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This article is a biography of Nikola Tesla.

Early years

Tesla was born "at the stroke of midnight" with lightning striking during a summer storm. He was born in Smiljani near Gospić, Lika, (the a Military Frontier of Austro-Hungarian Empire, now in Croatia). The midwife commented, "He'll be a child of the storm," to which his mother replied, "No, of light." Tesla was baptised in the Old Slavonic Church rite. His Baptism Certificate reports that he was born on June 28 (Julian calendar; July 10 in the Gregorian calendar), and christened by the Serb orthodox priest, Toma Oklobdžija.

His Serb father, the Rev. Milutin Tesla, was a priest in the Orthodox Metropolitanate of Karlovci which gathered to Serbs of the "Greek-rite" as they were legally referred to in Austria-Hungary at the time. His mother, Đuka Mandić, from a prominent Serb family of the Banija, made home craft tools. He was one of five children, having one brother and three sisters. His godfather, Jovan Drenovac, was a Captain in the Krajina army. His family moved to Gospić in 1862. Tesla went to school in Karlovac (Austria-Hungary), then studied electrical engineering at the Austria Politechnic in Graz, Austria (1875). While there, he studied the uses of alternating current. He also developed a telephone repeater (or amplifier).

In 1881 he moved to Budapest to work for the telegraph company, American Telephone Company. On the opening of the telephone exchange in Budapest, 1881, Tesla became the chief electrician to the telephone company, later engineer to the Yugoslav government and the country's first telephone system. Tesla invented a precursor to modern wireless telephone, known as a telephone repeater](or sometimes an amplifier). The device could act as an audio speaker (not an audio transducer). The device had its resonance tuned to a particular frequency of other repeaters to communicate between each. In 1916, Tesla described the prior developed audio transducers. According to Tesla, it was the "... implest ways the low frequency gave audible notes. placed a conductor, a wire or a coil, and then Tesla would get a note characteristics of the audible note". The audible sounds were of the quality of the telephones diaphragms of that period of time. The invention was never patented nor released publicly (till years later by Tesla himself). The device also contained the characteristics of modern wireless telephones.

For a while he stayed in Maribor. He was employed at his first job as an assistant engineer. Tesla suffered a nervous breakdown during this time. In 1882 he moved to Paris to work as an engineer for the Continental Edison Company. He worked designing improvements to electric equipment. In the same year, Tesla conceived of the induction motor and began developing various devices that use rotating magnetic fields (for which he received patents in 1888). Tesla visualized the rotating fields and thereby designed the induction motor. Tesla hastened from Paris to his mother's side as she lay dying, arriving hours before her death in 1882. Her last words to him were, "You've arrived, Nidzo, my pride." After her death, Tesla fell ill. He spent two to three weeks recuperating in Gospić and Tomingaj. All his life, Tesla kept a home-spun embroidered travel bag from his mother.

Middle years

In 1884, leaving the warfare of his birthplace behind, Tesla moved to the United States of America to accept a job with the Edison Company in New York City. He arrived in the US with 4 cents to his name, a book of poetry, and a letter of recommendation (from Charles Batchelor, his manager in his previous job).

Early employment

Tesla worked for Thomas Edison for a time. Edison offered him $50,000 for improvements in Edison's DC dynamos. Tesla worked nearly a year to redesign the inferior construction. Upon returning to Edison and inquiring about the $50,000, Edison replied, "Tesla, you don't understand our American humor." Tesla resigned. In 1886, Tesla formed his own company, Tesla Electric Light & Manufacturing. The initial financial investors disagreed with Tesla on his plan for an alternating current motor and eventually relieved Tesla of his duties at the company. Tesla was unemployed for a time.

Tesla worked on the streets of New York as a common laborer from 1886 to 1887 to raise capital to eat and for his next project. In 1887, he constructed the initial brushless alternate-current induction motor. He demonstrated the brushless two-phase one-fifth horsepower (150 W) induction motor to the American Institute of Electrical Engineers (now IEEE) in 1888. Also in 1888, he developed the principles of his Tesla coil. In the same period, he began working with Westinghouse, Westinghouse's Pittsburgh labs. Westinghouse listened to Tesla's ideas for polyphase systems. These systems would allow alternating current electricity to be transmitted over large distances.

