2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/40310The equations for variation of the Stokes parameters and intensity of photons propagating in a medium, whose optical properties may be described by the permittivity tensor, are derived. Classification of different cases of photon propagation is suggested on a basis of these equations.11 pages, Latex, typos (text, Eq30,37) corrected, Eq41 addedHigh Energy Physics - PhenomenologyAstrophysicsCondensed MatterOpticstext