Beschreibung:

EINSTEIN, Albert (1879-1955). Autograph correspondence card signed ('Albert') to Michele Besso, [postmarked Berlin, 28 August 1918]. In German, 1½ pages, 140 x 89mm (small loss to lower right corner). Address panel bearing Einstein's autograph return address ('Abs[ender]. A. Einstein'). Provenance : by descent from Michele Besso. On the origin of the great theories, including special and general relativity. In re-reading Besso's last letter, Einstein finds something which almost infuriates him – Besso has suggested that the role of speculation was more important than that of the empirical in the development of the theory of relativity. But the conclusion Einstein draws is almost exactly the opposite: 'that a theory, in order to deserve trust, must be constructed on the basis of generalisable facts '. He then goes to list as some 'old examples' five of the key theories in physics, with their empirical underpinning: 'The fundamentals of thermodynamics on the impossibility of perpetual motion. Mechanics on the empirically proven law of inertia. Special relativity on the invariability of the speed of light. Maxwell's equations for the vacuum, which again for their part rest on empirical foundations. Relativity for a uniform translation is an experienced fact . General relativity: equality between inert mass and weight '. He concluded 'A really usable and profound theory has never been discovered by absolutely pure speculative means' – though Maxwell's hypothesis on displacement current is the closest thing to an exception. Published (in French and German) in Pierre Speziali (ed. and tr.). Albert Einstein. Michele Besso. Correspondance 1903-1955 . Paris: Hermann, 1972. No. 47.