THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



MA Y 1884. 



XXXIX. On the Second Spectrum of Hydrogen. 

 By Dr. B. Hasselberg*. 



[Plate X. figs. 1-3.] 



PLUCKER and Hittorf, in their celebrated paper "On 

 the Spectra of Ignited Gases and Vapours " |, were 

 the first to call attention to the remarkable system of lines 

 which almost always appears, together with the characteristic 

 hydrogen-lines H a H^ H y and H 5 , in tubes containing hydrogen, 

 under small pressure, when traversed by the electric discharge. 

 These groups of lines, which are distributed through the whole 

 spectrum from H a to H y , but are especially bright and cha- 

 racteristic in the neighbourhood of I), have since been made 

 the subject of numerous investigations, especially to decide 

 the question of their origin, since the views of the discoverer 

 upon this point had been rendered doubtful by later experi- 

 ments. The result of these investigations was not altogether 

 satisfactory, since even now the question can hardly be re- 

 garded as settled. On the contrary, two opposite opinions 

 upon this point are held by spectroscopists, one of which, held 

 by Pliicker, Hittorf, and Wtillner, represents the lines in 

 question as a spectrum belonging to hydrogen at a low tem- 

 perature ; whilst the second, represented by Berthelot, Ang- 

 strom, Salet, and recently Ciamician, finds the source of these 



* Translated from the Memoires de V Academic Imperiale des Sciences 

 de St. Peter shoar g , vol. xxx. No. 7. 

 t Phil. Trans. 1864. 



Phil. Mag. S. 5. Vol. 17. No. 107, May 1884. Z 



