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The Story Book of Science by  Jean Henri Fabre

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CHAPTER LV

DAY AND NIGHT

[257]

"I
T seems to me," said Claire, "we have lost sight of the hearth that turns with its lighted fire-brands 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, [258] 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 [259] 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 [260] 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 upright, we shall be upside-down. In that inconvenient position why don't we feel uncomfortable? Why are we not thrown down? So as not to fall, it seems to me, we ought to be obliged to cling to the ground in desperation."

"Your observation is right," returned Uncle Paul, "but only in a certain degree. Yes, it is true that twelve hours from now we shall be in an inverse position; our heads will be toward that point in space to which our feet are now turned. But despite this inversion there will be no danger of our falling, nor even the slightest inconvenience of any kind; for our heads will always be up, that is to say toward the sky, since the sky surrounds the terrestrial globe everywhere; our feet will always be down, that is to say resting on the ground. Understand thoroughly, once for all, that to fall is to rush toward the ground, and not into surrounding space. So that notwithstanding all the evolutions of our globe, as we are always on the earth, feet on the ground, head toward the sky, we are always in an upright position, without any unpleasant feeling, without any danger of falling."

[261] "Does the terrestrial globe turn very fast?" Emile inquired.

"It turns on its axis once in twenty-four hours. Therefore any point in its middle region, the region that makes the longest journey, travels in the same time forty millions of meters, that is to say a journey equal to the circuit of the earth, or 462 meters a second. That is about the speed of a cannon-ball as it leaves the cannon's mouth, or about thirty times the speed of the fastest locomotive. Mountains, plains, seas, apparently fixed in their places for time and for eternity, are perpetually chasing one another in a circle, with the formidable speed of more than one-tenth of a league a second."

"And yet everything seems to us to be stationary."

"Without the jolting of the car should we not think we were standing still when the train carries us with such frightful speed? Well, the rapid movement of the earth is at the same time so gentle that it is impossible to be aware of it except by the apparent motion of the stars."

"By rising to a certain height in a balloon," said Jules, "we ought to see the earth turning under us. Seas and their islands, continents with their empires, forests, and mountains, ought in succession to come under the eyes of the observer, who in twenty-four hours sees the turning of the whole earth. What a magnificent spectacle that must be! What a journey, so wonderful and with so little fatigue! When the rotation brings back one's own country, one descends and it is accomplished. In [262] twenty-four hours, without changing place, one has seen the whole world."

"Yes, I agree with you, it would be an admirable way to see countries. To this spot where we are other peoples will come, brought by the rotation; seas, distant regions, snowy mountains will take our place; and to-morrow at the same hour we shall be here again. Where we are talking now, in the shade of the juniper-trees, first will pass the sea, the somber Atlantic, which will replace our conversation by the grand voice of its waves. In less than an hour the ocean will be here. Some large war-vessel, with its triple row of guns, will float perhaps, all sails set, over the spot we are occupying. The sea has passed. Now we have North America, the great Canadian lakes, and the interminable prairies where the red-skinned Indians hunt buffaloes. The sea begins again, much larger than the Atlantic; it takes nearly seven hours to pass. What line of islands is this where fishermen wrapped in furs are drying herrings? They are the Koorile Isles, south of Kamchatka. They pass quickly; we scarcely have time to give them a glance. Now it is the turn of the yellow-faces—the Mongolians and Chinese, with slanting eyes. Oh! what curious things we could see here! But the ball is always turning, and China is already in the distance. The sandy plateaus of Central Asia and mountains higher than the clouds come next. Here are the pastures of the Tartars, with neighing herds of mares; here are the grassy plains of the Caspian with the flat-nosed Cossacks; then southern Russia, Austria, Germany, Switzerland, [263] and finally France. Let us descend quickly, get on to our feet; the earth has finished its rotation.

"Do not for an instant, my little friends, think that this giddy spectacle of the earth passing with the rapidity of a cannon-ball would be visible to any but spiritual eyes. By rising into the upper air in a balloon, as Jules said, it does at first seem as if we ought to see the earth turning and lands and seas passing under our feet. Nothing of the kind takes place, for the atmosphere turns with the terrestrial globe and drags the balloon in the general rotation, instead of leaving it at rest, as would be necessary if the observer were to have successively under his eyes the different regions of the earth."


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