Hans Christian Ørsted (1777–1851) was a Danish physicist who made one of the luckiest — and most important — accidental discoveries in science, and he made it in the middle of a lecture, in front of his students. In one twitch of a compass needle he revealed that electricity and magnetism, long thought to be totally separate, are secretly the same story.

The work behind the fame

Ørsted found that an electric current flowing through a wire makes a compass needle swing — proof that a current creates a magnetic field around itself. That single observation is the seed of every electromagnet ever built, from the buzzer in a doorbell to the giant magnets that lift cars in a scrapyard. He launched the whole field of electromagnetism, and the unit of magnetic field strength in the old CGS system, the oersted, still carries his name.