Hair hygrometer

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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Online ID:	000-100-102-709-C
Image Rights Holder:	National Museums Scotland
Project:	0098: National Museums Scotland Project description \| View all records in project
Ref:	National Museums Scotland T.1967.14
Date:	1790 c. 1790
Material:	Brass cylinders, mahogany box. Inscription: Haas & Hurter, LONDON
Dimensions:	11.63" L x 2.38" D
What:	Hygrometer, hair / box
Subject:	10. METEOROLOGY (Departmental Classification)
Who:	Haas and Hurter, London (Maker)
Where:	England, London
Event:
Description:	Hair hygrometer, in a mahogany box, by Haas and Hurter of Londonc. 1790
References:	Middleton, W. E. Knowles, Invention of the Meteorological Instruments. Baltimore, 1969, p 110 Reis, A. Estacia dos, Uma Oficina de instrumentos matematicos e nauticos (1800-65), Lisbon: 1991, p 65 & fig 9
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