The ionosphere ( /aɪˈɒnəsfɪər/) is a part of the upper atmosphere, from about 85 km to 600 km altitude, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.^[1]

Relationship of the atmosphere and ionosphere

Geophysics[link]

The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km to more than 1000 km. It owes its existence primarily to ultraviolet radiation from the Sun.

The lowest part of the Earth's atmosphere, the troposphere extends from the surface to about 10 km (6.2 mi). Above 10 km is the stratosphere, followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer. At heights of above 80 km (50 mi), in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The number of these free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma which is referred to as the ionosphere. In a plasma, the negative free electrons and the positive ions are attracted to each other by the electromagnetic force, but they are too energetic to stay fixed together in an electrically neutral molecule.

Ultraviolet (UV), X-Ray and shorter wavelengths of solar radiation are ionizing, since photons at these frequencies contain sufficient energy to dislodge an electron from a neutral gas atom or molecule upon absorption. In this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher (of the order of thousand K) than the one of ions and neutrals. The reverse process to Ionization is recombination, in which a free electron is "captured" by a positive ion, occurs spontaneously. This causes the emission of a photon carrying away the energy produced upon recombination. As gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together. The balance between these two processes determines the quantity of ionization present.

Ionization depends primarily on the Sun and its activity. The amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is a diurnal (time of day) effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation. The activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions). There are also mechanisms that disturb the ionosphere and decrease the ionization. There are disturbances such as solar flares and the associated release of charged particles into the solar wind which reaches the Earth and interacts with its geomagnetic field.

The ionospheric layers[link]

Ionospheric layers.

At night the F layer is the only layer of significant ionization present, while the ionization in the E and D layers is extremely low. During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F₁ layer. The F₂ layer persists by day and night and is the region mainly responsible for the refraction of radio waves.

D layer[link]

The D layer is the innermost layer, 60 km to 90 km above the surface of the Earth. Ionization here is due to Lyman series-alpha hydrogen radiation at a wavelength of 121.5 nanometre (nm) ionizing nitric oxide (NO). In addition, with high Solar activity hard X-rays (wavelength < 1 nm) may ionize (N₂, O₂). During the night cosmic rays produce a residual amount of ionization. Recombination is high in the D layer, the net ionization effect is low, but loss of wave energy is great due to frequent collisions of the electrons (about ten collisions every msec). As a result high-frequency (HF) radio waves are not reflected by the D layer but suffer loss of energy therein. This is the main reason for absorption of HF radio waves, particularly at 10 MHz and below, with progressively smaller absorption as the frequency gets higher. The absorption is small at night and greatest about midday. The layer reduces greatly after sunset; a small part remains due to galactic cosmic rays. A common example of the D layer in action is the disappearance of distant AM broadcast band stations in the daytime.

During solar proton events, ionization can reach unusually high levels in the D-region over high and polar latitudes. Such very rare events are known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region. In fact, absorption levels can increase by many tens of dB during intense events, which is enough to absorb most (if not all) transpolar HF radio signal transmissions. Such events typically last less than 24 to 48 hours.

E layer[link]

The E layer is the middle layer, 90 km to 120 km above the surface of the Earth. Ionization is due to soft X-ray (1-10 nm) and far ultraviolet (UV) solar radiation ionization of molecular oxygen (O₂). Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10 MHz and may contribute a bit to absorption on frequencies above. However, during intense Sporadic E events, the E_s layer can reflect frequencies up to 50 MHz and higher. The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer rapidly disappears because the primary source of ionization is no longer present. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer.

This region is also known as the Kennelly-Heaviside Layer or simply the Heaviside layer. Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861–1939) and the British physicist Oliver Heaviside (1850–1925). However, it was not until 1924 that its existence was detected by Edward V. Appleton.

[edit] E_s

The E_s layer (sporadic E-layer) is characterized by small, thin clouds of intense ionization, which can support reflection of radio waves, rarely up to 225 MHz. Sporadic-E events may last for just a few minutes to several hours. Sporadic E propagation makes radio amateurs very excited, as propagation paths that are generally unreachable can open up. There are multiple causes of sporadic-E that are still being pursued by researchers. This propagation occurs most frequently during the summer months when high signal levels may be reached. The skip distances are generally around 1,000 km (620 mi). Distances for one hop propagation can be as close as 900 km (560 mi) or up to 2,500 km (1,600 mi). Double-hop reception over 3,500 km (2,200 mi) is possible.

