Reversals of the Earth’s Magnetic Field. Vine and Matthews’ Hypothesis

Gilbert, Queen Elizabeth’s physician, discovered that the Earth’s magnetic field was similar to that of a uniformly magnetized sphere; it is also equivalent to the field of a small magnet or ‘dipole’ placed at the centre. Actually the field varies continually; if its annual mean is taken and if it is developed in spherical harmonics as was done by Gauss, it is found to be almost exclusively of internal origin, and it is found that the leading terms, by much the largest, correspond exactly to the field of a magnetic dipole, currently inclined at 11.5° to the geographical axis.