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

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1alſo inſtead of the Chord that rolleth about the Cylinder C, place
there a ſmall Wheel with teeth or Coggs, that may turn another
greater, and by that means multiply the power of the Force as
much as one ſhall pleaſe, without having any thing to deduct of
the ſame, ſave only the difficulty of moving the Machine, as in the
others.
The SCREW, Cochlea.
When once the Force of the Capſten and of the In­
clined Plane is underſtood, that of the Screw is eaſie
to be computed, for it is compoſed only of a Plane
much inclined, which windeth about a Cylinder: and if this Plane
be in ſuch manner Inclined, as that the Cylinder ought to make
v. gr. ten turns to advance forwards the length of a foot in the
Screw, and that the bigneſs of the Circumference of the Circle
213[Figure 213]
which the Force that turneth it
about doth deſcribe be of ten
feet; foraſmuch as ten times ten
are one hundred, one Man alone
ſhall be able to preſs as ſtrongly
with this Inſtrument, or Screw, as
one hundred without it, provided
alwaies, that we rebate the Force
that is required to the turning
of it.
Now I ſpeak here of Preſſing rather than of Raiſing, or Remo­
ving, in regard that it is about this moſt commonly that the Screw
is employed, but when we would make uſe of it for the raiſing of
Weights, inſtead of making it to advance into a Female Screw, we
joyn or apply unto it a Wheel of many Coggs, in ſuch ſort
made, that if v. gr. this Wheel have thirty Coggs, whilſt the Screw
maketh one entire turn, it ſhall not cauſe the Wheel to make more
than the thirtieth part of a turn, and if the Weight be faſtned to
a Chord that rowling about the Axis of this Wheel ſhall raiſe it but
one foot in the time that the Wheel makes one entire revolution,
and that the greatneſs of the Circumference of the Circle that is
deſcribed by the Force that turneth the Screw about be alſo of ten
ſeet, by reaſon that 10 times 30 make 300, one ſingle Man ſhall be
able to raiſe a Weight of that bigneſs with this Inſtrument, which
is called the Perpetual Screw, as would require 300 men with­
out it.
Provided, as before, that we thence deduct the difficulty that
we meet with in turning of it, which is not properly cauſed by the
Ponderoſity of the Weight, but by the Force or Matter of the In­

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