Dalton, John

(b. Eaglesfield, Cumberland, England, 6 September 1766; d. Manchester, England, 27 July 1844)

physics, chemistry, meteorology.

If the provincial Dissenter of dubiously middle–class background, obscure education, and self–made opportunity is the characteristics figure of late eighteenth–century English natural philosophy, then John Dalton is the classic example of the species. John was the second son of a modest Quaker weaver, Joseph Dalton, and Mary Greenup. The Daltons can be traced back in west Cumberland at least to the late sixteenth century. From that time the family seems to have owned and farmed a small amount of land. Joseph, himself a younger son, had no holding until his elder brother died without issue in 1786. The property Joseph then inherited passed at his death the following year to Jonathan, his elder son. Only when Jonathan, a bachelor, died in 1834 did the then considerably augmented acreage finally pass to John Dalton, who by that time had independently accumulated wealth sufficient to his own frugal and celibate ways.

In the eighteenth century, west Cumberland enjoyed considerable prosperity as a mining and trading area, with an important series of coastal ports engaged in local and overseas commerce. George Fox had earlier seen his first major evangelistic success in this region, whole villages and families (including the Daltons) undergoing conversion to his doctrines. The area was thus peculiarly important within the developing international life of the Society of Friends. Strong links were forged between these Northern Friends, Quaker manufacturers in the Midlands, London Quaker merchants, and Philadelphia residents. This network of connections, coupled with the sect’s strong emphasis on education and the interest in natural philosophy displayed by so many of its members, is the key to understanding the peculiarly favorable context in which Dalton grew and matured as a scientific thinker.

Although his father appears to have been somewhat feckless, his mother came from a more prosperous local family, and John was strongly influenced by her determination and tenacity. He made rapid progress in the village Quaker school, which he himself unsuccessfully took over at the age of twelve. He also quickly attracted the attention of Elihu Robinson, the most prominent of the local Friends and a naturalist of no mean stature. Robison’s encouragement is reflected in the story of how John at the age of thirteen copied out verbatim an issue of the Ladies’ Diary, a popular but by no means trivial annual devoted to mathematics and philosophy.

At this time Dalton’s future seemed uncertain, and he was of necessity put to work as a laborer on the local small–holdings. In 1781 he was rescued by an invitation to replace his elder brother as assistant in a Kendal boarding school, forty miles away.

The school to which Dalton moved was newly built and equipped by the Quakers. The list of benefactors was headed by John Fothergill, the London physician and a personal friend of Robinson, and included such wealthy Midland entrepreneurs as Abraham Darby and Richard Reynolds. More immediately important than the web of contacts the benefactors’ list displays was the use that the school’s first pricipal made of the £150 available for the library. George Bewely, himself a distant cousin of Dalton, was quick to purchase not only Newton’s Principia, but also the supporting texts of Gravesande, Pemberton, and Thomas Rutherforth. Later purchases included Musschenbroek’s Natural Philosophy, the six–volume Works of the Honourable Robert Boyle, and Buffon’s Natural History, among others. The collection was rounded out with various items of apparatus, including a two–foot reflecting telescope, a double microscope, and (for £21) a double–barreled air pump with its subsidiary equipment.

Dalton did not feel such valuable resources as these worth even a mention in the accounts of his early life that he was later to authorize for publication. Nor did he refer to the stimulus available to such a talented and enterprising youth from the continued flow of Quaker visitors. He also forgot to include the public lectures given by itinerant natural philosophers (Kendal being, among other things, an important staging post on the coach route from London to Scotland). Typical of the courses available was that of John Banks in 1782. In a seven–week stay in Kendal, Banks offered “twelve lectures, which include the most useful, interesting and popular parts of philosophy,” the lectures being illustrated by extensive apparatus. Despite his failure to acknowledge their influence, Dalton obviously modeled his own subsequent public courses on lectures such as these.

What Dalton did acknowledge was the presumably still greater stimulus he found in the library, learning, and enthusiasm of another Kendal Quaker, John Gough, the blind natural philosopher of Wordsworth’s Excursion. As Dalton explained in a 1783 letter to Peter Crosthwaite, a Keswick Friend and fellow naturalist:

John Gough is… a perfect master of the Latin, Greek, and French touges… Under his tuition, I have since4 acquired a good knowledge of them. He understands will all the different branches of mathematics… He knows by the touch, taste, and smell, almost every plant within twenty miles of this place… He is a good proficient in astronomy, chemistry, medicine, etc… He has the advantage of all the books he has a mind for… He and I have been for a long time very intimate; as our pursuits are common—viz, mathematical and philosophical…

Under Gough’s tuition Dalton made rapid progress in mathematics, meteorology, and botany. Emulating his master, he began to keep a daily meteorological record in1787, a task he continued steadfastly until the day he died. He also carefully compiled a stillextant eleven–volume Hortus siccus. And from 1787on this “teacher of the mathematics in Kendal” enjoyed an increasing reputation for his successes in the yearly puzzles and prize competitions of the Ladies’ Dairy and Gentleman’s Dairy.

In 1785 Geroge Bewley withdrew form the Kendal school. Jonathan and John Dalton thereupon took over as joint principals, and their sister Mary moved from Eaglesfield to become housekeeper. Despite his increased responsibilities at the school, John was soon offering his own first series of public lectures in Kendal. The lectures treated mechanics, optics, pneumatics, astronomy, and the use of the globes, with the aid of the school’s apparatus. Yet even with such new outlets for his energy and curiosity, John was obviously becoming restless within the confines of a local scientific community whose lessons he had mastered and whose possibilities he had so fully explored. In 1790 he wrote to Bewley, Robinson, and his uncle Thomas Greenup, a London barrister, to seek advice on his prospects in medicine and law (the Society of Friends having no clergy).

Dalton argued that “very few people of middling genius, or capacity for other business” become teachers. His own desire for a profession with “expectation of greater emolument” led to his queries, especially about the feasibility of studying medicine at Edinburgh. The replies were not enthusiastic. Greenup in particular chose to say that medicine and law were “totally out of the reach of a person in thy circumstances” and that Dalton should rather aim at moving in the humbler sphere of apothecary or attorney, where with a little capital and great industry he might perhaps be able to establish himself. Despite this discouragement, such an ambitious and talented young man was not to be confined to a Kendal school.

In 1791 Dalton again offered a public lectures. In 1792 he paid his first visit to London, ostensibly for the annual meeting of the Society of Friends. Shortly afterwards he was appointed professor of mathematics and natural philosophy in the “New College,” which Socinian- and Unitarian–oriented Dissenters had recently established in the dramatically expanding town of Manchester, following the demise of the nearby Warrington Academy, at which Joseph Priestley had once taught.

Initially, Dalton seems to have been well pleased with the Manchester appointment. Reporting on his new situation to Robinson, his early patron, he explained:

There is in this town a large library [Chetham’s], furnished with the best books in every art, science and language, which is open to all gratis; when thou are apprised of this and such like circumstances, thou considerest me in my private apartments, undisturbed, having a good fire, and a philosophical apparatus around me, thou wilt be able to form an opinion whether I spend my time in slothful inactivity of body and mind.

Despite the availability of library and apparatus, teaching duties seem to have absorbed Dalton’s energies in his early years in Manchester. Called upon to offer college–level mathematics and natural philosophy for the first time, he soon found himself expected to cover chemistry as well. As he ruefully noted, it was “often expedient to prepare my lectures previously.” In addition there was the necessary “attendance upon students 21 hours in the week.” Walking tours tours in the summer vacation, regular local and occasional regional Quaker meetings, return visits to his beloved Lake District and, in 1796, a further set of Kendal lectures served to more than fill out the remaining time.

