Shipud writes "200 years ago today (Oct. 21) John Dalton revolutionized chemistry by starting the process of turning it into an exact science. He presented the Table of Atomic Weights, at the Manchester literary and Philosophical Society. Dalton's work proposed atoms exist: and not just as an explanatory or philosophical tool. His theory laid the foundations for the periodic table of the elements (1869, Mendeleev), and indeed to all modern chemistry. The molecular weight of compounds is today measured in Daltons, the weight of a hydrogen atom. Read more about Mr. Dalton in today's Nature: a man of many interests, whose atomic theory preceded experimental evidence by a century. Read also about Daltonism -- and why it is named after him."