Nikola Tesla/Middle years
Menlo Park 
In 1884, 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) to Thomas Edison.
The letter read simply "I know two great men, and you are one of them. This young man is the other". Tesla's work for Edison began with simple electrical engineering. Eventually Tesla earned the respect of Edison and offered to undertake a complete re-design of the Edison company's DC dynamos. After Tesla described the nature of the benefits from his proposed modifications, Edison offered him US$50,000 if they were successfully completed.
Tesla worked for nearly a year to redesign them and gave the Edison company several enormously profitable new patents in the process. When Tesla inquired about the $50,000, Edison replied to him, "Tesla, you don't understand our American humor", and reneged on his agreement, offering a raise in Tesla's salary of $10 per week as a compromise - at which rate it would have taken almost 100 years to earn the money Edison had originally promised. Tesla resigned on the spot. In some accounts of the final confrontation, Tesla did not say a single word to Edison but simply turned his back on the inventor and walked off the premises. Edison would receive US patent 328572 for an improved commutator and, later, would gain US patent 373584 for a dynamo-electric machine (which includes an extra coil and utilizes a field of force) among other patents which Tesla may be responsible for.
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 him of his duties at the company. Tesla worked in New York as a common laborer from 1886 to 1887 to feed himself and raise capital for his next project.
In 1887, he constructed the initial brushless alternate-current induction motor, which he demonstrated to the American Institute of Electrical Engineers (now IEEE) in 1888. Also in 1887, he developed the principles of his Tesla coil and began working with George Westinghouse at Westinghouse's Pittsburgh labs. Westinghouse listened to his ideas for polyphase systems which would allow transmission of AC electricity over large distances
The first efficient and practical electromechanical generator patented by Nikola Tesla in 1891 was U.S. Patent 447921. This is the first small rotating machine, called the alternator. Nikola Tesla's U.S. Patent 447920, "Method of Operating Arc-Lamps" (March 10, 1891), describes an alternator that produces high frequency current, around 10,000 cycles per second (hertz). His intention was to suppress the disagreeable sound of power-frequency harmonics produced by arc lamps operating on frequencies within the range of human hearing. The produced alterations (or pulsations) was in the longwave broadcasting range (very low frequency band).
World Columbian Exposition 
The International Exposition was held was held in Chicago in 1893 to celebrate the 400th anniversary of Christopher Columbus's discovery of the New World. It was the first to have a large portion of its grounds devoted electrical exhibits. It was an historical moment and the beginning of a revolution, as Nikola Tesla and George Westinghouse introduced the public to electrical power by providing alternating current to illuminate the Exposition. The general public observed firsthand the qualities and abilities of alternating current power. All the exhibits were from commercial enterprises. Thomas Edison, Brush, Western Electric, and Westinghouse 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, armed with Tesla's alternating current system, proposed to illuminate the exposition for half that price. Tesla's high-frequency high-voltage lighting produced more efficient light with quantitatively 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 in Tesla's works. Westinghouse's proposal was chosen over the inferior direct current system to power the fair. General Electric banned the use of Edison's lamps in Westinghouse's plan, in retailiation for losing the bid. Westinghouse's company quickly designed a double-stopper lightbulb (sidestepping Edison's patents) and was able to light the fair.
The Westinghouse Company displayed several polyphase systems. The exhibits included a switchboard, polyphase generators, step-up transformers, transmission line, step-down transformers, commercial size induction motors and synchronous motors, and rotary direct current converters (including an operational railway motor). The working scaled system allowed the public a view of a system of polyphase power which could be transmitted over long distances, and be utilized, including the supply of direct current. Meters and other auxiliary devices were also present.
Tesla displayed his phosphorescent lighting, powered without wires by high-frequency fields. Tesla displayed the first practical phosphorescent lamps (a precursor to fluorescent lamps). Tesla's lighting inventions exposed to high-frequency currents would bring the gases to incandescence. Tesla also displayed the first neon lights. His innovations in this type of light emission were not regularly patented.
Also among the exhibits was Tesla's demonstration, most notably the "Egg of Columbus". This device explains the principles of the rotating magnetic field and his induction motor. The Egg of Columbus consisted of a polyphase field coil underneath a plate with a copper egg positioned over the top. When the sequence of 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 a 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 continued to explain the working mean of the production of constant period electric currents (not resorting to spark gaps or breaks), and how to produce these with mechanisms which are reliable.
