The analysis of a long series of l a t i t u d e observations carriedout in t h e International Latitude Station has allowed a very careful studyof forced motion due to meteorological effects and of t h e remaining motionascribed to the free nutation of an elastic Earth. The discussion of theseobservations has, however, led to the discovery of the existence of longterm components in polar motion (<•• 8). These results have recently beenconfirmed by Proverbio et al. (u ).In this work, the

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... es observed in t h e period 1900.0 - 1969.0 reducedto a single homogeneous system are analyzed separately for t h e five stationsof the ILS. The analysis of this q u a n t i t y points up t h e existence of twodifferent long term components in polar motion of about 16 and 26 years.One possible interpretation of these phenomena is based on " beat " phenomenabetween the n u t a t i o n of the mantle and the inner core of the E a r t h