It is shown that the anisotropic permeability of the magnetic particles constituting an artificial dielectric provides an explanation for the rotation of the plane of polarization and the variation of the attenuation of a plane‐polarized electromagnetic signal propagating through the dielectric in the presence of a longitudinal magnetic field. The attenuation curve is found to be readily explainable from the nature of variation of the power transmitted into the particles. A more detailed agreement between experimentally observed rotation, attenuation, and computed values is shown to follow if Lewin's formulas for the permeability and permittivity of an artificial dielectric is assumed to be valid also for circularly polarized signals. The effect of the size and permeability of the metal particles on the figure of merit of rotation is also discussed.