  Using the linear fractional transformation, connecting effective
conductivities sigma_{e} of isotropic two-phase systems with and without
magnetic field, explicit approximate expressions for sigma_{e} in a magnetic
field are obtained. They allow to describe sigma_{e} of various inhomogeneous
media at arbitrary phase concentrations x and magnetic fields. the x-dependence
plots of sigma_e at some values of inhomogeneity and magnetic field are
constructed. Their behaviour is qualitatively compatible with the existing
experimental data. The obtained results are applicable for different two-phase
systems (regular and nonregular as well as random), satisfying the symmetry and
self-duality conditions, and admit a direct experimental checking.