On 26 March 1800 Dalton announced his intention to resign his teaching position at the close of the session, for reasons that remain obscure. Perhaps he was dissatisfied with the college’s radical posture, perhaps unsettled by its faculty changes and uncertain future, perhaps unhappy that he remained the lowest paid of the three professors (receiving £52.10.0 annual salary, plus approximately £ 50 in fees), perhaps quite simply confident in his own popularity and teaching abilities. The following September the Manchester Mercury advertised the opening of his private “Mathematical Academy,” offering tuition in mathematics experimental philosophy, and chemistry. Success came quickly to the academy. Within two years Dalton could drily observe, “My Academy had done very well for me hitherto. I have about eight or nine day pupils at a medium, at ten guineas per annum, and am now giving upwards of twenty lessons per week, privately, at two shillings each besides. I am not yet rich enough to retire, notwithstanding.” Private teaching of this fashion more than adequately supported him for the rest of his days. Far from being regarded as a degrading chore, his activity in this respect was typical of that of a host of lower–to middle–class Dissenters whose academies and popular lectures formed one of the major strengths of English science throughout this period of embryonic professionalization. Self–help, private initiative, technological curiosity, and utilitarian attitudes were characteristics of that Industrial Revolution science which is both exemplified in Dalton’s work and encapsulated by his lifetime.

Within five years of leaving the New College Dalton had completed in essential outline the work on which his major and enduring scientific reputation was to rest: the law of gaseous expansion at constant pressure (also called Charles’s law after its independent—msdash;and earlier—French discoverer); the law of partial pressures in gaseous systems; and the chemical atomic theory (which for the first time gave significance to and provided a technique for calculation the relative weights of the ultimate particles of all known chemical, whether elements or compounds). Despite this brilliant efflorescence of creative thought, Dalton’s achievements can be properly appreciated only when seen against the background of his earlier research and writing.

When he moved from Kendal to Manchester, Dalton also entered a far wider and more demanding scientific world. Indicative of new horizons and new opportunities was his election on 17 October 1794 to membership in the Manchester Literary and Philosophical Society, then in its first great productive epoch, to which Dalton was to contribute so substantially. His sponsors were Thomas Henry, translator of Lavoisier’s Opuscules; Thomas Percival, pioneer sanitary reformer and medical statistician; and Robert Owen, entrepreneur and visionary socialist. And within a month of his election, Dalton was reading the society his first major paper, on some “Extraordinary Facts Relating to the Vision of Colours, with Observation."

The paper is an excellent example of the careful observation, bold theorizing, and dogmatic belief which together characterize Dalton’s work. The paper provided the first systematic notice and attempted explanation of the existence of color blindness, a defect which John shared with his brother Jonathan. Collecting information from other people similarly afflicted, Dalton was able to give a careful account of the actual phenomenon. His explanation of his own failure to see red was in terms of the supposed blue (that is, red–ray absorbing) nature of the aqueous medium of his eye. Characteristically, Dalton refused to entertain Thomas Young’s later alternative explanation. He even went so far as to instruct that his own eye be dissected after death to confirm his hypothesis—a dissection duly undertaken, with the opposite result. If the theory now seems inadequate, the meticulous detail and bold speculations on an important and neglected phenomenon were enough to establish the newly elected member’s place in the front ranks of Mancherster’s burgeoning group of natural Philosophers.

In contrast to this brilliant early investigation, Dalton’s other major scientific achievements present many puzzling problems of chronology and interpretation. His background and scientific formation is ill understood. It is clear that the standard accounts, with their straight line of development from Isaac Newton’s speculations on the fundamental particles of matter in the thirty–first query of the Opticks to John Dalton’s chemical atomic theory a century later, are woefully inadequate. Their replacement by a more careful and convincing narrative is not yet possible, but some tentative outlines may be indicated.

Although not a Newtonian in any simple sense, Dalton was deeply indebted to the British tradition of textbook and popular Newtonianism, pervasive throughout the later eighteenth century. This tradition, at once empirical and speculative, placed great stress on the uniformity (i.e., inertial homogeneity) and “internal structure” of matter and the role in nature of those short–range attractive and repulsive forces everywhere associated with, if not necessarily inherent properties of, that matter. In the hands of more sophisticated thinkers, the path from homogeneity, internal structure, and short–range forces gradually led through the “nutshell” view of matter elaborarated by Newton’s immediate disciples, to the subtle curves of the Abbé Bosšscaron;ković and the “materialistic” immaterialism of Joseph Priestly. Scottish common–sense philosophy provided one possible answer to the doubts and paradoxes thus arrived at, while some more conservative and evangelical thinkers turned instead to the heterogeneous matter, indivisible atoms, and ethereal fluids of the consciously “revisionist” disciples of John Hutchinson. The shifting political and theological currents of the 1780’s, and more especially the 1790’s; the association of Priestley’s ideas with materialism; and the pressures on chemical theory inherent in the dramatic technological advances of the period have not yet recieved any sustained investigation. Thus, for instance, the resonances between Dalton’s philosophical position on the nature and properties of matter and the teachings of the Hutchinsonians may more easily be noted than explained. It is one of the curiosities of historical exegesis that the intellectual and philosophical context and consequences of what was for a century the dominant scientific theory of matter—the chemical atomic theory—has been so little studied. The situation is better when we turn to the more limited questions of the chronology and logic of the directly scientific and experimental work which fed and helped to fashion Dalton’s evolving theoretical concerns.

Besides his mathematical interests, Dalton was early involved in natural history, the compiling of meteorological records, and the construction of barometers, thermometers, rain gauges, and hygrometers. His daily weather records over a five–year period and those of his friends John Gough (also in Kendal) and Peter Crosthwaite (in Keswick) were to form the basis of Dalton’s first book, the Meteorological Observations and Essays (1793), which well displays the interests, ambitions and energy of the young provincial natural philosopher. The work, which was already with the printer before he left Kendal, provides tables of barometric pressure temperature, wind, humidity, and rainfall, besides detailing the occurrence of snow, thunder, and the aurora borealis. All these constitute the Observations. As such, they testify to Dalton’s patience and diligence. Far more interesting are the Essays, in which the empirical is made the servant of the speculative.

The essays include a theory of trade winds, anticipated by George Hadley, as Dalton discovered on his move to Manchester with its more adequate libraries; a theory of the aurora borealis, similarly anticipated by Anders Celsius and by Edumund Halley; speculations about variations in barometric pressure, anticipated by Jean Deluc; and ideas on evaporation which include the germs of his own later chemical atomic theory.

Dalton’s earliest meteorological researches had not unnaturally awakened a deep and abiding interest in the theory of rain and in the state of water vapor in the atmosphere. The Meteorological Observations even went so far as to advance “a theory of the state of vapour in the atmosphere, which as far as I can discover, is entirely new, and will be found, I believe, to solve all the phenomena of vapour we are acquainted with.” The theory was that “evaporation and the condensation of vapour are not the effects of chymical affinities, but that aqueous vapour always exists as a fluid sui generis, diffused among the rest of the aerial fluids…there is no need to suppose a chymical attraction in the case.”