The successful demonstration of alternating current lighting at the Exposition dispelled doubts about the usefulness of the polyphase alternating current system developed by Westinghouse and Tesla.
Colorado Springs 
In 1899, Tesla decided to move and began research in Colorado Springs, Colorado, where he could have room for his high-voltage high-frequency experiments. He chose this location primarily because of the frequent thunderstorms, the high altitude (where the air, being at a lower pressure, had a lower dielectric breakdown strength, making it easier to ionize), and the dryness of the air (minimizing leakage of electric charge through insulators). Also, the property was free and electric power available from the El Paso Power Company. Today, magnetic intensity charts also show that the ground around his lab possesses a denser magnetic field than 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. It consists of 500 pages of handwritten notes and nearly 200 drawings, recorded chronologically between June 1, 1899 and January 7, 1900, as the work occurred, containing explanations of his experiments. He was developing a system for wireless telegraphy, telephony and the transmission of power, experimented with high-voltage electricity and the possibility of wireless transmitting and distributing large amounts of electrical energy over long distances. He also conceived a system for geophysical exploration--seismology--which he called telegeodynamics, based on his reciprocating mechanical oscillator patented in 1894, and explained that a long sequence of small explosions could be used to find ore and 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. The lab was established on Knob Hill, east of the Colorado School for the Deaf and Blind and one mile (1.6 km) east of downtown. Its primary purposes were experiments with high frequency electricity and other phenomena, and secondary--research into wireless transmission of electrical power. Tesla's design of the lab was a building fifty feet by sixty feet (15 by 18 m) with eighty-foot (24 m) ceilings. A one-hundred-forty-two foot (43 m) conducting aerial with a thirty-inch (76 cm) copper-foil covered wooden ball was erected on the roof. The roof was rolled back to prevent fire from sparks and other dangerous effects of the experiments. The laboratory had sensitive instruments and equipment.
Tuned circuits 
Tesla also constructed many smaller resonance transformers and discovered the concept of tuned electrical circuits. He also developed a number of coherers for separating and perceiving electromagnetic waves and designed rotating coherers which he used to detect the unique types of electromagnetic phenomenon he observed. They had a mechanism of geared wheels driven by a coiled spring-drive mechanism which rotated small glass cylinders. These experiments were the final stage of years of work on synchronized tuned electrical circuits.
These transceivers were constructed to demonstrate how signals could be "tuned in". Tesla logged in his 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, which 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. A few years later, George Westinghouse stopped funding Tesla's research when Tesla showed him that he could offer free electricity to the whole world by simply "ramming a stick in the earth in your backyard". Westinghouse said he would go bankrupt if that happened.
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 (40 km). He transmitted signals several kilometres and lit neon tubes conducting through the ground. He researched ways to transmit energy wirelessly over long distances (utilizing the ionosphere and the ground's telluric currents via transverse waves, to a lesser extent, and, more readily, longitudinal waves). He transmitted extremely low frequencies through the ground as well as between the Earth's surface and the Kennelly-Heaviside layer. He received patents on wireless that developed standing waves by this method. In his experiments, he made mathematical calculations and computations based on his experiments and discovered that the resonant frequency of the Earth was approximately 8 Hz (Hertz). In the 1950s, researchers confirmed resonant frequency was in this range (interesting to note, Theta brain waves also cycle in this range).
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 25 February 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 — 25 February 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 transceiver 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 initial 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.
On March 21, 1900, Tesla was granted US685012 patent for the means for increasing the intensity of electrical oscillations. The United States Patent Office classification system currently denotes that this patent pretains to superconductivity technology (Class 505/825). Within this patent it describes the increase intensity and duration of electric oscillations of a low temperature resonating circuit. w:Carl von LindeCarl von Linde and William Hampson, both commercial researchers, nearly at the same time filed for patents on the Joule-Thomson effect. Linde's patent was the climax of 20 years of systematic investigation of establish facts, using a regenerative counterflow method. Hampson's designs was also of a regenerative method. It is believed that Tesla had intended that Linde's machine would be used to attain the cooling agents.
Wardenclyffe Tower 
Tesla began planning the Wardenclyffe Tower facility ca. 1898, and in 1901, construction began on the land near Long Island Sound. Architect Stanford White designed the Wardenclyffe facility main building. The tower was designed by W.D. Crow, an associate of White. Funding for Tesla's project was provided by influential industrialists and other venture capitalists. The project was initially backed by the wealthy J. P. Morgan (he had a substantial investment in the facility, initially investing $150,000).
