= Cloud chamber
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A <cloud chamber> contains <supersaturated vapor>. <Ionization> along a <charged particle>'s path supplies sites for <nucleation>; the resulting <liquid> drops scatter <light> and reveal the trail. The observed objects are drops, not magnified <particles>. Its beauty is that a spatially distributed microscopic interaction becomes a visible geometrical record.
Two ways of making <supersaturated vapor> must be distinguished. An <expansion cloud chamber> rapidly increases the <volume (thermodynamics)> of moist <gas>, producing a temporary sensitive interval through cooling by <adiabatic expansion>. A <diffusion cloud chamber> maintains a cold base and a warmer <vapor> supply, producing a continuously replenished sensitive layer through <diffusion> and a <temperature gradient>.
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