1. Kayser, H. (Handbuch der Spektroskopie, Vol. 6, Hirzel, Leipzig 1912, pp. 636/54).
2. Twyman, F.; Smith, D. M. (Wavelength Tables for Spectral Analysis, Hilger, London 1931, pp. 1/180).
3. McLennan, J. C.; Cohen, E. (Trans. Roy. Soc. Can. Sect. 3 20 [1926] 365/76).
4. Allin, E. J. (Trans. Roy. Soc. Can. Sect. 3 21 [1927] 231/5).
5. Moore, B. E. (Astrophys. J. 30 [1909] 144/66).