Why Does The Sky Appear Blue?

            A blanket of air called atmosphere, surrounds our earth. It is mainly composed of nitrogen, oxygen, carbon dioxide, dust particles, water vapors and other gases. The light coming to us from the sun has to travel through this atmosphere.

The Sky

            We all know that the sun is the main source of light for earth. When the sunlight passes through the atmosphere, it is scattered by the dust particles, water vapor and air molecules in all the directions. This is the reason why light is all around after the sunrise.

            Do you know that the sunlight is composed of seven colors- violet, indigo, blue, green, yellow, orange and red? When the sunrays pass through the atmospheric molecules, the violet, indigo and blue colors get scattered most and the red color least of them. Therefore, when we look at the sky, the light that enters our eyes mainly consists of violet, indigo and blue colors. The mixture of these three colors is almost blue. That is why the sky appears blue.

            If the earth had no atmosphere, the sky would have just appeared dark. This fact is clear when we look at the sky from the surface of the moon. It appears dark since there is no atmosphere in the moon. Similarly, the sky appears dark when we look form a spacecraft, because there are no light scattering particles in the higher space.

How Does an Electric Bulb Give Out Light?

            The moment we switch on an electric bulb in a dark room in the night, the whole room is illuminated with light and all the articles kept there become clearly visible. Do you know how light is given out from the bulb?

Electric Bulb

            The American scientist Thomas Edison developed the first electric bulb of the world in the year 1878. In making this bulb, he utilized the principle that light and heat are produced when electricity is passed through wires. Actually, the electric bulb converts electrical energy into heat and light energy. Such light sources are called incandescent lamps. To begin with, a coil of very fine platinum wire was sealed in glass bulb used by Edison. When the two ends of this coil were connected to the electric supply, it became red-hot and started glowing. Lamps made by Edison could not become popular because platinum wires were very costly.

            Subsequently, many changes were made in the filament materials used in the electric bulbs. For some time, carbon filaments were used. Later on, filaments made up of tungsten and tantalum metals came into use. Since the melting points of these metals are very high, filament made form them do not easily burn out.

            In the modern electric bulb, the coiled tungsten filament is sealed in a glass bulb. Each end of the filament is welded to a thick wire. These thick wires are then passes through a glass pillar. Two ends of these wires are soldered with contact pads. To prevent the two ends form coming in contact with each other, insulating material is filled in the metal cap. The air inside the glass bulb is removed and filled with a mixture of argon and nitrogen gases. Thus, it prevents the evaporation of metal form the filament and protects it form melting. This mixture also increases the efficiency.

            When electric current flows through the filament, it first becomes red-hot and then white. This glowing white filament gives us the light. The power of bulb is measured in watts. A medium-sized room needs a 100 watts bulb.

            While handling bulb, we should not shake it because the filament is likely to break due to the jerks. Once the filament is broken, the bulb becomes useless. While fixing bulbs in their holders, one should keep the relevant switches off to avoid any possibility of electric shocks.

Why Does Iron Get Rusty?

            You may have noticed that when an iron object is kept exposed to the atmosphere for along time, it acquires a brownish red cover. This is known as rust. Rust is a substance that forms on the surfaces of iron ad steel articles when they are exposed to damp air. Rust is a hydrated form of iron oxide.

Iron nails getting rusted

            Rusting occurs when the oxygen in the air unites with iron by a process known as oxidation. It is also called corrosion. But rusting is not only a process of oxidation because part form oxygen, moisture is also necessary to produce the change. The complex rusting process is an electrochemical reaction that is speeded up by the presence of salts and acids. That is why rusting is more severe in coastal regions ad industrial areas where the air may contain acidic sulphur dioxide fumes.

            Rust not only corrodes the surface but also weakens the metal. Small cells are set up in the corroding metal. It occurs mainly at grain boundaries of metals and where it stressed. A prolonged exposure to moist air causes rusting in iron materials, and holes in iron sheets.

