Final answer:
Cathode rays are negatively charged and deflected by a magnetic field, suggesting the presence of electrons. J.J. Thomson's experiments led to the discovery of the electron as a fundamental component of all atoms.
Step-by-step explanation:
Cathode rays are negatively charged and deflected by a magnetic field, suggesting the presence of electrons. J.J. Thomson's experiments with cathode rays demonstrated that these particles had a net negative charge and a mass-to-charge ratio that was independent of the nature of the metal electrodes or the gas. This led to the discovery of the electron as a fundamental component of all atoms.