Winlock & Huddleston Psychrometer

Two thermometers, one kept wet, showed how fast water evaporated, which told how humid the air was.

Date: 1873
Maker: John S. F. Huddleston; Joseph Winlock
Place: United States: Massachusetts, Boston
Dimensions: overall: 14 3/4 in x 8 1/2 in x 4 in; 37.465 cm x 21.59 cm x 10.16 cm
Museum: National Museum of American History

Patent model for Joseph Winlock and John S F. Huddleston, "Psychrometer," U.S. Patent 149,176 (March 31, 1874). Joseph Winlock was a professor of astronomy at Harvard College, and John S. F. Huddleston was a thermometer and barometer maker in Boston. The wet bulb thermometer is mounted on a brass plate that is marked "HUDDLESTON BOSTON" and graduated every degree Fahrenheit from +10 to +115. The dry bulb thermometer is missing.

The wooden tower holds a rotating chart that indicates relative humidity, and carries a brass plate graduated every degree from +6 to +113. The patent described "a simple, efficient, and convenient means of determining the relative humidity of the atmosphere or the dew-point, so called, without calculation."

The museum's own record (Smithsonian, National Museum of American History)