Gravesande, Willem Jacob 's, An essay on perspective

Table of contents

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[151.] Remarks.
[152.] Method III.
[153.] Operation.
[154.] Demonstration.
[155.] H I: T H:: a X: a T.
[156.] Prob. III.
[157.] Operation.
[158.] Demonstration.
[159.] Prob. IV.
[160.] Method II.
[161.] Operation.
[162.] Method III.
[163.] Remarks.
[164.] CHAP. VII. Of Shadows.
[165.] Of Solar Shadows. Problem I.
[166.] Operation.
[167.] Proe. II.
[168.] Remarks.
[169.] Problem III.
[170.] Of the Shadows of a ſmall Light. Prob. IV.
[171.] Problem V.
[172.] Remarks.
[173.] CHAP. VIII. Of mechanically ſhortning the Operations of Perſpective. 1. WHEN the perſpective Plane is ſup-pos’d perpendicular or upright. Problem I.
[174.] Operation.
[175.] Method II.
[176.] Prob. II.
[177.] Operation.
[178.] Method II.
[179.] Method III.
[180.] The Demonſtration of the two laſt Ways.
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              <pb o="74" file="0132" n="152" rhead="An ESSAY"/>
            the Lines themſelves, and T the Accidental Point
              <lb/>
            oſ Perpendiculars to the Geometrical Plane.</s>
            <s xml:id="echoid-s1760" xml:space="preserve"/>
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        <div xml:id="echoid-div268" type="section" level="1" n="140">
          <head xml:id="echoid-head146" xml:space="preserve">
            <emph style="sc">Operation</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1761" xml:space="preserve">Continue the Line A B until it meets the
              <lb/>
            Baſe Line in G, and draw the Line G D, which
              <lb/>
            cut in a and b by Lines drawn from A and B to
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            the Eye. </s>
            <s xml:id="echoid-s1762" xml:space="preserve">Then draw the Lines a F and T b In-
              <lb/>
            terſecting each other in X; </s>
            <s xml:id="echoid-s1763" xml:space="preserve">and a x will be the
              <lb/>
            Appearance ſought.</s>
            <s xml:id="echoid-s1764" xml:space="preserve"/>
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        <div xml:id="echoid-div269" type="section" level="1" n="141">
          <head xml:id="echoid-head147" xml:space="preserve">
            <emph style="sc">Demonstration</emph>
          .</head>
          <p>
            <s xml:id="echoid-s1765" xml:space="preserve">Becauſe a b is the Repreſentation of A
              <note symbol="*" position="left" xlink:label="note-0132-01" xlink:href="note-0132-01a" xml:space="preserve">43.</note>
            the Appearance of the inclin’d Line is one Part
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            of a F. </s>
            <s xml:id="echoid-s1766" xml:space="preserve">But the Extremity of the inclin’d Line
              <lb/>
            is in a Perpendicular to the Geometrical Plane
              <lb/>
            raiſed at the Point B; </s>
            <s xml:id="echoid-s1767" xml:space="preserve">therefore the Repreſen-
              <lb/>
            tation of the ſaid Extremity is in T b, and con-
              <lb/>
            ſequently x in the Interſection of this Line and
              <lb/>
            a F.</s>
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        <div xml:id="echoid-div271" type="section" level="1" n="142">
          <head xml:id="echoid-head148" xml:space="preserve">
            <emph style="sc">Method</emph>
          III.</head>
          <p>
            <s xml:id="echoid-s1769" xml:space="preserve">91. </s>
            <s xml:id="echoid-s1770" xml:space="preserve">Draw F H thro’ the Accidental Point of
              <lb/>
            the inclin’d Lines, parallel to the Baſe Line,
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            and equal to o F in Fig. </s>
            <s xml:id="echoid-s1771" xml:space="preserve">48. </s>
            <s xml:id="echoid-s1772" xml:space="preserve">then a is the Perpen-
              <lb/>
              <note position="left" xlink:label="note-0132-02" xlink:href="note-0132-02a" xml:space="preserve">Fig. 49.</note>
            dicular of the Foot of the inclin’d Line whoſe
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            Perſpective a x may be found as directed n. </s>
            <s xml:id="echoid-s1773" xml:space="preserve">70.</s>
            <s xml:id="echoid-s1774" xml:space="preserve"/>
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