Electrons were discovered through a series of experiments involving cathode ray discharge tubes. Relatively high voltages were supplied across the electrodes of these tubes, resulting in the flow of current through the tube. The current flowed from the cathode (the negative electrode) to the anode (the positive electrode). This flow is commonly known as a cathode ray. Despite being invisible, the behaviour of cathode rays could be observed with the use of phosphorescent or fluorescent materials. Cathode rays travelled in straight lines when they were not under the influence of any magnetic or electrical fields. Thomson proposed that the electrons were embedded in a uniform sphere that contained both the positive charge and most of the mass of the atom, much like raisins in the plum pudding or chocolate chips in a cookie
Rutherford showed unambiguously that Thomson’s model of the atom was incorrect. Rutherford’s results were not consistent with a model in which the mass and positive charge are distributed uniformly throughout the volume of an atom. He found there is a nucleus. The behaviour of cathode rays was observed to be similar to that of negatively charged particles. Therefore, it was inferred that cathode rays were made up of numerous negatively charged particles, which were later named electrons. The properties and characteristics of cathode rays were found to be independent of the materials used in the construction of the electrodes. The modern atomic theory establishes the concepts of atoms and how they compose matter.