Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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ſeth to be raiſed by a leſſer, are the Pulley, the Inclined Plane, the
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Wedg, the Capſten, or Wheel, the Screw, the Leaver, and ſome
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others, for if we will not apply or compare them one to another,
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we cannot well number more, and if we will apply them we need
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not inſtance in ſo many.</
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>The PVLLEY,
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Trochlea.
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>Let A B C be a Chord put about the Pulley D, to which let
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the Weight E be faſtned; and firſt, ſuppoſing that two
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men ſuſtain or pull up equally each of them one of the
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ends of the ſaid Chord:
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it is manifeſt, that if the
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Weight weigheth 200
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pounds, each of thoſe
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men ſhal employ but the
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half thereof, that is to ſay,
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the Force that is requiſite
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for ſuſtaining or raiſing
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of 100 pounds, for each
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of them ſhal bear but the
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half of it.</
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>Afterwards, let us ſup
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poſe that A, one of the
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ends of this Chord, being
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made faſt to ſome Nail,
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the other C be again ſu
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ſtained by a Man; and it
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is manifeſt, that this Man in C, needs not (no more than before)
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for the ſuſtaining the Weight E, more Force than is requiſite for
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the ſuſtaining of 100 pounds: becauſe the Nail at A doth the
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ſame Office as the Man which we ſuppoſed there before. </
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>In fine,
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let us ſuppoſe that this Man in C do pull the Chord to make the
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Weight E to riſe, and it is manifeſt, that if he there employeth
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the Force which is requiſite for the raiſing of 100 pounds to the
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height of two feet, he ſhall raiſe this Weight E of 200 pounds to
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the height of one foot: for the Chord A B C being doubled, as it
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is, it muſt be pull'd two feet by the end C, to make the Weight E
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riſe as much, as if two men did draw it, the one by the end A,
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and the other by the end C, each of them the length of one foot
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only.</
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>There is alwaies one thing that hinders the exactneſs of the Cal
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culation, that is the ponderoſity of the Chord or Pulley, and the
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difficulty that we meet with in making the Chord to ſlip, and in
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bearing it: but this is very ſmall in compariſon of that which </
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