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Feature Article 1856–1943 Nikola Tesla the original ‘mad scientist’ L ast month, our final entry concerned Tesla’s application for multiple radio patents in 1897 and some of the controversy surrounding his claims predating some of Marconi’s, despite Tesla not having demonstrated any real radio communications. Here is what happened after that: Ignition system for gasoline engines 1898 In 1898, Tesla obtained US Patent 609,250 for a spark plug for petrol engines – see Fig.14. Teleautomatics 1898 The first article in this two-part series, published last month, introduced prolific inventor Nikola Tesla and covered his life and developments until 1898 before we ran out of space. This article picks up where that one left off and also covers some overarching topics, like his contributions to AC electricity and some of his misconceptions. Part 2 by Dr David Maddison, VK3DSM Tesla received US Patent 613,809 for a remote-controlled vehicle in 1898 (Fig.15), titled “Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles”. Based on this, he demonstrated a remotecontrolled 1m-long boat at Madison Square Garden in New York City as part of the first annual Electrical Exhibition. The boat was controlled by an operator with a transmitter (see Fig.16). The receiver used a device called a coherer, an early type of radio signal detector containing metal filings that came into contact with each other when a radio signal was received, changing its resistance. Once a signal was received, the device had to be reset by shaking it or using a ‘clapper’ attached to an electromagnet. Such a device could only detect the presence or absence of a signal, like in Morse code; such a binary output was ideal for this application. One of Tesla’s inventions was a coherer that continuously rotated to reset it, although he does not use the term “coherer”. The boat contained a motor for propulsion and one for a servo mechanism. The boat could steer, start, stop, go forwards or backwards or light one of two lamps. To control the boat, there was a mechanism that, upon detecting the radio signal, moved a set of electrical contacts to the next of several positions that would execute the predefined manoeuvre. This represented the state of the rudder, motor and lighting. Radio signals from Mars 1899 Tesla on the cover of Electrical Inventor magazine, February 1919. The lead image is based on a photo of Tesla from around 1900 demonstrating wireless power transmission. He is holding a partially evacuated glass bulb that’s glowing due to the electric field from a nearby Tesla coil. See https://w.wiki/AZMz Tesla believed that radio signals he received in 1899 in Colorado may have been from Mars (see Fig.17). In 1909, he wrote: To be sure, we have no absolute proof 58 Practical Electronics | November | 2025 The Life of Nikola Tesla, part two that Mars is inhabited... Personally, I base my faith on the feeble planetary electrical disturbances which I discovered in the summer of 1899, and which, according to my investigations, could not have originated from the sun, the moon, or Venus. Further study since has satisfied me they must have emanated from Mars – https://pemag.au/link/aby4 Some have suggested that the signals Tesla was receiving were, in fact, from Marconi’s (or others’) radio experiments. Fig.14: Tesla’s ignition system for petrol engines. Source: https:// patents.google. com/patent/ US609250A Tesla Experimental Station 1899 to 1900 In 1899, Tesla established the Tesla Experimental Station in Colorado Springs, Colorado, and used it for one year. He moved there because he wanted a high altitude for his experiments in wireless electricity transmission and more space than his Manhattan laboratory. His main focus was on high-frequency, high-voltage experiments. He built the largest Tesla coil to date, with a diameter of 15m, to be configured as a “magnifying transmitter”. This was a variation of the Tesla coil with an antenna (see Fig.18) tuned to the supposed resonant frequency of the Earth to create standing waves of electrical energy. The idea was to harvest them with an appropriate antenna and receiver. The magnifying transmitter was a three-coil, triple-resonant design. This coil reportedly had a 300kW power rating and generated millions of volts at 150kHz. This was to be the prototype for his magnifying transmitter at the Wardenclyffe Tower. Tesla produced electric arc discharges up to 41m long. He had a deal with the local power company to provide large or unlimited amounts of power (he occasionally damaged their generators!). Tesla wrote that he had produced 20MV at 1000-1100A (we assume that was current drawn from the mains supply) and that he had learned how to produce 100MV (see p196, https:// pemag.au/aby0). Tesla also wrote that lightning arrestors on buildings within a 19 km radius were “bridged with continuous arcs” and that he lit handheld incandescent lights 15-30m from his laboratory when the oscillator was running at 4MV. Apparently, the light filament often broke due to the resulting vibrations. Practical Electronics | November | 2025 Fig.15: a remote-controlled boat described by Tesla’s US Patent 613,809 (top: plan view, bottom: the vessel in the water). Fig.16: a model of Tesla’s boat in the Nikola Tesla Museum in Belgrade. The museum website (https://tesla-museum.org/en/ qr-en/exhibit-049) gives no information about when the model was made, but clear acrylic wasn’t invented until the 1930s. Source: https://w.wiki/AbUv Fig.17: a newspaper article titled “Nicola Tesla Promises Communication with Mars” from The Times (Richmond, Virginia, USA) on January 13th, 1901, page 8. Source: The Times, January 13th 1901 – https://pemag.au/link/abyo 59 Feature Article Fig.18: an exterior view of the Colorado Springs laboratory. The antenna mast was telescopic and 43m tall. Source: https://w.wiki/AbUx Fig.19: Tesla’s “magnifying transmitter” at his Colorado Springs facility, around 1899. This photo was a long-exposure photo taken in a darkened room with a double exposure showing Tesla sitting on a chair. Source: https://w.wiki/AbUw 60 Tesla stated that when he energised the large transmitter coil, butterflies were caught in the field and flew around in circles as if trapped in a hurricane. He also noted sparks in the sand when walking “some distance from the building”, saying: At night a continuous stream of tiny sparks could be seen between the heels and the earth and between the grains of sand. When I operated with undamped waves, the oscillator being perfectly silent (no streamers whatever), a horse at a distance of perhaps onehalf a mile, would become scared and gallop away the instant the switch was thrown on... When using damped waves the roar was so strong that it could be plainly heard ten miles away. Fig.19 was a long-exposure photo taken in a darkened room. The arcs are for demonstration purposes, deliberately induced and were not a normal part of the operation of this machine. The discharge was reported to be deafening and that “sparks an inch long can be drawn from a water main at a distance of three hundred feet from the laboratory”. The laboratory was torn down in 1904, and the contents were sold to pay off debts. Energy harvesting 1901 In 1901, Tesla was granted US Patent 685,957 for supposedly harvesting energy from sources such as “ultra-­ violet light, cathodic, Roentgen rays, or the like”. Wardenclyffe Tower 1901 to 1906 Wardenclyffe was Tesla’s last major laboratory (see Figs.20 & 21). It was built in Long Island, New York and was intended for trans-Atlantic wireless communications. Later, he wished to extend it for wireless power transmission in accordance with his theories. Banker JP Morgan was the main financial backer for this project, but he refused to continue funding it. So it was abandoned in 1906, never having become operational. The tower was, to some extent, an extension of Tesla’s Colorado Springs experiments in an attempt to implement the World Wireless System for transmitting electric power. Tesla believed that if he injected current into the Earth at the right frequency, he could get the Earth’s natural charge to resonate and establish standing waves, which could be utilised to harvest electricity remotely. At Wardenclyffe, iron pipes were sunk 37m into the ground, and the tower was 57m tall. The tower was believed to be also intended to have ultraviolet lights on top, possibly to create an ionised pathway to conduct electricity to the upper atmosphere. After JP Morgan’s final refusal to continue to fund the project, Wikipedia Practical Electronics | November | 2025 The Life of Nikola Tesla, part two notes, “newspapers reported that the Wardenclyffe tower came alive shooting off bright flashes lighting up the night sky. No explanation was forthcoming from Tesla or any of his workers as to the meaning of the display, and Wardenclyffe never seemed to operate again” (also see the website www.teslasociety.com/warden.htm). Even before the tower project’s failure, investors had lost interest in Tesla. They were more interested in Marconi, who transmitted a Morse code wireless signal from England to Newfoundland in 1901. The failure of the Wardenclyffe project led Tesla to have a nervous breakdown in 1905. Apart from the withdrawal of financial