434 BELL SYSTEM TECHNICAL JOURNAL 



nated b\- the letters 5, p, d, f (or their capital, or Gothic, or Greek 

 equivalents).'" A spectroscopist using these symbols generally writes 

 the serial number of the le%el before the letter, with a comma between, 

 thus: (1,5) and (2,p) and (3,f/). Or the columns may be designated 

 by their values of the numeral k. which is then commonly written as a 

 subscript to the serial number. These s\'mboIs have at least the 

 ad\antage of being comparativeh' ti,\ed. It is far otherwise with the 

 serial numbers. One might expect that the level having the greatest 

 energy-value in a particular column would be called Number 1, and 

 the successive ones Number 2, Number 3, and so forth towards the 

 convergence-limit. Unfortunately (though for not a bad reason) 

 the habit is to designate the first levels of the successive columns by 

 the order-numbers 1, 2, 3 and 4, successi\ely; so that their respective 

 symbols are (l,s); {2,p); (Z,d) and (4,/). These are the symbols I 

 have affixed in Fig. 6; but they are not the only ones, as the order- 

 numbers have jumped up and down several times to satisfy the ex- 

 igencies of new atom-models. It would be unprofitable to confuse 

 the reader with further details, at least at this point. The important 

 things to remember are three: that the symbol for each stalionar\- 

 state must contain one index for its column and another for its place 

 in its column — that the former index is usually one of the specified 

 letters — that the latter index is a number, usually beginning with 

 1, 2, 3, 4 for the first le\'el in the 5, p, </,/ columns, respectively, and 

 ascending along the column in unit steps. 



E 6. Names and Features of the Most Noted Line-Series 



Every line in every series, according to Bohr's fundamental idea, 

 corresponds to a transition or "combination" between two stationary 

 states of the atom — -to a transition from an initial state to a final state. 

 The atom possesses more energy in the initial state than in the final 

 state (we are speaking of emission-spectra only). Hence the energy- 

 value of the initial state, reckoned as it usually is from the energy of 

 the ionized atom as zero, is algebraically higher and ariihmeticalh' 

 lower than the energy-value of the final state. 



The various lines of any one line-series have this in common : they 

 correspond to transitions from \arious initial states which however 

 all lie in one and the same colimui, into one final state which is the 

 same for all and lies in an adjacent column. Each line-series thus 



"The symbol b is sometimes used instcail of/. For the columns following to the 

 right of the /-column there are various notations, particularly/',/",/'" and g, /i, i. 

 See also footnote 21. 



