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

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SIMP. I think ſo, if ſo be the moveable be of a matter
durable.
SALV. 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?
SIMP. Becauſe the inclination of grave bodies is to move
wards the centre of the Earth, and onely by violence upwards
wards the circumference; and the inclining ſuperficies is that
which acquireth vicinity to the centre, and the aſcending one,
remoteneſſe.
SALV. Therefore a ſuperficies, which ſhould be neither
clining nor aſcending, ought in all its parts to be equally
ſtant from the centre.
But is there any ſuch ſuperficies in the
World?
SIMP. There is no want thereof: Such is our Terreſtrial
Globe, if it were more even, and not as it is rough and
nous; but you have that of the Water, at ſuch time as it is calm
and ſtill.
SALV. 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.
SIMPL. It ſhould ſeem to be ſo.
SALV. And that ſtone which is on the round top, doth not it
move, as being together with the ſhip carried about by the
cumference of a Circle about the Centre; and therefore
quently by a motion in it indelible, if all extern obſtacles be
removed?
And is not this motion as ſwift as that of the ſhip.
SIMPL. Hitherto all is well. But what followeth?
SALV. Then in good time recant, I pray you, that your laſt
concluſion, if you are ſatisfied with the truth of all the
miſes.
SIMPL. 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
diments 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