John received his early education from his father and from John Fletcher, teacher of the Quaker school at Eaglesfield, on whose retirement in 1778 he himself started teaching. This youthful venture was not successful, the amount he received in fees being only about five shillings a week, and after two years he took to farm work. But he had received some instruction in mathematics from a distant relative, Elihu Robinson, and in 1781 he left his native village to become assistant to his cousin George Bewley, who kept a school at Kendal. There he passed the next twelve years, becoming in 1785, through the retirement of his cousin, joint manager of the school with his elder brother Jonathan. About 1790 he seems to have thought of taking up law or medicine, but his projects met with no encouragement from his relatives and he remained at Kendal till, in the spring of 1793, he moved to Manchester. Mainly through John Gough, a blind philosopher to whose aid he owed much of his scientific knowledge, he was appointed teacher of mathematics and natural philosophy at the New College in Moseley Street (in 1880 transferred to Manchester College, Oxford), and that position he retained until the removal of the college to York in 1799, when he became a public and private teacher of mathematics and chemistry.
During his residence in Kendal, Dalton had contributed solutions of problems and questions on various subjects to the Gentlemen's and Ladies' Diaries, and in 1787 he began to keep a meteorological diary in which during the succeeding fifteen years he entered more than 200,000 observations. His first separate publication was Meteorological Observations and Essays (1793), which contained the germs of several of his later discoveries; but in spite of the originality of its matter, the book met with only a limited sale. Another work by him, Elements of English Grammar, was published in 1801. In 1794 he was elected a member of the Manchester Literary and Philosophical Society, and a few weeks after election he communicated his first paper on Extraordinary facts relating to the vision of colours, in which he gave the earliest account of the optical peculiarity known as Daltonism or colour-blindness, and summed up its characteristics as observed in himself and others (including his brother). Besides the blue and purple of the spectrum he was able to recognize only one colour, yellow, or, as he says in his paper, that part of the image which others call red appears to me little more than a shade or defect of light; after that the orange, yellow and green seem one colour which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow. This paper was followed by many others on diverse topics on rain and dew and the origin of springs, on heat, the colour of the sky, steam, the auxiliary verbs and participles of the English language and the reflection and refraction of light. In 1800 he became a secretary of the society, and in the following year he presented the important paper or series of papers, entitled Experimental Essays on the constitution of mixed gases; on the force of steam or vapour of water and other liquids at different temperatures, both in Torricellian vacuum and in air; on evaporation; and on the expansion of gases by heat. The second of these essays opens with the striking remark, There can scarcely be a doubt entertained respecting the reducibility of all elastic fluids of whatever kind, into liquids; and we ought not to despair of effecting it in low temperatures and by strong pressures exerted upon the unmixed gases further. After describing experiments to ascertain the tension of aqueous vapour at different points between 32° and 212° F, he concludes from observations on the vapour of six different liquids, that the variation of the force of vapour from all liquids is the same for the same variation of temperature, reckoning from vapour of any given force. In the fourth essay he remarks, I see no sufficient reason why we may not conclude that all elastic fluids under the same pressure expand equally by heat and that for any given expansion of mercury, the corresponding expansion of air is proportionally something less, the higher the temperature. It seems, therefore, that general laws respecting the absolute quantity and the nature of heat are more likely to be derived from elastic fluids than from other substances. He thus enunciated the law of the expansion of gases, stated some months later by Gay-Lussac. In the two or three years following the reading of these essays, he published several papers on similar topics, that on the Absorption of gases by water and other liquids (1803), containing his Law of partial pressures.
But the most important of all Dalton's investigations are those concerned with the Atomic Theory in chemistry, with which his name is inseparably associated. It has been supposed that this theory was suggested to him either by researches on olefiant gas and carburetted hydrogen or by analysis of protoxide and deutoxide of azote both views resting on the authority of Dr Thomas Thomson (1773-1852), professor of chemistry at Glasgow University. But from a study of Dalton's own laboratory notebooks, discovered in the rooms of the Manchester society, Roscoe and Harden (A New View of the Origin of Dalton's Atomic Theory, 1896) conclude that so far from Dalton being led to the idea that chemical combination consists in the approximation of atoms of definite and characteristic weight by his search for an explanation of the law of combination in multiple proportions, the idea of atomic structure arose in his mind as a purely physical conception, forced upon. him by study of the physical properties of the atmosphere and other gases. The first published indications of this idea are to be found at the end of his paper on the Absorption of gases already mentioned, which was read on October 21 1803 though not published till 1805. Here he says:
Why does not water admit its bulk of every kind of gas alike? This question I have duly considered, and though I am not able to satisfy myself completely I am nearly persuaded that the circumstance depends on the weight and number of the ultimate particles of the several gases.He proceeds to give what has been quoted as his first table of atomic weights, but on p. 248 of his laboratory notebooks for 1802-1804, under the date 6th of September 1803, there is an earlier one in which he sets forth the relative weights of the ultimate atoms of a number of substances, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time. It appears, then, that confronted with the problem of ascertaining the relative diameter of the particles of which, he was convinced, all gases were made, he had recourse to the results of chemical analysis. Assisted by the assumption that combination always takes place in the simplest possible way, he thus arrived at the idea that chemical combination takes place between particles of different weights, and this it was which differentiated his theory from the historic speculations of the Greeks. The extension of this idea to substances in general necessarily led him to the law of combination in multiple proportions, and the comparison with experiment brilliantly confirmed the truth of his deduction; (A New View, etc., pp. 50, 51). It may be noted that in a paper on the; Proportion of the gases or elastic fluids constituting the atmosphere, read by him in November 1802, the law of multiple proportions appears to be anticipated in the words; The elements of oxygen may combine with a certain portion of nitrous gas or with twice that portion, but with no intermediate quantity, but there is reason to suspect that this sentence was added some time after the reading of the paper, which was not published till 1805.
