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When were the First Mechanical Clocks Made?

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The first mechanical clocks are believed to have been made in China in 1088 AD. Later in 1200s, they were first made in Europe. Such clocks made in Europe were driven by a weight on the end of a cord wound round a drum. As the drum rotated, it turned the hands of the clock. The earliest known clock was made in Spain in 1276 AD and the oldest mechanical clock that still works is in Salisbury cathedral in Britain. It was made in 1368. These clocks had devices called escapements to keep the hands turning at the correct rate, so that the clocks depicted the correct time.
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What are Deciduous Trees?

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T he deciduous trees are the ones that lose their leaves in autumn. These trees are largely the broad-leaved trees of the northern hemisphere. Winter in this region is very harsh, so the trees shed their leaves in autumn to spend the winter in a state of dormancy . They do so to conserve water, by avoiding transpiration through leaves. There is frost all around and the roots get no water from the soil. Maples , magnolias, oaks, beech are some deciduous trees.
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Which Mammals Fly in the Dark?

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B ats are the only mammals which can truly fly in the dark. They are nocturnal and so are active and fly at night. The wing of a bat is different from the wing of a bird. It is a skin-like membrane, the patagium , stretched between enormously long arm and hand finger bones. Most bats are insectivorous while some are fruits-eating. The vampire bats feed on the blood of large mammals and some others feed on mice, voles, frogs and fish. Bats are able to find their prey and avoid obstacles in the dark by using a sound radar system called echolocation. They emit very high-pitched pulses of sound called ultrasound which cannot be heard by us. The sound waves bounce back to the bat after hitting an object . The bat hears the patterns of these echoes and analyses it to give a 'sound picture‘ of the object and the surroundings.
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What is the Sun's Corona?

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When the moon passes completely in front of the Sun during an eclipse, a glowing halo shines out. This is known as Corona or Sun's atmosphere. But it, in no way, resembles our atmosphere. It has a temperature of a million degrees centigrade and is a million times thinner than air. Normally , it hides from the view due to the Sun's brilliance except during an eclipse The Corona contains hydrogen, nitrogen oxygen and other common elements. They are very hot and scattered far apart. Unlike our atmosphere, which is held to the Earth by gravity, corona is pouring off into space at a speed of about 400Km/s. These clouds of atoms pass the planets and the Sun towards the stars. This movement of atomic particles is called solar wind.
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What are Flatworms?

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F latworms are flat, simple-bodied worm like animals ranging from the size Of a few millimetres to larger tropical forms. These worms are largely found in temperate and tropical regions of the world. They live under the stones and leaves , in freshwater streams and ponds. A few of them also live on land. Flatworms can regenerate themselves and if a worm is cut into few pieces , each piece will grow into a new flatworm. Some flatworms are parasites. For example the flukes and tapeworms.
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