The feild and armature work together to make the Hoover vacuum motor turn.The coils on them generate the opposing magnetic feilds needed to make the motor work.The feild winding on the horseshoe shaped feild core are in series with the armature-the electric power fed to the motor flows thru the feild coil before flowing thru the armature-hence a series wound motor-a workhorse in the small applaince and power tool industry-so named becuase such a motor can work from AC or DC power.Or another terms-the feild=stator,Armature=rotor for AC motor terms.If you fed a DC voltage into the feild assembly shown you would have an electromagnet.The soft iron core doesn't retain the magnetic feild when the power is off.The armature,rotor oare the parts of the motor that turn and allow the motor to do work.The feild,stator remain stationary-provides a magnetic feild.