( 480 ) 



acc'oi-diug to Rvdukrg-Schustkr. So a differential series makes the 

 impression of a subordinate series, because it coiivei-fies to the same 

 root (see Lilhinm). 



Tlie fact that //^ consists of 2 comi)onents whose distance is 0.14 

 — Hr: of 2 components whose distance is 0.08 A. U. according to 

 MiCHKLsoN points to the fact that we have not to do with a constant 

 frequency difference, and pleads against the character of a sub- 

 ordinate series '). 



The lines of this differential series again give differential \ibrations 

 namely those measured by Paschkn 18751,3 (1) and 12817,6 (1,5). 



Within the possible error of obser\ation these lines are represented 



1II9G75 109675 109675 109675 



by n = — and it ■=^ and mav, thei-e- 



^ 9 16 9 25 



;.i= 18751,6 ;.i— 12818,7 



fore be considered as differential vibrations between the first line of 

 the differenlfal series with the second and third line of this series or 

 also as differential vibrations between the second line of the prin- 

 cipal series with the third and fourth lines of the principal series. 

 RiTZ ') concludes from the |»resence of these lines that Bat.mer's^ 

 formula must be written with two whole order numbers thus 



.^ / 1 1 \ 



n = 109675 n^'l and ///=3, 4 etc. and /i=:3, //?=:4, 5 etc. 



\n- m'^ J 



No ol>jection can be made against this way of representation'); 

 for an explanation of the sj)ectial phenomenon, however, it is desir-. 

 able to draw attention to the presence of differential vibrations. 



In this connection it is also very remai'kable that the line 1216,0 



one of the infenst^st lines measured by Lyman ^) in the extreme ultra- 



109675 

 violet, is the first term of the series n = 10\)Q7d . 



For m =z 1 we find h = 1215,6. 



Of late F. Paschen has continued to contribute to our knowledge 

 of the line spectra by giving a number of excellent measurements 

 in the infra-red '). In Paschen's papers attention is drawn to a 

 number of combinations in the spectra of Thallium, Aluminium, Zinc, 



1) GF. Kayser und Runge, HandbucU der Spectroscopie, Bd. II, p. 572. 



2) W. RiTZ, Phys. Zeitschr. 16, 1908, p. 524. 



'^) Except this that only the terms m = 4 and m = 5 have been observed. 



^) Th. LxMan, Astrophys. Journ. 23, 1906, p. J 81. Ritz draws attention to 

 this Une in his paper on Magnetische Alomfelder und Serienspeklren Ann. d. 

 Phys. 25, 1908, p. 067. 



5) F Paschen, Ann. d. Phys- 27, 1908, p. 537; 29, 1909, p. 625; 30, 1909, 

 p. 740; 33, 1910; 35, 1911, p. 860; 36, 1911. p. 191. 



