On the Electrodynamics of Moving Bodies
Abstract
It is known that Maxwell's electrodynamics---as usually understood at
the present time---when applied to moving bodies, leads to asymmetries
which do not appear to be inherent in the phenomena. Take, for
example, the reciprocal electrodynamic action of a magnet and a
conductor. The observable phenomenon here depends only on the
relative motion of the conductor and the magnet, whereas the customary
view draws a sharp distinction between the two cases in which either
the one or the other of these bodies is in motion. For if the magnet
is in motion and the conductor at rest, there arises in the
neighbourhood of the magnet an electric field with a certain definite
energy, producing a current at the places where parts of the
conductor are situated. But if the magnet is stationary and the
conductor in motion, no electric field arises in the neighbourhood of
the magnet. In the conductor, however, we find an electromotive
force, to which in itself there is no corresponding energy, but which
gives rise---assuming equality of relative motion in the two cases
discussed---to electric currents of the same path and intensity as those
produced by the electric forces in the former case.