The “War of the Currents:” Edison vs. Tesla


In 1865, James Clerk Maxwell produced a unified theory of electromagnetism.  One of the major pieces of input into Maxwell’s theory was the principle of magnetic induction, which had been discovered by Michael Faraday just a few years earlier.  The process of magnetic induction is generated by a time-varying magnetic field.  When a conducting loop is placed inside the changing magnetic field, an electric current is induced to flow through the loop.  So a current will flow through a conducting loop without any attached battery or power source. Immediately following Faraday’s discovery, it was possible to produce electric motors and generators which relied on magnetic induction.  These discoveries in turn led to applications that opened up new fields in applied physics.  One of the major new applications was the use of electric currents to provide lighting in factories and homes. 

In the U.S. and Europe, many people researched ways to make electric lighting a major industry.  One of the first Americans to study this area was Thomas Alva Edison, who had achieved fame as the “Wizard of Menlo Park” for the number of inventions created and patented in Edison’s Menlo Park research laboratory.  As we will see, Edison produced the first inexpensive and long-lived incandescent light bulb.  After patenting his electric light, Edison then designed and patented methods of producing and distributing electric power.  In this, Edison relied on direct-current or DC power. 

Edison’s main American rival was George Westinghouse.  Like Edison, Westinghouse was also a noted inventor and entrepreneur.  Westinghouse had made a fortune on his system of air brakes for railroad cars.  George Westinghouse then expanded his research into the production of electric power.  Unlike Edison, Westinghouse bet on alternating-current or AC power.  In the 1880s, Westinghouse and Edison were engaged in a battle for supremacy in the installation of electric power.  The competition between the two systems was intense, and led to each side denigrating the production system of the other. 

This competition was so heated that it became known as “the War of the Currents.”  In this post we will review the major features of the War of the Currents and will also discuss the major players, in particular Thomas Edison and Nikola Tesla, a colleague of Westinghouse.  The “War of the Currents” has been described by many as a major scientific feud – which form of electric power was better, AC or DC?  However, we will also consider a contrary view – namely, whether the feud over AC or DC was actually more an economic and public-relations battle than a scientific controversy. 

One of the reasons that the “War of the Currents” was so interesting is that a key battleground in that feud was the Niagara Falls Power Project.  One of us (TL) grew up in Niagara Falls, and used to clamber around the Niagara Gorge as a child.  The subject of the “War of the Currents” was of great interest at the time, and it continues to give a fascinating glimpse of a struggle between several different corporations in the early days of electric power. 

A Primer on Electricity & Magnetism:

In this post we will be discussing a number of features of electricity and magnetism.  Here, we will introduce some basic features of electricity and magnetism that are necessary to understand the concepts being discussed.  First, a conductor is a material that contains electrons or objects with an electric charge that are relatively free to move through the material.  For example, in a copper wire some of the electrons in the copper are free to move when they experience an electric or magnetic force.  In a battery, chemical reactions occur that break molecules into ions, where some of the ions have a net negative charge while other ions have a net positive charge. 

An insulator is a material where the molecules are generally electrically neutral.  When a moderate electric field is applied to an insulator, no charged particles flow through the system.  An electric current is a measure of the rate at which electric charges flow through a conductor.  If a total amount of charge dq flows through a conductor in time dt, then the current I is defined by

I = dq/dt        (1)

Charge will move through a conductor when the conductor experiences an electric potential difference V.  This is shown schematically in Fig. 1.  The relationship between V and the resulting current I is

V = I R;   I = V/R       (2)

Figure 1: A schematic showing a solid conducting material.  The molecules of the material contain some electrons that are free to move when subjected to an electric force.  The top figure shows the material with the free electrons; the bottom figure shows the free electrons moving and producing an electric current when an electric force is applied to the material.

Eq. (2), called Ohm’s Law, says that the current I is proportional to the applied voltage V.  The quantity R is called the “resistance” of the conductor.  For a given voltage V, the current I is inversely proportional to the resistance R.  For example, a battery is a device that uses a chemical reaction to produce an electric potential difference V between the two poles of the battery (for example, the top and bottom of a 1.5-Volt AA battery).  If one hooks up a conducting wire with resistance R between the top and bottom plates of the battery, a current will flow through the wire.  With a constant V, the current I will be approximately constant and will be given by Eq. (2), I = V/R. 

The “power” in an electric circuit is the rate at which energy flows through the circuit.  Given an electric potential V and current I, the power P is given by

P = V I = I2 R              (3)

We will also use electric and magnetic fields to discuss electric currents and potentials.  If a charge q is placed in a region with electric field E, then the force on that charge is given by

F = q E            (4)

Forces and fields are vectors, that is they have both magnitude and direction.  In Eq. (4), the electric force on a positive charge will be in the same direction as the field, while a negative charge will experience a force exactly opposite the direction of the field.  Figure 2 shows the electric field lines produced by a single positive charge.  The field lines originate at the location of the charge and are directed radially outward.

Figure 2:  The electric field lines due to a positive point charge.  The electric field lines are straight lines that originate at the charge and travel radially outward from the charge.

There are also magnetic fields.  Permanent magnets can produce magnetic fields.  Figure 3 shows the magnetic fields lines for a permanent bar magnet.  Whereas electric field lines originate from a positive charge and terminate on a negative charge, magnetic field lines form closed loops with no “source” and no “sink.”  If a moving electric charge q is placed in a magnetic field B, the magnetic force on that charge is proportional to q, B and the speed v of the charge.  The magnetic force is perpendicular to both the velocity vector v and the magnetic field vector B.  This relationship yields the unusual properties that the magnetic force on a stationary charge is zero, and the magnetic force is also 0 if v and B are collinear. 

Figure 3:  The magnetic field lines for a bar magnet. Note that the magnetic field lines form closed loops (the loops are completed inside the magnet, but are not shown there) that do not cross one another.

For a while, electric and magnetic phenomena were considered two distinct and different types of forces.  However, in 1831 Michael Faraday discovered that a changing magnetic field was capable of inducing an electric current in a nearby circuit.  This demonstrated a connection between magnetic and electric forces.  Then in 1864, James Clerk Maxwell postulated that, in analogy to magnetic induction, a changing electric field would be capable of producing a magnetic force.  The following year, Maxwell wrote down a set of equations that unified electricity and magnetism into a single field called electromagnetism.  Maxwell’s equations were a revolutionary step in that they took two areas formerly thought to be separate and unified them.  This was a discovery analogous to Isaac Newton’s demonstration that gravity on Earth (terrestrial gravity) was the same force that caused the Moon to orbit the Earth and the Earth to orbit the Sun. 

The discoveries of Faraday and Maxwell led directly to the development of machines that utilized those electromagnetic (EM) principles.  Figure 4 shows the schematics of an electric motor.  An electric current is run through a loop of wire that is immersed in a magnetic field (the loop is between the poles of a magnet).  The wire loop experiences a torque from the magnetic field that causes the loop to rotate.  The loop is connected to contacts called “brushes;” after every half turn of the loop, the direction of the current is reversed.  This keeps the loop rotating in the same direction.  The rotating loop can be connected to a crank that will rotate along with the loop.  Such a device converts the energy carried by an electric current into the mechanical kinetic energy of the rotating crank. 

Figure 4:  A schematic drawing of an electric motor.  A loop of wire carries an electric current.  The wire loop is immersed in a magnetic field.  The wire loop experiences a torque that causes the loop to rotate.  The loop is connected to contacts called “brushes;” the contacts cause the direction of the current in the wire to reverse every half-turn of the loop.  This keeps the loop rotating in the same direction.  The rotating loop can be connected to a crank that rotates along with the loop.  In a motor, the energy carried by the electric current is converted into rotational kinetic energy that can be used to perform work.

Figure 5 shows the operation of a generator.  It looks extremely similar to the AC motor of Fig. 4. However, in this case the input is the kinetic energy of the rotating crank.  This causes a loop of wire to rotate in the magnetic field.  The changing magnetic flux then induces an alternating current in the loop of wire.  Here, the input of mechanical kinetic energy is turned into the output of an alternating current in the wire.  This current could then be transported to another area where the current could be used for lighting, heating or other purposes. 

Figure 5:  Schematic diagram of an alternating current generator.  A rotating crank causes a conducting loop of wire to rotate in the presence of a magnetic field.  The changing magnetic flux induces a current in the loop of wire.  In a generator, rotational kinetic energy is turned into electrical energy.

