Who was Nikola Tesla? What he really invented

Nikola Tesla was a Serbian-American engineer and inventor, born in 1856 in what is now Croatia and died in New York in 1943, whose induction motor and polyphase system helped make alternating current (AC) the way the world sends electricity. He also built the Tesla coil, demonstrated radio control and chased wireless power. Much of what the internet now says about him is exaggerated or invented.

In short

• Tesla's lasting achievement is the AC induction motor and the polyphase system, which George Westinghouse licensed in 1888 and built into the grid.
• AC won because transformers can raise its voltage for long lines, which cuts the energy lost as heat.
• He did pioneering radio and wireless work, but he did not invent AC, did not single-handedly invent radio, and never built "free energy" or a death ray.

Who was Tesla, in brief?

Tesla was born on 10 July 1856 in Smiljan, a village in the Military Frontier of the Austrian Empire, to a Serbian Orthodox priest's family. He studied engineering at the polytechnic in Graz without finishing, worked for a telephone exchange in Budapest in 1881, and then for an Edison company in Paris. In June 1884 he sailed to New York and worked at the Edison Machine Works for about six months before leaving over pay.

After a failed first company, he patented his AC motor in 1887 and 1888 and sold the rights to Westinghouse. The 1890s were his peak: a laboratory in Manhattan, lectures that made him famous, and the Tesla coil. From 1901 he poured everything into a wireless tower at Wardenclyffe on Long Island, which failed. He spent his last decades in New York hotels, short of money, and died alone in his room at the Hotel New Yorker on 7 January 1943. The SI unit of magnetic flux density, the tesla, has carried his name since 1960.

What did Tesla actually invent?

His central invention was a motor with no brushes or commutator, the worn-out sliding contacts that DC motors needed. Tesla fed two or more alternating currents, timed out of step, into a ring of coils, which made a magnetic field that rotates. The rotating field drags the rotor around by inducing currents in it. This induction motor is simple and sturdy, and descendants of it still run fans, pumps, factory machines and many electric cars. The Italian physicist Galileo Ferraris reached the rotating field independently at about the same time.

Tesla filed seven US patents on polyphase motors and transmission in late 1887. In July 1888 Westinghouse licensed them for $60,000 in cash and stock plus a royalty of $2.50 per horsepower, as PBS records. When Westinghouse's company hit a financial crisis in 1891, Tesla gave up the royalty. In 1893 Westinghouse lit the World's Columbian Exposition in Chicago with AC and displayed the Tesla polyphase system in its Great Hall of Electricity. In 1895 its polyphase generators began running at Niagara Falls, and from November 1896 they sent power to Buffalo, about 40 km away.

His other work spread wide. The Tesla coil, from 1891, is a transformer that produces very high voltages at high frequency. In 1898 he steered a model boat by radio at Madison Square Garden, an early demonstration of remote control. He experimented with X-ray tubes, wireless lighting and tuned radio circuits.

Why did alternating current win?

AC won because of a simple fact about wires: the energy they waste as heat depends on the square of the current. Power is voltage times current, so the same power can be sent as high voltage with low current, or low voltage with high current. A transformer, which works only with a current that changes, can step AC voltage up for the long line and back down for the home.

Here is a worked example. Send 100 kilowatts down a line whose wires have a total resistance of 5 ohms.

Line voltage	Current (power ÷ voltage)	Heat lost (current² × resistance)	Share lost
1,000 volts	100 amps	50,000 watts	50%
10,000 volts	10 amps	500 watts	0.5%
100,000 volts	1 amp	5 watts	0.005%

Ten times the voltage cuts the loss a hundredfold. Thomas Edison's direct current (DC) systems of the 1880s could not change voltage cheaply, so they ran at low voltage and their power stations had to sit within a mile or so of their customers. AC could be generated at a waterfall and sent to a city. Today power electronics can convert DC voltages too, and high-voltage DC lines now carry power over very long distances, as the US Department of Energy notes. The grid itself stayed AC.

What was the "war of the currents"?

The war of the currents was a commercial fight in the late 1880s, mainly between Edison's companies and Westinghouse. Edison, whose business rested on DC patents, campaigned that AC was deadly. An engineer named Harold Brown electrocuted animals in public to make the point and, with a secretly bought Westinghouse generator, supplied the current for the first electric chair, which killed William Kemmler at Auburn Prison in New York on 6 August 1890. The Chicago fair of 1893 and Niagara Falls settled the matter. By 1896 even General Electric, formed partly from Edison's company, was building AC.

Tesla supplied the motor patents but was not the main combatant. The popular picture of a personal Tesla-versus-Edison duel is a later story.

What is myth and what is true?

Tesla attracts more myths than almost any other scientist. Some began with his own later claims, others online.

Claim	What the record shows
Tesla invented alternating current	No. AC generators and transformers existed before him, and Westinghouse was already building AC lighting systems. Tesla's contribution was the practical AC motor and polyphase system
Edison cheated him out of $50,000	The story comes from Tesla's own 1919 memoir, decades later. He did quit the Edison Machine Works after about six months over a bonus he felt he was owed; what was promised, and by whom, is unclear
Tesla, not Marconi, invented radio	Radio had many inventors. Tesla's 1897 tuning patents mattered, and in 1943 the US Supreme Court struck down key claims of Marconi's patent because earlier work by Oliver Lodge, John Stone Stone and Tesla came first. The court did not name Tesla the inventor of radio
He built a free-energy machine that was suppressed	No. Wardenclyffe was meant to send messages and power wirelessly using generators; it needed fuel like any power plant, never worked as planned, and lost funding when J. P. Morgan declined to put in more than his $150,000
He built a death ray	He described a particle-beam weapon to reporters from 1934 but never showed one. An MIT engineer, John G. Trump, examined his papers for the US government after his death and concluded that his late work did "not include new, sound, workable principles or methods" for what he promised
He was cheated of a 1915 Nobel Prize shared with Edison	Newspapers reported the rumor in 1915; the prize went to William and Lawrence Bragg, and neither man was ever awarded one

A quick test for any Tesla claim: if it rests on what Tesla told reporters late in life, or on a web page with no date or document, treat it as doubtful.

Why does Tesla matter?

Tesla's motor and the AC system it made practical are part of the reason electricity reached factories and homes far from any power station. His work on tuned circuits fed into radio, and the coil he built is still used to teach and demonstrate high-voltage physics. He was a gifted, original engineer who worked mostly by imagining machines in detail before building them.

He was also an inventor who promised more than he delivered, and a poor businessman. Like Albert Einstein, he became a symbol larger than his work. The test that sorts the two, a claim checked against documents and measurements, is the core of how science works. The grid his motor helped build now powers the computers that spread the myths about him.

Check yourself

• Without looking back, explain why raising a line's voltage tenfold cuts its losses a hundredfold.
• What exactly did Tesla's induction motor do that earlier motors couldn't?
• What did the 1943 Supreme Court decision on Marconi's patent actually decide?

Sources

• Tesla: Master of Lightning, War of the Currents — PBS, 2000
• The War of the Currents: AC vs. DC Power — U.S. Department of Energy, 2014
• Marconi Wireless Telegraph Co. of America v. United States, 320 U.S. 1 (1943) — Legal Information Institute, Cornell Law School
• Tesla: Master of Lightning, The Missing Papers — PBS, 2000
• Nikola Tesla Museum — Nikola Tesla Museum, Belgrade
• Nikola Tesla — Wikipedia