Editing Electrostatic generator (section)

===Influence machines===

====History====
Frictional machines were, in time, gradually superseded by the second class of instrument mentioned above, namely, ''influence machines''. These operate by [[electrostatic induction]] and convert mechanical work into electrostatic energy by the aid of a small initial charge which is continually being replenished and reinforced. The first suggestion of an influence machine appears to have grown out of the invention of [[Alessandro Volta|Volta]]'s ''[[electrophorus]]''. The electrophorus is a single-plate [[capacitor]] used to produce imbalances of [[electric charge]] via the process of electrostatic induction.

The next step was when [[Abraham Bennet]], the inventor of the gold leaf [[electroscope]], described a "''doubler of electricity''" (Phil. Trans., 1787), as a device similar to the electrophorus, but that could amplify a small charge by means of repeated manual operations with three insulated plates, in order to make it observable in an electroscope. In 1788, [[William Nicholson (chemist)|William Nicholson]] proposed his rotating doubler, which can be considered as the first rotating influence machine. His instrument was described as "an instrument which by turning a winch produces the two states of electricity without friction or communication with the earth". (Phil. Trans., 1788, p.&nbsp;403) Nicholson later described a "spinning condenser" apparatus, as a better instrument for measurements.

[[Erasmus Darwin]], W. Wilson, G. C. Bohnenberger, and (later, 1841) J. C. E. Péclet developed various modifications of Bennet's 1787 device. [[Francis Ronalds]] automated the generation process in 1816 by adapting a pendulum bob as one of the plates, driven by clockwork or a steam engine – he created the device to power his [[Electric telegraph#First working systems|electric telegraph]].<ref>{{Cite book|title=Sir Francis Ronalds: Father of the Electric Telegraph|last=Ronalds|first=B.F.|publisher=Imperial College Press|year=2016|isbn=978-1-78326-917-4|location=London}}</ref><ref>{{Cite journal|last=Ronalds|first=B.F.|date=2016|title=Sir Francis Ronalds and the Electric Telegraph|journal=International Journal for the History of Engineering & Technology|volume=86|pages=42–55|doi=10.1080/17581206.2015.1119481|s2cid=113256632}}</ref>

Others, including [[Tiberius Cavallo|T. Cavallo]] (who developed the "[[Cavallo multiplier]]", a charge multiplier using simple addition, in 1795), [[John Read (inventor)|John Read]], [[Charles Bernard Desormes]], and [[Jean Nicolas Pierre Hachette]], developed further various forms of rotating doublers. In 1798, The German scientist and preacher Gottlieb Christoph Bohnenberger, described the [[Bohnenberger machine]], along with several other doublers of Bennet and Nicholson types in a book. The most interesting of these were described in the "Annalen der Physik" (1801). [[Giuseppe Belli (physicist)|Giuseppe Belli]], in 1831, developed a simple symmetrical doubler which consisted of two curved metal plates between which revolved a pair of plates carried on an insulating stem. It was the first symmetrical influence machine, with identical structures for both terminals. This apparatus was reinvented several times, by [[C.&nbsp;F. Varley]], that patented a high power version in 1860, by [[Lord Kelvin]] (the "replenisher") 1868, and by A.&nbsp;D. Moore (the "dirod"), more recently. Lord Kelvin also devised a combined influence machine and electromagnetic machine, commonly called a [[mouse mill]], for electrifying the ink in connection with his [[siphon recorder]], and a water-drop electrostatic generator (1867), which he called the "''[[water-dropping condenser]]''".

