HOW DO BACTERIA COME FROM

HOW DO BACTERIA COME FROM?
Bacteria are living beings ) organisms ) so small that they can be seen only with a microscope which enlarges several hundred times. Therefore, they are called ''micro-organisms''.
Long before people were able to see bacteria, they knew about the results of bacteria at work. For example, people knew about the results of bacteria at work. For example, people knew that wine ferments, milk turns sour, and dead plants and animals decay. But people had superstitious or religious beliefs as to why this happened. Today, we know that bacteria are all about us-in the air, in water, in food, on the skin, and even inside the body. Bacteria multiply by splitting in half. There are no males or females among bacteria. If they have the right conditions and food for living, they will simply multiply and keep on multiplying.
Bacteria have only one cell which is more like that of a plant than an animal. The outside is a skinlike cover, or ''membrane,'' which is not waterproof. The inside is filled with a material called ''protoplasm'' and usually does not have a single center, or nucleus.
The outside cover is important because any chemical used to destroy the bacteria must be able to pass through the membrane. Around the whole is a slimy material which can change shape and oftern forms tiny threadlike tails, called ''flagella.'' Bacteria can move, although they have no feet. Some move by waving the flagella, and others seem to move by shortening and lengthening the cell, the way worms move.
Bacteria, as we know, cause diseases which we call ''infections.'' But bacteria can also be very helpful and useful to human beings.

WHAT IS A MINERAL

 WHAT IS A MINERAL?
A ''mineral'' is any substance found in the earth's crust that does not come from a living thing.
Sometimes petroleum, coal, and limestone are called minerals, but since they were made from plants or animals which lived on the earth a long time ago, they are not really minerals.
Minerals are usually divided into two groups, metallic and nonmetallic. Examples of metallic minerals are hematite ( iron ), bornite ( copper ), and bauxite ( aluminum ). The non-metallic minerals include quartz, asbestos, and calcite. Minerals are usually found n forms called ''crystals.''
It is easy to confuse minerals and rocks, but there is a difference. A mineral has a definite composition. The chemical make-up of a mineral is almost always the same, no matter where it is. So a mineral foud in any part of the world will have the same luster, hardness, and other properties.
Rocks, however, are made up of mixtures of several minerals.For example, granite is a rock made up of minerals like quartz, feldspar, mica and others. But a piece of granite found in one place might have different amounts of these minerals from a piece of granite in another place.
Minerals are found in many places. They may be found in rocks or in sands and gravels. And they are formed in many different ways. Many minerals crystallized or hardened years ago from a very hot, melted mass of rock, called '' a magma.'' Diamond, mica, and feldspar are examples of minerals that formed from moten magma.
Certain minerals, chiefly because of their beauty and scarcity, are very valuable. These are called ''gems'' Some examples of valuable gem minerals are diamond, garnet, topaz, and zircon.
Some minerals, on the other hand, are found almost everywhere. The most common mineral is quartz. There are about 200 different kinds of quartz and it is found in almost every part of the earth.

WHAT IS EINSTEIN'S THEORY OF RELATIVITY

WHAT IS EINSTEIN'S THEORY OF RELATIVITY?
When this theory was first published, it was said that it could be understood by only a dozen or so scientists in the whole world! So obviously, we cannot even begin to try to explain it in any technical detail in this website. But it should be useful to have a general idea of what Einstein was dealing with, the problem he was concerned with.
Everybody knows from experience that all motion is ''relative.'' This means that it can only be measured in relation to something else. For example, you're sitting in a railroad train and you look out the window. As you see things moving by quickly, you know you're in motion. But ther's a man sitting opposite you, and relative to him you're not moving at all!
So the existence of motion can have meaning only when it is considered relative to something which is fixed. That's the first basic part of Einstein's theory. We may state it as: The motion of a body traveling at uniform speed through space cannot be detected by observation made on that body alone.
The second basic part of Einstein's theory said that the only absolute unchanging quantity in the universe was the speed of light. Now, we know this to be about 186,000 miles per second. But it is really a fantastic idea to be able to imagine that this cannot change. here is why this is so strange: If a car is going at 60 miles an hour, we mean that its speed, measured by a someone standing still, is 60 miles an hour, we mean that its speed, measured by a someone standing still, is 60 miles per hour. If itt passes a car traveling in the same direction at 40 miles per hour, it passes it at a speed of 20 miles per hour. And if the second car, instead of traveling in the same direction, were coming to meet it, they would pass each other at a speed of 100 miles per hour.
Now, according to Einstein, it the speed of a ray of light were measured in the same way ( for example, if we were racing in one direction and it was going the opposite way ), it wouldn't make any difference! That ray of light would still pass at about 186,000 miles per second. This is only the rough, general idea of what Einstein was dealing with in his theory of relativity.Among other things he deal with were mass and energy and how they can be transformed into each other.

