View source for Timeline of electromagnetism and classical optics

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{{Use dmy dates|date=March 2021}}
'''[[Timeline]] of [[electromagnetism]] and classical [[optics]]''' lists, within the [[history of electromagnetism]], the associated theories, technology, and events.

==Early developments==
[[File:Thales Lebiedzki Rahl.jpg|thumb|Detail of the right-hand facade fresco, showing [[Thales of Miletus]], [[National and Kapodistrian University of Athens]].]]
[[File:Cardano, Girolamo – De subtilitate, 1559 – BEIC 3024364.jpg|thumb|[[Girolamo Cardano]], ''De subtilitate'']]

* 28th century BC – [[Ancient Egypt]]ian texts describe [[electric fish]]. They refer to them as the "Thunderer of the [[Nile]]", and described them as the "protectors" of all other fish.<ref name="moller">{{citation|title=Review: Electric Fish|first1=Peter|last1=Moller|journal=BioScience|volume=41|issue=11|date=December 1991|pages=794–6 [794]|doi=10.2307/1311732|jstor=1311732|last2=Kramer|first2=Bernd}}</ref>
* 6th century BC – [[Greek philosophy|Greek]] philosopher [[Thales of Miletus]] observes that rubbing fur on various substances, such as [[amber]], would cause an attraction between the two, which is now known to be caused by [[static electricity]]. He noted that rubbing the amber buttons could attract light objects such as hair and that if the amber was rubbed sufficiently a spark would jump.<ref name=Baigrie>{{Citation
 | last =Baigrie
 | first =Brian
 | title =Electricity and Magnetism: A Historical Perspective
 | publisher =Greenwood Publishing Group
 | page=1
 | year =2007
 | isbn =978-0-313-33358-3
}}</ref><ref name=stewart>{{Citation| first = Joseph | last= Stewart| title = Intermediate Electromagnetic Theory| publisher = World Scientific| year = 2001| isbn = 9-8102-4471-1 | page=50}}</ref>
* 424 BC [[Aristophanes]]' "lens" is a glass globe filled with water.([[Seneca the Younger|Seneca]] says that it can be used to read letters ''no matter how small or dim'')<ref name=King>''The history of the telescope'' by Henry C. King, Harold Spencer Jones Publisher Courier Dover Publications, 2003 Pg 25 {{ISBN|0-486-43265-3}}, {{ISBN|978-0-486-43265-6}}</ref>
* 4th century BC [[Mozi|Mo Di]] first mentions the [[camera obscura]], a pin-hole camera.
* 3rd century BC [[Euclid]] is the first to write about reflection and refraction and notes that light travels in straight lines<ref name=King/>
* 3rd century BC – The [[Baghdad Battery]] is dated from this period. It resembles a [[galvanic cell]] and is believed by some to have been used for [[electroplating]], although there is no common consensus on the purpose of these devices nor whether they were, indeed, even electrical in nature.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/sci/tech/2804257.stm |first=Arran |last=Frood  |title=Riddle of 'Baghdad's batteries' |newspaper=BBC News |date=27 February 2003 |access-date=20 October 2015}}</ref>
* 1st century AD – Pliny in his Natural History records the story of a shepherd Magnes who discovered the magnetic properties of some iron stones, "''it is said, made this discovery, when, upon taking his herds to pasture, he found that the nails of his shoes and the iron ferrel of his staff adhered to the ground.''"<ref>{{cite book|url=http://data.perseus.org/citations/urn:cts:latinLit:phi0978.phi001.perseus-eng1:1.dedication |author=Pliny the Elder |title=The Natural History |chapter=Dedication|series=Perseus Collection: Greek and Roman Materials|publisher=Department of the Classics, Tufts University |access-date=20 October 2015}}</ref>
* 130 AD. – [[Ptolemy|Claudius Ptolemy]] (in his work ''Optics'') wrote about the properties of light including: [[Reflection (physics)|reflection]], [[refraction]], and [[color]] and tabulated [[angle]]s of [[refraction]] for several media
* 8th century AD – Electric fish are reported by [[Islamic geography|Arabic naturalists]] and [[Islamic medicine|physicians]].<ref name="moller"/>

== Middle Ages ==
* 1021 – [[Ibn al-Haytham]] (Alhazen) writes the ''[[Book of Optics]]'', studying [[Visual perception|vision]].
* 1088 – [[Shen Kuo]] first recognizes [[magnetic declination]].
* 1187 – [[Alexander Neckham]] is first in Europe to describe the magnetic compass and its use in navigation.
* 1269 – [[Pierre de Maricourt]] describes [[magnet|magnetic pole]]s and remarks on the nonexistence of [[Magnetic monopole|isolated magnetic poles]]
* 1282 – [[Al-Ashraf Umar II]] discusses the properties of magnets and dry compasses in relation to finding [[qibla]].<ref>{{Cite journal|last=Schmidl|first=Petra G.|year=1996–1997|title=Two Early Arabic Sources On The Magnetic Compass|journal=Journal of Arabic and Islamic Studies|volume=1|pages=81–132}}</ref>
* 1305 – [[Theodoric of Freiberg]] uses crystalline spheres and flasks filled with water to study the [[Reflection (physics)|reflection]] and refraction in raindrops that leads to primary and secondary [[rainbow]]s
* 14th century AD – Possibly the earliest and nearest approach to the discovery of the identity of [[lightning]], and [[electricity]] from any other source, is to be attributed to the [[Arabs]], who before the 15th century had the [[Arabic language|Arabic]] word for lightning (''raad'') applied to the [[electric ray]].<ref name="EncyclopediaAmericana">''The [[Encyclopedia Americana]]; a library of universal knowledge'' (1918), New York City: Encyclopedia Americana Corp.</ref>
* 1550 – [[Gerolamo Cardano]] writes about electricity in ''De Subtilitate'' distinguishing, perhaps for the first time, between electrical and magnetic forces.{{citation needed|date=September 2020}}

