All,

I believe there is an error in the FMES spreadsheet just posted.  The 
correct natural frequency for a "pot and tube" tiltmeter/horizontal 
seismometer is:

(omega nought)^2 = ((3/2) g)/(2L +l(R^2/r^2)),

where g is acceleration due to gravity, L is height of liquid in the 
pot, l is length of the tube, R is pot radius and r is tube radius.  The 
complication is due to non-uniform speed of liquid flow in a tube, 
maximum at the center, zero in contact with the tube.  Steen and Casey, 
Theory of the Manometer Accelerometer, Rev Sci Instr, Nov., 1953, 
p1021-1028.  gives a complete derivation.

Chuck Burch
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