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

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1their parts do draw by Lines of Direction, which all concur in one
and the ſame Point; and Forces and their parts may be underſtood
to draw in ſuch ſort that all the Lines of Direction are parallel to
each other.
In the ſecond place, we ſuppoſe that a Force and its Line of Di­
rection abiding alwaies in the ſame poſition, as alſo the Center
of the Ballance or Leaver, be the Arm what it will that is drawn
from the Center of the Ballance to the Line of Direction, the
Force drawing alwaies in the ſame faſhion, will alwaies produce
the ſame Effect.
As, in this ſecond Figure, the Center of the Ballance being A,
the Force B, and the Line of Direction
223[Figure 223]
B F prolonged, as occaſion ſhall re­
quire, in which the Arms A G, A C, and
A F do determine, in this poſition let
the Line B F be faſtned to the Arm
A F, or A C, or to another Arm drawn
from the Center A to the Line of Di­
rection ^{*} B F: we ſuppoſe that this

Force B ſhall alwaies work the ſame
Effect upon the Ballance.
And if
drawing by the Arm A C it make an
Equilibrium with the Force D drawing by the Arm A E, when
ever it ſhall draw by the Arms A F or A G, it ſhall likewiſe make
an Equilibrium with the Force D drawing by the Arm A E. This
Principle although it be not expreſly found in Authors, yet it is
tacitly ſuppoſed by all thoſe that have writ on this Argument, and
Experience conſtantly confirmeth it.
* In the Original
it is writ, but by
the miſtake of
the Tranſcriber,
a la ligue de di­
rection A F.
If the Arms of a Ballance or Leaver are directly placed the one to
the other, and that being equal they ſuſtain equal Forces, of which
the Angles of Direction are Right An­
224[Figure 224]
gles, theſe Forces do alwaies weigh
equally upon the Center of the Bal­
lance, whether that they be near to the
ſame Center, or far diſtant, or both
conjoyned in the Center it ſelf; as in
this Figure the Ballance being E D,
the Center A, the equal Arms A D
and A E, let us ſuſtain equal Forces H and I, of which the Angles

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