WHAT IS SMOKE?

Smoke is the result of incomplete combustion of the certain fuels. This means that if most of our common fuels were able to burn completely, we would have no smoke!

Most fuel consists of carbon, hydrogen, oxygen nitrogen, a little sulphur, and perhaps some mineral ash. Now if these fuels would burn complete, the final product would be carbon dioxide, water vapor, and free nitrogen, all of which are harmless. If sulphur is preset, small quantities of sulphur dioxide are also given off, and when this comes in contact with air and moisture, it becomes a corrosive acid.

For complete combustion, a fuel must have enough air for full oxidation at a high temperature. These conditions are difficult to obtain, especially with solid fuels, and the result is smoke. Anthracite and coke can be burned without producing smoke because they have no volatile matter.

But bituminous coals decompose at rather low temperatures so that gases and tarry matter are freed; they combine with dust and ash and produce smoke.

The air in any city is full of suspended solid particles, but not all of this is smoke. It may contain dust, vegetable matter, and other materials. All of those gradually settle under the force of gravity. In small towns or suburbs, probably about 75 to 100 tons of these deposits settle down per square mile during a year. In a big industrial city, the deposits may be 10 times as great!

Smoke can do a great deal of harm. It damages health, property, and vegetation. In big industrial towns, it lowers the intensity of the sunshine, especially the ultraviolet rays which are essential to health.

If the wind didn’t spread the smoke, big industrial towns would probably have fog every day. In fact, where smoky fog occurs, it often happens that the death rate goes up for lung and heart diseases.

The effect of smoke on vegetation is especially harmful. It interferes with the “breathing” of plants and screens off needed sunlight. Quite often, the acid in the smoke destroys plants directly!

Today, many cities are waging active campaigns to cut down on smoke or to prevent it from doing damage.

WHY IS A DESERT DRY?

What is a desert? A desert is a region where only special forms of life can exist. All deserts have a shortage of moisture, which means the life that exists in them must be able to get along with almost no water.

The amount of rainfall largely controls the amount and kinds of plan life in a region. Forests grow where there is much rain. Grassland grows where the rainfall is less. Where there is still less rain, only scattered, specialized desert plants can live.

Sahara in Africa

The hot deserts near the Equator, such as the Sahara in Africa, lie in subtropical land where the air settles downward, becoming warmer and drier as it does so. Lands in these areas are dry, even though they are next to the ocean. The same is true of deserts in northwest Africa and Western Australia.

Deserts farther away from the Equator are generally caused by the great distance from the sea and its moist winds, and by the mountains between the desert and the sea. These mountain barriers may catch rainfall on their seaward side but the interior, leeward region remains dry.

This is known as "the rain shadow" effect. The deserts of Central Asia lie in the rain shadow of the great Himalayan ranges and the plateau of Tibet. The deserts of the Great Basin, in Western United States, lie in the rain shadow of high mountain ranges on their west, such as the Sierra Nevada.

Deserts differ greatly in appearance. Where sand is abundant, the winds may build sand hills or dunes. These are sand deserts. Rock deserts consist mostly of bare rock, which forms fantastic cliffs and hills, or rough, jagged plains. Other deserts, like much of Southwestern United States, include barren Rocky Mountains and dry plains of soil and gravel. The wind sweeps away finer soil and the stones which are left form a gravelly surface called "a desert pavement."

Most deserts have some sort of plant and animal life. Desert plants often have little or no leaf surface to reduce evaporation of water from the plant. Or they have thorns or spines to discourage animals from eating them. Animals which can live in deserts can go for long periods without water and get liquid from plants or night dew.

IS THE SOUTH POLE AS COLD AS THE NORTH POLE?

To most of us, the regions of both the North as South Poles are lands of great mystery. We have a vague idea of what they're like, and we imagine that they must be very similar to each other.

The strange thing is that differences between the Antarctic region (South Pole Area) and the Arctic region (North Pole Area) are greater than heir similarities! The South Pole area consists chiefly of continent called Antarctica. This ice-snow-covered continent s nearly twice as large as the United States. By contrast, the North Pole region consists of the Arctic Ocean surrounded by margins of North America, Europe and Asia.

