I found it at:
http://www.fsm.physics.uwa.edu.au/RSI.pdf
Charles R. Patton

 Chris Chapman wrote:
'Ground tilt seismic spectrum measured with a new high sensitivity
rotational spectrometer'. A N Luiten & Al. Rev.Sci. Instrum. V68 (4),
April 1997  pp 1889-1893 has a sensitive beam balance system and it is
somewhere on the Web. I downloaded it, but am not now sure from where...
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