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JJ考古，请楼主确认！谢谢！ 第二篇：一种异常准确的机械钟。（难，高分区）
第一段：说这种钟可以说是世界上最后的机械钟了，而且有两个，一个在爱丁堡，一个在某observing station.（记不清了，但此处无题）。这种钟就两个钟摆（pendulum）, the first 在一个真空（vacuum）的容器中（此处对真空有题），另一个来管钟的各指针（大概是这个意思）。第一个钟摆会适时第第二个钟摆信号，来进行适度调整。这个钟就是靠这个运行的
第二段：主要讲这种钟如何准确，有一些数字。最后一句说，利用这个钟测出了日月引力对地环转速的影响（这有一题）
第三段：讲在1984年做的一个试验，将这种机械种与automatic clock做比较，结果发现（一堆数字比较）。后又说日月引对，不但能影响海潮，还能影响陆地。而这种引力会使机械种有一定的误差。
第四段：主要讲日月引力怎么样对陆地也造成影响（好像没什么题）。
主题：引出机械钟+表述其精准性+精准性实验+继续描述精准性。
考题：
1）What is truth about the first pendulum (in the first paragraph)? 基金主人选和真空有关的
2）Which of the following can NOT be experimented in 1984? 基金主人选了一个更准确的钟。
3）What does this clock coincidentally find? 基金主人选地球转速因引力而不同。（有人说这个选项有问题） 因为原文说的是seasonal rotation. 但是答案里面是year one year 的rotation。所以没选这个，那个人选的是对大陆，海洋的tidal都有影响。（请大家确认）
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网上找到的，据说仿真度较高，请大家仔细阅读
The Shortt clock had two pendulums. The first, known as the master, swung freely in an evacuated case. Its only job was to synchronize the swing of the second pendulum, called the slave, which was housed in a neighboring cabinet. Every 30 seconds the slave sent an electrical signal to give a nudge to the master. In return, via an elaborate electromechanical link, the master ensured that the slave never got out of step.
Shortt clocks were standard provision in astronomical observatories of the 1920s and 1930s, and are credited with keeping time to better than 2 milliseconds a day. Many were on record as losing or gaining no more than 1 second a year – a stability of one part in 30 million. The first indications of seasonal variations in the Earth’s rotation were gleaned by the use of Shortt clocks.
In 1984  ierre Boucheron carried out a study of a Shortt clock which had survived in the basement of the US Naval Observatory since 1932. Using the modern optical sensing equipment instead of the electromechanical coupling, he measured its rate against the observatory’s atomic clocks for a month. He found that it was stable to 200 microseconds a day over this period, equivalent to two to three parts in a billion. What is more, the data also reveal that the clock was sensing the distortion of the Earth due to tides from the Moon and the Sun. | 
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发表于 2009-7-21 23:33:00
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