more positive charge inside its orbit (see Gauss's law). Electrons were free to rotate in rings that were further stabilized by interactions among the electrons, and spectroscopic measurements were meant to account for energy differences associated with different electron rings. As for the properties of matter, Thomson believed they arose from electrical effects. He further emphasized the need of a theory to help picture the physical and chemical aspects of an atom using the theory of corpuscles and positive charge. Thomson attempted unsuccessfully to reshape his model to account for some of the major spectral lines experimentally known for several elements. After the scientific discovery of radioactivity, Thomson decided to address it in his model by stating: ... we must face the problem of the constitution of the atom, and see if we can imagine a model which has in it the potentiality of explaining the remarkable properties shown by radio-active substances ... Thomson's model changed over the course of its initial publication, finally becoming a model with much more mobility containing electrons revolving in the dense field of positive charge rather than a static structure. Despite this, the colloquial nickname "plum pudding" was soon attributed to Thomson's model as the distribution of electrons within its positively charged region of space reminded many scientists of raisins, then called "plums", in the common English dessert, plum pudding. In 1909, Hans Geiger and Ernest Marsden conducted experiments where alpha particles were fired through thin sheets of gold. Their professor, Ernest Rutherford, expected to find results consistent with Thomson's atomic model. However, when the results were published in 1911, they instead implied the presence of a very small nucleus of positive charge at the center of each gold atom. This led to the development of the Rutherford model of the atom. Immediately after Rutherford published his results, Antonius van den Broek made the intuitive proposal that the atomic number of an atom is the total number of units of charge present in its nucleus. Henry Moseley's 1913 experiments (see Moseley's law) provided the necessary evidence to support Van den Broek's proposal. The effective nuclear charge was found to be consistent with the atomic number (Moseley found only one unit of charge difference). This work culminated in the solar-system-like Bohr model of the atom in the same year, in which a nucleus containing an atomic number of positive charges is surrounded by an equal