For use with Geissler tubes, spectrum analysis tubes, or various cathode tubes for demonstrates of high voltage characteristics. Coils consist of enameled copper wire wound on a solenoid. Ruhmkorff commentator allows primary current to be bath reversed and switched on and off, and with make and break point. Metal discharge electrodes with Bakelite handles are mounted on two thick, insulated, perspex sheets fixed at each end of the solenoid. Complete assembly is mounted on a sturdy, wooden base with color-coded, 4mm socket terminals for electrical connection and an ON/OFF switch. Produced spark up to 10cm. Recommended for use with spectrum analysis tubes, our, no. 3500. Also available are other ranges in sparks lengths 5, 10, 25, 50mm.