190 Sir Isaac Newton’s BookII.

nets Jupiter and Saturn; because they act in that manner.But now the fame thing will be evident by drawing no etherconsequence from what is seen in those planets, than that thepower, by which the primary planets act on their secondary,is extended from the primary through the whole interval be-tween, so that it would act in every part of the intermediatespace. In Jupiter and Saturn this power is so far from beingconfined to a small extent of distance, that it not only reachesto several satellites at very different distances, but also fromone planet to the other, nay even through the whole plane-tary system \ Consequently there is no appearance of reason,why this power should not act at all distances, even at thevery surfaces of these planets as well as farther off. But fromhence it follows, that the power, which retains the moonin her orbit, is the same, as causes bodies near the surface ofthe earth to gravitate. For since the power, by which theearth acts on the moon, will cause bodies near the surfaceof the earth to descend with all the velocity they are soundto do, it is certain no other power can act upon thembesides; because if it did, they must os necessity descendswifter. Now from all this it is at length very evident,that the power in the earth, which we call gravity, ex-tends up to the moon, and decreases in the duplicate pro-portion of the increase os the distance from the earth.

7. This finishes the discoveries made in the action ofthe primary planets upon their secondary. The next thing

* Sec Ch. II. § 6.

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