F layer[link]

The F layer or region, also known as the Appleton layer extends from about 200 km to more than 500 km above the surface of Earth. It is the densest point of the ionosphere, which implies signals penetrating this layer will escape into space. At higher altitudes the amount of oxygen ions decreases and lighter ions such as hydrogen and helium become dominant, this layer is the topside ionosphere. Here extreme ultraviolet (UV, 10–100 nm) solar radiation ionizes atomic oxygen. The F layer consists of one layer at night, but during the day, a deformation often forms in the profile that is labeled F₁. The F₂ layer remains by day and night responsible for most skywave propagation of radio waves, facilitating high frequency (HF, or shortwave) radio communications over long distances.

From 1972 to 1975 NASA launched the AEROS and AEROS B satellites to study the F region.^[2]

Ionospheric model[link]

An ionospheric model is a mathematical description of the ionosphere as a function of location, altitude, day of year, phase of the sunspot cycle and geomagnetic activity. Geophysically, the state of the ionospheric plasma may be described by four parameters: electron density, electron and ion temperature and, since several species of ions are present, ionic composition. Radio propagation depends uniquely on electron density.

Models are usually expressed as computer programs. The model may be based on basic physics of the interactions of the ions and electrons with the neutral atmosphere and sunlight, or it may be a statistical description based on a large number of observations or a combination of physics and observations. One of the most widely used models is the International Reference Ionosphere (IRI)^[3] (IRI 2007), which is based on data and specifies the four parameters just mentioned. The IRI is an international project sponsored by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI).^[4] The major data sources are the worldwide network of ionosondes, the powerful incoherent scatter radars (Jicamarca, Arecibo, Millstone Hill, Malvern, St. Santin), the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets. IRI is updated yearly. IRI is more accurate in describing the variation of the electron density from bottom of the ionosphere to the altitude of maximum density than in describing the total electron content (TEC).Since 1999 this model is "International Standard" for the terrestrial ionosphere (standard TS16457).

Anomalies to the "ideal" model[link]

Ionograms allow deducing, via computation, the true shape of the different layers. Nonhomogeneous structure of the electron/ion-plasma produces rough echo traces, seen predominantly at night and at higher latitudes, and during disturbed conditions.

Winter anomaly[link]

At mid-latitudes, the F₂ layer daytime ion production is higher in the summer, as expected, since the Sun shines more directly on the Earth. However, there are seasonal changes in the molecular-to-atomic ratio of the neutral atmosphere that cause the summer ion loss rate to be even higher. The result is that the increase in the summertime loss overwhelms the increase in summertime production, and total F₂ ionization is actually lower in the local summer months. This effect is known as the winter anomaly. The anomaly is always present in the northern hemisphere, but is usually absent in the southern hemisphere during periods of low solar activity.

Equatorial anomaly[link]

Electric currents created in sunward ionosphere.

Within approximately ± 20 degrees of the magnetic equator, is the equatorial anomaly. It is the occurrence of a trough of concentrated ionization in the F₂ layer. The Earth's magnetic field lines are horizontal at the magnetic equator. Solar heating and tidal oscillations in the lower ionosphere move plasma up and across the magnetic field lines. This sets up a sheet of electric current in the E region which, with the horizontal magnetic field, forces ionization up into the F layer, concentrating at ± 20 degrees from the magnetic equator. This phenomenon is known as the equatorial fountain.

Equatorial electrojet[link]

The worldwide solar-driven wind results in the so-called Sq (solar quiet) current system in the E region of the Earth's ionosphere (ionospheric dynamo region) (100–130 km altitude). Resulting from this current is an electrostatic field directed E-W (dawn-dusk) in the equatorial day side of the ionosphere. At the magnetic dip equator, where the geomagnetic field is horizontal, this electric field results in an enhanced eastward current flow within ± 3 degrees of the magnetic equator, known as the equatorial electrojet.

Ionospheric perturbations[link]

X-rays: sudden ionospheric disturbances (SID)[link]

When the Sun is active, strong solar flares can occur that will hit the sunlit side of Earth with hard X-rays. The X-rays will penetrate to the D-region, releasing electrons that will rapidly increase absorption, causing a High Frequency (3 - 30 MHz) radio blackout. During this time Very Low Frequency (3 – 30 kHz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it. As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out ends as the electrons in the D-region recombine rapidly and signal strengths return to normal.

Protons: polar cap absorption (PCA)[link]

Associated with solar flares is a release of high-energy protons. These particles can hit the Earth within 15 minutes to 2 hours of the solar flare. The protons spiral around and down the magnetic field lines of the Earth and penetrate into the atmosphere near the magnetic poles increasing the ionization of the D and E layers. PCA's typically last anywhere from about an hour to several days, with an average of around 24 to 36 hours.

