Hans Christian Oersted

The Danish physicist Hans Christian Oersted (1777-1851) was the first to notice the interaction of electric current and the magnetic needle, thereby initiating the study of electromagnetism.

Hans Oersted was born on Aug. 14, 1777, in Rudköbing on the island of Langeland. Hans received his education from some friendly towns-people, but what was lacking in the way of competent teachers was amply supplemented by Oersted's extraordinary thirst for knowledge. In 1794 he went to Copenhagen and matriculated in science at the university in the fall of that year. The completion of his training in pharmacy came in 1797. Two years later he received his doctorate for a dissertation in which a new and competent theory of alkalies was proposed.

Oersted began his teaching career at the University of Copenhagen as lecturer in pharmacy. In 1801 he went abroad and sought out some of the best philosophic and scientific minds in Germany, the Netherlands, and France, where he spent the winter of 1802/1803. One of the things he immediately realized was the excitement created everywhere by Alessandro Volta's development of the electric battery 2 years earlier. Oersted's attention to this advance was evidence of his ambition to occupy eventually the chair of physics at his university. In 1803 his application was rejected. Clearly he was more of a chemist or pharmacist than physicist. But he kept experimenting and publishing, not only in chemistry but also in physics. His ingenious analysis of Chladni's acoustic figures finally secured for him the position of professor extraordinarius (associate) of physics in 1806. Three years later he published the first volume, dealing with mechanics, of a longer work planned to cover all areas of natural philosophy (physics).

During 1812 and 1813 Oersted visited in Germany and France. While in Berlin he published in German his Views of the Chemical Laws of Nature Obtained through the More Recent Discoveries. It came out the next year in French translation under the revealing title Researches on the Identity of Chemical and Electrical Forces. Oersted spoke in his Researches about the identity of magnetism and electricity with such assurance that he seemed predisposed to be the discoverer of electromagnetism. In the eighth chapter he noted the close analogies between the properties of magnetic and electric fields, their equally universal presence in nature, and certain reciprocal actions between them such as the loss of magnetism in steel due to rise in temperature and the simultaneous increase of the metal's electrical conductivity. He concluded, "An attempt should therefore be made to see whether electricity, in its most latent stage, has any effect on the magnet as such."

Oersted was also aware of the fact that lightning often resulted in the magnetization of pieces of iron, even to the point of altering the polarity of compass needles. He spent years in search of an elusive goal as he systematically vitiated his work by expecting the magnetic effect to be in the direction of the flow of the current. During those years of search, Oersted blossomed into a most sought-after lecturer both within and outside the university. In recognition of his consummate versatility in scientific matters, he was appointed the leader of a geological survey party charged with the exploration of the island of Bornholm.

In the spring of 1820 Oersted was giving a series of lectures on the interaction between electricity and magnetism before an advanced group of students. The responsiveness of the audience proved to be stimulating, and he was prompted to demonstrate the experimental evidence in support of one of his conjectures. It concerned the possible action of electric discharge on a magnetic needle placed near the circuit. As he expected a discharge through incandescence to be most effective, he inserted in the circuit a very thin platinum wire right above the magnetic compass. "The effect," he wrote, "was certainly unmistakable, but still it seemed to me so confused that I postponed further investigation to a time when I hoped to have more leisure." He resumed the experiments in July, carefully repeating all the steps in the presence of a group of colleagues and students. On July 21 he dispatched to scientists, universities, and learned societies throughout Europe the account of his findings in a four-page essay written in Latin, Experimenta circa effectum conflictus electrici in acum magneticam (Experiments about the Effects of an Electrical Conflict [Current] on the Magnetic Needle).

In the essay Oersted noted the dependence of the extent of the needle's motion on the strength of the battery, on the direction of the current in the wire, and on the needle's position with respect to the wire. He found that no effect was noticeable when the wire was perpendicular to the plane of the magnetic meridian. From the dip of the needle, he concluded that the magnetic effect existed in closed circles and not in spirals around the wire. He also found that neither metal plates nor wood nor stoneware would, when interposed between the wire and the needle, screen the effect. This meant that "the transmission of effects through all these matters has never before been observed in electricity and galvanism [current]. The effects, therefore, which take place in the conflict of electricity [current] are very different from the effects of the [static] electricities."

In his account of his discovery given in 1821, Oersted merely cared to correct the belief that the magnetic needle was in its actual position accidentally. It was only 10 years after the event that he emphasized, in the third person, in an article prepared for the Edinburgh Encyclopedia that "In composing the lecture, in which he was to treat of the analogy between magnetism and electricity, he conjectured, that if it were possible to produce any magnetical effect by electricity, this could not be in the direction of the current, since this had been so often tried in vain, but that it must be produced by a lateral action." In the same article Oersted also expressed his surprise over the fact that he failed to resume his experiments for 3 months and that those present were not impressed at all as the needle made the historic movement. One of the witnesses later claimed it was by chance that the compass needle was almost under the wire in the desired position.

The impact of Oersted's discovery on the scientific world was enormous. According to Oersted's own count, more than a hundred scientists published their comments and researches on electromagnetism during the first 7 years following its discovery. Oersted was showered with honors and awards. The Royal Society of London gave him the Copley Medal, and the French Academy awarded him a prize of 3,000 gold francs. But his greatest satisfaction was undoubtedly the spectacular growth of a new branch of physics, electromagnetism, which was to have revolutionary impact on modern culture.

Oersted was 43 when he made his great discovery. For the rest of his life he held the position of a leader in science. He had a major role in the establishment of the Royal Polytechnic Institute in 1829, of which he became the first director.

Further Reading on Hans Christian Oersted

The most authoritative and exhaustive biography of Oersted is the book-length essay by Kirstine Meyer in her edition of H. C. Oersted: Scientific Papers (3 vols., 1920). A detailed biography by one of Oersted's contemporaries is in Bessie Zaban Jones, ed., The Golden Age of Science: Thirty Portraits of the Giants of 19th-Century Science by Their Scientific Contemporaries (1966). For additional material on Oersted's work and the general historical background see Edmund Taylor Whittaker, A History of the Theories of Aether and Electricity (1910; 2 vols., rev. ed. 1951), and Bern Dibner, Oersted and the Discovery of Electromagnetism (1961; 2d ed. 1963).

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