I came back to Sommerfeld and I had a fellowship which kept me alive and I served as the second assistant to Sommerfeld, and whenever... especially whenever an American came, he was assigned to me; 'You take care of him.' And one of them... there were two important Americans who came to Sommerfeld at the time. One was Kirkwood, who was a very substantial person in physical chemistry. And the other was Lloyd Smith who was younger and - he was just my age - and wanted to have a problem in quantum mechanics. So I asked him to do the theory of excited states in Helium, and he did that very well, to his satisfaction and my satisfaction, and he became important for me later on in life. I also had some... I think I had two doctorate students. One of them was Henneberg, who did for me a thesis on the scattering of electrons by heavy atoms, angular distribution and all that, which I think was a very good paper and Henneberg unfortunately was sent to the front in the Second World War and was killed in that.