Seeking 'to derive the whole basis of physics' with the same deductive approach he once used for general relativity.

Einstein has not made as much progress [with his Unified Field Theory] as his sister Maja has led Besso to believe: 'The recent advances are of a purely mathematical nature. I have succeeded with my collaborator Dr Mayer in systematicallly going through all field laws which identically fulfil two divergence relations. This is less straightforward than the Riemann case. But the mathematical system is rather more natural than Riemann's ...'. He will explain in more detail when they see each other. 'The path to a physical testing is in no way simple; but the whole conception is natural and must in any case be completely thought through ... It is uncommonly appealing to try to derive the whole basis of physics in a similarly deductive way, as general relativity succeeded in doing for gravitation'. Einstein hopes to stop and see Besso in Berne on his way to Zurich; he apologises for such a short letter, as he is 'terribly overburdened with writing'.