The Collaborative International Dictionary of English v.0.48:

Electro-magnetic \E*lec`tro-mag*net"ic\, a.
   Of or pertaining to electromagnetism.
   [1913 Webster]

   Electro-magnetic engine, an engine in which the motive
      force is electro-magnetism.

   Electro-magnetic theory of light (Physics), a theory of
      light which makes it consist in the rapid alternation of
      transient electric currents moving transversely to the
      direction of the ray.
      [1913 Webster]