fomething from two other fects of philosophers, whose extreme obfcurity feems to have prevented them from acquiring themselves any extensive reputation: the one was that of Cratylus and Heraclitus ; the other was that of Xenophanes, Parmenides, Meliffus, and Zeno. To pretend to rescue the system of any of those antefocratic fages, from that oblivion which at present covers them all, would be a vain and useless attempt. What seems, however, to have been borrowed from them, fhall fometimes be marked as we go along. There was still another school of philofophy, earlier than Plato, from which, however, he was fo far from borrowing any thing, that he feems to have bent the whole force of his reafon to difcredit and expose its principles. This was the Philosophy of Leucippus, Democritus, and Protagoras, which accordingly seems to have submitted to his eloquence, to have lain dormant, and to have been almost forgotten for fome generations, till it was afterwards more fuccefsfully revived by Epicurus. SECTION IV. The Hiftory of Aftronomy. OF their greatness and beauty, the most universal objects of the curiosity of mankind. Those who furveyed the heavens with the most careless attention, neceffarily distinguished in them three different forts of objects; the Sun, the Moon, and the Stars. These last, appearing always in the fame fituation, and at the fame distance with regard to one another, and seeming to revolve every day round the earth in parallel circles, which widened gradually from the poles to the equator, were naturally thought to have all the marks of being fixed, like like fo many gems, in the concave fide of the firmament, and of being carried round by the diurnal revolutions of that folid body: for the azure sky, in which the ftars feem to float, was readily apprehended, upon account of the uniformity of their apparent motions, to be a folid body, the roof or outer wall of the universe, to whofe infide all thofe little fparkling objects were attached. The Sun and Moon, often changing their distance and fituation, in regard to the other heavenly bodies, could not be apprehended to be attached to the fame sphere with them. They affigned, therefore, to each of them, a fphere of its own; that is, fuppofed each of them to be attached to the concave fide of a folid and transparent body, by whose revolutions they were carried round the earth. There was not indeed, in this cafe, the fame ground for the suppofition of such a sphere as in that of the Fixed Stars; for neither the Sun nor the Moon appear to keep always at the same distance with regard to any one of the other heavenly bodies. But as the motion of the Stars had been accounted for by an hypothesis of this kind, it rendered the theory of the heavens more uniform, to account for that of the Sun and Moon in the fame manner. The sphere of the Sun they placed above that of the Moon; as the Moon was evidently feen in eclipses to pass betwixt the Sun and the Earth. Each of them was supposed to revolve by a motion of its own, and at the same time to be affected by the motion of the Fixed Stars. Thus, the Sun was carried round from eaft to weft by the communicated movement of this outer sphere, which produced his diurnal revolutions, and the viciffitudes of day and night; but at the fame time he had a motion of his own, contrary to this, from weft to eaft, which occafioned his annual revolution, and the continual shifting of his place with regard to the Fixed Stars. This motion was more easy, they thought, when carried on edgeways, and not in direct oppofition to the motion of the outer fphere, which occafioned the in clination clination of the axis of the sphere of the Sun, to that of the sphere of the Fixed Stars; this again produced the obliquity of the ecliptic, and the consequent changes of the seasons. The moon, being placed below the sphere of the Sun, had both a shorter course to finish, and was less obftructed by the contrary movement of the sphere of the Fixed Stars, from which fhe was farther removed. She finished her period, therefore, in a fhorter time, and required but a month, inftead of a year, to complete it. The Stars, when more attentively furveyed, were some of them obferved to be lefs conftant and uniform in their motions than the reft, and to change their fituations with regard to the other heavenly bodies; moving generally eaftwards, yet appearing fometimes to ftand ftill, and fometimes even to move weftwards. Thefe, to the number of five, were distinguished by the name of Planets, or wandering Stars, and marked with the particular appellations of Saturn, Jupiter, Mars, Venus, and Mercury. As, like the Sun and Moon, they seem to accompany the motion of the Fixed Stars from east to weft, but at the fame time to have a motion of their own, which is generally from weft to eaft; they were each of them, as