Maximum entropy spectral analysis has been applied to the annual mean magnetic data around London for the years 1939--1974. These data were compiled by Malin and Bullard. The existence of a ~60-year spectral line is clearly found. In addition, cross power spectral density analyses using a two-channel maximum entropy method were applied to both the variations of the annual mean declination around London from 1900 to 1974 and the fluctuations of the Earth's rotation rate from 1876 to 1974. The coherence is high (0.98), and the phase angle indicates that the changes of the magnetic declinations around London lag behind the fluctuations of the Earth's rotation rate by 20¿4 years. ¿ American Geophysical Union 1989