John Dalton

John Dalton was born on September 6, 1766, in the village of Eaglesfield in Cumberland, in the northwest of England. His father, Joseph Dalton, worked as a weaver, and the family belonged to the Religious Society of Friends, the Quakers ^[1]. That affiliation shaped Dalton's entire life. Quakers were barred from the English universities of Oxford and Cambridge, which admitted only members of the Church of England, so the path to formal higher education was closed to him from the start ^[2].

What Eaglesfield lacked in institutions it made up for in individual teachers. Dalton attended the local Quaker school, and his early aptitude drew the attention of Elihu Robinson, a prosperous Quaker neighbour and amateur meteorologist who tutored the boy in mathematics and natural philosophy ^[1]. The lessons took hold. At roughly twelve years of age Dalton began teaching in the village school himself, an arrangement that seems startling now but was not unheard of in rural eighteenth century England ^[2].

In 1781 he moved to Kendal, about forty miles away, to join his older brother Jonathan in teaching at a Quaker boarding school. There he came under the influence of John Gough, a blind scholar of remarkable range who instructed Dalton in Latin, Greek, French, and mathematics ^[3]. Gough also passed on the habit that would define Dalton's working life: the daily recording of weather observations. Dalton began his meteorological diary in 1787 and maintained it without interruption for fifty seven years, entering more than 200,000 observations by the time of his death ^[1].

Anyone asking who was John Dalton in 1793 would have received a modest answer: a provincial schoolteacher with a new book. That year he published Meteorological Observations and Essays, a compilation of his weather records together with essays on the aurora borealis, evaporation, and the behaviour of the atmosphere ^[3]. The same year he accepted a post teaching mathematics and natural philosophy at New College in Manchester, a dissenting academy founded to serve students excluded from the established universities ^[2].

Manchester proved decisive. The city was industrialising rapidly, and its Literary and Philosophical Society gave men of science a forum regardless of religion or social rank. Dalton was elected a member in 1794 and remained associated with the society for the rest of his life, eventually serving as its president from 1817 until his death ^[4]. Within weeks of joining he read his first major paper, Extraordinary Facts Relating to the Vision of Colours, in which he described his own inability to distinguish red from green ^[1].

The paper was the first systematic scientific study of colour blindness. Dalton proposed, incorrectly, that the fluid inside his eyeball was tinted blue, and he directed that his eyes be examined after his death to test the idea. The examination disproved his hypothesis, but the condition became widely known as Daltonism, a name still used in several languages. In 1995, a century and a half later, DNA extracted from his preserved eye tissue confirmed that he had deuteranopia, a deficiency of the retinal receptors sensitive to medium wavelengths of light ^[5].

In 1800 he resigned from New College, which was in financial difficulty, and supported himself thereafter as a private tutor in mathematics and chemistry. The independence suited him. Freed from institutional duties, he gave his mornings to pupils and his remaining hours to experiment ^[2].

Dalton's route to atomic theory ran through the weather. His long preoccupation with the atmosphere led him to ask how gases mix, and in 1801 he formulated what is now called Dalton's law of partial pressures: in a mixture of gases, each gas exerts the same pressure it would exert if it occupied the container alone, and the total pressure is the sum of these individual pressures ^[3]. The law remains a staple of chemistry and physics teaching more than two centuries later.

From gases he moved to the composition of compounds. Dalton observed that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other stand in ratios of small whole numbers, a regularity known as the law of multiple proportions ^[6]. To explain it he revived and transformed an ancient idea. Matter, he argued, consists of indivisible atoms; all atoms of a given element are identical in weight; atoms of different elements differ in weight; and chemical compounds form when atoms combine in fixed whole number ratios ^[1].

The crucial innovation was quantitative. Philosophers since Democritus had speculated about atoms, but Dalton attached a measurable property, relative weight, to each kind. In 1803 he drew up the first table of relative atomic weights, taking hydrogen as unity, and he presented the full theory in A New System of Chemical Philosophy, published in parts beginning in 1808 ^[6]. Many of his individual values were wrong, partly because he assumed the simplest possible formulas (water, for instance, as one hydrogen atom joined to one oxygen atom), yet the framework survived every correction. Among John Dalton achievements, the atomic theory stands first: it gave chemists a common accounting system for matter and made chemical formulas and equations possible ^[3].

