Oscillating engine

from The Collaborative International Dictionary of English v.0.48

Oscillating current \Os"cil*lat`ing current\ (Elec.)
   A current alternating in direction.
   [Webster 1913 Suppl.]

   {Oscillating engine}, a steam engine whose cylinder
      oscillates on trunnions instead of being permanently fixed
      in a perpendicular or other direction. --Weale.
      [1913 Webster]