Editing Electric charge (section)

== History ==
{{See also|History of electromagnetic theory|Electricity#History}}
[[File:Bcoulomb.png|thumb|Coulomb's [[torsion balance#Torsion balance|torsion balance]]]]
From ancient times, people were familiar with four types of phenomena that today would all be explained using the concept of electric charge: (a) [[lightning]], (b) the [[torpedo fish]] (or electric ray), (c) [[St Elmo's Fire]], and (d) that [[amber]] rubbed with [[fur]] would attract small, light objects.<ref>{{cite book |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1954 |title=The development of the concept of electric charge: Electricity from the Greeks to Coulomb |url=https://archive.org/details/developmentofcon0000roll|url-access=registration |location=Cambridge, MA |publisher=[[Harvard University Press]] |page=[https://archive.org/details/developmentofcon0000roll/page/n18 1] }}</ref> The first account of the {{em|amber effect}} is often attributed to the ancient Greek mathematician [[Thales of Miletus]], who lived from c. 624 to c. 546 BC, but there are doubts about whether Thales left any writings;<ref>{{cite book |last=O'Grady |first=Patricia F.|author-link=Patricia O'Grady |date=2002 |title=Thales of Miletus: The Beginnings of Western Science and Philosophy |url=https://books.google.com/books?id=ZTUlDwAAQBAJ|publisher=Ashgate |page=8 |isbn= 978-1351895378}}</ref> his account about amber is known from an account from early 200s.<ref name=DL/> This account can be taken as evidence that the phenomenon was known since at least c. 600 BC, but Thales explained this phenomenon as evidence for inanimate objects having a soul.<ref name=DL>{{cite web| url = https://en.wikisource.org/wiki/Lives_of_the_Eminent_Philosophers/Book_I#Thales_24| title = Lives of the Eminent Philosophers by Diogenes Laërtius, Book 1, §24}}</ref> In other words, there was no indication of any conception of electric charge. More generally, the ancient Greeks did not understand the connections among these four kinds of phenomena. The Greeks observed that the charged amber buttons could attract light objects such as [[hair]]. They also found that if they rubbed the amber for long enough, they could even get an [[electric spark]] to jump,{{citation needed|reason=cannot find any source for this claim|date=April 2018}} but there is also a claim that no mention of electric sparks appeared until late 17th century.<ref>{{cite journal |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1953 |journal=American Journal of Physics|volume=21|issue=5 |doi=10.1119/1.1933449|page=348|title=The Prenatal History of Electrical Science|bibcode=1953AmJPh..21..343R}}</ref> This property derives from the [[triboelectric effect]].
In late 1100s, the substance [[jet (lignite)|jet]], a compacted form of coal, was noted to have an amber effect,<ref>{{cite journal |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1953 |journal=American Journal of Physics|volume=21|issue=5 |doi=10.1119/1.1933449|page=351|title=The Prenatal History of Electrical Science|bibcode=1953AmJPh..21..343R}}</ref> and in the middle of the 1500s, [[Girolamo Fracastoro]], discovered that [[diamond]] also showed this effect.<ref>{{cite journal |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1953 |journal=American Journal of Physics|volume=21|issue=5 |doi=10.1119/1.1933449|page=353|title=The Prenatal History of Electrical Science|bibcode=1953AmJPh..21..343R}}</ref> Some efforts were made by Fracastoro and others, especially [[Gerolamo Cardano]] to develop explanations for this phenomenon.<ref name=Roller356>{{cite journal |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1953 |journal=American Journal of Physics|volume=21|issue=5 |doi=10.1119/1.1933449|page=356|title=The Prenatal History of Electrical Science|bibcode=1953AmJPh..21..343R}}</ref>