WHAT IS ENERGY

WHAT IS ENERGY?
As you know from reading the news columns, the greatest goal of science today is to obtain energy from the atom to enable man to live a life of peace and plenty. The mere idea that this can be done is one of the greatest steps forward in the history of human thought!
Albert Einstein was the first man to set up a theory that measured matter in terms of energy. In other words, he showed that matter could be changed into energy. This changed our whole way of looking at the physical world.Matter became secondary; energy became the most important thing in the physical world.
What is energy? Energy is the ability to do work. Energy is that which stands back of forces, and makes the forces possible. Let's try to understand this by considering the automobile.
To make the motor go, a force must be used. Something must provide that force. That something is energy. Where does it come from? It comes from the petrol, and the energy is let loose by burning the petrol in the cylinder. This energy puts certain forces into operation, forces which produce motion through the gears and wheels of the car. The result is that the engine does work, and energy has made it possible.
There are two kinds of energy, potential and kinetic. Firest let's understand potential energy. In the case of petrol, the molecules are held together by electrical forces. Energy is stored in these molecules, potential energy. When the petrol explodes, that potential energy is used up.
Another example of potential enegy is a suspended weight. There is stored-up energy in the weight which we can release just by letting it drop.Water at the top of a falls or behind a dam also has potential energy is used up.
Now suppose the weight drops, or the water goes down over the falls. The mere fact that it is moving at a certain speed enables it to do work, and this energy is called ''kinetic energy.'' It is energy that is derived from the weight of a moving body and its speed. As a body falls, it loses potential energy and gains kinetic energy. But the amount gained is exactly equal to the amount lost. In fact, the total amount of energy in the universe is alwasys the same. We can't create it or destroy it. What we do, whether we use falling water, coal, or tha atom, is change it from one form to another.

Hedgehog

There are thought to be 16 different species of hedgehog found around the world although, oddly enough, there are no species of hedgehog that are native to Australia and no living species of hedgehog that are native to North America. The spikes of the hedgehog are hollow hairs that are made from the protein keratin (the same stuff that human hair and fingernails are made from), and unlike the spikes of the porcupine, the spikes of the hedgehog cannot be removed easily. The spikes of the hedgehog also differ from the spikes of the porcupine as the hedgehog spikes are not poisonous or barbed.
 
 

When baby hedgehogs get to a certain age, the young hedgehog will shed the softer baby spikes that are then replaced with the stronger and darker spikes of theadult hedgehog. Hedgehogs have also been known to shed a number of spikes when the hedgehog is under extreme stress or if the hedgehog is poorly.

Hercules beetle

There are thirteen known species of Hercules beetle found in the jungles of South America and the Hercules beetle was named for it's sheer size as some males have been known to reach nearly 7 inches in length. Although it is quite rare for these beetles to get quite so big, the average adult Hercules beetle is usually between four and fifteen centimetres long depending on the species. The most distinctive feature of the Hercules beetle has to be the enormous horn-like pincers which protrude from the forehead of the males. These horns can grow longer than the Hercules beetle's body and are mainly used for solving disputes with other male Hercules beetles. Female Hercules beetles do not have horns but their bodies are thought to be larger, but shorter than their male counterparts.

Hermit Crab

The hermit crab has a soft under-body which it protects by carrying a shell on its back. The shell of the hermit crab is not its own, but one that belonged to another animal. As hermit crabs grow, they continue to find larger shells to accomodate their increasing size. Hermit crabs are omnivorous animals that eat pretty much anything they can find in the surrounding water. Small fish and invertebrates including worms, are the most common prey for the hermit crab along with plankton and other food particles in the water.

