IX.

A Shock in Copenhagen

The next steps in understanding electricity unfolded in Copenhagen, Denmark. In 1820 Hans Christian Oersted made a key discovery. Oersted created an electric current in the usual manner, with wires connecting one terminal of a battery to the other. He placed a compass needle, a magnet, near the circuit. When the current flowed, the compass needle veered from pointing to Earth’s magnetic North Pole—its normal position—to taking an odd position at right angles to the wire. Oersted worried about this effect until it dawned on him that, after all, a compass is designed to detect magnetic fields. He realized that the current in the wire must be producing a magnetic field. Oersted had discovered a connection between electricity and magnetism: Currents produce magnetic fields. Magnets, of course, also produce magnetic fields, and their ability to attract pieces of iron had been well studied. The news traveled across Europe and created a great stir.

Using this information, Parisian scientist André Marie Ampère found a mathematical relationship between a current and its magnetic field. The strength and direction of the magnetic field depended upon the strength and direction of the current and on the shape of the wire carrying the current. By a combination of mathematical reasoning and hastily executed experiments, Ampère generated a storm of controversy. Out of this controversy eventually emerged a prescription for calculating the magnetic field produced by an electric current through any configuration of wire, whether the wire was straight, bent, formed into a circular loop, or wound densely on a cylindrical form. Ampère found that a current passing through two straight wires produces two magnetic fields, and these fields can push on each other. This discovery was profound, as it made possible Faraday's experiments with magnetic induction, which is the creation of a current in a conductor when the conductor is moved through a magnetic field, or when the strength of a current in a stationary conducting loop is made to vary. These experiments, in turn, led to the development of the electric motor.

Oersted, like so many other scientists, drove toward unification, simplification, and reduction. He believed that gravity, electricity, and magnetism were all different manifestations of a single force, which is why his discovery of a direct connection between two of these forces was so exciting. Ampère, too, looked for simplicity; he essentially tried to eliminate magnetism by considering it an aspect of electricity in motion, a field of study that would later become known as electrodynamics. The discoveries of Oersted and Ampère served as springboards for the work of Faraday, one of the most unlikely scientists and successful experimenters of all time.