Today is the birthday of physicist Henry Cavendish, born in 1731 and known for his discoveries about the composition of air, water, and earth. In 1766 Cavendish demonstrated the existence of hydrogen, or "inflammable air," and he showed that carbon dioxide, or "fixed air," was produced both by fermentation and by the action of acid on marble. The next year he determined from an analysis of London pump water that calcareous matter could be held in solution--that is, he discovered calcium bicarbonate. By 1783 he had discovered that the composition of the atmosphere is constant at a given time and place, and soon thereafter established that water was a compound. Cavendish determined the density of Earth in 1798. And while studying electricity, he discovered inductive capacity--that electrostatic charge is confined to the conducting surface. The great Cavendish Laboratory in Cambridge, United Kingdom, is named in his honor.
[Source: Trevor I. Williams, Ed., A Biographical Dictionary of Scientists (John Wiley & Sons, New York, ed. 3, 1982).]