W. Schroder et Hj. Treder, ON HIDE MAGNETIC ANALOG OF ERTEL VORTICITY THEOREM, Zeitschrift fur Naturforschung. A, A journal of physical sciences, 52(1-2), 1997, pp. 210-211
The relativistic formulation of Hide's ''magnetic analogue'' of Ertel'
s potential vorticity theorem is Dirac's ''new classical theory of ele
ctrons''.