How did arithmetic originate?

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Why does cork float on water?

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How did the various religions originate?

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Why are diamonds so precious?

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How can stamp collection be profitable?

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When were the world fairs started?

We do not have definite information about the beginning of the fairs. But in ancient times when there were no means of communication and man had to go long distances in search of articles of daily needs, the traders used to assemble on a fixed day at a fixed place to sell articles of daily use. People used to purchase articles of their needs in exchange for animal hides or grains.
With the advancement in the modes of communication, the commercial importance of the fairs decreased, and they came to be organised for entertainment and on cultural occasions. With the growth of civilization and industrial progress, fairs became the means of demonstrating the progress and achievements of any country. In the 19th century, fairs became symbols of international co-operation and friendship. They began to be called world fairs.
The first world fair was set up in 1851 in the Hyde Park of London. For this purpose a building named 'Crystal Palace' was constructed. The building was made of iron and glass. this fair went on for 141 days and 6 million 39 thousand and 195 people saw it. It was destroyed in a fire in 1936. The first international fair of America was organised in New York in 1853. Twenty-three countries participated in it and five thousand people set up their stalls. But this did not become very successful. After this, America organised a big fair in 1876 on the occasion of the centenary celebrations of American Independence at Pensylvania. America exhibited in this fair articles developed by it. In this very fair Graham Bell demostrated for the first time the telephone developed by him. After this, the world's biggest fair spot was constructed in New York in 1939-40. This was constructed on a piece of land measuring 1216.5 acres. In 1964-65 a world fair was organised at this place, which was visited by 51 million, 6 lakhs, 7 thousand and 37 people. Around 60 million people saw the Expo.' 70 fair organised at Osaka. This fair went on form March 1970 to September 1970. In India the first world fair, Asia-72, was organised at Pragati Maidan in Delhi in 1972 and was visited by millions of people. Now-a-days international book fairs are also held every year.

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Why do birds preen their feathers?

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Do giants live on earth?

In many parts of Europe and Asia, there are legends of the existence of giants in ancient times. We also read many stories in magazines and newspapers about demons and giants. After reading these stories, one feels that giants exist in some parts of the world. Since many races of pygmies are found on earth,
it is logical to think that there may be races of giants on the earth as well. In fact, giants have existed in myths and story books only. There is no scientific evidence that such people ever actually existed.
Enough variations are noticed in the heights of human beings of the world. Most of the people are of normal heights but the people of some races, such as Eskimos, Lapps and certain Indian tribes in South America, are dwarfs. Some of the native tribes of eastern Africa, have an average height of 2 metres. But they cannot be treated as demons or giants.
In fact, we all know of giants who appear in circuses and side shows. How did they get to be so tall? They are usually the persons suffering from abnormalities. Thy become abnormally tall due to the excess formation of hormones by pituitary gland. The pituitary gland regulates growth. Sometimes, it developes a tumor which makes the gland larger. This larger gland then begins to produce large quantity of hormones. One of these hormones is the growth hormone, which has an effect on the size of the organs and the skeleton of the body.
When excess of this hormone is produced body keeps on growing. In such a case, the height of the individual may go up to 2 1/2 metres. This condition is known as giantism.

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What causes an echo?

When we speak loudly in a big empty hall or in a temple, we hear our own sound repeatedly. This is called echo. An echo can also be heard by shouting near a deep ditch or a well. The thunder of clouds, is another example of echo.

We know that sound travels from one place to another in the form of waves. The velocity of sound in the air is (340 metres 1100 ft) per second. When we speak, the sound waves emanating from our mouth spread out in all the directions. When these waves meet a wall or some other obstacle in their way, they are reflected back. These reflected waves are heard by us as an echo. Hence echo is produced when sound waves are reflected by some obstacle.
To hear an echo, it is essential that the obstacle reflecting the sonund waves must be situated at least 17 metres or 55 feet from us. This is because, the effect of sound persists on our ears for one-tenth of a second. If some sound signal has reached the ears and within one tenth of a second another sound signal reaches our ears, it will not be distinguished because during this period the effect of the earlier sound is persisting in the ear. Sound travels about 34 metres or 110 ft in one-tenth of a second. As such, if the object reflecting the sound waves is situated 17 metres away from the speaker, the time taken for the sound to travel this distance, from the speaker's mouth to the object and back to him would be one-tenth of a second and the reflected sound can be distinguished by our ear as an echo.
All objects do not reflect sound. There are some materials like wood, jute, cardboard etc. which absorb sound.
Today we find that in modern buildings the architects use methods and materials which reduce echoes and favour good sound transmission. Auditoriums are now built with rounded corners and few large flat surfaces. This prevents sound waves from being reflected to any one position. They are scattered in many directions and the only sounds heard are those sent out from the source. Some fibre boards having many holes are used for making rooms sound proof. By the use of these materials the sound waves are either absorbed or scattered so the production of echo is reduced.

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Where have Seven Wonders of the world gone?

We have often heard about the seven great wonders of the world. Would you like to know what are these seven wonders? They are: The Pyramids of Egypt, The Hanging Gardens of Babylon, The Tomb of Mousolus, The Temple of Diana, the Colossus of Rhodes of Helios,

The Statue of God Zeus and The light House of Pharos near Alexandria. Out of these seven wonders, the Pyramids of Egypt are preserved only. The story behind their construction is very interesting.

The only preserved wonder-The Pyramids of Egypt were made some 5000 years ago. In fact, these are the tombs of the Egyptian ruler. The biggest pyramid is located at Gizeh, a small town near Cairo. This is the tomb of Pharaoh Cheops and his queen. Its area is 750 sq.ft. Its base forms a square and its height is approximately around 451 ft. 2 million stone slabs are fitted in this tomb. It is said that it was completed by more than one lakh labourers who worked for 20 years.

The second wonder was the hanging gardens of Babylon. Around 2500 years ago, the king of that place, Nebuchadnezzar made beautiful gardens on the walls on all sides of a palace to fulfil his queen's wishes. These gardens were quite high from the normal surface and they had to be watered by hot water. Up to the year 514 A.D., these gardens were intact, but Persia attacked Babylon that year and destroyed these walls and gardens.
The third wonder was the tomb of Mousolus, theruler of Halicarnassus which was constructed by his queen after his death. This was approximately 30 metres high and had on its top statues showing the king and queen riding a horse driven chariot. Within a short period of its construction, this tomb was demolished in the attack by Alexander the Great. Later in 1857, an English traveller went there and brought back wth him the statueof the king which is still preserved in the British museum.

The fourth wonder of the world was the temple of Diana at Ephesus with its roof resting on 19 metres high pillar. This temple was constructed in the year 350 B.C. in Eastern Turkey. At that time this temple was considered so sacred that people would feel secure after depositing their wealth and precious possessions in this temple. In the year 262 A.D. Goths burnt down this temple.

The fifth wonder of the world was a bronze statue colossus of Rhodes of Helios. Approximately 30 metres high, this was located at Rhodes island. This was constructed in the year 280 B.C. but 56 years after its construction, this statue was destroyed in an earthquake.

