John Dalton pioneered the development of modern atomic theory and was the first scientist to study color blindness. Dalton’s groundbreaking discoveries on atomic weight, size, mass, and other properties of atoms in chemical elements changed chemistry. Additionally, Dalton’s atomic theory enabled scientists to understand how atoms of various elements interact with each other. Dalton’s primary research on color blindness led to greater study by others on the subject.  


As a young man, Dalton had several mentors who helped him develop a passion for mathematics and meteorology. Dalton learned how to use meteorological instruments and the process of recording weather records. Dalton kept a diary of his recordings for nearly 60 years and wrote around 200,000 observations over the years. His work inspired greater scientific study in meteorology. 


In 1794, Dalton became a member of the Manchester Literary and Philosophical Society where he wrote his first paper on "extraordinary facts relating to the vision of colours.” Dalton and his brother were both color blind, so he recognized that color blindness was hereditary. Because of Dalton’s discoveries, red-green color blindness is still often referred to as “Daltonism.”


Dalton’s most significant research was his atomic theory in chemistry. Dalton’s theory identified that elements are made of small particles called atoms, and atoms of the same element are the same in size, mass, and other properties, while atoms of different elements differ in size, mass, and other properties. Additionally, Dalton’s experiments with gases led to his discovery and creation of Dalton’s Law of Partial Pressure, which stated that the total pressure of a combination of gases is the sum of the partial pressures of each individual gas in the combination.


Dalton grew up as a Quaker Christian. He remained Quaker throughout his life and kept to the Quaker doctrine. Sir Humphry Davy, a fellow scientist and contemporary of Dalton, said of his faith,“John Dalton was a very singular Man, a Quaker by profession & practice: He has none of the manners or ways of the world.”