Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667
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1that I fear I ſhall have but a ſmall part of it left free and
gaged, to apply to the principal matter that is treated of, and
which of it ſelf is but even too obſcure and intricate: So that
I intreat you to vouchſafe me, having once diſpatcht the buſineſs
of the ebbings and flowings, to do this honour to my houſe (and
yours) ſome other dayes, and to diſcourſe upon the ſo many other
Problems that we have left in ſuſpence; and which perhaps are
no leſs curious and admirable, than this that hath been diſcuſſed
theſe dayes paſt, and that now ought to draw to a
cluſion.
SALV. I ſhall be ready to ſerve you, but we muſt make more
than one or two Seſſions; if beſides the other queſtions reſerved
to be handled apart, we would diſcuſſe thoſe many that pertain
to the local motion, as well of natural moveables, as of the
ed: an Argument largely treated of by our Lyncean
mick. But turning to our firſt purpoſe, where we were about to
declare, That the bodies moving circularly by a movent virtue,
which continually remaineth the ſame, the times of the
tions were prefixt and determined, and impoſſible to be made
longer or ſhorter, having given examples, and produced
ments thereof, ſenſible, and feaſible, we may confirm the ſame
truth by the experiences of the Celeſtial motions of the Planets;
in which we ſee the ſame rule obſerved; for thoſe that move by
greater Circles, confirm longer times in paſſing them.
A moſt
pertinent obſervation of this we have from the Medicæan
nets, which in ſhort times make their revolutions about Jupiter:
Inſomuch that it is not to be queſtioned, nay we may hold it for
ſure and certain, that if for example, the Moon continuing to be
moved by the ſame movent faculty, ſhould retire by little and
little in leſſer Circles, it would acquire a power of abreviating
the times of its Periods, according to that Pendulum, of which in
the courſe of its vibrations, we by degrees ſhortned the cord, that
is contracted the Semidiameter of the circumferences by it paſſed.
Know now that this that I have alledged an example of it in the
Moon, is ſeen and verified eſſentially in fact.
Let us call to mind,
that it hath been already concluded by us, together with Coperni-

cus, That it is not poſſible to ſeparate the Moon from the Earth,
about which it without diſpute revolveth in a Moneth: Let us
remember alſo that the Terreſtrial Globe, accompanyed alwayes
by the Moon, goeth along the circumference of the Grand Orb
about the Sun in a year, in which time the Moon revolveth about
the Earth almoſt thirteen times; from which revolution it
eth, that the ſaid Moon ſometimes is found near the Sun; that is,
when it is between the Sun and the Earth, and ſometimes
much more remote, that is, when the Earth is ſituate between

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