Thomson used the cathode ray tube to discover the electron. The Cathode Ray Tubes consists of several elements starting with a vacuum tube sealed to keep air out of it. On one side of the inside of the tube there is a cathode and an anode. The cathode is a negatively-charged conductor, and the anode is a positively-charged conductor. Electrons, which have a negative charge, flow off the cathode and are attracted towards the anode. A small hole in the anode allows some electrons to pass through it, creating a beam of electrons. On the opposite side of the tube is a coating that glows when struck by the electrons.