Detection of Solar and Lunar Tidal Forces via Non-resonant Oscillations of A Pendulum

The FFT power spectrum of time deflection data from a pendulum bob shows a broad structure in the micro-Hz regime is consistent with non-resonant response due to forced acceleration. Harmonic analyses of pass Butterworth filtered data and the horizontal components of the theoretical tidal forces were compared. We conclude that the observed diurnal and semi-diurnal oscillations with about 10 micro-gal amplitude are due to solar and lunar tides. Our results presented here clearly indicate that under the appropriate conditions the horizontal forces are also present and have to be accounted for and provide useful information. To the best of our knowledge this is the first reported detection of the horizontal tides with a pendulum.