This is a long-period horizontal seismometer, likely built for the World Wide Standard Seismological Network (WWSSN) in the early 1960s. The WWSSN was designed to detect underground nuclear tests. Further information about this type of instrument can be found at the Smithsonian's National Museum of American History (http://americanhistory.si.edu/collections/search/object/nmah_1445876 ).
Image courtesy of the AVO/ADGGS.