Meteorology Dalton's early life was influenced by a prominent Quaker, Elihu Robinson, a competent
meteorologist and instrument maker, from Eaglesfield,
Cumberland, who interested him in problems of mathematics and meteorology. During his years in Kendal, Dalton contributed solutions to problems and answered questions on various subjects in ''
The Ladies' Diary and the Gentleman's Diary''. In 1787 at age 21 he began his meteorological diary in which, during the succeeding 57 years, he entered more than 200,000 observations. He rediscovered
George Hadley's theory of atmospheric circulation (now known as the
Hadley cell) around this time. In 1793 Dalton's first publication,
Meteorological Observations and Essays, contained the seeds of several of his later discoveries but despite the originality of his treatment, little attention was paid to them by other scholars. A second work by Dalton,
Elements of English Grammar (or
A new system of grammatical instruction: for the use of schools and academies), was published in 1801.
Measuring mountains After leaving the
Lake District, Dalton returned annually to spend his holidays studying meteorology, something which involved a lot of hill-walking. Until the advent of aeroplanes and
weather balloons, the only way to make measurements of temperature and humidity at altitude was to climb a mountain. Dalton estimated the height using a
barometer. The
Ordnance Survey did not publish maps for the Lake District until the 1860s. Before then, Dalton was one of the few authorities on the heights of the region's mountains. He was often accompanied by
Jonathan Otley, who also made a study of the heights of the local peaks, using Dalton's figures as a comparison to check his work. Otley published his information in his map of 1818. Otley became both an assistant and a friend to Dalton.
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. As both he and his brother were
colour blind, he recognised that the condition must be hereditary. Although Dalton's theory was later disproven, his early research into colour vision deficiency was recognized after his lifetime. Examination of his preserved eyeball in 1995 demonstrated that Dalton had
deuteranopia, a type of
congenital red-green color blindness in which the gene for medium wavelength sensitive (green)
photopsins is missing.
Gas laws In 1800, Dalton became secretary of the Manchester Literary and Philosophical Society, and in the following year he presented an important series of lectures, entitled "Experimental Essays" on the constitution of mixed gases; the
pressure of steam and other
vapours at different temperatures in a
vacuum and in
air; on
evaporation; and on the
thermal expansion of gases. The four essays, presented between 2 and 30 October 1801, were published in the
Memoirs of the Literary and Philosophical Society of Manchester in 1802. The second essay opens with the remark, After describing experiments to ascertain the pressure of steam at various points between , Dalton concluded from observations of 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, He enunciated
Gay-Lussac's law, published in 1802 by
Joseph Louis Gay-Lussac (Gay-Lussac credited the discovery to unpublished work from the 1780s by
Jacques Charles). In the two or three years following the lectures, Dalton published several papers on similar topics. "On the Absorption of Gases by Water and other Liquids" (read as a lecture on 21 October 1803, first published in 1805) contained his law of partial pressures now known as
Dalton's law. as depicted in John Dalton's
A New System of Chemical Philosophy (1808) on page 546, 547 and 589.
