common Center of Gravity, as well that of the Earth, as that 
of the Moon, are to defcribe feveral Epicycles. And, for that 
Reafon fails of giving any clear account of this Menjlrual Pe- 
riod. (And in like manner, he propofeth the Confideration as 
well of the Earths Aphelium and feriheliumy as of the yEquinoBi- 
al and Soijlitml Points^ in order to the finding a Reafon of the 
j^mualViaffitudQS', but doth not fix upon any thing, in which 
himfelf can Acquiefce : And therefore leaves it hi medio 3^% he 
found it. ) • 
It had been more agreeable to the J^z^^oi Staticks, if he 
had^ f as I do, ) fo conlidered the Earth and Moon as two parrs 
of the fame movable, ( not fo, as he doth, altam in Centro et /e- 
quentem pnecife revolutionem axis^ aliam remotius ac velut in cireum" 
ferentia, but, ) fo, as to make neither of them the Center, but 
both out of it, defcribing Epicycles about it: Like as, when 
a long ftick thrown in the Air, whofe one end is lieavyer than 
the other, is whirled about, fo as that the End, which did firft fly 
foremoft , becomes hindmoft ; the proper line of motion of 
this whole Body is not that, which iMlefcribed by either End, 
but that, which is defcribed by a middle point between them ; 
about which point each end, in whirlfiig,defcribes an Epicycle, 
And indeed, in the prefent cafe, it is not the Epicycle defcribed 
by the Moon, bint that, defcribed by the Earth, which gives the 
Menjlrual Viciffitudes of motion to the Water 5 which would, 
as to thisjbe the fame, if the Earth fo move, whether there were 
any Moon to move or not ; nor would the Moons Motion, (up- 
pofing the Earth to hold on its own courfe , any whit concern 
the motion of the Water. 
But now,(after all our Phyfical,or Statical Confiderations)the 
cleareft Evidence for |his Hypothefis (if it can be had) will be 
fromCeieftial Obfervations. As for inftance ^ (fee F/V.5.) Sup- 
pofing the San at S; the Earths place in its Annual Orb at T- and 
"Mars (in oppofition to the Sun^or near itj at M : From whence 
J/<isr/ fhould appear in the Zodiackatyi and will at Full moon 
befeen there tobe; the Moon being at C and the Earth at c: 
(and the like at the New-moon. ) But if the Moon be in the 
Firft quarter at A, and die Earth at a ; Mars will be feen, not at 
y.^ but at a J too flov;: And when the Moon "is at B, and the 
Earth at b, Mars will be feen at ; yet coo flow : till at the Full- 
mo oD;,, 