            Rust can be removed by scrubbing the iron or steel or by using grinding abrasives. There are two basic methods to prevent rusting. The iron or steel may be coated with paint, plastic, or a corrosion resistant metal such as tin or zinc so that oxygen is stopped form reaching the iron or steel beneath. Chemically coated paper wrapped around metal objects also prevents rusting. The metal may also be alloyed with corrosion resistant metals such as nickel and chromium.

How does a Thermos Flask Work?

            The thermos flask is a special kind of bottle in which hot liquids like tea and milk remain hot and cold items like ice and cold water remain cold for a long time. Sir James Dewar first invented this flask in 1892. That is why it is also known as the Dewar flask. It consists of a double walled glass bottle. These walls are silvered form inner side. The space between the walls is evacuated with the help of a vacuum pump and sealed.

Thermos Flask

Internal Structure of Thermos Flask

            Do you know how this bottle helps in keeping the hot things hot and cold ones cold? Normally, a hot substance becomes cold by losing its heat to the surroundings having a lower temperature. Similarly a cold substance becomes hot by absorbing heat from the surroundings having higher temperature. The function of the thermos flask is to prevent the flow of heat to and from the bottle. We know that heat can flow from one place to another by three modes- conduction, convention and radiation. The thermos flask prevents the flow of heat by any of these modes. The flask is made up of glass, which is a bad conductor of heat. Hence heat does not flow by conduction. Since there is a vacuum between the walls of the bottle, flow of heat by convection is also ruled out. Due to the silvering of the walls, heat is not lost by radiation. As a result, hot things kept in a thermos flask do not become cold and cold ones do not become hot for a long time.

How are Millions of Substances Made from Only a Few Elements?

            Today there are over a million of articles used for different purposes of life. There are a numerous man-made objects but the number of naturally occurring stable elements on the earth is 92 only. Although scientists have discovered 118 elements in all up to February 2007, only 26 of these have been artificially made in the laboratories. These artificial elements are unstable in nature. The atoms of the other 92 elements are stable. Then how are millions of substances are made form these elements?

            All substances available in the universe are made by the combination of atoms of these 92 elements. The atoms of different elements combine with one another in various proportions and keep on forming countless substances. Some of the important elements are – iron, gold, silver, copper, aluminum, sodium, potassium metallic elements, oxygen, nitrogen, chlorine, carbon and sulphur non-metallic elements. All the elements of atoms and the atoms of the same elements are alike. Two or more atoms combine with each other to make molecules. For example, two atoms of hydrogen one molecule of water. Even a very small quantity of water consists of innumerable molecules. Similarly, one atoms of sodium combines with one atoms of chlorine to make one molecule of the common salt or sodium chloride.

            Now the question arises- how is it possible for the atoms combine with one another to form compounds? They mainly combine in two different ways. To understand the processes of combination, we have to know the structure of an atom.

            The central portion of every atom is positively charged and is called the nucleus. The electrons of the atom revolve round the nucleus in different orbits. Electrons are negatively charge particles. In the first kind of combination, one atom donates some of its electrons to the other making a bond between then and these results in the formation of a new material. In the second type of combination, one atom makes a bond with another atom by mutual sharing of electrons. In both these combinations only the electrons of the outermost orbits participate. Do you know how does the exchange or sharing of electrons create new materials?

            In the formation of common salt, one electron of the sodium atoms is donated to one atom of chlorine. This transfer of electron makes sodium atoms a positive ion and chlorine atom a negative ion. There exists an electrostatic force of attraction between these ions. This force of attraction binds the two atoms together and thus a molecule of common salt is formed. Similarly in the formation of water, oxygen and hydrogen, atoms have a mutual sharing of electrons by which a force of attraction exists between them, which binds the atoms together. As a result, water is formed.

            In another example of chemical bonding, one carbon atom combines with two oxygen atoms to make one molecule of carbon dioxide. Similarly one atom of nitrogen combines with three atoms of hydrogen to make one large molecule of ammonia gas. Carbon is one such element, which combine with large number of elements and forms the maximum number of compound called organic materials. Those compounds which do not contain carbon are called inorganic.

            The Russian scientist, Dmitri Mendeleev, classified all elements into several groups in 1895 he published the periodic table showing all the elements in their respective groups.

Why do Women have a Sweet Voice?