A transformer is an extremely useful inductive device for transporting electrical energy.  The basic operation of a transformer is shown in Fig. 6.  An iron core is shown as an open rectangle, with wires wrapped around both sides of the core.  The wire on the right or “primary” side of the core contains a primary current IP and voltage VP.  The input current must vary with time; in general this will be a sinusoidal or AC current.  The changing current induces a time-varying magnetic field throughout the iron core.  The changing magnetic field then induces a time-varying current in the secondary wire.  The magnitude of the secondary voltage Vs is related to the primary voltage VP as the number of turns on the secondary NS to the turns on the primary NP, i.e.

VS/VP = NS/NP           (5)

In Fig. 6, NS is twice NP, then the magnitude of the secondary voltage will be two times greater than the voltage on the primary circuit.  The figure shows that Vs is twice that of VP, that is 220 V to 110 V. However, the power across a transformer remains constant because there is no transfer of energy from the primary to the secondary; from Eq. (3), this implies the equation

VS IS = VP IP     (6)

Figure 6:  The operation of a transformer.  Two sets of wires, a primary set on the right and secondary on the left, are wrapped around an iron core. A time-varying current on the primary produces a varying magnetic field in the core.  That in turn produces a time-varying current on the secondary.  The voltage in the secondary coils is related to the voltage in the primary by the ratio of the number of turns on the secondary to the turns on the primary.

From Eq. (3), if you run a current I through a wire with resistance R, the amount of electrical power lost to heat in the wire will be I2R.  In transporting AC electricity over large distances, sinusoidal electric currents are first produced by an AC generator as shown in Fig. 5.  The resulting current is then run through a “step-up” transformer, one that has many more turns on the secondary than on the primary.  The resulting voltage on the secondary is much greater than on the primary (hence, we have high voltage transmission lines), so by Eq. (6) the secondary current is much smaller than the primary current.  From Eq. (3), by greatly decreasing the current, the energy lost to heating of the wire is very small. This is especially important for transport over long distances because the resistance of the transmission lines increases with their length.

Thomas Edison

Thomas Alva Edison was one of the great applied scientists and entrepreneurs of the late 19th and early 20th centuries.  Edison was born in 1847 and raised in Port Huron, Michigan, as the last of seven children.  Although he attended school for only a few months, Edison was home-schooled by his mother, a former teacher. 

Figure 7:  A photograph of the inventor Thomas Alva Edison.

Edison quickly showed a talent for sales and marketing.  As a youth, he sold newspapers and food on trains from Port Huron to Detroit.  By age 13, he was earning $50 a week profit, a princely sum at the time.  He used his earnings to purchase chemicals and equipment that he used to set up a home laboratory.  Edison next got a job as a telegraph operator.  There, he invented a system that would allow the operator to send two to four telegraph messages simultaneously.  Edison sold the rights to his device to Western Union for $10,000, and he used the profits to establish an industrial research laboratory in Menlo Park, New Jersey. 

Edison’s Early Inventions:

Edison supervised an ever-growing number of staff at his Menlo Park facility.  Edison divided his staff into various teams, and he directed each team to carry out research in specific areas, or to work on improvements to existing technologies.  Edison would then patent his inventions.  Over his lifetime, Edison obtained 1,063 patents on a wide range of topics.  Nearly all his patents were in the areas of chemical, mechanical or electrical processes.  Each of those patents would afford his laboratory 17 years of protection, and Edison zealously protected his intellectual property.  He was frequently involved in lawsuits regarding patent rights for his inventions. 

Figure 8:  Workers at Thomas Edison’s research laboratory at Menlo Park, New Jersey. 

Edison was known for working around the clock.  He rarely spent time at home and was found at his laboratory at all hours of the day and night.  Edison had great stamina – he could work for days at a stretch on his inventions.  Edison claimed that he rarely slept, but he took regular 20-minute naps. Although he was known to embellish aspects of his life, it is true that he worked extremely long hours. 

One of Edison’s first major accomplishments was his invention of the phonograph in 1877.  Sounds were recorded on tinfoil, which surrounded a grooved cylinder.  The sound quality of Edison’s initial phonograph was mediocre, and the recordings could only be played a few times.  Nevertheless, Thomas Edison became a household name for his invention.  He took his phonograph to Washington, D.C. where he made demonstrations to President Rutherford B. Hayes, members of Congress and the National Academy of Sciences.  There, Edison displayed his remarkable gift of showmanship.  Joseph Henry, the president of the National Academy and one of America’s most distinguished scientists, described Edison as “The most ingenious inventor in this country … or any other.”   The media began calling him “the wizard of Menlo Park.” 

Edison’s next major accomplishment was the development of improved microphones to be used in the telegraph industry and in the development of residential phones.  Here, Edison’s lab was in competition with many other inventors, including Alexander Graham Bell.  Edison eventually came up with a method that used two metal plates with carbon granules in between the plates.  The carbon passed a direct current between the plates.  When sound waves passed through the system, the carbon changed its resistance; thus, by measuring changes in the current one could reproduce the sound.  Edison patented his device and successfully defended his patent against the claims of other inventors.  Edison’s carbon microphone was used by the Bell Telephone System for nearly 70 years. 

The Edison Electric Company:

In 1878, a division of Thomas Edison’s Menlo Park laboratories began working on issues in electricity.  He first concentrated on improving the incandescent light bulb.  Early bulbs were inadequate for two major reasons: long-lived bulbs tended to have extremely expensive filaments (platinum filaments were one of the most successful); while bulbs with inexpensive filaments tended to be extremely short-lived, with many lasting for only minutes before the filament burned out.  Many early incandescent bulbs required an extremely high current to operate, and the short life of the filaments was related to the high current they carried.  

Edison’s electricity group experimented with literally thousands of candidates for a long-lived incandescent bulb that could operate on low current.  In 1879, Edison filed a patent for an electric lamp that used a “carbon filament or strip coiled and connected to platina contact wires.”  Within the next year Edison was able to produce a carbonized bamboo filament that operated under low currents and would last more than 1,200 hours.  In Dec. 1878, he formed the Edison Electric Light Company in New York City for the purpose of producing and distributing light bulbs.  Among his financial backers were J.P. Morgan and the Vanderbilt family.  The first public demonstration of Edison’s incandescent light bulb was made at his Menlo Park factory on Dec. 31, 1879.  Edison boasted that “We will make electricity so cheap that only the rich will burn candles.” 

Next, Edison created an electric utility company to control the production and distribution of electricity.  His electric utility was based on earlier utilities that had been formed in the coal and gas industries.  In Dec. 1880, he created the Edison Illuminating Company.  Next, he patented a method for the distribution of electricity.  In Sept. 1882, Edison turned on his Pearl Street generating system, and began distributing 110-Volt DC power to 59 customers in lower Manhattan. 

Edison’s goal was to make his name synonymous with electricity.  He wanted to replicate his electricity-generating stations in cities across America.  And he staked his reputation on his DC power systems.  As the most widely-recognized scientist-inventor in the nation, Thomas Edison convinced a number of American cities to award him contracts for electricity generation and distribution.  At first, Edison achieved a great deal of success.  He won contracts to set up DC generating and distributing stations in a number of American cities. 

However, Edison’s system had some notable drawbacks.  He could only transport the electricity that he generated over a distance of one mile.  This meant that he had to build many generating stations in order to supply even the center of a city.  People who lived in rural areas had no access to Edison’s lighting.  In addition, Edison buried underground the expensive copper wires used to distribute his electricity; and finally, customers had access to only a single voltage, the 110 Volts from his generating stations. 

Soon, Edison found that he had competition from companies that were generating AC power.  After a few technological breakthroughs, AC electricity had several advantages over DC power.  First, it could be transmitted over very large distances.  Second, the voltage and current could be modified by using transformers.  And third, AC electricity was carried by cables mounted on telephone poles.  The net result was that AC power became much cheaper than DC power.  Edison had the option of fighting AC electricity or switching.  He chose to fight.  The fight between Thomas Edison for DC power, and the duo of George Westinghouse and Nikola Tesla for AC power, is summarized in our section “The War of the Currents.” 


Edison’s labs designed a fluoroscope, a machine that uses X-rays to make radiographs.  The original substance used for fluoroscopes was barium platinocyanide; however, this produced only very faint images.  Edison discovered that screens made of calcium tungstate could produce much brighter images than the original screens.  The type of screen manufactured by Edison labs is still in use today.  However, Edison and one of his assistants, Clarence Dally, both were injured by radiation from their X-ray research.  Edison’s vision was seriously affected by his exposure.  However, Dally fared much worse; he developed cancer from his exposure to high levels of radiation, and he died at age 39.  

