2013年12月大学英语四级阅读范文2
备考英语四级的同学不难发现，阅读是英语四级考试中非常重要的一部分，阅读理解题想要拿到比较理想的成绩，就要掌握阅读考试技巧，加强练习，不断提高自身的阅读能力。小编在此为大家整理了关于2013年12月大学英语四级阅读范文的资料，希望对大家有所帮助!
The accuracy of cientific observations and calculations is always at the mercy of the scientist's timekeeping methods. For this reason,scientists are interested in devices that give promise of more precise timekeeping.
In their search for precision, scientists have turned to atomic clocks that depend on various vibrating atoms or molecules to supply their "ticking" .This is possible because each kind of atom or molecule has its own characteristic rate of vibration. The nitrogen atom in ammonia , for example, vibrates or "ticks" 24 billion times a second.
One such atomic clock is so accurate that it will probaly lose no more than a second in 3000 years. It will be of great improtance in fields such as astronomical is a sesium atom that vibrates 9.2 billion times a second when heated to the temperature of boiling water.
An atomic clock that operates with an ammonia molecue may be used to check the accuracy of predictions based on Einstein's relativity theories, according to which a clock in motion and a clock at rest should keep time differently. Placed in an orbiting satellite moving at a speed of 18000 miles an hour, the clock could broadcast its time readings to a ground station, where they would be compared with the readings on a similar model. Whatever differences develop would be checked against the differences predicted
编辑推荐：