Editing Charles Wheatstone (section)

== Wheatstone bridge ==
In 1843 Wheatstone communicated an important paper to the Royal Society, entitled 'An Account of Several New Processes for Determining the Constants of a Voltaic Circuit.' It contained an exposition of the well known balance for measuring the electrical resistance of a conductor, which still goes by the name of [[Wheatstone bridge|Wheatstone's Bridge]] or balance, although it was first devised by [[Samuel Hunter Christie]], of the Royal Military Academy, Woolwich, who published it in the ''Philosophical Transactions'' for 1833.<ref>[https://archive.org/details/philtrans06307436 S. Hunter Christie, ''The Bakerian Lecture: Experimental Determination of the Laws of Magneto-electric Induction in different masses of the same metal, and its intensity in different metals.'', Philosophical Transactions of the Royal Society of London, vol. 123, 1833, pp. 95–142].</ref> The method was neglected until Wheatstone brought it into notice.<ref>[https://archive.org/details/philtrans09981490 Charles Wheatstone, ''The Bakerian Lecture: An Account of Several New Instruments and Processes for Determining the Constants of a Voltaic Circuit'', Philosophical Transactions of the Royal Society of London, vol. 133, 1843, pp. 303–327].</ref>

His paper abounds with simple and practical formulae for the calculation of currents and resistances by the law of [[Georg Simon Ohm|Ohm]]. He introduced a unit of resistance, namely, a foot of copper wire weighing one hundred grains (6.5 g), and showed how it might be applied to measure the length of wire by its resistance. He was awarded a medal for his paper by the Society.<ref>"The Genesis of the Wheatstone Bridge" by Stig Ekelof discusses [[Samuel Hunter Christie|Christie's]] and Wheatstone's contributions, and why the bridge carries Wheatstone's name. Published in "Engineering Science and Education Journal", volume 10, no 1, February 2001, pp. 37–40.</ref> The same year he invented an apparatus which enabled the reading of a thermometer or a barometer to be registered at a distance by means of an electric contact made by the mercury. A sound telegraph, in which the signals were given by the strokes of a bell, was also patented by Cooke and Wheatstone in May of that year.