On January 20-21, 1964, the Institute for Space Studies of the Goddard Space Flight Center, National Aeronautics and Space Administration, was host to an international group of astronomers, physicists, and Earth scientists, gathered to discuss the Earth-Moon system. This was the sixth in a continuing series of interdisciplinary meetings on topics in space physics held at the Institute. The conference was organ ized by G.J.F. MacDonald, of the University of California at Los Angeles, and by R.H. ...