The invention of radio communication was preceded by many decades of establishing theoretical underpinnings, discovery and experimental investigation of radio waves, and engineering and technical developments related to their transmission and detection. These developments allowed Guglielmo Marconi to turn radio waves into a wireless communication system.
The idea that the wires needed for electrical telegraph could be eliminated, creating a wireless telegraph, had been around for a while before the establishment of radio-based communication. Inventors attempted to build systems based on electric conduction, electromagnetic induction, or on other theoretical ideas. Several inventors/experimenters came across the phenomenon of radio waves before its existence was proven; it was written off as electromagnetic induction at the time.
The discovery of electromagnetic waves, including radio waves, by Heinrich Hertz in the 1880s came after theoretical development on the connection between electricity and magnetism that started in the early 1800s. This work culminated in a theory of electromagnetic radiation developed by James Clerk Maxwell by 1873, which Hertz demonstrated experimentally. Hertz considered electromagnetic waves to be of little practical value. Other experimenters, such as Oliver Lodge and Jagadish Chandra Bose, explored the physical properties of electromagnetic waves, and they developed electric devices and methods to improve the transmission and detection of electromagnetic waves. But they did not apparently see the value in developing a communication system based on electromagnetic waves.
In the mid-1890s, building on techniques physicists were using to study electromagnetic waves, Guglielmo Marconi developed the first apparatus for long-distance radio communication.Bondyopadhyay, Prebir K. (1995) "Guglielmo Marconi – The father of long distance radio communication – An engineer's tribute", 25th European Microwave Conference: Volume 2, pp. 879–85 On 23 December 1900, the Canadian-born American inventor Reginald A. Fessenden became the first person to send audio (wireless telephony) by means of electromagnetic waves, successfully transmitting over a distance of about a mile (1.6 kilometers,) and six years later on Christmas Eve 1906 he became the first person to make a public wireless broadcast.
By 1910, these various wireless systems had come to be called "radio".
Wireless communication theories and methods previous to radio
Before the discovery of electromagnetic waves and the development of radio communication, there were many wireless telegraph systems proposed and tested.Sterling, Christopher H. & O'Dell, Cary (2011) The Concise Encyclopedia of American Radio, Routledge, p. 238 In April 1872 William Henry Ward received for a wireless telegraphy system where he theorized that convection currents in the atmosphere could carry signals like a telegraph wire.Sterling & O'Dell (2011), page 239 A few months after Ward received his patent, Mahlon Loomis of West Virginia received for a similar "wireless telegraph" in July 1872.Sterling, Christopher H. (ed.) (2003) Encyclopedia of Radio ( Volume 1) Page 831Lee, Thomas H. (2004) The Design of CMOS Radio-Frequency Integrated Circuits pp. 33–34. The patented system claimed to utilize atmospheric electricity to eliminate the overhead wire used by the existing telegraph systems. It did not contain diagrams or specific methods and it did not refer to or incorporate any known scientific theory.
In the United States, Thomas Edison, in the mid-1880s, patented an electromagnetic induction system he called "grasshopper telegraphy", which allowed telegraphic signals to jump the short distance between a running train and telegraph wires running parallel to the tracks.(, Means for Transmitting Signals Electrically, US 465971 A, 1891 In the United Kingdom, William Preece was able to develop an electromagnetic induction telegraph system that, with antenna wires many kilometers long, could transmit across gaps of about . Inventor Nathan Stubblefield, between 1885 and 1892,"History of the Radio Industry in the United States to 1940", by Carole E. Scott, State University of West Georgia (eh.net) also worked on an induction transmission system.
A form of wireless telephony is recorded in four patents for the photophone, invented jointly by Alexander Graham Bell and Charles Sumner Tainter in 1880. The photophone allowed for the transmission of sound on a beam of light, and on 3 June 1880, Bell and Tainter transmitted the world's first wireless telephone message on their newly invented form of light telecommunication.Carson, Mary Kay (2007) Alexander Graham Bell: Giving Voice To The World, Sterling Biographies, New York: Sterling Publishing Co., Inc., pp. 76–78. .
In the early 1890s Nikola Tesla began his research into high-frequency electricity. Tesla was aware of Hertz's experiments with electromagnetic waves from 1889 onO'Neill, James (1944) Prodigal Genius: The Life of Nikola Tesla, page 86Seifer, Marc (1996) Wizard: The Life and Times of Nikola Tesla, p. 1721 but doubted they existed, and agreed with the prevailing scientific thought at that time that they probably only travel in straight lines, making them useless for long range transmission.
