Henry Cavendish
Henry Cavendish
Born	(1731-10-10)10 October 1731 Nice, France
Died	24 February 1810(1810-02-24) (aged 78) London, England
Nationality	United Kingdom
Fields	Chemistry, physics
Alma mater	University of Cambridge
Known for	Discovery of hydrogen Measured the Earth's density

Henry Cavendish FRS (10 October 1731 – 24 February 1810) was a British scientist noted for his discovery of hydrogen or what he called "inflammable air".^[1] He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and gave the element its name. Cavendish is also known for the Cavendish experiment, his measurement of the Earth's density, and early research into electricity.

Biography[link]

Henry Cavendish was born on 10 October 1731 in Nice, France, where his family was living at the time. His mother was Lady Anne Grey, daughter of Henry Grey, 1st Duke of Kent and his father was Lord Charles Cavendish, son of William Cavendish, 2nd Duke of Devonshire. The family traces its lineage across eight centuries to Norman times and was closely connected to many aristocratic families of Great Britain.

At age 11, Cavendish was a pupil at Peter Newcome's School in Hackney. At age 18 (on 24 November 1749) he entered the University of Cambridge in St Peter's College, now known as Peterhouse, but left four years later on 23 February 1753 without graduating.^[2][3] His first paper, "Factitious Airs", appeared thirteen years later, in 1766.

Cavendish was silent and solitary, and was viewed as somewhat eccentric by many. He only communicated with his female servants by notes and formed no close personal relationships outside his family. By one account, Cavendish had a back staircase added to his house in order to avoid encountering his housekeeper because he was especially shy of women. The contemporary accounts of his personality have led some modern commentators, such as Oliver Sacks, to speculate that he had Asperger syndrome, though he may merely have been painfully shy. His only social outlet was the Royal Society Club, whose members dined together before weekly meetings. Cavendish seldom missed these meetings, and was profoundly respected by his contemporaries. However his shyness made those who "sought his views... speak as if into vacancy. If their remarks were...worthy, they might receive a mumbled reply, but more often than not they would hear a peeved squeak (his voice appears to have been high-pitched) and turn to find an actual vacancy and the sight of Cavendish fleeing to find a more peaceful corner"^[4] He also enjoyed collecting fine furniture exemplified by his purchase of a set of "ten inlaid satinwood chairs with matching cabriole legged sofa".^[5]

Because of his asocial and secretive behaviour, Cavendish often avoided publishing his work, and much of his findings were not even told to his fellow scientists. In the late nineteenth century, long after his death, James Clerk Maxwell looked through Cavendish's papers and found things for which others had been given credit. Examples of what was included in Cavendish's discoveries or anticipations were Richter's Law of Reciprocal Proportions, Ohm's Law, Dalton's Law of Partial Pressures, principles of electrical conductivity (including Coulomb's Law), and Charles's Law of Gases.

A manuscript "Heat", tentatively dated between 1783 and 1790, describes a "mechanical theory of heat". Hitherto unknown, the manuscript was analyzed in the early 21st century. Historian of science Russell McCormmach proposed that "Heat" is the only 18th century work prefiguring thermodynamics. Theoretical physicist Dietrich Belitz concluded that in this work Cavendish "got the nature of heat essentially right."^[6]

Cavendish died in 1810 (as one of the wealthiest men in Britain) and was buried, along with many of his ancestors, in the church that is now Derby Cathedral and the road he used to live on in Derby has been named after him. The University of Cambridge's Cavendish Laboratory was endowed by one of Cavendish's later relatives, William Cavendish, 7th Duke of Devonshire (Chancellor of the University from 1861 to 1891).

Gases and the atmosphere[link]

Cavendish's apparatus for making and collecting hydrogen^[1]

Cavendish is considered to be one of the so-called pneumatic chemists of the eighteenth and nineteenth centuries, along with, for example, Joseph Priestley, Joseph Black, and Daniel Rutherford. By combining metals with strong acids, Cavendish made hydrogen (H₂) gas, which he isolated and studied. Although others, such as Robert Boyle, had prepared hydrogen gas earlier, Cavendish is usually given the credit for recognizing its elemental nature.

