Why do the Eyes of Some Animals Shine in the Dark?

            Have you ever seen a cat sitting in the dark? Though its body may not be visible, its yellow eyes shine in the darkness. The eyes of many other animals like tiger, leopard, and lion also shine in the night, just like the eyes of a cat.

Eyes of cats, tigers, lions, leopards, etc.,shine in the night

            The eyes of these animals have a thin layer of a special crystalline substance, which reflects the light falling on it. This reflected light is the cause of the shine. In the night, even the smallest amount of light falling on this crystalline surface gets reflected and thus eyes who can see things clearly in darkness are called nocturnal animal.

            Studies made on cats have shown that behind the retina of eyes, there is a crystalline layer called the luminous tape turn, which reflects light. Due to this layer, a cat can see clearly in dim light ad its eyes shine in the dark when light is directed on them. Many animals do not have this crystalline layer; hence their eyes do not shine in the dark.

            It has been observed that the color of the shine varies in different animals. It depends upon the number of blood vessels present in their eyes. If the number of blood vessels is large, the color of the sine is red and if the number of blood vessels is less, the color of the shine is white or pale yellow.

Do Plants Move?

            One of the fundamental difference between plants and animals is that animals can move form one place to another, whereas plants lack mobility. But this is not true of all kinds of plants, because there are some plants which move on their own. For example, slime moulds have amoeba-like movement by which they move from one place to another. Some types of algae have whip-like flagella, which they use to paddle themselves through water.

Certain lower plants are capable of moving

            Many plants, particularly, the lower ones, produce mobile male gametes that swim about in order to find eggs to fertilize. Euglena is a protozoan, which is capable of swimming. A part from these exceptions, the movement of plants is usually confined to the movement of some parts of it while the plant itself remains fixed at one place.

            There are three basic types of plant movements-tropisms, nutations and nastic movements.

            A tropism is a growth response towards or away from something caused by a specific environmental stimulus. The direction of growth is determined by the stimulus, it is called positive tropism and when away from the stimulus, it is known as negative tropism.

            Tropisms are caused by special growth hormones called auxins. In most of the cases, the stimulus causes the auxins to accumulate on one side of an affected organ. This causes the cells on that side to grow and divide more quickly than the cells on the other side. As a result, the organ moves away from the side with the maximum auxins.

            There are several types of tropism phototropism is a growth response to the stimulus of light. Auxins are concentrated on the side away from the light. This causes stems and leaves to grow towards light and roots to grow away from light. Geotropism is the growth due to the Earth’s gravity. Roots show positive geotropism, while stems show negative geotropism. Similarly, hydrotropism is the growth response of a plant to the stimulus of water. Roots grow towards water and often cover great distances to reach areas of moist soil.

            Nutation is the spiral movement exhibited by the tips of certain stems during growth which enables a climbing plant to find a suitable support.

            Nastic movement is caused b an external stimulus, such as light or temperature, but the movement is independent of the source. This movement is neither towards nor away forms a stimulus. For example, some flowers open in daylight and close at night. You must have noticed the leaves of touch-me-not (mimosa pudica) dropping when touched by hand or stick or when an insect sits on it. This is also an example of nastic movement.

What is Regeneration?

            Would it not be wonderful if people who lost an arm or a leg or even a finger in an accident could simply grow another one in its place? But this does not happen in case of human beings. However, you will be surprised to know that there is some living beings in which a new limb develops at the same point from where the original limb has been lost. Development of a new body part in place of a lost one is known as regeneration.

Starfish

            If one arm of a starfish is cut off or destroyed, it is regenerated. Hydra, lizards, sponges, newts and earth worms also possess this capability of regeneration. If the tail of a lizard is cut, a new tale develops there.

            The ability of regeneration varies in different creatures. Living beings with complicated structures have lesser ability of regeneration. Man and other mammals have a complex constitution. That is why they have lesser ability of regeneration. Mammals can replace hair, nails and skin. They can also repair broken bones and other damaged tissues. In some species, new tissues grow from the surface of the wound replacing the damaged tissues. Sometimes, the tissues that an organism regenerates are different form the original ones. The regenerated structure may be smaller and weaker than the original one.

