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

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1not move, and ſo he ſhall not be bound to ſhew how that in
cending it continueth all the way vertically over one point, for
that it will not do any ſuch thing.
SIMP. Very well; But if grave bodies, and light can have no
principle, either internal or external of moving circularly, than
neither can the terreſtrial Globe move with a circular motion: and
thus you have the intent of the Author.
SALV. I did not ſay, that the Earth had no principle, either
interne, or externe to the motion of gyration, but I ſay, that I do
not know which of the two it hath; and yet my not knowing it
hath not a power to deprive it of the ſame; but if this Author
can tell by what principle other mundane bodies are moved round,
of whoſe motion there is no doubt; I ſay, that that which
keth the Earth to move, is a vertue, like to that, by which Mars
and Jupiter are moved, and wherewith he believes that the ſtarry
Sphere it ſelf alſo doth move; and if he will but aſſure me, who is
the mover of one of theſe moveables, I will undertake to be able
to tell him who maketh the Earth to move.
Nay more; I will
undertake to do the ſame, if he can but tell me, who moveth the
parts of the Earth downwards.
SIMP. The cauſe of this is moſt manifeſt, and every one knows
that it is gravity.
SALV. You are out, Simplicius, you ſhould ſay, that every
one knowes, that it is called Gravity: but I do not queſtion you
about the name, but the eſſence of the thing, of which eſſence
you know not a tittle more than you know the eſſence of the
mover of the ſtars in gyration; unleſſe it be the name that hath
been put to this, and made familiar, and domeſtical, by the many

experiences which we ſee thereof every hour in the day,: but not
as if we really underſtand any more, what principle or vertue that
is which moveth a ſtone downwards, than we know who moveth
it upwards, when it is ſeparated from the projicient, or who
veth the Moon round, except (as I have ſaid) onely the name,
which more particularly and properly we have aſſigned to the
tion of deſcent, namely, Gravity; whereas for the cauſe of
cular motion, in more general termes, we aſſign the Vertue
ſed, and call the ſame an Intelligence, either aſſiſting, or informing;
and to infinite other motions we aſcribe Nature for their cauſe.
We know no more
who moveth grave
bodies downwards;
than who moveth
the Stars round,
nor know we any
thing of theſe
ſes, more than the
names impoſed on
them by us.
SIMP. It is my opinion, that this Author asketh far leſſe than
that, to which you deny to make anſwer; for he doth not ask
what is nominally and particularly the principle that moveth
grave and light bodies circularly, but whatſoever it be, he
reth to know, whether you think it intrinſecal, or extrinſecal:
For howbeit, v. gr. I do not know, what kind of thing that gravity
is, by which the Earth deſcendeth; yet I know that it is an intern

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