Observations made in various batch and continuously operated inclined settlers are reported. The systems considered are the so‐called ‘‘low aspect ratio’’ devices in which the width of the vessel is large enough such that the presence of the enclosing walls does not affect the dynamic phenomena. The principal aim of these experiments was to test the predictions of the recent theoretical papers of Shaqfeh and Acrivos [Phys. Fluids29, 3935 (1986);30, 960 (1987)] concerning the laminar base state convective flow and accompanying instability wave growth under conditions in which inertial effects play an important role. The observations confirm that the theory predicts various characteristics of the laminar flow both quantitatively and qualitatively and that, within the range of experimental conditions, the more recent linear stability theory qualitatively describes the salient features of the instability wave growth in these systems.