Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

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      <text>
        <body>
          <chap>
            <pb xlink:href="040/01/861.jpg" pagenum="168"/>
            <p type="main">
              <s>
                <emph type="italics"/>
              Let the Horizontal Lines be A F the upper, and C D the low­
                <lb/>
              er; between which let the Perpendicular A C, and inclined
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              Plane D F, be cut in B; and let A R be a Mean-Proportional
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              between the whole Perpendicular C A, and the upper part A B; and
                <lb/>
              let F S be a Mean-proportional between the whole Inclined Plane D F,
                <lb/>
              and the upper part B F. </s>
              <s>I ſay, that the Time of the Fall along the
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              whole Perpendicular A C hath the ſame proportion to the Time along
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              its upper part A B, with the lower of the Plane, that is, with B D,
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              as A C hath to the Mean-proporti­
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              onal of the Perpendicular, that is
                <emph.end type="italics"/>
                <lb/>
                <figure id="id.040.01.861.1.jpg" xlink:href="040/01/861/1.jpg" number="104"/>
                <lb/>
                <emph type="italics"/>
              A R, with S D, which is the ex­
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              ceſſe of the whole Plane D F above
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              its Mean-proportional F S. </s>
              <s>Let a
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              Line be drawn from R to S, which
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              ſhall be parallel to the two Horizon­
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              tal Lines. </s>
              <s>And becauſe the Time of
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              the Fall along all A C, is to the
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              Time along the part A B, as C A is
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              to the Mean proportional A R, if we ſuppoſe A C to be the Time of
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              the Fall along A C, A R ſhall be the Time of the Fall along A B,
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              and R C that along the remainder B C. </s>
              <s>For if the Time along A C
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              be ſuppoſed, as was done, to be A C it ſelf the Time along F D ſhall
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              be F D; and in like manner D S may be concluded to be the Time a­
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              long B D, after F B, or after A B. </s>
              <s>The Time therefore along the
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              whole A C, is A R, with R C; And the Time along the inflected
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              Plane A B D, ſhall be A R, with S D: Which was to be proved.
                <emph.end type="italics"/>
              </s>
            </p>
            <p type="main">
              <s>
                <emph type="italics"/>
              The ſame happeneth, if inſtead of the Perpendicular, another
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              Plane were taken, as ſuppoſe N O; and the Demonstration is the
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              ſame.
                <emph.end type="italics"/>
              </s>
            </p>
            <p type="head">
              <s>PROBL I. PROP. XIII.</s>
            </p>
            <p type="main">
              <s>A Perpendicular being given, to Inflect a Plane
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              unto it, along which, when it hath the ſame
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              Elevation with the ſaid Perpendicular, it may
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              make a Motion after its Fall along the Per­
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              pendicular in the ſame Time, as along the
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              ſame Perpendicular
                <emph type="italics"/>
              ex quiete.
                <emph.end type="italics"/>
              </s>
            </p>
            <p type="main">
              <s>
                <emph type="italics"/>
              Let the Perpendicular given be A B, to which extended to C,
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              let the part B C be equal; and draw the Horizontal Lines
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              C E and A G. </s>
              <s>It is required from B to inflect a Plane reach­
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              ing to the Horizon C E, along which a Motion, after the Fall out
                <emph.end type="italics"/>
              </s>
            </p>
          </chap>
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