Cavendish observed that hydrogen, which he called "inflammable air", reacts with oxygen, then known as "dephlogisticated air", to form water. James Watt and Antoine Lavoisier made a similar observation, resulting in a controversy as to who should receive credit for it. Cavendish however resisted Lavoisier's theory of chemical compounds, and attempted to explain his experiment in terms of phlogiston.^[7][8]

Cavendish also accurately determined the composition of Earth's atmosphere. In a 1785 paper, he described experiments in which hydrogen and ordinary air were combined in known ratios, and then exploded with a spark of electricity. In each case, Cavendish observed both the formation of water and that the gas volume after the explosion was always less than it was before it. By careful measurements he was led to conclude that, "common air consists of one part of dephlogisticated air [oxygen], mixed with four of phlogisticated [nitrogen]".^[9][10]

The same paper described an experiment in which Cavendish was able to remove, in modern terminology, both the oxygen and nitrogen gases from a sample of atmospheric air until only a small bubble of unreacted gas was left in the original sample. From this experiment Cavendish concluded that not more than 1/120 of the Earth's atmosphere was other than oxygen and nitrogen.^[11] Although a seemingly small fraction, about 100 years later William Ramsay and Lord Rayleigh showed that this residual gas contained argon, an element that was unknown at the time.

Density of the Earth[link]

In addition to his achievements in chemistry, Cavendish is also known for the Cavendish experiment, the first to measure the force of gravity between masses in a laboratory and to produce an accurate value for Earth's density. His work led others to accurate values for the gravitational constant (G) and Earth's mass. Based on his results, one can calculate a value for G of 6.754 × 10⁻¹¹N-m²/kg²,^[12] which compares favourably with the modern value of 6.67428 × 10⁻¹¹N-m²/kg².^[13]

The equipment Cavendish used was designed and built by geologist John Michell, who died before he could begin the experiment. The apparatus was sent in crates to Cavendish, who completed the experiment in 1797 – 1798,^[4] and published the results.^[14] Cavendish noticed that Michell's apparatus would be sensitive to temperature differences and induced air currents so he made modifications by isolating the apparatus in a separate room with external controls and telescopes for making observations.^[15]

The experimental apparatus consisted of a torsion balance to measure the gravitational attraction between two 350-pound lead spheres and a pair of 2-inch 1.61-pound lead spheres.^[4] Using this equipment, Cavendish found that the Earth's average density is 5.48 times greater than that of water. John Henry Poynting later noted that the data should have led to a value of 5.448,^[16] and indeed that is the average value of the twenty-nine determinations Cavendish included in his paper.^[17]

Books often describe Cavendish's work as a measurement either of the gravitational constant (G), or of the Earth's mass. Since these are related to the Earth's density by a trivial web of algebraic relations, none of these sources are wrong, but they do not match the exact word choice of Cavendish,^[18][19] and this mistake has been pointed out by several authors.^[20][21] Cavendish's stated goal was to measure the Earth's density, although his result obviously calculates G in order to do so.

The first time that the constant got this name was in 1873, almost 100 years after the Cavendish experiment, but the constant was in use since the time of Newton.^[22] Cavendish's results obviously also give the Earth’s mass.

Cavendish performed his experiment in an outbuilding in the garden of his Clapham Common estate. For years afterward, his neighbours would point out the building and tell their children that it was where the world was weighed.^[5]

Electrical research[link]

Cavendish wrote papers on electrical topics for the Royal Society^[23][24] but the bulk of his electrical experiments did not become known until they were collected and published by James Clerk Maxwell a century later, in 1879, long after other scientists had been credited with the same results. According to the 1911 edition of Encyclopædia Britannica, among Cavendish's discoveries were the following:^[25]

• The concept of electric potential, which he called the "degree of electrification"
• An early unit of capacitance, that of a sphere one inch in diameter
• The formula for the capacitance of a plate capacitor
• The concept of the dielectric constant of a material
• The relationship between electric potential and current, now called Ohm's Law. (1781)
• Laws for the division of current in parallel circuits, now attributed to Charles Wheatstone
• Inverse square law of variation of electric force with distance, now called Coulomb's Law^[26]

Selected writings[link]

• Cavendish, Henry (1921). Scientific Papers. 1. Cambridge: Cambridge University Press. http://www.archive.org/details/scientificpapers01caveuoft.  - edited by James Clerk Maxwell and revised by Joseph Larmor
• Cavendish, Henry (1921). Scientific Papers. 2. Cambridge: Cambridge University Press. http://www.archive.org/details/scientificpaper00cavegoog.  - edited by James Clerk Maxwell and revised by Joseph Larmor
• Cavendish, Henry (1879). The Electrical Researches of the Honourable Henry Cavendish. Cambridge: Cambridge University Press. http://books.google.com/?id=3gYJAAAAIAAJ&pg=PR24&dq=cavendish+henry#PPR3,M1.  - edited by James Clerk Maxwell

See also[link]

• Timeline of hydrogen technologies

Notes and references[link]

Further reading[link]

• Cavendish, Christa Jungnickel and Russell McCormmach, American Philosophical Society, 1996, ISBN 0-87169-220-1, 414 pp.
• Cavendish: The Experimental Life, Christa Jungnickel and Russell McCormmach, Bucknell University Press, 1999, ISBN 0-8387-5445-7, 814 pp.

