1879 G. H. Darwin in (Royal Soc.) 171 713 On the Secular Changes in the Elements of the Orbit of a Satellite revolving about a Tidally Distorted Planet.
1880 G. H. Darwin in (Royal Soc.) 172 513 In considering the effects of tidal friction the theory has been throughout adopted that the tidally-disturbed body is homogeneous and viscous.