|Galilei, Galileo Dialogues on two world systems 1661, tr. Salusbury, Thomas|
therefore if that stone let fall from the round top, ought to fol
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
The project ac
cording to Aristo
tle, is not moved by
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 pro
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 operatio
nes; and therefore not onely of projected, but of all other pre
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 se
patated from the projicient, will you admit of the impressed ver
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 im
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 project.
Operation of the
medium in continu
ing the motion of
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.