External links[link]

Wikiquote has a collection of quotations related to: Henry Cavendish

• The Life of the Honourable Henry Cavendish by George Wilson, London, 1851.
• Experiments on Air by Henry Cavendish, Edinburgh: William F. Clay (1893) - Alembic Club reprint number 3.
• "The Mean Density of the Earth" by J. H. Poynting, London: Charles Griffin and Company (1894).
• The Laws of Gravitation: Memoirs by Newton, Bouguer and Cavendish, edited and translated by A. Stanley MacKenzie, New York: American Book Company (1900).
•  Chisholm, Hugh, ed. (1911). "Cavendish, Henry". Encyclopædia Britannica (11th ed.). Cambridge University Press. 

Nikola Tesla
Tesla, aged 37, 1893, photo by Napoleon Sarony
Born	(1856-07-10)10 July 1856 Smiljan, Austrian Empire (Croatian Military Frontier)
Died	7 January 1943(1943-01-07) (aged 86) Manhattan, New York, USA
Residence	Manhattan, New York, USA Karlovac, Croatia Budapest, Hungary
Citizenship	Austrian Empire (10 July 1856 – 29 October 1918)[citation needed] United States (30 July 1891 – 7 January 1943)
Fields	Electrical engineering Mechanical engineering
Institutions	Edison Machine Works Tesla Electric Light & Manufacturing Westinghouse Electric & Manufacturing Co.
Alma mater	Graz University of Technology Charles University in Prague
Known for	Alternating current Bifilar coil Death ray Electrogravitics Induction motor Particle beam weapon Rotating magnetic field Teleforce Tesla coil Tesla electric car Tesla principle Tesla turbine Tesla's Egg of Columbus Tesla's oscillator Telegeodynamics Terrestrial stationary waves Wireless technology
Influences	Ernst Mach
Influenced	Gano Dunn
Notable awards	Order of St. Sava (1892) Elliott Cresson Medal (1894) Edison Medal (1916) John Scott Medal (1934)
Signature

Nikola Tesla (Serbian Cyrillic: Никола Тесла; 10 July 1856 – 7 January 1943) was a Serbian-American inventor, physicist, mechanical engineer, electrical engineer, and futurist. He was an important contributor to the use of commercial electricity, and is best known for developing the modern alternating current (AC) electrical supply system. His many revolutionary developments in the field of electromagnetism in the late 19th and early 20th centuries were based on the theories of electromagnetic technology discovered by Michael Faraday. Tesla's patents and theoretical work also formed the basis of wireless communication and the radio.

Born in the village of Smiljan (now part of Gospić, present day Croatia), Tesla was a subject of the Austrian Empire by birth and later became an American citizen.^[1] Because of his 1894 demonstration of short range wireless communication through radio^[2] and as the eventual victor in the "War of Currents", he was widely respected as one of the greatest electrical engineers who worked in America.^[3] He pioneered modern electrical engineering and many of his discoveries were of groundbreaking importance. In the United States during this time, Tesla's fame rivaled that of any other inventor or scientist in history or popular culture.^[4] Tesla demonstrated wireless energy transfer to power electronic devices in 1891,^[5] and aspired to intercontinental wireless transmission of industrial power in his unfinished Wardenclyffe Tower project.

Tesla became reclusive towards the end of his life, living alone in a New York City hotel room and only appearing occasionally to make unusual statements to the press.^[6][7] Because of his pronouncements and the nature of his work over the years Tesla gained a reputation in popular culture as the archetypal "mad scientist".^[8][9] He died with little money to his name.^[10]

Tesla's work fell into relative obscurity after his death but since the 1990s his reputation has experienced a popular culture comeback.^[11] In 2005 he was listed amongst the top 100 nominees in the TV show "The Greatest American", an open access popularity poll conducted by AOL and The Discovery Channel.

The SI unit measuring magnetic field B (also referred to as the magnetic flux density and magnetic induction), the tesla, was named in his honor (at the CGPM, Paris, 1960).

