In E.E. "Doc" Smith's fictional Lensman series, the Bergenholm generator is the key to faster-than-light transportation. It functions by rendering an object inertialess so that it instantly takes on an analogue of terminal velocity: that is, the speed and direction of motion in which frictional resistance from the medium it is travelling through is equal and opposite to the applied force, such as the force of a ship's jets. The maximum speed possible with the Bergenholm drive depends on the force exerted by a ship's jets, the density of matter around the ship, and even the size and streamlining of the ship. Thus, intergalactic space travel is possible in reasonably short time, because the matter in intergalactic space is less dense than in interstellar space.