jan 1, 1897 - Discovery of Electrons
J. J. Thompson began to experiment with cathode ray tubes in the late 19th century. He placed two oppositely charged plates on either side at the end of the tube. The cathode rays deflected the negatively charged plate which led him to believe the ray consisted of negatively charged particles. He came to the conclusion that these negative subatomic particles can be found within the atom.
Added to timeline:
Development and Discovery of Atomic Theory, the Periodic Table, and Radiation