Fundamental Physical Constants and Conversion Factors

This section provides a summary of important units for geomagnetism and geoelectricty. In addition, a summary of conversion factors and fundamental units of relevance to earth and planetary science are presented for reference. Despite the sentiment expressed above by Vigoureux, it still seems that plenty of us slave over SI units in geomagnetism. There is probably no other scientific discipline in which the topic of units generates so much endless discussion and confusion than in magnetism. Before the late 1970’s, practically all the geophysical literature in geomagnetism and paleomagnetism used the Gaussian CGS system of units. The CGS system is a perfectly sound, intemally consistent, system of units, but, like all systems of units and dimensions, is totally arbitrary. As the name implies, the cgs system is based on three base units: centimeter, gram, and second. All other units are derived from these three. The Gaussian cgs system is based on two earlier systems, the electrostatic units (esu) and electromagnetic units (emu). Electrostatic units were defined by Coulomb’s law describing the force between two electrical charges. Similarly, electromagnetic units were defined by the force between two magnetic charges or two current-carrying wires. One consequence of this dichotomy is that the dimen-