&ook IV. of Naturhl Philosophy. 239

Altho’ these Disturbances, arising from the 1274^S'lons of the Planets upon each other, be very small,a nd altho’ those which happen in a different Po-rtion of the Planets, do in some measure com-pensate each other, yet the Proportion in whichdie Force which keeps the Planets in their Orbits^creases, is a little chang’d by these Actions, sothat it does not decrease exactly in an inverse Ra-tio of the Square of the Distance; therefore al-tho* the Orbits are at rest as to Sense, after atpeat many Revolutions, a small Change is obferv’dhz their Situation*. * z 43

From all this it follows, that if we suppose the 9Z 9Janets at first once projected at the Distances 12 1 5from the Sun, at which they are mov’d, they will,hy the Laws already explain’d, persevere in thoseMotions ; and the Eccentricity of the Orbits de-pends upon the Celerity and Direction of the firstProjection ; but these Motions may be preserv’dv ery long by reason of the small Resistance of theCelestial Matter.

It is also plain, why, by Lines drawn to theCenter of the Sun, they describe Area’s propor-tionable to the Times ; namely, because all otherCravities in the System are very small in respectso the Gravity towards the Sun* ; therefore by *1-65this Gravity alone it is that they are retain’d intheir Orbits; whence follows this Proportion ofthe Area’s*. And also the Motion in-elliptic* 225kines, which are carried on very slowly, followsfrom the Law of Gravity ; and these LinesWould also be immoveable, if the Planets gra-stated only towards the Sun * ; but this flow * 241Motion of the Orbits is deduc’d from the Action » 2oSct the Planets upon one another*. Now in re- *1214.fpect to the Proportion which is observ’d be-tween the Cubes of the Distances and the Squares°f the periodical Times, it is also deduc’d from

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