Do Ants Too have Their Kingdoms?

Ants are insects that belong to the Hymenoptera order. Scientists have studied more than two thousand species of ants that exist all over the world. Most ants are no bigger than an inch.

            Ants are social animals and have their own kingdoms, which mean that they live together in large colonies or groups. Some colonies may contain over millions of ants. Most colonies make nests in the ground or in dead trees. There are three kinds of ants in each colony-----egg-laying queens, males who don to work and a corp of female workers. An ant colony contains many cells or lives in one and lays eggs in another. Next door is the hatching room, where the grubs turn into pupa and are carried into another room to develop. There are chambers for storing food also. An ant colony may contain several queens, each with its own suite of rooms. Worker ants collect food, feed the young ants and build the nest. Some species of ants also have female soldier ants. They protect the nest.

            Army ants are a type of ants found in the tropical jungles. Thousands of them march in a narrow band to a different place every day, and eat any animal that comes in their way. They eat away the flesh off the bones of dead animal very quickly.

            Ants have the capacity to do many things. They are able to travel long distances away from their nest and find their way back, because they follow their own chemical trails. Ants are very strong. They can lift things that weigh 50 times more than their own body weight.

How does an Owl See Clearly at Night?

Have you ever seen an owl in daytime? An owl is a nocturnal bird of prey; no wonder we rarely see it during the daytime. In fact, owls come to life at night and are an apt example of nocturnal birds. Birds which can see better at night than during the day are known as nocturnal birds.

            On the other hand, birds that can see better during the day than in the night are called diurnal.

            About 130 species of owls are found around the world. In some countries, they are treated as auspicious birds, while in others they are regarded as symbols of wealth and wisdom. An owl has a large head and equally big eyes, short neck, broad wings and sharp claws.

            What is peculiar about owls is that they can see more clearly at night than during the day and have an exceptionally good hearing power.

            You must be very curious as to how nocturnal birds in general and owls in particular can see so clearly at night.

            To understand this, it is essential to know how human beings see things. Light scattered by an object is focused on to the retina of our eyes by the lenses inside the eyes.

            An inverted image of the object is formed on the retina, which is carried to the brain by optic nerves. The brain inverts this upside- down image, and thus we see the object as true object.

            The owl’s eyes are large, forward pointing and have four special features due to which it can see more clearly at night.

            Firstly, the distance between the les of its eye and the retina is more than the distance in case of the human eyes. Due to this, the image formed on the retina is bigger in size.

            Secondly, the number of rods ad cones special cells which help in clarity of vision in the owl’s retina is very large---almost 10,000 per square millimeter compared to 2,000 per square millimeter in our eyes. Thus, the owl can see five times more than us.

            Thirdly, its eyes have a red—colored material, chemically a protein, which makes its eyes more sensitive to light.

            Fourthly, the pupils of its eyes can dilate more, thus allowing even the smallest amount of light to enter the eyes. Because of these four factors, an owl can see more clearly in darkness. Due to the extreme sensitivity of its eyes to light, objects appears too bright and uncomfortable to it in the day light. Surprisingly enough, an owl can rotate its head by 180 degrees, i.e., it can turn its head to see at what is at the back of its head.

What is the Principle on Which an Autopilot Works?

           Can an aircraft fly on its own while the pilot takes his hands off the controls and rests? Today it is possible, and most modern aircraft have autopilots. It is a device operated b a computer that takes over the controls of the aircraft and guides it. An aircraft can fly without the pilot touching the controls. These autopilots can even control takeoffs and landings.

            The principles on which an autopilots works is similar to the automatic steering system of ships, but here three gyroscopic sensors and their associated equipment are used to control the three variables in an aircraft that help it move.

            An aircraft with autopilot has the following parts:

            1. Ailerons control rolls  2. Elevators controls pitch   3. Rudder controls yaw    4. Gyroscopic altitude sensors   5. Computer    6. Radio or radar receiver      7. Servo motor rubber

            These three variables are yaw, pitch and roll. The complex autopilot system uses an onboard computer, which activates servomotors for introducing necessary corrections. A radio or radar link between the computer and the ground controls at the airport assists the aircrafts in takeoffs and landings.

