Editing Cavendish experiment (section)

==Reformulation of Cavendish's result to ''G'' ==
The formulation of [[Newton's law of universal gravitation|Newtonian gravity]] in terms of a gravitational constant did not become standard until long after Cavendish's time. Indeed, one of the first references to ''G'' is in 1873, 75 years after Cavendish's work.<ref>{{cite journal |last1=Cornu |first1=A. |last2=Baille |first2=J. B. |date=1873 |url=http://gallica.bnf.fr/ark:/12148/bpt6k3033b/f954.image |title=Détermination nouvelle de la constante de l'attraction et de la densité moyenne de la Terre |language=fr |trans-title=New Determination of the Constant of Attraction and the Average Density of Earth |journal=C. R. Acad. Sci. |location=Paris |volume=76 |pages=954–958 }}</ref>

Cavendish expressed his result in terms of the density of the Earth. He referred to his experiment in correspondence as 'weighing the world'. Later authors reformulated his results in modern terms.<ref>[https://books.google.com/books?id=ZrloHemOmUEC&pg=PA353 Boys 1894], p. 330 In this lecture before the Royal Society, Boys introduces ''G'' and argues for its acceptance</ref><ref>[https://books.google.com/books?id=dg0RAAAAIAAJ&pg=PA4 Poynting 1894], p. 4</ref><ref>[https://books.google.com/books?id=O58mAAAAMAAJ&pg=PA1 MacKenzie 1900], p. vi</ref>
:<math>G = g\frac{R_\text{earth}^2}{M_\text{earth}} = \frac{3g}{4\pi R_\text{earth}\rho_\text{earth}}\,</math>
After converting to [[SI]] units, Cavendish's value for the Earth's density, 5.448&nbsp;g&nbsp;cm<sup>−3</sup>, gives
:''G'' = {{val|6.74e-11|u=m<sup>3</sup>&nbsp;kg<sup>–1</sup>&nbsp;s<sup>−2</sup>}},<ref>{{cite journal|first=Adam |last=Mann |title=The curious case of the gravitational constant |date=September 6, 2016 |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=36 |pages=9949–9952 |doi=10.1073/pnas.1612597113 |doi-access=free |pmid=27601579 |pmc=5018785 }}</ref>
which differs by only 1% from the 2014 [[CODATA]] value of {{val|fmt=none|6.67408e-11|u=m<sup>3</sup>&nbsp;kg<sup>−1</sup>&nbsp;s<sup>−2</sup>}}.<ref>{{cite journal |first=Jennifer Lauren |last=Lee |title=Big G Redux: Solving the Mystery of a Perplexing Result |date=November 16, 2016 |journal=NIST |url=https://www.nist.gov/news-events/news/2016/11/big-g-redux-solving-mystery-perplexing-result}}</ref>
Today, physicists often use units where the gravitational constant takes a different form. The [[Gaussian gravitational constant]] used in space dynamics is a defined constant and the Cavendish experiment can be considered as a measurement of this constant.
In Cavendish's time, physicists used the same units for mass and weight, in effect taking ''g'' as a standard acceleration. Then, since ''R''{{Sub|earth}} was known, ''ρ''{{sub|earth}} played the role of an inverse gravitational constant. The density of the Earth was hence a much sought-after quantity at the time, and there had been earlier attempts to measure it, such as the [[Schiehallion experiment]] in 1774.