Final answer:
Cathode rays consist of charged particles called electrons.
Step-by-step explanation:
Cathode rays consist of charged particles called electrons. British physicist J. J. Thomson proved this by demonstrating that cathode rays could be deflected by magnetic or electric fields. By measuring the extent of the deflection, Thomson was able to calculate the mass-to-charge ratio of the particles, which was found to be independent of the nature of the metal electrodes or the gas.