显然，试图解释和预测磁场变化的地球物理学家必须了解外核发生了什么。
Clearly, geophysicists who seek to explain and forecast changes in the field must understand what happens in the outer core.
1832年，也就是迈克尔·法拉第发现磁场变化会产生电场的那一年，一位年轻的法国工程师为一种新的、效率更高的水车申请了专利。
In 1832, the year of Michael Faraday's discovery that a changing magnetic field produces an electric field, a young French engineer patented a new and more efficient waterwheel.
传感器成功探测到心跳所伴随的微弱而规则的磁场变化。
The sensor successfully detected the weak but regular magnetic pattern of the heartbeat.
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