On 30 July 1891, at the age of 35, Tesla became a naturalized citizen of the United States. He told many of his companions that he valued the citizenship more than any scientific honors that he had acquired. In the same year, Tesla established his South Fifth Avenue laboratory in New York. Later, Tesla established his Houston Street laboratory in New York at 46 E. Houston Street. He lit electric lamps wirelessly at both of the New York locations, providing evidence for the potential of wireless power transmission.
It is debated whether Tesla was the first to discover the electron. On 26 August 1891, Tesla published his article "Reply to J.J. Thomson's note," in "Electrical Engineer, New York." In this article, Tesla claimed that his experiments proved the existence of small charged particles, while J.J. Thomson denied this. Five years later, Thomson proved the existence of electrons through another experiment.
In 1892, Tesla was awakened from a dream in which his mother had died. Tesla rushed to his mother's side as she lay dying, arriving from Paris hours before her death. Her last words to him were: "You've arrived, Nidžo, my pride." He returned to Europe for her funeral. After her death, Tesla became ill and spent two to three weeks recuperating in Gospić and the village of Tomingaj.
When Tesla was 36 years old, Tesla's first patents for the polyphase power system were granted. He continued research of the system and rotating magnetic field principles. Tesla served, from 1892 to 1894, as the vice president of the American Institute of Electrical Engineers, the forerunner (along with the Institute of Radio Engineers) of the modern-day IEEE. From 1893 to 1895, he investigated high frequency alternating currents. He generated AC of one million volts using a conical Tesla coil and investigated the skin effectin conductors, designed tuned circuits, invented a machine for inducing sleep, invented a cordless gas dischargelamp, and transmitted electromagnetic energy without wires, putatively building the first radio transmitter. In St. Louis, Missouri, Tesla made a demonstration related to radio communication in 1893. Addressing the Franklin Institute in Philadelphia, Pennsylvania and the National Electric Light Association, he described and demonstrated in detail its principles. Tesla's demonstrations were written about widely through various media outlets. Tesla also investigated harvesting energy that is present throughout space. He believed that it was merely a question of time until men would succeed in attaching their machinery to the very wheelwork of nature, stating: "Ere many generations pass, our machinery will be driven by a power obtainable at any point of the universe."
Westinghouse won the bid to electrify the 1893 World's Columbian Exposition in Chicago with alternating current. ThisWorlds Fair devoted a building to electrical exhibits. It was a key event in the history of AC power as Westinghouse and Tesla demonstrated the safety and reliability of alternating current to the American public. At the Columbian Exposition, Tesla demonstrated a series of electrical effects in a lecture he had performed throughout America and Europe. This included using high-voltage, high-frequency alternating current to light a wireless gas-discharge lamp. An observer noted:
Within the room was suspended two hard-rubber plates covered with tin foil. These were about fifteen feet apart, and served as terminals of the wires leading from the transformers. When the current was turned on, the lamps or tubes, which had no wires connected to them, but lay on a table between the suspended plates, or which might be held in the hand in almost any part of the room, were made luminous. These were the same experiments and the same apparatus shown by Tesla in London about two years previous, "where they produced so much wonder and astonishment".
Tesla also explained the principles of the rotating magnetic field and induction motor by demonstrating how to make a copper egg stand on end in his demonstration of the device he constructed known as the "Egg of Columbus".
The Tesla generator was developed by Tesla in 1895, in conjunction with his developments concerning theliquefaction of air. Tesla knew from Lord Kelvin's discoveries that more heat is absorbed by liquefied air when it is re-gasified and used to drive something than is required by theory; in other words, that the liquefaction process is somewhat anomalous or 'over unity'. Just before Tesla's completion of his work and the filing of a patent application, Tesla's laboratory burned down, destroying all his equipment, models and inventions. Immediately after the fire, Carl von Linde, in Germany, filed a patent application for the same process.
A "world system" for "the transmission of electrical energy without wires" that depended upon the electrical conductivity of the earth was proposed, in which transmission in various natural media with current that passes between the two points are used to power devices. In a practical wireless energy transmission system using this principle, a high-power ultraviolet beam might be used to form a vertical ionized channel in the air directly above the transmitter-receiver stations. The same concept is used in virtual lightning rods and the electrolaserelectroshock weapon, and has been proposed for disabling vehicles..
In the late 1880s, Tesla and Thomas Edison became adversaries in part because of Edison's promotion of direct current (DC) for electric power distribution over the more efficient alternating current advocated by Tesla and Westinghouse. Until the development of the induction motor, AC's advantages for long distance high voltage transmission were counterbalanced by the inability to operate motors on AC. As a result of the "War of Currents", Edison and Westinghouse went nearly bankrupt, so in 1897, Tesla released Westinghouse from contract, providing Westinghouse a break from Tesla's patent royalties. Also, in 1897, Tesla researched radiation, which led to setting up the basic formulation of cosmic rays.
In 1897, at age 41, Tesla filed the first radio patent (U.S. Patent 645,576). A year later, he demonstrated a radio-controlled boat to the US military, believing that the military would want things such as radio-controlled torpedoes. Tesla claimed to have developed the "Art of Telautomatics", a form of robotics, as well as the technology of remote control.In 1898, he demonstrated a radio-controlled boat to the public during an electrical exhibition at Madison Square Garden. Tesla called his boat a "teleautomaton". This same year, Tesla devised an "electric igniter" or spark plug for internal combustion gasoline engines. He was awarded U.S. Patent 609,250, "Electrical Igniter for Gas Engines", on thismechanical ignition system. Before the end of the century, Tesla lived in the Gerlach Hotel (later renamed The Radio Wave building) at 49 West 27th Street Lower Manhattan, where he conducted radio wave experiments. Acommemorative plaque was placed on the building in 1977 to honor his work. Remote radio control remained a novelty until World War I and afterward, when a number of countries used it in military programs.