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The BBC has a good article about John Dalton on its site. In 1803 John Dalton demonstrated that atoms must exist - and so set chemistry to become a modern science. He formulated a way to denote chemical elements and their compounds. This enabled science to gain an understanding of the properties and interactions of different substances.
His standing in society of the time is astonishing. While still alive, a statue was erected in 1838 in Manchester in the UK by public subscription. It cost 2,000 guineas. For the time this was a vast amount of money. When he died, Manchester gave him a huge funeral. It is said that 40,000 people filed by his coffin.
John Dalton 1766-1844 (born Eaglesfield, Cumberland, England)