of the ſaid four Points will be ſo many Points of
              <lb/>
            Appearance ſought. </s>
            <s xml:id="echoid-s1190" xml:space="preserve">And by drawing two other
              <lb/>
            Lines, as i h and 9 m, and proceeding as be-
              <lb/>
            fore, the Repreſentation of ſo many more Points
              <lb/>
            will be had.</s>
            <s xml:id="echoid-s1191" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s1192" xml:space="preserve">Note, Becauſe a part of the Torus is hid by
              <lb/>
              <note position="right" xlink:label="note-0089-01" xlink:href="note-0089-01a" xml:space="preserve">Fig. 32.</note>
            the Column, therefore to avoid uſeleſs Operations,
              <lb/>
            a Circle muſt be deſcribed about the Center A,
              <lb/>
            with the Radius 36, cutting the Arc B C A in
              <lb/>
            the Points T and O, and the Lines STY and SOZ
              <lb/>
            muſt be drawn; </s>
            <s xml:id="echoid-s1193" xml:space="preserve">then all the Points as F and H,
              <lb/>
            falling between the Lines TY and O Z are uſeleſs,
              <lb/>
            and L and M not coming under this Obſervation
              <lb/>
            muſt only be uſed; </s>
            <s xml:id="echoid-s1194" xml:space="preserve">Note alſo, that there is no
              <lb/>
            neceſſity to determine Geometrically </s>
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