Joseph John "J.J." Thomson discovered the electron in 1897 by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged and that the mass of each particle was much smaller than that of any known atom. Thomson went on to propose a model for the structure of the atom, which he likened to plum pudding. The negative electrons represented the raisins in the pudding, and the dough contained the positive charge. Thomsons model of the atom explained some of the electrical properties of the atom due to the electrons but failed to recognize the positive charges in the atom as particles. In 1911, Ernest Rutherford, a former student of J.J. Thomson, proved Thomsons plum pudding structure incorrect. Thomsons work also led to the invention of the mass spectrograph. Thomson received the Nobel Prize in Physics in 1906 for his work exploring the electrical conductivity of various gases.