The sixth wonder of the world was the statue of God Zeus situated at Olympia. This was made by the famous sculptor Phidias in the year 450 B.C. The clothes of this 9 metres (over 30 feet) high statue were made of gold. Its body was made of ivory and the eyes of precious diamonds. This statue was destroyed by the followers of Christianity.

The seventh wonder of the world was the famous light house constructed in Pharos, a peninsula near Alexandria, Egypt. The tower of white marble was completed about 280 B.C. From pictures it seems to have been over 120 metres high with a ramp leading to the top where a beacon was kept during day and night. It remained standing until the 12th cent. A.D.

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How was the calendar started?

In the beginning of the civilisation, when man observed the sun rising and setting, he felt the occurrence of the day and night. The idea of the month came with the observation of the phases of the moon. And probably the change in the seasons gave birth to the idea of the year.
Finally with the development of science, man came to know things more correctly. He defined the period of one revolution of the earth round the sun as one year. The time taken by the moon in completing one revolutionroundthe earth was called a month and the time taken by the earth to complete one rotation on its axis was called a day.
In the initial calendars of Egypt, one year used to have 12 months, with one month having 30 days. The extra days were added to the year in the end to make it exactly equal to 365 days. The people of Greece used the lunar calendar according to which an additional period of three months used to be added to every eighth year. In the year 432 B.C the astronomer Meton found out that 235 lunar months exactly fit into 19 years.
The first major step in the direction of the development of calendars was taken by the Roman ruler Julius Caesar in 46 B.C. He took Greek astronomer Sosigenes help in this work. this calendar was based on the timetaken by the earth in completing one revolution round the sun. this was named as the solar calendar. the earth completes one revolution round the sun in 365.25 days, hence this period was taken as one year. The astronomers of Caesar defined a year as consisting of 365 days and every fourth year consisted of 366 days so that one-fourth of a day left out every year was compensated in thefourth year. this fourth year was called the 'leap year'. Any year divisible by the number 4 was taken to be a leap year. 365 days of the year were divided into twelve months. The months January, March, May, July, August, October and December consisted of 31 days each, while April, June, September and November consisted of 30 days each. The month February was taken a consist of 28 days, whereas in the leap year it would have 29 days. This calendar continued for 1600 years. However, later a mistake of 10 days was detected in these calculations, because the earth actually takes 365.2422 days to complete one revolution of the sun. As such it was natural that a difference of 7.8 days should have taken place over a period of 1000 years. To remove this deficiency, Gregory made an improvement in 1582 according to which the century years (100,200,300 etc.) Which were not divisible by the number 400, would not be made leap years i.e. February month would contain only 28 days in such century years. Accordingly the years 1700, 1800, 1900 had February of 28 days only, but the year 2000 would have February of 29 days. This is called theGregorian calendar and is in use all over the world.
The second calendar in use is the lunar calendar which is based on the movement of the moon. Since the moon takes 29 1/2 days to complete one revolution of the earth, it takes 354 days (29 1/2 * 12) for twelve such revolutions. As such the lunar year, consisting of 354 days, in less than the solar year by 11 days. This way a difference of 33 days occurs in every three years. This difference is removed by making every third lunar year consisting of 13 montsh. This additional one month is called 'Malmas' in Hindi. To make up for the days of the month, theactual numbering of the lunar days is advanced or deferred for the necessary adjustment. On 22nd March, 1957, the Government of India introduced the Shaka Calendar based on the lunar System as the Official Calendar. The Shaka era is behind the Christian era by 78 years.
In addition to these two calendar, some countries have other kinds of calendars also, which are used by them for religious purposes of those countries.

You have already read that while making the calendar, the 365 days of a year were divided into 12 months. These months have been named as January, February, March, April, May, June, July, August, September, October, November and December. Do you know how they got these names?

    January is the first month of the year. It's name originated from the Roman god Janus' name. The Romans think that this god has two faces-one for seeing into past and other into future.
    February is named after the Roman festival Februa.
    March is named after the warrior god of the Romans Mars.
    April is probably derived from the Latin word Epirer which means'to open'. Since the         spring season falls in this month and there is blossoming in trees and         plants, this month has been named April.
    May is derived from the Roman goddess Myma's name.
    The origin of June is not definitely known but probably this has been derived from the name of Juno-the goddess of heavens.
    July is named after Julius Caesar, who was born in this month. He was the first man who made big contributions to the development of the modern calendar.
    August is named after king Augustus of Rome who had won many victories in this month.
    September finds its origin in the Latin word 'Septem' meaning 'seventh'. This was the seventh month in the old Roman calendar.
    October comes outof theRoman word 'Octo' meaning eight. In the old Roman calendar this was the eighth month.
    November originates from the Latin word 'Novem', meaning nine. This was the ninth month in the old Roman calendar.
    December is derived from the Latin word 'Decem', meaning tenth. This was the tenth month in the old Roman calendar.

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How was the needle invented?

Needle is a tiny thing, but is really very useful. Had there been no needle, we would never have got our clothes stitched. It has been serving the mankind for thepast thousands of years. The excellently stitched clothes you see today speak of the marvel of the needle. Not only this, millions of people earn their livelihood in the world with the help of the needle.

We do not have definite information regarding the invention of the needle. But this much is certain that in the early stages when man had started covering his body with barks and hides, he would have felt the necessity of the needle to stitch them. And naturally he would have made some needle-like thing to do this job. In ancient times, needles were made from bones, ivory, wood, bronze and thorns. These needles were very ugly and had no holes at the end. For several hundred years man used needles made from bones. These were provided with holes at one end.
Chinese were first to manufacture steel needles. From China these needles reached Europe. This way production of steel needles was started in Nuremberg (Germany) in the fourteenth century. During the reign of Elizabeth I, a person named Elias Grouse of Germany taught the making of needles to the people of England. Now needles are manufactured in every country of the world. England and France stand first and second in the manufacturing of the needles respectively. Even though the needle is a very small thing and machines are used in its production, yet the needle passes through the hands of twenty people during the production stages.
On the 20th March 1971, a girl studentof Wistershire (England) established a world record of inserting thread in the hole of an extremely small needle 3795 times in two hours. The record is still unsurpassed.

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How was the circulation of currency started?

Generally the word currency denotes conins and paper notes issued by a government for buying an article. Today currency forms the basis of all the trade in the world.

