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!