The design criteria of a proposed ac magnetohydrodynamic (mhd) generator are discussed. It is found that electrical losses to the moving fluid are serious unless the duct length‐to‐width ratio is greater than about 30. Two developments of such a generator are suggested. The first would provide a solution to the problem of power output from a segmented‐electrode generator. The second development, that of capacitive power transfer at the electrode‐fluid interface, would have many benefits, but its application is found to be severely restricted by the limited dielectric strength of materials.