Early years[link]

Nikola Tesla was born to Serbian parents in the village of Smiljan, Austrian Empire near the town of Gospić, in the territory of modern-day Croatia. His baptismal certificate reports that he was born on 28 June (N.S. 10 July) 1856 to father Milutin Tesla, a priest in the Serbian Orthodox Church.^[12] His mother was Đuka Tesla, née Mandić, whose father was also a Serbian Orthodox priest.^[13] She was talented in making home craft tools and memorized many Serbian epic poems, but never learned to read.^[14] Tesla's biographer John O'Neill relates that "the Tesla and Mandić families originally came from the western part of Serbia near Montenegro."^[15]

Nikola was the fourth of five children, having one older brother (Danilo, who was killed in a horse-riding accident when Nikola was five) and three sisters (Milka, Angelina and Marica).^[16] His family moved to Gospić in 1862. Tesla attended school at Higher Real Gymnasium in Karlovac.^[17] He finished a four-year term in the span of three years.^[18]

Nikola Tesla's house (parish hall) in village Smiljan where he was born and the church where his father served (present day Croatia).

Tesla went on to study electrical engineering at the Austrian Polytechnic in Graz (1875). While there, he studied the uses of alternating current. Some sources say he received Baccalaureate degrees from the university at Graz.^[19][20][21] However, the university says that he did not receive a degree and did not continue beyond the first semester of his third year, during which he stopped attending lectures.^{[22][23][24][25]} In December 1878, Tesla left Graz and broke all relations with his family. His friends thought that he had drowned in the Mur River. He went to Marburg, (today's Maribor, in Slovenia), where he was first employed as an assistant engineer for a year. He suffered a nervous breakdown during this time. Tesla was later persuaded by his father to attend the Charles-Ferdinand University in Prague, which he attended for the summer term of 1880. Here, he was influenced by Ernst Mach. However, after his father died, he left the university, having completed only one term.^[26]

Nikola Tesla c. 1879 at age 23, and his passport from 1883

Tesla engaged in reading many works, memorizing complete books, supposedly having a photographic memory.^[27] Tesla related in his autobiography that he experienced detailed moments of inspiration. During his early life, Tesla was stricken with illness time and time again. He suffered a peculiar affliction in which blinding flashes of light would appear before his eyes, often accompanied by visions. Much of the time the visions were linked to a word or idea he might have come across, at other times they would provide the solution to a particular problem he had been encountering; just by hearing the name of an item, he would be able to envision it in realistic detail. Modern-day synesthetes report similar symptoms. Tesla would visualize an invention in his mind with extreme precision, including all dimensions, before moving to the construction stage; a technique sometimes known as picture thinking. He typically did not make drawings by hand, instead just conceiving all ideas with his mind. Tesla also often had flashbacks to events that had happened previously in his life; these began during his childhood.^[27]

In 1880, he moved to Budapest to work under Tivadar Puskás in a telegraph company,^[28] the National Telephone Company. There, he met Nebojša Petrović, a young, Serbian inventor who lived in Austria. Although their encounter was brief, they did work on a project together using twin turbines to create continual power. On the opening of the telephone exchange in Budapest, 1881, Tesla became the chief electrician to the company, and was later engineer for the country's first telephone system. He also developed a device that, according to some, was a telephone repeater or amplifier, but according to others could have been the first loudspeaker.^[29]

Drawing from U.S. Patent 381968, illustrating principle of Tesla's alternating current motor

Working for Edison in France and the U.S[link]

In 1882 he moved to Paris, to work as an engineer for the Continental Edison Company, designing improvements to electric equipment brought overseas from Edison's ideas. According to Tesla's autobiography, in the same year he conceived of his induction motor and began developing various devices that use rotating magnetic fields for which he received patents in 1888. The paternity of the invention remains controversial since a prototype induction motor was demonstrated in Europe in 1885 by Galileo Ferraris.^{[30][31][32][33]} Ferraris published his findings in 1888.

On 6 June 1884, Tesla first arrived in the United States, in New York City^[34] with little besides a letter of recommendation from Charles Batchelor, a former employer. In the letter of recommendation to Thomas Edison, it is claimed that Batchelor wrote, 'I know two great men and you are one of them; the other is this young man', but the exact contents of the letter is disputed in McNichol's book. Edison hired Tesla to work for his Edison Machine Works. Tesla's work for Edison began with simple electrical engineering and quickly progressed to solving some of the company's most difficult problems. Tesla was even offered the task of completely redesigning the Edison company's direct current generators.^[35]

In 1885 Tesla claimed he could redesign Edison's inefficient motor and generators, making an improvement in both service and economy. According to Tesla, Edison remarked "There's fifty thousand dollars in it for you - if you can do it".^[36] This has been noted as an odd statement from an Edison whose company was stingy with pay and did not have that sort of cash on hand.^[37] After months of work when Tesla finished the task and inquired about payment Edison claimed he was only joking replying, "Tesla, you don't understand our American humor".^[38][39] Edison offered a $10 a week raise over Tesla's US$18 per week salary, but Tesla refused it and immediately resigned.^[36]

