Alluard Hygrometer

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Emile Alluard, professor of physics at the University of Clermont-Ferrand and director of the meteorological observatory on the nearby Puy-de-Dôme, described this type of hygrometer in 1878. A modification of Regnault's instrument, it consists of a square vessel made of polished nickel-plated brass; at either side of the vessel, but not touching it, are strips of similar material. In use, the vessel would be filled with ether, and this ether would be cooled by evaporation by means of an aspirating bulb. When dew appears on the shiny surface of the vessel, a thermometer in the vessel indicates the temperature of the ether at that point. A second thermometer (lacking in this example) measures the ambient temperature.
Robert A. Millikan described the Alluard hygrometer as being one of the "most perfect forms of the dew-point hygrometer" in his Mechanics, Molecular Physics and Heat, a popular college text first published in 1903, that aimed "to present Physics as a science of exact measurement." The illustration on p. 167 shows an Alluard hygrometer made by William Gaertner, a German immigrant who settled in Chicago and who specialized in precision instruments.
This example is marked "WM. GAERTNER & CO. CHICAGO." It was made between 1898 and 1923, when the firm traded as Wm. Gaertner & Co. It came to the Smithsonian from Kalamazoo College.
Ref: M. Alluard, "Nouvel Hygromètre a Condensation," Journal de Physique et le Radium 7 (1878): 328-330.
Currently not on view
date made
early 20th century
Gaertner Scientific Corporation
place made
United States: Illinois, Chicago
overall: 31 cm x 13 cm; 12 7/32 in x 5 1/8 in
overall: 11 1/8 in x 4 1/2 in; 28.2575 cm x 11.43 cm
ID Number
catalog number
accession number
Credit Line
Kalamazoo College
See more items in
Medicine and Science: Physical Sciences
Measuring & Mapping
Thermometers and Hygrometers
Data Source
National Museum of American History


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