            You may have noticed that the voice of women is generally sweeter than that of men. Even boys have a feminine voice till the age of eleven or twelve years. But later it starts becoming deeper. The voice of girls, however, does not change much with age.

Women have a sweet voice of the absence of testosterone, a hormone responsible for variations in the vocal cords

            Normally the age between eleven to thirteen years is knows as the puberty age. During this period, some of our glands produce sex hormones. These hormones bring many changes in the bodies of boys and girls. In boys, they are responsible for arms, auxiliary hair, pubic hair and facial hair. The voice of boys starts becoming deeper. Their bodies produce a hormone called testosterone which is mainly responsible for changing the length and thickness of the vocal cords. This also affects the larynx. As a result, a man’s larynx becomes larger than that of a woman. Men have vocal cords longer than those in women. Due to this, the frequency or pitch of man’s voice becomes lower than woman’s and hence the male voice becomes deeper than that of female.

            Though this hormone is not produce in the girls, yet a slight change takes place in their voice also. This change occurs mainly due to the further growth of their throat, mouth, nose and upper jaw.

How is Icebergs Formed?

            Icebergs are those gigantic pieces of gloating ice that we mostly see in national geographic channel on our television or in books. In the southern hemisphere, the Antarctic ice sheet overflows its land support to form shelves of ice on the sea; huge pieces, as much as 200 kilometers across, break to form icebergs. In northern hemisphere, icebergs are generally not over 150 meters across. However, most icebergs are from some 20 glaciers on the west coast of Greenland. Do you know how these giant icebergs are formed? When glaciers, drifting from mountains and valleys reach the sea, sea waves and tides break them into big pieces. These big pieces of ice are called icebergs. However, there are some glaciers, which do not break even after floating for long distances in the sea, and appear like mountains of ice.

The major portion of an Iceberg is hidden under the sea

            The sizes of the different icebergs vary. The smallest iceberg measures 5 to 6 meters in length and breadth while the bigger ones can be hundreds of meter long. Some iceberg with lengths and breadths of half a kilometer have been seen floating in the oceans. As ice is lighter than water, the icebergs float on the surface. Their one-tenth part remains above water and the remaining under water. For example, if a 50 meter high iceberg is seen above water, then 450 meters of it will be under water. These icebergs contain huge quantities of snow. Some of them may contain 200,000,000 tons of ice. As an iceberg floats, some of the ice melts and pieces break off. Eventually, it completely disappears.

            Because of their huge weight and volume, the icebergs do not move in the sea on their own. They are pushed by the sea waves or tides. They are very dangerous for ships. A collision with the icebergs can cause a shipwreck. Though they can be detected with the help of modern instruments, mishaps do take place occasionally. On April 14, 1912, a ship named titanic was broken into pieces when it collided with an iceberg. This ship was sailing to New York; 1513 passengers, who were aboard this ship lost their lives.

            A similar accident took place on January 30, 1959 when the ship Hans Hedtoft collided with an iceberg in southern Greenland and was wrecked. Now the United States and other countries have formed an international ice patrol. The patrol uses ships, planes, and radars to locate icebergs.

What is Smoke?

            Whenever wood, coal or some other substance burns, smoke is emitted. Smoke is produced due to the incomplete combustion of fuels. If complete combustion of fuels takes place, no smoke will be produced. In fact, smoke is a colloid of solid particles in gaseous form.

Smoke is produced by incomplete combustion

            Most of the fuels contain carbon, hydrogen, oxygen, nitrogen and small quantities of sulphur. When any fuel burns, we get carbon dioxide, water vapor, nitrogen and traces of sulphur dioxide. For the complete combustion of fuels, a large quantity of oxygen is required because burning is a process of oxidation. Due to the lack of oxygen, fuels do not burn completely. As a result of this, smoke is produced. Smoke mainly consists of carbon dioxide, water vapor and carbon particles. When the number of carbon particles present in the smoke is large, it appears grey or dark. These very carbon particles get deposited on the walls of the chimneys. This deposit is called soot.

