Sparking devices comprising an electric circuit including relatively fixed and movable electrodes, the movable electrode being adapted to make and break the circuit, as in the preceding make-and-break subclasses, and the operation thereof depending immediately upon the piston of the engine with which the device is used. In the devices in this subclass the movable electrode is either carried by the
working piston or is located in the clearance space of the engine, and said electrode when not carried by the piston is generally operated directly by the piston or by a projection thereon as it comes into contact with the movable electrode near the end of the compression-stroke.
