  In the framework of the perturbation theory an expression suitable for
calculation of the effective conductivity of 3-D inhomogeneous metals in
uniform magnetic field $H$ is derived. For polycrystals of metals with closed
Fermi surfaces in high magnetic fields the perturbation series defining the
longitudinal and the hall elements of the perturbation series can be summed
allowing us to obtain the exact expression for the leading terms of all these
elements of the effective conductivity tensor.
