The torque exerted by circularly polarized radiation can be demonstrated and measured in a simple microwave motor experiment. A small electric dipole, delicately suspended in a circular waveguide, continuously rotates under the torque influence of an incident circularly polarized wave of low power. A component of the wave energy scattered from the dipole experiences a natural downshift in frequency equal to twice the dipole rotation frequency. This intrinsic change in wave energy completely accounts for the power extracted from the wave in turning the dipole against damping forces. The experiment is a macroscopic model of a rotational mechanism through which spectral shifts can arise in nature, and appears to be analogous to the rotational Raman effect with linear molecules. Since the interaction between wave and dipole is reversible, the energy (frequency) of an interacting circularly polarized wave is increased whenever the direction of rotation of the scattering dipole opposes the torque of the wave. Through this mechanism, energy can be transferred from one circularly polarized wave to a second of higher frequency but of less intensity. This corresponds to the generation of an anti-Stokes line.