Berlin, 9 March 1917

'The curvature of space is irregular, so that light rays travel in a medium filled with streaks'.

'Your suggestion about relativity is right. But the little book is finished, the proof corrections almost completed, so that I can make no further use of it': Einstein is rather dissatisfied with the way his book has come out, finding it rather wooden – in future he might leave the writing part to someone else with 'more facility in self-expression and a better sense of order'. Besso will have received Einstein's article 'Cosmological considerations on the general theory of relativity': 'It is at least a proof that general relativity can lead to a system free of contradictions. Until now there was always the fear that 'infinity' would hide insoluble contradictions. Unfortunately there seems little prospect of being able to verify the propositions in reality. If one relies upon the researches of astronomers about the density of distribution of stars, one comes to the order of magnitude R=10⁷ light years, whereas visibility reaches only as far as R=10⁴ light years ... One mustn't forget that the curvature of space is irregular, so that light rays travel in a medium filled with streaks ['mit Schlieren']'. Some recent work on quanta has brought him back to the idea of a spatial quantum aspect to radiant energy: 'But I have a feeling that the actual joke which the eternal riddle-maker poses for us here has not yet been grasped'.

Einstein is putting off a projected visit to Zurich until the summer, a time at which a journey is easier on 'my creaking carcass' – the doctor has diagnosed him with gall stones: 'water cure, strict diet ... I am in fact feeling much better, no longer in pain and I look healthier’. He is however deeply pessimistic about the political situation (after three years of war), sensing pathological aspect to the general outlook, and comparing the times to 'witch-hunts and similar outbursts of religious madness'.