well as those two great lamps of heaven, apprehended to be attached to the infide of a folid concave and tranfparent sphere, which had a revolution of its own, that was almoft directly contrary to the revolution of the outer heaven, but which, at the fame time, was hurried. along by the fuperior violence and rapidity of this last. This is the system of concentric Spheres, the first regular system of Aftronomy, which the world beheld, as it was taught in the Italian fehool before Ariftotle and his two cotemporary philofophers, Eudoxus and Callippus, had given it all the perfection which it is capable of receiving. Though rude and inartificial, it is capable of connecting together, in the imagination, the grandeft and the most feemingly feemingly disjointed appearances in the heavens. The motions of the most remarkable objects in the celeftial regions, the Sun, the Moon, and the Fixed Stars, are fufficiently connected with one another by this hypothefis. The eclipfes of these two great luminaries are, though not so easily calculated, as easily explained, upon this ancient, as upon the modern fyftem. When these early philosophers explained to their difciples the very fimple caufes of those dreadful phænomena, it was' under the feal of the most facred fecrecy, that they might avoid the fury of the people, and not incur the imputation of impiety, when they thus took from the gods the direction of those events, which were apprehended to be the most terrible tokens of their impending vengeance. The obliquity of the ecliptic, the confequent changes of the seasons, the viciffitudes of day and night, and the different lengths of both days and nights, in the different feafons, correfpond too, pretty exactly, with this ancient doctrine. And if there had been no other bodies difcoverable in the heavens befides the Sun, the Moon, and the Fixed Stars, this old hypothefis might have stood the examination of all ages, and have gone down triumphant to the remotest posterity. If it gained the belief of mankind by its plausibility, it attracted their wonder and admiration; fentiments that ftill more confirmed their belief, by the novelty and beauty of that view of nature which it presented to the imagination. Before this system was taught in the world, the earth was regarded as, what it appears to the eye, a vast, rough, and irregular plain, the bafis and foundation of the universe, furrounded on all fides by the ocean, and whose roots extended themselves through the whole of that infinite depth which is below it. The fky was confidered as a folid hemifphere, which covered the earth, and united with the ocean at the extremity of the horizon. The Sun, the Moon, and all the heavenly bodies rose out of the eastern, climbed up the convex fide of the heavens, and de fcended fcended again into the western oceán, and from thence, by fome subterraneous paffages, returned to their first chambers in the east. Nor was this notion confined to the people, or to the poets who painted the opinions of the people: it was held by Xenophanes, the founder of the Eleatic philofophy, after that of the Ionian and Italian schools, the earliest that appeared in Greece. Thales of Miletus too, who, according to Ariftotle, represented the Earth as floating upon an immense ocean of water, may have been nearly of the fame opinion; notwithstanding what we are told by Plutarch and Apuleius concerning his aftronomical difcoveries, all of which muft plainly have been of a much later date. To those who had no other idea of nature, befides what they derived from fo confufed an account of things, how agreeable muft that fyftem have appeared, which reprefented the Earth as diftinguished into land and water, felf-balanced and fufpended in the centre of the univerfe, furrounded by the elements of Air and Ether, and covered by eight polifhed and criftalline Spheres, each of which was diftinguished by one or more beautiful and luminous bodies, and all of which revolved round their common centre, by varied, but by equable and proportionable motions. It feems to have been the beauty of this fyftem that gave Plato the notion of fomething like an harmonic proportion, to be difcovered in the motions and diftances of the heavenly bodies; and which fuggefted to the earlier Pythagoreans, the celebrated fancy of the Mufick of the Spheres: a wild and romantic idea, yet fuch as does not ill correspond with that admiration, which so beautiful a system, récommended too by the graces of novelty, is apt to inspire. Whatever are the defects which this account of things labours under, they are fuch, as to the first observers of the heavens could not readily occur. If all the motions of the Five Planets cannot, the greater part of them may, be easily connected by it; they and all their motions are the leaft remarkable objects in the heavens; the |