Spectrum of Erbium. 169* 



to Welsbach and Co., U.S.A., for a very pure sample of erbium, which 

 they presented to the Natural Philosophy Dept. X-ray analysis showed 

 that there was no discernable impurity. 



References. 



(1) Stenstrom, Dissertation Lund, 1919. 



(2) D. L. Webster, Physical Review 7, 599, 1916. 



(3) D. L. Webster, (I.e.). 



(4) Coster, Zeitschr. f. Phys. 185, 1921. 



(5) Atombau und Spektrallinien, 3 ed., 1922. 



(6) Proc. Nat. Acad. 6, 477, 1920. 



(7) Journ. de Phys., 1916. 



(8) Phys. Rev., 14, Dec, 1919. 



(9) Phys. Zeitschr., 20, p. 252, 1919. 



(10) Phil. Mag. 28, p. 266. 1914. • 



