THROUGHOUT the preceding chapters we have reasoned as if the earth were the whole universe. Indeed, almost all men believed that such was the case, from the first establishment of society until the last century. Great mathematical knowledge, profound study, and highly perfected optical instruments are requisite to rectify the false ideas, the errors, and the illusions which are the result of a simple view of the earth and the sky. Great efforts of the mind, and a very difficult struggle against the testimony of our senses are necessary to the recognition that the earth moves, and that the sun is motionless. In order to distinguish the place and the office of each of those softly beaming globes, in the midst of the uniformity of aspect presented by the stars which shine during the night, patient and severe observations, transmitted and repeated from age are indispensable, and, in addition, an excellent scientific method. Let us therefore not be surprised that men have taken so much time to comprehend the ordering of the universe, and that they had only the most childish conception of them for thousands of years. The ancients, the Greeks, the Romans, the Egyptians, knew nothing of the universe, except the earth (nor did the Orientals, with the exception of some truly learned men, who had divined the general mechanism of the universe by methods unknown to us, but they concealed their knowledge from the profane). These ancients could speak of only a small portion of the globe: of Europe, Asia, and the North of Africa. The remainder was a dead letter for the peoples of antiquity. After them, and following their example, the first Christians reduced the universe to what they knew of it; they believed there was but one world, because they saw only one. The earth was for them the universe. In the stars they saw only brilliant spots, like silver nails in the celestial vault, to enhance the azure, and charm the eyes of men in the quiet of the night. The moon was the natural beacon of the earth. In the sky there was a shining track followed by the sun, and the torch of day was no larger than the beacon of night. The celestial region which spread itself above the sun and the moon was the Empyrean of the ancients, the Paradise of the Christians and the Mussulmans. It was at once the sojourn of clouds and of light, the habitation of the elect of God, of the saints and the just. Under the earth, and in its interior, were immense abysses, gulfs, and cavities, the dark dwellings of the damned.