When ac generators were driven by reciprocating engines one of the major problems in the operation of machinery was hunting. The periodic tions in torque applied to the generators caused periodic variations in speed. The resulting periodic variations in voltage and frequency were transmitted to the motors connected to the system. Oscillations of the motors caused by the variations in voltage and frequency sometimes caused the motors to lose syn-chronism entirely if their natural frequency of oscillation coincided with the frequency of oscillation caused by the engines driving the generators. Damper windings were first used to minimize hunting by the damping action of the losses resulting from the currents induced in the damper windings by any relative motion between the rotor and the rotating field set up by the armature current. The use of turbines has reduced the problem of hunting, although it is still present where the prime mover is a diesel engine.