Why do We Wear Seat Belts in a Car?

            It has become compulsory for everyone to fasten seat belts while traveling in a car, in most cities of India. According to this rule, if the front seat passenger or driver is found without a fastened seat belt, a penalty has to be paid. It is a new rule I India, but this rule has been existing in the developed countries since long. Do you know why we have to wear seat belts?

Seat Belt

            Seat belts are a very important safety device for a car driver as well s for the person sitting on the front set. If your car stops suddenly or hits another car, the belts hold you in your seat and help to protect you against serious injuries. Let us take a situation in which two cars are moving at 60 kilometers per hour. If these cars hit each other, the force of collision will be 120 kilometers per hour. In such a case, if you are wearing a set belt, you will not be throwing against the windscreen. The belt will hold you in your place. You must just experience a jerk.

            On the other hand, if you have not fastened the seat belt, you could be hurled through the windscreen. As a result, your face might get cut badly. It is also possible that you are thrown out of the car onto the road, and suffer serious injuries. As a driver, without a seat belt, you could also crash into the steering wheel.

            Seat belts have saved many lives all over the world. Nowadays, belts for rear-set passengers are also becoming mandatory.

What is a Cable Car?

            Have you ever traveled in a cable car? A cable car is a cabin hung from cable slung between towers. Cableways are usually made in hilly terrain across steep cliffs where roads are difficult to make our traveling takes a long time. They are also called ropeways. These are very common in Switzerland. You can see ropeways in India, (Haridwar and Mussoorie).

Cable Car

            Most cable cars run in pairs in such a way that the power needed to make one work is used by the other. Besides, counterbalancing is also achieved. This is known as funicular system. Each cable car hung’s forma steel suspension cable by means of a metal frame. The metal frame has grooved wheels that rest on the cable.

            A haulage cable pulls each car along. This cable is fixed to the cars and looped around a drum at the top of the cableway. An electric motor at the top hauls the cable to one side and pulls it out on the other, so that as one car goes up another comes down.

            Brakes may act on a third cable to stop the car. The journey by cable car offers a beautiful bird’s eye view of the landscape below.

How does a Jet Engine Work?

            A jet engine works on the principle of Newton’s third law of motion, that is, every action has an equal and opposite reaction. Its working can be compared to the action of a boat in which the boatman pushes the water back with his oar, thereby getting a forward thrust which moves the boat forward.

A Jet Engine

            In simple words, according to Newton’s law, the action of pushing the water backwards produces the opposite reaction of the forward movement of the boat. Similarly, a jet engine ejects pushes backward gases to the rear at a high speed, and the resulting opposite reaction gives a forward motion to the aircraft. But how is this gas produced and how is it released with such a great force?

            Jet engines burn fuel to make hot gases. The hot gases blast out form the rear nozzle at high speed, thus pushing the engine forward at an equal speed.

            All jet engines have means of injecting fuel into the combustion chamber. There the burnt fuel produces a great amount of hot gases. It is like an explosion. These hot gases are released from the rear of the engine with great force, which pushes the engine forward. As the engines are fixed to the aircraft, the entire aircraft moves forward. This forward force is called thrust.

            The forward thrust is similar to the motion of an air-filled balloon when the air form it is released suddenly. The balloon moves in the direction, opposite to that of the nozzle from which the air escapes. The force or thrust of air is responsible for pushing the balloon in the opposite direction.

            Rockets also work on the same principle. The main difference between jets and rockets is the source of oxygen. A jet engine takes oxygen form the air through intake nozzles, but a rocket carries its own oxygen supply in the far of liquid oxygen in tank or in the form of solid fuel. Jet engines have compressors to compress the sucked in air before it is mixed with the fuel and burnt in the combustion helps to increase the force of explosion in the engine, thereby producing greater thrust.

How do Planes Take Off and Land Vertically?

            One of the most exciting developments in aircraft technology has been the VTOL aircraft. VTOL means vertical take off and landing planes. The most successful aircraft of this type has been the British made harrier jump jet.

