John Dalton FRS (6 September 1766 – 27 July 1844) 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).
Dalton was born into a Quaker family at Eaglesfield, near Cockermouth in Cumbria, 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 from 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.[1] 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.
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 discolouration of the liquid medium of the eyeball. In fact, a shortage of colour perception in some people had not even been formally described or officially noticed until Dalton wrote about his own. Although Dalton's theory lost credence in his own lifetime, the thorough and methodical nature of his research into his own visual problem was so broadly recognized that Daltonism became a common term for colour blindness. Examination of his preserved eyeball in 1995 demonstrated that Dalton actually had a less common kind of colour blindness, deuteroanopia, in which medium wavelength sensitive cones are missing (rather than functioning with a mutated form of their pigment, as in the most common type of colour blindness, deuteroanomaly). 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.
Five main points of Dalton's Atomic Theory
Elements are made of tiny particles called atoms.
All atoms of a given element are identical.
The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative weights.
Atoms of one element can combine with atoms of other elements to form chemical compounds; a given compound always has the same relative numbers of types of atoms.
Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.
Dalton proposed an additional "rule of greatest simplicity" that created controversy, since it could not be independently confirmed.
When atoms combine in only one ratio, "..it must be presumed to be a binary one, unless some cause appear to the contrary".
This was merely an assumption, derived from faith in the simplicity of nature. No evidence was then available to scientists to deduce how many atoms of each element combine to form compound molecules. But this or some other such rule was absolutely necessary t