Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/237

 it will passe any further, or else that there it would immediately stand still, and move no further?

I believe that it would continue to move a great way further.

But this motion beyond the centre, would it not be upwards, and according to your assertion preternatural, and violent? And yet on what other principle do you make it to depend, but only upon the self same, which did carry the ball to the centre, and which you called intrinsecal, and natural? Finde, if you can, another external projicient, that overtaketh it again to drive it upwards. And this that hath been said of the motion thorow the centre, is also seen by us here above; for the interne impetus of a grave body falling along a declining superficies, if the said superficies be reflected the other way, it shall carry it, without a jot interrupting the motion, also upwards. A ball of lead that hangeth by a thread, being removed from its perpendicularity, descendeth spontaneously, as being drawn by its internal inclination, and without any interposure of rest, passeth beyond the lowest point of perpendicularity: and without any additional mover, moveth upwards. I know that you will not deny, but that the principle of grave bodies that moveth them downwards, is no less natural, and intrinsecal, than that principle of light bodies, which moveth them upwards: so that I propose to your consideration a ball of lead, which descending through the Air from a great altitude, and so moving by an intern principle, and comming to a depth of water, continueth its descent, and without any other externe mover, submergeth a great way; and yet the motion of descent in the water is preternatural unto it; but yet nevertheless dependeth on a principle that is internal, and not external to the ball. You see it demonstrated then, that a moveable may be moved by one and the same internal principle, with contrary motions.

I believe there are solutions to all these objections, though for the present I do not remember them; but however it be, the Author continueth to demand, on what principle this circular motion of grave and light bodies dependeth; that is, whether on a principle internal, or external; and proceeding forwards, sheweth, that it can be neither on the one, nor on the other, saying; Si ab externo; Deusne illum excitat per continuum miraculum? an verò Angelus, an aër? Et hunc quidem multi assignant. Sed contra[In English thus] If from an externe principle; Whether God doth not excite it by a continued Miracle? or an Angel, or the Air? And indeed many do assign this. But on the contrary.

Trouble not your self to read his argument; for I am