Tesla, in need of work, eventually found himself digging ditches for a short period of time for the Edison company. He used this time to focus on his AC polyphase system.^[40]

Middle years[link]

Wireless transmission of power and energy demonstration during his high frequency and potential lecture of 1891 Electromechanical devices and principles developed by Nikola Tesla: Various devices that use rotating magnetic fields (1882) The Induction motor, rotary transformers, and "high" frequency alternators The Tesla coil,[41] his magnifying transmitter, and other means for increasing the intensity of electrical oscillations (including condenser discharge transformations and the Tesla oscillators[42][43]) Alternating current long-distance electrical transmission system[44] (1888) and other methods and devices for power transmission Systems for wireless communication (prior art for the invention of radio) and radio frequency oscillators[45] Robotics and the electronic logic gate[46] Electrotherapy Tesla currents[47][48][49] Wireless transfer of electricity and the Tesla effect[50][51] Tesla impedance phenonomena[52] Tesla electro-static field Tesla principle Bifilar coil Telegeodynamics Tesla insulation Tesla impulses[53] Tesla frequencies[41] Tesla discharge[41] Forms of commutators and methods of regulating third brushes Tesla turbines (e.g., bladeless turbines) for water, steam and gas and the Tesla pumps Tesla igniter Corona discharge ozone generator Tesla compressor X-rays Tubes using the Bremsstrahlung process Devices for ionized gases and "Hot Saint Elmo's Fire".[54] Devices for high field emission Devices for charged particle beams Phantom streaming devices[55] Arc light systems Methods for providing extremely low level of resistance to the passage of electric current (predecessor to superconductivity) Voltage multiplication circuitry Devices for high voltage discharges Devices for lightning protection VTOL aircraft Dynamic theory of gravity Concepts for electric vehicles Polyphase systems

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 laborer from 1886 to 1887 to feed himself and raise capital for his next project. In 1887, he constructed a brushless alternating current induction motor, which he demonstrated to the American Institute of Electrical Engineers (now IEEE) in 1888. In the same year, he developed the principles of his Tesla coil, and began working with George Westinghouse at Westinghouse Electric & Manufacturing Company's Pittsburgh labs. Westinghouse listened to his ideas for polyphase systems which would allow transmission of alternating current electricity over long distances.

In April 1887, Tesla began investigating what would later be called X-rays using his own single terminal vacuum tubes (similar to his patent #514,170). This device differed from other early X-ray tubes in that it had no target electrode. The modern term for the phenomenon produced by this device is bremsstrahlung (or braking radiation). It is now known that this device operated by emitting electrons from the single electrode through a combination of field electron emission and thermionic emission. Once liberated, electrons are strongly repelled by the high electric field near the electrode during negative voltage peaks from the oscillating HV output of the Tesla Coil, generating X rays as they collide with the glass envelope. He also used Geissler tubes. By 1892, Tesla became aware of the skin damage that Wilhelm Röntgen later identified as an effect of X rays.

In the early research, Tesla devised several experimental setups to produce X-rays. Tesla held that, with his circuits, the "instrument will [... enable one to] generate Roentgen rays of much greater power than obtainable with ordinary apparatus".^[56]

He also commented on the hazards of working with his circuit and single-node X-ray-producing devices. Of his many notes in the early investigation of this phenomenon, he attributed the skin damage to various causes. He believed early on that damage to the skin was not caused by the Roentgen rays, but the ozone generated in contact with the skin, and to a lesser extent, nitrous acid. Tesla incorrectly held that x-rays were longitudinal waves, such as those produced in waves in plasma. There are known examples of this and these plasma waves can occur in the situation of force-free magnetic fields.^[57][58] His hypotheses and experiments were confirmed by others.^[59]

Tesla continued research in the field. He performed several experiments prior to Roentgen's discovery (including photographing the bones of his hand; later, he sent these images to Roentgen) but did not make his findings widely known; much of his research was lost in the 5th Avenue laboratory fire of March 1895.

Tesla demonstrated wireless energy transmission as early as 1891. The Tesla effect is a term for an application of this type of electrical conduction (that is, the movement of energy through space and matter, not just the production of voltage across a conductor).^[50][60]

American citizenship[link]

Tesla demonstrated a radio-controlled boat on 1898 U.S. Patent 613,809, named Method of an Apparatus for Controlling Mechanism of Moving Vehicle or Vehicles

On 30 July 1891, at the age of 35, he became a naturalized citizen of the United States. Tesla established his South Fifth Avenue laboratory in New York in the same year. 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.^[61]

Soon thereafter, in 1892,^[62] Tesla was awakened from a dream in which his mother had died.^[63] He returned to Europe for her funeral. After her death, Tesla fell ill. He spent two to three weeks recuperating in Gospić and the village of Tomingaj near Gračac, his mother's birthplace.

