page_title: Kristian Birkeland
section_title: Research
hierarchical_section_title: Kristian Birkeland / Research
context_page_description: Kristian Olaf Bernhard Birkeland was a Norwegian scientist. He is best remembered for his theories of atmospheric electric currents that elucidated the nature of the aurora borealis. In order to fund his research on the aurorae, he invented the electromagnetic cannon and the Birkeland–Eyde process of fixing nitrogen from the air. Birkeland was nominated for the Nobel Prize seven times.
context_section_description: Birkeland organized several expeditions to Norway's high-latitude regions where he established a network of observatories under the auroral regions to collect magnetic field data. The results of the Norwegian Polar Expedition conducted from 1899 to 1900 contained the first determination of the global pattern of electric currents in the polar region from ground magnetic field measurements. The discovery of X-rays inspired Birkeland to develop vacuum chambers to study the influence of magnets on cathode rays. Birkeland noticed that an electron beam directed toward a magnetised terrella was guided toward the magnetic poles and produced rings of light around the poles and concluded that the aurora could be produced in a similar way. He developed a theory in which energetic electrons were ejected from sunspots on the solar surface, directed to the Earth, and guided to the Earth's polar regions by the geomagnetic field where they produced the visible aurora. This is essentially the theory of the aurora today.
  Birkeland proposed in 1908 in his book The Norwegian Aurora Polaris Expedition 1902–1903 that polar electric currents, today referred to as auroral electrojets, were connected to a system of currents that flowed along geomagnetic field lines into and away from the polar region. Such field-aligned currents are known today as Birkeland currents in his honour. He provided a diagram of field-aligned currents in the book, and this diagram was reproduced on the back of the Norwegian 200 kroner 7th series banknote in the lower right corner, and his terrella experiment is shown on the front at the left with a portrait of Birkeland on the right. The book on the 1902–1903 expedition contains chapters on magnetic storms on the Earth and their relationship to the Sun, the origin of the Sun itself, Halley's comet, and the rings of Saturn.
  Birkeland's vision of what are now known as Birkeland currents became the source of a controversy that continued for over half a century, because their existence could not be confirmed from ground-based measurements alone. His theory was disputed and ridiculed at the time as a fringe theory by mainstream scientists, most notoriously by the eminent British geophysicist and mathematician Sydney Chapman who argued the mainstream view that currents could not cross the vacuum of space and therefore the currents had to be generated by the Earth. Birkeland's theory of the aurora continued to be dismissed by mainstream astrophysicists after his death in 1917. It was notably championed by the Swedish plasma scientist Hannes Alfvén, but Alfvén's work in turn was also disputed by Chapman.
  Proof of Birkeland's theory of the aurora only came in 1967 after a probe was sent into space. The crucial results were obtained from U.S. Navy satellite 1963-38C, launched in 1963 and carrying a magnetometer above the ionosphere. Magnetic disturbances were observed on nearly every pass over the high-latitude regions of the Earth. These were originally interpreted as hydromagnetic waves, but on later analysis it was realized that they were due to field-aligned or Birkeland currents.
  The scale of Birkeland's research enterprises was such that funding became an overwhelming obstacle. Recognizing that technological invention could bring wealth, he developed an electromagnetic cannon and, with some investors, formed a firearms company. The coil-gun worked, except the high muzzle velocities he predicted (600 m/s) were not produced. The most he could get from his largest machine was 100 m/s, corresponding to a disappointing projectile range of only 1 km. So he renamed the device an aerial torpedo and arranged a demonstration with the express aim of selling the company. At the demonstration, one of the coils shorted and produced a sensational inductive arc complete with noise, flame, and smoke. This was the first failure of any of the launchers that Birkeland had built. It could easily have been repaired and another demonstration organized.
  However, fate intervened in the form of an engineer named Sam Eyde. At a dinner party only one
caption: Kristian Birkeland and his terrella experiment
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