Line-spectrum of Hydrogen in the Oxyhydrogcn Flame. 371 



If the hydrogen and nitrogen mixtures stood alone, there 

 would be a presumption that the law of the logarithmic curves 

 originated in proportionality of LV.and C.P. to temperature. 



But this law does not hold for any of the other mixtures; and 

 in the marsh-gas mixtures the I.V. is certainly constant 

 through most of the range. 



It seems possible that the increased l.V. for higher carbon 

 densities may be due to temperature. But I am rather in- 

 clined to look in the direction of molecular behaviour. 



XLI. Note on Plucker's supposed Detection of the Line- 

 spectrum of Hydrogen in the Oxyhydrogen Flame. By G. 

 D. Livbing, V.P.R.S.* 



IN a paper published in Poggendorf's Annalen (1862, 4th 

 ser. vol. xxvi. p. 48) Plucker stated that the flame of a 

 mixture of oxygen and hydrogen, when the latter was slightly 

 in excess, showed the two lines of hydrogen H a and H^. 



The passage in which this statement occurs is an episode in 

 a paper on recurrent electric discharges in gases at low pres- 

 sure, and is given by way of confirmation of the author's 

 theory that the illumination of gases by the electric discharge 

 is due to the high temperature of the discharge. 



This statement seems to have been generally accepted on 

 Plucker's authority ; but no one else, so far as I can learn, 

 has ever succeeded in seeing, or in photographing, any of the 

 lines of hydrogen in the spectrum of a flame. Nevertheless 

 no one has, I believe, distinctly challenged the correctness of 

 the statement, and it is still currently taken to be true, and 

 inferences have been drawn from it (as to the condition of the 

 solar atmosphere and other matters) which become untenable 

 if Plucker was mistaken. Plucker's authority is so great that 

 every one hesitates to call any observation of his in question . 

 Moreover, it is difficult to prove a negative. For one to suc- 

 ceed with an experiment when another fails is nothing un- 

 common. Still spectroscopy has made long strides since 

 18(32, and the interests of science demand that the evidence 

 on this question should be reviewed. 



Two years after the publication of Plucker's paper, Dibbits, 

 also a good observer, published in the same journal (Pogg. 

 Ann. 5th ser. vol. ii. p. 497) an account of his observations of 

 the spectrum of the flame of hydrogen burning in air, in 

 oxygen, in nitrous and in nitric oxides, and in chlorine. In 



* Communicated by the Author. 