Geomagnetic storms[link]

A geomagnetic storm is a temporary intense disturbance of the Earth's magnetosphere.

• During a geomagnetic storm the F₂ layer will become unstable, fragment, and may even disappear completely.
• In the Northern and Southern pole regions of the Earth aurorae will be observable in the sky.

Lightning[link]

Lightning can cause ionospheric perturbations in the D-region in one of two ways. The first is through VLF (Very Low Frequency) radio waves launched into the magnetosphere. These so-called "whistler" mode waves can interact with radiation belt particles and cause them to precipitate onto the ionosphere, adding ionization to the D-region. These disturbances are called Lightning-induced Electron Precipitation (LEP) events.

Additional ionization can also occur from direct heating/ionization as a result of huge motions of charge in lightning strikes. These events are called Early/Fast.

In 1925, C. F. Wilson proposed a mechanism by which electrical discharge from lightning storms could propagate upwards from clouds to the ionosphere. Around the same time, Robert Watson-Watt, working at the Radio Research Station in Slough, UK, suggested that the ionospheric sporadic E layer (Es) appeared to be enhanced as a result of lightning but that more work was needed. In 2005, C. Davis and C. Johnson, working at the Rutherford Appleton Laboratory in Oxfordshire, UK, demonstrated that the Es layer was indeed enhanced as a result of lightning activity. Their subsequent research has focussed on the mechanism by which this process can occur.

Radio application[link]

DX communication, popular among amateur radio enthusiasts, is a term given to communication over great distances. Thanks to the property of ionized atmospheric gases to refract high frequency (HF, or shortwave) radio waves, the ionosphere can be utilized to "bounce" a transmitted signal down to ground. Transcontinental HF-connections rely on up to 5 bounces, or hops. Such communications played an important role during World War II. Karl Rawer's most sophisticated prediction method^[1] took account of several (zig-zag) paths, attenuation in the D-region and predicted the 11-year solar cycle by a method due to Wolfgang Gleißberg.

Mechanism of refraction[link]

When a radio wave reaches the ionosphere, the electric field in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Some of the radio-frequency energy is given up to this resonant oscillation. The oscillating electrons will then either be lost to recombination or will re-radiate the original wave energy. Total refraction can occur when the collision frequency of the ionosphere is less than the radio frequency, and if the electron density in the ionosphere is great enough.

The critical frequency is the limiting frequency at or below which a radio wave is reflected by an ionospheric layer at vertical incidence. If the transmitted frequency is higher than the plasma frequency of the ionosphere, then the electrons cannot respond fast enough, and they are not able to re-radiate the signal. It is calculated as shown below:

Failed to parse (Missing texvc executable; please see math/README to configure.): f_{critical} = 9 \times\sqrt{N}

where N = electron density per m³ and f_critical is in Hz.

The Maximum Usable Frequency (MUF) is defined as the upper frequency limit that can be used for transmission between two points at a specified time.

Failed to parse (Missing texvc executable; please see math/README to configure.): f_{muf} = \frac{f_{critical}}{ \sin \alpha}

where Failed to parse (Missing texvc executable; please see math/README to configure.): \alpha

= angle of attack, the angle of the wave relative to the horizon, and sin is the sine function.

The cutoff frequency is the frequency below which a radio wave fails to penetrate a layer of the ionosphere at the incidence angle required for transmission between two specified points by refraction from the layer.

Other applications[link]

The open system electrodynamic tether, which uses the ionosphere, is being researched. The space tether uses plasma contactors and the ionosphere as parts of a circuit to extract energy from the Earth's magnetic field by electromagnetic induction.

Measurements[link]

Ionograms[link]

Ionograms show the virtual heights and critical frequencies of the ionospheric layers and which are measured by an ionosonde. An ionosonde sweeps a range of frequencies, usually from 0.1 to 30 MHz, transmitting at vertical incidence to the ionosphere. As the frequency increases, each wave is refracted less by the ionization in the layer, and so each penetrates further before it is reflected. Eventually, a frequency is reached that enables the wave to penetrate the layer without being reflected. For ordinary mode waves, this occurs when the transmitted frequency just exceeds the peak plasma, or critical, frequency of the layer. Tracings of the reflected high frequency radio pulses are known as ionograms. Reduction rules are given in: "URSI Handbook of Ionogram Interpretation and Reduction", edited by William Roy Piggott and Karl Rawer, Elsevier Amsterdam, 1961 (translations into Chinese, French, Japanese and Russian are available).

