München 2019 – scientific programme

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GP: Fachverband Geschichte der Physik

GP 6: Tools and Technologies of physics research

GP 6.4: Talk

Tuesday, March 19, 2019, 15:45–16:15, HS 9

Saussure's hair hygrometer: the art of measuring atmospheric humidity — •Fischer Stéphane — Musée d'histoire des sciences de Genève

Among the many instruments invented or perfected by the Swiss naturalist Horace-Bénédict de Saussure (1740-1799) the hair hygrometer is undoubtedly the instrument that has had the greatest commercial success with more than 150 copies sold.

Saussure first made many experiments in laboratory. He is one of the first to highlight the phenomenon of relative humidity (percentage of humidity compared to the saturating value). The results of his experiments are published in 1783 in his *Essai sur l*hygrométrie*, considered as a reference work in the field.

To validate its work and so that its results can be reproduced by its peers, Saussure sells its hygrometer throughout Europe accompanied by an explanatory note on its operation.

Thereafter, Saussure uses his hygrometer to perform many measurements in the field. During his ascent to Mont Blanc in 1787, he observed that the total humidity decreases with altitude. Measuring the moisture content of the atmosphere was one of Saussure's main activities. As such, it can be considered a pioneer of modern meteorology.

On the basis of these considerations, the Musée d*histoire des sciences de Genève, which conserves the instrument*s collection of Saussure, including several hair hygrometers, plans to reproduce some hygrometric experiments carried out by the Genevan naturalist at the end of the 18th century.