Another big difference is that man, animals and plants have slowly migrated northward to North Pole region, as they have adapted them-selves to polar environment. But the South Pole region, separated by hundreds of miles of ocean from all continents except South America, has no land animals and no native population. The plant life is so scare there that the only things growing are lichens mosses, grasses and a few flower-in plants.

By the way, one of the reasons why the penguin can continue to live in this area so happily is that it has no land enemies to contend with.

What about the climate in the Antarctic region? It has two chief characteristics: Low temperatures even summer and the world's greatest blizzards in winter. In the North Pole area, air currents rise from the surrounding waters and help raise the temperature a bit. But in Antarctica, which has a huge icecap spreading over most of it, large, cold, high-pressure air masses develop, and so the climate is much more severe that in the North Pole region.

Even during the summer months, the average temperature in Antarctica is below freezing! Now and then, during some summer days, the temperature may rise to 40 degrees, but on the other hand temperatures below zero may also occur right in the middle of the summer. And in the winter, the temperature at the South Pole averages from 10 to 30 degrees below ZERO!

WHAT IS A RAINBOW?

A RAINBOW is one of the most beauiful sights in nature, and man has long wondered what makes it happen. Even Aristotle, the great Greek Philosopher, tried to explain the rainbow. He thought it was a reflection of the sun's rays by the rain, and he was wrong!

Sunlight, or ordinary white light, is really a mixture of all the colors. You have Probably seen what happens when light trikes the beveled edge of a mirror, or a soap bubble. The white light is broken up into different colors. We see red, orange, yellow, green, blue and violet.

An object that can break up light in ths way is called "a prism". The colors that emerge from a band of stripes, each color grading into the one next to it. This band is called "a spectrum".

A rainbow is simply a great curved spectrum, or band of colors, caused by the breaking-up of light which has passed through raindrops. the rain-drops act as prisms.

A rainbow is seen only during showers, when rain is falling and the sun is shining at the same time. you have to be in middle,

the sun behind you, the rain in front of you, or you can't see rainbow! The sun shines over your shoulder into the raindrops, which break up the light into a spectrum, or band of colors. The sun, your eyes, and the center of the arc of the rainbow must all be in straight line!

If the sin is too high in the sky, its impossible to make such a straight line. That's why rainbows are seen only in the early morning or late afternoons. A morning rainbow means the sun is shining in the west and rain is falling in the east.

Superstitious people used to believe that a rainbow was a sigh of bad luck. They thought that souls went to heaven on the bridge of rainbow, and when a rainbow appeared it meant someone was going to die!

WHY DOES THUNDER FOLLOW LIGHTNING?

LIGHTNING and THUNDER must have been among the first things about nature that mystified and frightened primitive man. When he saw the jagged tones of lightning in the sky and heard the claps and rumbles of thunder, he believed the gods were angry and that the lightning and thunder were a way of punishing man.

To understand what lighting and thunder actually are, we must recall a fact we know about electricity. We know that things become electrically charged-either positively or negatively. A positive charge has a great attraction for a negative one.

As the charges become greater, this attraction becomes stronger. A point is finally reached where the strain of being kept apart becomes too great for the charges whatever resistance holds them apart, such as air, glass, or other insulating substance, is overcome or "broken down". A discharge takes place to relieve the strain and make the two bodies electrically equal.

This is just what happens in the case of lighting. A cloud containing countless drops of moisture may become oppositely charged with respect to another cloud or the earth. When the electrical pressure between the two becomes great enough to break down the insulation of air between them, a lightning flash occurs. The discharge follows the path which offers the least resistance. That's why lightning often zigzags.

The ability of air to conduct electricity varies with its temperature, density, and moisture. Dry air is a pretty good insulator, but very moist air is a fair conductor of electricity. That's why lightning often stops when the rain begins falling. The moist air forms a conductor along which a charge of electricity may travel quietly and unseen.