In contrast to [[astronomy]], [[mechanics]], and [[optics]], which had been studied quantitatively since antiquity, the start of ongoing qualitative and quantitative research into electrical phenomena can be marked with the publication of ''[[De Magnete]]'' by the English scientist [[William Gilbert (astronomer)|William Gilbert]] in 1600.<ref>{{cite book|last1=Roche|first1=J.J.|title=The mathematics of measurement|date=1998|publisher=The Athlone Press|location=London|isbn=978-0387915814|page=62}}</ref> In this book, there was a small section where Gilbert returned to the amber effect (as he called it) in addressing many of the earlier theories,<ref name=Roller356/> and coined the [[Neo-Latin]] word ''electrica'' (from {{lang|grc|ἤλεκτρον}} (ēlektron), the [[ancient Greek|Greek]] word for ''amber''). The Latin word was translated into English as {{em|electrics}}.<ref>{{cite book |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1954 |title=The development of the concept of electric charge: Electricity from the Greeks to Coulomb |url=https://archive.org/details/developmentofcon0000roll|url-access=registration |location=Cambridge, MA |publisher=[[Harvard University Press]] |pages=[https://archive.org/details/developmentofcon0000roll/page/6 6–7] }}<br/>
{{cite book |last= Heilbron| first= J.L.|title= Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics|publisher= University of California Press|year= 1979|page= 169|isbn= 978-0-520-03478-5|url= https://books.google.com/books?id=UlTLRUn1sy8C&pg=PA169}}</ref> Gilbert is also credited with the term ''electrical'', while the term ''electricity'' came later, first attributed to Sir [[Thomas Browne]] in his [[Pseudodoxia Epidemica]] from 1646.<ref>{{cite book |last1=Brother Potamian |last2=Walsh |first2=J.J.|date=1909 |title=Makers of electricity|url=https://archive.org/details/cu31924004627059 |location=New York|publisher=[[Fordham University Press]] |page=[https://archive.org/details/cu31924004627059/page/n81 70] }}</ref> (For more linguistic details see [[Etymology of electricity]].) Gilbert hypothesized that this amber effect could be explained by an effluvium (a small stream of particles that flows from the electric object, without diminishing its bulk or weight) that acts on other objects. This idea of a material electrical effluvium was influential in the 17th and 18th centuries. It was a precursor to ideas developed in the 18th century about "electric fluid" (Dufay, Nollet, Franklin) and "electric charge".<ref name=Baigrie11>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=11}}</ref>

Around 1663 [[Otto von Guericke]] invented what was probably the first [[electrostatic generator]], but he did not recognize it primarily as an electrical device and only conducted minimal electrical experiments with it.<ref>{{cite journal|last1=Heathcote|first1=N.H. de V.|title=Guericke's sulphur globe |journal=Annals of Science |date=1950| volume=6|issue=3| page=304|doi=10.1080/00033795000201981}}<br/>{{cite book  |title=Electricity in the 17th and 18th centuries: a study of early Modern physics  |last=Heilbron |author-link=John L. Heilbron  |first=J.L. |year=1979 |publisher=[[University of California Press]] |isbn=0-520-03478-3 |pages=215–218 |url=https://books.google.com/books?id=UlTLRUn1sy8C&pg=PA215}}</ref> Other European pioneers were [[Robert Boyle]], who in 1675 published the first book in English that was devoted solely to electrical phenomena.<ref name=Baigrie20>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=20}}</ref> His work was largely a repetition of Gilbert's studies, but he also identified several more "electrics",<ref name=Baigrie21>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=21}}</ref> and noted mutual attraction between two bodies.<ref name=Baigrie20/>

In 1729 [[Stephen Gray (scientist)|Stephen Gray]] was experimenting with [[static electricity]], which he generated using a glass tube.  He noticed that a cork, used to protect the tube from dust and moisture, also became electrified (charged).  Further experiments (e.g., extending the cork by putting thin sticks into it) showed—for the first time—that electrical effluvia (as Gray called it) could be transmitted (conducted) over a distance.  Gray managed to transmit charge with twine (765 feet) and wire (865 feet).<ref name=Baigrie27>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=27}}</ref>   Through these experiments, Gray discovered the importance of different materials, which facilitated or hindered the conduction of electrical effluvia.  [[John Theophilus Desaguliers]], who repeated many of Gray's experiments, is credited with coining the terms [[electrical conductor|conductors]] and [[electrical insulation|insulators]] to refer to the effects of different materials in these experiments.<ref name=Baigrie27/> Gray also discovered electrical induction (i.e., where charge could be transmitted from one object to another without any direct physical contact).   For example, he showed that by bringing a charged glass tube close to, but not touching, a lump of lead that was sustained by a thread, it was possible to make the lead become electrified (e.g., to attract and repel brass filings).<ref name=Baigrie28>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=28}}</ref> He attempted to explain this phenomenon with the idea of electrical effluvia.<ref>{{cite book |last= Heilbron| first= J.L.|title= Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics|publisher= University of California Press|year= 1979|page= 248|isbn= 978-0-520-03478-5|url= https://books.google.com/books?id=UlTLRUn1sy8C&pg=PA248}}</ref>

