About ten years ago I began to investigate tidal friction and its influence on the evolution of the Earth-Moon system, and I first describe the model used. Following the ideas of G. H. Darwin, I treated the system as a two-body problem. The Moon raises tides on the Earth and the two bulges of the tidal ellipsoid, because of the rotation of the Earth, revolve twice daily. The line joining them forms an angle
ψ
with the line joining their centres; this is a measure of the dissipation of energy. The Moon, considered as a point mass, exerts a retarding couple on the deviated tidal ellipsoid. Contrary to Darwin, I have limited myself to the case of small angles
ψ
, but I have allowed for arbitrary changes of the other parameters of the orbit, for example, changes of the obliquity ∊ between the earth’s axis and the pole of the orbit as well as changes of the eccentricity.
28 December Early History of the Earth-Moon System