448 Prof. Wiillner on M. Goldstein's Observations 



There are some other points arising out of the long memoir 

 of M. Gernez, especially on the subject of superheating, that call 

 for comment, but must be deferred to another occasion on account 

 of the great length of this paper. 



Highgate, N. May 10, 1875. 



LII. Remarks on M. Goldstein's Observations on Spectra of 

 Gases. By Professor Wullner, of Aachen *. 



IN the Monatsbericht of the Konigl. Akademie der Wissen- 

 schaften for August last are described by M. Goldstein 

 observations on gas- spectra f, which are said to prove that my 

 explanation of the band- and line-spectra observed in one and 

 the same gas (Pogg. Ann. vol. cxlvii. p. 321) is untenable. My 

 explanation was to this effect — that from an illuminating gas a 

 band-spectrum is always obtained when a thick layer of gas is 

 made use of as the source of light^ but the line-spectrum when 

 only a few molecules of the gas are ignited. I deduce this from 

 experiments which showed that in tubes filled with rarefied gases 

 the line-spectrum always and only appeared when the induction- 

 current traversed the tube in the form of a proper spark, but 

 the band-spectrum when the discharge was without a spark. 

 In my experiments at that time the sparkless discharge was 

 that which I afterwards (Pogg. Ann. Jubelband) named the 

 luminous tuft : it gives light which more or less fills the entire 

 tube ; the proper spark ignites a minimum quantity of mole- 

 cules, only those which lie in the line of the spark. 



The experiments of M. Goldstein which are said to contradict 

 my explanation consist, so far as I understand his description, 

 essentially in this : — In the circuit in which is the spectral tube 

 he produces an interruption at one plaee, so that there the in- 

 duction-current passes in sparks ; sometimes he also inserts a 

 Leyden jar ; and then he observes the spectra of the tube. He 

 expects under these circumstances line-spectra must appear in 

 the tube, but finds, as a rule, in tubes filled with air, the band- 

 spectrum, and only when the air presents greater resistance a 

 mixed spectrum of bands and lines. No detailed description is 

 given of his observations on hydrogen ; he merely remarks (p. 

 602), " The observations on hydrogen correspond.'" He specifies, 

 however, that, of two tubes simultaneously placed in the circuit, 

 one containing air, and the other hydrogen, the former gives the 

 band-spectrum, and the latter the line-spectrum. As the same 



* Translated from the Monatshericht der Koniglich Preussischen Aka- 

 demie der Wissenschaften zu Berlin, December 18/4. 

 t See Phil. Mag, for May 18/5, pp. 333-345. 



