Dalton's table of elements,1806-1807.
© Science Museum / Science & Society Picture Library
Replica produced in 1925 from the original held by the Manchester Literary and Philosophical Society. John Dalton (1766-1844) formulated the atomic theory to explain chemical reactions, based on the concept that the atoms of different elements are distinguished by differences in their weights. This theory has influenced scientific thought for more than a century and a half.