In June 1902, Tesla moved his laboratory operations from his Houston Street laboratory to Wardenclyffe. However, in 1903, when the tower structure was near completion, it was still not yet functional due to last-minute design changes that introduced in an unintentional defect. When Morgan wanted to know "Where can I put the meter?", Tesla had no answer. Tesla's vision of free power did not agree with Morgan's worldview. Construction costs eventually exceeded the money provided by Morgan, and additional financiers were reluctant to come forth. By July 1904, Morgan (and the other investors) finally decided they would not provide any additional financing. Morgan also encouraged other investors to avoid the project. In May 1905, Tesla's patents on alternating current motors and other methods of power transmission expired, halting royalty payments and causing a severe reduction of funding to the Wardenclyffe Tower. In an attempt to find alternative funding, Tesla advertised the services of the Wardenclyffe facility, but he met with little success. By this time, Tesla had also designed the Tesla turbine at Wardenclyffe and produced Tesla coils for sale to various businesses.
By 1905, since Tesla could not find any more backers, most of the site's activity had to be shut down. The main hall continued to be used for blackface minstrel shows until October of that year. Employees were laid off in 1906, but parts of the building remained in use until 1907. In 1908, the property was foreclosed for the first time. Tesla procured a new mortgage from the proprietor of the Waldorf-Astoria Hotel, George C. Boldt. The facility was partially abandoned around 1911, the tower structure eventually becoming deteriorated. Between 1912 and 1915, Tesla's finances unraveled, and when the funders wanted to know how they were going to recapture their investments, Tesla was unable to give satisfactory answers. Newspaper headlines of the time labeled it "Tesla's million-dollar folly." The facility's main building was breached and vandalized around this time. Collapse of the Wardenclyffe project may have contributed to the mental breakdown Tesla experienced during this period. Coupled to the personal tragedy of Wardenclyffe was the earlier 1895 unexplained fire in Tesla's Houston Street laboratory. In this fire, he lost much of his equipment, notes and documents. This produced a state of severe depression for Tesla.
In 1915, legal ownership of the Wardenclyffe property was transferred to George Boldt for a $20,000 debt. Demolition and salvaging of the tower occurred in 1917. However, the main building remains standing to this day. Tesla was not in New York during the tower's destruction. George Boldt wished to make the property available for sale. New York papers reported that the tower had been destroyed by order of the government to prevent its use by foreign agents. In 1917, the United States government may have aided the destruction of the Wardenclyffe Tower, ostensibly because it was believed it could provide a navigational landmark for German submarines. The facts neither support nor discount either claim. On April 20, 1922 Tesla lost an appeal of judgment versus his backers in the second foreclosure. This effectively locked Tesla out of any future development of the facility.
Fight for radio 
In 1904, the US Patent Office reversed its decision and awarded Guglielmo Marconi the patent for radio. Tesla began his fight to re-acquire his radio patent. Later in 1909, Marconi was awarded the Nobel Prize for radio. Tesla was deeply resentful. So in 1915, Tesla filed a lawsuit against Marconi.
Tesla always disputed the claim that Marconi invented radio and he gave a simple reason for this position. It was that radio is not an invention: "It was evident to me in 1888 that wireless transmission of energy, if it could ever be accomplished, is not an invention; it is an art. Bell's telephone, Edison's phonograph, or my induction motor were inventions, but the wireless transmission of energy is an art that requires a great many inventions in combination.", (Nikola Tesla, 1916, in Ed. Anderson, Leland, 'Nikola Tesla On His Work With Alternating Currents And Their Application to Wireless Telegraphy, Telephony, and Transmission of Energy, Published 1992). Seen in this context, some believe that it is Tesla's lecture and patent record from 1888 onwards that contains the fundamental information on the '....great many inventions...' that form the basis for modern radio and wireless technology.
An ongoing lawsuit regarding the patent battle was finally resolved in Tesla's favor in 1944, one year after his death. This decision was based on the facts of the 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 and others the formal recognition in order to nullify any claims Marconi would have to compensation (as the earlier award to Marconi nullified any claims Tesla would have for compensation).
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 (and, later alone, in Nobel Prize of 1915). Tesla's rumored nominations 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.