Cathode rays (also called an electron beam or e-beam) are streams of electrons observed in vacuum tubes, i.e. evacuated glass tubes that are equipped with at least two metal electrodes to which a voltage is applied, a cathode or negative electrode and an anode or positive electrode. They were discovered by German scientist Johann Hittorf in 1869 and in 1876 named by Eugen Goldstein kathodenstrahlen (cathode rays). Electrons were first discovered as the constituents of cathode rays. In 1897 British physicist J. J. Thompson showed the rays were composed of a previously unknown negatively charged particle, which was named electron.

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