24 Maiheinatical Elements Book 1^ '

very Jlowly whilst the Earth comes towards it W")swiftly.

Whence it fbllows, that the Earth is cattieround the Sun, lest it should fall upon the Sun bythat very violent Motion whereby it h retain £in its Orbit.

This Motion of the Earth is also deduc’d fr olsl

the fame Principles another way.

Two Bodies that are carried towards one afl °^ther by any Force, will at last concur, or c °^tinually recede from one another, unless eachthem de so mov’d as to have a centrifugal F° rCequal to the Force whereby it is carried tov^*”the other Body; but as the Bodies which A ^vitate towards one another j tend towards ea # ,i2 5 other with equal Forces *, or what is the l" air > e ’* 65 with Celerities that are inversly as the1235 titles of Matter*, these Bodies cannot P e \ Q f S248 vere in their Motions about one another,both of them be so mov’d as to have equal ^trifugal Forces* which does not happen, unthey both revolve in equal times about their c° ^mon Center of Gravity ; that is, if this Prop®tion be applied to the Sun and Earth, unless^both move about a Point, whose distance y .the Center of the Sun is to its distance y r ^the Center of the Earth, as the Qu antlt XMatter in the Earth is to the Quantity of M . fter in the Sun, they cannot persevere in r

234 Motions about one another*: This Point, .

2 3 5 Center of Gravity , most of consequencevery near to the Sun’s Center. Now 11 _which soever of these Bodies moves, _itveres in its Motion about the other, it son. ,that both of them are affected by the Mot>^above-mention’d, and that the Sun is