On the quantum theory of radiation and the structure of the atom

by Niels Bohr

[19] Fowler, Phil. Trans. Roy. Soc. A. 214. p. 225 (1914).

[20] Fowler, loc. cit. p. 262, see also II. p. 15.

[21] Stark, loc. cit. pp. 67-75.

[22] Rau, loc. cit.

[23] Franck & Hertz, Verh. d. D. Phys. Ges. xv. p. 34 (1918).

[24] Cuthbertson, Proc. Roy. Soc. A. lxxxiv. p. 18 (1910).

[25] Franck and Hertz, Verh. d. D. Phys. Ges. xvi. pp. 457, 512 (1914).

[26] Paschen, Ann. d. Phys. xxxv. p. 860 (1911).

[27] Stark, Ann. d. Phys. xlii. p. 239 (1913).

[28] This value is of the same order of magnitude as the value 12.5 volts recently found by McLennan and Henderson (Proc. Roy. Soc, A. xci. p. 485, 1915) to be the minimum voltage necessary to produce the usual mercury spectrum. The interesting observations of single-lined spectra of zinc and cadmium given in their paper are analogous to Franck and Hertz’s results for mercury, and similar considerations may therefore possibly also hold for them.