Dalton, John 1766-1844
English chemist and natural philosopher

Born in Eaglesfield, Cumbria, he received his early education at a Quaker school there and began teaching at the age of 12. In 1793 he moved to Manchester and taught mathematics at New College in Moseley Street (a predecessor of Manchester College, Oxford) but after about six years turned to private teaching and scientific research. In 1787 he began a lifelong meteorological journal, recording over 200,000 observations. In 1794 he described colour blindness (Daltonism), exemplified partly by his own case. In his chemical and physical research Dalton was a crude experimentalist, but his results led him to his atomic theory, on which his fame rests. Of particular importance were his studies showing that in a mixture of gases each gas exerts the same pressure as it would if it were the only gas present in the given volume (Dalton's law). This led to the interpretation of chemical analyses in terms of the relative weights of the atoms of the elements involved and to the laws of chemical combination. His atomic theory recognized that all matter is made up of combinations of atoms, the atoms of each element being identical. He concluded that atoms could be neither created nor destroyed, and that chemical reactions take place through the rearrangement of atoms.

Bibliography: H E Roscoe, John Dalton and the Rise of Modern Chemistry (1895)