==17th century==
* 1600 – [[William Gilbert (astronomer)|William Gilbert]] publishes ''De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure'' ("On the Magnet and Magnetic bodies, and on that Great Magnet the Earth"), Europe's then current standard on electricity and magnetism. He experimented with and noted the different character of electrical and magnetic forces. In addition to known ancient Greeks' observations of the electrical properties of rubbed amber, he experimented with a needle balanced on a pivot, and found that the needle was non-directionally affected by many materials such as alum, arsenic, hard resin, [[Jet (lignite)|jet]], glass, gum-mastic, mica, rock-salt, sealing wax, slags, sulfur, and precious stones such as amethyst, [[beryl]], diamond, opal, and sapphire. He noted that electrical charge could be stored by covering the body with a non-conducting substance such as silk. He described the method of artificially magnetizing iron. His [[terrella]] (little earth), a sphere cut from a lodestone on a metal lathe, modeled the earth as a lodestone (magnetic iron ore) and demonstrated that every lodestone has fixed poles, and how to find them.<ref>{{cite book |first=Henry Smith |last=Williams |title=A history of science |volume=2 |url=http://www.worldwideschool.org/library/books/sci/history/AHistoryofScienceVolumeII/chap18.html |chapter=Part IV. William Gilbert and the Study of Magnetism |publisher=Worldwide School |access-date=20 October 2015 |url-status=dead |archive-url=https://web.archive.org/web/20080117174223/http://www.worldwideschool.org/library/books/sci/history/AHistoryofScienceVolumeII/chap18.html |archive-date=17 January 2008 }}</ref> He considered that gravity was a magnetic force and noted that this mutual force increased with the size or amount of lodestone and attracted iron objects. He experimented with such physical models in an attempt to explain problems in [[navigation]] due varying properties of the [[magnetic compass]] with respect to their location on the earth, such as [[magnetic declination]] and magnetic inclination. His experiments explained the [[Dip circle|dipping of the needle]] by the magnetic attraction of the earth, and were used to predict where the vertical dip would be found. Such magnetic inclination was described as early as the 11th century by [[Shen Kuo]] in his ''Meng Xi Bi Tan'' and further investigated in 1581 by retired mariner and [[Compasssmith|compass maker]] [[Robert Norman]], as described in his pamphlet, ''The Newe Attractive.'' The gilbert, a unit of [[magnetomotive force]] or [[magnetic scalar potential]], was named in his honor.
* 1604 – [[Johannes Kepler]] describes how the eye focuses light
* 1604 – Johannes Kepler specifies the laws of the rectilinear propagation of light
* 1608 – first [[telescope]]s appear in the Netherlands
* 1611 – [[Marko Dominis]] discusses the rainbow in ''De Radiis Visus et Lucis''
* 1611 – Johannes Kepler discovers [[total internal reflection]], a small-angle refraction law, and thin [[lens (optics)|lens]] optics,
* c1620 – the first [[Optical microscope#Compound microscope|compound microscope]]s appear in Europe.<ref>{{cite book|author1=Albert Van Helden|author2=Sven Dupré|author3=Rob van Gent|title=The Origins of the Telescope|url=https://books.google.com/books?id=XguxYlYd-9EC&pg=PA24|year=2010|publisher=Amsterdam University Press|isbn=978-90-6984-615-6|page=24}}</ref>
* 1621 – [[Willebrord van Roijen Snell]] states his [[Snell's law]] of refraction
* 1630 – [[Cabaeus]] finds that there are two types of [[electric charge]]s
* 1637 – [[René Descartes]] quantitatively derives the angles at which primary and secondary rainbows are seen with respect to the angle of the [[Sun]]'s elevation
* 1646 – [[Sir Thomas Browne]] first uses the word ''electricity'' is in his work [[Pseudodoxia Epidemica]].
* 1657 – [[Pierre de Fermat]] introduces the [[Fermat's principle|principle of least time]] into optics
* 1660 – [[Otto von Guericke]] invents an early electrostatic generator.
* 1663 – [[Otto von Guericke]] (brewer and engineer who applied the barometer to weather prediction and invented the air pump, with which he demonstrated the properties of atmospheric pressure associated with a vacuum) constructs a primitive electrostatic generating (or friction) machine via the [[triboelectric effect]], utilizing a continuously rotating sulfur globe that could be rubbed by hand or a piece of cloth. [[Isaac Newton]] suggested the use of a glass globe instead of a sulfur one.
* 1665 – [[Francesco Maria Grimaldi]] highlights the phenomenon of [[diffraction]]
* 1673 – Ignace Pardies provides a wave explanation for refraction of light
* 1675 – [[Robert Boyle]] discovers that electric attraction and repulsion can act across a vacuum and do not depend upon the air as a medium. Adds resin to the known list of "electrics."
* 1675 – [[Isaac Newton]] delivers his [[Isaac Newton's early life and achievements#The composition of white light|theory of light]]
* 1676 – [[Ole Rømer]] proves that [[speed of light]] is finite, by observing [[Jupiter]]'s [[Natural satellite|moon]]s
* 1678 – [[Christiaan Huygens]] states [[Huygens' principle|his principle]] of wavefront sources and demonstrates the refraction and diffraction of light rays.

