Editing Electrostatic generator (section)

===Friction machines===<!-- This section is linked from [[Van de Graaff generator]] -->

====History====
[[File:Elektrisiermaschine.jpg|thumb|right|222px|Typical friction machine using a glass globe, common in the 18th century]]

[[File:Electrostatic generator Teylers Museum.jpg|thumb|222px|Martinus van Marum's [[Large electrostatic generator (Teylers)|Electrostatic generator]] at [[Teylers Museum]]]]

The first electrostatic generators are called ''friction machines'' because of the [[friction]] in the generation process. A primitive form of frictional machine was invented around 1663 by [[Otto von Guericke]], using a sulphur globe that could be rotated and rubbed by hand. It may not actually have been rotated during use and was not intended to produce electricity (rather cosmic virtues),<ref>See:
* Heathcote, N. H. de V. (1950) "Guericke's sulphur globe", ''Annals of Science'', '''6''' : 293–305. [[doi:10.1080/00033795000201981]]
* Zeitler, Jürgen (2011) "Guerickes Weltkräfte und die Schwefelkugel", ''Monumenta Guerickiana'' '''20'''/'''21''' : 147–156.
* {{cite book|last=Schiffer|first=Michael Brian|title=Draw the Lightning Down: Benjamin Franklin and Electrical Technology in the Age of Enlightenment|year=2003|publisher=Univ. of California Press|isbn=0-520-24829-5|url=https://archive.org/details/drawlightningdow00mich|url-access=registration|pages=[https://archive.org/details/drawlightningdow00mich/page/18 18]-19}}</ref> but inspired many later machines that used rotating globes. [[Isaac Newton]] suggested the use of a glass globe instead of a sulphur one.<ref>[[Opticks|Optics, 8th Query]]</ref> About 1706 [[Francis Hauksbee]] improved the basic design,<ref>{{cite book|last=Hauksbee|first=Francis|title=Psicho-Mechanical Experiments On Various Subjects|year=1709|publisher=R. Brugis}}</ref> with his frictional electrical machine that enabled a glass sphere to be rotated rapidly against a woollen cloth.<ref name=ODNB>{{cite ODNB|first=Stephen|last=Pumfrey|title=Hauksbee, Francis (bap. 1660, d. 1713)|date=May 2009| url=http://www.oxforddnb.com/view/article/12618|access-date=2011-12-11|doi=10.1093/ref:odnb/12618}}</ref>

Generators were further advanced when, about 1730, Prof. [[Georg Matthias Bose]] of Wittenberg added a collecting conductor (an insulated tube or cylinder supported on silk strings). Bose was the first to employ the "[[prime conductor]]" in such machines, this consisting of an iron rod held in the hand of a person whose body was insulated by standing on a block of resin.

In 1746, [[William Watson (scientist)|William Watson]]'s machine had a large wheel turning several glass globes, with a sword and a gun barrel suspended from silk cords for its prime conductors. [[Johann Heinrich Winckler]], professor of physics at [[Leipzig]], substituted a leather cushion for the hand. During 1746, [[Jan Ingenhousz]] invented electric machines made of plate glass.<ref>Consult Dr. [[Joseph Constantine Carpue|Carpue]]'s [https://archive.org/details/b22042684 'Introduction to Electricity and Galvanism'], London 1803.</ref> Experiments with the electric machine were largely aided by the invention of the [[Leyden Jar]]. This early form of the [[capacitor]], with conductive coatings on either side of the glass, can accumulate a charge of electricity when connected with a source of electromotive force.

The electric machine was soon further improved by [[Andrew Gordon (Benedictine)|Andrew (Andreas) Gordon]], a Scotsman and professor at Erfurt, who substituted a glass cylinder in place of a glass globe; and by Giessing of Leipzig who added a "rubber" consisting of a cushion of woollen material. The collector, consisting of a series of metal points, was added to the machine by [[Benjamin Wilson (painter)|Benjamin Wilson]] about 1746, and in 1762, [[John Canton]] of England (also the inventor of the first pith-ball electroscope) improved the efficiency of electric machines by sprinkling an amalgam of tin over the surface of the rubber.<ref name="EncyclopediaAmericana">Maver, William Jr.: "Electricity, its History and Progress", The Encyclopedia Americana; a library of universal knowledge, vol. X, pp. 172ff. (1918). New York: Encyclopedia Americana Corp.</ref> In 1768, [[Jesse Ramsden]] constructed a widely used version of a plate electrical generator.{{clarify|date=August 2018}}

In 1783, Dutch scientist [[Martin van Marum]] of Haarlem designed a [[large electrostatic generator (Teylers)|large electrostatic machine]] of high quality with glass disks 1.65 meters in diameter for his experiments. Capable of producing voltage with either polarity, it was built under his supervision by [[John Cuthbertson (instrument maker)|John Cuthbertson]] of Amsterdam the following year. The generator is currently on display at the [[Teylers Museum]] in Haarlem.
 
In 1785, N. Rouland constructed a silk-belted machine that rubbed two grounded tubes covered with hare fur. [[Edward Nairne]] developed an electrostatic generator for medical purposes in 1787 that had the ability to generate either positive or negative electricity, the first of these being collected from the prime conductor carrying the collecting points and the second from another prime conductor carrying the friction pad. The [[Winter machine]]{{clarify|date=August 2018}} possessed higher efficiency than earlier friction machines.

In the 1830s, [[Georg Ohm]] possessed a machine similar to the Van Marum machine for his research (which is now at the [[Deutsches Museum]], Munich, Germany). In 1840, the [[Woodward machine]] was developed by improving the 1768 Ramsden machine, placing the prime conductor above the disk(s). Also in 1840, the [[Armstrong Hydroelectric Machine|Armstrong hydroelectric machine]] was developed, using steam as a charge carrier.

====Friction operation====
The presence of [[surface charge]] imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomenon of the [[triboelectric effect]]. Rubbing two non-conductive objects can generate a great amount of static electricity. This is not the result of friction; two non-conductive surfaces can become charged by just being placed one on top of the other. Since most surfaces have a rough texture, it takes longer to achieve charging through contact than through rubbing. Rubbing objects together increases amount of adhesive contact between the two surfaces. Usually [[Insulator (electricity)|insulators]], e.g., substances that do not conduct electricity, are good at both generating, and holding, a surface charge. Some examples of these substances are [[rubber]], [[plastic]], [[glass]], and [[pith]]. [[conductor (material)|Conductive]] objects in contact generate charge imbalance too, but retain the charges only if insulated. The charge that is transferred during contact electrification is stored on the surface of each object. Note that the presence of [[electric current]] does not detract from the electrostatic forces nor from the sparking, from the [[corona discharge]], or other phenomena. Both phenomena can exist simultaneously in the same system.