What about thunder? When there is a discharge of electricity, is causes the air around it to expand rapidly and then to contract. currents of air rush about as this expansion and contraction take place. The violent collisions of these currents of air are what we hear as thunder. The reason thunder rolls and rumbles when it is far away is that the sound waves are reflected back and forth from cloud to cloud.

Since light travels at about 186,284 miles per second and sound at about 1100 feet per second through air, we always see the flash first and then the thunder later.

WHAT IS STORM?

Even though man has become a powerful creature, able to control mighty forces, nature can still strike terror into his heart when she ships up a storm! What is storm?

Whenever there is something taking place in the weather of a violent nature, it is a storm. At sea, a storm may be strong wind or gale. Inland, a storm usually means there is weather situation that is marked by heavy rain, and often by lighting, thunder and strong winds.

A storm in the latitudes where the United States lies usually covers an area hundreds of miles across. It represents vast circular whirls of air roaring about a central point of low atmospheric pressure.

Such storms begin where cold dry masses of air moving southward from Arctic regions are met by warm moist air masses moving northward from the tropics. At certain places, great tongues of the warm air thrust their way into cold. The tip of such a warm air tongue becomes a spot a low atmospheric pressure, toward which the winds blow, and the storm area develops around it.

Where the cold and warm air masses actually meet, they mix only slightly. The lighter warm air climbs up and over the cold air along a sloping surface. This cools the warm moist air, it becomes saturated, clouds form, and the result may be rain or snow.

In the Northern Hemisphere, the earth's rotation causes the winds to be deflected toward the right, so the "whirl" of the storm is counterclockwise. In fact, it's like a whirlwind on a huge scale.

Typhoons and hurricanes north of the Equator usually originate in late summer or fall over warm tropical water. They move westward and northwestward in a path that curves to the right. A tornado is a violent whirlwind. It begins as a black, funnel-shaped cloud that accompanies a larger thunderstorm area. The tip of the funnel may be only a few hundred feet wide but it destroys whatever it touches. The destruction is caused by the terrific speed of the wind and the terrific reduction in atmospheric pressure. Walls of houses are sucked out and the buildings collapse! Tornadoes are so destructive that in regions where they occur often, people have built special places to hide from their danger.

HOW DOES WATER CHANGE TO ICE?

If you've ever noticed a pond, lake or river freeze, you've seen a sheet of ice begin to form over the top of the water.

Do you realize that if ponds, lakes and rivers froze from the bottom up, instead of from the top down, many important things about our life would be quite different? Not only would it change the climate of the world, but certain creatures who live in the water would disappear altogether!

Here is how the water in a pond changes into ice: When the air above the pond grows cold, it cools off the top layer of water, too. This coldness makes the water heavier than the warmer layers underneath and the cold water sinks down. This process goes on and on until all the water in the pond has reached a temperature of about 39 degrees Fahrenheit.

But our temperature is still dropping! When the top layer of water becomes colder than 39 degrees, it remains on top. The reason is that water cooled to below 39 degrees actually becomes lighter!

We now have the top layer of water ready to start freezing. So when the temperature remains at the freezing point of 32 degrees, or if it goes below that, tiny crystals begin to form.

Each of these crystals has six rays, or points. As they join together they form ice and soon a whole sheet of ice appears on top of the water. Sometimes the ice is clear, sometimes its cloudy. Why? The reason is that when each drop of water freezes, it sets free a tiny bubble of air. This bubble sticks to the arms of the crystal. As more crystals form, the bubble caught and we have cloudy ice.

If the water under the ice is moving, the little air bubbles are grouped together into clear ice.

Water is one of the few substances that do not shrink when changed from liquid so solid. When water is frozen into ice it expends by one-ninth, so that nine quarts of water give you ten quarts of solid ice! When automobile radiators and water lines crack in winter, it's because the water freezes and there is no room for the ice!

WHY DOES FROST FORM ON WINDOWS?

Children who live in places where the winter get cold love to see frost on the windows. some of the patterns are quite beautiful and look like intricate designs on trees or leaves.

