(a8i) 
For which, this consideration of the Common Center of Gravity 
of the Earth and Moon , is fo proper a remedy ( efpecially if it 
fhali be found precifeiy to anfwer thofe Phcenomena , which I 
have not Examined, but am very apt to believe J that it is fo 
far from being, with me, an Objection againft it, that it is one 
of the reafons, which make me inclinable to introduce it. 
I mu ft before I leave this, add one Confideration more. 
That if we fhali upon thefe Confiderations think itreafonable, 
tli lis to confider the Common Center of Gravity of the Earth and 
Aloon-, it may as well be thought reafonable, that the like Con- 
fideration fhould be had of Jupiter and his four Satellite j^vthich 
according to the Complication of their feveral motions, will 
fomewhat change the pofition of Jupiter ,as to that Common cen~ 
ter of Gravity of all thefe Bodies ; which yet, becaufe of their 
frnailnefs, may chance to be fo little, as that, at this diftance, 
.the change of this apparent place may not be difcernable. And 
what is laid of Jupiter , is in the like manner to be underftood 
of Saturne and his Satelles , difcovered by Hugenius : For all 
thefe Satellites are to their Principals , as fo many Moons to the 
Earth. And I do very well remember, in the Letters forecited, 
Mr. Horrocks exprefleth fome fuch little inequalities in Saturnes 
motion, of which he could not imagine what account to give, 
as if (to ufe his Expreffion) this crabbed Old Saturn had defpi- 
fedhis Youth. Which, for ought I know , might well enough 
have been accounted for , if at that time the Satelles of Saturn 
had been difcovered, and that Mr .Horrocks had thought of fnch 
a motion as the Common Center of Gravity of Saturn and his Compa- 
nioned be conGderable,as to the guidingof his motion. 
Yoju have now, in obedience to your Commands , an Ac- 
count of my thoughts, as to this matter, though yet immature 
and unpolifhed : What ufe you will pleafe to make of them , I 
fhali leave to your prudence,Scc. 
An A P P E N D I X, written by way of Letter to the publiflier j 
Being an Anfwer to fome Objections > made by feveral Perfons 3 to 
the precedent Difcourfe. 
I Received yours > and am very well contented, that objecti- 
ons be made againft my Plypotheps concerning Tydes • being 
P p 2 pro- 
