Abstract
In homeotropically aligned nematics with negative dielectric anisotropy the
electrohydrodynamic instability occurs above a bend Fréedericksz
transition. In the presence of a magnetic field 
parallel to the liquid
crystal slab, ordered roll patterns with a well-defined uniform wave vector
id appear above the onset of convection. By rotating the cell
around an axis perpendicular to the slab by a small angle α, one can
manipulate the system into a state with wave vector
= id + Δ, where Δ is
roughly perpendicular to id. We have studied experimentally
the motion of defects, which then move essentially perpendicular to the rolls.
The direction as well as the magnitude of the velocity as a function of
Δ agrees with predictions of the weakly nonlinear theory.
In particular, we obtain evidence for the nonanalyticity for
Δ → 0.