Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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tarding, as being contrary to nature; and would be longer or
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ſhorter, according to the greater or leſs impulſe, and according to
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the greater or leſs acclivity.</
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>SALV. </
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>It ſeems, then, that hitherto you have explained to me
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the accidents of a moveable upon two different Planes; and that
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in the inclining plane, the grave moveable doth ſpontaneouſly
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ſcend, and goeth continually accelerating, and that to retain it in
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reſt, force muſt be uſed therein: but that on the aſcending plane,
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there is required a force to thruſt it forward, and alſo to ſtay it in
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reſt, and that the motion impreſſed goeth continually diminiſhing,
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till that in the end it cometh to nothing. </
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<
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>You ſay yet farther,
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that in both the one and the other caſe, there do ariſe differences
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from the planes having a greater or leſs declivity or acclivity; ſo
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that the greater inclination is attended with the greater velocity;
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and contrariwiſe, upon the aſcending plane, the ſame moveable
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thrown with the ſame force, moveth a greater diſtance, by how
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much the elevation is leſs. </
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>Now tell me, what would befall the
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ſame moveable upon a ſuperficies that had neither acclivity nor
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declivity?</
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>SIMPL. </
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>Here you muſt give me a little time to conſider of an
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anſwer. </
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<
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>There being no declivity, there can be no natural
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nation to motion: and there being no acclivity, there can be no
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reſiſtance to being moved; ſo that there would ariſe an
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rence between propenſion and reſiſtance of motion; therefore,
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methinks it ought naturally to ſtand ſtill. </
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>But I had forgot my
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ſelf: it was but even now that
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Sagredus
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gave me to underſtand
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that it would ſo do.</
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<
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>SALV. </
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>So I think, provided one did lay it down gently: but
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if it had an
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impetus
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given it towards any part, what would
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low?</
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>SIMP. </
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>There would follow, that it ſhould move towards that
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part.</
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>SALV. </
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>But with what kind of motion? </
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>with the continually
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accelerated, as in declining planes; or with the ſucceſſively
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tarded, as in thoſe aſcending.</
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>SIMP. </
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>I cannot tell how to diſcover any cauſe of acceleration,
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or retardation, there being no declivity or acclivity.</
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>SALV. Well: but if there be no cauſe of retardation, much
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leſs ought there to be any cauſe of reſt. </
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<
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>How long therefore
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would you have the moveable to move?</
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<
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>SIMP. </
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<
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>As long as that ſuperficies, neither inclined nor
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ned ſhall laſt.</
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<
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>SALV. </
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>Therefore if ſuch a ſpace were interminate, the motion
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upon the ſame would likewiſe have no termination, that is, would
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be perpetual.</
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