X-rays and friendships

In April 1887, Tesla began investigating what would later be called X-rays using his own devices as well as Crookes tubes. He did this by experimenting with high voltages and vacuum tubes. His technical publications indicate that he invented and developed a special single-electrode X-ray tube. Tesla's tubes differed from other X-ray tubes in that they had no target electrode. He stated these facts in his 1897 X-ray lecture before the New York Academy of Sciences. The modern term for this is the bremsstrahlung process, in which a high-energy secondary X-ray emission is produced when charged particles (such as electrons) pass through matter.

In 1891, Tesla became a naturalized American citizen. Also in this year, Tesla established his Houston Street laboratory in New York. He lit vacuum tubes wirelessly in the lab, providing evidence for the potential of wireless power transmission. Around this time, Tesla developed a close and lasting friendship with author and humorist Mark Twain. They spent quite a bit of time together in Tesla's lab and other areas. Tesla's closest friends were writers and artists. Tesla's also befriended R. A. Jonson, who adapted several poems of the Serbian poet Jovan Jovanović Zmaj (and which were translated into English by Tesla).

When he was 36 years old, the first patents concerning the polyphase power system were granted. He continued researching rotating magnetic field principles and polyphase power distribution. By 1892, Tesla became aware of certain characteristics later identified by Wilhelm Conrad Röntgen as effects of X-rays. He performed several experiments (including taking photographs of the bones of his hand) but did not make his findings widely known. Much of his research was lost in the 1895 Houston Street lab fire. He did obtain pictures of the human body with X-rays and subsequently sent the images to Röntgen. His later X-ray experimentation by vacuum high field emissions led him to alert the scientific community first to the biological hazards associated with X-ray exposure.

Wireless and the AIEE

Tesla served as the Vice-President of AIEE, the American Institute of Electrical Engineers (now part of the IEEE) from 1892 to 1894. From 1893 to 1895, Tesla investigated high frequency alternating currents. He generated one million volts of alternating currents using a conical Tesla coil. He developed the skin effect in circuitry, designed tuned circuits, invented a machine for inducing sleep, cordless gas discharge lamps, and transmitted electromagnetic energy without wires, effectively building the first radio transmitter.

In St. Louis, Missouri, Tesla made the first public demonstration of radio communication in 1893. Addressing the Franklin Institute in Philadelphia, Pennsylvania and the National Electric Light Association, he described and demonstrated in detail the principles of radio communication. The apparatus he used contained all the elements that were incorporated into radio systems before the development of the vacuum tube.

World's Fair Exposition

Main article: World Columbian Exposition

At the 1893 World's Fair, the World Columbian Exposition, in Chicago, Illinois, celebrating the 400th anniversary of Christopher Columbus' first voyage to America, an international exposition was held, in which, for the first time, a building was devoted to electrical exhibits. It was a historic event and the beginning of a revolution as Tesla and Westinghouse introduced visitors to AC power by providing AC energy to illuminate the World Columbian Exposition. The public at large observed firsthand the qualities and abilities of AC power. All the exhibits were from commercial enterprises. Edison, Brush, Western Electric, and Westinghouse all had exhibits. General Electric Company (backed by Edison and J.P. Morgan) proposed to power the electric fair with direct current at the cost of one million dollars.

Westinghouse proposed, armed with Tesla's AC system, to illuminate the exposition for half as much. Tesla's high-frequency high-voltage lighting produced more efficient light with less heat. A two-phase induction motor was driven by current from the main generators to power the system. Edison tried to prevent the use of his light bulbs with Tesla's system. GE banned the use of Edison's lamps in Westinghouse's exhibits. Still, Westinghouse's proposal was chosen over the inferior DC system to power the fair.

Westinghouse displayed several polyphase systems. The exhibits included a switchboard, polyphase generators, step-up and step-down transformers, transmission line, commercial size induction motors, commercial size synchronous motors, and rotary direct current converters (one of which was operating a railway motor). The working-scale system allowed the public a view of a system of polyphase power which could transmit long distances. Meters and other auxiliary devices were also present.

Tesla displayed the first neon light tubes at the exposition, demonstrating his phosphorescent lighting powered without wires by high-frequency fields. Tesla's lighting inventions exposed to high-frequency currents would bring the gases to incandescence. Tesla displayed the first practical phosphorescent lamps (a precursor to fluorescent lamps). His innovations in this type of light emission were not regularly patented.

