Discovery of the Four Fundamental Particles
Protons were known as the nuclei of hydrogen atoms.
Electrons were discovered in 1897 by J. J. Thompson. He showed that
"cathode rays" were much lighter than hydrogen atoms.
Neutrons were proposed by Rutherford in 1920. James Chadwick confirmed their
existence in 1932.
Photons were proposed as a model of light by Einstein in 1905.