John Dalton, an English chemist, author of the atomic theory, and of that of the constitution of mixed gases, born at Eaglesfield, near Cockermouth, in Cumberland, Sept. 5, 1766, died in Manchester, July 27, 1844. With his parents, he belonged to the society of Friends. He received his first instruction at the school of his native village, and in 1781 became usher in a school at Kendal, where he remained till 1793, when he was appointed professor of mathematics and natural philosophy in the New college at Manchester, which was removed to York in 1799. He continued his lessons in private schools for years, occasionally giving lectures on the physical and experimental sciences in neighboring towns and cities. In 1788 he began a series of important meteorological observations, and in 1793 published his first separate work, entitled "Meteorological Observations and Essays." This was one of his favorite pursuits, and he continued to collect and record meteorological observations until his death. In 1794 he gave an account of a singular defect in his own vision which rendered him incapable of distinguishing certain colors; green, red, purple, and blue, all appearing alike to him.

He supposed this peculiarity to be due to the color of the retina or of the fluids of the eye; but after his death no abnormal coloration was discovered on dissection. This defect of vision, which is not very uncommon, has sometimes been called Daltonism since the publication of his paper. (See Colob-Blindness.) He wrote numerous articles for the "Gentleman's and Lady's Diary," the "Memoirs of the Manchester Society," "Nicholson's Journal," the "Philosophical Magazine," and the " Transactions of the Royal Society of London." In 1801 he published "Elements of English Grammar." In 1802 he wrote six dissertations for the Memoys of the Manchester Society," in one of which he unfolded his celebrated theory of the " Constitution of Mixed Gases." The leading feature of this theory is that gases which do not form new chemical compounds act on each other as a vacuum, diffusing themselves among each other by their own elasticity. The greater part of Dalton's experiments were made to ascertain the influence of heat in the production of physical and chemical phenomena; and much of the progress of modern science in this department is due to his researches.

Other subjects treated in these papers were "The Force of Vapor of Water and other Fluids at Different Temperatures in the Torricellian Vacuum, and other Atmospheric Pressure," and "The Theory of Evaporation and the Expansion of Gases by Heat." These writings display profound reasoning based on accurate observations, and have rendered great service to pneumatic chemistry and modern investigations on the specific gravity of gases. His-celebrity, however, rests mainly on his atomic theory, which he began to work out in 1803, and explained in lectures in 1804. This theory was fully propounded in his "New System of Chemical Philosophy," the first volume of which appeared in 1807, and the second in 1810, followed by a third in 1827. (See Atomic Theory.) In his papers on subjects connected with meteorology, he has left valuable remarks on evaporation, rain, the aurora borealis, winds, and dew. His observations on the latter contain the principles of Dr. Wells's theory of dew, and of Daniell's hygrometer. In 1821 he was elected fellow of the royal society, and in 1826 received a gold medal from that society for discoveries in science. In 1822 he visited France, where he was received with much distinction.

In the reign of William IV. the English government gave him a pension of £150 a year, which was subsequently increased to £300.