Moving Pictures:

Thomas Edison’s laboratories developed the first motion picture cameras.  One of his employees, William Kennedy Dickson, was responsible for many of the photographic and optical advances from Edison’s labs.  The camera would advance film rapidly, so that it could take 20-30 frames per second of a moving object.  Edison collaborated with photographic pioneer George Eastman on the design of film that would advance steadily around a cylinder, take individual frames rapidly, and be sufficiently strong to minimize breakage of the film. 

Figure 10:  An example of an early kinetoscope.  This machine would run and display a short film produced by Thomas Edison’s motion picture company.  Banks of kinetoscopes, each showing a different short film, were assembled in “penny arcades,” storefronts that would show short film loops. 

The developed moving picture film was then run through a small peep-hole device called a kinetoscope.  Beginning in May 1891, Edison’s labs produced a number of very short films that could be installed in kinetoscopes.  Edison then opened “penny arcades.”  These were storefronts that housed a series of kinetoscopes, each one running a different film loop.  Each of these films typically lasted for only a few seconds.  Below is a video that describes the kinetoscope, shows one of the first penny arcade installations, and also shows a few of the famous early film loops. 

The public response to the videos was electric (but neither AC nor DC).  People found the films irresistible, and the penny arcades were a smash hit.  The success of the kinetoscopes kick-started a world-wide film industry.  It is interesting that Edison initially focused on the peep-hole kinetoscope that could only be viewed by a single person at a time.  He was convinced that his penny arcades would be more profitable than designing machines that would show a film to a large audience. 

However, Edison’s labs also worked on moving-picture machines to show films in theaters.  In 1896, Edison sold the rights to project moving pictures to Thomas Armat’s Vitascope.  This company made public screenings of short films in theaters.  Again, this project found enthusiastic audiences both in the U.S. and around the world.  Edison simultaneously made audio recordings of some of his films.  The audio was then played back simultaneously on a separate machine. Edison’s audio cylinders were hand-cranked so that they synchronized with the video. 

Around the turn of the 20th century, the motion picture exploded around the globe.  Europe particularly embarked on a new film industry, with film companies established in Britain, France, Germany and Belgium.  Edison established the first film studio, the Black Maria in West Orange, New Jersey.  His film company made 1,200 films, most of them being extremely short subjects.  Among these were The Kiss in 1896, The Great Train Robbery in 1903, and Frankenstein in 1910.  In 1908, Edison established the Motion Picture Patents Company.  A group of nine film studios joined together with the Patents Company to protect their patent rights. 

Thomas Edison also made notable contributions to the mining industry. In the 1870s he developed a process to extract iron from low-grade deposits.  The deposits were pulverized and then crushed into dust.  The dust was then sent through a series of giant magnets that picked up the dust.  In 1901, Edison set up mining operations outside Sudbury, Ontario.  Although he discovered an important lode, the Falconbridge ore body, he was never successful in extracting the ore, and he abandoned the site in 1903. 

Edison’s Philosophical Views:

Thomas Edison was a freethinker.  One of his heroes was Thomas Paine.  Edison described Paine’s views as follows: “Paine has been called an atheist, but atheist he was not.  Paine believed in a supreme intelligence, as representing the idea which other men often express by the name of deity.”  This appears to describe Edison’s philosophical views as well.  After Edison outlined his own views in a magazine article, he was accused of being an atheist.  He denied that, but said that he believed in Nature, which he described as “the supreme intelligence that rules matter … Nature made us – nature did it all, not the gods of the religions.”  Edison further remarked “It is doubtful in my opinion if our intelligence or soul or whatever one may call it lives hereafter as an entity or disperses back again from whence it came.” 

Edison was also a vegetarian, and a strong supporter of women’s suffrage.  One of the things he was most proud of was his disinclination to build weapons of war.  He said, “I am proud of the fact that I never invented weapons to kill.”  This was despite many requests that Edison’s laboratories take on military contracts.  Edison described his views on this matter: “Nonviolence leads to the highest ethics, which is the goal of all evolution.  Until we stop harming all other living things, we are still savages.” 

Edison died of complications from diabetes in October 1931.  He was lauded as one of the greatest inventors in history.  He had assembled large groups of applied scientists, and under Edison’s direction they had made contributions to several different emerging fields.  Thomas Edison was a genius at identifying key areas that were ripe for new technologies.  In the case of the phonograph and motion pictures, he was able to make seminal contributions that opened up entire fields of commerce.  In other areas such as electricity, he made improvements in existing technologies (such as the incandescent light bulb), and then patented, marketed and distributed his products.  Much like his good friend Henry Ford (who worked for Edison as an engineer before inventing the assembly line), Edison was able to develop products that revolutionized areas of technology. 

Thomas Edison received a number of awards for his inventions.  In addition, many awards are named after Mr. Edison. Here are just a few.  In 1915 the American Institute of Electrical Engineers (now the IEEE) awarded the Edison Medal “for a career of meritorious achievement in electrical science, electrical engineering or the electric arts.” In the Netherlands, the Edison Medal is awarded for achievements in music.  And the American Society of Mechanical Engineers bestows the Thomas A. Edison Patent Award for a patent that demonstrates a significant impact on the practice of mechanical engineering. 

Nikola Tesla

Nikola Tesla would become one of the great inventors and applied scientists of the 19th and 20th centuries.  He was born in the Austrian Empire (in an area that is now part of Croatia) in July 1856.  Tesla apparently had an eidetic (“photographic”) memory, and was able to visualize complex concepts – in fact, in school he was accused of cheating because he worked out integral calculus problems in his head.  It is reported that Tesla was able to memorize complete books, and in addition he was fluent in seven languages (English, French, German, Hungarian, Italian, Czech and Serbo-Croatian – eight if you include Latin). 

Figure 11:  Inventor and applied scientist Nikola Tesla. 

Tesla was inspired by his high school physics teacher, whose demonstrations of electro-magnetic (EM) phenomena gave him the desire to master this field of study.  At the Imperial-Royal Technical College in Graz, Tesla was motivated by lectures on electromagnetism by one of his professors.  Strangely enough, for someone as bright at Tesla and gifted with a photographic memory, Tesla began failing his courses in his third year and left Graz without a degree.  There is speculation that he might have spent his last year gambling and womanizing.

Like Edison, Tesla was able to work for long periods without resting.  He claimed that he never slept more than two hours a night.  On occasion he was known to work in his laboratory for 84 hours straight.  Tesla also had expensive tastes in food, lodging and clothes.  As we will see, when he was prosperous he could afford these luxuries; however, he did not cut back when his finances went south, and this caused him to end up deeply in debt at various points in his life.    

Tesla did return to college at Charles-Ferdinand University in Prague, but he never enrolled as a full-time student.  After that, his knowledge of science was all self-taught.  In 1881, Tesla was appointed as the chief electrician at the Budapest Telephone Exchange.  In 1882, he obtained a position at Continental Edison in Paris, where he worked on installing incandescent lighting throughout the city.  There his mastery of equipment and his creativity, particularly with motors and dynamos, was noticed. 

When Charles Batchelor of the Con Ed staff was appointed to manage the Edison Machine Works factory in New York, he brought Tesla with him.  Tesla was assigned to devise a system for installing arc lighting in New York.  This proved to be a difficult task because arc lighting required very high voltages, whereas Edison’s direct-current (DC) system used low voltages. 

After six months working at the Edison Machine Works, Tesla resigned from that company.  He received venture capital from two investors and opened his own company, Tesla Electric Lighting & Manufacturing.  At this company, it appears that Tesla was further refining inventions that he had worked on at Edison Machine Works.  Tesla subsequently installed his DC arc lighting system in Rahway, New Jersey, to general acclaim. 

Unfortunately, in 1886 Tesla’s financial backers decided to open their own utility company, and abruptly withdrew their financial support.  This was a disaster for Tesla; as he had traded his patent rights for stock in his company, he was left penniless and with no patent rights.  At some point, Tesla was working as a ditch digger and earning $2 per day.  However, in 1887 Tesla found investors who bankrolled his Tesla Electric Company in Manhattan. 

Tesla developed an induction motor that ran on alternating current (AC), rather than Edison’s DC system.  Tesla utilized polyphase currents that generated a rotating magnetic field.  Below is a diagram of currents from three conductors in a three-phase system.  The currents generate a rotating magnetic field that turns a motor. 

Figure 12:  Diagram of three alternating electric currents in a three-phase system.  Each current is one-third of a wavelength out of phase.  Together the three currents produce a rotating magnetic field that can be used to power an electric motor.

