ccrniiig the Seas Ebbing and Flowing : Had I not been already 
too tedious, I fhould now proceed to give a further reafon, 
why I do introduce this confideration ot the Common Center of 
Gravity in reference to A flrmomical Accounts . For indeed, that 
which may poffibly feem at firft to be an Objection againji it, is 
with me one rea(on/<?r it. 
It may be thought perhaps, that if the Earth fliould thus de- 
fcribe an Epicycle about theCommon Center of Gravity,it would 
(by this its change of placej difturbe the Ceelefiial motions ^ and 
make the apparent places of the Planets , clpecially fome of 
them 5 different from what they would otherwifc be. For 
though fo fmall a removal of the Earth, as the Epicycle would 
caufe(erpecially \i \t% Semidiameter Ihould not be above i\ of 
the Earths Semidiameter) would fcarce be fenfible (if at all)to 
the remoter Planets ^ yet as to the nearer it mighty 
Now though what GaliUo anfwers to a tike Objedtfon in his 
Eypothefis ; (that its poffible there may be fome fmall difference, . 
which Aflronomers have not yet been fo accurate, as to obferve) 
might here perhaps ferve the turn s Yet my anfwer is much 
otherwife 5 to wit, that fuch difference hath been obferved.and 
hath very much puzzeled Afirmomtn to give an account of. 
About which you will find Mr, Morroc\s ( in fome of his Let- 
ters, whereof I did formerly, upon the Command of the B.oyal 
Society^ make an ExtraB) was very much perplexed ; and was 
f ain^ for want of other relief 5 to have recourfe to fomewhat 
like Kjplers amicable jF/'^r^/, which did according to the feve- 
ral pofitions of the Moon 3 accelerate or retard the Moon's 
motion • which amicable Fibres he had no affcdlion to at all ( as 
there appears ) if he could any other wares give account of 
thofe little inequalities ; ami would much rather (I doubt not) 
have embraced this Notion of the Common Center of Gravity, 
to falve the Plmmmenon^ had it come to his mindj or been fug- 
geflcd to him. And you find,that other Afironomers have been 
feen to bring in (fome upon one fuppofxtioUj fome upon ano- 
ther) feme kind of Menjirual j^quation, to folve the inequalities 
of the Moons motion, according iohtv SynodicalKtvoXmion^ 
or different Afpedts { of New-moon^FuU Moon, &c.) befide 
what concerns her own Periodical motion* 
For 
