Sir J.J. Thomson discovered electrons through his experiments with cathode rays in 1897, proving that the fundamental unit of electricity was over 1000 times smaller than an atom. He was awarded the 1906 Nobel Prize in Physics for this discovery and for his work on the conduction of electricity in gases. Throughout his career, Thomson made several other contributions including discovering the natural radioactivity of potassium in 1905 and demonstrating that hydrogen had only a single electron per atom in 1906.