=====Holtz machine=====
[[File:Holtz influence machine.jpg|thumb|160px|Holtz's influence machine]]

Between 1864 and 1880, [[Wilhelm Holtz|W. T. B. Holtz]] constructed and described a large number of influence machines which were considered the most advanced developments of the time. In one form, the [[Holtz machine]] consisted of a glass disk mounted on a horizontal axis which could be made to rotate at a considerable speed by a multiplying gear, interacting with induction plates mounted in a fixed disk close to it. In 1865, [[August Toepler|August J. I. Toepler]] developed an influence machine that consisted of two disks fixed on the same shaft and rotating in the same direction. In 1868, the [[Schwedoff machine]] had a curious structure to increase the output current. Also in 1868, several mixed friction-influence machine were developed, including the [[Kundt machine]] and the [[Carré machine]]. In 1866, the [[Piche machine]] (or [[Bertsch machine]]) was developed. In 1869, H. Julius Smith received the American patent for a portable and airtight device that was designed to ignite powder. Also in 1869, sectorless machines in Germany were investigated by [[Johann Christian Poggendorff|Poggendorff]].

The action and efficiency of influence machines were further investigated by [[Francesco Rossetti|F. Rossetti]], [[Augusto Righi|A. Righi]], and [[Friedrich Kohlrausch (physicist)|Friedrich Kohlrausch]]. [[Éleuthère Mascart|E. E. N. Mascart]], [[A. Roiti]], and [[E. Bouchotte]] also examined the efficiency and current producing power of influence machines. In 1871, sectorless machines were investigated by Musaeus. In 1872, [[Righi's electrometer]] was developed and was one of the first antecedents of the Van de Graaff generator. In 1873, Leyser developed the [[Leyser machine]], a variation of the Holtz machine. In 1880, Robert Voss (a Berlin instrument maker) devised a form of machine in which he claimed that the principles of Toepler and Holtz were combined. The same structure become also known as the ''Toepler–Holtz'' machine.

=====Wimshurst machine=====
{{Main|Wimshurst machine}}
[[File:Wimshurst.jpg|thumb|A small Wimshurst machine]]
In 1878, the British inventor [[James Wimshurst]] started his studies about electrostatic generators, improving the Holtz machine, in a powerful version with multiple disks. The classical Wimshurst machine, that became the most popular form of influence machine, was reported to the scientific community by 1883, although previous machines with very similar structures were previously described by Holtz and Musaeus. In 1885, one of the largest-ever Wimshurst machines was built in England (it is now at the [[Museum of Science and Industry (Chicago)|Chicago Museum of Science and Industry]]). The [[Wimshurst machine]] is a considerably simple machine; it works, as all influence machines, with electrostatic induction of charges, which means that it uses even the slightest existing charge to create and accumulate more charges, and repeats this process for as long as the machine is in action. Wimshurst machines are composed of: two insulated disks attached to pulleys of opposite rotation, the disks have small conductive (usually metal) plates on their outward-facing sides; two double-ended brushes that serve as charge stabilizers and are also the place where induction happens, creating the new charges to be collected; two pairs of collecting combs, which are, as the name implies, the collectors of electrical charge produced by the machine; two Leyden Jars, the capacitors of the machine; a pair of electrodes, for the transfer of charges once they have been sufficiently accumulated. The simple structure and components of the Wimshurst Machine make it a common choice for a homemade electrostatic experiment or demonstration, these characteristics were factors that contributed to its popularity, as previously mentioned.<ref>{{cite web|last=De Queiroz|first=A. C|title=Operation of the Wimshurst Machine|year=2014|url=http://www.coe.ufrj.br/~acmq/whyhow.html}}
* {{cite web|last=MIT|title=MIT Physics Demo – The Wimshurst Machine|website=[[YouTube]] |year=2010|url= https://www.youtube.com/watch?v=Zilvl9tS0Og| archive-url=https://web.archive.org/web/20130320163625/http://www.youtube.com/watch?v=Zilvl9tS0Og&gl=US&hl=en| archive-date=2013-03-20 | url-status=dead}}
* {{cite web|last=Weisstein|first=E. W|title=Wimshurst Machine – from Eric Weisstein's World of Physics|year=1996–2007|url=http://scienceworld.wolfram.com/physics/WimshurstMachine.html}}
* {{cite web|last=Von Slatt|first=J|title=Jake's Wimshurst Machine and How to Build It! (Part 1)|year=2012|url=http://steampunkworkshop.com/how-build-wimshurst-influence-machine-part-1/}}</ref>

