John Dalton was born on September 6, 1766 into a modest Quaker family in Cumberland, England. John received his early education from his father, a weaver, and from John Fletcher, the teacher at the Quaker school in Eaglesfield, England. Upon Fletcher’s retirement in 1778, John took over teaching at Eaglesfield at the tender age of 12. John earned his living for most of his life as a teacher and public lecturer, moving to Kendal in 1781, and finally to Manchester, England in 1793 where he spent the remainder of his life.

     In the early days of his career, Dalton was influenced by a wealthy Quaker who was a capable meteorologist and instrument maker, and who nurtured John’s interest in mathematics and meteorology. In fact, Dalton’s first scientific work, begun in 1787, was to keep a diary of meteorological observations of the climate of the lake district in which he lived. Dalton recorded observations in this diary until the end of his life, at which time it held over 200,000 entries.

     Dalton’s early studies on gases led to development of the law of partial pressures (now known as Dalton's law), which states that the total pressure of a mixture of gases equals the sum of the pressures of the gases in the mixture. In addition, he formulated the theory that the chemical combination of different elements occurs in simple numerical ratios by weight, which led to the development of the laws of definite and multiple proportions.

     In 1803, already having attained a significant scientific reputation, Dalton developed his masterpiece on atomic theory. In the now classic paper, A New System of Chemical Philosophy (1808-1827), Dalton stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). While some of Dalton’s conclusions have proven incorrect, his work formed the foundation for later scientific research.

     Along with his other research, Dalton became interested in color blindness, a condition that he and his brother shared. In 1794 Dalton published an essay "Extraordinary Facts Relating to the Vision of Colors," in which he postulated that deficiency in color perception was caused by discoloration of the liquid medium of the eyeball. Although Dalton's theory lost credence in his own lifetime, the meticulous, systematic nature of his research was so broadly recognized that Daltonism became a common term for color blindness.