JOHN, LL.D., the illustrious author of the Atomic Theory of Chemistry and of the Constitution of Mixed Gases, was born September 6, 1766, at Eaglesfield, in the vicinity of Cockermouth in Cumberland. Like his parents, he was a member of the religious sect of the Society of Friends, and for a long period supported himself by the humble office of usher to a school at Kendal until 1793; when, through the recommendation of Mr Gough the blind philosopher of that town, he obtained the appointment of professor of mathematics and natural philosophy in a college or seminary established at Manchester, which was removed to York in 1799. From the commencement of the present century, Dalton fixed his residence in Manchester, although he sometimes publicly explained the doctrine of chemical philosophy in a few other places. Some have confounded this great philosopher with another Dalton, an ingenious self-taught individual, who for many years was well known in England as an itinerant lecturer on experimental science. It is painful to reflect that John Dalton, one of the most acute and original philosophers that have adorned our age, should have been for many years compelled to earn his subsistence by the irksome task of conveying the elements of instruction to the minds of both sexes. But Dalton was of too independent a spirit to be beholden to others for what he could obtain by his own exertions; was of a contented disposition, and lived amid a select society of tried friends, who admired his talents, and esteemed him as a man; continuing to employ his leisure hours in those interesting philosophical investigations which have given him a lasting reputation. He was successively the secretary, vice-president, and president of the Philosophical Manchester Society; and among its highly interesting memoirs, the papers of Dalton, both for their number and their value, occupy a most important place.

His earliest papers consisted of contributions to that remarkable and able periodical termed The Lady's Diary. In after years he enriched the Memoirs of the Manchester Society, Nicholson's Journal, the Philosophical Magazine, and the Transactions of the Royal Society, with numerous contributions.

In 1793 appeared his earliest separate publication, Meteorological Essays, a favourite subject, on which he continued to collect and record observations to the period of his death. In the following year he gave an account of a singular defect in his own vision which rendered him incapable of distinguishing certain colours, as green and scarlet. In conversation with the writer of this notice, he stated how he first became aware of this peculiarity of his vision. When a boy he had gone to see a review of troops, and being surprised to hear those around expatiating on the gorgeous effect of the military costume, he asked, "In what a soldier's coat differed from the colour of the grass on which he trod?" The derisive laugh and exclamations of his companions now first led him to suspect that he did not see like other people. (See Colour Blindness.)

His daily employment as a teacher of youth no doubt drew his attention to the want then subsisting of a suitable English grammar, and led to his publication in 1801 of Elements of English Grammar—a subject very foreign to those on which his powerful mind was usually exerted; yet it shows marks of that precision and comprehensive grasp with which he could handle everything which he investigated.

In the Manchester Memoirs for 1802, we find six dissertations by Dalton; and in these he unfolded his beautiful theory of the constitution of mixed gases; of which the characteristic feature is the proof 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. This philosophical view, for some time strenuously opposed by different chemists, is now universally received. Another subject discussed by him was very important—"On the force of Vapour of Water and other Fluids at different Temperatures in the Torricellian Vacuum, and under Atmospheric Pressure," which included the "Theory of Evaporation and the Expansion of Gases by Heat." The simple experiments by which Dalton illustrated those subjects, and the profound reasoning by which his views were supported, established the philosophical reputation of our author, and have been of infinite service to the progress of pneumatic chemistry, especially in the refined modern investigations on the specific gravity of gases.

But the high reputation of Dalton mainly reposes on the Atomic Chemical Theory, which he began to develop in 1803, and illustrated by numerous observations in succeeding years. Yet from the inherent difficulties of the subject,

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1 Chalmers' Biographical Dictionary, art. Dalrymple, vol. xi. p. 229. See also Life of Lord Hailes, in the Edinburgh Magazine and Literary Miscellany, March 1793; the brief memoir by Dr Charles Stuart, prefixed to the second and third editions of the Reply to Gibbon; and the "Sermon on the Death of Lord Hailes," preached at Inveresk, by Alexander Carlyle, D.D., Edin, 1792, &c. and, perhaps, from some want of perspicuity in his explanations, it was not at once adopted by philosophers; and we are in this country chiefly indebted for luminous views of this grand theory to the labours of the late Professor Thomson of Glasgow, of the late Dr Henry of Manchester, and its early adoption by Dr Wollaston; while the masterly analysis of Berzelius placed the doctrine of Dalton on a stable foundation. The atomic theory is a consequence of the investigations of Ritter which that laborious experimentalist did not perceive, and was obscurely indicated in a paper of Dr Higgins; but it is now acknowledged that we owe to Dalton the first development of its general principles, and the important consequences of its application to the explanation of chemical and natural phenomena. It is not too much to assert that we are indebted to the atomic theory for much of the recent progress in many branches of physical science.

This theory was fully propounded by Dalton in his New System of Chemistry, of which the first volume appeared in 1807, the second in 1810, and these were followed by a third in 1827. These important volumes contained the elements of the mathematical principles of the science.

In his other papers on subjects connected with meteorology, he has left us valuable remarks on evaporation, rain, the aurora borealis, winds, and dew. His observations on the latter contain the principles of Dr Wells's beautiful Theory of Dew, and of Daniell's Hygrometer.

In 1822 he visited France, where he was received with that distinction which was due to so eminent a philosopher. He was afterwards elected a corresponding member, and finally a foreign associate of the French Institute. He was also a foreign member of the Royal Academies of Berlin and Munich, and of the Natural History Society of Moscow. In 1834 the university of Edinburgh did itself honour by conferring on him the degree of LL.D. In the reign of William IV, he received from the government a pension of L150, which was subsequently increased to L200 a-year.

In person Dr Dalton was of middle stature, and vigorous, though not robustly formed. His powerful intellect was disciplined by patient observation and composure; and he had a happy facility in seizing the relations of physical subjects. His early habits as a member of the Society of Friends had given him a quiet, grave demeanour, but without austerity; and he possessed a manly independence of character, without superciliousness. His high moral worth will live in the remembrance of all who had the pleasure of knowing him, as well as the kindness with which he always accommodated his conversation to the comprehension of those who sought his acquaintance.

This eminent man had long enjoyed excellent health; but he had two attacks of paralysis in 1837, and a third attack carried him off on the 27th July 1844.

His principal contributions to physical science will be noticed under Atmosphere, vol. iv.; Aurora Borealis, vol. iv.; Atomic Theory and chemical researches, under Chemistry. See also articles Evaporation, Heat, Mercurial Chronometers, Repulsive Power of the Particles of Air, Magnetism, and Elasticity and Density of Steam. For further details of Dalton's life, see the excellent biography by Dr Charles Henry.