Instead of using radio waves, Tesla's efforts were focused on building a conduction-based power distribution system,Carlson, W. Bernard (2013). Tesla: Inventor of the Electrical Age. Princeton University Press. . pp. 178–79 although he noted in 1893 that his system could also incorporate communication. His laboratory work and later large-scale experiments at Colorado Springs led him to the conclusion that he could build a conduction-based worldwide wireless system that would use the Earth itself (via injecting very large amounts of an electric current into the ground) as the means to conduct the signal very long distances (across the Earth), overcoming the perceived limitations of other systems. He went on to try to implement his ideas of power transmission and wireless telecommunication in his very large but unsuccessful Wardenclyffe Tower project.Regal (2005) p. 23
Development of electromagnetism
Experiments and theory Various scientists proposed that electricity and magnetism were linked. Around 1800 Alessandro Volta developed the first means of producing an electric current. In 1802 Gian Domenico Romagnosi may have suggested a relationship between electricity and magnetism but his reports went unnoticed.Sandro Stringari, Robert R. Wilson (2000), "Romagnosi and the discovery of electromagnetism" , Rendiconti Lincei: Scienze Fisiche e Naturali, serie 9, vol. 11, issue 2, pp. 115–36.Roberto de Andrade Martins (2001), "Romagnosi and Volta’s pile: early difficulties in the interpretation of Voltaic electricity", in Fabio Bevilacqua, Lucio Fregonese (eds), Nuova Voltiana: Studies on Volta and his Times, Volume 3, Pavia / Milano: Università degli Studi di Pavia / Ulrico Hoepli, 2001, pp. 81–102. In 1820 Hans Christian Ørsted performed a simple and today widely known experiment on electric current and magnetism. He demonstrated that a wire carrying a current could deflect a magnetized compass needle.Ørsted, Hans Christian (1997). Karen Jelved, Andrew D. Jackson, and Ole Knudsen, translators from Danish to English. Selected Scientific Works of Hans Christian Ørsted, , pp. 421–45 Ørsted's work influenced André-Marie Ampère to produce a theory of electromagnetism. Several scientists speculated that light might be connected with electricity or magnetism.
In 1831, Michael Faraday began a series of experiments in which he discovered electromagnetic induction. The relation was mathematically modelled by Faraday's law, which subsequently became one of the four Maxwell equations. Faraday proposed that electromagnetic forces extended into the empty space around the conductor, but did not complete his work involving that proposal. In 1846 Michael Faraday speculated that light was a wave disturbance in a "force field".
Expanding upon a series of experiments by Felix Savary,Gluckman, Albert Gerard, "The Discovery of Oscillatory Electric Current" , Journal of the Washington Academy of Sciences, March 1990, pp. 16–25. between 1842 and 1850 Joseph Henry performed experiments detecting inductive magnetic effects over a distance of .Fleming, J. A. (1908) The Principles of Electric Wave Telegraphy, London: New York and Co. (cf., Joseph Henry, in the United States, between 1842 and 1850, explored many of the puzzling facts connected with this subject, and only obtained a clue to the anomalies when he realized that the discharge of a condenser through a low resistance circuit is oscillatory in nature. Amongst other things, Henry noticed the power of condenser discharges to induce secondary currents which could magnetize steel needles even when a great distance separated the primary and secondary circuits.)See The Scientific Writings of Joseph Henry, vol. i. pp. 203, 20:-i; also "Analysis of the Dynamic Phenomena of the Leyden Jar", Proceedings of the American Association for the Advancement of Science, 1850, vol. iv. pp. 377–78, Joseph Henry. The effect of the oscillatory discharge on a magnetized needle is summarized in this review.Ames, J. S., Henry, J., & Faraday, M. (1900). The Discovery of Induced Electric Currents, New York: American book. (cf. Page 107: "On moving to Princeton, in 1832, [Henry] [...] investigated also the discharge of a Leyden jar, proved that it was oscillatory in character, and showed that its inductive effects could be detected at a distance of two hundred feet, thus clearly establishing the existence of electro-magnetic waves.") He was the first (1838–42) to produce high frequency AC electrical oscillations, and to point out and experimentally demonstrate that the discharge of a capacitor under certain conditions is oscillatory, or, as he puts it, consists "of a principal discharge in one direction and then several reflex actions backward and forward, each more feeble than the preceding until equilibrium is attained". This view was also later adopted by Helmholtz,Helmholtz, Hermann (1847) "Über die Erhaltung der Kraft", Berlin the mathematical demonstration of this fact was first given by Lord Kelvin in his paper on "Transient Electric Currents".Thomson, William (June 1853) "On Transient Electric Currents", Philosophical Magazine and Journal of Science, Fourth series, volume 5, pp. 393–405.Fessenden, Reginald (1908) "Wireless Telephony", Transactions of the American Institute of Electrical Engineers (volume 27, part 1), 29 June 1908, pp. 553–630
Maxwell and the theoretical prediction of electromagnetic waves Maxwell and electromagnetic waves
Between 1861 and 1865, based on the earlier experimental work of Faraday and other scientists and on his own modification to Ampere's law, James Clerk Maxwell developed his theory of electromagnetism, which predicted the existence of electromagnetic waves. In 1864 Maxwell described the theoretical basis of the propagation of electromagnetic waves in his paper to the Royal Society, "A Dynamical Theory of the Electromagnetic Field." This theory united all previously unrelated observations, experiments and equations of electricity, magnetism, and optics into a consistent theory. His set of equations—Maxwell's equations—demonstrated that electricity, magnetism, and light are all manifestations of the same phenomenon, the electromagnetic field. Subsequently, all other classic laws or equations of these disciplines were special cases of Maxwell's equations. Maxwell's work in electromagnetism has been called the "second great unification in physics", after Newton's unification of gravity in the 17th century.Nahin, Paul J. (1992), "Maxwell's Grand Unification", IEEE Spectrum 29(3): 45.