cloud chamber
noun [ C ] physics specialized uk/ˈklaʊd ˌtʃeɪm.bər/ us/ˈklaʊd ˌtʃeɪm.bɚ/
云室（一种充满气体的设备，在其内部，比原子小的物质粒子经过时，气体会凝成液滴，液滴的出现证明这种微粒的存在）
a device containing a gas in which units of matter smaller than atoms are shown to be present by the small drops of liquid that they produce