==18th century==
* 1704 – [[Isaac Newton]] publishes ''[[Opticks]]'', a corpuscular theory of light and colour
* 1705 – [[Francis Hauksbee (scientist)|Francis Hauksbee]] improves von Guericke's [[electrostatic generator]] by using a glass globe and generates the first sparks by approaching his finger to the rubbed globe.
* 1728 – [[James Bradley]] discovers the [[Aberration of light|aberration]] of starlight and uses it to determine that the [[speed of light]] is about 283,000&nbsp;km/[[second|s]]
* 1729 – [[Stephen Gray (scientist)|Stephen Gray]] and the Reverend [[Granville Wheler]] experiment to discover that electrical "virtue", produced by rubbing a glass tube, could be transmitted over an extended distance (nearly 900&nbsp;ft (about 270&nbsp;m)) through thin iron wire using silk threads as insulators, to deflect leaves of brass. This has been described as the beginning of electrical communication.<ref name=Clark>{{cite book|last1=Clark|first1=David H.|last2=Clark|first2=Stephen P.H.|title=Newton's tyranny : the suppressed scientific discoveries of Stephen Gray and John Flamsteed|url=https://archive.org/details/newtonstyrannysu00clar|url-access=registration|date=2001|publisher=Freeman|location=New York|isbn=9780716747017}}</ref>{{Page needed|date=October 2015}} This was also the first distinction between the roles of conductors and insulators (names applied by [[John Theophilus Desaguliers|John Desaguliers]], mathematician and [[Royal Society]] member, who stated that Gray "has made greater variety of electrical experiments than all the philosophers of this and the last age.")<ref name=Clark/>{{Page needed|date=October 2015}} Georges-Louis LeSage built a [[electrical telegraph|static electricity telegraph]] in 1774, based upon the same principles discovered by Gray.
* 1732 – [[C. F. du Fay]] Shows that all objects, except metals, animals, and liquids, can be electrified by rubbing them and that metals, animals and liquids could be electrified by means of an electrostatic generators
* 1734 – [[C. F. du Fay|Charles François de Cisternay DuFay]] (inspired by Gray's work to perform electrical experiments) dispels the effluvia theory by his paper in Volume 38 of the ''Philosophical Transactions of the Royal Society'', describing his discovery of the distinction between two kinds of electricity: "resinous", produced by rubbing bodies such as amber, copal, or [[Lac (resin)|gum-lac]] with silk or paper, and "vitreous", by rubbing bodies as glass, rock crystal, or precious stones with hair or wool. He also posited the principle of mutual attraction for unlike forms and the repelling of like forms and that "from this principle one may with ease deduce the explanation of a great number of other phenomena." The terms resinous and vitreous were later replaced with the terms "positive" and "negative" by [[William Watson (scientist)|William Watson]] and Benjamin Franklin.
* 1737 – [[C. F. du Fay]] and [[Francis Hauksbee the younger]]{{citation needed|date=May 2013}} independently discover two kinds of frictional electricity: one generated from rubbing glass, the other from rubbing resin (later identified as positive and negative electrical charges).
* 1740 – [[Jean le Rond d'Alembert]], in ''Mémoire sur la réfraction des corps solides'', explains the process of [[refraction]].
* 1745 – [[Pieter van Musschenbroek]] of Leiden (Leyden) independently discovers the [[Leyden jar|Leyden (Leiden) jar]], a primitive [[capacitor]] or "condenser" (term coined by Volta in 1782, derived from the Italian ''condensatore''), with which the transient electrical energy generated by current friction machines could now be stored. He and his student Andreas Cunaeus used a glass jar filled with water into which a brass rod had been placed. He charged the jar by touching a wire leading from the electrical machine with one hand while holding the outside of the jar with the other. The energy could be discharged by completing an external circuit between the brass rod and another conductor, originally his hand, placed in contact with the outside of the jar. He also found that if the jar were placed on a piece of metal on a table, a shock would be received by touching this piece of metal with one hand and touching the wire connected to the electrical machine with the other.
* 1745 – [[Ewald Georg von Kleist]] of independently invents the capacitor: a glass jar coated inside and out with metal. The inner coating was connected to a rod that passed through the lid and ended in a metal sphere. By having this thin layer of glass insulation (a [[dielectric]]) between two large, closely spaced plates, von Kleist found the energy density could be increased dramatically compared with the situation with no insulator. [[Daniel Gralath]] improved the design and was also the first to combine several jars to form a battery strong enough to kill birds and small animals upon discharge.
* 1746 – [[Leonhard Euler]] develops the wave theory of light refraction and dispersion
* 1747 – [[William Watson (scientist)|William Watson]], while experimenting with a Leyden jar, observes that a discharge of static electricity causes [[electric current]] to flow and develops the concept of an electrical potential ([[voltage]]).
* 1752 – [[Benjamin Franklin]] establishes the link between lightning and electricity by the flying a kite into a thunderstorm and transferring some of the charge into a Leyden jar and showed that its properties were the same as charge produced by an electrical machine. He is credited with utilizing the concepts of positive and negative charge in the explanation of then known electrical phenomenon. He theorized that there was an electrical fluid (which he proposed could be the [[Luminiferous ether#The history of light and aether|luminiferous ether]], which was used by others before and after him, to explain the [[wave theory of light]]) that was part of all material and all intervening space. The charge of any object would be neutral if the concentration of this fluid were the same both inside and outside of the body, positive if the object contained an excess of this fluid, and negative if there were a deficit. In 1749 he had documented the similar properties of lightning and electricity, such as that both an [[electric spark]] and a lightning flash produced light and sound, could kill animals, cause fires, melt metal, destroy or reverse the polarity of magnetism, and flowed through conductors and could be concentrated at sharp points. He was later able to apply the property of concentrating at sharp points by his invention of the lightning rod, for which he intentionally did not profit. He also investigated the Leyden jar, proving that the charge was stored on the glass and not in the water, as others had assumed.
* 1753 – C. M. (of Scotland, possibly Charles Morrison, of Greenock or Charles Marshall, of Aberdeen) proposes in 17 February edition of Scots Magazine, an electrostatic telegraph system with 26 insulated wires, each corresponding to a letter of the alphabet and each connected to electrostatic machines. The receiving charged end was to electrostatically attract a disc of paper marked with the corresponding letter.
* 1767 – [[Joseph Priestley]] proposes an electrical inverse-square law
* 1774 – [[Georges-Louis LeSage]] builds an electrostatic telegraph system with 26 insulated wires conducting Leyden-jar charges to pith-ball electroscopes, each corresponding to a letter of the alphabet. Its range was only between rooms of his home.
* 1784 – [[Henry Cavendish]] defines the [[electromagnetic induction|inductive capacity]] of [[dielectrics]] (insulators) and measures the specific inductive capacity of various substances by comparison with an air condenser.
* 1785 – [[Charles-Augustin de Coulomb|Charles Coulomb]] introduces the [[Coulomb's law|inverse-square law of electrostatics]]
* 1786 – [[Luigi Galvani]] discovers "animal electricity" and postulates that animal bodies are storehouses of electricity. His invention of the voltaic cell leads to the invention the electric battery.
* 1791 – [[Luigi Galvani]] discovers galvanic electricity and [[bioelectricity]] through experiments following an observation that touching exposed muscles in frogs' legs with a scalpel which had been close to a static electrical machine caused them to jump. He called this "animal electricity". Years of experimentation in the 1780s eventually led him to the construction of an arc of two different metals (copper and zinc for example) by connecting the two metal pieces and then connecting their open ends across the nerve of a frog leg, producing the same muscular contractions (by completing a circuit) as originally accidentally observed. The use of different metals to produce an electrical spark is the basis that led Alessandro Volta in 1799 to his invention of his voltaic pile, which eventually became the [[Battery (electricity)|galvanic battery]].<ref>{{cite book|first=Henry Smith |last=Williams |title=A history of science |volume=3|url=http://www.worldwideschool.org/library/books/sci/history/AHistoryofScienceVolumeIII/chap46.html |chapter=VII. The Modern Development of Electricity and Magnetism|publisher=Worldwide School |access-date=20 October 2015}}</ref>
* 1799 – [[Alessandro Volta]], following Galvani's discovery of galvanic electricity, creates a [[voltaic pile|voltaic cell]] producing an electric current by the chemical action of several pairs of alternating copper (or silver) and zinc discs "piled" and separated by cloth or cardboard which had been soaked brine (salt water) or acid to increase conductivity. In '''1800''' he demonstrates the production of light from a glowing wire conducting electricity. This was followed in 1801 by his construction of the first [[electric battery]], by utilizing multiple voltaic cells. Prior to his major discoveries, in a letter of praise to the Royal Society 1793, Volta reported Luigi Galvani's experiments of the 1780s as the "most beautiful and important discoveries", regarding them as the foundation of future discoveries. Volta's inventions led to revolutionary changes with this method of the production of inexpensive, controlled electric current vs. existing frictional machines and Leyden jars. The electric battery became standard equipment in every experimental laboratory and heralded an age of practical applications of electricity.<ref name=Clark/>{{Page needed|date=October 2015}} The unit [[volt]] is named for his contributions.
* 1800 – [[William Herschel]] discovers [[infrared radiation]] from the Sun.
* 1800 – [[William Nicholson (chemist)|William Nicholson]], [[Anthony Carlisle]] and [[Johann Ritter]] use electricity to decompose water into hydrogen and oxygen, thereby discovering the process of [[electrolysis]], which led to the discovery of many other elements.
* 1800 – [[Alessandro Volta]] invents the [[voltaic pile]], or "battery", specifically to disprove Galvani's animal electricity theory.

