Kite experiment

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An artistic rendition of Franklin's kite experiment painted by Benjamin West.

The kite experiment was a scientific experiment which was proposed and may have been conducted by Benjamin Franklin with the assistance of his son William Franklin. The experiment's purpose was to uncover the unknown facts about the nature of lightning and electricity.

Background

In 1750, the electrical nature of lightning was the subject of public discussion in France, with a dissertation of Denis Barbaret receiving a prize in Bordeaux; Barbaret proposed a cause in line with the triboelectric effect. The physicist Jacques de Romas also wrote a memoir that year with similar ideas. Franklin had listed a dozen analogies between lightning and electricity in his notebooks at the end of 1749.[1] Speculations of Jean-Antoine Nollet had led the issue being posed as a prize question at Bordeaux in 1749. De Romas later defended his own electrical kite proposal as independent of Franklin's.[2]

Lightning rod experiments

In 1752, Franklin proposed an experiment with conductive rods to attract lightning to a Leyden jar, an early form of capacitor. Such an experiment was carried out in May 1752 at Marly-la-Ville in northern France by Thomas-François Dalibard.[3] An attempt to replicate the experiment killed Georg Wilhelm Richmann in Saint Petersburg in August 1753; he was thought to be the victim of ball lightning.[4] Franklin himself is said to have conducted the experiment in June 1752, supposedly on the top of the spire on Christ Church in Philadelphia.

Franklin's Kite Experiment

Franklin's kite experiment was performed in Philadelphia in June 1752, according to the account by Priestly.[5] Franklin described the experiment in the Pennsylvania Gazette in October 19, 1752,[6][7] without mentioning that he himself had performed it.[8] This account was read to the Royal Society on December 21 and printed as such in the Philosophical Transactions.[5] A more complete account of Franklin's experiment was given by Joseph Priestley in 1767, who presumably learned the details directly from Franklin, who was in London at the time Priestley wrote the book.[5]

The BEP engraved the vignette Franklin and Electricity (c. 1860) which was used on the $10 National Bank Note from the 1860s to 1890s.

Franklin realized the dangers of using conductive rods and instead used the conductivity of a wet hemp string attached to a kite. This allowed him to stay on the ground and the kite was less likely to electrocute him. According to the account, Franklin kept the silk string of the kite dry at his son's end to insulate him while the hemp string to the kite was allowed to get wet in the rain to provide conductivity. A house key belonging to Benjamin Loxley was attached to the hemp string and connected to a Leyden jar; a silk string was attached to this, held by Franklin's son William who flew the kite (while standing inside a doorway to keep himself and the silk string dry). Franklin assumed that the Leyden jar would accumulate electricity from the lightning. The kite was not struck by visible lightning; had it done so, Franklin would almost certainly have been killed.[9] However, Franklin did notice that loose threads of the kite string were repelling each other and deduced that the Leyden jar was being charged. He moved his hand near the key and observed an electric spark,[5] proving the electric nature of lightning.[10]

Modern controversy

The standard account of Franklin's experiment is disputed by science historian Tom Tucker in 2003.[11] According to Tucker, Franklin never performed the experiment, and the kite as described is incapable of performing its alleged role.[12]

In an investigation by the television series MythBusters using a lightning simulator, the team showed that if lightning had actually hit the kite, Franklin would have received a fatal current through his heart. Nevertheless, they confirmed that certain aspects of the experiment were feasible—specifically, the ability of a kite with sufficiently damp string to receive and send to the ground the electrical energy delivered by a lightning strike.[9]

Because of the danger inherent in the kite experiment, it has become illegal in certain locales.[clarification needed][13]

References

  1. ^ Pierre Zweiacker (November 24, 2011). Sacrée foudre !: Ou la scandaleuse invention de Benjamin F. (in French). Presses polytechniques et universitaires romandes. p. 165. ISBN 978-2-88074-943-9. Retrieved October 29, 2012.
  2. ^ J. L. Heilbron (1979). Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics. University of California Press. p. 351 note 32. ISBN 978-0-520-03478-5. Retrieved October 29, 2012.
  3. ^ Jessica Riskin (December 15, 2002). Science in the Age of Sensibility: The Sentimental Empiricists of the French Enlightenment. University of Chicago Press. p. 101. ISBN 978-0-226-72078-4. Retrieved October 29, 2012.
  4. ^ Vladimir A. Rakov; Martin A. Uman (January 8, 2007). Lightning: Physics and Effects. Cambridge University Press. p. 656. ISBN 978-0-521-03541-5. Retrieved October 29, 2012.
  5. ^ a b c d National Archives, The Kite Experiment, 19 October 1752. Retrieved February 6, 2017
  6. ^ Benjamin Franklin, "The Kite Experiment", printed in The Pennsylvania Gazette, October 19, 1752. In The Papers of Benjamin Franklin, The American Philosophical Society and Yale University; digital edition by The Packard Humanities Institute, Volume 4, page 360a. Retrieved February 6, 2017
  7. ^ Historical Society, Benjamin Franklin History. Retrieved February 6, 2017
  8. ^ Steven Johnson (2008) The Invention of Air, p. 39 ISBN 978-1-59448-401-8. Retrieved February 6, 2017
  9. ^ a b "Franklin Discovered Electricity with Kite". Mythbusters. April 11, 2012. Retrieved July 30, 2016.
  10. ^ Julian Rubin, Benjamin Franklin - Master of Electricity: The Kite Experiment and the Invention of the Lightning Rod (article about Franklin and the experiment). Retrieved February 6, 2017
  11. ^ Bolt of Fate by Tom Tucker Public Affairs books 2003
  12. ^ Robert Matthews, "Benjamin Franklin 'faked kite experiment' ", The Telegraph, June 1, 2003. (Accessed February 6, 2016)
  13. ^ "St. Louis, Missouri, Code of Ordinances: Chapter 15.155 - KITES". Retrieved September 28, 2013.

External links

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