In 1891 a tall, dark, and handsome man strode onto the stage in the lecture hall at Columbia University in New York City. Grasping a brass ball in each hand, the man touched the terminals of a high-voltage, high-frequency transformer (what is today called a Tesla coil). For a moment, 250,000 volts raced across the surface of his body, causing him to be surrounded by what one newspaper called “the Effulgent Glory of Myriad Tongues of Electric Flame.”

View Images Nikola Tesla calmly takes notes while a man-made electrical storm erupts overhead in his laboratory in Colorado Springs, Colorado. He worked at this lab in 1899 and built the world’s largest Tesla coil there. Photograph by BETTMANN, CORBIS/GETTY



Yet after a few moments, the man stepped away from the apparatus, the electrical aura dissipated, and to the delight of the audience, he was unharmed. Who was this man and why did he take this risk?

The man was Nikola Tesla, inventor of the alternating current (AC) motor. Tesla took the risk to demonstrate the safety of AC. For the past several years, the Edison Electric Light Company had been waging a campaign against AC. Its direct current (DC) systems had been losing market share to Tesla’s friends at the Westinghouse Electric Company, and in response, the Edison group had decided to challenge the safety of AC through sensational stories in the newspapers. Tesla hoped, through his dramatic demonstration, to disarm the negative publicity. In the late 1880s, when electricity was the“Wild West”of technology, no one knew what kind of system was going to succeed.

View Images In 1876, tired of arguing with Newark landlords, Edison decided to build his own laboratory in the tiny village of Menlo Park, New Jersey, located 25 miles southwest of New York City. Working with craftsmen and scientists, Edison turned out “a minor invention every ten days and a big thing every six months or so.” Among the big things coming out of tiny Menlo Park were an improved telephone transmitter, the phonograph, and, of course, the incandescent lamp. Even though his years in Menlo Park were productive, Edison moved to New York City in 1882 to manage his new lighting enterprise, and Menlo Park was abandoned. Photograph by D. R. FRAZIER, ALAMY/ACI

Frequently, technological controversies—the race between two inventions vying for widespread acceptance—are resolved through rational means: one invention might be cheaper than the other, another could be accepted because it’s safer than the alternative, and still other inventions succeed because of standards set by engineers or government regulators.

Yet every so often, controversies don’t work out so neatly, and that’s what happened when Tesla and Edison fought over the future of electric power distribution. It was a battle that involved gruesome demonstrations, juvenile name-calling, and attempts to outlaw AC. In the end, though, cooler engineering heads prevailed, and, because of its ability to distribute electric power widely and cheaply, AC won the day.

Let there be light

The common belief that Thomas Edison singlehandedly invented electric lighting in 1879 isn’t true. The first electric light was the arc light, invented by Sir Humphry Davy in 1807. Inspired by the electric battery invented by Alessandro Volta in 1800, Davy had built a huge electric battery in the basement of the Royal Institution in London. To demonstrate the power of his battery, Davy connected the battery terminals to two carbon rods. When he separated the carbons by a tiny distance, the current jumped the gap and gave off a bright light. Over the next 50 years (1810s-1860s), inventors worked to develop arc lamps with electromechanical regulators that maintained the exact gap needed between the carbons to create the bright light. But their efforts were limited as long as they had to rely on batteries; to expand, they needed a new source of electric current.

View Images Michael Faraday, 19th-century English chemist, physicist, and inventor. Photograph by GRANGER/CORDON PRESS

That new source was the dynamo or generator. In 1831 Michael Faraday (who had started his career as Davy’s lab assistant) showed that if you moved a conductor through a magnetic field where the motion was at right angles to the magnetic field, then a current would be induced in the conductor. Seizing on Faraday’s principle of electromagnetic induction, ingenious instrument makers began fashioning new machines that could be cranked by hand or powered by a steam engine to produce a strong electric current. (See also: Where do new ideas come from?)