For this frost to form on the windowpanes-as well as on trees and grass-certain condition are necessary. Frost is made up of tiny crystals of frozen water. It forms when air that has a lot of moisture in it is cooled below the freezing temperature of water. This temperature, which we call "the freezing point," is 32 degrees Fahrenheit and zero degree centigrade, at sea level.

When air becomes cooler, it cannot hold as much water as before. The excess water condenses on such object as the windowpane. Now, if the temperature falls below 32 degrees Fahrenheit, this water becomes crystallized. in other words, it freezes into a coating of interlocked crystals of water.

What causes the patterns to appear in the frost on the windowpanes? For one thing, the tiny crystals have a certain structure which gives them a pattern. In addition, there may be create the designs that "jack Frost" makes on your windows.

White frost, which is often called "hoarfrost," is of two kinds: granular and crystalline. Granular frost is simply frozen fog. The crystalline frost, which we have described, is formed directly from the water vapor in the air. It goes right from being a gas to being a solid, without going through the liquid state.

Frost , as you know, can be a serious danger for the farmer by killing buds or ripening fruit. Actually, it is not the  frost itself, but the freezing of the plant juices that it is harmful. So farmers have had to develop ways of preventing frost to save their crops. One way is to cover the plants with a light cloth to prevent radiation of heat. Smudge pots in orchards cover the tree with thick smoke, and this also helps the plants hold in their heat.

So while you enjoy seeing the work of "jack Frost," remember that it may serious damage to millions of pounds worth of crops.

WHY DO SNOWFLAKES HAVE SIX SIDES?

One of the most beautiful objects formed by nature is a snowflake. It would take most of us a long time to “design” a shape as beautiful as a single snowflake. Yet in an ordinary snowstorm, billions upon billions of snowflakes fall to the earth-and no two are exactly alike!

Snow, as you may know, is just frozen water. In fact, you may ask why snow is white if it’s just frozen water. Shouldn’t it be colorless? The white appearance is caused by the fact that the many surfaces in all the ice crystals that make up a snowflake reflect light, and we therefore see it as white.

When water freezes, it forms crystals. This simply means that the molecules come together in a special arrangement, or geometrical form, and we call this “a Crystal.”

It so happens that a water molecule consists of three units-two atoms of hydrogen and one of oxygen. So when it crystallizes, it has to form either three-sided or sis-sided figures.

The water that freezes to form snow is in the form of water vapor in the atmosphere. As it freezes, the crystals that form are so small that they are invisible, but when snow is being formed, these crystals are carried up and down in the atmosphere by air currents.

As they move up and down, a group of crystals begin to collect around something. It might be around a speck of dust, or around a tiny drop of water. The group of crystals gets larger and larger, so that soon there might be hundreds of crystals gathered around one nucleus.

When such a group becomes large enough, it begins to float down toward the ground and we call it “a snowflake.” Some snowflakes are more than an inch in diameter! The size of a snowflake depends on the temperature. The colder the temperature, the smaller the snowflakes that will form.

Did you know that in many parts of the world snow has fallen that has been blue, green, red, and even black? This is due to the presence of certain fungi or dust in the air around which the snowflakes formed.

WHAT IS DEW?

You would imagine that dew is a very simple phenomenon of nature, easily understood and explained. Yet strangely enough, exactly what dew is have long been misunderstood, and whole books have been written on the subject!

Since the days of Aristotle until about 200 years ago, it was believed that dew “fell,” somewhat like rain. But dew doesn’t fall at all! The most familiar form of dew, seen on the leaves of plants, is now known not to be all dew! So you see, there have been many wrong ideas about dew.

In order to understand what dew is, we have to understand something about the air around us. All air holds a certain amount of moisture. Warm air can hold much more water vapor than cold air. When the air comes in contact with a cool surface, some of that air becomes condensed and thee moisture in it is deposited on the surface in tiny drops. This is dew.