Incoherent scatter radars[link]

Incoherent scatter radars operate above the critical frequencies. Therefore the technique allows to probe the ionosphere, unlike ionosondes, also above the electron density peaks. The thermal fluctuations of the electron density scattering the transmitted signals lack coherence, which gave the technique its name. Their power spectrum contains information not only on the density, but also on the ion and electron temperatures, ion masses and drift velocities.

Solar flux[link]

Solar flux is a measurement of the intensity of solar radio emissions at a frequency of 2800 MHz made using a radio telescope located in Dominion Radio Astrophysical Observatory, Penticton, British Columbia, Canada.^[5] Known also as the 10.7 cm flux (the wavelength of the radio signals at 2800 MHz), this solar radio emission has been shown to be proportional to sunspot activity. However, the level of the Sun's ultraviolet and X-ray emissions is primarily responsible for causing ionization in the Earth's upper atmosphere. We now have data from the GOES spacecraft that measures the background X-ray flux from the Sun, a parameter more closely related to the ionization levels in the ionosphere.

• The A and K indices are a measurement of the behavior of the horizontal component of the geomagnetic field. The K index uses a scale from 0 to 9 to measure the change in the horizontal component of the geomagnetic field. A new K index is determined at the Boulder Geomagnetic Observatory 40°08′15″N 105°14′16″W / 40.137558°N 105.237875°W / 40.137558; -105.237875.
• The geomagnetic activity levels of the Earth are measured by the fluctuation of the Earth's magnetic field in SI units called teslas (or in non-SI gauss, especially in older literature). The Earth's magnetic field is measured around the planet by many observatories. The data retrieved is processed and turned into measurement indices. Daily measurements for the entire planet are made available through an estimate of the ap index, called the planetary A-index (PAI).

Scientific research on ionospheric propagation[link]

Scientists also are exploring the structure of the ionosphere by a wide variety of methods, including passive observations of optical and radio emissions generated in the ionosphere, bouncing radio waves of different frequencies from it, incoherent scatter radars such as the EISCAT, Sondre Stromfjord, Millstone Hill, Arecibo, and Jicamarca radars, coherent scatter radars such as the Super Dual Auroral Radar Network (SuperDARN) radars, and using special receivers to detect how the reflected waves have changed from the transmitted waves.

A variety of experiments, such as HAARP (High Frequency Active Auroral Research Program), involve high power radio transmitters to modify the properties of the ionosphere. These investigations focus on studying the properties and behavior of ionospheric plasma, with particular emphasis on being able to understand and use it to enhance communications and surveillance systems for both civilian and military purposes. HAARP was started in 1993 as a proposed twenty year experiment, and is currently active near Gakona, Alaska.

The SuperDARN radar project researches the high- and mid-latitudes using coherent backscatter of radio waves in the 8 to 20 MHz range. Coherent backscatter is similar to Bragg scattering in crystals and involves the constructive interference of scattering from ionospheric density irregularities. The project involves more than 11 different countries and multiple radars in both hemispheres.

Scientists are also examining the ionosphere by the changes to radio waves, from satellites and stars, passing through it. The Arecibo radio telescope located in Puerto Rico, was originally intended to study Earth's ionosphere.

Ionospheres on other planets and Titan[link]

The atmosphere of Titan includes an ionosphere.^[6] It ranges from about 1100 to 1300 km in altitude, and contains carbon compounds.

Planets with ionospheres (incomplete list):

Ionosphere of Venus

Ionosphere of Uranus

History[link]

Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland (now in Canada) using a 152.4 m (500 ft) kite-supported antenna for reception. The transmitting station in Poldhu, Cornwall used a spark-gap transmitter to produce a signal with a frequency of approximately 500 kHz and a power of 100 times more than any radio signal previously produced. The message received was three dits, the Morse code for the letter S. To reach Newfoundland the signal would have to bounce off the ionosphere twice. Dr. Jack Belrose has recently contested this, however, based on theoretical and experimental work.^[7] However, Marconi did achieve transatlantic wireless communications beyond a shadow of doubt in Glace Bay, Nova Scotia one year later.

In 1902, Oliver Heaviside proposed the existence of the Kennelly-Heaviside Layer of the ionosphere which bears his name. Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Heaviside's proposal, coupled with Planck's law of black body radiation, may have hampered the growth of radio astronomy for the detection of electromagnetic waves from celestial bodies until 1932 (and the development of high frequency radio transceivers). Also in 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties.