In denying the chemical attraction of water for air in which it was “dissolved,” Dalton was of course flouting the orthodox and Newtonian view that short–range attractive and repulsive forces were the appropriate media for explaining the process. In support of such a view, chemists could quote no less an authority than Lavoisier. Dalton, with his habit of looking upon all empirical phenomena from a mathematical point of view, was not the one to worry about this. His experiments seemed to show that the absorption of water vapor by air was not pressure dependent, i.e., “that a cubic foot of dry air, whatever its density be, will embibe the same weight of vapour if the temperature be the same.” Such a conclusion (in modern terminology, the vapor pressure of water is constant at constant temperature) could not easily be reconciled with belief in evaporation as a chemical process. Hence Dalton, the mathematically inclined meteorologist, simply abandoned the chemistry.

In the appendix to the work, he went even further, saying that “the vapour of water (and probably of most other liquids) exists at all times in the atmosphere in an independent state.” As the quotation shows, Dalton was not afraid to generalize his ideas. The visual nature of his thinking and the essential continuity in his own ideas from before 1793 right down to 1808 is apparent from his supporting statements. Dalton argued that it was an error to assume chemical combination was necessary if water vapor was to exist in the open atmosphere below 212°F. The error arose from assuming that “air pressing upon vapour condenses the vapour equally with vapour pressing upon vapour, a supposition we have no right to assume, and which I apprehend will plainly appear to be contradictory to reason, and unwarranted by facts; for, when a particle of vapour exists between two particles of air let their equal and opposite pressures upon it be what they may, they cannot bring it nearer to another particle of vapour.”

The ideas that in a mixture of gases every gas acts as an independent entity (Dalton’s law of partial pressures) and that the air is not a vast chemical solvent were thus first stated in the Meteorological Observations. The statements brought no immediate reaction. This was only to be expected, Dalton’s argument being so tentative and undeveloped, the ideas themselves so curious in a world off all–pervasive chemical forces, and the author and vehicle of publication so comparatively obscure.

Three papers that Dalton read to the Manchester Literary and Philosophical Society in 1799 and 1800 (in which year he became the society’s secretary) show how much the question of water vapor continued to exercise him. In the first paper he discussed the balance in nature between rain, dew, river–water runoff, and evaporation. In the course of this discussion, he provided the earliest definition of the dew point. Then followed two competent, but more pedestrian, papers on heat, in which his firm belief in a fluid of heat is well–displayed and his complete acceptance of the particular caloric theory of William Irvine and Adair Crawford is apparent. The really dramatic development came in the summer of 1801. By 14 September, Dalton was confident enough in his ideas to write to William Nicholson’s recently established monthly Journal of Natural Philosophy, Chemistry and the Arts. It showed no hesitation in publishing his “New Theory of the Constitution of Mixed Aeriform Fluids, and Particularly of the Atmosphere.”

That Dalton was convinced of the value of his ideas is apparent. The rough sketch of his theory of mixed gases printed in Nicholson’s Journal was quickly supplemented in three papers to the Manchester society. These included the first clear statement that “When two elastic fluids, denoted by A and B, are mixed together, there is no mutual repulsion amongst their particles; that is, the particles of A do not repel those of B, as they do one another. Consequently, the pressure or whole weight upon any one particle arises solely from those of its own kind.” The debt of this generalized “new theory” to his 1793 picture of water vapor in air is obvious. So too is the debt of Dalton’s thinking, with its static, particulate gas, to the passage in Newton’s Principia (bk. II, prop.23) which discusses the properties that such a gas would have.

Besides this first formal enunciation of the law of gaseous partial pressures, the papers also contained important information on evaporation and on steam pressure, as well as Dalton’s independent statement of Charles’s law that “all elastic fluids expand the same quantity by heat.”

While Dalton’s earlier statements had passed unnoticed, the reaction to his 1801 pronouncements was rapid and widespread. The three papers in the Manchester Memoirs were abstracted and reprinted on the Continent. Discussion was immediate and lively. C. L. Berthollet, then in the midst of his Newtonian affinity investigations, scornfully dismissed Dalton’s diagrammatic representation of the new theory of mixed gases as “un tableau d’imagination,” while Humphry Davy quickly sought the judgment of a friend on these “new and very singular” ideas. Even the Literary and Philosophical Society was uncertain what to make of its secretary’s dismissal of chemical affinity as a force acting in the atmosphere. More damagingly, the first edition of Thomas Thomson’s highly successful System of Chemistry (1802) was highly critical. Dalton quickly wrote to the two major monthly scientific journals of the day, rebutting Thomson’s criticism; but clearly it was not argument that was needed so much as convincing experimental proof of his beliefs. To provide such proof became Dalton’s major aim, and hence the efficient cause of the chemical atomic theory. What began as a particular interest in meteorology thus ended up as a powerful and wide–ranging new approach to the whole of chemistry, although the transition was by no means sudden.

One thing Dalton did in order to provide support for his heavily attacked theory of mixed gases was to begin an experimental inquiry into the proportions of the various gases in the atmosphere. This inquiry accidentally raised the whole question of the solubility of gases in water. By 12 November 1802 he had discovered enough to read to the Manchester Society his paper “On the Proportion of the Several Gases or Elastic Fluids, Constituting the Atmosphere; With an Enquiry into the Circumstances Which Distinguish the Chymical and Mechanical Absorption of Gases by Liquids.” When read, although not when published, it contained the statement that carbon dioxide “is held in water, not by chemical affinity, but merely by the pressure of the gas… on the surface, forcing it into the pores of the water.” The researches on solubility thus led to an extension of his mechanical ideas.

It seems that it was this extension of Dalton’s ideas that provoked his close friend, the Edinburgh–trained chemist William Henry, to begin his own rival and chemically orthodox series of experiments to ascertain the order of affinities of gases for water. Measured with reference to this objective, the experiments were not a success. However, within a month Henry found what Dalton had failed to see—namely that at a given temperature the mass of gas absorbed by a given volume of water is directly proportional to the pressure of the gas (Henry’s law). Aware of this work and quick to see its relevance to his own ideas, Dalton was able to point out faults in Henry’s procedure. One consequence was the latter’s public admission that “the theory which Mr. Dalton has suggested to me on this subject, and which appears to be confirmed by my experiments, is that the absorption of gases by water is purely a mechanical effect.”

In the light of such exciting developments, we can appreciate why Dalton continued to grapple with “The Absorption of Gases by Water and Other Liquids.” A paper with that title, presented to the Manchester Society in October 1803, made it clear that although his theory of mixed gases was much strengthened by the new evidence from solubility studies, “The greatest difficulty attending the mechanical hypothesis arises from different gases observing different laws.” Or, to put the problem in its crudest form, why does water not admit its bulk of every kind of gas alike? To answer this question Dalton proposed that

… the circumstance depends upon the weight and number of the ultimate particles of the several gases; Those whose particles are lightest and single being least absorbable and the others more according as they increase in weight and complexity… An enquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new; I have lately been prosecuting this enquiry with remarkable success. The principle cannot be entered upon in this paper; but I shall just subjoin the results, as far as they appear to be ascertained by my experiments.

And thus it was that this paper closed with the very first list of what we would now call atomic weights.

Dalton’s method of calculating the relative weights of ultimate particles was simplicity itself. Despite their appeal to more orthodoxly Newtonian chemists, the measurement or calculation of interparticle affinity forces held no interest for him. Instead, his mechanistic visual, and realist view of atoms was joined with prevailing vogue for numerical calculation and with the common assumption of one–to-one combination, in such a way as to yield wholly new insights.