support by JP Morgan, Tesla may have had doubts about whether his science was correct. Biographer Bernard Carlson wrote: Tesla faced a serious dilemma... Either he was wrong or nature was wrong. Wireless electricity transmission 1905 In the January 7th 1905 issue of Electrical World and Engineer, Tesla wrote about how he saw wireless transmission of electricity as a means of furthering world peace (p85, https:// pemag.au/aby0). Wireless communications 1905 In 1905, he received US Patent 787,412 for the “Art of transmitting electrical energy through the natural mediums”. He described “stationary waves” from lightning at a 25-70km wavelength that “may be propagated in all directions over the globe”. He proposed reproducing this to transmit messages and establish positional data. He anticipated that resonances would occur at greater than 6Hz. Predictions 1911 According to the New York American on the 3rd of September 1911, Tesla’s “World System” (Fig.22) would perform the following tasks. We will comment on the status of each. • Television, making it possible to see any object at any distance. > Yes. • Universal twenty-four-hour daylight by wireless illumination. > No, although there is plenty of night-time lighting. • Instantaneous transmission of typed or hand-written characters all over the world. > Yes. • Operation of flying machines by wireless power. > No, but solar-powered aircraft exist, as do some experimental remotely-­powered drones. For more details, see the Silicon Chip magazine article on Aerial Platforms (August 2023; siliconchip.au/Article/15894). • Navigation of ships through fogs and channels by wireless “tuned” compasses. > Yes. • Communication with Mars. > Yes, in the sense that we can send and receive radio signals to and from spacecraft on Mars. • Operation of all manufacturing and transportation machinery. > Yes, if it means remote wireless or autonomous operation of machinery. • Every clock and watch in the world set and regulated by wireless at certain time each day. > Yes, that is certainly possible now. • Universal telephony, making it possible to speak at any distance. > Yes. • A perfect government secret signal service by exclusive wireless waves. > It is essentially possible now by using strong encryption. • Simultaneous operation of all stock tickers throughout the world. > Yes. • Universal system of musical transmission on atmospheric currents. > Not exactly, although radio can transmit music over very long distances. • Irrigation and fertilization of arid lands by wireless power. > No, that amount of wireless power is not practical. • The magnetizing of enemy’s battleships to attract torpedoes. > No, although magnetism is used to detect ships. Fig.20: a newspaper article about Wardenclyffe Tower from the New-York American, May 22nd, 1904. Source: https://w.wiki/AbUz Fig.21: Wardenclyffe Tower in 1904. The tower was 57m tall but was never finished due to a lack of funding. The top of the tower was meant to be a smooth dome. Source: https://w. wiki/AbU$ Practical Electronics | November | 2025 61 Feature Article • Reproduction of drawings and photographs at any distance. > Yes. • Absolutely exclusive telegraphy and telephony. > Yes (encrypted communications). Tesla turbine 1913 In 1913, Tesla received US Patent 1,061,206 for a novel bladeless turbine in which the working fluid impinged tangentially on a stack of discs. The fluid causes the discs to rotate via the laminar flow of the fluid at the disc surface, and thus, it extracts energy from the working fluid, such as steam or water (see Figs.23 & 24). The fluid enters the stack of discs at the edge and is exhausted at the centre. The turbine was said to be more efficient, simpler, could run faster and at higher temperatures than bladed axial turbines of the time. It could also be used as a pump. The turbine has seen little commercial application, probably because its advantages have been difficult to realise in practice. For more on this, see the video titled “The Tesla Turbine & How it Works” at https://youtu.be/mrnul6ixX90 Wireless transmission of electricity 1914 In 1914, Tesla was granted US Patent 1,119,732, which improved upon his previous power transmission schemes. While the size of the power transmission structure shown in Fig.25 is not specified, we expect it would be a large tower similar to what was (incompletely) built at Wardenclyffe and similar to the modern one pictured in Fig.26. Speedometer 1916 In 1916, Tesla was granted US Patent 1,209,359 for a speedometer. He licensed it to Waltham Watch, which sold 60,000 copies. Wardenclyffe Tower dismantled 1917 In 1917, the metal tower was demolished