Abstract: The specification discloses a motor activated by a combination of fluid pressure, such as air, and gravity. The motor comprises a rotor, the shaft of which carries a cylindrical shell divided into an even number of sectors or cells. Each cell contains an envelope or bag of elastomeric material which communicates through a transverse passage in the shaft with the bag of a diametrically opposite cell. Each connected pair of bags contains a supply of high density liquid, such as Mercury, sufficient to fill one bag. A rotary valve carried on the shaft outboard of the shaft bearings controls admission and release of fluid pressure to and from the cells in the cylindrical shell via longitudinal passages in the shaft communicating therewith to sequentially supply fluid pressure to the cells to expel the liquid from bags in lower cells to bags in upper cells, thereby producing a torque on the rotor due to gravity acting on the Mercury in the upper cells.