Rühmkorff, Heinrich Daniel (1803–1877)

German-born French instrumentmaker who invented the Rühmkorff induction coil in 1851, a type of transformer for direct current that outputs a high voltage from a low-voltage input.

Rühmkorff was born in Hannover and went to Paris in 1819. Working as a porter in the laboratory of physicist Charles Chevalier (1804–1850), he became interested in electrical equipment and soon began to manufacture scientific instruments. He opened his own workshop in 1840, and eventually became famous throughout Europe for his scientific apparatus.

Rühmkorff's first notable invention was a thermoelectric battery 1844. The principles of the induction coil had been worked out by English scientist Michael Faraday in 1831. Rühmkorff's induction coil consisted of a central cylinder of soft iron on which were wound two insulated coils: an inner primary coil comprising only a few turns of relatively thick copper wire, and an outer secondary coil with a large number of turns of thinner copper wire. An interrupter automatically made and broke the current in the primary coil, thereby inducing an intermittent high voltage in the secondary coil.