“IT seems to me,” said Claire, “we have lost sight of the hearth that turns with its lighted firebrands around the lark.”

“On the contrary, we are closer to it than ever. If the sun, which is thirty-eight millions of leagues from us, were to go around the earth every day, do you know how far it would have to go in a minute? More than 100,000 leagues. But this incomprehensible speed is nothing. The stars, as I have just told you, are so many suns, comparable to ours in volume and brilliancy; only they are much farther away, and that is what makes them appear so small. The nearest is about thirty thousand times as distant as the sun. Accordingly, in order to go around the earth in twenty-four hours, as it appears to do, it would have to move at the rate of thirty thousand times 100,000 leagues a minute. And how would it be with other stars a hundred times, a thousand times, a million times farther away—stars which, despite their distance, would all have to accomplish their journey around the earth always in exactly twenty-four hours? And remember, furthermore, the prodigious size of the sun. You want it, the giant, the colossus, beside which the earth is only a lump of clay, to circle at an impossible speed in infinite space, in order to give light and heat to our planet; you want thousands and thousands of other suns, quite as large and immensely farther off—in a word, the stars—to accomplish also, with velocities increasing according to the distance, a daily journey around this humble terrestrial globe! No! no! such an arrangement is contrary to reason; to allow it is to want to make the firebrands, the hearth, the whole house, turn around a little bird on a spit.”

“Then it is the earth that turns, and we turn with it,” Claire again interposed. “In consequence of this movement the sun and stars seem to us to move in the opposite direction, like trees and houses when we are on the train. Since the sun seems to go around the earth from east to west in twenty-four hours, it is a proof that the earth turns on its axis from west to east in twenty-four hours.”

“The earth turns in front of the sun in a manner to present its different parts successively to the rays of that body; it pirouettes on its axis like a top. Moreover, while it thus rotates in twenty-four hours, it revolves around the sun in the interval of a year. In playing with a top you find a good example of two analogous movements executed together. When the top turns on its point, not moving from the same place—in short, when it sleeps—it has only the movement of rotation. But in throwing it in a certain way, you know better than I that it circles on the ground while turning on its point. In that instance, it represents in a small way the double movement of the earth. Its rotation on its point represents the whirling motion of the earth on its axis; its course on the ground represents the earth’s revolution around the sun.

“You can familiarize yourself in another way with the double movement of the terrestrial globe, as follows: place in the middle of a room a round table, and on that table a lighted candle to represent the sun. Then circle around the table, pirouetting on your toes. Each of your pirouettes corresponds to a turn of the earth on its axis, and your course around the table corresponds to its journey around the sun. Notice that in turning on your toes you present in succession to the rays of the candle the front, one side, the back, and the other side of your head, which in our experiment may represent the terrestrial globe; so that each one of its parts is in turn in the light or in the shade. The earth does the same: in turning it presents one after the other its different regions to the rays of the sun. It is day for the region that sees the sun, night for the opposite region. That is the very simple cause of day and night. In twenty-four hours the earth makes one rotation on its axis. Of these twenty-four hours the duration of the day and night is composed.”

“I understand very well the cause of the alternation of day and night,” said Jules. “It is day for the half of the earth that sees the sun, night for the opposite half. But as the globe turns, each country comes in succession to face the sun while others pass into the unlighted half. The lark that turns on the hearth presents, in the same way, each of its sides in turn to the heat of the flame.”

“One might almost say,” remarked Emile, “it is day for the half of the lark next to the fire, and night for the other half.”

“One difficulty still perplexes me,” Jules continued. “If the earth turns around once in every twenty-four hours, in half of that time we ought to make a half-turn with the globe that carries us, and find ourselves upside-down. At this moment we have our heads up, feet down; twelve hours later it will be just the opposite: our heads will be down and our feet up. We are up............