( -t73 ) 



Tlie first linr (6240.1) of lliis (lillt'i-ciitial st'i-ies «>i\'es again (liffcr- 

 ential vil)ratioiis with tlio first liiu's of the two suhoidiiiate series. 

 The first cüliiniii contains the lines of the subordinate series ; (1, I S.S.) 

 denotes the I''' line of the first suboi'dinate series; the 2"'^ column 

 gives the frequency difierence with the line B240,l, tlu' first line of 

 the differential series. 



The second line of the differential series 4635,9 gives a differential 

 vibration with (1, I S. S.) (2, D. S.) — (1,1 S. S.) = 21571 — 16384 = 

 = 5187 Xi, = 19278,7 . X„. = 19290 (P. 5) '■'). 



Bergmann discovered a number of lines forming a series in the 

 infra-red of the alkali-metals. The root of this new series is derived 

 from the first subordinate sei'ies just as the root of the subordinate 

 series according to Rydbkrg — Schuster is found from the i)rincii)al 

 series, viz. root subordinate series — root Bergm. series = first line of 

 the first subordinate series. For Lithium 



Root B.S. = 28581,8 — 16379,3 = 12202,5 '). 



The formula n = 12202,5 



1096' 

 ÖM^3) 



; m = 'ï;2 gives ^) ;. = 18696 



1) P. = Paschen. Bergmann gives 12235. 



2) F. Paschen, Ann. d. Physik, 33, 1910, p. 724. 



•') 28581,8 has been borrowed from the paper of Nov. 1906. These values have 



been reduced to vacuum according to determinations of the dispersion of the air 



of Kayser and Runge. 



109675 

 *) This is the original Rydberg formula. Whether the formula 7i=A 



m-\-a-\-- 



must be used for Bergmann's series cannot be decided as yet, which will be treated 

 further on under Caesium. Rixz gives the formula (3, d, cï) — (m, Pi — 2h> ^i — ^-2)1 

 m = 4,5, .... (loc.cil. p. 522, case 5) for these lines, ni — n^ however is almost 

 zero and px — IJ.^ i^ moreover so small* that these constants exert hardly any 