In accord with the postulates of his theory of mixed gases, Dalton assumed that when two elements A and B come together in reaction, it is the mutual repulsion of the atoms of B that is the critical factor in controlling what happens, rather than any attraction between A and B. Thus, assuming spherical atoms of equal size, twelve atoms of B can theoretically come into contact(react) with one atom of A. In practice the most likely outcome is a one–to-one combination of A and B. Two atoms of B combining with one of A is also possible but less likely, since the atoms of B have a mutual repulsion to overcome, even though they will automatically take up positions on opposite sides of A. Three atoms of B to one of A involve greater repulsive forces, a corresponding triangular disposition, and so on. Thus if only one chemical compound of elements A and B is known, it is natural to assume it has the composition AB. If there are two compounds, they are most likely to be AB and AB₂ and so on. In this way Dalton’s theoretical views provided a rationale for deciding on both the formulas of compounds and on their three–dimensional molecular structures. Armed with such a mechanical view of combining ratios, it was a simple matter for him to argue from the knowledge that eight ounces of oxygen combined with one of hydrogen, to the statement that the relative weights of their ultimate particles were as eight to one.

Just how little Dalton or anyone else realized the implications of his work is seen from public reaction to his tables. Although published in the Manchester Memoirs and reprinted in the monthly scientific journals, his table of weights—unlike his theory of mixed gases—aroused no reaction at all. When printed by themselves, tables of weight numbers appeared to be just further obscure and unexplained variations on the widely known tables of affinity numbers current at that time. Even when accompanied by an explanation of their significance, a favorable reception was by no means certain. In December 1803, thanks to a slip in his arithmetic, Dalton, in London to lecture at the Royal Institution, was able to show Humphry Davy how the various oxides of nitrogen might be given formulas and particle weights that were in harmony with the latter’s own experimental results. Yet Davy, true to his deeper Newtonian vision, simply dismissed these ideas as speculations “rather more ingenious that important.”

This lack of enthusiasm for the chemical possibilities of his work must have been a blow to Dalton, for Davy was after all a highly capable and serious chemist. It is not clear, however, that Dalton himself had yet fully grasped the wider implications of his work. In 1804 he did succeed in arriving at formulas for various hydrocarbons which were agreeable both to his calculating system and to his own now rapidly increasing chemical experiments. But 1804 was notable chiefly for controversy over the mixed gases theory and particularly over its denial of weak chemical affinity forces. Continuing criticism of the theory—and the failure of particle weight studies to provide the hoped–for clinching evidence—caused Dalton to revise his ideas on mixed gases during the course of 1805. This revision seems to have strengthened the slowly deepening conviction that his work on particle weights, although not a success in its original purpose, was of fundamental importance as the basis for his New System of Chemical Philosophy.

In the syllabuses of the public lectures he gave in London late in 1803, in Manchester early in 1805, and in Edinburgh in April 1807, we can trace the slow shifting of Dalton’s interest away from mechanics, meteorology, and mixed gases, toward chemistry. By March 1807 he was writing to Thomas Thomson to offer an Edinburgh lecture course. This was to be on his recent experimental inquiries, including chemical elements or atoms with their various combinations, and would reveal “my latest results, some of which have not yet been published or disclosed in any way, & which I conceive of considerable importance.” The lectures duly took place. Dalton’s introduction left no doubt as to his awareness that he spoke to the foremost scientific audience of the day. Equally, there was no doubt as to his own estimate of the importance of his ideas. He quickly informed his hearers that he was about to exhibit “a new view of the first principles or elements of bodies and their combinations” and that this view, if established, “as I doubt not it will in time, will produce the most important changes in the system of chemistry, and reduce the whole to a science of great simplicity, and intelligible to the meanest understanding.”

The lectures in Edinburgh were little short of a manifesto for the New System. That their reception was favorable we know from the dedication attached to the first part of that work when it finally appeared, just over a year later. With the publication of the second part in 1810, and more especially with Thomas Thomson’s and W. H. Wollaston’s 1808 papers showing the practical power of his approach, the chemical atomic theory was finally launched. The theory was Dalton’s last creative piece of scientific thinking, although he continued active work in several fields for though he continued active work in several fields for more than a quarter century. The main thrust of much of this work was in providing experimental measurements of atomic weights of known chemical compounds. The enormity of this task and Dalton’s reluctance to take other people’s results on trust are symbolized by his failure ever to complete those later parts of the New System which were to embody his results (although vol. II, pt. 1 did belatedly appear in 1827).

Before leaving Dalton’s scientific work, mention must be made of his attitude to chemical atomism. The equation of the concepts “atom” and “chemical element” is usually held to be one of the most important aspects of his achievement. It was certainly one that led to controversy and debate throughout the nineteenth century. Dalton’s work not only provided a new, fundamental, and enormously fruitful model of reality for the chemist. It also gave focus and rationale to those weight studies that had become of steadily increasing importance to chemistry through the previous two generations. Even so, the systematic utilization and extension of Dalton’s ideas on atomic weights was to be plagued by methodological problems, problems only slowly resolved through the work of Gay–Lussac, Avogadro, and Cannizzaro. Dalton’s ideas on the real physical existence and actual nature of chemical atoms were to prove even more trouble–some, initiating a continuing nineteenth–century debate that was terminated only by the work of Rutherford and Soddy.

The syllabus for his course of lectures at the Royal Institution in December 1803, soon after the first measurement of relative particle weights, speaks in thoroughly orthodox fashion of “Properties of matter. Extension–impenetrability-divisibility–inertia-various species of attraction and repulsion. Motion–forces-composition of forces–collision. Pendulums.” Yet by the spring of 1805, under pressure from the continuing success of his chemical investigations, Dalton’s public position was changing. The newly discovered syllabus for his Manchester lectures lists “General properties of matter–extension-divisibility–original ideas on the division of matter into elements and their composition–solidity-mobility–inertia.” By this time also, one whole lecture was devoted to the elements of bodies and their composition. Tantalizingly, no manuscript survives to enlighten us about the “original ideas on the division of matter into elements” that the syllabus promised. It seems reasonable to suppose, however, that as Dalton slowly came to appreciate the far wider chemical utility of his researches on the relative weights of ultimate particles so he increasingly felt the need to define the nature of these ultimate particles. Because of his background and context, the move to explicit avowal of chemical atoms and heterogeneous matter was a comparatively simple one to make.

It was in the 1807 Edinburgh syllabus that direct mention was first made of indivisible particles or atoms. Lectures 3.4 and 5 of Dalton’s now deliberately propagandizing course were devoted to the chemical elements. The syllabus spoke of elastic fluids, liquids, and solids as consisting of indivisible particles or atoms of matter, surrounded with atmospheres of heat. Even this statement was not as unambiguous as might be supposed. Of the eighteen elastic fluids known to Dalton, fifteen were, by his own reckoning, compounds. Thus Dalton was in part using the word “atom” in the commonplace and acceptable sense of “smallest particle possessing a given nature.” In this sense, “atom” was merely a term for a particle which was divisible only with the loss of its distinguishing chemical characteristics. Yet Dalton’s position was not so clear–cut. He was also beginning not only to think but to speak in public of chemical atoms in the more radical sense of solid and indivisible particles.

