SOME CONTEMPOR.fRV .{m.lXCr.S IX rilVSICS rill 445 



represent the enery;y-(litTerence between the new stationary state 

 (Icnotetl by the index m, and the original slalionar\' state. The rules 

 are compriseil in the formula, 



and ill the selection-principle. In the fornuila // stands for the 

 magnetic t'leld; w is a factor equal within experimental error to e/4rnr 

 (/i = mass of the electron) and commonly identified with it. in has two 

 or more \aliies spacetl one unit .ijiarl (for instance, I and •>. (ir ." and 

 -i. or 1 and and -1). 



The selection principle is as follows: The only transitions 'iuliich cor- 

 rrspiniil !o ih fthtl !iiir\ art' llio'ic in whiih m rlunii^cs hy unity or not 



I __ ^ i, tU-l.l oTi spi'ctrum lliu-^. I', /rem, 111, Jri,', 



t'ranktin Institute) 



at all: Am=0,±l. This is the selection-primiple for tlic magnetic 

 qnatititm number. 



If we allow m to assume onh- two \alues, this i)rinciple Incomes 

 nugatory. If on the other hand, we aflopt the principle, m can assume 

 an>' number of values whatever, provided onh' lhc\' are spaced at unit 



Fig. 10 — More complicated effects of magnetic fields on spectriiin lini>. 

 (P. Zeeman, I.e.) 



intervals; it makes no difference with the observed lines wheltier there 

 are two or two hundred new stationary states for every original one. 

 This is convenient for theorizing. In dealing with the Zeeman effect 

 in general, and not merely with these special "normal" ca.ses, it is 

 neces.sary to assume that oi is not restricted to the particular value 