The possibility of using arc lights to illuminate streets and large buildings spurred other electricians to improve the generator, and in 1876, Charles Brush in Cleveland designed a DC generator that powered four arc lights in a series circuit. Brush’s powerful lights were used to illuminate streets, factories, and shops, including Wanamaker’s department store in Philadelphia.

Arc lighting was great for illuminating streets and large buildings. Indeed, it’s still used today in the powerful searchlights that are beamed skyward to announce the opening of a new store or movie.

View Images This 1889 engraving by William Allen Rogers for Harper’s Weekly magazine shows New York’s burgeoning night life along Grand Avenue, thanks to the illumination from electric arc lights. Photograph by DE AGOSTINI, GETTY

Edison and incandescent lighting

But arc lighting was not useful if one wanted a smaller, softer electric light. Recognizing that customers would buy an electric light similar to existing gas lights, Edison decided in 1878 to drop his work at Menlo Park on the telephone and phonograph and plunge into a field he knew nothing about—electric lighting. (See which of Thomas Edison's predictions about the future came true.)

View Images This bulb from 1879 contains a single carbon filament that glowed when current passed through it. Photograph by SSPL, Getty

To create a smaller lamp, Edison decided to rely on incandescence—an object’s ability to glow when heated. Once it reaches a critical temperature, the object not only glows but can emit bright light. To take advantage of incandescence, Edison experimented initially with platinum. Because this metal has a high melting point, Edison assumed that he could pass a current through a platinum filament, and the heat would cause the filament to incandesce. However, he discovered that oxygen attacked and weakened the platinum when it was heated. To overcome this problem, Edison placed the metal filament in a vacuum bulb.

While the vacuum improved the performance of his lamps, platinum was still too costly and also had a low electrical resistance, which meant his future system would need large and expensive copper cables. Fortunately, Edison realized that he could overcome the need for large copper distribution mains by increasing the resistance of each lamp and putting them in parallel circuits.

The challenge now became finding a high-resistance filament. For several months in 1879, Edison and his team tried dozens of materials, only to find that the lampblack carbon Edison had been using in his telephone transmitters was the ideal material. As one newspaper report described the Eureka moment:

Sitting one night in his laboratory reflecting on some of the unfinished details, Edison began abstractedly rolling between his fingers a piece of compressed lampblack until it had become a slender thread. Happening to glance at it, the idea occurred to him that it might give good results as a burner if made incandescent. A few minutes later the experiment was tried, and to the inventor’s gratification, satisfactory, although not surprising results were obtained. Further experiments were made, with altered forms and composition of the substance, each experiment demonstrating that the inventor was upon the right track.

View Images In this Currier & Ives print from the late 1800s, Edison (left) and Charles Brush, inventor of the arc lamp, are shown as rivals over lighting up New York. Photograph by MPI, GETTY

In October 1879 Edison and his staff conducted their first successful experiments by putting a carbon filament in a vacuum, and they were able to bring it to incandescence since there was no oxygen to cause the filament to burn. By New Year’s Eve, Edison was demonstrating lamps using carbonized cardboard filaments to large crowds at his Menlo Park laboratory. (Watch Thomas Edison reflect on the concept of genius and Nikola Tesla in Nat Geo's 2015 documentary.)

But to commercialize his incandescent lamp, Edison now had to design an entire electrical system to power it, which he modeled after the gas lighting systems used in large cities. Gas systems included central stations, underground conductors, meters, and lamp fixtures. Edison built his first central station on Pearl Street in lower Manhattan in 1882. The area included the Wall Street financial district and the offices of New York’s newspapers, ensuring that Edison had access to both financiers and the media.

Before installing the station, he had his men survey the district to find out how many gas and kerosene lamps were used that might be replaced by his new lights. To offset the high costs of the copper mains needed to carry power to his lights, Edison designed his DC system for densely populated urban centers, and it was most efficient serving customers within a mile of the central station.

