 A passage from §3 of Einstein’s first complete exposition of the general theory of relativity (1916a) appeared to provide further grist for the mill of Machian positivism. There Einstein grandly declared that his requirement of general covariance for the gravitational field equations (i.e., that they remain unchanged under arbitrary, but suitably continuous, transformation of the spacetime coordinates), “takes away from space and time the last remnant of physical objectivity”. An accompanying heuristic reflection on the reasoning behind this claim seemed nothing less than an endorsement of Mach’s phenomenalism. “All our space-time verifications”, Einstein wrote, “invariably amount to a determination of space-time coincidences…”. This is because, Einstein presumed, all results of physical measurement ultimately amount to verifications of such coincidences, such as the observation of the coincidence of the second hand of a clock with a mark on its dial, or the point-like mark of a particle made on a detection screen. Observing that such (topological) relations alone are preserved under arbitrary coordinate transformation, Einstein concluded that “all our physical experience can ultimately be reduced to such coincidences”. To Mach’s followers, Einstein’s illustrative reflection was nothing less than an explicit avowal of the centerpiece of Mach’s phenomenalist epistemology, that sensations (Empfindungen), directly experienced sensory perceptions, alone are real and knowable. Thus Josef Petzoldt, a Machian philosopher and editor of the 8th edition of Mach’s Mechanics , the first to appear after the general theory of relativity, noted that Einstein’s remarks meant that the theory “rests, in the end, on the perception of the coincidence of sensations” and so “is fully in accord with Mach’s world-view, which is best characterized as relativistic positivism” (1921: 516).