The Eötvös Effect, named after Hungarian nobleman and physicist Baron Roland von Eötvös, is an longitudinal effect which affects gravimeters and occurs when a vessel is traveling eastwards or westwards. In the early 1900s, a German team from the Institute of Geodesy in Potsdam carried out gravity measurements on moving ships in the Atlantic, Indian and Pacific Oceans. While studying their results Eötvös noticed that the readings of the gravimeter were slightly lower when the boat moved eastwards, and slightly higher when it moved westward.
An Effect of Gravimetry
It is found that a gravimeter is a low-frequency seismometer, and that the theory of gravimetry is based on a theoretical assessment of the background noise in the subseismic band. The patterns of the tides and other phenomena can be pulled out of the background noise, and are assumed to be due to "gravity". See: Gravimetry
In connection with the above, The Eötvös Effect is an effect which adds or subtracts anthropogenic and microseismic noises to the gravimeter when a vessel moves eastwards or westwards. Although the cause of the noise is unknown, it is suggested that it may be related to the stars, tides, or even the 'great ocean conveyor belt', all of which make regular westwards motions across the earth. A vessel going against this noise would pick up greater noise than a vessel which goes with the noise.