Gray's discoveries introduced an important shift in the historical development of knowledge about electric charge.  The fact that electrical effluvia could be transferred from one object to another, opened the theoretical possibility that this property was not inseparably connected to the bodies that were electrified by rubbing.<ref name=Baigrie35>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=35}}</ref> In 1733 [[Charles François de Cisternay du Fay]], inspired by Gray's work, made a series of experiments (reported in ''Mémoires de l'[[Académie Royale des Sciences]]''), showing that more or less all substances could be 'electrified' by rubbing, except for metals and fluids<ref>{{cite book |last1=Roller |first1=Duane |last2=Roller |first2=D.H.D.|date=1954 |title=The development of the concept of electric charge: Electricity from the Greeks to Coulomb |url=https://archive.org/details/developmentofcon0000roll|url-access=registration |location=Cambridge, MA |publisher=[[Harvard University Press]] |page=[https://archive.org/details/developmentofcon0000roll/page/40 40] }}</ref> and proposed that electricity comes in two varieties that cancel each other, which he expressed in terms of a two-fluid theory.<ref>[http://www.sparkmuseum.com/BOOK_DUFAY.HTM Two Kinds of Electrical Fluid: Vitreous and Resinous – 1733. Charles François de Cisternay DuFay (1698–1739)] {{webarchive|url=https://web.archive.org/web/20090526211225/http://www.sparkmuseum.com/BOOK_DUFAY.HTM |date=2009-05-26}}. sparkmuseum.com</ref> When [[glass]] was rubbed with [[silk]], du Fay said that the glass was charged with ''[[glass|vitreous]] electricity'', and, when amber was rubbed with fur, the amber was charged with ''[[resin]]ous electricity''. In contemporary understanding, positive charge is now defined as the charge of a glass rod after being rubbed with a silk cloth, but it is arbitrary which type of charge is called positive and which is called negative.<ref>{{cite book |last1=Wangsness |first1=Roald K. |title=Electromagnetic Fields |edition=2nd |date=1986 |location=New York |publisher=Wiley |page=40|isbn=0-471-81186-6}}</ref> Another important two-fluid theory from this time was proposed by [[Jean-Antoine Nollet]] (1745).<ref>{{cite book |last= Heilbron| first= J.L.|title= Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics|publisher= University of California Press|year= 1979|pages= 280–289|isbn= 978-0-520-03478-5|url= https://books.google.com/books?id=UlTLRUn1sy8C&pg=PA169}}</ref>