In the beginning of the civilisation, whenever somebody wanted to buy anything, he would barter it with food grains, tobacco, hides, salt etc. In villages and under-developed countries this system is still prevailing. It is known as barter economy. Such a system used to cause lot of inconvenience to people. Thus, to overcome this difficulty, man started using gold and silver bars. However, it was not possible to determine the purity and value of these metals.
Around 700 B.C, King Gaijes of Lydia (today's Turkey) started coins' circulation made from an alloy named 'electrum'. This consisted of 25% of silver and seventy-five percent gold. These coins were shaped like beans. And when Greeks came across these coins, they found them very useful in their day-to-day business. They also started using such coins. In a very short period, this systembecame popular in many countries of the world. Later, gold and silver coins were replaced by copper coins.
The use of coins solved many problems, but their use in larger quantity proved inconvenient because of their weight. As a result, currency notes were invented. The Chinese were the first to use paper currency. They started its circulation around 119 years B.C. The notes were circulated bya a bank which used to guarantee the payment of the amount mentioned on these notes. In the modern time Stockholm's Bank of Sweden was the first to issue currency notes in July 1661. Today along with notes, even cheques have come into use. In this way, facilities for monetary exchange have considerably improved. In India the first note was printed during Sher Shah Suri's reign.

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Why is the census taken?

Census operation is now common in almost all the countries of the world. Nothing can be definitely said as to how and when it was started. But it seems that man realised the importance of census when he started living in larger groups. It is said that the population of the world was 85 million in the year 4000 B.C.
It is evident from this fact that the system of census was very much developed at that time also. After all, why is the census taken? The reasons for this have been different at different times. In ancient times, the king used to have census with a view to assess the number of people fit for fighting in wars. Another purpose for having census was collection of revenue. Previously, there were probably these two main reasons for conducting census, but now it has acquired greater importance.
Census helps in presenting a clear picture of different aspects of population. This helps the government in the preparation and execution of plans relating to education, health, employment etc. Census tells whether the population is increasing or decreasing. The knowledge of rate of birth helps in the formation of plans to cater to the needs of people in future. It also gives the ratio of urban to rural population. It is also helpful in holding elections, because it is on the basis of population only that the number of voters is fixed. Besides, census helps very much in improving law and order, economic, social and other conditions too.
The first census in our country was conducted in 1872. Since then it has been repeated every ten years. the latest has been the census of 1981.

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How are the pearls formed?

Pure pearls are very precious. You will be surprised to know that these are made by a small sea-creature, oyster. This can crawl on the ground also. The biggest tragedy with this little creature is that fish of the sea or the bigger members of its own family eat it away. When the oyster comes to the sea shore to save its life man eats it. In order to protect itself, it forms a hard shell around its own body. Pearls are made within this hard cover.
The discovery of pearls is an interesting story. Around four thousand years ago a Chinese was suffering from hunger. To quench his hunger he opened some oysters to find some eatables. Inside on oyster he found one round shining small ball. This shining thing was later on called pearl.
Whenever by chance a sand particle goes inside the shell of an oyster, it starts depositing layers after layers of the shell material on this particle. These layers are made up of calcium carbonate. After some-time the formation of the pearl inside the shell is completed. The pearl so formed is round, white and shining. This is called pure pearl. However, the pearls are not essentially white only. Their colours may be black or pink also. Man has now developed some techniques of making artificial pearls. Under these techniques sand particles are introduced inside the shell. After two or three years, when the shell is taken out of water, a pearl is found inside it. These pearls are called cultured pearls. Since pure natural pearls are very costly, generally we purchase pearls developed by these artificial techniques. On the 7th May, 1934 a pearl was found in Phillippines measuring 23 cm long with a diameter of 13 cm. This pearl weighed about 6 kg.

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What is rubber?

The history of rubber is as old as that of nature. Rubber is obtained from special type of plants. Three million years old fossils of the rubber producing plants have been found. It is a highly elastic organic material. It can be stretched eight times to its original length. A while liquid called latex comes out of the trees from which the rubber is made.

When this liquid is dried up we get rubber. Rubber so obtained is called natural rubber. In fact, there are more than four hundred kinds of plants from the juice of which rubber can be made. Each kind of plant gives a different yield of rubber. The plant which gives the hightest yield of rubber is called 'Hevea-Brasiliensis'. It is approximately thirty five metres high. Another high yielding plant is Castilla.
The real development in rubber production took place in the eighteenth century when the samples of rubber giving plants reached America. There is a very interesting story about rubber. When Columbus made his second voyage, he saw the children of the residents of Haiti Island playing with a ball which used to bounce. This ball was taken to Europe. One English scientist named Joseph Gestley observed that pencil writings could be erased by rubbing with this material. Hence it was named rubber.
In the nineteenth century, the use of rubber increased considerably because of its unique properties. It became difficult to fulfill the increasing world demand from the natural rubber. Hence scientists started developing synthetic rubber. The production of artificial rubber was started for the first time in Germany during the First World War. After that synthetic rubber was produced in other countries also. Today about fifty percent of the rubber is produced by synthetic process in the world.
Rubber is very useful for us. Various items of our daily use are made from it. Tyres, tubes, pipes, rain-coats, carpets and water-proof clothes are all made from rubber. Insulation of electric wires is done by coating them with thin layers of rubber. It is soluble in some organic liquids, hence it can be moulded in any form. Today its uses have increased so much that during 1972 the total world production of natural and artificial rubber was 3.1 and 5.3 million tons respectively.

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How the postal system started?

We are all familiar with the importance of the postal system. It is because of this that we are able to receive letters written by our friends and relatives from England or America in six to seven days. Similarly it takes only 2-3 days for the letters to reach us from Bombay, Calcutta or some other places.

All this is the marvel of the postal system. Mail vans, trains and Aeroplanes carry letters sent by us. Millions of people are engaged in this carrying of letters from one place to another.
In the ancient times, man had private arrangements for sending his messages from one place to another. During the 16th century, the governments took over the postal system. There were three main reasons for this. The first reason was the governments' intention to keep an eye on the suspicious messages. The second aim was to earn money through the postal system and the third aim was the welfare of the people. Now the service to the people is prime factor behind the postal system. Up to 1609, special messengers appointed by the governments used to carry letters. In 1680, a businessman of London started his own postal system for the city and its suburbs. In 1840, the entire structure of the postal system in England was modified. This very year postal stamps were issued and postal rates were made uniform for the entire country. Other countries of the world also followed the English system and so the postal system was established throughout the world. Today America has the biggest postal system. It has about 7.5 lac employees and some 100000 million letters are handled by the system every year. In India the postal system was started in 1854. The Air Mail service was started on the 10th February 1911. The postal system of India is considered better than that of America as far as facilities are concerned.

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What is malaria and how it spreads?

