( 470 ) 



Physics. — "Summational and dljf'ennüal cihnitions in line spectra". 

 I»v Dr E. E. MoGENDORFF. (Communicated by Prof. P. Zekman). 



(Communicated in the meeting of Oct. 28, 1911.) 



Tlie supposition that in line spectra combinational vil)ra(ions occur, 

 analogous to the well known combinational tones, which have been 

 fully investigated by von Helmhoi.tz ^), is not new. 



To account for the great number of pairs of lines (doublets) with 

 constant frequency ditference, which have been observed in man}- 

 spectra, V.A.Julius*) has assumed the existence of summational and 

 difFerentional vibrations. 



If in the iiifi'a-i-ed lines occur of the frequency: 



they can give' the combinations: 



"1 + "3 , «2 + "s ; ", r "4 ' "s + «4 Ï "1 + "s . "a + "5 ^'^• 

 in the visible spectrum, and evidently these lines show the difference 

 of frequency n^ — n,. 



The hypothesis of Juuus is not tenable because no intense lines 

 have been observed in the infra-red which could give rise to sum- 

 mational vibi'ations of so great intensity as the first doublet of a 

 [irincipal series ^e. g. the well-known />)-lines of ya). Shortly after 

 it was shown by Rydbek(;, Kaysek, and Runge that in many line 

 spectra series occur, while it has ap|)eared from the ZEK^MAN-effect 

 that we have to do with })airs of series which run pai-aliel. 



After a great many lines had been measured in the infra-red by 

 Moll '), Bergmann ^), and Paschen *), the situation of these lines was 

 accounted for by RiTZ b}- the aid of the spectral formula given 

 by him "). 



RiTz's combinations consist for the greater part in taking sum- 

 mations and differences of observed frequencies, as Ritz himself 



1) Helmholtz, Poggend. Ann. 99, p. 532, 1856. 



■-) V. A. Julius, The linear spectra of the elements. Verb, der Kon Ak. v. Wet. 

 te Amsterdam, Dl. 26. 



^) W. J. H. Moll, Onderzoek van uUra-roode spectra, Thesis for the doctorate, 

 Ut-echt, 1907. 



■*) A. Bergmann, Beitrage zur Kennlnis der ullraroten Emissionsspeklra der 

 Alkaliën. Inaug. Diss. Jena 1907. 



^) F. Paschen. Kennlnis ullraroter Linienspectra, Ann. d. Phys. Vol. 27, p. 537 — 

 571, 1908. 



6) W. Ritz, Ann. d Physik. 12, p. 264, 1903 (inaug. Diss.) and Pbysik. Zeit- 

 schrifl, 16, 190>i, p. 521. 



