  The Popper-Szilard engine attaches a pulley and weight to each side of the partition, but positions a floor beneath the engine in such a way that when the partition is in the centre of the box, both weights are resting on the floor and the pulley is taut. The partition has a hole in it, allowing the molecule access to both sides of the engine. At an arbitrary time, the hole is blocked, without any measurement performed on the location of the molecule. The collisions of the molecule against the partition will now exert a force on one or the other weight, lifting it against gravity.