1. For general accounts of the development of quantum theory see: Mehra J, Rechenberg H (1982) The historical development of quantum theory. Springer, New York; Kuhn TS (1978) Black-body theory and the quantum discontinuity 1894–1912. Oxford University Press, Oxford: (b) An excellent historical and scientific exposition, at a somewhat advanced level: Longair MS (1983) Theoretical concepts in physics. Cambridge University Press, Cambridge, chapters 8–12
2. A great deal has been written speculating on the meaning of quantum theory, some of it serious science, some philosophy, some mysticism. Some leading references are: (a) Whitaker A (1996) Einstein, Bohr and the quantum dilemma. Cambridge University Press; (b) Stenger VJ (1995) The unconscious quantum. Prometheus, Amherst; (c) Yam P (1997) Scientific American, June 1997, p. 124; (d) Albert DZ (1994) Scientific American, May 1994, p. 58; (e) Albert DZ (1992) Quantum mechanics and experience. Harvard University Press, Cambridge, MA; (f) Bohm D, Hiley HB (1992) The undivided universe. Routledge, New York; (g) Baggott J (1974) The meaning of quantum theory. Oxford University Press, New York; (h) Jammer M (1974) The philosophy of quantum mechanics. Wiley, New York; (i) Particularly on the reality of orbitals: Mulder P (2011) Hyle 17(1):24
3. Levine N (2014), Quantum chemistry, 7th edn, Prentice Hall, Engelwood Cliffs
4. Sitzung der Deutschen Physikalischen Gesellschaft, 14 December 1900, Verhandlung 2, p. 237. This presentation and one of October leading up to it (Verhandlung 2, p. 202) were combined in: Planck M (1901) Annalen Phys 4(4):553
5. (a) Klein MJ (1966) Physics Today 19:23; (b) For a detailed account of Planck’s role in and attitude to the birth of quantum theory see Brown BR (2015) Planck: Driven by Vision, Broken by War. Oxford University Press, and references therein; particularly chapter 10