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Motional Induction
電磁感應
Last time, we talked about "motional induction," a phenomenon by which the ocean generates a magnetic field.
上次，我們提到過動生電磁感應：海洋產生磁場的一種現象。
It works like this: earth has its own magnetic field. The ocean has plenty of charged atoms in it, in the form of dissolved salt. These atoms are in motion because the ocean flows.
地球有自己的磁場，海洋有無數溶解鹽形式的帶電原子，隨著海洋運動而運動。
Charged atoms moving through a magnetic field will induce an electric current. And an electric current will, in turn, create another magnetic field. The ocean should generate its own magnetic field.
在磁場中運動的帶電原子會引起電流，而電流反過來又回形成另一個磁場。這樣海洋應該就形成了自己的磁場。
You said should. How could we know this "motional induction" is happening?
你說“應該”，我們怎么知道這種動生電磁感應確有其事？
Direct evidence came in 2003 from scientists working at the University of Washington and a research institute in Potsdam, Germany. These researchers used a magnetometer on board an orbiting satellite.
直到2003年，華盛頓大學和德國波茲坦的某研究學院研究人員將磁力計放在軌道衛星上，證實海洋的磁場真是存在。
First, they figured out what the magnetic field of the planet should be. After subtracting this figure, they found there was still some leftover magnetic field.
最初，磁力計上的數據讓科學家以為是地球磁場作用的。而后，他們發現除去這個因素后，仍然有磁場存在。
Next, the team made a computer model of what kind of magnetic field the ocean should generate through motional induction. Sure enough, their prediction matched the excess magnetic field measured by the satellite.
研究人員又電腦模擬在動生電磁感應讓海洋產生哪種磁場，當然，科學家的推論和衛星上測出的“另一個”磁場吻合。
The satellite also found that magneticintensity over the oceans peaked every twelve and a half hours, but not over the land. Can you guess why?
衛星還發現，海洋磁場每隔12個半小時就會出現高峰，但是地球磁場不受影響。你能猜到原因嗎？
Every twelve hours... Oh,I get it—tides!
每隔12個半小時？我知道了！答案是潮汐。
Exactly right! The tides rise and fall every twelve and half hours, just as that extra magnetic energy swells and diminishes. This is very strong evidence that motional induction is real... and the ocean has its own magnetism.
完全正確！潮汐每隔12個半小時潮起潮落，正好和“另一個”磁場高低峰吻合。這正是磁場感應存在的真憑實據，海洋確實有自己獨特的磁力。
