J.J. Thompson

In 1897 the British physicist Joseph John Thomson discovered the electron through a series of experiments using a cathode-ray tube. He studied the behavior of electric discharge in a high-vacuum cathode-ray tube, and he interpreted the deflection of the rays by electrically charged plates and magnets as evidence of electrons. In 1904 Thomson contributed his version of the atomic model as a sphere of positive matter in which electrons are positioned by electrostatic forces. His atomic model is called the plum pudding model because he predicted the positive and negative particles balanced each other out without an pattern or structure, because the nucleus had not been discovered.
"Joseph John Thomson | Chemical Heritage Foundation." Joseph John Thomson | Chemical Heritage Foundation. Chemical Heritage Foundation, n.d. Web. 04 Oct. 2015. <http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/thomson.aspx>.