Gravesande, Willem Jacob 's, An essay on perspective

Page concordance

< >
Scan Original
31 10
32 11
33 12
34 13
35 14
36 15
37 16
38
39
40
41 17
42 18
43 19
44 20
45
46
47
48 21
49 22
50 23
51 24
52
53
54
55 25
56 26
57
58
59
60 27
< >
page |< < (33) of 237 > >|
    <echo version="1.0RC">
      <text xml:lang="en" type="free">
        <div xml:id="echoid-div120" type="section" level="1" n="66">
          <p>
            <s xml:id="echoid-s850" xml:space="preserve">
              <pb o="33" file="0065" n="72" rhead="on PERSPECTIVE."/>
            firſt found ; </s>
            <s xml:id="echoid-s851" xml:space="preserve">and then if Lines be drawn
              <note symbol="*" position="right" xlink:label="note-0065-01" xlink:href="note-0065-01a" xml:space="preserve">47.</note>
            the Repreſentation of the Vertex touching the
              <lb/>
            Repreſentation of the Baſe, the Repreſentation
              <lb/>
            of the Cone will be had.</s>
            <s xml:id="echoid-s852" xml:space="preserve"/>
          </p>
          <p>
            <s xml:id="echoid-s853" xml:space="preserve">But ſince, according to this Manner, we are
              <lb/>
            obliged to find the Perſpective of all the Baſe;
              <lb/>
            </s>
            <s xml:id="echoid-s854" xml:space="preserve">whereas it often cannot be all ſeen; </s>
            <s xml:id="echoid-s855" xml:space="preserve">we may de-
              <lb/>
            termine, by the following Method, what Part
              <lb/>
            of the Baſe is viſible, and ſo only find the Re-
              <lb/>
            preſentation thereof. </s>
            <s xml:id="echoid-s856" xml:space="preserve">And then, to compleat
              <lb/>
            the Cone, we draw Lines from the Extremities
              <lb/>
            of the viſible Part of the Baſe, to the Repreſen-
              <lb/>
            tation of the Vertex.</s>
            <s xml:id="echoid-s857" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div123" type="section" level="1" n="67">
          <head xml:id="echoid-head72" style="it" xml:space="preserve">53. To determine the viſible Part of the Baſe of
            <lb/>
          a Cone.</head>
          <p>
            <s xml:id="echoid-s858" xml:space="preserve">Let the Circle L I F be the Baſe of a Cone
              <lb/>
              <note position="right" xlink:label="note-0065-02" xlink:href="note-0065-02a" xml:space="preserve">Fig. 21.</note>
            in the Geometrical Plane, and A the Center
              <lb/>
            thereof.</s>
            <s xml:id="echoid-s859" xml:space="preserve"/>
          </p>
        </div>
        <div xml:id="echoid-div125" type="section" level="1" n="68">
          <head xml:id="echoid-head73" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s860" xml:space="preserve">Aſſume P Q ſomewhere in the Baſe Line,
              <lb/>
            equal to the Semidiameter of the Circle L F;
              <lb/>
            </s>
            <s xml:id="echoid-s861" xml:space="preserve">and from the Point P, raiſe P D G perpendicu-
              <lb/>
            lar to the Baſe Line, meeting the Horizontal
              <lb/>
            Line in G; </s>
            <s xml:id="echoid-s862" xml:space="preserve">and in this Perpendicular, make
              <lb/>
            P D equal to the Height of the Cone; </s>
            <s xml:id="echoid-s863" xml:space="preserve">and draw
              <lb/>
            the Line Q D H, meeting the Horizontal Line
              <lb/>
            in H. </s>
            <s xml:id="echoid-s864" xml:space="preserve">Then, about the Point A as a Center,
              <lb/>
            and with the Radius G H, draw the Circle B C E; </s>
            <s xml:id="echoid-s865" xml:space="preserve">
              <lb/>
            and from the ſaid Point A, draw a Line to the
              <lb/>
            Station Point S: </s>
            <s xml:id="echoid-s866" xml:space="preserve">Biſect A S in R; </s>
            <s xml:id="echoid-s867" xml:space="preserve">and about
              <lb/>
            R, as a Center, with the Radius R A, deſcribe
              <lb/>
            the Circular Arc B A C, cutting the Circle BEC
              <lb/>
            in the Points B and C. </s>
            <s xml:id="echoid-s868" xml:space="preserve">Draw the Lines B A F,
              <lb/>
            and C A L; </s>
            <s xml:id="echoid-s869" xml:space="preserve">and the viſible Portion, (L I F) </s>
          </p>
        </div>
      </text>
    </echo>
Impressum