Rise of alternating current

Edison was right that there was a huge market for smaller electric lights that could take the place of gas lamps, and he enjoyed significant profits from his incandescent system through the 1880s. Although Edison pioneered the development of incandescent lighting, he was unable in the early 1880s to keep rival inventors from entering this lucrative market. But the biggest challenge facing Edison was the fact that his system was only economical in towns and cities where there was a densely populated downtown—in those situations, there were enough customers who could offset the cost of laying the copper mains required for his system.

View Images This woodcut shows one of the central power stations in New York built by the Edison Light Company in 1882. Photograph by AKG, ALBUM

Yet in America, there were numerous towns that had the money for electric lighting but the population was too spread out to warrant installing an Edison system. Whoever could tap into this larger market was sure to make a fortune!

Recognizing this, George Westinghouse decided to develop an alternating current (AC) lighting system. Westinghouse reckoned that if he raised the voltage (say to 1,000 volts) used to transmit the current, he could reduce the size of the copper mains. However, since bringing 1,000 volts into people’s houses could be dangerous, Westinghouse had his engineers borrow a device invented in Europe, the transformer, which could step down the voltage from 1,000 to 110 V.

But transformers only worked with alternating current, meaning that Westinghouse’s new system would be a radical departure from Edison’s prevailing DC system. In Edison’s DC system, the voltage was constant (typically 110 V), which was relatively safe for consumers. Installation of DC systems was straightforward because linemen could rely on the practices commonly used in DC telephone and telegraph systems.

View Images Born in New York in 1846, George Westinghouse was a lifelong entrepreneur and inventor, transforming the railroad and power industries. Before his death in 1914, he had more than 360 patents in his name. Photograph by BIANCHETTI, CORBIS/GETTY

In the new Westinghouse AC system, however, the voltage on the transmission lines would alternate between a maximum of a positive 1,000 and negative 1,000 volts, meaning that there was greater danger of electrocution for linemen stringing the new power lines. The higher voltages also demanded that Westinghouse Electric engineers needed to develop better insulation and new safety measures. And because AC could transmit power economically over longer distances, it was worthwhile to address these safety issues.

So, circa 1887, AC looked very promising to electrical engineers. Yet they soon realized that they had an economic problem on their hands. Ideally, an AC system should cover an entire city but that meant that the power plant and network would cost hundreds of thousands of dollars, and to offset that investment, it would be good if the plant could deliver electricity 24 hours a day, 7 days a week. To do that, engineers realized they would need a motor that would consume power during the day—a motor that could be used in streetcars, factories, elevators, and all sorts of applications.

Tesla and the AC motor

At this critical juncture—1887—a tall, dark, and handsome man turned up with just the right invention, an AC motor. His name was Nikola Tesla.

Tesla was born in 1856 to a Serbian family living in what is today Croatia. Tesla’s father was a Serbian Orthodox priest who hoped his son would follow in his footsteps. As a teenager, however, Nikola was stirred by a faith in science and instead studied engineering at the Joanneum Polytechnic School in Graz, Austria. (Here are five surprising facts about Nikola Tesla.)

At Graz, Tesla became interested in developing a new electric motor. All motors have two sets of electromagnets. One set is stationary (called the stator) and the other is mounted on a rotating shaft (called the rotor). Adjusting the current fed to each set can create similar magnetic poles facing each other in the stator and rotor. When that happens, the two sets of magnets repel each other, and the shaft of the motor will turn.

View Images Tesla’s induction motor was at the center of the battle of the currents. Its innovative design and resulting efficiency would revolutionize the power industry in the late 19th century. Photograph by Lebrech Music, Album

While watching how a DC motor sparked during a demonstration in his physics class, Tesla suggested that the commutator (the rotating switch feeding electricity to the rotor in the motor) should be eliminated. His physics professor thought he was crazy to propose such a motor, but Tesla persisted. Over the next few years, Tesla puzzled about how to make a sparkfree motor. Rather than build an actual motor, Tesla pictured everything in his mind. In 1882, while living in Budapest, Tesla hit upon the perfect idea during a walk in a city park. Rather than changing the magnetic poles in the rotor, he envisioned the idea of using a rotating magnetic field in his motor.

