The unit of electro-motive force; -- defined by the
   International Electrical Congress in 1893 and by United States Statute
   as, that electro-motive force which steadily applied to a conductor
   whose resistance is one ohm will produce a current of one ampere. It is
   practically equivalent to / the electro-motive force of a standard
   Clark's cell at a temperature of 15¡ C.