Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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Rectangle F H deſcribeth whilſt it draweth the Weight D along
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the Plane B A, by the means of a Chord parallel to this Plane, and
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paſſing about the Pulley E, in ſuch ſort, that H G, that is the height
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of this Rectangle, is equal to B A, along which the Weight D is to
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move, whilſt it mounteth to the height of the Line C A. </
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>And N O
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repreſents the firſt Dimenſion of ſuch another Force, that is de
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ſcribed by the Rectan
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gle N P, in the time that
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it is raiſing the Weight
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L to M. </
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>And I ſuppoſe
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that L M is equal to B A,
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or double to C A; and
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that N O is to F G, as
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O P is to G H. </
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>This
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done, I conſider that at
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ſuch time as the Weight
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D is moved from B to
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wards A, one may ima
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gine its Motion to be
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compoſed of two others, of which the one carrieth it from B R to
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wards C A, (to which operation there is no Force required, as all
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thoſe ſuppoſe who treat of the Mechanicks) and the other raiſeth
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it from B C towards R A, for which alone the Force is required:
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inſomuch that it needs neither more nor leſs Force to move it
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along the Inclined Plane B A, than along the Perpendicular C A.
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>For I ſuppoſe that the unevenneſſes,
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&c.
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of the Plane do not
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at all hinder it, like as it is alwaies ſuppoſed in treating of this
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matter.</
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>So then the whole Force F H is employed only about the raiſing
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of D to the height of C A: and foraſmuch as it is exactly equal to
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the Force N P, that is required for the raiſing of L to the Height
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of L M, double to C A, I conclude by my Principle that the
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Weight D is double to the Weight L. </
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>For in regard that it is
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neceſſary to employ as much Force for the one as for the other,
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there is as much to be raiſed in the one as in the other; and no
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more knowledge is required than to count unto two for the
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knowing that it is alike facile to raiſe 200 pounds from C to A,
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as to raiſe 100 pounds from L to M: ſince that L M is double
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to C A.</
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>You tell me, moreover, that I ought more particularly to ex
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plain the nature of the Spiral Line that repreſenteth the Plane
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equally enclined, which hath many qualities that render it ſuffi
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ciently knowable.</
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