Some of Tesla's closest friends were artists. He befriended Century Magazine editor Robert Underwood Johnson, who adapted several Serbian poems of Jovan Jovanović Zmaj (which Tesla translated). Also during this time, Tesla was influenced by the Vedic philosophy (i.e., Hinduism) teachings of the Swami Vivekananda; so much so that, after his exposure to Hindu-Vedic thought, Tesla started using Sanskrit words to name some of his fundamental concepts regarding matter and energy.^[64]

Nikola Tesla's AC dynamo-electric machine (Electric generator) used to generate AC which is used to transport electricity across great distances. It is contained in U.S. Patent 390,721.

When Tesla was 36 years old, the first patents concerning 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 effect in conductors, designed tuned circuits, invented a machine for inducing sleep, invented a cordless gas discharge lamp, and transmitted electromagnetic energy without wires, building the first radio transmitter.^{[citation needed]} In St. Louis, Missouri, Tesla made a demonstration related to radio communication in 1893.^{[citation needed]} 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 when 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."^[65]

At the 1893 World's Fair, the World's Columbian Exposition in Chicago, an international exposition was held which, for the first time, devoted a building to electrical exhibits. It was a historic event as Tesla and George Westinghouse introduced visitors to AC power by using it to illuminate the Exposition. On display were fluorescent lamps developed by Westinghouse^[66] and single node bulbs. 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".^[67]

Tesla also explained the principles of the rotating magnetic field and induction motor by demonstrating how to make an egg made of copper 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 the liquefaction 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'.^[68] 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.^[69]

A "world system" for "the transmission of electrical energy without wires" that depends 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.^{[citation needed]} The same concept is used in virtual lightning rods and the electrolaser electroshock weapon,^[70] and has been proposed for disabling vehicles.

Also 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.^{[citation needed]} 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.^[71]

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.^[72] 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".^[73] In the same year, Tesla devised an "electric igniter" or spark plug for Internal combustion gasoline engines. He gained U.S. Patent 609,250, "Electrical Igniter for Gas Engines", on this mechanical ignition system. Tesla lived in the former Gerlach Hotel, renamed The Radio Wave building, at 49 W 27th St. (between Broadway and Sixth Avenue), Lower Manhattan, before the end of the century where he conducted the radio wave experiments. A commemorative 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.

Colorado Springs[link]

Publicity picture of Nikola Tesla sitting in his laboratory in Colorado Springs with his "Magnifying transmitter" generating millions of volts. The arcs are about 7 meters (23 ft) long. (Tesla's notes identify this as a multiple exposure photograph.)

An experiment in Colorado Springs. This bank of lights is receiving power by means of electrodynamic induction from a nearby transmitter

A Colorado Springs experiment: here a grounded tuned coil in resonance with a distant transmitter illuminates a light near the bottom of the picture.

In 1899, Tesla decided to move and began research in Colorado Springs, Colorado in a lab located near Foote Ave. and Kiowa St.,^[74] where he would have room for his high-voltage, high-frequency experiments. Upon his arrival he told reporters that he was conducting wireless telegraphy experiments transmitting signals from Pikes Peak to Paris. Tesla's diary contains explanations of his experiments concerning the ionosphere and the ground's telluric currents via transverse waves and longitudinal waves.^[75] At his lab, Tesla proved that the earth was a conductor, and he produced artificial lightning (with discharges consisting of millions of volts, and up to 135 feet long).^[76] Tesla also investigated atmospheric electricity, observing lightning signals via his receivers. Reproductions of Tesla's receivers and coherer circuits show an unpredicted level of complexity (e.g., distributed high-Q helical resonators, radio frequency feedback, crude heterodyne effects, and regeneration techniques).^[77] Tesla stated that he observed stationary waves during this time.^[78]

Tesla researched ways to transmit power and energy wirelessly over long distances (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 transceivers 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 hertz (Hz). In the 1950s, researchers confirmed that the resonant frequency of the Earth's ionospheric cavity was in this range (later named the Schumann resonance).

In Colorado Springs Tesla carried out various long distance wireless transmission-reception experiments. Tesla effect is the application of a type of electrical conduction (that is, the movement of energy through space and matter; not just the production of voltage across a conductor). Through longitudinal waves,^{[citation needed]} Tesla transferred energy to receiving devices. He sent electrostatic forces through natural media across a conductor situated in the changing magnetic flux and transferred electrical energy to a wireless receiver.

