CHAP. V.

Of the Periodical Motion of the Secondary Planets.

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AVING confidered the Periods of the Primary Planets; let us next caft our eye upon those of their Secondaries. And among these we shall find the fame compleat order and harmony as among the laft. Thus Saturn's five Moons, and Jupiter's four, and our own about the Earth, have each of them their determinate times, fome longer, fome fhorter intervals of time, in the fame due proportion, as I fpake of among the Primaries.

BESIDES which, there is another thing very confiderable in this Periodical Motion of those Secondary

Pla

Planets, and that is, that it is mixt with a kind of cochleous Direction towards one or other Pole of the Primary Planet; by which means every Satellite by gentle degrees changeth its Latitude, and makes its vifits towards each Pole of its Primary. This is well known among the Circumjovials for inftance, that they all have a flow and gradual progress, firft towards one, then back again towards the other Pole of Jupiter : and that each Satellite hath its Latitude greater and greater according as it is farther or farther from Jupiter's Body. Accordingly the Latitude of each Circumjovial, affigned by the di ligent and fagacious Caffini (4), after 12 years obfervations, are thefe, The greatest Latitude of the First,

(4) Les Hypoth, & les Tables des Satel. de fupiter, 4. in the French Academift's large Collection.

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or Nearest, exceeds not a third part of Jupiter's Semidiameter: that of the Second, furpaffeth but a little of a quarter of its Diameter: that of the Third a little exceeds three quarters of the Diameter: and that of the Fourth, or Outermost goes beyond Jupiter's Poles by a third part of the Semidiameter. All which mutations, he faith, are performed in the space of 12 years. Thus the famous Caffini. But I have my self observed a greater vagation in the Third Satellite, that it advanced near to, if not even with the very Limb, or Pole of Jupiter, and that its Stay in Jupiter's Shadow, or the Duration of its Eclipfe at that time,was less than is commonly affigned unto it, as it is reasonable to imagine it should be, because the Satellite had only the outfide of the Conè of Jupiter's Shadow, and confequently a leffer part thereof to pass tho rough at that time.

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As to the end and use of this fo obfervable a tendency in the Secondaries towards each Pole of their Primaries, we may guess at it from what hath been faid of the like tendency of the Primaries towards the Sun,on which our Seasons do depend: So thofe Secondaries moving in like manner to each Pole, effect fome of the grand Works of the divine Providence from Pole to Pole, illuminate all parts of their respective Globes, contract the length of their Nights (as fhall be fhewn in proper place,) move their Waters, and excite their Tides, and perform other fuch great Works of Nature as with good reafon we attribute to the influx of our Moon here in our own Globe.

AND can fuch well contrived, fuch useful Motions, that the World could not fubfift without, that Nature could not do its grand Works without, can these be other than the

Fiat

Fiat of an infinitely indulgent as well as wife CREATOR! Could this confonancy be fo universal,among all the Globes we can bring within ourView, could their Periods and Distances be in the fame due Proportion all the Universe over, their Motions all fo alike, had they not had the fame Contriver and Maker! But I fhall close this argument with the Reflection of the most ingenious Mr.Molyneux (5), who speaking of the fefquiplicate proportion of both the Primary and Secondary Planets, thus concludes. And from hence may we justly fall into the deepest admiration, that one and the fame Law of Motion should be observed in Bodies fo vastly diftant from each other, and which feem to have no dependence or correfpondence with each other. This doth moft evidently demonftrate that they were‹

(5) Dioptr. Nov. Par. 2. c. 6. Sect. 12.