Airplane Take Off 

            Normal twin-jet aircraft have the jet engines fixed horizontally at the sides of the aircraft, or to the wings. Single jet engine aircraft have the engine built into the fuselage of the aircraft. In both, air is sucked in form the front, mixed with fuel in the compression chamber and the exhaust gases are ejected from the rear, thrusting the plane forward. VTOL planes make use of the same process, but their jet engines can be temporarily re-positioned vertically. The exhaust is directed downwards and the resultant thrust is directed upwards.

            Normally the same engines that produce lift are used to propel the aircraft forward. This is done by realigning the engines angle of tilt.

            VTOL aircraft are used mainly for military purposes. Very powerful engines are required for vertical take off, and therefore they produce a lot of noise. Some types of VTOL planes have separate engines to provide lift and for forward propulsion.

            These aircraft do not need long runways for takeoff and landing. They need a small piece of level ground or deck space on an aircraft carrier not much longer than its own length, and once it is in the air, it can fly at supersonic speeds. Since their wings can usually be folded when in storage, they are ideal for use on aircraft carriers where space is limited, and are perfect for reconnaissance or attack roles, as evidenced in their use by the USA in operation Iraqi freedom.

Can We Measure Intelligence?

Most scientists define intelligence as the ability of learn, understand and analyze things, accompanied by a good memory and imagination. This implies that intelligence is a mixture of several abilities. We know that intelligence levels differ form person to person depending upon the aforesaid traits.

            Today, neither has the above definition of intelligence been universally accepted nor do the various tests to measure it, have a common appeal. In spite of the difficulties, there is one method widely used to measure intelligence-the intelligence Quotient (IQ) test.

            IQ is the abbreviation of psychological phenomenon called intelligence quotient. It is expressed as a number. The IQ of an individual is obtained by dividing his mental age – it is determined by the performance on a standardized intelligence test – by his chronological age, and multiplying the result by 100.

The formal is: IQ = mental age/ real age *100

            The mental age of an individual is determined with the help of different tests. Persons are classified under different categories depending on their IQ scores. The following table shows a generally accepted classification of different categories of people in relation to their IQ scores.

Classification table

IQ range                                            category

140 or above                                     genius

                                                            Gifted

                                                            Very intelligent

70 to 140                                            bright averages

                                                            Average intelligence

Below 69 to 139                                mentally retarded

            At one time, many psychologists believed that everyone had some degree of inborn intelligence. It was also believed that intelligence was a natural trait like blue eyes, sharp nose, etc., and could be ascertained in a single test. But a French psychologist, Alfred Binet, exploded this myth. He developed a test that helped distinguish between intelligent and dull children. His first tests were tried on some French school children in 1905. Later in 1915, a German psychologist William Stern and a US psychologist Lewis Terman adopted these tests.

            Many psychologists believe that these intelligence tests are not the rue indicators of one’s intelligence level and do not give a complete picture of the factors that make up intelligence. For example, some tests measure what one has learnt but not how quickly one has learnt. We know that the grasping power among different people is different. They differ in their ability to understand and remember ideas. They also differ in the use of their knowledge and earlier experiences to solve problems. Hence, till today there is no fully accepted definition of intelligence.

            It has been, however, concluded that intelligence mainly depends on heredity and the environment. Every person is born with certain mental abilities. The development of that ability may be activated or slowed down by his or her background. The socialization process, which includes the environment, plays an important role in shaping one’s intelligence. A child becomes a quick learner in areas which he experiences and observers in his day-to-day life. A child who is constantly ridiculed or beaten up may develop a complex due to which he may not be able to develop his intellectual abilities fully. Many children who face discrimination because of race or physical defects fail to develop their mental abilities. Form these facts; it is clear hat intelligence is not a natural trait like blue eyes. There is not a single trait that can be called intelligence, nor any single factor which determines it.

Where is the Alhambra?

            The Alhambra is a palace and fortress at Granada in Spain overlooking the river Darro. It stands on hill below the Sierra Nevada Mountains. It was built by the moors-the Muslim kings who occupied Spain in the middle ages. The moors were the inhabitants of Mauretania, an African province of the Roman Empire. Today, it is known as Morocco. The construction of Alhambra began in 1248 and was completed in 1354.