Blue Heron

The great blue heron found inhabiting parts of North America and as far west as the Galapagos Islands is the largest species of heron in the world and can measure nearly a meter in height. The smallest species of heron in the world is the green heron measuring less than 50 cm tall. The green heron is most commonly found in North America and Central America, and occasionally in Hawaii. All 64 different species of heron are very similar in body shape but not in size and colour. All herons have long pointed beaks which helps them to grab fish out of the water, along with long necks and thin, long legs both of which are useful to the heron as it lives it's waterside lifestyle. Herons also have enormous wings that can be nearly double the size of the heron's body.

Highland cattle

Highland cattle originally come from Scotland. Highland cattle can now be found in Europe, North America and Australia, where the highland cattle are all commonly farmed for their meat but some people also use the long hair of the highland cattle. Highland cattle have adapted to living in such harsh terrains as highland cattle have a large, strong build and a thick double layer of long orange hair. Highland cattle also have two horns on the tops of their heads which the highland cattle use to dig through thick snow to find the vegetation that lies underneath and the highland cattle also use their horns in order to defend themselves from oncoming predators and other rival highland cattle.

WHY DO COWS GIVE MILK

WHY DO COWS GIVE MILK?
People have used milk for food from ancient times, and have developed certain animals to supply large amounts of milk. We depend on cows to supply most of our milk, but in Spain, for example, the sheep is one of the chief milk-producing animals.

Many desert tribes depend on the camel for milk, and in Egypt, they use water buffaloes. In Peru, the llama is a milk-producing animal. People in many countries use goat's milk.

Milk is the fluid secreted by the mammary glands of the animal are food for their young in the period immediately after birth. It takes the place of the blood which supplied the young with nutrition before it was born. In fact, it is exactly like blood, only without the red blood cells and the blood pigment.
The composition of milk varies quite a bit, depending on the species of the animal which produces it. But milk always contains fat, protein, carbohydrate, and minerals. Goat's milk, for instance, contains twice as much fat as cow's milk, and the milk of reindeer contains five times as much fat as cow's milk!
The milk of every animal also contains various salts according to the needs of its young. The more rapid the growth of the newborn, the more salts in the mother's milk. A cow doubles its original weight at birth in 47 days, but a human being does it in 180 days. That's why cow's milk is too rich in proteins and salts and must be diluted for feeding newborn children.

The milk produced by cows varies depending on many factors. One, of course, is the breed of cow and the constitution of the individual cow. Another is the time between milkings. The last milk to be drawn at each milking is richer in fat then the rest. So, if a cow has not been completely milked, it will probably have fatter milk next time.
Since green food is the main source of vitamins for the cow summer milk is usually richer than winter milk, when the cow can't walk about in the pasture. About 110 grams of food solids are contained in each litre of milk. The most important solids are the butterfat, the casein, the milk sugar, and the minerals.

WHAT IS THE FASTEST FOUR-LEGGED ANIMAL

WHAT IS THE FASTEST FOUR-LEGGED ANIMAL?
Man is very proud of his speed. After all, don't we zoom through space faster than sound itself can travel? Don't we fly across oceans in a few hours?
What man should really be proud of in these cases is his brain, which has enabled him to develop machines that can go at fantastic speeds. For when it comes to his body, he is very far indeed from being the speed champion among mammals. In fact, he ranks quite low.

Let's take a look at the speeds at which some four- legged creatures can travel. We must remember, however, that many animals capable of great speed cannot sustain this speed for a long time. Man himself, who can run 22 to 25 miles (35 to 40 kilometer) per hour, can hold this during a race such as a 200 metre dash, but not in a longer race! Also, these speeds are not scientifically exact. They are based on reports and observations which various people have made at different times. But they give you a pretty accurate idea of how animals compare in speed.

The champ of them all is the cheetah, a kind of leopard; it has reached 70 miles per hour! The black-buck comes next at 65 miles per hour. At about 60 miles per hour, we have the Mongolian gazelle and the Pronghorn antelope. Any of these animals mentioned would outdistance all other mammals is a race of over a mile or so.