==19th century==

===1801–1850===
* 1801 – [[Johann Wilhelm Ritter|Johann Ritter]] discovers [[ultraviolet radiation]] from the Sun
* 1801 – [[Thomas Young (scientist)|Thomas Young]] demonstrates the [[wave nature]] of light and the principle of [[Interference (wave propagation)|interference]]<ref name=whittaker106107>{{Cite book|last=Whittaker|first=Edmund Taylor|url=https://en.wikisource.org/wiki/A_History_of_the_Theories_of_Aether_and_Electricity/Chapter_4#106|title=A History of the Theories of Aether and Electricity|chapter=Chapter IV: The luminiferous medium, from Bradley to Fresnel |year=1910|pages=106–107}}</ref>
* 1802 – [[Gian Domenico Romagnosi]], Italian legal scholar, discovers that electricity and magnetism are related by noting that a nearby voltaic pile deflects a magnetic needle. He published his account in an Italian newspaper, but this was overlooked by the scientific community.<ref>{{cite book|last=Martins|first=Roberto de Andrade|chapter=Romagnosi and Volta's pile: early difficulties in the interpretation of Voltaic electricity|editor-last1=Bevilacqua|editor-first1=Fabio|editor-last2=Fregonese|editor-first2=Lucio|title=Nuova Voltiana: Studies on Volta and his Times|location=Pavia |publisher=Ulrico Hoepli |volume=3 |pages=81–102}}</ref>
* 1803 – Thomas Young develops the [[Double-slit experiment]] and demonstrates the effect of [[interference (wave propagation)|interference]].<ref>{{Cite book|last=Whittaker|first=Edmund Taylor|url=https://en.wikisource.org/wiki/A_History_of_the_Theories_of_Aether_and_Electricity/Chapter_4#108|title=A History of the Theories of Aether and Electricity|chapter=Chapter IV: The luminiferous medium, from Bradley to Fresnel |year=1910|page=108}}</ref>
* 1806 – [[Alessandro Volta]] employs a voltaic pile to decompose potash and soda, showing that they are the oxides of the previously unknown metals potassium and sodium. These experiments were the beginning of [[electrochemistry]].
* 1808 – [[Étienne-Louis Malus]] discovers [[Polarization (waves)|polarization]] by reflection
* 1809 – Étienne-Louis Malus publishes the law of Malus which predicts the light intensity transmitted by two polarizing sheets{{citation needed|date=September 2020}}
* 1809 – [[Humphry Davy]] first publicly demonstrates the electric [[arc lamp|arc light]].
* 1811 – [[François Jean Dominique Arago]] discovers that some quartz crystals continuously rotate the electric vector of light
* 1814 – [[Joseph von Fraunhofer]] discovered and studied the dark absorption lines in the [[spectrum]] of the sun now known as [[Fraunhofer lines]]
* 1816 – [[David Brewster]] discovers stress [[birefringence]]
* 1818 – [[Siméon Poisson]] predicts the [[Arago spot|Poisson-Arago bright spot]] at the center of the shadow of a circular opaque obstacle
* 1818 – [[François Jean Dominique Arago]] verifies the existence of the Poisson-Arago bright spot
* 1820 – [[Hans Christian Ørsted]], Danish physicist and chemist, develops an experiment in which he notices a compass needle is deflected from [[Magnetic declination|magnetic north]] when an electric current from the battery he was using was switched on and off, convincing him that magnetic fields radiate from all sides of a live wire just as light and heat do, confirming a direct relationship between electricity and magnetism. He also observes that the movement of the compass-needle to one side or the other depends upon the direction of the current.<ref>{{Cite book|last=Whittaker|first=Edmund Taylor|url=https://en.wikisource.org/wiki/A_History_of_the_Theories_of_Aether_and_Electricity/Chapter_3#84|title=A History of the Theories of Aether and Electricity|chapter=Chapter III: Galvanism: From Galvani to Ohm |year=1910|pages=84–85}}</ref> Following intensive investigations, he published his findings, proving that a changing electric current produces a magnetic field as it flows through a wire. The [[oersted]] unit of magnetic induction is named for his contributions.
* 1820 – [[André-Marie Ampère]], professor of mathematics at the École Polytechnique, demonstrates that parallel current-carrying wires experience magnetic force in a meeting of the [[French Academy of Science]], exactly one week after Ørsted's announcement of his discovery that a magnetic needle is acted on by a voltaic current.<ref>{{Cite book|last=Whittaker|first=Edmund Taylor|url=https://en.wikisource.org/wiki/A_History_of_the_Theories_of_Aether_and_Electricity/Chapter_3#87|title=A History of the Theories of Aether and Electricity|chapter=Chapter III: Galvanism: From Galvani to Ohm |year=1910|page=87}}</ref> He shows that a coil of wire carrying a current behaves like an ordinary magnet and suggests that electromagnetism might be used in telegraphy. He mathematically develops [[Ampère's force law|Ampère's law]] describing the magnetic force between two electric currents. His mathematical theory explains known electromagnetic phenomena and predicts new ones. His laws of electrodynamics include the facts that parallel conductors currying current in the same direction attract and those carrying currents in the opposite directions repel one another. One of the first to develop electrical measuring techniques, he built an instrument utilizing a free-moving needle to measure the flow of electricity, contributing to the development of the [[galvanometer]]. In '''1821''', he proposed a telegraphy system utilizing one wire per "galvanometer" to indicate each letter, and reported experimenting successfully with such a system. However, in '''1824''', [[Peter Barlow (mathematician)|Peter Barlow]] reported its maximum distance was only 200 feet, and so was impractical.{{citation needed|date=October 2015}} In '''1826''' he publishes the ''Memoir on the Mathematical Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience'' containing a mathematical derivation of the electrodynamic force law. Following Faraday's discovery of electromagnetic induction in 1831, Ampère agreed that Faraday deserved full credit for the discovery.
* 1820 – [[Johann Salomo Christoph Schweigger]], German chemist, physicist, and professor, builds the first sensitive galvanometer, wrapping a coil of wire around a graduated compass, an acceptable instrument for actual measurement as well as detection of small amounts of electric current, naming it after Luigi Galvani.
* 1821 – [[André-Marie Ampère]] announces his theory of electrodynamics, predicting the force that one current exerts upon another.
* 1821 – [[Thomas Johann Seebeck]] discovers the [[thermoelectric effect]].
* 1821 – [[Augustin-Jean Fresnel]] derives a mathematical demonstration that polarization can be explained only if light is ''entirely'' transverse, with no longitudinal vibration whatsoever.
* 1825 – [[Augustin Fresnel]] phenomenologically explains optical activity by introducing circular birefringence
