Henry Cavendish FRS (/ˈkævəndɪʃ/ KAV-ən-dish; 10 October 1731 – 24 February 1810) was an English experimental and theoretical chemist and physicist.

A shy man, Cavendish was distinguished for great accuracy and precision in his researches into the composition of atmospheric air, the properties of different gases, the synthesis of water, the law governing electrical attraction and repulsion, a mechanical theory of heat, and calculations of the density (and hence the mass) of the Earth.

At the age of 18 (on 24 November 1748) he entered the University of Cambridge in St Peter's College, now known as Peterhouse, but left three years later on 23 February 1751 without taking a degree (at the time, a common practice).

Lord Charles Cavendish spent his life firstly in politics and then increasingly in science, especially in the Royal Society of London.

In 1773, Henry joined his father as an elected trustee of the British Museum, to which he devoted a good deal of time and effort.

Soon after the Royal Institution of Great Britain was established, Cavendish became a manager (1800) and took an active interest, especially in the laboratory, where he observed and helped in Humphry Davy's chemical experiments.

[6] Although others, such as Robert Boyle, had prepared hydrogen gas earlier, Cavendish is usually given the credit for recognising its elemental nature.

[7] Also, by dissolving alkalis in acids, Cavendish produced carbon dioxide, which he collected, along with other gases, in bottles inverted over water or mercury.

He described a new eudiometer of his invention, with which he achieved the best results to date, using what in other hands had been the inexact method of measuring gases by weighing them.

The Scottish inventor James Watt published a paper on the composition of water in 1783; controversy about who made the discovery first ensued.

[7] In 1785, Cavendish investigated the composition of common (i.e. atmospheric) air, obtaining impressively accurate results.

[12][13] In the 1890s (around 100 years later) two British physicists, William Ramsay and Lord Rayleigh, realised that their newly discovered inert gas, argon, was responsible for Cavendish's problematic residue; he had not made an error.

[14] The London house contained the bulk of his library, while he kept most of his instruments at Clapham Common, where he carried out most of his experiments.

The apparatus Cavendish used for weighing the Earth was a modification of the torsion balance built by geologist John Michell, who died before he could begin the experiment.

Cavendish's electrical and chemical experiments, like those on heat, had begun while he lived with his father in a laboratory in their London house.

[32] Cavendish died at Clapham on 24 February 1810[2] (as one of the wealthiest men in Britain) and was buried in the church that is now Derby Cathedral, alongside many of his ancestors.

Cavendish inherited two fortunes that were so large that Jean Baptiste Biot called him "the richest of all the savants and the most knowledgeable of the rich".

By one account, Cavendish had a back staircase added to his house to avoid encountering his housekeeper, because he was especially shy of women.

The contemporary accounts of his personality have led some modern commentators, such as Oliver Sacks, to speculate that he was autistic.

However, his shyness made conversation difficult; guests were advised to wander close to him and then speak as if "into vacancy.

[37] He also enjoyed collecting fine furniture, exemplified by his purchase of a set of "ten inlaid satinwood chairs with matching cabriole legged sofa".

[38] Because of his asocial and secretive behaviour, Cavendish often avoided publishing his work, and much of his findings were not told even to his fellow scientists.

In the late nineteenth century, long after his death, James Clerk Maxwell looked through Cavendish's papers and found observations and results for which others had been given credit.

Theoretical physicist Dietrich Belitz concluded that in this work Cavendish "got the nature of heat essentially right".

[39] As Cavendish performed his famous density of the Earth experiment in an outbuilding in the garden of his Clapham Common estate, his neighbours would point out the building and tell their children that it was where the world was weighed.