'The boldest dreams have now been fulfilled. General covariance. The perihelion movement of Mercury wonderfully exact...'.

The triumph of general relativity: in four magisterial papers submitted to the Prussian Academy of Sciences between 4 and 25 November, Einstein had set out the key elements of the general theory of relativity. In this postcard to his closest friend, he rejoices in his theory's success: 'I sent you the papers today. The boldest dreams have now been fulfilled. General covariance. The perihelion movement of Mercury wonderfully exact. The latter is completely secure from an astronomical standpoint, for Newcomb's mass determinations of the inner planets are from periodic (not constant) perturbations. This time the nearest way was the right one but Grossman and I believed that the conservation laws were not fulfilled, and that Newton's law did not result in the first approximation. You will be surprised by the appearance of the g₁₁ ... g₃₃'s'.

The postcard opens with news of an intended journey to Switzerland, now that he has been assured that his eldest son, Hans Albert, wishes to spend time with him. Einstein signs off the letter 'greetings ... from your / happy but rather worn out / Albert' ('Grüssen ... von Deinen / zufriedenen aber ziemlich kaputen / Albert').