Читать книгу Round the Year with Enid Blyton—Winter Book - Enid blyton - Страница 4

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Have you had any snow in your town or village yet this winter? If you live in the North of Britain possibly the snow is lying outside now! In the South we sometimes have no snow at all until the winter is far advanced—and even then it may not lie very long. Do you like watching a snow-storm? It is a strange feeling to stand at the window and look upwards when the snow is falling—there are such thousands of white snowflakes for ever appearing out of the leaden sky, falling steadily, silently downwards.

Why do we get frost and snow? Isn’t it a curious thing to find all the puddles turned to ice one morning, or to see the world covered in white? What makes the frost come on the window-pane, the rime cover the trees, the snow fall thick from the sky?

I expect you have a Fahrenheit thermometer in your classroom. Pass it round carefully and look at it. Look at the number 32 on it. What is printed just by it? Yes, the word Freezing. The mercury in the glass tube is far higher than that, of course, because your room is warm; but if you put your thermometer outside one cold night the silver mercury would gradually fall in the tube, and perhaps it would show freezing-point—it would sink right down to number 32. And then a strange thing would begin to happen to all the water and to all the moisture around. It would freeze.

What do we mean when we say that water freezes? In some way that is stranger than magic, and more powerful than machinery, each drop of water finds itself turned into ice. At freezing-point all the puddles in the road freeze, all the ponds are covered with ice, dripping water becomes solid and hangs from roofs in the form of icicles.

You cannot pick water up and hold it in your fingers—but you can hold it when it is solid ice. It breaks very easily when you drop it, for it is brittle.

Do you know if water takes up more room when it is liquid or when it is solid? Would a cupful of water turn into exactly the same amount of ice, or would there be less in the cup—or more? Who knows?

It is a curious thing that water, when frozen into ice, gets bigger, and takes up more room than before! Would you like to prove this for yourselves? It is quite easy. Get a lemonade or medicine bottle and fill it quite full with water. Cork it tightly and put it outside on a frosty night. In the morning your bottle will be broken!

ICICLES HANGING FROM A ROOF. THE SNOW ON THE BARN MELTED, AND AS THE WATER DRIPPED OFF, IT FROZE INTO ICICLES BECAUSE THE TEMPERATURE WAS FALLING AGAIN

The frost broke it. The water in your bottle froze hard, and grew bigger as it turned into ice. It wanted more room—but there wasn’t any more room in the bottle! So it burst the glass, and thus your bottle was broken. What strength the frost had!

I am sure you have sometimes had pipes burst in frosty weather. What makes them burst? A great many people will say, “Oh, the thaw burst the pipes!” But they are wrong, aren’t they? It is the frost that bursts the pipes. The water in the pipes freezes hard and wants more room to expand as it freezes. It cannot find any more space, so it bursts our pipes—but we do not know then that they are burst, because the water inside is changed to ice, which cannot flow out of the holes made by the bursting—and only when the thaw comes and the ice changes back to water and trickles out of the holes do we see that our pipes need mending! The thaw shows us the bursts in our pipes, but it is the frost that does the damage!

The farmer welcomes the frost in winter-time, for it works better than a score of farm-labourers for him. Did you see the great clods in the fields in the autumn? If you did, perhaps you wondered how in the world young plants could possibly grow.

The frost breaks up the clods for the farmer. It freezes the moisture inside them, and when the frozen moisture tries to expand and find more room it breaks up the clods! The next time you walk by that field and tread on a clod you will find that it crumbles away to powdery earth—just right for tiny seeds to grow in when spring-time comes.

Have you seen the beautiful scrolls and ferns that the frost designs on your window-pane at night? Perhaps this very morning you got up and went to look out of the window—and you couldn’t see out because it was all “frosted over”! The frost had come in the night and put pictures on the window. How did it do it? Well, as we slept we breathed out warm breath, and some of it went to the window-pane in the form of water-vapour. The window-pane was cold and the frost lurked just outside. As soon as our breath touched the glass it froze, and as it froze there came the lovely patterns made of ice-crystals that you saw when you woke up this morning.

