On his deep attachment to his colleagues in Berlin, especially Max Planck; and on the contrasting roles of the empirical and the speculative in physics.

Einstein has been offered a dual post at the University and Polytechnic of Zurich, which he has declined after considerable soul-searching: 'I hardly need say that I feel more in sympathy with the general conditions [in Zurich]. But if you could see what fine relationships have formed between my closest colleagues and myself (especially Planck) and how accommodating everyone here has been and still is to me, if you recall that my papers first achieved an impact through the understanding that they found here, then you will surely understand that I cannot decide to turn my back on this place'. A further consideration is the personal difficulties that would arise from close proximity to his estranged wife, Mileva, and their children in Zurich. Life in Berlin offers less stress of this sort: 'Here everyone approaches me only up to a certain distance, so that life proceeds in an almost frictionless way; this much I have learnt in life'. Because of his deep attachment to Zurich, he has most uncharacteristically offered a compromise, of going there for two periods of 4-6 weeks each year to offer cycles of 12 lectures, remunerated only to the extent of his expenses.

Einstein is delighted by Besso's remarks on the role of empirical knowledge and speculation in physics: 'I would just like to add that it doesn't work to enter Riemann's achievement as pure speculation. Gauss's achievement is the formulation of the positioning laws of rigid rods on a given surface ... Riemann's generalisation to the multidimensional is admittedly a purely speculative act; but it nevertheless rests on Gauss's conception of the measuring rod'.