 As Einstein’s principal research activity turned, after 1919, to the pursuit of a geometrical theory unifying gravitation and electromagnetism, his philosophical pronouncements increasingly took on a more realist or at least anti-positivist coloration. Lecturing at the Sorbonne in April 1922 (1922: 28), Einstein pronounced Mach “un bon mécanicien” (probably a reference to Mach’s views of the relativity of inertia) but “un déplorable philosophe”. Increasingly, Einstein’s retrospective portrayals of the genesis of general relativity centered almost entirely on the success of a strategy emphasizing mathematical aesthetics (see Norton 2000, Ryckman 2014, and  §5).  Positivists and operationalists alike continued to point to the Einstein analysis of simultaneity as relativity theory’s fundamental methodological feature. One, ruefully noting the difficulty of giving an operationalist analysis of the general theory, even suggested that the requirement of general covariance “conceals the possibility of disaster” (Bridgman 1949: 354). Finally there was, for Einstein, an understandable awkwardness in learning of Mach’s surprising disavowal of any role as forerunner to relativity theory in the Preface, dated 1913, to Mach’s posthumous book (1921) on physical optics. Though Einstein died without knowing differently, a recent investigation has built a strong case that this statement was forged after Mach’s death by his son Ludwig, under the influence of a rival guardian of Mach’s legacy and opponent of relativity theory, the philosopher Hugo Dingler (Wolters 1987).