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ArrowØrsted's Compass

Oersted's Compass

Compasses had been steering people in the right direction for many centuries when, in the year 1820, one particular compass made a very different sort of revelation to an unsuspecting Danish science professor. The surprising event went down in history as one of the greatest milestones in electricity and magnetism.

One evening, while getting ready to give a lecture at the University of Copenhagen, Hans Christian Ørsted noticed the magnetized needle of a small desktop compass suddenly swing into activity. Ørsted knew, of course, that the needle would realign itself with the Earth’s magnetic field if you moved it. But, oddly, the compass had been sitting still when the needle deflected. The professor noticed, also, that whenever he connected or disconnected the circuit he was working with to a voltaic pile, the magnetized needle (which was near the wire of the circuit) moved. The strange phenomenon, Ørsted realized that April night, meant that electricity and magnetism were somehow linked.

Ørsted penned a short paper describing his findings. This publication was the first indication most scientists had regarding the electricity-magnetism connection, and thus it marks the birth of the field known as electromagnetics. Yet another man — an Italian named Gian Domenico Romagnosi — made the same observation about 18 years earlier. Romagnosi’s 1802 account of the discovery appeared as a newspaper article in Italy, but failed to make much of an impact on the scientific community. Ørsted and most of his contemporaries had never heard of Romagnosi or his experimental findings.

The Dane did not suffer the same fate. When Ørsted announced his discovery, the world listened. Within a matter of months, a number of other scientists made several important conclusions regarding electromagnetics. In fact, less than a week after he learned of Ørsted’s work, French scientist André-Marie Ampère composed the first of a series of treatises that theoretically addressed electromagnetism. Ampère also carried out his own experiments, from which he found that parallel wires experience attraction or repulsion that depends upon the direction of the currents flowing through them (if the currents in the wires flow in the same direction, attraction results; opposing currents produce repulsion). Additional advances in the field made by François Arago, Siméon-Denis Poisson and others quickly followed. Ørsted himself made no more important contributions to electromagnetism; most of his successes were in the realm of chemistry.

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