SOME COXTEMPOR-tRY ADWANCES IN PHYSICS- VlII 425 



in which 



v/in, = f ri'qui'iir\' of the limit of the scries = i? '4 



R s'.iiuliiiK for a cert.iiii conslant. TIuti- is another series of lines 

 in the iihraviolel part of the same siiectriim, whereof llie fre(|nencics 

 are etinal conscriiti\ely to 



V = VU„-R \, V,im-R''^, l-^m-/?. Iti. etc. (2) 



in which 



Vlim = R, 



R having the same value as before. The utter simplicity of the 

 terms to l>e subtracted from vum in eacii of these cases, not to speak 

 of the related form of the expres.sions for k;,™, suggests like simple 

 laws in other fields of physics that in this formulation of the facts 

 .something highly important has been partially unveiled. There are 

 certain other series in the spectrum of hydrogen, and inspecting them 

 all one is led to the rule that ei'ery frequency emitted by the hydrogen 

 atom can be calculated by inserting different pairs of integers in the 

 places of m and n /// the formula 



The case of the ionized-helium '■' atom is quite as simple. Kvery fre- 

 quency emitted by this atom can be calculated by assigning different 

 pairs of integer values to the constants m and n in the formula 



= 4/? 



ih-l^- <« 



Line-series have been found in the spectra of many other elements. 

 Some of them are as strikingly outstanding as the line-series in the 

 sfK-ctrum of hydrogen, and converge upon limits scarcely less easy 

 to locate; for instance, the "principal" series of the spectrum of 

 sotlium (Fig. 3). Most are by no means so obvious; often they are 

 involved in the midst of a luxuriant jungle of unrelated or otherwise- 

 related lines. Most spectra conceal their structures from the un- 

 practised eye, as a tone-poem of Strauss its themes or an opera of 

 the Ring its Leitmotiv from the ine.xperienced ear. Long training 

 and a skilled judgment are required in the deciphering of spectra, 

 except in the few untypically simple cases; and usually the arrange- 

 ment of lines into series which the spectroscopist presents must be 



" The reader may take this, for the time being, simply as the name of a particular 

 element. 