Before Tesla, inventors had always designed electric motors so that the magnetic field of the stator was kept constant and the magnetic field in the rotor was changed by means of a commutator. Tesla’s insight was a reverse of standard practice. In his motor, Tesla got exactly the right sequence by switching the current on and off in the individual electromagnets in the stator, thus creating a rotating magnetic field. As the magnetic field in the stator rotated, it would induce an opposing electric field in the rotor, thus causing it to turn. Tesla surmised in Budapest that the rotating magnetic field could be created using AC instead of DC, but at the time he did not know how to accomplish this.

Over the next five years, Tesla struggled to acquire the practical knowledge needed to perfect his motor. After helping install a telephone exchange in Budapest, he moved to Paris to work for the Continental Edison Company installing lighting systems in major European cities. In 1884 Tesla was transferred to the Edison Machine Works in New York. There, he had little personal contact with Edison and was assigned the task of designing an arc lighting system. After a payment dispute over his designs, Tesla quit in disgust.

Working with backers from Rahway, New Jersey, Tesla introduced his own arc lighting system, but the company soon folded and Tesla was forced to work as a ditchdigger. In the midst of hardship, though, he mustered the energy needed to file a patent for a thermomagnetic motor. This invention attracted the attention of Charles F. Peck and Alfred S. Brown, who had made a fortune on Wall Street. Intrigued by Tesla’s inventions, Peck and Brown rented a laboratory for Tesla in downtown Manhattan in 1886. (Can you put names to the faces of these 13 titans of the arts and sciences?)

Tesla devoted himself to perfecting the thermomagnetic motor, but when it proved unworkable, Peck encouraged him to return to his AC motor. Building on his vision in Budapest, Tesla now experimented with using several alternating currents in his motor. In doing so, he was a maverick since engineers at Westinghouse Electric and elsewhere used only one alternating current in their systems. In 1887 Tesla discovered that he could produce a rotating magnetic field by using two separate alternating currents fed to pairs of coils on opposing sides of the stator. Modern engineers would say that Tesla’s motor was running on“two-phase current.” Elated that he was finally able to make his rotating magnetic field work, Tesla filed patents broadly covering AC motors as well as the idea that multiphase AC could transmit power over long distances.

View Images Because AC current was more efficient than DC for transmitting over long distances , Westinghouse could use his power plants, like the one above, to serve more people over larger areas than was possible for Edison’s system. Photograph by BETTMANN, CORBIS/GETTY



As it became clear that Tesla had come up with a promising AC motor, his patrons began to think about how to promote it. For Peck and Brown, the name of the game was not to manufacture Tesla’s motor but rather to sell the patents to the highest bidder. To get the right “buzz” going about Tesla’s motor, Peck and Brown arranged for Tesla to give a lecture in 1888 at the American Institute of Electrical Engineers. Their plan worked. Following this lecture, George Westinghouse purchased Tesla’s patents for $200,000; in today’s dollars, this deal would be worth $5 million.

Battle of the currents

Now equipped with an AC system that could power lamps and motors, Westinghouse eagerly took on his major rival, the Edison Electric Light Company. In particular, Westinghouse went after contracts for the very places that the Edison DC system could not serve—the towns and cities where the population was spread out over a wide area. Drawing on the fortune he had made manufacturing railroad air brakes and signal systems, Westinghouse underbid Edison in competing for contracts. Indeed, determined to catch up with Edison, Westinghouse frequently offered to build new power stations below cost.

The Westinghouse tactics appalled Edison. Born and raised in the Midwest, he had a simple view of business deals: A customer should be charged what it actually cost to make the equipment plus a modest profit. Intentionally losing money to undercut a rival seemed unfair. In 1888, after losing major contracts for lighting Denver and Minneapolis, one of Edison’s managers, Francis Hastings, decided to retaliate by attacking the safety of the Westinghouse Electric AC system.

