1. "An Atlas of Representative Stellar Spectra," p. 85. For a more complete investigation of the absorption in the Class A stars, see Hartmann, Physik. Zeit., 18, 429, 1917.
2. Astrophys. Jour., 29, 100, 1909.
3. Lick Obs. Bull., 9, 54, 1917; also Publ. Lick Obs., 13, 256, 1918.
4. Hubble, Publ. Astron. Soc. Pacific, 32, 155, 1920.
5. Ann. Chim. et Phys., (8), 9, 361, 1906.