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The Story Book of Science by  Jean Henri Fabre

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CHAPTER XLI

CLOUDS

[181]

T
O finish his talk on lightning, the next morning Uncle Paul told them about clouds. The occasion, moreover, was very favorable. In one part of the sky great white clouds like mountains of cotton were piled up. The eye was delighted with the soft outlines of that celestial wadding.

"You remember," he began, "all those fogs that on damp autumn and winter mornings cover the earth with a veil of gray smoke, hide the sun, and prevent our seeing a few steps in front of us?"

"Looking into the air, you could see something like fine dust of water floating," said Claire; and Jules added:

"We played hide and seek with Emile in that kind of damp smoke. We could not see each other a few steps away."

"Well," resumed Uncle Paul, "clouds and fog are the same thing; only fog spreads about us and shows for what it is, gray, damp, cold; while clouds keep more or less above us and take on, with distance, a rich appearance. There are some of dazzling whiteness, like those you see over there; others of a red color, or golden-hued, or like fire; still others of the color of ashes, and others that are black. The color changes, too, from moment to moment. At sunset [182] you will see a cloud begin with being white, then turn scarlet, then shine like a pile of embers, or like a lake of melted gold, and finally become dull and turn gray or black, according as the sun's rays strike it less and less. All that is a matter of illumination by the sun. In reality, clouds, however splendid in appearance, are formed of a damp vapor like that of fog. We can assure ourselves of this by a near approach."

"People can then mount as high as the clouds, Uncle?" Emile asked.

"Certainly. All one needs is a pair of legs stout enough to climb to the top of a mountain. Often then clouds are under one's feet."

"And you have seen clouds underneath you?"

"Sometimes."

"That must be a very beautiful sight."

"So beautiful that words cannot express it. But it is not exactly a pleasure if the clouds mount and envelop you. You can be very much embarrassed by the obscurity of the fog alone. You lose your way; you become confused, without suspecting any danger in the most dangerous places, at the risk of falling into some abyss; you lose sight of the guides, who alone know the way and could save you from a false step. No, all is not roses up among the clouds. You will perhaps learn that some day to your cost. Meanwhile let us transport ourselves in imagination to the top of a cloud-capped mountain. If circumstances are favorable, here is what we shall see:

"Above our heads the sky, perfectly clear, presents no unusual appearance; the sun shines there [183] in all its brilliancy. Down there at our feet, almost in the plains, white clouds spread themselves out. The wind sweeps them before it and drives them toward the summit. There they are, rolling and mounting up the side of the mountain. One would think they were immense flocks of cotton pushed up the slope by some invisible hand. Now and then a ray of sunlight penetrates their depths and gives them the brilliancy of gold and fire. The beautiful clouds behind which the sun disappears at its setting are not richer. What brilliant tints, what soft suppleness! They mount higher and higher. Now they roll up like a shining white band around the top of the mountain, and hide the view of the plain from us. Only the point where we are projects above the cloud-curtain, like an islet above the sea. At last this point is invaded, we are in the bosom of the clouds. Warm tints, soft outlines, striking views—all have disappeared. It is now only a dark fog that saturates with moisture and makes us feel depressed. Ah, if some breath of wind would make haste and sweep away these disagreeable clouds!

"That, my little friends, is what one does not fail to wish when one is in the clouds, which, so beautiful at a distance, are nothing but gloomy fog when close at hand. The spectacle of the clouds should be seen from afar. When in our curiosity we wish to examine certain appearances too closely, we sometimes find them deceptive; but we also find that, under a secondary brilliancy, which serves to adorn the earth, they hide realities of the first importance. The marvels of the clouds are only an appearance, [184] an illusion of light; but under this illusion are concealed the reservoirs of rain, source of the earth's fecundity.
[Illustration]
Cirrus
God, by whom the smallest details of creation have been ordered, willed that the most common but also most necessary substances should serve as an ornament to the earth in spite of their really humble aspect; and he clothes them with a prestige dependent on the distance from which we are to contemplate them. The gray vapor of the clouds gives us rain. That is its chief utility. The sun illuminates it, and that suffices to transform it into a celestial tapestry in which the astonished eye finds the splendor of purple, gold and fire. That is its ornamental function.

"The height maintained by clouds is very variable and is generally less than you might suppose. There are clouds that lazily trail along the ground; they are the fogs. There are others that cling to the sides of moderately high mountains, and still others that crown the summits. The region where they are commonly found is at a height varying from 500 to 1500 meters. In some rather rare instances they rise to nearly four leagues. Beyond that eternal serenity reigns; clouds never mount there, thunder never rumbles, and snow, hail, and rain never form.

"Those clouds are called 'cirrus' that look sometimes like light flocks of curly wool, sometimes like drawn-out-filaments of dazzling whiteness, sharply [185] contrasting with the deep blue of the sky. They are the highest of all the clouds. They are often a league high. When cirrus clouds are small and rounded and closely grouped in large numbers, so as to look like the backs of a flock of sheep, the sky thus covered is said to be dappled. It is usually a sign that the weather is going to change.

"The name 'cumulus' is given to those large white clouds
[Illustration]
Cumulus
with round outlines which pile up, during the heat of summer, like immense mountains of cotton-wool. Their appearance presages a storm."

"Then the clouds we see over there next to the mountains," queried Jules, "are cumulus? They look like piles of cotton. Will they bring us a storm?"

"I think not. The wind is driving them in another direction. The storm always takes place in their neighborhood. There! Hear that?"

A sudden light had just flashed through the flocks of the cumulus. After rather a long wait the noise of the thunder reached them, but greatly weakened by distance. Questions came quickly from Jules's and Emile's lips: "Why does it rain over there, and not here? Why does the noise of the thunder come after the lightning? Why—"

"We are going to talk about all that," said Uncle Paul; "but first let us learn the other forms of clouds. 'Stratus' is
[Illustration]
Stratus
applied to clouds disposed in [186] irregular bands placed in tiers on the horizon at sunrise or sunset. They are clouds that, in the fading daylight, especially in autumn, take the glowing tints of melted metals and of flame. The red stratus of the morning are followed by rain or wind.

"Finally, we give the name 'nimbus' to a mass of dark clouds of a uniform gray, so crowded together that it is impossible to distinguish one cloud from another. These clouds generally dissolve into rain. Seen from a distance, they often look like broad stripes extending in a straight line from heaven to earth. They are trails of rain.

"Now, Emile may ask his questions."


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