Sir Joseph J. Thomson, who had done so much to investigate the structure of the atom experimentally, wanted to devise an atomic model that would explain all the known properties of atoms. Since most of the mass of the atom was in the positively charged portion, he considered the atom to be a spherical distribution of positive charge with electrons bound on the outside surfaces by spring-like forces that allowed the atoms to move about. The Thomson theory predicted that practically all of the alpha particles would be found within very few degrees of their original direction, since most of the time the alpha particle would find positive charges nearly equally spaced on all sides.