for its scrap metal value to help pay Tesla’s debts and the property was foreclosed in 1922. The original brick building remains and has been converted into a museum and educa- tional science centre, partly with the aid of Elon Musk. See: https://teslasciencecenter.org/ Finding hidden submarines 1917 In his proposal to find enemy submarines, he wrote, “I believe this magnetic method of locating or indicating the presence of an iron or steel mass might prove very practical in locating a hidden submarine.” This article was published in The Electric Experimenter in August 1917. It turned out to be a practical idea, used widely during WW2. Allis-Chalmers 1918-1920 During this period, Tesla worked with the steam and gas turbine manufacturer Allis-Chalmers, testing 200kW and 500kW steam turbines. The results were unsatisfactory, and Tesla also said the working conditions were poor, so the collaboration soon ended. Tesla fluid valve 1920 In 1920, Tesla was awarded US Patent 1,329,559 for a “valvular conduit”, Fig.23: a drawing of the Tesla turbine. Source: Open Source Ecology – siliconchip.au/ link/abyp Fig.22: an illustration from the article in the “New York American” of 3rd of September, 1911 on Tesla’s “World Wireless System”, entitled “To Turn Earth into One Gigantic Dynamo”. Source: https://teslauniverse.com/nikola-tesla/ articles/turn-earth-one-gigantic-dynamo Fig.24: a Tesla turbine on display at the Nikola Tesla Museum, Belgrade. Source: https://w.wiki/AbV2 62 Practical Electronics | November | 2025 The Life of Nikola Tesla, part two which causes the fluid flow to be relatively unimpeded in one direction but highly impeded in the opposite direction. It is the fluid equivalent of a diode (see Fig.27). The device has no moving parts and is scalable from microfluidic applications upward. However, the fluid needs a certain minimum flow speed for it to work effectively. Today, there is renewed interest in the valve and its applications, including its use in microfluidics (see the article on that in the August 2019 issue of Silicon Chip at siliconchip.au/Article/11762). Xiaomi uses it in its “loop liquidcool technology” for mobile phones (https://pemag.au/link/aby5). It is also used in a steam mop (https://youtu.be/ rYdtf90CcJQ) and a blood viscometer (https://pemag.au/link/aby6). Sulfur processing 1923 In 1923, Tesla was granted two US Patents (645,568 & 645,569) for treating and transporting sulfur, but he failed to pay the fees, and the patents were withdrawn. VTOL aircraft 1928 In 1928, Tesla received his final patent, US Patent 1,655,114 for what he described as “a new type of flying machine, designated ‘helicopterplane’, which may be raised and lowered vertically and driven horizontally by the same propelling devices” – see Fig.28. Electric car (hoax) 1931 There were claims that in 1931, Tesla made an electric car powered by a “cosmic energy power receiver” without a battery. These are false and no such machine was ever made. Ocean & geothermal energy 1931 Tesla suggested improvements to existing ideas to harvest geothermal energy from within the Earth. His idea was to pump water down a borehole, where the internal heat of the Earth at sufficient depth would turn it into steam, after which it returns and drives a turbine to generate electricity, condenses and is then returned Fig.28: Tesla’s “helicopter-plane” drawing from US Patent 1,655,114. to the borehole to continue the cycle (see Fig.29). He also suggested improvements to existing ideas for energy generation by harvesting heat differentials between the deep and shallow parts of the ocean. A working fluid would be vaporised at a higher temperature, drive a turbine, and then condense at a lower temperature. Breaking up tornadoes 1933 In 1933, Tesla proposed using a radio-controlled aircraft to carry Fig.25: the terminal structure, coil, capacitor and other components for radiating electrical energy, from Tesla’s 1914 US Patent 1,119,732 regarding wireless power transmission. Fig.26: Tesla’s Wardenclyffe wireless power transmission tower (1901) and Viziv’s tower (2018). Source: Stack Exchange – https://pemag.au/link/abyq Fig.27: at the top, fluid travels from left to right and is blocked because part of the fluid stream is turned around and interferes with the other part. Below that, fluid is travelling from right to left and is unimpeded. Source: https://w.wiki/AbV3 Practical Electronics | November | 2025 63 Feature Article Fig.29: Nikola Tesla proposed improvements to existing ideas for geothermal energy (L) and oceanic energy (R) harvesting. Originally published in Everyday Science and Mechanics, December 1931. Source: www.eenewseurope.com/ en/slideshow-the-other-things-tesladiscovered-invented 2017 Silicon Chip magazine article on “Rail Guns and Electromagnetic Launchers” (siliconchip.au/Article/10897). Predictions 1934 explosives into the funnel of a tornado to break it up (p251, https:// pemag.au/aby0). Wirelessly powered aircraft 1934 In a 1934 article (p268, https://pemag. au/aby0), Tesla proposed that aircraft would be powered by wirelessly transmitted electricity (Fig.30), among other futuristic proposals. Telegeodynamics 1934-1941 According to the Tesla Science Foundation, from 1934 to 1941, Tesla worked on what he termed “telegeodynamics”. This concerned the transmission of mechanical energy through the Earth via mechanical oscillators. He offered it to various companies, but they were not interested. No practical outcome seems to have arisen from this work. Teleforce 1934 In 1934, Tesla described a proposed defensive “beam” weapon (also called the “Death-Beam”, https://pemag.au/ link/aby7) he called “Teleforce”. The invention was said to be “Powerful Enough to Destroy 10,000 Planes 250 Miles Away”. It comprised an open-ended vacuum tube from which small charged particles of metal or other materials were fired (not subatomic particles). These were accelerated to a high velocity by a large potential difference of perhaps 50MV. For Tesla’s description, see: www.teslaradio.com/pages/ teleforce.htm Similar experimental weapons have now been developed; see the December 64 In Modern Mechanix and Inventions, July 1934, Tesla wrote: We are on the threshold of a gigantic revolution, based on the commercialization of the wireless transmission of power. Motion pictures will be flashed across limitless spaces... The same energy (wireless transmission of power) will drive airplanes and dirigibles from one central base. In rocket-propelled machines... it will be practicable to attain speeds of nearly a mile a second (3600 m.p.h.) through the rarefied medium above the stratosphere... We will be enabled to illuminate the whole sky at night... Eventually we will flash power in virtually unlimited amounts to planets. Dynamic theory of gravity 1937 For his 81st birthday, he announced he had developed a “Dynamic Theory of Gravity”. He wrote “that it will put an end to idle speculations and false conceptions, as that of curved space”, but no further work on this was published. Tesla passes away 1943 Tesla passed away on the 7th of January 1943, aged 86. US Government takes Tesla’s papers 1943 After Tesla passed away, the US Government came to his room and took many of his papers. While this is the subject of numerous conspiracy theories, bear in mind that this was in the midst of World War 2. The most likely explanation is that they wanted any material related to the proposed Teleforce weapon or anything else that might be useful for the war effort. If a weapon such as Teleforce had been possible, it would have greatly benefitted the Allied war effort. Dr John G. Trump (the uncle of Donald Trump) of the US National Defense Research Committee examined Tesla’s papers and reported: [Tesla’s] thoughts and efforts during at least the past 15 years were primarily of a speculative, philosophical, and somewhat promotional character often concerned with the production and wireless transmission of power; but did not include new, sound, workable principles or methods for realizing such results. Zenneck surface waves much later in 2018 Tesla’s dream of global wireless power transmission is not over. Jonathan Zenneck proposed ‘surface waves’ in 1907. They represent vertically polarised electromagnetic waves at certain planar boundaries, such as the surface of the Earth. They have been proposed as a means of wireless power transfer. Power delivery with Zenneck waves was demonstrated in 2020, although only along conducting surfaces and only over a distance of up to 15m – see https://pemag.au/link/aby8 We are not suggesting that the idea is technologically or scientifically valid for global power delivery; however, Tesla’s dream of wireless power delivery at a large scale remains alive with others. In 2018, Baylor University in Texas announced a collaboration with Viziv Technologies LLC (https://pemag.au/ link/aby9). A power transmission tower was built in Texas; see Fig.26. Unfortunately, Viziv filed for bankruptcy in 2020. See the related article at https://pemag.au/link/abya and the videos: • “Texzon Utilities - Imagine a world without wires” – (https://youtu. be/7mZErR_ZR3E) • “Texzon Zenneck Wave Wireless Power Transmission” – (https://youtu. be/vQTYaL9jCMo) • “Viziv Technologies sends power without wires” – (https://youtu.be/ jK5XUptZDEs). Tesla’s