Under certain conditions, a heat source applied to the free surface of an aqueous solution will produce (a) rapid surface flow from all directions towards the region of contact (b) a rise in the surface below the heat source (c) a downward current from the elevation. A theoretical analysis of the phenomenon is provided under the assumptions that the process takes place in a shallow layer under steady-state conditions, the induced flow being two-dimensional and symmetrical about a vertical plane in which the heat source is assumed to lie. The process is shown to be characterised by a discriminant which depends on the rates of heat and mass transfer along the layer, Prandtl, Schmidt and Reynolds numbers and the Marangoni numbers for temperature and concentration changes.