Digital TeslaEverything you need to know about Nikola Tesla.

Glossary

The terms behind the story, in plain language.

Alternating current (AC)

Electric current that periodically reverses direction. Tesla’s polyphase AC system made it practical to generate power at a plant, step it up to high voltage for long-distance transmission, and step it down for safe use — the architecture of the modern grid.

Direct current (DC)

Electric current that flows in one direction only. Edison’s system; excellent for batteries and electronics, but in the 1880s it could not be efficiently transmitted over distance at the voltages then usable.

War of Currents

The late-1880s–1890s commercial battle between Edison’s DC and the Westinghouse/Tesla AC systems. AC won on technical and economic merits — above all the transformer, which DC lacked. Edison’s side ran a notorious propaganda campaign, including the promotion of the AC-powered electric chair.

Rotating magnetic field

The principle Tesla conceived (by his account, 1882): two or more out-of-phase alternating currents create a magnetic field that rotates, dragging a rotor with it. The foundation of the induction motor and the polyphase generator.

Polyphase system

An AC system using multiple currents out of phase with each other (typically two or three phases). Tesla’s 1888 patents covered the complete polyphase system: generation, transmission, and motors.

Induction motor

A motor whose rotor is driven by electromagnetic induction from the rotating magnetic field — no brushes, no commutator, no electrical connection to the rotor. Rugged and simple; the dominant industrial motor type to this day.

Commutator

The rotating switch in DC motors and generators that reverses current to keep the rotor turning. A source of sparking, wear, and maintenance — the thing Tesla’s brushless AC motor eliminated.

Transformer

A device that steps AC voltage up or down. The key enabler of long-distance AC transmission — and the component Edison’s DC system had no equivalent for.

Tesla coil

Tesla’s 1891 resonant transformer for producing high voltage at high frequency. Used in early radio transmitters, and still in physics demonstrations and plasma research.

Resonance

The phenomenon of a system oscillating with large amplitude at its natural frequency. Tesla exploited electrical resonance in the Tesla coil and the magnifying transmitter; he also speculated — far beyond the evidence — about mechanical resonance effects.

Magnifying transmitter

Tesla’s Colorado Springs apparatus: a giant Tesla coil intended to pump electrical energy into the Earth itself, which he believed could act as a conductor for worldwide power transmission. It produced spectacular discharges; it never transmitted usable power.

Wardenclyffe

Tesla’s unfinished wireless station at Shoreham, Long Island (1901–06): a 187-foot wooden tower, funded by J.P. Morgan’s $150,000, meant for transatlantic signaling and — Tesla hoped — wireless power. Abandoned for lack of funds; demolished 1917.

Telautomaton

Tesla’s term for his radio-controlled devices, from the 1898 Madison Square Garden boat demonstration — the first public showing of wireless remote control.

High frequency

In Tesla’s era, alternating currents oscillating thousands to millions of times per second — the domain of his most spectacular experiments and lectures, and the technical basis of radio.

X-rays

Discovered by Röntgen in 1895. Tesla quickly produced some of America’s earliest X-ray images and, unusually early, warned of their dangers — after reportedly suffering burns from exposure.

Bladeless turbine

Tesla’s 1913 turbine using smooth disks and fluid friction instead of blades. Elegant in theory; the materials of the day couldn’t withstand the operating stresses, and it was never commercialized.

Teleforce

Tesla’s 1930s proposal for a particle-beam weapon — the origin of the “death ray” legend. Announced repeatedly to birthday press conferences; never built, and no government is documented to have taken it up.

“Free energy”

A phrase Tesla never used for his own work. He did not claim perpetual motion or costless power; his wireless schemes were meant to transmit power that would be metered and billed. The “suppressed free energy” story is internet mythology — see Myth vs. Record.

Patent

A government grant of exclusive rights to an invention. Tesla held roughly 300 patents worldwide (exact counts vary with how continuations and foreign filings are counted); the 1888 U.S. polyphase patents are his most consequential.

Royalty

A per-unit payment to a patent holder. Westinghouse’s 1888 license reportedly included royalties of $2.50 per horsepower of Tesla-motor capacity — the obligation Tesla later released during Westinghouse’s cash crisis.

Niagara (Adams Power Plant)

The hydroelectric plant at Niagara Falls built to the Westinghouse AC design on Tesla’s polyphase principles; operating from 1896, it was the first large-scale AC power system and the practical proof of Tesla’s system.

Colorado Springs

Tesla’s 1899–1900 experimental station for high-voltage, high-frequency research. Source of the famous lightning photographs and the Colorado Springs Notes — and of many later myths.

The tesla (unit)

The SI unit of magnetic flux density, symbol T, named for Nikola Tesla in 1960. One tesla is a very strong field — an MRI scanner runs at 1.5–3 T.

Serbian Orthodox

The church of Tesla’s family and upbringing; his father Milutin was a priest. Tesla himself was not conventionally devout as an adult, but he spoke respectfully of the tradition.

Office of Alien Property

The U.S. government office that seized Tesla’s papers after his 1943 death (he died a U.S. citizen, but the seizure was precautionary wartime procedure). MIT’s John G. Trump reviewed the papers and reported nothing of military significance.

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