Authors: International Astronomical Union, from symposium No. 32. Organized by the IAU in cooperation with IUGG held in Stresa, Italy, 21-25 of March, 1967
Publisher: R. Reidel Publishing Company, New York, 1968
Condition: Very good
"A study of the International Latitude Service (ILS) results for 1900 to 1966 indicates that the secular motion of the mean pole is real and that within the errors of observation the five stations located near parallel t3908' are not undergoing crustal displacements in lqtitude. An empirical, 24-yr librational motion found in 1960 was continued from 1960 to 1966. The progressive motion of the mean pole is about 0'.'0034/yr towards longitude 650 west. Homogeneous data for studying changes in relative longitudes do not exist because similar observations for time have not been made. However, programs of observations of the same stars with instruments on nearly the same parallel and which determine both time and latitude, such as the photographic zenith tube and astrolabe, have recently been organized. These observations will help to determine whether continental drift is occurring. The irregular variation in speed of rotation of the earth has been determined with high accuracy since 1955.5 by a comparison of Universal Time with Atomic Time. Sudden changes in acceleration occur, but not sudden changes in speed of rotation. The difference, Universal Time minus Atomic Time, can be well represented by arcs of parabol~s. The changes from one parabola to another do not coincide with changes in the motion of the mean pd'e. However, a much longer period of observation than is now available will be required to see if there is any correlation."