They are expressed in the most plain and simple terms, wherein those people are not mercurial enough to discover above one interpretation: and to write a comment upon any law, is a capital crime.
Jonathan Swift. Gulliver's Travels Into Several Remote Regions of the World (1726)
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A mercurial man Who fluttered over all things like a fan.
Byron.
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Rick: So in conclusion: you're both equally mercurial, overly sensitive, clingy, hysterical, bird-brained homunculi; and I honestly can't even tell the two of you apart half the time [...].
Adult Swim. Rick and Morty, season 2: A Rickle in Time
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In Lagos, the harmattan was a mere veil of haze, but in Nsukka, it was a raging, mercurial presence; the mornings were crisp, the afternoons ashen with heat, and the nights unknown.