            Smoke is the biggest pollutant of air and is very harmful to our health. To day, it has become a major problem in the cities. If it does not get scattered by wind, the atmosphere of the cities becomes highly foggy. Smoke is particularly harmful for the heart and lungs and is the cause of many diseases. It is also harmful to the eyes.

            However, in certain respects, smoke is useful also. It is used to protect orchards form cold. In wars, smoke helps in camouflaging. It is also helpful in rain formation by enabling the water vapor to condense on its particles. But the harmful effects of smoke often over ride the positive effects.

When did The Construction of Bridges Start?

            In ancient times, rivers or large water bodies were natural divisions or borders between tow distant lands. Later, people probably found that a fallen log across a stream provided them with a useful footbridge. In jungle areas, they could make a simple foot bridge out of ropes of vines twisted together. When people began to fine then the log and vine bridges could not carry carts and wagons, or large number of people across wider spans, they began to improve their bridges to meet their needs.

Beam Bridges

Arch Bridges

            The most primitive form is the beam or girder bridge consisting of a rigid beam resting at either end on piers. The span may be increased by the use of beams.

            This eventually led to creation of truss bridges. These were mainly wooden or metal framework designed for greater strength.

            As per written records, the first bridge of wooden beams resting on stone piers was built in 2230 B.C. across the river Euphrates in Babylon. After this, an arched bridge of stone was constructed across Anio River in Italy about 600 B.C.

            Gradually a lot of improvements were made in the art and science of building bridges. In 1779, the first metal bridge was built over Severn River in England. In 1887, the first reinforced concrete bridge was built over river Rhine in Germany. The oldest bridge is in Florence, Italy.

            Today due to the advancement in technology, engineers and architects are able to construct very long and strong bridges. Usually bridges are divided into four categories: 1. Girder or Beam Bridges, 2. Arced Bridges, 3. Suspension Bridges and 4. Movable bridges. Nowadays, the bridges are being built over very wide rivers. The construction of double strayed bridges too has become easy. One storey of such bridges is used for road transportation and the other for trains. The most common temporary bridges are pontoon or floating bridge comprising floating bridge comprising floating members that support a continuous roadway.

            Did you know that the longest bridge in the world is humbler estuary bridge of England? A sum of 67 million pounds was spent on its construction. The world’s widest long-span bridge is the Sydney harbor bridge of Australia. It is 502.9 meters long and 48 meters wide. The highest bridge of the world built over Arkansas River of USA stands 321 meters 1053 feet above the sea level.

Why does Bread have Pores?

            Bread is a popular food eaten in almost all countries of the world. Their ingredients vary form country to country. In most of the countries, however, bread is made form wheat or rye flour. In some places it is also made form rice, barley, potatoes, peas and beans.

Bread have Pores

            According to the recorded history, the making of bread first started around 300 B.C. in Egypt. This was also the time when yeast was discovered. These days, the common bread is made form dough prepared by kneading flour with water. A little yeast, sugar ad salt are added to it. The yeast causes the dough to rise by forming bubbles of carbon dioxide gas in it. The dough is then moulded into the shape of a loaf and baked in a loaf tin in the oven.

            In the process of baking, the gaseous bubbles burst resulting in small pores inside the bread. It is mainly the yeast. Baking soda, which is the mixture of tartaric acid and sodium bicarbonate is used in the preparation of cakes.

            When this mixture is added to the dough and it is baked, carbon dioxide is baking causing small pores. Breads are white or brown depending on whether white or brown flour is used.

Why The Leaning Tower of Pisa does not fall?

            The Leaning tower of Pisa is one of the most amazing structures in the world. Located in the city of Pisa, Italy, it is visited by hundreds of people every day. Very few people know the reason of its leaning. Made of whit marble, this structure has walls 4 meters thick at its base. It has 8 floors and is 54.5 meters high and measures 15.8 meters round the bases. There is a stairway, which leads to the top and has 300 steps. From its top, it is possible to get a breath taking view of the city and the sea, which is 10 kilometers away.

The Leaning Tower of Pisa 

            Now the question arises- what makes this tower lawn and why does it not fall? Plumb line form the top is meters away from the base, i.e. it leans over by 4 meters. If we drop a ball from its top, it would hit the ground 4 meters away from its base.