The lion, surprisingly enough, can change after his enemy at a speed of 50 miles, but he can't keep it up. A deer which most of us consider a very fast animal, only goes at about 45 or 50 miles an hour, and that's about the speed of a race horse!

Another animal that is used in racing, the Greyhound, goes at about 35 to 40 miles- only a few miles faster than a grizzly bear! And an elephant has been known to make a dash at 25 miles an hour!

HOW WERE THE MOUNTAINS MADE

HOW WERE THE MOUNTAINS MADE?
Because mountains are so big and grand, man thinks of them as unchanging and everlasting.But Gelolgists,the scientists who study mountains,can prove that mountains do change, and that they are not everlasting.
Certain changes in the earth's surface produced the mountains , and they are constantly being destroyed and changed. Boulders are broken from mountain sides by freezing water; soil and rock particles are carried away by rainwash and streams.In time, even the highest mountains are changed to rolling hills or plains.

Geologists divide mountains into four classifications , according to how they are formed. All mountains, however , are the result of violent changes in the earth's surface, most of which happened millions of years ago.

Folded mountains were made of rock layers, squeezed by great pressure into large folds. In many places in such mountains , you can see the rock layers curving up and down in arches and dips, caused by the sqeezing and pressure on the earth's surface.The Appalachian Mountains and the Alps of Europe are examples of folded mountains.

In dome mountains, the rock layers were forced up to make great pressure from below the earth's surface, lifted these rock layers.The Black Hills of south Dakota are examples of dome mountians.
Block mountains are the result of breaks,or faults, int earth's crust.Huge parts of the earth's surface, entire ''blocks'' of rock, were raised up or tilted at one time. The Sierra Nevada Range of Clifonia is a block that is 400 miles long and 80 miles wide!
Volcanic mountains are built of lave,ash, and cinders poured out from within the earth. The usual volcano is cone-shaped with a large hole, or crater, at the top. Among the famous volcanic mountains are Mounts Ranier, Shasta, and Hood in the United States, Fujiyama in Japan , and Vesuvius in Italy.
Many mountain ranges have been formed by more than one of the ways described. In the Rockies are mountains made by folding, faulting, doming, and even erosion of lava!

WHAT IS THE JET STREAM

WHAT IS THE JET STREAM?
Nowadays, the word ''jet'' is very much in the news, and you might imagine that 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. Wings 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 region) we can say that, in general, cold air is transported from the poles toward the Equator, and warm air from the Equator toward the Poles. This flow doesn't take place in smooth surrents, 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 existance of semi-permanent.

WHERE DO MOST EARTHQUAKES OCCUR

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 region 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 contast, 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.

WHAT IS HUMIDITY

WHAT IS HUMIDITY?
If ou put a pitcher of ice water on a table and let it stand a while, what happens? Moisture gathers on the outside of the pitcher. Where does this moiture 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 th cold surface of the pitcher and thus became visible. But water capor in the air is in visible. 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 ''relative 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 wheter 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 evaporative power of the air depends on the temperature, and absolute humidity doen't indicate anything about the evaporative 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.

WHAT IS FOG

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

Off the coast of Newfoundland, which is one of the foggist parts of the world, fogs are formed by the passage of damp, warm air over the cold water flowing south from the 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 DO SNOWFLAKES HAVE SIX SIDES

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. In fact, you may ask why snow is white if it's just frozen water. Shouldn't in 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.

HOW DOES THE WEATHERMAN KNOW WHAT TO SAY

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 condenses 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 meteorological data weather forecasts are produced.
The maps which the weather experts srudy show them many things: places where the air pressure is equal,

WHY DO SUNSETS LOOK RED

WHY DO SUNSETS LOOK RED?

A beautiful red  sunset, the colors warm and glowing, is one of the loveliest sights we can imagine. And sometimes, when we look at it we might say, "see how red the sun is!"
But, of course, we know that the sun itself hasn't become red or changed in any way. It merely looks that way to us at that particular time of day. In fact, at that very moment people are looking at that same sun thousands of miles to the west and it doesn't look red to them at all.
What produces the colors of a sunset is the distance that the sunlight must travel through our atmosphere. the lower it is, the more of our earth's atmosphere does that light travel through.

