from the Confi deration of 'the Common tenter of gravity of tb$- 
Earth and Moon, This being by feveral Learned Men lookc 
upon, as a very rational Motionjt w?is thought fit to offer it by 
the Prefs to the Publick , that other Intelligent Perfons alfo 
might the more conveniently and at their leifure examine the 
Conjeblure (the Author, fuch is his Modefty, prefenting it no o- 
therwife) and thereupon give in their Tenfe , and what Diffi- 
culties may occur to them about it , that fo it may be either 
confirm’d or laid alide accordingly 5 As the Propofer- him felf 
expreily deiires in the Difcourfe , we now, without any more 
Preamble , are going to fubjoyn, as it was by him addrefled , by 
way of Letter, from Oxford to Mr. Boyle April 25* 1 666 . and 
afterwards communicated to the F*. Society, as follows : 
Y Ou were earneft 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 others concerning the Common Center of • 
Gravity of the: Earth and Moon, in order to halving the Phenomena 
as well of the Seas Ebbing and Flowing -, as of fome perplexities 
in Agronomical Obfervations of the Places of the Celeftial Bo* 
dies. 
How much the World , and the great Bodies therein, are 
manag’d according to the Laws of Motion , anti Static \ Principles , 
and with how much more of clearnefs and fatisfadfion , many 
of the more abftrufe Phenomena have been halved on fuch 
Principles, within this laft Century of years, than formerly they 
liad been j I need not difcourfe to you, who are well verfed in 
it. For , fiiice that GaltfdL and (after him) Torricelho, and o- 
th'ers, have applied Mechanic}^ Principles to the halving of Pki~ 
lofophicalD ifficulties ; Natural Philofophy is well known t© have 
been rendered more intelligible, and to have made amuck 
greater progrefs in lefs than an hundred years, than before for 
many ages* 
The Seas Ebbing and Flowing, hath fo great a connexion with 
the Moons motion, that in a manner all Philofophers (whatever 
other Catifes they hayejoyned with, it ) have attributed much 
of its eaufe to the Motin'^which either by Jome occult quality, 
.or 
