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Heinrich Daniel Ruhmkorff (Rühmkorff) (January 15, 1803 in Hanover – December 19, 1877 in Paris) was a German instrument maker who commercialised the induction coil (often referred to as the Ruhmkorff coil.)
Ruhmkorff was born in Hanover. He changed the "ü" to "u" in his name when living abroad. After an apprenticeship with a German mechanic, he moved to England. Biographies say that he worked with the inventor Joseph Bramah, but this is unlikely since Bramah died in 1814. He may, though, have worked for the Bramah company. In 1855, he set up a shop in Paris, where he gained a reputation for the high quality of his electrical apparatus.
Although Ruhmkorff is often credited with the invention of the induction coil, it was in fact invented by Nicholas Callan in 1836. Ruhmkorff's first coil, which he patented in 1851, utilized long windings of copper wire to achieve a spark of approximately 2 inches (50 mm) in length. In 1857, after examining a greatly improved version made by an American inventor, Edward Samuel Ritchie, Ruhmkorff improved his design (as did other engineers), using glass insulation and other innovations to allow the production of sparks more than 30 centimetres long. Ruhmkorff patented the first version of his induction coil in 1851, and its success was such that in 1858 he was awarded a 50,000-franc prize by Napoleon III for the most important discovery in the application of electricity. He died in Paris in 1877.
In several of Jules Verne's science-fiction novels, so-called "Ruhmkorff lamps" are mentioned. These were an early form of portable electric lamp. The lamp consisted of a Geissler tube that was excited by a battery-powered Ruhmkorff induction coil. Initially the lamp generated white light by using a Geissler tube filled with carbon dioxide. However, the carbon dioxide tended to break down. Hence in later lamps, the Geissler tube was filled with nitrogen (which generated red light), and the glass was replaced with glass containing uranium salts (which fluoresced with a green light).
Intended for use by miners, the lamp was actually developed both by Alphonse Dumas, an engineer at the iron mines of Saint-Priest and of Lac, near Privas, in the départment of Ardèche, France, and by Dr. Camille Benoît, a medical doctor in Privas. In 1864, the French Academy of Sciences awarded Dumas and Benoît a prize of 1,000 francs for their invention.
This lamp could be considered as a predecessor of modern fluorescent lanterns, because as in the "Ruhmkorff lamp," portable actual ones use an inverter (oscillator + step-up transformer) to convert low voltage DC current from dry cells or storage batteries to AC or even pulsating current at a voltage high enough as to ionize the fluorescent tube and power it at the required nominal power. This one has no nitrogen nor C02, neither uranium glass; instead a modern fluorescent tube is filled with argon at a very low pressure, along with a few milligrams of mercury. Their electrodes are usually consituted by a triple wounded tungsten wire covered with electron emitting substances, as alkaline metal oxides, that easily give free electrons to aid to ionizing, striking and sustaining the electric arc. The inner walls of the tube are coated with a thin layer of fluorescent substances that when excited by the 253,7 nM line of UV radiation from mercury arc, emit visible light, usually in the range of 6500ºK (daylight). The spectral characteristics (coloration) of such a light depends entirely on the chemical nature of those "phosphors."
Modern inverters for portable fluorescent lanterns don't rely on electromechanical and electromagnetic vibrating switching contacts to produce the required current interruptions on primary circuit to provide induced voltages through the secondary winding as occur in Ruhmkorff coils; instead, the primary of the transformer is switched by means of one or two transistors oscillating at frequencies of tens or even hundreds of thousand cycles per second which results in smaller and lighter devices having also a very good efficiency in lumens/watt for a given battery consumption or a longer battery charge life for a given light flux when compared with incandescent lamps, but the principle remains the same as in the Dumas & Benoit original mining electric lamp.
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