AtomicTheory Time Line By upt150223 400 democritus He found the atom. 400 bc. Jan 1, 1803 John Dalton Dalton's Atomic Theory Jan 1, 1859 J. Plucker Cathode Ray Tube Jan 1, 1897 J.J. Thomson Discovered the electron Jan 1, 1922 Niels Bohr Bohr Planetary Model Jan 1, 1926 Ernest Rutherford Gold Foil Experiment Model / Rutherford Model