Second Spectrum of Hydrogen. 339 



After the foregoing explanation I cannot but regard the 

 explanation of Berthelot's spectrum given by Pliicker and 

 AY illlner as by far the best founded. In this opinion I am 

 still further confirmed by numerous experiments of my own. 

 That nevertheless this view has not yet received universal 

 assent, is indeed perhaps not share! by the majority of spec- 

 troscopists, is seen from the circumstance that Ciamician* has 

 recently given Berthelot's explanation as the correct one, and 

 that Schusterf regards the question as still open. This last 

 circumstance has induced Wullnerif also to undertake now 

 experiments upon this subject, the results of which require 

 further notice here in conclusion. 



Wullner's experiments are designed to show directly that 

 the spectrum of acetylene is quite different from the second 

 spectrum of hydrogen, and could not be confused with it. For 

 this purpose acetylene, prepared from cuprous acetvlide with 

 careful observation of the precautions necessary to secure the 

 purity of the product, was introduced into a spectral tube, ex- 

 hausted to a pressure of 1 or '2 millimetres. The spectroscopic 

 examination of the greenish-white light produced bythe passage 

 of the induced current revealed a somewhat complicated spec- 

 trum, which Wiillner considers to be that of acetylene ; and 

 the difference between which and that of hydrogen he further 

 endeavours to show by means of a complete description based 

 upon measurements. That there is a difference there is no 

 doubt, but not because the spectrum belongs to acetylene, the 

 spectrum oi' which is altogether different, but because it is 

 formed by the simple superposition of the spectra of carbonic 

 oxide and of hydrogen ; of which last spectrum, just because 

 of this superposition, only the strongest lines are perceptible. 

 In order to show this, I here compare Wiillner's description 

 of the spectrum with the measurements of the carbonic-oxide 

 spectrum made by Angstrom and Thalcn, and with those of 

 the second hydrogen spectrum made by myself, omitting 

 nevertheless those spectral regions which, according to Wiill- 

 ner, form the boundary of the bright carbon-oxide bands on 

 the more refrangible side of the spectrum, since these, under 

 varying circumstances, have no significance as characteristic 

 of the spectrum. The wave-lengths of the lines here given of 

 the second hydrogen spectrum are taken from complete tables 

 of wave-lengths of this spectrum given further on. 



* Wlen. Site. Ber. lxxxii. part ii. p. 425 (1880). 

 t Report of the British Association, L88Q, p. 287j 

 X Wiedemann's Annalai, xiv. p. 855 (1881). 



