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Why did Tesla make his coil in the first place?  What was it that he was trying to accomplish?  Other than just the fun of making one, do they have any practical purposes?

One of Tesla's high-frequency power supplies for use with fluorescent and single-terminal lamps.Tesla built his first oscillator as a tool for studying high-frequency electrical phenomena.  He also constructed high-frequency electrical alternators for the same purpose.  When it comes to describing practical applications for this type of electrical power supply, top on my list is high-frequency electric lighting.  Tesla's investigations in the area of high-voltage RF power processing techniques resulted in the very first high-efficiency, high-frequency lighting ballasts.  He experimented with both fluorescent- and incandescent-type lamps, as well as high-frequency arc lighting.  Some of the modern electronic fluorescent ballasts which first appeared in the late 1980s have great similarities to those he developed in the 1890s, the principal difference being replacement of the mechanical switching mechanism with a solid-state device.

An early single-terminal incandescent lamp.Early on in the course of his research Tesla made another remarkable discovery.  Using the principle of electrical resonance he found that it is possible to eliminate one of the two conductors normally used to carry current from the power supply to the electrical load.  He created a light bulb specifically designed to be used in this manner, called the carbon button lamp  It was generally based upon the dual-terminal tubes developed by William Crooks.  He also developed a single-wire electric motor that could be operated in much the same manner.  This involves attaching a metal plate to one of the high-voltage power supply terminals in place of one of the connecting wires.  The electrical capacitance at the load, the refractory button or in the case of the motor a second metal plate, serves to complete the circuit through "electrostatic induction," sometimes referred to as 'capacitive coupling.' [The Inventions, Researches and Writings of Nikola Tesla]

A system for the conversion and transmission of electrical energy.In operating various devices with his high-frequency power supply using only one connecting wire he realized the load can placed at some distance from the power supply and still function properly.  This is what Tesla called the transmission of electrical energy through one wire without return.  While a load connected to only one of the high-potential terminals does not form a closed circuit, in the ordinary acceptance of the term the circuit is closed in the sense that a return path is established back to the secondary by so called displacement currents.  This return path is directly between the two metal plates.  At greater distances the capacitive coupling to ground predominates at both the transmitter and the receiver ends of the circuit.  Instead of using individual capacitor plates at the transmitting and receiving ends it is also possible to make the connection directly to ground, completing the circuit entirely through the earth.  The accompanying illustration of a one-wire power transmission system is from Tesla's U.S. Patent No. 593,138 titled "Electrical Transformer," covering the Tesla coil resonance transformer.

Illustrating arrangement with a Lenard X-ray tube for safe working at close range.His work with the single terminal incandescent lamp led him to investigate other phenomena associated with vacuum tubes including the generation and physical properties of X rays.  Tesla was one of the first researchers to alert the scientific community to some of the biological hazards associated with X-ray exposure.  Tesla's more advanced tubes differ from typical X-ray tubes in that they have no target electrode and produce X rays through vacuum high-field emission and a process known as Bremsstrahlung.  His work in this area set the stage for the development of high-energy particle accelerators. [Nikola Tesla: Lecture Before The New York Academy of Sciences, April 6, 1897]

A device for producing ozone including a high potential transformer.When standing in the same room as an operating Tesla coil, one might observe the presence of the aromatic gas ozone.  Tesla took advantage of this operating characteristic by designing a device for the production of ozone in unlimited amount (U.S. Pat. #568,177, Sept. 22, 1896).  Tesla observed that with some additional energy and certain modifications it is possible to efficiently induce a reaction between oxygen and relatively inert nitrogen.  In the industrial processes for the fixation of atmospheric nitrogen, the resulting gaseous oxides are reacted with other substances to form solid nitrogen compounds. [Dr. Nikola Tesla Complete Patents]

A high-frequency alternator used in the transmission of signals.As Tesla's research progressed, he placed additional emphasis on finding a solution to one of the most vexing problems of his erathe development of a practical system for wireless telegraphy and telephony.  Some preliminary experiments with  high-frequency alternators connected to an aerial and ground showed promising results towards this end.  He next replaced the alternator with his resonance transformer and achieved even better results.  When used as a radio transmitter it was demonstrated that Tesla's oscillator, with its tuned primary and secondary circuits, was able to produce radio waves thousands of times more powerful than the simple spark-coil transmitter used by Heinrich Hertz just a few years before handa practical application indeed! [Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power]

Used in receivers, this small mechanical and electrical oscillator provided a small AC current of constant frequency.In spite of this initial success Tesla was clearly not satisfied with his results.  Further improvements included the development of techniques for obtaining frequency stability, selectivity, immunity to interference, and security of communications.  It is a footnote to history that a portion of this work with high-power radio-frequency oscillators involved the first electronic implementation of the AND logic function.  The resulting U.S. Patents # 723,188 & # 725,605 for wireless signaling cover logic gates in general and also describe the basic principles of frequency-hopping and frequency-division multiplexing in wireless spread spectrum telecommunications.  See Wireless Remote Control and the Electronic Computer Logic Gate for an exhibit in the U.S. patent interference "Nikola Tesla vs. Reginald A. Fessenden, Interference No. 21,701, Systems of Signaling" showing a circuit diagram of an electronic AND logic gate used by Tesla in 1899. [Nikola Tesla: Guided Weapons & Computer Technology]

While many of Tesla's innovations are embodied in our present apparatus for wireless telecommunications there are certain elements which have not been incorporated.  In Tesla's own words, "devices of this kind, to be most effective and efficient, should be designed with due regard to the physical properties of this planet and the electrical conditions obtaining on the same." [
The True Wireless]

Created 12/3/2006; last revised 10/27/2012

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