Daniell Hygrometer

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John Frederic Daniell, a young English natural philosopher, described this type of hygrometer in 1820. It consists of two glass balls, one partially filled with ether and the other covered with muslin, connected by a thin tube from which the air has been evacuated. There is a thermometer in the tube above the ball with the ether, and another on the supporting stand. When a few drops of ether are poured onto the muslin, their evaporation chills the covered ball; that in turn causes the ether vapor inside the instrument to condense, thereby cooling the other ball and causing dew to form on its surface.
The stand of this example is wood. The interior thermometer has a paper inside the stem that is graduated every degree from +13 to +120. The exterior thermometer is mounted on a white porcelain plate that is marked "Fahrenheit" and graduated every degree from -20 to +122.
This example came from the United States Military Academy, and may date from the middle years of the nineteenth century.
Ref: J. F. Daniell, "On a new Hygrometer, which Measures the Force and Weight of Aqueous Vapour in the Atmosphere, and the Corresponding Degree of Evaporation," Quarterly Journal of Science 8 (1820): 298-336.
Currently not on view
overall: 9 11/32 in; 23.7236 cm
overall: 10 1/4 in x 7 1/4 in x 5 in; 26.035 cm x 18.415 cm x 12.7 cm
ID Number
catalog number
accession number
Credit Line
U.S. Military Academy
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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