The temperature of the cool surface, however, has to drop below a certain point before dew will form. That point is called “the dew point.” For example, if you place water in a grass or a polished metal container, dew may not collect on the surface. If you place some ice in the water, dew may still not collect until the surface of the glass or container is brought down to a certain point.

How does dew form in nature? First, there has to be moisture-laden warm air. This air must come into contact with a cool surface. Dew doesn’t form on the ground or sidewalk, because it still remains warm after having been heated by the sun. But it may form on grasses or plants which have become cool.

Then why did we say that the dew seen on plants is really not dew? The reason is that while a small part of the moisture seen on plants in the morning is dew, most of it-and in some cases all of it- has really come from the plant itself! The moisture comes out through the pores of the leaves. It is a continuation of the plant’s irrigation process for supplying the leaves with water from the soil. The action starts in the daytime, so that the surface of the leaf should be able to withstand the hot sun, and it simply continues into the night.

In some places in the world, enough dew is deposited every night for it to be collected in dew ponds and used as a water supply for cattle!

HOW FAST DOES SOUND TRAVEL?

Every time a sound is made, there is some vibrating object somewhere. Something is moving back and forth rapidly. Sound starts with a vibrating object.

But sound must travel in something. It requires something to carry the sound from its source to the hearer. This is called “a medium.” A medium can be practically anything-air, water, objects, even the earth. The Indians used to put their ears to the ground to hear a distant noise!

No medium-no sound. If you create a vacuum, space containing no air or any other substance, sound cannot travel through it. The reason for this is that sound travels in waves. The vibrating objects cause the molecules or particles in the substance next to them to vibrate. Each particle passes on the motion to the particle next to it, and the result is sound waves.

Since the mediums in which sound travels can range from wood to air to water, obviously the sound waves will travel at different speeds. So when we ask how fast does sound travel, we have to ask: In what?

The speed of sound in air is about 1,100 feet per second (750 miles per hour). But this is when the temperature is 32 degrees Fahrenheit. As the temperature rises, the speed of sound rises.

Sound travels much faster in water than in air. When water is at a temperature of 46 degrees Fahrenheit, sound travels through it at about 4,708 feet per second, or 3,210 miles per hour. And in steel, sound travels at about 11,160 miles per hour!

You might imagine that a loud sound would travel faster than a weak sound, but this isn’t so. Nor is the speed of sound affected its pitch (high or low). The speed depends on the medium through which it is traveling.

If you want to try an interesting experiment with sound, clap two stones together when you are standing in the water. Now go under water and clap those two stones together again. You’ll be amazed how much better sound travels through water than through air!

What Is Fog?

A fog is a cloud in contact with the ground. there is no basic difference between a fog and a cloud floating high in the atmosphere. When a cloud is near or on the surface of the earth or sea, it is simply called "FOG".

The commonest fogs are those seen at night and in the early morning over the lowlands and small bodies of water. They usually are caused by a cold current of air from above striking down upon the warmer surface of the land or water.

In the autumn they are very common, because the air is cooling faster day by day the land or the water. On still nights after dark, thin layers of fog often form close to the ground in low places. As the earth cools at night, the lower air gets cooler. where this cooler air meets the moist warmer air just above, fog forms.

As the general rule, city fogs are much thicker than country fogs. City air is full of dust and soot that mingle with tiny particles of water to form a thicker blanket.

Off the coast of Newfoundland, which is one of the foggiest parts of the world, fogs are formed by the passage of dump, warm air over the cold water flowing south from Arctic Circle, The chill of the water condenses the moisture of the air into tiny drops of water. These drops are not big enough to fall as rain. They remain in the air as fog.

San Francisco fogs are formed in the opposite way. There a cool morning breeze blows over warm sand dunes, and if rain has moistened the sand the night before, a thick fog bank of evaporated moisture forms.

The reason fogs often seem denser than clouds is that the droplets are smaller in a fog. A large number of small drops absorb more light than a smaller number of large drops (as found in clouds), and thus it seems denser to us.

Why Does Iron Get Rusty?

