Why does an Electric Bulb Give off Light?

A light bulb gives off light because an electric current is passed through its filament, a thread of tungsten metal thinner than a human hair, which then becomes white hot.

Sir Joseph Swan (1828-1914) in England and Thomas Alva Edison (1847-1931) in the United States constructed the first incandescent electric lamps in 1879. They succeeded in preventing the rapid burning up of the filament by oxidation, but their problem lay in the choice of a suitable material for the filament.

Edison sat in his laboratory watching a filament of charred cotton thread glow in a glass bulb, which had been exhausted of air, for 40 hours. But the thread was too fragile to sustain the heat provided by the electric current. A material was needed that would stand great heat, for the hotter the filament, the brighter is the light given by the lamp.

But even with the present day use of tungsten, the problem still remains in that the more a filament is heated, the sooner it will burn away. To solve this problem, gas discharge lamps were invented.

These consist of glass tubes filled with sodium or mercury vapor, or neon gas. At each end of the tubes are electrodes, or contacts. When an electric current is applied to one of the contacts it passes through the gas to the other contact, causing the gas to glow and give out light.

Why are Ice Skates made of Steel?

Ice Skate blades are made of steel for three reasons.

1. First because steel is immensely strong, hard and resistant to wear.
2. Second, because it is a relatively low conductor of heat.
3. And third, because it can be sharpened to a keen edge.

A skate blade has to resist tremendous pressure because it is hollow-ground, so that only the edges rest on the ice.

The smooth gliding movement associated with skating is made possible by thin film of water on the ice produced by heat friction as the blade strikes the surface. As it is relatively poor conductor of heat, the steel allows the heat to remain for a longer time at the edge of the blade, thus ensuring the necessary film of water.

There are specially designed blades for different kinds of ice-skating. The figure skater's blade is hollow ground and curved with saw-like teeth at the toe to enable the skater to get a better grip on the ice when carrying out certain movements.

The speed skater uses a thinner blade, about 16-17 inches long, sharpened, with a flat surface. This type of blade gives the racer a longer stroke.

Where was the wheel invented?

The earliest wheels discovered so far were found in graves at Kish and Susa, two ancient Mesopotamian cities. These wheels are believed to date from 3,500 B.C. They were made from three planks, clamped together with copper clasps. This kind of wheel also existed in ancient times in Europe and the Near East. No one is sure where the wheel was invented, but this archeological evidence suggests it was probably in ancient Mesopotamia.

A wheel with proper spokes was not invented until after 2,000 B.C. There are records of this wheel in northern Mesopotamia, central Turkey, and north east Persia. By the 15th Century B.C., spoke wheels were being used on chariots in Syria, Egypt, and the western Mediterranean.

The solid wheel was used mostly in farming. Tripartite wheels - wheels with three spokes - were being used in the Bronze Age in Denmark, Germany, and northern Italy for carts.

The invention of the wheel made it possible for people to transport heavy objects much more easily. It also enabled them to travel farther and trade with each other more easily, and so find out about other countries and customs.

Where was the First Radio Signal sent from?

Guglielmo Marconi is usually credited with sending the first radio message. Marconi was born in Bologna, Italy. He came to England in 1896 and obtained a British patent for his wireless telegraphy system. In 1897 he established a radio transmitter on the roof of the Post Office at St. Martins-le-Grand in London, and sent a message a distance of a few hundred yards.

He continued to improve his apparatus and in 1898 radio was installed aboard a ship at sea, the East Goodwin lightship off the south-east coast of England. In the following year wireless messages were sent across the English Channel.

The first radio transmission across the Atlantic was on December 12, 1901 from a station on the cliffs at Poldhu, in Cornwall, and the message, three dots representing the letter S in the Morse code, was picked up at St. John's in Newfoundland.

The existence of radio waves was first demonstrated by Heinrich Hertz, a German professor, in 1887. Marconi based his experiments on Hertz's research.

What makes the Ring around the Moon?

The ring around the moon is the glow, or halo, which surrounds any light visible in intense darkness. Technically the ring is known as the moon's albedo.

It is faint because of the roughness of the moon's surface. This reduces the light reflected by the moon to slightly less than 0.1% of the amount it receives from the sun and other stars.