In 1887, Weinhold modified the Leyser machine with a system of vertical metal bar inductors with wooden cylinders close to the disk for avoiding polarity reversals. [[M. L. Lebiez]] described the [[Lebiez machine]], that was essentially a simplified [[Voss machine]] (''L'Électricien'', April 1895, pp.&nbsp;225–227). In 1893, Louis Bonetti patented a machine with the structure of the Wimshurst machine, but without metal sectors in the disks.<ref>Bonetti, "Une machine électrostatique, genre Wimshurst, sans secteurs et invisible" [An electrostatic machine of the Wimshurst type, without visible sectors], French patent no. 232,623 (issued: September 5, 1893). See: ''Description des machines et procédés pour lesquels des brevets d'invention ont été pris'' … (Descriptions of machines and processes for which patents of invention have been taken … ), 2nd series, vol. 87, part 2 (1893), section: Instruments de précision: Production et transport de l'électricité, [http://babel.hathitrust.org/cgi/pt?id=coo.31924062420827;view=1up;seq=385 page 87.]</ref><ref>See also:
* (Anon.) (April 14, 1894) [http://www.dbnl.org/arch/_lan015189401_01/pag/_lan015189401_01.pdf#page=305 "Machines d'induction électrostatique sans secteurs"] (Electrostatic induction machines without sectors), ''La Nature'', '''22''' (1089) : 305–306.
* English translation of ''La Nature'' article (above): (Anon.) (May 26, 1894) [https://archive.org/stream/scientific-american-1894-05-26/scientific-american-v70-n21-1894-05-26#page/n4/mode/1up/ "Electrostatic induction machines without sectors,"] ''Scientific American'', '''70''' (21) : 325-326.
* S. M. Keenan (August 1897) [https://books.google.com/books?id=Z9RLAAAAYAAJ&pg=PA316 "Sectorless Wimshurst machines,"] ''American Electrician'', '''9''' (8) : 316–317
* [http://www.coe.ufrj.br/~acmq/bonetti.html Instructions for building a Bonetti machine]
* G. Pellissier (1891) [https://archive.org/stream/journaldephysiq57physgoog#page/n454/mode/1up "Théorie de la machine de Wimshurst"] (Theory of Wimshurt's machine), ''Journal de Physique théoretique et appliquée'', 2nd series, '''10''' (1) : 414–419. On p. 418, French lighting engineer Georges Pellissier describes what is essentially a Bonetti machine: " ''...&nbsp;la machine de Wimshurst pourrait, en effet, être construite avec des plateaux de verre unis et des peignes au lieu de brosses aux extrémités des conducteurs diamétraux. L'amorçage au départ devrait être fait à l'aide d'une source étrangère, placée, par example, en face de A<sub>1</sub>, à l'extérieur.''" (...&nbsp;Wimshurst's machine could, in effect, be constructed with plain glass plates and with combs in place of brushes at the ends of the diametrical conductors. The initial charging could be done with the aid of an external source placed, for example, opposite and outside of [section] A<sub>1</sub> [of the glass disk].) Pellissier then states that "the role of the metallic sectors of the Wimshurst machine seems to be primarily, in effect, to facilitate its automatic starting and to reduce the influence of atmospheric humidity."</ref> This machine is significantly more powerful than the sectored version, but it must usually be started with an externally applied charge.

=====Pidgeon machine=====
In 1898, the [[Pidgeon machine]] was developed with a unique setup by [[W. R. Pidgeon]]. On October 28 that year, Pidgeon presented this machine to the Physical Society after several years of investigation into influence machines (beginning at the start of the decade). The device was later reported in the ''Philosophical Magazine'' (December 1898, pg. 564) and the ''Electrical Review'' (Vol. XLV, pg. 748). A Pidgeon machine possesses fixed electrostatic inductors arranged in a manner that increases the electrostatic induction effect (and its electrical output is at least double that of typical machines of this type [except when it is overtaxed]). The essential features of the Pidgeon machine are, one, the combination of the rotating support and the fixed support for inducing charge, and, two, the improved insulation of all parts of the machine (but more especially of the generator's carriers). Pidgeon machines are a combination of a Wimshurst Machine and Voss Machine, with special features adapted to reduce the amount of charge leakage. Pidgeon machines excite themselves more readily than the best of these types of machines. In addition, Pidgeon investigated higher current "triplex" section machines (or "double machines with a single central disk") with enclosed sectors (and went on to receive British Patent 22517 (1899) for this type of machine).

