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37. TIME KEEPER The latitude of one’s position can be easily determined from the sun, but finding the longitude is much more difficult. Since the earth rotates about its axis once every 24 hours, it is clear that a difference in longitude corresponds to a difference in measured time. Hence the mariners of old required a time-piece which would keep very accurate time – a chronometer. The choice of Greenwich, the construction of the first chronometer, and the use of the old time balls all make for interesting reading.
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