【单选题】
Finding Longitude
From ancient times, sea voyagers were able to calculate latitude with reasonable accuracy. They did this at night by measuring the angle of the pole star above the horizon and at noon by measuring the angle of the sun above the horizon. However, the problem of calculating longitude, or degrees east or west of a meridian line running north to south from pole to pole, was intractable.Even on land this calculation was difficult. In the 1600s, an Italian scientist published tables giving the times of the eclipses of Jupiter’s moons. From these tables it was possible to calculate longitude east or west of a given point by comparing the local time at which eclipses happened with the time given in the tables. This breakthrough did not, however, help ocean navigation. The unstable conditions aboard ships made precise observation of Jupiter’s satellites a near impossibility. Other methods, including measuring the observed distance between the moon and particular stars, gave flawed results.
In practice, mariners tended to revert to a system called dead reckoning. This involved finding position by measuring speed based on observing a knotted rope thrown overboard, and a careful attention to changes of direction based on compass readings. Often calculations were excessively inaccurate leading to shipwrecks and failure to reach destinations. In 1714 after a small fleet was wrecked with a huge loss of life, theBritish government established a prize of 20,000 pounds for whoever could find an accurate method of determining longitude at seA、
John Harrison, anEnglish clock maker, thought that he could build a reliable clock that would keep time at sea, although most scientists of the period did not believe such a clock could be built. Their skepticism was well founded; the movement of a ship, the constant changes of temperature, and the moist conditions made accurate timekeeping an impractical dream. Nevertheless, Harrison persevereD、The idea behind his approach was that a sailor could read the time on a clock set correctly in the home port. On a voyage the time would be checked on that clock at noon (when the sun was at the highest point) on the ship.Every four minutes of difference would indicate one degree of longitude.
Harrison worked for seven years on his first marine clock. The committee responsible for judging the success of candidates for the prize was dubious about the design, but agreed to a sea trial. This test was successful enough that Harrison was awarded money to continue development. Two more versions, today known as H2 and H3, were built over the next several years. The H2 version was not sea tested due to the danger of it failing into Spanish hands during the War of theAustrian Succession. The latter creation was abandoned by Harrison when he became dissatisfied with its performance.
Harrison then worked diligently for thirteen more years and produced, at sixty-six years of age, a masterpiece of ingenuity.
This differed greatly in appearance from its forerunners.
It was only a little over five inches in diameter, whereas the other designs had been heavy instruments that needed to be hung from stout timbers. Mechanically, it was also a radically innovative design, using oil as a lubricant and finely worked wheels and pinions.
After a two-month trip to Jamaica, H4 was determined to have lost only a few seconds. In terms of distance, this represented only about one or two miles of error.
Clearly this latest apparatus had proved itself to be the best candidate yet for the prize.Due to professional jealousy by some committee members, t
网考网参考答案：D
网考网解析：
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From ancient times, sea voyagers were able to calculate latitude with reasonable accuracy. They did this at night by measuring the angle of the pole star above the horizon and at noon by measuring the angle of the sun above the horizon. However, the problem of calculating longitude, or degrees east or west of a meridian line running north to south from pole to pole, was intractable.Even on land this calculation was difficult. In the 1600s, an Italian scientist published tables giving the times of the eclipses of Jupiter’s moons. From these tables it was possible to calculate longitude east or west of a given point by comparing the local time at which eclipses happened with the time given in the tables. This breakthrough did not, however, help ocean navigation. The unstable conditions aboard ships made precise observation of Jupiter’s satellites a near impossibility. Other methods, including measuring the observed distance between the moon and particular stars, gave flawed results.
In practice, mariners tended to revert to a system called dead reckoning. This involved finding position by measuring speed based on observing a knotted rope thrown overboard, and a careful attention to changes of direction based on compass readings. Often calculations were excessively inaccurate leading to shipwrecks and failure to reach destinations. In 1714 after a small fleet was wrecked with a huge loss of life, theBritish government established a prize of 20,000 pounds for whoever could find an accurate method of determining longitude at seA、
John Harrison, anEnglish clock maker, thought that he could build a reliable clock that would keep time at sea, although most scientists of the period did not believe such a clock could be built. Their skepticism was well founded; the movement of a ship, the constant changes of temperature, and the moist conditions made accurate timekeeping an impractical dream. Nevertheless, Harrison persevereD、The idea behind his approach was that a sailor could read the time on a clock set correctly in the home port. On a voyage the time would be checked on that clock at noon (when the sun was at the highest point) on the ship.Every four minutes of difference would indicate one degree of longitude.
Harrison worked for seven years on his first marine clock. The committee responsible for judging the success of candidates for the prize was dubious about the design, but agreed to a sea trial. This test was successful enough that Harrison was awarded money to continue development. Two more versions, today known as H2 and H3, were built over the next several years. The H2 version was not sea tested due to the danger of it failing into Spanish hands during the War of theAustrian Succession. The latter creation was abandoned by Harrison when he became dissatisfied with its performance.
Harrison then worked diligently for thirteen more years and produced, at sixty-six years of age, a masterpiece of ingenuity.
It was only a little over five inches in diameter, whereas the other designs had been heavy instruments that needed to be hung from stout timbers. Mechanically, it was also a radically innovative design, using oil as a lubricant and finely worked wheels and pinions. After a two-month trip to Jamaica, H4 was determined to have lost only a few seconds. In terms of distance, this represented only about one or two miles of error. Clearly this latest apparatus had proved itself to be the best candidate yet for the prize.Due to professional jealousy by some committee members, t网考网参考答案：D
网考网解析：
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