pThis volume is the first English resource to shed light on the philosophy of Joseph Petzoldt 1862-1929, the main pupil of Ernst Mach and founder of the iGesellschaft fr wissenschaftliche Philosophiei, later the association of Berlin logical positivists. A central figure in the early debate on the theory of relativity, his work was praised by Einstein himself. pTracing the development of Petzoldt's ideas, starting from his early acceptance of materialism and Kantian agnosticism, Chiara Russo Krauss presents a comprehensive reconstruction of his philosophy in the context of the German milieu. She examines his attempt to develop a new philosophy following Gustav Fechner and the empiriocriticism of Richard Avenarius and Ernst Mach. In the final chapter, she sets out how Petzoldt proposed relativistic positivism as the official interpretation of Einstein's relativity. pBy illuminating key elements of Petzoldt's work, this is a valuable case study for students and scholars of philosophy of