In 1912, the U.S. Congress imposed the Radio Act of 1912 on amateur radio operators, limiting their operations to frequencies above 1.5 MHz (wavelength 200 meters or smaller). The government thought those frequencies were useless. This led to the discovery of HF radio propagation via the ionosphere in 1923.

In 1926, Scottish physicist Robert Watson-Watt introduced the term ionosphere in a letter published only in 1969 in Nature:

We have in quite recent years seen the universal adoption of the term ‘stratosphere’..and..the companion term ‘troposphere’... The term ‘ionosphere’, for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series.

Edward V. Appleton was awarded a Nobel Prize in 1947 for his confirmation in 1927 of the existence of the ionosphere. Lloyd Berkner first measured the height and density of the ionosphere. This permitted the first complete theory of short wave radio propagation. Maurice V. Wilkes and J. A. Ratcliffe researched the topic of radio propagation of very long radio waves in the ionosphere. Vitaly Ginzburg has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere.

In 1962 the Canadian satellite Alouette 1 was launched to study the ionosphere. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS -A and -B in 1972 and 1975, all for measuring the ionosphere.

See also[link]

• Geophysics
  • Van Allen radiation belt
  • Schumann resonances
  • International Reference Ionosphere
  • Volland-Stern Model
  • ionospheric dynamo region
• Radio
  • Earth-Ionosphere waveguide
  • Fading
  • Line-of-sight propagation
  • Ionospheric absorption
• Related
  • Tether propulsion
  • Canadian Geospace Monitoring
  • Pioneer Venus project
  • Nozomi
  • New Horizons
  • Soft gamma repeater
  • TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics)
  • International Geophysical Year
  • Upper Atmospheric Lightning
• Lists
  • List of astronomical topics
  • List of electronics topics
  • List of plasma (physics) articles

Notes[link]

References[link]

• Corum, J. F., and Corum, K. L., "A Physical Interpretation of the Colorado Springs Data". Proceedings of the Second International Tesla Symposium. Colorado Springs, Colorado, 1986.
• Davies, K., 1990. Peter Peregrinus Ltd, London. ISBN 0-86341-186-X Ionospheric Radio.
• Grotz, Toby, "The True Meaning of Wireless Transmission of power". Tesla : A Journal of Modern Science, 1997.
• Hargreaves, J. K., "The Upper Atmosphere and Solar-Terrestrial Relations". Cambridge University Press, 1992,
• Kelley, M. C, and Heelis, R. A., "The Earth's Ionosphere: Plasma Physics and Electrodynamics". Academic Press, 1989.
• Leo F. McNamara. (1994) ISBN 0-89464-804-7 "Radio Amateurs Guide to the Ionosphere".
• Rawer,K.:"Wave Propagation in the Ionosphere". Kluwer Academic Publ., Dordrecht 1993 ISBN 0-7923-0775-5.
• D. Bilitza, "International Reference Ionosphere 2000,".Radio Science 36, #2, pp 261–275, 2001.
• J. Lilensten et P.-L. Blelly: Du Soleil à la Terre, Aéronomie et météorologie de l'espace, Collection Grenoble Sciences, Université Joseph Fourier Grenoble I, 2000. ISBN 978-2-86883-467-6
• P.-L. Blelly and D. Alcaydé, Ionosphere, in: Y. Kamide/A. Chian, Handbook of the Solar-Terrestrial Environment, Springer-Verlag Berlin Heidelberg, pp. 189–220, 2007. doi:10.1007/11367758_8
• H. Volland, Atmospheric Electrodynamics, Springer Verlag, Berlin, 1984.

External links[link]

Wikimedia Commons has media related to: Ionosphere

Look up ionosphere in Wiktionary, the free dictionary.

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]

Theoretical inventions[link]

Another of Tesla's theorized inventions is commonly referred to as Tesla's Flying Machine, which appears to resemble an ion-propelled aircraft.^[104] Tesla claimed that one of his life goals was to create a flying machine that would run without the use of an airplane engine, wings, ailerons, propellers, or an onboard fuel source. Initially, Tesla pondered about the idea of a flying craft that would fly using an electric motor powered by grounded base stations. As time progressed, Tesla suggested that perhaps such an aircraft could be run entirely electro-mechanically. The theorized appearance would typically take the form of a cigar or saucer.^[105]

Personal life[link]

Nikola Tesla's father Milutin, Serbian Orthodox priest in the village of Smiljan.

