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

Table of figures

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            <pb xlink:href="040/01/192.jpg" pagenum="174"/>
            <p type="main">
              <s>SIMP. </s>
              <s>I ſaid ſo, and alſo confeſſe the reſt: and do now plainly
                <lb/>
              underſtand that the ſtone will not ſeparate from the Earth, for
                <lb/>
              that its receſſion in the beginning would be ſuch, and ſo ſmall,
                <lb/>
              that it is a thouſand times exceeded by the inclination which the
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              ſtone hath to move towards the centre of the Earth, which
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              tre in this caſe is alſo the centre of the wheel. </s>
              <s>And indeed it muſt
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              be confeſſed that the ſtones, the living creatures, and the other
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              grave bodies cannot be extruded; but here again the lighter things
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              beget in me a new doubt, they having but a very weak propenſion
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              of deſcent towards the centre; ſo that there being wanting in
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              them that faculty of withdrawing from the ſuperficies, I ſee not,
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              but that they may be extruded; and you know the rule, that
                <emph type="italics"/>
              ad
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              deſtruendum ſufficit unum.
                <emph.end type="italics"/>
              </s>
            </p>
            <p type="main">
              <s>SAVL. </s>
              <s>We will alſo give you ſatisfaction in this. </s>
              <s>Tell me
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              therefore in the firſt place, what you underſtand by light matters,
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              that is, whether you thereby mean things really ſo light, as that
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              they go upwards, or elſe not abſolutely light, but of ſo ſmall
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              vity, that though they deſcend downwards, it is but very ſlowly;
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              for if you mean the abſolutely light, I will be readier than your
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              ſelf to admit their extruſion.</s>
            </p>
            <p type="main">
              <s>SIMP. </s>
              <s>I ſpeak of the other ſort, ſuch as are feathers, wool,
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              ton, and the like; to lift up which every ſmall force ſufficeth:
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              yet nevertheleſſe we ſee they reſt on the Earth very quietly.</s>
            </p>
            <p type="main">
              <s>SALV. </s>
              <s>This pen, as it hath a natural propenſion to deſcend
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              wards the ſuperficies of the Earth, though it be very ſmall, yet I
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              muſt tell you that it ſufficeth to keep it from mounting upwards:
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              and this again is not unknown to you your ſelf; therefore tell me
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              if the pen were extruded by the
                <emph type="italics"/>
              Vertigo
                <emph.end type="italics"/>
              of the Earth, by what
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              line would it move?</s>
            </p>
            <p type="main">
              <s>SIMP. </s>
              <s>By the tangent in the point of ſeparation.</s>
            </p>
            <p type="main">
              <s>SALV. </s>
              <s>And when it ſhould be to return, and re-unite it ſelf to
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              the Earth, by what line would it then move?</s>
            </p>
            <p type="main">
              <s>SIMP. </s>
              <s>By that which goeth from it to the centre of the
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              Earth.</s>
            </p>
            <p type="main">
              <s>SALV. </s>
              <s>So then here falls under our conſideration two
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              ons; one the motion of projection, which beginneth from the
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              point of contact, and proceedeth along the tangent; and the
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              ther the motion of inclination downwards, which beginneth from
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              the project it ſelf, and goeth by the ſecant towards the centre; and
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              if you deſire that the projection follow, it is neceſſary that the
                <emph type="italics"/>
                <lb/>
              petus
                <emph.end type="italics"/>
              by the tangent overcome the inclination by the ſecant: is it
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              not ſo?</s>
            </p>
            <p type="main">
              <s>SIMP. </s>
              <s>So it ſeemeth to me.</s>
            </p>
            <p type="main">
              <s>SALV. </s>
              <s>But what is it that you think neceſſary in the motion
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              of the projicient, to make that it may prevail over that </s>
            </p>
          </chap>
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