1. Jacob Bekenstein, “Astronomical Consequences and Tests of Relativistic Theories of Variable Rest Masses,” Comments on Astrophysics8, no. 4 (1979), 89–98.
2. Max Planck, A Survey of Physical Theory (New York: Dover Publications, 1960), 18. See also Nadia Robotti and Massimiliano Badino, “Max Planck and the ‘Constants of Nature,’” Annals of Science58, no. 2 (2001), 137–62.
3. On Zöllner’s number, see Helge Kragh, “Zöllner’s Universe,” Physics in Perspective14, no. 4 (2012), 392–420. And for the early anticipations of the fine-structure constant, Helge Kragh, “Magic Number: A Partial History of the Fine-Structure Constant,” Archive for History of Exact Sciences57, no. 5 (2003), 395–431. I have described Eddington’s theory in Helge Kragh, “Eddington’s Dream: A Failed Theory of Everything,” in Information and Interaction: Eddington, Wheeler, and the Limits of Knowledge, ed. Dean Rickles and Ian Durham, 45–58 (Basel: Springer, 2017).
4. Philip Mirowski, “Looking for those Natural Numbers: Dimensionless Constants and the Idea of Natural Measurement,” Science in Context5, no. 1 (1992), 165–88.
5. John D. Barrow, The Constants of Nature: From Alpha to Omega (London: Jonathan Cape, 2002); Jean-Philippe Uzan and Roland Lehoucq, Les Constantes Fondamentales (Paris: Belin, 2005); Helge Kragh, Higher Speculations: Grand Theories and Failed Revolutions in Physics and Cosmology (Oxford: Oxford University Press, 2011), 167–82.