final decades Arguably, Tesla’s best work was done before about 1900. His final years, until his passing in 1943, involved him living off a small stream of royalties, giving annual press conferences, writing articles about the future of technology and living in seclusion, depression and poverty. Practical Electronics | November | 2025 The Life of Nikola Tesla, part two There was a revival of interest in his work in the 1970s and beyond, some of it from counterculturalists who believed in “free energy”. Today, most people know Tesla’s name, in part due to Elon Musk’s influence. His legacy also inspires other creative scientists and engineers who are prepared to dream and ‘push the boundaries’. Tesla’s mistakes and misconceptions While he was a genius, Tesla evidently made mistakes and had misconceptions. Among these were: • He did not accept Einstein’s theory of curved spacetime • He did not accept Maxwell’s equations • He believed he had measured faster-­than-light speeds • He did not believe in electrons and thought that atoms were the smallest units of matter • He believed that the ‘aether’ transmitted electric currents • He did not believe the splitting of atoms resulted in the liberation of energy The aether was once thought to fill the universe and be the medium through which light and gravity were transmitted. The existence of the “luminiferous aether”, which transmitted light, was disproven by the Michelson–­ Morley experiment in 1887, and subsequent experiments. Some of these misconceptions are remarkable, given his highly successful early work with electricity and magnetism. Tesla also said of nuclear energy, “The idea of atomic energy is illusionary but it has taken a powerful hold on the mind and there are still some who believe it to be realizable”. In an article in the Electrical Experimenter of February 1919, he also wrote that the moon does not rotate on its axis (p14 of https://pemag.au/ link/abyd). However, it was known at the time that it did. In fact, it rotates in synchrony with the Earth, so we always see the same side of the moon. World Wireless System flaws It is certainly possible to transmit power wirelessly; we see it every day in things like mobile phone wireless chargers. They are based on ‘near field’ effects that occur close to the transmitting device. In the near field, the electric and magnetic field components of an electromagnetic wave can exist independently of each other, while in the ‘far field’, the electric and magnetic fields are perpendicular to each other. Far-field charging techniques are also available, but they require strongly focused beams such as lasers or microwaves. What Tesla demonstrated as wireless power transmission involved either Fig.30: an illustration from the July 1934 Modern Mechanix and Inventions magazine of a proposed electric aircraft, to be powered wirelessly. Fig.31: the future of warfare, as envisaged by Tesla and illustrated by Frank R. Paul in 1922. This image ties together some of Tesla’s ideas, such as wireless power transmission, radio and teleautomatons (remotely operated vehicles). Few people would be hurt in this war, as it would be mostly between remote-controlled machines. Source: https://w.wiki/AbV4 Practical Electronics | November | 2025 65 Feature Article capacitive coupling (such as when a fluorescent tube illuminates near a high-voltage power line) or inductive coupling (like in an air-cored transformer). These are near-field phenomena and do not work at extended distances beyond a few tens of metres and certainly not worldwide. Besides, the energy of electromagnetic waves decreases with the distance from the antenna. Tesla also incorrectly believed that the entire Earth could be made to electrically resonate in the manner of an LC circuit. He thought that, by injecting current into the Earth at its resonant frequency from a grounded Tesla coil with a capacitance, standing waves could be established around the Earth that could be received at their nodal points anywhere on Earth with an antenna tuned to resonance. Another idea Tesla had was to hoist both transmitting and receiving power antennas high up into the atmosphere on balloons, to about 9100m, where he thought the rarefied air would be sufficiently electrically conductive to transmit electric power, with the Earth being the return circuit. That idea would not be practical; the ionosphere (not discovered until 1924), where the atmosphere does become electrically conductive, starts about 48km above the surface. Tesla and alternating current Contrary to popular belief, Tesla did not invent the concept of AC electricity. The first AC generator was invented in 