The basic operation of a simple AC motor was shown in Fig. 4.  The rotating coil converts electromagnetic energy driving the current into the rotational kinetic energy of the loop of wire.  A drawback of the simple AC motor shown in Fig. 4 is that the system requires very high voltages to produce significant amounts of mechanical energy.  The high voltage can cause sparking at the brushes; in the earliest motors the sparking could cause breakdowns or fires in the systems.  In addition, the brushes needed frequent maintenance to avoid breakdowns.  A much more stable system is the induction motor, where the electric current is induced in the rotating coils rather than being supplied to them.  Tesla’s system involved induction motors with alternating magnetic fields supplied by a polyphasic AC current.  Tesla’s 1888 patent for his induction motor is shown in Fig. 13. 

Figure 13:  Nikola Tesla’s 1888 patent application for an induction motor.  This motor was widely used in the electric power industry.

The Tesla Electric Company widely publicized its AC generating system, through a May 1888 demonstration at a meeting of the American Institute of Electrical Engineers.  George Westinghouse, CEO of the Westinghouse Electric & Manufacturing Company, became aware of Tesla’s system and realized that this induction motor would be ideal for Westinghouse’s own AC system.  Westinghouse paid the Tesla Electric Company a substantial amount of cash to market their system, and he hired Tesla as a consultant at Westinghouse Electric for a fee equivalent to nearly $60,000 per month in today’s dollars.  

It appeared that Tesla had achieved the financial independence he had sought, and in addition it seemed that this arrangement would provide him with plenty of cash to broaden his research into new areas.  Unfortunately, Westinghouse found itself in a heated competition with the two major electrical energy producers, Edison Electric with its DC power, and another AC-generating company Thomson-Houston.  The three firms were all competing to gain a monopoly on contracts to electrify major cities.  This began a cutthroat competition among the firms that is now called the “war of the currents.”  We will review the war of the currents in the next section of this post.  Each company made strong claims regarding the superiority of its own systems, while bad-mouthing the reliability and safety of the competing firms. 

To make matters worse, a worldwide financial panic in 1890 saw cities cutting back on their spending.  The recession forced Westinghouse to scale back his operations.  This left Tesla without much of the financial support he had been promised by Westinghouse.  In 1896, Westinghouse gave Tesla a lump-sum payment of $216,000 in return for his patent rights.  This was part of a patent-sharing agreement between Westinghouse Electric and General Electric (a company created by the merger of Edison Electric and Thomson-Houston). 

The Tesla Coil:

Tesla then developed an AC device now called the Tesla Coil.  This was a system that used transformers to produce extremely high voltages with low current and high frequency.  The basic operation of a transformer was shown in Fig. 6.  Wires are wrapped around two sides of a magnet.  An alternating current is applied to the “primary” side.  This causes an induced voltage and alternating current in the secondary wires. 

The magnitude of the secondary voltage Vs is related to the primary voltage VP as the number of turns on the secondary NS to the turns on the primary NP, as shown by Eq. (5). Thus, if NS is 100 times NP, then the magnitude of the secondary voltage will be 100 times greater than the voltage on the primary circuit.  But from Eq. (6), the power across a transformer remains constant.  If the voltage in the secondary increases by a factor 100, the current in the secondary would be 100 times smaller than the primary current.  By creating a system with a huge number of turns on the secondary, Tesla was able to produce exceptionally large voltages on the secondary.  Tesla then developed a system that coupled a transformer with a capacitor and an air gap on the primary side, as shown in Fig. 14. 

Figure 14:  A circuit diagram for a Tesla coil.  The primary circuit contains a wire with a “spark gap” of air, coupled to a current loop and a transformer.  The secondary contains a wire with many more turns than the primary.  On the primary, the electric charge builds up on the sides of the capacitor, until the potential difference across the air gap is so large that a spark crosses the air gap.  This produces a very large change in voltage across the primary coil.  This induces an even larger voltage across the secondary coil, sufficient to send large sparks through the air.

The capacitor can be thought of as a sponge, that soaks up electric charges of opposite signs on the plates of the capacitor.  The voltage difference across the capacitor is the same as the voltage difference between the two balls on opposite sides of the air gap.  For sufficiently small voltages, no current will flow across the air gap, as under normal voltages the air is an insulator.  However, after a certain time the voltage across the air gap will be so great that a spark will shoot across the air gap.  The spark is caused by electrons flowing across the air gap, as shown in Fig. 15.  The spark causes a large change in voltage on the primary over a very short time.  Since the number of turns on the secondary is much greater than those on the primary, this will cause a much larger voltage difference on the secondary side. 

Figure 15: Normally, air is an insulator and electric currents will not flow through air.  However, if a sufficiently high voltage difference is formed across an air gap, a beam of electrons (a “spark”) will suddenly flow across the air gap.

This very large voltage can produce a very large spark from the secondary coil.  Figure 16 shows Tesla seated in a room with a Tesla coil that is producing massive sparks.  However, since the current associated with those sparks is tiny, they generally are not a health hazard. 

Figure 16: Nikola Tesla demonstrating a Tesla coil.  The device shown schematically in Fig. 15 will produce large sparks in the air.  The sparks are produced by a very high voltage, but combined with a very low current.

Now, the gigantic sparks produced in Tesla’s demo are primarily for visual effect.  However, the physics of the Tesla coil, involving AC currents, transformers, capacitors and induced voltages, had many practical applications.  The Tesla coil could produce electromagnetic fields of extremely high voltage, high frequency, and very low current.  Many present-day devices such as televisions and radios utilize devices based on the physics principles of the Tesla coil. 

Tesla widely displayed his Tesla coil in public demonstrations.  He could produce spectacular lightning bolts that traveled across a stage.  At the same time, he realized that variations of his devices might be used to transport signals across great distances without the use of wires.  He was never able to convert his ideas into useful devices, but he had anticipated the advent of wireless transmission of signals. 

The Columbian Exposition:

Westinghouse and Tesla had great success at the 1893 World’s Columbian Exposition in Chicago (which was originally timed to take place on the 400th anniversary of Columbus’ ‘discovery’ of the New World in 1492).  First, Westinghouse won a competition with Edison to light the Exposition with electrical power.  In addition to the fact that Westinghouse was able to convince the exposition jury that his AC electricity was superior, his bid for lighting the exposition was nearly 40% lower than Edison’s.  This resulted in a tremendous publicity coup for Westinghouse, as the Exposition was designed to highlight the latest in technology, and electric lighting was a spectacular feature of the fair.

Figure 17:The lighting display produced by Westinghouse and Tesla at the 1893 Columbian Exposition. Their AC system was able to power banks of fluorescent lights, and to light up the night. Visitors to the Exposition, most of whom relied on gas lights and candles for illumination, found the display to be awe-inspiring.

Also, Tesla put on demonstrations at the Electricity Building at the Exposition.  For one of his demonstrations, audience members could come onstage and hold a fluorescent light bulb.  When Tesla turned on his AC generators, the bulbs would light up, even though they were not connected to any wires.  The demonstrations were tremendously powerful in convincing people that AC-generated electricity was safe and reliable.  This was extremely important; as we will see in the “War of the Currents” section, Edison was making strong claims that AC power was dangerous and potentially deadly. 

Perhaps Tesla’s greatest achievement was the installation of an AC system to generate electricity at Niagara Falls, New York.  The basic idea was to divert some water from the upper Niagara River, above the falls, and then to let that water fall over the cliff above the lower rapids below the falls.  The water would gain kinetic energy as it fell, and the question was how best to convert this into electrical energy.  We will discuss this in detail in our section on the “War of the Currents.”  Suffice it to say that the AC-based system of Westinghouse and Tesla was deemed to be a better bet than the DC-based system championed by Edison.  A major role was played by Lord Kelvin (William Thomson), a physics professor at Glasgow and a world leader in electromagnetic theory.  Kelvin would later be an advisor to the Niagara Power project.  He had attended the Columbian Exposition in Chicago, where he had personally seen the Westinghouse-Tesla electrical generating system.   

A crucial aspect of the AC-based system was the use of transformers (shown in Fig. 6) to produce the electrical voltage and current.  The falling water would be used to turn turbines.  Energy from the spinning turbines was used to produce alternating-current electricity.  The electricity would then be carried by wires to the locations of factories or homes.  When electricity is carried over current-carrying wires, the currents heat the wires, and this heat represents energy lost in the system.  From Eq. (3), the amount of power P lost in a wire carrying current I is proportional to the square of the current in the wire.  In an AC circuit, the heat loss is minimized by making the current I as small as possible.  This is achieved by using a “step-up” transformer at the generating station.  This greatly increases the voltage V, and subsequently decreases the current I to a tiny level.  This results in minimal power losses, even when the electrical power is transmitted for very long distances. When the electricity reaches its destination, it is run through a “step-down” transformer, which decreases the voltage to the value desired at the end location.  For most homes that voltage is either 110 V or 220 V. 