All of us are familiar with malaria. More than two million people of the world die of this disease every year. This disease is found in all the countries of the world, but is more common in Central and South America, Far East Asia, Central Africa, countries around the Mediterranean Sea, hot belt areas and places situated on the seashores.
Previously it was believed tht malaria is caused by a poisonous gas produced in dark and damp places. The word 'malaria' is derived from an Italian word meaning 'foul air'. It was Sir Ronald Ross who for the first time in 1902 conclusively proved that malaria is caused by mosquitoes. He was awarded Nobel Prize for this discovery.
Scientific experiments have proved that malaria is caused by a parasite known as Plasmodium. the parasites of malaria are carried by the female anopheles mosquito in its belly which is connected with salivary gland. When the female anopheles mosquito bites some healthy peson, the parsites of malaria enter his blood alongwith the saliva. These parasites attack the red blood corpuscles and destroy them. As a result man gets shivering and high fever. These are the main symptoms of malaria. If not properly treated, red blood corpuscles become scarce and there is obstruction in the veins of the brain. Thus patient can die.
Malaria can be easily treated now. When somebody suffers from malaria, he is given chloroquin tablets. Doctors advise primaquin tablets also for protection from malaria attacks.
Health experts are of the opinion that malaria will be eradicated from this earth one day. They say that in order to stop this disease, it is essential to eliminate anopheles mosquitoes. To fulfil this aim, health organisations from all over the world and governments of many countries have made joint programmes. Under this programme the following advice has been offered to prevent occurrence of malaria.
To prevent malaria, DDT insecticides should be sprayed to destroy the anopheles mosquitoes. Accumulation of water should be prevented so that mosquitoes may not breed there. Mosquito nets should be used while sleeping in the night. At the time of sleeping, the exposed part of the body should be massaged with mustard oil. Kerosene oil should be sprayed over stagnant pools of water. Flit should be sprayed in dark spots of the house. This is the way to stop the transmission of malaria parasites from persons suffering from this disease to healthy persons via mosquitoes.

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How do we get wool from the sheep?

We wear warm clothes during the winter. These clothes are made of wool. We get wool from the sheep. Hair grow on the body of the sheep as they do on our head. This hair of the sheep is called wool. The wool protects the sheep from cold in winter. Do you know how wool is obtained from the sheep?

The hair of a sheep are cut once in a year. When the winter is about to end and the summer is round the corner, the sheep does not require hair. At that time only, the hair of the sheep are clipped by large scissors. The hair so clipped contain thorns, dirt and vegetable oils. To clean it, the hair are made into balls and tied with wool twine. Now, this wool is cleaned. Thereafter, the wool is combed to straighten out the curls. Next it is spun into yarn. The wool yarn is then made into cloth by weaving or knitting.
Nobody knows when man first tamed the sheep. But records reveal that the primitive man had domesticated sheep for both wool and meat. After the passage of centuries, man has now been able to breed many varieties of the sheep. Some of them are valuable for their wool and others for their meat. A species of sheep named 'Merino', found in Spain and Africa is highly productive in wool. Its whole body except legs and nose is covered with hair. Now Merino sheep are found in the United States of America and Australia also which produce large quantities of superior wool. Wool obtained from Merino sheep is very warm.
Today, Australia is the biggest producer of wool in the world. Thirty percent of world's wool is obtained from Australia alone. The United States of America ranks next to Australia. The U.S. produces 300 million pounds of wool every year.

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How is copper useful to us?

After gold, copper was the first metal to be discovered by man. History reveals that it was used by the man in stone age. It is found in nature in solid or granule form and it is possible that it was discovered in this state only. Man had started using copper instruments, weapons and ornaments around 6000 B.C By 4000 B.C.
the mining of copper had begun. For thousands of years copper was the only metal used by him. Later, when he came to know that bronze, an alloy of copper, Zinc and tin is harder than copper, it was used for making utensils, weapons and ornaments.
Copper is a metal of red colour. Native copper is found in small quantities. Most of it occurs in the combined state as sulphides, carbonates, silicates and oxides. Copper pyrite is its most important ore. About 50% of the world's supply of copper comes from copper pyrite.
During the last hundred years the use of copper has increased tremendously. Large quantities of copper are used by the electrical industry for making wires, because of its softness and tenacity. It is a very good conductor of electricity and heat. Thousands of tons of copper is used all over the world for making electric wires every year. This is also used for making motor and dynamo coils. Copper coins have been long in vogue throughout the world.
Copper easily makes alloy with other metals. Bronze and brass are its main alloys. Bronze contains 90% copper, 4% tin and the remaining 6% zinc, glass and nickel. Brass has 70% copper and 30% zinc. Both these alloys are very useful. Many varieties of utensils, as well as items of industrial use, are made of these two alloys. Copper also makes an alloy with aluminium which is called aluminium bronze.
Copper makes many compounds with other elements too. All its compounds are poisonous and hence they are used as insecticides. Copper has become so useful that every country has been trying to increase its production. You will be surprised to know that its production rose to approximately 6.5 million tons in 1970 from about 4.1 million tons in 1961. The usefulness of copper can be guessed from it.

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What is helium gas?

Most of the gases can be prepared in the laboratory but there are some gases which are found in nature only. Helium is one of them. It is an inert gas. It is odourless and tasteless. Helium has some special characteristics due to which it has proved very useful for us.

Next to hydrogen it is the second lightest gas but it has a speciality that unlike hydrogen it is not inflammable. On account of its lightness and non-inflammability, it is used in weather balloons. It is used by air force, army and navy. Helium is also used to ease the breathing difficulties of asthmatic patients. Deep sea divers are given a mixture of oxygen and helium for breathing so that after coming back, they do not suffer with bends. This is also used to weld aluminium. A mixture of helium and neon is used to produce laser beams. Helium can be liquefied at -268.4 degree centigrade and hence liquid helium is used in low temperature work.
This gas was discovered in 1868 independently by English scientists Sir Joseph Norman Lockyer and Pierre Janssen. While studying the solar spectrum to find the elements present in the sun, they came across some lines which were not observed earlier. These lines suggested the presence of a new element in the sun. This element was named as Helium after the Greek word '    ' meaning 'the sun'. Thereafter, scientists made efforts to know if helium was present in the earth's atmosphere. They detected helium in the atmosphere, but in very small quantities. Atmospheric air contains only one part in 186,000 parts, i.e., 0.0005239 percent.
There are some places in America like Texas, New Mexico, Kansas etc. where the amount of helium present in the atmosphere goes upto 8%. It is also found in Canada, Africa and the Sahara desert. America is the biggest seller of helium to other countries, since it is the world's richest source of this gas. In earlier times this gas was very costly, but now it has become quite cheap.

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How is oxygen useful to us?

Without oxygen there would have been no life on this earth. Without it no living being-trees, plants or animals-can survive. Hence it will not be a misnomer to call it a life-giver. Do you know what it is and why it is absolutely essential for us?

