Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

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1Weight G hanging at F, it hath been already demonſtrated, that
the ſaid Force D hath to the Weight ſo by it ſuſtained, that ſame
proportion which the Diſtance F C hath to the Diſtance C D:
Which is ſubduple proportion: Therefore the Moment D is ſub­
duple to the Moment of half of the Weight G ſuſtained by it:
Wherefore it followeth, that it is the fourth part of the Moment
of the whole Weight.
And in the ſame manner the ſame thing is
demonſtrated, of the Moment B; and it is but reaſonable, that the
Weight G being ſuſtained by the four points, A, B, C, D, each of
them ſhould feel an equall part of the Labour.
Let us come now to apply this Conſideration to Pullies, and let
the Weight X be ſuppoſed to hang at the two Pullies A B and D E
Rope, as we ſee, I D E H G A B, ſuſtaining the whole Machine in
the point K.
Now I ſay, that placing the Force in L, it ſhall be able
to ſuſtain the Weight X, if ſo be, it be equal to the fourth part of
it.
For if we do imagine the two Diameters D E and A B, and the
Weights hanging at the middle points F and C, we ſhall have two
Leavers like to thoſe before deſcribed, the Fulciments of which an­
ſwer to the points D and A.
Whereupon the Force placed in B,

or if you will, in L, ſhall be able to ſu­
ſtain the Weight X, being the fourth
part of it: And if we adde another Pul­
ley above the other two, making the
Rope or Cord to paſs along L M N, trans­
ferring the Force L into N, it ſhall be
able to bear the ſame Weight gravitating
downwards, the upper Pulley neither aug­
menting or diminiſhing the Force, as hath
been declared.
And we will likewiſe
note, that to make the: Weight aſcend the

four Ropes B L, E H, D I, and A G
ought to paſs, whereupon the Mover will
be to begin, as much as thoſe Ropes are
long; and yet nevertheleſs the Weight
ſhall move but only as much as the length
of one of them: So that we may ſay by
way of advertiſement, and for confirma­
tion of what hatn been many times ſpo­
ken, namely, that look with what proportion the Labour of the

Mover is diminiſhed, the length of the Way, on the contrary, is
encreaſed with the ſame proportion
* Or four parts
of the ſame Rope
* The word Gy­
rilla ſignifieth a
Shiver, Rundle,
or ſmall Wheel
of a Pulley, tran­
ſlated by we
ſometimes Pul­
ley, ſometimes
Nut or Girill.
But if we would encreaſe the Force in ſexcuple proportion, it
will be requiſite that we adjoyn another ^{*} ſmall Pulley or Gyrill
to the inferiour Pulley which that you may the better underſtand