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

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1check that is immoveable, they ſhall fly out with great
ſity: the ſame effect following in that caſe, which we ſee dayly
to fall out in a boat that running a ſwift courſe, runs a-ground, or
meets with ſome ſudden ſtop, for all thoſe in the boat, being

prized, ſtumble forwards, and fall towards the part whither the
boat ſteered.
And in caſe the Earth ſhould meet with ſuch a
check, as ſhould be able to reſiſt and arreſt its vertigo, then indeed
I do believe that not onely beaſts, buildings and cities, but
tains, lakes and ſeas would overturn, and the globe it ſelf would
go near to ſhake in pieces; but nothing of all this concerns our
preſent purpoſe, for we ſpeak of what may follow to the motion
of the Earth, it being turn'd round uniformly, and quietly about
its own centre, howbeit with a great velocity.
That likewiſe
which you ſay of the ſlings, is true in part; but was not alledged
by Salviatus, as a thing that punctually agreed with the matter
whereof we treat, but onely, as an example, for ſo in groſs it may
prompt us in the more accurate conſideration of that point,
ther, the velocity increaſing at any rate, the cauſe of the
ction doth increaſe at the ſame rate: ſo that v. g. if a wheel of
ten yards diameter, moving in ſuch a manner that a point of its
circumference will paſs an hundred yards in a minute of an hour,
and ſo hath an impetus able to extrude a ſtone, that ſame impetus
ſhall be increaſed an hundred thouſand times in a wheel of a million
of yards diameter; the which Salviatus denieth, and I incline to his
opinion; but not knowing the reaſon thereof, I have requeſted it
of him, and ſtand impatiently expecting it.
Graming the
urnal vertigo of
the Earth, & that
by ſome ſudden ſtop
or obſtacle it were
arreſted, houſes,
mountains
ſelves, and perhaps
the whole Globe
would be ſhaken n
pieces.
SALV. I am ready to give you the beſt ſatisfaction, that my
abilities will give leave: And though in my firſt diſcourſe you
thought that I had enquired into things eſtranged from our
poſe, yet nevertheleſſe I believe that in the ſequel of the diſpute,
you will find that they do not prove ſo.
Therefore let Sagredus
tell me wherein he hath obſerved that the reſiſtance of any
able to motion doth conſiſt.
SAGR. I ſee not for the preſent that the moveable hath any
internal reſiſtance to motion, unleſſe it be its natural inclination
and propenſion to the contrary motion, as in grave bodies, that
have a propenſion to the motion downwards, the reſiſtance is to
the motion upwards; and I ſaid an internal reſiſtance, becauſe
of this, I think, it is you intend to ſpeak, and not of the external
reſiſtances, which are many and accidental.
SALV. It is that indeed I mean, and your nimbleneſſe of wit
hath been too hard for my craftineſſe, but if I have been too
ſhort in asking the queſtion, I doubt whether Sagredus hath been
full enough in his anſwer to ſatisſie the demand; and whether
there be not in the moveable, beſides the natural inclination to the

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