6.  B. Lehnert, in Ref. 1, Vol. 114(2).  B. Lehnert and S. Roy,
        Extended Electromagnetic Theory (World Scientific, Singapore,
        1998).
  7.  M. Sachs, in Ref. 1, Vol. 114(1) and in T.W. Barrett and D.
        M. Grimes, eds., Advanced Electromagntism (World Scientific,
        Singapore, 1995).
   8.  M.W. Evans, in Ref. 1, Vol. 114(2).