The opposite way. width the ancients thus took to study the Heavens and the Earth,. observing the one, and dreaming, as one may say, over the other, though a striking sistency, is not diffieult to be explained.
No information at all could be obtained in astronomy, without regnlar and assiduous ob servation, and without instruments capable of measuring angles, and of measuring time, either directly or indirectly. The steadiness and regularity of the'celestial-motions seem ed to invite the most scrupulous attention. On the other hand, as terrestrial objects were always at hand, and spontaneously falling under men's view, it seemed unnecessary to take much trouble to beoome acquainted with them, and as for applying measures, their irregu larity appeared to render every idea of such proceeding nugatory. The Aristotelian phi losophy particularly favoured this prejudice, by representing the earth, and all things on its surface, as full of irregularity and confusion, while the principles of heat and cold, dry ness and. moieties, were in a state of perpetual warfare. The unfortunate division of tioninto natant' and violent, and the distinction, still more unfortunate, between the pro perties of motion and of body, in the heavens and on the earth,' prevented all intercourse between the astronomer and the naturalist, and all transference of the maxims of the one to the speculations of the other.
Though, on account of this inattention to experiment; nothing like the true system of natural philosophy was known to the ancients, there are, nevertheless, to be found in their writings many brilliant conceptions, several fortunate conjectures,. and gleams of the light which was afterward, to be se generally diffused.
Ada xagoras and. Empedoeles, for example, taught that the moon shines. by light. borrow ed from the sun, and were led.to that not only from the phases of the moon, but from its light being weak, and unaccompanied by heat. That it was .a habitable body, ate the earth, appears. to- be a doctrine as old as Orpheus ; some lines, ascribed to that poet, representing the .moon as an. earth, with Mountains- and cities on. its surface. - , Democritua spots-on the face of the moon to arise from the inequalities of the surface, andirom.-the shadows of the more elevated parts projected on the plains. Every oneknowa•how conformable this is to the discoveries made by the telescope: Plutarch considers the velocity of the moon's motion as the cause which prevents that body from Sailing to the just as •the- motion • of a stone -in ' I sling prevents it from ` falling. to. 4he •ground. pe comparison is, in a certain degree; just, and Clearly implies
the notion of centrifugal -force ; and gravity may also be considered, as pointed at for the • cause which gives the moon a tendency.to. the. earth. Here, therefore, a foundation was . • laid for the true philosophy of the celestial motions ; but it was laid without effect. It Was merely the conjecture of an ingenious mind, wandering through the regions of possibility, guided by no evidence, and having nd principle which could give stability to its opinions. Democritus, and the authors of that physical system which Lucretius has so beautifully il lustrated, were still more fortunate in some of their conjectures. They taught that the Milky Way is the light of a great number of small stars, very close to one another ; a mag nificent conception, which the latest improvements of the telescope have fully verified. Yet, as if to convince us that they derived this knowledge from no pure or certain source, the same philosophers maintained, that the sun and the moon are bodies no larger than they appear to us to be.
Very just notions concerning comets were entertained by some of the ancients. The Chaldean considered those bodies as .belonging to the same order with the planets ; and this was also the opinion of Anaxagoras, Pythagoras, and Democritus. The remark of Se neca on this subject is truly philosophical, and contains a prediction which has been fully accomplished : " Why do we wonder that comets, which are so rare a spectacle in the world, observe laws which to us are yet unknown, and that the beginning and end of mo tions, so seldom observed, are not yet fully understood ?"—Veniet tem pus, quo ista que mine latent, in dies extrahat, et longioris cevi diligentia : ad inquisitionem tdntorum (etas una non sufficit. Veniet tempos, quo posteri nostri tam aperta nos nescisse miren, tour .' It was, however, often the fate of such truths to give way to error. The comets, which these ancient philosophers had ranked so justly with the stars, were degraded by Aristotle into meteors floating in the earth's atmosphere ; and this was the opinion con cerning them which ultimately prevailed.