This animation illustrates a hypothetical scenario
in which an enormous dip needle (a compass whose needle
can osciallate in a vertical plane) is placed on the
surface of the earth and oscillates undamped in the
earth's field. The oscillation is of course a result
of the interaction between the magnetic field of the
earth and the magnetic field generated by the dip needle.
If the needle's oscillatons were damped, it would align
itself along the local magnetic field. Note how the
total field is stretched and compressed as the needle
oscillates, in keeping with the Maxwell stresses that
cause the oscillation of the dip needle.