Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667
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              roof, if we remove it far from perpendicularity, and then let it go,
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              have you not obſerved that, it declining, will paſs freely, and well
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              near as far to the other ſide of the perpendicular?</s>
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              <s>SAGR. </s>
              <s>I have obſerved it very well, and find (eſpecially if the
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              plummet be of any conſiderable weight) that it riſeth ſo little leſs
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              than it deſcended, ſo that I have ſometimes thought, that the
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              ſcending arch is equal to that deſcending, and thereupon made it
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              a queſtion whether the vibrations might not perpetuate themſelves;
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              and I believe that they might, if that it were poſſible to remove
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              the impediment of the Air, which reſiſting penetration, doth ſome
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              ſmall matter retard and impede the motion of the
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              pendulum,
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              though indeed that impediment is but ſmall: in favour of which
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              opinion the great number of vibrations that are made before the
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              moveable wholly ceaſeth to move, ſeems to plead.</s>
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              The motion of
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              grave
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              penduli
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              might be
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              ted, impediments
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              being removed.
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              <s>SALV. </s>
              <s>The motion would not be perpetual,
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              Sagredus,
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              though the impediment of the Air were totally removed, becauſe
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              there is another much more abſtruſe.</s>
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              <s>SAGR. </s>
              <s>And what is that? </s>
              <s>as for my part I can think of no
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              other?</s>
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              <s>SALV. </s>
              <s>You will be pleaſed when you hear it, but I ſhall not
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              tell it you till anon: in the mean time, let us proceed. </s>
              <s>I have
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              propoſed the obſervation of this
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              Pendulum,
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              to the intent, that you
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              ſhould underſtand, that the
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              impetus
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              acquired in the deſcending
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              arch, where the motion is natural, is of it ſelf able to drive the
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              ſaid ball with a violent motion, as far on the other ſide in the like
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              aſcending arch; if ſo, I ſay, of it ſelf, all external impediments
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              being removed: I believe alſo that every one takes it for granted,
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              that as in the deſcending arch the velocity all the way increaſeth,
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              till it come to the loweſt point, or its perpendicularity; ſo from
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              this point, by the other aſcending arch, it all the wav diminiſheth,
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              untill it come to its extreme and higheſt point: and diminiſhing
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              with the ſame proportions, where with it did before increaſe, ſo that
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              the dgrees of the velocities in the points equidiſtant from the point
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              of perpendicularity, are equal to each other. </s>
              <s>Hence it ſeemeth
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              to me (arguing with all due modeſty) that I might eaſily be induced
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              to believe, that if the Terreſtrial Globe were bored thorow the
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              centre, a Canon bullet deſcending through that Well, would
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              quire by that time it came to the centre, ſuch an impulſe of
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              city, that, it having paſſed beyond the centre, would ſpring it
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              wards the other way, as great a ſpace, as that was wherewith it had
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              deſcended, all the way beyond the centre diminiſhing the velocity
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              with decreaſements like to the increaſements acquired in the
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              ſcent: and the time ſpent in this ſecond motion of aſcent, I
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              lieve, would be equal to the time of deſcent. </s>
              <s>Now if the
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              able by diminiſhing that its greateſt degree of velocity which it </s>
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