Galilei, Galileo
,
Mechanics
,
1665
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of the Members and Muſcles, and as we uſe to ſay, by Force of
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Armes, beſides the extern Weight, we are to lift up the Weight of
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our own Armes, in which greater pains is required. </
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<
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>Conclude we,
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therefore, that this upper Pulley doth not bring any Facility to the
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Force ſimply conſidered, but onely to the manner of applying it:
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but if we ſhall make uſe of the like Machine
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in another manner, as we are now about to
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declare; we may raiſe the Weight with di
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minution of Forces: For let the Pulley
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B D C be voluble about the Center E placed
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in it's Frame B L C, at which hang the
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Grave G; and let the Rope A B D C F
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paſſe about the Pulley; of which let the end
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A be faſtned to ſome fixed ſtay, and in the
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other F let the Force be placed; which
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moving to wards H ſhall raiſe the Machine
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B L C, and conſequently the Weight G:
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and in this operation I ſay, that the Force in
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F is the half of the Weight ſuſtained by it.
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>For the ſaid Weight being kept to Rights by the two ^{*} Ropes A B
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and F C, it is manifeſt, that the Labour is equally ſhared betwixt
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the Force F and the Fulciment A: and more ſubtilly examining the
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nature of this Inſtrument, if we but continue forth the Diameter
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B E C, we ſhall ſee a Leaver to be made, at the midſt of which, that
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is at the point E, the Grave doth hang, and the Fulciment cometh
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to be at the end B, and the Force in the Term C: whereupon, by
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what hath been above demonſtrated, the Force ſhall have the ſame
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proportion to the Weight, that the Diſtance E B hath to the Di
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ſtance; Therefore it ſhall be the half of the ſaid Weight: And
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becauſe the Force riſing towards A, the Pulley turneth round,
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therefore that Reſpect or Conſtitution which the Fulciment B and
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Center E, on which the Weight and Term C, in which the Force
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is employed do depend, ſhall not change all the while; but yet in
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the Circuinduction the Terms B and C happen to vary in number,
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but not in vertue, others and others continually ſucceeding in their
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place, whereby the Leaver B C cometh to be perpetuated. </
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<
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>And
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here (as hath been done in the other Inſtruments, and ſhall be in
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thoſe that follow) we will not paſſe without conſidering how that
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the journey that the Force maketh, is double to the Moment of the
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Weight. </
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<
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>For in caſe the Weight ſhall be moved ſo far, till that
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the Line B C come to arrive with it's points B and C, at the points
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A and F, it is neceſſary that the two equal Ropes be diſtended in
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one ſole Line F H, and conſequently, when the Weight ſhall have
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aſcended along the Intervall B A, the Force ſhall have been moved
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twice as far, that is, from
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F
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unto H. </
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<
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>Then conſidering that the </
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