Also in the exhibits were Tesla's demonstrations, most notably the "Egg of Columbus". This device explains the principles of the rotating magnetic field and his induction motor. The Egg consisted of a polyphase field coil underneath a plate with a copper egg positioned over the top. When the sequence of the coils were energized, the magnetic field arrangement inductively created a rotation on the egg and made it stand up on end (appearing to resist gravity).

On August 25, Elisha Gray introduced Tesla for the delivery of a lecture on mechanical and electrical oscillators. Tesla explained his work for efficiently increasing the work at high frequency of reciprocation. As Electrical Congress members listened, Tesla delineated mechanisms which could produce oscillations of constant periods irrespective of the pressure applied and irrespective of frictional losses and loads. He explained the working means of producing constant period electric currents (not resorting to spark gaps or breaks) and how to produce these with reliable mechanisms.

The Exposition's illumination with electricity using Tesla's and Westinghouse's alternate current removed any doubt of the utility of the polyphase alternating current.

War of currents

Main article:War of Currents

During this time, direct current was the standard, and Edison was not disposed to lose all his patent royalties to a former employee. Adversaries due to Edison's promotion of DC for electric power distribution over the more efficient alternating current advocated by Tesla, Edison (or, reportedly, one of his employees) employed the tactics of misusing Tesla's patents to construct the first electric chair for the state of New York in order to promote the idea that alternating currents were deadly.

In his work with the rotary magnetic fields, Tesla devised the system for transmission of power over long distances. He partnered with George Westinghouse to commercialize this system. Westinghouse had previously bought the rights to Tesla's polyphase patents and other patents for AC transformers. Experts announced proposals to harness the Niagara Falls for generating electricity. Against General Electric and Edison's proposal, Tesla's AC system won the international Niagara Falls Commission contract. The commission was led by Lord Kelvin and backed by entrepreneurs (such as J.P. Morgan, Lord Rothschild, and John Jacob Astor). Work began in 1893 on the Niagara Falls generation project and Tesla's technology was applied to generate electromagnetic energy from the falls.

Some doubted that the system would generate enough electricity to power industry in Buffalo. Tesla was sure it would work, saying that Niagara Falls had the ability to power the entire eastern U.S. On November 16, 1896, the first transmission of electrical power between two cities was sent from Niagara Falls to industries in Buffalo from the first commercial two-phase power plants (known as hydroelectric generators) at the Edward Dean Adams Station.

The hydroelectric generators were built by Westinghouse Electric Corporation from Tesla's AC system patent designs. Tesla's system designs alleviated the limitations of the previous DC methods. The nameplates on the generators bear Tesla's name. He also set the 60 hertz standard for North America. It took five years to complete the whole facility.

With the financial backing of George Westinghouse, Tesla's AC replaced DC, enormously extending the range and improving the safety and efficiency of power distribution. Tesla's Niagara Falls system marked the end of Edison's roadmap for electrical transmission. Eventually, Edison's GE company converted to the AC system. Tesla's contributions to the modern world are widely regarded as more important and long-lasting, by some, than those of his nemesis and one-time employer, Thomas Edison.

Designs and Colorado

When Tesla was 41 years old, he filed the first basic radio patent (No. US645576). A year later, he demonstrated a remote controlled boat to the US military. Tesla believed that the military would want things such as radio-guided torpedoes. These devices had an innovative coherer and a series of logic gates. Mark Twain wrote Tesla over the demonstrations, though the military took little interest. Radio remote control remained a novelty until the Space Age. At the age of 42, Tesla devised an electric igniter for gasoline engines. His designs are nearly identical to ideas which deal with the same process which modern internal combustion engines use.

In 1899, Tesla traveled to Colorado Springs to continue his research into high-voltage, high frequency alternating current electricity. He was developing a system for wireless telegraphy, telephony and the transmission of power. He also conceived of a system for geophysical exploration--seismology--which he called telegeodynamics, based his reciprocating mechanical oscillator Tesla patented in 1894. He claimed that it could be used to identify underground ore deposits.

