Historical background of chemistry, modern period, Karl Wilhelm Schill, 1742-1786, Schill discovered oxygen, although Joseph Priestley published his findings first, an identified malibdenum, tungsten, barium, hydrogen, and chlorine, among others. Henry Cavendish, 1731-1810, Cavendish is credited with the discovery of hydrogen gas. His contributions to the understanding of gases, the composition of water, and Earth's density were groundbreaking. John Dalton, 1766-1844, John Dalton made significant contributions to the development of modern atomic theory and the understanding of gases. Joseph Louis Gay-Lusac, 1778-1850, he advanced the understanding of gases and the relationship between pressure, temperature, and volume. His discoveries and laws laid the groundwork for the development of modern gas laws and thermodynamics.