On Analysis of the Secular Variation

It is noted that the time-scale of the secular variation of the geomagnetic field is rather short compared with the electromagnetic diffusion times appropriate to the earth's core. It is therefore suggested that the secular variation is primarily due to the rearrangement of pre-existing lines of force emanating from the core, and not due to the creation of new (or destruction of old) flux tubes by electromagnetic diffusion. The theoretical consequences of this idea are fully examined.