Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/154

 I think so, if so be the moveable be of a matter durable.

That hath been already supposed, when it was said, that all external and accidental impediments were removed, and the brittlenesse of the moveable in this our case, is one of those impediments accidental. Tell me now, what do you think is the cause that that same Ball moveth spontaneously upon the inclining plane, and not without violence upon the erected?

Because the inclination of grave bodies is to move towards the centre of the Earth, and onely by violence upwards towards the circumference; and the inclining superficies is that which acquireth vicinity to the centre, and the ascending one, remotenesse.

Therefore a superficies, which should be neither declining nor ascending, ought in all its parts to be equally distant from the centre. But is there any such superficies in the World?

There is no want thereof: Such is our Terrestrial Globe, if it were more even, and not as it is rough and montainous; but you have that of the Water, at such time as it is calm and still.

Then a ship which moveth in a calm at Sea, is one of those moveables, which run along one of those superficies that are neither declining nor ascending, and therefore disposed, in case all obstacles external and accidental were removed, to move with the impulse once imparted incessantly and uniformly.

It should seem to be so.

And that stone which is on the round top, doth not it move, as being together with the ship carried about by the circumference of a Circle about the Centre; and therefore consequently by a motion in it indelible, if all extern obstacles be removed? And is not this motion as swift as that of the ship.

Hitherto all is well. But what followeth?

Then in good time recant, I pray you, that your last conclusion, if you are satisfied with the truth of all the premises.

By my last conclusion, you mean, That that same stone moving with a motion indelibly impressed upon it, is not to leave, nay rather is to follow the ship, and in the end to light in the self same place, where it falleth when the ship lyeth still; and so I also grant it would do, in case there were no outward impediments that might disturb the stones motion, after its being let go, the which impediments are two, the one is the moveables inability to break through the air with its meer impetus onely, it being deprived of that of the strength of Oars, of which it had