Possessing an eidetic memory, Nikola Tesla was a polyglot, and along with his native tongue he also spoke Czech, English, French, German, Hungarian, Italian, and Latin.^[106]

During his second year of study at Graumltz, Tesla developed a passion for (and became very proficient at) billiards, chess and card-playing, sometimes spending more than 48 hours in a stretch at a gaming table.^[107][108] Tesla by nature required little sleep, claiming to never sleep more than two hours.^[109] On one occasion at his laboratory Tesla worked for a period of 84 hours without sleep or rest.^[110]

Tesla may have suffered from obsessive-compulsive disorder, and had many unusual quirks and phobias. He did things in threes, and was adamant about staying in a hotel room with a number divisible by three. Tesla was physically revolted by jewelry, notably pearl earrings.^[111] He was fastidious about cleanliness and hygiene, and was by all accounts mysophobic.

Tesla was obsessed with pigeons, ordering special seeds for the pigeons he fed in Central Park and even bringing injured ones into his hotel room to nurse them back to health. Tesla was an animal-lover, often reflecting contentedly about a childhood cat, "The Magnificent Mačak." Tesla never married. He was celibate and claimed that his chastity was very helpful to his scientific abilities.^[27] Nonetheless there have been numerous accounts of women vying for Tesla's affection, even some madly in love with him. Tesla, though polite, behaved rather ambivalently to these women in the romantic sense.

Tesla was prone to alienating himself and was generally soft-spoken. However, when he did engage in a social life, many people spoke very positively and admiringly of him. Robert Underwood Johnson described him as attaining a "distinguished sweetness, sincerity, modesty, refinement, generosity, and force." His loyal secretary, Dorothy Skerrit, wrote: "his genial smile and nobility of bearing always denoted the gentlemanly characteristics that were so ingrained in his soul." Tesla's friend Hawthorne wrote that "seldom did one meet a scientist or engineer who was also a poet, a philosopher, an appreciator of fine music, a linguist, and a connoisseur of food and drink."

Nevertheless, Tesla could be harsh at times; he openly expressed his disgust for overweight people, once firing a secretary because of her weight.^[112] He was quick to criticize others' clothing as well, on several occasions directing a subordinate to go home and change her dress.^[27]

Tesla was widely known for his great showmanship, presenting his innovations and demonstrations to the public as an artform, almost like a magician. This seems to conflict with his observed reclusiveness; Tesla was a complicated figure. He refused to hold conventions without his Tesla coil blasting electricity throughout the room, despite the audience often being terrified, though he assured them everything was perfectly safe.

Mark Twain in Tesla's lab, early 1894

In middle age, Tesla became close friends with Mark Twain. They spent a lot of time together in his lab and elsewhere.

Tesla remained bitter in the aftermath of his dispute with Edison. The day after Edison died the New York Times contained extensive coverage of Edison's life, with the only negative opinion coming from Tesla, who was quoted as saying:

He had no hobby, cared for no sort of amusement of any kind and lived in utter disregard of the most elementary rules of hygiene  ... His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90 percent of the labor. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense.^[113]

Shortly before he died, Edison said that his biggest mistake had been in trying to develop direct current, rather than the superior alternating current system that Tesla had put within his grasp.^[114]

Tesla was good friends with Robert Underwood Johnson. He had amicable relations with Francis Marion Crawford, Stanford White, Fritz Lowenstein, George Scherff, and Kenneth Swezey. He ripped up a Westinghouse contract that would have made him the world's first billionaire, in part because of the implications it would have on his future vision of free power, and in part because it would run Westinghouse out of business, and Tesla had no desire to deal with the creditors.^{[citation needed]}

Tesla lived the last ten years of his life in a two-room suite on the 33rd floor of the Hotel New Yorker, room 3327. There, near the end of his life, Tesla showed signs of encroaching senility, claiming to be visited by a specific white pigeon daily. Several biographers note that Tesla viewed the death of the pigeon as a "final blow" to himself and his work.

Tesla believed that war could not be avoided until the cause for its recurrence was removed, but was opposed to wars in general. However, Tesla came to find exceptions in which he thought certain situations and wars were justifiable.^[115] Tesla sought to reduce distance, such as in communication for better understanding, transportation, and transmission of energy, as a means to ensure friendly international relations.^[116]

Tesla was a life-long bachelor. Like many of his era, he became a proponent of an imposed selective breeding version of eugenics. His opinions stemmed from a belief that humans already interfered with the natural "ruthless workings of nature", rather than conceptions of a "master race" or inherent superiority of one person over another. His advocacy of it was however to push it further. In a 1937 interview, he stated:

