Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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contrary term, another intrinſick and natural quality, which
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keth it averſe to motion. </
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<
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>Therefore tell me again; do you not
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think that the inclination
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v. </
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of grave bodies to move
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wards, is equal to the reſiſtance of the ſame to the motion of
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jection upwards?</
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The inclination of
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grave bodies to the
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motion downwards,
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is equal to their
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reſiſtance to the
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motion upwards.
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<
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>SAGR. </
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>I believe that it is exactly the ſame. </
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>And for this reaſon
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I ſee that two equal weights being put into a ballance, they do
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ſtand ſtill in
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equilibrium,
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the gravity of the one reſiſting its
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ing raiſed by the gravity wherewith the other preſſing
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wards would raiſe it.</
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>SALV. </
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>Very well; ſo that if you would have one raiſe up the
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other, you muſt encreaſe the weight of that which depreſſeth,
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or leſſen the weight of the other. </
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<
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>But if the reſiſtance to
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ing motion cunſiſt onely in gravity, how cometh it to paſſe, that
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in ballances of unequal arms, to wit in the ^{*}
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Stiliard,
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a weight
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ſometimes of an hundred pounds, with its preſſion downwards,
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doth not ſuffice to raiſe up on of four pounds; that ſhall
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poiſe with it, nay this of four, deſcending ſhall raiſe up that
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of an hundred; for ſuch is the effect of the pendant weight upon
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the weight which we would weigh? </
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>If the reſiſtance to motion
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reſideth onely in the gravity, how can the arm with its weight of
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four pounds onely, reſiſt the weight of a ſack of wool, or bale of
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ſilk, which ſhall be eight hundred, or a thouſand weight; yea
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more, how can it overcome the ſack with its moment, and raiſe
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it up? </
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<
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>It muſt therefore be confeſt
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Sagredus,
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that here it maketh
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uſe of ſome other reſiſtance, and other force, beſides that of
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ſimple gravity.</
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* A portable
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lance wherewith
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market-people
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weigh their
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modities, giving it
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gravity by
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ving the weight
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farther from the
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cock: call'd by the
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Latines,
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Campana
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trutina.
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<
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>SAGR. </
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>It muſt needs be ſo; therefore tell me what this
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cond virtue ſhould be.</
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<
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>SALV. </
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>It is that which was not in the ballance of equal
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arms; you ſee then what variety there is in the Stiliard; and
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on this doubtleſſe dependeth the cauſe of the new effect.</
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<
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>SAGR. </
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<
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>I think that your putting me to it a ſecond time, hath
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made me remember ſomething that may be to the purpoſe. </
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<
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>In
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both theſe beams the buſineſs is done by the weight, and by the
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motion; in the ballance, the motions are equal, and therefore the
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one weight muſt exceed it in gravity before it can move it; in the
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ſtiliard, the leſſer weight will not move the greater, unleſs when
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this latter moveth little, as being ſlung at a leſſer diſtance, and the
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other much, as hanging at a greater diſtance from the lacquet or
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cock. </
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<
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>It is neceſſary therefore to conclude, that the leſſer weight
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overcometh the reſiſtance of the greater, by moving much, whilſt
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the other is moved but little.</
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<
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>SALV. </
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<
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>Which is as much as to ſay, that the velocity of the
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moveable leſs grave, compenſateth the gravity of the moveable
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more grave and leſs </
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