Dalton communicated his atomic theory to Dr Thomson, who by consent included an outline of it in the third edition of his System of Chemistry (1807), and Dalton gave a further account of it in the first part of the first volume of his New System of Chemical Philosophy (1808). The second part of this volume appeared in 1810, but the first part of the second volume was not issued till 1827, though the printing of it began in 1817. This delay is not explained by any excess of care in preparation, for much of the matter was out of date and the appendix giving the author's latest views is the only portion of special interest. The second part of vol. ii. never appeared.
Altogether Dalton contributed 116 memoirs to the Manchester Literary and Philosophical Society, of which from 1817 till his death he was the president. Of these the earlier are the most important. In one of them, read in 1814, he explains the principles of volumetric analysis, in which he was one of the earliest workers. In 1840 a paper on the phosphates and arsenates, which was clearly unworthy of him, was refused by the Royal Society, and he was so incensed that he published it himself. He took the same course soon afterwards with four other papers, two of which On the quantity of acids, bases and salts in different varieties of salts and On a new and easy method of analysing sugar, contain his discovery, regarded by him as second in importance only to the atomic theory, that certain anhydrous salts when dissolved in water cause no increase in its volume, his inference being that the salt enters into the pores of the water.
As an investigator, Dalton was content with rough and inaccurate instruments, though better ones were readily attainable. Sir Humphry Davy described him as a very coarse experimenter, who almost always found the results he required, trusting to his head rather than his hands. In the preface to the second part of vol. i. of his New System he says he had so often been misled by taking for granted the results of others that he determined to write as little as possible but what I can attest by my own experience, but this independence he carried so far that it sometimes resembled lack of receptivity. Thus he distrusted, and probably never fully accepted, Gay-Lussac's conclusions as to the combining volumes of gases; he held peculiar and quite unfounded views about chlorine, even after its elementary character had been settled by Davy; he persisted in using the atomic weights he himself had adopted, even when they had been superseded by the more accurate determinations of other chemists; and he always objected to the chemical notation devised by J. J. Berzelius, although by common consent it was much simpler and more convenient than his cumbersome system of circular symbols. His library, he was once heard to declare, he could carry on his back, yet he had not read half the books it contained.
Before he had propounded the atomic theory he had already attained a considerable scientific reputation. In 1804 he was chosen to give a course of lectures on natural philosophy at the Royal Institution in London, where he delivered another course in 1809-1810. But he was deficient, it would seem, in the qualities that make an attractive lecturer, being harsh and indistinct in voice, ineffective in. the treatment of his subject, and ;singularly wanting in the language and power of illustration. In 1810 he was asked by Davy to offer himself as a candidate for the fellowship of the Royal Society, but declined, possibly for pecuniary reasons; but in 1822 he was proposed without his knowledge, and on election paid the usual fee. Six years previously he had been made a corresponding member of the French Academy of Sciences, and in 1830 he was elected as one of its eight foreign associates in place of Davy. In 1833 Lord Grey's government conferred on him a pension of £150, raised in 1836 to £300. Never married, though there is evidence that he delighted in the society of women of education and refinement, he lived for more than a quarter of a century with his friend the Rev. W. Johns (1771-1845), in George Street, Manchester, where his daily round of laboratory work and tuition was broken only by annual excursions to the Lake District and occasional visits to London, a surprising place and well worth ones while to see once, but the most disagreeable place on earth for one of a contemplative turn. to reside in constantly. In 1822 he paid a short visit to Paris, where he met many of the distinguished men of science then living in the French capital, and he attended several of the earlier meetings of the British Association at York, Oxford, Dublin and Bristol. Into society he rarely went, and his only amusement was a game of bowls on Thursday afternoons. He died in Manchester in 1844 of paralysis. The first attack he suffered in 1837, and a second in 1838 left him much enfeebled, both physically and mentally, though he remained able to make experiments. In May 1844 he had another stroke; on July 26 he recorded with trembling hand his last meteorological observation, and on the 27th he fell from his bed and was found lifeless by his attendant. A bust of him, by Chantrey, was publicly subscribed for him and placed in the entrance hall of the Manchester Royal Institution.
Dalton had requested that his eyes be examined after his death, in an attempt to discover the cause of his colour-blindness; he had hypothesised that his aqueous humour might be coloured blue. Postmortem examination showed that the humours of the eye were perfectly normal. However, an eye was preserved at the Royal Institution, and a 1990s study on DNA extracted from the eye showed that he had lacked the pigment that gives sensitivity to green; the classic condition known as a deuteranope.