Wherever you live, television pictures come to you from broadcasting stations located in various cities around the country. But they may get to you in several different ways. Many programs are transmitted from a local television mast. They go to the mast from the broadcasting stations along cable or via radio links. Then from the mast, the programs come to …

Grains of sand are really very tiny particles of rock. It takes time and a special kind of weather to turn rock into sand. Rain, frost, and wind can do the job. On beaches, the tide hitting against the rocks forms sand. Salt water, too, forms sand by dissolving minerals in the rocks. Since rocks are made up of minearals …

Lichens are found throughout the world, often occupying areas where no other plant can become established. They are found in their greatest numbers in the Alpine and Arctic regions, where they are the dominant form of vegetation. Lichens are the products of two distinct groups of plants. Together fungi and algae (seaweed is an algae) combine to produce lichens. Most …

Cork is the thick and spongy bark of the cork oak tree. These trees don’t grow to be very tall but they have quite thick trunks. Taking the cork bark off the tree can only be done every ten years, but about forty-five pounds, or about twenty-two kilograms of cork can be stripped off one tree at a time, so …

Nowhere-it simply changes into other substances. That is what burning does to everything. The moment you put a match to the wick, you start a change in the candle by turning the solid wax into a liquid. The liquid wax rises to the wick by an irresistible process called capillarity, the simplex example of which is the way blotting paper …

Cowrie shells are widely distributed and possibly the favourites among shell collectors because of their polished enamel-like surfaces and their beautiful colored patterns. The cowrie appears in all the warmer seas of the globe. But the great cowries, the tiger cowrie and the orange cowrie are natives of tropical regions. They crawl slowly, browsing on weeds, and are shy creatures …

If you have a pair of jeans, you will know that what they are made of is a cloth called denim; but do you know where the word comes from? At first, it was used to describe a serge cloth made in Nimes, France – the original name was ‘serge de Nimes’. Gradually, these last two names were shortened and …

We know that the Earth’s crust and the top part of the mantle are split into rigid sections, called plates, which are up to 70-100 km (43-62 miles) thick. Beneath the plates, temperatures are high and the rocks are semi-molten. Currents in the molten material are moving the plates about. Plates are moving apart along the ocean ridges. When they …

Spacecraft cannot carry large supplies of fuel and these aren’t any filling station in space. Instead, many have large panels of solar cells. These capture sunlight and turn it into electricity. The sun always shines in space, so there is always electricity to power the spacecraft. Some space probes travel to the outer planets far from the Sun. There the …

The first sound you hear, the one which says ‘lub’ is caused by the rapid closure of the valve between the auricles and the ventricles (auriculo-ventricular valves). This sound, rather like a door closing, is accompanied by a dull murmur, caused by the contraction of the ventricular muscles. The second sound is caused by the closing of the arterial valves. …