  This paper is devoted to topological phenomena in normal metals with rather
complicated Fermi surface. The results of the article are based on the deep
topological theorems concerning the geometry of non-compact plane sections of
level surfaces of periodic function in 3-dimensional Euclidean space which are
the quasi-classical electron orbits in the presence of homogeneous magnetic
field. The main result is that the observation of electrical conductivity in
strong magnetic fields can reveal such nontrivial topological characteristics
of Fermi surface as integral planes, connected with conductivity tensor and
locally stable under small rotations of magnetic field. This planes are
connected with generic non-closed orbits on the Fermi surface. Some non-generic
situations are also discussed.