Colorado Springs and his diary

In 1899, Tesla decided to move and began conducting research in Colorado (near Colorado Springs), where he could have room for his high-voltage high-frequency experiments. After searching the country for a new location, Tesla chose Colorado Springs for his next series of experiments, primarily because of the frequent electrical storms and the thinness of the air (reducing its dielectric level), making it more conductive. Also, the property was free and electric power was available from the El Paso Power Company. Today electromagnetic intensity charts from the geological survey also show that the ground around his lab possesses a denser field than most of the surrounding area. Tesla reached Colorado Springs on May 17, 1899. Upon his arrival he told reporters that he was conducting experiments transmitting signals from Pikes Peak to Paris.

Tesla kept a diary of his experiments in the Colorado Springs lab where he spent nearly nine months. The diary consists of handwritten notes and date between June 1, 1899 and January 7, 1900. There are explanations (as seen in the photographs taken during this time) of his experimental work. It consists of 500 pages and nearly 200 drawings and is recorded chronologically as the work occurred. He experimented with high-voltage electricity and the possibility of transmitting and distributing large amounts of electrical energy over long distances without using wires. He also conceived the science of telegeodynamics, now known as seismology, and explained that a long sequence of small explosions could be used to find ore underground and could create earthquakes large enough to destroy the Earth. He did not experiment with this as he felt there would not be "a desirable outcome".

Laboratory construction

Tesla, a local contractor, and several assistants commenced the construction of the laboratory shortly after arriving in Colorado Springs. Tesla established his lab on Knob Hill in Colorado Springs, (east of the Colorado School for the Deaf and Blind and one mile east of downtown). The primary purpose of the laboratory was to experiment with high frequency electricity and other phenomena. The Colorado Springs lab's secondary purpose was to research wireless transmission of electrical power.

Tesla's design for the lab consisted of a building fifty feet by sixty feet with eighty-foot ceilings. A one-hundred-forty-two foot conducting aerial with a thirty-inch copper-foil-covered wooden ball was erected on the roof of the lab. The design also implemented a roof that rolled back to prevent fire from sparks and other dangerous effects from the experiments. The laboratory possessed sensitive instruments and equipment.

Magnifying transmitter

The Colorado Springs lab possessed the largest Tesla Coil ever built, known as the "Magnifying Transmitter". This was not identical to the classic Tesla Coil. According to accounts, Tesla managed to transmit tens of thousands of watts of power without wires using the magnifier. Tesla posted a large fence around the coil with a sign, "Keep Out - Great Danger". Tesla's Magnifying Transmitter, at fifty-two feet in diameter, generated millions of volts of electricity and produced lightning bolts more than one-hundred feet long (30.5 metres). It was a three-coil magnifying system requiring alternative forms of analysis than lumped-constant coupled resonant coils presently described to most. The Magnifying Transmitter resonated at a natural quarter wavelength frequency. Tesla worked the magnifying transmitter in a continuous-wave mode and in a partially damped-wave resonant mode.

The Magnifying Transmitter produced thunder which was heard as far away as Cripple Creek. He became the first man to create electrical effects on the scale of lightning. People near the lab would observe sparks emitting from the ground to their feet and through their shoes. Some people observed electrical sparks from the fire hydrants (Tesla for a time grounded out to the plumbing of the city). The area around the laboratory would glow with a blue corona (similar to St. Elmo's Fire). One of Tesla's experiments with the Magnifying Transmitter destroyed Colorado Springs Electric Company's generator by backfeeding the city's power generators, and blacked out the city. The city had a backup generator and company officials denied Tesla further access to their feed if he did not repair the city's primary generator at his own expense. The generator was working again in a few days.

Tuned circuits

Tesla constructed many smaller resonance transformers in his lab and discovered the concept of tuned electrical circuits. Tesla also developed a number of coherers for separating and perceiving electromagnetic waves. In his Colorado experiments, he designed rotating coherers. These were used to detect the unique types of electromagnetic phenomenon observed by Tesla. Tesla's rotating coherer had a mechanism of geared wheels that were driven by a coiled spring-drive mechanism, which was used to rotate small glass cylinders. These experiments were the final stage of years of work related to synchronized electrical tuned circuits.

These transceivers were constructed to demonstrate how signals could be "tuned in". Tesla logged in the diary on July 3, 1899, that a separate resonance transformer tuned to the same high frequency as a larger high-voltage resonance transformer would transceive energy from the larger coil, acting as a transmitter of wireless energy. This data was used to confirm Tesla's patent for radio during later disputes in the courts. These air core high-frequency resonate coils were the predecessors of systems from radio to radar and medical magnetic resonance imaging devices.

