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

Table of figures

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              <s>SVPPOSITION.</s>
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              <s>
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              I ſuppoſe that the degrees of Velocity acquired by the
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              ſame Moveable upon Planes of different inclinations
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              are equal then, when the Elevations of the ſaid
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              Planes are equal.
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              <s>By the Elevation of an inclined Plane he meaneth the Per­
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              pendicular, which from the higher term of the ſaid Plane
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              falleth upon the Horizontal Line produced along by the
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              lower term of the ſaid Plane inclined: as for better underſtanding;
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              the Line A B being parallel to the Horizon, upon which let the two
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              Planes C A, and C D be inclined:
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              the Perpendicular C B falling up­
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              on the Horizontal Line B A the
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              Author calleth the Elevation
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              of the Planes C A and C D;
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              and ſuppoſeth that the degrees of
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              Velocity of the ſame Moveable
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              deſcending along the inclined Planes C A and C D, acqui­
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              red in the Terms A and D are equal, for that their Elevation is
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              the ſame C B. </s>
              <s>And ſo great alſo ought the degree of Velocity be
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              underſtood to be which the ſame Moveable falling from the Point
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              C would acquire in the term B.</s>
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              <s>SAGR. </s>
              <s>The truth is, this Suppoſition hath in it ſo much of pro­
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              bability, that it deſerveth to be granted without diſpute, alwaies
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              preſuppoſing that all accidental and extern Impediments are re­
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              moved, and that the Planes be very Solid and Terſe, and the Move­
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              able in Figure moſt perfectly Rotund, ſo that neither the Plane,
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              nor the Moveable have any unevenneſs. </s>
              <s>All Contraſts and Im­
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              pediments, I ſay, being removed, the light of Nature dictates to
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              me without any difficulty, that a Ball heavy and perfectly round
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              deſcending by the Lines C A, C D, and C B would come to the
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              terms A D, and B with equal
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              Impetus's.
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              <s>SALV. </s>
              <s>You argue very probably; but over and above the pro­
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              bability, I will by an Experiment ſo increaſe the likelihood, as that
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              it wants but little of being equal to a very neceſſary Demonſtrati­
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              on. </s>
              <s>Imagine this leafe of Paper to be a Wall erect at Right-angles
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              to the Horizon, and at a Nail, faſtned in the ſame, hang a Ball or
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              Plummet of Lead, weighing an ounce or two, ſuſpended by the
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              ſmall thread A B, two or three yards long, perpendicular to the
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              Horizon: and on the Wall draw an Horizontal Line D C, cutting </s>
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