But first, let's remind ourselves that sunlight is a mixture of light of all colors. Normally, this mixture of light appears as white to our eyes. But the atmosphere has molecules of air, dust, water vapor, and other impurities present in it. As the light passes through them, different colors are scattered by these particles. Now, it so happens our atmoshere scatters out violet, blue, and green light more than it does the reds and yellows. So when the sun is low, this scattering leaves more reds and yellows for us to see and we have a reddish sunset.
By the way, this scattering of light also explanis why the sky liiks blue, Violet and blue light have short waves and are scattered about 10 times more than red light waves by our atmoshere. This means that the red rays go straight through our atmosphere, while the blue waves don't come through directly but are scattered by the air, water, and dust particles. It is this scattered light that we see as the blue sky when we look up.

WHY DID ASTRONOMERS THINK THERE MIGHT BE LIFE ON MARS

WHY DID ASTRONOMERS THINK THERE MIGHT BE LIFE ON MARS?

As you know,scientists are now conducting all kinds of experiments to see if life can be found anywhere else in the universe.Naturally,it is easier to explore our own solar system for signs of life than it is to probe outer space.And one of the places where some scientists thought a form of life might have been found is the planet Mars.
Why did they pick Mars? Well, Mars is considered to be a sort of twin of our own planet earth. It is the next planet beyond the earth in distance from the sun.Mars is about half the diameter of the earth and it rotates arount the in just under two years.But Mars has a day that is almost equal in lenght to our day here on earth.
In observing Mars,astronomers have noticed certain things that indicate a form of life may be possible there.First of all,Mars seasons like the earth,In face,as the seasons change on Mars,there seem to be changes on its surface.The dark areas get stronger in the spring and summer,and the colour changes from bluish-green to yellow.Could this be vegetation?
Astronomers also believe that there is at least a small amount of water vapor in the atmosphere of Mars,and this would be helpful in supporting life.Then,too,in 1887 an Italian astronomer,Giovanni Schiaparelli,reported seeing marking on the surface of Mars that resembled canals."Could these have been built by Martians in order to carry water from the polar regions to desert areas?" scientists wondered.
In 1976 two American Viking space probes landed on the surface of Mars.The instuments in the space probes searche the surrounding soil for signs of life and radioed their results back to earth.These reults showes that either there are germs in the soil or that the soil is very unusual and not like that on earth.If life does exist on Mars it would be a very simple form of life.

WHY ARE THERE DIFFERENT KINDS OF CLOUDS

WHY ARE THERE DIFFERENT KINDS OF CLOUDS?
Here is how cloud are formed: Warm air,landen with moisture ,arises noto the sky.When it gets to a certain height,the warm air cools.At the cooler temperature it can no longer hold all its moisture in the form of water vapor.So the extra moisture changes into small drpos of water,or bits of ice,and this forms clouds.
No two clouds are exactly alike,and they are always changing their shape.The reason we have different types of clouds is that cloud formation takes place at different heights and temperatures.And clouds will be composed fo different particles.depending on their height and temperature.
The highest cloud are called "noctilucent" clouds.They may be up as high as 30 to 50 miles! The next highest are called"nacreous," or "mother-of-pearl" clouds.They're 12 to 18 miles high.They are very thin,beautifully coloured clouds composed of dust or water drops,and they are seen only after sunest,at night,or before sunrise.
The next highest clouds,which are five or more miles above the earth,are called"cirrus" clouds,"cirrostratus" clouds, and "cirrocumulus" clouds.The cirrus are feathery and threadlike, the cirrostratus are thin, whitish sheets, and the cirrocumulus are small,round clouds which form "mackerel" patterns in the sky. All these clouds are made of tiny bits of ice.
Lower clouds are made of little drops of water,The highest of these,the altocumulus clouds,are about two to four miles abouve the earth,and are levels are the altostratus clouds,which often cover the whole sky with a greyish veil through which the sun and moon whine as spots of pale light.
Lower still,about a mile high,are the stratocumulus clouds,large and lumpy.At the same level are the rain clouds,the nimbostratus,thick,dark,and shapeless.Very low,less than 610 metres above the ground,are the stratus clouds,which are sheets of high fog.Two other kinds of clouds,the cumulus and the cumulonimbus,are the big,fat, "cauliflower" clouds that bring thunder and stroms.