            Originally, it was intended as a bell tower for the cathedral, which is nearby. Its construction was started in 1174 A.D. and completed in 1350 A.D. when the construction started no body though that it would lean, but it started leaning as soon as the third storey was completed. The foundation of the tower was laid in sand and this may explain why it leans. Since the tower started leaning, the plan for its construction was modified and then the tower was completed.

            Since 1918, yearly measurements have been made. These measurements show that the leaning is increasing. During the last one hundred years the tower has leaned another 30 centimeters.

            But why does it not fall even while leaning? According to science, anything will remain stable as long as the vertical line drawn from the centre of gravity passes through it base. The centre of gravity is that point where the whole mass of the body is supposed to be concentrated. Till today the vertical line from the centre of gravity has bee falling within the base of this tower. That is why it has not fallen. It is believed that when the tower leans further and the line from its centre of gravity passes out of its base, it will fall down.

            However, by using different new methods and techniques, engineers and technologists are now trying to arrest further leaning of the tower.

What is a Mirage?

            You must have seen it in movies when a person has been traveling in the desert for many days. He is suddenly delighted to see a pool of water in the distance. When he goes closer he realism that there is no water at all. What he saw was a mirage. The desert deer also gets a similar impression. They run hear and there in search of this illusory water and finally die of thirst. A similar phenomenon is observed when we drive on a concrete road on a hot summer day. Mirage is simply an optical illusion. Do you know how it is caused?

Mirage of a tree in the desert

            This optical illusion is caused by total internal reflection of light. During the summer, the earth’s surface becomes very hot. These heats up the sir in its vicinity but the upper layers of the atmosphere remain cool. Since hot air is always lighter than cold air, the air near the earth’s surface becomes lighter than the air of the upper layers. In scientific terms, the refractive index of hot air is less than that of cold air. As such, the refractive index goes on increasing as we go above the earth’s surface up to a certain height.

            In such circumstances, when the light rays coming from trees and plants enters from a medium of higher refractive index to a medium of lower refractive index, they get deviated form their path. This phenomenon is called refraction of light. As the rays travel more distance of varying refractive index, the angle of refraction goes on increasing and a stage comes when it becomes more than 90 degrees. At that stage the refracted light goes back into the medium from which is had started. This is called the total internal reflection of light.

            As a result of this reflection, the images of the trees and plants appear inverted, giving an impression as if these images have been reflected by water. This gives rise to the illusion of the presence of pool of water. This is what is known as a mirage.

            Sometimes another kind of illusion producing the opposite effect takes place. Over cold artic waters, a layer of cold air may lie under a layer of warm air. This causes the light to bend downward. For example a ship beyond the horizon may appear to be lifted into the sky. This optical illusion is known as looming.

How Can We Reach The Bottom of The Sea?

            Man has always been curious about the various secrets hide in spaces beyond his reach. He has tried to find out these secrets of the universe. From the very beginning, man has been interested in exploring the bottom of the sea. He has been anxious to know about varies substances found on the seabed. Do you know how man goes inside the sea to explore its depths?

A Bathyscaphe can take on a journey to the bottom of the sea

            A special vessel called ‘bathyscaphe’ is used for going into the deep sea. A Swiss scientist named August Piccard in the late 1940s developed this vessel. The first bathyscaphe was fabricated in Belgium between 1946 and 1948. However after a few trips to the sea it broke down in 1948. After this, the second bathyscaphe was made. It made its first voyage as it went down to the depth of 4,000 meters in the Atlantic Ocean on February 15, 1954.

            Jacques Piccard, son of August Piccard made an improved bathyscaphe which went to a depth of 10,916 meters inside the Pacific Ocean on January 23, 1960. This broke the previous world record. The name of this bathyscaphe was Trieste.

            A bathyscaphe has two main parts. One part, made of steel is called cabin. It can accommodate two people. The other part made of some light metal, floats on water. It stores gasoline and two air vessels. To enable the bathyscaphe to move on the surface of the sea, these vessels are filled with air. However, before taking it into the sea, the vessels are filled with water. And the weight of this water causes it amount of air and water in these vessels it can be taken to the desired depth. Nowadays, this vessel the use of battery powered motors provides this helps to study the marine research in a shorter period.

