Note that the counting of editions is different in London and Princeton. Born’s and McCrea’s reviews refer to the 4th
London edition which contained the famous Appendix II for the first time and was published in April 1950 (after a 3rd
edition in 1946 with an appendix on cosmology corresponding to the appendix of the 2nd Princeton edition of 1946).
Methuen’s 5th edition came out in London in July 1951 [154], the 6th in 1956. Princeton’s 3rd edition
appeared also in 1950, containing Appendix II as well, the 4th edition in (March) 1953, the 5th in 1955. A further
complication is that, in 1950 a further printing of the 3rd Princeton edition appeared [150*] in which a mistake in
Appendix II was corrected (cf. [490*], p. 138, letter Pauli to Strauss; footnote 3 by K. von Meyenn). Although,
on the back side of the title page in Methuen’s 4th edition it is claimed: “This edition and the Princeton
University Press third edition are identical” [151], Appendix II in the American and the British editions of
1950 are quite different! If translations into other languages with several editions by themselves are referred to
by authors (like to the Italian translation, published by Einaudi), it becomes even harder to give a reliable
reference.