The lamented Dr. P. S. Epstein, a gifted pupil of Sommerfeld, who—like Mosely—fell a martyr to the World War, succeeded in applying the quantum dynamics to the Stark effect, whereby the motions of the electron in producing the H-beta (in the blue-green) and H-gamma (in the violet) lines observed, “are accounted for with great accuracy” (Loring, “Atomic Theories,” Page 67). It may be said in conclusion, that the most promising attempts fully to explain the phenomena of the Zeeman and Stark effects seem to be made from the point of view of Planck’s Quantum Theory of Light. On the other hand, it must be admitted that there has not been, so far as I can ascertain, any theory proposed which explains _all_ of the phenomena involved. FOOTNOTES: [23] For a good summary of the main results concerning the Zeeman effect, see von Auerbach, Felix, “_Moderne Magnetik_,” Leipsic, 1921. An excellent account of the quantum treatment of the Zeeman effect may be found in Chapter XV (Series Spectra) of Dr. N. R. Campbell’s “Modern Electrical Theory, Supplementary Chapters,” Cambridge University Press, 1921. [24] It seems that this phenomenon had previously been observed by M. Fievez. (Cf. Michelson, Dr. Albert A., “Light Waves and Their Uses,” Page 107.) “He thought that each separate line was doubled or quadrupled.” Lockyer, in 1866, observed that some of the lines in a sun spot spectrum were widened. Prof. Charles Young and W. M. Mitchell observed that some of the lines were even double, but it was not suspected that these phenomena were caused by a strong magnetic field in sun-spots, brought about by free electrons being driven around in a vortex movement. In fact, Mitchell referred to the doublets as “reversals.” [25] Zeeman, “_Les Lignes Spectrales et les Theories Modernes_,” _Scientia_, January 1, 1921, Page 18 (Vol. XIX, No. CV—I). [26] Hale, “Ten Years Work of a Mountain Observatory,” Pages 29-30, Washington, D. C. (Carnegie Institution of Washington), 1915. See also, Babcock, Harold D., “The Zeeman Effect for Chromium,” _Contributions from Mount Wilson Observatory_, Vol. II, Paper No. 52; also “The Correspondence between Zeeman Effect and Pressure Displacement for the Spectra of Iron, Chromium and Titanium,” Arthur S. King, Loc. cit., Paper No. 46; and “The Zeeman Effect on the Sun,” Adriaan van Maanen, _Publications of the Astronomical society of the Pacific_, Page 24, Vol. XXXIV, No. 197 (February, 1922). [27] Zeeman, _Loc. cit._, Page 18. See also the classical monograph by the same author, “Researches in Magneto-Optics,” London, 1913. [28] Millikan, _Physical Review_, 2, 143 (1913); “The Electron,” 1917 (revised edition, 1924). See also, _Proceedings of the National Academy of Sciences_, 3, 314 (1917). [29] “The New Heavens,” Page 70, New York, 1922. [30] Cf. Stark, “_Die Atomionen chemischere Elemente und ihre Kanastrahlenspektra_,” Berlin, 1913. See also, “_Elektrische Spektralanalyse chemischen Atome_,” Leipsic, 1914.