balls: Substituting F into the first equation above gives To find the torsion coefficient () of the wire, Cavendish measured the natural resonant oscillation period T of the torsion balance: Assuming the mass of the torsion beam itself is negligible, the moment of inertia of the balance is just due to the small balls: , and so: Solving this for , substituting into (1), and rearranging for G, the result is: Once G has been found, the attraction of an object at the Earth's surface to the Earth itself can be used to calculate the Earth's mass and density: Definitions of terms References Sources Establishes that Cavendish didn't determine G. Discusses Michell's contributions, and whether Cavendish determined G. Review of gravity measurements since 1740. External links Cavendish’s experiment in the Feynman Lectures on Physics Sideways Gravity in the Basement, The Citizen Scientist, July 1, 2005. Homebrew Cavendish experiment, showing calculation of results and precautions necessary to eliminate wind and electrostatic errors. "Big 'G'", Physics Central, retrieved Dec. 8, 2013. Experiment at Univ. of Washington to measure the gravitational constant using variation of Cavendish method. . Discusses current state of measurements of G. Model of Cavendish's torsion balance, retrieved Aug. 28, 2007, at Science Museum, London. Physics experiments 1790s in science 1797 in science 1798 in science Geodesy Gravity Royal Society