1. Einstein to Marić [early August 1899], in John Stachel, ed., The Collected Papers of Albert Einstein. Vol. 1. The Early Years 1879–1902 (Princeton: Princeton University Press, 1987), pp. 220–221, on p. 220; translated somewhat differently by Anna Beck (Princeton: Princeton University Press, 1987), p. 129.
2. Albert Einstein, Lettres à Maurice Solovine (Paris: Gauthier-Villars, 1956), p. viii; Letters to Solovine (New York: Citadel Press, 1993), pp. 8–9; Gerald Holton, Einstein, History, and Other Passions (Woodbury, N.Y.: AIP Press, 1995), p. 84; David Cahan, “The Young Einstein’s Physics Education: H.F. Weber, Hermann von Helmholtz, and the Zurich Polytechnic Physics Institute,” in Don Howard and John Stachel, ed., Einstein: The Formative Years, 1879–1909 (Boston, Basel, Berlin: Birkhäuser, 2000), pp. 43–82, esp. pp. 59–74.
3. Hermann Helmholtz, Über die Erhaltung der Kraft, eine physikalische Abhandlung (Berlin: G. Reimer, 1847): reprinted in Wissenschaftliche Abhandlungen. Erster Band (Leipzig: Johann Ambrosius Barth, 1882), pp. 12–75. Fabio Bevilacqua, “Helmholtz’s Ueber die Erhaltung der Kraft: The Emergence of a Theoretical Physicist,” in David Cahan, ed., Hermann von Helmholtz and the Foundations of Nineteenth-Century Science (Berkeley, Los Angeles, London: University of California Press), pp. 291–333.
4. Hermann Helmholtz, “Messungen über den zeitlichen Verlauf der Zuckung animalischler Muskeln und die Fortpflanzungsgeschwindigkeit der Reizung in den Nerven” [1850], reprinted in Wissenschaftliche Abhandlungen, Zweiter Band (Leipzig: Johann Ambrosius Barth, 1883), pp. 764–843.
5. Hermann Helmholtz, “Ueber die Methoden, kleinste Zeittheile zu messen, und ihre Anwendung für physiologische Zwecke” [1850], in ibid., pp. 862–880. Claude Debru, “Helmholtz and the Psychophysiology of Time,” Science in Context 14 (2001), 471–492. For the question of “lost time,” see Michel Meulders, Helmholtz: From Enlightenment to Neuroscience. Translated and edited by Laurence Garey (Cambridge, Mass. and London: The MIT Press, 2010), pp. 89–106.