... man's new sense of pity began to interfere with the ruthless workings of nature. The only method compatible with our notions of civilization and the race is to prevent the breeding of the unfit by sterilization and the deliberate guidance of the mating instinct .... The trend of opinion among eugenists is that we must make marriage more difficult. Certainly no one who is not a desirable parent should be permitted to produce progeny. A century from now it will no more occur to a normal person to mate with a person eugenically unfit than to marry a habitual criminal.^[117]

In 1926, Tesla commented on the ills of the social subservience of women and the struggle of women toward gender equality, indicated that humanity's future would be run by "Queen Bees". He believed that women would become the dominant sex in the future.^[118]

In his later years Tesla became a vegetarian. In an article for Century Illustrated Magazine he wrote: "It is certainly preferable to raise vegetables, and I think, therefore, that vegetarianism is a commendable departure from the established barbarous habit." Tesla argued that it is wrong to eat uneconomic meat when large numbers of people are starving; he also believed that plant food was "superior to [meat] in regard to both mechanical and mental performance". He also argued that animal slaughter was "wanton and cruel".^[119]

In his final years he suffered from extreme sensitivity to light, sound and other influences.^[120]

Death[link]

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Gilded urn with Tesla's ashes, in his favorite geometrical object of sphere, Nikola Tesla Museum, Belgrade.

Tesla died on 7 January 1943 at age 86 from heart thrombus, alone in room 3327 of the New Yorker Hotel.^[121] A few days after Tesla's death, the information center of the Yugoslav royal government-in-exile released a statement giving a short review of Tesla's achievements and the schedule for his memorial service and funeral. The speech, written by Louis Adamic, was read in a live broadcast on Radio New York by the mayor of New York City, Fiorello La Guardia, on 10 January 1943. The remains of Nikola Tesla were taken to Campbell cemetery. The protocol anticipated the funeral service would be conducted on 12 January in the Cathedral of Saint John the Divine in Manhattan.^[122] Bishop William T. Manning delivered the introductory and the last prayer in English. The funeral service was conducted in the name of the Serbian Orthodox Church by priest Dusan Sukletovic, the superior of the Church of St. Sava of the New York parish. The bereaved family members present at the funeral were Sava Kosanovic and Nikola Trbojevic. A state funeral was attended by 2000 people. Tesla's casket was draped with U. S. and Yugoslav flags. The pallbearers were Nobel prize winners. Telegrams of condolence were received from many notables including the First Lady of the United States, Mrs Eleanor Roosevelt and Vice-President Henry A. Wallace. Tesla's body was cremated and his ashes taken to Belgrade, Serbia, then-Yugoslavia in 1957. The urn containing his ashes was placed in the Nikola Tesla Museum in Belgrade. Despite having sold his AC electricity patents, Tesla died with significant debts. Later that year the US Supreme Court upheld Tesla's patent number 645576 in a ruling that served as the basis for patented radio technology in the United States.^[123]

Soon after his death Tesla's safe was opened by his nephew Sava Kosanović. Shortly thereafter Tesla's papers and other property were impounded by the United States' Alien Property Custodian office in Tesla's compound at the Manhattan Warehouse, even though he was a naturalized citizen.

Dr. John G. Trump was the main government official who went over Tesla's secret papers after his death in 1943. At the time, Trump was a well-known electrical engineer serving as a technical aide to the National Defense Research Committee of the Office of Scientific Research & Development, Technical Aids, Div. 14, NTRC (predecessor agency to the CIA's Office of Scientific Intelligence). Trump was also a professor at M.I.T., and had his feelings hurt by Tesla's 1938 review and critique of M.I.T.'s huge Van de Graaff generator with its two thirty-foot towers and two 15-foot-diameter (4.6 m) balls, mounted on railroad tracks—which Tesla showed could be out-performed in both voltage and current by one of his tiny coils about two feet tall.^{[124][dubious – discuss]} Trump was asked to participate in the examination of Tesla's papers at the Manhattan Warehouse & Storage Co. Trump reported afterwards that no examination had been made of the vast amount of Tesla's property that had been in the basement of the New Yorker Hotel ten years prior to Tesla's death, or of any of his papers, except those in his immediate possession at the time of his death. Trump concluded in his report that there was nothing that would constitute a hazard in unfriendly hands.