Up until about 1745, the main explanation for electrical attraction and repulsion was the idea that electrified bodies gave off an effluvium.<ref>{{cite encyclopedia |last1=Heilbron |first1=John  |editor-last1=Heilbron |editor-first1=John |title=Leyden jar and electrophore |date=2003 |publisher=Oxford University Press |location=New York |isbn=9780195112290 |page=459 |encyclopedia=The Oxford Companion to the History of Modern Science}}</ref>
[[Benjamin Franklin]] started electrical experiments in late 1746,<ref name=Baigrie38>{{cite book|last=Baigrie|first=Brian |title=Electricity and magnetism: A historical perspective|year=2007|publisher=Greenwood Press|location=Westport, CT|page=38}}</ref> and by 1750 had developed a one-[[fluid theory of electricity]], based on an experiment that showed that a rubbed glass received the same, but opposite, charge strength as the cloth used to rub the glass.<ref name=Baigrie38/><ref>{{cite journal |last1=Guarnieri |first1=Massimo |title=Electricity in the Age of Enlightenment |journal=IEEE Industrial Electronics Magazine |date=2014 |volume=8 |issue=3 |page=61|doi=10.1109/MIE.2014.2335431|s2cid=34246664 }}</ref> Franklin imagined electricity as being a type of invisible fluid present in all matter and coined the term {{em|charge}} itself (as well as [[Electrical battery|battery]] and some others<ref>{{Cite web|url=https://spark.iop.org/electric-charge-and-current-short-history|title=Electric charge and current - a short history &#124; IOPSpark}}</ref>); for example, he believed that it was the [[glass]] in a [[Leyden jar]] that held the accumulated charge. He posited that rubbing insulating surfaces together caused this fluid to change location, and that a flow of this fluid constitutes an electric current. He also posited that when matter contained an excess of the fluid it was {{em|positively}} charged and when it had a deficit it was {{em|negatively}} charged.  He identified the term {{em|positive}} with vitreous electricity and {{em|negative}} with resinous electricity after performing an experiment with a glass tube he had received from his overseas colleague Peter Collinson. The experiment had participant A charge the glass tube and participant B receive a shock to the knuckle from the charged tube. Franklin identified participant B to be positively charged after having been shocked by the tube.<ref name="Franklin1747">{{cite letter |first= Benjamin |last=Franklin |recipient=Peter Collinson |date=1747-05-25 |subject=Letter to Peter Collinson, May 25, 1747 |url=http://www.benjamin-franklin-history.org/letter-from-benjamin-franklin-to-peter-collison-dated-may-25-1747/ |access-date=2019-09-16}}</ref> There is some ambiguity about whether [[William Watson (scientist)|William Watson]] independently arrived at the same one-fluid explanation around the same time (1747). Watson, after seeing Franklin's letter to Collinson, claims that he had presented the same explanation as Franklin in spring 1747.<ref>{{cite journal |last1=Watson |first1=William |title=Some further inquiries into the nature and properties of electricity |journal=Philosophical Transactions of the Royal Society of London |date=1748 |volume=45 |page=100 |doi=10.1098/rstl.1748.0004 |s2cid=186207940 |doi-access= }}</ref> Franklin had studied some of Watson's works prior to making his own experiments and analysis, which was probably significant for Franklin's own theorizing.<ref name=Cohen66>{{cite book |last1=Cohen |first1=I. Bernard |title=Franklin and Newton |date=1966 |publisher=Harvard University Press |location=Cambridge, MA |pages=390–413 |edition=reprint |url=https://archive.org/details/franklinnewtonin0000cohe/page/390/mode/2up}}</ref> One physicist suggests that Watson first proposed a one-fluid theory, which Franklin then elaborated further and more influentially.<ref>{{cite book |last1=Weinberg |first1=Steven |author-link = Steven Weinberg | title=The discovery of subatomic particles |date=2003 |publisher=Cambridge University Press |isbn=9780521823517 |page=13 |edition=rev}}</ref> A historian of science argues that Watson missed a subtle difference between his ideas and Franklin's, so that Watson misinterpreted his ideas as being similar to Franklin's.<ref>{{cite book  |title=Electricity in the 17th and 18th centuries: a study of early Modern physics  |last=Heilbron |author-link=John L. Heilbron  |first=J.L. |year=1979 |publisher=[[University of California Press]]|isbn=0-520-03478-3 |pages=344–5 |url=https://books.google.com/books?id=UlTLRUn1sy8C&pg=PA344}}</ref> In any case, there was no animosity between Watson and Franklin, and the Franklin model of electrical action, formulated in early 1747, eventually became widely accepted at that time.<ref name=Cohen66/> After Franklin's work, effluvia-based explanations were rarely put forward.<ref>{{cite book |last1=Tricker |first1=R.A.R |title=Early electrodynamics: The first law of circulation |url=https://archive.org/details/earlyelectrodyna0000tric |url-access=registration |date=1965 |publisher=Pergamon |location=Oxford |isbn=9781483185361 |page=[https://archive.org/details/earlyelectrodyna0000tric/page/2 2]}}</ref>

