The diamagnetic theory of undisturbed terrestrial‐magnetic variations

In an earlier paper 2 the writer outlined a theory of the terrestrial‐magnetic variations based on diamagnetism existing in the upper atmosphere. The diamagnetism of the region was shown to follow from simple considerations of the motion of ions or electrons which spiralled about the Earth's magnetic field as a result of their thermal agitation. It is the purpose of this paper to extend the original ideas and supply certain evidence supporting the theory that was not advanced in the original paper. It has been shown 2 that the intensity of magnetization I of an ion gas due to the thermal agitation of the ions is given by urn:x-wiley:00968013:media:tma31313:tma31313-math-0001 where N is the number of ions of all kinds per cubic centimeter, m the mass of the ion, V the component of the velocity of the ion perpendicular to the impressed magnetic field H , κ the Boltzmann constant, and T the absolute temperature. These relations have been deduced on the assumption that the free‐path is long and it becomes necessary to establish a criterion for the existence of long free‐paths. The free‐path, λ, of an ion in a gas made up of N molecules or ions per cubic centimeter, and having a kinetic‐ theory diameter σ is given by