OF THE COPERNICAN SYSTEM.

THE next fyftem is the Pythagorean or Copernican, being invented as fome imagine by Pythagoras himself. But Diogenes Laertius exprefsly faith, that Pythagoras's opinion was, That the world was round, containing the earth in the midst of it. And by Pliny's account of " Pythagoras, his diftances, and orders of the planets, this feems to have been his opinion. But the fame Laertius affirms Philolaus, the Pythago. rean, την Γήν κινέεσθαι κατα κύκλον, πρώτον ειπείν οι δε, Ἱκεταν Συρακησίον φασιν to have been the frit that faid the earth was moved in a circle; but fome fay Hicetas the Syracufian, So Plutarch in his life of Numa, speaking of Numa's building the temple of Vefta, faith, he built it round, and that a continual fire was kept therein, in imitation of the figure of the earth, or rather of the whole world itself, the middle of which the Pythagoreans (not Pythagoras) take to be the feat of fire.

This fyftem (whoever was the inventor of it) Copernicus, a canon of Tourain, restored about, the beginning of the 15th century, and was followed therein by many confiderable men, as Rheticus, Mæftlinus, Kepler, Rothman, Bullialdus, Lanfberge, Heigonius, Schickard,

Gaffendus, Galilæo, and others. The laft of which (by the ill-will and inftigation of Pope Urban III. as it is supposed) had the misfortune to fall under the cenfure of, and to have his Copernican tenets condemned by the inquifition, and was forced to abjure them. The particulars of which, if the reader hath a mind to fee, he may find them in Riccioli's Almagest.<

According to this fyftem, the fun is fuppofed to be in the centre, and the heavens and earth to revolve round about him, according to their feveral periods: firft Mercury in near 88 days; then Venus in fomewhat above 224 days; then' the earth with its fatellite the Moon, in 365 days; then Mars in about 687 days; then Jupiter with his four moons in about 4333 days; and laftly, Saturn in fomewhat above 10759 days, with his five or more moons revolving about him. And beyond, or above all thefe, is the firmament, or the region of the fixt ftars, which are all fuppofed to be at equal distances from their centre the fun.

This is the Copernican fyftem, which I have given a scheme of in Fig. 2. And fo far as this fyftem relates to the motion of the earth, and the fun refting in the centre, I prefer it to the

Lib. ix. Sect. 4. Chap. 40.

Ptolemaic

1

Ptolemaic hypothefis on thefe five following ac

counts:

1. Becaufe it is far more agreeable to nature, which never goes a round-about way, but always acts by the most compendious, eafy, and fimple methods. And in the Copernican way, that is performed by one, or a few eafy revolutions, which, in the other way, is made the work of the whole heavens, and of many ftrange and unnatural orbs, Thus the diurnal motion is accounted for, by one revolution of the earth, which all the whole heavens are called in for, in the other way; fo for the periodical motions of the planets, their ftations, retrogradations, and direct motions, they are all accounted for by one eafy, fingle motion round the fun; for which, in the Ptolemaic way, they are forced to invent divers ftrange, unnatural, interfering eccentrics and epicycles. An hypothefis fo bungling and monftrous, as gave occafion to a certain king to fay, if he had been of God's council, when he made the heavens, he could have taught him how to have mended his work.

2. As the Copernican is far more cafy and agreeable to nature than the Ptolemaic fyftem, fo it is far more complete, and anfwerable to the various phænomena of the planets; feveral of which

M 4

which the Ptolemaic hypothefis either very auk. wardly folves, or doth not at all come up to. I might inftance here in divers particulars relating to Venus and Mercury, as why the earth is never between them and the fun, which the Ptolemaic fyftem gives no tolerable account of, and but poor accounts of other of their phænomena, as alfo of thofe of the moon and the other planets. I might fhew also how incoherent and improper the motions affigned to the heavenly bodies are in the Ptolemaic way, as that the moon fhould move round once in a month, the other planets in fuch and fuch periods as are affigned to them; the firmament or fixt ftars, in 25 or 26000 years; the sphere beyond that in 1700 years; the tenth sphere in 3400 years; and the outermost of all, the primum mobile, which moves all the reft, in only 24 hours, Which are motions fo unproportional, and difagreeable, that are fufficient to fubvert the whole hypothefis. But it would be endless to enter into a detail of fuch incoherences and improprieties as the Ptolemaic fyftem abounds with.

3. The prodigious and inconceivable rapidity affigned by the Ptolemaic to the heavens, is by the Copernican scheme taken off, and a far more eafy and tolerable motion fubftituted in its room, For is it not a far more eafy motion for the earth

to

to revolve round its own axis in 24 hours, than for fo great a number of far more maffy, and far diftant globes, to revolve round the earth in the fame space of time? If the maintainers of the Ptolemaic fyftem do object against the motion of the earth, that it would make us dizzy, and shatter our globe to pieces, what a precipitant, how terrible a rapidity must that of the heavens be? What a velocity muft the fun have to run its course, at the distance of 21 or 22 femidiameters of the earth? What a velocity must that of the fixt ftars, efpecially that of the primum mobile be, at far greater diftances than the fun is ?

4. It is an inconteftible argument of the fun being the centre of the planets about him, and not the earth; that their motions and distances respect the fun, and not the earth. For with regard to the fun, the primary planets have a very due motion, in proportion to their feveral diftances; that is, their motions round the fun, are in fefquiplicate proportion to their distances from him; but this proportion doth not hold at all with relation to the earth. But as for the fecondary planets, round Saturn, Jupiter, and the earth, it is very certain that they have the. same respect to their primaries, as these primaries have to the fun; that is, the fquares of their

revolutions