This is a digital reprint of the revised 1976 edition of this classic work. It examines seismology, gravity, the strength of the shell, the variation of latitude and the figure of the Moon. The chapter on tidal friction is largely rewritten and what now seem to be the three most reliable estimates of the true secular acceleration of the Moon agree in suggesting that the provisional estimate in the last edition should be considerably increased. The criticism of theories of continental drift, convection and plate tectonics is much expanded. A new appendix pinpoints directions for future...