The transformer only works with alternating current systems.  It is not possible to use this trick with DC current.  For this reason, direct-current electricity is transported at the same current level that is used at the end station.  Power losses in DC circuits are thus very large; the result is that DC current can only be transported a short distance from the generating station.  In Edison’s DC systems, that distance was roughly one mile.  Thus, electricity had to be generated within a mile of the locations where it was used. 

The Niagara Falls project turned out to be a great success.  The power generated from the turbines at the bottom of the Niagara Gorge was initially sent to Buffalo, NY, about 20 miles from the Falls.  However, subsequent expansions of the turbines and generators eventually allowed power to be sent as far as New York City.  At present, the Niagara Falls hydroelectric plants provide electrical power to much of the Northeastern United States. 

Figure 18:  The Niagara Power plant in the early part of the 20th century.  At the time of its completion, the Niagara power project was the largest in the U.S.  Initially, it generated electric power for the upstate New York region; however, with later upgrades it now supplies electricity to much of the Northeastern U.S. and Canada.

Other Tesla Projects: 

Around 1894, Tesla became aware of “invisible radiant energy;” he had noted that film had been damaged in his lab, and he began investigating the source of this energy.  It is speculated that Tesla may have seen images produced by what became known as X-rays, even before Wilhelm Roentgen’s 1895 announcement of this novel radiation.  Tesla made modifications to his Tesla coil to build machines that would produce X-rays. 

Tesla made some interesting observations regarding X-rays.  However, he also came to some incorrect conclusions that diminished his contributions to the field.  He noted that the X-rays produced skin damage.  However, he incorrectly attributed this damage to the ozone that was produced by X-rays passing through air, rather than being produced by the X-rays themselves.  Also, he maintained that the X-rays were longitudinal radiation (in a longitudinal wave, the vibrations of the field are in the same direction as the propagation of the radiation).  In fact, X-rays are a form of transverse electromagnetic radiation, as is visible light; the only difference is that X-rays have a much higher frequency than visible light or microwaves.   

Tesla also experimented on radio-controlled devices.  In 1898, he tried without success to convince the military that he could produce a radio-controlled torpedo.  Tesla also carried out many experiments in attempts to develop wireless transmission of electrical power.  Tesla’s ideas about wireless communications could have had a revolutionary impact had he been able to produce useful devices.  However, he spent a good fraction of his time attempting projects to send electrical signals through the Earth. 

Tesla’s Nobel Prize? 

On November 6, 1915, a news report from London stated that Thomas Edison and Nikola Tesla had jointly been awarded the 1915 Nobel Prize in Physics.  However, nine days later it was announced that the prize had been awarded to William Henry Bragg and Lawrence Bragg for their use of X-rays to analyze crystal structure.  This led to much speculation over whether the prize had initially been offered to Edison and Tesla.  Some biographers of Tesla have claimed that the Nobel Committee had indeed offered the prize to Edison and Tesla.  It was speculated that both Edison and Tesla had argued to the Nobel Committee that the other was unworthy of the award.  It was further suggested that both men said they would refuse the prize if the other person shared it.  Finally, there has been some speculation that the wealthy Edison refused the prize specifically so that Tesla would not receive the $20,000 monetary stipend that accompanied the award.  Eventually, neither Edison nor Tesla ever won a Nobel Prize, although it is known that Edison was one of the nominees for the award in 1915, and that Tesla was a nominee for the award in 1937. 

Nikola Tesla’s Unconventional Beliefs:

In many respects, Tesla was self-taught in science.  He relied heavily on his own intuition and his ability to construct ingenious machines.  However, this left him with some notable lapses in his scientific knowledge.  For example, Tesla refused to believe that atoms had a substructure, i.e., an atomic nucleus made up of protons and neutrons, surrounded by electrons.  As a result, Tesla denied that atoms contained sub-units called electrons, and he refused to believe that electric currents were frequently caused by the motion of electrons.  In Tesla’s view, atoms could not be broken down into smaller components, despite experimental discoveries of electrons and the atomic nucleus by his contemporaries J.J. Thomson (1897) and Ernest Rutherford (1911), respectively. 

Tesla also believed in the reality of the “luminiferous ether;” that is, he believed that space was permeated with this transparent substance, and that light waves traveled with a characteristic speed through the ether.  Tesla’s views contradicted Einstein’s special theory of relativity, which stated that the ether did not exist, and also postulated that the speed of light was the same with respect to all observers. 

Tesla also disagreed with Einstein’s general theory of relativity.  In this theory, gravity can be viewed as a ‘warping’ of space-time in the vicinity of matter.  Tesla stated that “To say that in the presence of large bodies space becomes curved is equivalent to stating that something can act upon nothing.  I, for one, refuse to subscribe to such a view.”  For roughly 45 years, Tesla claimed to be working on his own theory of gravity.  In 1937, Tesla wrote in a letter that he had achieved a “dynamic theory of gravity.”  This theory, he claimed, would “put an end to idle speculations and false conceptions, as that of curved space.”  He claimed to have worked out his theory “in all details,” and promised that he would soon announce it to the world.  This theory was never forthcoming, and no details were found in Tesla’s papers following his death. 

Tesla was also an outspoken advocate for eugenics.  He was a secular humanist, and one of his beliefs was that religion had interfered with “the ruthless workings of nature.”  A misplaced sense of pity motivated by religion had allowed society to tolerate procreation by the unfit.  Tesla stated that “The only method compatible with our notions of civilization and the race is to prevent the breeding of the unfit by sterilization and the deliberate guidance of the mating instinct.”  Tesla argued that improvement of the race required that “We must make marriage more difficult.  Certainly no one who is not a desirable parent should be permitted to produce progeny.  A century from now it will no more occur to a normal person to mate with a person eugenically unfit than to marry a habitual criminal.”  

Tesla’s Later Years:

In 1899, Tesla set up a laboratory in Colorado Springs.  He was able to build Tesla coils outdoors at very high altitude, where he was able to build much larger coils than in his old lab in New York City.  There, Tesla carried out several experiments in wireless transmission.  He caused a sensation in 1900 when he began receiving electromagnetic signals that he believed originated from another planet.  Newspapers published breathless articles claiming that Tesla had discovered communications from Mars.  It is now believed that Tesla was receiving signals from another researcher who was generating radio signals; some believe that he may have picked up signals from Guglielmo Marconi’s radio transmissions from Europe. 

Eventually, Marconi succeeded in transmitting an electromagnetic signal from England to Newfoundland.  At that point, Tesla requested a large contribution from his major financier, J.P. Morgan.  Tesla proposed to build a much more powerful transmitting system than Marconi’s.  However, Morgan had seen very little return from his previous investment with Tesla, and Tesla had been scooped by Marconi.  Thus, Morgan turned down Tesla’s repeated requests for funds. 

In 1917, Tesla proposed a method to detect submarines underwater by bouncing high-frequency EM waves off the submerged object and observing the reflected waves.  Tesla’s methods anticipated the later development of radar; however, a fatal flaw in his reasoning was his (incorrect) belief that radio waves would propagate long distances through water.  In 1928, Tesla proposed an airplane that would take off by initially flying straight up, and then converting to horizontal flight.  Although he made very little progress on a workable model, he had anticipated today’s VTOL (vertical takeoff and landing) planes. 

Over the years, Tesla’s sources of funding dried up.  However, he maintained his habit of living in expensive hotels and frequenting exclusive restaurants.  Eventually, he settled on an unusual lifestyle.  He would live in an upscale hotel and dine at its restaurant.  Over time, he would run up a gigantic tab.  He was able to maintain this for many months because of his reputation as a genius.  However, eventually he would be evicted and sued by the hotel.  He would then move to another hotel and begin again. 

In 1934, having been evicted from a few hotels, Nikola Tesla arrived at the New Yorker Hotel, where he would remain for the rest of his life.  He was supported by a monthly grant from Westinghouse Electric.  The company knew that he would refuse to accept charity, so the money was described as a consulting fee, even though Tesla did no more work for Westinghouse. 

From time to time, Tesla would report stupendous breakthroughs, but they never materialized.  In 1932, he announced the invention of a motor that would run on cosmic rays.  Next, he announced the discovery of a new form of energy.  With this energy, he claimed he could devise a motor that would cost almost nothing to run and would last for 500 years.  In 1934, he claimed to have invented a “death ray.”  He alleged that he had developed an oscillator that could destroy the Empire State Building using only 5 pounds of air pressure.

