  We compare polarization properties of the cyclotron, and relativistic dipole
radiation of electrons moving in the magnetic field on a helix with
ultra-relativistic longitudinal and non-relativistic transverse velocity
components. The applicability of these models in the case of accretion onto a
neutron star is discussed. The test, based on polarization observations is
suggested, to distinguish between the cyclotron, and relativistic dipole origin
of features, observed in X-ray spectra of some X-ray sources, among which the
Her X-1 is the most famous.
