Abstract: A rotatable machine for operation as a compressor or a motor. A stator rotates a rotor positioned therewithin. The rotor variably limits the radial section of an annular space or room. The rotor carries a series of blades rotatably mounted thereon and positioned within the room. The machine includes control means impelling the blades to oscillating movement synchronized with the rotation of the rotor such that the blades move themselves as a function of the angular position of the rotor and thereby divide the room into partitions, each having the shape of a segment of a crown.