. . "At the bottom, the inner periphery closely conforms to the shape of the image field, e.g., rectangular though this need not be the case.The liquid is confined in the reservoir by a gas seal 16 between the bottom of the seal member 12 and the surface of the substrate W. The gas seal is formed by gas, e.g. air or synthetic air or N.sub.2 or an inert gas, provided under pressure viainlet 15 to the ga" . . .