Magnetic Moments of Sunspots

Abstract
Simple approximate representations of the magnetic fields of sunspots by dipoles or ring currents are considered, and expressions deduced for the magnetic moment of a sunspot in terms of its area and its maximum central magnetic field strength. These are extended to include sunspot groups, and a function (SS-MM) is defined as the arithmetical sum of the equivalent moments of all visible groups. Statistical treatment by Chree's method of superposed epochs provides some indication of a 27-day interval between recurrences of fluctuations in SS-MM.