Galilei, Galileo - Mechanics

Galilei, Galileo, Mechanics, 1665

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That which in all Demonſtrative Sciences is neceſſary to be
obſerved, we ought alſo to follow in this Diſcourſe, that is;
to propound the Definitions of the proper Terms of this
Art, and the primary Suppoſitions, from which, as from ſeeds full
of fecundity, may of conſequence ſpring and reſult the cauſes,
and true Demonſtrations, of the Nature of all the Mechanick
Engines which are uſed, for the moſt part about the Motions of
Grave Matters, therefore we will determine, firſt, what is GRA-
VITIE.

We call GRAVITIE then, That propenſion of moving
naturally downwards, which is found in ſolid Bodies, cauſed by
the greater or leſſe quantity of matter, whereof they are conſti-
tuted.

MOMENT is the propenſion of deſcending, cauſed not ſo
much by the Gravity of the moveable, as by the diſpoſure which
divers Grave Bodies have in relation to one another; by means of
whichMoment, we oft ſee a Body leſs Grave counterpoiſe another
of greater Gravity: as in the Stiliard, a great Weight is raiſed by
a very ſmall counterpoiſe, not through exceſs of Gravity, but
through the remoteneſſe from the point whereby the Beam is up-
held, which conjoyned to the Gravity of the leſſer weight adds
thereunto Moment, and Impetus of deſcending, wherewith the
Moment of the other greater Gravity may be exceeded. MO-
MENT then is that IMPETUS of deſcending, compounded
of Gravity, Poſition, and the like, whereby that propenfion may
be occaſioned

The CENTER of GRAVITY we define to be that point
in every Grave Body, about which conſiſt parts of equall Moment:
ſo that, imagining ſome Grave Body to be ſuſpended and ſuſtain-
ed by the ſaid point, the parts on the right hand will Equilibrate
thoſe on the left, the Anteriour, the Poſteriour, and thoſe above
thoſe below; ſo that be it in any whatſoever fite, and poſition,
provided it be ſuſpended by the ſaid CENTER, it ſhall ſtand
ſtill: and this is that point which would gladly unite with the
univerſall Center of Grave Bodies, namely withthat of the Earth,
if it might thorow ſome free Medium deſcend thither. From
whence we take theſe Suppoſitions.

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