[14] This, however, is probably a temporary state of affairs. Certain Pasons for quantum transitions are already known. See J. Franck and P. Jordan, Anregung von Quaniensprüngen durch Stösse, Berlin, 1926; also P. Jordan, Kausalität und Statistik in der modernen Physik, Naturwissenschaften, Feb. 4, 1927. [15] See Sommerfeld, op. cit., pp. 232 ff. [16] This is not the same phenomenon as in the case of the orbit of Mercury. The latter depends upon the general theory of relativity, the former upon the special theory. [17] Sommerfeld, op. cit., pp. 467 ff. [18] The principal papers setting forth this theory are: 1. W. Heisenberg, Ueber quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen. Zeitschrift für Physik, 33, pp. 879-893, 1925. 2. M. Born and P. Jordan, Zur Quantenmechanik. Ibid. 34, pp. 858-888, 1925. 3. M. Born, W. Heisenberg, and P. Jordan, Zur Quantenmechanik II. Ibid. 35, pp. 557-615, 1926. 4. P. A. M. Dirac, The Fundamental Equations of Quantum Mechanics. Proc. Royal Soc., Series A, vol. 109, No. A752, pp. 642-653, 1925. 5. W. Heisenberg, Ueber quantentheoretische Kinematik und Mechanik. Mathematische Annalen, 95, pp. 683-705, 1926. 6. W. Heisenberg, Quantenmechanik. Naturwissenschaften, 14 Jahrgang. Heft 45, pp. 989-994. I shall quote these papers by the above numbers. I am much indebted in this matter to Mr R. H. Fowler, F.R.S. [19] This is the assumption, mentioned above, that an atom or electron at time can be represented by a collection of terms of the form: [20] Annales de Physique, 3, 22, 1925. [21] Annalen der Physik, 1926. Four papers, 79, pp. 361, 489, 734; 80, p. 437. [22] Nature, Sp. 25, 1926, p. 441. See also Fowler, "Matrix and Wave Mechanics." ib. Feb. 12, 1927. [23] Gyromagnetic Electrons and a Classical Theory of Atomic Structure and Radiation. By Louis Vessot King. F.R.S., Macdonald Professor of Physics, McGill University. Louis Carrier, Mercury Press, 1926. [Pg 48] CHAPTER V THE SPECIAL THEORY OF RELATIVITY