Image: Quartz gravimeter pendulums

Description: Photo of quartz gravimeter pendulums used in the gravimeter instrument designed by Gulf Research and Development Co. in 1929. Accurate to less than 1 milligal, the Gulf instrument was the most accurate commercial gravimeter into the 1950s. The pendulums are 10.7 inches long and had a period of about 0.89 sec. They were mounted in a sealed vacuum tank and swung synchronized, 180° out of phase, to cancel out swaying of the support. Fused quartz was used because of its small thermal expansion, but stray electrostatic charges on the pendulums had to be removed by exposure to a radioactive salt before use. Alterations to image: removed aliasing artifacts (striped lines) from scanning of original halftone image using GREYCstoration filter in Gimp.
Title: Quartz gravimeter pendulums
Credit: Downloaded 2009-05-09 from Victor F. Lenzen, Robert P. Multauf (1964) 'Paper 44: Development of gravity pendulums in the 19th century' in United States National Museum Bulletin 240: Contributions from the Museum of History and Technology, reprinted in Bulletin of the Smithsonian Institution, 1964, Smithsonian Institution Press, USA, p.337, fig.29 on Google Books. Credited in text to US Coast and Geodetic Survey.
Author: US Coast and Geodetic Survey
Permission: Original work of US Government
Usage Terms: Public domain
License: Public domain
Attribution Required?: No