Details cont.

Foucault's "fixity" assertion remains true for any model pendulum governed by purely harmonic restoring forces even if the pendulum motion is not the restricted
motion resulting from a release from rest as shown in Fig. 2. Indeed, the most general motion of an harmonic pendulum has in common with the special motion in Fig.
2 the property that it will always appear as an ellipse in a fixed orientation in the frame of the stars. In the frame of the earth these different elliptical motions take on
the patterns shown in Fig. 5.

Fig. 5

As in Fig. 2, the Coriolis precession is greatly exaggerated.

Fig. 6
Figure 6 corresponds to purely back and forth, i.e. linear, motion in the star fixed frame.
Fig. 7
Figures 5 and 7 are orbits that have oppositely directed elipticity yet all three precess at the same rate and in the same direction.

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Pendulum