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
terrella, a model of the Earth consisting of a spherical magnet, 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 week later, Eyde told Birkeland that there was an industrial need for the biggest flash of lightning that can be brought down to Earth in order to make
artificial fertilizer. Birkeland's reply was, "I have it!" There were no more attempts to sell the firearms company, and he worked with Eyde only long enough to build a plasma arc device for the
nitrogen fixation process. The pair worked to develop the prototype furnace into a design that was economically viable for large-scale manufacture. The resulting company,
Norsk Hydro, hugely enriched Norway, and Birkeland then enjoyed adequate funding for research, his only real interest. The
Birkeland–Eyde process is relatively inefficient in terms of energy consumption. Therefore, in the 1910s and 1920s, it was gradually replaced in Norway by a combination of the
Haber process and the
Ostwald process. In 1913, Birkeland may have been the first to predict that plasma was ubiquitous in space. He wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in 'empty' space." In other words, the solar wind consists of both negative electrons and positive ions. The first complete map of the statistical location of
Birkeland currents in the Earth's polar region was developed in 1974 by A.J. Zmuda and J.C. Armstrong and refined in 1976 by T. Iijima and T.A. Potemra As a scholar with wide interests, Birkeland joined the control commission of NSFPS (Norwegian Society For Psychic Research). The 299 members of the society included, by 1922, people like prime minister
Gunnar Knudsen, as well as a wide range of doctors, professors and shipowners. The society arranged circles experimenting with dancing tables and
automatic writing, but attracted more attention arranging controlled experiments with invited foreign
mediums. In 1912 it was the alleged medium
Etta Wriedt from
Detroit, famous for her "spirit
trumpet", who was exposed as a fraud. Mrs Wriedt's "trumpet" should have been speaking with the "spirit voice" of, among others,
Hypatia, but in Norway the "trumpet blows" were exposed as explosions produced by
potassium and
water. Professor Birkeland exclaimed on that occasion, "I'm supposedly against all
witch burnings, but a teeny weeny one in honour of Mrs Wriedt would not have been in the way." ==Legacy==