an English chemist and physicist who first isolated key chemical compounds. In 1766 he published a paper entitled "Three Papers containing Experiments on Factitious Airs," in which he identified what he called "inflammable air" (later termed hydrogen by Antoine Lavoisier) and "fixed air" (or carbon dioxide) as substance distinct from air. In 1783 he demonstrated that the composition of air was constant regardless of the geographic region or altitude sampled. Cavendish discovered nitric acid (HNO3) and proved that water was not an element but made up of gases. Cavendish also used a sensitive torsion balance (the Cavendish balance) to measure the value of the gravitational constant G. This allowed him to calculate the mass of the Earth. Henry Cavendish was an eccentric scientist who published his findings only sporadically, thus leaving some of his significant discoveries unknown until long after his death.