Wave number of maximal growth in viscous magnetic fluids of arbitrary depth

An analytical method within the frame of linear stability theory is present ed for the normal field instability in magnetic fluids. It allows us to cal culate the maximal growth rate and the corresponding wave number for any co mbination of thickness and viscosity of the fluid. Applying this method to magnetic fluids of finite depth, these results are quantitatively compared to the wave number of the transient pattern observed experimentally after a jumplike increase of the field. The wave number grows linearly with increa sing induction where the theoretical and the experimental data agree well. Thereby, a long-standing controversy about the behavior of the wave number above the critical magnetic held is tackled.