* 1825 – [[William Sturgeon]], founder of the first English Electric Journal, ''Annals of Electricity'', found that an iron core inside a helical coil of wire connected to a battery greatly increased the resulting magnetic field, thus making possible the more powerful [[electromagnet]]s utilizing a [[Ferromagnetism|ferromagnetic]] core. Sturgeon also bent the iron core into a U-shape to bring the poles closer together, thus concentrating the magnetic field lines. These discoveries followed Ampère's discovery that electricity passing through a coiled wire produced a magnetic force and that of [[François Arago|Dominique François Jean Arago]] finding that an iron bar is magnetized by putting it inside the coil of current-carrying wire, but Arago had not observed the increased strength of the resulting field while the bar was being magnetized.
* 1826 – [[Georg Simon Ohm]] states his [[Ohm's law]] of [[electrical resistance]] in the journals of Schweigger and Poggendorff, and also published in his landmark pamphlet ''Die galvanische Kette mathematisch bearbeitet'' in '''1827'''. The unit [[ohm (unit)|ohm]] (Ω) of electrical resistance has been named in his honor.<ref>{{cite web|access-date=13 April 2021|url=https://mathshistory.st-andrews.ac.uk/Biographies/Ohm/|publisher= St. Andrews University|title=Georg Simon Ohm}}</ref>
* 1829 & 1830 – [[Francesco Zantedeschi]] publishes papers on the production of electric currents in closed circuits by the approach and withdrawal of a magnet, thereby anticipating Michael Faraday's classical experiments of 1831.
* 1831 – [[Michael Faraday]] began experiments leading to his discovery of the law of [[electromagnetic induction]], though the discovery may have been anticipated by the work of Francesco Zantedeschi. His breakthrough came when he wrapped two insulated coils of wire around a massive iron ring, bolted to a chair, and found that upon passing a current through one coil, a momentary electric current was induced in the other coil. He then found that if he moved a magnet through a loop of wire, or vice versa, an electric current also flowed in the wire. He then used this principle to construct the [[Dynamo|electric dynamo]], the first electric power generator. He proposed that electromagnetic forces extended into the empty space around the conductor, but did not complete that work. Faraday's concept of lines of flux emanating from charged bodies and magnets provided a way to visualize electric and magnetic fields. That mental model was crucial to the successful development of electromechanical devices which were to dominate the 19th century. His demonstrations that a changing magnetic field produces an electric field, mathematically modeled by [[Faraday's law of induction]], would subsequently become one of [[Maxwell's equations]]. These consequently evolved into the generalization of [[Field (physics)|field theory]].
* 1831 – [[Macedonio Melloni]] uses a [[thermopile]] to detect infrared radiation
* 1832 – [[Pavel Schilling|Baron Pavel L'vovitch Schilling]] (Paul Schilling) creates the first electromagnetic telegraph, consisting of a single-needle system in which a code was used to indicate the characters. Only months later, Göttingen professors [[Carl Friedrich Gauss]] and [[Wilhelm Eduard Weber|Wilhelm Weber]] constructed a telegraph that was working two years before Schilling could put his into practice. Schilling demonstrated the long-distance transmission of signals between two different rooms of his apartment and was the first to put into practice a binary system of signal transmission.
* 1833 – [[Heinrich Lenz]] states [[Lenz's law]]: if an increasing (or decreasing) magnetic flux induces an [[Electromotive force|electromotive force (EMF)]], the resulting current will oppose a further increase (or decrease) in magnetic flux, i.e., that an induced current in a closed conducting loop will appear in such a direction that it opposes the change that produced it. Lenz's law is one consequence of the principle of [[conservation of energy]]. If a magnet moves towards a closed loop, then the induced current in the loop creates a field that exerts a force opposing the motion of the magnet. Lenz's law can be derived from [[Faraday's law of induction]] by noting the negative sign on the right side of the equation. He also independently discovered [[Joule's first law|Joule's law]] in '''1842'''; to honor his efforts, Russian physicists refer to it as the "Joule-Lenz law."
* 1833 – [[Michael Faraday]] announces his law of [[electrochemical equivalent]]s
* 1834 – [[Heinrich Lenz]] determines the direction of the induced [[electromotive force]] (emf) and [[Electric current|current]] resulting from [[electromagnetic induction]]. [[Lenz's law]] provides a physical interpretation of the choice of sign in [[Faraday's law of induction]] (1831), indicating that the induced emf and the change in flux have opposite signs.
* 1834 – [[Jean-Charles Peltier]] discovers the [[Peltier effect]]: heating by an electric current at the junction of two different metals.
* 1835 – [[Joseph Henry]] invents the [[relay|electric relay]], which is an electrical switch by which the change of a weak current through the windings of an electromagnet will attract an armature to open or close the switch. Because this can control (by opening or closing) another, much higher-power, circuit, it is in a broad sense a form of electrical amplifier. This made a practical electric telegraph possible. He was the first to coil insulated wire tightly around an iron core in order to make an extremely powerful electromagnet, improving on William Sturgeon's design, which used loosely coiled, uninsulated wire. He also discovered the property of [[self inductance]] independently of Michael Faraday.
[[File:International Morse Code.svg|right|thumb|180px|Chart of the International [[Morse code]] letters and numerals.]]
* 1836 – [[William Fothergill Cooke]] invents a mechanical telegraph. '''1837''' with [[Charles Wheatstone]] invents the [[Cooke and Wheatstone telegraph|Cooke and Wheatstone needle telegraph]].  '''1838''' the Cooke and Wheatstone telegraph becomes the first commercial telegraph in the world when it is installed on the [[Great Western Railway]].
* 1837 – [[Samuel Morse]] develops an alternative electrical telegraph design capable of transmitting long distances over poor quality wire. He and his assistant [[Alfred Vail]] develop the [[Morse code]] signaling alphabet. In '''1838''' Morse successfully tested the device at the Speedwell Ironworks near [[Morristown, New Jersey]], and publicly demonstrated it to a scientific committee at the [[Franklin Institute]] in [[Philadelphia]], Pennsylvania. The first electric telegram using this device was sent by Morse on 24 May, '''1844''' from Baltimore to Washington, D.C., bearing the message "[[Book of Numbers|What hath God wrought]]?"
* 1838 – [[Michael Faraday]] uses Volta's battery to discover [[cathode ray]]s.
* 1839 – [[Alexandre Edmond Becquerel]] observes the [[photoelectric effect]] with an electrode in a conductive solution exposed to light.
* 1840 – [[James Prescott Joule]] formulates [[Joule's first law|Joule's Law]] (sometimes called the Joule-Lenz law) quantifying the amount of heat produced in a circuit as proportional to the product of the time duration, the resistance, and the square of the current passing through it.
* 1845 – [[Michael Faraday]] discovers that light propagation in a material can be influenced by external [[magnetic field]]s ([[Faraday effect]])
* 1849 – [[Hippolyte Fizeau]] and [[Jean-Bernard Foucault]] measure the speed of light to be about 298,000&nbsp;km/s