Multiple disk machines and "triplex" electrostatic machines (generators with three disks) were also developed extensively around the turn of the 20th century. In 1900, [[F. Tudsbury]] discovered that enclosing a generator in a metallic chamber containing [[compressed air]], or better, [[carbon dioxide]], the [[Electrical insulation|insulating properties]] of compressed gases enabled a greatly improved effect to be obtained owing to the increase in the breakdown voltage of the compressed gas, and reduction of the leakage across the plates and insulating supports. In 1903, [[Alfred Wehrsen]] patented an [[ebonite]] rotating disk possessing embedded sectors with button contacts at the disk surface. In 1907, [[Heinrich Wommelsdorf]] reported a variation of the Holtz machine using this disk and inductors embedded in celluloid plates (DE154175; "[[Wehrsen machine]]"). Wommelsdorf also developed several high-performance electrostatic generators, of which the best known were his "Condenser machines" (1920). These were single disk machines, using disks with embedded sectors that were accessed at the edges.

====Van de Graaff====
{{Main|Van de Graaff generator}}
The Van de Graaff generator was invented by American physicist [[Robert J. Van de Graaff]] in 1929 at [[Massachusetts Institute of Technology|MIT]] as a particle accelerator.<ref name="Van de Graaff">{{cite journal
 | last1 = Van de Graaff
 | first1 = R. J.
 | last2 = Compton
 | first2 = K. T. 
 | last3 = Van Atta
 | first3 = L. C. 
 | title = The Electrostatic Production of High Voltage for Nuclear Investigations
 | journal = Physical Review
 | volume = 43
 | issue = 3
 | pages = 149–157
 | publisher = American Physical Society
 | date = February 1933
 | url = http://web.ihep.su/dbserv/compas/src/van%20de%20graaff33/eng.pdf
 | doi = 10.1103/PhysRev.43.149
 | access-date = August 31, 2015|bibcode = 1933PhRv...43..149V }}</ref> The first model was demonstrated in October 1929. In the Van de Graaff machine, an insulating belt transports electric charge to the interior of an insulated hollow metal high voltage terminal, where it is transferred to the terminal by a "comb" of metal points. The advantage of the design was that since there was no electric field in the interior of the terminal, the charge on the belt could continue to be discharged onto the terminal regardless of how high the voltage on the terminal was. Thus the only limit to the voltage on the machine is [[ionization]] of the air next to the terminal. This occurs when the electric field at the terminal exceeds the [[dielectric strength]] of air, about 30&nbsp;kV per centimeter. Since the highest electric field is produced at sharp points and edges, the terminal is made in the form of a smooth hollow sphere; the larger the diameter the higher the voltage attained. The first machine used a silk ribbon bought at a five and dime store as the charge transport belt. In 1931 a version able to produce 1,000,000 volts was described in a patent disclosure.

The Van de Graaff generator was a successful particle accelerator, producing the highest energies until the late 1930s when the [[cyclotron]] superseded it. The voltage on open air Van de Graaff machines is limited to a few million volts by air breakdown. Higher voltages, up to about 25&nbsp;megavolts, were achieved by enclosing the generator inside a tank of pressurized insulating gas. This type of Van de Graaff particle accelerator is still used in medicine and research. Other variations were also invented for physics research, such as the [[Pelletron]], that uses a chain with alternating insulating and conducting links for charge transport.

Small Van de Graaff generators are commonly used in [[science museum]]s and science education to demonstrate the principles of static electricity. A popular demonstration is to have a person touch the high voltage terminal while standing on an insulated support; the high voltage charges the person's hair, causing the strands to stand out from the head.