Anchor

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Anchor A device which prevents a vessel from drifting. The flukes or arms of an anchor dig into the seabed, thus resisting a horizontal pull; it is made fast to the ship by a heavy cable, usually of studded chain. >>

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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 is a Geostationary Orbit?

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Artificial satellites sent from the Earth orbit around the earth. The ones near the Earth orbit faster than the ones far away. A satellite 35,900 Km above the Earth's surface, takes 24 hours to orbit once. The satellite is always above the same point on the Earth's surface as the planet rotates. Geostationary orbit is also called as geosynchronous ' orbit. Such satellites are used to receive telephone and television signals and retransmit them over long distances.
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Why are Some Tree Frogs so Colourful?

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A bout 500 species of frogs spend their lives on tree tops. Some South American tree frogs are very brightly coloured to warn predators that they are extremely poisonous to eat. All the amphibians have mucous glands in their skin to keep themselves moist. In some frogs, these glands also produce a poison so deadly that it can paralyze a bird or monkey instantly. South American Indians use secretions from golden arrow-poison frogs to poison the tips of their hunting arrows.
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Black Panther

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Africa and Asia, black panthers are black-coated leopards, and in North, Central, and South America, they're dark-coated jaguars. In other words, “black panther” is an umbrella term used to refer to any leopard or jaguar with an unusually dark coat. Black panthers are not specific species, but refer to the blackened individuals of several panthers. Cats, especially large species, usually find some black individuals with different colors from the original ones. Leopards with normal coat color can produce the same litter cubs with black coat and normal coat color. Descendants who give birth to normal coat colors have less impact on survival than albinism, so melanism is more common than albinism, and species living in rain forests or bushes may even be more conducive to survival due to melanism. Under the bright light, the blackened leopard can find that the body hair is not pure black, but dark brown with different shades, and it can still recognize the unique markings of various le...
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When were the First Spinning Machines Invented?

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People in the olden days used to spin thread by hand . They pulled fibres out of cotton and wool and twisted them together into thread. Spinning machines were invented in Britain in the 1700s. These machines had rollers turning at different speeds to twist the fibres into yarn. James Hargreaves in 1764 produced the first successful spinning machine. It was the hand-powered jenny which produced thin yarn. Richard Arkwright's water frame of 1769, powered by water wheels, gave a sturdy thread. Samuel Crompton combined these two spinning machines in 1779 , to make the spinning mule, which could spin many kinds of yarn. These machines were the precursors of the Industrial Revolution . 
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