===1851–1900===
* 1852 – [[George Gabriel Stokes]] defines the [[Stokes parameters]] of polarization
* 1852 – [[Edward Frankland]] develops the theory of [[valence (chemistry)|chemical valence]]
* 1854 – [[Gustav Robert Kirchhoff]], physicist and one of the founders of [[spectroscopy]], publishes [[Kirchhoff's circuit laws|Kirchhoff's Laws]] on the conservation of electric charge and energy, which are used to determine currents in each branch of a circuit.
* 1855 – [[James Clerk Maxwell]] submits ''On Faraday's Lines of Force'' for publication containing a [https://archive.org/stream/scientificpapers01maxw#page/202/mode/2up mathematical statement] of [[Ampère's circuital law]] relating the curl of a magnetic field to the electrical current at a point.
* 1861 – the [[First Transcontinental Telegraph|first transcontinental telegraph system]] spans North America by connecting an existing network in the eastern United States to a small network in California by a link between Omaha and Carson City via Salt Lake City. The slower Pony Express system ceased operation a month later.
* 1864 – [[James Clerk Maxwell]] publishes his papers on a dynamical theory of the [[electromagnetic field]]
* 1865 – [[James Clerk Maxwell]] publishes his landmark paper [[A Dynamical Theory of the Electromagnetic Field]], in which [[Maxwell's equations]] demonstrated that electric and [[magnetism|magnetic]] forces are two complementary aspects of [[electromagnetism]]. He shows that the associated complementary electric and magnetic fields of electromagnetism travel through space, in the form of waves, at a constant velocity of 3.0 × 10<sup>8</sup> m/s. He also proposes that light is a form of electromagnetic radiation and that waves of oscillating electric and magnetic fields travel through empty space at a speed that could be predicted from simple electrical experiments. Using available data, he obtains a velocity of 310,740,000&nbsp;m/s and states "This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other [[radiation]]s if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws."
* 1866 – the first successful '''transatlantic telegraph system''' was completed. Earlier submarine cable transatlantic cables installed in 1857 and 1858 failed after operating for a few days or weeks.
* 1869 – [[William Crookes]] invents the [[Crookes tube]].
* 1873 — The [[British Science Association#Electrical standards|British Association]] establishes the units volt, ampere, and ohm.<ref>[[Fleeming Jenkin]] (1873) [https://babel.hathitrust.org/cgi/pt?id=mdp.39015067305402&view=1up&seq=5&skin=2021 Report of the Committee on Electrical Standards] via [[HathiTrust]]</ref>
* 1873 – [[Willoughby Smith]] discovers the [[photoelectric effect]] in metals not in solution (i.e., selenium).
* 1871 – [[Lord Rayleigh]] discusses the blue sky law and sunsets ([[Rayleigh scattering]])
* 1873 – J. C. Maxwell publishes [[A Treatise on Electricity and Magnetism]] which states that light is an electromagnetic phenomenon.
* 1874 – German scientist [[Karl Ferdinand Braun]] discovers the "unilateral conduction" of crystals.<ref>Braun, Ferdinand (1874) [http://gallica.bnf.fr/ark:/12148/bpt6k152378/f580.image.langEN "Ueber die Stromleitung durch Schwefelmetalle"] (On current conduction in metal sulphides), ''Annalen der Physik und Chemie'', '''153''' : 556–563.</ref><ref>[https://web.archive.org/web/20060211010305/http://chem.ch.huji.ac.il/~eugeniik/history/braun.htm Karl Ferdinand Braun]. chem.ch.huji.ac.il</ref> Braun patents the first [[diode|solid state diode]], a crystal [[rectifier]], in '''1899'''.<ref>{{cite web |url=http://encyclobeamia.solarbotics.net/articles/diode.html |title=Diode |publisher=Encyclobeamia.solarbotics.net |url-status=dead |archive-url=https://web.archive.org/web/20060426020137/http://encyclobeamia.solarbotics.net/articles/diode.html |archive-date=26 April 2006 }}</ref>
* 1875 – [[John Kerr (physicist)|John Kerr]] discovers the electrically induced birefringence of some liquids
* 1878 – [[Thomas Edison]], following work on a "multiplex telegraph" system and the phonograph, invents an improved incandescent light bulb. This was not the first electric light bulb but the first commercially practical incandescent light. In '''1879''' he produces a high-resistance lamp in a very high vacuum; the lamp lasts hundreds of hours. While the earlier inventors had produced electric lighting in lab conditions, Edison concentrated on commercial application and was able to sell the concept to homes and businesses by mass-producing relatively long-lasting light bulbs and creating a complete system for the generation and distribution of electricity.
* 1879 – [[Joseph Stefan|Jožef Stefan]] discovers the [[Stefan–Boltzmann law|Stefan–Boltzmann radiation law]] of a [[black body]] and uses it to calculate the first sensible value of the temperature of the Sun's surface to be 5700 [[Kelvin|K]]
* 1880 – Edison discovers [[thermionic emission]] or the Edison effect.
* 1882 – Edison switches on the world's first electrical power distribution system, providing 110 volts [[direct current]] (DC) to 59 customers.
* 1884 – [[Oliver Heaviside]] reformulates Maxwell's original mathematical treatment of electromagnetic theory from twenty equations in twenty unknowns into four simple equations in four unknowns (the modern vector form of [[Maxwell's equations]]).
* 1886 – [[Oliver Heaviside]] coins the term ''[[inductance]]''.
* 1887 – [[Heinrich Hertz]] invents a device for the production and reception of electromagnetic (EM) radio waves. His receiver consists of a coil with a spark gap.
* 1888 – Introduction of the [[induction motor]], an electric motor that harnesses a [[rotating magnetic field]] produced by [[alternating current]], independently invented by [[Galileo Ferraris]] and [[Nikola Tesla]].
[[File:Albert Einstein ETH-Bib Portr 05937.jpg|thumb|right|180px|[[Albert Einstein]] in the [[Deutsches Patent- und Markenamt|patent office]], Bern Switzerland, 1905]]

