  It will be shown that the rotation of the Earth in the Earth-Moon system can
be detected by comparing the deflection of a Foucault pendulum at noon on the
one hand and at midnight on the other hand. More precisely, on 21 June the
midnight experiment would give a deflection about 4% larger than at noon. In
other words, with a Foucault pendulum having an accuracy of the order of 1% one
should be able to identify this effect through a single measurement. Moreover,
if the experiment is repeated on N successive days, the division of the error
bar by the square-root of N which comes with the averaging process will allow
identification of the Moon effect even with a pendulum of poorer accuracy, say
of the order of a few percent. In spite of the fact that this effect appears
fairly easy to detect, it does not seem that its observation has attracted much
attention so far. We hope that this paper will encourage some new observations.
