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. Although cathode rays themselves are invisible, they cause a phosphorescent screen to glow when they strike it - making it possible for us to see their path. Cathode rays are deflected by a magnet, indicating that they are electrically charged.