follows:
\begin{equation}
H(\mbox {\boldmath $\kappa$},{\bf N}, t) = -\left(\frac {\partial S}{\partial
t}\right)_{\bf N}  \qquad
\kappa_\alpha =
\left(\frac {\partial S}{\partial N^\alpha}\right)_t .
\ee        %29
      We call
{\boldmath $\kappa$} {\it the invariant
quasimomentum}, because all
physical quantities, written as functions of {\boldmath $\kappa$}, are
periodic
with a constant period $2 \pi$ (not $2\pi { \bf a}^\alpha$).
\par
    Let us consider the local dispersion law $\eps (\mbox {\boldmath
$\kappa$},
g^{\alpha \beta})$ as a function of the invariant quasimomentum and the
metrical tensor $g^{\alpha \beta}$. Since it coincides with the Hamiltonian,
one has
\begin{equation}
\eps(\mbox{\boldmath $\kappa$},g^{\alpha\beta}, t) = -\left(\frac {\partial
S}{\partial t}\right)_{\bf N}  \qquad
\kappa_\alpha =
\left(\frac {\partial S}{\partial N^\alpha}\right)_t.
\ee        %30
    Now let us consider a real electron which is executing a quasiclassical
motion. Its wave function in the new variables has the form
\begin{equation}
\psi ({\bf N},t) \sim
exp\left\{\frac{i}{\hbar}S_0({\bf N},t)\right\}
\ee       %31
where
$\dx S_0({\bf N},t)$ is the classical action. The transformation law for the
action follows from the transformation properties of the phase of the wave
function under Galilean transformations [9]:
\begin{equation}
S = S_0 + m{\bf \dot u r} - m{\dot u}^2/2
\ee      %32
where  $m$ is the mass of a free particle.
\par
    The Hamiltonian and the quasimomentum in 