2] is interesting since it is the RFCN frequency, closest to the motion we are studying.
Now if the resonant frequency of RFCN changes, the curve representing T([sigma]) shifts horizontally, and the value T([sigma]) for any forced term with frequency [sigma] also changes.
leading to the value of the resonance RFCN period equal to [P.
The main difference between the direct and indirect determination of RFCN apparent and resonance period respectively is that
The inevitable conclusion is that the observed changes of the apparent RFCN period coming from the direct determination must be caused by an additional excitation.
FCN] are the complex terrestrial frequencies of Chandler wobble and RFCN, respectively.