had no affection to at all (as
there appears) if he could any other waies give account of those little
inequalities; and would much rather (I doubt not) have embraced this Notion
of the Common Center of Gravity, to salve the _Phaenomenon_, had it come to
his mind, or been suggested to him. And you find, that other _Astronomers_
have been seen to bring in (some upon one supposition, some upon another)
some kind of _Menstrual AEquation_, to solve the inequalities of the Moon's
motion, according to her _Synodical_ Revolution, or different Aspects (of
New-moon, Full Moon, &c.) beside what concerns her own _Periodical_ motion.
{281}

For which, this consideration of the _Common Center of Gravity of the Earth
and Moon_, is so proper a remedy (especially if it shall be found precisely
to answer those _Phaenomena_, which I have not Examined, but am very apt to
believe) that it is so far from being, with me, an Objection against it,
that it is one of the reasons, which make me inclinable to introduce it.

I must before I leave this, add one Consideration more, That if we shall
upon these Considerations think it reasonable, thus to consider the _Common
Center of Gravity of the Earth and Moon_; it may as well be thought
reasonable, that the like Consideration should be had of _Jupiter_ and his
four _Satellites_, which according to the Complication of their several
motions, will somewhat change the position of _Jupiter_, as to that _Common
center of Gravity_ of all these Bodies; which yet, because of their
smallness, may chance to be so little, as that, at this distance, the
change of his apparent place may not be discernable. And what is said of
_Jupiter_, is in the like manner to be understood of _Saturne_ and his
_Satelles_, discovered by _Hugenius_: For all these _Satellites_ are to
their _Principals_, as so many Moons to the Earth. And I do very well
remember, in the Letters forecited, Mr. _Horrocks_ expresseth some such
little inequalities in _Saturnes_ motion, of which he could not imagine
what account to give, as if (to use his Expression) this crabbed _Old
Saturn_ had despised his _Youth_. Which, for ought I know, might well
enough have been accounted for, if at that time the _Satelles_ of _Saturn_
had been discovered, and that Mr. _Horrocks_ had thought of such a notion
as the _Common Center of Gravity_ of _Saturn_ and his _Companion_, to be
considerable, as to the guiding of his motion.

You have now, in obedience to yo