jan 1, 1911 - Gold Foil Experiment/Discovery of the Nucleus
Rutherford discovered these charges by conduction an experiment in which he fired particles at a sheet of gold foil and measured the deflection of the particles. This resulted in the discovery of the nucleus and positive charge in an atom. This disproved Thompsons model of an atom when he released his findings to the public in 1911.
Added to timeline:
Development and Discovery of Atomic Theory, the Periodic Table, and Radiation