In the Colorado Springs lab, Tesla observed unusual signals that he later thought may have been evidence of extraterrestrial radio wave communications coming from Venus or Mars.^[79] He noticed repetitive signals from his receiver which were substantially different from the signals he had noted from storms and earth noise. Specifically, he later recalled that the signals appeared in groups of one, two, three, and four clicks together. Tesla had mentioned that he thought his inventions could be used to talk with other planets. There have even been claims that he invented a "Teslascope" for just such a purpose. It is debatable what type of signals Tesla received or whether he picked up anything at all. Research has suggested that Tesla may have had a misunderstanding of the new technology he was working with,^[80] or that the signals Tesla observed may have been non-terrestrial natural radio source such as the Jovian plasma torus signals.^[81]

Tesla left Colorado Springs on 7 January 1900. The lab was torn down ca. 1905 and its contents sold to pay debts. The Colorado experiments prepared Tesla for the establishment of the trans-Atlantic wireless telecommunications facility known as Wardenclyffe near Shoreham, Long Island.

Wardenclyffe years[link]

In 1900, with US$150,000 (51% from J. Pierpont Morgan), Tesla began planning the Wardenclyffe Tower facility. In June 1902, Tesla's lab operations were moved to Wardenclyffe from Houston Street. The tower was dismantled for scrap during World War I.^[82]

On his 50th birthday in 1906, Tesla demonstrated his 200 hp (150 kW) 16,000 rpm bladeless turbine. During 1910–1911 at the Waterside Power Station in New York, several of his bladeless turbine engines were tested at 100–5000 hp.

Nobel prize and Tesla[link]

Since the Nobel Prize in Physics was awarded to Guglielmo Marconi for radio in 1909, Thomas Edison and Tesla were mentioned in a press dispatch as potential laureates to share the Nobel Prize of 1915, leading to one of several Nobel Prize controversies. Some sources have claimed that because of their animosity toward each other neither was given the award, despite their scientific contributions; that each sought to minimize the other's achievements and right to win the award; that both refused ever to accept the award if the other received it first; and that both rejected any possibility of sharing it.^[14][83]

In the years after these rumors, neither Tesla nor Edison won the Prize (although Edison did receive one of 38 possible bids in 1915, and Tesla did receive one bid out of 38 in 1937).^[84] Earlier, Tesla alone was rumored to have been nominated for the Nobel Prize of 1912. The rumored nomination was primarily for his experiments with tuned circuits using high-voltage high-frequency resonant transformers.

Later years[link]

In 1915, Tesla filed a lawsuit against Marconi attempting, unsuccessfully, to obtain a court injunction against Marconi's claims. After Wardenclyffe, Tesla built the Telefunken Wireless Station in Sayville, Long Island. Some of what he wanted to achieve at Wardenclyffe was accomplished with the Telefunken Wireless. In 1917, the facility was seized and torn down by the Marines, because it was suspected that it could be used by German spies.

The Wardenclyffe Tower facility

Before World War I (1914-1918), Tesla looked overseas for investors to fund his research. When the war started, Tesla lost the funding he was receiving from his patents in European countries. After the war ended, Tesla made predictions regarding the relevant issues of the post-World War I environment, in a printed article (20 December 1914). Tesla believed that the League of Nations was not a remedy for the times and issues. 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 undoubtedly hurt what was left of his reputation.

At this time, he was staying at The Waldorf-Astoria Hotel, renting in an arrangement for deferred payments. Eventually, the Wardenclyffe deed was turned over to George Boldt, proprietor of the Waldorf-Astoria, to pay a US$20,000 debt. In 1917, around the time that the Wardenclyffe Tower was demolished by Boldt to make the land a more viable real estate asset, Tesla received AIEE's highest honor, the Edison Medal.

Tesla, in August 1917, first established principles regarding frequency and power level for the first primitive radar units.^[85]

In 1934, Émile Girardeau, working with the first French radar systems, stated he was building them "according to the principles stated by Tesla". By the 1920s, Tesla was reportedly negotiating with the United Kingdom government about a ray system.^{[citation needed]} Tesla had also stated that efforts had been made to steal the so called "death ray".^{[citation needed]} It is suggested that the removal of the Chamberlain government ended negotiations.^{[citation needed]}

On Tesla's 75th birthday in 1931, Time magazine put him on its cover. The cover caption noted his contribution to electrical power generation. Tesla received his last patent in 1928 for an apparatus for aerial transportation which was the first instance of VTOL aircraft. By the end of 1931, Tesla released "On Future Motive Power" which covered an ocean thermal energy conversion system. In 1934, Tesla wrote to consul Janković of his homeland. The letter contained a message of gratitude to Mihajlo Pupin who had initiated a donation scheme by which American companies could support Tesla. Tesla refused the assistance, choosing instead to live on a modest pension received from Yugoslavia, and to continue his research.

