The definition of a desert is a place where the lack of moisture makes it impossible for anything but a few special life forms to grow. This applies not only to hot places, like the
How many times have you heard someone say, ‘I think I’ will go out for a breath of fresh air”? Have you ever stopped to think what this means in our industrialized world? Of course, if you happen to be living high up among the mountains where there is little or no industry and few people your chances of finding fresh air are quite good. But what of the build-up areas of Britain and Europe or America? Even if you have not experienced it yourself, we expect you have heard of smog. This word is a mixture of the words ‘smoke’ and ‘fog’, which is very apt because smog really is smoky fog. London was once famed for its ‘pea-soupers’, that is, fog containing so much, sulfurous waste that it resembled the yellowish green color of pea soup and was almost as difficult to breathe and see through. These smogs usually occurred during the early months of winter when the fogs that would normally be present at that time of year became contaminated with all the smoke from cars and factory chimneys.
It is interesting to note how much influence pollution of the air, at first by smells of household waste and later by pollution, has influenced the distribution of people in cities like London. As you probably know, London has an ‘East end’ and ‘West end’ until quite recently the East end has been by far the poorer half of the city. This is because winds usually blow from west to east carrying the dirty air with them. People who could afford to choose where they wanted to live went to the western side leaving the smelly east for those with smaller incomes. In Los Angeles, in America, which is also famed for its smog’s, the prevailing winds are from east to west so that the London situation is reversed.
Today, many industrial countries have introduced ‘Clean Air Acts’ preventing the burning of ordinary coal in homes in certain areas and controlling the amount of smoke that factories can release. This means that some areas, such as London, Certainly have air containing much lees dust and dirt, and smogs are almost a thing of the past. In general, however, the air in our countries is far from fresh. The millions of cars on the road pour vast quantities of poisonous carbon monoxide gas into the atmosphere. It has even been suggested that if supersonic flight became popular, with the ‘planes flying at such hi8gh altitudes. The upper atmosphere could be affected in such a way as to permit deadly cosmic rays to reach the Earth.
The next time that you see some plants or trees next to a busy road, take a closer look at the leaves. You will probably find that they are covered with a film of black, oily dust. Remember that this is the same air that we are all breathing.
Read more...You must realize that the Earth provided us with all the raw materials swallowed up by our industries. Many of these materials are minerals. The word ‘mineral’ is used to denote any substance obtained by mining. It is clear that the words mine and mineral have similar origins. You might expect that minerals would be spread throughout the Earth, and indeed, this does happen. Occasionally, however, minerals may accumulate in sufficient quantities for man to be able to remove them comparatively easily. When this situation arises, the deposits are usually known as ores or ore bodies. The minerals associated with the ores that have no real economic value are usually referred to as gangue minerals, the consequent scarcity of them, and improved methods of mining and refining, material that was once thrown on the spoil heaps can now provide valuable sources.
Ores can occur in a variety of ways. With ores or iron, for example, the same ore can arise as a result of different methods of concentration. Many ores other than iron are formed in association with magma tic process. If you remember the way in which magma cools and forms crystals. It will come as no surprise to you to learn that metals such as chromium and nickel result from the settling into bands of the relevant crystals as the magma cools. There are often watery solution charged with minerals coming from magmas and these also provide supplies of metals such as mercury or copper. Both these minerals are in short supply, and in fact, deposits of mercury are almost completely confined to areas in Spain. Not all ores have been formed by igneous activity, however. Important deposits of iron in England have resulted from concentration by sedimentary process. Deposits known as placers are typical sedimentary ores. Of course, oil and coal must be considered as economic minerals and these have obviously resulted from sedimentation.
The sea may one day provide much of the world’s minerals. It has been known for some time that there is great richness of gold in the sea but as yet it has not been worthwhile nor even possible to exploit this mineral wealth. Even uncommon metals like vanadium, which is used for the nosecones of spacecraft, is concentrated in the blood of an unexciting sea animal – the sea cucumber.
Read more...Our galaxy, vast island of stars though it is, is only one of millions of similar galaxies scattered throughout space as far away as we can see through our telescopes. The nearest galaxies to our galaxies are two small satellite galaxies called the Magellanic clouds. They can be seen only in the southern hemisphere, and look like pieces torn out of the Milky Way. A large nearby galaxy is the Andromeda galaxy, which can be seen with the naked eye as a faint patch. It is over 2 million light – years away.
Galaxies come in many shapes. Many are spiral. Elliptical galaxies look like globular clusters of stars, and irregular galaxies such as the Magellanic Clouds have no particular structure. About a hundred million galaxies can be seen with the largest telescopes. Galaxies, like stars, tend to form clusters and our galaxy is one of a cluster of over tweny7 that include the Andromeda Galaxy.
The time it takes for the Earth to make one rotation has been divided into 24 parts, known as hours. This division was made to give us a fixed unit of time.
