This paper presents the results of an experimental investigation of thermocapillary and thermogravitational flows in a horizontal layer much thicker than the hydrodynamic boundary layer at the free surface. There is a linear heat source beneath the free surface and a heat sink at the opposite vertical face. At a constant heat flux, boundary layers develop at the free horizontal and the cooling vertical surfaces. Velocity and temperature profiles measured in the boundary layers are presented. Analytical solutions are obtained for the boundary layer at the cooling surface and beyond the boundary layers. The patterns of periodic thermocapillary flows for periods shorter than 24 s are studied : the actual and mean temperatures, the actual and mean values of the friction coefficient at the free surface, the variance of temperature fluctuations, space-time correlation functions, and the boundaries of the propagation of periodic flows.