Oxygen is a gaseous element. This was first discovered by Lavoisier and Priestley. It is a colourless, tasteless and odourless gas. In the atmosphere the air contains 21% oxygen, 78% nitrogen and rest one percent other gases. In the earth's crust, it is found in the form of oxides of metals, the proportion being up to 50%. At - 185 degree centigrate under right pressure it can be liquefied. In the liquid state its colour becomes light blue. At - 219 degree centigrate, it can be converted into solid state.
In the laboratory, this is obtained by heating the mixture of potassium chlorate and manganese dioxide. From the atmosphere, it is obtained by the fractional distillation of air. The air is compressed to two hundred times the normal atmospheric pressure and passed through a narrow hole into a chamber. As the pressure is suddenly dropped, the air is liquefied and collected in the chamber. The nitrogen gas is separated from this by a special method and oxygen is left in the liquid state.
Oxygen is very useful to us in many ways. All the living beings use oxygen for breathing. Trees and plants take oxygen in the night for survival. By burning oxygen gas along with the acetylene gas, a high temperature flame is produced. This flame is used for welding and cutting metals. Oxygen is also used as a fuel in space vehicles.
When patients have breathing difficulties, oxygen is given to them to ease this trouble. It is also used for breathing purposes while climbing mountains or diving in the sea. This helps in the oxidation of food in our body which ultimately gives us energy. Our fuel burns due to oxygen and the aquatic animals survive with its help.
We cannot breathe in pure oxygen for long. Fresh air is essential for us because it contains more oxygen and breathing in fresh air makes us feel fresh and active. Thus, we should keep open the doors and windows of our rooms for fresh air. we should not cover our face while sleeping as this stops the fresh air from reaching in.
We feel suffocated in big crowds because the quantity of oxygen becomes less there. During winter, one should not sleep in a closed room by burning coal. The burning of coal converts the oxygen into carbon dioxide and carbon monoxide. Carbon monoxide is a poisonous gas and very injurious to health.

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How is liquid converted into vapour?

It is commonly observed during the rainy season that water falling on roads and streets disappears after few hours. Similarly, in summer, wet clothes dry up very soon. Do you know where this water goes? This water gets converted into vapour. Conversion of water into vapour is called evaporation.

How does evaporation take place? Every substance is made up of very small particles called molecules. These molecules are held together by strong forces of attraction called cohesive forces are opposed by the repulsive forces caused due to the motion of molecules. As long as the cohesive forces are far greater than the repulsive forces the substance remains in the solid state. When the substance is heated up, it absorbs heat energy due to which the molecules are set up in rapid motion. This motion starts counterbalancing the cohesive force, that is, this force tries to separate them apart. When the repulsive force generated by the motion of molecules equals the cohesive force, matter changes from solid to liquid state. If the liquid is still heated, the molecules move still faster and when the force due to increased motion exceeds the cohesive force, the molecules of the liquid become free and escape into the air. It is how the liquid is converted into vapour. The liberation of the molecules from the liquid surface and going into the air is called evaporation.
This explains the drying up of the clothes. If the wet clothes are put in the sun, they dry up faster because at the higher temperature the motion of molecules becomes faster and the evaporation is also faster. Evaporation takes place at all temperatures but the rate of evaporation increases with the rise in temperature. It takes place more rapidly when the air is dry. That is why clothes dry up more quickly on a dry day than on a damp cloudy day.

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How is silicon useful to us?

Silicon is a non-metallic element. It is not found in nature in a pure form. Pure silicon is a hard, deep black or brown coloured material. It shines like metals, and is crystalline in nature. At Ordinary temperature it does not react with other elements, but at higher temperature it makes compounds with other elements.
The earth's crust has 28% silicon whereas china clay contains 50% silicon. It is also found in rocks, sands, water, bones, etc. Sand has a large quantity of silicon.
Silicon is extracted from the compound silicon dioxide. When silicon dioxide is heated in an electric furnace, oxygen is removed and silicon is seperated from silicon dioxide.
Most of silicon is found in e form of silica which is another name of silicon dioxide. It is a compound of silicon and oxygen. Quartz, jasper, milky stone and sand-all are different forms of silica. Silicate is another compound of silica. Mica and asbestos are found in the form of silicates.
Silicates are very useful to us. They are used in making many kinds of glasses, enamels, china clay, etc. Sodium silicate is used in the making of soaps, prevention of the rotting of wood and eggs and in dyeing. It is also used for smoothening and for making artificial rubber.
Silicon in its pure form is used in photocells, transistors and othert electronic parts. A compound of silicon and carbon called silicon carbide or carborundum is used for polishing metals. By mixing silicon in steel, its utility is enhanced. Silicon is also used for making semiconductors which have proved very useful in our life. Silicon mixed with sand and earth is used for making bricks.

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Why do hot things burn us?

An object is said to be hot if its temperature is more than our body temperature. If we touch such an object, heat flows from it to our body and we feel its sensation. Similarly, an object is said to be cold if its temperature is lower than our body temperature.
When we touch it, heat flows from our body into that object. Do you know why it happens like that?
We know that our body is made up of cells. And consequently these cells are made up of molecules. At normal body temperature these molecules are in motion. When a hot substance touches some part of our body, the fast moving molecules of that substance accelerate the motion of the molecules of the cells in the affected part. And when the molecules of cells stand the fast vibrations the cells start breaking up. It is the breaking up of the cells that gives the burning sensation. To repair the damaged cells, the blood circulation becomes faster in the affected area. That is why the affected part becomes red.
When the temperature of the object touching the body is very high, a large number of cells and nerves break up. The heat of the substance dehydrates cells of the skin and they break up. This is called burning.
Sometimes very hot substances destroy the fat, molecules and bones. This causes deeper wounds in the body. The scars caused by such burning are removed by grafting the skin from some other parts of the body.

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How is dew formed?

In the early hours of morning you might have seen small drops of water on grass, plants and trees shining like pearls in the sun's rays. These water-drops are called dew. Quite often people think that dew drops, like rain water, fall on the earth from sky during night but this is not true.

Dew drops are formed due to condensation of water vapours. Air around us contains water vapours which we call moisture or humidity. Hot air contains more moisture as compared to cold air. During the night when the hot air comes into contact with some cold surface, water vapour present in it condenses on the cold surface in the form of droplets. These tiny drops of water are called dew drops. The process of dew formation can be seen in a simple experiment. Take a tumbler and place it on a table. Now put some ice or ice-cooled water inside the tumbler. You will notice that after some time on the outer surface of the tumbler small drops of water have appeared. These water drops are formed by the condensation of the water vapours present in the air. Exactly in the same way when the trees, plants and grass become cold during night, the water vapours of the air condense on them in the form of dew.
The dew formation is more when the sky is clear and less when it is cloudy. This is so, because there is more evaporation of water when the sky is clear and the trees and plants are also colder during night thus the dew formation is more. But when it is cloudy, trees and plants do not become cold in the night and hence there is less dew formation. As the sun rises high in the sky, these dew evaporate into air.

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When were newspapers started?

Newspaper is the most effective medium of communication in the mordern world today. Millions of newspapers are published in the world. Do you know when newspapers were started and how much effort did it take to bring them to the present form?