We take as a reference point the moment when the Sun is at its highest point in the sky (when the sun is at its highest point in the sky (when the shade is at its minimum).This is called mid-day, or
However, this does not happen at the same moment on each part of the Earth because the Earth is turning all the time. Therefore, when it is mid-day in
Ordinary railway lines usually look as they are laid on level ground. In reality most stretches of railway track have a slight gradient, so that during a journey of any reasonable length, a train will be running up and down a number of very gradual slopes. However, there is a define limit to the degree of steepness a train can manage going up hill before its wheels start to skid on the tracks. In mountainous areas especially, it is not always possible to avoid gradients which a normal train simply could not climb, even by carrying the track through deep cuttings and tunnels. To overcome this difficulty rack railways have been built. Locomotives intended to run over such sections of track have a toothed, or cog, wheel fitted between the normal running wheels. This connects with third rail, also toothed, fitted to the track itself. This is the rack, its cog wheel engages the rack rail and so holds the train to the track with no risk of skidding.
For many years railway engineers have been thinking about new kinds of track for trains to run along. The parallel metal rail tracks with which we are familiar are not very efficient by modern standards. Because wheels are needed to move the trains along, a good deal of power is lost through friction in the moving parts. Ordinary railway tracks also set a limit to the speed that trains can go, especially round curves. They take up a lot of room, and they are expensive to build and keep in good repair.
Some trains, such as those operated on the Paris Metro, run very efficiently on rubber tyres. Other even more interesting advances in this field have been the experiments with monorail systems. Monorail means ‘one rail’, and several types of train have been designed which are suspended from an elevated monorail track. Spectacular results, in terms of speed and comfort, have been achieved.
Yet other trains have been built which sit astride a single metal or concrete track and slide along it. Called aero-trains, they have been designed to move like hovercraft. An even more advanced idea is to suspend a train from a monorail by magnetizing the rail. In all these cases there is hardly any friction to overcome, and much greater safety.
Sometimes the former Russian rulers, the tsars, used the Cossack cavalry to crush rebellions among the peasants. At other times the Cossacks were the pride of the Russian army, and could always be relied upon to strike fear into the hearts of the enemy. They were especially effective during Napoleon’s invasion of
When a doctor takes a pulse he is felling the patient’s hear-beat. If the heart is beating faster than normal it may be a sign – like a rise in temperature – of illness somewhere in the body. For signs of illness in the heart itself a more careful check is usually needed.
The working of the heart is controlled by electrical impulses, and each part of its-the various valves where blood flows in a out – produces its own electrical wave pattern. By attaching electrical terminal points to the outside of the chest and connecting these to an electrocardiograph, these wave patterns can be observed. For when the electrocardiograph is switched on, an automatic device like pen moves up and down over a special sheet of graph paper, recording each wave impulse. This shows exactly the pattern of each complete heart beat. If anything is wrong with the heart, it will be shown by irregularities in these patterns. The pattern sheets or electrocardiograms can then be kept by doctors and compared over a period of time, which is extremely useful in the treatment of heart illness.
If an astronaut leaves his spacecraft during a journey, he cannot walk about in the ordinary way. There is nothing but empty space. There is not even any gravity to pull him in one particular direction. He can only guide himself by the same means as the spacecraft itself – by rocket propulsion. So when astronauts do leave their spacecraft during a flight – perhaps to help in docking operations with another spacecraft – they carry specially designed hand rockets with them. If they point the rocket exhaust in one direction, and give the engine a burst of power, they will move in the opposite direction. In this way they can steer themselves.
The Red Cross was found by a Swiss, Jean Henri Dunant, after he had witnessed the terrible plight of the wounded at the Battle of Solferino in 1859, Five years later, in 1864, the first Geneva convention was called to establish a code of conduct for nations at war, and Dunant obtained the convention’s agreement that both wounded soldiers and medical services should be treated as neutrals.
The flag chosen to represent the international medical service that grew out of dunant’s work was a red cross on a white background, this being the reverse colours of the Swiss flag. It also gave the organization its name. In Muslim countries, however, the flag is a red crescent on a white background, to distinguish it clearly from the Christian symbol of a crucifix.
The indoor game of ‘real’ tennis was played in the middle ages. During the 19th century it over flowed on to the lwn where players made up their own rules. In 1874 Major Walter Wing field invented rules for lawn tennis. Even by 1890, however, ‘real’ tennis rackets were still being used.
The Olympic Games is the biggest sporting event in the world. It takes place every four years, each time in a different country. Amateur sportsmen and women from over 100 nations take part. There are about 20 sports, of which the most important are track and field athletics.
The idea for these competitive events came from Ancient Greece. And the spirit of the games has always been one of true sportsmanship; that is, fair competition, without the aid of cheating in any form. However, competition is so fierce these days that it is hard for competitors to live up to these ideals.
