Abstract
Instantaneous phase and amplitude of a time dependent given function f(t) can be calculated by the method of Goodman (1960). It is interesting to see how the instantaneous phase and amplitude of ILS (International Latitude Service) and BIH (Bureau International de l'Heure) data change with time. These calculated instantaneous phase and amplitude are shown in Fig. 3, 4, 5, 6. In Fig. 3, 4 we find sudden phase changes in 1927 and 1942. Such a sudden phase change may be considered to be related with the excitation of the Earth's free damped nutations. It is, however, not clear what kind of natural phenomena are related with the excitation. Earthquake occurrences do not seem to be related with the excitation of the Chandler wobble.