The following year the first part of the New System was to say that chemical analysis and synthesis is only the separating and rejoining of existing particles, the actual creation and destruction of matter being beyond the reach of chemical agency. Such a statement was thoroughly orthodox. What was new was the further insistence that “We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen” In this way Dalton first made formal claim for the privileged status of his chemical atoms. The particle of hydrogen was not to be seen as the complex result of an ordered and intricate internal structure but as the given solid, the planet.

Just why Dalton should have moved to this position of reserving privileged status for his chemical atoms is not fully obvious. No doubt he felt the need of some philosophical justification for his concentration on particle weights at a time when the list of known elements was under renewed, electrochemical, attack. Lavoisier’s reforms had by no means settled the question of which substances should be admitted to the status of chemical element. Between 1800 and 1812 no less than fifteen new chemicals were added to the list of eighteen previously known elements. We can therefore appreciate how widely acceptable was Davy’s impatient belief that whereas the power of nature was limited the powers of the chemist’s analytical instruments were capable of indefinite increase, so that “there is no reason to suppose that any real indestructible principle has yet been discovered.”

Having adopted a position, Dalton was not one to settle for half measures. His second lecture series at the Royal Institution, in 1810, was clearly designed to defend and vindicate his now widely known and controversial ideas against Davy and a host of critics. In these lectures he first publicly abandoned the unity of matter. Dalton was prepared to admit how “it has been imagined by some philosophers that all matter, however unlike, is probably the same thing.” However, on the excellent principle that attack is the best form of defense, he calmly asserted that “this does not appear to have been [Newton’s] idea. Neither is it mine. I should apprehend there are a considerable number of what may be called elementary principles, which can never be metamorphosed, one into another, by any power we can control.”

Still on the offensive, Dalton reiterated the same beliefs in print in Nicholson’s Journal in 1811. He insisted that “atoms of different bodies may be made of matter of different densities.” The examples he offered was that “mercury, the atom of which weighs almost 170 times as much as that of hidrogen, I should conjecture was larger, but by no means in proportion of the weights,” Once again the opposition was disarmed with the bland assertion that Newton had a better claim to be heard than either Dalton or his critics. And Newton was quoted as saying in the thirty–first query of the Opticks that “God is able to create particles of matter of several sizes and figures, and in several proportions to the space they occupy, and perhaps of different densities and forces…at least I see nothing of contradiction in all this.”

The interesting thing about this quotation is what Dalton chose to omit from it. Newton did not allow that the matter of our own world was heterogeneous, as the missing words—"and thereby to vary the laws of Nature, and make worlds of several sorts in several parts of the universe"—make plain. But Dalton was obviously concerned to utilize Newton in his own defense, not to quote him accurately. It was polemically useful to cite the Opticks in favor of elementary principles which could not be metamorphosed and atoms of different bodies made of matter of different densities; however the roots of such thinking would seem much more complex than Dalton’s public defense suggests. Hence the unwillingness of so many chemists to embrace chemical atoms, the utility of which they appreciated, but the ontological base of which they could not understand. This utility, particularly in its visual aspect, was to prove enormous, especially later in the century, when organic chemistry knew its greatest triumphs. Indeed the eventual successes of the chemical atomic theory were so great as to hide from many subsequent chemists and commentators the ambiguities and uncertainties of Dalton’s own writings on the subject. The result is that we still do not possess an adequate understanding of the development of Dalton’s own thought, the context in which the first debates on chemical atomic theory took place, or the earlier traditions underlying the continuing unease of the later nineteenth century.

While Dalton’s creative science stands at the center of his achievement, other facets of his life are of equal interest. The most obvious are his role in the Manchester Literary and Philosophical Society, his activity in other societies, his civil recognition, his public lecture course, and his changing place in the mythology of science. Each reflects a different light on the professionalization of the scientific enterprise.

The Manchester Literary and Philosophical Society, England’s oldest continuing scientific society apart from the Royal Society of London, was founded in 1781. The first, it was also the foremost of the rash of such societies founded in the growing manufacturing centers of England as the Industrial Revolution progressed. Boldly provincial, utilitarian, and technological in its orientation, it nourished creative science of the highest caliber, of which John Dalton’s work is the best–known but by no means the solitary example. While Dalton was ultimately to bring great prestige to it, the society in its turn played an early and critical a role in his intellectual development.

The “Lit and Phil” offered legitimation, audience, encouragement, and reward to the scientific practitioner at a time when science still enjoyed little public recognition as a profession. Not only did the society offer an extensive and up–to-date library, a vehicle of publication (the Manchester Memoirs, which were eventually to contain twenty–six of the 117 papers Dalton read before the “Lit and Phil”), and, from 1800, a home for Dalton’s apparatus and experimental labors. It also offered critical encouragement and personal reward. This last may be seen objectified and institutionalized in Dalton’s rise form member, to secretary, to vice–president(1808), and finally to president (1817), in which capacity he ruled the society firmly but efficiently for the remaining twenty–seven years of his life.

If the Manchester group provided the essential environment for the flowering of Dalton’s abilities, other scientific societies were more peripheral to his life. Dalton showed considerable reluctance to be a candidate for election to the Royal Society. In 1810 he rebuffed Davy’s approaches, and he was finally elected in 1822 only when some friends proposed him with out his knowledge. He submitted but four papers to the Transactions. (When, in 1839, the last of these papers was rejected for publication, he had it privately printed with the added lament that"Cavendish, Davy, Wollaston and Gilbert are no more”) Although one of the first two recipients of the Royal Medal in 1826, in recognition of his chemical atomic theory, he appears to have been almost completely indifferent to the Society’s affairs. This indifference reflects in part the gulf in social class and professional stance between the provincial teacher committed to his science and the still largely amateur, cosmopolitan, and dilettante orientation of the Royal Society. Dalton’s attitude may be seen in his comment to Charles Cabbage that if the latter’s reformists tract on The Decline of Science (1830) “should stimulate the officers and other active members of the Royal Society to the performance of their duties it may be of essential service to the promotion of science.” Only in 1834, when he himself was at last enjoying widespread social recognition as the archetype of the dedicated and successful man of science, did Dalton finally make his formal bow at the society.

A sharp contrast appears between John Dalton’s attitude to the Royal Society and his response to other groups whose socializing functions were more clearly subordinated to the recognition of professional merit and the promotion and dissemination of science. Thus, in 1816 he willingly accepted his election as a corresponding member of the French Académie des Sciences. In 1822 he even went so far as to visit Paris, where he “had the happiness to know” such preeminent men of science as Laplance, Berthollet, Gay Lussac, Théenard, Argo, Cuvier, Brequet, Dugong, and Ampère. During this visit he took his seat at a meeting of the Academy, being introduced by GayLussac, then president. He also dined at Arcueil with the members of Berthollet’s informal but influential scientific coterie. In 1830 he enjoyed the further honor of being elected one of the eight foreign associates of the Academy, filling the place made available by the death of Davy.

