像水銀一樣停不下來的人
把那一滴水銀的動作搬到人身上。它滑得快、抓不住，用在情緒上就成了「說變就變」，用在腦子上就成了「反應靈活」。同一個動作，兩種評價；決定語氣的是後面接的名詞。
adjective · C1
Changing mood suddenly and without warning, so that other people cannot guess how you will be an hour later.
情緒多變
核心畫面
Hold the picture of liquid mercury, the silver metal that will not sit still. Tip a drop onto a table and it runs; try to press it down and it splits and slides away. It is bright, it is fast, and it is impossible to keep in one shape. English even gave it a second name, quicksilver, which means 'living silver'. Every use of mercurial can be held next to that drop: the chemistry one names the metal itself, and the two about people borrow the way it moves.
可以想成桌上那一滴水銀：亮亮的銀色，怎麼也停不下來。滴到桌面它就跑；想用手壓住它，它就散開、從指縫滑走。它亮、它快、…更多收起
可以想成桌上那一滴水銀：亮亮的銀色，怎麼也停不下來。滴到桌面它就跑；想用手壓住它，它就散開、從指縫滑走。它亮、它快、它沒有固定的形狀。英文給它另一個名字 quicksilver，字面是「活的銀」。mercurial 的每一種用法，都可以擺到這一滴旁邊看：講化學的那個說的是金屬本身，講人的那兩個借走的是它移動的樣子。From the word’s history
Mercurial comes from Latin mercuriālis, 'belonging to the god Mercury'. The packet also records Mercury as the Roman god of commerce, communication, and trickery, and the same name is carried by the planet and by the metal, which is why one adjective can cover a chemical and a character.
mercurial 來自拉丁文 mercuriālis，意思是「屬於羅馬神 Mercury 的」（依 Wiktionary 詞源）。資料同時記載 Mercury 是掌管商業、溝通與機巧的神，而這個名字後來也落在行星和水銀這個金屬上。所以同一個形容詞才會既能講化學品，又能講一個人的性情。這裡談的是概念上的相通，不是主張其中一個意思在歷史上先於另一個。
Wiktionary etymology and sense notes supplied in this evidence packet (source_ref kaikki:3f6f69a190036ae4:332884707)
From the picture
Also in this word
adjective · C2
Containing mercury, or made with a compound of mercury; also used of harm caused by mercury.
含汞的