There is no subject within the whole range of knowledge so universally interesting as that of a Plurality of Worlds. It commands the sympathies, and appeals to the judgment of men of all nations, of all creeds, and of all times; and no sooner do we comprehend the few simple facts on which it rests, than the mind rushes instinctively to embrace it. Before the great truths of Astronomy were demonstrated—before the dimensions and motions of the planets were ascertained, and the fixed stars placed at inconceivable distances from the system to which we belong, philosophers and poets descried in the celestial spheres the abodes of the blest; but it was not till the form and size and motions of the earth were known, and till the condition of the other planets was found to be the same, that analogy compelled us to believe that these planets must be inhabited like our own.

Although this opinion was maintained incidentally by various writers both on astronomy and natural religion, yet M. Fontenelle, Secretary to the Academy of Sciences in Paris, was the first individual who wrote a work expressly on the subject. It was published in 1686, the year before Sir Isaac Newton gave his immortal work, the Principia, to the world. It was entitled Conversations on the Plurality of Worlds, and consisted of five chapters with the following titles.