Archimedes Texts

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.