The physical theory of the Earth's magnetic and electric phenomena.—No. IV: On the origin of the Earth's magnetism

Abstract

42. In the previous number, the hypothesis was set up (§29) that “the Earth is chiefly an electromagnet, the magnetizing currents being outside and consisting of negative electric currents circulating overhead in the same general direction as that of the Earth's rotation, namely, from west to east.” The external currents are revealed by the harmonic analysis of the magnetic elements observed on the Earth's surface (§37). Starting with these currents, it was found that, qualitatively, the Earth, if paramagnetic, would be magnetized by them in the general direction in which it is actually found to be and that quantitatively, the magnetization of our planet can be accounted for, if its average magnetic permeability is on the order of 135 for a magnetizing force of about 0.0024 C. G. S. This value while high was shown not to be impossible and, in fact, it is not as great as has been thought necessary in order to account for the Earth's magnetism electromagnetically; as these researches progress it is quite likely that the value will receive some modification.