mechanical hygrometer

https://doi.org/10.1351/goldbook.M03801
An apparatus containing an element (hair, goldbeater's skin, carbon-@F02366@) whose dimension or mass varies as a function of its water content.
Source:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2195 [Terms] [Paper]