亨
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亠
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口
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了
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Mnemonic symbol: American scientist Joseph Henry.
Before Henry (亨) invented inductance he used to hang out with Hamlet (h) a lot in front of the engine ((e)ng1). One day he observed Hamlet shifting a mandarin (口) from a price cup (了) to a beret (亠) and vice versa, which gave him the idea of putting an iron core into an electromagnet.
哼
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亨
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口
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In front of the engine ((e)ng1), Joseph Henry (亨) finally has the idea how to build his coil and exclaims "hurrah!", accidentally throwing away Hamlet's (h) mandarin (口) so Hamlet just says "humph!" (哼).