Variations in the rate of rotation of the Earth.
Variations observed in the length of the day can be divided into three types: seasonal, irregular, and long-term. The astronomical data examined here for the years 1956-1969 suggest that the seasonal terms hitherto assumed are slightly in error, that the irregular variations probably share the same source with the seasonal variations, and that the long-term variations may be linked to earthquake activity.
Challinor
R A
RA