1. Bohr to Ehrenfest, May 5, 1918, Museum Boerhaave, ESC1, S5, 152.
2. Ehrenfest to Lorentz, August 25, 1913, Museum Boerhaave, ESC7, S4, 198.
3. J. M. Burgers, Het Atoommodel van Rutherford-Bohr (Haarlem: De Erven Loosjes. 1918).
4. N. Bohr, “On the Quantum Theory of Line-Spectra,” Det Kongelige Danske Videnskabernes Se1skab. Skrifter. Naturvidenskabelig og mathematisk Afdeling 8. Raekke, IV. 1, Parts 1–2 (1918), 1–100; reprinted in Niels Bohr Collected Works. Vol. 3. The Correspondence Principle (1918–1923) (Amsterdam, New York, Oxford: North-Holland Publishing Company, 1976), pp. 67–166.
5. Ehrenfest to Einstein, May 8, 1918; reprinted in The Collected Papers of Albert Einstein. Vol. 8. The Berlin Years: Correspondence, 1914–1918. Part B. 1918, edited by Robert Schulmann, A.J. Kox, Michel Janssen, and József Illy (Princeton: Princeton University Press, 1998), pp. 756–767; translated by Ann M. Hentschel (Princeton: Princeton University Press, 1998), pp. 555–556.