John Dalton

Verified Timeline

Lore & Background

In 1794, shortly after his arrival in Manchester, Dalton was elected a member of the Manchester Literary and Philosophical Society, 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, 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. 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 second essay opens with the 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.' His paper '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. Arguably the most important of all Dalton's investigations are concerned with the atomic theory in chemistry. 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.

Reader's Guide

Dalton's significance lies in his transformation of chemistry from a qualitative to a mathematical science. By proposing that each chemical element consists of identical atoms of characteristic weight and that compounds form in fixed whole-number proportions, he provided a quantitative framework that became the basis of modern chemical thought. His work on gas laws, including the first empirical law of partial pressures (Dalton's law), and his studies of vapor pressure and gas solubility advanced physics and meteorology. His investigation into his own color blindness led to the first scientific description of the condition, still known as Daltonism in several languages. Elected a Fellow of the Royal Society in 1822 and awarded its Royal Medal in 1826, Dalton was the first British scientist to develop a quantitative atomic theory and a key figure in the transition of chemistry to a mathematical discipline. His legacy endures in the atomic model, stoichiometry, and the understanding of gas behavior.

Did You Know?

• Dalton kept daily weather observations for over fifty years, entering more than 200,000 observations in his meteorological diary from 1787.
• He rediscovered George Hadley's theory of atmospheric circulation (the Hadley cell) around 1787.
• Dalton estimated mountain heights using a barometer, and before the Ordnance Survey published maps for the Lake District in the 1860s, he was one of the few authorities on the region's mountain heights.
• Examination of Dalton's preserved eyeball in 1995 demonstrated that he had deuteranopia, a type of congenital red-green color blindness where the gene for medium wavelength sensitive (green) photopsins is missing.
• Dalton's first publication, *Meteorological Observations and Essays* (1793), contained the seeds of several of his later discoveries.