When you leave a piece of iron for a few days in a place it's damp or wet, a covering of rust forms over it just as if someone had come along and painted that reddish color on it.

What is rust? Why does it form in iron and steel? Rust is iron oxide. It is created when iron "burns" by uniting with oxygen dissolved in water.

This means that unless there is moisture in the air, or water is actually present, the oxygen is not dissolved in water and rust cannot begin to form.

When a drop of rain falls on a bright iron surface, the drop will remain clear for a short time. But the iron and the oxygen in the water soon begin to unite and form iron oxide, or rust, inside the drop. The drop will turn a reddish color and the rust is suspended in the water. When the drop evaporates, the rust will remain and form a reddish coat on the iron itself.
Once started, rust will spread even in dry air. This is because the rough spot of rust helps whatever moisture there is in the air to condense; it attracts the moisture and holds it. That's why it's easier to prevent rust from starting than to prevent it from spreading once it has started.

Since iron and steel articles often have to be stored for long periods of time, the problem of preventing rust is an important one. Sometimes such articles are coated with a special paint or plastic film. But what would you do if you had keep the insides of battleships rust-free when these ships are not in use? Govt. has solved it by using dehumidifiers. These are machines that draw moist air out of the compartments of the ship and replace it with dry air. Rust never gets a chance to start!

What is Humidity?

If you put a pitcher of ice water on a table and left it stands a while, what happens? Moisture gathers on the outside of the pitcher. Where does this moisture come from? It comes from the air.

The fact is there is always moisture in the air in the form of water vapor. In the case of the ice pitcher, the vapor condensed on the cold surface of the pitcher and thus became visible. But water vapor in the air is invisible. And the word “humidity” simply means the presence of water vapor in the air. It is found everywhere, even over great deserts.

This means, of course, that we always have humidity, but the humidity is not always the same. We have several ways of expressing the humidity, and two of them are “absolute humidity’ and humidity.” Let’s see what each means.

“Absolute humidity” is the quantity of water vapor in each unit volume of air. There are so many grains per cubic foot of air. But for most practical purposes, this doesn’t tell us very much. If you want to know whether you’ll feel comfortable or not, the answer “four grains per cubic foot” won’t tell you whether the air will feel dry or humid. The more easily moisture from your body can evaporate into the air, the more comfortable you’ll be. The evaporate power doesn’t indicate anything about the evaporate power of the air.

Relative humidity is expressed as a percentage. “One hundred per cent” stands for air which is saturated or completely filled with water vapor. The higher the temperature, the greater the quantity of water vapor air can hold. Thus, on a hot day, a “90 per cent relative humidity” means an awful lot of moisture in the air- a day that will make you mighty uncomfortable.

Where Does The Wind Come From?

There are two ways of looking at the wind and where it comes from. One is in terms of your immediate neighborhood, and one is in terms of the world and the big winds that blow over it.

Differences in pressure may exist in a small region around you, and you will have a local wind blowing. Of you live near the shore, you have an example of this every day. During the day, the land becomes heated, the air above it rises, and cool winds come in from the water to take its place. At night, the land becomes colder that the water, the warm air rises over the water, and the breeze blows out from the land to take the place of the rising warm air.

What is true in our immediate neighborhood is true on a much larger scale of the winds that blow over the earth. The warmest place on earth is around the Equator. So there is always a belt of warm air rising from this region. This belt of warm air flows out to the north and south and sinks again at certain latitudes, which are called “the horse latitudes.” This sinking air flows out along the surface of the earth toward the Equator and the Poles.

If the earth were not rotating, these winds would be north winds or south winds. But the spinning of the earth makes all winds in the Northern Hemisphere deflect to the right and in the Southern Hemisphere to the left. The winds blowing from the horse latitudes toward the Equator are called “the trade winds.” Those blowing toward the Poles are called “the westerlies.” The United States is largely in the zone of the westerlies.

There are other “prevailing” or common winds in other parts of the worlds. But as you can see, the wind does come from somewhere- and it comes from there because of every definite reasons caused by the way air over the earth is heated.

What Is The Jet Stream?

