Electromagnet

Before 1824, magnets were permanent—they either had magnetism or they didn't. William Sturgeon changed that by creating the first magnet that could be switched on and off with electric current. His electromagnet was a simple device: a bar of iron wrapped with wire. When current flowed through the wire, the iron became magnetic. When the current stopped, the magnetism vanished. This controllable magnetism would become the foundation of the electrical age.

The adjacent possible for the electromagnet required Ørsted's 1820 discovery that electric current creates a magnetic field. Ampère had already shown that coiling wire concentrated this field. Sturgeon's insight was to put something magnetic inside the coil. Iron, composed of tiny magnetic domains pointing in random directions, normally has no net magnetism. But when placed in a magnetic field, those domains align, amplifying the field enormously. A wire coil wrapped around an iron core produced far more magnetic force than the wire alone.

Sturgeon, an English shoemaker turned electrical engineer, demonstrated his invention in 1825 at the East India Company's Military Seminary in Addiscombe, where he lectured on science. His seven-ounce electromagnet could lift nine pounds—an astonishing ratio. He varnished the iron to insulate it, allowing tighter wire windings, and bent the core into a horseshoe shape to concentrate the magnetic poles. The design principles he established—insulated cores, tight windings, pole concentration—would guide electromagnet construction for the next two centuries.

Sturgeon's device had a limitation: his wire was bare copper, so he couldn't layer windings without short circuits. Joseph Henry in America solved this in 1827 by wrapping the wire itself in silk insulation, enabling multi-layer coils that multiplied magnetic strength. Henry's improved electromagnet could lift 750 pounds—nearly a hundred times Sturgeon's achievement.

The electromagnet enabled technologies that depended on controllable magnetic force. Telegraph sounders used electromagnets to click out Morse code. Electric motors required electromagnets to create the rotating fields that produced continuous motion. Electric clocks, typewriters, loudspeakers, and countless other devices followed. Where permanent magnets were fixed and passive, electromagnets could be switched, pulsed, modulated, and reversed at will.

The cascade of inventions enabled by the electromagnet illustrates how a fundamental component can spawn an entire technological ecosystem. Sturgeon's wrapped iron bar was to the electrical age what the transistor would later be to the electronic age: a building block so versatile that nearly everything else depended on it.