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

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1
SUPPOSITIONS.
Any Grave Body, (as to what belongeth to it's proper ver­
tue) moveth downwards, ſo that the Center of it's Gravity
never ſtrayeth out of that Right Line which is produced
from the ſaid Center placed in the firſt Term of the Motion unto
the univerſal Center of Grave Bodies.
Which is a Suppoſition
very manifeſt, becauſe that ſingle Center being obliged to endea­
vour to unite with the common Center, it's neceſſary, unleſſe ſome
impediment intervene, that it go ſeeking it by the ſhorteſt Line,
which is the Right alone: And from hence may we ſecondarily
ſuppoſe
Every Grave Body putteth the greateſt ſtreſſe, and weigheth
moſt on the Center of it's Gravity, and to it, as to its proper ſeat,
all Impetus, all Ponderoſity, and, in ſome, all Moment hath re­
courſe.
We laſtly ſuppoſe the Center of the Gravity of two Bodies e­
qually Grave to be in the midſt of that Right Line which conjoyns
the ſaid two Centers; or that two equall weights, ſuſpended in
equall diſtence, ſhall have the point of Equilibrium in the common
Center, or meeting of thoſe equal Diſtances.
As for Example,
the Diſtance C E being equall to the Diſtance E D, and there be­
ing by them two equall weights ſuſpended, A and B, we ſuppoſe
the point of Equilibrium to be in the point E, there being no
greater reaſon for inclining to
one, then to the other part.
But

here is to be noted, that the Di­
ſtances ought to be meaſured
with Perpendicular Lines, which
from the point of Suſpenſion E,
fall on the Right Lines, that from
the Center of the Gravity of the
Weights A and B, are drawn to
the common Center of things
Grave; and therefore if the Diſtance E D were tranſported into
E F, the weight B would not counterpoiſe the weight A, becauſe
drawing from the Centers of Gravity two Right Lines to the Cen­
ter of the Earth, we ſhall ſee that which cometh from the Center
of the Weight I, to be nearer to the Center E, then the other
produced from the Center of the weight A.
Therefore our ſaying
that equal Weights are ſuſpended by [or at] equal Diſtances, is
to be underſtood to be meant when as the Right Lines that go from
their Centers & to ſeek out the common Center of Gravity, ſhall be
equidiſta nt from that Right Line, which is produced from the ſaid