* 1888 – [[Heinrich Rudolf Hertz|Heinrich Hertz]] demonstrates the existence of electromagnetic waves by building an apparatus that produced and detected UHF radio waves (or microwaves in the UHF region). He also found that radio waves could be transmitted through different types of materials and were reflected by others, the key to [[radar]]. His experiments explain [[Reflection (physics)|reflection]], [[refraction]], [[Polarization (waves)|polarization]], [[Interference (wave propagation)|interference]], and [[velocity]] of electromagnetic waves.
* 1893 – [[Victor Schumann]] discovers the [[vacuum ultraviolet]] spectrum.
* 1895 – [[Wilhelm Conrad Röntgen]] discovers [[X-ray]]s
* 1895 – [[Jagadis Chandra Bose]] gives his first public demonstration of electromagnetic waves
* 1896 – [[Arnold Sommerfeld]] solves the half-plane [[diffraction]] problem
* 1897 – [[J. J. Thomson]] discovers the [[electron]].
* 1899 – [[Pyotr Lebedev]] measures the [[pressure of light]] on a solid body.
* 1900 – The [[Liénard–Wiechert potential]]s are introduced as time-dependent (retarded) electrodynamic potentials
* 1900 – [[Max Planck]] resolves the [[ultraviolet catastrophe]] by suggesting that [[black-body radiation]] consists of discrete packets, or [[quantum|quanta]], of energy.  The amount of energy in each packet is proportional to the frequency of the electromagnetic waves.  The constant of proportionality is now called [[Planck's constant]] in his honor.

