Kite experiment

From Wikipedia, the free encyclopedia
Jump to: navigation, search
An artistic rendition of Franklin's kite experiment painted by Benjamin West.

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

Background[edit]

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 physician 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[edit]

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 [3] by Thomas-François Dalibard. An attempt to replicate the experiment killed Georg Wilhelm Richmann in Saint Petersburg in August 1753, thought to be the victim of ball lightning.[4] Franklin himself conducted the experiment in June 1752, supposedly on the top of the spire on Christ Church in Philadelphia.

Kite experiment[edit]

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 a kite. The increased height allowed him to stay on the ground and the kite was less likely to electrocute him. According to the legend, Franklin kept the string of the kite dry at his end to insulate him while the rest of the string was allowed to get wet in the rain to provide conductivity. A key was attached to the string and connected to a Leyden jar, which Franklin assumed would accumulate electricity from the lightning. The kite wasn't struck by visible lightning (had it done so, Franklin would almost certainly have been killed) but Franklin did notice that the strings of the kite were repelling each other and deduced that the Leyden jar was being charged. Franklin reportedly received a mild shock by moving his hand near the key afterwards, because as he had estimated, lightning had negatively charged the key and the Leyden jar, proving the electric nature of lightning[5]

Fearing that the test would fail, or that he would be ridiculed, Franklin only took his son to witness the experiment, and then published the accounts of the test in third person.[6]

De Romas pursued his priority claim to the kite experiment. He had it recognised by the Bordeaux Academy, and then the Académie française in Paris.[3]

Modern Controversy[edit]

In one episode of the television series MythBusters the hosts tried to emulate a variation on the story of this famous experiment in which Franklin was to have received the lightning arc directly from the key attached to the kite string. Even though they declared the myth "busted" and that Franklin would have been killed if he had done the experiment, they confirmed that certain aspects of the experiment were feasible.[7]

  • "You can get electricity down a [wet] kite string."
  • Electricity will NOT travel down a dry kite string.
  • The key will conduct a static charge, even when NOT struck by lightning.

Because of the danger inherent in the kite experiment, it has become illegal in certain locales.[8]

External links[edit]

  • Philosophical Transactions: A Letter of Benjamin Franklin, Esq; to Mr. Peter Collinson, F. R. S. concerning an Electrical Kite. Phil. Trans. 1751–1752 47, 565–567; (PDF)

References[edit]

  1. ^ (French) Pierre Zweiacker (24 November 2011). Sacrée foudre !: Ou la scandaleuse invention de Benjamin F.. Presses polytechniques et universitaires romandes. p. 165. ISBN 978-2-88074-943-9. Retrieved 29 October 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 29 October 2012. 
  3. ^ a b Jessica Riskin (15 December 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 29 October 2012. 
  4. ^ Vladimir A. Rakov; Martin A. Uman (8 January 2007). Lightning: Physics and Effects. Cambridge University Press. p. 656. ISBN 978-0-521-03541-5. Retrieved 29 October 2012. 
  5. ^ An article about Franklin and the experiment
  6. ^ Carl Van Doren's account of the experiment, based on Franklin's recounting
  7. ^ Mythbusters. "Franklin vlieger mythbuster". 
  8. ^ "St. Louis, Missouri, Code of Ordinances: Chapter 15.155 - KITES". Retrieved 28 September 2013.