[Illustration: Asteroids. Jupiter. Saturn. Uranus. Neptune.
Fig. 5.--Size of the Planets Jupiter, Saturn, Uranus, and Neptune compared with the Earth.]
This rapid glance at our solar system in its entirety, proves that the earth is not in possession of any privilege. The part which she plays in the economy of the universe is equally fulfilled by other stars, and there is nothing to justify the pre-eminence assigned to her by the ancients. She is not the largest, the warmest, or the brightest of the planets. She simply forms a portion of a group of stars, and is but one individual of that group.
These considerations tend to lead us to a very important deduction. Since the earth is in no way distinguished from the other planets of our solar system, there must exist in other planets the things which are found on our globe; air, water, a hard soil, rivers and seas, mountains and valleys. Even vegetation and forests ought to be there, regions covered with verdure and with shade. So there surely ought to exist in the other planets, animals, and even men, or at least creatures superior to animals, corresponding to our human type.
But is this possible? is it true? are the planets which, like the earth, and together with it, turn round the sun, constituted physically as the earth is? Are they covered with vegetable growth? are they tenanted by animals and by beings belonging to the human type?
This grave question has been profoundly discussed by M. Camille Flammarion, in a work entitled _Pluralité des Mondes Habités_, and in a later publication, _Les Mondes Imaginaires et les Mondes Réels_. It would be outside the province of this book to follow the author through the various scientific considerations, from which he reasons that the planets which form a portion of our solar system, are, like the earth, the scene of life, organization, thought, and feeling. In the 17th century, Fontenelle and Huygens had successfully approached this successful problem, which M. Camille Flammarion has lately treated with especial care and development, invoking the lessons of contemporaneous astronomy and physics, which refer to the subject. We therefore refer the reader, who wishes to be instructed upon the question of the possibility of the planets being inhabited, to M. Flammarion's works.