WHAT IS NEBULA

WHAT IS NEBULA?
If you have seen pictures of nebulae in books,great spirals and whirlpools and clouds-don't expect to find anything like that in the sky.Most of the nebulae are so faint that they cannot be seen without a telescope.The word"nebulae," by the way, is really the Latin word for "mists" because they looked like mists when first observed through small telescopes.
There are two chief classes of nebulae,the galctic and the extragalactic.The galactic nebulae are found in our own galaxy (the Milky Way) and are composed of dust and gas.Since "extra" means "outside," the extra-galactic nebulae are outside our own galaxy. They are made up largely of stars.
The galactic nebulae number less than 2,000. This means that most of the nebulae known to man are outside our own galaxy.How many are there? For all we know,there may be millions of them out there in the vast space beyond the Milky Way.
The extragalactic nebulae are sometimes called "island universes" or "galaxies." This means that if someone were looking at our own galaxy from out there he might well see it as nebula.
The extragalactic nebulae have various forms.Some are irregular or elliptical.The most numerous are the spirals,THe spirals,like our own galaxy,are made up of a large number of stars.big gaseous clouds, and vast tracts of dust.These nebulae usually have a nucleus in the center and from this, arms extend in spiral fashion.The spiral nebula Andromeda is the nearest to earth and the largest and brightest nebula known.It gives out about 1,500,000,000 times as much light as our sun!

WHICH IS THE DEEPEST OCEAN

WHICH IS THE DEEPEST OCEAN?
In many ways, the oceans still remain a great mystery to us.We don't even know how old the oceans are.It seems certain that in the first stages of the earth's growht no oceans existed.
Today, man is exploring the bottoms of the oceans to learn more about them.Covering the floor of the ocean to a depth of 3.660 metres  is a soft,oozy mud.It is made up of the limy skeltons of tiny sea animals.The floor of the deep,dark regions of the sea,where the water is more than four miles of tiny deep is covered by a fine,rusty coloured ooze called "red clay." It is made up of tiny parts of skeltons of animals,the coverings of tiny plants, and volcanic ash.
The way the depth of oceans is measured today is by sending down sound waves whch are reflected back from the bottom.The depth is found by measuring the time it takes for the sound wave to make the round trip and dividing this time in half.
Based on these measurements,we have a pretty good idea of the average depth of various oceans, and also the deepest point in each one.The ocean which has the greatest average depth is the Pacific Ocean.This is 4,281 metres,Next in average depth is the Indian ocean which has an average of 3.963.The Atlantic is third with an average depth of 3,926 metres.The Baltic Sea is at the other extreme, with an average depth of only 55 metres!
The single deepest spot so far known is in the Pacific near Guam,with a depth of 10,790 metres.The next deepest spot is in the Atlantic off Puerto Rico where it measures 9,219.Hundson Bay,which is larger than many seas,has its deepest point at only 183 metres!

WHY DOES WATER FLOW OUT OF A SPRING

WHY DOES WATER FLOW OUT OF A SPRING?
All the water that flows out of every spring once fell as rain.The rain water soaks into the soil and enters into rocks through cracks.Of course,much of the rain water remains near the surface and evaporates into the air,or plants absorb it through their roots.
The rest of the rain water is drawn downward by gravity,and it goes as far down as the openings in the rocks will allow.Below the surface of the land,but at a different depth in each place,there is a zone where all the openings in the rocks are completely filled with water.This is called "the ground water zone." The upper surface of this water is called "the water table."
A spring occurs when water finds a natural opening in the ground that is below the water table.That's why most springs are in valleys or low places.The ground water escapes as spring water through the cracks in the rocks along the sides or bottoms of these low places.A spring doesn't defy gravity; it is always flowing down from some water level above it.
Some springs receive water from deep within the water zone.These usually flow all year and are called "permanent" springs. Other springs have their openings near the water table.They usually flow only in the rainy season when the water table is at its highest.These are called "intermittent" springs.
Since all spring water passes through rocks during its underground travels, all spring water carries some mineral matter, such as sulphur or lime. Springs that have water containing an unusual amount of mineral matter are called "mineral" springs.
In some places,especially in areas where there have been volcanoes, the water in springs has been in contact with hot,underground rocks.This type of spring is called a "thermal'' or ''hot'' spring.
An artesian well is quite different from a spring. In an artesian well,the rain water sinks down into the ground until it reaches a layer of porous rock or sand that is buried between two layers of solid rock. Pressure is built up around this water,and when a hole is bored down to reach it, the water escapes with a gush. The well must be driven at a point lower than that at which the water enters the ground.

