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

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1without impediment by this Line, the Force and the Line ſhall
take ſome certain poſition in which they ſhall reſt, and the Line
ſhall of neceſſity be ſtreight, let that Line be termed the Pendant,
or Line of Direction of the Force. And let the Point by which it is
faſtned to the Fulciment be called the Point of Suſpenſion: which
may ſometimes be the Arm of a Leaver or Ballance; and then let
the Line drawn from the Center of the Fulciment of the Leaver
or Ballance to the Point of Suſpenſion be named the Diſtance or
the Arm of the Force: which we ſuppoſe to be a Line fixed, and
conſidered without Gravity.
Moreover, let the Angle comprehen­
ded betwixt the Arm of the Force and the Line of Direction be
termed the Angle of the Direction of the Force.
After theſe Definitions we lay down for a Principle, that in the
Leaver, and in the Ballance, Equal Forces drawing by Arms
that are equal, and at equall Angles of Direction, do draw equal­
And if in this Poſition they draw one againſt the other they
ſhall make an Equilibrium: but if they draw together, or towards
the ſame part, the Effect ſhall be double.
If the Forces being equal, and the Augles of Direction alſo
equal, the Arms be unequal, the Force that ſhall be ſuſpended at
the greater Arm ſhall work the greater Effect.
As in this Figure, the Center of the Ballance or Leaver being A,
222[Figure 222]
if the Arms A B and A C are equal,
as alſo the Angles A B D, and A C E,
the equal Forces D and E ſhall
draw equally, and make an Equili­
brium. So likewiſe the Arm A F be­
ing equal to A B, the Angle A F G
to the Angle A B D, and the Force
G to D, theſe two Forces ^{*} G and D

draw equally; and in regard that
they draw both one way, the Effect
ſhall be double.
* In the M. S.
Copy it is C and
In the ſame manner the Forces G and E ſhall make an Equilibri­
um; as alſo I and L ſhall counterpoiſe, if (being equal) the Arms
A K and A H, and the Angles A H T, and A K L be equal.
The ſame ſhall befall in the Forces P and R, if all things be
diſpoſed as before.
And in this caſe we make no other diſtinction
betwixt Weights and other Forces ſave only this, that Weights all
tend towards the Center of Grave Bodies, and Forces may be un­
derſtood to tend all towards all parts of the Univerſe, with ſo
much greater or leſſer Impetus than Weights. So that Weights and

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