Thomson was born in Cheetham Hill, Manchester, England, on December 18, 1856. He was the son of a bookseller who specialized in antique books. At the age of 14, he enrolled at Owen's College (now the University of Manchester). Thomson's original plans to study engineering were interrupted two years later when his father died and the family was no longer able to afford the additional fees needed for his engineering studies. Instead, Thomson decided to major in mathematics and the physical sciences. In 1876, he earned a scholarship at Trinity College, Cambridge, and graduated second in his mathematics class four years later. Thomson remained at Cambridge in various positions for the rest of his life.

The discovery for which Thomson is best known is that of the electron. The research leading to that discovery had two different origins. The first involved atomic theory. A popular view of the atom in the 1880s...