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Nikola Tesla and alternating current
1856–1943; AC motor patents 1888· Person· Tools, energy & materials
Well documentedSolid records, physical evidence or scientific consensus.
Serbian-American inventor whose alternating-current motor and system, backed by Westinghouse, helped AC win the 'war of the currents'.
See it on the Technology & Medicine map →How it works
Born in Smiljan (now Croatia) to a Serbian family, Tesla worked briefly for Edison's company in New York in 1884, then went his own way. In 1888 he patented a polyphase induction motor: currents in staggered phases create a rotating magnetic field that spins the motor without brushes. George Westinghouse bought the patents. Combined with transformers developed by Lucien Gaulard, John Gibbs and William Stanley, AC lit the 1893 Chicago World's Fair and carried power from Niagara Falls.
Why it mattered
Tesla's induction motor gave AC a practical use beyond lighting. Versions of it still drive most of the world's fans, pumps and factory machines.
Legacy and how we know
His 1888 US patents, including 381,968; his May 1888 lecture to the American Institute of Electrical Engineers; Westinghouse contracts. The Nikola Tesla Museum in Belgrade holds his papers.
Still unknown or debated
Galileo Ferraris in Italy built a rotating-field motor at about the same time, so credit is shared. Tesla's later claims about wireless power and 'death rays' were never proven.
Connections (3)
▸Nikola Tesla and alternating current helped make AC the standard for Electric power and the gridWell documented
The connection
Alternating current can be stepped up by transformers to high voltage for efficient long-distance lines, then stepped down for use. What AC lacked was a good motor. Tesla's induction motor, bought by Westinghouse in 1888, filled that gap. With transformers developed by others, it made AC the winner, proven at Niagara Falls in 1895–96.
When and how
Westinghouse's works in Pittsburgh, 1888–93; the 1893 Chicago World's Fair; the Adams Power Plant at Niagara Falls, which sent AC to Buffalo, about 40 km away, from 1896.
How we know
Tesla's patents, Westinghouse contracts and the Niagara project's 1893 choice of a polyphase AC system are well documented.
Debates and open questions
Credit for AC is shared: Gaulard and Gibbs, William Stanley, Galileo Ferraris, Mikhail Dolivo-Dobrovolsky (three-phase power) and Westinghouse engineers all contributed. Tesla's role is often overstated in popular accounts.
▸Nikola Tesla and alternating current rivalled Thomas EdisonWell documented
The connection
Tesla worked for Edison's company in New York in 1884 and left after a pay dispute, believing in AC, which Edison dismissed. In the late-1880s 'war of the currents', Edison's camp warned AC was deadly, while Westinghouse, using Tesla's patents, sold AC systems. AC won; Edison's company, merged into General Electric in 1892, switched to it.
When and how
New York, 1884–1893: Tesla's months at the Edison Machine Works in 1884; Harold Brown's anti-AC campaign from 1888; the first electric-chair execution, using AC, in 1890.
How we know
Letters, newspapers and company records document the campaign, though the rivalry was mostly Edison versus Westinghouse; Tesla and Edison rarely clashed directly.
Debates and open questions
Tesla's story that Edison reneged on a promised $50,000 bonus rests on Tesla's own account, and the personal feud is often exaggerated in popular culture.
▸Nikola Tesla and alternating current claimed priority over Marconi for RadioDebated
The connection
In the 1890s Tesla built high-frequency coils, demonstrated wireless signaling and a radio-controlled boat, and filed radio-related patents from 1897. In 1943, months after Tesla died, the US Supreme Court voided key claims of Marconi's tuning patent, citing earlier work by Tesla, Oliver Lodge and John Stone Stone.
When and how
Tesla's New York lab, 1891–98, including his remote-controlled boat shown at Madison Square Garden in 1898; the Supreme Court decision of June 21, 1943.
How sure are we?
Tesla's 1897 patent filings and lectures are documented, but the 1943 ruling settled a patent dispute partly about government damages; it did not name Tesla as radio's inventor.
Debates and open questions
Whether Tesla's devices could send usable signals over long distances, as Marconi's did, is disputed; most historians credit radio to many contributors rather than one inventor.