Abstract: The thin optical display panel of any convenient area formed of a plurality of pixel elements, each element comprising a pair of small, thin cavities in each transparent surface of the panel. Two cavities in each element are interconnected by a small conduit and one cavity in the conduit is filled with conductive opaque fluid, such as mercury or the like. The fluid in the conduit is subjected to a transverse, reversible magnetic field and a transverse, reversible current so that the fluid may be selectively and rapidly transferred between the cavities by electromagnetic pumping action. The indicia on the surfaces of the display panel are formed by appropriate selection of the directions of either the magnetic field or the transverse current in the many elements forming the panel.