Abstract: Switches operated by gas, preferably controlled electrothermally, include a capillary tube closed at both ends with a conductive liquid piston dividing the tube into two chambers each filled with a non-oxidizing gas. A pair of electrical contact points are disposed within the capillary tube with the piston positioned to, at selected intervals, contact both points simultaneously. In one embodiment of the switches, a closed glass capillary tube contains a pair of aligned nickel wires with ends selectively contacted simultaneously by a mercury piston or globule providing a circuit-closing position for the switch. The switch is set in the circuit-closing position by applying heat to a non-oxidizing gas within one end of the capillary tube. The switch is then reset to a circuit-opening position at any desired time by applying heat to a non-oxidizing gas within the other end of the capillary tube.