Imatges de pÓgina
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What is a frith? A frith, or estuary, is the part of a river towards its mouth which is affected by the tide. It may be considered as an arm of the sea.

THE AIR.

Harriet, is there any thing about you besides the things which you can see? Yes, all around me there is air, which is invisible.

How can you be made sensible, that you are surrounded by air? If I swing my hand fast, the air can be felt; and when I run, my face feels its gentle resistance.

What is air? It is that subtle fluid, which enables mankind and the animals to breathe; the element that encompasses the earth.

What is the air called, when it moves slowly, or with a strong motion? In either case it is denominated wind.

How can you tell, when the air is in motion? I can see little particles of dust moving: the leaves of the trees move also, and other things.

What is a breeze? A gentle motion of the air.

What is a gale? It is when the wind blows stronger than in a breeze; yet not tempestuous.

What is a tempest? A violent wind, a hurricane.

Does the wind ever do any injury? When it rises into a violent storm, it prostrates fields of grain, trees, fences, barns, houses, and destroys vessels, by which means the lives of human beings are sometimes destroyed.

Does the wind ever do any good? Its utility is immense, in carrying away smoke and unwholesome air; and in rendering the atmosphere cool and pleasant. It is also instrumental of great good, by bringing clouds and showers which water the ground. On the water it is highly useful, by propelling vessels in their different courses.

Of what use is air? It enables us to breathe, and is essential to animal life. When we inhale, the air into our lungs, our bosoms swell, which would occasion great distress, if it were not immediately exhaled.

Why cannot any person live long under the water? Because, in that element, there is not a sufficient portion of air to enable him to continue breathing.

Why do fishes die shortly after being taken out of the

water? Because they are so constituted, as to require a constant supply of water, and a comparatively small quantity of air to support life.

Suppose a person should be shut up in a small tight place, where there was but little air, what would become of him? He would soon die, for the want of a sufficient supply of air for breath and sustenance.

Which way does the air go that we breathe? Upwards; because it is a little heated, and rendered lighter than the common air.

What is our breath? The air, when inhaled or drawn into the lungs, is our breath; but when it is exhaled, or breathed out, it is no more our breath; for it mingles with the common air. What makes fire burn? Air.

What artificial aid is sometimes used to make the air go to the fire fast? The bellows.

What natural aid will increase the air? Our mouths.

What bears up the clouds? The air, in which they float somewhat as a stick of wood does in the water.

How do birds fly in the air? They strike it so frequently with their wings, and with such force, that they are borne up, and carried about in the atmosphere with entire safety.

If the air had been made much heavier and thicker than it is, would it have been as well for us? It would not; for we then should have experienced great difficulties to breathe and live.

Suppose it had been made much lighter and thinner, what then? It would not have supported the birds and clouds, nor animal life.

Suppose there were no air? Then the birds could not fly any more; the clouds would fall down to the ground; the fire would all go out; and all animals and people would die.

HEAT AND COLD.

Charles, how can you tell, whether any thing is hot or cold? By the sense of touch, or feeling.

What is the difference between hot and warm? Any thing which is a little heated, is rendered warm; but to become hot, it must be heated greatly. Warm implies a moderate temperature of heat; hot, its increase to an excessive degree.

What is the meaning of the terms, cool and cold? In a

comparative view cold implies a greater degree, or state of coldness than the term, cool, does.

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Suppose ice is placed near the fire, or lead put into it, what change takes place? They become melted, or dis1 solved.

Can wax, tallow, and iron be melted by heat? They can. Will every thing which is solid, melt by heat? It will not: wood is reduced to ashes, or calcined.

Suppose that water, or milk, is placed, where it is very cold, what change is effected? It freezes, or is congealed. Will oil and quicksilver harden by cold? They will, if it is very cold indeed.

Will every thing which is liquid, harden by cold? No; alcohol, spirits of turpentine, of nitre, &c. will not.

If you should put hot iron into cold water, what changes would take place? The iron would be cooled, and the water warmed.

What, if you should put cold iron into hot water? The iron would be warmed, and the water cooled.

What, if you put your hand upon a cold stone? My hand is cooled, and the stone warmed.

