156 
Physics. — “Translation series in line-spectra.” By T. vaN LOHUIZEN, 
(Communicated by Prof. P. ZEEMAN). 
(Communicated in the meeting of May 25, 1912). 
In my preceeding communication’) I told already how I had suc- 
ceeded in discovering series in the spectra of Tin and Antimony by 
making use of a model which was the result of a spectral formula 
found by me empirically, which formula was based on the fundamen- 
tal thought: ‘Every series in a line-spectrum of whatever element 
can be represented by one and the same curve when the frequen- 
cies are considered as function of the parameter, and the curve 
refers every time to another system of axes.” 
I will now show how this fundamental thought may be serviceable 
to arrange the series of systems of the different elements in better 
order. It is true that some order has already been brought in the 
great material of observation®) by the discovery of numerous 
series by Rypsmra, Kayser and Runge and others, and recently 
particularly by the “Kombinationsprinzip’, discovered by Ritz, but 
it is exactly this great number of series and combinations that 
threatens to destroy the order and bring confusion. If we consult, 
e. g. a treatise by Dunz*) which was recently published, we 
find there a great quantity of material of observation arranged 
according to Rrrz’s spectral formula and the ‘‘Kombinationsprinzip”’, 
but it appears already very soon that specially for the numerous 
combinations the order leaves a good deal to be desired. It is impossible 
to have a survey of the matter. That this way of arrangement is 
not the only one, is shown by Mocrnporrr *) in his communication 
on “Summational and differential vibrations in line-spectra’, in which 
most of the combinations are indicated as summational and differential 
vibrations. Though the system is by no means lucid here either, 
yet we will for a. moment retain the idea of differential vibrations. 
Already before PascHeN*) had about the same idea when he says: 
“Die Linien eines Seriensystems sind darstellbar durch eine Anzahl 
von Termen, deren Differenzen die Wellenzahlen (bzw. Schwingungs- 
zahlen) existierender Linien geben.” 
The first thought of this sentence is already found in Rypsrre, 
where he takes the asymptote of the principal series as a special 
1) These Proc. p. 31. 
2) Cf. Kayser, Handbuch der Spectroscopie Bd. V and Exner and Hascuex, Die 
Spektren der Elemente bei normalem Druck. 
3) Unsere Kenntnisse von den Seriengesetzen der Linienspektra. 
4) Proc. Royal Acad. Amst. Nov. 25, 1911. 
5) Jahrbuch der Radioaktivität und Elektronik Bd. 8, Heft 1. 