According to recorded facts, the first newspaper of the world was published in China around 1000 years ago. Its name was 'Tching Pao' which meant 'news of the capital'. The government used to communicate main events to the public with its help.The second newspaper of the world was the 'Acta Diurna'which meant 'Daily Happenings'. These two arethe oldest newspapers as per recorded history.
The first daily newspaper of the world was the 'Morning Post' which started in London in 1772. After this, another daily newspaper 'The London Times', started its publication from London itself and it is published even today.
The first newspaper of India-'The Bengal Gazette' started on 29th January 1780. Later its name was changed to 'The English Man'. Today, in addition to those published in English, newspapers are published in all the Indian languages.
Today, around 500 million people in the world purchase newspapers everyday. More than eight thousand newspapers are published in Russia alone. They are read by 120 to 130 million people. Russia publishes the largest number of newspapers in the world.
The first newspaper to cross the one million circulation mark was 'Les Petit Journal' of Paris which did it in 1886. In 1970 the 'Ashashi Shimbun'-a newspaper of Japan reached the circulation of 10 millions. The biggest edition of one single newspaper was taken out by the  'New York Times' on October 10, 1971, having 15 sections, 972 pages and 102 million lines of advertisements. It weighed 3.5 kg and was priced at 50 cents.

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What is quicksand?

Quicksand is a peculiar creation of nature. Though it has an ordinary appearance, yet it is very dangerous. From a distance, you cannot distinguish between ordinary soil and quicksand. By mistake, however, if some body enters quicksand, he will slowly go down and finally sink in it.
Once you are trapped in quicksand, it is very difficult to get out of it. Quicksand can devour anything big or small. Do you know what quicksand is, how it is formed and how to save oneself if trapped in it?
Broadly speaking, quicksand is a type of slush, but its depth is much more. Quicksands are normally formed on such river banks and sea shores where the earth's crust contains layers of clay with huge quantities of sand above. Water waves deposit water into this mixture of clay and sand. The inner layers of the clay prevent the water from draining away. Slowly and slowly this stagnated water starts rotting and converts the entire soil into deep slush. It becomes pasty. It is how quicksand is formed.
Quicksand contains more of water than soil. Hence people can swim in it. But it is dangerous to swiftly move hands and legs the moment you are trapped in it. On the contrary you should make slow movements and allow water to accumulate around you. You will find it easier to swim in this accumulated water and come alive to the solid ground on the bank. This way you can save yourself from quicksand.

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When were the advertisements started?

Advertisement have become a part of our lives. Thousands of goods are advertised through the media like radio, television and the press. They help to popularise the products among the consumers and buyers and give a boost to sales.

Today, in all the countries of the world, there are advertising agencies which advertise goods in many attractive ways. Besides increasing the sale of goods, advertisements are also used to make the public vigilant. Moreover, by keeping certain legal checks on advertisements, the tendency to cheat and indulge in malpractices can be curbed to some extent. In many countries, private or social service organisations issue advertisements informing the people about prevention or check of fire, rehabilitation of the handicapped, the traffic rules and control of crimes etc.
Do you know how did they start? From ancient times when man started trade, he adopted methods to convey to his customers his goods' qualities. In the beginning, the traders used to attract customers by shouting the specialities of the goods. After some time, traders and manufacturers started using walls for this purpose. In the year 1450, when printing was started, the trader's task in this regard became easy. In 1460, William Caxton, for the first time, published an advertisement of a religious book. And with the start of newspapers there came a revolution in the world of advertisements.
Now, not only traders but also politicians, social workers, publishers and government agencies use advertisements to convey their message to the public. In the world billions of rupees are spent every year on advertisements. In 1968, the United States of America alone had spent 1800 million dollars on advertising. Similarly, West Germany had spent 400 million dollars, Japan 150 million dollars, Britain 120 million dollars and France and Canada 100 million dollars each.
Today, the number of advertisements is so large that people are unable to give more attention to them. As a result of tremendous competition among manufacturers the advertisements contain various types of assurances and offers of gifts. In India, advertisement on radio started with the Vividh Bharati Vigyapan Seva (Vividh Bharati Advertisement Service) on November 15, 1967. On television this service was started on January 4, 1976. Today advertisement is regarded not only an art, but also a science. Keeping in view the tastes and habits of the customers, various kinds of advertisement are prepared so that more and more customers are attracted towards them.

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What is Nobel Prize?

Nobel prizes are awarded every year and the winners of this prize are talked about throughout the world. Their life-sketch and works are published in the newspapers. Their names are heard on radio and television. After all what is a Nobel prize and why it is given so much importance?

Under this prize, the prize-winner gets a gold medal, a certificate and a large sum of money. The Nobel prize is the world's most important prize. This prize is given to persons with most outstanding contributions in six fields, namely- Physics, Chemistry, Literature, Physiology or Medicine, Peace and Economics. Economics was added in the list in 1969 for the first time. One prize is awarded in every field. If there are more than one recipients of the prize in one field, the prize money is equally distributed amongst all the winners.
Do you know how the Nobel prize was started? This is surprisingly true that this prize was instituted by a man who was the founder of the science of destruction. This scientist was Alfred Bernhard Nobel. The Nobel prize is given after his name. He was born in Stockholm on 21st October, 1833 and he died on 10th December 1896. His father was also a scientist. Though he was a citizen of Sweden, yet he was educated in Russia. He invented the explosive called dynamite. This material was widely used for breaking rocks, digging petrol wells and of course in wars. For his valuable discovery, Nobel became world famous. He earned huge sums of money on account of this material. At the time of his death, he left behind a fabulous sum of 9,20,000/- dollars. He left a Will indicating that the interest on this money should be distributed as prizes to persons for their outstanding works in Physics, Chemistry, Medical Science, Literature and Peace. This prize was named as Nobel prize. The first Nobel prize was given to Rontgen on 10th December 1901 for his outstanding research in X-rays. The prize money was 40,000/- dollars. Even though the prize money is not large, yet the winners of this prize are treated with great respect all over the world.
Nobel prizes are awarded by a council called 'Nobel Foundation of Sweden'. The Royal Academy of Sciences, Stockholm selects the best scientists of the year in the fields of Physics and Chemistry. The Caroline Institute of Stockholm selects the best man in the field of Medical Science, while the Swedish Academyof Literature does it for literature. Similarly a cojmmittee of five persons appointed by the Parliament of Norway selects the best persons for peace.
Till now many outstanding people of the world have already received the Nobel prize. Some of them are: Albert Einstein, George Bernard Shaw, Rabindra Nath Tagore, Sir C.V. Raman, hargobind Khorana, Mother Teresa etc.
The youngest man to receive this prize was Sir William Lawrence Bragg of England, who received the NObel prize for Physics at the age of 25 in 1915.
Nobelbecame so famous in the world that the 102nd element was named as Nobelium after him. There is an institution in Sweden which has also been named after him as Nobel Institute of Sweden.

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Why was the Great Wall of China built?

We all have heard the name of the Great Wall of China. this is the longest wall of the world, being more than 2694.4 kilometers (1684 miles) long. Its height ranges from 4.57 to 9.2 meters (15 to 30 feet)

while thickness is 9.75 meters (32 feet). The costruction of this great wall was started in the year 221 B.C. and it took almost 15 years to complete this work. This was built of stones and bricks. Now the question arises: what was the necessity of costructing such a huge wall?
This great wall was built to protect China from Mongol invaders. About the year 246 B.C. China was divided amongst small provinces. King Shih Huang Li united different provinces of China into an empire. To the north of this empire lived barbaric Mongols and theking felt that at any time they might attack his empire. To protect China from this danger he ordered the construction of a huge wall. So a wall starting from Shanhi Kuan in the bay of Pohai to Chiakuman in Kansuwas constructed.