THE LOVELY FERN-PATTERN MADE BY THE FROST ON A WINDOW-PANE DURING THE NIGHT

How is snow made? It isn’t frozen rain, because that would come down as small hailstones. It is frozen water-vapour—frozen clouds! In winter-time the clouds often float through very cold air, and it sometimes happens that instead of turning into raindrops, as they usually do, they change from water-vapour into tiny ice-crystals. The crystals join together and make snowflakes. These are too heavy to float about the sky, so down they come. They are so soft and so light that, although there may be thousands of snowflakes falling around us, we never hear a sound.

Have you ever seen an ice-crystal? I should like you to see one, because I know you will be surprised at its lovely shape. To see crystals properly, you want a piece of black cloth. Catch a snowflake on it and look at it through a small magnifying glass.

You will see that the flake is made of tiny, glittering crystals—and every one of them has six sides! Catch as many as you like and count the number of points they have, and you will always find six, or a multiple of six. Some of the crystals are feathery-looking, some are star-shaped, others are plain—but all are exquisitely fragile and delicate.

Choose a day when there is not much wind when you catch your snowflakes, as otherwise they will be bruised by being blown about, and you will not be able to see clearly the lovely shapes of the crystals.

The snow acts as a warm blanket to the earth. Perhaps you are surprised to hear that something so cold should give warmth to things!

WHAT FROST CRYSTALS LOOK LIKE UNDER A MAGNIFYING GLASS. EACH HAS SIX SIDES

If you weighed a pound of water and compared it with a pound of snow, you would be surprised to see what an enormous amount of snow had to go to make up the pound, compared with the water. What makes snow so bulky? It is the air entangled in the snowflakes! Think of feathers, or of wool—each of those weighs very light, and a great deal of them has to be piled on the scales before the weight of a pound is reached. They, too, have air entangled in them. A little bird’s body gives out heat and warms the air in its feathers, and these keep the air in—and the heat too—so the bird is always warm, no matter how cold the outer air is. Its feathers entangle the warm air and won’t let it get away.

Fur does the same, and so does wool. And now, how does snow keep the earth warm? Can you think? It keeps it warm because it doesn’t let what heat there is in the ground get away! It holds it there, entangled in the six-sided crystals. The frost in the air above the snow may get harder and harder—but the bitter cold cannot touch the tender plants below the snow! The flakes are keeping their heat in, just as our woolly blankets at night keep our heat in, and make us feel warm.

When warmer days come, the snow melts and the plants drink their blanket! It trickles down to their roots and so is of use to them in another way.

Hoar frost is not frozen dew. The moisture in the layer of air next to the ground becomes frozen instead of turning into drops of dew. If we look at hoar-frost closely we shall see that it is a feathery layer of ice formed on blades of grass, twigs, leaves and so on. It is very beautiful.

When the weather is misty and very cold at the same time, the mist freezes, and we see that everything outside becomes covered with a thick layer of tiny ice-needles. This we call Rime.

When snow falls through air that is warmer than freezing-point it begins to melt—and we find that a mixture of snow and water is falling on us. This is called Sleet.

Hail is made of rain-drops frozen into balls of ice. As you know, hail-stones are very often far bigger than drops of rain, and this is because in their travels through very cold air more and more layers of ice have been added to each hail-stone, so that when at last they reach earth they may be very large indeed, and do a great deal of damage.

THINGS TO DO

1.

The very first chance you have, catch a snowflake on something dark and look at it closely—with a magnifying glass if you can. Count its sides.

2.

Draw a snow-crystal or a snow-scene.

3.

How does the frost help the farmer?

4.

How does the snow help the plants to face a bitter winter?

5.

Why do our pipes burst in frosty weather?