Propagation and resonance

On July 3, 1899, Tesla discovered terrestrial stationary waves within the earth. He demonstrated that the Earth behaves as a smooth polished conductor and possesses electrical vibrations. He experimented with waves characterized by a lack of vibration at points, between which areas of maximum vibration occur periodically. These standing waves were produced by confining waves within constructed conductive boundaries. Tesla demonstrated that the Earth could respond at predescribed frequencies of electrical vibrations. At this time, Tesla realized that it was possible to transceive power around the globe.

Tesla conducted experiments contributing to the understanding of electromagnetic propagation and the Earth's resonance. It is well documented (from various photos from the time) that he lit hundreds of lamps wirelessly at a distance of up to twenty-five miles (forty kilometres). He transmitted signals several miles and lit neon tubes conducting through the ground. He researched ways to utilize the ionosphere to transmit energy wirelessly over long distances. He transmitted extremely low frequencies through the earth and portions of the ionosphere, called the Kennelly-Heaviside layer, in his experiments. Tesla made mathematical calculations and computations based on his experiments and discovered that the resonant frequency of this area was approximately eight hertz. In the 1950s, researchers confirmed the resonant frequency was in this range. He also produced the effects that are now referred to as "free electron lasers."

Cosmic waves

In the Colorado Springs lab, Tesla recorded what he concluded were extraterrestrial radio signals and announced his findings in some of the scientific journals of the time. His announcements and data were rejected by the scientific community who did not believe him. He notes measurements of repetitive signals from his receiver which are substantially different from the signals he had noted from storms and earth noise. Specifically, he later recalled that the signals appeared in groups of clicks 1, 2, 3, and 4 clicks together. He stated in the article "A Giant Eye to See Round the World", of Feburary 25, 1923, that:

"Twenty-two years ago, while experimenting in Colorado with a wireless power plant, I obtained extraordinary experimental evidence of the existence of life on Mars. I had perfected a wireless receiver of extraordinary sensitiveness, far beyond anything known, and I caught signals which I interpreted as meaning 1--2--3--4. I believe the Martians used numbers for communication because numbers are universal." Albany Telegram — February 25, 1923

Clearly, Tesla felt the signal groups originated on the planet Mars. In 1996 Corum and Corum published an analysis of Jovian plasma torus signals which indicate that there was a correspondence between the setting of Mars at Colorado Springs, and the cessation of signals from Jupiter in the summer of 1899 when Tesla was there. Further, analysis by the Corums indicate that Tesla's transciever was sensitive in the 18 KHz gap in the Kennelly-Heaviside layer which would have allowed that reception from Jupiter. Therefore, there is evidence the signals Tesla noticed came from Jupiter, among other possible sources. Tesla spent the latter part of his life trying to signal Mars.

It is important to recognize that when he says he "recorded" these signals, it is meant that he wrote down the data and his impressions of what he had heard. He did release reports at the time. Tesla’s inital announcement of the existence of extraterrestrial radio signals was in 1899. In March of 1907, Tesla wrote about signaling to Mars in Harvard Magazine and how it was a problem of electrical engineering. Additional descriptions come from remembrances twenty years later. All this was met with resistance and disbelief by his contemporaries.

Colorado departure

Tesla left Colorado Springs on January 7, 1900. The lab was torn down, broken up, and its contents sold to pay debts. The Colorado experiments prepared Tesla for his next project, the establishment of a wireless power transmission facility that would be known as Wardenclyffe.

Wardenclyffe

Main article: Wardenclyffe Tower

In 1900, Tesla began planning the Wardenclyffe Tower facility. In 1901, the construction began on land near Long Island Sound. The architect Stanford White designed the Wardenclyffe facility main building. Tesla's project was funded by influential industrialists and other venture capitalists. In June 1902, Tesla's lab operations were moved to Wardenclyffe from Houston Street. In 1903, the tower structure neared completion, although it was not yet functional due to a design error. In Electrical World and Engineer (March 5, 1904), Tesla reportedly determined the mode of ball lightning formation and produced them artificially.