As the first AC systems were installed, there were inevitably accidents in which linemen were electrocuted by the higher voltages used in these new systems. With a little encouragement from Hastings and the Edison company, newspapers quickly picked up these grisly AC accidents. To accelerate the process, however, Hastings found a willing ally in Harold P. Brown. A consulting engineer who had somehow been double-crossed by Westinghouse Electric, Brown was eager for revenge. With the blessing of the Edison managers, Brown organized demonstrations for reporters at Edison’s laboratory in West Orange, New Jersey, in which stray dogs were electrocuted using Westinghouse Electric AC equipment.

View Images Beginning in the 18th century, legal thinkers in Europe and America came to believe that execution for crimes should be more humane, if possible. In the United States a series of botched hangings in the 1880s prompted reformers to seek a new form of capital punishment. In Buffalo, New York, Dr. Alfred P. Southwick, a dentist, undertook a study of how much electricity was required to kill stray dogs and then designed a system to electrocute criminals. An initial jolt of electricity was passed through the head to cause unconsciousness and brain death and a second jolt caused fatal damage to the vital organs. Southwick’s electric chair was first used for capital punishment in 1890. Photograph by GRANGER, CORDON PRESS

Brown’s biggest publicity coup was to arrange for AC to be used for capital punishment. In New York State physicians and reformers had become concerned that hanging was a cruel form of punishment and were seeking an alternate method of execution. Brown convinced them that electrocution by AC was more humane than hanging, and surreptitiously he purchased a used Westinghouse Electric AC generator. Installed at Auburn prison, this Westinghouse machine was used to execute a convicted murderer, William Kemmler, in 1890. Naturally, Brown and the Edison company made sure the headlines read that Kemmler had been“Westinghoused.”

Brown personally dared George Westinghouse to take shocks from his AC generator at increasing voltages while Brown took shocks from an Edison DC machine. Perhaps worried that his friend Westinghouse might take up this challenge, Tesla decided during his 1891 lecture to demonstrate the safety of AC by taking 250,000 volts across his body. Because of the high frequency of the current generated by his newly invented Tesla coil, the current traveled across the surface of Tesla’s body and did not harm his internal organs.

Complementing this publicity campaign, the Edison company also fought Westinghouse on a legislative front. Representatives of the Edison group lobbied several state legislatures to limit the maximum voltage of electrical systems to 300 volts, and they came very close to getting laws passed in Virginia and Ohio.

AC prevails

But while the Edison organization fought in the court of public opinion, Westinghouse and Tesla prevailed in the realm of engineering and business. First, the Westinghouse company decided to dramatically demonstrate its AC system by providing power to tens of thousands of lights at the 1893 World’s Columbian Exposition in Chicago. Visitors not only were enthralled by the beauty of the nighttime illumination but also grew convinced that AC was the future.

View Images The World’s Columbian Exposition took place in Chicago in 1893. Spectators from all over the country flocked to the shores of Lake Michigan to marvel at the newest inventions and trends in the United States. Photograph by GRANGER, CORDON PRESS

Second, in parallel with the World’s Fair, Tesla worked behind the scenes to convince the Wall Street financiers of a giant hydroelectric power plant at Niagara Falls that they should use AC to transmit power to cities across New York State. Through a series of letters and meetings, Tesla persuaded the bankers that AC would allow them to provide electricity to a wider geographic area. At the same time, Tesla kept Westinghouse informed of how the Niagara project was progressing so that Westinghouse could bid on the contract for designing and equipping the power station. In recognition of his contributions to Niagara, the bankers asked Tesla to speak at the banquet celebrating the opening of the power plant in 1896.

After Niagara, the basic pattern of the American electrical industry was established. For much of the 20th century, AC power has been generated and distributed on a massive scale by investor-owned utilities for use by businesses and residential customers. Because the capital costs of building new plants is so high and the marginal profits in selling power is so low, utilities have generally sought to build ever larger networks—first across cities, then entire states, and eventually regions covering multiple states. In doing so, they continue to rely on the multiphase AC technology pioneered by Tesla and Westinghouse.