A porous wall through which a flow of gas is established forming a layer supporting
a liquid mass is strengthened partly to stiffen it and partly to control the shape
of the lower surface of the supported liquid. Chambers containing different pressures
can be formed, and possibly, separated by some of these strengthening parts to
improve the equalisation by reducing the pressure at the center. Finally, capillaries
may pass through the plate to measure the pressure or provide additional equalisation
of the thickness of the layer by a suction device.
