Mendenhall Gravity Pendulum Apparatus

Thomas C. Mendenhall, who became superintendent of the U.S. Coast and Geodetic Survey in 1889, introduced a new gravity apparatus that was substantially smaller than earlier gravimetric instruments and, he hoped, more reliable. Mendenhall’s apparatus had a set of short and invariable pendulums, an airtight brass chamber in which the pendulums could be swung, and a flash apparatus with telescope for observing the coincidence between a pendulum and the beats of a chronometer. In 1894 the Survey used Mendenhall apparatus to determine the force of gravity at 26 stations along the 39th parallel from the Atlantic coast to Utah. The trial was deemed successful, and this type of apparatus remained in use until the 1930s.
The pendulum of the Mendenhall apparatus was made of a copper-aluminum alloy, with a flat stem supporting a lenticular bob. It had a period of about 2 seconds, so designed that a coincidence between the pendulum and a chronometer would occur every 5 or 6 minutes. Each apparatus was provided with three pendulums. If discrepancies appeared in the results, the faulty pendulum could be detected as well as a dummy pendulum equipped with a thermometer.
The Coast and Geodetic Survey transferred this example to the Smithsonian in 1958, describing it as “essentially a boiled-down version of the original." Its pendulums have periods of about 3 seconds. The Museum also has a Michelson interferometer that was used to determine the flexure of the pendulum support, and was adapted for this purpose in 1907.
Ref: Victor Lenzen and Robert Multhauf, "Development of Gravity Pendulums in the 19th Century," United States National Museum Bulletin 240 (1965): 331-334.
C. H. Swick, Modern Methods of Measuring the Intensity of Gravity (Washington, D.C.: United States Coast and Geodetic Survey, 1921).
T. C. Mendenhall, "Determination of Gravity with the New Half-Second Pendulum," Report of the Superintendent of the U.S. Coast and Geodetic Survey for 1890-91, Part 2, pp. 503-564.
W. H. Burger, "The Measurement of the Flexure of Pendulum Supports with the Interferometer," Report of the Superintendent of the U.S. Coast and Geodetic Survey for 1909-1910, Appendix 6.
Currently not on view
Object Name
gravity pendulums (Mendenhall apparatus)
date made
pendulums: 3 1/2 in; 8.89 cm
brass chamber: 7 in; 17.78 cm
place made
United States: District of Columbia
ID Number
accession number
catalog number
Measuring & Mapping
U.S. Coast & Geodetic Survey
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Medicine and Science: Physical Sciences
Data Source
National Museum of American History, Kenneth E. Behring Center
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