抄録
Using the variational calculus method in a previous paper, we calculate the free periods of torsional oscillations for two earth models. In the model I, the earth is assumed to be composed of homogeneous mantle and core. In the model II, we hane used the mantle strucure infered by Jeffreys and Bullen. In each model, we calculate the periods when the core is fluid or perfectly rigid. In the fluid core model, we have also worked out the periods when the coupling between the mantle and core is perfect or zero. Present study will show that in order to get useful informations on the rigidity of the core or the strength of coupling between the mantle and core by this kind of study, we must make the observations of free periods with the accuracy of several ten seconds.
