SOME CONTEMPORARY AIH-ANCES IN PHYSICS-yill 4.13 



l>cl<)n^s to one p.irlit'iil.ir llii.il ^t.iit-, .iiul in unt- |).irti< til.ir ciilinnii of 

 initial stalt-s. 



The linc-sories consisting of transitions into the state (\,s), or 

 Urmimtting upon (1,5) as the phrase sometimes is, hears the name of 

 principal series. Its consecutive lines are: {\,s) — (2,p)\ (1,5) — (3,^); 

 (1,5) — (4, p) and so forth. The>' are signified by the blue arrows'of 



A7.irmiili Quaiiiuin Number 



Fig. 7 — .Vnotht-r way of mapping the staliunarj' states of sodium 



Fig. 6. The general symbol for this series is (1,5) — (»/,/>); which will 

 be quite intelligible. The (1,5) level is the normal state of the att)m; 

 consequently, the various lines of the principal series correspond to 

 transitions, by which the atom regains its normal state after a tempo- 

 rary e.xile from it. It is probably for this reason that the series is 

 prominent enough to have received the name principal from the 

 spectroscopists. 



Two series terminate upon the {2,p) level. One of these consists of 