==20th century==
* 1904 – [[John Ambrose Fleming]] invents the [[thermionic]] [[diode]], the first electronic [[vacuum tube]], which had practical use in early [[radio receivers]].
* 1905 – [[Albert Einstein]] proposes the [[Special Relativity|Theory of Special Relativity]], in which he rejects the existence of the [[Luminiferous aether|aether]] as unnecessary for explaining the propagation of electromagnetic waves. Instead, Einstein asserts ''as a [[postulate]]'' that the speed of light is constant in all [[inertial|inertial frames of reference]], and goes on to demonstrate a number of revolutionary (and highly counter-intuitive) consequences, including [[time dilation]], [[length contraction]], the [[relativity of simultaneity]], the [[relativistic mass|dependence of mass on velocity]], and the [[mass-energy equivalence|equivalence of mass and energy]].
* 1905 – Einstein explains the [[photoelectric effect]] by extending Planck's idea of light quanta, or [[photons]], to the absorption and emission of [[photoelectrons]].  Einstein would later receive the [[Nobel Prize in Physics]] for this discovery, which launched the [[quantum mechanics|quantum revolution]] in physics.
* 1911 – [[Superconductivity]] is discovered by [[Heike Kamerlingh Onnes]], who was studying the resistivity of solid mercury at cryogenic temperatures using the recently discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistivity abruptly disappeared. For this discovery, he was awarded the Nobel Prize in Physics in 1913.
* 1919 – [[Albert A. Michelson]] makes the first interferometric measurements of stellar diameters at [[Mount Wilson Observatory]] (see [[history of astronomical interferometry]])
* 1924 – [[Louis de Broglie]] postulates the wave nature of [[electrons]] and suggests that [[Matter wave|all matter has wave properties]].
* 1946 – [[Martin Ryle]] and Vonberg build the first two-element astronomical radio interferometer (see [[history of astronomical interferometry]])
* 1953 – [[Charles H. Townes]], [[James P. Gordon]], and [[Herbert J. Zeiger]] produce the first [[maser]]
* 1956 – [[Hanbury-Brown and Twiss effect|R. Hanbury-Brown and R.Q. Twiss]] complete the [[interferometer|correlation interferometer]]
* 1959 – [[Sheldon Glashow]], [[Abdus Salam]], and [[John Clive Ward]] merge electromagnetism and the [[weak interaction]] in [[Standard Model]], into [[electroweak interaction]] 
* 1960 – [[Theodore Maiman]] produces the first working [[laser]]
* 1966 – [[Oleg D. Jefimenko|Jefimenko]] introduces [[Jefimenko's equations|time-dependent (retarded) generalizations of Coulomb's law and the Biot–Savart law]]
* 1999 – M. Henny and others demonstrate the fermionic Hanbury Brown and Twiss experiment

==See also==
* [[History of electromagnetic theory]]
* [[History of optics]]
* [[History of special relativity]]
* [[History of superconductivity]]
* [[Timeline of luminiferous aether]]

==References==
{{Reflist}}

==Further reading==
* [https://www.perseus.tufts.edu/hopper/text?doc=Plin.+Nat.+toc&redirect=true The Natural History ''Pliny the Elder, The Natural History from Perseus Digital Library'']
* [http://www.aip.org/history/electron/ The Discovery of the Electron] ''from the [[American Institute of Physics]]''
* [https://web.archive.org/web/20060504042244/http://www.chemsoc.org/chembytes/ezine/2003/russell_aug03.htm Enterprise and electrolysis...] ''from the [[Royal Society of Chemistry]] (chemsoc)''
* [http://www.worldwideschool.org/library/catalogs/bysubject-sci-history.html Pure Science-History], Worldwide School

==External links==
{{commons category|Electromagnetism}}
* [http://www.tuc.nrao.edu/~demerson/bose/bose.htm The Work of Jagadis Chandra Bose: 100 Years of MM-Wave Research]
* [http://www.ias.ac.in/resonance/Feb1998/pdf/Feb1998AiB.pdf Jagadis Chandra Bose and His Pioneering Research on Microwaves]
{{History of physics}}

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[[Category:Electromagnetism| Timeline]]
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[[Category:Physics timelines|Electromagnetism and Classical Optics]]
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