Nowadays, the word “jet” is very much in the news, and you might imagine that all the “jet stream” has something to do with jet planes. This isn’t the case at all!

The jet stream is part of the system of winds that surround the earth, so let’s start with the subject of winds. Winds are currents of air that move parallel to the surface of the earth and close to it.

The movement of winds is chiefly caused by the existence of areas of different pressure, and winds always blow from areas of high pressure to areas of low pressure.

If we look at it from an over-all point of view (not from local regions) we can say that, in general, cold air is transported from the Poles toward the Equator, and warm air from the Equator towards the Poles. This flow doesn’t take place in smooth currents, but forms a system of rather turbulent streams. There are various conditions that decide what happens in each specific region. There may be local sources of heat which affect the pressure. The way the land and water and mountains are distributed can decide which way the local winds blow.

Finally, there is the existence of semi-permanent high-pressure areas in certain places. This means that in these regions there tends t be a high-pressure area most of the time. They are called “anticyclones” and wind currents locally are decided by them.

Now, this gives you a general idea of how winds blow and some of the things affect them. But all of this concerns winds that are quite close to the earth, in the lower layers of the atmosphere. As you know, the earth is surrounded by atmosphere that may go as high as 1,500 miles up. In the higher levels of the atmosphere, different wind conditions exist. Here they usually move with much greater speed than near the surface. At a height of about 30,000 feet, currents of air move with such speed that they a special name- “the jet stream”! The speed of the jet stream ranges from 100 to 200 miles per hour.

Why Do We Have Different Seasons?

Since earliest times, man has been curious about the changing of the seasons. Why is it warm in summer and cold in winter? Why do the days gradually grow longer in the spring? Why are the nights so long in winter?

We all know the earth resolves around the sun, and at the same time it revolves on its own axis. As it moves around the sun, it’s also spinning like a top. Now if the axis of the earth (the line from the North Pole through the South Pole) were at right angles to the path of the earth around the sun, we would have no such things as different seasons, and all the days of the year would be of equal length.

But the axis of the earth is tilted. The reason for this is that a combination of forces is at work on the earth. One is the pull of the sun, the other is the pull of the moon; the third is the spinning action of the earth itself. The result is that the earth goes around the sun in a tilted position. It keeps that same position all year, so that the earth’s axis always points in the same direction, toward the North Star.

This means that during part of the year the North Pole tilts toward the sun and part of the year way form it. Because of this tilt, the direct rays of the sun sometimes fall on the earth north of the Equator, sometimes directly on the Equator, and sometimes south of the equator. These differences in the way the direct rays of the sun strike the earth because the different seasons in different parts of the world.

When the Northern Hemisphere is turned toward the sun, the countries north of the equator have their summer season, and the countries south of the Equator have their winter season. When the direct rays of the sun fall on the Southern Hemisphere, it is their summer and it is winter in the Northern Hemisphere. The longest and shortest days of each year are called “the summer solstice’ and “winter solstice.”

There are two days in the year when night and day are equal all over the world. They come in the spring and fall, just halfway between the solstices. One is the autumnal equinox, which occurs about September 23, and the other is spring equinox, which occurs about March 21.

How Does The Weatherman Know What To Say?

All the conditions of the atmosphere are “weather.” Whether it’s hot or cold, dry or wet, sunny or cloudy, windy or still, it’s “weather.” The weather is changeable from day to day, and the total effect during a year is called “the climate.”

There are many complicated reasons for changes in the weather, but the most important influence is the sun. The sun’s heat evaporates water and warms the air, so that rising currents of warm air carry water vapor into the sky. There the air cools and the vapor condense into rain. These things happen gently or violently. When they take place violently, we have storms.

In Great Britain there are approximately 200 weather reporting stations and roughly the same number spread over the rest of Europe. In addition, “weather ships” stationed in the Atlantic and special aircraft on regular patrol send back systematic reports on weather conditions. From this and other meteorolical data weather forecasts are produced.