Did the king achieve his goal? Unfortunately-no, because the wall was broken at many places and Mongols got an opportunity to attack China. The purpose of constructing the wasll ould never be fulfilled. Still many parts of the wall are broken. Now the Chinese have even taken to farming beyond the wall.

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What is the Red Cross and how was it born?

The Red Cross is an international humanitarian organisation.Initially its field of activity was confined to looking after soldiers wounded in wars.But now it works for alleviation of all forms of human suffering.Almost all the countries of the worlds branches of Red Cross which works both during war and peace.

It serves helpless people without any discrimination on grounds of caste,creed or nationality.During peace time,its activities are:to give first aid,to prevent accidents,to keep drinking water safe,to train nurses and midwives,to look after maternity and child welfare centres, to establish hospital hospitals, to set up blood etc.This organisation is a friend of the entire humanity.
The story of the origin of the Red Cross is very interesting.The founder of this orgnisation was Jean Henri Dunant.On June 24,1859,he had gone to the city of Lavardi in connection with his business.At that time,the city was the focal point of the continuing war between France and Austria.Thousands of men and women injured in war were seen in great pains.Many of them were dying for want of first aid.This heart-rending sight had a great impact on his mind.He forget his own workand dedicated himself to the service of the distressed people .His efforts saved many lives.
After this war he made an appeal telling the people of the world that soldiers wounded in wars were helpless people and human beings it was the duty of everybody to help them.This appeal had a great impact on the people and in the international conference held in Geneva in 1864,fourteen coutries accepted the establishment of Red Cross.The flag of switzerland had a white cross against red background changing it ,a 'red cross' against a white background,the name and flag to this organisation was given. Thus Red Cross came into  existence.
The Red Cross has three organs. The first is the International Committee of the Red Cross. It is an independent committee of twenty-five citizens of Switzerland. Its main office is situated in Geneva. The second organ is the league of the Red Cross Societies while the third is the National Red Cross Societies.
During wars, the International Committee of the Red Cross works as an intermediary between the National Red Cross societies and the countries involved in the wars. It looks after the prisoners of war in their camps and arranges relief for them. It takes care of their mail and establishes contact with their relatives. This organisation also serves the people affected by cyclones, epidemics, famines etc.

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Why do watches have jewels?

Whenever somebody purchases a watch he often enquiries about the number of jewels in it. The number of jewels is inscribed or printed on the outer cases or the dial of the watch. It is commonly believed that the larger the number of jewels, the better and more durable the watch will be.
Would you like to know what are jewels and why are they fitted into watches?
A good watch is one which gives correct time and does not easily go out of order. If you open a watch, you will notice that the internal mechanism of the watch is very complicated. It has many big and small parts of different kinds. A watch contains roughly 211 parts. Amongst these parts, is a small wheel which is always in motion. Along with it, there is a hair-like wire which is called spring. When we wind the spring, the watch starts ticking. The energy stored in the spring by winding is used for running the watch. In addition to this wheel, there are many other wheels, which are constantly rotating. These wheels move the hour, minute and second hands. The axles of these wheels rest on pivots. When the wheels rotate, friction is generated between the axles and the pivots. Due to this friction, pivots and axles can wear out soon and then the watch will show incorrect time, and finally stop working. To reduce this friction, small pieces of some very hard but smooth materials are used as pivots. These small pieces are called jewels. In general, the materials to be used as jewels are ruby and sapphire. They are precious stones next to diamond in hardness. The axles of the wheels of the watches pivoted on these jewels go on rotating without experiencing much friction. Because of hardness, these jewels do not wear out and the watch does not go out of order easily. Hence jewels are used in the watches for their longer life.

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Why does the rising and the setting sun appear red?

When the sun rises in the morning, it appears like a red ball. As the day advances, the colour appears white, but at the time of sunset in the evening, the colour again appears red. Do you know why it is so?

We know that the earth revolves round the sun. The part of the earth receiving the sunlight is lighted and we say it is day in that part. We also know that the white sunlight comprises seven colours-violet, indigo, bleu, green, yellow, orange and red in the morning and evening, when the sun is near the horizon, the rays have to travel a longer path in the atmosphere to reach us than in the noon. The distance travelled by the sun rays in the atmosphere in the morning and evening is fifty times more than that in the noon. The dust, smoke and water vapours present in the atmosphere scatter away these colours differently. Violet is scattered most and red is scattered least. Therefore, the amount of red light which reached our eyes is maximum. As a result the sun appears red while rising and setting.

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How did America get its name?

Today America is regarded as the most affluent and powerful country of the world. Its development is mainly a story of last two hundred years. Earlier it was divided into 13 small colonies. We know that America was discovered by Columbus. Then why was it not named after him?

It is a matter of chance. The story as to how America was named is very interesting.
The world famous Italian traveller Columbus, set out on a sea voyage in search of India. He reached some island in the morning of October 12, 1492. He landed over and named it after the name of King Ferdinand and Queen Isabella of Spain as "San Salvador". This island was just a small part of America. Now it is called the Watling Island. He misunderstood it as India and started calling its inhavitants as Indians. Even today they are called Indians. From there he wanted to go to Japan, but instead he reached Cuba & Hispaniola. Disappointed with his failure to locate India, Columbus returned to Spain on March 13, 1493.
On his second voyage, which he started on September 24, 1493, he discovered several virgin islands like Puerto Rico and Jamaica. But he did not succeed in locating India. In his third journey in 1498, he discovered Trinidad and touched South America.
During this period a Spanish sailor named Amerigo Vespucci announced that he is the first person to have landed at the mainland of SOuth America which he did on June 16, 1497. However, experts are of the opinion that Amerigo had not gone on a voyage till 1499. In 1499 Aloso de Ojeda accompanied by Florentine Amerigo Vespucci sailed up to the Orinoco straits and discovered Venezuela. During 1501-1502 Vespucci himself directed a sea voyage under the Portugese banner and discovered the shores of Brazil. It became clear to Vespucci that part of the land considered by Columbues as a portion of Asia was in fact a continent of the New World. In the beginning of the year 1500, Vespucci's writings got wide circulation and he got the credit of becoming the first European to have discovered South America. A German geographer named Waldsee Miller, named the territory of Brazil as America in honour of 'Amerigo' Vespucci. This very name caught people's attention and the entire world started using this name.

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Are the molecules of all substances in motion?

