In the fall of 1931, Fermi and Orso Mario Corbino organized in Rome an international conference on nuclear physics, which was sponsored by the Royal Academy of Italy. Fermi invited Rossi to give an introductory talk on cosmic rays. In the audience were Robert Millikan and Arthur Compton, both of whom had won the Nobel prize in physics, in 1923 and 1927, respectively. During the 1920s, Millikan, who is famous for his oil drop experiment, made extensive measurements of the mysterious radiation discovered by Hess. He coined the name "cosmic rays" and proposed that they were photons created by the fusion of hydrogen in interstellar space. He was not pleased by the presentation of evidence that most observed cosmic rays are energetic charged particles. Later, Rossi wrote: