L so ] 



VII. Atomic T] i e or y and Low Voltaoe Arcs in C cesium Vapour. 

 By Paul D. Foote, Ph.D., and W. F. Meggers, Ph.D.* 



[Plate I.] 

 I. Theoretical. 



THE spectrum of caesium is characterized by the principal 

 doublet series l'5s—mpi, where m = 2, 3, 4, etc.; the 

 1st subordinate series 2p L — md and 2p 2 — rnd', where m = 3, 

 4, 5, etc. ; the 2nd subordinate series 2p^—ms, where m=2'5 9 

 35, 4o'5, etc. ; the Bergmann series M — mAp and 3d'—mAp 9 

 where ??i = 4, 5, 6, etc.; satellites to the 1st subordinate 

 series; and certain combination lines, those known lying in 

 the far infra-red f. 



The spectroscopic data are sufficient to permit a schematic 

 representation of the caesium atom, as illustrated in fig. 1. 



Fig. 1. 



- Convergence- Pein. Series 1.5 S'— 1 st and 2 nQ Sub.Senes 2 p t and 2 p 2 — Bergmann Series id — 

 3-87 volts 



To 



3.18 



2.71 



5Pr 



4P. 



3P. 



6d 



S-ap 



4.5 S 



5d 



5Ap 



3.5 S 



4Af> 



4d 



2.5 S 



3d 



3.4 3.5 3.6 



loq. wave number 



3.8 



3.9 



4.1 



4.2 



4.3 



44 



4.5 



Schematic representation of caesium atom. 



This method was suggested to the writers by Dr. Raymond T. 

 Birge; and, regardless o£ the theory of atomic structure, 

 it affords a precise picture of the possible series lines in the 

 spectrum of an element — a much clearer picture than may be 



* Communicated by the Authors, and published by permission of the 

 Director Bureau of Standards. 



t The above notation is that employed by Dunz in his tabtes, except 

 that for convenience we have written p± for p x and p 2 when both lines 

 are referred to. 