In 1904, the United States Patent Office awarded the patent for radio to Guglielmo Marconi, though his work is based on Tesla's widely-discussed demonstration years prior. In May 1905, some of Tesla's patents expired, stopping the royalty payments and causing severe reduction to the funding of the Wardenclyffe Tower. Tesla advertised services of the Wardenclyffe facility to find alternative funding to little success. Around 1910, Tesla designed the Tesla turbine at Wardenclyffe and produced Tesla coils for sale to various businesses to generate funding. He developed a 200 horsepower (150 kW) 16,000 revolutions-per-minute bladeless turbine. It was shown to an audience on his fiftieth birthday.

Of the 700-plus patents accumulated by Tesla, the most controversial today is his Wardenclyffe Tower. The tower was meant to be the start of a global system for wireless telecommunications and a national (and later global) system of towers broadcasting power to users as radio waves. A second plant was to be built in England. It was also intended as a demonstration of wireless electrical power distribution. Instead of supplying electricity through a current grid system, users would simply "receive" power through antennas on their roofs. At the time the power grid was quite limited in terms of who it reached and the proposed system represented a way of significantly reducing the cost of "electrifying" the countryside.

Though never completed successfully in Tesla's lifetime due to lack of funding, and finally dismantled for scrap during wartime, its principles are currently being implemented by a U.S. military project in Alaska, spanning several hundred acres. However, Project HAARP, as it is called, targets a different objective. While Tesla's tower was to be his supreme test of the applicability of transmitted power, HAARP is being used to study ionospheric effects on radio communication. Wardenclyffe also provides a basis for a current search for practical applications for focused wave and particle beams, such as the laser and maser.

In the financial panic of 1907, Tesla set Westinghouse free from payments on his patents over the induction motor for a nominal sum of money. Diminished in strength by the "War of the Currents," the Westinghouse Company survived due to Tesla's act of generosity. Between 1912 and 1915, Tesla's finances unraveled. Newspapers of the time labeled Wardenclyffe "Tesla's million-dollar folly."

Nobel rumors

Due to the fact that the Nobel Prize was awarded to Marconi for radio in 1909, it was believed that Tesla and Edison were to share the Nobel Prize of 1912 (or 1915; some accounts differ). Tesla's rumored nomination for the Nobel Prize in Physics was primarily for his experiments with tuned circuits using high-voltage high-frequency resonant transformers. It was possible that Tesla was told of the plans of the physics award committee and let it be known that he would not share the award with Edison.

Later years

Prior to the First World War, Tesla looked overseas for investors to fund his research. When the war started, Tesla lost funding he was receiving from his European patents. Wardenclyffe Tower was also demolished towards the end of WWI. Tesla had predicted the relevant issues of the post-World War I environment (a war which theoretically ended) in a printed article (December 20, 1914). Tesla believed that the League of Nations was not a remedy for the times and issues. In 1915, Tesla filed a lawsuit against Marconi attempting, unsuccessfully, to obtain a court injunction against the claims of Marconi. Around 1916, Tesla filed for bankruptcy because he owed so much in back taxes. He was living in poverty.

Tesla started to exhibit pronounced symptoms of obsessive-compulsive disorder in the years following. He became obsessed with the number three. He often felt compelled to walk around a block three times before entering a building, demanded a stack of three folded cloth napkins beside his plate at every meal, etc. The nature of OCD was little understood at the time and no treatments were available, so his symptoms were considered by some to be evidence of partial insanity and this probably hurt what was left of his reputation. This obsessive-compulsive behavior may have originated from the observations over repeated polyphase systems in nature that Tesla researched.

At this time, he was staying at the Waldorf-Astoria, renting in an arrangement for deferred payments. In 1917, around the time that the Wardenclyffe Tower was demolished, Tesla received the highest and most significant honor the IEEE can award to any person who uses scientific knowledge to solve practical problem, the Edison Medal. The incongruities between what might have been and the situation at hand probably did not pass without notice by Tesla.

Radar

Tesla, in August 1917, first established principles regarding frequency and power level for the first primitive radar units in 1934. In the 1917 The Electrical Experimenter, he stated the principles of modern military radar in detail. His study of high-voltage, high-frequency alternating current led to this development. He had formed the concept of using radio waves to detect objects at a distance.

Tesla stated,

"For instance, by their use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed."