Tesla's famous telegram exchange with Vladko Maček is preserved in the Technical Museum in Zagreb, Croatia

In 1936, replying to a birthday telegram from Vladko Maček, Tesla said he was "equally proud" of his "Serbian origin and Croatian homeland",^[86] a phrase often paraphrased in conciliatory context at modern-day joint Croatian-Serbian Tesla celebrations.^[87] In addition, in the same telegram, Tesla wrote "Long live all Yugoslavs."^{[citation needed]} When others tried to co-opt him into ethnic and other conflicts in Yugoslavia, Tesla once replied: "If your hate could be turned into electricity, it would light up the whole world."^[86]

Field theories[link]

When he was 81, Tesla stated he had completed a "dynamic theory of gravity".^[88] He stated that it was "worked out in all details" and that he hoped to soon give it to the world.^[89] The theory was never published.

The bulk of the theory was developed between 1892 and 1894, during the period that he was conducting experiments with high frequency and high potential electromagnetism and patenting devices for their use. Reminiscent of Mach's principle, Tesla stated in 1925 that:

Nikola Tesla, with Ruđer Bošković's book Theoria Philosophiae Naturalis, sits in front of the spiral coil of his high-frequency transformer at East Houston Street, New York.

There is no thing endowed with life—from man, who is enslaving the elements, to the nimblest creature—in all this world that does not sway in its turn. Whenever action is born from force, though it be infinitesimal, the cosmic balance is upset and the universal motion results.

Tesla was critical of Einstein's relativity work, calling it:

...[a] magnificent mathematical garb which fascinates, dazzles and makes people blind to the underlying errors. The theory is like a beggar clothed in purple whom ignorant people take for a king ... its exponents are brilliant men but they are metaphysicists rather than scientists ...^[90]

Tesla also argued:

I hold that space cannot be curved, for the simple reason that it can have no properties. It might as well be said that God has properties. He has not, but only attributes and these are of our own making. Of properties we can only speak when dealing with matter filling the space. 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.^[91]

Tesla also believed that much of Albert Einstein's relativity theory had already been proposed by Ruđer Bošković, stating in an unpublished interview:

...the relativity theory, by the way, is much older than its present proponents. It was advanced over 200 years ago by my illustrious countryman Ruđer Bošković, the great philosopher, who, notwithstanding other and multifold obligations, wrote a thousand volumes of excellent literature on a vast variety of subjects. Bošković dealt with relativity, including the so-called time-space continuum ...'.^[92]

Directed-energy weapon[link]

Later in life, Tesla made remarkable claims concerning a "teleforce" weapon.^[93] The press called it a "peace ray" or death ray.^[94][95] In total, the components and methods included:^{[96][97][dubious – discuss]}

• An apparatus for producing manifestations of energy in free air instead of in a high vacuum as in the past. This, according to Tesla in 1934, was accomplished.
• A mechanism for generating tremendous electrical force. This, according to Tesla, was also accomplished.
• A means of intensifying and amplifying the force developed by the second mechanism.
• A new method for producing a tremendous electrical repelling force. This would be the projector, or gun, of the invention.

Tesla worked on plans for a directed-energy weapon from the early 1900s until his death.^{[dubious – discuss]} In 1937, Tesla wrote a treatise entitled "The Art of Projecting Concentrated Non-dispersive Energy through the Natural Media", which concerned charged particle beams.^{[98][dubious – discuss]} Tesla published the document in an attempt to expound on the technical description of a "superweapon that would put an end to all war." This treatise describing the particle beam is currently in the Nikola Tesla Museum archive in Belgrade. It describes an open-ended vacuum tube with a gas jet seal that allows particles to exit, a method of charging particles to millions of volts, and a method of creating and directing nondispersive particle streams (through electrostatic repulsion).^{[98][dubious – discuss]}

His records indicate that the device is based on a narrow stream of atomic clusters of liquid mercury or tungsten accelerated via high voltage (by means akin to his magnifying transformer). Tesla gives the following description concerning the particle gun's operation:

[The nozzle would] send concentrated beams of particles through the free air, of such tremendous energy that they will bring down a fleet of 10,000 enemy airplanes at a distance of 200 miles from a defending nation's border and will cause armies to drop dead in their tracks.^[99]

Tesla described the weapon as being able to be used against ground based infantry or for antiaircraft purposes.^[100] Tesla tried to interest the US War Department in the device.^[101] He also offered this invention to European countries.^[102] None of the governments purchased a contract to build the device. He was unable to act on his plans.^[103]