Instrument used to measure the water vapour content of the atmosphere.
See: capacitance hygrometer, dew point hygrometer, electrical hygrometer, electrolytic hygrometer, frost point hygrometer, mechanical hygrometer, psychrometric hygrometer
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2195 (https://doi.org/10.1351/pac199062112167)