John Dalton FRS (Bengali: জন ডালটন) was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness (sometimes referred to as Daltonism, in his honour). He was born in 6th September 1766 and died in 27 July 1844.Early life
John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth, Cumberland, England. The son of a weaver, he joined his older brother Jonathan at age 15 in running a Quaker school in nearby Kendal.
Around 1790 Dalton seems to have considered taking up law or medicine,
but his projects were not met with encouragement from his relatives – Dissenters
were barred from attending or teaching at English universities – and he
remained at Kendal until, in the spring of 1793, he moved to Manchester. Mainly through John Gough, a blind philosopher and polymath to whose informal instruction he owed much of his scientific knowledge, Dalton was appointed teacher of mathematics and natural philosophy at the "New College" in Manchester, a dissenting academy.
He remained in that position until 1800, when the college's worsening
financial situation led him to resign his post and begin a new career in
Manchester as a private tutor for mathematics and natural philosophy.
Dalton's early life was highly influenced by a prominent Eaglesfield Quaker named Elihu Robinson, a competent meteorologist and instrument maker, who got him interested in problems of mathematics and meteorology. During his years in Kendal, Dalton 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 57 years, he entered more than 200,000 observations. He also rediscovered George Hadley's theory of atmospheric circulation (now known as the Hadley cell) around this time. Dalton's first publication was Meteorological Observations and Essays
(1793), which contained the seeds of several of his later discoveries.
However, in spite of the originality of his treatment, little attention
was paid to them by other scholars. A second work by Dalton, Elements of English Grammar, was published in 1801.
Colour blindness
In 1794, shortly after his arrival in Manchester, Dalton was elected a member of the Manchester Literary and Philosophical Society, the "Lit & Phil", and a few weeks later he communicated his first paper on "Extraordinary facts relating to the vision of colours", in which he postulated that shortage in colour perception was caused by discoloration of the liquid medium of the eyeball.
Atomic theory
In 1800, Dalton became a secretary of the Manchester Literary and
Philosophical Society, and in the following year he orally presented an
important series of papers, entitled "Experimental Essays" on the
constitution of mixed gases; on the pressure of steam and other vapours at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases. These four essays were published in the Memoirs of the Lit & Phil in 1802.
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 pressure of steam at
various points between 0 and 100 °C (32 and 212 °F), Dalton concluded
from observations on the vapour pressure
of six different liquids, that the variation of vapour pressure for all
liquids is equivalent, for the same variation of temperature, reckoning
from vapour of any given pressure.
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.
Public and personal life
Before he had propounded the atomic theory, he had already attained a
considerable scientific reputation. In 1803, 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. However,
some witnesses reported that he was deficient 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, Sir Humphry Davy asked him to offer himself as a candidate for the fellowship of the Royal Society,
but Dalton declined, possibly for financial reasons. However, 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 Académie des Sciences, and in 1830 he was elected as one of its eight foreign associates in place of Davy. In 1833, Earl Grey's government conferred on him a pension of £150, raised in 1836 to £300.
Dalton never married and had only a few close friends, all in all as a Quaker he lived a modest and unassuming life.
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. In 1822 he paid a short visit to
Paris, where he met many distinguished resident scientists. He attended
several of the earlier meetings of the British Association at York, Oxford, Dublin and Bristol.
Five main points of Dalton's atomic theory
- Elements are made of extremely small particles called atoms.
- Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
- Atoms cannot be subdivided, created, or destroyed.
- Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
- In chemical reactions, atoms are combined, separated, or rearranged.