In fall 1943, Tesla was crossing the street outside the New Yorker Hotel when he was struck by a taxi.  He sustained serious injuries, although he refused to see a doctor.  Apparently, Tesla never fully recovered from his injuries.  In Jan. 1944, Nikola Tesla was found dead in his room at the New Yorker.  The cause of death was listed as coronary thrombosis. He was 86 years old.  After Tesla’s death, the FBI seized his belongings; they were apparently looking for his death ray or for any machines that could have military uses. 

The FBI turned Tesla’s belongings over to MIT professor John G. Trump (the uncle of former president Donald Trump).  Trump concluded that Tesla’s devices and notes “did not include new, sound, workable principles or methods for realizing such results.”  After his death, Tesla was lauded as one of the great scientists and inventors of his time.  He had nearly 300 patents for his inventions.  Tesla often worked by himself, and had only a few close friends.  However, in his middle age he was good friends with Mark Twain.  One of his friends Julian Hawthorne said that “Seldom did one meet a scientist or engineer who was also a poet, a philosopher, an appreciator of fine music, a linguist, and a connoisseur of food and drink.” 

Tesla invented several of the turbines, generators and induction motors that are now staples of the AC electrical power industry.  Many of his designs were revolutionary; his skill and ambition made it possible to generate vast amounts of power at Niagara Falls, and to transmit it for very long distances.  Tesla also anticipated later breakthroughs in wireless transmission.  Because of his lack of formal education, Tesla was largely self-taught.  Occasionally, this would cause him to make elementary mistakes.  However, in many cases this gave him a rare ability to “think outside the box,” and helped lead him to unique insights in the field of applied electromagnetism. 

The “War of the Currents”

The so-called “war of the currents” played out during the 1880s and 1890s.  It involved a number of companies that were competing for the lion’s share of the booming market for electricity.  After Thomas Edison produced the first commercially viable incandescent lights, he formed the Edison Electric Company.  Edison’s system used direct-current (DC) power.  This system produced a constant electric current from the generating point to the point where the electricity was used for lighting, running motors, etc.  As a result, the current could not be transported for long distances, otherwise power losses from heating the wires became too great.  The Edison Electric Company typically located its generating stations within a mile of the point of usage. 

The Edison electrical system tended to use copper wires that were buried underground, and the voltage at the generating plant was the same as that used in factories or homes.  For the center of a city, provided that underground wiring could be laid, the Edison system worked fairly well.  Edison’s electrical plants produced rather low voltage, and his Edison Electric company generally focused on incandescent lighting in residences and indoors in factories.  Because his DC power could only supply electricity over limited distance, Edison set up generating stations in the center of relatively large cities.  People who lived in rural areas were simply out of luck in obtaining DC power; and even in cities, the location of Edison’s generating stations ensured that there were “pockets” of residential neighborhoods that had no electric power. 

As we have mentioned, AC generating plants could produce electricity at a source, and then greatly increase the voltage (and decrease the current) by means of a step-up transformer.  When the electricity reached its terminus, a step-down transformer could decrease the voltage to the value used in a home or factory.  Many of the early applications of AC electricity were for arc lighting.  This was used for outdoor streets, factory yards, or the interior of large factories.  Whereas DC systems used 110-Volt circuits and the current-carrying wires were generally installed underground, arc lighting by AC electricity used much higher voltages, often in the range of 3,500 Volts.  The AC wires were strung along poles high above ground level.  At that high voltage, sparking could cause fires or short the wires, and it could be quite dangerous to come in contact with live wires. 

The growth of AC electricity was bolstered by a number of European technological developments.  The “step-up” and “step-down” transformers were greatly improved by a group of Hungarian engineers working at the Ganz Works in Hungary.  Most transformers in use today rely on techniques developed at Ganz. 

In 1884 George Westinghouse, who had made his name by developing air brakes for railroads, began to diversify into electrical power.  Initially, Westinghouse began by developing DC systems.  However, Westinghouse had a big disadvantage.  Since Edison had patented nearly every aspect of DC power generation and incandescent light bulbs, Westinghouse was constantly fighting with Edison over patent rights.  Westinghouse then read about European developments in AC systems.  He realized that AC power had several advantages over DC. 

Figure 19:  Engineer and entrepreneur George Westinghouse.  Westinghouse initially developed air brakes for railroads, then branched out to produce and distribute electricity, in collaboration with Nikola Tesla.

By 1888, Westinghouse’s AC-powered electricity was rapidly gaining popularity.  By the end of 1887, Westinghouse had built 68 AC-generating facilities, compared to 121 by Edison Electric.  And another company that produced AC electricity, the Thomson-Houston company, had another 22 facilities. Edison realized that his own electric company was in danger of being scooped by AC power.  As early as 1886, just as Westinghouse was beginning to install AC systems, Edison claimed “Just as certain as death, Westinghouse will kill a customer within six months after he puts in a system of any size. He has got a new thing and it will require a great deal of experimenting to get it working practically.” For the next few years, Edison continued to assert that AC was inherently dangerous, and that it posed a serious threat to human health.  This set off a series of claims and counter-claims regarding AC electricity. 

Edison’s allegations occurred at a time when there was considerable uneasiness about the safety of AC power.  In locations such as New York City, areas above the streets were often clogged with hundreds of wires strung on poles.  Some were for electricity, others were telephone or telegraph lines, and they formed a dense network of cables.  Cables were often poorly insulated or badly constructed.  Cables for arc lighting often carried 3,000 Volts or more, and these could cause danger of electrocution if they were touched.  In addition, the high voltages associated with arc lighting would also cause sparks that could ignite fires.  Large AC generators at that time tended to use large “commutator brushes,” as shown in Fig. 5. Those large brushes required frequent maintenance; they would sometimes short out, and in addition they could cause large sparks that occasionally set off fires. So, the public was inclined to view with concern the machinery and cables that were used in AC electricity. 

A crucial event was the Blizzard of March 1888 in New York City.  Snow and ice accumulated on wires, bringing down telephone poles and their wires.  This is shown in Fig. 20. Telegraph, telephone and electric lines became so tangled that they had to be sawed apart.  A few workers were electrocuted in untangling this mess; and this heightened the public concern regarding the dangers of electric wires.  As Edison buried the copper wires used to distribute his DC currents, he was able to attack AC electricity for its unsafe power lines. 

Figure 20:  A series of tangled cables that were downed during a blizzard in New York City in March 1888.  A number of workers and New York citizens were killed when they came into contact with cables carrying high-voltage AC currents.

However, Thomas Edison’s claims about the dangers of AC power were seriously misleading.  To prove his point, Edison conspired with the operators of humane societies to electrocute animals.  In part, this was because electrocution was believed to be a more humane method of euthanizing animals than other techniques.  However, Edison and his confederates made a point of always euthanizing animals using AC power.  Furthermore, a confederate of Edison gave public demonstrations intended to prove that AC electricity could be lethal, while DC electricity was safe.  He carried out presentations where animals would be killed with 300 V of AC electricity, while 300 V of DC electricity would only shock them. 

Animals can be electrocuted if electric current passes through their body.  Provided that the current flows along the outside of the body, electrocution will generally not occur.  Thus, there are cases where a person could be exposed to very large voltages and still survive.  Many people are struck by lightning at phenomenally high voltages; provided that the current flows only on the outside of the body, they may survive the lightning strike. The danger from electric currents depends on the frequency of the EM waves.  For most residential purposes the frequency of AC electricity is about 60 Hertz (60 cycles per second).  If electricity enters the body, the current may disrupt the heart and thus cause death.  Electricity can also disrupt the brain, and a frequency of 60 Hertz can interfere with brain processes.  DC currents are likely to be somewhat less deadly than AC electricity.  So, Edison’s contention that DC currents were not fatal at lower voltages than AC currents was not entirely false. 

A major source of allegations about the dangers of AC power was a New York electrical engineer named Harold Brown.  Brown also alleged that AC power was hazardous to health.  He stated that “Among electric lighting men [a wire carrying AC currents] is appropriately called ‘undertaker’s wire’, and the frequent fatalities it causes justify the name.” To prove this, he conducted public demonstrations where animals were killed with AC electricity.  For example, on July 30, 1888, Brown gave a demonstration at Columbia College in New York to an audience of 700 government officials and electricians.  Brown hooked up electrodes to a dog’s front and rear paws; he then administered a series of electric shocks to the animal. 

Initially, he administered shocks of DC current ranging from 100 to 1,000 Volts.  The dog jumped at each shock but remained alive.  He then repeated this with AC current.  At 300 Volts, the dog immediately died.  When he attempted to repeat these measurements on a second dog, a representative from the ASPCA halted the demonstration and fined Brown $250.  Undeterred, Brown conducted further demonstrations with dogs and cats.  In making his claims, Brown was secretly collaborating with Thomas Edison.  Furthermore, he invariably used equipment from Westinghouse Electric to murder these animals. 

