Soviet Station Hair Hygrometer Joins the Collection
A 1970 M-19 hair hygrometer from the Riga Gidrometpribor plant has been added to the collection.
The new arrival is a station hair hygrometer manufactured in October 1970 by the Riga Gidrometpribor plant, one of the factories that supplied instruments to the hydrometeorological service of the USSR. The M-19 was a standard fixture of the psychrometric shelter at Soviet weather stations, where it served as the main source of humidity readings in winter, when frost made the psychrometer unreliable.
The instrument works on a principle introduced by Horace Bénédict de Saussure in 1783: a single degreased human hair lengthens and contracts with changes in relative humidity, and a lever with a counterweight turns these tiny movements into the sweep of a long steel pointer across an arc-shaped enamel scale. The scale carries the factory's monogram between stylised wings, the inscription "Made in the USSR" and the date of manufacture.
The hygrometer has survived in complete condition, together with its original cardboard factory case. A full description is available on the instrument's page.