Why do Objects Appear Colored?

            Do you known why an apple or tomato appears red the grass green and the milk white when they are all illuminated by the sunlight have you wondered why in the dark all objects look black? In face the color of objects depends upon the color it reflects.

Tomato 

An apple 

Milk

            The sunlight which appears to be white actually comprises seven colors- violet, indigo, blue, green, yellow, orange, and red. In sunlight an apple or tomato appears red because it reflects only the red component of light and absorbs the test. Grass appears green because it reflects only the green color and absorbs all other colors present in the sunlight. A white shirt or milk appears white because it reflects all the color of the sunlight. And a black board appears black because it absorbs all the colors of white light and reflects none.

            To prove this phenomenon focus red light on a white shirt and you will see that it becomes red. White objects take the color of light falling on it. Similarly if we see an apple in red or white light it will appear red but in green or blue light it would appear black. It cannot reflect any other color but red and therefore looks white. This is how the various objects get their color.

Does a Black Cat Bring Bad Luck?

            Have you someone telling you that a black cat crossing the road is a bad omen and you should not walk on the road if the cat has just passed by? Do you know why a cat in general and a black cat in particular are considered inauspicious?

A Black Cat

            Superstitions have taken various forms over the centuries but one of the most common superstitions that still prevail is that of the black cat. Many people all over the world regard the sight of a black cat as inauspicious.

            The thought that a black cat is inauspicious is a mere superstition. This superstition goes back to a belief of thousands of years. The ancient Egyptians worshipped cats.  They had a goddess called past whose head resembled that of a cat. They believed this goddess had nine lives. Whenever a black cat died in Egypt, its dead body was preserved as a mummy remains of thousands of black cats have bee recovered fro, a cemetery of Egypt. Killing a ct was then considered an offence, punishable with a death sentence. Thus, people had a great fear of the sight of a black cat.

            During the middle ages witches and witch doctors used the skull of a black cat to prepare mysterious medicines. As a result people started thinking that bad omen. People have believed in this superstition for many centuries. The cat is a pet animal being domesticated from past 5,000 years.

Which Animals Resemble Man?

            We all knew that man has evolved from animals over thousands of years. As a result there are few other animals which resemble man in different aspects. Gorilla, Chimpanzee and Orangutan are some of the animals which resemble man in many respects. These are a kind of monkeys without a tail. They are found in the dense jungles of Africa and Asia.

Gorilla

            Among these animals the chimpanzee has the closest resemblance to man. In fact the bone structure of all these animals has many similarities to that of man. The number of their teeth and the constitution are similar to ours. Like human beings they also have wrinkles. On their forehead and their skulls are also similar to ours. Even their blood is like ours. However they cannot speak like us. They eat flowers, leaves stem, fruits, insects and birds eggs.

Chimpanzee

            Gorillas re generally as tall as human beings but heavier and stronger. They live in groups of 20 to 30. The young ones live with their parents till they become adults. Young gorillas sleep on trees while the adults sleep on the ground. They are generally peace loving animals but once teased of wounded, they start beating their breasts. They can produce a drumming sound from their mouth and their skin is black.

Orangutan

            Chimpanzee is the cleverest of all these animals. It can imitate many habits of man. Its body is covered with black hair. Unlike gorilla and chimpanzee the orangutan is almost completely arboreal. It has bony cursers over the top of its skull. Its forehead is higher than that of gorilla and chimpanzee the lips protrude and the eras are small. All these animals belong to the same groups to which we belong.

How is Submarines Detected under the Sea?

            You may have heard about submarines earlier. They are not visible from the surface of water. But have you wondered how this sonar mainly consists of two parts the transmitter and the receiver. Both these parts are submerged under seawater. The transmitter with the help of a transducer produces sound waves of high frequencies. These waves are called ultrasonic waves and cannot be heard by human ears. The transmits these waves in pulses in all the directions. Whenever these pulses strike some object inside the seawater waves are then receiver by the receiver. The time taken for the waves to reach the object the object and come back to receiver is measured. Half of this time when multiplied by the speed of sound in seawater gives the distance of the objects. This instrument consists a display device also which accurately shows the distance and the position of the of objects.