The Alhanbra

            In Arabic, the word Alhambra means the red castle. It is probably derived from the color of the bricks of which the outer walls are built. The palace was built during the reigns of Al Ahmar and his successors. The outer wall and its 13 towers enclose the palace and the gardens. Its lace-like molding on walls and ceilings contain words from the Koran, the holy book of Islam.

            After 1492, when the moors were driven out, much of the interior was spoiled and the furniture ruined. King Charles V, who ruled again form 1516 to 1556, rebuilt portions of it in the renaissance style and destroyed part of the Alhambra to build and Italianate palace designed by Pedro de Manchaca in 1526. In 1812, the French blew some of the towers up during the Napoleonic wars, and in 1821 an earth quake caused further damage. The restoration of the building was again undertaken in 1828 and continues till today.

            The principal courts of the palace include the court of the myrtles and the court of the lions. The latter has been named because in the centre is a fountain of lions- an alabaster basin supported by twelve white marble lions-emblems of strength and courage. The most important parts of the Alhambra are the ‘Hall of Ambassadors’, an exceptionally grand reception room, and the ‘Hall of the Two Sisters’ with its outstanding example of stalactite work.

            Of the outlying buildings, the most important is the genera life. The villa probably dates back to the end of the 13^th century.

Why do Formed Moving Wheels of Cars in Movies Sometimes Appear to Turn Backwards?

             Have you ever taken care to notice the rotation of wheels? While seeing a movie or a television, you my notice that the wheels of speeding automobiles sometimes appear turning backwards. Do you know why forward moving wheels appear to be moving backwards?

Wheels of cars in movies sometimes appear turning backwards

            To understand this strange  optical effect, you have to understand the basic underlying principle of the motion picture. The film projected on the screen consists of a series of individual pictures. These pictures are joined together in such a manner that you can see them one after another in rapid succession. But there is a very small time, a fraction of a second, between each frame of picture when the screen is completely dark. Usually 32 pictures are shown on the screen per second, and they appear continuous because the impression of an image lasts for 1/16^th of a second on the retina of our eye. This phenomenon of the image remaining on the retina for 1/16^th of a second is called persistence of vision. Modern movies are shot at 24 frames per second to make the individual images blend smoothly into one another, when viewed.

            In the case of moving wheels, each individual picture shows the automobile moving along the road. However, if the wheel does not make a complete turn form one still picture to the next, it appears as if the wheel is moving backwards. For example, if we watch the top edge of the wheel in one picture, and if the edge does not make a complete turn in the next picture, but instead completes three-fourth of a turn, it looks as if the wheel turned one-fourth backward. Now in the third picture, with the wheel making only three-fourth of a turn, the top edge visible in the first picture is directly at the bottom. Again it appears, as if the wheel has turned one-fourth backwards. Thus the automobile continues moving forward and wheels continue to appear to be moving backwards. This is called the stroboscopic effect. This is nothing but an optical illusion.

What was the Stone Age?

            The Stone Age probably began more than three million years ago. It faded away some 5000 years ago and was followed by the Bronze Age. This period has been described as the landmark in the human history when man learned to make and use stone tools. This was followed by the metal age when man learnt the use of metals. Use of metals marks the end of Stone Age.

Stone Age Man and Woman

            The stone age has bee divided into three periods- the Paleolithic or old stone age, the Mesolithic or middle stone age and the Neolithic or new stone age.

            The Paleolithic or the Old Stone Age began with the appearances of the first hominids or man-like forms such as the australopithecines. The Paleolithic men were all hunters. Their tools were crude and made by flaking stones. The oldest Paleolithic tools are about 2,500,000 years old. It is likely, that apart form the stone tools, and the earliest hominids also used tools fabricated form wood and bones. The Pleistocene epoch began about 2,500,000 years ago and lasted until about 10,000 years ago during the latter part of the Old Stone Age; people learned the art of making paintings on cave walls. They had also learned the art of sculpture.

            The Mesolithic period or the middle Stone Age usually refers to that period when certain advancement started in about 8000 B.C in north-western Europe. It lasted until about 2700 B.C. during this period, better stone tools were made. The hunters used tiny flakes of flint in arrows and harpoons.

