RUHMKORFF, HEINRICH DANIEL

born , Jan. 15, 1803, Hannover, Hanover died Dec. 20, 1877, Paris German mechanic who invented the Ruhmkorff coil, a type of induction coil that could produce sparks more than 1 foot (30 centimetres) in length. After apprenticeship to a German mechanic, Ruhmkorff worked in England with Joseph Brahmah, inventor of the hydraulic press. In 1855 he opened his own shop in Paris, which became widely known for the production of high-quality electrical apparatus. There he built a number of improved induction coils, including one in 1851 that was awarded a 50,000-franc prize in 1858 by Emperor Napoleon III as the most imporant discovery in the application of electricity. Ruhmkorff's coils, which produced high-voltage current within a secondary armature winding, were used for the operation of Geissler and Crookes tubes as well as for detonating devices. Ruhmkorff's doubly wound induction coil later evolved into the alternating-current transformer.