444 BELL SYSTEM TECHNICAL JOURNAL 



This is the common character of the alkali elements Li, Na, K, Rb 

 and Cs, which occupy the first column of the periodic table; prob- 

 ably also for the noble metals which share this column, but the data 

 are few. For elements of the second column of the periodic table 

 there are two complete systems of stationary states, each having 

 its own s-column, its own />-column, its own rf-column, and all the 

 rest. In one system, all the groups in e\ery column reduce to single 

 levels; it is a singlet system; in the other, all the groups in the 5-column 

 are single levels, all the groups in the other column are triads of 

 levels or "triplet terms;" it is a "triplet system." The complc\it\- 

 mounts up stage by stage as we cross the periodic table of the ele- 

 ments from left to right, and soon becomes terrific. 



E 9. Effect of Magnetic Field on the Stationary States 



When a magnetic field is applied to a radiating gas, most of the 

 lines of its spectrum are replaced by triplets (Fig. 9), or by even richer 

 groups of lines (Fig. 10). By a somewhat loose usage the lines are said 

 to be resolved into three or more components. This is the "Zeeman 

 effect." There is a multitude of empirical rules about these compo- 

 nents, their spacings, the way in which their number and their spacings 

 vary from one line to another, and other features. According to the 

 new fashion, however, we focus our attention not on the component 

 lines, but on the stationary states which are inferred from them. 



The effect of a magnetic field may be described by saying that it 

 replaces each stationary state (with a few e.xceptions) by two or 

 more new ones. Each of these new states requires four symbols to 

 designate it; the symbols n, k and j for the original stationary state, 

 and a new symbol tn to denote its place in the resulting group. As 

 heretofore, when every stationary state is connected with e\ery other 

 by an arrow and the corresponding lines are sought, it is found that 

 some of the lines are missing. Still another selection principle is 

 therefore to be sought, and the values of the new numeral ni are to 

 be so adjusted — if possit)Ie — that the selection-principle can be read 

 easily from them. When so adjusted m is called the magnetic quantum- 

 number. 



In certain cases the empirical rules for the components whereby 

 the magnetic field replaces the indi\idual lines are simple; and the 

 derived rules for the new stationary states which arise out of the 

 original ones when the magnetic field is applied are correspondingh' 

 simple. These are the cases of "normal" Zeeman effect (the ad- 

 jective "normal" may be an entirely misleading choice). Let A Um 