            During the Neolithic or new Stone Age, farming and the manufacture of pottery were widespread in Europe. The new Stone Age began in the Middle East about 9000 years ago. The people in the new Stone Age manufactured smooth axe heads of ground stone as they learned to grind ad polish stones. The domestication of animals was an important factor in Neolithic life as was agriculture.

            This was the period when mining also came to be practiced. By this time, agriculture had started and the people started making villages. The Stone Age ended when people learned the use of metals.

            When the Europeans discovered America, most of Native Americans red Indians were living in a Neolithic age. Some Australian aborigines and tribes in New Guinea and on some of the Andaman Islands still lead a Stone Age life.

Why Egypt is Called the Gift of the Nile?

            Do you know which the longest river of the world is? It is none other that the river Nile of Africa. The river Nile is considered the life of Egypt and Sudan. It flows for 4145 miles 6671 kilometers through north east Africa. It flows from the mountains of Tanganyika to the Mediterranean Sea.

The Nile River

            Egypt is called the gift of the Nile because the valley of Nile is extremely fertile mainly due to the yearly floods and it was this fertility that made its ancient people prosperous and helped them survive calamities. Had it not been for the Nile, Egypt would have bee a barren land many years ago.

            The ancient religion of the Egyptians was based on the Nile, and the lives of the ancient Egyptians centered on the river. It is on the banks of this river that one of the oldest civilizations of the world flourished. This ancient Nile valley civilization goes back to more than 5000 B.C. the headwater lakes-Victoria, Albert and Edward- are in the tropical country, south of the equator.

            Most of the rain there falls during the winter months. The great lakes hold this water and feed it into the Nile gradually during the entire year.

            The Blue Nile and Atbara are the rivers that mainly cause floods. Humus and mud are distributed by the flood waters along the banks of the lower Nile. So the land regains a green oasis that would have been a desert otherwise.

            Did you know that 95% of Egypt’s population lives along the bank of river Nile, which is less than one-thirteenths of Egypt’s entire land? The construction of the Aswan high dam has made the Nile more useful. The dam regulates the floodwaters, generates hydroelectric power and irrigates thousands of acres of formerly unproductive land.

            Lake Victoria ranks as the Nile’s largest source. The river sabot along with others flows into the Nile and increases its volume considerably. From here onwards, it is called the White Nile. The Blue Nile is the longest tributary of the Nile and has its source in Ethiopia like Lake Tana. At Khartoum, the blue and white Nile comes together.

            There are six navigable cataracts between this place and the sea. In Sudan, the cataracts are used to produce an enormous quantity of electricity. They are circumnavigated by waterways.

            The two very big dams built on the Nile, and the cataracts are the main source of a large part of Egypt’s electric power.

How was the Grand Canyon Formed?

            The Grand Canyon in Arizona, USA, is a natural wonder of the world. It is famous all over for its colorful rocks ad majestic spectacle. At certain points, it appears like a magic city of rocks, with temples, towers and castles of dazzling colors. Do you know how this great wonder was formed?

Grand Canyon

            The Grand Canyon was formed by the continuous erosion of the Colorado River valley. The mighty force of Colorado River cut out this great gorge over thousands of years ago. Even now, year after year, the rushing waters of the Colorado River continue to cut deeper into the bottom of the gorge. This is the deepest gorge in the world.

            The Grand Canyon is about 347.2 kilometers long, and extends up to 20 kilometers wide and its depth is 2 kilometers at places.

            For years, the Colorado River has slowly cut through the high plateaus of northern Arizona, exposing strata of earth that are millions of years old. These strata re of great interest to geologists, because they offer an insight into a long stretch of earth’s history.

            At the bottom of the canyon, where the Colorado River flows, is an ancient Precambrian rock that contains fossils of primitive algae. The fossils of dinosaurs, elephants, trees and other organisms of those times are found in the higher strata. The most recent rocks occur at the top of the canyon. The chain of links of the fossils provides an idea about the evolutionary process.