Atomic theory Arguably the most important of all Dalton's investigations are concerned with the
atomic theory in chemistry. While his name is inseparably associated with this theory, the origin of Dalton's atomic theory is not fully understood. The theory may have been suggested to him either by researches on
ethylene (
olefiant gas) and
methane (
carburetted hydrogen) or by analysis of
nitrous oxide (
protoxide of azote) and
nitrogen dioxide (
deutoxide of azote), both views resting on the authority of
Thomas Thomson. From 1814 to 1819, Irish chemist
William Higgins claimed that Dalton had plagiarised his ideas, but Higgins' theory did not address relative atomic mass. Recent evidence suggests that Dalton's development of thought may have been influenced by the ideas of another Irish chemist
Bryan Higgins, who was William's uncle. Bryan believed that an atom was a heavy central particle surrounded by an atmosphere of
caloric, the supposed substance of heat at the time. The size of the atom was determined by the diameter of the caloric atmosphere. Based on the evidence, Dalton was aware of Bryan's theory and adopted very similar ideas and language, but he never acknowledged Bryan's anticipation of his caloric model. However, the essential novelty of Dalton's atomic theory is that he provided a method of calculating relative atomic weights for the chemical elements, which provides the means for the assignment of molecular formulas for all chemical substances. Neither Bryan nor William Higgins did this, and Dalton's priority for that crucial innovation is uncontested. The main points of Dalton's atomic theory, as it eventually developed, are: • 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. In his first extended published discussion of the atomic theory (1808), Dalton proposed an additional (and controversial) "rule of greatest simplicity". This rule could not be independently confirmed, but some such assumption was necessary in order to propose formulas for a few simple molecules, upon which the calculation of atomic weights depended. This rule dictated that if the atoms of two different elements were known to form only a single compound, like hydrogen and oxygen forming water or hydrogen and nitrogen forming ammonia, the molecules of that compound shall be assumed to consist of one atom of each element. For elements that combined in multiple ratios, such as the then-known two oxides of carbon or the three oxides of nitrogen, their combinations were assumed to be the simplest ones possible. For example, if two such combinations are known, one must consist of an atom of each element, and the other must consist of one atom of one element and two atoms of the other. 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 molecules. But this or some other such rule was absolutely necessary to any incipient theory, since one needed an assumed molecular formula in order to calculate relative atomic weights. Dalton's "rule of greatest simplicity" caused him to assume that the formula for water was OH and
ammonia was NH, quite different from our modern understanding (H2O, NH3). On the other hand, his simplicity rule led him to propose the correct modern formulas for the two oxides of carbon (CO and CO2). Despite the uncertainty at the heart of Dalton's atomic theory, the principles of the theory survived.
Relative atomic weights s as depicted in John Dalton's
A New System of Chemical Philosophy (1808) on page 238 Dalton published his first table of relative
atomic weights containing six elements (hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus), relative to the weight of an atom of hydrogen conventionally taken as 1. Compounds were listed as binary, ternary, quaternary, etc. (molecules composed of two, three, four, etc. atoms) in the
New System of Chemical Philosophy depending on the number of atoms a compound had in its simplest, empirical form. Dalton hypothesised the structure of compounds can be represented in whole number ratios. So, one atom of element X combining with one atom of element Y is a binary compound. Furthermore, one atom of element X combining with two atoms of element Y or vice versa, is a ternary compound. Many of the first compounds listed in the
New System of Chemical Philosophy correspond to modern views, although many others do not. Dalton used his own symbols to visually represent the atomic structure of compounds. They were depicted in the
New System of Chemical Philosophy, where he listed 21 elements and 17 simple molecules.
Other investigations Dalton published papers on such diverse topics as rain and dew and the origin of springs (hydrosphere); on heat, the colour of the sky, steam and the
reflection and
refraction of light; and on the grammatical subjects of the
auxiliary verbs and
participles of the English language.
Experimental approach As an investigator, Dalton was often content with rough and
inaccurate instruments, even though better ones were obtainable. Sir
Humphry Davy described him as "a very coarse experimenter", who "almost always found the results he required, trusting to his head rather than his hands." On the other hand, historians who have replicated some of his crucial experiments have confirmed Dalton's skill and precision. In the preface to the second part of Volume I of his
New System, he says he had so often been misled by taking for granted the results of others that he determined to write "as little as possible but what I can attest by my own experience", but this independence he carried so far that it sometimes resembled lack of receptivity. Thus he distrusted, and probably never fully accepted,
Gay-Lussac's conclusions as to the combining volumes of gases. He held unconventional views on
chlorine. Even after its elementary character had been settled by Davy, he persisted in using the atomic weights he himself had adopted, even when they had been superseded by the more accurate determinations of other chemists. He always objected to the chemical notation devised by
Jöns Jacob Berzelius, although most thought that it was much simpler and more convenient than his own cumbersome system of circular symbols. == Other publications ==