The result is that the moon's reflected light as seen on earth amounts to only half a millionth of direct sunlight. Its faint, mysterious and gauzy halo was considered by ancient peoples to be like the illumination round the heads of their gods.

Why does Iron go red when Heated?

Iron goes red when heated because its atoms radiate vibratory waves of an electrodynamic nature which are visible as light at a sufficiently high temperature. At 800 degrees Centigrade the iron is at low-red heat. But as the heat increases the iron will turn bright red, and finally white-hot and molten.

Heat is passed through the iron by conduction - the contact of one iron particle with another with no visible movement of the particles. The heat which is given off as light when iron glows red hot can be reconverted into heat by the substance on to which it falls.

When iron is heated to a temperature below 300 degrees Centigrade it gives off invisible rays of infra-red radiation which are similar in nature to light. But they do not contain quite enough energy per unit (photon) to stimulate the optic nerve and so seen by the human eye.

Why were the Galapagos Islands Important to Charles Darwin

In 1831 Charles Darwin sailed in HMS Beagle on an expedition which would take him to the Galapagos Islands. On arrival he was so impressed by the animal life that the islands inspired many of his ideas on evolution, in particular his monumental work The Origin of Species.

Here he had proof for his views on natural selection. In front of his eyes were albatross and cormorant that could not fly, and giant land tortoises weighing over 500 pounds and considered among the oldest living creatures on earth.

There were also such extra-ordinary curiosities as four-eyed fish and tame finches which would use sticks as tools to obtain food. Also, Darwin discovered a species of penguin unlike any others and large spiny iguanas, the only lizards that take to water.

The Galapagos Islands are in the Pacific Ocean, off the coasts of Ecuador and Peru, in South America.

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What is a Prime Number?

A prime number is one that cannot be split up by division. Think of 11. Twice six is 12, three fours are 12. But the only number you can divide by 11 is one, and when you have done that you still have 11 left.

Prime numbers lie at the very roots of arithmetic, and have always fascinated those concerned with figures. Choose at random 17, 23, 29, 41 take the sequence as far as you like, and you will never find a prime number divisible by another. Over the centuries the world's finest mathematicians have tried to do so and failed - although they have also been unable to prove that no such number exists.

That is because there is an infinity of prime numbers, and in theory, anything may happen in infinity. But so far the theorists have not even been able to find a rule governing the gaps between prime numbers, which is a great mathematical mystery.

Why Don't Cranes Topple Over?

Cranes do not topple over because their jibs or booms are counter-balanced at the opposite end from the lifted load, thus keeping the center of gravity over the base.

The first cranes were simply long poles fixed in the ground at an angle, with a pulley at the top through which passed a rope. They were called "cranes" because they looked rather like the neck of the bird with the same name.

The derrick crane, which looks like a gallows, is named after Dick Derick, a 17th century Hangman. In the middle of the 18th century, steam engines began to be used on cranes, while today the lifting may be done by varieties of power.

Jib cranes may be portable, being mounted on a wheeled carriage, or they may be self-propelled. Gantry canes with long booms are used for unloading ships while overhead cranes are used in factories. Goliath cranes, with steel towers at either side, capable of lifting 200 tons are used at some atomic power stations.

What is the Doppler Effect?

Christian Johan Doppler (1803-1853) was an Austrian scientist born in Salzburg who made an important discovery about the effects of sound and light when the sources are moving in relation to the observer. You may find the Doppler effect easier to understand if you consider what happens to the noise of a train as it approaches you and then fades away.

The Doppler principle states that the pitch of a sound is changed, if the object emitting it is moving relative to the observer. The light emitted, being a moving source, is changed in colour, as seen by a relatively stationary observer.

In each case the actual sound and light frequency remains constant. That is to say, a diesel locomotive traveling at a constant speed will be producing exactly the same engine noise or "note" whether it is half a mile or a 100 yards from you. But as it gets closer, a change of tone appears.

The second part of the principle can be applied to the change in colour of a moving star. A more complex example is the Doppler navigational system for aircraft, which requires no ground installation. In a typical system, four separate beams of microwave energy are radiated from an antenna on the aircraft to the surface of the earth, and some of the energy is reflected back. The frequency of the reflected signal from each beam is shifted by an amount proportional to the plane's speed. This information is processed by a computer and enables the pilot to fix his position.

