Art. II. — The Spectra of Oxygen, Sulphur and Selenium, 

 and their Atomic Weights. 



By L. rum MEL. 



[Read 9th March, 1899.] 



The researches of Messrs. Runge and Paschen (Wiedemann's 

 Annalen der Physik und Chemie fiir 1897, 8th Heft, pp. 641 and 

 following) have revealed the existence of novel sets of spectra 

 of great regularity, free from bands and differing, save for a 

 few prominent lines, from the spectra of the same elements as 

 observed by Pluecker, Hittorf and Huggins. The new spectra 

 were obtained, when pure Oxygen or the acids of Sulphur 

 and Selenium were heated in Geissler tubes to a temperature 

 approaching 500°C. over a Bunsen burner while under the 

 influence of an induction current and an air pump. Under 

 these conditions the capillary part of the tube resolved itself 

 into a pure line spectrum, while the wider parts showed a 

 mixture of lines and faint bands. The line spectra of the three 

 metalloids were arranged in triplets, forming two secondary series 

 with indications of a primary series. With Selenium each 

 triplet line seems to be sub-divided into two or more finer lines. 

 The spectrum of Oxygen differed from those of Sulphur and 

 Selenium by showing two additional secondary series of very 

 close doublets with rudimentary members of a primary series. 



Among the elements whose spectra have been arranged into 

 distinct series Helium is the only one, which, like Oxygen, yields 

 t7V0 sepai'ate sets of spectral series ; and it may therefore be 

 presumed that in both cases similar causes are bringing about 

 the same results. Helium being regarded as a compound, con- 

 sisting of Helium proper and Parheliuni, which slightly differ in 

 density, although no complete separation has yet been effected, 

 it follows in reason that Oxygen must likewise be a compound. 



To show that this conception does not clash with the investiga- 

 tions of the chemist, I beg to quote Debus (Liebig's Annalen der 

 Chemie, 1888, Band 2'l-4, p. 14-4) who, after treating exhaustively 



