Geomagnetic field: Westward drift

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The westerly drift of the Earth's magnetic field was first described by Edmund Halley in 1692. Halley noted that many of the changes in the field that had been observed in the previous century, such as the shift in the position of no variation from Cape d'Agulhas to the meridian of St. Helena (about 23° in 90 years), could be accounted for by a slow westward rotation of the internal part of the Earth, Halley's suggestion of a westward drift has since proved to be remarkably foresighted as magnetic field features have continued to move westward during the succeeding three centuries. Furthermore, as a result of theoretical calculations, the source of the field is now widely attributed to dynamo action in the Earth's fluid core with part of the core bodily moving westward carrying features of the field alongwith it as part of the dynamo process. Alternatively the westward drift may be associated with hydro-magnetic wave propagation inside the core, again as par ...