29B Sir I S A A C N E W T O N’s Book IV.

as the greatness of the force impressed on those vast bodies,some of which are many times greater than our earth, shewsthe power, its just quantity, varied regularly in the differentdistances of the planets, and its proper direction, /hew the skillof the firjl mover,

5. We may suppose that all the matter of which the systemconsists was formed first in one mast, where now the centre ofgravity of the whole system is found ; that of this mass variousbodies were formed, and separated from each other to properdistances, where they received their projectile motions ; andthat the powers which separated and moved, them observed thelaw of nature that requires an equality between action and re-action, and is observed in all the actions of powers at pre-sent : and thus these motions would begin, and continue forever, without producing any motion in thecentre of gravity ofthe system,

6. When the bodies were thus moved in their just orbits, wemay conceive some of them to have been subdivided again, byactions observing the fame laws, into several other bodies, whichin like manner, were formed into lester systems ; as that of theearth and moon,, those of Jupiter and Saturn and their fateslites. There is not any of these quieseent in its particularsystem ; the earth and moon.move about their, common centreof gravity, while it is carried with a regular motion round thecentre of gravity of the whole system.. The fame is to be saidof Jupiter and Saturn, and. their satellites; and.it is certainfrom the laws of nature, that the motions in any lester systemabout its centre of gravity , and. the motion of that centre aboutthe centre of gravity of the whole system, interfere not with*each other. A lester system being thus formed, one of thebodies, that compose, it might be. subdivided into lester bodies-

that: