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Hair hygrometer

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probably made in London

Hair hygrometer
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A hair hygrometer measures atmospheric humidity, using human hair as its hydroscopic, or moisture-absorbing, material. This example was made around 1790, probably by Haas & Hurter, scientific instrument makers based in London.

The hygrometer has a circular dial signed 'Haas & Hurter/LONDON'. Below the dial is the hydroscopic element encased in brass cylinders. As moisture is absorbed or evaporates, the hair lengthens or shortens, turning the pointer.

This instrument is adapted from a design published by the Swiss Horace Benedict de Saussure (1740-99) in 1783. Jacob Bernhard Haas (1753-1828) was in partnership with Johann Heinrich Hurter (1734-1799) in London between around 1790 and 1795.

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