Henry Cavendish used a torsion balance to infer the mean density of the Earth. Nearby lead masses exert a gravitational force on smaller masses carried by a suspended horizontal arm. The wire's restoring torque opposes the resulting angular displacement; the arm's oscillation period calibrates that response. Moving the attracting masses to opposite sides reverses the deflection. Comparing this measured gravitational force with terrestrial gravity then determines the mean density of the Earth. To reduce convection caused by uneven heating, he enclosed the apparatus and observed its scale through telescopes from outside the room.[ref]
Experiments to Determine the Density of the Earth by Henry Cavendish. 1798, pp. 469–475: apparatus, oscillation calibration, reversed positions and thermal-air-current precautions
Experimental natural philosopher who measured terrestrial gravitational attraction and inferred the mean density of Earth in 1798.
Portrait of Henry Cavendish
. Wellcome Library, London / Wellcome Collection; after a drawing by Alexander in the British Museum. CC BY 4.0, via Wikimedia Commons. Source.
Henry Cavendish (1731–1810) was a British scientist, chemist, and physicist known for his work in the fields of gas chemistry and electricity. He is best remembered for discovering hydrogen, which he called "inflammable air," and for measuring the density of the Earth in his famous experiment, known as the Cavendish experiment. This experiment allowed for the first accurate determination of the gravitational constant and the mass of the Earth.
New to topics? Read the docs here!