The diagnostic method proposed by Landi Degl'Innocenti and Landolfi (1982), based on the observation of circular polarization, has been generalized to derive the thermodynamic properties of unresolved magnetic elements in the solar atmosphere. The final aim is to derive the height dependence of several parameters of the flux tube atmosphere. A perturbation method based on the concept of response function for the Stokes profiles introduced by Landi Degl'Innocenti and Landi Degl'Innocenti (1977) is used. The preliminary results of inverting V-profiles by an iterative standard least-squares techniques, which allows the magnetic 1-D atmosphere to be found consistent with simulated data, is presented.