La Relatività Generale di Einstein nel suo sviluppo storico
A detailed historical analysis of the development of Einstein’s Generai Relativity from 1907, year of his first paper on gravitation, to 1915, the conclusive year of his work, shows that the turning point of the development was the transformation of the classical gravitational theory into a Riemanian theory of space-time. The equivalence principle played a fundamental role. Einstein built the theory by recurrent generalizations. His use of correspondence rules, i.e. the requirement that the new theory reduced to the classical theory and to special relativity when limiting values were assigned to some parameters, restricted the number of the possible generalizations.