The lines of force encvircling a permanent magnet or a moving charged element: The magnetic field is present in and around the Earth.

The intensity of the magnetic field at the Earth's surface is approximately 0.32 gauss at the equator and 0.62 gauss at the north pole.

A "gauss" is equivalent to 1 maxwell per square centimeter, and a "Maxwell" is equivalent to the flux that produces one abvolt in a one-turn circuit when the flux is reduced to zero at a uniform rate in one second, while a "flux" is the electric or magnetic field lines of force that traverse a given cross-sectional area.