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John Harrison

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  • John Harrison 1693~1776 - John Harrison is famous as the inventor of the first chronometer - a clock for finding time at sea - and for the reluctance of the Board of Longitude to award his prize. Born in Foulby, near Wakefield, he moved to Barrow-on-Humber soon after. John's father was a joiner, and he was also churchwarden and parish clerk. He was trained in his father's shop and learned about the tuning of bells and sang in the choir. His interest in music was to be influential in the development of his scientific ideas. He married in 1718, and his son John was born a few months later. By this time he was specialising in making clocks, helped by his youngest brother, James. Two innovations date from this time. One was the grid-iron pendulum which used linked rods of brass and steel for the pendulum, and have different rates of expansion thus keeping the length of the pendulum and the going rate of the clock even at all temperatures. Later he was to incorporate this idea into his watches as a bimetallic strip, which is still used in thermostats. The other innovation was the grasshopper escapement, which can be seen in the clock he made for the stables at Brocklesby Park, which is still in good working order. John's first wife died in May 1726 and in November he married again. They moved to a house on the Barton Road and had two more children, William, born 1728, and Elizabeth, born 1732. By this time John was working on a clock that could be used at sea, and which could be submitted to the Board of Longitude to claim the prize of £20,000 set up by the Act of 1714. John took his designs to the Astronomer Royal, Halley, who sent him to George Graham. In 1736 his first sea-clock was sent for official trials to Lisbon. The results were good enough for further funding, and John moved to London to work on his second machine. This was finished in 1737 but did not do well in tests. He began a third machine. It was not ready for trials until 1761, but by then Harrison had made a deck watch that had much better performance. This was taken by William for the trial. By this time, the Rev Nevil Maskelyne, who was soon to become Astronomer Royal, was also a candidate for the longitude prize, with the Lunar Distance Method of finding longitude, using new tables by Tobias Mayer. As a result the Board of Longitude put every obstacle they could think of to prevent a "mechanic" like Harrison claiming the award, even after a second successful trial watched by Maskelyne in Barbados in 1764. Harrison had to produce detailed drawings, and make two more watches. One of these was tested by King George III himself in his Observatory at Kew. Eventually Harrison was paid the money owing to him, not by the Board of Longitude but by a special Act of Parliament. In 1775, when he was 82, John Harrison wrote an account of his life's work. More information on Harrison's life and work can be found in John Harrison and the Problem of Longitude, by Heather and Mervyn Hobden, seventh edition (ISBN 1 871443 25 3) published by The Cosmic Elk, which is on sale at Jews's Court, Steep Hill, Lincoln.
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