Abstract: A linear mercury-wetted switch is housed within a hollow, elongated, sealed, cylindrical tube having a pair of mercury-wetted, spaced contacts which can be bridged by a conforming but spaced electromagnetically driven contact element in the form of a slider or armature which slides longitudinally inside the tube on the mercury on the surfaces of the contacts. The slider has a conductive surface for closing the electrical circuit through mercury films carried on and between the surfaces of the slider and the contacts. The slider does not go to the end of the cylinder to contact the end wall. The contacts and the armature are of conforming contour of appropriate dimensions in cross-section so that they slide one within the other. The usual armature slips over the exterior of the contacts. The envelope can also be an electrode connected to the armature by a layer of mercury and the armature can ride upon the support provided by the mercury riding on the interior of the sealed tube.