In 1894, J.J. Thomson, an English physicist, began a series of experiments that would resolve the controversy about cathode rays and lead to the discovery of the first subatomic particle. By constructing a cathode ray tube with the deflector plates inside the glass tube (at right), Thomson discovered --in direct contradiction with Hertz (Heinrich Hertz shows that cathode rays are not deflected by electrically charged metal plates, which would seem to indicate (incorrectly) that cathode rays cannot be charged particles.)-- that cathode rays could be deflected by an electric field. Thomson’s tube design allowed him to determine the ratio of the cathode ray particle’s charge to its mass. We will use Beyond Labz for this experiment.