1832 by Hippolyte Pixii, as mentioned in our article on the History of Electronics (February 2025, p55). However, André-Marie Ampère convinced him to convert it to pulsed DC. According to the book The Electric Light from 1884 (p238, https://pemag. au/link/abye), around 1856, due to frustration with failed commutators on a generator, they were dispensed with, resulting in the successful use of AC for lighting, such as arc lights. However, Tesla did invent many successful AC machines. electric project, at which Tesla’s generators were used. This ensured the future of AC. During the war of the currents, and even afterwards, some residences in New York had both DC and AC outlets, which looked the same! The last DC utility service in New York was shut down in 2007, see: www. edisontechcenter.org/NYC.html War of the currents Tesla had studied and was aware of Hertzian radio waves. However, he believed Hertz’s theories were incorrect and that Hertzian waves were not suitable for anything but short-range communications, such as under 2km. He also thought they behaved like light and would go straight into space rather than travel long distances on Earth. Tesla was more interested in wireless long-distance electricity transmission than in communications. However, in 1893, he noted that his proposed wireless electricity transmission system could also be used for communications. Tesla also incorrectly believed, as some others did at the time, that radio behaved much like the familiar telegraph system and that a return circuit was required, with radio waves travelling through the air and a return path of current through the Earth. While the Earth plays an important role in a radio system by providing a reference potential and allowing a small amount of current to flow through it, radio signals do not ‘return’ via that path. He incorrectly believed that radio waves could travel losslessly through the Earth. Tesla also had an idea of producing non-Hertzian “longitudinal electromagnetic waves” in the manner of sound waves, which he called “electromagnetic thrusts”. Radio waves are, in fact, transverse. The war of the currents lasted from the late 1880s to the early 1890s and basically concerned which of the two electrical systems would dominate large-scale electricity distribution. These were AC, represented by George Westinghouse (and Tesla), and DC, represented by Thomas Edison. AC was ideal for long-distance distribution because, at high voltages, it had low transmission losses and it was easy to change the voltage for use by the consumer with a low-cost, reliable transformer. DC systems had high losses at low voltages and would have required vast numbers of local power stations since DC voltage conversion was not practical. Edison promoted the safety of DC compared to the dangers of AC. Edison and Westinghouse’s other rival, Thomson-­Houston Electric Company, even colluded to ensure the first electric chair was powered by a Westinghouse AC generator to ‘prove’ how dangerous AC was. In 1893, Westinghouse won the contract for lighting at the Chicago World Fair, at which Tesla’s inventions were demonstrated, and won most of the contract for the Niagara Falls hydro- Links and References ● Nikola Tesla and the Planetary Radio Signals: https://radiojove.gsfc.nasa.gov/ education/educationalcd/Books/Tesla.pdf (K. L. Corum & J. F. Corum, 2003). ● Tesla’s autobiography from 1919: www.tfcbooks.com/tesla/my_inventions.pdf ● Plans to make your own Tesla turbine: www.instructables.com/Tesla-Turbine ● The Nikola Tesla Museum in Belgrade: https://tesla-museum.org/en/home/ ● A 301-page collection of some of Tesla’s writings, called “Tesla Said”, is described as “the most comprehensive single volume of Tesla’s writings”: https://archive.org/ details/nikolateslajohnt.ratzlaffteslasaid ● Tesla: Inventor of the Electrical Age, W. Bernard Carlson, Princeton University Press (2015). ● The Tesla Memorial Society of New York: www.teslasociety.com ● The Tesla Science Center at Wardendclyffe: https://teslasciencecenter.org ● The Tesla Collection, a comprehensive compilation of newspaper and periodical material: https://teslacollection.com 66 Tesla and radio Tesla’s “lost files” There are many conspiracy theories related to Tesla’s documents, which the US Government took after his passing. After they found nothing of practical use for the war effort (such as the “death ray”), the papers were released to Tesla’s relative, Sava Kosanović. He took them, along with Tesla’s entire estate (packed into 80 trunks) to Belgrade, Serbia in 1952, and they now reside in the Nikola Tesla Museum in Belgrade. PE Practical Electronics | November | 2025