  The two dimensional Rashba Hamiltonian is investigated using the momentum
representation.One finds that the SU(2) transformation which diagonalizes the
Hamiltonian gives rise to non commuting Cartesian coordinates for K=0 and zero
otherwise.This result corresponds to the Aharonov -Bohm phase in the momentum
space.
  The Spin -Hall conductivity is given by $\frac{e}{4\pi}$ which disagree with
the result $\frac{e}{8\pi}$ given in the literature.Using Stokes theorem we
find that the Spin -Hall current is carried equally by the up and down
electrons on the Fermi surface.
  We identify the Magnetic current and find that for an electric field with a
finite Fourier component in the momentum space a non zero Spin -Hall current is
obtained.For the electric field which is constant in space, the orbital
magnetic current cancels the spin current.
  In order to measure the Spin-Hall conductance we propose to apply a magnetic
field gradient $\Delta H_{2}$ in the $i=2$ direction and to measure a Charge-
Hall current $\frac{e}{h}(\frac{g}{2})\mu_{B}\Delta H_{2}$ in the $i=1$
direction.
