Aitken dust counter

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Aitken dust counter

(
Or Aitken nucleus counter.) An instrument developed by John Aitken for determining the dust content of the atmosphere.

A sample of air is mixed in an expandable chamber with a larger volume of dust-free air containing water vapor. Upon sudden expansion, the air in the chamber cools adiabatically below its dewpoint, and droplets form with the dust particles as nuclei. A portion of these droplets settle on a ruled plate in the instrument and are counted with the aid of a microscope.
See dust counter.

Aitken, J. 1923. Collected Scientific Papers. 236–246.