Tesla proposed to use electromagnetic waves to determine the relative position, speed, and course of a moving object and other modern concepts of radar. He had proposed it might help find submarines (which it isn't well-suited for), though it was first applied successfully to find aircraft (after their later proliferation) and surface ships during World War II. Emil Girardeau, working with the first French radar systems, stated he was building radar systems "conceived according to the principles stated by Tesla".

By the twenties, Tesla was reportedly negotiating with the United Kingdom government under Prime Minister Chamberlain about a ray system. Tesla had also stated that efforts had been made to steal the "death ray" (though they had failed). The Chamberlain government was removed, though, before any final negotiations occurred. The incoming Baldwin government found no use for Tesla's suggestions and ended negotiations.

1930s

On Tesla's seventy-fifth birthday in 1931, Time magazine put him on its cover. The cover caption noted his contribution to electrical power generation. In 1935, many of Marconi's patents relating to the radio were declared invalid by the United States Court of Claims. The Court of Claims decided that the prior work of Tesla (specifically US645576 and US649621) had anticipated Marconi's later works. Tesla got his last patent in 1928 on January 3, an apparatus for aerial transportation which was the first instance of VTOL aircraft. In 1934, Tesla wrote to consul Janković of his homeland. The letter contained the message of gratitude to Mihajlo Pupin who initiated a donation scheme by which American companies could support Tesla. Tesla refused the assistance, and chose to live by a modest pension received from Yugoslavia and to continue researching.

Dynamic theory of gravity

When he was eighty-one, Tesla challenged Albert Einstein's theory of relativity, announcing he was working on a dynamic theory of gravity and argued that a field of force was a better concept and did away with the curvature of space. Unfortunately the theory was never published, but Tesla may have been developing a theory about gravity waves. This theory provides a basis for plasma cosmology.

Death and afterwards

Tesla died alone in the hotel New Yorker of heart failure, some time between the evening of January 5 and the morning of January 8, 1943. Despite selling his AC electricity patents, he was essentially destitute and died with significant debts.

At the time of his death, Tesla had been working on some form of teleforce weapon, or death ray, the secrets of which he had offered to the United States War Department on the morning of January 5. It appears that his proposed death ray was related to his research into ball lightning and plasma. He was found dead 3 days later and, after the FBI was contacted by the War Department, his papers were declared to be top secret.

Immediately after Tesla's death became known, the Federal Bureau of Investigation instructed the Office of Alien Property to take possession of his papers and property, despite his US citizenship. All of his personal effects were seized on the advice of presidential advisors. J. Edgar Hoover declared the case "most secret," because of the nature of Tesla's inventions and patents. Tesla's Serbian-Orthodox family and the Yugoslav embassy struggled with American authorities to gain these items after his death due to the potential significance of some of his research. Eventually, his nephew, Sava Kosanovich, got possession of some of his personal effects (which are now housed in the Nikola Tesla Museum in Belgrade, Yugoslavia). Tesla's funeral took place on January 12, 1943 at the Cathedral of Saint John the Divine in Manhattan, New York City.

Tesla always disputed the claim that Marconi invented radio. An ongoing lawsuit regarding this was finally resolved in Tesla's favor after his death. This decision was based on the fact that there was prior work existing before the establishment of Marconi's patent. At the time, the United States Army was involved in a patent infringement lawsuit with Marconi regarding radio, leading some to posit that the government granted Tesla the patent in order to nullify any claims Marconi would have to compensation (as, some posit, the government's initial granting to Marconi the patent right in order to nullify any claims Tesla had for compensation).

In 1976, a bronze statue of Tesla was placed at Niagara Falls.

Perhaps because of Tesla's personal eccentricity and the dramatic nature of his demonstrations, conspiracy theories about applications of his work persist. The common Hollywood stereotype of the "mad scientist" mirrors Tesla's real-life persona, or at least a caricature of it—which may be no accident considering that many of the earliest such movies (including the first movie version of Mary Shelley's Frankenstein) were produced by Tesla's old rival, Thomas Edison. There are at least two films describing Tesla's life. In the first, arranged for TV, Tesla was portrayed by Rade Šerbedžija. In 1980, Orson Welles produced a Yugoslavian film named Tajna Nikole Tesle (The Secret of Nikola Tesla).