1. A. Einstein,Ideas and Opinions (Crown, New York, 1963), p. 270.
2. A. Einstein,Ann. Phys. 49, 769 (1916); English translation inThe Principle of Relativity, Perrett and Jeffrey, eds. (Dover, New York), pp. 111?164.
3. G. Holton, inThe Twentieth Century Sciences, Holton, ed. (Norton, New York, 1972), esp. pp. 365?366.
4. H. Goenner, inErnst Mach, Cohen and Seeger, eds. (D. Reidel, Dordrecht-Holland, 1970).
5. A. Hermann (ed.),Albert Einstein/Arnold Sommerfeld Briefwechsel (Schabe, Basel, 1968), pp. 102?103.