Abstract
We measure the surface order parameter Ss at the interface between the nematic liquid crystal p-methoxy-benzylidine-p-n-butyl-aniline and a rough glass plate. Roughness is induced by oblique evaporation of SiO. We observe a critical decrease of Ss when the surface roughness increases, just above the transition from planar to oblique orientation. This experiment supports the ordoelectric model to explain the oblique orientation of the nematic liquid crystal.