Mendenhall Gravity Pendulum Apparatus
date: label: date made
content: 1889-1930
name: label: Associated Name
content: U.S. Coast & Geodetic Survey
notes: label: Description
content: 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.
label: Description
content: 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.
label: Description
content: 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.
label: Description
content: Ref: Victor Lenzen and Robert Multhauf, "Development of Gravity Pendulums in the 19th Century," <i>United States National Museum Bulletin</i> 240 (1965): 331-334.
label: Description
content: C. H. Swick, <i>Modern Methods of Measuring the Intensity of Gravity</i> (Washington, D.C.: United States Coast and Geodetic Survey, 1921).
label: Description
content: T. C. Mendenhall, "Determination of Gravity with the New Half-Second Pendulum," <i> Report of the Superintendent of the U.S. Coast and Geodetic Survey for 1890-91</i>, Part 2, pp. 503-564.
label: Description
content: W. H. Burger, "The Measurement of the Flexure of Pendulum Supports with the Interferometer," <i>Report of the Superintendent of the U.S. Coast and Geodetic Survey for 1909-1910</i>, Appendix 6.
label: Location
content: Currently not on view
place: label: place made
content: United States: District of Columbia
setName: label: See more items in
content: Medicine and Science: Physical Sciences
label: See more items in
content: Measuring & Mapping
creditLine: label: Credit Line
content: U.S. Department of Commerce. Coast and Geodetic Survey
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: PH.315810
label: accession number
content: 221202
label: catalog number
content: 315810
objectType: label: Object Name
content: gravity pendulums (Mendenhall apparatus)
physicalDescription: label: Measurements
content: pendulums: 3 1/2 in; 8.89 cm
label: Measurements
content: brass chamber: 7 in; 17.78 cm
label: Measurements
content: overall; brass chamber: 7 in x 9 in x 7 7/8 in; 17.78 cm x 22.86 cm x 20.0025 cm
label: Measurements
content: overall; small box: 4 in x 8 1/2 in x 6 1/2 in; 10.16 cm x 21.59 cm x 16.51 cm
label: Measurements
content: overall; large box: 9 3/8 in x 19 7/16 in x 12 7/8 in; 23.8125 cm x 49.37125 cm x 32.7025 cm