“And,” continued Michel, “do we not know that in 1861 the earth passed through the tail of a comet? Or let us suppose a comet whose power of attraction is greater than that of the sun. The terrestrial orbit will bend toward the wandering star, and the earth, becoming its satellite, will be drawn such a distance that the rays of the sun will have no action on its surface.” “That _might_ happen, indeed,” replied Barbicane, “but the consequences of such a displacement need not be so formidable as you suppose.” “And why not?” “Because the heat and cold would be equalized on our globe. It has been calculated that, had our earth been carried along in its course by the comet of 1861, at its perihelion, that is, its nearest approach to the sun, it would have undergone a heat 28,000 times greater than that of summer. But this heat, which is sufficient to evaporate the waters, would have formed a thick ring of cloud, which would have modified that excessive temperature; hence the compensation between the cold of the aphelion and the heat of the perihelion.” “At how many degrees,” asked Nicholl, “is the temperature of the planetary spaces estimated?” “Formerly,” replied Barbicane, “it was greatly exagerated; but now, after the calculations of Fourier, of the French Academy of Science, it is not supposed to exceed 60° Centigrade below zero.” “Pooh!” said Michel, “that’s nothing!” “It is very much,” replied Barbicane; “the temperature which was observed in the polar regions, at Melville Island and Fort Reliance, that is 76° Fahrenheit below zero.” “If I mistake not,” said Nicholl, “M. Pouillet, another savant, estimates the temperature of space at 250° Fahrenheit below zero. We shall, however, be able to verify these calculations for ourselves.” “Not at present; because the solar rays, beating directly upon our thermometer, would give, on the contrary, a very high temperature. But, when we arrive in the moon, during its fifteen days of night at either face, we shall have leisure to make the experiment, for our satellite lies in a vacuum.” “What do you mean by a vacuum?” asked Michel. “Is it perfectly such?” “It is absolutely void of air.” “And is the air replaced by nothing whatever?” “By the ether only,” replied Barbicane. “And pray what is the ether?” “The ether, my friend, is an agglomeration of imponderable atoms, which, relatively to their dimensions, are as far removed from each other as the celestial bodies are in space. It is these atoms which, by their vibratory motion, produce both light and heat in the universe.”