  We investigate the growth of a pattern of liquid crests emerging in a layer
of magnetic liquid when subjected to a magnetic field oriented normally to the
fluid surface. After a steplike increase of the magnetic field, the temporal
evolution of the pattern amplitude is measured by means of a Hall-sensor array.
The extracted growth rate is compared with predictions from linear stability
analysis by taking into account the proper nonlinear magnetization curve M(H).
The remaining discrepancy can be resolved by numerical calculations via the
finite-element method. By starting with a finite surface perturbation, it can
reproduce the temporal evolution of the pattern amplitude and the growth rate.
The investigations are performed for two magnetic liquids, one with low and one
with high viscosity.