            Each year, more than 2 million tourists visit the grand canon to see this wonderful place. In 1919, the United States government created the grand canon national park, to preserve the wealth of the plant and animal life that has become a part of this unique environment.

What is Ozone Gas?

            You may have often heard about the ozone layer depletion but do you know what ozone is? Ozone is a allotrope of oxygen gas in which each molecule contains three atoms of oxygen with its chemical formula O3. The three atoms are arranged in a triangular shape. Although the molecule of ozone contain only oxygen atoms, their number and arrangement differ form those of oxygen gas.

Ozone layer protects life on Earth from harmful ultraviolet rays

            Ozone is light blue in color and as a pungent smell. The characteristic smell can be experienced near running electric motors. It is poisonous gas, differing considerably from oxygen in its chemical properties. It is found in the atmosphere in very small quantities, the highest concentration being at high attitudes where it is formed by the reaction of ultraviolet rays on oxygen.

            Ozone can be obtained artificially by passing ordinary oxygen through a tube where it is subjected to a silent electrical discharge. The electrodes are covered with insulating materials glass or mica so that the discharge currents are kept low, and high voltage pulses are supplied between the electrodes. This method is used so that oxygen acquires the energy it needs to form ozone but it ensure that at the same time ozone does not become hot enough to enable the molecule to break up into ordinary oxygen.

            Ozone is a very powerful oxidizing agent. It is used to sterilize water, to purify air, to decolorize foods, and act bleach. Its ozonide-forming property is used in several industrial processes in the manufacture of drugs and in plasticizing materials.

            An ozone layer in the atmosphere absorbs much of the sun’s harmful ultraviolet rays and consequently saves the animal and plant life of earth. This is due to the fact that the ultraviolet rays spoil the vegetation and cause diseases like cataract and skin cancer.

            Depletion of ozone layer in the atmosphere may also lead to variations in global rainfall, ecological disturbances and dwindling of global food supplies. The discovery of holes in the ozone layer has created a great concern among the scientists.

            Depletion of ozone is cased by CFCs (chloro fluoro carbons), which are liberated from refrigerators, fire extinguishers and aerosol sprayers. A global measure to eliminate the use of CFCs is currently afoot by banning these propellant gases for other harmless ones.

How did the use of Christmas Trees Begin?

            What are the first two things that come into your mind when you think of Christmas? I’m sure it is –Santa Claus and the Christmas tree. Do you know when and how the use of the Christmas tree began?

Christmas Tree

            The Christmas tree is an evergreen tree, usually, a balsam or Douglas fir, decorated with lights, tinsels and festoons as a part of Christmas festivities. The Christmas tree has its roots in the customs of ancient Egyptians, Chinese and Hebrews who treated the wraths and garlands of evergreen trees as a symbol of eternal life. The Romans draped their temples with green branches of trees. Tree worship, common among the pagan Europeans, survived even after their conversion to Christianity. These included the customs of decorating their housed in the New Year to scare away the devil and to set up a tree for the birds flying around this time.

            The modern Christmas tree originated in West Germany. The main prop used in popular medieval play about Adam and eve was a fir tree hung with apples paradise tree representing the Garden of Eden.

            The Germans used to set up a paradise tree in their home son December 24, the religious feast day of Adam and eve. They hung wafers on it. They also used a Christmas pyramid- a triangular construction of wood with shelves to hold Christmas figurines, candles and a star. By the 16^th century, the Christmas pyramid and the paradise tree had merged and the result was the modern Christmas tree. In northern Europe, a tree is the central feature of Christmas decorations.

            The custom became wide spread among the German Lutherans by the 18^th century. Later, it was introduced in England by the German Prince Albert, the husband of Queen Victoria in the mid-19^th century.

            The Victorian tree was decorated with candles, candies and fancy cakes that hung form the branches by ribbon and paper chains. Prince Albert had the first such Christmas tree set up at Windsor castle in 1841.

            The German immigrants brought this tradition to wider use in the United States in the 17^th century. By the 19^th century, these trees soon came at peak of fashion in America. They also became popular in Austria, Switzerland, Poland and Holland. In China and Japan, the Christmas trees, introduced by US missionaries in the 19^th and 20^th centuries, were decorated with beautiful paper designs.

