Sequicentenary of Gauss's first measurement of the absolute value of magnetic intensity

Abstract

The geomagnetic field and its changes with time are major tools for probing the Earth’s deep interior. It is therefore particularly appropriate that the Royal Society Discussion Meeting on the Earth’s core should coincide with the 150th anniversary of the first absolute measurement of the intensity of the geomagnetic field. This was only one of Carl Friedrich Gauss’s many contributions, both direct and indirect, to geomagnetism. For example, it was Gauss who devised the methods of least squares and of spherical harmonic analysis. With Weber, he applied these to the geomagnetic field to show that it was nearly all of internal origin. Gauss was also the initiator of, and an active participant in, the ‘Gottingen Magnetic Union’, a scheme for the simultaneous observation of the magnetic field at widespread sites from which has developed the present worldwide network of magnetic observatories. The particular achievement that we commemorate here was the determination by Gauss of the horizontal intensity of the geomagnetic field in units related to the millimetre, milligram and second. (This was one tenth of the unit that subsequently bore his name.) At that time he was working towards a universal system of units for all physical quantities and conceived the original idea that magnetic intensity can be measured in terms of mass, length and time.