In fall 1888, the magazine Electrical Engineer published Harold Brown’s assertion that AC electricity from Westinghouse had caused at least 30 deaths.  George Westinghouse challenged Brown’s claim, and the magazine investigated this issue.  They found that only 2 of the 30 deaths mentioned by Brown could be attributed to Westinghouse’s equipment. 

Next, Brown and Edison constructed an “electric chair” to execute criminals who had received the death penalty.  They capitalized on the belief that electrocution was a more humane form of execution than previous methods: hanging; a firing squad; or injection of lethal chemicals.  However, Brown and Edison argued that the electric chair demonstrated that AC power was potentially lethal. Engineers constructed a wooden chair with restraints that connected it to AC electricity.  The generator that powered this circuit was conspicuously labeled “Westinghouse Electric” (the generator was surreptitiously obtained, as Westinghouse was understandably opposed to allowing his equipment to be used as a means of portraying AC power as lethal). 

Figure 21: The electric chair used in the state of Florida to execute criminals who had been sentenced to death.  Harold Brown and Thomas Edison offered the electric chair as proof that AC electricity was inherently dangerous and potentially lethal.

In September 1888, the New York Medico-Legal Commission met with Harold Brown in West Orange, New Jersey.  There, Brown had set up a demonstration for the committee.  Brown electrocuted four calves and a horse using 750 Volts of AC electricity.  Figure 22 shows Brown electrocuting the horse.  Thomas Edison, who was colluding with Brown in these matters, attended the demonstration.  Not only did Edison remark that this demo showed the dangers of AC electricity, he suggested a term to be used for victims of electrocution – they were “Westinghoused.”  Following Brown’s demo, the Commission recommended that 1,000 – 1,500 Volts of AC electricity be used for the electric chair.  Newspaper reports emphasized the fact that the electric chair voltages were only half the amounts used for arc lighting. 

Figure 22:  A drawing showing Harold Brown executing a horse using AC electricity.  A schematic diagram of the electrical circuit is also shown.

Unfortunately, the first use of an “electric chair” for an execution did not go well.  On Aug. 6, 1890, convicted murderer William Kemmler was executed at New York’s Auburn Prison.  Kemmler received 1,000 Volts of AC current, but it did not kill him.  The generator had to be re-charged and Kemmler next received a 2,000-Volt shock.  “Blood vessels under the skin ruptured and bled, and the areas around the electrodes singed.  The entire execution took about eight minutes.”   George Westinghouse later commented that “They would have done better using an axe,” and a reporter who witnessed the execution wrote “It was an awful spectacle, far worse than hanging.”  

The Curious Case of Topsy the Elephant:

Topsy the elephant had been captured in Southeast Asia and shipped to the U.S. when she was a baby.  She was then exhibited in various circuses.  Many reports attest to the fact that she was brutally treated by several trainers.  At some point she killed at least one of her trainers.  Later in her life she ended up at Luna Park on Coney Island.  In 1903, the staff decided to euthanize Topsy.  They discussed various means to execute the animal, and eventually settled on hanging.  However, the Society for Prevention of Cruelty to Animals protested this as inhumane.  After negotiations with the SPCA, it was agreed that they would use a combination of methods, including poisoning and electrocution. 

On Jan. 4, 1903, the Luna Park staff fed Topsy poisoned carrots, and staff from Edison Electric Company fitted her with copper elements attached to her legs.  The event had been publicized, attracting a crowd of 1,500 people and a film crew from Edison’s moving picture company.  Topsy was subjected to a jolt of 6,600 volts of AC electricity, and she immediately keeled over.  The film of Topsy’s execution has circulated and can be found today, although we will not provide you with a link.   

Since the elephant’s execution was arranged by staff from Edison’s electric company and the event filmed by his film company, many people believe that Topsy’s death was part of Edison’s effort claiming that the AC power associated with Westinghouse was inherently dangerous.  The episode seems to jibe with the campaign by Harold Brown (who conspired with Thomas Edison), who staged a series of public electrocutions of cats, dogs, cattle and horses using Westinghouse’s AC electricity. 

However, there are problems with this claim.  First, even though Edison’s electric and movie companies were involved in Topsy’s killing, there is no direct evidence that Edison was present at this event; furthermore, no papers in Edison’s archives make any mention of Topsy.  Finally, by 1903 the “war of the currents” had been over for more than a decade.  By this point, Edison would have had almost nothing to gain from this stunt.  After 1892, it was almost universally accepted that AC electricity was superior to DC because of the ease with which AC power could be transported over long distances.  Soon after this, Edison himself would express remorse that he had not embraced AC power at a much earlier date, so that he could have emerged triumphant in the area of electricity generation. 

So, although the ‘Topsy’ story appeared to be part of Edison’s campaign against AC electricity, there is no direct proof of his involvement with this event, and several reasons to doubt that this was staged by Edison. 

Edison Loses the AC-DC Battle:

During the 1880s, Thomas Edison used his daunting scientific reputation and economic power in an attempt to persuade American cities that his DC power was both safer and more reliable than the AC power associated with Westinghouse and Tesla.  However, the scales began to tip rapidly in Westinghouse’s favor.  First, in August 1889 there was a burglary at Harold Brown’s office in New York City.  Among papers stolen from Brown were a series of letters that outlined in great detail the collusion between Edison and Brown.  This was very damaging to Edison, who had repeatedly denied any direct involvement with Brown. 

Next, Nikola Tesla’s induction motors and generators did away with the commutator brushes in earlier devices.  This removed several unsafe features previously associated with AC power.  Next, the adoption of “step-up” and “step-down” transformers from the Ganz group allowed AC electricity to travel large distances from the power source to cities and residential homes.  Edison’s DC power, on the other hand, could only travel a mile or less from the generating station.  For Edison, this required installation of many generating stations, in addition to the cost of running transmission wires underground.  In cities, Westinghouse was able to provide residential lighting at much lower prices than Edison; and in rural areas AC power was the only possible choice. 

Figure 23: Some of the indoor lighting provided by Westinghouse and Tesla at the 1893 Columbian Exposition in Chicago.  Electric lighting was one of the most impressive displays of new technology at this World’s Fair.

As we mentioned earlier, a major triumph for Westinghouse and Tesla was winning the competition to supply electricity to the Columbian National Exposition in Chicago in 1893.  This was crucial in two respects: first, the million attendees at the Exposition were awed by the lavish displays of electricity, as shown in Figs. 17 and 23.  For most of the Exposition visitors, electric lighting was something new, as they were accustomed to gas lamps on streets, and either gas lamps or candles in their homes. The Columbian Exposition was intended to demonstrate new technologies to the American public, and the electric lighting of the Fair was a tremendous public-relations success.  In addition, the displays by Nikola Tesla at the Electricity Pavilion at the Exposition were also spectacular.  Spectators were wowed at being able to hold a light bulb in their hand and have it light up using wireless transmission.  Also, Tesla was able to produce eye-popping bolts of lightning using his Tesla coils (see Fig. 16). 

The next major coup for Westinghouse was the competition to design the system for producing electricity from the kinetic energy of water that traveled over the cliffs below Niagara Falls.  Previously, a canal had been built that diverted some water from above the Falls.  The canal traveled parallel to the cliffs of the Niagara Gorge.  Water was then diverted to fall over the gorge.  The falling water then powered a series of mills and other companies.  Figure 24 shows the Niagara Gorge region before installation of the electric power generating facility. 

Figure 24: Prior to the Niagara Power Project, a canal had diverted water from above the Falls.  Water from the canal fell over the Niagara Gorge, where it powered a number of mills and factories, as shown in this photo.

In 1892, a competition was launched to determine the most efficient method of electricity generation from the water falling over the Niagara Gorge.  An “International Niagara Commission,” chaired by renowned physicist Lord Kelvin, met in London to review proposals for this project.  Seventeen proposed projects were reviewed; they ranged from a system using pneumatic pressure to one requiring ropes, springs and pulleys.  There were also proposals to use direct current electricity, including one endorsed by Thomas Edison. However, the commission rejected all seventeen of the power-generating proposals.   

The commission then invited George Westinghouse to submit a proposal using AC power generation for the Niagara Power project.  The Westinghouse proposal made widespread use of Tesla’s inventions and patents for high-power generators and motors.  A major benefit favoring Westinghouse over Edison was the scientific expertise of the Niagara Power Commission.  With lawyers and businessmen, Edison could use his fame and reputation to cast doubt on AC power.  But against Lord Kelvin, one of the world’s greatest authorities on electromagnetism, Edison’s claims could be easily refuted.  Besides, Lord Kelvin had previously visited the Columbian National Exposition and had observed Westinghouse’s AC system in action. 

