^^^^ (116^) 
Bbm the Coufideration of the Common Center of Gravity of the 
Earth and A^toon, This being by feveral Learned Men lookt 
upon, as a very rational Notion, it was thought fit to offer it by 
the Pr^fs to the^Pubhck , that other Incelligent Perfons alfo 
might the more conveniently and at their leifurc examine the 
Conjecture (the Author, fuch is his Modefty^^refenting it no o- 
therwife) and thereupon give in their fenie, and vi^hat Diffi. 
cullies may occur to them about it'^j jhat fo it may be either 
confirm'd or laid afide accordingly 5 As the Propofer himfelf 
exprefly defires in the Difcourfe , we now, without any more 
Preamble, are going to fubjoyn, as it was by him addrefled , by 
wayofLetter, from Oxford to Mr, Boyle April 2^^1666, and 
afterwards communicated to the Fw Society, as follows : 
*y Ou were carneft with me , when you laft went from hence^^. 
that I would put in writing fomewhat of that,which at divers 
times, thefe three or four years laft paft, I have been difcourf- 
ing with your felf and othejrs concerning the Common Center of 
Gravity of the Earth and Moon, in order to lalving tht Phanomenn 
*as oi xht S eas Ehhifig and Flomngy a^ offome perplexities 
in Agronomical Okfervations of the Places of the CeleftiaJ Bo- 
dies. Xii i 
How much the World , and the great Bodies therein, are 
managed according to the Lams af Motion, and Static\Princ2plej, 
and with how much more of clearnefs and fatisfadion, many 
of the more abljrufe Phmomena have been falved^ on fucli 
PrincipleSjtvithintlus laft Century of years^than formerly they 
bad been j I need nordifcourfe to you, who are well verfed in 
it. For , fince that GaliUo^ and (after him) Torricellie^ and o- 
thers, have applied Mechanie}^Vtmcx^\Q% to the falving of Phh 
lofophical Di&:uhks', Natural Philo/opky i$ well known t© have 
been rendered more intelhgible, and to have made a much, 
greater progrefs in lefs than an hundred years, than before for 
many ageSi „ ' - 
The Seas Ebhing and Flowing, hath fo great a connexion with 
the Meow/ motion, that in a manner all Philofophers (whatever 
other Caufes they have joyned with it ) have attributed much., 
of its caufe to the M0ons^ which either by lome occult quality, 
or. 