When did the Scout Movement Begin?

            The scout movement started in 1908, after a book called scouting for boys, was written by the then inspector general of cavalry in the British army, Lt. Col. Sir Robert Baden Powell. Although the author’s basic intention was only to formulate certain guiding principles to be followed by the existing youth organizations, it gave rise to a new movement. In fact, Baden Powell came to be known as the father of the scout movement.

International Scout Insignia

            Baden Powell arranged an experimental camp o brown sea island in Poole Harbour, Dorset, and put his ideas into practice. He believed that the youths should organize themselves in to small groups of six or seven under a leader. Their training should add another dimension to their education by teaching them the art of mapping, signaling rope knotting, first-aid and all other skills needed in camping and outdoor activities.

            A boy becomes a scout by joining a scout troop any time between the age of 11 and 16. before being accepted as a scout, he has to take an oath that he would do his duty to god and his country or sovereign, help other people at all times and obey the scout laws.

            The scout laws are: 1. a scout is to be trusted, 2. a scout is loyal, 3. a scout is friendly and considerate, 4. a scout is a brother to all other scouts, 5. a scout has courage in all difficulties, 6. a scout makes good use of his time and cares for others possessions and property, 7. a scout has respect for himself and for others.

            Almost of the entire scout activities are based on the patrol, which is the primary unit in scouting. The patrol leader takes part in planning ad running of activities. This does not mean that each patrol works on its own. The patrols regularly come together for troop meetings and activities. The scouts from different patrols may even work for a particular proficiency badge in which they share a common interest. The traditional scouting activities are hiking camping and pioneering.

            Scouting today is a world wide movement. There is a Boy Scout’s world committee, elected by the Boy Scout world’s Conference, which comprises all National Member Associations and meets every two years.

What is Semaphore?

            Do you know what was used for signaling from high towers, and transmitting messages between distant points before the invention of telegraph? It was semaphore. Semaphore is a Greek word meaning signal carrier it is a method used for signaling or conveying information by changing the position of a flag, light, etc. the first such system was developed by Cloude Chappe of France in 1794 that employed a ser of arms that were pivoted on a post. The arms were mounted on towers built 8 to 16 kilometers apart. The messages were read with the help of telescope.

The Semaphore signaling system

            Modern semaphores include movable arms or rows of light, simulating arms, which are displayed form towers and are used to signal railroad trains. The continuance of the use of semaphore for signaling is still found in the Indian railways.

            The ships on sea still use the semaphore signaling system to communicate messages. This involves human arms holding a small flag in each hand. When humans send the messages, the sender usually moves the flags in his hands at different angles to indicate the letters of the alphabet.

What is the International Date Line?

            The earth is divided into 24 one-hour zones 15 degrees longitude for each hour, which make one full day on earth. Since earth rotates eastward, the time on the clock progresses westward round the world. Thus 12 o’ clock noon occurs in London (0 degree longitude) five hours before it doe sin Washington D.C (75 degree west of London), and eight hours before at San Francisco 120 degrees west of London. So, when it is noon I London, it is midnight at the International Date Line.

The International Date Line extends from North Pole to South Pole

            The International Date Line is an imaginary line extending from the North Pole to the South Pole. It passes thorough the Pacific Ocean. As the earth rotates, each day begins and ends on this line. Whenever it passes over land or divides countries, it is diverted to pass over the Pacific Ocean.

            The line deviates east of the 180 longitude to pass through the Bering Strait to include eastern Siberia and then westward to include the Aleutian islands with Alaska. South of the equator, it bulges eastwards again to allow various island groups to have the same day as that of New Zealand.

            The earth is divided vertically into 360 longitudes (180 degrees east and 180 degrees west), zero degrees longitude passes through Greenwich and 180 degrees longitude is called the International Date Line. On either side of the International Date Line, the time is the same but there is a difference of 24 hours.

            It is for this reason that a traveler moving westward across the line sets his calendar back by one day, and a person crossing form west to east will have to advance his calendar by a day. In short, it implies that if you cross the date line going eastward, you gain a day while those traveling westward lose a day.