Around the 1900s, Sir John James Tomson claimed that atoms contain both protons and electrons, protons have a positive charge and electrons have an equal negative charge. protons are heavy and electrons are light.
Model: Plum Pudding or Raisin Bun, the dough is the protons and the fruit is the electrons.
Experiment: Cathode Ray Tube (CRT), where the shadow presented itself told him which was heavier, and that they were there.