Submarines are detected by sending high frequency sound waves through sonar

            Sonar however is not a foolproof system. The sounds produced by some aquatic animals like fishes and whales sometimes interfere with its transmissions and can be misleading about the position of the objects. The enemy submarines can be detected by this equipment and thus can be destroyed. These days there are various kinds of sonar being used for studding the objects under water. Sonar’s also help in large scale fishing by locating those spots where large groups of fishes are present. Nowadays blue green laser pulses are also being used for underwater detection of submarines and torpedoes. Laser based devices also work on the echo sounding principle just as sonar works.

How Can We Test The Purity of Milk?

            In these days of adulteration milk is one of the main sufferers in terms of purity because it is often mixed with other substances that make it impure. But we can find out about the purity of milk. How do we do that?

Lactometer

            The instrument used to assess the purity of milk is called a lactometer. It is a cylindrical vessel made by blowing a glass tube. One end of the glass tube is blown in the from of a bulb and filled with mercury. The other end is blown in the from of a thin tube and sealed. For calibration it is dipped in pure milk. The point up to which it sinks in the pure milk is marked after that it is put in water and is marked at the point up to which it sinks in water. It sinks less in milk than in water because milk is denser than water. The portion between ‘M’ and ‘W’ is divided into there parts and marked as 3, 2 and 1 to indicate the level of purity.

            Whenever we want to test the purity of milk, the instrument is put in milk. If it sinks up to the mark M the milk is pure. If the milk is not pure but mixed with water, it would sinks to a mark higher than M undersea ships can be directed? The main device used to detect and locate objects like submarines and torpedoes under the seawater is called sonar the word sonar is an acronym for sound navigation and ranging. This instrument is particularly useful in sea warfare. However in peacetime also it is used in shops and submarines. It can locate objects at distance ranging from 100 meters up to 10 kilometers.

            When the instrument stands at the mark 3, the milks 75% pure. At the mark 2, the purity is only 50%. Mark 1 indicates a purity of 25% only.

            Even though lactometer is generally used to measure the purity of milk, it is nor a very relievable instrument. It has been observer that in the case of skimmed milk the lactometer fails to give the correct assessment of the purity if the density of the skimmed milk is made equal to that of the pure milk adding water in an appropriate proportion.

Why We Cannot Fly Like Birds?

            An obvious answer to this question by any layman will be “we cannot fly like birds because we do not have natural wings”. However this answer does not explain this question completely because even if we attach artificial wings to our arms we are still unable to fly. Then how do the birds fly?

Human beings cannot fly because they do not have a streamlined body

            Birds have wings to assist them in flying. Apart from this they have very light frames and their bones are also light. Moreover they have air sacs which further reduce their body weight.

            The muscles of birds are quite strong in comparison to their body weight. They have a streamlined body which enables them to fly swiftly because air offers less resistance to such objects. With the help of their strong muscles they can they can easily fly with their wings. But than we do not have any air sac and our muscles are not comparatively strong enough. Hence we cannot flap the artificial wings.

            Birds having lighter bodies can fly more easily while heavy birds the cock face difficulties in flying for examples the cock and peacock cannot fly very high. There are also birds like ostrich and penguin which are even heavier. These birds cannot fly at all. They can merely run. Similarly we cannot fly like birds even if we attach artificial wings to our arms.

What is a Dragon?

            Everyone has heard of dragons these mythical creatures are used in almost every fantasy story. Do you know what exactly a dragon. Dragon is a legendary dreadful monster that never existed in reality. It is a musical beast born out of people’s imagination ling time ago. The belief in this creature apparently arose without the slightest knowledge on the part of the ancients about the gigantic, prehistoric dragon like reptiles.

Dragon

            The word ‘Dragon’ come the Greek word garcon which was used for a large serpent. But dragon as a monster is depicted as a huge fire breathing bat winged scaly lizard or snake with a barbed tail. In later period it mostly remained in the shape of a snake. In the eastern world where shake are large and deadly a dragon symbolized evil. But in the west it was accepted both as a symbol of good and evil depending on circumstances. The Christians and Jews perceived it as evil and dangerous. In Christian art dragon represented sin and sorrow.  