It is now known that the Franklin model was fundamentally correct. There is only one kind of electrical charge, and only one variable is required to keep track of the amount of charge.<ref name="one-kind">{{cite web |url=http://www.av8n.com/physics/one-kind-of-charge.htm |title=One Kind of Charge |last=Denker |first=John |date=2007 |website=www.av8n.com/physics |archive-url=https://web.archive.org/web/20160205132208/http://www.av8n.com/physics/one-kind-of-charge.htm |archive-date=2016-02-05 |url-status=dead }}</ref>

Until 1800 it was only possible to study conduction of electric charge by using an electrostatic discharge.  In 1800 [[Alessandro Volta]] was the first to show that charge could be maintained in continuous motion through a closed path.<ref>{{cite book|first=Andrew |last=Zangwill|title=Modern Electrodynamics|year=2013| page=31 | publisher=Cambridge University Press|isbn=978-0-521-89697-9}}</ref>

In 1833, [[Michael Faraday]] sought to remove any doubt that electricity is identical, regardless of the source by which it is produced.<ref>{{cite journal |last1=Faraday |first1=Michael |date=1833 |title=Experimental researches in electricity — third series |journal=Philosophical Transactions of the Royal Society of London |volume=123 |pages=23–54 |doi=10.1098/rstl.1833.0006 |s2cid=111157008 |url=https://royalsocietypublishing.org/doi/abs/10.1098/rstl.1833.0006}}</ref>  He discussed a variety of known forms, which he characterized as common electricity (e.g., [[static electricity]], [[piezoelectricity]], [[Electromagnetic induction|magnetic induction]]),  voltaic electricity (e.g., [[electric current]] from a [[voltaic pile]]), and animal electricity (e.g.,  [[bioelectricity]]).

In 1838, Faraday raised a question about whether electricity was a fluid or fluids or a property of matter, like gravity. He investigated whether matter could be charged with one kind of charge independently of the other.<ref>{{cite journal |last1=Faraday |first1=Michael |date=1838 |title=Experimental researches in electricity — eleventh series |journal=Philosophical Transactions of the Royal Society of London |volume=128 |page=4 |doi=10.1098/rstl.1838.0002 |s2cid=116482065 |quote=§1168|doi-access= }}</ref> He came to the conclusion that electric charge was a relation between two or more bodies, because he could not charge one body without having an opposite charge in another body.<ref>{{cite book |last1=Steinle |first1=Friedrich |editor1-last=Buchwald |editor1-first=Jed Z. |editor2-last=Fox |editor2-first=Robert |title=The Oxford Handbook of the history of physics |date=2013 |publisher=Oxford University Press |page=560 |chapter=Electromagnetism and field physics}}</ref>

In 1838, Faraday also put forth a theoretical explanation of electric force, while expressing neutrality about whether it originates from one, two, or no fluids.<ref>{{cite journal |last1=Faraday |first1=Michael |date=1838 |title=Experimental researches in electricity — fourteenth series |journal=Philosophical Transactions of the Royal Society of London |volume=128 |pages=265–282 |doi=10.1098/rstl.1838.0014 |s2cid=109146507 |doi-access=free }}</ref>  He focused on the idea that the normal state of particles is to be nonpolarized, and that when polarized, they seek to return to their natural, nonpolarized state.

In developing a field theory approach to electrodynamics (starting in the mid-1850s), [[James Clerk Maxwell]] stops considering electric charge as a special substance that accumulates in objects, and starts to understand electric charge as a consequence of the transformation of energy in the field.<ref name="Buchwald">{{cite book |last1=Buchwald |first1=Jed Z. |editor1-last=Buchwald |editor1-first=Jed Z. |editor2-last=Fox |editor2-first=Robert |title=The Oxford Handbook of the history of physics |date=2013 |publisher=Oxford University Press |page=575|chapter=Electrodynamics from Thomson and Maxwell to Hertz}}</ref> This pre-quantum understanding considered magnitude of electric charge to be a continuous quantity, even at the microscopic level.<ref name="Buchwald"/>