A solenoid in which the coil is positioned inside a housing of magnetic material. The housing has a tubular projection forming a recess in the inside of the end wall along the axis of the coil, one end of the plunger projecting beyond the coil into the recess when the plunger is in the energized position. The portion of the plunger that extends into the recess is tapered to obtain a constant force-displacement characteristic for the full travel of the plunger.