2 6 6 D O C . 1 4 7 S P A C E A N D T I M E [8]At this point in the original text Einstein indicates a note he has appended at the foot of the page: “Dies kommt in dem Satz zum andeutungsweisen Ausdruck: Die Gerade ist die kürzeste Verbindung zweier Punkte. Dieser Satz figurierte oft als Definition der Geraden, trotzdem diese Definition im logischen Gewebe der Deduktionen keine Rolle spielte.” [9]In previous epistemological writings, Einstein distinguished between axiomatic and practical geom- etry. See, e.g., Einstein 1917a (Vol. 6, Doc. 42), pp. 1–2 Einstein 1921c (Vol. 7, Doc. 52), pp. 3–6 and Einstein 1925g (Vol. 14, Doc. 220), pp. 16–17. [10]A similar line of argument can be found in Einstein 1921c (Vol. 7, Doc. 52) Einstein 1924n (Vol. 14, Doc. 321), pp. 1690–1691 and Einstein 1925g (Vol. 14, Doc. 220), pp. 16–17. Here, how- ever, Einstein gives particular emphasis to the fact that the main reason that the use of rods and clocks is problematic is their incommensurability with atomic particles. See Giovanelli 2014 for more details. [11]At this point in the original text, Einstein indicates a note he has appended at the foot of the page: “Aenderung der Richtung der Koordinaten¢richtungen²achsen unter Wahrung der Orthogona- lität.” [12]At this point in the original text, Einstein indicates a note he has appended at the foot of the page: “Vgl. den Artikel über „Zeit“.” [13]Einstein usually identifies the existence of a gravitational field with the nonconstancy of the (see Einstein 1916e [Vol. 6, Doc. 30], p. 779). [14]For a detailed discussion of the premise that special relativity holds in infinitesimal regions see Einstein 1916e (Vol. 6, Doc. 30), sec. 4. [15]In 1854, Bernhard Riemann (1826–1866) developed the geometry of complex surfaces named after him. It was only published posthumously as Riemann 1867. [16]For similar statements about curved surfaces being locally Euclidean see, e.g., Einstein 1917a (Vol. 6, Doc. 42), p. 61 Einstein 1921c (Vol. 7, Doc. 52), p. 10 Einstein 1922c (Vol. 7, Doc. 71), p. 40 and Einstein 1925g (Vol. 14, Doc. 220), p. 20. [17]For similar popular presentations of Gauss’s theory of surfaces in terms of the behavior of little rods, see Einstein 1917a (Vol. 6, Doc. 42), pp. 59–61 and Einstein 1922c (Vol. 7, Doc. 71), pp. 40– 42. For the importance of Gauss’s theory of curved surfaces in the emergence of general relativity, see Vol. 4, the editorial note, “Einstein’s Research Notes on a Generalized Theory of Relativity,” pp. 192–199. [18]A reference to the “Einstein cylinder world” introduced in Einstein 1917b (Vol. 6, Doc. 43). For further details, see Vol. 8, the editorial note, “The Einstein-De Sitter-Weyl-Klein Debate,” pp. 351–357. [19]For a similar account of the emergence of the notion of time, see Einstein 1922c (Vol. 7, Doc. 71), pp. 1–2. [20]This definition of “clock” appeared for the first time in Einstein’s writings in Einstein 1910a (Vol. 3, Doc. 2), p. 21. For later instances, see the 1912–1914 “Manuscript on the Special Theory of Relativity” (Vol. 4, Doc. 1), p. 22 and Einstein 1915b (Vol. 4, Doc. 21), p. 708. gμν