Wolfgang Pauli took up his duties as professor in Zurich at the end of April 1928. Before accepting the post he had insisted on the appointment of an assistant, and wrote to Ralph Kronig on 22 November, ‘I would like to ask you, for the moment quite tentatively, if in principle you would agree to accept this position … your task would be:

1. Every time I say something, to contradict me with detailed arguments.
2. To animate somewhat the scientific activity with modern ideas.

Looking back (this photo dates from 1955), Kronig considered his time in Zurich, ‘not only as one of the most instructive, but also as one of the most exhilarating periods’ of his life. He added, ‘One of my tasks, not agreed upon beforehand, was to watch out that Pauli should limit his consumption of ice cream at Sprüngli’s Konditorei at the Paradeplatz where we often went in the afternoon.'