Vibrating Armature Engine
  "[The figure] represents an instrument in which an armature, A, is made to vibrate backwards and forwards above the poles of an electromagnet, M. The armature, when on one side, is attracted to the poles until it arrives directly over them. As it reaches this position, the circuit is broken by the break-piece, and the bar moves on by the momentum it has acquired, for some distance. The circuit is then renewed, and it moves back toward the poles. The arrangement of the break-piece is such, that the current circulates while the armature is approaching the poles on either side, and is interrupted while it is receding from them. A continuous vibration is thus occasioned, which imports motion to a fly-wheel, and to a hammer, which strikes the bell seen in the cut." (from the 1851 edition of the Manual of Magnetism, pp 210-211) 

   This appparatus is at Hampden-Sydney College in Virginia.

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