What is an Alchemist?

An alchemist was an early student of the science of chemistry. According to one theory the the word "alchemy" is derived from Khem, the ancient name for Egypt. That country was the source of a great deal of the pioneer work in the various sciences.

Much of the early work of the alchemists is frowned on by today's scientists because it was bound up with experiments to find the "elixir of life" and the "philosopher's stone" which would turn all base metals into gold. The alchemists also studied magic and astrology.

However, we have to thank the alchemists for such words as "hermetically sealed", alcohol, and alkali, and for the discoveries of sulphuric, nitric, and hydrochloric acids, and of metals such as antimony, bismuth and arsenic.

The "hermetic art" is another name for alchemy. Hermes Trismegistus was the name given by the Greeks to the Egyptian god of alchemy. Thus hermetic sealing is derived from the method of airtight sealing used by alchemists in their experiments.

The alchemists also associated the planets with certain metals and used the astrological symbol as a shorthand sign for the metal. The sun stood for gold, the moon for silver, Venus for Copper, Mars for iron, Jupiter for tin and Saturn for Lead.

Why is a Screw so Strong?

The screw provides a means of converting a small force into a large one. Once in use, it allows pressure to be applied from different directions. These factors give the screw its relative strength as compared with a nail of the same size.

In the first case, the force applied to a screw is like the smaller force necessary to lift an object up an inclined plane rather than straight up. In a screw a form of inclined plane is provided by the spiral groove, called a thread, which cut round the shaft. By contrast the force applied to a nail can be compared with lifting an object straight up. If it were possible to unwind an inch-long screw, you would find that it was longer than an inch-long nail.

In the second case, the holding power of a screw or nail in a piece of wood depends on the pressure exerted on its shank by the wood fibres. A screw creates a far stronger grip because it presents a much greater surface area to the pressure of the wood.

Why do Some Liquids Burn?

Some liquids will burn because when their molecules mix with the oxygen in the air the mixture becomes combustible. The application of heat promotes the necessary chemical reaction to put the molecules into more violent motion, so that they collide at high speed. The jolt loosens the bonds and makes it easier for the molecules to rearrange themselves and escape from the liquid to form a vapour, mixing with oxygen in the air.

The most important liquid which will burn is crude mineral oil from which petrol and paraffin are produced. Others include tar and creosote, and the very explosive nitro-glycerine.

When did Talking Movies Start?

The first talking movie were produced in France before 1900 by Léon Gaumont. They were short films, starring great performers such as Sarah Bernhardt, in which the moving pictures were synchronized with a gramophone record. By 1912 Eugene Lauste had discovered the basic method for recording sound on film, while Thomas Edison produced several one-reel talking pictures in the United States. An American, Lee de Forest, improved the system.

In all of this, public showed interest until the presentation on October 6, 1927 of the Jazz Singer. This was a silent picture, starring Al Jolson, with four talking and singing interludes. Jolson's electric personality and the very much improved sound began a movie revolution. Within the year every important picture was being produced as a "talkie". By 1930, silent films were a thing of the past, and many films stars found themselves has-beens because their voices recorded badly.

Where Will Water Not Boil?

Water will boil anywhere, but it boils at different temperatures in different places. For example, it will boil at a lower temperature up a mountain than at sea level.

The boiling point of water is the temperature at which its vapour pressure becomes equal to the outside atmospheric pressure. As the atmospheric pressure is always changing so the boiling point of water will vary from day to day. Water boils at 100 degree Centigrade only when the atmospheric pressure outside is at the "standard value".

At Quito in Ecuador, which is about 2700 meters (8800 feet) above sea level, water boils at 90 degree centigrade.

People who explore in mountainous regions find a pressure cooker very useful. The time required to cook food can be greatly reduced if the boiling point of the water is raised. The pressure cooker does this, since it is an aluminum container fitted with a sealing ring but with a loaded pin-valve which allows steam to escape. The valve can be set at varying pressures, enabling the food to be cooked at a temperature of about 120 degree Centigrade.