disappear; and a third fort fhew themselves one time with more, and another time with a leffer Luftre. Hipparchus is faid to have obferved one; but in the Year 1572, we know that a new one appeared in the Chair of Caffiopea; in 1600, in the Breaft of the Swan; in 1604, in the right Heel of the Serpentarius; 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 feen before, are now invifible; and Hevelius fays, in his Præcurfor, that they fought in vain for five Stars, whofe Places however Tycho Brahe had defcribed full an Age before: Concerning which, the faid Gregory gives us a farther Account in the Act. Lipf. 1691. p. 8o. 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 Act. Lipf. 1703. p. 213. and how their Magnitude is remarkably changed in others, at least with respect to their Light. The Reader may likewife note what has been mention'd concerning Kirchius in the aforesaid Tranfactions of Leipfick, 1687. p. 647, fince we cannot stand here to reckon up all thofe Particulars. SECT. LX. 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 ftand ftill for a time; which, to those that have not inquired into their Courses, looks like Wandering; tho' thofe that do underftand it, know, that with refpe&t to the Sun they anly proceed forwards, but yet occafion the fame Appear 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 ftiled the lowest, viz. Mercury D, and Venus C, 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 oppofite 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 these Planets, we must again endeavour to diveft our felves of those Prejudices which we have fuck'd in as it were with our Mother's Milk, and by which we are taught to imagine, that thefe 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 these Planets, which at the best do represent 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 hinder us from forming a right Concep tion of their true Magnitudes. SECT. LXI. 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 ferr'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 refpe&t to the Sun GD K. According to his Obfervations we find the Diameter of the Sun to be, 110 times greater than that of the Earth than that of Mercury 308 than that of Venus than that of Mars than that of Jupiter A. D. C. E. F. than that of Saturn's Ring G I. and that of the Ring 24 times bigger than the Diameter of the Globe of Saturn H. From whence it follows, if these 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 1 of 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 these comes 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 Reason 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 this Ring GI, 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 observed to circulate about the faid Planet and its Ring. SECT. LXII. The Times of the Planets Revolutions and Diftances from the Sun. Now the Times in which these Planets finish their refpective 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 consult the Aftro nomers. The Distances of these Planets from the Sun, are likewife reckoned in the following manner: Upon the Suppofition 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. 1. 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 2 Diameters of the Earth; Mercury will be 4000; Venus 7000; Mars 15000; Jupiter 51000; and Saturn 95000; and proportionably fo much 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 used the smallest Numbers, because we would proceed with the greater Certainty. SECT. LXIII. The Velocity of Venus and Jupiter. I, Now let the Atheist confider, that notwithftanding the contemptible Notions he has of these 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 fmaller than that of the Earth; and, which is amazing, it moves about the Sun with a Swiftnefs, 146 times greater than than that of a Bullet, fhot out of a Cannon. To give likewife an Inftance of one of the remoteft Planets, let him contemplate that of Jupiter, which is a Globe. 8000 times as big as this of the Earth; and let him confider, First, how great a Distance it must be from him, when fo vaft a Body fhall 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. LXIV. 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 no thing |