J. J. Thomson. Image provided by Edgar Fahs Smith Collection, University of Pennsylvania Library. Sir Joseph John (J. J.) Thomson (1856–1940) Before J. J. Thomson’s discovery of the electron, the atom was thought to be indivisible. Thomson’s first observation of subatomic particles contributed greatly to a revolution in our understanding of atoms that had tremendous ramifications for chemistry. Born in the suburbs of Manchester, England, Thomson studied engineering before turning to mathematical physics. He was fascinated by electromagnetism among other things, building his theories on those of James Clerk Maxwell. He had attempted the Victorian equivalent of a grand unified theory even before his discovery of the electron, and in this theory attempted to account for the valencies of different elements. It was during his study of cathode rays that Thomson, ever thinking of electromagnetism, discovered electrons. Thomson spent his entire career at Cambridge University, where he devoted himself equally to classroom teaching and research. He received the Nobel Prize for physics in 1906 and was knighted in 1908.