Events at Physics
brought about by new methods for incorporating observations and theory, akin to those used in meteorology and oceanography. In 1950 Sir Edward Bullard wrote an influential paper entitled "The westward drift of the Earth's magnetic field", with coauthors C Freedman, H Gellman and J Nixon. A comprehensive study of observations was tied together with the then nascent dynamo theory to infer properties
of the dynamics of the core. Sixty years on, we have a much enriched understanding of the theory of convectively driven dynamos, and an even more comprehensive database of observations stretching back several centuries. Equally important are the new satellite observations that provide global coverage with unprecedented accuracy over the last decade. In this talk I will try to show how the interplay between theory and observation can lead to beter understanding of the dynamical regime in the core.