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

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1ſeth to be raiſed by a leſſer, are the Pulley, the Inclined Plane, the
Wedg, the Capſten, or Wheel, the Screw, the Leaver, and ſome
others, for if we will not apply or compare them one to another,
we cannot well number more, and if we will apply them we need
not inſtance in ſo many.
The PVLLEY, Trochlea.
Let A B C be a Chord put about the Pulley D, to which let
the Weight E be faſtned; and firſt, ſuppoſing that two
men ſuſtain or pull up equally each of them one of the

ends of the ſaid Chord:
it is manifeſt, that if the
Weight weigheth 200
pounds, each of thoſe
men ſhal employ but the
half thereof, that is to ſay,
the Force that is requiſite
for ſuſtaining or raiſing
of 100 pounds, for each
of them ſhal bear but the
half of it.
Afterwards, let us ſup­
poſe that A, one of the
ends of this Chord, being
made faſt to ſome Nail,
the other C be again ſu­
ſtained by a Man; and it
is manifeſt, that this Man in C, needs not (no more than before)
for the ſuſtaining the Weight E, more Force than is requiſite for
the ſuſtaining of 100 pounds: becauſe the Nail at A doth the
ſame Office as the Man which we ſuppoſed there before.
In fine,
let us ſuppoſe that this Man in C do pull the Chord to make the
Weight E to riſe, and it is manifeſt, that if he there employeth
the Force which is requiſite for the raiſing of 100 pounds to the
height of two feet, he ſhall raiſe this Weight E of 200 pounds to
the height of one foot: for the Chord A B C being doubled, as it
is, it muſt be pull'd two feet by the end C, to make the Weight E
riſe as much, as if two men did draw it, the one by the end A,
and the other by the end C, each of them the length of one foot
only.
There is alwaies one thing that hinders the exactneſs of the Cal­
culation, that is the ponderoſity of the Chord or Pulley, and the
difficulty that we meet with in making the Chord to ſlip, and in
bearing it: but this is very ſmall in compariſon of that which