The maps which the weather experts study show them many things: places where the air pressure is equal, places of equal temperature, directions of local winds, cloudy or clear skies, rain or snow, the amount rainfall, and regions where the air pressure is higher or lower than normal.

The weatherman can also tell from looking at the map what is likely to happen under the conditions that exist. He knows that low pressure indicate storms, because cold air is moving in to replace warm rising air that is laden with moisture. High pressures indicate fair weather.

In the Northern Hemisphere, the winds around a high-pressure area blow outward in a direction similar to that followed by the hands of a clock.
In a low-pressure area they blow inward in a counterclockwise direction. Thus the directions the winds will take can be predicted. The weatherman also knows how fast these pressure areas are moving across the country.

Knowing all these things, and having reports of the weather in most parts of the country before him, the weatherman begins to get a pretty good idea of what to say about the weather that’s coming to your area!

Where Do Most Earthquakes Occur?

If you could look at a map that showed the entire surface of the earth and where earthquakes occur most often, you’d see a wavy ribbon that twisted up and down as it twisted around the earth. Some parts are missed entirely; others seem to have a habit of having frequent earthquakes.

The single reason of the earth that has the most frequent earthquakes is Japan. There is an earthquake there almost every day of the year! Of course, most of these are very minor quakes and do no damage at all. Another region which has frequent earthquakes is the Mediterranean area. By contrast, consider the New England States. There have been no destructive earthquakes there since the Ice Age, many thousands of years ago!

The explanation for this is that the crust of the earth is not the same everywhere. In certain regions, the crust has not quite settled down firmly, and there is a “fault.” A fault is a break in the rocks of the earth’s crust. Where the break exists, one rock mass rubs against another with great force and friction. The energy of this rubbing is changed to vibration in the rocks.

While this vibration may travel thousands of miles, the earthquake is strongest, as you might imagine, right along the line of the fault made by the shifting of the earth blocks. The sides of the fault may move up and down against each other, or the sides of the fault may shift lengthwise.

Most of the changes that take place on the surface of the earth after an earthquake are seen along this fault line. The part of the fault line where the vibration is felt most strongly is called “the epicenter” of the earthquake. And if this is near a city, the destruction may be very great. The loss of life is usually due to falling buildings and fires that may be started by broken gas mains under streets.

The earthquake regions of the earth and the areas of recent volcanic activity are roughly the same. This is because both of these are regions where the earth’s crust is not at rest.

Why Do Volcanoes Appear only In Certain Places?

There are no volcanoes near New York City or London or Paris-nor are there likely to be any in the future. Yet there are parts of the world where there are several volcanoes quite near each other.

Central America, bordering the Pacific Ocean, is one of the most active volcano areas of the world. In fact, more than two-thirds of the active volcanoes and a large number of those which have been extinct for only a short time are found around the borders of the Pacific Ocean!

The reason is simply this: The earth’s crust in these areas must be “weak” or have weak spots in relation to the earth’s crust in other parts of the world. For without a weak spot in the crust of the earth, a volcano couldn’t come into being.

Here is how a volcano is born: As you know, the center of the earth is hot. The deeper you go under the surface of the earth, the higher the temperature. At a depth of about 20 miles, it is so hot (1,000 to 1,100 degrees centigrade) that most rocks found there simply melt.

When rock melts, it expands and needs more space. In certain areas of the worlds, new mountain ranges have recently been formed (new in terms of thousands of year). Under and near these new mountain ranges, the pressure is less than elsewhere. It is a kind of “weak spot”
in the earth’s solid crust.

So the molten rock, which is called “magma,” expands into these parts and a local reservoir of the molten rock is formed. This material rises along the cracks formed by the uplift. When the pressure in the reservoir of molten rock becomes greater than the strength of the roof over it, it bursts forth as a volcano. The eruption lasts until the gas is gone.

The material that comes out of a volcano is mainly gaseous, but large quantities of molten rock (which we call “lava”) and solid particles that look like cinders and ash are also thrown out. The eruption is really a gas explosion, but some of the lava becomes finely powered and makes the eruption look like black smoke.