An even clearer case of Dalton’s willing involvement with serious scientific endeavor is seen in his attitude to the British Association for the Advancement of Science. One of the few men of scientific distinction present at the 1831 foundation meeting in York, he played an active role in the Association’s affairs. He chaired the chemistry, mineralogy, electricity, and magnetism committee in 1832;was vice president and chairman of the chemistry section in 1833; and in 1834 was deputy chairman, and in 1835 vice–president, of the chemistry and mineralogy committee. In 1836 he was again vice–president of the chemistry section and became a vice–president-elect of the Association. His activity was abruptly halted by two severe paralytic attacks in April 1837. The attacks left Dalton a semi–invalid for the rest of his days, unable to undertake the strenuous traveling necessary to follow the Association in its journeyings. When the annual meeting came to Manchester in 1842, he was too feeble to take on the role of president. The sentiments expressed at that time, however, and the presidential address that followed his death in 1844 leave no doubt as to Dalton’s importance to the early life of the Association. His involvement clearly illustrates one way in which England’s emerging group of professional scientists was seeking to create and consolidate the institutional forms their professional life demanded.

Dalton’s later life also illustrates the growing recognition that society was beginning to offer the man of science. Impeccable scientific credentials, a blameless personal life, and in old age a calm and equable temperament all combined to make Dalton a peculiarly suitable recipient of civil honor. In 1832, in connection with the British Association meeting in the town, the University of Oxford conferred on him the honorary degree of D. C. L. In 1834 he received an Edinburgh L. L. D. under similar circumstances. Thanks to the efforts of Charles Babbage, William Henry, and others, he was awarded a government pension of £150 per annum in 1833; the amount was doubled in 1836. Meanwhile, Manchester was not to be outdone in recognition of its adopted savant: A committee raised £2,000 for a statue, and in May 1834 Dalton duly went to London to sit for the fashionable sculptor Chantrey. The esteem newly granted the successful man of science is seen in the way that “the Quaker Doctor” was even presented at Court in the course of this visit.

If Dalton in old age enjoyed widespread recognition and honor, he also knew a rather different public role throughout his life. His earliest public lectures in Kendal were in the tradition of those broadly popular performances by itinerant lecturers on natural philosophy, of which the importance to the developing structure of British science has yet to be fully appreciated. His lectures at the Royal Institution in 1803 were of similar type, although reflecting more closely Dalton’s own special concerns. His later courses were often more directly based on his own immediate research interests, reflecting in part the growing sophistication and expertise of the potential audience. The range and importance of this aspect of Dalton’s work may be seen from a (probably incomplete) listing of the courses he gave: in Manchester in 1805 and 1806; Edinburgh and Glasgow in 1807; Manchester in 1808; London in 1810; Manchester in 1811 and 1814; Birmingham in 1817; Manchester in 1820; Leeds in 1823; Manchester in 1825, 1827, 1828, 1829, 1834, and 1835. From 1824 he was also lecturer in pharmaceutical chemistry for Thomas Turner’s Manchester School of Medicine and Surgery, an association continued for at least six years. Among other things, these varied lecture courses added substantially to Dalton’s income—for instance, the Royal Institution paid him eighty guineas, while his first Manchester lectures showed a profit of £58.2.0.

With such an extensive repertoire in addition to his teaching and research, Dalton over the years built up a substantial collection of apparatus. If his predilection was for bold generalizations and elegantly simple experimental tests, he had a considerable range of equipment available, whether in Kendal, at the Manchester New College, or in his laboratory at the Literary and Philosophical Society. In addition, he knew that success as a public lecturer demanded adequate demonstrations. Thus, on one visit to London alone (in 1805) he spent £200 on lecture equipment. The young Benjamin Silliman, while on his first European tour, expressed a suitable awe at the elaborate experiments accompanying Dalton’s subsequent Manchester lectures.

Many writers on Dalton have exaggerated the supposed poverty of his training and his lack of experimental equipment. Similarly, the oft–told story of his contempt for books would seem without foundation. His early acquaintance with John Gough, the facilities of the Kendal school, and his eager appreciation of Manchester’s libraries all speak of his thirst for, and appreciation of, a wide range of knowledge and information. The sale catalog of his belongings confirms the picture. Despite the excellent libraries so freely available to him. Dalton’s own collection eventually contained no less than 700 volumes, largely but by no means solely restricted to science.

In all these ways—lectures, apparatus, books—John Dalton reveals the incipient professionalism of a new class in English science. Without benefit of Oxford, Cambridge, or medicine, from which natural knowledge had previously drawn its devotees, such men as he could not afford a casual or dilettante attitude toward their work. His livelihood and entrée to more rewarding social circles depended too acutely on that mixture of entrepreneurial talent and professional scientific competence which one may also see displayed in the careers of Humphry Davy and Michael Faraday.

If his public activity knew no tumultuous crises, Dalton’s private life waseven more unruffled. As an active and ambitious youth, he had little free time. His Kendal thoughts on trying medicine or law were encouraged by the knowledge that the emoluments of a Quaker school–master “are not sufficient to support a small family with the decency and reputation I could wish.” By 1794 he was saying instead that “my head is too full of triangles, chymical processes, and electrical experiments, etc., to think much of marriage.” Lacking a wife and family of his own, he became deeply attached to several relatives and associates. His brother Jonathan, William Henry, Peter Ewart, and Peter Clare were among his closest friends. In addition, his frequent walking tours, lecture trips, and visits to Quaker meetings made him known to a wide circle, although his quiet and reserved manner was often mistaken for indifference or uncouthness by strangers, especially in his later years.

When Dalton died in July 1844, he was accorded a civic funeral with full honors. His body first lay in state in Manchester Town Hall for four days while more than 40,000 people filed past his coffin. The funeral procession included representatives of the city’s major civic, commercial, and scientific bodies, and shops and offices were closed for the day as a mark of respect. This attention was in part a measure of Dalton’s intellectual stature and in part a display of civic pride by what in his lifetime had become the preeminent provincial city. It was also a recognition of the new and growing importance of the man of science both to the nation at large and, more especially, to its manufactures and commerce.

This recognition unfortunately did not ensure a competent biography. W. C. Henry, Dalton’s literary executor, eventually produced a hurried and careless work that has not yet been adequately replaced. The interest displayed in Dalton by members of Manchester University’s flourishing school of chemistry late in the nineteenth century did lead to some new studies; these studies, however, systematically under–valued Dalton’s youthful experiences. Instead they concentrated heavily on chemistry and on finding an account of the origins of the chemical atomic theory that would emotionally and heuristically satisfy the desire to see in Dalton the lonely pioneer chemist remote from, but also anticipating, Manchester’s later glory. The confusion thus generated is not yet dispersed. Even so, we can now recognize that John Dalton is best viewed not as the uncouth and ill–educated amateur they saw but as an early provincial prototype of that fateful invention of the nineteenth century, the professional scientist.

BIBLIOGRAPHY

Dalton’s three published books are Meteorological Observations and Essays (London, 1793; 2nd ed., 1834); Elements of English Grammar (Manchester, 1801; 2nd ed., London 1803); and the classic New System of Chemical Philosophy (London, pt. 1, 1808; pt. 2, 1810; vol. II, pt. 1, 1827; 2d ed. of pt. 1, 1842). His considerable output of papers, notes, etc. is adequately catalogued in A. L. Smyth, John Dalton 1766–1844. A Bibliography of Works by and About Him (Manchester, 1966). Smyth also provides a useful guide to the enormous secondary literature and an adequate, but incomplete, list of surviving Dalton manuscripts. The great bulk of the manuscripts was destroyed in World War II, but important extracts from Dalton’s scientific notebooks are available in H. E. Roscoe and A. Harden, New View of the origins of Dalton’s Atomic Theory… Now for the First Time Published from Manuscript (London, 1896), repr. with an intro. by A. Thackray (New York, 1970). A valuable record of current scholarly opinion on Dalton’s achievements is available in the bicentennial volume entitled John Dalton and the Progress of Science, D. S. L. Cardwell, ed,. (Manchester, 1968). Also relevant is the closing section of A. Thackray, Atoms and Powers: An Essay on Newtonian Matter–Theory and the Development of Chemistry (Cambridge, Mass., 1970). Two recent popular biographies of Dalton are F. Greenaway. John Dalton and the Atom (London, 1966), and E. Patterson, John Dalton and the Atomic Theory (New York, 1970).

