Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/156

 therefore if that stone let fall from the round top, ought to follow 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.

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 projection.

It cannot be properly called a motion of projection.

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?

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 nullae sunt operationes; and therefore not onely of projected, but of all other preternatural 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.

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 separated from the projicient, will you admit of the impressed vertue, or will you make another attempt to overthrow it?

The operation of the medium being removed, I see not how one can have recourse to any thing else save the faculty impressed by the mover.

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.

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.