HOW WERE THE MOUNTAINS MADE

HOW WERE THE MOUNTAINS MADE?
Because mountains are so big and grand, man thinks of them as unchanging and everlasting.But Gelolgists,the scientists who study mountains,can prove that mountains do change, and that they are not everlasting.
Certain changes in the earth's surface produced the mountains , and they are constantly being destroyed and changed. Boulders are broken from mountain sides by freezing water; soil and rock particles are carried away by rainwash and streams.In time, even the highest mountains are changed to rolling hills or plains.
Geologists divide mountains into four classifications , according to how they are formed. All mountains, however , are the result of violent changes in the earth's surface, most of which happened millions of years ago.
Folded mountains were made of rock layers, squeezed by great pressure into large folds. In many places in such mountains , you can see the rock layers curving up and down in arches and dips, caused by the sqeezing and pressure on the earth's surface.The Appalachian Mountains and the Alps of Europe are examples of folded mountains.
In dome mountains, the rock layers were forced up to make great pressure from below the earth's surface, lifted these rock layers.The Black Hills of south Dakota are examples of dome mountians.
Block mountains are the result of breaks,or faults, int earth's crust.Huge parts of the earth's surface, entire ''blocks'' of rock, were raised up or tilted at one time. The Sierra Nevada Range of Clifonia is a block that is 400 miles long and 80 miles wide!
Volcanic mountains are built of lave,ash, and cinders poured out from within the earth. The usual volcano is cone-shaped with a large hole, or crater, at the top. Among the famous volcanic mountains are Mounts Ranier, Shasta, and Hood in the United States, Fujiyama in Japan , and Vesuvius in Italy.
Many mountain ranges have been formed by more than one of the ways described. In the Rockies are mountains made by folding, faulting, doming, and even erosion of lava!

WHAT ARE FOSSILS

                                                         WHAT ARE FOSSILS?
The study of fossils is so important in helping man learn about his own past and that of animals who lived millons of years ago that it has developed into a separate science called ''palenontology''.
Fossils are not, as some people think, the remains of bodies buried ages ago. Actually, there are three diffenent kinds of fossils. The first is part of the actual body of the organism, which has been preserved from decay, and which appears just as it was originally.But fossils may also be just the cast or mold of the shape of the body, which remains after the body of the plant or animal has been removed,And fossils may merely be the footprints or trails that animals have left as they moved over the soft muds or clays.
When a fossil is found that consists  of part of the organism itself, it is usually only the hard parts, such as shells or skeletons, that are preserved.The spfter parts are destroyed by decay. Yet, in some cases, even such soft-bodied animals as jellyfish, which are 99 percent water, have left perfect fossils of themslves in rocks! And certain fossils found encased in ice not only have the skeleton preserved but also the flesh and skin on the bones.
Fossils have nothing to do with size. For instance, the fossils of tiny ants which lived millions of years ago can be found perfectly preserved in amber. The chances for animals being preserved as fossils depend mostly on where they lived. The most numerous of all fossils are water animals vecause when the die their bodies are quickly covered over by mud and so kept from decaying. Land animals and plants are exposed to the destroying action of the air and weather.
It is chiefly through the study of fossils that we know about animal life as it existed millions and hundreds of millions of years ago. For example, fossils taken from certain rocks tell us that millions of years ago there was an age of Reptiles,with monsters so huge that they were 24 metres long and weighed 36 tonnes. These were the dinosaurs. And our entire knowledge about the earliest bird, called ''the archaeopteryx,'' is based on just two fossils of it that have been found!