Where made: 
61 × 33 × 33 cm

H.W. Cox Ltd/London
Patent No. /16926
Harry W Cox & Co. Ltd.
Consists of two concentric coils of wire wound on a cylindrical core of soft iron wires impregnated with paraffin wax, all mounted on a hollow base containing a capacitor (which is constructed from sheets of tin foil separated by paraffin paper). Contains a flat spring contact breaker but also has terminals to which a mercury break may be connected. A polarity change switch is missing. The primary (inner) coil consists of two or more layers of thick silk covered copper wire impregnated with paraffin wax placed in an ebonite tube. The secondary coil is divided into sections separated by ebonite disks (to prevent discharge within the coil), each containing many turns of very thin, fine silk covered copper wire impregnated with paraffin wax also encased in ebonite. This is terminated in two discharging rods. When a small voltage (12 volts, say) is placed across the primary coil, a large one is induced across the secondary coil (105 volts). It is possible because of the large number of turns in the secondary coil, the concentrated magnetic field (due to the iron core and the close of the coils), and the abrupt and rapid interruptions (due to the contact breaker). The coil was invented in 1851 by Heinrich Daniel Ruhmkorff (1803-1877), who was a German instrument maker in Paris. It was popular for energizing discharge tubes and in particular for generating x-rays (which were discovered in 1895 by Roentgen). Harry Cox died of x-ray induced cancer.