Cavendish experiment

Henry Cavendish’s 1798 torsion-balance experiment measured the gravitational attraction between lead spheres and yielded Earth’s mean density.

Torsion balance: A measuring device that infers small forces from the twist of a suspended object. A suspended rod and its fibers converted the spheres’ attraction into a measurable angular deflection.
Henry Cavendish: An English natural philosopher and chemist whose experiments included measuring gravitational attraction between lead spheres. Cavendish reported the 1798 experiment and calculated Earth’s mean density.
Measurement of the gravitational constant: Experimental determination of the constant that sets the strength of gravitational interactions. Modern versions refine the same strategy of measuring attraction between known masses.
Gravitational constant: The proportionality constant setting the strength of gravity in Newton’s law of universal gravitation. Cavendish reported Earth’s mean density, not a value for this constant.
Torsion pendulum: A body suspended from a fiber that oscillates when twisted and released. The balance’s oscillation period helped determine the fiber’s resistance to twisting.
John Michell: An English natural philosopher who designed a torsion-balance apparatus for measuring gravitational attraction. Michell devised the experiment’s apparatus, which Cavendish completed after Michell’s death.
Earth's mass: The total mass of Earth, inferred from gravitational measurements and models of its interior. Earth’s mass follows from its measured mean density and volume.
Schiehallion experiment: An eighteenth-century geophysical experiment that estimated Earth’s density from the gravitational pull of a mountain. It inferred Earth’s density from astronomical deflection, rather than attraction between laboratory spheres.
Gravitational force: The mutual attraction between objects with mass or energy. The experiment detected gravitational attraction between laboratory-sized lead masses.
Philosophical Transactions of the Royal Society: A scientific journal published by the Royal Society of London since 1665. Cavendish published his account in this journal in 1798.

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