28 Hermann W. Vogel on Lockyer's 



part of a paraffin-flame would be a much better unit of light 

 than the present standard candle, particularly as distances 

 would be measured from the diaphragm and not from the 

 flame, by which error due to the curvature of the flame would 

 disappear. 



Grosmont House, Hampton Wick. 



III. On Lockyer's Theory of Dissociation. 

 By Hekmann W. Vogel*. 



IN February 1880 I took an opportunity to criticise, on the 

 ground of my observations of the spectrum of chemically 

 pure hydrogen, Lockyer's view that calcium is dissociated at 

 a very high temper a turef. Lockyer takes for his starting- 

 point, inter alia, that in the spectra of the so-called white 

 stars, photographed by Huggins, only the first of the two 

 calcium-lines H/ and H" is present, and accordingly advances 

 the theory that calcium at a high temperature separates into 

 two substances X and Y, of which the first gives the line H 7 , 

 the other the line W, and that, in the stars alluded to, only 

 the first exists. I showed, on the contrary, that hydrogen 

 possesses, besides the four well-known readily seen lines, 

 another, singular line with extremely intense photographic 

 action, which nearly coincides with Fraunhofer's line B 7 , and 

 that we are so much the more entitled to hold that the sup- 

 posed calcium-line observed by Huggins is the fifth hydrogen- 

 line, as the known lines of hydrogen are especially well 

 developed in the spectra of those stars, and also the ultra- 

 violet star-lines observed by Huggins coincide with the ultra- 

 violet hydrogen-lines photographically fixed by mej. 



Lockyer, however, has not given up his notion about disso- 

 ciation, but has sought in spectroscopy for new evidence in 

 favour of it. 



He remarks that, inter alia, in the spectrum of the sun- 

 spots certain iron-lines appear widened, others not, and, 

 further, that many of them, as X4918 and A 4919*7, do not 

 occur in the spectrum of the protuberances (which show other 

 lines of iron), but certainly do in the spectrum of the spots, 

 while in these, again, iron-lines which the former contain are, 

 under some circumstances, wanting ; and he then continues, 



* Translated from the Sitzungsberichte der Koniglich Preussischen Aka- 

 demie der Wissenschaften zu Berlin, Nov. 2, 1882, pp. 905-907. 

 t Proc. Koy. Soc. xxviii. p. 157. 

 X Monatsb. d. Berliner Akad. d. Wtssensch. 1880, p. 192. 