            The form and appearance of dragon varied from place to place. The Babylonian dragon had four legs while the biblical dragon was described as a many headed creature like the Greek hydra. In wartimes it was used as an emblem representing velour. In the 20^th century the dragon was officially incorporated in the armorial bearings of the Prince of Wales. The Chinese dragon known as lungs appears as the national symbol of china. The Japanese as well as Chinese dragons are usually wingless. Dragon images are also used in the north eastern states of India as well as in Bhutan during different festivals.

            The komodo dragons found in some Indonesian islands are in fact very large lizards. However the dragons in their general sense are still mythical figures.

Who Created Frankenstein’s Monster?

           Frankenstein’s monster is one of the most popular monsters ever created. In the 18^th and 19^th centuries, with an element of horror became quite popular among the masses.

Mary Shelly

            An Englishman named Horace Walpole first introduced horror as a permanent feature in most of his writing during the 1760s.

Frankenstein’s Monster

            Since then many writers started writing such stories including science fictions with amazing success. The Frankenstein monster is one such example of horror fiction that attained worldwide popularity.

            The story of Frankenstein was first published in 1818, which had a scientific flavor along with imagination. It was about the creation of a monster that ultimately destroys its creator. With its elaborate narrations of mystery horror outrage madness and spirit of revenge this character maintains the trend first started by Walpole. The basic idea behind the cremation of the monastery was to show the power of science how a dead person can be brought to life and the subsequent induced in the monster make it a reactive and suffering creature who wavers between good and evil.

            But do you know who was the creator of the muster the creation of this well known monster was marry Shelley Wollstonecraft the daughter of Williams Godwin and second wife of the famous poet Shelley. She was born on 30^th august 1797 in London. She spent much of her life editing her husband works after his death. Among the other novels she wrote the most famous was life and adventure of construction.

            However in spite of her many notable works her name is mainly attached to the creature she portrayed in Frankenstein. This novels was transformed in to feature films in many versions all over the world.

            Mary Shelley died on February 1, 1851 at the age of 54.

When did People First Use Money?

            Money has always fascinated man ever since ancient times. Money has come to become the most important thing in the world. Aristotle observed that man is a social being who established certain norms and regulations for his social interaction. Man employed money as a mode of exchange to facilitate such social dealings for his economical aspect.

Indian Rupees

US Dollars

            In primitive societies, when people wanted to buy anything, they had to give something else in return for it. For example, if a potter wanted to buy rice form a farmer, he offered him earthenware in exchange offer rice. The farmer would accept them because he needed pots. This was called the barter system, which involved goods in exchange of goods.

            During those times goods served the purpose of money. But with the development of trade, the barter system could not meet the growing demands of convenient exchange system for buying and selling. People started using token or symbolic goods in exchange all over the world. American Indians used beads of shells, Fijians used whale’s teeth and North Americans used tobacco in their exchange system. The roman army men were provided salt for their services. But when was the coin first used as currency?

            The precise origin of money in the form of coins is not clearly known. According to the available sources, the earliest coins were minted in about 800 B.C. when Indians who lived in Asia used stamped pieces of metal as a medium of exchange. Some believe that the Chinese used coins even earlier coins were preferred because they were easy to carry and durable.

            The early coins were of irregular shape and were stamped with rough designs. The money value of coins depended on the value of the metal that the coins were made of coins were mostly made of gold, silver or copper because they were precious and durable metals.

            The use of paper currency was known to china as early as in the 9^th century but it did not develop in Europe until the 17^th century. The governments of different countries favored the use of paper currencies and coins to simplify the monetary dealings. It helped, because what mattered was the money value printed or stamped on them and not their real value. This is because the printed value on the currencies denoted their purchasing power as assured by the government. People accept a coin or currency in payment not because they value the coin itself but because they have confidence in the authority that issued it.

            As coins are heavy and bulky, larger payments are made in paper money issued by the proper legal authority.