When Michael Faraday and Joseph Henry independently discovered the principle of electric induction in 1831, they started a chain of events that led to alternating current electricity, without which modern technology could not function.

Both Faraday and Henry were building upon a discovery made in 1820 by Hans Christian Oersted. He found that an electric current flowing through a wire created a magnetic field. This was the first discovery linking electricity and magnetism, and it galvanized scientists into a frenzy of research.

A few scientists, notably Faraday and Henry, followed a path of research that might have appeared to be totally backward to that of their colleagues. If electricity could create a magnetic field, the theory went, the procedure should be reversible; a magnetic field should be able to create electricity.

Faraday and Henry discovered that moving a magnet through a closed coil of wire did, indeed, "induce...