English chemist and physicist Henry Cavendish (1731-1810), depicted in this 19th-century engraving, was an important pioneer in the chemistry of gases, electricity, and Newtonian physics. His most celebrated work was the discovery of the composition of water; he stated that “water consists of dephlogisticated air (oxygen) united with phlogiston (hydrogen).” By what is now known as the Cavendish experiment, he determined that the density of the earth was 5.45 times as great as the density of water, a calculation very close to the 5.5268 established by modern techniques.

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