Every substance is made up of very tiny particles called molecules. A molecule is the smallest part of the matter that can exist independently and exhibits all the properties of that matter. For example, if we take a molecule of sugar, it will exhibit all the properties of sugar such as taste, shape, colour etc.
Molecules of different substances differ in size. Some are only few billionths of a centimeter in size while some other molecules are thousands of times larger. Molecules of gases are small in size. One cubic centimeter of air contains about 2.5 *10 to the power 19 (25,000,000,000,000,000,000) molecules.
Even though a tiny piece of matter contains a very large number of molecules, yet there are empty spaces in between them. Molecules of matter are constantly in random motion. As the temperature increases, the motion of the molecules also increases. the hotter the substance, the faster is the motion of the molecules. Molecules of a gas move very fast in comparison to the molecules of liquids and solids. Even the molecules of ice are in motion. Now the question arises: when molecules of all the substances are in motion, why don't substances appear shaky? The reason is: there exists a force of attraction between the molecules which keeps them together. If this force is not present, the molecules of matter will scatter away in all directions.
When heat is given to the molecules of a solid, the speed of the molecules increases and the force of attraction decreases. If we continue adding heat, the speed of the molecules would be still faster and the solid will change into liquid and finally to gaseous state.

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Why is gold so costly?

From ancient times, gold has symbolised affluence. The statues and temples of our gods and goddesses are decorated with gold ornaments. Kings and emperors always gave great importance to gold. Man has always shown a great affinity for gold. After all what is so special about gold that it has always been costly and day by day it is becoming costlier?

The preciousness of a substance depends on many factors. First of all it is its rarity. Secondly, the cost of an item depends upon its utility. Thirdly, the cost of a substance is related to its beauty. Fourthly, substances which are least affected by natural changes are also expensive. Gold is an element that contains all the four qualities. It is a rare metal found in very small quantities. Its colour and shine are very attractive. It is not affected by heat, cold, wind and humidity. No wonder, it is a costly metal.
Gold is a shining metal of yellow colour and found in nature in very small quantity. It is found in both free and combined states. To extract gold from its ores is a costly process. Once a small rock of seventy and a half kilogram found in Victoria, Australia yielded seventy kilograms of pure gold. But such rocks are rarely available. Gold is taken out of gold mines in extremely small quantity. It is traceable in sea water also, but its extraction is uneconomical.
About ten percent of the total gold production of the world is used in ornaments. It is used in medicines also. Till 1914, currencies of different countries were exchanged in terms of gold only. Even today the entire international trade is conducted with the help of gold. It is used in dentistry also. It is a soft and malleable metal, hence it can be easily converted into thin leaves. Thin layers of gold can be coated on other metals also. Some other metals like copper etc., are mixed in it to make it hard. It is unaffected by acids and alkalies but dissolves in aqua regia.
Gold is a means of accumulating wealth. Since the price of gold is increasing constantly, people purchase it and hoard it instead of currency notes.
Africa, Russia and the United States of Amarica are the biggest producers of gold in the world. The gold mines of India are situated in Karnataka.

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What causes baldness in people?

There are many theories regarding baldness. Some people treat baldness as the indication of arrival of old age while some are of the view that bald men are intelligent. Baldness is also treated as a sign of richness. Some people think that bald men are fools. Whatever may be the significance of baldness,
one thing is certain that by losing hair, man is deprived of that beauty which otherwise he would have.
Baldness or alopecia is mainly of two types: permanent and temporary. Heredity, age and male sex hormone (androgens) production are three main factors causing permanent baldness. Other causes of permanent baldness are scar producing skin diseases, injuries, inborn lack of hair development and severe injury to hair growing centres by chemical or physical agents.
Temporary baldness may be due to high fever, typhoid, pneumonia, influenza etc. Hair starts falling due to weakness also. Baldness caused by disease and weakness can be cured by nutritive diets and tonics. X-rays, ingestion of metals and drugs, malnutrition, skin disease and endocrine disorders are some other causes of temporary baldness.
Baldness can be controlled to some extent by proper care of hair and balanced diet. No successful drugs or therapies have yet been developed to treat baldness.

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How is dust useful to us?

Most of the people think that dust is very harmful to us. But this is not true. Dust also is very useful to us.Before we go through the uses of dust, it is essential to know as to what dust is and how it is formed?

Every solid substance is composed of very small particles.
When these small particles of matter are scattered, they become dust particles. For example, if we go on breaking a brick or a stone into small pieces, they will turn into small particles. These particles get mixed with air and are called dust particles. The air carries dust particles from one place to another. There are different ways by which dust is formed. When solids break, dust is formed. Smoke generated by the burning of coal, wood, petrol etc. also produces dust. Dust particles also come from dead plant and animal matter, sea salt, desert, volcanic sand etc. The particles of the earth's surface also fly in air in the form of dust.
The biggest use of the dust particles is that they help in the formation of the rains. The water-vapour in the clouds condense on the dust particles in the form of water-drops. These drops fall on the earth as rains. The absence of dust particles can delay the rain. Likewise, mist, fog etc. are also formed due to the presence of dust particles.
The dust particles present in atmosphere reflect the sun-rays in all directions. Due to this reflection, even after the sun set, there is not complete darkness for one to two hours. The appearance of red colour at the sunrise and sunset is due to dust particles and water vapours. The beautiful rays of the sun seen in the twiligt is also due to dust particles. Thus we see that the dust particles which are regarded as useless by people are really very useful.

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How do we remember things?

The processes of learning, memory and understanding are directly related to behaviour. Almostall human behaviour is learned. Learning takes place all the time. The brain keeps a trace of all the events taking place in our life.

According to psychologists there are four kinds of learning. Classical conditioning is the simplest kind of learning. Ivan Pavlov studied it during early 1900s. He offered a dog food and at the same time rang a bell. The sight of food made the dog's mouth water. Pavlov called this an unconditioned response because it was not learned. Soon, however, ringing the bell was enough to cause the dog's mouth to water. This was called conditioned response. Classical conditioning is often called respondent learning.
Another form of learning is called instrumental learning. Often a person learns to do something as a result of what happens after the person does it.
Multiple response learning is third type and happens when a skill is learned. A sequence of simple things must first be learned. Using a typewriter is our kind of multiple-response learning. At first, a person has to type letter by letter. With practice, the person learns to type word by word or phrase by phrase.
Fourth type of learning is insight learning. It means solving a problem through understanding how the different parts of a problem fit together. A simple example is that of a young child wanting to climb on top of a table. The child may use a stool to get on to chair and then use the chair to climb onto the table.
There are two basic theories to explain as how we memories events. According to one theory, memory is said to be stored in the brain as a memory trace. When we learn or experience something, impulses are generated in the nerves of the brain. These impulses impart their effects in the brain in the form of a record. According to the other theory, sensations created by learning produce some permanent changes in the brain which remain there in the form of memory. According to some biologists, the R.N.A. (ribo-nucleic acid) present in the brain keeps the record of events. It has been observed that the quantity of R.N.A present in the brain keeps o increasing from the age of three to the age of forty. During these years, the memory of the man also increases. The quantity of R.N.A is almost constant from the age of 40 to 55 or 60. Therefore man's memory is almost constant during this period. After the age of 60, the quantity of R.N.A. starts decreasing and so does the memory.
The only effective way of remembering something is to repeat it many times. Interest is very important. Boring things are much more difficult to remember than something that we understand and are interested in. Motivation or wanting to do something, is also important.

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