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

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1therefore if that ſtone let fall from the round top, ought to
low the motion of the ſhip, that effect ſhould be aſcribed to the
Air, and not to the vertue impreſſed.
But you preſuppoſe that
the Air doth not follow the motion of the ſhip, but is tranquil.
Moreover, he that letteth it fall, is not to throw it, or to give
it impetus with his arm, but ought barely to open his hand and let
it go; and by this means, the ſtone, neither through the vertue
impreſſed by the projicient, nor through the help of the Air,
ſhall be able to follow the ſhips motion, and therefore ſhall be
left behind.
The project
cording to
tle, is not moved by
vertue impreſſed,
but by the medium.
SALV. I think then that you would ſay, that if the ſtone be
not thrown by the arm of that perſon, it is no longer a
jection.
SIMPL. It cannot be properly called a motion of projection.
SALV. So then that which Ariſtotle ſpeaks of the motion, the
moveable, and the mover of the projects, hath nothing to do
with the buſineſſe in hand; and if it concern not our purpoſe,
why do you alledg the ſame?
SIMP. I produce it on the oceaſion of that impreſſed vertue,
named and introduced by you, which having no being in the
World, can be of no force; for non-entium nullæ ſunt
nes; and therefore not onely of projected, but of all other
ternatural motions, the moving cauſe ought to be aſcribed to the
medium, of which there hath been no due conſideration had;
and therefore all that hath been ſaid hitherto is to no purpoſe.
SALV. Go to now, in good time. But tell me, ſeeing that
your inſtance is wholly grounded upon the nullity of the vertue
impreſſed, if I ſhall demonſtrate to you, that the medium hath
nothing to do in the continuation of projects, after they are
patated from the projicient, will you admit of the impreſſed
tue, or will you make another attempt to overthrow it?
SIMP. The operation of the medium being removed, I ſee not
how one can have recourſe to any thing elſe ſave the faculty
preſſed by the mover.
SALV. It would be well, for the removing, as much as is
poſſible, the occaſions of multiplying contentions, that you
would explain with as much diſtinctneſſe as may be, what is that
operation of the medium in continuing the motion of the
Operation of the
medium in
ing the motion of
the project.
SIMP. The projicient hath the ſtone in his hand, and with
force and violence throws his arm, with which jactation the
ſtone doth not move ſo much as the circumambient Air; ſo that
when the ſtone at its being forſaken by the hand, findeth it ſelf
in the Air, which at the ſame time moveth with impetouſity, it
is thereby born away; for, if the air did not operate, the ſtone
would fall at the foot of the projicient or thrower.