How it began
Hans Christian Oersted, born in Rudkobing in 1777, held a post at the University of Copenhagen from 1806. On April 21, 1820, while setting up a lecture demonstration there, he noticed that a compass needle near a wire moved when he connected the wire to a battery. The movement was so slight that the audience did not notice. He experimented for three more months and on July 21, 1820, published his results in a pamphlet.
Before it existed
By the end of the 18th century scientists knew many electrical and many magnetic effects, but most believed they were distinct forces. There were hints of a link, since a compass struck by lightning could reverse polarity. An Italian, Gian Domenico Romagnosi, had reported a similar observation in a newspaper in 1802, but it made little impact, and Oersted and most of his contemporaries had never heard of it.
How it works
An electric current in a wire produces a magnetic force around it, which turns a nearby magnetized needle away from north. Oersted used a voltaic pile of 20 copper rectangles. He found the effect with various kinds of wire, saw the needle swing the opposite way when he reversed the current, and noted that wood or glass placed between the wire and the compass did not shield it. He called the effect an "electric conflict."
What changed first
The pamphlet, circulated privately to physicists and scientific societies, caused an immediate sensation. Less than a week after learning of it, Andre-Marie Ampere wrote the first of a series of treatises on electromagnetism and showed that parallel wires attract or repel depending on the direction of their currents. Further advances by Francois Arago, Simeon-Denis Poisson and others followed within months.
What lasted
About a decade later Michael Faraday showed the reverse effect, that a changing magnetic field induces an electric current. James Clerk Maxwell then formally unified electricity and magnetism in his equations. The National MagLab describes Oersted's paper as the birth of electromagnetics.
