John Dalton

John Dalton (born 5 or 6 September 1766, died 27 July 1844) was an English chemist, physicist, and meteorologist. He is best known for creating the foundation of modern atomic theory and stoichiometric chemistry. Drawing on older concepts about matter being indivisible and his own careful measurements of how elements combine, Dalton argued that every chemical element is made of identical atoms with a specific weight. He also stated that compounds form when atoms of different elements join in simple, whole-number ratios. His 1808 book *A New System of Chemical Philosophy* laid out a clear atomic model, gave relative atomic weights and a system of symbols, and provided the quantitative basis that guided chemistry in the 1800s and still underpins modern chemical science.

Dalton was also a pioneer in meteorology and physics. He recorded daily weather observations for more than fifty years, developed the first empirical law of partial pressures (now called Dalton's Law), and explored gas behavior through his research on vapor pressure and gas solubility. His investigation of his own color blindness produced the first scientific account of the condition—still called Daltonism in several languages—and helped create experimental methods linking perception to physiology. 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 moving chemistry from a qualitative to a mathematical science.

**Early life**

Dalton was born on 5 or 6 September 1766 into a Quaker family in Eaglesfield, near Cockermouth, in Cumberland, England. His father was a weaver. He got his early education from his father and from Quaker John Fletcher, who ran a private school in the nearby village of Pardshaw Hall. Because his family was too poor to support him for long, Dalton began earning a living at age ten, working for a wealthy local Quaker named Elihu Robinson.

**Scientific work**

**Meteorology**

Dalton’s early life was shaped by Elihu Robinson, a skilled meteorologist and instrument maker from Eaglesfield who sparked his interest in mathematics and weather science. While living in Kendal, Dalton contributed solutions to problems and answered questions in *The Ladies' Diary* and the *Gentleman's Diary*. In 1787, at age 21, he started a meteorological diary, eventually recording more than 200,000 observations over 57 years. Around this time, he independently rediscovered George Hadley’s theory of atmospheric circulation (the Hadley cell). His first publication, *Meteorological Observations and Essays* (1793), contained the seeds of several later discoveries, but other scholars paid little attention to its originality. He also published *Elements of English Grammar* in 1801.

**Measuring mountains**

After leaving the Lake District, Dalton returned each year for holidays to study meteorology, which involved a lot of hill-walking. Before airplanes and weather balloons, the only way to measure temperature and humidity at altitude was to climb a mountain. Dalton used a barometer to estimate heights. The Ordnance Survey did not publish maps of the Lake District until the 1860s, so Dalton was one of the few authorities on the heights of the region’s mountains. He often worked with Jonathan Otley, who also studied local peak heights, using Dalton’s figures to check his own work. Otley published his findings in a map in 1818 and became both an assistant and a friend to Dalton.

**Colour blindness**

In 1794, shortly after moving to Manchester, Dalton was elected to the Manchester Literary and Philosophical Society (the "Lit & Phil"). A few weeks later, he presented his first paper, "Extraordinary facts relating to the vision of colours," in which he suggested that color perception shortages were caused by discoloration of the eye’s liquid medium. Because both he and his brother were color blind, he recognized the condition was hereditary. Although his theory was later disproven, his early research into color vision deficiency was recognized after his death. Examination of his preserved eyeball in 1995 showed that Dalton had deuteranopia, a type of congenital red-green color blindness where the gene for medium-wavelength-sensitive (green) photopsins is missing. People with this condition see every color mapped to blue, yellow, or gray—or, as Dalton wrote, "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."

**Gas laws**

In 1800, Dalton became secretary of the Manchester Literary and Philosophical Society. The following year, he presented a series of lectures called "Experimental Essays" on the constitution of mixed gases; the pressure of steam and other vapors at different temperatures in a vacuum and in air; on evaporation; and on the thermal expansion of gases. These four essays, given between 2 and 30 October 1801, were published in the *Memoirs of the Literary and Philosophical Society of Manchester* in 1802. The second essay begins 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 un..."