Can you tell me what is meant by the phrases, warm day and cold day; warm weather and cold weather? They denote that the air all around us, is either warm or cold.

Why is it so much warmer in summer than in winter? Because the sun is then more nearly over our heads. His rays come to the earth more directly in summer; and more obliquely in winter, which occasions the principal changes of the temperature of the weather, or the extremes of cold and heat.

What makes our bodies warm? Friction, which is occasioned by the action of the blood throughout the system, and by the action of the lungs in respiration.

Do not our clothes really make our bodies warm by generating heat? They do not: they merely serve to keep them from becoming cold, by preventing their coming constantly in contact with the surrounding air.

Why do people increase the quantity of bed clothes for their covering during a very cold night? To protect their bodies from the keenness of the air, and to confine the heat which they produce; and thus are they kept comfortably warm.

If you were to wrap a stone in flannels and furs would they make it warm? They would not; but, if the stone should

be previously warmed, they would serve to keep it from cooling fast.

Suppose the heated stone should not be wrapt up, what then? The surrounding air would move away, and the stone would be continually exposed to the approaching cold air. Thus, if a cold wind should blow upon a piece of hot iron, it would cool faster than a similar piece would, protected from the constant approach and contact of the air. In like manner, if a warm wind should blow upon a piece of ice, or upon a snow-ball, it would melt faster than it would to be kept constantly in a cool place.

What is the effect, if you run, or walk very fast? It makes me quite warm in consequence of the increased motion and

exertion.

Suppose you rub your hands together some time, what then? They are made warmer than usual by the contact of action.

If you should rub two pieces of wood together hard and fast for some time, what would be the effect? The sides in contact would be heated by the friction.

Now my child, listen, whilst I tell you a few things. If you wet any thing in cold water, it will be warmer, when it is drying; but, if it be wet in warm water, it will become cooler by drying.

If you blow in your hands with your mouth, when they are very cold, they will grow warm; but, if you blow in them, when they are quite warm, your breath will serve to make them cool, as your breath is cooler, or not so warm as your hands, when heated.

THE WEATHER, THUNDER, LIGHTNING, &c.

Charles, can you mention some of the different kinds of weather? Clear, cold, cloudy, chilly, fair, foggy, frosty, hot, rainy, sultry, stormy, warm, and windy weather.

What can you say about the shape and size of the drops of rain? Their form is globular or round; and they are of different sizes.

In what direction does the rain fall to the ground? Sometimes perpendicularly, and at other times obliquely.

What is the difference between a shower and a storm? A shower is soon past: a storm is violent, or of longer duration.

Which falls through the air swiftest, snow, rain, or hail? Hail does; and snow comes the slowest.

Why? Because hail is of the greatest density or solidity; and snow is of the least.

What great good is done by rain? The air is purified; the water upon the earth is rendered salubrious; and in warm weather, by it vegetation is produced.

Do the rivers in winter freeze solid to the bottom? They do not.

Why? Because the weather grows warm again, before the water which is deep becomes sufficiently cold to the bottom for freezing.

How is snow formed? By vapours freezing in the air. How is hail formed? By water freezing in the air after it is formed into large drops. Hail cannot be formed, unless the air is very cold. The reason that we ever have hail in the summer, is, that it is sometimes sufficiently cold to freeze high in the air, whilst it is warm near the ground. If snow should be formed in the sky in very warm weather, it would melt, before it would reach the ground: but as hail is much more solid and heavy, it falls quicker, frequently before it is melted.

Are thunder and lightning always really together? They are.-Do we always see the lightning, and hear the thunder at the same time? We do not.

Why? Because they are sometimes at a considerable distance from us; and, as light proceeds much swifter than sound, so the light of the lightning comes to us quicker than the sound of the thunder; hence we frequently see the lightning first.

When we see a flash of lightning, what then? Unless it be at a great distance, we may expect to hear it thunder instantly.

When the lightning and thunder are near together, or come in quick succession, what are we to conclude? That neither of them is far distant; but both near us.

When a cloud is coming up in the day time, which do we notice first? The thunder, because the bright light of the day prevents us from seeing the lightning as soon, unless the flash be very vivid.

When a cloud comes up in the night, which is first noticed? The lightning, because the darkness makes it appear brighter, and the more readily discerned.

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