AGU American Geophysical Union BIH Bureau International de l'Heure FAGS Federation of Astronomical and Geophysical Services lAG International Association of Geodesy IAU International Astronomical Union ICSU International Council of Scientific Unions ILS International Latitude Service IPMS International Polar Motion Service International Union of Geodesy and Geophysics IUGG PZT Photographic Zenith Tube UNESCO United Nations Educational, Scientific and Cultural Organization INTRODUCTION The hypothesis of continental drift has become of increasing interest to geophysicists in recent years. The...