John Dalton

Today is the 250th birthday of chemist John Dalton, who laid the foundation for modern atomic theory. He was born in 1766 in Eaglesfield, England. Dalton’s scientific contributions began soon after he took a teaching job in Manchester. He was elected a member of the Manchester Literary and Philosophical Society and promptly published a study on color blindness, the first scientific paper on the subject. Dalton was also passionate about meteorology, keeping detailed weather records every day from 1787 until his death in 1844. His careful study of the atmosphere led him to conclude that air is actually a mixture of various gases that each exert pressure. He then deduced that different elements have atoms of different size and mass—a radical proposal, considering that scientists going back to ancient Greece believed that all atoms are alike. Dalton proposed that chemistry involves the combination of indivisible atoms in simple, whole-number ratios to make chemical compounds. His atomic theory had flaws, yet it preceded direct evidence of atoms by about a century.

Date in History: 6 September 1766