After the FBI was contacted by the War Department, his papers were declared to be top secret. The personal effects were sequestered on the advice of presidential advisers; J. Edgar Hoover declared the case most secret, because of the nature of Tesla's inventions and patents.^[125] One document stated that "[he] is reported to have some 80 trunks in different places containing transcripts and plans having to do with his experiments [...]". Altogether, in Tesla's effects, there were the contents of his safe, two truckloads of papers and apparatuses from his hotel, another 75 packing crates and trunks in a storage facility, and another 80 large storage trunks in another storage facility. The Navy and several "federal officials" spent two days microfilming some of the material at the Office of Alien Properties storage facility in 1943, and that was it, until Oct., 1945.^[126]

Tesla's family and the Yugoslav embassy struggled with the American authorities to gain these items after his death because of the potential significance of some of his research. Eventually Mr. Kosanović won possession of the materials, which are now housed in the Nikola Tesla Museum.^[127]

Literary works[link]

Apart from doing pure work on inventing things, Tesla also wrote a number of books and articles for magazines and journals.^[128] Among his books are My Inventions: The Autobiography of Nikola Tesla, The Fantastic Inventions of Nikola Tesla and The Tesla Papers.

A number of Tesla's writings are freely available on the web,^{[129][130][131]} including the article The Problem of Increasing Human Energy which he wrote for The Century Magazine,^[132][133] and the article Experiments With Alternate Currents Of High Potential And High Frequency published in his book Inventions, Researches and Writings of Nikola Tesla.^[134][135]

Legacy and honors[link]

Nikola Tesla on contemporary 100 Serbian dinar banknote.

Nikola Tesla Corner in New York

• The tesla (symbol T) – compound derived SI unit of magnetic flux density.^[136]
• Tesla – a crater on the far side of the moon of 26 kilometers in diameter at −2,0° width, −132.0° height.^[137]
• 2244 Tesla – a minor planet.^[137]
• TPP Nikola Tesla – the largest power plant in Serbia.
• The rock band Tesla takes its name from Nikola Tesla.^[138]
• An electric car company, Tesla Motors, named their company in tribute to Tesla.^[139]
• The Belgrade Nikola Tesla Airport is named in his honor.^[140]
• Google honoured Tesla on his birthday on 10 July 2009 by displaying a doodle in the Google search home page, that showed the G as a tesla coil.^[141][142]
• The Czechoslovakian electro-technical company Tesla
• Tesla Motors, a manufacturer of electric cars based in Palo Alto, California, is named for him.
• The street sign “Nikola Tesla Corner” at the corner of the 40th Street and 6th Avenue in Manhattan
• The United States Postal Service honored Tesla with a commemorative stamp in 1983.
• Tesla was inducted into the Inventor’s Hall of Fame in 1975.
• The Nikola Tesla Award^[143]

Monuments[link]

Nikola Tesla monument by Les Drysdale in Niagara Falls, Ontario.

The Nikola Tesla Memorial Centre located in his birthplace of Smiljan near the town of Gospić in Croatia opened in 2006 features a statue of Tesla designed by sculptor Mile Blažević.^[144][145] On 7 July 2006 on the corner of Masarykova and Preradovićeva streets in the Lower Town area in Zagreb the monument to Tesla was unveiled. This monument was designed by Ivan Meštrović in 1952 and was transferred from the Zagreb-based Ruđer Bošković Institute where it had spent previous decades.

A monument to Tesla was established at Niagara Falls, New York. This monument, sculpted by Frano Kršinić and portraying Tesla reading a set of notes, was presented to the United States by Yugoslavia in 1976 and is an identical copy of the monument standing in front of the University of Belgrade Faculty of Electrical Engineering. Another monument to Tesla, featuring him standing on a portion of an alternator, was established at Queen Victoria Park in Niagara Falls, Ontario, Canada. The monument was officially unveiled on 9 July 2006 on the 150th anniversary of Tesla's birth. The monument was sponsored by St. George Serbian Church, Niagara Falls, and designed by Les Drysdale of Hamilton, Ontario. Drysdale's design was the winning design from an international competition.

In 1994, acting on the advice of the President's Advisory Council on Historic Preservation, a formal nomination process was initiated by the Tesla Wardenclyffe Project seeking placement of the Wardenclyffe laboratory-office building and the Tesla tower foundation on both the New York State and National Registers of Historic Places. This would result in the creation of a monument to Tesla out of the Wardenclyffe site itself.^[146]

Portrayals in popular culture[link]

Nikola Tesla has appeared in popular culture as a character in books, films, radio, TV, music, live theatre, comics and video games. The lack of recognition received by Tesla during his own lifetime has made him a tragic and inspirational character well suited to dramatic fiction. The impact of the technologies invented by Tesla is a recurring theme in several types of science fiction.

See also[link]

Electronics portal

• Electrical Experimenter
• List of Tesla patents
• Timeline of low-temperature technology

References[link]

Notes[link]