Granular material, contained in a long, inclined cylinder, slowly rotating about its axis, forms a flat surface whose intersection with the cylinder is an ellipse. We postulate that the granular material falls in a thin layer along the line of steepest descent in the surface, which line is inclined at the angle of repose to the horizontal; the granular material then rotates with the cylinder in 'solid body' motion. With no axial flow, each particle remains in the same plane normal to the axis of the cylinder. The predicted length of the ellipse, measured in the direction of the axis of the cylinder, is in excellent agreement with experiments using sand or TiO2. The same theory is applied to granular material in a dish granulator operated at low speed, so the bed surface is hat. The theory for no-flow gives results for the position of the bed surface which are in fair agreement with published data at small feed rate. For the case when centrifugal accelerations are small, but not negligible, theory is given which predicts their effect.