Kiel (Germany), 24 May 1924

'Dwelling almost uninterruptedly on the quantum problem'.

'Scientifically I am dwelling almost uninterruptedly on the quantum problem, and really think I am on the right track ... The best thing I have achieved in recent times was the paper of 1917 in the Physikal. Zeitschrift [on the quantum theory of radiation]. My new efforts are aimed at the unification of quanta and the Maxwellian field'; the most important experiments in recent years have been by Stern and Gerlach, as well as one by Compton, 'the first proves the unique existence of quantum states, the second the reality of the momentum of light quanta'.

Einstein has sent his published papers to the Swiss National Library in Berne, to preempt the disorder in his papers which was likely to follow the departure for married life of his stepdaughter Ilse. Otherwise he is healthy and well, and he is delighted with his sons, so that the Nobel Prize money (which he had passed to Mileva as part of their divorce settlement) is unlikely to spoil them. Politically things are calmer, and he is much less bothered by the public, thankfully. Einstein also recalls his 'wonderful journey to Japan' in late 1922, 'during which I for the first time saw a healthy human society, whose members live entirely for it'. He enjoys his regular visits to Kiel, working on technical projects at the Anschütz-Kaempfe gyrocompass factory.