  Several dynamical processes may induce considerable electric currents in the
atmospheres of magnetic chemically peculiar (CP) stars. The Lorentz force,
which results from the interaction between the magnetic field and the induced
currents, modifies the atmospheric structure and induces characteristic
rotational variability of the hydrogen Balmer lines. To study this phenomena we
have initiated a systematic spectroscopic survey of the Balmer lines variation
in magnetic CP stars. In this paper we continue presentation of results of the
program focusing on the high-resolution spectral observations of A0p star \aur
(HD 40312). We have detected a significant variability of the H$\alpha$,
H$\beta$, and H$\gamma$ spectral lines during full rotation cycle of the star.
This variability is interpreted in the framework of the model atmosphere
analysis, which accounts for the Lorentz force effects. Both the inward and
outward directed Lorentz forces are considered under the assumption of the
axisymmetric dipole or dipole+quadrupole magnetic field configurations. We
demonstrate that only the model with the outward directed Lorentz force in the
dipole+quadrupole configuration is able to reproduce the observed hydrogen line
variation. These results present new strong evidences for the presence of
non-zero global electric currents in the atmosphere of an early-type magnetic
star.
