Gulf Gravimeter

Gravimeters (gravity meters) are extremely precise instruments that measure the earth’s gravity at a specific location. Gravimeters are often used by prospectors to locate subterranean deposits of valuable natural resources (mainly petroleum) as well as by geodesists to study the shape of the earth and its gravitational field. Differences in topography, latitude, or elevation—as well as differences in subterranean density—all affect the force of gravity. Commonly, gravimeters are composed of a weight hanging on a zero-length spring inside a metal housing to negate the influence of temperature and wind. Generally gravity is then measured by how much the weight stretches the spring, although this object tweaks this arrangement.
The Gulf Research & Development Corp. began work on a gravimeter in November 1932, and conducted their first field trials in March 1935. The gravimeter soon supplanted Gulf's pendulum equipment; and by the end of the decade, with 18 instruments in the field, Gulf was fairly described as "the most aggressive of the major oil companies in the early application of gravimeter surveys to petroleum exploration." Gulf gravimeters often achieved results accurate to 0.05 milligal. With slight modification, they could be used under water.
The Gulf gravimeter was designed by a young Ph.D. physicist named Archer Hoyt (1905-ca. 1938) who, after trying various designs, chose an unastized instrument with a heliacal spring. This instrument does not measure the change of length of a spring with change of gravity, but rather the rotation (or unwinding) of the lower end of the spring. Hoyt used a thin ribbon for the spring, rather than the thin wire that had been used in earlier instruments of this sort. The mass at the bottom of the spring held a mirror whereby the angular rotation could be measured. Hoyt received three patents on October 4, 1938. One (#2,131,737) described the gravimeter itself. The second (#2,131,738) described the optical system. The third (#2,131,739) described the helical ribbon spring measuring apparatus. All were assigned to the Gulf Research and Development Corp.
The original Gulf gravimeter weighed over 90 lbs. The instrument that the Gulf Research & Development Corp donated to the Smithsonian in 1966 seems to be a later model designed for demonstration purposes.
Ref: E. A. Eckhardt, "A Brief History of the Gravity Method of
Prospecting for Oil," Geophysics 5 (1940): 231-242.
R. D. Wyckoff, "The Gulf Gravimeter," Geophysics 6 (1941): 13-33.
L. L. Nettleton, Geophysical Prospecting for Oil (New York,1940), pp.27-29.
Currently not on view
overall: 51 cm x 17.7 cm; 20 1/16 in x 6 15/16 in
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Work and Industry: Agriculture
Measuring & Mapping
Natural Resources
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National Museum of American History, Kenneth E. Behring Center


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