Galileo Ferraris

1847-1897

The Italian physicist who discovered the rotating magnetic field independently of Tesla, demonstrating two-phase induction motors and proving the principle that underlies AC machines worldwide.

Galileo Ferraris was born in 1847 in Livorno Vercellese, in the Kingdom of Sardinia. He earned a master's in engineering and became an assistant in technical physics near the Royal Italian Industrial Museum in Turin, an institution later absorbed into the Politecnico di Torino. A careful, methodical experimenter, he investigated the rotating magnetic field independently of Nikola Tesla, arriving at the same fundamental discovery from a different direction at almost the same moment.

Ferraris showed that two stationary coils set at right angles, driven by alternating currents shifted ninety degrees in phase, produce a magnetic field that rotates in space. He built working prototypes of two-phase AC motors that turned on this principle, with no electrical contact to the rotating part. He presented his results to the Royal Academy of Sciences in Turin on 11 March 1888, just two months before Tesla was granted his US induction-motor patent. Engineering histories of the period consistently credit Ferraris and Tesla as having made the discovery independently.

In a choice that shaped his legacy, Ferraris never patented his motor work. He saw the rotating field more as a scientific discovery to be shared than as property to be owned, and he published an extensive monograph on the open-circuit transformers of Gaulard and Gibbs. He helped found Italy's first school of electrical engineering and became the first president of the Italian Electrotechnical Association. He died young, in 1897. In 2021 the IEEE honored his rotating-field and early induction-motor work with a Milestone plaque.

Whether you trace the lineage through Tesla or Ferraris, the rotating magnetic field is the bedrock of AC machines. Ferraris's two-coil, ninety-degree-phase demonstration is essentially the textbook picture of how a polyphase stator creates a turning field. That same picture is what motor-control engineers reproduce electronically today: an inverter feeds phase-shifted currents into a stator to synthesize a rotating field that pulls the rotor around. Ferraris proved the idea was real and sound, and then gave it freely to the world.

Fun facts

Ferraris demonstrated the rotating magnetic field in Turin in March 1888, two months before Tesla received his US patent. Contemporary engineers explicitly recognized them as independent discoverers of the same principle.
He deliberately chose not to patent his induction-motor work, treating the rotating field as a scientific gift to be shared rather than a commercial monopoly to be defended.
His textbook picture of the rotating field is elegantly simple: just two stationary coils with perpendicular axes, fed by currents ninety degrees out of phase. That minimal setup is still how the principle is taught and how inverters synthesize a turning field today.