His honours accumulated slowly, then all at once. The Royal Society elected him a fellow in 1822 and awarded him one of its first Royal Medals in 1826 for the atomic theory ^[4]. The French Academy of Sciences named him a foreign associate, and in 1832 the University of Oxford conferred an honorary doctorate on the Quaker who could never have enrolled there as a student ^[2].

Dalton never married. He lived for more than a quarter of a century as a lodger in the household of the Reverend William Johns, a Unitarian minister in Manchester, and his routine scarcely varied: tutoring, laboratory work, the daily weather reading, and a game of bowls on Thursday afternoons ^[2]. Contemporaries described him as plain in dress and manner, reserved with strangers, and indifferent to fashion or luxury, traits consistent with his lifelong Quaker practice ^[1].

His colour blindness supplied the one famous anecdote of his private life. Quakers dressed in sober colours, yet Dalton is said to have once appeared in a bright red garment, unable to perceive that its hue was anything but drab. Whatever the truth of particular stories, he was frank about the condition in print and treated his own eyes as experimental instruments ^[5].

He remained close to his brother Jonathan, who shared his defective colour vision, and he kept up his connections to Cumberland throughout his life. Money never interested him much. Even after the British government granted him a civil list pension in 1833, raised in 1836, he continued the same frugal habits he had learned as a weaver's son ^[4].

Recognition arrived in forms that sat oddly with Dalton's plain faith. In 1834 he was presented at court to King William IV, an occasion requiring dress that no Quaker could ordinarily wear; the difficulty was resolved by his appearing in the scarlet robes of his Oxford doctorate, a colour his eyes rendered inoffensively muted ^[2]. Manchester raised money for a statue of him by the sculptor Francis Chantrey, which was installed while he was still alive, a rare tribute for a working scientist ^[4].

His health began to fail in 1837, when he suffered the first of several strokes that left his speech impaired and his hand unsteady. He nevertheless kept working. The meteorological diary continued, and he made his final entry, recording the rainfall, on July 26, 1844, the evening before he died ^[1].

Dalton died in Manchester on July 27, 1844, at the age of 77. The city's response revealed how far the weaver's son had travelled: his body lay in state in Manchester Town Hall, where tens of thousands of people filed past, and the funeral procession to Ardwick Cemetery stretched for the better part of a mile ^[4]. It was an extraordinary civic farewell for a man who had spent his life avoiding display.

Modern chemistry is written in Dalton's grammar. The idea that elements consist of atoms with characteristic masses, combining in fixed ratios, underlies chemical formulas, stoichiometry, and the periodic table that Dmitri Mendeleev organised a generation later ^[6]. Twentieth century physics revised the details, showing that atoms are divisible and that isotopes of one element differ in mass, but these were refinements of a picture Dalton had made thinkable in the first place ^[3].

His name is embedded in the vocabulary of science. The dalton (symbol Da) is the standard unit of atomic and molecular mass, used daily in chemistry and molecular biology, and Dalton's law of partial pressures appears in every introductory textbook and in practical fields from anaesthesiology to scuba diving ^[6]. Daltonism remains a common term for red green colour blindness, and his 1794 paper is treated as the founding document of the scientific study of colour vision ^[5].

Manchester has kept his memory in stone and in institutions. Streets, buildings, and lecture series in the city bear his name, and the Manchester Literary and Philosophical Society preserves his association as its longest serving president ^[4]. Readers of any John Dalton biography tend to notice the same striking fact: a man barred from university by his religion, trained largely by a blind tutor and his own weather notebook, supplied the central organising idea of an entire science. Among the more memorable John Dalton facts is that his eye, preserved to test his own theory of his colour blindness, ended up confirming a genetic diagnosis 150 years after his death ^[5].