HAIR HYGROMETER, English, c. second quarter 19th century, signed “Watkins & Hill, London.” The open framework is constructed of clear lacquered brass, 8-3/4″ (22 cm) tall overall, with suspension ring and mounts for the mechanism. It is fitted with a circular scale of relative humidity divided every unit from 0 to 100, and ends marked D(ry) and M(oist). An index pointer is driven by central double pulley, the pulley drawn counter-clockwise by string attached to a tight bundle of very fine hair, and clockwise by string attached to a long finely wound preload spring. The hair is secured, at the base of the instrument, to an adjustable calibration screw. If the air dries out, the hair shrinks, pulling on the string and rotating the index arm counterclockwise against the spring tension. Condition is very fine complete with the original shaped wood case lined in purple cloth and bound in red Morocco leather. This is a good early example of the hygrometer form designed by Jean-Andre De Luc but here activated by a fine bundle of hair rather than by a strip of whalebone. Hair was in fact the province of Horace Benedict de Saussure, and controversy between the two scientists raged for years in the late 18th century (see Middleton, 1969).
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David and Yola Coffeen both have enjoyed academic careers, as planetary astronomer and as linguist/educator. But since 1982 (yes, 1982!) they have been full-time dealers in early scientific and medical instruments, under the name Tesseract. Selling primarily by catalogue (over 100 issued so far) they also have a web presence at www.etesseract.com, and can be contacted at firstname.lastname@example.org.