A structure associated with a layer of liquid that is confined by two horizontal parallel plates, in which the lateral dimensions are much larger than the width of the layer. Before heating the liquid is homogeneous. However, if after heating from below the temperatures of the plates are T₁ and T₂, at a critical value of the temperature gradient Δ‎T = T₁ – T₂ the liquid abruptly starts to convect. The liquid spontaneously organizes itself into a set of convection rolls, i.e. the liquid goes round in a series of ‘cells’, called Bénard cells. The cell is named after the French physicist Henri Bénard (1874–1939), who discovered this structure while investigating convection in liquids in 1900.