On the value of energy in his new paper on thermodynamics, thoughts on the size of ions in cathode radiation, and scathing criticism of Berne University.

Einstein excuses himself for not having written (in fact, he had been sick with diphtheria): 'I should have written so many letters in the last few days – that is my excuse, and it goes for all of them, for I haven't written a single one'. He goes on to discuss in detail a specific equation from his recently-published paper on the foundations of thermodynamics ['Eine Theorie der Grundlagen der Thermodynamik', published in Annalen der Physik, II, 1903], responding (evidently to a criticism by Besso) that 'The condition that E [the energy of the system] should be the only integral of the equations of the given form is no limitation, for I free myself from it in the consideration of the "adiabatically" influenced system'.

Besso has written a note about cathode radiation, and Einstein suggests that he calculate the absolute size of the ions, which he suggests would be 'a simple matter. I would have done it myself, but I do not have the necessary literature or time'. Returning to Besso's comments on his thermodynamics paper, Einstein remarks, 'If you look at my paper more closely, you will find that the assumption of the energy principle and the fundamental atomistic idea do not suffice in themselves to explain the second law': he sets out the coordinate system which must be used additionally. 'If that is true, then the whole generalisation attained in my last paper consists in the elimination of the concept of force as well as in the fact that E can possess arbitrary form (yet not altogether)'. The letter ends with a pungent criticism of the University of Berne, where Einstein had recently tried and failed to become a Privatdozent: 'The university here is a pigsty. I won't lecture there, as it would be a shame to waste my time'.