By 1931, cosmic ray research had become a primary arena for experimental physics and was receiving enormous attention in newspapers around the world. As the person who had introduced the term “cosmic ray” in 1925, American physicist Robert Millikan was a leading experimenter in the field. During a visit to Berlin he was received by the leading theoretical physicists of the day. From left to right: Walther Nernst (thermochemistry), Albert Einstein (general relativity), Max Planck (quantum theory), Robert Millikan (elementary electronic charge and photoelectric effect), and Max von Laue (X-rays).