Heinrich D. Ruhmkorff (1803 -1877) was a mechanic and electrical researcher who invented the Ruhmkorff's coil, a type of induction coil that could produce sparks more than 1 foot (30 centimetres) in length. This coil was used in the first radio transmitters and some other primitive electrical and electronic devices. Used also for generating X-rays (discovered in 1895).
Rsf: http://chem.ch.huji.ac.il/history/ruhmkorff.htm