A physicist found a particle smaller than the atom — and broke the atom apart

In 1897, J.J. Thomson fired cathode rays through a vacuum tube and showed they were streams of particles thousands of times lighter than any atom, deflected by electric and magnetic fields. He had found the electron, the first subatomic particle ever identified, proving atoms were not the indivisible building blocks their name implied.

— J. J. Thomson, Cathode Rays — Philosophical Magazine, Series 5, Vol. 44, 1897