On the apparent secular accelerations of the Moon and the Sun

The discussion of tidal friction in the Earth-Moon system given in successive editions ofThe Earth by Jeffreys is shown to contain a serious dynamical error. When the treatment is corrected, it shows that the moment of inertia of the Earth must be changing. The apparent secular accelerations of the Moon and Sun require a diminishing moment of inertia, and the rate is in agreement with the phase-change hypothesis for the nature of the core.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.