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| Keywords: Quartz gravimeter pendulums.jpg 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 <br /><br /> Alterations to image removed aliasing artifacts striped lines from scanning of original halftone image using GREYCstoration filter in Gimp Downloaded 2009-05-09 from http //books google com/books id A1IqAAAAMAAJ pg RA2-PA317 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 1964 US Coast and Geodetic Survey Original work of US Government PD-USGov Pendulums Gravimetry | ||||