Arnold Thackray

Dalton, John

ENGLISH CHEMIST
1766–1844

The fundamental idea of modern chemistry is that matter is made up of atoms of various sorts, which can be combined and rearranged to produce different, and often novel, materials. The person responsible for "this master-concept of our age" (Greenaway, p. 227) was John Dalton. He applied Newton's idea of small, indivisible atoms to the study of gases in the atmosphere and used it to advance a quantitative explanation of chemical composition. If French chemist Antoine Lavoisier started the chemical revolution, then it was Dalton who put it on a firm foundation. His contemporary, the Swedish chemist Jöns J. Berzelius, said: "If one takes away from Dalton everything but the atomic idea, that will make his name immortal."

John Dalton was born on or about September 6, 1766, to Quaker parents, in Eaglesfield, a remote village in the north of England. He was largely self-educated, and learned most of his mathematics and science by teaching others. He studied mathematics in a local school until the age of 11, started his own school at the age of 12, and at 15 joined his brother Jonathan in teaching at, and later running, a Quaker school in Kendal. The Quakers were a small dissenting (from the established Church of England) sect, and Dalton was thus a nonconformist, like the scientists Joseph Priestley and Michael Faraday. Dalton was taught and influenced by fellow Quakers Elihu Robinson, a wealthy instrument maker, and John Gough, a blind polymath. In Kendal Gough taught the young Dalton Latin, Greek, French, mathematics, and science, and in return Dalton read to him from books and newspapers. Gough encouraged Dalton to study natural phenomena and to keep a meteorological journal, which Dalton began on March 24, 1787. Dalton maintained this journal methodically for the rest of his life, making his last meteorological observations on his deathbed. He made over 200,000 measurements over a period of fifty-seven years, and a neighbor in Manchester is supposed to have said that she was able to set her clock by Dalton's daily appearance to take the temperature. Dalton's meteorological observations launched his scientific career and provided the material for his first book, Meteorological Observations and Essays (1793).

In 1793 Dalton moved to Manchester, becoming professor of mathematics and natural philosophy at New College. He stayed there until 1799, at which time he resigned in order to devote more time to research. He continued to teach private pupils in order to earn a living. According to legend, a visiting French scientist once traveled to Manchester to meet the famous Dalton. He had difficulty in finding him, finally locating him in a small house in an obscure street. He then had to wait while Dalton finished teaching a lesson in mathematics to a small boy.

Dalton stayed in Manchester for the rest of his life, and it was there that he did most of his important work, the results of which were published in the Memoirs of the Manchester Literary and Philosophical Society (MLPS). His first scientific paper, published by the MLPS in 1798, described his red-green color blindness. Dalton is said to have purchased for his mother a pair of what he thought were dull-colored stockings—Quakers did not wear bright colors—which she could not wear because they were scarlet. This misadventure motivated Dalton to investigate his color recognition deficiency. He was the first to describe red-green color blindness, sometimes known as Daltonism.

Dalton's study of the atmosphere, prompted by his weather measurements, led him in 1803 to his law of partial pressures (in a mixture of gases, each gas acts as an independent entity), and subsequently to the study of the combining of elements. He compared marsh gas (methane, CH₄) with olefiant gas (ethane, C₂H₄), and found that ethane contained exactly double the mass of carbon to the same mass of hydrogen. It is this relationship between the two gases that guided him to his law of multiple proportions. He imagined a chemical atomic model, whereby one atom of an element could combine only with one, two, or three atoms (and so on) of a second element, the combinations forming distinct compounds. He visualized atoms as small hard balls and constructed small wooden models to illustrate how they combined. He invented symbols that enabled him (and others) to notate chemical formulas ✷. Dalton drew up the first list of atomic weights. Dalton's ideas about atoms and their combinations were first aired in 1803 at meetings of the MLPS, mentioned in Thomas Thomson's System of Chemistry (1807), and finally published by Dalton in his most important book, New System of Chemical Philosophy (1808).

✷ See an image of Dalton's symbols in the Atoms article.

Dalton's most significant work was done between 1795 and 1805, but fame came later—when the importance of his atomic theory was realized. He became a member of the Royal Society in 1822, received its first Royal Medal in 1826, and was honored with a state pension in 1833, among other honors. He died on July 27, 1844, and 40,000 people attended his funeral.

see also Berzelius, JÖns Jakob; Faraday, Michael; Lavoisier, Antoine; Priestley, Joseph.

Peter E. Childs

Bibliography

Cardwell, D. S. L., ed. (1968). John Dalton and the Progress of Science. Manchester, U.K.: Manchester University Press.

Greenaway, Frank (1966). John Dalton and the Atom. London: Heinemann.

Henry, William C. (1854). Life of Dalton. London: The Cavendish Society.

Millington, J. P. (1906). John Dalton. London: J. M. Dent.

Internet Resources

LeMoyne College, Department of Chemistry. Classic Chemistry compiled by Carmen Giunta. "John Dalton (1766–1844): A New System of Chemical Philosophy [excerpts]." Available from <http://webserver.lemoyne.edu/faculty/giunta/Dalton.html>.

Walnut Valley (California) Unified School District. Diamond Bar High School. "John Dalton." Available from <http://dbhs.wvusd.k12.ca.us/AtomicStructure/Dalton.html>.

Walnut Valley (California) Unified School District. Diamond Bar High School. "Photo Gallery." Available from <http://dbhs.wvusd.k12.ca.us/Gallery/>.

John Dalton

The English chemist John Dalton (1766-1844) provided the beginnings of the development of a scientific atomic theory, thus facilitating the development of chemistry as a separate science. His contributions to physics, particularly to meteorology, were also significant.

John Dalton was the youngest of three surviving children of a Quaker handloom weaver. He was born about Sept. 6, 1766 (no exact record exists), in Eaglesfield. Until he was 11, he attended school, then at the age of 12 became a teacher. For about a year he next worked as a farm helper, but at 15 he returned to teaching, privately for the most part, pursuing it as a career for the remainder of his life.

In his work Dalton used relatively simple equipment and has been accused of being "a very coarse experimenter." However, he had a gift for reasoning and for drawing correct conclusions from imperfect experiments. He himself attributed his success primarily to simple persistence.

Studies in Meteorology

Dalton's lifelong interest in meteorology did much to make that study a science. He began keeping records of the local weather conditions—atmospheric pressure, temperature, wind, and humidity—in 1787 and maintained them for 57 years until his death. During this time he recorded more than 200,000 values, using equipment which for the most part was made by him.

Dalton's interest in the weather gave him a special interest in mixtures of gases, and his earliest studies were concerned with atmospheric physics. The formulation of his law of partial pressures (Dalton's law) was announced in 1803. It defined the pressure of a mixture of gases as the sum of the pressures exerted by each component solely occupying the same space. In 1800 he studied the heating and cooling of gases resulting from compression and expansion, and in 1801 he formulated a law of the thermal expansion of gases. His work on water vapor concentration in the atmosphere, using a homemade dew-point hygrometer, and his 1804 study of the effect of temperature on the pressure of a vapor brought him international fame.

