Galilei, Galileo
,
Mechanics
,
1665
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than the Diſtance A C; that is, as the Force is leſſe than the
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Weight.</
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>Theſe Principles being declared, we will paſſe to the Contem
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plation of Pullies, the compoſition and ſtructure of which, together
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with their uſe, ſhall be deſcribed by us. </
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>And firſt let us ſuppoſe the
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^{*} Little Pulley A B C, made of Mettall or hard Wood, voluble a
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bout it's Axis which paſſeth thorow it's Center D, and about this
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Pulley let the Rope E A B C be put,
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at one end of whichlet the Weight E
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hang, and at the other let us ſuppoſe
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the Force F. </
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>I ſay, that the Weight
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being ſuſtained by a Force equall to
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it ſelf in the upper Nut or Pulley
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A B C, bringeth ſome benefit, as the
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moving or ſuſtaining of the ſaid
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Weight with the Force placed in F:
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For if we ſhall underſtand, that from
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the Center D, which is the place of the Fulciment, two Lines be
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drawn out as far as the Circumference of the Pulley in the points
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A and C, in which the pendent Cords touch the Circumference, we
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ſhall have a Ballance of equal Arms which determine the Diſtance
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of the two Suſpenſions from the Center and Fulciment D: Where
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upon it is manifeſt, that the Weight hanging at A cannot be ſuſtain
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ed by a leſſer Weight hanging at G, but by one equal to it; ſuch
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is the nature of equal Weights hanging at equal Diſtances. </
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>And
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although in moving downwards, the Force F cometh to turn about
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the Pulley A B C, yet there followeth no alteration of the Alti
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tude or Reſpect, that the Weight and Force have unto the two
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Diſtances A D and D C, nay, the Pulley encompaſſed becometh a
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Ballance equal to A C, but perpetuall. </
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>Whence we may learn,
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how childiſhly
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Ariſtotle
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deceiveth himſelf, who holds, that by making
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the ſmall Pulley A B C bigger, one might draw up the Weight with
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a leſſer Force; he conſidering that upon the enlargement of the
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ſaid Pulley, the Diſtance D C encreaſed, but not conſidering that
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there was as great an encreaſe of the other Diſtance of the Weight,
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that is, the other Semidiameter D A. </
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>The benefit therefore that may
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be drawn from the Inſtrument above ſaid, is nothing at all as to the
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diminution of the labour: and if any one ſhould ask how it hap
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pens, that on many occaſions of raiſing Weights, this means is made
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uſe of to help the Axis, as we ſee, for example, in drawing up the
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Water of Wells; it is anſwered, that that is done, becauſe that
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by this means the manner of employing the Force is found more
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commodious: for being to pull downwards, the proper Gravity of
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our Arms and other parts help us, whereas if we were to draw
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the fame Weight upwards with a meer Rope, by the ſole ſtrength </
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