of the Swan; in 1604, in the right Heel of the Serpentanius; and feveral others may be found in Gregory, Lib. II. Sect. 30. as alfo in Mercator and Whifton, that give us an account of them and their Number. Some again, that had been seen before, are now invifible; and Hevelius fays, in his Præcurfor, that they fought in vain for five Stars, whofe Places however Tycho Braché had defcribed full an Age before: Concerning which the faid Gregory gives us a farther account in the A&t. Lipf. 1691. p. 80. as alfo how a Star belonging to the Neck of the Whale has often difappeared, and fhewn itself again in the fame Place at different times; See Alt. Lipf. 1703, p. 213. and how their Magnitude is remarkably changed in others, at leaft with respect to their Light. The Reader may likewise note what has been mention'd concerning Kirchius in the aforefaid Tranfactions of Leipfick, 1687. p. 647, fince we cannot ftand here to reckon up all thofe Particulars.

SECT. LIX. Concerning the Planets.

LET us now proceed to the Planets or Wandering Stars, fo called, because they appear to us who live upon the Earth A, (Tab. XXII. Fig. 1, and 2.) to move fometimes quick, other-times flow; now forwards, then backwards, and another while to stand still for a time; which, to those that have not inquired into their Courfes, looks like Wandering; tho' thofe that do understand it, know, that with refpect to the Sun they only proceed forwards, but yet occafion the fame Appearances, for which the Aftronomers have accounted.

All the Planets, as we have faid before, do move about the Sun S but two, which are therefore filed the loweft, viz. Mercury D, and Venus C,

perform

perform their Revolution in fuch a manner, that as they are feen from the Earth, they appear always on the fame fide with the Sun: Whereas the three other, Mars E, Jupiter F, Saturn H, are feen from the Earth A, fometimes on the fame fide, and fometimes on the opposite fide of the Sun, as you may obferve on the abovemention'd two Figures of this Table.

Now in order to form a right Notion of thefe Planets, we must again endeavour to diveft our felves of thofe Prejudices which we have fuck'd in as it were with our Mother's Milk, and by which we are taught to imagine, that these great Bodies are about the fize of the Marbles we play'd with when we were Children, or fomewhat lefs, and that they are but a very fmall Distance from us; and we are yet the more confirmed in the fame, by the Figures that Aftronomers are wont to give us of thefe Planets, which at the beft do reprefent to us the Proportion of their Distances, but in a very small Compafs, and do rarely or never fhew us their Bodies in comparison of their real Magnitudes, which likewife confiderably helps to prevent our Conceptions thereof.

SECT. LX. The Magnitude of the Planets.

THAT famous Aftronomer Mr. Huygens, in order to improve our Notions concerning the Planets, did at the latter end of his Life draw their Magnitudes in a particular Figure in proportion to that of the Sun, which we have therefore tranfferr'd from his Autom. Planet. to our Tab. XXIII. Fig. 2. where the Earth A, and the Moon by it at B, and fo the reft of the Planets are reprefented in their proportionable Bigneffes with respect to the Sun G DK. According to his Obfervations

than that of Jupiter

D.

C.

E

F.

3

than that of Saturn's Ring GI.

and that of the Ring 24 times bigger than the Diameter of the Globe of Saturn H.

From whence it follows, if thefe Planets are compared with the Earth, which is best known

to us,

I. That the Earth is not quite 3 times fo thick, and confequently not quite 27 times as big as the Planet Mercury D.

II. That Venus C is about 1 as thick, and confequently as big as the Earth itself.

III. That Mars E, is fmaller than the Earth, fo that the Diameter of the latter will make rof the former, and confequently contains 3 as much Matter as the Globe of Mars.

IV. That Jupiter F, has 20 times as great a Diameter, and 8000 times as large a Bulk as that of the Earth.

It has likewife four Satellites or Moons about it, each of which does not feem leffer than the whole Earth: See Huygens Cofm. p. 101.

V. After thefe come Saturn H, which, what no Body could ever have thought or fufpected, is furrounded with a Ring GI, that is flat and very thin in proportion to its Magnitude: There is a Space between that Ring and the Body of the Planet, which it encompaffes without any Contiguity like a Vault or Ceiling; for which reafon this Difpofition of Saturn with its Ring, being viewed from different parts of the Earth, is wont to reprefent a very different Figure. The Diameter

of

of this Ring G I, is according to the foregoing Computation about 30 times as large as the Diameter of the Earth, and therefore if it were a Globe, it would contain about 27,000 times the quantity of this Globe of the Earth.

The Diameter of Saturn itfelf is about 13 times as big as the Earth's, and confequently the Body of that Planet is 2197 times as large as the whole Earth; befides which there are five Moons that are obferved to circulate about the faid Planet and its Ring.

SECT. LXI. The Times of the Planet's Revolutions and Distances from the Sun.

Now the Times in which these Planets finifh their respective Circulations about the Sun, have been obferved as follows: That of Mercury, in three Months; of Venus, in about 7 Months; of Mars, in almoft two Years; of Jupiter in 12 Years; and that of Saturn, in about 30 Years, all of 'em computed as near as may be,

We fhall here pafs by the Satellites; they who defire to know the Time of their Revolutions about Jupiter and Saturn, may confult the Aftro

nomers.

The Diftances of thefe Planets from the Sun are likewife reckoned in the following manner : Upon the fuppofition that the Distance of the Earth from the Sun is 10, that of Mercury is hardly 4, Venus 7, Mars 15, Jupiter 51, and Saturn 95 of the fame Parts: See Gregory Aftron. Lib. I. Sect. 1. So that the Distance of our Earth from the Sun being, according to Caffini and Flamftead (for the more convenient Calculation) 10000 Diameters of the Earth; Mercury will be 4000; Venus 7000; Mars 15000; Jupiter 51000; and Saturn 95000; and proportionably fo much

greater

greater if with Mr. Huygens we account the Distance of the Sun to be 12000, or with Mr. la Hire 17000 of the faid Diameters. We have here ufed the fmalleft Numbers, because we would proceed with the greater Certainty.

SECT, LXII. The Velocity of Venus and Jupiter.

Now let the Atheist confider, that notwithftanding the contemptible Notions he has of thefe Heavenly Bodies, which he looks upon as no bigger than they are reprefented in Tab. XXII. Fig. 1, and 2; and in Tab. XXIII. Fig. 2. yet Venus, the Evening and Morning Star, is a Globe not much smaller than that of the Earth; and, which is amazing, it moves about the Sun with a Swiftness, 146 times greater than that of a Bullet, fhot out of a Cannon. To give likewife an Inftance of one of the remotest Planets, let him contemplate that of Jupiter, which is a Globe 8000 times as big as this of the Earth; and let him confider, Firft, how great a Distance it must be from him, when fo vaft a Body shall appear as fmall as one of our Childrens Marbles And Secondly, what a Force is neceffary to move fuch a prodigious Globe along the Heavens, the Motion of which we find to be 54 times fwifter than a Cannon-bullet's.

SECT. LXIII. The Calculation of the Revolutions of the aforefaid Planets.

THIS may perhaps feem fomewhat whimfical and incredible too to ignorant Perfons; but those who understand Aftronomy know that nothing need be advanced by Conjecture or Gueffing, when one compares the Magnitude and Diftance of the Planets with that of the Sun; but

that