Developing the Atomic Theory

The formulation of the atomic theory, Dalton's greatest achievement, was developed gradually, almost inadvertently, through a series of observations resulting from his preoccupation with gases. It began with an attempt to explain why the constituents of a gaseous mixture remain homogeneously mixed instead of forming layers according to their density. The theory was first alluded to in a paper presented before the Manchester Literary and Philosophical Society in 1803 on the absorption of gases by water and other liquids. In the last section of the paper was the first table of atomic weights. The acceptance of his theory prompted Dalton to expand it further, and finally he published it in his New System of Chemical Philosophy (1808). Although William Higgins claimed priority over Dalton, the consensus is that Dalton conceived the idea that the atoms of different elements are distinguished by differences in their weight. As contrasted to others who may have vaguely glimpsed the principle, Dalton presented it as a universal and consistent fact and applied it to the explanation of chemical phenomena.

Other, less significant contributions were his pioneering investigation of thermal conductivity in liquids and his 1794 paper in which he discussed color blindness.

Later Life

Dalton lived a simple life, kept to the doctrines of his Quaker faith, and never married. During most of his life he had little money and was almost excessively economical; however, by tutoring and doing routine chemical work at low pay his few wants were met. He had no flair for lecturing: his voice was rather harsh, and he was inclined to be rather stiff and awkward in manner. He is said to have had no grace in conversation or in writing. Despite his lack of these social assets, he apparently lived a quite happy life and had many friends.

In 1810 Dalton refused an invitation to join the Royal Society but was finally elected in 1822 without his knowledge. As his fame grew, he received many honors, including a doctor's degree from Oxford in 1832, at which time he was presented to King William IV. For this occasion he had to wear the famous scarlet regalia of Oxford, which fortunately looked gray to his color-blind eyes and therefore was acceptable to him as an orthodox Quaker.

In 1837 he suffered a damaging stroke; the following year another left him with impaired speech. A final stroke came on the night of July 26, 1844.

Further Reading

The most recent biography of Dalton is Frank Greenaway, John Dalton and the Atom (1966). See also L. J. Neville-Polley, John Dalton (1920), and Bernard Jaffe, Crucibles (1930). The background for Dalton's work, its influence, and biographical and historical material are contained in David Stephen L. Cardwell, ed., John Dalton and the Progress of Science (1968), which comprises essays presented by Dalton scholars at a conference marking the bicentenary of Dalton's birth. Dalton's scientific achievements are summarized in James R. Partington, History of Chemistry, vol. 3 (1962). A. L. Smyth, John Dalton, 1766-1844: A Bibliography of Works by and about Him, was published in 1966. □

John Dalton

1766-1844

English Chemist, Physicist and Meteorologist

John Dalton proposed the atomic theory of matter as a result of his investigations of the atmosphere. By viewing matter as made up of indivisible particles each with their own particular weight, Dalton offered a way to understand chemical reactions. This led to the rapid development of chemistry in the nineteenth century.

Dalton was born into a family of devout Quakers in a small village in the Lakes District of northwest England. His Quaker heritage, with its emphasis on education and interest in science, played a key role in Dalton's life. After completing all the schooling he could obtain in his village, Dalton left in 1781 to replace his elder brother as an assistant in a Quaker boarding school in Kendal, the principal town in the Lakes District. The school had a very good library as well as scientific equipment that allowed Dalton to continue his education by reading and experimentation.

While in Kendal Dalton was befriended by a fellow Quaker, John Gough. Although blind, Gough was highly educated and had a particular interest in the natural sciences. He tutored Dalton in mathematics, meteorology, botany, Latin, Greek, and French. Dalton also began taking on teaching duties in Kendal and giving public lectures on various scientific matters, a practice he would continue through out his life. In 1792 Dalton was appointed to the position of professor of mathematics and natural philosophy at New College in Manchester. He spent the next eight years teaching various subjects before resigning in 1800 to open his own school offering private instruction in mathematics, experimental science, and chemistry.

By 1805 Dalton had essentially produced an outline of his most important contributions, his two laws concerning the gaseous state and the atomic theory of matter. What led to these discoveries was Dalton's attempt to try to understand certain aspects of the atmosphere. In particular, why was the atmosphere a homogeneous mixture of gases instead of layers of gases arranged according to their weight, the heaviest at the bottom and the lightest on the top? Another question was how water vapor could be absorbed in the atmosphere. The key to these problems was Dalton's belief in the particulate nature of matter, a concept that had been accepted by many of his contemporaries.

Dalton's insight was that the mixing of gases need not be a chemical reaction and that gases existed independently of each other in the atmosphere. This mechanical explanation for the mixing of gases led Dalton to propose in 1801 his law of partial pressures. Dalton generalized that in any mixture of gases, each component acted independently. A further principle stated by Dalton was that at constant pressure all gases will expand equally given the same quantity of heat. A similar principle was discovered by the French physicist Jacques Charles (1746-1823), who is generally given credit for this instead of Dalton.

Dalton's unorthodox view that chemical attraction was not a force in the atmosphere was met with much criticism and disbelief. In attempting to find experimental proof for his mechanical concept of the mixing of gases, Dalton relied on the work of his friend William Henry (1774-1836), who studied the effect of pressure on the amount of gas that could be dissolved in water at constant temperature. Henry's experiments showed that the amount was related to the pressure, thus showing that mixing of gases in the atmosphere had to be a mechanical phenomenon. Dalton found in his own experiments that the nature of the substance played a role in terms of how much could be dissolved at a constant pressure. What distinguished one substance from another was its mass; thus, Dalton believed that it was the size of the particles (atoms) that was the crucial determinant of an element's chemical properties. In 1803 Dalton published these results along with his measurement of the relative weights of different gases, in the process producing the first atomic weight table.

Dalton quickly realized that the concept of elements as being ultimately made up of atoms, with each atom having a unique atomic weight, was a way to explain why compounds such as water have a constant composition. Dalton also explained how atoms could react with other atoms in more than one ratio by weight and produce a series of compounds, an observation that fueled acceptance of Dalton's atomic theory.

Dalton's theory appeared in print in A New System of Chemical Philosophy, published in two parts in 1808 and 1810. Dalton was to contribute little new after 1810 and spent the rest of his life developing the theory by making measurements of atomic weights and public lectures. Dalton lived the balance of his life in Manchester and received many honors, including election to the Royal Society (1822), the Royal Society medal (1826), and honorary degrees from Oxford (1832) and Edinburgh (1834). On his death in 1844 more than 40,000 people filed past his coffin and a public funeral was held.

MARTIN D. SALTZMAN

Dalton, John (1766–1844). Chemist, atomist, quaker, and Manchester intellectual, Dalton's first interests were in meteorology and in colour blindness: being colour blind himself, he made the first scientific study of the phenomenon. From 1794 he worked at the Manchester Literary and Philosophical Society, taking private pupils to augment his income. In 1803–4 he lectured at the Royal Institution in London, and met Humphry Davy; but metropolitan life did not attract him. He wondered why the atmosphere was not a sandwich, with the densest gas at the bottom, and began thinking about the nature of the particles of matter. He concluded that each chemical element has distinct atoms, and began to work out structures of compounds, using simplicity rules. His was the first testable atomic theory, transforming chemistry in subsequent years.

David Knight