I have remarked in the twentieth book of my Astronomy, that in every period of time it has been believed that the planets were inhabited, on account of their resemblance to the earth. The idea of the plurality of worlds is expressed in the Orphics, those ancient Grecian poems attributed to Orpheus (_Plut. de Placitis Philosoph. l. 2, cap. 13_.) Proclus has preserved some verses in which we find that the writer of the Orphics places mountains, men, and cities in the moon. The Pythagoreans, such as Philolaüs, Hicetas, Heraclides, taught that the stars were all worlds. Several ancient philosophers even admitted an infinity of worlds beyond the reach of our sight. Epicurus, Lucretius, and all the Epicureans were of the same opinion; and Metrodorus thought it as absurd to imagine but one world in the immensity of space, as to say that only one ear of corn could grow in a great extent of country. Zeno of Eleusis, Anaximenes, Anaximander, Leucippus, Democritus, asserted the same thing: in short, there were some philosophers who, although they did not consider the rest of the planets inhabited, placed inhabitants in the moon; such were Anaxagorus, Xenophanes, Lucian, Plutarch, (_De Oracular. defectu. De Facie in orbe Lunæ_,) Eusebius, Stobius. We may see a long list of the ancients who have treated on the subject, in Fabricius, (_Biblio. Græcæ, t. 1. cap. 20_.) and in the Mémoire de Bonamy (Acad. des Inscriptions, tom. ix.) Hevelius appeared as firmly persuaded of this opinion in 1647, when he talked of the difference between the inhabitants of the two hemispheres of the moon: he calls them _selenitæ_, and examines at length all the phœnomena observed in their planet, after the example of Kepler (_Astron. Lunaris_.) It was maintained at Oxford, in certain themes which are mentioned in the News of the Republic of Letters, June 1784, that the system of Pythagoras on the inhabitants of the moon was well founded: two years afterwards Fontenelle discussed this subject in his agreeable work. There are farther details of the different astronomical opinions at the end of Gregory's book. For the objections, we may refer to Riccioli. (_Almagestum, tom. 1, p. 188, 204_). In 1686 the Plurality of Worlds was adorned by Fontenelle with all the beauties of which a philosophical work was susceptible. Huygens (who died in 1695) in his book entitled Cosmothéoros, published in 1698, likewise enters largely into the subject. The resemblance between the earth and the other planets is so striking, that if we allow the earth to have been formed for habitation, we cannot deny that the planets were made for the same purpose; for if there is, in the nature of things, a connection between the earth and the men who inhabit it, a similar connexion must exist between the planets and beings who inhabit them.