ndz uge der Relativitantheorie. Braunschweig: Vieweg (originally Vier Vorlesungen ubcr Relativitatstheoric, 1922: the talks were given in 1921). See Alexander Afriat Ermenegildo Caccese. The relativity of inertia and reality of nothing. p 8. philsci-archive.pitiedu/4450/1/Inenia.pdf., from which the quote in the footnote was taken.