Figure 25 is a schematic illustration of the general principles of a hydro-electric plant.  A dam is built to hold back a large body of water.  Water is sent down a long tunnel or penstock; the water gains kinetic energy as it moves to lower elevation.  The fast-moving water flows past a turbine and starts the turbine rotating.  The energy of the rotating turbine is used to power a generator (shown in Fig. 26), which converts this kinetic energy to alternating-current electrical energy.   The electricity is then carried by power lines over long distances.  At the generating station, “step-up” transformers produce very high voltage and extremely small current.  Because the current is so low, the high-voltage power lines lose very little energy to heat dissipation (see Eq. 3).   Then, at the final destination, “step-down” transformers decrease the voltage to its final value in homes or factories; this is generally 110 V in the U.S. 

Figure 25: A schematic illustration of the operation of a hydroelectric power plant.  A dam holds a large body of water.  Water is sent down a long tunnel where it gains kinetic energy.  The water then activates a turbine, and the rotational kinetic energy of the turbine activates a generator, which produces electric power.

Figure 26: A bank of generators at the Niagara Falls Power Project built by Westinghouse using Tesla’s designs.  The generators produce electric power that is then transported by high-voltage lines to the northeastern United States.

Figure 27: A label on the first generators used at the Niagara Falls Power project.  The generators were built by the Westinghouse company using patents that had been secured by Nikola Tesla.

The original Niagara Falls Power Company supplied electricity to the city and to Buffalo, NY, about 20 miles away.  Later upgrades to the power grid allowed power to be transmitted as far as New York City.  There have since been major power plants constructed on both the American and Canadian sides of the Falls.  Electric power generated at the Falls now supplies electricity to much of the power grid of the Northeast United States, as well as Northeastern Canada. 

By the end of the 19th century, it was well established that AC power held a great advantage over the DC power espoused by Edison.  A number of cities that had initially installed DC electricity from Edison Electric replaced their systems with AC power.  A few factories retained their own DC generating systems for relatively long periods of time; and some small electrical systems such as elevators continued to run on DC power well into the 20th century.  One of the final holdouts was New York City’s Broadway theaters; they operated on DC power as late as 1975.  However, when the musical A Chorus Line introduced computerized lighting controls and thyristors for dimming, Broadway’s other theaters finally converted to AC power.  On Nov. 14, 2007, New York’s Consolidated Edison shut down the last remaining DC power generators.  Customers who still used DC were supplied with AC-to-DC rectifiers.  In San Francisco, Pacific Gas & Electric still provides DC power to a handful of customers, mainly for operating elevators. 

In 1892, Thomas Edison’s financial backers J.P. Morgan and Anthony Drexel forced the Edison Electrical Company and another major electricity company, Thomson-Houston, to merge to form a single new company.  Although Edison initially insisted that the merged company had to contain the name “Edison,” he lost that battle and the merged company was called the General Electric Company.  At this time, General Electric switched over to AC electricity, a clear sign that the DC-AC battle had been resolved in favor of alternating current. 

The formation of General Electric was the culmination of a major series of mergers amongst electric companies.  The hundreds of small electric companies across the country rapidly merged into large conglomerates such as Westinghouse and General Electric.  The New York Edison electric generating company in lower Manhattan became part of Consolidated Gas in the late 1800s.  As electric sales began to dwarf those of gas, that company incorporated as Consolidated Edison in 1936. 

There is a movie, called The Current War, based on the Edison-Tesla-Westinghouse conflict. It was released in 2017 and stars Benedict Cumberbatch as Edison, Nicholas Hoult as Tesla, and Michael Shannon as Westinghouse. Much of the movie is fact-based. The movie received mixed reviews, and the events reviewed in the movie are best appreciated if one knows the details of this conflict beforehand.


The “war of the currents” is often described as a bitter scientific feud.  However, we prefer to view it as an economic power struggle.  Having invented the incandescent light bulb, Thomas Edison proceeded to invent and patent a vast array of devices to produce and transport electricity.  The Edison Electric Company zealously protected its intellectual property.  A phalanx of lawyers guarded his inventions against patent infringement, whether real or imagined.  And since Edison Electric had a head start on most other electric companies, competitors found themselves paying large sums of money to purchase rights from Edison, and to defend themselves against patent-infringement lawsuits.  In fact, one of the reasons that George Westinghouse was initially drawn to AC electricity is that he thought it would not be subject to lawsuits from Edison (Westinghouse was wrong here – he spent considerable time and money defending his AC devices from lawsuits by Edison). 

Initially, many cities signed up for Edison’s DC power because they were convinced by Edison’s assurances and his fame as an inventor.  After Westinghouse entered the electric-power field, scientists and engineers realized the enormous advantages of AC power.  Edison and Westinghouse found themselves competing to install electric power in cities, and Edison saw a direct threat to his dream of extending his electric-power stations across the U.S. As Edison began to lose customers to Westinghouse, he hit upon the idea of branding AC power as inherently dangerous and potentially lethal. 

One might ask: at what point did it become clear to Edison that his claims about AC electricity were false or misleading?  One would have to think that he realized this either from the start, or very soon after he made these claims.  Edison secretly conspired with Harold Brown, who carried out public demonstrations where animals were killed with AC electricity.  In these demonstrations, Brown went to great lengths to show that 300 V of AC electricity would kill an animal, while the same voltage of DC power was not lethal.  Edison also claimed that it was extremely difficult to properly ground AC circuits; thus, a person in their home might be electrocuted if they touched a doorknob or piece of metal that was not properly grounded.  In his campaign, Edison called AC electricity “the electrocutioner’s currents.”     

For a short period of time, Edison’s claims were effective.  He used his great prestige to convince cities that they should use his own DC generating stations to provide electricity to light their homes and power their streetcars.  And he was helped by the fact that arc lighting powered by AC electricity was responsible for fires and deaths of workers who touched improperly grounded wires.  Edison suffered a major setback when it was revealed that he was secretly conspiring with Harold Brown.  However, a turning point was reached when Westinghouse’s AC electricity, using machines patented by Tesla, won the commission to light the 1893 Columbian Exposition in Chicago.  Westinghouse next won a competition to build AC generators and transformers for the Niagara Falls Power Commission.  Those events happened at almost the same time that Thomas Edison’s financial backers, led by J.P. Morgan, forced him to merge his Edison Electrical Company with a rival group, the Thomson-Houston Company, that utilized AC electricity.  After that, the giant electrical conglomerate General Electric that was formed from this union focused almost exclusively on AC electricity. 

In summary, we agree with the statement by Ivy Roberts on her “Local Public Square” site: “The battle of the currents was never really about determining which system was best.  It was, instead, a rivalry between two industrial giants, with helpless animals and line workers as collateral damage.” 

The “War of the Currents” thus ended with a complete victory by the AC Westinghouse-Tesla firm over Edison’s DC power generation.  However, Edison was able to console himself with the reputation and fortune that he made from his invention of the phonograph, the incandescent electric bulb, and the motion picture industry.

Source Material:

Wikipedia, Thomas Alva Edison

Wikipedia, Nikola Tesla

Wikipedia, George Westinghouse  

Wikipedia, War of the Currents  

Tesla Science Center, Columbian Exposition  

Anna Sproule, Thomas Alva Edison: the World’s Greatest Inventor, Blackbirch Press, 2000. 

The Franklin Institute, The Wizard of Menlo Park,

National Park Service, Thomas Edison

Ivy Roberts, The Dirty Industrial Rivalry That Determined Whether America’s Electricity Would be AC or DC, Zocalo Public Square, June 5, 2019

Nathan Chandler, Why Did Edison Electrocute an Elephant?  How Stuff Works,

Tony Long, Jan. 4, 1903: Edison Fries an Elephant to Prove His Point, Tony Long, Wired, Jan. 4, 2000

Library of Congress, Inventing Entertainment: The Early Motion Pictures and Sound Recordings of the Edison Companies,

John Joseph O’Neill, Prodigal Genius: The Life of Nikola Tesla, Ives Washburn, 1944

Nikola Tesla: The Genius Who Lit The World, documentary film, 1994

PBS, Tesla: Life and Legacy – Poet and Visionary,

The Tesla Science Center at Wardenclyffe

Paul Ratner, Why Nikola Tesla’s Greatest Achievement May Be in Niagara Falls

Wikipedia, Niagara Falls Hydraulic Power and Manufacturing Company

Mark Essig, Edison and the Electric Chair: A Story of Light and Death, Bloomsbury Publishing, 2009. 

Jill Jonnes, Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World, Random House 2003